Decoding neural activity to assess individual latent state in ecologically valid contexts.

Objective.Currently, there exists very few ways to isolate cognitive processes, historically defined via highly controlled laboratory studies, in more ecologically valid contexts. Specifically, it remains unclear as to what extent patterns of neural activity observed under such constraints actually manifest outside the laboratory in a manner that can be used to make accurate inferences about latent states, associated cognitive processes, or proximal behavior. Improving our understanding of when and how specific patterns of neural activity manifest in ecologically valid scenarios would provide validation for laboratory-based approaches that study similar neural phenomena in isolation and meaningful insight into the latent states that occur during complex tasks.Approach.Domain generalization methods, borrowed from the work of the brain-computer interface community, have the potential to capture high-dimensional patterns of neural activity in a way that can be reliably applied across experimental datasets in order to address this specific challenge. We previously used such an approach to decode phasic neural responses associated with visual target discrimination. Here, we extend that work to more tonic phenomena such as internal latent states. We use data from two highly controlled laboratory paradigms to train two separate domain-generalized models. We apply the trained models to an ecologically valid paradigm in which participants performed multiple, concurrent driving-related tasks while perched atop a six-degrees-of-freedom ride-motion simulator.Main Results.Using the pretrained models, we estimate latent state and the associated patterns of neural activity. As the patterns of neural activity become more similar to those patterns observed in the training data, we find changes in behavior and task performance that are consistent with the observations from the original, laboratory-based paradigms.Significance.These results lend ecological validity to the original, highly controlled, experimental designs and provide a methodology for understanding the relationship between neural activity and behavior during complex tasks.

Subsurface phosphorus and nitrogen loss following liquid dairy manure and commercial fertilizer application on a clay soil in northwest Ohio.

Nutrient source has been the focus of much debate regarding the re-eutrophication of Lake Erie, despite that only 20% of nutrients applied to crops in the Western Lake Erie Basin (WLEB) originate from organic sources. However, limited data and assessments exist on the subsurface tile drainage water quality comparison between organic (liquid dairy manure) and commercial (mono-ammonium phosphate [MAP]) sources in crop production systems. Subsurface tile drainage, dissolved reactive phosphorus (DRP) and total phosphorus (TP) losses in tile drainage discharge following equal phosphorus (P) based applications of liquid dairy manure and MAP were assessed using a before-after control-impact design and 4 years of data from a paired field system located in northwest Ohio. Nitrate-nitrogen (NO3 - -N ) and total nitrogen (TN) losses were also examined to supplement the P findings; however, due to dissimilar nitrogen application rates, losses were assessed in a different context. No significant differences (p > 0.05) were detected in drainage discharge volumes or TP loads between the control and impact sites. However, statistically significant increases (p < 0.05) were measured for mean daily DRP, NO3 - -N, and TN loads from the dairy manure site. While significant, mean daily DRP differences between commercial (MAP) and liquid dairy manure treatments were only on the order of 0.01 g DRP ha-1 . Assuming current manure application extent and rates, when accumulated annually across the WLEB watershed, these losses are equivalent to less than 1% of target loads. These findings also help to inform nutrient management stewardship as it relates to nutrient source. Furthermore, additional research across a range of soil characteristics and cropping managements should be explored as well as the impacts of other livestock manure nutrients.

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

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

Connecting soil characteristics to edge-of-field water quality in Ohio.

