Chesapeake Bay eutrophication: scientific understanding, ecosystem restoration, and challenges for agriculture

Phosphorus speciation in manure and fertilizer impacted Mid-Atlantic coastal plain soils

Historical applications of manures and fertilizers at rates exceeding crop P removal in the Mid-Atlantic region (United States) have resulted in decades of increased water quality degradation from P losses in agricultural runoff. As such, many growers in this region face restrictions on future P applications. An improved understanding of the fate, transformations, and availability of P is needed to manage P-enriched soils. We paired chemical extractions (i.e., Mehlich-3, water extractable P, and chemical fractionation) with nondestructive methods (i.e., x-ray absorption near edge structure [XANES] spectroscopy and x-ray fluorescence [XRF]) to investigate P dynamics in eight P-enriched Mid-Atlantic soils with various management histories. Chemical fractionation and XRF data were used to support XANES linear combination fits, allowing for identification of various Al, Ca, and Fe phosphates and P sorbed phases in soils amended with fertilizer, poultry litter, or dairy manure. Management history and P speciation were used to make qualitative comparisons between the eight legacy P soils; we also speculate about how P speciation may affect future management of these soils with and without additional P applications. With continued P applications, we expect an increase in semicrystalline Al and Fe-P, P sorbed to Al (hydro)oxides, and insoluble Ca-P species in these soils for all P sources. Under drawdown scenarios, we expect plant P uptake first from semicrystalline Al and Fe phosphates followed by P sorbed phases. Our results can help guide management decisions on coastal plain soils with a history of P application.

Modeling the importance of fish condition, overall health, and disease on the fecundity of White Perch in the Choptank River

OBJECTIVE

Modeling of fecundity with allometric, nutritional, and environmental covariates has increased sensitivity of reproductive metrics in many fish species. In estuaries with heavy anthropogenic influence, resident species often experience sublethal health impacts because of increased stress, which can include increases in gonadal pathology, intersex, or potential reproductive failure. This study models the fecundity of the estuarine species White Perch Morone americana in response to health parameters identified as signals of habitat stress, including gross pathology presentation, nutritional condition, and disease presence.

METHODS

Subpopulation fecundity in the Choptank River (Maryland) of the Chesapeake Bay was estimated using stereological fecundity sampling methods and modeled using information-theoretic approaches of model selection. Nutritional and health parameters identified through health assessment techniques, specific somatic indices, and disease presence were selected as covariates.

RESULT

Nutrition demonstrated limited influence on model fit as compared to models with only conventional allometric variables such as weight and length. Of the health variables, gross pathology and somatic indices showed minimal influence on selection, but mycobacterial infection, a chronic condition in the Chesapeake Bay among temperate basses, showed measurable influence. Models with mycobacteriosis included were 40 times more likely the best fit when compared to models with only allometric parameters.

CONCLUSION

Whether this has a region-wide influence on all subpopulations will require further research and sampling of the magnitude of mycobacteriosis infection.

Field-scale nutrient loss assessment following cover crop and manure rate change

Eutrophication due to elevated nitrogen (N) and phosphorus (P) loss from croplands remains one of the most pressing water quality issues throughout the world. Understanding the effect of implementing conservation management practices is critical for meeting nutrient reduction goals as well as informing conservation programs and policies. A before-after-control-impact (BACI) analysis was used to evaluate the individual and combined effect of cover crops and manure application rate on discharge and nutrient loss using six water years (WY2014-WY2019) of measured data across four distinct drainage zones (1X-NCC; 1X-CC; 2X-NCC; 2X-CC) within an Ohio, USA, crop production field. White mustard significantly reduced mean monthly nitrate (NO₃^--N) concentration regardless of manure application rate (i.e., 65 m³ ha^-1 and 130 m³ ha^-1). However, neither the use of white mustard, doubling manure rate, or the combination of the two had a significant impact on mean monthly drainage discharge, dissolved-reactive P (DRP), or total P (TP) loss. Seasonal analysis confirmed that NO₃^--N concentration in the cover crop zones was signficantly less in fall, winter, and spring. However, significant increases in spring discharge, NO₃^--N, DRP, and TP loads as well as TP concentration were noted with cover crop and greater manure rate treatments. These findings confirm that cover crops have a reducing effect on NO₃^--N concentration but may not have any effect on addressing P concerns. Further research is warranted; however, this study highlights that the resource concern (e.g., N or P) should be considered prior to implementing cover crops as a conservation management practice.

A new method for phosphate purification for oxygen isotope ratio analysis in freshwater and soil extracts using solid-phase extraction with zirconium-loaded resin

RATIONALE

Phosphate (PO₄ ) oxygen isotope (δ¹⁸ O_PO4 ) analysis is increasingly applied to elucidate phosphorus cycling. Due to its usefulness, analytical methods continue to be developed and improved to increase processing efficiency and applicability to various sample types. A new pretreatment procedure to obtain clean Ag₃ PO₄ using solid-phase extraction (SPE) with zirconium-loaded resin (ZrME), which can selectively adsorb PO₄ , is presented and evaluated here.

METHODS

Our method comprises (1) PO₄ concentration, (2) PO₄ separation by SPE, (3) cation removal, (4) Cl^- removal, and (5) formation of Ag₃ PO₄ . The method was tested by comparing the resulting δ¹⁸ O_PO4 of KH₂ PO₄ reagent, soil extracts (NaHCO₃ , NaOH, and HCl), freshwater, and seawater with data obtained using a conventional pretreatment method.

RESULTS

PO₄ recovery of our method ranged from 79.2% to 97.8% for KH₂ PO₄ , soil extracts, and freshwater. Although the recovery rate indicated incomplete desorption of PO₄ from the ZrME columns, our method produced high-purity Ag₃ PO₄ and accurate δ¹⁸ O_PO4 values (i.e., consistent with those obtained using conventional pretreatment methods). However, for seawater, the PO₄ recovery was low (1.1%), probably due to the high concentrations of F^- and SO₄ ^2- which interfere with PO₄ adsorption on the columns. Experiments indicate that the ZrME columns could be regenerated and used repeatedly at least three times.

CONCLUSIONS

We demonstrated the utility of ZrME for purification of PO₄ from freshwater and soil extracts for δ¹⁸ O_PO4 analysis. Multiple samples could be processed in three days using this method, increasing sample throughput and potentially facilitating more widespread use of δ¹⁸ O_PO4 analysis to deepen our understanding of phosphorus cycling in natural environments.

Phytoplankton assemblage and chlorophyll a along the salinity gradient in a hypoxic eutrophic tropical estuary-Ulhas Estuary, West Coast of India

Phytoplankton assemblage and chlorophyll a along the salinity gradient and oxygen zonation were studied in Ulhas Estuary. Oxic condition exist in euhaline region of the estuary that receives oxygenated coastal waters, while, poly-meso-oligohaline region is hypoxic due to the accumulation of voluminous amount of pollutants from industrial effluents, domestic/sewage and agricultural discharges. Additionally, anthropogenically generated nutrients enhanced phytoplankton biomass (chlorophyll a) and their senescence also led to hypoxia. The dominance of diatoms (>70%) was observed in the euhaline-oxic region, while a tremendous decrease in their contribution (18%) was observed in the oligohaline region. Meso to oligohaline region of the estuary is governed by cyanophytes and chlorophytes due to their affinity towards low salinity and high dissolved inorganic nutrients. Carlson's Trophic State Index (TSI) further substantiated the estuary as eutrophic. Additionally, the study could identify the adaptation of cyanophytes and chlorophytes in oxygen deficient water.

Impact of Agricultural Non-Point Source Pollution on River Water Quality: Evidence From China

Identifying the effect of agricultural non-point source pollutants on water quality is very important for water pollution management. This study used NH3N as an indicator to empirically study the influence of fertilizer application on river water quality based on panel data of 46 prefecture-level cities and 18 state-controlled water quality monitoring points through which the main streams of Yangtze River and Yellow River flow from 2004 to 2019. It is found that: (1) An increase in agricultural fertilizer application amount will exacerbate water pollution, and the worsening water quality in the upper watershed and the influence of precipitation will lead to transboundary water pollution in the lower watershed. (2) The amount of fertilizer application and fertilizer application intensity had a threshold effect on river water quality pollution. When the former exceeded the threshold value of 11.496 tons, and the latter exceeded the threshold value of 7.991 ton/km2, the positive effect of fertilizer application on pollutants in rivers was further enhanced. (3) The amount of fertilizer applied had a long-term effect on water quality through a lagged effect, and as the number of lags increased, the accumulative effect of the negative influence gradually rose. Based on the findings of the empirical study, it is proposed that the inter-basin and inter-regional synergy should be formed in the prevention and control of agricultural non-point source pollution, and the overall top-level design of agricultural subsidies and agricultural environmental policies in the areas along the basin should be considered.

