Agricultural Tile Drainage Research Articles

Mapping agricultural tile drainage in the US Midwest using explainable random forest machine learning and satellite imagery

There has been an increase in tile drained area across the US Midwest and other regions worldwide due to agricultural expansion, intensification, and climate variability. Despite this growth, spatially explicit tile drainage maps remain scarce, which limits the accuracy of hydrologic modeling and implementation of nutrient reduction strategies. Here, we developed a machine-learning model to provide a Spatially Explicit Estimate of Tile Drainage (SEETileDrain) across the US Midwest in 2017 at a 30-m resolution. This model used 31 satellite-derived and environmental features after removing less important and highly correlated features. It was trained with 60,938 tile and non-tile ground truth points within the Google Earth Engine cloud-computing platform. We also used multiple feature importance metrics and Accumulated Local Effects to interpret the machine learning model. The results show that our model achieved good accuracy, with 96 % of points classified correctly and an F1 score of 0.90. When tile drainage area is aggregated to the county scale, it agreed well (r2 = 0.69) with the reported area from the Ag Census. We found that Land Surface Temperature (LST) along with climate- and soil-related features were the most important factors for classification. The top-ranked feature is the median summer nighttime LST, followed by median summer soil moisture percent. This study demonstrates the potential of applying satellite remote sensing to map spatially explicit agricultural tile drainage across large regions. The results should be useful for land use change monitoring and hydrologic and nutrient models, including those designed to achieve cost-effective agricultural water and nutrient management strategies. The algorithms developed here should also be applicable for other remote sensing mapping applications.

Microbial diversity and gene abundance in denitrifying bioreactors: A comparison of the woodchip surface biofilm versus the interior wood matrix.

Excessive amounts of nitrogen (N) and phosphorus (P) can lead to eutrophication in water sources. Woodchip bioreactors have shown success in removing N from agricultural runoff, but less is known regarding P removal. Woodchip bioreactors are subsurface basins filled with woodchips installed downgradient of agricultural land to collect and treat drainage runoff. Microorganisms use the woodchips as a carbon (C) source to transform N in the runoff, with unresolved biological impacts on P. This study aims to explore microbial communities present in the bioreactor and determine whether milling woodchips to probe the microbial communities within them reveals hidden microbial diversities or potential activities. Metagenomic sequencing and bioinformatic analyses were performed on six woodchip samples (i.e., three unmilled and three milled) collected from a 10-year-old woodchip bioreactor treating agricultural tile drainage. All samples had similar DNA purity, yield, quality, and microbial diversity regardless of milling. However, when sequences were aligned against various protein libraries, our results indicated greater relative abundance of denitrification and P transformation proteins on the outside of the woodchips (unmilled), while the interior of woodchips (milled) exhibited more functional gene abundance for carbohydrate breakdown. Thus, it may be important to characterize microbial communities both within woodchips, and on woodchip surfaces, to gain a more holistic understanding of coupled biogeochemical cycles on N, P, and C in woodchip bioreactors. Based on these findings, we advise that future microbial research on woodchips (and potentially other permeable organic materials) examine both the surface biofilm and the interior organic material during initial studies. Once researchers determine where specific proteins or enzymes of interest are most prevalent, subsequent studies may then focus on either one or both aspects, as needed.

Phosphorus removal from agricultural tile drainage effluent with activated alumina in novel adsorption reactors.

Subsurface tile drains under agricultural field crops are a major source of phosphorus (P) discharge to aquatic ecosystems, contributing to the eutrophication of surface waters. Adsorption reactors for P removal from drainage water (P-reactors) could reduce P outflow from agricultural land but were rarely studied in cold, temperate climates. In our study, four low-cost P-reactors were installed in agricultural fields in south-central Québec, Canada. Activated alumina (AA) beads were used as P-adsorptive material, and the reactors were connected to tile drain outlets. Paired water samples (39 events) from reactor inlets and outlets were analyzed for P species and other physicochemical parameters during one calendar year to assess the P removal from tile drain effluent in the P-reactors. Collectively, the P-reactors retained approximately half (48%) of the total mass of P flowing through the tile drains, mostly (92%) as particulate P. The mass of AA beads adsorbed 11% of the dissolved-P fractions. Results are interpreted in the context of the field drainage area and will require adjustments to the P-reactor design to accommodate larger fields. The P-reactors remained structurally intact throughout all four seasons in a cold temperate climate, showing the potential of simple, inexpensive P-reactors to reduce P concentration in tile drain effluent.

