Less Agricultural Phosphorus Applied in 2019 Led to Less Dissolved Phosphorus Transported to Lake Erie

Role of particle size-dependent copper bioaccumulation-mediated oxidative stress on Glycine max (L.) yield parameters with soil-applied copper oxide nanoparticles

Increased impetus on the application of nano-fertilizers to improve sustainable food production warrants understanding of nanophytotoxicity and its underlying mechanisms before its application could be fully realized. In this study, we evaluated the potential particle size-dependent effects of soil-applied copper oxide nanoparticles (nCuO) on crop yield and quality attributes (photosynthetic pigments, seed yield and nutrient quality, seed protein, and seed oil), including root and seed Cu bioaccumulation and a suite of oxidative stress biomarkers, in soybean (Glycine max L.) grown in field environment. We synthesized three distinct sized (25 nm = S [small], 50 nm = M [medium], and 250 nm = L [large]) nCuO with same surface charge and compared with soluble Cu2+ ions (CuCl2) and water-only controls. Results showed particle size-dependent effects of nCuO on the photosynthetic pigments (Chla and Chlb), seed yield, potassium and phosphorus accumulation in seed, and protein and oil yields, with nCuO-S showing higher inhibitory effects. Further, increased root and seed Cu bioaccumulation led to concomitant increase in oxidative stress (H2O2, MDA), and as a response, several antioxidants (SOD, CAT, POX, and APX) increased proportionally, with nCuO treatments including Cu2+ ion treatment. These results are corroborated with TEM ultrastructure analysis showing altered seed oil bodies and protein storage vacuoles with nCuO-S treatment compared to control. Taken together, we propose particle size-dependent Cu bioaccumulation-mediated oxidative stress as a mechanism of nCuO toxicity. Future research investigating the potential fate of varied size nCuO, with a focus on speciation at the soil-root interface, within the root, and edible parts such as seed, will guide health risk assessment of nCuO.

New phosphorus losses via tile drainage depend on fertilizer form, placement, and timing

Agricultural phosphorus (P) losses are harmful to water quality, but knowledge gaps about the importance of fertilizer management practices on new (recently applied) sources of P may limit P loss mitigation efforts. Weighted regression models applied to subsurface tile drainage water quality data enabled estimating the new P losses associated with 155 P applications in Ohio and Indiana, USA. Daily discharge and dissolved reactive P (DRP) and total P (TP) loads were used to detect increases in P loss following each application which was considered new P. The magnitude of new P losses was small relative to fertilizer application rates, averaging 79.3 g DRP ha-1 and 96.1 g TP ha-1 , or <3% of P applied. The eight largest new P losses surpassed 330 g DRP ha-1 or 575 g TP ha-1 . New P loss mitigation strategies should focus on broadcast liquid manure applications; on average, manure applications caused greater new P losses than inorganic fertilizers, and surface broadcast applications were associated with greater new P losses than injected or incorporated applications. Late fall applications risked having large new P losses applications. On an annual basis, new P contributed an average of 14% of DRP and 5% of TP losses from tile drains, which is much less than previous studies that included surface runoff, suggesting that tile drainage is relatively buffered with regard to new P losses. Therefore old (preexisting soil P) P sources dominated tile drain P losses, and P loss reduction efforts will need to address this source.