Identifying and Aligning Ecosystem Services and Beneficiaries Associated with Best Management Practices in Chesapeake Bay Watershed

Ecosystem restoration may require implementing programs or best management practices (BMPs) in areas that are geographically far from the target ecosystem. Stakeholders in these areas may feel disconnected from the target ecosystem or may not have a clear understanding of local benefits from implemented practices. To achieve widespread participation in restoration efforts, it is important to engage stakeholders located where BMPs need to be implemented to identify and consider their local priorities and impacts. Here, we demonstrate use of a structured decision-making approach to identify ecosystem services associated with BMPs in the Chesapeake Bay watershed and connect them with the priorities of stakeholders they benefit. We follow a four-step approach to define the bounds of the decision context, identify ecosystem services and beneficiaries relevant to that decision context, engage stakeholders to understand priorities, and identify potential metrics and indicators. Our approach highlights the utility of different tools, such as ecosystem service classification systems and the Final Ecosystem Goods and Services (FEGS) Scoping Tool, in engaging stakeholders to identify, communicate, and prioritize ecosystem services. The results demonstrate a method by which to connect large-scale regional restoration efforts, and the managers overseeing such efforts, with the priorities of local communities where programs will be implemented. This work will help Chesapeake Bay restoration partners identify and promote management actions that will provide the most value for communities throughout the watershed, while also benefiting restoration of Chesapeake Bay.

Bacterial Indicators Are Ubiquitous Members of Pelagic Microbiome in Anthropogenically Impacted Coastal Ecosystem

Coastal zones are exposed to various anthropogenic impacts, such as different types of wastewater pollution, e.g., treated wastewater discharges, leakage from sewage systems, and agricultural and urban runoff. These various inputs can introduce allochthonous organic matter and microbes, including pathogens, into the coastal marine environment. The presence of fecal bacterial indicators in the coastal environment is usually monitored using traditional culture-based methods that, however, fail to detect their uncultured representatives. We have conducted a year-around in situ survey of the pelagic microbiome of the dynamic coastal ecosystem, subjected to different anthropogenic pressures to depict the seasonal and spatial dynamics of traditional and alternative fecal bacterial indicators. To provide an insight into the environmental conditions under which bacterial indicators thrive, a suite of environmental factors and bacterial community dynamics were analyzed concurrently. Analyses of 16S rRNA amplicon sequences revealed that the coastal microbiome was primarily structured by seasonal changes regardless of the distance from the wastewater pollution sources. On the other hand, fecal bacterial indicators were not affected by seasons and accounted for up to 34% of the sequence proportion for a given sample. Even more so, traditional fecal indicator bacteria (Enterobacteriaceae) and alternative wastewater-associated bacteria (Lachnospiraceae, Ruminococcaceae, Arcobacteraceae, Pseudomonadaceae and Vibrionaceae) were part of the core coastal microbiome, i.e., present at all sampling stations. Microbial source tracking and Lagrangian particle tracking, which we employed to assess the potential pollution source, revealed the importance of riverine water as a vector for transmission of allochthonous microbes into the marine system. Further phylogenetic analysis showed that the Arcobacteraceae in our data set was affiliated with the pathogenic Arcobacter cryaerophilus, suggesting that a potential exposure risk for bacterial pathogens in anthropogenically impacted coastal zones remains. We emphasize that molecular analyses combined with statistical and oceanographic models may provide new insights for environmental health assessment and reveal the potential source and presence of microbial indicators, which are otherwise overlooked by a cultivation approach.

Water quality and hydraulic performance of biochar amended biofilters for management of agricultural runoff

This research evaluated the effect of biochar amendment rate on nitrogen species and organic carbon removals and hydraulic performance in biofilter columns treating dairy farm runoff. Initial studies compared the performance of sand columns amended with two types of biochar with different specific surface area (SA) and cation exchange capacity (CEC) with an un-amended sand column. The results showed that biochar enhanced N-species removal due to its unique physicochemical properties. In subsequent tests, two biofilter columns with different biochar fractions (20% and 50% by volume) were operated at varying hydraulic loading rates and antecedent dry conditions. Total nitrogen, ammonia, organic nitrogen and organic carbon removals were significantly higher in the column with the higher biochar fraction. The high CEC of biochar increased ammonium retention during the application period, allowing for nitrification during the antecedent dry periods (ADPs) when aerobic conditions developed in the media pores. High biochar SA also resulted in greater retention of DON and DOC by adsorption. A variable saturation flow model of biochar amended biofiltration was developed using HYDRUS-1D software. The model was calibrated using data from conservative tracer and moisture content studies. Model results showed that the high microporous structure of the biochar increases the time needed to reach full saturation, lowers the saturated conductivity and increases the hydraulic retention time in the medium. This calibrated model can be used to design field scale biofilter systems for managing agricultural runoff.

Long-Term Mississippi River Trends Expose Shifts in the River Load Response to Watershed Nutrient Balances Between 1975 and 2017

Excess nutrients transported by the Mississippi River (MR) contribute to hypoxia in the Gulf of Mexico. Nutrient balances are key drivers to river nutrient loads and represent inputs (fertilizer, manure, deposition, wastewater, N-fixation, and weathering) minus outputs (nutrient uptake and removal in harvest, and N emissions). Here, we quantified annual changes in nitrogen (N) and phosphorus (P) river loads and nutrient balances at the MR Outlet and documented that the river load response to watershed nutrient balances shifted between 1975 and 2017. Annual nutrient balances and river loads were positively correlated between 1975 and 1985, but after, a disconnect between both the N and P balances and river loads emerged, and the subsequent river load patterns were different for N versus P. We evaluated the relative impacts of legacy nutrients and other latent factors, for which data were not available, on river nutrient load trends. Our analysis showed that in the case of N, latent factors were potentially just as important in explaining changes in river nutrient loads over time as N balances, and in the case of P, they were even more important. We hypothesized that these factors included implementation of best management practices, changes in watershed buffering capacity, the effects of tile drainage, or increased precipitation. Our analytical approach shows promise for the investigation of drivers of water quality trends that are not well-represented in typical national scale geospatial datasets.

The Chesapeake Bay Program Modeling System: Overview and Recommendations for Future Development

The Chesapeake Bay is the largest, most productive, and most biologically diverse estuary in the continental United States providing crucial habitat and natural resources for culturally and economically important species. Pressures from human population growth and associated development and agricultural intensification have led to excessive nutrient and sediment inputs entering the Bay, negatively affecting the health of the Bay ecosystem and the economic services it provides. The Chesapeake Bay Program (CBP) is a unique program formally created in 1983 as a multi-stakeholder partnership to guide and foster restoration of the Chesapeake Bay and its watershed. Since its inception, the CBP Partnership has been developing, updating, and applying a complex linked modeling system of watershed, airshed, and estuary models as a planning tool to inform strategic management decisions and Bay restoration efforts. This paper provides a description of the 2017 CBP Modeling System and the higher trophic level models developed by the NOAA Chesapeake Bay Office, along with specific recommendations that emerged from a 2018 workshop designed to inform future model development. Recommendations highlight the need for simulation of watershed inputs, conditions, processes, and practices at higher resolution to provide improved information to guide local nutrient and sediment management plans. More explicit and extensive modeling of connectivity between watershed landforms and estuary sub-areas, estuarine hydrodynamics, watershed and estuarine water quality, the estuarine-watershed socioecological system, and living resources will be important to broaden and improve characterization of responses to targeted nutrient and sediment load reductions. Finally, the value and importance of maintaining effective collaborations among jurisdictional managers, scientists, modelers, support staff, and stakeholder communities is emphasized. An open collaborative and transparent process has been a key element of successes to date and is vitally important as the CBP Partnership moves forward with modeling system improvements that help stakeholders evolve new knowledge, improve management strategies, and better communicate outcomes.

Climate-resilient strategies for sustainable management of water resources and agriculture

Warming of the earth is considered as the major adverse effect of climate change along with other abnormalities such as non-availability of water resources, decreased agriculture production, food security, rise in seawater level, glaciers melting, and loss of biodiversity. Over the years, decreased agriculture production and water quality degradation have been observed due to climatic abnormalities. Crop production is highly sensitive to climate. It gets affected by long-term trends in average rainfall and temperature, annual climate variations, shocks during different stages of growth, and extreme weather events. Globally, the areas sown for the major crops of barley, maize, rice, sorghum, soya bean, and wheat have all seen an increase in the percentage of area affected by drought as defined in terms of the Palmer Drought Severity Index since the 1960s, from approximately 5-10% to approximately 15-25%. Increase in temperature will be observed in terms of wheat yield losses - 5.5 ± 4.4% per degree Celsius for the United States, - 9.1 ± 5.4% per degree Celsius for India, and - 7.8 ± 6.3% per degree Celsius for Russia as these countries are more vulnerable to temperature increase. Water management through increasing storage capacity (or rainwater storage), fair policies for water supply and distribution, river health, and watershed management can reduce the negative effects of climate change on water resource availability. Similarly, climate change-resistant crop development, water management in irrigation, adapting climate-smart agriculture approach, and promoting indigenous knowledge can ensure the food security via increasing agricultural yield. Technical intervention can equip the farmers with the scientific analyses of the climatic parameters required for the sustainable agriculture management. These technologies may include application of software, nutrient management, water management practices, instruments for temperature measurement and soil health analysis etc. Holistic efforts of the stakeholders (farmers, local society, academia, scientists, policy makers, NGOs etc.) can provide better results to reduce the risks of climate change on agriculture and water resources as discussed in this paper. Graphical abstract.