Removal of selected sulfonamides and sulfonamide resistance genes from wastewater in full-scale constructed wetlands

Sulfonamides are high-consumption antibiotics that reach the aquatic environment. The threat related to their presence in wastewater and the environment is not only associated with their antibacterial properties, but also with risk of the spread of drug resistance in bacteria. Therefore, the aim of this work was to evaluate the occurrence of eight commonly used sulfonamides, sulfonamide resistance genes (sul1–3) and integrase genes intI1–3 in five full-scale constructed wetlands (CWs) differing in design (including hybrid systems) and in the source of wastewater (agricultural drainage, domestic sewage/surface runoff, and animal runs runoff in a zoo). The CWs were located in low-urbanized areas in Poland and in Czechia. No sulfonamides were detected in the CW treating agricultural tile drainage water. In the other four systems, four sulfonamide compounds were detected. Sulfamethoxazole exhibited the highest concentration in those four CWs and its highest was 12,603.23 ± 1000.66 ng/L in a CW treating a mixture of domestic sewage and surface runoff. Despite the high removal efficiencies of sulfamethoxazole in the tested CWs (86 %–99 %), it was still detected in the treated wastewater. The sul1 genes occurred in all samples of raw and treated wastewater and their abundance did not change significantly after the treatment process and it was, predominantly, at the level 105 gene copies numbers/mL. Noteworthy, sul2 genes were only found in the influents, and sul3 were not detected. The sulfonamides can be removed in CWs, but their elimination is not complete. However, hybrid CWs treating sewage were superior in decreasing the relative abundance of genes and the concentration of SMX. CWs may play a role in the dissemination of sulfonamide resistance genes of the sul1 type and other determinants of drug resistance, such as the intI1 gene, in the environment, however, the magnitude of this phenomenon is a matter of further research.

Nutrient release in drainage discharge from organic soils under two different agricultural water management systems

AbstractThe release of available nitrogen (N) and phosphorus (P) from agricultural tile drainage contributes to eutrophication in water bodies. To mitigate the harmful impact of nutrient release, drainage water management (DWM) has been proposed as a beneficial management practice that will limit N and P in tile drainage discharge. This study, conducted in the organic soils of the Holland Marsh, Ontario, assessed the nutrient water quality for 2 years (2015–2016) under DWM systems: controlled drainage (CD) comprising a series of stackable gates to manually control the water table level; and pumped drainage (PD) which uses a submersible pump within a collector well that discharges effluent when activated. The latter is the common method of field drainage in the Holland Marsh, however, there is limited comparable research for either DWM system. The data were separated into growing and fallow seasons as well as winter, spring, and summer seasons for trend analysis (winter: October–February; spring: March–May; summer: June–September). The nitrate (NO3‐N) concentrations, under CD, were found to be on average higher during the winter season (7.64 mg L−1) compared to the growing season (3.76 mg L−1). Furthermore, total N concentrations are positively correlated to discharge (R > 0.55). The average total P concentration increased during the summer period following fertilization; however, there was no correlation between P and drainage discharge throughout the duration of the study. The P concentrations depended more on nutrient inputs, rather than the discharge under CD. The log regression statistical relationship showed significant differences in nutrient levels compared to the mean at both sites, however, greater differences were found under CD. Under PD, the NO3‐N concentrations showed significant seasonal trends between the spring and winter (Pr > t: 0.0061) and summer (Pr > t: <0.0001). Overall, both CD and PD can reduce the amount of tile drain discharge, but the concentrations of N and P are not significantly reduced.