Soil health and water quality improvement are major goals of sustainable agricultural management systems, yet the connections between soil health and water quality impacts remain unclear. In this study we conducted an initial exploratory assessment of the relationships between soil chemical, physical, and biological properties and edge-of-field water quality across a network of 40 fields in Ohio, USA. Discharge, dissolved reactive P (DRP), total P (TP), and nitrate (NO3 ) losses associated with precipitation events via surface runoff and tile drainage were monitored. Agronomic soil tests and a suite of soil health indicators were measured, then predictive relationships between the field average soil properties and tile drainage and surface runoff discharge and DRP, TP, and nitrate loads were explored with random forest and multiple linear regression approaches. Among the soil health indicators, water extractable C and N were consistently found to be positively related to tile nitrate loads, but other soil health indicators had little or inconsistent importance for water quality impacts. Several other soil properties were important predictors, particularly soil P pools for surface and tile DRP and TP losses as well as Mehlich-3 (M3) extractable Fe and Al for surface and tile discharge. Thus, we did not observe strong evidence that soil health was associated with improved edge-of-field water quality across the edge-of-field monitoring network. However, additional studies are needed to definitively test the relationships between a broader array of soil health metrics and water quality outcomes.

Influence of climate, topography, and soil type on soil extractable phosphorus in croplands of northern glacial-derived landscapes.

Delineating the relative solubility of soil phosphorus (P) in agricultural landscapes is essential to predicting potential P mobilization in the landscape and can improve nutrient management strategies. This study describes spatial patterns of soil extractable P (easily, moderately, and poorly soluble P) in agricultural landscapes of the Red River basin and the southern Great Lakes region. Surface soils (0-30 cm) and select deeper cores (0-90 cm) were collected from 10 cropped fields ranging in terrain (near-level to hummocky), soil texture (clay to loam), composition (calcareous to noncalcareous), and climate across these differing glacial landscapes. Poorly soluble P dominated (up to 91%) total extractable P in the surface soils at eight sites. No differences in the relative solubilities of soil extractable P with microtopography were apparent in landscapes without defined surface depressions. In contrast, in landscapes with pronounced surface depressions, increased easily soluble P (Sol-P), and decreased soil P sorption capacity were found in soil in wetter, low-slope zones relative to drier upslope locations. The Sol-P pool was most important to soil P retention (up to 28%) within the surface depressions of the Red River basin and at sites with low-carbonate soils in the southern Lake Erie watershed (up to 28%), representing areas at elevated risk of soil P remobilization. This study demonstrates interrelationships among soil extractable P pools, soil development, and soil moisture regimes in agricultural glacial landscapes and provides insight into identifying potential areas for soil P remobilization and associated P availability to crops and runoff.

Cover crops differentially influenced nitrogen and phosphorus loss in tile drainage and surface runoff from agricultural fields in Ohio, USA.

Nitrogen (N) and phosphorus (P) loss from crop production agriculture is transported to adjacent and downstream water bodies, resulting in negative environmental impacts including harmful and nuisance algal blooms. Cover crops are a conservation management practice that replaces bare soil with vegetation outside of the cash crop growing season, purportedly reducing N and P loss by increasing water and nutrient demand in agroecosystems. In this study, we compared nitrate (NO3--N), total N (TN), dissolved reactive P (DRP), and total P (TP) loads in subsurface (tile) drainage and surface runoff from fields with cover crop management (CC) and fields without cover crop management (NoCC) using continuous monitoring data from 40 agricultural fields located throughout northcentral Ohio, United States (US). We found that average monthly tile NO3--N and TN loads from CC fields were ~50% less than NoCC fields, while average monthly tile discharge, DRP, and TP loads did not differ between CC and NoCC fields. Cover crops also did not significantly influence average monthly surface metrics. Cover crops reduced monthly totals of tile NO3--N and TN loads by ~1.0-2.6 kg N ha-1 from January to June (winter and spring), coinciding with critical periods of nutrient loss from agroecosystems in the midwestern US, but increased monthly totals of tile DRP (by 0.4-12.1 g DRP ha-1) and TP (by 1.2-31.6 g TP ha-1) loads during some months. We found similar patterns at the annual time scale whereby CC fields had lesser cumulative annual totals of tile NO3--N and TN but greater cumulative annual totals of tile DRP and TP. These results show that the influence of cover crops on N loads, but not P, were consistent across temporal scales of examination, demonstrating that cover crops effectively increased N demand and mitigated N losses from agricultural fields. The variable influence of cover crops on P loads underscores the need for greater understanding of the factors and mechanisms that control P loss in systems that include cover crop management. Furthermore, these findings stress the importance of identifying and selecting conservation management practices tailored to the natural resource concern.

