Atmospheric deposition of phosphorus to land and freshwater

Atmospheric wet and dry phosphorus deposition in Lake Erhai, China

Lake Erhai is a potentially phosphorus (P)-limited lake and its water quality may have been affected by atmospheric P deposition. However, there have been few studies on atmospheric P deposition in this lake. In this study, we established five wet deposition monitoring sites and two dry deposition monitoring sites around Lake Erhai to quantify the wet and dry deposition of total phosphorus (TP), including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) from July 2022 to June 2023. Wet deposition fluxes of P species were collected by automatic rainfall collection instrument, and dry deposition fluxes were estimated using airborne concentration measurements and inferential models. The results reveal that among the different P components, DOP had the highest contribution (50%) to wet TP deposition (average all sites 12.7 ± 0.7 mg P m2/yr), followed by PP (40%) and DIP (10%). Similarly, DOP (51%) was the major contributor to dry TP deposition (average two sites 2.4 ± 0.9 mg P m2/yr), followed by DIP (35%) and PP (14%). Wet deposition dominated the annual total TP deposition (wet plus dry), accounting for approximately 83%. The key seasons for dry deposition were spring and autumn, which accounted for 64% of the annual total dry TP deposition. In comparison, wet deposition was significantly higher in the summer, accounting for 73% of the annual total wet TP deposition. The results of the potential source contribution function and concentration-weighted trajectories analysis indicate that local source emission and long-range transport from surrounding cities jointly exerted a substantial influence on aerosol P concentrations, particularly in the eastern and northwestern regions of the lake. These findings provide a comprehensive understanding of the different P components in atmospheric deposition, which is beneficial for developing effective strategies to manage the P cycle in Lake Erhai.

Characterizing Spatiotemporal Variability in Phosphorus Export across the United States through Bayesian Hierarchical Modeling

Phosphorus inputs from anthropogenic activities are subject to hydrologic (riverine) export, causing water quality problems in downstream lakes and coastal systems. Nutrient budgets have been developed to quantify the amount of nutrients imported to and exported from various watersheds. However, at large spatial scales, estimates of hydrologic phosphorus export are usually unavailable. This study develops a Bayesian hierarchical model to estimate annual phosphorus export across the contiguous United States, considering agricultural inputs, urban inputs, and geogenic sources under varying precipitation conditions. The Bayesian framework allows for a systematic updating of prior information on export rates using an extensive calibration data set of riverine loadings. Furthermore, the hierarchical approach allows for spatial variation in export rates across major watersheds and ecoregions. Applying the model, we map hotspots of phosphorus loss across the United States and characterize the primary factors driving these losses. Results emphasize the importance of precipitation in determining hydrologic export rates for various anthropogenic inputs, especially agriculture. Our findings also emphasize the importance of phosphorus from geogenic sources in overall river export.

Vicuña antipredator diel movement drives spatial nutrient subsidies in a high Andean ecosystem

Large animals could be important drivers of spatial nutrient subsidies when they ingest resources in some habitats and release them in others, even moving nutrients against elevational gradients. In high Andean deserts, vicuñas (Vicugna vicugna) move daily between nutrient-rich wet meadows, where there is abundant water and forage but high risk of predation by pumas (Puma concolor), and nutrient-poor open plains with lower risk of predation. In all habitats, vicuñas defecate and urinate in communal latrines. We investigated how these latrines impacted soil and plant nutrient concentrations across three habitats in the Andean ecosystem (meadows, plains, and canyons) and used stable isotope analysis to explore the source of fecal nutrients in latrines. Latrine soils had higher concentrations of nitrogen, carbon, and other nutrients than did nonlatrine soils across all habitats. These inputs corresponded with an increase in plant quality (lower C:N) at latrine sites in plains and canyons, but not in meadows. Stable isotope mixing models suggest that ~7% of nutrients in plains latrines originated from vegetation in meadows, which is disproportionately higher than the relative proportion of meadow habitat (2.6%) in the study area. In contrast, ~68% of nutrients in meadow latrines appear to originate from plains and canyon vegetation, though these habitats made up nearly 98% of the study area. Vicuña diel movements thus appear to concentrate nutrients in latrines within habitats and to drive cross-habitat nutrient subsidies, with disproportionate transport from low-lying, nutrient-rich meadows to more elevated, nutrient-poor plains. When these results are scaled up to the landscape scale, the amount of nitrogen and phosphorus subsidized in soil at plains latrines was of the same order of magnitude as estimates of annual atmospheric nitrogen and phosphorus deposition for this region (albeit far more localized and patchy). Thus, vicuña-mediated nutrient redistribution and deposition appears to be an important process impacting ecosystem functioning in arid Andean environments, on par with other major inputs of nutrients to the system.

Attributing Atmospheric Phosphorus in the Himalayas: Biomass Burning vs Mineral Dust

Atmospheric phosphorus is a vital nutrient for ecosystems whose sources and fate are still debated in the fragile Himalayan region, hindering our comprehension of its local ecological impact. This study provides novel insights into atmospheric phosphorus based on the study of total suspended particulate matter at the Qomolangma station. Contrary to the prevailing assumptions, we show that biomass burning (BB), not mineral dust, dominates total dissolved phosphorus (TDP, bioavailable) deposition in this arid region, especially during spring. While total phosphorus is mainly derived from dust (77% annually), TDP is largely affected by the transport of regional biomass-burning plumes from South Asia. During BB pollution episodes, TDP causing springtime TDP fluxes alone accounts for 43% of the annual budget. This suggests that BB outweighs dust in supplying bioavailable phosphorus, a critical nutrient, required to sustain Himalayas' ecological functions. Overall, this first-hand field evidence refines the regional and global phosphorus budget by demonstrating that BB emission, while still unrecognized, is a significant source of P, even in the remote mountains of the Himalayas. It also reveals the heterogeneity of atmospheric phosphorus deposition in that region, which will help predict changes in the impacted ecosystems as the deposition patterns vary.

Atmospheric Dry and Wet Deposition of Total Phosphorus to the Great Lakes

Quantifying atmospheric loadings of total phosphorus (TP) to freshwater environments is essential to improve understanding of its fate and transport, and to mitigate the effects of excessive levels in freshwater ecosystems. To date, atmospheric deposition of TP in the U.S. is poorly characterized due to the lack of long-term deposition observations. Here, we integrate several historical datasets to develop an estimate of dry and wet deposition to the Great Lakes region. For dry deposition, we use TP concentrations in fine particulate matter (PM2.5) samples from fourteen land-based IMPROVE sites (2013-2020) upwind of the Great Lakes to provide new fine particle phosphorus dry deposition estimates. For wet deposition, we use TP concentrations in wet-only precipitation samples collected at eleven land-based sites (2001-2009) in the Great Lakes region. For both wet and dry deposition, a seasonal cycle is evident with higher concentrations in warmer and wetter months when compared to colder months. Additionally, there is an increasing gradient from north to south in wet deposition, likely driven by both higher precipitation and increased emissions near southern sites. Despite different sampling time periods, these updated observations can provide further constraints on the TP loadings to each of the five Great Lakes. We estimate annual deposition of TP to Lakes Superior, Michigan, Huron, Erie and Ontario at 526, 702, 495, 212, and 185 MTA per year, which is lower than prior estimates for Lakes Superior, Erie and Ontario, comparable for Lake Huron, and about two times greater for Lake Michigan. When considering only the contribution of fine particulate PM to the dry deposition, wet deposition dominated over dry at all lakes except for Lake Huron. However, prior global estimates suggest greater contributions from larger particles (PM10 and PM100), yet observations to validate these estimates over the Great Lakes are not available. Our findings indicate that dry deposition of a range of particle sizes are needed to constrain the total atmospheric deposition of TP over the Great Lakes.