Management pathways for the successful reduction of nonpoint source nutrients in coastal ecosystems

Eutrophication remains a threat to coastal habitats and water quality worldwide. The U.S. Clean Water Act resulted in reductions of nutrient loading from point sources but management of nonpoint sources (NPS) of nutrients remains challenging despite efforts over at least three decades. The hydrological factors, best management practices (BMPs) and regulatory mechanisms that target nutrient NPS and improve coastal ecosystem function are poorly understood. We identified three case study sites in the U.S. with sufficient NPS management and monitoring history to quantify changes in estuarine habitat and water quality following BMP implementation and regulation targeting nutrient NPS. Utilizing publicly available data, we compared sites that are geographically distant and hydrologically distinct. We found that BMPs targeting NPS loads from surface waters into Roberts Bay (Florida) and Newport Bay (California) significantly reduced nutrient concentrations and harmful algal blooms within ~20 years. Improvements occurred despite concurrent human population growth within both watersheds. Conversely, we found that the majority of BMPs implemented within the Peconic Estuary (New York) watershed targeted surface waters despite a dominance of nitrogen inputs (97%) from groundwater and atmospheric sources. Declines in habitat and water quality in Peconic Estuary may be due to a failure to control the dominant nutrient sources and the long residence time of nitrogen in groundwater. Compared to surface water, reducing groundwater and atmospheric nutrients face greater technical and financial challenges. Improvements to Peconic Estuary may occur with further reductions in surface water inputs and as nutrients leach out of the groundwater. Although the effectiveness of specific NPS BMPs has been examined at small spatial scales, our study is the first to quantify improvements at a watershed scale. We showed that successful NPS management pathways are those which targeted the dominant sources of nutrients to coastal ecosystems and applied multiple BMPs within watersheds.

Framework of multi-level regionalization schemes based on non-point source pollution to advance the environmental management of small watersheds

Regionalization exerts an important guiding role for sound environmental management, regional development, and schemes toward regionalizing ecological function, involving multiple levels. This paper formulated a framework for a detailed regionalization approach using the Ashi River watershed, China, as case study. Human activities, especially agriculture non-point source pollution (ANPS) and social factors, were identified as main factors. The results indicated that (1) the export coefficient model (ECM) can be used to determine ANPS loads in the watershed as well as total nitrogen and total phosphorus loads. (2) The minimum cumulative resistance model (MCR) showed that the middle and lower reaches had high risk for ANPS occurrence. (3) Based on the identified key factors, the watershed was divided into level IV and combined with existing level III using cluster analysis. Corresponding management countermeasures were proposed. This provides a scientific basis for pollution control planning and for management measures.

A three-dimensional mechanistic model of Prorocentrum minimum blooms in eutrophic Chesapeake Bay

Planktonic Prorocentrum, common harmful dinoflagellate, are increasing in frequency, duration, and magnitude globally, as exemplified by the number of blooms of P. minimum in Chesapeake Bay that have nearly doubled over the past 3 decades. Although the dynamics of transport and seasonal occurrence of this species have been previously described, it has been challenging to predict the timing and location of P. minimum blooms in Chesapeake Bay. We developed a new three-dimensional mechanistic model of this species that integrates physics, nutrient cycling and plankton physiology and embedded it within a coupled hydrodynamic-biogeochemical model originally developed for simulating water quality in eutrophic estuarine and coastal waters. Hindcast simulations reproduced the observed time series and spatial distribution of cell density, in particular capturing well its peak in May in the mid-to-upper part of the estuary. Timing and duration of the blooms were mostly determined by the temperature-dependent growth function, while mortality due to grazing and respiration played a minor role. The model also reproduced the pattern of overwintering populations, which are located in bottom waters of the lower Bay, and are transported upstream in spring by estuarine flow. Blooms develop in the mid-upper parts of the estuary when these transported cells encounter high nutrient concentrations from the Susquehanna River and favorable light conditions. Diagnostic analysis and model-sensitivity experiments of nutrient conditions showed that high nitrogen:phosphorus conditions favor bloom development. The model also captured the observed interannual variations in the magnitude and spatial distribution of P. minimum blooms.

Elevated temperature inhibits Mycobacterium shottsii infection and Mycobacterium pseudoshottsii disease in striped bass Morone saxatilis

Mycobacteriosis occurs with high prevalence in the wild striped bass Morone saxatilis of Chesapeake Bay, USA. Etiologic agents of mycobacteriosis in this system are dominated by Mycobacterium pseudoshottsii and Mycobacterium shottsii, both members of the M. ulcerans/M. marinum clade of mycobacteria. Striped bass occupying Chesapeake Bay during summer months where water temperatures regularly approach and occasionally exceed 30°C are thought to be near their thermal maximum, a condition hypothesized to drive high levels of disease and increased natural mortality due to temperature stress. M. shottsii and M. pseudoshottsii, however, do not grow or grow inconsistently at 30°C on artificial medium, potentially countering this hypothesis. In this work, we examine the effects of temperature (20, 25, and 30°C) on progression of experimental infections with M. shottsii and M. pseudoshottsii in striped bass. Rather than exacerbation of disease, increasing temperature resulted in attenuated bacterial density increase in the spleen and reduced pathology in the spleen and mesenteries of M. pseudoshottsii infected fish, and reduced bacterial densities in the spleen of M. shottsii infected fish. These findings indicate that M. pseudoshottsii and M. shottsii infections in Chesapeake Bay striped bass may be limited by the thermal tolerance of these mycobacteria, and that maximal disease progression may in fact occur at lower water temperatures.

Examining sources and pathways of phosphorus transfer in a ditch-drained field

Understanding the processes that mobilize and transport dissolved phosphorus (P) during storms is critical to managing P in flat landscapes with open ditch drainage and legacy soil P. In this study, we used routine baseflow monitoring and intensive storm sampling at a ditch-drained site on Maryland's Lower Eastern Shore (July 2017-September 2018) to assess whether concentration-discharge (C-Q) relationships and chemical and isotopic hydrograph separation could provide insight into the processes that mobilize and transport dissolved P in ditch drainage. Using a segmented regression model, we determined that long-term C-Q relationships for dissolved P differed above and below a discharge threshold of 6.4 L s^-1 . Intensive storm sampling revealed that small storms (n = 3) occurring at or below the discharge threshold generally exhibited complex hysteresis and dissolved P dilution patterns that were consistent with deeper (>122 cm) groundwater inputs with low dissolved P concentrations (0.04 mg L^-1 ). In contrast, large storms occurring well above the discharge threshold (n = 4) induced rising water tables and preferential flow pathways that most likely tapped dissolved P-enriched shallow (<20 cm) soil waters (0.89 mg L^-1 ), producing consistent clockwise hysteresis and dissolved P flushing patterns. Notably, chemical and isotope hydrograph separation during two of the largest storms revealed significant event water fractions (59-68%) that strongly suggested a role for the rapid delivery of dissolved P via preferential flow pathways. Findings highlight the need to mitigate vertical P stratification as a means for reducing dissolved P flushing from ditch-drained landscapes with legacy P.

Atmospheric nitrogen deposition in the Chesapeake Bay watershed: A history of change

The Chesapeake Bay watershed has been the focus of pioneering studies of the role of atmospheric nitrogen (N) deposition as a nutrient source and driver of estuarine trophic status. Here, we review the history and evolution of scientific investigations of the role of atmospheric N deposition, examine trends from wet and dry deposition networks, and present century-long (1950-2050) atmospheric N deposition estimates. Early investigations demonstrated the importance of atmospheric deposition as an N source to the Bay, providing 25%-40% among all major N sources. These early studies led to the unprecedented inclusion of targeted decreases in atmospheric N deposition as part of the multi-stakeholder effort to reduce N loads to the Bay. Emissions of nitrogen oxides (NO_x) and deposition of wet nitrate, oxidized dry N, and dry ammonium ( NH 4 + ) sharply and synchronously declined by 60%-73% during 1995-2019. These decreases largely resulted from implementation of Title IV of the 1990 Clean Air Act Amendments, which began in 1995. Wet NH 4 + deposition shows no significant trend during this period. The century-long atmospheric N deposition estimates indicate an increase in total atmospheric N deposition in the Chesapeake watershed from 1950 to a peak of ~15 kg N/ha/yr in 1979, trailed by a slight decline of <10% through the mid-1990s, and followed by a sharp decline of about 40% thereafter through 2019. An additional 21% decline in atmospheric N deposition is projected from 2015 to 2050. A comparison of the Potomac River and James River watersheds indicates higher atmospheric N deposition in the Potomac, likely resulting from greater emissions from higher proportions of agricultural and urban land in this basin. Atmospheric N deposition rose from 30% among all N sources to the Chesapeake Bay watershed in 1950 to a peak of 40% in 1973, and a decline to 28% by 2015. These data highlight the important role of atmospheric N deposition in the Chesapeake Bay watershed and present a potential opportunity for decreases in deposition to contribute to further reducing N loads and improving the trophic status of tidal waters.