Controls on subsurface nitrate and dissolved reactive phosphorus losses from agricultural fields during precipitation-driven events.

The magnitude of nitrogen (N) and phosphorus (P) exported from agricultural fields via subsurface tile drainage systems is determined by site-specific interactions between weather, soil, field, and management characteristics. Here, we used multiple regression analyses to evaluate the influence of 29 controls of precipitation event-driven discharge, nitrate (NO3--N) load, and dissolved reactive P (DRP) load from subsurface tile drains, leveraging a unique dataset of ~7000 precipitation events observed across 40 agricultural fields (n = 190 site years) instrumented to collect continuous water quality samples. We calculated marginal effects of significant controls and assessed the modifying influence of event rainfall, duration, and intensity, and antecedent precipitation. Tile discharge was strongly and positively influenced by previous 7-day precipitation and total rainfall and negatively influenced by daily temperature and tile spacing. Both tile NO3--N and DRP loads were positively influenced by transport and source variables, including event discharge and total fertilizer applied as well as soil test P (STP) in the case of tile DRP load; factors with the strongest negative influence on tile NO3--N and DRP loads were related to time of year. The strength and direction of both positive and negative controls also varied with precipitation characteristics. For example, the positive influence of event discharge on nutrient loads lessened as event duration, event intensity, and previous 7-day precipitation increased, while the positive influence of N and P sources strengthened, particularly in response to extreme (or maximum) events. Results here demonstrate the predominant role of transport and source controls while accounting for interactive effects among site-specific characteristics and underscore the importance of storm dynamics when managing N and P loss from agricultural fields.

Legacy phosphorus concentration-discharge relationships in surface runoff and tile drainage from Ohio crop fields.

Legacy phosphorus (P) in agricultural soils can be transported to surface waters via runoff and tile drainage, where it contributes to the development of harmful and nuisance algal blooms and hypoxia. However, a limited understanding of legacy P loss dynamics impedes the identification of mitigation strategies. Edge-of-field data from 41 agricultural fields in northwestern Ohio, USA, were used to develop regressions between legacy P concentrations (C) and discharge (Q) for two P fractions: total P (TP) and dissolved reactive P (DRP). Tile drainage TP concentration (CTP ) and DRP concentration (CDRP ) both increased as Q increased, and CTP tended to increase at a greater rate than CDRP . Surface runoff showed greater variation in C-Q regressions, indicating that the response of TP and DRP to elevated Q was field specific. The relative variability of C and Q was explored using a ratio of CVs (CVC /CVQ ), which indicated that tile drainage TP and DRP losses were chemodynamic, whereas losses via surface runoff demonstrated both chemodynamic and chemostatic behavior. The chemodynamic behavior indicated that legacy P losses were strongly influenced by variation in P source availability and transport pathways. In addition, legacy P source size influenced C, as demonstrated by a positive relationship between soil-test P and the CTP and CDRP in both tile drainage and surface runoff. Progress towards legacy P mitigation will require further characterization of the drivers of variability in CTP and CDRP , including weather-, soil-, and management-related factors.

Impacts of preferential flow and agroecosystem management on subsurface particulate phosphorus loadings in tile-drained landscapes.