Using isotopic tracers to enhance routine watershed monitoring – Insights from an intensively managed agricultural catchment

Experimental (research-based) and non-research-based watershed monitoring programs often differ with respect to sampling frequency, monitored variables, and monitoring objectives. Isotopic variables, which are more commonly incorporated in research-based programs, can provide an indication of water sources and the transit time of water in a catchment. These variables may be a valuable complement to traditional water quality monitoring variables and have the potential to support improved hydrologic process-related insights from long term monitoring programs that typically have low resolution sampling. The purpose of this investigation is to explore the utility of incorporating isotopic variables (specifically δ18O, δ2H, and 222Rn) into routine monthly sampling regimes by comparing insights gained from these variables to monitoring only specific conductivity and chloride. A complete annual cycle of monthly groundwater and surface water monitoring data collected from the Upper Parkhill watershed in southwestern Ontario, Canada was used to characterize baseline watershed conditions, evaluate watershed resilience to climate change, and examine contamination vulnerability. Study results provide an improved understanding of appropriate tracer use in agricultural regions with isotopic variables able to provide important insights into the seasonality of hydrologic phenomena, such as the timing of groundwater recharge. A comparison of monitoring variables to present-day hydro-meteorological conditions suggests the importance of a winter dominated hydrologic regime and the potential influence of changes in precipitation on groundwater-surface water interactions. Estimated transit time dynamics indicate the likelihood for rapid contaminant transport through surface and shallow subsurface flow and highlight the possible effects of agricultural tile drainage. The sampling approach and data analysis methods adopted in this study provide the basis for improving routine watershed monitoring programs in agricultural regions.

The retention of nitrogen and phosphorus in aboveground biomass of plants growing in constructed wetlands treating agricultural drainage

Three horizontal subsurface flow constructed wetlands (CW1, CW2 and CW3) for treatment of agricultural tile drainage water were built in 2018. Two wetlands were filled with a mixture of washed gravel and birch woodchips (10:1 volume ratio), in the third one the layer of woodchips was on top of a gravel layer. All wetlands were planted with Gyceria maxima and Phalaris arundinacea in parallel bands and parallel to water flow. Four-year study (2019–2022) was aimed at the amount of nutrients retained in aboveground plant biomass. The results revealed that the biomass of both species was lower as compared to biomass of these species growing in constructed wetlands for municipal sewage. Due to low aboveground macrophyte biomass, the nitrogen and phosphorus standing stocks were low (maximum 1.3 g P m−2 and 11.1 g N m−2). When comparing the nitrogen standing stocks with the inflow annual loadings and removed load, it represented on average only 2.38% of the removed load and 0.85% of the inflow load because of very high inflow loading (1298, 866 and 842 g N m−2 yr−1 in CW1, CW2 and CW3, respectively). On the other hand, the respective values for phosphorus amounted to 43.9% and 21.6% due to very low inflow loading (8.8, 6.6 and 6.0 g P m−2 yr−1 in CW1, CW2 and CW3, respectively). The study confirmed that plant contribution to nutrient removal in constructed wetlands expressed as removal percentage is strongly affected by inflow loading. The study also revealed that under low load conditions the plant uptake may substantially contribute to nutrient removal.

Climate change effects on denitrification performance of woodchip bioreactors treating agricultural tile drainage

Denitrifying woodchip bioreactors (WBRs) are a nature-based technology that are increasingly used to control nonpoint source nitrate (NO3−) pollution in agricultural catchments. The treatment effectiveness of WBRs depends on temperature and hydraulic retention time (HRT), both of which are affected by climate change. Warmer temperatures will increase microbial denitrification rates, but the extent to which the resulting benefits to treatment performance may be offset by intensified precipitation and shorter HRTs is not clear. Here, we use three years of monitoring data from a WBR in Central New York State to train an integrated hydrologic-biokinetic model describing links among temperature, precipitation, bioreactor discharge, denitrification kinetics, and NO3− removal efficiencies. Effects of climate warming are assessed by first training a stochastic weather generator with eleven years of weather data from our field site, and then adjusting the distribution of precipitation intensities according to the Clausius-Clapeyron relationship between water vapor and temperature. Modeling results indicate, in our system, faster denitrification rates will outweigh the influence of intensified precipitation and discharge under warming, leading to net improvements in NO3− load reductions. Median cumulative NO3− load reductions at our study site from May - October are projected to increase from 21.7% (interquartile range 17.4%–26.1%) under baseline hydro-climate to 41.0% (interquartile range 32.6–47.1%) with a + 4 °C change in mean air temperature. This improved performance under climate warming is driven by strong nonlinear dependence of NO3− removal rates on temperature. Temperature sensitivity may increase with woodchip age and lead to stronger temperature-response in systems like this one with a highly aged woodchip matrix. While the impacts of hydro-climatic change on WBR performance will depend on site-specific properties, this hydrologic-biokinetic modeling approach provides a framework for assessing climate impacts on the effectiveness of WBRs and other denitrifying nature-based systems.