Messaging on Slow Impacts: Applying Lessons Learned from Climate Change Communication to Catalyze and Improve Marine Nutrient Communication

Building publics' understanding about human-environmental causes and impacts of nutrient pollution is difficult due to the diverse sources and, at times, extended timescales of increasing inputs, consequences to ecosystems, and recovery after remediation. Communicating environmental problems with "slow impacts" has long been a challenge for scientists, public health officials, and science communicators, as the time delay for subsequent consequences to become evident dilutes the sense of urgency to act. Fortunately, scientific research and practice in the field of climate change communication has begun to identify best practices to address these challenges. Climate change demonstrates a delay between environmental stressor and impact, and recommended practices for climate change communication illustrate how to explain and motivate action around this complex environmental problem. Climate change communication research provides scientific understanding of how people evaluate risk and scientific information about climate change. We used a qualitative coding approach to review the science communication and climate change communication literature to identify approaches that could be used for nutrients and how they could be applied. Recognizing the differences between climate change and impacts of nutrient pollution, we also explore how environmental problems with delayed impacts demand nuanced strategies for effective communication and public engagement. Applying generalizable approaches to successfully communicate the slow impacts related to nutrient pollution across geographic contexts will help build publics' understanding and urgency to act on comprehensive management of nutrient pollution, thereby increasing protection of coastal and marine environments.

Nutrient limitation of phytoplankton in Chesapeake Bay: Development of an empirical approach for water-quality management

Understanding the temporal and spatial roles of nutrient limitation on phytoplankton growth is necessary for developing successful management strategies. Chesapeake Bay has well-documented seasonal and spatial variations in nutrient limitation, but it remains unknown whether these patterns of nutrient limitation have changed in response to nutrient management efforts. We analyzed historical data from nutrient bioassay experiments (1992-2002) and data from long-term, fixed-site water-quality monitoring program (1990-2017) to develop empirical approaches for predicting nutrient limitation in the surface waters of the mainstem Bay. Results from classification and regression trees (CART) matched the seasonal and spatial patterns of bioassay-based nutrient limitation in the 1992-2002 period much better than two simpler, non-statistical approaches. An ensemble approach of three selected CART models satisfactorily reproduced the bioassay-based results (classification rate = 99%). This empirical approach can be used to characterize nutrient limitation from long-term water-quality monitoring data on much broader geographic and temporal scales than would be feasible using bioassays, providing a new tool for informing water-quality management. Results from our application of the approach to 21 tidal monitoring stations for the period of 2007-2017 showed modest changes in nutrient limitation patterns, with expanded areas of nitrogen-limitation and contracted areas of nutrient saturation (i.e., not limited by nitrogen or phosphorus). These changes imply that long-term reductions in nitrogen load have led to expanded areas with nutrient-limited phytoplankton growth in the Bay, reflecting long-term water-quality improvements in the context of nutrient enrichment. However, nutrient limitation patterns remain unchanged in the majority of the mainstem, suggesting that nutrient loads should be further reduced to achieve a less nutrient-saturated ecosystem.

Seasonal and temporal factors leading to urea-nitrogen accumulation in surface waters of agricultural drainage ditches

Urea-nitrogen (N) is commonly applied to crop fields, yet it is not routinely monitored despite its association with reduced water quality and its ability to increase toxicity of certain phytoplankton species. The purpose of this work was to characterize temporal fluctuations in urea-N concentrations and associated environmental conditions to infer sources of urea-N in agricultural drainage ditches. Physicochemical properties and N forms in ditch waters were measured weekly during the growing seasons of 2015-2018. Fertilizer application was only associated with spring peaks of urea-N concentrations in ditches next to cornfields, whereas summer peaks in ditches adjacent to corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] fields were not associated with fertilizer applications. Environmental conditions of warmer temperatures, lower dissolved oxygen concentrations, and lower redox potentials were correlated with higher urea-N concentrations. In 2018, peaks of urea-N and ammonium-N during the summer co-occurred with peaks of dissolved organic N and total dissolved N, suggesting they might be associated with the breakdown of organic matter and with the turnover of the organic N pool. Although the highest urea-N concentrations occurred when ditch surface waters were hydrologically disconnected from nearby streams, heavy rainfalls can potentially flush accumulated urea-N into coastal waters, where it may affect algal bloom toxicity. Therefore, implementation of available drainage ditch management practices is recommended, but these strategies need to be optimized for targeting periods with high rainfall that coincide with fertilizer additions as well as for periods with low rainfall that promote stagnant water conditions.

Otolith fingerprints reveals potential pollution exposure of newly settled juvenile Sparus aurata

Coastal ecosystems are increasingly threatened by a wide range of human activities. Fish otolith chemistry, by creating a unique specific signature, can be used as a natural tag for determining life stage dispersal, spatial connectivity and population structure. In this study, we tested whether differences in otolith composition among juveniles of gilthead sea bream, Sparus aurata, could enable their proper allocation to polluted areas based on higher concentrations of elements related to contaminants. Otoliths were embedded, sectioned and analysed by LA-ICP-MS in line scan mode. Multivariate analysis confirmed clear separation between sites and elements. Samples from the site under the strongest anthropogenic impact from industrial and agricultural river input were characterized by higher values of Pb/Ca and Zn/Ca. However, these relatively low values likely do not have a negative effect on S. aurata recruitment, though they could serve for identifying the contribution of polluted nurseries to stock dynamics.

Riparian buffer effectiveness as a function of buffer design and input loads

Although many agricultural watersheds rely heavily on riparian buffer adoption to meet water quality goals, design and management constraints in current policies create adoption barriers. Based on focus group feedback, we developed a flexible buffer design paradigm that varies buffer width, vegetation, and harvesting. Sixteen years of daily-scale nutrient and sediment loads simulated with the Soil and Water Assessment Tool (SWAT) were coupled to the three-zone Riparian Ecosystem Management Model (REMM) to compare the effectiveness of traditional, policy-based buffer designs with designs that are more flexible and integrate features important to local farmers. Buffer designs included (i) 10 m grass, (ii) 15 m grass, (iii) 15 m deciduous trees, (iv) 30 m grass and trees, (v) 30 m grass and trees with trees harvested every 3 yr, and (vi) 30 m grass and trees with grass harvested every year. Allowing harvesting in one zone of the buffer vegetation (either trees or grasses) minimally affected water quality, with annual average percent reductions differing by <5% (p > .05; 76-78% for total nitrogen [TN], 51-55% for total phosphorus [TP], and 68% for sediment). Under the highest input loading conditions, buffers with lower removal efficiencies removed more total mass than did buffers with high removal efficiencies. Thus, by focusing on mass reduction in addition to percent reduction, watershed-wide buffer implementation may be better targeted to TN, TP, and sediment reduced. These findings have important implications for informing flexible buffer design policies and enhanced placement of buffers in watersheds impaired by nutrient and sediment.

Demonstrating efficacy of rural land management actions to improve water quality - How can we quantify what actions have been done?

Despite several decades of encouraging land management actions to improve water quality on rural land, we are still struggling to accurately quantify what management actions have been implemented, where these actions have been used and the intensity of implementation. This is largely because standardised approaches to recording and reporting of land management actions have not been established, resulting in a lack of robust information that can be used to determine the effectiveness and longevity of these actions at a catchment or larger scale. Better information on the effectiveness of different land management actions will provide land managers with more certainty that their investments in land management actions will make a difference. We reviewed a total of 91 global publications and proceedings between 1989 and 2019 which assessed the complexities related to recording and reporting sustainable land use actions with a focus on freshwater ecosystems in rural areas in the developed world. We then summarised these complexities (i.e., temporal and spatial lag-effects, confidentiality issues, lack of data robustness) and mined the literature about methodologies on how actions can be measured, how to address the challenges with doing this and recommended a suite of indicators of land management actions that could be standardised and widely used to improve water quality. Our review of literature identified numerous sources describing land management actions, but little information on standardised indicators of location, scale and intensity of the most common actions. Some common actions are measured using a wide variety of incompatible approaches (e.g., riparian management is often indicated by length of fencing, width of vegetated buffer strips, proportion of the catchment with stock exclusion), whereas other indicators of land management action are at such a high level (e.g., costs) that they do not provide information on the actions used. The scale/intensity of land management efforts is often not reported spatially with information typically restricted to small scales such as single point location information, making it difficult, if not impossible to determine the scale of actions within a catchment relative to a given water quality monitoring site.