Environment and Host Genetics Influence the Biogeography of Plant Microbiome Structure

To understand how microbiota influence plant populations in nature, it is important to examine the biogeographic distribution of plant-associated microbiomes and the underlying mechanisms. However, we currently lack a fundamental understanding of the biogeography of plant microbiomes across populations and the environmental and host genetic factors that shape their distribution. Leveraging the broad distribution and extensive genetic variation in duckweeds (the Lemna species complex), we identified key factors that governed plant microbiome diversity and compositional variation geographically. In line with the microbial biogeography of free-living microbiomes, we observed higher bacterial richness in temperate regions relative to lower latitudes in duckweed microbiomes (with 10% higher in temperate populations). Our analyses revealed that higher temperature and sodium concentration in aquatic environments showed a negative impact on duckweed bacterial richness, whereas temperature, precipitation, pH, and concentrations of phosphorus and calcium, along with duckweed genetic variation, influenced the biogeographic variation of duckweed bacterial community composition. Analyses of plant microbiome assembly processes further revealed that niche-based selection played an important role (26%) in driving the biogeographic variation of duckweed bacterial communities, alongside the contributions of dispersal limitation (33%) and drift (39%). These findings add significantly to our understanding of host-associated microbial biogeography and provide important insights for predicting plant microbiome vulnerability and resilience under changing climates and intensifying anthropogenic activities.

Global water use efficiency saturation due to increased vapor pressure deficit

The ratio of carbon assimilation to water evapotranspiration (ET) of an ecosystem, referred to as ecosystem water use efficiency (WUEeco), is widely expected to increase because of the rising atmospheric carbon dioxide concentration (Ca). However, little is known about the interactive effects of rising Ca and climate change on WUEeco. On the basis of upscaled estimates from machine learning methods and global FLUXNET observations, we show that global WUEeco has not risen since 2001 because of the asymmetric effects of an increased vapor pressure deficit (VPD), which depressed photosynthesis and enhanced ET. An undiminished ET trend indicates that rising temperature and VPD may play a more important role in regulating ET than declining stomatal conductance. Projected increases in VPD are predicted to affect the future coupling of the terrestrial carbon and water cycles.

Ericoid mycorrhizal fungi mediate the response of ombrotrophic peatlands to fertilization: a modeling study

Ericaceous shrubs adapt to the nutrient-poor conditions in ombrotrophic peatlands by forming symbiotic associations with ericoid mycorrhizal (ERM) fungi. Increased nutrient availability may diminish the role of ERM pathways in shrub nutrient uptake, consequently altering the biogeochemical cycling within bogs. To explore the significance of ERM fungi in ombrotrophic peatlands, we developed the model MWMmic (a peat cohort-based biogeochemical model) into MWMmic-NP by explicitly incorporating plant-soil nitrogen (N) and phosphorus (P) cycling and ERM fungi processes. The new model was applied to simulate the biogeochemical cycles in the Mer Bleue (MB) bog in Ontario, Canada, and their responses to fertilization. MWMmic_NP reproduced the carbon(C)-N-P cycles and vegetation dynamics observed in the MB bog, and their responses to fertilization. Our simulations showed that fertilization increased shrub biomass by reducing the C allocation to ERM fungi, subsequently suppressing the growth of underlying Sphagnum mosses, and decreasing the peatland C sequestration. Our species removal simulation further demonstrated that ERM fungi were key to maintaining the shrub-moss coexistence and C sink function of bogs. Our results suggest that ERM fungi play a significant role in the biogeochemical cycles in ombrotrophic peatlands and should be considered in future modeling efforts.

Improving the phosphorus budget of European agricultural soils

Despite phosphorus (P) being crucial for plant nutrition and thus food security, excessive P fertilization harms soil and aquatic ecosystems. Accordingly, the European Green Deal and derived strategies aim to reduce P losses and fertilizer consumption in agricultural soils. The objective of this study is to calculate a soil P budget, allowing the quantification of the P surpluses/deficits in the European Union (EU) and the UK, considering the major inputs (inorganic fertilizers, manure, atmospheric deposition, and chemical weathering) and outputs (crop production, plant residues removal, losses by erosion) for the period 2011-2019. The Land Use/Cover Area frame Survey (LUCAS) topsoil data include measured values for almost 22,000 samples for both available and total P. With advanced machine learning models, we developed maps for both attributes at 500 m resolution. We estimated the available P for crops at a mean value of 83 kg ha^-1 with a clear distinction between North and South. The ratio of available P to the total P is about 1:17. The inorganic fertilizers and manure contribute almost equally as P inputs (mean 16 ± 2 kg P ha^-1 yr^-1 at 90 % confidence level) to agricultural soils, with high regional variations depending on farming practices, livestock density, and cropping systems. The P outputs came mainly from the exportation by the harvest of crop products and residues (97.5 %) and, secondly, by erosion. Using a sediment distribution model, we quantified the P fluxes to river basins and sea outlets. In the EU and UK, we estimated an average surplus of 0.8 kg P ha^-1 yr^-1 with high variability between countries with some regional variations. The P annual budget at regional scale showed ample possibility to improve P management by both reducing inputs in regions with high surplus (and P soil available) and rebalancing fertilization in those at risk of soil fertility depletion.

Molecular Characterization of Organophosphorus Compounds in Wildfire Smoke Using 21-T Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry

We present a detailed molecular characterization of organophosphorus compounds in ambient organic aerosol influenced by wildfire smoke. Biomass burning organic aerosol (BBOA) is an important source of phosphorus (P) to surface waters, where even a small imbalance in the P flux can lead to substantial effects on water quality, such as eutrophication, algal blooms, and oxygen depletion. We aimed to exploit the ultrahigh resolving power, mass accuracy, and sensitivity of Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) to explore the molecular composition of an ambient BBOA sample collected downwind of Pacific Northwest wildfires. The 21-T FT-ICR MS yielded 10 533 distinct formulae, which included molecular species comprising C, H, O, and P with or without N, i.e., organophosphorus compounds that have long been quantified in wildfire smoke but have not yet been characterized at the molecular level. The lack of detailed molecular characterization of organophosphorus compounds in BBOA is primarily due to their inherently low concentrations in aerosols and poor ionization efficiency in complex mixtures. We demonstrate that the exceptional sensitivity of the 21-T FT-ICR MS allows qualitative analysis of a previously uncharacterized fraction of BBOA without its selective concentration from the organic matrix, exemplifying the need for ultrahigh-resolution tools for a more detailed and accurate molecular depiction of such complex mixtures.

