Phosphorus (P) management remains a challenge in agricultural watersheds. The Choptank River Conservation Effects Assessment Project watershed, located in Maryland and Delaware and draining to the Chesapeake Bay, contains legacy soil P from historical dairy and poultry manure applications. These practices elevated soil P beyond crop needs, contributing to persistent P export to aquatic ecosystems. We assessed spatial P distribution and analyzed GIS (Geographic Information Systems)‐derived landscape features driving legacy P movement on a farm (47 ha). We hypothesized that P accumulates in drained lowlands and depressional areas due to gravity‐driven processes that accelerate P‐enriched water to receiving waters via overland flow. In collaboration with the US Department of Agriculture Legacy P project, we collected 105 soil samples (0‐ to 5‐cm and 5‐ to 15‐cm depths) and 14 ditch sediment samples across five topographic openness classes from a farm with >100 years of dairy manure application. Average Mehlich‐III P concentrations were 218 and 179 mg kg −1 at 0‐ to 5‐cm and 5‐ to 15‐cm depths, respectively, with legacy areas defined by P content > 100 mg kg −1 . Soil P and clay particle size were positively correlated ( r = 0.42, p < 0.05), increased as landscape openness decreased, and were negatively correlated with topographic openness (ranging from −0.2 to −0.4, p < 0.05), indicating accumulation of P and clay in low‐lying areas. These patterns suggest that historical field‐level managements have primarily shaped P distribution, while hydrologic and landscape properties further influence its redistribution via transport pathways and drainage. These findings support the development of landscape models to map critical source areas in low‐relief watersheds and guide targeted mitigation in high‐risk P export zones.

Concentrated animal feeding operations (CAFOs), such as poultry farms, contribute significantly to air pollution, particularly ammonia (NH3) and particulate matter (PM) emissions. Vegetative environmental buffers (VEBs) offer a sustainable, cost-effective, and low-maintenance solution for mitigating NH3 and PM emissions from CAFOs, and some previous studies showed that pollutant concentrations behind the VEBs were substantially reduced compared with concentration directly from the source. However, due to the lack of a controlled dataset for non-VEB situations, the net effect of VEBs could hardly be assessed. Thus, the dataset from the previous study was used to develop a methodology for quantitatively evaluating the efficacy of VEBs in reducing NH3 and PM emissions from a poultry house, and to distinguish the net pollutant reduction achieved by VEBs from those resulting merely from atmospheric dilution and dispersion. The results showed that VEB can effectively mitigate air pollutants emissions and attributes enhanced ground-level reductions of NH3 (72.7 % +/- 9.1 %), total suspended particle (TSP) (61.9 % +/- 10.0 %), PM10 (62.5 % +/- 9.9 %) and PM2.5 (94.6 % +/- 6.5 %). In addition, VEB demonstrated better mitigation performance during daytime. Meteorological conditions showed no correlation with pollutant concentrations or enhanced reduction ratios while significant positive correlations between reductions of NH3 and PM were also observed. These results demonstrated that VEBs are effective in reducing NH3 and PM emissions from poultry houses. The results from this study will inform conservation practice guidelines and assist land managers in employing VEBs for poultry house emitted air pollution reductions.

Metolachlor is the most heavily used member of acetanilide herbicides, which are noted for forming highly soluble metabolites in root zone soils soon after field application. The two primary metabolites of metolachlor, metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid (MOXA), retain the same chiral chemistry as their source and are important tracers of nitrate loading from agricultural cropland. New analytical methods for separating the isomers of MESA and MOXA, enable studies assessing changes in the abundance of atropisomer pairs of the carbon chiral enantiomers in environmental samples. These changes were documented starting with the atropisomers in the parent metolachlor structure, leading to soil-degraded metabolites, and then in samples collected over 3 years from 15 subwatersheds in the Upper Choptank River Watershed. The influence of drainage differences, %hydric soil and slope, across the watershed strongly correlate with shifts in atropisomer abundance ratios, especially for those enantiomers of MOXA and MESA with axial aS rotations. The hypothesis is that differentiating atropisomer chiral shifts occur as the compounds exit to receiving waters. These findings offer a novel tool to study the transport of these important tracers of cropland-influenced groundwater.