Recent research on tile-drainage has placed emphasis on dissolved reactive phosphorus (DRP) delivery and transport pathways but less emphasis on particulate P (PP), resulting in its exclusion from agricultural water management models. In this study, we quantified the fluxes, mechanisms, and factors driving PP delivery into tiles through statistical analysis of a long-term hydrologic and water quality dataset. The dataset includes 5 yr of surface and tile discharge, total P (TP), DRP, total nitrogen (TN), and dissolved inorganic N concentrations from two edge-of-field study sites with contrasting soil and management practices. Hydrograph recession techniques were coupled with multiple linear regression for understanding hydrologic flow pathways, and empirical mode decomposition (EMD) time-series analysis was used to determine the significance of PP seasonality processes and the effect of management practices. The analysis of hydrologic flow pathways demonstrated that quickflow contributed 66 and 36% of subsurface discharge in the clay and loam sites, respectively. Phosphorus loading analysis showed that macropore flow plays a significant role in PP delivery to subsurface P loading and that PP significantly contributed to TP and DRP delivery; however, greater PP loadings were observed at the clay site despite greater subsurface discharge and soil test P levels at the loam site. Furthermore, PP delivery was significantly affected by environmental conditions and management practices. We highlight the efficacy of hydrograph recession analysis for identifying macropore and diffuse drainage, of P/N ratios to characterize sediment delivery mechanisms in tiles, and of EMD to detect management impacts on TP and DRP at the field scale.

Injury frequency and severity in crayfish communities as indicators of physical habitat quality and water quality within agricultural headwater streams.

Crayfishes (Decapoda) are common inhabitants of agricultural headwater streams in the Midwestern USA that have been impacted by physical habitat degradation and contamination by agricultural pollutants. The frequency and severity of injuries within crayfish communities are indicators of crayfish aggression, which is influenced by physical, chemical, and biotic factors. Previous studies have not evaluated the relationships of the frequency and severity of crayfish injuries with physical habitat quality, water quality, and biotic factors within agricultural headwater streams. Understanding these relationships will assist with determining if crayfish injury variables can serve as an indicator of physical habitat quality or water quality in these small degraded streams. We sampled crayfishes, documented the frequency and type of injuries, and measured instream habitat and water chemistry in 2014 and 2015 within 12 agricultural headwater streams in Indiana, Michigan, and Ohio. We documented five native crayfish species from 1641 adult captures. The most abundant species were Faxonius rusticus, Faxonius immunis, and Faxonius propinquus. Linear mixed effect model analyses indicated that four crayfish injury response variables were positively correlated (p < 0.05) with crayfish density, physical habitat quality, and water velocity diversity and that crayfish injury response variables were more strongly correlated with crayfish density than physical habitat quality or water quality. Our results indicate that response variables describing the severity and frequency of crayfish injuries can be effective indicators of physical habitat quality in agricultural headwater streams.

Conservation implications of fish-habitat relationships in channelized agricultural headwater streams.

Channelized agricultural headwater streams are common throughout agricultural watersheds in the midwestern United States. Understanding fish-habitat relationships within these streams will provide information that can assist with developing conservation and restoration strategies for these degraded streams. From spring 2006 to fall 2010, we collected fishes and measured riparian habitat, instream habitat, and water chemistry variables from seven sites in Cedar Creek, Indiana, and 14 sites in Upper Big Walnut Creek, Ohio. We found that fish community structure was more strongly correlated with instream habitat than riparian habitat or water chemistry in both watersheds. We also observed interrelationships among instream habitat, watershed size, and fish communities within both watersheds that suggest that the hydrological changes that occur with increasing watershed size are the underlying factor for fish community changes that occur with increasing watershed size. Our results suggest that conservation and restoration efforts within channelized agricultural headwater streams in the midwestern United States, where nutrients and herbicide concentrations are low, need to address physical habitat degradation to positively influence fish community structure.

Internal Phosphorus Storage in Two Headwater Agricultural Streams in the Lake Erie Basin.