Coupling nitrate capture with ammonia production through bifunctional redox-electrodes

Nitrate is a ubiquitous aqueous pollutant from agricultural and industrial activities. At the same time, conversion of nitrate to ammonia provides an attractive solution for the coupled environmental and energy challenge underlying the nitrogen cycle, by valorizing a pollutant to a carbon-free energy carrier and essential chemical feedstock. Mass transport limitations are a key obstacle to the efficient conversion of nitrate to ammonia from water streams, due to the dilute concentration of nitrate. Here, we develop bifunctional electrodes that couple a nitrate-selective redox-electrosorbent (polyaniline) with an electrocatalyst (cobalt oxide) for nitrate to ammonium conversion. We demonstrate the synergistic reactive separation of nitrate through solely electrochemical control. Electrochemically-reversible nitrate uptake greater than 70 mg/g can be achieved, with electronic structure calculations and spectroscopic measurements providing insight into the underlying role of hydrogen bonding for nitrate selectivity. Using agricultural tile drainage water containing dilute nitrate (0.27 mM), we demonstrate that the bifunctional electrode can achieve a 8-fold up-concentration of nitrate, a 24-fold enhancement of ammonium production rate (108.1 ug h−1 cm−2), and a >10-fold enhancement in energy efficiency when compared to direct electrocatalysis in the dilute stream. Our study provides a generalized strategy for a fully electrified reaction-separation pathway for modular nitrate remediation and ammonia production.

Flow analysis and hydraulic performance of denitrifying bioreactors under different carbon dosing treatments

Denitrifying bioreactors are an effective approach for removing nitrate from a variety of non-point wastewater sources, including agricultural tile drainage. However, compared to alternate mitigation approaches such as constructed wetlands, nitrate removal in bioreactors may decline with time and low temperature, resulting in poor long-term nitrate removal rates. To address the low nitrate removal rates in bioreactors, the addition of an external carbon source has been found to be an effective method for enhancing and maintaining nitrate removal rates. While carbon dosing has led to a significant improvement in nitrate removal, some of the possible adverse effects of carbon dosing, such as clogging and reduction in hydraulic efficiency, remain unknown and need to be investigated. Using observations from both field and mesocosm trials, we compared the hydraulic performance of bioreactors with and without carbon dosing. The pilot-scale field bioreactor (58 m3 total woodchip volume, 25 m3 saturated volume, referred to as field bioreactor in this work) treated drainage water from a paddock of a dairy farm. The bioreactor received an exogenous carbon dose of 8% methanol (v/v) at 10 mL min−1 and 5 mL min−1 in the 2020 and 2021 drainage seasons, respectively. The field bioreactor had a statistically higher hydraulic conductivity in 2018 when not carbon-dosed of 4601 m day−1, reducing to 1600 m day−1 in 2021 which was the second year of carbon dosing. Field observations could not establish whether the addition of liquid carbon could affect the bioreactor's internal hydraulics performance, such as actual hydraulic retention time (AHRT), despite a significant decline in hydraulic conductivity in the field bioreactor. Separate experiments on replicated bioreactor mesocosms were conducted to investigate the effects of carbon dosing on the internal hydraulic parameters of bioreactors. These mesocosm bioreactors had previously been used to study the long-term effects of methanol dosing on bioreactor performance, such as nitrate removal under steady-state conditions. The mesocosm and field bioreactors shared some characteristics, such as the use of methanol as an external carbon source, but the mesocosm experiments were hydrologically controlled contrary to the field bioreactor's transient operating conditions. We found that methanol dosing in either carbon or nitrate limiting conditions had no significant effects (p-value >0.05) on internal hydraulic parameters (e.g., effective utilization of media) when compared to control bioreactors. The present study offers insight into the long-term hydraulic performance of bioreactors and may help develop small-footprint bioreactors that incorporate external carbon dosing.