Dynamic characteristics of net anthropogenic phosphorus input and legacy phosphorus reserves under high human activity - A case study in the Jianghan Plain

The increase of phosphorus (P) input related to human activities is one of the main reasons for eutrophication. Notably, in areas with high population densities and intensive agricultural activities, eutrophication has occurred frequently in the Jianghan Plain, so quantitative evaluation of anthropogenic P input is of great significance for the formulation of P pollution control measures. This study estimated net anthropogenic P input (NAPI), riverine total P exports (TP exports), and the pool of P stored in the terrestrial system (legacy P reserves) at the county scale from 1990 to 2019 in the Jianghan Plain. The results showed that NAPI increased from 2645 kg·km^-2·yr^-1 in 1991 to 5812 kg·km^-2·yr^-1 in 2014, and then decreased to 4509 kg·km^-2·yr^-1 in 2019. Non-point sources were the main form of NAPI, of which 75-96% came from agricultural systems. Meanwhile, P fertilizer input was the largest source of NAPI. It is worth noting that the contribution of seed P input in some counties, such as Jiangling County, is relatively high, even exceeding that of net food/feed P input. The P fertilizer application and livestock density were the main drivers for NAPI change. Only 3% of NAPI was exported into rivers, so a large amount of legacy P accumulated in the terrestrial system. An empirical model incorporating NAPI components, cultivated land area ratio, and annual precipitation was established. Based on this model, the average contribution of annual NAPI and the sum of legacy P and natural background sources to TP exports were calculated to be 71% and 29%, respectively. So it is necessary to control P pollution by improving fertilizer use efficiency and enhancing manure management. The results provide a scientific basis for targeted solutions to the sources of P nutrient and its control measures in the middle reach of the Yangtze River.

Weak impact of nutrient enrichment on peat: Evidence from physicochemical properties

Atmospheric deposition of nitrogen (N) and phosphorus (P) far exceeding the pre-industrial levels have the potential to change carbon (C) dynamics in northern peatlands. However, the responses of soil C concentration and organo-chemical composition to different rates and durations of nutrient enrichment are still unclear. Here, we compared the short- (3 years) and long-term (10 years) effects of N and P fertilizations on the physicochemical properties of peat and porewater in a bog-fen complex in northern China. Our results showed that the short-term fertilization increased Sphagnum moss cover, while the expansion of vascular plants was observed owing to the long-term fertilization. The preserved soil C did not vary considerably after the short- and long-term fertilizations. The harsh soil conditions may impede the decomposition of organic matters by soil microorganisms during the short-term fertilization. For the long-term fertilization, the input of high-phenolic litters owing to vascular plant expansion likely exerted an important control on soil C dynamics. These processes constrained the variation in soil C concentrations when the addition rate and cumulative amount of external N and P increased, which will advance our understanding and prediction of the resilience of soil C storage to imbalanced nutrient enrichment of N and P in northern peatlands.

Grazing by wild red deer can mitigate nutrient enrichment in protected semi-natural open habitats

Eutrophication through atmospheric nutrient deposition is threatening the biodiversity of semi-natural habitats characterized by low nutrient availability. Accordingly, local management measures aiming at open habitat conservation need to maintain habitat-specific nutrient conditions despite atmospheric inputs. Grazing by wild herbivores, such as red deer (Cervus elaphus), has been proposed as an alternative to mechanical or livestock-based measures for preserving open habitats. The role of red deer for nutrient dynamics in protected open habitat types, however, is yet unclear. Therefore, we collected data on vegetation productivity, forage removal, quantity of red deer dung and nutrient concentrations in vegetation and dung from permanent plots in heathlands and grasslands (eight plots à 225 m² per habitat type) on a military training area inhabited by a large population of free-ranging red deer over one year. The annual nutrient export of nitrogen (N) and phosphorus (P) by red deer grazing was higher than the nutrient import through red deer excreta, resulting in an average net nutrient removal of 14 and 30 kg N ha⁻¹ a⁻¹ and 1.1 and 3.3 kg P ha⁻¹ a⁻¹ in heathlands and grasslands, respectively. Even when considering approximate local atmospheric deposition values, net nutrient depletion due to red deer grazing seemed very likely, notably in grasslands. Demonstrating that grazing by wild red deer can mitigate the effects of atmospheric nutrient deposition in semi-natural open habitats similarly to extensive livestock grazing, our results support the idea that red deer are suitable grazing animals for open habitat conservation.

The evolving role of weather types on rainfall chemistry under large reductions in pollutant emissions

Long-term change and shorter-term variability in the atmospheric deposition of pollutants and marine salts can have major effects on the biogeochemistry and ecology of soils and surface water ecosystems. In the 1980s, at the time of peak acid deposition in the UK, deposition loads were highly dependent on prevailing weather types, and it was postulated that future pollution recovery trajectories would be partly dependent on any climate change-driven shifts in weather systems. Following three decades of substantial acidic emission reductions, we used monitoring data collected between 1992 and 2015 from four UK Environmental Change Network (ECN) sites in contrasting parts of Great Britain to examine the trends in precipitation chemistry in relation to prevailing weather conditions. Weather systems were classified on the basis of Lamb weather type (LWT) groupings, while emissions inventories and clustering of air mass trajectories were used to interpret the observed patterns. Concentrations of ions showed clear differences between cyclonic-westerly-dominated periods and others, reflecting higher marine and lower anthropogenic contributions in Atlantic air masses. Westerlies were associated with higher rainfall, higher sea salt concentrations, and lower pollutant concentrations at all sites, while air mass paths exerted additional controls. Westerlies therefore have continued to favour higher sea salt fluxes, whereas emission reductions are increasingly leading to positive correlations between westerlies and pollutant fluxes. Our results also suggest a shift from the influence of anthropogenic emissions to natural emissions (e.g., sea salt) and climate forcing as they are transported under relatively cleaner conditions to the UK. Westerlies have been relatively frequent over the ECN monitoring period, but longer-term cyclicity in these weather types suggests that current contributions to precipitation may not be sustained over coming years.

Distribution Characteristics and Controlling Factors of Soil Total Nitrogen: Phosphorus Ratio Across the Northeast Tibetan Plateau Shrublands

Nitrogen (N) and phosphorus (P) stoichiometry have significant effects on nutrient cycles in terrestrial ecosystems. However, our understanding of the patterns and the driving factors of soil N:P ratios in the Tibetan Plateau shrublands remains limited. Our study aimed to quantify the distribution of soil N:P ratio and its controlling factors based on soil, plant, and climate factors from 59 sites in shrublands across the northeast Tibetan Plateau. The kriging interpolation method was used to quantify the soil N:P distribution. Spatially, the soil N:P ratio was higher in the south than in the north and lower in the west than in the east. The soil N:P ratio in the northeast Tibetan Plateau shrublands was mainly explained by edaphic factors, which also played an important role in regulating the effects of plant and climate factors on soil N:P ratios. Mean annual precipitation, instead of mean annual temperature, significantly controlled the soil N:P ratios, and its effect on the pattern of soil N:P ratios differed between alpine shrublands and desert shrublands. The N:P ratios of different organs in shrublands also played different roles in shaping the soil N:P ratios in alpine and desert shrublands. These results provide support for the hypothesis that edaphic factors were the dominant drivers of spatial variation in soil N:P ratios across the northeast Tibetan Plateau shrublands, and our study contributes to a deeper understanding of biogeochemical cycling at high altitudes.