Phosphorus speciation during anaerobic digestion and subsequent solid/liquid separation

This study aims to investigate the effect of anaerobic digestion (AD) on P species and how the different species are distributed in the digestate and digestate fractions, i.e. liquid and solid fractions. To do so, six full scale AD plants were used in this work and representative biomass samples were collected for investigation. P fractionation proceeded by adopting fractionation protocols consisting in step-by-step extraction with different solvents, (i.e. NaHCO₃, HCl and NaOH-EDTA). Subsequently P species in the different fractions were identified by using ³¹PNMR. On average, AD did not substantially affect P speciation that depended on the P-fraction content of feeds. A high NaHCO₃ fraction content in the ingestate determined, also, a high content of this fraction in the digestate, with consequently lower contents of both P-HCl and P-NaOH-EDTA, i.e. digestate P-fraction contents represented an inheritance of P speciation in the ingestate. A feed effect was observed in single plants. Highest pig/cow slurry content in the feeds seemed to decrease readily soluble P (extracted with NaHCO₃) content and increased P associated with both organic matter and amorphous Fe/Al in the digestate. Again, using a large amount of digestate in the feed increased P-soluble content in the digestate. ³¹P NMR analyses revealed that inorganic P compounds dominated the spectra of all biomasses and fractions, with orthophosphate as the predominant species. When present, organic phosphorus compounds were typically represented by monophosphate esters, DNA and phospholipids, with a predominance of monophosphate esters.

Waste nutrients from U.S. animal feeding operations: Regulations are inconsistent across states and inadequately assess nutrient export risk

Livestock production in the United States has been transformed over the past several decades, largely as a result of widespread development of industrial-scale mass production facilities, termed Animal Feeding Operations (AFOs). These facilities generate massive amounts of animal waste that can concentrate in small areas. Animal wastes from AFOs have led to high levels of nutrients and other pollutants in nearby surface waters, as well as groundwater. The environmental problems associated with these disposal practices have led to federal and state modifications to the rules and regulations governing waste practices. We summarize the federal guidelines for AFO nutrient management, focusing on swine, and compare the regulations of four AFO-rich states in different regions of the USA. Furthermore, we discuss inconsistencies among regulations and regulatory gaps, and identify issues with waste nutrient management practices that lead to environmental degradation in watersheds hosting AFOs. Finally, we address these shortcomings and the need to implement policy updates that would alleviate some of these environmental and human concerns.

Factors driving nutrient trends in streams of the Chesapeake Bay watershed

Despite decades of effort toward reducing nitrogen and phosphorus flux to Chesapeake Bay, water-quality and ecological responses in surface waters have been mixed. Recent research, however, provides useful insight into multiple factors complicating the understanding of nutrient trends in bay tributaries, which we review in this paper, as we approach a 2025 total maximum daily load (TMDL) management deadline. Improvements in water quality in many streams are attributable to management actions that reduced point sources and atmospheric nitrogen deposition and to changes in climate. Nutrient reductions expected from management actions, however, have not been fully realized in watershed streams. Nitrogen from urban nonpoint sources has declined, although water-quality responses to urbanization in individual streams vary depending on predevelopment land use. Evolving agriculture, the largest watershed source of nutrients, has likely contributed to local nutrient trends but has not affected substantial changes in flux to the bay. Changing average nitrogen yields from farmland underlain by carbonate rocks, however, may suggest future trends in other areas under similar management, climatic, or other influences, although drivers of these changes remain unclear. Regardless of upstream trends, phosphorus flux to the bay from its largest tributary has increased due to sediment infill in the Conowingo Reservoir. In general, recent research emphasizes the utility of input reductions over attempts to manage nutrient fate and transport at limiting nutrients in surface waters. Ongoing research opportunities include evaluating effects of climate change and conservation practices over time and space and developing tools to disentangle and evaluate multiple influences on regional water quality.

A scientometric review of the research on the impacts of climate change on water quality during 1998-2018

Research on the impacts of climate change on water quality helps to better formulate water quality strategies under the challenge of an uncertain future, which is critical for human survival and development. As a result, in recent years, there has been growing attention given to research in the field, and the attention has led to an increasing number of publications, which is why a systematic literature review on this topic has been proposed in the current paper. This study reviewed 2998 related articles extracted from the Science Citation Index-Expanded (SCI-E) database from 1998 to 2018 to analyse and visualize historical trend evolution, current research hotspots, and promising ideas for future research by combining a traditional literature review, bibliometric analysis, and scientific knowledge mapping. The results revealed that the impacts of climate change on water quality mainly included the aggravation of eutrophication, changes in the flow, hydrological and thermal conditions, and the destruction of ecosystems and biodiversity. Further exploration of the influence mechanism of climate change on cyanobacteria is an emerging research topic. Additionally, the water quality conditions of shallow lakes and drinking water are promising future research objects. In the context of climate change, the general rules of water quality management and the scientific planning of land use are of great significance and need to be further studied. This study provides a practical and valuable reference for researchers to help with the selection of future research topics, which may contribute to further development in this field.

Headwater stream condition and nutrient runoff: Relating SWAT to empirical ecological measures in an agricultural watershed in Pennsylvania

Managing nonpoint sources of nutrients and sediments is the primary challenge for improving conditions in the Susquehanna-Chesapeake basin. Aquatic macroinvertebrates are widely used indicators of stream ecological integrity, but the relationship between nutrient runoff and macroinvertebrate response remains indistinct. Logistical and financial hurdles hinder collection of high-resolution empirical nutrient data, but landscape-based models like the Soil and Water Assessment Tool (SWAT) offer a more practical approach. Nutrient runoff was simulated with SWAT for a small, upland, agricultural Pennsylvania watershed. Three levels of ecological assessment were used to interpret SWAT results. Macroinvertebrate communities (intensive) were sampled at 14 sites and described using an Index of Biotic Integrity (IBI). Biological integrity was moderately degraded in many reaches. The Stream-Wetland-Riparian (SWR) Index (rapid) and landscape metrics (remote) also indicated prevalent agricultural stressors. Baseflow nitrate grab samples, collected once per season, showed no significant relationship with IBI score. Thirty spatiotemporal scales of nutrient data were extracted from SWAT for phosphorus, nitrate, and organic nitrogen. Best subsets regression was performed on IBI scores using SWAT, land cover, and SWR variables. Results were significant (p < .001) with high R² values (84.8 and 86.2), signifying a negative relationship between instream nutrient concentration and IBI score. This study demonstrates the viability of SWAT as an alternative to in-field nutrient sampling, the value of spatiotemporal scale in model outputs, and the importance of site condition variables in relating nutrients to stream ecological health.

Vertical water renewal in a large estuary and implications for water quality

Estuaries are a special transition zone subject to both riverine and marine processes, where environmental issues, e.g. water pollution, eutrophication and hypoxia, have become an increasing cause of concern in recent decades. The vertical transport of water and material is an intrinsic process in estuarine environments, with the atmosphere and seabed being the upper and lower boundaries. However, vertical water renewal in estuaries is not fully understood despite its significance to the estuarine environment being widely recognized. In the present study, the vertical water renewal process in a large estuary is investigated using the concept of water age. A three-dimensional water age model is built based on a hydrodynamic model, in which the age of a water parcel is defined as the time interval since it last touched the air-water interface, and thus indicates the renewal duration from the free surface. Water renewal durations, especially when relatively long, can provide insight into environmental and water quality issues, e.g. a low dissolved oxygen (DO), that can have a significant impact on ecosystem functioning. Results showed that the water age in the Pearl River Estuary (PRE) was characterized by significant spatial distributions and seasonal variations, which depends heavily on the water density stratification, as indicated by the Richardson number. During the wet season, the bottom water age was large at the lower reach of the estuary, up to 8 days, whereas the maximum bottom age during the dry season was ~1 day at the upper reach. Based on the quantification of vertical renewal, a new approach was proposed, and used to successfully evaluating DO depletion. The data and method would benefit for future environmental management, eco-biological restoration and related policy-making, especially when oxygen-based pollution is considered.

