Subsurface Drainage Water Research Articles

Nutrient losses from subsurface drainage systems in Latvia

Artificial subsurface drainage systems are a common water management practice to remove excess water from agricultural land in the Baltic and Nordic countries. Unfortunately, these systems also serve as nutrient transport pathways from agricultural fields to downstream waterbodies. The objective of this study was to determine the status of subsurface drainage water in the context of implementation of the European Union (EU) Water Framework Directive (WFD) and EU Nitrate Directive (ND), to investigate the impact of hydrology and mineral fertilizer application on nutrient losses through subsurface drainage systems and to evaluate the possible effects of climate change on drainage and nutrient loss. This research was conducted from 1995 through 2013 at the agricultural run-off–monitoring sites in Berze and Mellupite. Continuous-flow measurement data and composite water samples were collected on a monthly basis for assessment of total nitrogen (TN), nitrate–nitrogen (NO3–N) and total phosphorus (TP) in drainage water. Results from the study indicated that the mean annual NO3–N concentration was slightly below the threshold level defined by ND, while TN concentrations exceeded the threshold level for good chemical status of water according to WFD. Differences in TN losses were mainly driven by the hydrologic behaviour at the study sites rather than by mineral fertilizer application rates, whereas TP losses under similar application rates were affected by open inlets for surface water accumulation. The comparison of meteorological data for the research period (1995–2013) with the long-term mean (1950–1994) showed a pronounced evidence of climate change. The mean annual precipitation amount has increased at both Berze and Mellupite monitoring sites by 36 mm and 42 mm, respectively, compared to the long-term mean for 1950–1994. Meanwhile, the mean annual temperature during the research period was 7.3°C for Berze and 6.4°C for Mellupite, which is 1.4°C and 0.6°C warmer than long-term mean.

Modeling nitrate removal in a denitrification bed

Denitrification beds are promoted to reduce nitrate load in agricultural subsurface drainage water to alleviate the adverse environmental effects associated with nitrate pollution of surface water. In this system, drainage water flows through a trench filled with a carbon media where nitrate is transformed into nitrogen gas under anaerobic conditions. The main objectives of this study were to model a denitrification bed treating drainage water and evaluate its adverse greenhouse gas emissions. Field experiments were conducted at an existing denitrification bed. Evaluations showed very low greenhouse gas emissions (mean N2O emission of 0.12 μg N m−2 min−1) from the denitrification bed surface. Field experiments indicated that nitrate removal rate was described by Michaelis–Menten kinetics with the Michaelis–Menten constant of 7.2 mg N L−1. We developed a novel denitrification bed model based on the governing equations for water flow and nitrate removal kinetics. The model evaluation statistics showed satisfactory prediction of bed outflow nitrate concentration during subsurface drainage flow. The model can be used to design denitrification beds with efficient nitrate removal which in turn leads to enhanced drainage water quality.

Heterotrophic denitrification constrains the upper limit of dissolved N2O-nitrate concentration ratio in agricultural groundwater

Indirect emission of nitrous oxide (N2O) through groundwater and surface drainage is commonly estimated based on the apparent positive relationship between the concentrations of nitrate ([NO3−]) and dissolved N2O ([N2O]) for regional and national assessments. Field observations of the ratio of [N2O]–[NO3−], however, rarely follow such relationship due to the complexity in N2O dynamics. Here we hypothesized that the temporal variation in [N2O] involves a phase shift as a function of [NO3−] during heterotrophic denitrification (HD) based on the fact that high [NO3−] inhibits N2O reduction to dinitrogen. We tested this hypothesis using the long-term, high frequency dataset of subsurface drainage water from the lysimeters under a cultivated soil in Japan. We identified the cases where [N2O] increased under high [NO3−] conditions (phase 1) and decreased under low [NO3−] conditions (phase 2) during the non-rainy periods. When [NO3−] exceeded 20.4 mg N L−1 across the entire dataset, we found the positive correlation between [N2O] and the concentration of dissolved carbon dioxide ([CO2]), an end-product of HD, in accordance with phase 1. When [NO3−] was 28.3 mg C L−1, we found the positive correlation between [N2O] and [NO3−], which agrees with phase 2. With this phase shift, [N2O]–[NO3−] ratio increased (phase 1) and reached a plateau (phase 2). Our results suggest that the progress of HD, especially phase 1, contributes to the increases in [N2O]–[NO3−] ratio and thus site-specific emission factor of N2O, EF5g.