Internal phosphorus (P) in sediments plays an important role in the nutrient dynamics of lakes, sometimes long after external loads have been reduced. Similarly, internal P sources may drive the nutrient dynamics of small agricultural streams that drain to larger rivers and lakes, despite best management practices intended to reduce external P loads from adjacent fields. Here, internal P concentrations were measured with sequential extraction on cores collected in spring and summer from two small agricultural streams in the drainage basin of Lake Erie, a large, eutrophic lake experiencing increasing SRP loads. Average total extractable P concentrations were similar to within 5% during spring and summer, but mobile P binding fractions nearly doubled in summer, possibly due to accelerated rates of organic matter mineralization or iron reduction beneath suboxic, stagnant surface waters. One site had chronically greater internal P concentrations by 25-75%, despite the implementation of best management practices such as grass buffers. The site also had more aquatic vegetation that restricted the flow, less dissolved oxygen in surface water, and greater organic matter in sediments during both seasons, suggesting that variations in hydrology, sediment composition, and vegetation influence hot spots of P retention throughout small agricultural streams.

DRG microstimulation evokes postural responses in awake, standing felines.

OBJECTIVE: We have demonstrated previously that microstimulation in the dorsal root ganglia (DRG) can selectively evoke activity in primary afferent neurons in anesthetized cats. This study describes the results of experiments focused on characterizing the postural effects of DRG microstimulation in awake cats during quiet standing. APPROACH: To understand the parameters of stimulation that can affect these postural shifts, we measured changes in ground reaction forces (GRF) while varying stimulation location and amplitude. Four animals were chronically implanted at the L6 and L7 DRG with penetrating multichannel microelectrode arrays. During each week of testing, we identified electrode channels that recruited primary afferent neurons with fast (80-120 m s-1) and medium (30-75 m s-1) conduction velocities, and selected one channel to deliver current-controlled biphasic stimulation trains during quiet standing. MAIN RESULTS: Postural responses were identified by changes in GRFs and were characterized based on their magnitude and latency. During DRG microstimulation, animals did not exhibit obvious signs of distress or discomfort, which could be indicative of pain or aversion to a noxious sensation. Across 56 total weeks, 13 electrode channels evoked behavioral responses, as detected by a significant change in GRF. Stimulation amplitude modulated the magnitude of the GRF responses for these 13 channels (p  < 0.001). It was not possible to predict whether or not an electrode would drive a behavioral response based on information including conduction velocity, recruitment threshold, or the DRG in which it resided. SIGNIFICANCE: The distinct and repeatable effects on the postural response to low amplitude (<40 µA) DRG microstimulation support that this technique may be an effective way to restore somatosensory feedback after neurological injuries such as amputation.

Phosphorus Availability in Western Lake Erie Basin Drainage Waters: Legacy Evidence across Spatial Scales.

The Western Lake Erie Basin (WLEB) was inundated with precipitation during June and July 2015 (two to three times greater than historical averages), which led to significant nutrient loading and the largest in-lake algal bloom on record. Using discharge and concentration data from three spatial scales (0.18-16,000 km), we contrast the patterns in nitrate (NO-N) and dissolved reactive phosphorus (DRP) concentration dynamics and discuss potential management implications. Across all scales, NO-N concentration steadily declined with each subsequent rainfall event as it was flushed from the system. In contrast, DRP concentration persisted, even on soils at or below agronomic P levels, suggesting that legacy P significantly contributes to nutrient loads in the WLEB. These findings highlight the need to revisit current P fertility recommendations and soil testing procedures to increase P fertilizer use efficiency and to more holistically account for legacy P.

Modified APEX model for Simulating Macropore Phosphorus Contributions to Tile Drains.

The contribution of macropore flow to phosphorus (P) loadings in tile-drained agricultural landscapes remains poorly understood at the field scale, despite the recognized deleterious impacts of contaminant transport via macropore pathways. A new subroutine that couples existing matrix-excess and matrix-desiccation macropore flow theory and a modified P routine is implemented in the Agricultural Policy Environmental eXtender (APEX) model. The original and modified formulation were applied and evaluated for a case study in a poorly drained field in Western Ohio with 31 months of surface and subsurface monitoring data. Results highlighted that a macropore subroutine in APEX improved edge-of-field discharge calibration and validation for both tile and total discharge from satisfactory and good, respectively, to very good and improved dissolved reactive P load calibration and validation statistics for tile P loads from unsatisfactory to very good. Output from the calibrated macropore simulations suggested median annual matrix-desiccation macropore flow contributions of 48% and P load contributions of 43%, with the majority of loading occurring in winter and spring. While somewhat counterintuitive, the prominence of matrix-desiccation macropore flow during seasons with less cracking reflects the importance of coupled development of macropore pathways and adequate supply of the macropore flow source. The innovative features of the model allow for assessments of annual macropore P contributions to tile drainage and has the potential to inform P site assessment tools.