External Phosphorus Loading in New Lakes

The water quality of lakes is highly dependent on external phosphorus (P) loading. The vast external loadings from sewage and other wastewater discharge that European lakes have historically received have been dramatically reduced today by improved wastewater treatment. Gaining knowledge of the catchment characteristics that influence external P-loading should enable predictions of the achievable water quality of lakes. In this study, we tested this proposition. Data from 90 new Danish lakes show no apparent relationship between the mean summer P-concentration and the size or land use of the catchments. The external P-loading and resulting annual P-concentration were further investigated on a representative subset of 12 of the new lakes, using six methods. Three of the methods used empirical estimates of P-transport from catchments, based on the national average P-transport, runoff-dependent P-transport, and crop-dependent P-transport, and the other three methods used different empirical models tested on the lakes. External P-loading was reliably predicted by several of the methods. The predictions of the annual P-concentration were highly dependent on the inclusion of annual runoff. However, the predicted P-concentrations were generally overestimated, most pronounced for the nutrient-poor and most recently established lakes. In these lakes, internal P-loading was found to be the most important factor in predicting achievable water quality.

Temporal Trends of Phosphorus in Urban Atmospheric Aerosols

Air particulate samples collected from a Canadian urban area station showed seasonal trend of the phosphorus with peak levels observed for April-June periods and levels not significantly changed between 2007 and 2015. The phosphorus measured as total phosphorus (TP) in digested aqueous extracts showed an exponential increase with daily temperature (R2=0.544, N=474), with the best correlation observed for the 2010 subset (R2=0.727, N=55). The temperature correlation was not observed with the total suspended particles (TSP). Longer dry periods during spring-summer months favored higher P level on aerosols. The temperature and precipitation pattern dependence indicate a possible climate change influence on the aerosol P levels. The unchanged yearly aerosol TP content does not directly reflect the dropping trend observed in surface water after 1990s from the same area during spring-summer periods.

Hierarchical systems integration for coordinated urban-rural water quality management at a catchment scale

Managing river quality is important for sustainable catchment development. In this study, we present how catchment management strategies benefit from a coordinated implementation of measures that are based on understanding key drivers of pollution. We develop a modelling approach that integrates environmental impacts, human activities, and management measures as three hierarchical levels. We present a catchment water management model (CatchWat) that achieves all three hierarchical levels and is applied to the Cherwell Catchment, UK. CatchWat simulations are evaluated against observed river flow and pollutant data including suspended solids, total nitrogen, and total phosphorus. We compare three competing hypotheses, or framings, of the catchment representation (integrated, urban-only, and rural-only framings) to test the impacts of model boundaries on river water quality modelling. Scenarios are formulated to simulate separate, combined and coordinated implementation of fertiliser application reduction and enhanced wastewater treatment. Results show that models must represent both urban and rural pollution emissions to accurately estimate river quality. Agricultural activities are found to drive river quality in wet periods because runoff is the main pathway for rural pollutants. Meanwhile, urban activities are the key source of pollution in dry periods because effluent constitutes a larger percentage of river flow during this time. Based on this understanding, we identify a coordinated management strategy that implements fertiliser reduction measures to improve river quality during wet periods and enhanced wastewater treatment to improve river quality during dry periods. The coordinated strategy performs comparably to the combined strategy but with higher overall efficiency. This study emphasises the importance of systems boundaries in integrated water quality modelling and simulating the mechanisms of seasonal water quality behaviour. Our key recommendation is that incorporating these mechanisms is required to develop coordinated strategies for river water quality management, that can ultimately lead to more efficient and sustainable catchment management.

Natural forests promote phosphorus retention in soil

Soil phosphorus (P) availability often limits plant productivity. Classical theories suggest that total P content declines at the temporal scale of pedogenesis, and ecosystems develop toward the efficient use of scarce P during succession. However, the trajectory of ecosystem P within shorter time scales of succession remains unclear. We analyzed changes to P pools at the early (I), middle (II), and late (III) stages of growth of plantation forests (PFs) and the successional stages of natural forests (NFs) at 1969 sites in China. We found significantly lower P contents at later growth stages compared to earlier ones in the PF (p < .05), but higher contents at late successional stages than in earlier stages in the NF (p < .05). Our results indicate that increasing P demand of natural vegetation during succession, may raise, retain, and accumulate P from deeper soil layers. In contrast, ecosystem P in PF was depleted by the more rapidly increasing demand outpacing the development of a P-efficient system. We advocate for more studies to illuminate the mechanisms for determining the divergent changes, which would improve forest management and avoid the vast degradation of PF ecosystems suffering from the ongoing depletion of P.

Earth, Wind, Fire, and Pollution: Aerosol Nutrient Sources and Impacts on Ocean Biogeochemistry

A key Earth system science question is the role of atmospheric deposition in supplying vital nutrients to the phytoplankton that form the base of marine food webs. Industrial and vehicular pollution, wildfires, volcanoes, biogenic debris, and desert dust all carry nutrients within their plumes throughout the globe. In remote ocean ecosystems, aerosol deposition represents an essential new source of nutrients for primary production. The large spatiotemporal variability in aerosols from myriad sources combined with the differential responses of marine biota to changing fluxes makes it crucially important to understand where, when, and how much nutrients from the atmosphere enter marine ecosystems. This review brings together existing literature, experimental evidence of impacts, and new atmospheric nutrient observations that can be compared with atmospheric and ocean biogeochemistry modeling. We evaluate the contribution and spatiotemporal variability of nutrient-bearing aerosols from desert dust, wildfire, volcanic, and anthropogenic sources, including the organic component, deposition fluxes, and oceanic impacts.

Anthropogenic and Climate-Exacerbated Landscape Disturbances Converge to Alter Phosphorus Bioavailability in an Oligotrophic River

Cumulative effects of landscape disturbance in forested source water regions can alter the storage of fine sediment and associated phosphorus in riverbeds, shift nutrient dynamics and degrade water quality. Here, we examine longitudinal changes in major element chemistry and particulate phosphorus (PP) fractions of riverbed sediment in an oligotrophic river during environmentally sensitive low flow conditions. Study sites along 50 km of the Crowsnest River were located below tributary inflows from sub-watersheds and represent a gradient of increasing cumulative sediment pressures across a range of land disturbance types (harvesting, wildfire, and municipal wastewater discharges). Major elements (Si2O, Al2O3, Fe2O3, MnO, CaO, MgO, Na2O, K2O, Ti2O, V2O5, P2O5), loss on ignition (LOI), PP fractions (NH4CI-RP, BD-RP, NaOH-RP, HCI-RP and NaOH(85)-RP), and absolute particle size were evaluated for sediments collected in 2016 and 2017. While total PP concentrations were similar across all sites, bioavailable PP fractions (BD-RP, NaOH-RP) increased downstream with increased concentrations of Al2O3 and MnO and levels of landscape disturbance. This study highlights the longitudinal water quality impacts of increasing landscape disturbance on bioavailable PP in fine riverbed sediments and shows how the convergence of climate (wildfire) and anthropogenic (sewage effluent, harvesting, agriculture) drivers can produce legacy effects on nutrients.

