Groundwater Coordinating Council And Agency-Funded Research Highlights

GCC-Funded Research

GCC-Funded Research

A complete compilation of all GCC-funded projects can be found at UW Water Resources Institute's searchable repository. While the application of the results is broad, some areas where the results of state-funded groundwater research and monitoring projects have been successfully applied to groundwater problems in Wisconsin include the following:

Pesticides Background Serious concerns about pesticide contamination were first raised in 1980 when aldicarb, a pesticide used on potatoes, was detected in groundwater near Stevens Point. The DNR, Department of Agriculture Trade and Consumer Protection (DATCP) and other agencies responded to concerns by implementing monitoring programs and conducting groundwater surveys, initially testing exclusively for aldicarb1,2, but soon expanding to other pesticides and pesticide metabolites3. DATCP also developed rules to restrict aldicarb use in areas vulnerable to groundwater contamination. Sampling surveys in the late 1980s and early 1990s showed that atrazine, a popular, commonly used corn herbicide, was particularly prevalent in groundwater across the state4,5. Special projects were conducted to investigate how and why atrazine reaches groundwater. Notably, researchers funded by the Wisconsin Groundwater Research and Monitoring Program (WGRMP) discovered that normal field application of atrazine – not just point spills and misuse – was an important source of atrazine in groundwater6,7. Occurrences of atrazine were also found in monitoring and private drinking water wells. A subsequent study found that atrazine was present in 12% of Grade A Dairy Farm wells. The last three decades have seen increased use of neonicotinoid insecticides. A FY20-FY21 project by UW-Stevens Point conducted sampling for neonicotinoids in groundwater-fed streams. Two sampling methods - traditional grab samples and time-integrative POCIS (polar organic compound integrative samplers) samples were collected, with findings that grab samples at baseflow conditions and POCIS samples provided similar results. The authors also constructed a linear regression model of percentage of the entire groundwater contributing area that was agricultural land cover proximate to the streams and neonicotinoid concentrations, finding that the model explained about 60% of the variation in concentrations. This suggests that neonicotinoid concentrations will continue to increase in groundwater-fed streams over the next several decades. In total, the GCC has funded over 30 studies on pesticides - including 14 on atrazine - on the sources, groundwater susceptibility and presence of pesticides in our groundwater. Outcomes Aldicarb was withdrawn from use in Wisconsin. Low-cost screening methodologies for detecting the presence of atrazine and its break-down products in drinking water were developed. Knowledge from the intensive research and monitoring efforts allowed DATCP to adopt management strategies for reducing atrazine contamination and create the Atrazine Rule. Follow-up studies demonstrated that where atrazine use has been prohibited by the Atrazine Rule, there is a clear reduction in atrazine levels, which generally drop below the groundwater standard in 2 - 7 years. Many farmers would like the option to use atrazine in these areas, but they have adapted well to growing corn without it. A 2010 DATCP survey found that the vast majority of farmers in atrazine prohibition areas have not observed a decrease in yield, and that most believe it’s not more difficult to control weeds with other alternatives. The survey found that there is an even split in those who think weed control is more vs. less costly without atrazine8. By far, the most popular alternatives to atrazine are glyphosate-containing products such as Roundup. From a groundwater perspective, this is fortunate since glyphosate binds very tightly to soil and thus is generally not considered a groundwater threat. There are concerns, however, that overuse of glyphosate may lead to glyphosate-resistant weeds. Results from the FY20-FY21 UW-Stevens Point study of neonicotinoid insecticides in groundwater-fed streams results suggest that neonicotinoid concentrations will continue to increase in groundwater-fed streams over the next several decades. Learn More Pesticides DATCP - Atrazine

Arsenic Background Naturally-occurring arsenic was discovered in Winnebago & Outagamie Counties groundwater in 1989 during a routine investigation conducted by the DNR. Follow up sampling by DNR and reports from nearby homeowners revealed a pressing need to determine the distribution and frequency of the problem. As a result, the DNR, the Department of Health Services (DHS) and local health officials teamed with researchers funded by the WGRMP to sample thousands of private wells in Winnebago and Outagamie counties and analyze where and why arsenic levels were elevated1,2. Researchers first identified the geologic formation, then the chemical reactions responsible for the situation3,4,5,6. In the early 2000s, the US EPA lowered the MCL for arsenic from 50 ppb to 10 ppb (the current standard), which raised concerns for schools and residents in southeastern Wisconsin that had been observing arsenic levels in the 10-50 ppb range. Initial testing by the DNR and the Wisconsin Geological and Natural History Survey (WGNHS) revealed that the geochemical explanations for arsenic contamination in northeastern Wisconsin could not explain the problem in southeastern Wisconsin7, so the WGRMP funded further research to analyze the new situation and develop more appropriate guidelines8,9,10,11. Sampling of thousands of private wells shows that approximately 4% of private wells in WI exceeded the 10 ppb federal drinking water standard for arsenic. More than 15 GCC-funded studies have documented arsenic above the 10 ppb state groundwater quality enforcement standard for arsenic in groundwater in every Wisconsin county. Outcomes Innovative and inexpensive arsenic removal technology for public & private water supplies has been developed. Detection methods for arsenic were improved, including the development of an on-site measurement apparatus which reduced costs. Improved understanding of how chlorine disinfection, which is often used to treat microbial biofilms (slime) in wells, can affect the release of arsenic12 has been an important research outcome. Shock chlorination of private wells is now limited in much of northeastern Wisconsin because it has a strongly oxidizing effect that encourages the release of arsenic from sulfide minerals. Well chlorination has been found to not affect arsenic bound to iron compounds in groundwater environments such as southeastern Wisconsin. In these settings, well disinfection may reduce arsenic levels by controlling microbes that contribute to iron dissolution. Revised well-disinfection techniques have been developed to ensure that arsenic levels are kept below safe drinking water standards when treating wells for bacteria. The DNR has established a Special Well Casing Depth Area for arsenic contamination, and developed well construction guidelines, to protect drinking water supply wells in parts of northeastern Wisconsin where naturally-occurring arsenic is present in groundwater. Residents in parts of the state where naturally-occurring arsenic is present in groundwater have been provided information on the health risks of arsenic in drinking water and informed of low-cost arsenic testing options. Educational materials have been developed to help homeowners reduce arsenic levels in their drinking water supply. Information about people with long-term exposure to arsenic has been gathered in one of the largest epidemiological studies ever conducted in Wisconsin13,14. Educational outreach has been provided to well drillers to continue to improve well drilling and construction techniques that minimize arsenic levels in private wells. Learn More Arsenic Arsenic Research