Effects of maquis clearing on the properties of the soil and on the near-surface hydrological processes in a semi-arid Mediterranean environment

Many hillslopes covered with maquis in the semi-arid Mediterranean environment have been cleared in recent decades. There is little information on what effect this has on the hydrology of the soil. We compared the hydraulic properties of the soil and the subsurface hydrological dynamics on two adjacent sites on a hillslope. One site was covered with maquis, the other with grass. The grass started to grow some 10 years ago, after the maquis had been cleared and the soil had been ploughed. Our study found that the hydraulic properties and the hydrological dynamics of the maquis and the grassed soil differed greatly. The grassed soil had less organic matter and higher apparent density than did the soil covered in maquis. Moreover, the maquis soil retained more water than the grassed soil in the tension range from saturation to 50 cm of water. Infiltration tests performed in summer and in winter indicated that the field saturated hydraulic conductivity (K<sub>fs</sub>) of the maquis soil was higher than that of the grassy soil. However the data showed that the K<sub>fs</sub> of the two soils changed with the season. In the maquis soil the K<sub>fs</sub> increased from summer to winter. This was assumed to be due to water flowing more efficiently through wet soil. By contrast, in the grassy soil the K<sub>fs</sub> decreased from summer to winter. This was because the desiccation cracks closed in the wet soil. As result, the influence of the land use change was clear from the K<sub>fs</sub> measurements in winter, but less so from those in the summer. Changes in land use altered the dynamics of the infiltration, subsurface drainage and soil water storage of the soil. The maquis soil profile never saturated completely, and only short-lived, event based perched water tables were observed. By contrast, soil saturation and a shallow water table were observed in the grass covered site throughout the wet season. The differences were assumed to be due to the high canopy interception of the maquis cover, and to the macropores in the grassed soil being destroyed after the maquis had been cleared and the soil ploughed. The results of this work are helpful for predicting the changes in the hydraulic properties of the soil and in the near-surface hydrological processes in similar Mediterranean environments where the natural vegetation has been cleared. These changes must be taken into consideration when developing rainfall-runoff models for flood forecasting and water yield evaluation.

Simulating coupled surface and subsurface water flow in a tile-drained agricultural catchment

Summary The impact of shallow tile drainage networks on groundwater flow patterns, and associated transport of chemical species or sediment particles, needs to be quantified to evaluate the effects of agricultural management on water resources. A current challenge is to represent tile drainage networks in numerical models at the scale of a catchment for which proper simulation and reproduction of subsurface drainage water dynamics are essential. This study investigates the applicability of various tile drainage modeling concepts by comparing their results to a reference model. The models were setup for a 3.5 ha regularly monitored tile-drained area located in the clayey till Lillebaek catchment in Denmark, where the main input of water to the streams originates from subsurface drainage. Several simulations helped identify the most efficient way of modeling tile-drained areas using the integrated surface water and groundwater HydroGeoSphere code, which also simulates one-dimensional water flow in tile drains. The aim was also to provide insight on the design of larger scale models of complex tile drainage systems, for which computational time can become very large. A reference model that simulated coupled surface flow, groundwater flow and flow in tile drains was setup and showed a rapid response in drain outflow when precipitation is applied. A series of additional simulations were performed to test the influence of flow boundary conditions, temporal resolution of precipitation data, conceptual representations of clay tills and drains, as well as spatial discretization of the mesh. For larger scale models, the simulations suggest that a simplification of the geometry of the drainage network is a suitable option for avoiding highly discretized meshes. Representing the drainage network by a high-conductivity porous medium layer reproduces outflow simulated by the reference model. This approach greatly reduces the mesh complexity and simulation time and thus represents an alternative to a discrete representation of drains at the field scale, but specifying the hydraulic properties of the layer requires calibration against observed drain discharge.