Modeling and measurements of ammonia from poultry operations: Their emissions, transport, and deposition in the Chesapeake Bay

The goal of this study is to determine how much ammonia/nitrogen is being deposited to the Maryland Eastern Shore land and the Chesapeake Bay from poultry operations on Maryland's Eastern Shore. We simulated the fate of ammonia/nitrogen emitted (using emission factors from the U.S. EPA in conjunction with Carnegie-Mellon University) from 603 poultry facilities using the air quality model, AERMOD. The model domain was approximately 134 km by 230 km (and covers the full land area of Maryland's Eastern Shore), with a horizontal resolution of 2 km by 2 km. Ammonia concentration observations were made at 23 sites across Maryland's Eastern Shore during two periods (September and October 2017) in order to calibrate the model. An ammonia deposition velocity of 2.4 cm/sec was selected based on the sensitivity analysis of results for the simulation of a large poultry facility, and this value fell within the range of measurements reported in the scientific literature downwind of Concentrated Animal Feeding Operations (CAFOs). The ammonia deposition velocity of 2.4 cm/s leads to an estimated total annual ammonia deposition of 11,100 Megagrams/year (10,600 Mg/yr deposition to land, and 508 Mg/yr deposition to water (1 Mg = 1,000,000 g = 1.1023 US Tons)). In addition, model simulations indicate that ~72.4% of ammonia emissions from poultry animal feeding operations would be deposited within the modeling domain. However, this deposited ammonia/nitrogen may be transported through waterways from the land mass and ground water to the Chesapeake Bay. A comprehensive sensitivity analysis of the assumed ammonia deposition velocity (ranging from 0.15 to 3.0 cm/s) on estimated ammonia annual deposition is provided. Using the lower limit of an ammonia deposition velocity of 0.15 cm/s gives much smaller estimated total annual ammonia deposition of 2,040 Mg/yr (1,880 Mg/yr deposition to land and 163 Mg/yr deposition to water).

Combining field phosphorus runoff risk assessments with whole-farm phosphorus balances to guide manure management decisions

Phosphorus (P) loss from agricultural fields contributes to water quality degradation. A phosphorus index (PI) is a tool that scores fields based on P loss potential. Recently, a new transport × best or beneficial management practice (BMP) approach was proposed for the New York PI (NY-PI), which first scores fields using landscape-based transport factors (raw scores) and then offers various BMPs to reduce the score (i.e., risk of P transport). The final score is assigned a management implication (N needs based, P removal based, or zero P application), taking into account field-specific soil-test P (STP) and the farm's whole-farm P balance. With farmer and nutrient management planner input and data on field-specific transport factors and whole-farm P balances of 18 New York dairy farms, we set coefficients for transport factors, BMPs related to P application, and STP limits and determined the impact of implementation of the new NY-PI on manure management options. Based on raw scores, the proposed NY-PI initially limited manure application to 51% of the total cropland area of the participating farms (28% N-based, 23% P-based). Implementation of BMPs (i.e., changing the method and ground cover or timing of P application) allowed 43-98% of the land area to receive manure at N-based rates. For farms with whole-farm P balances within the feasible limits set for New York, an additional 0-50% of the land base was classified as N-based management, depending on BMP selection. These results show the ability of the new NY-PI to limit P applications on fields with high transport risk while incentivizing adoption of BMPs and improvements in whole-farm P management.

Elucidation of soil phosphorus speciation in mid-Atlantic soils using synchrotron-based microspectroscopic techniques

Phosphorus deficiency and excess are concomitant problems in agricultural soils of the mid-Atlantic region. A fundamental understanding of soil P speciation is essential to assess P fate and transport in these soils. Current methods for soil P speciation often rely on sequential chemical extractions, which can introduce artifacts during analysis. To overcome limitations of current methods, this study evaluated synchrotron-based micro-focused X-ray fluorescence (µ-XRF) and X-ray absorption near-edge spectroscopy (µ-XANES) techniques to assess soil P speciation in agricultural soils collected from the mid-Atlantic region of the United States. Three soils with varying chemical and physical properties were analyzed with µ-XRF maps collected at high (12,000 eV) and tender (2240 eV) energies to evaluate colocation of P with Fe, Al, Ca, and Si in soil samples, and µ-XANES spectra were collected at the P K-edge for P hotspots. Combined µ-XRF and µ-XANES analysis was useful for identifying Ca phosphate, Fe phosphate, Al-sorbed P, and Fe-sorbed P species in heterogeneous soil samples. X-ray fluorescence maps were valuable to distinguish Al-oxide sorbed P from Fe-oxide sorbed P species. A low signal-to-noise ratio often limited µ-XANES data collection in regions with diffuse, low concentrations of P. Therefore, some P species may not have been detected during analysis. Even with varying degrees of self-absorption and signal-to-noise ratios in µ-XANES spectra, important inferences regarding P speciation in mid-Atlantic soils were made. This study highlights the potential of µ-XANES analysis for use in environmental and agricultural sciences to provide insights into P fate and transport in soils.

Effects of River Hydrology and Physicochemistry on Anchovy Abundance and Cymothoid Isopod Parasitism

The flow regime of a river is an important driver of many ecosystem components. However, few studies explore how differences in flow rates and water chemistry can influence communities of parasites and their hosts. Here, we investigate the impact of dissolved oxygen, pH, salinity, water temperature, and river flow on the abundance and prevalence of cymothoid isopod parasitism (Lironeca ovalis) of the Bay Anchovy (Anchoa mitchilli) in the Alafia and Hillsborough rivers of Tampa Bay (Florida). We also explore seasonality by comparing monthly samples preserved throughout 2005-2007. Although both the Alafia and Hillsborough rivers had similar average water temperatures and salinity, and similar wet and dry season cycles, the upstream damming of the Hillsborough River had numerous negative effects on water flow rate, dissolved oxygen content, and acidity. This disruption in water quality corresponded with a lower abundance of anchovy hosts, fewer free-swimming cymothoids, and low prevalence of anchovy parasitism. Anchovies were much more abundant in the Alafia River, but flow negatively affected abundance-a negative effect that could be mitigated by positive changes in water temperature, salinity, and pH. Flow rates also negatively affected free-swimming cymothoid abundance; however, water flow was less important in predicting their parasitism of anchovies. In Alafia, fewer anchovies were parasitized when dissolved oxygen was high and water acidity was low, but more were parasitized during the wet season. These findings corroborate predictions that flow can moderate habitat stability and complexity which, in turn, can impact opportunities for parasitism of host communities.

Phosphorus and the Chesapeake Bay: Lingering Issues and Emerging Concerns for Agriculture

Hennig Brandt's discovery of phosphorus (P) occurred during the early European colonization of the Chesapeake Bay region. Today, P, an essential nutrient on land and water alike, is one of the principal threats to the health of the bay. Despite widespread implementation of best management practices across the Chesapeake Bay watershed following the implementation in 2010 of a total maximum daily load (TMDL) to improve the health of the bay, P load reductions across the bay's 166,000-km watershed have been uneven, and dissolved P loads have increased in a number of the bay's tributaries. As the midpoint of the 15-yr TMDL process has now passed, some of the more stubborn sources of P must now be tackled. For nonpoint agricultural sources, strategies that not only address particulate P but also mitigate dissolved P losses are essential. Lingering concerns include legacy P stored in soils and reservoir sediments, mitigation of P in artificial drainage and stormwater from hotspots and converted farmland, manure management and animal heavy use areas, and critical source areas of P in agricultural landscapes. While opportunities exist to curtail transport of all forms of P, greater attention is required toward adapting P management to new hydrologic regimes and transport pathways imposed by climate change.

Modelling the influence of environmental parameters over marine planktonic microbial communities using artificial neural networks

Guanabara Bay is a tropical estuarine ecosystem that receives massive anthropogenic impacts from the metropolitan region of Rio de Janeiro. This ecosystem suffers from an ongoing eutrophication process that has been shown to promote the emergence of potentially pathogenic bacteria, giving rise to public health concerns. Although previous studies have investigated how environmental parameters influence the microbial community of Guanabara Bay, they often have been limited to small spatial and temporal gradients and have not been integrated into predictive mathematical models. Our objective was to fill this knowledge gap by building models that could predict how temperature, salinity, phosphorus, nitrogen and transparency work together to regulate the abundance of bacteria, chlorophyll and Vibrio (a potential human pathogen) in Guanabara Bay. To that end, we built artificial neural networks to model the associations between these variables. These networks were carefully validated to ensure that they could provide accurate predictions without biases or overfitting. The estimated models displayed high predictive capacity (Pearson correlation coefficients ≥0.67 and root mean square error ≤ 0.55). Our findings showed that temperature and salinity were often the most important factors regulating the abundance of bacteria, chlorophyll and Vibrio (absolute importance ≥5) and that each of these has a unique level of dependence on nitrogen and phosphorus for their growth. These models allowed us to estimate the Guanabara Bay microbiome's response to changes in environmental conditions, which allowed us to propose strategies for the management and remediation of Guanabara Bay.