Edge-Of-Field Evaluation of the Ohio Phosphorus Risk Index.

The Phosphorus Index (PI) has been the cornerstone for phosphorus (P)-based management and planning over the past twenty years, yet field-scale evaluation of many state PIs has been limited. In this study, P loads measured in surface runoff and tile discharge from 40 agricultural fields in Ohio with prevailing management practices were used to evaluate the Ohio PI. Annual P loads were highly variable among fields (dissolved reactive P: 0.03-4.51 kg ha, total P: 0.03-6.88 kg ha). Both measured annual dissolved reactive P ( = 0.36, < 0.001) and total P ( = 0.25, < 0.001) loads were significantly related to Ohio PI score. The relationship between measured load and PI score substantially improved when averaged annual field values were used (dissolved reactive P: = 0.71, total P: = 0.73), indicating that the Ohio PI should be utilized to evaluate average annual risk of P loss, rather than as an annual risk tool. Comparison between the Ohio PI and other established local and national metrics resulted in large differences in potential P management recommendations for the monitored fields. In the near term, revision of Ohio PI risk categories and management recommendations using local P loading thresholds is needed. To meet the minimum criteria for state PI tools, future research efforts should focus on using measured field data (i) to incorporate new input factors (i.e., P application timing and leaching potential) into the Ohio PI, and (ii) to calibrate and validate the Ohio PI to provide better P risk assessments and management recommendations.

Contributions of systematic tile drainage to watershed-scale phosphorus transport.

Phosphorus (P) transport from agricultural fields continues to be a focal point for addressing harmful algal blooms and nuisance algae in freshwater systems throughout the world. In humid, poorly drained regions, attention has turned to P delivery through subsurface tile drainage. However, research on the contributions of tile drainage to watershed-scale P losses is limited. The objective of this study was to evaluate long-term P movement through tile drainage and its manifestation at the watershed outlet. Discharge data and associated P concentrations were collected for 8 yr (2005-2012) from six tile drains and from the watershed outlet of a headwater watershed within the Upper Big Walnut Creek watershed in central Ohio. Results showed that tile drainage accounted for 47% of the discharge, 48% of the dissolved P, and 40% of the total P exported from the watershed. Average annual total P loss from the watershed was 0.98 kg ha, and annual total P loss from the six tile drains was 0.48 kg ha. Phosphorus loads in tile and watershed discharge tended to be greater in the winter, spring, and fall, whereas P concentrations were greatest in the summer. Over the 8-yr study, P transported in tile drains represented <2% of typical application rates in this watershed, but >90% of all measured concentrations exceeded recommended levels (0.03 mg L) for minimizing harmful algal blooms and nuisance algae. Thus, the results of this study show that in systematically tile-drained headwater watersheds, the amount of P delivered to surface waters via tile drains cannot be dismissed. Given the amount of P loss relative to typical application rates, development and implementation of best management practices (BMPs) must jointly consider economic and environmental benefits. Specifically, implementation of BMPs should focus on late fall, winter, and early spring seasons when most P loading occurs.

Surface runoff and tile drainage transport of phosphorus in the midwestern United States.