Pilot demonstration of concentrated solar-powered desalination of subsurface agricultural drainage water and other brackish groundwater sources

The energy–water nexus is addressed with the experimental demonstration of a solar-powered desalination process system. This system was designed for high-recovery treatment of subsurface agricultural drainage water as a reuse strategy as well as other brackish groundwater sources. These water sources may exhibit wide fluctuations in salinity and makeup and pose a high risk for operational troubles due to high scaling potential. A first-of-its-kind open-cycle vapor-absorption heat pump is coupled with a multiple-effect distillation train and a large parabolic trough solar thermal concentrator. Without the heat pump, the distillation operation showed a minimum thermal energy consumption of 261.87kWhth/m3. With the heat pump, the thermal energy consumption was reduced by more than 49% to 133.2kWhth/m3. This reduction in thermal energy requirement directly translates into a 49% reduction in solar array area required to power a process with the same freshwater production rate as a system without an integrated heat pump. An optimized design was modeled and the thermal energy performance of a commercial system is projected at 34.9kWhth/m3 using a 10-effect MED operating at 85% recovery.

Pesticide concentrations in frog tissue and wetland habitats in a landscape dominated by agriculture

Habitat loss and exposure to pesticides are likely primary factors contributing to amphibian decline in agricultural landscapes. Conservation efforts have attempted to restore wetlands lost through landscape modifications to reduce contaminant loads in surface waters and providing quality habitat to wildlife. The benefits of this increased wetland area, perhaps especially for amphibians, may be negated if habitat quality is insufficient to support persistent populations. We examined the presence of pesticides and nutrients in water and sediment as indicators of habitat quality and assessed the bioaccumulation of pesticides in the tissue of two native amphibian species Pseudacris maculata (chorus frogs) and Lithobates pipiens (leopard frogs) at six wetlands (3 restored and 3 reference) in Iowa, USA. Restored wetlands are positioned on the landscape to receive subsurface tile drainage water while reference wetlands receive water from overland run-off and shallow groundwater sources. Concentrations of the pesticides frequently detected in water and sediment samples were not different between wetland types. The median concentration of atrazine in surface water was 0.2μg/L. Reproductive abnormalities in leopard frogs have been observed in other studies at these concentrations. Nutrient concentrations were higher in the restored wetlands but lower than concentrations thought lethal to frogs. Complex mixtures of pesticides including up to 8 fungicides, some previously unreported in tissue, were detected with concentrations ranging from 0.08 to 1500μg/kg wet weight. No significant differences in pesticide concentrations were observed between species, although concentrations tended to be higher in leopard frogs compared to chorus frogs, possibly because of differences in life histories. Our results provide information on habitat quality in restored wetlands that will assist state and federal agencies, landowners, and resource managers in identifying and implementing conservation and management actions for these and similar wetlands in agriculturally dominated landscapes.

Controlled drainage and subirrigation – A water management option to reduce non-point source pollution from agricultural land

Losses of nutrients from arable land significantly contribute to the eutrophication of lakes and coastal waters. Consequently agricultural nutrient and water management strategies have been emphasized during the last decades. The problem of excessive drainage at certain times of the year in conventional drainage systems (CD) can in many cases be overcome by implementing controlled drainage strategies (CWT). The data for this paper is based on water management projects, at both plot and field scales, which have been carried out in Southern Sweden during the period 2002 to 2005. The studies included water table strategies in which the subsoil was subjected to various degrees of water status at different times of the year by means of controlled drainage system. They were run on one site with small plots and two sites with field scale plots, and each site consisted of one CD plot and three CWT plots.Compared to CD, CWT had lower subsurface runoff all years of measurement. Nitrogen (N) and phosphorus (P) concentrations in subsurface drainage water revealed no significant differences between CWT and CD. N and P losses, in contrast, tended to be lower in CWT than in CD, possibly due to lower runoff volumes in CWT. The yearly losses of NO3-N, Total-N, PO4-P and Total-P through the drainage system were on average 40% lower in CWT than in CD. The yield and N uptake by crops, in most measurements, were higher in CWT due to more water available during the cropping season and thereby improved N efficiency of the applied fertiliser. The results from the experiments revealed that controlled drainage has a potential to lower non-point source leaching of nutrients from agricultural land, improve N and P use efficiency and increase yields.

Stochastic approach to assess a nitrate process-factor in soil water

A process-factor was driven for the NO3--N concentration in the soil water. The process-factor was calculated to a catchment in Belgium. The NO3--N concentration in the surface water at the outlet of the catchment was used as Cs. The model was run on each individual field within the catchment for four consecutive winter periods. A Monte Carlo approach was used (i.e. the simulation was repeated 1500 times with new picks from the NO3--N distribution functions on October 1st considering the crop rotation. The results indicated that, the process-factor, calculated as the ratio of the simulated NO3--N concentration in the soil water at 90cm and the measured NO3--N concentration in the surface water, for the catchment is 2.35. Moreover, the proper management of crop nutrients (nutrient source, application rate and timing) is an important way to help control the loss of nutrients through surface runoff and subsurface drainage water.