Electrochemical ammonia production from nitrates in agricultural tile drainage: Technoeconomic and global warming analysis

AbstractNitrates from agricultural wastewater are harmful to human health and result in eutrophication. Several emerging electrochemical technologies have been developed independently to enable efficient recovery and recycling of nitrate waste; however, it remains unclear whether the implementation of such combined technologies can be economically viable. Herein, we perform technoeconomic and global warming potential analyses on several hypothetical nitrate capture and conversion systems for the recovery of nitrates from agricultural wastewater and conversion of nitrate to ammonia. The energy efficient technologies incorporated include: electrodialysis for nitrate separation, electrocatalysis for ambient ammonia production, and agrophotovoltaics as a clean energy source. Our technoeconomic analysis reveals that despite advancements in nitrate separation and conversion, capital investments for system installation cannot be recovered by the financial benefit of on‐site fertilizer production. Our analysis highlights the necessity of government intervention to promote nitrate abatement technologies to ensure environmental compliance and protect public health.

Constant carbon dosing of a pilot-scale denitrifying bioreactor to improve nitrate removal from agricultural tile drainage

Denitrifying bioreactors are effective tools for removing nitrate from agricultural drainage water. However, as woodchips age with time, a shortage of labile carbon supply limits nitrate removal by microbial denitrification when high nitrate pulses occur in drainage waters. In this study, we investigated the potential of methanol dosing at a constant rate to increase nitrate removal rates in a 58 m3 pilot-scale bioreactor (25 m3 saturated volume) installed on a dairy farm for two consecutive drainage seasons. The drainage water in the bioreactor had a mean hydraulic retention time (HRT) of 12.7 days and 13.5 days in the 2020 and 2021 drainage seasons. With 14.4 L of methanol solution (8% v/v) added per day, the seasonal nitrate removal rates were 8.6 g N m−3 d−1 in 2020 and 5.1 g N m−3 d−1 in 2021 when the methanol dosing rate was halved. Both rates (2020 and 2021) were enhanced as compared to seasonal rates of 0.67–1.60 g N m−3 d−1 in previous years (2017 and 2018) when the bioreactor was not dosed. When there were very large pulses of nitrate into the bioreactor, which exhausted added methanol, nitrate was observed at concentrations above limiting ranges (> 3 mg N L−1) at the outlet on several occasions in 2021. Cumulative nitrate load reductions of 1859 g N and 1620 g N occurred in 2020 and 2021, respectively, resulting in overall nitrate removal efficiencies of 85 and 73%, respectively.Methanol concentrations decreased by order of magnitude along the bioreactor length, from mean inlet concentrations of 327 mg CH3OH-C L−1 in 2020 (higher dosing rate) to concentrations of <50 mg CH3OH-C L−1 at the outlet. The mean methanol removal rates of 106 g CH3OH-C m−3 d−1 in 2020 and 109 g CH3OH-C m−3 d−1 in 2021. A 90% (2020) and 100% (2021) overall methanol removal efficiency was calculated. With methanol dosing, sulfate removal occurred in the bioreactor, with an average sulfate removal rate of 8.5 g SO42−-S m−3 d−1 in 2020 and 0.5 g SO42−-S m−3 d−1 in 2021. This work demonstrated that methanol additions to bioreactors could enhance denitrification rates even when nitrate was limiting without considerable losses of methanol being released to the receiving waters.