Phosphorus in the Clouds of Venus: Potential for Bioavailability

Aerosol phase elements such as phosphorus (P), sulfur (S), and metals including iron (Fe) are essential nutrients that could help sustain potential biodiversity in the cloud deck of Venus. While the presence of S and Fe in the venusian cloud deck has been broadly discussed (Zasova et al., 1981; Krasnopolsky, 2012, 2013, 2016, 2017; Markiewicz et al., 2014), less attention has been given to the presence of P in the aerosols and its involvement in the multiphase chemistry of venusian clouds and potential sources of P deposition in the venusian atmosphere. A detailed characterization of phosphorus atmospheric chemistry in the cloud deck of Venus is crucial for understanding its solubility and bioavailability for potential venusian cloud microbiota (Schulze-Makuch et al., 2004; Grinspoon and Bullock, 2007; Limaye et al., 2018). We summarize our current understanding of the presence of P in the clouds of Venus and its role in a hypothetical atmospheric (bio)chemical cycle. The results of the VeGa lander measurements are put into perspective with regard to nutrient limitation for a potential biosphere in venusian clouds. Our work combines the results of the VeGa measurements and focuses on P as an inorganic nutrient component and its potential sources and chemical behavior as part of multiple transformations of atmospheric chemistry. The VeGa data indicate that a plentiful phosphorus layer exists within a layer that reaches into the lower venusian clouds and exceeds minimum P abundances for terrestrial microbial life. Extreme acidification of airborne phases in the atmosphere of Venus may facilitate P solubilization and its bioavailability for a potential ecosystem in venusian clouds. Further sampling and P abundance measurements in the atmosphere of Venus would improve our knowledge of P speciation and facilitate determination of a bioavailable fraction of P detected in venusian clouds. The previous results deserve further experimental and modeling analyses to diminish uncertainties and understand the rates of atmospheric deposition of P and its role in a potential venusian cloud ecosystem.

Restoration, conservation and phytoplankton hysteresis

Phytoplankton growth depends not only upon external factors that are not strongly altered by the presence of phytoplankton, such as temperature, but also upon factors that are strongly influenced by activity of phytoplankton, including photosynthetically active radiation, and the availability of the macronutrients carbon, nitrogen, phosphorus and, for some, silicate. Since phytoplankton therefore modify, and to an extent create, their own habitats, established phytoplankton communities can show resistance and resilience to change, including managed changes in nutrient regimes. Phytoplankton blooms and community structures can be predicted from the overall biogeochemical setting and inputs, but restorations may be influenced by the physiological responses of established phytoplankton taxa to nutrient inputs, temperature, second-order changes in illumination and nutrient recycling. In this review we discuss the contributions of phytoplankton ecophysiology to biogeochemical hysteresis and possible effects on community composition in the face of management, conservation or remediation plans.

Nitrogen and phosphorus enrichment cause declines in invertebrate populations: a global meta-analysis

Human-driven changes in nitrogen (N) and phosphorus (P) inputs are modifying biogeochemical cycles and the trophic state of many habitats worldwide. These alterations are predicted to continue to increase, with the potential for a wide range of impacts on invertebrates, key players in ecosystem-level processes. Here, we present a meta-analysis of 1679 cases from 207 studies reporting the effects of N, P, and combined N + P enrichment on the abundance, biomass, and richness of aquatic and terrestrial invertebrates. Nitrogen and phosphorus additions decreased invertebrate abundance in terrestrial and aquatic ecosystems, with stronger impacts under combined N + P additions. Likewise, N and N + P additions had stronger negative impacts on the abundance of tropical than temperate invertebrates. Overall, the effects of nutrient enrichment did not differ significantly among major invertebrate taxonomic groups, suggesting that changes in biogeochemical cycles are a pervasive threat to invertebrate populations across ecosystems. The effects of N and P additions differed significantly among invertebrate trophic groups but N + P addition had a consistent negative effect on invertebrates. Nutrient additions had weaker or inconclusive impacts on invertebrate biomass and richness, possibly due to the low number of case studies for these community responses. Our findings suggest that N and P enrichment affect invertebrate community structure mainly by decreasing invertebrate abundance, and these effects are dependent on the habitat and trophic identity of the invertebrates. These results highlight the important effects of human-driven nutrient enrichment on ecological systems and suggest a potential driver for the global invertebrate decline documented in recent years.

Assessing agro-food system circularity using nutrient flows and budgets

Nutrient reuse and recycling is a key strategy towards more circular and sustainable food systems and depends on the specific conditions of the area under study, such as geography and the type of agricultural system. In this study we analysed nutrient flows and assessed the circularity of a livestock-dominated and export-oriented agro-food system at different system levels and spatial scales. We quantified the nitrogen (N), phosphorus (P) and potassium (K) flows and soil balances in the Belgian agro-food system at the sub-regional, regional and national scale, and assessed five P-based indicators that capture different aspects of circularity: total inputs, phosphorus use efficiency, share of reused to total input, recycling rate, and losses. We found that nutrient soil balances depend on the type of agricultural system: areas with intense livestock production accumulate up to 108 kgN/ha, 4.8 kgP/ha and 150 kgK/ha in their soil annually, whereas areas of mostly arable production have low N and K surpluses of <20 kg/ha and P deficits of < -10 kg/ha. We further found that Wallonia, the southern region of the country that is characterized by lower livestock densities and a partial reuse of sewage sludge, outperforms the Flemish region in the North in all five indicators. The food system in the whole of Belgium has a 34% phosphorus use efficiency rate and a 63% overall recycling rate, while 84% of the total inputs in agriculture are from secondary sources. Our results show that the type of production system is the most crucial determinant for circularity, and highlight the benefit of working at different levels and spatial scales to capture all aspects of circularity in agro-food systems.

Phosphorus Inventory for the Conterminous United States (2002-2012)

Published reports suggest efforts designed to prevent the occurrence of harmful algal blooms and hypoxia by reducing non-point and point source phosphorus (P) pollution are not delivering water quality improvements in many areas. Part of the uncertainty in evaluating watershed responses to management practices is the lack of standardized estimates of phosphorus inputs and outputs. To assess P trends across the conterminous United States, we compiled an inventory using publicly available datasets of agricultural P fluxes, atmospheric P deposition, human P demand and waste, and point source discharges for 2002, 2007, and 2012 at the scale of the 8-digit Hydrologic Unit Code subbasin (~1,800 km²). Estimates of agricultural legacy P surplus accumulated from 1945 to 2001 were also developed. Fertilizer and manure inputs were found to exceed crop removal rates by up to 50% in many agricultural regions. This excess in inputs has led to the continued accumulation of legacy P in agricultural lands. Atmospheric P deposition increased throughout the Rockies, potentially contributing to reported increases in surface water P concentrations in undisturbed watersheds. In some urban areas, P fluxes associated with human waste and non-farm fertilizer use has declined despite population growth, likely due, in part, to various sales bans on P-containing detergents and fertilizers. Although regions and individual subbasins have different contemporary and legacy P sources, a standardized method of accounting for large and small fluxes and ready to use inventory numbers provide essential infromation to coordinate targeted interventions to reduce P concentrations in the nation's waters.

Water quality assessment based on multivariate statistics and water quality index of a strategic river in the Brazilian Atlantic Forest

Fifty-four water samples were collected between July and December 2019 at nine monitoring stations and fifteen parameters were analysed to provide an updated diagnosis of the Piabanha River water quality. Further, forty years of monitoring were analysed, including government data and previous research projects. A georeferenced database was also built containing water management data. The Water Quality Index from the National Sanitation Foundation (WQI_NSF) was calculated using two datasets and showed an improvement in overall water quality, despite still presenting systematic violations to Brazilian standards. Principal components analysis (PCA) showed the most contributing parameters to water quality and enabled its association with the main pollution sources identified in the geodatabase. PCA showed that sewage discharge is still the main pollution source. The cluster analysis (CA) made possible to recommend the monitoring network optimization, thereby enabling the expansion of the monitoring to other rivers. Finally, the diagnosis provided by this research establishes the first step towards the Framing of water resources according to their intended uses, as established by the Brazilian National Water Resources Policy.