Sorption of selected pesticides on soils, sediment and straw from a constructed agricultural drainage ditch or pond

Buffer zones such as ponds and ditches are used to reduce field-scale losses of pesticides from subsurface drainage waters to surface waters. The objective of this study was to assess the efficiency of these buffer zones, in particular constructed wetlands, focusing specifically on sorption processes. We modelled the sorption processes of three herbicides [2-methyl-4-chlorophenoxyacetic acid (2,4-MCPA), isoproturon and napropamide] and three fungicides (boscalid, prochloraz and tebuconazole) on four substrates (two soils, sediment and straw) commonly found in a pond and ditch in Lorraine (France). A wide range of Freundlich coefficient (K fads) values was obtained, from 0.74 to 442.63 mg(1 - n) L (n) kg(-1), and the corresponding K foc values ranged from 56 to 3,725 mg(1 - n) L (n) kg(-1). Based on potential retention, the substrates may be classified as straw >> sediments > soils. These results show the importance of organic carbon content and nature in the process of sorption. Similarly, the studied pesticides could be classified according to their adsorption capacity as follows: prochloraz >> tebuconazole-boscalid > napropamide >> MCPA-isoproturon. This classification is strongly influenced by the physico-chemical properties of pesticides, especially solubility and K oc. Straw exhibited the largest quantity of non-desorbable pesticide residues, from 12.1 to 224.2 mg/L for all pesticides. The presence of plants could increase soil-sediment sorption capacity. Thus, establishment and maintenance of plants and straw filters should be promoted to optimise sorption processes and the efficiency of ponds and ditches in reducing surface water pollution.

Long-Term Effects of Poultry Manure Application on Nitrate Leaching in Tile Drain Water

A long-term study (1998 to 2009) was initiated on eleven tile-drained field plots, ranging in size from 0.19 to 0.47 ha, to investigate the effects of poultry manure application on subsurface drainage water quality in Iowa under a corn-soybean rotation system. The experimental treatments included poultry manure at rates of 168 kg N ha-1 (PM) and 336 kg N ha-1 (PM2), each with three replications; nitrogen application from chemical fertilizer, urea ammonium nitrate (UAN), at a rate of 168 kg N ha-1 with four replications; and a control treatment that received 0 kg N ha-1. Subsurface drainage (tile) flow volume was monitored, and drainage samples were collected and analyzed for nitrate-nitrogen (NO3-N). The results from this 12-year study show that NO3-N losses with tile drainage were more likely to occur during the early stages of crop production (April to June) and were more related to the monthly distribution of precipitation than the total rainfall amount. The overall results of this study indicate that applying poultry manure at 168 kg N ha-1 resulted in significantly lower flow-weighted nitrate concentrations (PM < UAN < PM2) and the lowest nitrogen losses to subsurface drain water compared to UAN and PM2 application(PM < UAN < PM2), as well as higher crop yields compared to UAN application. Therefore, it can be concluded that poultry manure application at a rate of 168 kg N ha-1 is an environmentally sound N application practice with good yield potential for corn and soybean production systems with poorly drained soils in the upper Midwest. Future work is recommended to identify new practices and technologies to reduce nitrate loss to water systems.

Fosfilt filters in an agricultural catchment: a long-term field-scale

Diffuse load mitigation is a prevailing global challenge due to the eutrophication of water bodies. We report here long-term nutrient removal performance of two on-site sand filters (F1 and F2) in southwestern Finland, established in the 1990s. The sand filters were enhanced with a layer of phosphorus binding material Fosfilt-s, a side product of titanium dioxide production. The monitoring periods were 4.5 and 3.5years for F1 and F2, respectively. F1 only worked for some months due to blockage of the crushed stone layer. After renovation (1999), the filter worked for a year but then the Fosfilt-s layer clogged and the filter increased suspended solids (SS) and dissolved reactive phosphorus (DRP) loads by 36% and 19% on average, respectively. Total P (PTOT) load was not affected. The structure and performance of F2 were more successful due to a better water distribution system. On average, 61% ofthe inflowing suspended solids, 37% of the PTOT and 45% of the DRP were removed during the monitoring period. We conclude that these filter types have the potential to be further developed into useful tools for nutrient load reduction. Development work should be focused on the treatment of subsurface drainage waters with high concentrations of dissolved nutrients, in particular. Long term field data is needed, because laboratory tests cannot fully simulate natural circumstances.