Evaluating Management Implications of the New York Phosphorus Index with Farm Field Information

Phosphorus (P) loss from agricultural fields can contribute to water quality degradation. The current New York P index (NY-PI) scores fields on the basis of P sources and field characteristics that reflect risk of P transport (a source × transport approach). Recently, a transport × best management practice (BMP) approach was proposed, which first scores fields using landscape-driven transport factors and then offers various BMPs to reduce the score (i.e., risk of P transport). To analyze the score distribution of the current NY-PI and the incentivizing potential of the proposed structure, a database of 33,327 agricultural fields in New York was assembled in collaboration with nutrient management planners and farmers. Under the current NY-PI, no additional P could be applied to 2% of the fields, while for 3% the application rates should not exceed annual crop P removal. Flow distance (field to stream) was a major driver for NY-PI scores. The current NY-PI relies heavily on soil test P to assess runoff risk, allowing some low-P fields to receive manure independent of transport risk. A scenario evaluation showed that the proposed NY-PI limits P application on fields with high transport risk while simultaneously incentivizing adoption of BMPs in such areas. In the absence of farm-level water quality data, a farm field database can help set P index coefficients and assess implications of a new P index. This study emphasizes the value of involving stakeholders in assessing nutrient management tools, as well as the importance of using an incentive-driven approach for protecting water resources.

Ocean warming along temperate western boundaries of the Northern Hemisphere promotes an expansion of Cochlodinium polykrikoides blooms

Since the early 1990s, ocean temperatures have increased and blooms of the icthyotoxic dinoflagellate Cochlodinium polykrikoides (a.k.a. Margalefidinium polykrikoides) have become more widespread across the Northern Hemisphere. This study used high-resolution (1-30 km), satellite-based sea surface temperature records since 1982 to model trends in growth and bloom season length for strains of C. polykrikoides inhabiting North American and East Asian coastlines to understand how warming has altered blooms in these regions. Methods provided approximately 180× greater spatial resolution than previous studies of the impacts of warming on harmful algae, providing novel insight into near shore, coastal environments. Along the US East Coast, significant increases in potential growth rates and bloom season length for North American ribotypes were observed with bloom-favourable conditions becoming established earlier and persisting longer from Chesapeake Bay through Cape Cod, areas where blooms have become newly established and/or intensified this century. Within the Sea of Japan, modelled mean potential growth rates and bloom season length of East Asian ribotypes displayed a significant positive correlation with rising sea surface temperatures since 1982, a period during which observed maximal cell densities of C. polykrikoides blooms have significantly increased. Results suggest that warming has contributed, in part, to altering the phenology of C. polykrikoides populations, potentially expanding its realized niche in temperate zones of the Northern Hemisphere.

Identification of Phosphorus Sources in a Watershed Using a Phosphate Oxygen Isoscape Approach

Identifying nonpoint phosphorus (P) sources in a watershed is essential for addressing cultural eutrophication and for proposing best-management solutions. The oxygen isotope ratio of phosphate (δ¹⁸O_PO4) can shed light on P sources and P cycling in ecosystems. This is the first assessment of the δ¹⁸O_PO4 distribution in a whole catchment, namely, the Yasu River Watershed in Japan. The observed δ¹⁸O_PO4 values in the river water varied spatially from 10.3‰ to 17.6‰. To identify P sources in the watershed, we used an isoscape approach involving a multiple-linear-regression model based on land use and lithological types. We constructed two isoscape models, one using data only from the whole watershed and the other using data from the small tributaries. The model results explain 69% and 96% of the spatial variation in the river water δ¹⁸O_PO4. The lower R² value for the whole watershed model is attributed to the relatively large travel time for P in the main stream of the lower catchment that can result in cumulative biological P recycling. Isoscape maps and a correlation analysis reveal the relative importance of P loading from paddy fields and bedrock. This work demonstrates the utility of δ¹⁸O_PO4 isoscape models for assessing nonpoint P sources in watershed ecosystems.

Halloysite Nanotubes as Adsorptive Material for Phosphate Removal from Aqueous Solution

In this study, we were aiming at testing halloysite nanotubes as an efficient adsorbent for the removal of phosphate from agricultural runoff. Adsorption of phosphate onto powder and granular form of halloysite nanotubes has been examined by using the classical batch method and diffusion experiments at room temperature. Different forms of halloysite nanotubes were investigated to explore the effect of structure on the adsorption of phosphate. The maximum adsorption efficiency was obtained for powder halloysite nanotubes (79.5%) and granular form (94.7%). It is believed that the pore space of the granular halloysite nanotubes accommodates phosphorus in addition to physico-chemically bound phosphate at surfaces. The pseudo-first order and pseudo-second order model fitted well the experimental kinetic data for both powder and granular form of halloysite nanotubes. The fit of the Freundlich isotherm model was superior as compared with the Langmuir approach, implying that the halloysite nanotubes are heterogeneous because of multiple surface groups and different pore structures. The two forms of halloysite nanotube tested have the abundant potential for removal of phosphate from agriculture runoff. Additional investigations at the pilot scale are, however, required to draw definite conclusions.

Leveraging Big Data Towards Functionally-Based, Catchment Scale Restoration Prioritization

The persistence of freshwater degradation has necessitated the growth of an expansive stream and wetland restoration industry, yet restoration prioritization at broad spatial extents is still limited and ad-hoc restoration prevails. The River Basin Restoration Prioritization tool has been developed to incorporate vetted, distributed data models into a catchment scale restoration prioritization framework. Catchment baseline condition and potential improvement with restoration activity is calculated for all National Hydrography Dataset stream reaches and catchments in North Carolina and compared to other catchments within the river subbasin to assess where restoration efforts may best be focused. Hydrologic, water quality, and aquatic habitat quality conditions are assessed with peak flood flow, nitrogen and phosphorus loading, and aquatic species distribution models. The modular nature of the tool leaves ample opportunity for future incorporation of novel and improved datasets to better represent the holistic health of a watershed, and the nature of the datasets used herein allow this framework to be applied at much broader scales than North Carolina.

Nutrient enrichment in wadeable urban streams in the Piedmont Ecoregion of the Southeastern United States

The U.S. Geological Survey (USGS) Southeastern Stream Quality Assessment (SESQA) collected weekly samples for nitrogen and phosphorus in 76 wadeable streams in the urbanized Piedmont Ecoregion of the Southeastern United States, during April–June 2014. Total nitrogen (TN) concentrations in excess of U.S. Environmental Protection Agency (EPA) guidelines and statistically greater than at reference locations indicated nitrogen-nutrient enrichment in streams draining poultry confined animal feeding operations (CAFO) or urban centers. Nitrate plus nitrite (NO₃ + NO₂) dominated TN species in urban/CAFO-influenced streams. Streams that drained poultry CAFO and Washington DC had statistically higher NO₃ + NO₂ concentrations than streams draining Atlanta, Charlotte, Greenville, or Raleigh. In contrast, total phosphorus (TP) concentrations in Atlanta and Washington DC streams statistically were comparable to and lower than, respectively, reference stream concentrations. Over 50% of TP concentrations in Greenville, Charlotte, Raleigh and CAFO-influenced streams exceeded the EPA guideline and reference-location mean concentrations, indicating phosphorus-nutrient enrichment. Urban land use, permitted point sources, and soil infiltration metrics best predicted TN exceedances. Elevated TN and NO₃ + NO₂ concentrations in urban streams during low flow were consistent with reduced in-stream dilution of point-source or groundwater contributions. Urban land use, permitted point sources, and surface runoff metrics best predicted TP exceedances. Elevated TP in CAFO and urban streams during high flow were consistent with non-point sources and particulate transport.

Impact of climate change and climate anomalies on hydrologic and biogeochemical processes in an agricultural catchment of the Chesapeake Bay watershed, USA

Nutrient export from agricultural landscapes is a water quality concern and the cause of mitigation activities worldwide. Climate change impacts hydrology and nutrient cycling by changing soil moisture, stoichiometric nutrient ratios, and soil temperature, potentially complicating mitigation measures. This research quantifies the impact of climate change and climate anomalies on hydrology, nutrient cycling, and greenhouse gas emissions in an agricultural catchment of the Chesapeake Bay watershed. We force a calibrated model with seven downscaled and bias-corrected regional climate models and derived climate anomalies to assess their impact on hydrology and the export of nitrate (NO₃-), phosphorus (P), and sediment, and emissions of nitrous oxide (N₂O) and di-nitrogen (N₂). Model-average (±standard deviation) results indicate that climate change, through an increase in precipitation and temperature, will result in substantial increases in winter/spring flow (10.6 ± 12.3%), NO₃- (17.3 ± 6.4%), dissolved P (32.3 ± 18.4%), total P (24.8 ± 16.9%), and sediment (25.2 ± 16.6%) export, and a slight increases in N₂O (0.3 ± 4.8%) and N₂ (0.2 ± 11.8%) emissions. Conversely, decreases in summer flow (-29.1 ± 24.6%) and the export of dissolved P (-15.5 ± 26.4%), total P (-16.3 ± 20.7%), sediment (-20.7 ± 18.3%), and NO₃- (-29.1 ± 27.8%) are driven by greater evapotranspiration from increasing summer temperatures. Decreases in N₂O (-26.9 ± 15.7%) and N₂ (-36.6 ± 22.9%) are predicted in the summer and driven by drier soils. While the changes in flow are related directly to changes in precipitation and temperature, the changes in nutrient and sediment export are, to some extent, driven by changes in agricultural management that climate change induces, such as earlier spring tillage and altered nutrient application timing and by alterations to nutrient cycling in the soil.