Nitrate Background Nitrate is the most widespread groundwater contaminant in Wisconsin. Statewide, about 10% of private well samples exceed the 10 part per million (ppm) safe drinking water level for nitrate. Around 90% of nitrogen inputs to groundwater in Wisconsin can be traced to agricultural sources. In 2019, sampling results from new well and pump work (from the years 2014 - 2018) was used to develop an estimate of the statewide costs to address nitrate over the 10 ppm health standard in private wells. The estimate was based on the assumption that private well owners who were over the nitrate health standard would choose to drill a new well to a depth where safe, below the nitrate health standard, water could be obtained (the preferred “safe at the source” method to address well contamination). The data analysis from 2019 showed that the estimated number of private wells exceeding the health standard for nitrate in Wisconsin was over 42,000, with a total cost estimate, to abandon those contaminated wells and replace them with new safe water supply wells, of over 446 million dollars. Nitrate has always been a core concern for GCC agencies. Since 1985, over 40 projects, or 10% of the total portfolio funded by the WGRMP, have investigated the occurrence, transport, removal or management of nitrogen in Wisconsin. Outcomes DHS expanded their health recommendation for nitrate from just pregnant women and children under 6 months, to include everyone drinking water with nitrate above the standard. In 2014, the private well code was changed to require sampling for nitrate in newly constructed wells and wells with pump work. Numerous studies show that nutrient management plans do not meet the health-based standard for Nitrate. A tool for viewing nitrate trends in Wisconsin’s Public Water Systems has been developed, in partnership with the DNR, by the UW-Stevens Point Center for Watershed Science and Education. This tool allows users to view summary statistics for public water system wells to see which systems may be changing over time and, if so, whether those changes show increasing or decreasing nitrate concentrations. Learn More Nitrate

Viruses, Bacteria and Pathogens Background Protecting drinking water from microbial contamination is a top public health priority. Limited statewide groundwater virus occurrence data exists because testing is expensive, not routinely performed, and levels cannot be reliably inferred from total coliform bacteria sampling results. Virus markers were found in deep bedrock wells that were thought to be protected, suggesting that deep groundwater may be more vulnerable to virus contamination than previously thought. Public water systems may be at an increased risk of being contaminated by viruses and other microbial agents. The incidence of virus contamination in private wells may affect 4-12% of private wells in the state. The GCC has funded 10 research projects on viruses because of concern of presence of viruses in drinking water wells. Outcomes Because of research funded by GCC, virus testing that used to take three months to complete can now be accomplished in an afternoon. Evidence indicating that disinfection with chlorine or ultraviolet light reduces the risk of illness from viruses and other microbial sources led DNR to amend a rule requiring disinfection of municipal drinking water supplies. That rule change, however, was repealed by the state legislature in 2011. Nationally, the EPA has included virus types found in Wisconsin research projects on a list of 30 unregulated contaminants being studied to gather information to support future drinking water protection regulations. Learn More Pathogens Detection and Monitoring of Microbiological Contaminants

Radium and other Naturally Occurring Elements Background In eastern Wisconsin, wells that draw from a very deep sandstone aquifer often have levels of radium above safe drinking water levels. High levels of radium in groundwater from the deep sandstone aquifer in eastern WI primarily affects public wells, as drilling a deep well that would reach this aquifer is usually prohibitively expensive for those having a private home water supply well constructed. In the early 2000s, the flow patterns and geochemistry of groundwater in southeastern Wisconsin became of great interest as large-scale pumping driven by growing communities outside Milwaukee began to dramatically change groundwater conditions. One puzzle to scientists was why radium levels were elevated to the east of the Maquoketa shale in this region but not to the west – conventional understanding of the sources of radium did not seem sufficient to explain observations. By the mid-1980s, regular monitoring of public water supplies in north central Wisconsin seemed to indicate that there was an increased risk of radionuclide contamination in wells drawing from the granite bedrock aquifer. This raised concern since, at the time, drilling to this deeper granite aquifer was viewed as the best alternative if wells in the shallow sand and gravel aquifer became contaminated by manmade sources. About 80 public water systems have exceeded a radionuclide drinking water standard at some point in time. A study of radium in groundwater, in the Cambrian-Ordovician aquifer system, was conducted in the vicinity of Madison in 2016 - 20172. This study evaluated radium occurrence in groundwater relative to several geochemical parameters, as well as the presence of naturally occurring radium “parent elements”, uranium and thorium, in aquifer bedrock units. The Cambrian-Ordovician aquifer in central Wisconsin is composed of an unconfined bedrock aquifer unit and a confined bedrock aquifer unit, separated by the Eau Claire shale aquitard. Radium parent radionuclides (238U and 232Th) were found associated with both the Eau Claire shale aquitard and bedrock layers in both unconfined and confined Cambrian-Ordovician aquifer units. The study found an association in the upper, unconfined aquifer unit, between elevated levels of radium in groundwater and relatively high levels of total dissolved solids (TDS). High TDS in groundwater, creates competition between radium and other dissolved ions for sorption sites, and is proposed as the explanation for the elevated groundwater radium found in the unconfined aquifer unit. Elevated groundwater radium in the lower, confined aquifer unit was found to be associated with very low groundwater dissolved oxygen (DO) levels. Dissolution of iron and manganese hydroxide radium adsorption sites occurs under low DO conditions and adsorbed radium can be mobilized into groundwater under these geochemical conditions. Seven studies have been funded by the GCC on Naturally Occurring Radioactive Elements, including Radium, since 1987. In Dane County, residents were surprised to learn in 2011 that hexavalent chromium (Cr-6) is present in Madison drinking water in very low concentrations. While trivalent chromium (Cr-3) is an essential trace nutrient in low concentrations, Cr-6 is a suspected carcinogen. As DHS responded to questions about the health effects of Cr-6, WGNHS quickly embarked on a sampling study to determine whether there was a naturally occurring source of chromium in the local bedrock formations1. A research project, funded through WGRMP, was conducted to study the occurrence and sources of strontium in groundwater in northeastern Wisconsin2. Very high levels of strontium in wells drawing water from the Cambrian Ordovician bedrock aquifer in the northeast part of the state were documented in the study. Outcomes After collecting and analyzing nearly 500 samples from this area in the late 1980s, the DNR showed that the granite bedrock aquifer is indeed a significant source of radionuclides, especially radon, and the DNR began taking steps to educate well owners and expand the investigation. Follow up work in other regions of the state by the DNR, WGNHS, and DHS also showed that while nearly all aquifers in the state contain some amount of radon (at or above 300 pCi/L), exceedingly high levels (over 4,000 pCi/L) are only found in granite, or in sand and gravel deposits derived from granite3 . A few studies by University of Wisconsin researchers at that time also noted unusually high levels of radium in eastern Wisconsin that seemed to be associated with the Maquoketa shale geologic formation4,5. The DNR has been working with public water systems since 2003 to ensure that they develop a compliance strategy and take corrective action on radium. Currently, fewer than 10 systems remain that are providing water in exceedance of the radium standards. The Wisconsin State Laboratory of Hygiene and other WGRMP-funded researchers have also made advances in sampling techniques and laboratory testing for radionuclide parameters, which tend to be very sensitive to collection and analysis methods. Studies have demonstrated how simple differences in approaches can cause one analysis to conclude a water sample is below the MCL while another can conclude the opposite about the same sample6,7. Following these findings, researchers have developed corrections and guidelines to ensure reported test results are as accurate as possible. Leveraging new models and knowledge about groundwater flow patterns in the Waukesha area, researchers at the University of Wisconsin evaluated the relationship between radium and sulfate minerals in the area, collecting much needed information on the geochemical conditions of the region in the process8,9. The need for compliance with radium drinking water standards is the main reason the city of Waukesha sought and received approval under the Great Lakes Compact for a diversion (with “return flow”) of Lake Michigan water. WGRMP-funded researchers at UW-Madison and the Wisconsin State Laboratory of Hygiene followed up with a project to explore what geochemical environments create ideal conditions for Cr-6 mobility in key geologic formations across the state10. Findings indicated that chromium naturally occurs in all formations, but only the upper aquifers seem to have the geochemical conditions to promote mobility of aqueous Cr-6. Research has shown that groundwater chemistry in the Cambrian Ordovician aquifer is influenced by deep regional bedrock faults, that have created aquifer groundwater “zones” with differing major ion chemistry. Strontium minerals (precipitated from Michigan geologic basin hydrothermal brines) in carbonate bedrock and interstitial cement in sandstone formations were determined to be the likely source of elevated strontium in northeastern Wisconsin groundwater. The heterogenous nature of bedrock strontium mineral deposition, and the influence of major faults on groundwater chemistry, were suggested as reasons for the observed variability in strontium concentrations in well water across the research study area. Strontium is emerging as a trace element of concern in eastern Wisconsin, particularly in the Brown and Outagamie county areas. A study detected strontium above the US EPA’s health advisory limit in about 63% of well samples from this area, but the full extent of groundwater with high strontium levels is not well documented, nor are the potential health effects. Learn More Groundwater Drawdowns Radionuclides