Trichloroethene (TCE) is a chlorinated solvent that can adversely affect human health. TCE-contaminated groundwater bioremediation relies on the presence of an active and diverse reductively dechlorinating microbial community. This process requires the presence of reduced conditions, which are also favorable to methanogens. Methanogens and dechlorinating bacteria can both use hydrogen for metabolism thus competition can arise. Previous studies have indicated that methanogens might also be beneficial for the dechlorinating microbial community since they can provide enzymes, cofactors and vitamins necessary for the metabolism. In this study, the methanogenesis inhibitors garlic oil (GO) and 2-chloroethanesulfonate (CES) were assessed for their effect on reductive dechlorination and methanogenesis in TCE contaminated groundwater. GO has been used in the field as a methanogenesis inhibitor but limited information is available on its effects on the microbial community. The results from this study indicated that GO did not impact the activity of the microbial community, while CES partially inhibited methanogenesis. At the assessed electron donor concentration (5 mM) neither of the compounds affected TCE dechlorination in the reactor microcosms. This information can be beneficial for decision-makers, when designing a TCE-bioremediation plan to assess the need for amendments to enhance long-term TCE dechlorination activity at the site.

The Long-Term Agroecosystem Research (LTAR) network is a collaborative initiative funded by the U.S. Department of Agriculture, Agricultural Research Service, aimed at advancing sustainable, resilient agriculture through coordinated research conducted on croplands, grazing lands, and integrated crop/livestock systems. Here we provide an overview of the LTAR network, highlighting its vision, mission, initiatives, recent network activities, and future directions. Network-level research is critical for developing contextually relevant solutions to the challenges faced by agricultural producers. Long-term data collection, stakeholder engagement, and the integration of scientific knowledge are needed to enhance agricultural productivity and its resiliency, environmental quality, profitability, and social well-being into the future.

The buffering of phosphorus (P) in the landscape delays management outcomes for water quality. If stored in labile form (readily exchangeable and bioavailable), P may readily pollute waters. We studied labile P and its intensity for >600 soils and sediments across seven study locations in the United States. Stocks of labile P were large enough to sustain high P losses for decades, indicating the transport-limited regime typical of legacy P. Sediments were commonly more P-sorptive than nearby soils. Soils in the top 5 cm had 1.3-3.0 times more labile P than soils at 5-15 cm. Stratification in soil test P and total P was, however, less consistent. As P exchange via sorption processes follows the difference in intensities between soil/sediment surface and solution, we built a model for the equilibrium phosphate concentration at net zero sorption (EPC0) as a function of labile P (quantity) and buffer capacity. Despite widely varying properties across sites, the model generalized well for all soils and sediments: EPC0 increased sharply with more labile P and to greater degree when buffer capacity was low or sorption sites were likely more saturated. This quantity-intensity-capacity relationship is central to the P transport models we rely on today. Our data inform the improvement of such P models, which will be necessary to predict the impacts of legacy P. Further, this work reaffirms the position of labile P as a key focus for environmental P management-a view Dr. Sharpley developed in the 1980s with fewer data and resources.