Efficient smartphone-based measurement of phosphorus in water

Agricultural runoff is one of the main sources of excess phosphorus (P) in different water bodies, subsequently leading to eutrophication and harmful algal blooms. To effectively monitor P levels in water, there is a need for simple measurement tools and extensive public involvement to enable regular and widespread sampling. Several smartphone-based P measurement methods have been reported, which extract red-green-blue (RGB) values from colorimetric reactions to build statistical regression models for P quantification. However, these methods typically require meticulous light conditions, involve initial equipment investment, and have undergone limited testing for large-scale applications. To overcome these limitations, this study developed a smartphone-based, equipment-free and facile P colorimetric analysis method. Following the standard procedure of the ascorbic acid approach, colorimetric reactions were captured by a smartphone camera, and RGB values were extracted using Python code for modeling. Different indoor light conditions, phone types, containers, and types of water samples were examined, resulting in a collection of 1922 images. The best regression model, employing random forest with RGB values and container types as inputs, achieved an R2 of 0.97 and an RMSE of 0.051 for P concentrations ranging from 0.01 to 1.0 mg P/L. Additionally, the optimal classification model could estimate the level of P below 0.1 mg P/L with an accuracy of 95.2 (or 77.4 % for <0.05 mg P/L). The strong performance of the developed models, which are also available freely online, suggests an easy and effective tool for more frequent P measurement and greater public involvement.

Unraveling spatial patterns and source attribution of nutrient transport: Towards optimal best management practices in complex river basin

A comprehensive understanding of nutrient transport patterns and clarification of pollutant sources' load contributions are critical prerequisites for developing scientific pollution control strategies in complex river basins. Here, we focused on the Minjiang River Basin (MRB) and employed the Soil and Water Assessment Tool (SWAT) model to systematically investigate the nitrogen (N) and phosphorus (P) loads from both point and non-point sources. Results revealed that the key source areas of N and P pollution in the MRB were predominantly located along the riverbanks, influenced by a combination of sediment, precipitation, agricultural activities such as fertilization. Our analysis indicated that soil nutrient loss, fertilization, and livestock farming were the major contributors to N and P inputs, accounting for over 70 % of the total input, followed by rural residential and urban point sources. Based on the identification of non-point source pollution as the primary load source, a multi-objective optimization was conducted using response surface methodology (RSM) coupled with the non-dominated sorting genetic algorithm-II (NSGA-II), resulting in the identification of optimal best management practices (BMPs) that achieve a reduction of 40.04 % in N load, 39.22 % in P load, and a net economic benefit of -1.13 billion yuan per year. Compared to the RSM and automated optimization results, the proposed management measures exhibited significant improvements in N and P load reduction and net benefits. Overall, the findings provide important insights for formulating agricultural management policies in the MRB and offering valuable implications for pollution management in other complex river basins.

Effect of foliar application of phosphorus nanoparticles on the performance and sustainable agriculture of sweet corn

Traditional phosphorus fertilizers are necessary for plant growth but about 80-90% are lost into the surrounding environment via irrigation, therefore nano-fertilizers have been developed as slow-release fertilizers to achieve sustainable agriculture. This trial investigated the impact of the foliar application of hydroxyapatite nanoparticles (HA-NPs) as a source of nano-phosphorus (P-NPs) on two cultivars of sweet corn (yellow and white) throughout two seasons. The morphology and structure of the prepared HA-NPs were characterized via transmission electron microscopy (TEM) and X-ray diffractometry (XRD). In addition, agro-morphological criteria, chemical contents (i.e., photosynthetic pigments, phenols, indoles, minerals, etc.), and genomic template stability percentage (GTS%) were evaluated in the produced sweet corn. The application of 50 mg/l HA-NPs improved the growth characteristics, yield per hectare, leaf pigments, and chemical content of yellow sweet corn, whereas the application of 100 mg/l of HA-NPs to white sweet corn enhanced the vegetative characteristics, production, photosynthetic pigments, phenols, and indoles. The difference in results may be due to the presence of a +ve unique band with SCoT-4 and SCot-2 primers at 1250 and 470 bp in yellow and white corn treated with 50 and 100 mg/l, respectively. The minimum GTS% was recorded at a concentration of 75 mg/l for both white and yellow corn. The HA-NPs can be applied as a foliar source of P-NPs to achieve agricultural sustainability.