Effectiveness of oat and rye cover crops in reducing nitrate losses in drainage water

Much of the NO3 in the riverine waters of the upper Mississippi River basin in the United States originates from agricultural land used for corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production. Cover crops grown between maturity and planting of these crops are one approach for reducing losses of NO3. In this experiment, we evaluated the effectiveness of oat (Avena sativa L.) and rye (Secale cereale L.) cover crops in reducing NO3 concentrations and loads in subsurface drainage water. The oat fall cover crop was broadcast seeded into living corn and soybean crops before harvest in late August or early September and was killed by cold temperatures in late November or early December The rye winter cover crop, which had already been used annually for four years, was planted with a grain drill after corn and soybean harvest, overwintered, grew again in the spring, and was killed with herbicides before main crop planting. These treatments were evaluated in subsurface-drained field plots with an automated system for measuring drainage flow and collecting proportional samples for analysis of NO3 concentrations from each plot. The rye winter cover crop significantly reduced drainage water NO3 concentrations by 48% over five years, but this was less than the 58% reduction observed in its first four years of use. The oat fall cover crop reduced NO3 concentrations by 26% or about half of the reduction of the rye cover crop. Neither cover crop significantly reduced cumulative drainage or nitrate loads because of variability in cumulative annual drainage among plots. Both oat and rye cover crops are viable management options for significantly reducing NO3 losses to surface waters from agricultural drainage systems used for corn and soybean production.

Development and application of a distributed modeling approach to assess the watershed-scale impact of drainage water management

Drainage water management, also known as controlled drainage, is the practice of using a water table control structure at the end of the subsurface drain pipe to reduce subsurface drainage, and thereby nitrate losses. Methods to quantify the potential effects of drainage water management for entire watersheds are needed to evaluate the impacts of large-scale adoption. A distributed modeling approach was developed to apply the field-scale DRAINMOD model at the watershed scale, and used to assess the impact of drainage water management on nitrate load from an intensively subsurface drained agricultural watershed in west central Indiana. The watershed was divided into 6460 grid cells for which drain spacing, soil parent material, and cropping pattern were estimated, resulting in 600 unique field conditions. The annual edge-of-field nitrate load from each grid cell was estimated as the product of DRAINMOD-predicted drain flow and the average annual nitrate concentration in drain flow, estimated from observations from related drainage sites in northern Indiana. Predicted monthly streamflow was in good agreement with the observed streamflow (Nash–Sutcliffe efficiency of 0.87 and 0.84 during the calibration and validation periods, respectively) and the predicted drain flow matched well with the measured drain flow (77.1cm vs. 77.8cm and 121.3cm vs. 128.4cm). Drainage water management decreased the average annual (1985–2009) predicted drain flow from 11.0 to 5.9cm, and the total nitrate load through subsurface drainage from 236 to 126ton (both about 47% reduction). The percent reduction in nitrate load varied between 40% and 53% for all combinations of drain spacing, soil parent material and cropping patterns, with drain spacing and soil parent material having a greater effect than cropping pattern. The methodology developed in this study showed potential for predicting the watershed-scale effects of subsurface drainage and drainage water management in drained agricultural watersheds.

Scale issues for assessment of nutrient leaching from agricultural land in Latvia

This paper deals with water quality assessment and recommendations for a classification system based on nitrogen (N) and phosphorus (P) concentrations. In order to evaluate the influence of agricultural intensity, climate and hydrology on water quality, the long-term data (from 1995 to 2009) collected in three Latvian diffuse pollution monitoring sites (Berze, Mellupite and Vienziemite) were analysed. Measurements were carried out within areas where agriculture was the main source of diffuse nutrient loading at four spatial scales, i.e. experimental plot, drainage field, small catchment and river. The available long-term data series shows large variations in nutrient concentrations, depending on the intensity of agricultural production system and the scale of measurements. The concentrations of total N are higher at the plot scale, decreasing when the spatial scale of measurements increase. The proposed simplified classification system (five classes) was based upon the assumption that good chemical status for rivers in agricultural areas represent concentrations of total N &amp;lt; 1.5 mg L−1 and total P &amp;lt; 0.075 mg L−1, while in small catchments total N &amp;lt; 2.5 mg L−1 and total P &amp;lt; 0.050 mg L−1 and in subsurface drainage water total N &amp;lt; 5.5 mg L−1 and total P &amp;lt; 0.020 mg L−1.