Innovative lab methods Background Groundwater quality testing can be expensive and limited analytical methods can be available. Projects funded by GCC have led to the development of new methods for groundwater evaluation and protection that take less time and are more cost-efficient. Outcomes Research funded by the GCC documented that holding times and higher temperatures do not affect the quality of E. coli bacteria samples. This finding led to a decrease in the number of samples rejected by laboratories and saved water systems a significant amount of time and money. The department estimates that water systems are saving $300,000 to $600,000 per year in shipping costs alone. Laboratory techniques that have made it possible to discern whether bacteria are from human, animal or other sources have been developed1,2. These microbial source tracking (MST) tools include tests for Rhodococcus coprophilus (indicative of grazing animal manure), Bifidobacteria (indicative of human waste) and Bacteroides (indicative of recent fecal contamination by either humans and/or grazing animals). Analysis has also been developed that can successfully detect bovine adenoviruses, that indicate bovine fecal contamination of groundwater3. The DNR has been using these tools as they become available to determine the source of fecal contamination in private wells. DNR and DATCP are working to find ways of controlling this major source of contamination and have established revised performance standards and prohibitions related to manure land application in areas of the state with carbonate bedrock and shallow soils. Virus testing that used to take three months to complete can now be accomplished in an afternoon. Improved detection techniques for arsenic have been developed, including the development of on-site measurement apparatus to reduce laboratory costs. Low-cost screening methodologies for detecting the presence of atrazine and its break-down products in drinking water have been developed.

Methylmercury Background Methylmercury (MeHg) is one of the most toxic and persistent substances in the environment. Funded research has focused on how MeHg forms from inorganic mercury deposited from atmospheric sources such as coal combustion. Measured MeHg concentrations are likely produced in situ and are not from legacy sources. The GCC has funded five studies on Methylmercury in groundwater. Outcomes Information advancing our understanding of mercury transport and methylation in groundwater that will help us interpret the watershed response to changing conditions in the hyporheic zone. Any variation in groundwater levels, whether due to climate change or conjunctive use of groundwater and surface waters, will likely influence MeHg production in both natural and engineered wetlands. Learn More Methylmercury Formed in Groundwater

Fracture flow and karst Background Karst features, including a variety of sinkholes, cavities and solution openings, commonly occur in carbonate rock (limestone and dolomite). Environmental problems associated with karst features include rapid groundwater contamination, unpredictable groundwater flow, difficulty in groundwater monitoring and unexpected failure or collapse of surface structures such as roads and foundations. There has been increased concern about the hazards and effects of karst features in many parts of Wisconsin, but little published information has been available. Fourteen studies have been funded through GCC regarding fracture flow and karst. Outcomes A karst database for the state has been created. This includes geophysical surveys near some of these features in order to characterize their depth and extent. The results of studies have been used by municipalities for planning purposes and selecting options for sinkhole remediation. A program of research and public education on groundwater movement in fractured rocks was developed and has provided assistance to various agencies facing carbonate-rock problems. Funded project led to the development of a professional short courses on fractured-rock hydrogeology. Learn More Karst and Shallow Carbonate Bedrock in Wisconsin