Phosphorus Speciation in Atmospherically Deposited Particulate Matter and Implications for Terrestrial Ecosystem Productivity

Chemical forms of phosphorus (P) in airborne particulate matter (PM) are poorly known and do not correlate with solubility or extraction measurements commonly used to infer speciation. We used P X-ray absorption near-edge structure (XANES) and ³¹P nuclear magnetic resonance (NMR) spectroscopies to determine P species in PM collected at four mountain sites (Colorado and California). Organic P species dominated samples from high elevations, with organic P estimated at 65-100% of total P in bulk samples by XANES and 79-88% in extracted fractions (62-84% of total P) by NMR regardless of particle size (≥10 or 1-10 μm). Phosphorus monoester and diester organic species were dominant and present in about equal proportions, with low fractions of inorganic P species. By comparison, PM from low elevation contained mixtures of organic and inorganic P, with organic P estimated at 30-60% of total P. Intercontinental PM transport determined from radiogenic lead (Pb) isotopes varied from 0 to 59% (mean 37%) Asian-sourced Pb at high elevation, whereas stronger regional PM inputs were found at low elevation. Airborne flux of bioavailable P to high-elevation ecosystems may be twice as high as estimated by global models, which will disproportionately affect net primary productivity.

Simulating long-term carbon nitrogen and phosphorus biogeochemical cycling in agricultural environments

Understanding how agricultural practices alter biogeochemical cycles is vital for maintaining land productivity, food security, and other ecosystem services such as carbon sequestration. However, these are complex, highly coupled long-term processes that are difficult to observe or explore through empirical science alone. Models are required that capture the main anthropogenic disturbances, whilst operating across regions and long timescales, simulating both natural and agricultural environments, and shifts among these. Many biogeochemical models neglect agriculture or interactions between carbon and nutrient cycles, which is surprising given the scale of intervention in nitrogen and phosphorus cycles introduced by agriculture. This gap is addressed here, using a plant-soil model that simulates integrated soil carbon, nitrogen and phosphorus (CNP) cycling across natural, semi-natural and agricultural environments. The model is rigorously tested both spatially and temporally using data from long-term agricultural experiments across temperate environments. The model proved capable of reproducing the magnitude of and trends in soil nutrient stocks, and yield responses to nutrient addition. The model has potential to simulate anthropogenic effects on biogeochemical cycles across northern Europe, for long timescales (centuries) without site-specific calibration, using easily accessible input data. The results demonstrate that weatherable P from parent material has a considerable effect on modern pools of soil C and N, despite significant perturbation of nutrient cycling from agricultural practices, highlighting the need to integrate both geological and agricultural processes to understand effects of land-use change on food security, C storage and nutrient sustainability. The results suggest that an important process or source of P is currently missing in our understanding of agricultural biogeochemical cycles. The model could not explain how yields were sustained in plots with low P fertiliser addition. We suggest that plant access to organic P is a key uncertainty warranting further research, particularly given sustainability concerns surrounding rock sources of P fertiliser.

An Assessment of the Performance of the PLUS+ Tool in Supporting the Evaluation of Water Framework Directive Compliance in Scottish Standing Waters

Phosphorus is one of the main causes of waterbodies in Scotland being at less than good ecological status (GES) in terms of the water framework directive (WFD). In Scotland, there are more than 8000 standing waters, defined as lakes and reservoirs that have a surface area of more than 1 hectare. Only about 330 of these are monitored routinely to assess compliance with the WFD. The export coefficient tool PLUS+ (phosphorus land use and slope) has been developed to estimate total phosphorus (TP) concentrations in the unmonitored sites; modelled values are then compared to WFD target concentrations for high, good, moderate, poor, and bad status to assess compliance. These type-specific or site-specific targets are set by the regulatory authority and form part of a suite of physical, chemical, and ecological targets that are used to assess GES, all of which must be met. During development, the PLUS+ tool was applied to 323 monitored catchments and 7471 unmonitored catchments. The efficacy of the tool was assessed against TP concentrations observed in 2014 and found to perform well in the rural catchments. 51% of standing waters had the same modelled and observed WFD class (i.e., High, Good, Moderate, Poor, Bad), and a further 40% of standing waters had a modelled WFD class that was within one class of observed water quality. The tool performed less well in catchments with larger inputs of TP from urban sources (e.g., sewage). The greatest deviations between measured and modelled classes were explained by the shortage of information on wastewater treatment works, fish farms, migratory birds, levels of uncertainty in TP measurements, and the amount of in-lake re-cycling of P. The limitations of the tool are assessed using data from six well documented case study sites and recommendations for improving the model performance are proposed.

Hydrology-driven environmental variability determines abiotic characteristics and Oribatida diversity patterns in a Sphagnum peatland system

We investigated oribatid mite communities in a Sphagnum-dominated boreal peatland system characterised by a mosaic of oligotrophic and meso-eutrophic areas. We aimed to determine the relative importance of environmental factors (pH, Sphagnum nutrient content, water table level, diversity of vascular plants and bryophytes in the surrounding plant community) and spatial variation in influencing abundance, diversity and community composition of aquatic and terrestrial oribatid mites. Among environmental variables, water table level (micro-topography), pH, and K in Sphagnum tissues were the main predictors of Oribatida community structure. Aquatic species were associated with pools; two terrestrial species-Hoplophthiracarus illinoisensis and Nothrus pratensis-were associated with oligotrophic hummocks; the rest of terrestrial species were associated with dryer mesotrophic and eutrophic habitats. Low water table depth (hummocks), high local plant diversity, and high P in Sphagnum tissues were predictors of high abundance of terrestrial Oribatida. Species richness of terrestrial Oribatida was linked with low water table and high plant diversity. For aquatic Oribatida abundance, water table depth was the single most important predictor variable. Plot trophic class (its status on the peatland poor-rich gradient assigned based on plant indicator species) was also a significant predictor of terrestrial Oribatida abundance, richness, and community structure. Spatial structuring was important for terrestrial Oribatida community composition, weak (P < 0.10) for terrestrial Oribatida abundance and richness, and not significant for aquatic Oribatida.

Critical Review of Eutrophication Models for Life Cycle Assessment

This paper evaluates the current state of life cycle impact assessment (LCIA) methods used to estimate potential eutrophication impacts in freshwater and marine ecosystems and presents a critical review of the underlying surface water quality, watershed, marine, and air fate and transport (F&T) models. Using a criteria rubric, we assess the potential of each method and model to contribute to further refinements of life cycle assessment (LCA) eutrophication mechanisms and nutrient transformation processes as well as model structure, availability, geographic scope, and spatial and temporal resolution. We describe recent advances in LCIA modeling and provide guidance on the best available sources of fate and exposure factors, with a focus on midpoint indicators. The critical review identifies gaps in LCIA characterization modeling regarding the availability and spatial resolution of fate factors in the soil compartment and identifies strategies to characterize emissions from soil. Additional opportunities are identified to leverage detailed F&T models that strengthen existing approaches to LCIA or that have the potential to link LCIA modeling more closely with the spatial and temporal realities of the effects of eutrophication.