LOSS OF NITROGEN WITH DRAINAGE WATER IN A LONG TERM FIELD EXPERIMENT

In a long term field experiment with different nitrogen rates the effect of nitrogen fertilization upon the concentration of nitrate and ammonia nitrogen in subsurface drainage water was studied in a period from 1997 to 2007. Increased rates of applied nitrogen led to higher average values of NO3--N concentration in drainage water. In treatments of up to 150 kg ha-1 N, average nitrate nitrogen subsurface runoff concentration was lower than 15 mg/L for the investigation period (1997 - 2007). Maximum average concentration increased to 25.8 mg/L NO3--N treated with 300 kg ha-1 N. Average ammonia nitrogen concentration ranged from 0.27 mg/L to 0.37 mg/L during the investigation period and were not in correlation with applied fertilization doses. Losses of nitrate and ammonia nitrogen through drainage water varied from 6.3 kg/ha to 28.4 kg/ha, and from 0.24 kg/ha up to 0.52 kg/ha, respectively, depending on nitrogen rate applied. Results substantiate the importance of investigating the influence of different nitrogen rates applied for fertilization of arable crops upon nitrogen leaching in the agroecological conditions of Croatia, especially in regions where intensive agricultural production is practiced.

ADAPT: Model Use, Calibration, and Validation

This article presents an overview of the Agricultural Drainage and Pesticide Transport (ADAPT) model and a case study to illustrate the calibration and validation steps for predicting subsurface drainage and nitrate-N losses from an agricultural system. The ADAPT model is a daily time step, field-scale water table management model that was developed as an extension of the GLEAMS model. The GLEAMS algorithms were augmented with algorithms for subsurface drainage, subsurface irrigation, deep seepage, and related water quality processes. Recently, a frost depth algorithm was incorporated to enhance the models capability to predict flow during spring and fall months. In addition to the normal GLEAMS output, ADAPT gives estimates of pesticides and nutrients in drainage. The model has four components: hydrology, erosion, nutrient transport, and pesticide transport. Predictions of surface runoff and subsurface drainage by ADAPT are very sensitive to hydrology input parameters, such as NRCS curve number, hydraulic conductivity, depth of the impeding layer, and hydraulic conductivity of the impeding layer. In the erosion component, slope, hydraulic length, and crop management are the most sensitive factors. Nutrients generally follow the trends in surface runoff and subsurface drainage. In addition, nitrogen and phosphorus concentrations in soil horizons are sensitive to nutrient losses. Recently, the ADAPT model was further calibrated and validated in southern Minnesota to evaluate impacts of subsurface drain spacing and depth, rate and timing of nitrogen application, and precipitation changes on water quality. ADAPT is written in FORTRAN, and the source code is available to interested model users. Considering the limited technical support and text editor-based input files, development of a user-friendly interface to create input files would greatly enhance ADAPTs acceptability by users involved in modeling agricultural systems equipped with subsurface drains.

Technical Note: Rational Polynomial Functions for Modeling E. coli and Bromide Breakthrough

Fecal bacteria peak concentrations and breakthrough times as affected by preferential flow to subsurface (tile) drainage systems following irrigation or rainfall are important when assessing the risk of contamination. Process-based, convective-dispersive modeling of microbial transport through preferential flow has been conducted. Likewise, regression modeling has been used to study solute transport (e.g., nitrate) under agricultural systems and can have advantages over process-based modeling, such as fewer or easier to determine parameters and easier determination of confidence intervals. However, empirical models (e.g., regression) have only rarely been used to investigate microbial transport. In addition, the selection of time response curves to empirically model simple, right skewed, single breakthrough events from field or laboratory data is generally an arbitrary choice and often considers only conventional distribution-shaped response curves, such as lognormal distributions. In this study, we evaluate four rational polynomial functions for modeling bromide and E. coli data from a single breakthrough event from a tile-drained field near Nashua, Iowa. Bromide and liquid swine manure were applied to the plot immediately prior to 42 mm of overhead sprinkler irrigation. E. coli and bromide concentrations were determined in subsurface drainage water samples collected for the next 24 h. Nonlinear iteratively re-weighted least squares regression procedures were used to model the breakthrough data. The maximum event value, time of occurrence, and event total were estimated from the parameters for each model. Selection of the best model was based on multiple performance criteria. A simple rational polynomial with a linear factor in the numerator and quadratic form in the denominator was the overall best choice for E. coli (R² = 0.92). A related fractional order form also known as the Gunary model was the best choice for bromide (R² = 0.93). In comparison, the more commonly assumed lognormal distribution described only 78% of the variation in E. coli and 68% of the variation in bromide, with a weighted mean square error 3.0 to 4.6 times larger than each selected rational polynomial model. In this experiment, the chosen models clearly tracked E. coli and bromide distribution better than the lognormal model.