Air pollutants from poultry production, such as ammonia (NH3) and particulate matter (PM), have raised concerns due to their potential negative impacts on human health and the environment. Vegetative environmental buffers (VEBs), consisting of trees and/or grasses planted around poultry houses, have been investigated as a mitigation strategy for these emissions. Although previous research demonstrated that VEBs can reduce NH3 and PM emissions, these studies used a limited number of samplers and did not examine concentration profiles. Moreover, the differences between daytime and nighttime emissions have not been investigated. In this study, we characterized emission profiles from a commercial poultry house using an array with multiple sampling heights and explored the differences between daytime and nighttime NH3 and PM profiles. We conducted three sampling campaigns, each with ten sampling events (five daytime and five nighttime), at a VEB-equipped poultry production facility. NH3 and PM samples were collected downwind from the ventilation tunnel fans before, within, and after the VEB. Results showed that ground-level concentrations beyond the VEB decreased to 8.0% ± 2.7% for NH3, 13% ± 4% for TSP, 13% ± 4% for PM10, and 2.4% ± 2.8% for PM2.5 of the original concentrations from the exhaust tunnel fan, with greater reduction efficiency during daytime than nighttime. Furthermore, pollutant concentrations were positively intercorrelated. These findings will be valuable for developing more effective pollutant remediation strategies in poultry house emissions.

Trichloroethylene (TCE) is a toxic organic compound, which can adversely affect human health. The chemical is one of the most frequently found contaminants in groundwater in the United States and around the world. A landfill in Maryland contaminated with high levels of TCE decades ago was added to the National Priority List (NPL) in 1994 for clean up. A biowall was installed on the site in 2013 to promote the bioremediation of TCE and subsequently of its degradation products. Six-year monitoring data indicated a steady removal of >99% groundwater TCE at the wall since installation. However, a concurrent buildup of intermediate byproducts was observed downgradient of the wall. An examination of the entire system was necessary to find the reason behind the inefficiency of the biowall. In this study, the background of the site, remediation plan, and installation were assessed. Monitoring data, including the concentration of TCE and its degradation byproducts, and geochemical and physical characteristics were evaluated to understand the conditions and challenges facing decision-makers of this project and possible options to improve biowall efficacy.

More than 40 leading US agricultural and water scientists developed a water research vision designed to address the most critical water and agricultural challenges in a changing climate to sustain agricultural production and natural systems. Water sustainability can only be realized by balancing the

Many groundwater aquifers around the world are contaminated with trichloroethene (TCE), which can be harmful to human and ecosystem health. Permeable Reactive Barriers (PRB) are commonly used to remediate TCE-contaminated groundwaters especially when a point source is ill defined. Using biosolids from wastewater treatment plants as a PRB filling material can provide a source of carbon and nutrients for dechlorinating bacterial activity. However, under the anaerobic conditions of the PRB, methanogenesis can also occur which can adversely affect reductive dechlorination. We conducted bench scale experiments to evaluate the effect of biosolids on TCE reductive dechlorination and found that methanogenesis was significantly higher in the reactors amended with biosolids, but that reductive dechlorination did not decrease. Furthermore, the microbial communities in the biosolid-enhanced reactors were more abundant with obligate dechlorinators, such as Dehalobacter and Dehalogenimonas, than the reactors amended only with the dechlorinating culture. The biosolids enhanced the presence and abundance of methanogens and acetogens, which had a positive effect on maintaining an efficient dechlorinating microbial community and provided the necessary enzymes, cofactors, and electron donors. These results indicate that waste materials such as biosolids can be turned into a valuable resource for bioremediation of TCE and likely other contaminants.

Single injection, chiral analysis of two abundant metolachlor metabolites, metolachlor ethanesulfonic acid (MESA) and metolachlor oxanilic acid (MOXA), was accomplished using 10 mL of water samples, modified from the original 1 L method for MESA analysis alone. These compounds revealed a temporal stamp corresponding to a conversion from racemic to S-enriched metolachlor that can be used to reduce uncertainty and equifinality in modeling watershed cropland response. They offer a dual tracer for watershed processing of nitrate that is derived from a common source and provides utility for sampling and consistency in tracing both time-weighted and long-term processes related to hydrology. Six matched grab sample results compared the 1 L and 10 mL procedures with less than a 12% difference. Average recoveries for the 10 mL method were 94% for the four isomers of MOXA and 96% for the three peaks of MESA. The 10 mL method increases the accessibility of this procedure for water age dating on a larger scale.