The midwestern United States offers some of the most productive agricultural soils in the world. Given the cool humid climate, much of the region would not be able to support agriculture without subsurface (tile) drainage because high water tables may damage crops and prevent machinery usage in fields at critical times. Although drainage is designed to remove excess soil water as quickly as possible, it can also rapidly transport agrochemicals, including phosphorus (P). This paper illustrates the potential importance of tile drainage for P transport throughout the midwestern United States. Surface runoff and tile drainage from fields in the St. Joseph River Watershed in northeastern Indiana have been monitored since 2008. Although the traditional concept of tile drainage has been that it slowly removes soil matrix flow, peak tile discharge occurred at the same time as peak surface runoff, which demonstrates a strong surface connection through macropore flow. On our research fields, 49% of soluble P and 48% of total P losses occurred via tile discharge. Edge-of-field soluble P and total P areal loads often exceeded watershed-scale areal loadings from the Maumee River, the primary source of nutrients to the western basin of Lake Erie, where algal blooms have been a pervasive problem for the last 10 yr. As farmers, researchers, and policymakers search for treatments to reduce P loading to surface waters, the present work demonstrates that treating only surface runoff may not be sufficient to reach the goal of 41% reduction in P loading for the Lake Erie Basin.

Phosphorus transport in agricultural subsurface drainage: a review.

Phosphorus (P) loss from agricultural fields and watersheds has been an important water quality issue for decades because of the critical role P plays in eutrophication. Historically, most research has focused on P losses by surface runoff and erosion because subsurface P losses were often deemed to be negligible. Perceptions of subsurface P transport, however, have evolved, and considerable work has been conducted to better understand the magnitude and importance of subsurface P transport and to identify practices and treatments that decrease subsurface P loads to surface waters. The objectives of this paper were (i) to critically review research on P transport in subsurface drainage, (ii) to determine factors that control P losses, and (iii) to identify gaps in the current scientific understanding of the role of subsurface drainage in P transport. Factors that affect subsurface P transport are discussed within the framework of intensively drained agricultural settings. These factors include soil characteristics (e.g., preferential flow, P sorption capacity, and redox conditions), drainage design (e.g., tile spacing, tile depth, and the installation of surface inlets), prevailing conditions and management (e.g., soil-test P levels, tillage, cropping system, and the source, rate, placement, and timing of P application), and hydrologic and climatic variables (e.g., baseflow, event flow, and seasonal differences). Structural, treatment, and management approaches to mitigate subsurface P transport-such as practices that disconnect flow pathways between surface soils and tile drains, drainage water management, in-stream or end-of-tile treatments, and ditch design and management-are also discussed. The review concludes by identifying gaps in the current understanding of P transport in subsurface drains and suggesting areas where future research is needed.

Event based analysis of chlorothalonil concentrations following application to managed turf.

Chlorothalonil concentrations exceeding acute toxicity levels for certain organisms have been measured in surface water discharge events from managed turf watersheds. The duration of exceedence and the timing of these events related to precipitation/runoff and time since application, however, have not been explored. Chlorothalonil concentrations were measured from discharge waters draining a managed turf watershed in Duluth, Minnesota, USA, between 2003 and 2009. The median chlorothalonil concentration was 0.58 µg/L. Approximately 2% of all measured concentrations exceeded the 7.6 µg/L median lethal concentration (LC50) acute toxicity level for rainbow trout. One-twentieth the LC50 concentration, equivalent to the level of concern (0.38 µg/L) for endangered species, was exceeded 31% of the time during the present study. The concentrations that exceeded the LC50 threshold were associated with eight rainfall/runoff events. Low dose exposures are a more important biological concern than acute occurrences. Exceedence concentrations associated with acute effects were significantly (p < 0.05) correlated to time since application and were measured only in the fall following extensive application. A conflict exists between the transportability of chlorothalonil as suggested by its chemical properties and the data collected in the present study. With respect to course-wide golf course application, avoiding application until after the major autumn rainfall period but before the first snow coverage is recommended to reduce occurrence of chlorothalonil concentrations that exceed toxic levels associated with acute and chronic levels of concern.