Techno-Economic Analysis of Phosphorus Removal Structures

Excess phosphorus (P) is a major pollutant in aquatic systems. Phosphorus removal structures, landscape-scale filters designed to capture dissolved P from runoff, drainage, and wastewater offer promise in curbing P pollution. While the environmental benefits of various P removal structures are well documented, the cost-effectiveness of each structure's ability to sequester P is lacking. In this study, we compare the cost-effectiveness of P removal of the most prominent P removal structures. Specifically, we calculate the average cost per kilogram (kg) of P removed by eight different P removal structures across a range of parameter assumptions. Absent constraints, we found that (1) larger structures that use (2) regionally available phosphorus sorption materials that are (3) byproducts of industrial production (e.g., metal shavings and steel slag) rather than manufactured are more cost-effective. The average cost of P removal for most structures varies from $100 to 1300 per kg in our baseline estimations, which is comparable to the average cost for wastewater treatment. This work provides further information to guide the optimal implementation of P removal structures for conservationists.

Watershed- and reach-scale drivers of phosphorus retention and release by streambed sediment in a western Lake Erie watershed during summer

Reducing phosphorus (P) concentrations in aquatic ecosystems, is necessary to improve water quality and reduce the occurrence of harmful cyanobacterial algal blooms. Managing P reduction requires information on the role rivers play in P transport from land to downstream water bodies, but we have a poor understanding of when and where river systems are P sources or sinks. During the summers of 2019 and 2021, we sampled streambed sediment at 78 sites throughout the Maumee River network (a major source of P loads to Lake Erie) focusing on the zero equilibrium P concentration (EPC₀), the soluble reactive phosphorus (SRP) concentration at which sediment neither sorbs nor desorbs P. We used structural equation modeling to identify direct and indirect drivers of EPC₀. Stream sediment was a P sink at 40 % and 67 % of sites in 2019 and 2021, respectively. During both years, spatial variation in EPC₀ was shaped by stream water SRP concentrations, sediment P saturation, and sediment physicochemical characteristics. In turn, SRP concentrations and sediment P saturation (PSR) were influenced by agricultural land use and stream size. Effect of stream size differed among years with stream size having a greater effect on SRP in 2019 and on PSR in 2021. Streambed sediment is currently a net P sink across the sites sampled in the Maumee River network during summer, but sediment at these locations, especially sites in headwater streams, may become a P source if stream water SRP concentrations decrease. Our results improve the understanding of watershed- and reach-scale controls on EPC₀ but also indicate the need for further research on how changes in SRP concentration as a result of conservation management implementation influences the role of streambed sediment in P transport to Lake Erie.

Spatio-temporal connectivity of the aquatic microbiome associated with cyanobacterial blooms along a Great Lake riverine-lacustrine continuum

Lake Erie is subject to recurring events of cyanobacterial harmful algal blooms (cHABs), but measures of nutrients and total phytoplankton biomass seem to be poor predictors of cHABs when taken individually. A more integrated approach at the watershed scale may improve our understanding of the conditions that lead to bloom formation, such as assessing the physico-chemical and biological factors that influence the lake microbial community, as well as identifying the linkages between Lake Erie and the surrounding watershed. Within the scope of the Government of Canada's Genomics Research and Development Initiative (GRDI) Ecobiomics project, we used high-throughput sequencing of the 16S rRNA gene to characterize the spatio-temporal variability of the aquatic microbiome in the Thames River-Lake St. Clair-Detroit River-Lake Erie aquatic corridor. We found that the aquatic microbiome was structured along the flow path and influenced mainly by higher nutrient concentrations in the Thames River, and higher temperature and pH downstream in Lake St. Clair and Lake Erie. The same dominant bacterial phyla were detected along the water continuum, changing only in relative abundance. At finer taxonomical level, however, there was a clear shift in the cyanobacterial community, with Planktothrix dominating in the Thames River and Microcystis and Synechococcus in Lake St. Clair and Lake Erie. Mantel correlations highlighted the importance of geographic distance in shaping the microbial community structure. The fact that a high proportion of microbial sequences found in the Western Basin of Lake Erie were also identified in the Thames River, indicated a high degree of connectivity and dispersal within the system, where mass effect induced by passive transport play an important role in microbial community assembly. Nevertheless, some cyanobacterial amplicon sequence variants (ASVs) related to Microcystis, representing less than 0.1% of relative abundance in the upstream Thames River, became dominant in Lake St. Clair and Erie, suggesting selection of those ASVs based on the lake conditions. Their extremely low relative abundances in the Thames suggest additional sources are likely to contribute to the rapid development of summer and fall blooms in the Western Basin of Lake Erie. Collectively, these results, which can be applied to other watersheds, improve our understanding of the factors influencing aquatic microbial community assembly and provide new perspectives on how to better understand the occurrence of cHABs in Lake Erie and elsewhere.