Groundwater/surface water interactions Background The upper surface of groundwater, referred to as the water table, can fluctuate in response to precipitation events and water withdrawals. During times of drought, local water tables can decline due to decreased groundwater recharge and increased water use (e.g. watering lawns, irrigating farm fields, municipal water supply). The result is that the water table can fall below, and disconnect from, surface water resources that rely on the water from the aquifer. The result of the disconnection can impact the ecosystems of groundwater-dependent surface water features such as springs, streams, wetlands and seepage lakes. The opposite can also occur, resulting in a higher-than-normal water table. Groundwater flooding occurs when frequent, sustained rainfall leads to excessive recharge of local groundwater levels and the water table rises above the land surface. Outcomes An inventory (and evaluation) of groundwater levels (e.g. wells) and groundwater-dependent surface water features (springs, lakes, and headwater streams) has been created. This inventory of features, and data associated with each feature, is displayed on the DNR’s Water Quantity Data Viewer. To understand the role of groundwater withdrawals on headwater streams, a groundwater flow model for the Little Plover River watershed in Portage County was completed. This model is a scientific tool for understanding the complexities of geology, groundwater recharge and discharge, surface-water flow, well development and the effects of water use on overall water balance. To understand the lake level variation and the extent groundwater withdrawals have on lakes, a study of three lakes in Waushara County (Central Sands Lakes Study) has been conducted. Learn More Groundwater/Surface Water Interactions

Emerging Groundwater Contaminants Background Emerging contaminants are compounds that are increasingly being detected in groundwater and may have harmful human health or environmental impacts. Emerging contaminants often enter groundwater in wastewater discharged or released from municipal, industrial or agricultural sources. Examples include perfluoroalkyl and polyfluoroalkyl substances (PFAS), pharmaceuticals and personal care products (including antibiotics, birth control pills, shampoos and detergents); and other broad classes of emerging contaminants such as viruses and agricultural pesticides and their metabolites (environmental break-down products). A FY 2021 GCC-funded study evaluated PFAS adsorption by selected Wisconsin aquifer sediments from five areas in Wisconsin. Sorption is when substances dissolved in water attach to solid aquifer material. Research has shown that sorption behavior among PFAS varies greatly, but that it can be higher when multi-valent cations such as iron are present. The PFAS problem is complex and widespread, and additional studies are needed. One area for further research is strategies to reduce the levels of PFAS potentially infiltrated to groundwater through the land application of biosolids. Research on the occurrence and health effects of these contaminants is important to characterize risk and to evaluate actions that may be taken to protect human and environmental health. In response to this need, over 20 studies have been funded by the GCC. Outcomes In Wisconsin law, there is an established process that facilitates the regular review of groundwater monitoring data and identification of contaminants of emerging concern (s. 160.27, Wis. Stats.). A fundamental component of this process is long-term groundwater monitoring data, so maintenance and expansion of current networks is an ongoing priority for the GCC. The occurrence of emerging contaminants in Wisconsin is not easily generalized, but several studies supported by the GCC have investigated the potential for emerging contaminants to enter groundwater from a variety of sources. WGRMP-funded projects have explored pathways of contaminant transport. One group of these studies investigated factors that affect the mobility and fate of antibiotics in the subsurface1-8. This body of work has helped describe under what conditions specific antibiotic compounds bind to soil, which is important for assessing the risk to groundwater from antibiotics in wastewater sources. A finding of the study of PFAS adsorption by selected Wisconsin aquifer sediments is that there is increased PFAS sorption in the presence of carbonate minerals. This finding is an important new finding for Wisconsin as large portions of the state have carbonate bedrock (karst) aquifers (and/or overlying calcareous sand aquifers). The results of this study will be detailed in a final report and publication in a scientific journal. Learn More Emerging Contaminants PFAS Emerging contaminants, including PFAS Pharmaceuticals, Personal Care Products and Endocrine Disrupting Compounds in Groundwater

Agency-Funded Research

Agency-Funded Research

Nitrate Initiatives

Multiple sampling programs have been carried out by the DNR, DATCP and the WGNHS to characterize the extent of nitrate contamination.

In addition to regular well sampling surveys performed by DATCP, DATCP supports the development of nutrient management plans (NMPs). These plans specify the amount and timing of nutrient sources applied to a field to optimize economic input. Approximately 31% of the agricultural land in Wisconsin is covered by an approved management plan (DATCP, 2015). All farms that apply nutrients to fields, including pastures, are required to have a nutrient management plan. DATCP provides financial assistance, free resources and training for farmers to encourage total coverage across the state.

DATCP estimated that in 2007, over 200 million pounds of nitrogen were applied to agricultural lands in excess of UW recommendations, a number that could be substantially reduced with broader adoption of NMPs. However, NMPs do not presently contain mechanisms specifically designed to assess potential nitrate loading to groundwater.

Numerous studies indicate that NMPs are not always effective at reducing nitrate levels to below the MCL. Even in the best-managed agricultural systems, over the long term (7 years) nearly 20% of nitrogen fertilizer bypasses plants and is leached to groundwater, which makes it likely that groundwater concentrations of nitrate-N at or above the MCL will continue to be a concern for Wisconsin residents. Nonetheless, there is still significant potential for improvement through increased adoption of NMPs, particularly if plans are specifically designed to result in less potential for nitrate leaching, such as incorporating crops into rotation that require less nitrogen inputs, keeping nitrogen inputs at the lower end of recommended ranges, the use of cover crops and utilizing perennial cropping practices.

The Nitrate Pilot Project

The Nitrate Pilot Project program was started by the DNR Drinking Water and Groundwater Program in 2012 to develop partnerships and collaborate with drinking water stakeholders, including the agricultural community, to evaluate strategies to reduce nitrate loading to groundwater while maintaining farm profitability. Projects have been established in collaboration with communities where municipal water systems were approaching unsafe levels of nitrate contamination. Key partners include the Wisconsin Rural Water Association, the UW System, WGNHS, the Wisconsin Land and Water Conservation Association, County Conservation and County Environmental Health departments, the USGS and others.

Common themes and challenges have emerged when looking at potential for land use changes in the vicinity of wells. Because nitrate is an acute contaminant, regulators, water suppliers and consumers need assurances that any mitigation efforts will be robust and reliable enough to assure a safe concentration of nitrate at the tap. Stakeholders need to know which conservation practices could achieve the needed water quality results, how intensively practices need to be applied, and any associated cost. In many cases, data on the efficacy of practices for protecting groundwater is either lacking or involves significant degrees of variability in the expected results. Tools do not presently exist to assist with formulation of NMPs and conservation practice regimes that will be protective of drinking water wells located downgradient of agricultural fields. Stakeholders also need to know the time period or “lag” between implementing practices in the field and the onset of water quality improvements at the tap. Traditional nutrient management planning and traditional wellhead protection planning are not designed or equipped to answer these questions.

This has led to the recommendation for the state, on a collaborative basis with all drinking water stakeholders, to engage in a process to develop new technical tools to facilitate the goal of protecting our sources of drinking water while maintaining profitable agricultural production, allowing local resource managers to create producer partnerships to implement new “groundwater protective” nutrient management plans in areas contributing recharge to potable wells.