Complete separation of the trans-enantiomers of the two most abundant, persistent polar metabolites of metolachlor, metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid (MOXA), was achieved using UPLC equipped with a reverse phase chiral column and trace detection with an electrospray triple quadrupole mass spectrometer. Various conditions that influenced the separation and instrumental signal were investigated to achieve the optimum separation and instrument response within an analysis time of less than 30 minutes. Different eluting solvent compositions for each metabolite were required for optimized separation of of the 4 enantiomers. Standard curves were responsive to less than 13 ng/mL and 8 ng/mL for the least plentiful MOXA and MESA enantiomers, respectively with a linear coefficient of determination greater than 0.998. Suitability of the method for quantification of the 4 mixed enantiomers of each was demonstrated using natural surface water samples collected from the Choptank River watershed in Eastern Maryland.•LC chiral separation parameters were varied to achieve optimal separation of the major enantiomers of the two metolachlor metabolites.•LC/MS-MS parameters were adjusted to maximize response and minimize analysis time.•Finished methods were used to quantitate enantiomers in archived stream water extracts from agricultural watersheds with corn/soybean production.

Monitoring and modeling of airborne particulate matter (PM) from low-altitude sources is becoming an important regulatory target as the adverse health consequences of PM become better understood. However, application of models not specifically designed for simulation of PM from low-altitude emissions may bias predictions. To address this problem, we describe the modification and validation of an air dispersion model for the simulation of low-altitude PM dispersion from a typical cotton ginning facility. We found that the regulatory recommended model (AERMOD) overestimated pollutant concentrations by factors of 64.7, 6.97 and 7.44 on average for PM2.5, PM10, and TSP, respectively. Pollutant concentrations were negatively correlated with height (p < 0.05), distance from source (p < 0.05) and standard deviation of wind direction (p < 0.001), and positively correlated with average wind speed (p < 0.001). Based on these results, we developed dispersion correction factors for AERMOD and cross-validated the revised model against independent observations, reducing overestimation factors to 3.75, 1.52 and 1.44 for PM2.5, PM10 and TSP, respectively. Further reductions in model error may be obtained from use of additional observations and refinement of dispersive correction factors. More generally, the correction permits the validated adjustment and application of pre-existing models for risk assessment and development of remediation techniques. The same approach may also be applied to improve simulations of other air pollutants and environmental conditions of concern.

Washing is essential in fresh-cut produce industry to remove debris and ensure desirable shelf life. The intensive water usage during washing and water scarcity in the production regions necessitate proper water reuse and reconditioning. However, the organic compounds accumulated in the water elevate chlorine demand (CLD) and chemical oxygen demand (COD), thus complicating food sanitization and subsequent water treatment. Hereby, we examined the major sources of COD and CLD during fresh-cut produce washing, and explored the mitigation of CLD by treating select water constituents for the first time. Results showed that sugars as the predominant composition contribute to over 80% of COD in the wash water, whereas minor constituents including proteins/ peptides, acids, and phenolic compounds account for over 80% of total CLD. The actual CLDs by those compounds depend highly on produce type. Moreover, while removing large molecules from the wash water led to the greatest CLD reduction for romaine lettuce, absorption of anionic molecules proved the most effective for iceberg lettuce, onion, and carrot wash water. This study suggests the possibility of mitigating CLD by more targetted and cost-effective water treatment procedures without the need for removing sugars. It also recommends prudent and product-specific design for produce sanitization and water treatments.