Potential of water quality wetlands to mitigate habitat losses from agricultural drainage modernization

Given widespread biodiversity declines, a growing global human population, and demands to improve water quality, there is an immediate need to explore land management solutions that support multiple ecosystem services. Agricultural water quality wetlands designed to provide both water quality benefits and wetland and grassland habitat are an emerging restoration solution that may reverse habitat declines in intensive agricultural areas. Installation of water quality wetlands in the Upper Midwest, USA, when considered alongside the repair and modification of aging agricultural tile drainage infrastructure, is a likely scenario that may mitigate nutrient pollution exported from agricultural systems and improve crop yields. The capacity of water quality wetlands to provide habitat within the wetland pool and the surrounding grassland is not well-studied, particularly with respect to potential habitat changes resulting from drainage infrastructure upgrades. For the current study, we produced spatially explicit models of 37 catchments distributed throughout an important region for agriculture and biodiversity, the Des Moines Lobe of Iowa. Four scenarios were considered - with and without improved drainage and with and without water quality wetlands - to estimate the net potential habitat implications of these scenarios for amphibians, grassland birds, and wild bees. Model results indicate that drainage modification alone will likely result in moderate direct losses of suitable amphibian habitat and large declines in overall habitat quality. However, inclusion of water quality wetlands at the catchment scale may mitigate these amphibian habitat losses while also increasing grassland bird and pollinator habitat. The impacts of water quality wetlands and drainage modernization on waterfowl in the region require additional study.

Reduction of Phosphorus Using Electric Arc Furnace Slag Filters in the Macatawa Watershed (Michigan)

Eutrophication is a major problem in lakes and rivers throughout the world. One such system is Lake Macatawa, located in West Michigan, which hydrologically connects to Lake Michigan. Lake Macatawa and its watershed suffer from excess phosphorus and sediment loads. The total maximum daily load for the lake calls for a total phosphorus (TP) reduction of 75%, which would reduce the water column total phosphorus concentration from 125 μg/L to 50 μg/L. Understanding how P moves through this landscape, into Lake Macatawa, and ultimately to Lake Michigan and the St. Lawrence Seaway, is critical to managing and controlling P runoff. A potentially significant source of P to Lake Macatawa occurs through agricultural tile drainage. Various best management practices (BMPs) have been implemented in the Macatawa watershed to reduce P loading, especially surface runoff, but their overall effectiveness has been limited. Electric arc furnace (EAF) slag, a waste product from the steel industry, can chemically bind P and has been used previously in agricultural settings. Three iron slag filters were installed at the end of agricultural tile lines in the Macatawa watershed and evaluated to assess their effectiveness in removing P, while also monitoring for the presence of potentially toxic chemicals leaching from the slag. After 1 year of slag filter performance, both SRP (soluble reactive phosphorus) and TP decreased in the tile drain effluent: percent reductions of soluble reactive phosphorus and TP ranged from 7.4% to 57.3% and 59.5–76.5%, respectively. Absolute concentrations of TP were reduced to between 100 and 329 μg/L, which still exceeds the 50 μg/L goal for Lake Macatawa. Concentrations of toxic metals, polycyclic aromatic hydrocarbons compounds, and cyanide all were at levels below drinking water standards. Our preliminary conclusions are that the installation of these filters should be targeted to areas where tile drain effluent P levels are very high (SRP &amp;gt; 250 μg/L) to obtain an optimal cost/benefit ratio. While they are not a panacea, when installed in combination with other BMPs (Best Management Practices), EAF slag filters may play an important localized role in reducing P to Lake Macatawa and farther downstream.

Sizing an open-channel woodchip bioreactor to treat nitrate from agricultural tile drainage and achieve water quality targets