Laboratory Evaluation of Porous Iron Composite for Agricultural Drainage Water Filter Treatment

Agricultural subsurface drainage waters containing nutrients (nitrate/phosphate) and pesticides are discharged into neighboring streams and lakes, frequently producing adverse environmental impacts on local, regional, and national scales. On-site drainage water filter treatment systems can potentially prevent the release of agricultural contaminants into adjacent waterways. A recently developed porous iron composite (PIC) product may have promise as a filter material for drainage water treatment. Therefore, a laboratory study was initiated to evaluate the feasibility of using PIC for this purpose. Laboratory experiments included saturated falling-head hydraulic conductivity tests, contaminant (nutrient/pesticide) removal batch tests, and saturated solute transport column tests. The saturated falling-head hydraulic conductivity tests indicate that the original PIC product by itself has a high enough hydraulic conductivity (>0.001 cm s-1) to make this material hydraulically practical for filter treatment use. PIC hydraulic conductivity can be further enhanced (>0.01 cm s-1) by utilizing only the portion of this material retained on a 100 mesh sieve (particle size > 0.15 mm). Batch test results carried out with spiked drainage water and either unsieved or 100 mesh sieved PIC showed nitrate reductions of greater than 30%, and 100% removal of the pesticide atrazine. Saturated solute transport column tests with spiked drainage water provided more insight on the effectiveness and efficiency of utilizing PIC for drainage water filter treatment. These column tests confirm that PIC is capable of nearly complete removal of atrazine, and significant nitrate reduction. Additionally, once the phosphate originally present within the PIC material is leached out, the PIC then exhibited ability to remove large quantities of phosphate. Consequently, these laboratory findings support employment of PIC for use within on-site agricultural drainage water filter treatment systems.

Laboratory Evaluation of Zero Valent Iron and Sulfur‐Modified Iron for Agricultural Drainage Water Treatment

Agricultural subsurface drainage waters containing nutrients (nitrate/phosphate) and pesticides are discharged into neighboring streams and lakes, frequently producing adverse environmental impacts on local, regional, and national scales. On‐site drainage water filter treatment systems can potentially prevent the release of agricultural contaminants into adjacent waterways. Zero valent iron (ZVI) and sulfur‐modified iron (SMI) are two types of promising filter materials that could be used within these treatment systems. Therefore, water treatment capabilities of three ZVI and three SMI filter materials were evaluated in the laboratory. Laboratory evaluation included saturated falling‐head hydraulic conductivity tests, contaminant removal batch tests, and saturated solute transport column experiments. The three ZVI and the three SMI filter materials, on average, all had a sufficient hydraulic conductivity greater than 1 × 10–3 cm/s. Batch test results showed a phosphate decrease of at least 94% for all tests conducted with the ZVI and SMI. Furthermore, the three SMI filter materials removed at least 86% of the batch test nitrate originally present, while batch tests for one of the ZVI filter materials exhibited an 88% decrease in the pesticide, atrazine. Saturated solute transport column experiments were carried on the best ZVI filter material, or the best SMI filter material, or both together, in order to better evaluate drainage water treatment effectiveness and efficiency. Results from these column tests additionally document the drainage water treatment ability of both ZVI and SMI to remove the phosphate, the ability of SMI to remove nitrate, and the ability of a select ZVI material to remove atrazine. Consequently, these findings support further investigation of ZVI and SMI subsurface drainage water treatment capabilities, particularly in regard to small‐ and large‐scale field tests.