Resolving new and old phosphorus source contributions to subsurface tile drainage with weighted regressions on discharge and season

Agricultural losses of dissolved reactive phosphorus (DRP) emanate from both historic P applications (i.e., "old P") and recently applied fertilizer (i.e., "new P"). Understanding the relative contributions of these sources is important for mitigating DRP losses from agriculture. This study provides a proof-of-concept for resolving new P vs. old P source contributions to DRP losses in subsurface tile drainage using edge-of-field water quality data and management records from eight fields in Ohio. Weighted regressions on discharge and season (WRDS) were fitted using data from periods without P fertilizer applications and then used to predict DRP losses in tile drainage during new P loss risk periods (default length, 90 d) after fertilizer applications. Differences between observed and predicted DRP concentrations during the new P loss risk period were attributed to the new P source. Remaining losses were attributed to the old soil P source. The WRDS model performance was modest (modified Kling-Gupta efficiency ranged from -0.074 to 0.484). New P sources contributed between 0 and 17% of overall DRP losses (average, 7%), with old soil P contributing 83-100%. Individual P fertilizer applications were associated with new DRP losses up to 192 g P ha^-1 . Increasing the length of the risk period for new P losses up to 180 d after fertilizer application marginally increased the estimated contribution of the new P source. The WRDS-based analysis provides a novel approach for resolving the contributions of new and old sources to edge-of-field DRP losses.

Modeling and assessing water and nutrient balances in a tile-drained agricultural watershed in the U.S. Corn Belt

Identifying the key processes and primary sources of water and nutrient losses is essential for water quantity and quality management in watersheds. This is especially true in the U.S. Corn Belt, which has been recognized as the primary region contributing nutrient loads to the Great Lakes and the Gulf of Mexico. A SWAT (Soil and Water Assessment Tool) model simulation was set up in an agricultural watershed with about 50% tile drainage area in the U.S. Corn Belt to study the water and nutrient balance components for the whole watershed and the corn-soybean rotation system. The SWAT model was improved to consider additional nitrogen and phosphorus loss paths from the soil. The model was comprehensively calibrated and validated for simulating monthly stream flow, total suspended solids (TSS), nutrient loads (including total Kjeldahl nitrogen (TKN), nitrate and nitrite nitrogen (NO_x-N), total phosphorus (TP) and orthophosphate phosphorus (orthoP)), actual evapotranspiration (ET_a), leaf area index (LAI) and annual crop yields in the watershed from 2011 to 2019. Results showed the model performance was very good for simulating the stream flow, TSS and ET_a, and acceptable for nutrient loads, LAI and crop yields. ET_a, surface runoff, lateral soil flow, tile drainage and percolation respectively accounted for 65%, 15%, 2%, 8% and 9% of the precipitation. Fertilizer was the main source of nitrogen and phosphorus input to the watershed, and harvested crops were the main paths removing nutrients. Surface runoff, tile drainage and percolation each contributed about 30% of total nitrogen losses to water, with surface runoff being dominated by organic nitrogen while tile drainage and percolation were dominated by nitrate nitrogen. Phosphorus losses were mainly through surface runoff, which resulted in 66% of the total losses and was dominated by organic phosphorus and soluble phosphorus. Representing about 49% of the watershed area, the corn-soybean rotation system contributed 83% and 88% of the total nitrogen and phosphorus inputs, respectively, to the watershed, as well as 64% and 46% of the nitrogen and phosphorus losses to the water system, respectively. The non-growing season (October to the next April) was identified as the critical period resulting in water and nutrient losses due to low evapotranspiration and plant uptake. Targeted management strategies for reducing nutrient loads in key hydrological paths were suggested.