Groundwater And Nitrogen Fertilizer Decision Support Tools

To help achieve groundwater protection in the context of nutrient management planning, the DNR is presently working with the USGS and UW system partners to develop a series of Groundwater and Nitrogen Fertilizer Decision Support tools (GW & Nitrogen DSTs) for use by communities needing source water protection resources, conservation departments, the agricultural community, and other drinking water stakeholders. Nitrogen fertilizer decision support tools will be developed and improved over time based on contributions from the full range of stakeholders. The goal is to create tools that are complementary to the existing Nutrient Management Planning programming in the state and that will illuminate management options that better protect groundwater while maintaining agricultural production. Starting with basic tools and progressing to more advanced applications over time, stakeholders will be engaged to develop collaborative solutions to existing data and research gaps, as well as barriers to adoption. Early products will focus on simple intuitive concepts, including nitrogen budget calculators that enable estimation of average annual leaching potential based on the difference between nitrogen inputs and outputs to the system. An example is the online application developed by the Central Wisconsin Groundwater Center using a mass balance approach. With minimal inputs (i.e. N fertilizer, yield, soil characteristics, etc.) the user can estimate the potential leachable nitrogen. Early evaluation shows that the calculator provides reasonable results for coarse textured soils in the Central Sands region where the challenge of estimating the change in nitrogen storage in soil is less critical. Features that can aid in planning to reduce leaching potential include the option to account for nitrogen in irrigation water, adding cover crops, and the ability to compare effect of varying fertilizer rates. A beta version of the calculator can be found here.

Future updates will utilize outputs from process-based models to increase realism and insight by incorporating nitrogen cycle drivers and simulation of the effects of weather variability. In source water protection areas where nitrate mitigation is needed, the objective is to couple an analysis of practices to reduce nitrate leaching potential with existing nutrient management planning tools already in use in Wisconsin. For example, a user might export nutrient management data from SnapPlus and process separately with a Nitrogen DST to explore options to reduce nutrient losses while maintaining productivity. Alternatively, future versions of SnapPlus could be programmed to include scripts that calculate potential nitrogen losses by pulling in needed data from a central nitrogen management scenario database that is pre-populated with best available data from field trials, the scientific literature and model runs that simulate effects of management practice and weather variation.

Because the nitrogen cycle is complex and there are many factors leading to nitrogen losses, we expect some nitrate leaching to occur even under optimal management, especially for nitrogen demanding crops. The goal is to provide reasonable expected ranges of the nitrate leaching below the root zone for common practices and to provide estimates of loss reductions for proposed conservation practices. By coupling loss estimates with groundwater transport DSTs we can facilitate groundwater management to assure potable wells located hydraulically downgradient of production fields can be maintained below the health-based standard for nitrate. To achieve the dual goal of source water protection and farm profitability, we must also quantify any tradeoffs in productivity. Where economic offsets can be expected to occur, quantification could serve as a basis for utilizing existing state and federal conservation practice funding sources in new ways that protect drinking water sources and the public health while enhancing local economies.

To upgrade the state’s capacity to reduce nitrogen losses and protect the health of most of the state population that relies on groundwater for drinking water, the goal is to better understand the extent of losses from current practices and illuminate options to reduce them. Concurrently, groundwater decision support tools in development will assist resource managers with identifying critical land areas based on outputs from groundwater flow models, and address common questions, such as the estimated time delay between practice implementation and expected water quality improvements at receptors. Groundwater DSTs will leverage existing research and groundwater models to make hydrogeologic information more available to decision-makers. Ultimately, these tools will help better utilize existing state and federal non-point pollution funding for conservation practices and can be incorporated into traditional watershed-based planning and implementation.

This long-term project provides a framework for continued development and improvement of nitrogen decision support as additional partners, research and data are incorporated over time. To be successful, drinking water stakeholders in the state, including the agricultural community, will need to share ownership and responsibility for continued development and improvement of these tools, just as we continually develop and improve the science supporting crop production. The integration of additional partners within a coordinated statewide research, planning, outreach and implementation effort is necessary to address the range of challenges to preventing excess nitrogen losses to our waters. The current Groundwater and Nitrogen Decision Support Tool development partnership seeks to expand collaboration with agencies, researchers, outreach specialists, decision support application developers and agricultural producers.

Learn more

• Abbotsford Pilot Project
• Video: Pilot project modeling analysis presentation to the Waupaca Common Council (starts at 1:01:42)
• A Groundwater-Flow Model and Effective Nitrate Calculator for Waupaca, Wisconsin
• Webinar: Nitrogen leaching in central sands: Regional & field-based estimation
• Video: Presentation on the Nitrogen Fertilizer Decision Support Tools project (starts at 41:33)

DATCP Surface And Groundwater Monitoring

Wisconsin DATCP performs routine monitoring for pesticides and nitrates to evaluate the occurrence of agrichemicals in surface water and groundwater. DATCP's Bureau of Laboratory Services analyzes samples for nitrate and more than 100 pesticide compounds using modern analytical methods. Sample collection and analysis have no cost for well owners. Annual summary reports of surface and groundwater monitoring programs are posted online.

Monitoring Programs

• Targeted Sampling Program: Tests groundwater from private wells in agricultural areas around the state to determine if pesticides are present and at what concentrations. Areas with an elevated risk for impact by agricultural chemicals are sampled annually. Samples are collected by DATCP and analyzed by DATCP's Bureau of Laboratory Services. Results are shared with the well owners and local county conservation departments, and they are used to evaluate new policy development.
• Field-Edge Monitoring Program: This program analyzes groundwater samples from monitoring wells installed within or near agriculture fields to evaluate whether agricultural practices are affecting groundwater quality. DATCP collaborates with growers around the state to install and maintain a network of groundwater monitoring wells. Groundwater collection occurs multiple times a year over several years to evaluate pesticide concentrations and potential trends. Observations and results help shape future policy and standards development.
• Surface Water Sampling Program: Represents a collaboration with the Wisconsin Department of Natural Resources (DNR) stream sampling programs. This program provides pesticide analyses on select stream streams typically located within agricultural or urban areas where pesticides are used. Samples are collected by DNR and DATCP, and analyzed by DATCP's Bureau of Laboratory Services. Data is used to evaluate impacts to surface water quality resulting from agricultural or urban runoff and groundwater discharge.
• Exceedance Well Sampling Program: Tests groundwater from private wells around the state where a state established groundwater quality standard (as defined by the Wis. Adm. Code Ch. NR 140) for a pesticide has been exceeded. Testing allows for long-term monitoring to evaluate the effectiveness of measures taken to protect groundwater over time.
• Statewide Survey: A randomized sampling of approximately 400 private drinking water wells for nitrate and pesticides. The survey is designed to provide a statistical snapshot of water quality at the time of sampling to measure the occurrence of pesticides and nitrate, and to evaluate changes in water quality over time. The survey is performed every 5 to 10 years. Five statewide surveys have been completed, with the most recent in 2016. Starting in March 2023, DATCP initiated an additional statewide survey. This survey is currently in progress and is expected to be completed by September 2023.
• Emerging Issues: This program seeks to identify new pesticide that pose a threat of becoming larger concerns for the agency. Pesticides that pose emerging concerns for groundwater contamination include neonicotinoid insecticides like imidacloprid, clothianidin and thiamethoxam, and the herbicide isoxaflutole.