Impact of two centuries of intensive agriculture on soil carbon, nitrogen and phosphorus cycling in the UK

This paper describes an agricultural model (Roth-CNP) that estimates carbon (C), nitrogen (N) and phosphorus (P) pools, pool changes, their balance and the nutrient fluxes exported from arable and grassland systems in the UK during 1800-2010. The Roth-CNP model was developed as part of an Integrated Model (IM) to simulate C, N and P cycling for the whole of UK, by loosely coupling terrestrial, hydrological and hydro-chemical models. The model was calibrated and tested using long term experiment (LTE) data from Broadbalk (1843) and Park Grass (1856) at Rothamsted. We estimated C, N and P balance and their fluxes exported from arable and grassland systems on a 5km×5km grid across the whole of UK by using the area of arable of crops and livestock numbers in each grid and their management. The model estimated crop and grass yields, soil organic carbon (SOC) stocks and nutrient fluxes in the form of NH₄-N, NO₃-N and PO₄-P. The simulated crop yields were compared to that reported by national agricultural statistics for the historical to the current period. Overall, arable land in the UK have lost SOC by -0.18, -0.25 and -0.08MgCha^-1y^-1 whereas land under improved grassland SOC stock has increased by 0.20, 0.47 and 0.24MgCha^-1y^-1 during 1800-1950, 1950-1970 and 1970-2010 simulated in this study. Simulated N loss (by leaching, runoff, soil erosion and denitrification) increased both under arable (-15, -18 and -53kgNha^-1y^-1) and grass (-18, -22 and -36kgNha^-1y^-1) during different time periods. Simulated P surplus increased from 2.6, 10.8 and 18.1kgPha^-1y^-1 under arable and 2.8, 11.3 and 3.6kgPha^-1y^-1 under grass lands 1800-1950, 1950-1970 and 1970-2010.

Long-term N and P additions alter the scaling of plant nitrogen to phosphorus in a Tibetan alpine meadow

Nitrogen and phosphorus are two important nutrient elements for plants. The current paradigm suggests that the scaling of plant tissue N to P is conserved across environments and plant taxa because these two elements are coupled and coordinately change with each other following a constant allometric trajectory. However, this assumption has not been vigorously examined, particularly in changing N and P environments. We propose that changes in relative availability of N and P in soil alter the N to P relationship in plants. Taking advantage of a 4-yr N and P addition experiment in a Tibetan alpine meadow, we examined changes in plant N and P concentrations of 14 common species. Our results showed that while the scaling of N to P under N additions was similar to the previously reported pattern with a uniform 2/3 slope of the regression between log N and log P, it was significantly different under P additions with a smaller slope. Also, graminoids had different responses from forbs. These results indicate that the relative availability of soil N and P is an important determinant regulating the N and P concentrations in plants. These findings suggest that alterations in the N to P relationships may not only alter plant photosynthate allocation to vegetative or reproductive organs, but also regulate the metabolic and growth rate of plant and promote shifts in plant community composition in a changing nutrient loading environment.

Human Perturbation of the Global Phosphorus Cycle: Changes and Consequences

The phosphorus (P) cycle is an important Earth system process. While natural P mobilization is slow, humans have been altering P cycle by intensifying P releases from lithosphere to ecosystems. Here, we examined magnitudes of which humans have altered the P cycles by integrating the estimates from recent literatures, and furthermore illustrated the consequences. Based on our synthesis, human alterations have tripled the global P mobilization in land-water continuum and increased P accumulation in soil with 6.9 ± 3.3 Tg-P yr^-1. Around 30% of atmospheric P transfer is caused by human activities, which plays a significant role than previously thought. Pathways involving with human alterations include phosphate extraction, fertilizers application, wastes generation, and P losses from cropland. This study highlights the importance of sustainable P supply as a control on future food security because of regional P scarcity, food demand increase and continuously P intensive food production. Besides, accelerated P loads are responsible for enhanced eutrophication worldwide, resulting in water quality impairment and aquatic biodiversity losses. Moreover, the P enrichment can definitely stimulate the cycling of carbon and nitrogen, implying the great need for incorporating P in models predicting the response of carbon and nitrogen cycles to global changes.

Phosphorus Speciation and Solubility in Aeolian Dust Deposited in the Interior American West

Aeolian dust is a significant source of phosphorus (P) to alpine oligotrophic lakes, but P speciation in dust and source sediments and its release kinetics to lake water remain unknown. Phosphorus K-edge XANES spectroscopy shows that calcium-bound P (Ca-P) is dominant in 10 of 12 dust samples (41-74%) deposited on snow in the central Rocky Mountains and all 42 source sediment samples (the fine fraction) (68-80%), with a lower proportion in dust probably because acidic snowmelt dissolves some Ca-P in dust before collection. Iron-bound P (Fe-P, ∼54%) dominates in the remaining two dust samples. Chemical extractions (SEDEX) on these samples provide inaccurate results because of unselective extraction of targeted species and artifacts introduced by the extractions. Dust releases increasingly more P in synthetic lake water within 6-72 h thanks to dissolution of Ca-P, but dust release of P declines afterward due to back adsorption of P onto Fe oxides present in the dust. The back sorption is stronger for the dust with a lower degree of P saturation determined by oxalate extraction. This work suggests that P speciation, poorly crystalline minerals in the dust, and lake acidification all affect the availability and fate of dust-borne P in lakes.

Long-term nutrient addition increased CH4 emission from a bog through direct and indirect effects

Peatlands are globally significant sources of atmospheric methane (CH₄). While several studies have examined the effects of nutrient addition on CH₄ dynamics, there are few long-term peatland fertilization experiments, which are needed to understand the aggregated effects of nutrient deposition on ecosystem functioning. We investigated responses of CH₄ flux and production to long-term field treatments with three levels of N (1.6-6.4 g m^-2 yr^-1 as NH₄NO₃), potassium and phosphorus (PK, 5.0 g P and 6.3 g K m^-2 yr^-1 as KH₂PO₄), and NPK in a temperate bog. Methane fluxes were measured in the field from May to August in 2005 and 2015. In 2015 CH₄ flux was higher in the NPK treatment with 16 years of 6.4 g N m^-2 yr^-1 than in the control (50.5 vs. 8.6 mg CH₄ m^-2 d^-1). The increase in CH₄ flux was associated with wetter conditions derived from peat subsidence. Incubation of peat samples, with and without short-term PK amendment, showed that potential CH₄ production was enhanced in the PK treatments, both from field application and by amending the incubation. We suggest that changes in this bog ecosystem originate from long-term vegetation change, increased decomposition and direct nutrient effects on microbial dynamics.

Performance of surface and subsurface flow constructed wetlands treating eutrophic waters

Three medium size constructed wetlands (CWs) with a total surface of 90ha are working since 2009 in the Albufera de Valencia Natural Park (Spain). Two of them are fed with eutrophic waters from l'Albufera Lake. Their objectives are both reduce the phytoplankton biomass and increase the biodiversity; consequently, improved water quality is returned to the lake. A "science based governance" of these CWs is ongoing inside the LIFE+12 Albufera Project to demonstrate the environmental benefits of these features. In this paper, results and relationships among hydraulic operation, physicochemical variables and plankton in two different CWs typologies, five free water surface CW (FWSCW) and one horizontal subsurface flow CW (HSSFCW), were analysed showing that CWs were capable of improving the water quality and biodiversity but showing clear differences depending on the CW type. The CWs worked under different hydraulic load rates (HLR) from <0.12 to 54.75myr^-1. Inflow water quality was typical from eutrophic waters with mean values of chlorophyll a (Chl a) about 22-90μgChlal^-1 and mean total phosphorus (TP) between 0.122 and 0.337mgl^-1. The main conclusion is that HSSFCW was much more efficient than FWSCW in the removal of organic matter, suspended solids and nutrients. The biological role of several shallow lagoons located at the end of the CWs has also been evaluated, showing that they contribute to increase the zooplankton biomass, a key factor to control the phytoplankton blooms.