Reducing the bioavailability of persistent organic contaminants in soil by incorporating carbonaceous material (CM) has been investigated and confirmed by numerous laboratory studies. However, the efficacy of these methods under more complex field conditions needs exploration. We conducted an 18-month, small-scale plot study (n = 7) to evaluate the ability of two CMs, a compost aged for four months and a compost aged for two years, to reduce the bioavailability of the highly aged organochlorine pesticides (OCPs) dichlorodiphenyltrichloroethane (DDT), its metabolites (together as DDx), and dieldrin in soil. The study was carried out in a former orchard where OCPs were routinely applied until they were banned in the early 1970s. Soil and earthworms were collected, contaminant concentrations were measured, and bioaccumulation factors (BAF) of the OCPs were calculated for the 28 subplots at multiple timepoints. A decrease in the uptake and bioaccumulation of the OCPs was observed with increasing soil concentration, i.e., the relationship between soil and worm concentrations was non-linear. In addition, substantial spatial variability in soil and earthworm concentrations were observed, which resulted in variable BAFs across the site. The soil treated with CMs, 14 subplots in total, showed varying effects on bioaccumulation: for DDx 8 showed a reduction, 4 showed no difference, and 2 showed an increase; and for dieldrin 6 showed a reduction, 5 showed no difference, and 3 showed an increase. Although this study showed some evidence that CM amendments may reduce bioaccumulation over time, the results were not statistically significant due to the spatial and temporal variability. This work illustrates the challenges of extrapolating laboratory results to onsite determinations and suggests that more robust methods are needed in calculating ecological risk assessments for indigenous animals, particularly for legacy sites with substantial spatial variability.

Dicamba is an important herbicide for controlling post-emergent resistant weeds in soybean farming. Recently, the scientific community and general public have further examined off-target transport mechanisms (e.g., spray drift, volatilization, and tank contamination) and the visual responses of soybeans to ultralow dicamba concentrations. This paper synthesizes key chemical concepts and environmental processes associated with dicamba formulations, transport mechanisms, drift measurements, and plant responses. This paper proposes additional areas of research and actions to increase our understanding and communicate the science findings, which should provide farmers with more robust tools and practices for sustainable dicamba use.

Estimating the transport of ammonia and particulate matter (PM) from ventilation tunnel fans of poultry houses is needed to develop effective mitigation strategies. However, field measurements are time-consuming and costly. Alternatively, air dispersion models can provide more information under a variety of conditions. Therefore, this study was conducted to modify and to validate the Gaussian plume model to predict poultry house plumes. The most notable modification was the addition of a virtual, emission-releasing point behind the exhaust tunnel fan. The modified model was validated using previously-reported field measurements. The fraction of predictions within a factor of two (FAC2) for both ammonia and PM observations was greatly improved compared with original model. In addition, the model performance was not sensitive to different sampling scenarios. This new model can be applied to other experiments and will be useful in evaluating the effectiveness of mitigation strategies for air pollutant emissions.

We previously discovered a method to estimate the groundwater mean residence time using the changes in the enantiomeric ratio of metolachlor ethanesulfonic acid (MESA), (2-[(2-ethyl-6-methylphenyl)(2-methoxy-1-methylethyl)amino]-2-oxoethanesulfonic acid), a metabolite of the herbicide metolachlor. However, many grab samples would be needed for each watershed over an extended period, and this is not practical. Thus, we examined the use of a polar organic chemical integrative sampler (POCIS) deployed for 28 days combined with a modified liquid chromatography-mass spectrometry LC-MS/MS method to provide a time-weighted average of the MESA enantiomeric ratio. POCISs equipped with hydrophilic-lipophilic-balanced (HLB) discs were deployed at five sites across the United States where metolachlor was used before and after 1999 and compared the effectiveness of the POCIS to capture MESA versus grab samples. In addition, an in situ POCIS sampling rate (Rs) for MESA was calculated (0.15 L/day), the precision of MESA extraction from stored POCIS discs was determined, and the effectiveness of HLB to extract MESA was examined. Finally, using molecular modeling, the influence of the asymmetric carbon of metolachlor degradation on the MESA enantiomeric ratio was predicted to be negligible. Results of this work will be used in projects to discern the groundwater mean residence times, to evaluate the delivery of nitrate-N from groundwater to surface waters under various soil, agronomic, and land use conditions, and to examine the effectiveness of conservation practices.