Abstract Woodchip bioreactors are capable of removing nitrate from agricultural runoff and subsurface tile drain water, alleviating human health hazards and harmful discharge to the environment. Water pumped from agricultural tile drain sumps to nearby ditches or channels could be cost-effectively diverted through a woodchip bioreactor to remove nitrate prior to discharge into local waterways. Sizing the bioreactor to achieve targeted outlet concentrations within a minimum footprint is important to minimizing cost. Determining the necessary bioreactor size should involve a hydrological component as well as reaction type and rates. We measured inflow and outflow nitrate concentrations in a pumped open-channel woodchip bioreactor over a 13-month period and used a tanks-in-series approach to model hydrology and estimate parameter values for reaction kinetics. Both zero-order and first-order reaction kinetics incorporating the Arrhenius equation for temperature dependence were modeled. The zero-order model fit the data better. The rate coefficients (k = 17.5 g N m−3 day−1 and theta = 1.12 against Tref = 20 °C) can be used for estimating the size of a woodchip bioreactor to treat nitrate in agricultural runoff from farm blocks on California's central coast. We present an Excel model for our tanks-in-series hydrology to aid in estimating bioreactor size.

Ecosystem services in Iowa agricultural catchments: Hypotheses for scenarios with water quality wetlands and improved tile drainage

Nutrient loads from agricultural runoff in the upper Midwest continue to contribute to Gulf Coast hypoxia and harmful algal blooms due to insufficient retention of nitrogen (N) and phosphorus (P) associated with row crop agriculture and highly productive soils. In the coming decades, much of the drainage infrastructure in this region will be rebuilt to modern design standards. At the same time, the region is developing and implementing strategies to reduce nutrient export. A group of Iowa stakeholders representing agricultural producers, land managers, and researchers met seven times in late 2018 and early 2019 and was asked to describe ecosystem service information needs that could support nutrient best management practice decisions in Iowa. The stakeholder group identified the importance and relevance of a catchment-scale (i.e., small watershed) analysis of a set of priority ecosystem services associated with agricultural tile drainage improvements and targeted water quality wetlands. Water quality wetlands are wetlands installed strategically to intercept agricultural drainage channels and receive runoff and tile drainage. These potential modifications were codified into four scenarios for literature analysis and hypothesis development including (1) a baseline, no change scenario representing the most prevalent current landscape with underperforming tile drainage infrastructure and degraded wetland functions; (2) upgrade of tile drainage infrastructure without a water quality wetland; (3) installation of a water quality wetland at the drainage district catchment scale but with no drainage improvements; and (4) a combination of adding a water quality wetland and tile drainage infrastructure upgrades at the catchment scale. Synthesizing published field-scale and modeling results across a collection of relevant studies suggests that the combined scenario of improved drainage paired with a water quality wetland may result in increased crop yields, habitat, pollination, and educational and cultural services as well as decreased global warming potential relative to the baseline scenario. Nitrate (NO₃^™) export will likely decrease in the combined scenario, depending on net agricultural export and wetland effectiveness. To better substantiate these findings, more catchment-scale research in the region is required, particularly in the areas of water quality, wetland carbon (C) sequestration, wetland habitat quality, and educational and cultural services. Additionally, research is needed to address the effect of upgrading drainage infrastructure on ecosystem services, as most reported ecosystem service effects have been for new drainage installations. Fully integrated assessments, particularly at the catchment scale, will be key to understanding how land management approaches like adding water quality wetlands and improved drainage affect both agricultural production and ecosystem services.

Slope stability of streambanks at saturated riparian buffer sites.

Saturated riparian buffers (SRBs) reduce nitrate export from agricultural tile drainage by infusing drainage water into carbon-rich riparian soils where denitrification and plant uptake occur. The water quality benefits from SRBs are well documented, but uncertainties about their effect on streambank stability have led to design standards that limit the maximum bank height and minimum buffer width, thus reducing the number of suitable candidate sites. In this study, the relationship between SRB design and streambank stability was examined through numerical slope stability modeling and validated using field sites. At the study sites, the addition of SRB flow increased the probability of failure by less than 3% for both simulated dry and rainfall scenarios. Furthermore, the simulations provide no evidence to support excluding potential sites based on bank height alone. Multivariate analysis of dimensionless parameters developed for SRB flow conditions was used to predict the factor of safety as a function of the SRB site and design conditions. The equation presented allows designers to assess the stability of a potential site where bank failure poses a heightened risk. The results of this study alleviate the need for extensive geotechnical evaluations at future SRB sites and could increase SRB implementation by expanding the range of eligible sites.