SWAT model application for evaluating agricultural conservation practice effectiveness in reducing phosphorous loss from the Western Lake Erie Basin

Lake Erie is threatened by eutrophication and harmful algal blooms due to excess nutrient loading from agricultural sources. Agricultural conservation practices (ACPs) have been developed and implemented to reduce nutrient losses but estimating ACP effectiveness is challenging. The Soil and Water Assessment Tool (SWAT) has been used to investigate ACP effectiveness for water quality improvement. Many SWAT applications have been developed by different investigators to evaluate ACP effectiveness for reducing nutrient, particularly phosphorus (P), loading in the agriculturally-dominated Western Lake Erie Basin (WLEB). Our objective is to establish what has been achieved by past modeling research and make suggestions for future applications and improvements. We synthesized the findings of 28 SWAT modeling studies within the WLEB. Models generally performed satisfactorily against accepted criteria for streamflow and sediment, but performance for P loads, like soluble reactive P, was mostly "unsatisfactory". The "unsatisfactory" performance maybe due to imperfections and idealizations in model formulations and/or parameterization. Thus, simulations of P transport and transformation processes need improvement. In addition, model parameter selection is the key part of model set-up. Most SWAT modeling studies used default values during initial set-up, then performed calibration and validation. It was found that the calibrated P related parameter values varied widely across different studies, even within the same watershed with some values unrealistic for the study areas. The phenomena of different combinations of model parameters producing similar outputs indicates equifinality. Equifinality in the baseline model may impact results when ACPs are incorporated. Furthermore, the unrealistic values used in ACP assessment undermine the credibility of ACP effectiveness. Future model applications should try to re-examine the calibrated P parameters and make sure they are realistic for the study area as well as reduce equifinality by constraining the model with characterization of watershed conditions, better understanding of hydrologic processes, and parameter values based on real-world observations. In summary, future model applications should focus on improving P transport and transformation processes, using measured watershed characteristics for parameterization, and improving reflections of climate change, which could result in more accurate assessments of ACP effectiveness to meet targeted goals.

Desorption Kinetics of Legacy Soil Phosphorus: Implications for Non-Point Transport and Plant Uptake

Soil phosphorus (P) solubility and kinetics partly control dissolved P losses to surface water and uptake by plants. While previous studies have focused on batch techniques for measuring soil P desorption kinetics, flow-through techniques are more realistic because they simulate P removal from the system, akin to runoff, leaching, and plant uptake. The objectives were to measure soil P desorption by a flow-through technique at two flow rates and several batch methods, and utilize both for understanding how flow rate impacts the thermodynamics and kinetics of soil P desorption. Desorption obeyed first-order kinetics in two different phases: an initial rapid desorption phase followed by a gradual release. Desorption was limited by equilibrium and the kinetics of physical processes as demonstrated by an interruption test. Dilution-promoted desorption occurred with increasing cumulative volume, which increased desorption rate via first-order kinetics. The batch tests that simulated cumulative solution volume and time of flow-through were similar to the flow-through results; however, the batch methods overestimated the desorption rates due to less limitations to diffusion. Fast flow rates desorbed less P, but at a greater speed than slow flow rates. The differences were due to contact time, cumulative time, and solution volume, which ultimately controlled the potential for chemical reactions to be realized through physical processes. The interaction between these processes will control the quantity and rate of desorption that buffer P in non-point drainage losses and plant uptake.