History Of Research Funding

History Of State Budget Funding Levels Specifically For Groundwater Research

GCC-funded groundwater research has been vital in protecting public health and in aiding agency groundwater management decisions. Over the history of the GCC, approximately $20 million dollars has been utilized on more than 500 projects. Graphs of state budget funding levels specifically for groundwater research (since FY91-93 for UWS and FY95-97 for DNR) are shown below. The solid blue line shows the actual authorized funding level through time, the dashed gray line shows the inflation-adjusted value of the initial funding level in today's dollars.

When adjusted for inflation using U.S. Bureau of Labor Statistics Consumer Price Index calculator, annual funding to DNR was $329,255 and UW $426,790. Restoring funds to this level would allow nearly half of annually submitted groundwater research proposals to be funded each year instead of the 1/6 to 1/4 typically funded over the last ten years.

Alternatively, increasing the funding to $500,000 each for DNR and UW would allow the joint solicitation program to better attract qualified researchers to address concerns such as PFAS, which is more expensive to test and research.

Additional consideration could be given to creating dedicated funding mechanisms for the departments of Agriculture, Trade and Consumer Protection; Health Services; and Safety and Professional Services to conduct groundwater research targeting the needs of each respective agency.

References cited

References Cited

Pesticides

1. Rothschild, E. R., R. J. Manser, M. P. Anderson. 1982. Investigation of aldicarb in ground water in selected areas of the Central Sand Plain of Wisconsin. Ground Water 20(4):437-445.
2. Kraft, G. 1990. Fate of aldicarb residues in a groundwater basin near Plover, Wisconsin. Ph.D. dissertation, Department of Soil Science, UW-Madison.
3. Postle, J. K. and Brey K. M. 1988. Results of the WDATCP groundwater monitoring for pesticides. Wisconsin groundwater management practice monitoring project, DNR-002. Available at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?id=EcoNatRes.PostleResults
4. LeMasters, G. S. and D. J. Doyle. 1989. Grade A dairy farm well water quality survey. Wisconsin groundwater management practice monitoring project, DNR-052. Available at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?id=EcoNatRes.LeMastersGrade
5. Cowell, S. E. and LeMasters G. S. 1992. Follow up to the grade A dairy farm well water quality survey. Wisconsin groundwater management practice monitoring project, DNR-070. Available at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?id=EcoNatRes.CowellFollow
6. Chesters, G., G. V. Simsiman, R. N. Fathulla, B. J. Alhajjar, R. F. Harris, J. M. Harkin, J. Levy. 1990. Degradation of atrazine, alachlor, metolachlor in soils and aquifer materials. Wisconsin groundwater management practice monitoring project, DNR-047. Available at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?id=EcoNatRes.ChestersDegradation ;
7. Chesters, G., J. Levy, D. P. Gustafson, H. W. Read, G. V. Simsiman, D. C. Liposcak, Y. Xiang. Sources and extent of atrazine contamination of groundwater at Grade A dairy farms in Dane County, WI. Wisconsin groundwater management practice monitoring project, DNR-065. Available at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?id=EcoNatRes.ChestersSources
8. DATCP. 2011. Final report on the 2010 Survey of Weed Management Practices in Wisconsin’s Atrazine Prohibition Areas. Wisconsin Department of Agriculture, Trade and Consumer Protection, ARM Pub 215. Available via email request at datcppublicrecords@wi.gov

Arsenic

1. Burkel, R.S. 1993. Arsenic as a naturally elevated parameter in water wells in Winnebago and Outagamie Counties, Wisconsin. Wisconsin groundwater management practice monitoring project, DNR-087. Available at http://digital.library.wisc.edu/1711.dl/EcoNatRes.BurkelArsenic
2. Burkel, R.S. and R.C. Stoll. 1995. Naturally occurring arsenic in sandstone aquifer water supply wells of northeastern Wisconsin. Wisconsin groundwater management practice monitoring project, DNR-110. Available at http://digital.library.wisc.edu/1711.dl/EcoNatRes.BurkelNaturally
3. Pelczar, J.S. 1996. Groundwater chemistry of wells exhibiting natural arsenic contamination in east-central Wisconsin. MS thesis. University of Wisconsin-Madison. Available at http://digital.library.wisc.edu/1793/53154
4. Simo, J.A., P.G. Freiberg, K.S. Freiberg. 1996. Geologic constraints on arsenic in groundwater with applications to groundwater modeling. Wisconsin groundwater management practice monitoring project, WR95R004.
5. Simo, J.A., P.G. Freiberg, M.E. Schreiber. 1997. Stratigraphic and geochemical controls on the mobilization and transport of naturally occurring arsenic in groundwater: Implications for water supply protection in northeastern Wisconsin. Wisconsin groundwater management practice monitoring project, DNR-129.
6. Gotkowitz, M.B., J.A. Simo, M. Schreiber. 2003. Geologic and geochemical controls on arsenic in groundwater in northeastern Wisconsin. Final report to the Wisconsin Department of Natural Resources, DNR-152. Available at https://wgnhs.uwex.edu/pubs/000831/
7. Gotkowitz, M.B. 2002. Report on the preliminary investigation of arsenic in groundwater near Lake Geneva, Wisconsin. Final report to the Wisconsin Department of Natural Resources, DNR-163. Available at http://wgnhs.uwex.edu/pubs/wofr200002/
8. Sonzogni, W.C., A. Clary, G. Bowman, J. Standridge, D. Johnson, M. Gotkowitz. 2003. Importance of disinfection on arsenic release in wells. Wisconsin groundwater management practice monitoring project, DNR-172. Available at http://digital.library.wisc.edu/1711.dl/EcoNatRes.SonzogniImport
9. Bahr, J.M., M.B. Gotkowitz, T.L. Root. 2004. Arsenic contamination in southeast Wisconsin: sources of arsenic and mechanisms of arsenic release. Wisconsin groundwater management practice monitoring project, DNR-174. Available at http://digital.library.wisc.edu/1711.dl/EcoNatRes.BahrArsenic
10. Root, T.L. 2005. Controls on arsenic concentrations in ground water from Quaternary and Silurian units in southeastern Wisconsin. Ph.D. diss., Department of Geology and Geophysics, University of Wisconsin – Madison.
11. West, N., M. Schreiber, M. Gotkowitz. 2012. Arsenic release from chlorine-promoted alteration of a sulfide cement horizon: Evidence from batch studies on the St. Peter Sandstone, Wisconsin, USA. Applied Geochemistry, 27(11):2215-2224.
12. Gotkowitz, M., K. Ellickson, A. Clary, G. Bowman, J. Standridge and W. Sonzogni, 2008. Effect of well disinfection on arsenic in ground water, Ground Water Monitoring and Remediation, 28: 60-67.
13. Knobeloch L. and H Anderson. 2002. Effect of arsenic-contaminated drinking water on skin cancer prevalence in Wisconsin’s Fox River Valley. Proceedings of the 5th International Conference on Arsenic Exposure, San Diego CA.
14. Zierold K, Knobeloch L, and H Anderson. 2004. Prevalence of chronic disease in adults exposed to arsenic-contaminated drinking water. American Journal of Public Health, 94(11):1936-1937. Available at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1448563/