Temporal variability in water and nutrient movement through vertisols into agricultural tile drains in the northern Great Plains

Agricultural tile drainage is expanding in the northern Great Plains of North America. Given ongoing environmental and political concerns related to the eutrophication of Lake Winnipeg in Canada and the potential for tile drains to transport significant quantities of nutrients from agricultural fields, an improved understanding of nutrient dynamics in tile drains in this region is needed. This study characterized seasonal patterns in tile flow and chemistry under variable hydroclimatic conditions and related this variance to temporal variability in soil hydraulic properties in a farm in southern Manitoba, Canada, from 2015 to 2017. Tile flow, soil hydraulic properties, and groundwater table position all varied seasonally, as did the chemistry of tile drain effluent. The majority of annual tile discharge, which occurred in late spring, appears to have been contributed by shallow groundwater, primarily through soil matrix pathways. At these greater tile flow rates, concentrations of soluble reactive phosphorus (SRP) and total phosphorus (TP) were low (&lt;0.03 mg L^–1 SRP, &lt;0.04 mg L^–1 TP), but concentrations of nitrate (NO₃-N) were high (20 to 25 mg L^–1 NO₃-N). In contrast, tile flows outside of this peak period appeared to be primarily attributed to preferential flow pathways through frozen (snowmelt) and dry soil cracks (summer). Phosphorus (P) concentrations were greater during snowmelt and summer (~0.05 mg L^–1 SRP, ~0.1 mg L^–1 TP) but did not produce significant nutrient loads due to the minimal tile discharge rates (&lt;1 mm d^–1). This work suggests that the expansion of tile drainage may not exacerbate water quality issues involving P in the northern Great Plains but may increase nitrogen (N) loads in local water bodies.

Initial Validation of a Replicated Field-scale Denitrifying Bioreactor Facility in a Boreal Environment

Denitrifying bioreactor technology, where a solid carbon source (woodchips) acts as a reactive medium to intercept agricultural tile drainage water, has been successfully used to convert N (NO3-) to di-nitrogen (N2) gas. Four replicated field-scale (24 m long x 3 m wide x 1 m deep), bioreactors were built and operated at the St. John’s Research and Development Centre and were successful at removing a notable amount of nitrate (N) from agricultural subsurface drainage water. The objective of this study was to investigate the internal flow dynamics of one of these field-scale bioreactors as a proxy for the others. The hydraulic conditions in the bioreactor system developed differently than expected; asymmetric flow rates led to long average hydraulic retention time (HRT) and a highly dispersed residence time distribution, which was revealed by a sodium chloride tracer test. To measure the internal flow a known amount of sodium chloride (salt) was added to water before it entered the bioreactor and samples were collected in 30 minutes intervals. The temperature of water samples taken from the inlet, outlet, and sample ports ranged from 14.5 to 18.4°C With a N removal of 62 to 66% the bioreactor proved at the same time to be very effective under the boreal environment of Newfoundland and Labrador (NL). Mass removal rate (MRR) was calculated to evaluate the performance of woodchip bioreactor. The average MRR was 3.87 gm-3day-1 and the highest was 7.19 gm-3day-1 respectively. The theoretical retention time was calculated to be approximately 10.64 h based on the active flow volume, the length and depth of the system. In comparison the observed retention was 18.18 h

Microwave Wireless Powering of Sensored Agricultural Tile Drainages

In this article, a new technique for wireless powering of agricultural sensors buried deep underground is introduced and experimentally investigated. In this technique, the agricultural drainage tiles are utilized as waveguides to carry electromagnetic (EM) energy over long distances. By using high-efficiency rectifiers, the propagating EM waves are then converted into dc power to charge the batteries of underground sensors. A prototype 1 GHz rectenna system is fabricated and implemented on an 8 in tile to prove this concept experimentally. Various measurements are conducted for both the rectenna and the entire tile system, including realistic scenarios such as partially covered tiles and tile in the presence of water. Considering the emerging digital agriculture, the proposed technique will open the potential for detailed underground geochemistry studies, which will allow us to better monitor the transport of liquids and gases through millions of miles of agricultural tile drainage networks.