Improving and calibrating channel erosion simulation in the Water Erosion Prediction Project (WEPP) model

The Water Erosion Prediction Project (WEPP) model has been widely used to assess the impacts of management practices and climate change on runoff and soil loss at both hillslope and watershed scales. However, the representation of channel erosion processes in WEPP has not been changed significantly since it was released. The current (WEPP v2012.8) and previous WEPP versions assume that channel input erodibility parameters are constant through time, which may lead to erroneous channel detachment predictions, especially for cropland with substantial tillage operations. In this research, the temporally constant values of channel erodibility and critical shear stress were replaced by daily updated values, using the same temporal erodibility and critical shear stress adjustments that are applied in hillslope profile simulations for rill detachment. Observed watershed-scale runoff and soil erosion data from six agricultural watersheds were used to calibrate and compare the WEPP model performance in simulating channel runoff volumes and soil losses before and after the modification. The research showed both WEPP v2012.8 and the modified WEPP model (WEPP_CE) could satisfactorily simulate event-based hydrology and soil erosion at the watershed outlets after calibration. The WEPP_CE model with temporally varying channel erodibility and critical shear stress values demonstrated improved representation of the physical processes in channel soil detachment. Continued improvement in the representation of channel erosion processes in WEPP and other process-based models is needed. The improved WEPP model can be used to evaluate the effectiveness of soil conservation practices on hydrology and erosion in further research.

How Effective Are Existing Phosphorus Management Strategies in Mitigating Surface Water Quality Problems in the U.S.?

Phosphorus is an essential component of modern agriculture. Long-term land application of phosphorous-enriched fertilizers and animal manure leads to phosphorus accumulation in soil that may become susceptible to mobilization via erosion, surface runoff and subsurface leaching. Globally, highly water-soluble phosphorus fertilizers used in agriculture have contributed to eutrophication and hypoxia in surface waters. This paper provides an overview of the literature relevant to the advances in phosphorous management strategies and surface water quality problems in the U.S. Over the past several decades, significant advances have been made to control phosphorus discharge into surface water bodies of the U.S. However, the current use of phosphorus remains inefficient at various stages of its life cycle, and phosphorus continues to remain a widespread problem in many water bodies, including the Gulf of Mexico and Lake Erie. In particular, the Midwestern Corn Belt region of the U.S. is a hotspot of phosphorous fertilization that has resulted in a net positive soil phosphorous balance. The runoff of phosphorous has resulted in dense blooms of toxic, odor-causing phytoplankton that deteriorate water quality. In the past, considerable attention was focused on improving the water quality of freshwater bodies and estuaries by reducing inputs of phosphorus alone. However, new research suggests that strategies controlling the two main nutrients, phosphorus and nitrogen, are more effective in the management of eutrophication. There is no specific solution to solving phosphorus pollution of water resources; however, sustainable management of phosphorus requires an integrated approach combining at least a reduction in consumption levels, source management, more specific regime-based nutrient criteria, routine soil fertility evaluation and recommendations, transport management, as well as the development of extensive phosphorus recovery and recycling programs.

One size does not fit all: Toward regional conservation practice guidance to reduce phosphorus loss risk in the Lake Erie watershed

Agricultural phosphorus (P) losses to surface water bodies remain a global eutrophication concern, despite the application of conservation practices on farm fields. Although it is generally agreed upon that the use of multiple conservation practices ("stacking") will lead to greater improvements to water quality, this may not be cost effective to farmers, reducing the likelihood of adoption. At present, wholesale recommendations of conservation practices are given; however, the application of specific conservation practices in certain environments (e.g., no-till with surface application, cover crops) may not be effective and can even lead to unintended consequences. In this paper, we present the Lake Erie watershed as a case study. The Lake Erie watershed contains regions with unique physical geographies that include differences in climate, soil, topography, and land use, which have implications for both P transport from agricultural fields and the efficacy of conservation practices in mitigating P losses. We define major regions within the Lake Erie watershed where common strategies for conservation practice implementation are appropriate, and we propose a five-step plan for bringing regionally tailored, adaptive, and cost-conscious conservation practice into watershed planning. Although this paper is specific to the Lake Erie watershed, our framework can be transferred across broader geographic regions to provide guidance for watershed planning.