Long-term nitrogen and phosphorus enrichment alters vegetation species composition and reduces carbon storage in upland soil

Reactive nitrogen (N) deposition can affect ecosystem processes, particularly in oligotrophic upland habitats. Phosphorus (P) addition has been proposed to reduce the effects of N enrichment on N leaching and acidification, since P limitation can reduce biomass production and consequent sequestration of reactive N. However, biodiversity is often reduced in more productive ecosystems and P limitation may protect against this effect. Responses to P availability in instances of high N deposition are poorly understood. This study investigated the ecosystem response to alleviation of P limitation, using a long-term nutrient addition experiment (1996-2012) three years after ceasing N inputs and 15years after a single P application. Substantial differences were observed in the structure and composition of vegetation species and above-ground vegetation biomass. Vegetation height was greater in the N+P addition treatments (+38% cf. control), with increased cryptogam cover (+47%), whereas N addition increased graminoid species cover (+68%). Vegetation diversity was significantly reduced by the addition of P (-21%), indicating that P limitation is likely to be an important mechanism that limits biodiversity loss in upland habitats exposed to chronic N deposition. Significant differences in soil C and N contents were also observed between treatments. Relative to control, the addition of N increased soil C (+11%) and N (+11%) pool sizes, whereas the addition of N and P reduced soil C (-12%) and N (-13%) pool sizes. This demonstrated the importance of P availability for upland ecosystem processes, and highlights the long-term effects of P addition on vegetation species composition and C storage. Thus, the addition of P cannot be endorsed as a method for reducing impacts of N deposition. Capsule: Phosphorus limitation is a major mechanism governing ecosystem processes in situations of high atmospheric nitrogen deposition.

Effects of atmospheric reactive phosphorus deposition on phosphorus transport in a subtropical watershed: A Chinese case study

Atmospheric phosphorus (P) deposition is not only an important external macronutrient source for aquatic ecosystems but also a major cause of high export coefficient (EC) values. However, there are limited numbers of studies in the literature that focus on estimating the deposition flux of reactive P (P_r). The aim of this study is to estimate the P_r deposition on the Xiangxi River watershed, and therefore, provide a comprehensive understanding about the P_r deposition on subtropical watersheds in China. Results have shown that maximal P_r deposition fluxes reached 12 kg km^-2 in our selected subtropical watershed. Furthermore, we found out the particulate phosphorus (PP) were dominating the total P_r deposition in the Xiangxi River watershed. According to our experiments, certain forms of P_r deposition were associated with high correlation coefficients with respect to the variation of rainfall intensity. Results also demonstrated that the dissolved organic phosphorus (DOP) and soluble reactive phosphorus (SRP) via wet deposition had large influences on the DOP and SRP concentrations in runoff, while the PO₄-P and PP via wet deposition only affected PO₄-P and PP loads through runoff discharge. Our experiments also shown that most parts of the P_r in runoff water was derived from rainfall and its magnitudes varied with land types. Results suggested that during the dry season, the P_r wet deposition not only was an important source for the P_r transport driven by runoff, but also was one of the most important influencing factors that dominated the P_r transport in subtropical watersheds.

A database of georeferenced nutrient chemistry data for mountain lakes of the Western United States

Human activities have increased atmospheric nitrogen and phosphorus deposition rates relative to pre-industrial background. In the Western U.S., anthropogenic nutrient deposition has increased nutrient concentrations and stimulated algal growth in at least some remote mountain lakes. The Georeferenced Lake Nutrient Chemistry (GLNC) Database was constructed to create a spatially-extensive lake chemistry database needed to assess atmospheric nutrient deposition effects on Western U.S. mountain lakes. The database includes nitrogen and phosphorus water chemistry data spanning 1964–2015, with 148,336 chemistry results from 51,048 samples collected across 3,602 lakes in the Western U.S. Data were obtained from public databases, government agencies, scientific literature, and researchers, and were formatted into a consistent table structure. All data are georeferenced to a modified version of the National Hydrography Dataset Plus version 2. The database is transparent and reproducible; R code and input files used to format data are provided in an appendix. The database will likely be useful to those assessing spatial patterns of lake nutrient chemistry associated with atmospheric deposition or other environmental stressors.

Mains water leakage: Implications for phosphorus source apportionment and policy responses in catchments

Effective strategies to reduce phosphorus (P)-enrichment of aquatic ecosystems require accurate quantification of the absolute and relative importance of individual sources of P. In this paper, we quantify the potential significance of a source of P that has been neglected to date. Phosphate dosing of raw water supplies to reduce lead and copper concentrations in drinking water is a common practice globally. However, mains water leakage (MWL) potentially leads to a direct input of P into the environment, bypassing wastewater treatment. We develop a new approach to estimate the spatial distribution and time-variant flux of MWL-P, demonstrating this approach for a 30-year period within the exemplar of the River Thames catchment in the UK. Our analyses suggest that MWL-P could be equivalent to up to c.24% of the P load entering the River Thames from sewage treatment works and up to c.16% of the riverine P load derived from agricultural non-point sources. We consider a range of policy responses that could reduce MWL-P loads to the environment, including incorporating the environmental damage costs associated with P in setting targets for MWL reduction, alongside inclusion of MWL-P within catchment-wide P permits.

Continental-Scale Increase in Lake and Stream Phosphorus: Are Oligotrophic Systems Disappearing in the United States?

We describe continental-scale increases in lake and stream total phosphorus (TP) concentrations, identified through periodic probability surveys of thousands of water bodies in the conterminous U.S. The increases, observed over the period 2000-2014 were most notable in sites in relatively undisturbed catchments and where TP was initially low (e.g., less than 10 μg L(-1)). Nationally, the percentage of stream length in the U.S. with TP ≤ 10 μg L(-1) decreased from 24.5 to 10.4 to 1.6% from 2004 to 2009 to 2014; the percentage of lakes with TP ≤ 10 μg L(-1) decreased from 24.9 to 6.7% between 2007 and 2012. Increasing TP concentrations appear to be ubiquitous, but their presence in undeveloped catchments suggests that they cannot be entirely attributed to either point or common non-point sources of TP.

Effects of acidic deposition on in-lake phosphorus availability: a lesson from lakes recovering from acidification

Lake water concentrations of phosphorus (P) recently increased in some mountain areas due to elevated atmospheric input of P rich dust. We show that increasing P concentrations also occur during stable atmospheric P inputs in central European alpine lakes recovering from atmospheric acidification. The elevated P availability in the lakes results from (1) increasing terrestrial export of P accompanying elevated leaching of dissolved organic carbon and decreasing phosphate-adsorption ability of soils due to their increasing pH, and (2) decreasing in-lake P immobilization by aluminum (Al) hydroxide due to decreasing leaching of ionic Al from the recovering soils. The P availability in the recovering lakes is modified by the extent of soil acidification, soil composition, and proportion of till and meadow soils in the catchment. These mechanisms explain several conflicting observations of the acid rain effects on surface water P concentrations.

Innovative methods in soil phosphorus research: A review

Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state-of-the-art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q-TOF MS/MS, high resolution-MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum-chemical modeling, microbial biomass P, enzymes activity, DGT, ³³P isotopic exchange, ¹⁸O isotope ratios). Required experimental set-ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.