Radionuclides & other naturally-occurring elements

1. Mathews, M., Gotkowitz, M., Ginder-Vogel, M. 2019. Effect of geochemical conditions on radium mobility in discrete intervals within the Midwestern Cambrian-Ordovician aquifer system. Wisconsin Groundwater Research and Monitoring Program - Final Report for Project number WR16R006. Available at: https://www.wri.wisc.edu/wp-content/uploads/FinalWR16R006.pdf
2. Gotkowitz, M.B., P.I. McLaughlin, J.D. Grande. 2012. Sources of naturally occurring chromium in bedrock aquifers underlying Madison, Wisconsin. Wisconsin Geological and Natural History Survey, Open-File Report 2012-08. Available at http://wgnhs.uwex.edu/pubs/wofr201208/
3. Luczaj, J., M. Zorn, J. Baeten. 2013. An Evaluation of the Distribution and Sources of Dissolved Strontium in the Groundwater of Eastern Wisconsin, with a Focus on Brown and Outagamie Counties. University of Wisconsin System Groundwater Research Report WR12R004. Available at https://www.wri.wisc.edu/wp-content/uploads/FinalWR12R004.pdf
4. Mudrey, M. G. and K. R. Bradbury. 1993. Distribution of radionuclides in Wisconsin groundwater. Wisconsin Geological and Natural History Survey, Open-File Report 1993-09. 19 p. Available at http://wgnhs.uwex.edu/pubs/wofr199309/
5. Taylor, R. W. and G. Mursky. 1990. Mineralogical and geophysical monitoring of naturally occurring radioactive elements in selected Wisconsin aquifers. Wisconsin groundwater management practice monitoring project, DNR-051. Available at http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?id=EcoNatRes.TaylorMineral
6. Weaver, T. R. and J. M. Bahr. 1991. Geochemical evolution in the Cambrian-Ordovician sandstone aquifer, eastern Wisconsin: Major ion and radionuclide distribution. Ground Water 29(3):350-356.
7. Sonzogni, W. C., D. M. Schleis, L. E. West. 1995. Factors affecting the determination of radon in groundwater. Wisconsin groundwater management practice monitoring project, DNR-111. Available at http://digital.library.wisc.edu/1711.dl/EcoNatRes.SonzogniFactors
8. Arndt, M. F., and L. West. 2004. A Study of the factors affecting the gross alpha measurement, and a radiochemical analysis of some groundwater samples from the state of Wisconsin exhibiting an elevated gross alpha activity. Wisconsin groundwater management practice monitoring project, DNR-176. Available at http://www.slh.wisc.edu/wp-content/uploads/2013/10/dnrfinal.pdf
9. Grundl, T. and M. Cape. 2006. Geochemical factors controlling radium activity in a sandstone aquifer. Ground Water 44(4):518-527.
10. Grundl, T., K. Bradbury, D. Feinstein, S. Friers, D. Hart. 2006. A Combined Hydrologic/Geochemical Investigation of Groundwater Conditions in the Waukesha County Area, WI. Wisconsin groundwater management practice monitoring project, WR03R002. Available at https://www.wri.wisc.edu/research/a-combined-hydrogeologic-geochemical-investigation-of-groundwater-conditions-in-the-waukesha-county-area-wi/
11. Gorski, P. M. Shafer, J. Hurley. 2015. Hexavalent Chromium (Cr(VI)) in Wisconsin Groundwater: Identifying factors controlling the natural concentration and geochemical cycling in a diverse set of aquifers. Wisconsin groundwater management practice monitoring project, WR12R005.

Innovative Lab Methods

1. Pedersen, J. T. McMahon, S. Kluender. 2008. Use of human and bovine adenovirus for fecal source tracking. Wisconsin groundwater management practice monitoring project, DNR-195. Available at http://digital.library.wisc.edu/1711.dl/EcoNatRes.KluenderUse
2. Long, S. and J.R. Stietz. 2009. Development and validation of a PCR-based quantification method for Rhodococcus coprophilus. Wisconsin groundwater management practice monitoring project, DNR-206. Available at http://digital.library.wisc.edu/1711.dl/EcoNatRes.LongProject
3. Sibley, S.D., T. L. Goldberg, J. A. Pederson. 2011. Detection of known and novel adenoviruses in cattle wastes using broad-spectrum primers. Applied and Environmental Microbiology, 77(14):5001-5008.