Chesapeake Bay's water quality condition has been recovering: Insights from a multimetric indicator assessment of thirty years of tidal monitoring data

To protect the aquatic living resources of Chesapeake Bay, the Chesapeake Bay Program partnership has developed guidance for state water quality standards, which include ambient water quality criteria to protect designated uses (DUs), and associated assessment procedures for dissolved oxygen (DO), water clarity/underwater bay grasses, and chlorophyll-a. For measuring progress toward meeting the respective states' water quality standards, a multimetric attainment indicator approach was developed to estimate combined standards attainment. We applied this approach to three decades of monitoring data of DO, water clarity/underwater bay grasses, and chlorophyll-a data on annually updated moving 3-year periods to track the progress in all 92 management segments of tidal waters in Chesapeake Bay. In 2014-2016, 40% of tidal water segment-DU-criterion combinations in the Bay (n = 291) are estimated to meet thresholds for attainment of their water quality criteria. This index score marks the best 3-year status in the entire record. Since 1985-1987, the indicator has followed a nonlinear trajectory, consistent with impacts from extreme weather events and subsequent recoveries. Over the period of record (1985-2016), the indicator exhibited a positive and statistically significant trend (p < 0.05), indicating that the Bay has been recovering since 1985. Patterns of attainment of individual DUs are variable, but improvements in open water DO, deep channel DO, and water clarity/submerged aquatic vegetation have combined to drive the improvement in the Baywide indicator in 2014-2016 relative to its long-term median. Finally, the improvement in estimated Baywide attainment was statistically linked to the decline of total nitrogen, indicating responsiveness of attainment status to the reduction of nutrient load through various management actions since at least the 1980s.

Agricultural conservation practices can help mitigate the impact of climate change

Agricultural conservation practices (CPs) are commonly implemented to reduce diffuse nutrient pollution. Climate change can complicate the development, implementation, and efficiency of agricultural CPs by altering hydrology, nutrient cycling, and erosion. This research quantifies the impact of climate change on hydrology, nutrient cycling, erosion, and the effectiveness of agricultural CP in the Susquehanna River Basin in the Chesapeake Bay Watershed, USA. We develop, calibrate, and test the Soil and Water Assessment Tool-Variable Source Area (SWAT-VSA) model and select four CPs; buffer strips, strip-cropping, no-till, and tile drainage, to test their effectiveness in reducing climate change impacts on water quality. We force the model with six downscaled global climate models (GCMs) for a historic period (1990-2014) and two future scenario periods (2041-2065 and 2075-2099) and quantify the impact of climate change on hydrology, nitrate-N (NO₃-N), total N (TN), dissolved phosphorus (DP), total phosphorus (TP), and sediment export with and without CPs. We also test prioritizing CP installation on the 30% of agricultural lands that generate the most runoff (e.g., critical source areas-CSAs). Compared against the historical baseline and with no CPs, the ensemble model predictions indicate that climate change results in annual increases in flow (4.5±7.3%), surface runoff (3.5±6.1%), sediment export (28.5±18.2%) and TN export (9.5±5.1%), but decreases in NO₃-N (12±12.8%), DP (14±11.5), and TP (2.5±7.4%) export. When agricultural CPs are simulated most do not appreciably change the water balance, however, tile drainage and strip-cropping decrease surface runoff, sediment export, and DP/TP, while buffer strips reduce N export. Installing CPs on CSAs results in nearly the same level of performance for most practices and most pollutants. These results suggest that climate change will influence the performance of agricultural CPs and that targeting agricultural CPs to CSAs can provide nearly the same level of water quality effects as more widespread adoption.

Worsened physical condition due to climate change contributes to the increasing hypoxia in Chesapeake Bay

There are increasing concerns about the impact of worsened physical condition on hypoxia in a variety of coastal systems, especially considering the influence of changing climate. In this study, an EOF analysis of the DO data for 1985-2012, a long-term numerical simulation of vertical exchange, and statistical analysis were applied to understand the underlying mechanisms for the variation of DO condition in Chesapeake Bay. Three types of analysis consistently demonstrated that both biological and physical conditions contribute equally to seasonal and interannual variations of the hypoxic condition in Chesapeake Bay. We found the physical condition (vertical exchange+temperature) determines the spatial and seasonal pattern of the hypoxia in Chesapeake Bay. The EOF analysis showed that the first mode, which was highly related to the physical forcings and correlated with the summer hypoxia volume, can be well explained by seasonal and interannual variations of physical variables and biological activities, while the second mode is significantly correlated with the estuarine circulation and river discharge. The weakened vertical exchange and increased water temperature since the 1980s demonstrated a worsened physical condition over the past few decades. Under changing climate (e.g., warming, accelerated sea-level rise, altered precipitation and wind patterns), Chesapeake Bay is likely to experience a worsened physical condition, which will amplify the negative impact of anthropogenic inputs on eutrophication and consequently require more efforts for nutrient reduction to improve the water quality condition in Chesapeake Bay.

Watershed export of fine sediment, organic carbon, and chlorophyll-a to Chesapeake Bay: Spatial and temporal patterns in 1984-2016

Chesapeake Bay has long experienced nutrient enrichment and water clarity deterioration. This study provides new quantification of loads and yields for sediment (fine and coarse grained), organic carbon (total, dissolved, and particulate), and chlorophyll-a from the monitored nontidal Chesapeake Bay watershed (MNTCBW), all of which are expected to drive estuarine water clarity. We conducted an integrated analysis of nine major tributaries to the Bay to understand spatial and temporal export patterns over the last thirty years (1984-2016). In terms of spatial pattern, export of these constituents from the MNTCBW was strongly dominated (~90%) by the three largest tributaries (i.e., Susquehanna, Potomac, and James). Among the nine tributaries, the ranking of constituent export generally follows the order of their watershed sizes, with other factors such as land use and reservoir playing important roles in some exceptions. In terms of partitioning, suspended sediment (SS) export was dominated by fine-grained sediment (SS_fine) in all nine tributaries; overall, ~90% of the MNTCBW SS is SS_fine. Total organic carbon (TOC) export was dominated by dissolved organic carbon (DOC) in all tributaries except Potomac River; overall, ~60% of the MNTCBW TOC is DOC. A comparison with literature shows that the MNTCBW SS and TOC yields were ~80% and ~60% of the respective medians of worldwide watersheds. In terms of temporal pattern, flow-normalized yields from the MNTCBW show overall increases in SS (both long-term [1984-2016] and short-term [2004-2016]), SS_fine (long-term and short-term), TOC (long-term), and chlorophyll-a (short-term). The rises in SS, SS_fine, and TOC were largely driven by Susquehanna River where Conowingo Reservoir's trapping efficiency has greatly diminished in the last twenty years. Overall, these new results on the status and trends of sediment, organic carbon, and chlorophyll-a provide the foundation for building potential linkages between riverine inputs and estuarine water clarity patterns.

Excessive application of pig manure increases the risk of P loss in calcic cinnamon soil in China

Soil phosphorus (P) is a critical factor affecting crop yields and water environmental quality. To investigate the degree of loss risk and forms of soil P in calcic cinnamon soil, the P fraction activities in soils were analysed using chemical methods, combined with an in situ field experiment. Seven treatments were set in this study, including control (unfertilized), no P fertilizer (No-P), mineral P fertilizer (Min-P), low (L-Man) and high (H-Man) quantities of pig manure, Min-P+L-Man, and Min-P+H-Man. The results showed that manure fertilizer could not only significantly increase maize yield but could also enhance the accumulation of soil P in organic and inorganic forms. After 23years of repeated fertilization, the soil Olsen-P contents respectively showed 64.7-, 43.7- and 31.9-fold increases in the Min-P+H-Man, Min-P+L-Man and H-Man treatments, while the soil Olsen-P in Min-P treatment only increased 23.7-fold. The soil Olsen-P thresholds ranged from 22.59 to 32.48mgkg^-1 in calcic cinnamon soil to maintain a higher maize yield as well as a lower risk of P loss. Therefore, long-term excessive manure application could obviously raise the content of soil Olsen-P and increase the risk of P loss in calcic cinnamon soil.