Emerging Contaminants

1. Gao, J. and J.A. Pedersen. 2005. Adsorption of sulfonamide antimicrobial agents to clay minerals. Environmental Science & Technology, 39:9509-9516.
2. Gao, J. and J.A. Pedersen. 2010. Sorption of sulfonamides to humic acid–clay complexes. Journal of Environmental Quality, 39:228–235.
3. Gu, C., K.G. Karthikeyan. 2005a. Interaction of tetracycline with aluminum and iron hydrous oxides. Environmental Science & Technology, 39:2660-2667.
4. Gu, C. and K.G. Karthikeyan. 2005b. Sorption of the antimicrobial ciprofloxacin to aluminum and iron hydrous oxides. Environmental Science & Technology, 39(23):9166-9173
5. Gu, C. and K.G. Karthikeyan. 2008. Sorption of tetracycline to humic-mineral complexes. Journal of Environmental Quality, 37:704–711.
6. Gu, C, K.G. Karthikeyan, S. D. Sibley, and J.A. Pedersen. 2007. Complexation of the antibiotic tetracycline with humic acid. Chemosphere, 66:1494–1501.
7. Sibley, S. D., and J.A. Pedersen. 2008. Interaction of the macrolide antimicrobial clarithromycin with dissolved humic acid. Environmental Science & Technology, 42:422–428.
8. Pedersen, J.A., K.G. Karthikeyan, and H.M Bialk. 2009. Sorption of human and veterinary antibiotics to soils. Natural Organic Matter and its Significance in the Environment. Wu, F.; Xing, B. (eds). Science Press: Beijing, China, pp. 276-299.

Nitrate Initiatives

• Brye, K. R., J.M. Norman, L.G. Bundy, and S.T. Gower, 2001. Nitrogen and carbon leaching in agroecosystems and their role in denitrification potential. J. Environ. Qual. 30(1): 58-70.
• Campbell, T.A., Booth, E.G., Gratton, C., Jackson, R.D. and Kucharik, C.J., 2022. Agricultural landscape transformation needed to meet water quality goals in the Yahara River watershed of southern Wisconsin. Ecosystems, pp.1-19.
• Cardiff, M., Schachter, L., Krause, J., Gotkowitz, M. and Austin, B., 2023. Quantifying Annual Nitrogen Loss to Groundwater Via Edge‐of‐Field Monitoring: Method and Application. Groundwater, 61(1), pp.21-34.
• Cassman, K.G., A. Dobermann, D. T. Walters. 2002. Agroecosystems, nitrogen-use efficiency, and nitrogen management. Ambio, 31: 132-140.
• Cassman, K. G., A. Dobermann, D. T. Walters, and H. Yang. 2003. Meeting cereal demand while protecting natural resources and improving environmental quality. Annual Review of Environment and Resources 28:315-58.
• Donner, S. D. and C. J. Kucharik, 2003. "Evaluating the impacts of land management and climate variability on crop production and nitrate export across the Upper Mississippi Basin." Global Biogeochemical Cycles, 17(3): 10.1028 / 2001GB1808.
• Donner, S. D., C. J. Kucharik, et al., 2004. The impact of changing land use practices on nitrate export by the Mississippi Basin. Global Biogeochemical Cycles, 18(GB1028, doi: 10.1029/2003GB002093).
• Donner, S. D., M. T. Coe, et al., 2002. "Modeling the impact of hydrological changes on nitrate transport in the Mississippi River Basin from 1955-1994." Global Biogeochemical Cycles, 16(3): 10.1029/2001GB001396.
• Donner, S.D and C.J. Kucharik, 2003. Evaluating the impacts of land management and climate variability on crop production and nitrate export across the Upper Mississippi Basin. Global Biogeochemical Cycles 17(3) 1085, doi:10.1029/2001GB001808, 2003.
• Donner S.D., and C.J. Kucharik, 2008. Corn-based ethanol production compromises goal of reducing nitrogen export by the Mississippi River. Proceedings of the National Academy of Sciences 105: 4513-4518. DOI: 10.1073/pnas.0708300105.
• Erickson, M.L., Yager, R.M., Kauffman, L.J. and Wilson, J.T., 2019. Drinking water quality in the glacial aquifer system, northern USA. Science of the Total Environment, 694, p.133735.
• Heineman, E.M. and Kucharik, C.J., 2022. Characterizing Dominant Field-Scale Cropping Sequences for a Potato and Vegetable Growing Region in Central Wisconsin. Land, 11(2), p.273.
• Juckem, P.F., Clark, B.R. and Feinstein, D.T., 2017. Simulation of groundwater flow in the glacial aquifer system of northeastern Wisconsin with variable model complexity (No. 2017-5010). US Geological Survey.
• Juckem, P.F. and Starn, J.J., 2021. Re‐Purposing Groundwater Flow Models for Age Assessments: Important Characteristics. Groundwater, 59(5), pp.710-727.
• Kraft, G.J. and Stites, W., 2003. Nitrate impacts on groundwater from irrigated-vegetable systems in a humid north-central US sand plain. Agriculture, Ecosystems & Environment, 100(1), pp.63-74.
• Kraft, G.J., Stites, W., Mechenich, D. and Balma, J.A., 1995. Port Edwards groundwater priority watershed: Groundwater resource and agricultural practice evaluation. Stevens Point, Wisconsin: Central Wisconsin Groundwater Center, University of Wisconsin-Stevens Point. https://www3.uwsp.edu/cnr-ap/watershed/Documents/portedwards_1995.pdf
• Kucharik, C.J., 2003. Evaluation of a process-based agro-ecosystem model (Agro-IBIS) across the U.S. cornbelt: simulations of the inter-annual variability in maize yield. Earth Interactions, 7: 1-33.
• Kucharik, C.J. and K.R. Brye, 2003. Integrated BIosphere Simulator (IBIS) yield and nitrate loss predictions for Wisconsin maize receiving varied amounts of nitrogen fertilizer. Journal of Environmental Quality, 32: 247-268.
• Masarik, K. C., J.M. Norman and K.R. Brye, 2014. Long-Term Drainage and Nitrate Leaching below Well-Drained Continuous Corn Agroecosystems and a Prairie. Journal of Environmental Protection. doi: 10.4236/jep.2014.54028
• Meisinger, J.J. and Randall, G.W., 1991. Estimating nitrogen budgets for soil‐crop systems. Managing nitrogen for groundwater quality and farm profitability, pp.85-124.
• Parsen, M., Juckem, P.F., Gotkowitz, M. and Fienen, M.N., 2019. Groundwater flow model for Western Chippewa County–Including analysis of water resources related to industrial sand mining and irrigated agriculture (No. B112). Wisconsin Geological and Natural History Survey.
• Shrestha, D., Masarik, K. and Kucharik, C.J., 2023. Nitrate losses from Midwest US agroecosystems: Impacts of varied management and precipitation. Journal of Soil and Water Conservation, 78(2), pp.141-153.