A 3-year total phosphorus (TP) budget was created for Walnut Creek, a ∼5200 ha agricultural watershed in central Iowa. The budget, developed from measures of streambank erosion, overland flow, baseflow, and flux to floodplain storage, was created with the specific goal of estimating in-channel storage contributions to annual TP loads-a component often poorly understood and rarely quantified at the watershed scale. Remobilization of in-channel sediment-bound P storage was estimated to dominate contribution to annual P loads, with overland flow the second greatest contributor. Streambanks represented only a minor contribution to loads and were surpassed in importance by baseflow dissolved P in drought years with reduced direct runoff. Although flux to floodplain storage was negligible, due to relatively low peak flows over the study's duration, and the degree of channel incision, the floodplain would represent a substantial P storage opportunity during years with greater peak flows. High-discharge events delivered the majority of the annual P load in two of the three study years, and the impact of these events is predicted to increase with progression of channel evolution and climate-driven increases in precipitation event intensity. Restoration of watershed hydrology (e.g., reduction of peak flows) and increased P flux to long-term floodplain storage through enhancement of channel-floodplain connectivity will have the greatest impact for decreasing annual P loads.

Converting agricultural landscapes to native ecosystems has long been known to improve water quality, especially in US Midwest basins struggling with nutrient and sediment pollution. While the benefits of restoration have been well documented at field scales, few restoration efforts have been substantial enough to be detected at a larger watershed scale. Walnut Creek in central Iowa is a notable exception, undergoing conversion of 45% of cropland in the downstream half of the basin to tallgrass prairie at the Neal Smith National Wildlife Refuge. This study examined the influence of this large-scale prairie reconstruction on streamflow, nitrate, and sediment in Walnut Creek (1995-2024) using monitoring records upstream and downstream of the restoration. Mean annual streamflow yield and baseflow index were found to be lower in the prairie portion of the basin (264 mm/year and 0.58) than in its unaltered upstream counterpart (292 mm/year and 0.66). Likewise, nitrate and suspended sediment concentration (SSC) levels exhibited greater reductions within the prairie portion of the basin. Nitrate yields and flow-weighted concentrations decreased at rates of -0.370 kg/ha/year and -0.131 mg/L/year, respectively, while SSC decreases were -48.8 kg/ha/year and -17.0 mg/L/year. These results align with the hypothesized effects of converting cropland to tallgrass prairie and suggest that restoration efforts have had an appreciable impact on Walnut Creek's streamflow and water quality. The study highlights the benefits of long-term monitoring for quantifying changes in flow and water quality driven by land cover change, as improvements can be difficult to detect due to interannual rainfall variability.

Recent efforts to address flooding have explored incorporating flow-reduction capabilities into existing infrastructure. Roadside ditches have historically been viewed as an underutilized component of flood reduction, and a two-stage design has been proposed that modifies a conventional trapezoidal ditch by incorporating bench insets along the main channel. While it is expected that this second stage becomes inundated during storm events, resulting in flow attenuation, the exact impacts of this design are unknown. This study quantified the impact of the two-stage design by modeling a roadside ditch corridor in eastern Iowa. An existing single-stage ditch was converted to a two-stage design, and a HEC-RAS model was constructed to investigate the ditch’s impacts for four design storms (1-year, 2-year, 5-year, and 10-year). In the modeled results, peak flow rates were reduced by 22%, 21%, 7.5%, and 4.3%, respectively, while water volume reductions were near 6%. Maximum velocities throughout the ditch corridor also decreased, with reductions spanning 32% (1-year)–45% (10-year). These results indicate that increased travel times and infiltration associated with the two-stage design provide hydrologic and hydraulic benefits by lessening flood and erosion risk. While further study is needed to verify this behavior through monitoring and modeling at other locations, our findings suggest that two-stage ditches can be a useful best management practice for the transportation community.

This study investigates the occurrence and distribution of fluoride in Iowa's groundwater and drinking water. Fluoride, added to community water supplies to prevent dental caries, can pose health risks at high concentrations. The U.S. Public Health Service recommends an optimal fluoride concentration of 0.7 mg/L, while the EPA sets a maximum contaminant level (MCL) at 4 mg/L and a secondary MCL at 2 mg/L. This research analyzes fluoride data from various sources, including the Iowa Department of Natural Resources and the US Geological Survey, covering 9,011 raw groundwater samples from 1931 and 2017 and 26,280 treated drinking water samples from 1934 to 2021. Fluoride concentrations in Iowa's groundwater ranged from <0.1 mg/L to 11.2 mg/L, with an average of 0.65 mg/L and a median of 0.35 mg/L. Approximately 69% of untreated raw source groundwater samples fell below the recommended 0.7 mg/L, while 7% exceeded the secondary MCL of 2 mg/L. Higher fluoride levels are associated with deeper wells and specific aquifers, such as the Cambrian-Ordovician and Mississippian. Treated public drinking water showed an average fluoride concentration of 0.87 mg/L, indicating a higher average of 0.24 mg/L (mean) compared to untreated groundwater due to fluoridation practices. Fluoride concentrations in treated water peaked between 1980 and 1999, then declined slightly after 2000 and more so when systems began aligning with the 2015 recommendation to lower the optimal level to 0.7 mg/L. This pattern reflects how regulatory guidance and water source management have influenced fluoride levels over time. This study highlights significant regional variability in fluoride levels, influenced by aquifer lithology, well depth, and water chemistry. Anthropogenic sources also contribute to fluoride concentrations. The findings underscore the need for tailored water management strategies to balance the benefits of fluoridation with the risks of excessive fluoride intake. This research provides valuable insights for public health agencies, water suppliers, and residents, aiming to optimize fluoride levels in Iowa's drinking water to ensure safety and efficacy.

Societal risks from flooding are evident at a range of spatial scales and climate change will exacerbate these risks in the future. Assessing flood risks across broad geographical regions is a challenge, and often done using streamflow time-series records or hydrologic models. In this study, we used a national-scale hydrological model to identify, assess, and map 16 different streamflow metrics that could be used to describe flood risks across 34,987 HUC12 subwatersheds within the Mississippi-Atchafalaya River Basin (MARB). A clear spatial difference was observed among two different classes of metrics. Watersheds in the eastern half of the MARB exhibited higher overall flows as characterized by the mean, median, and maximum daily values, whereas western MARB watersheds were associated with flood indicative of high extreme flows such as skewness, standardized streamflow index and top days. Total agricultural and building losses within HUC12 watersheds were related to flood metrics and those focused on higher overall flows were more correlated to expected annual losses (EAL) than extreme value metrics. Results from this study are useful for identifying continental scale patterns of flood risks within the MARB and should be considered a launching point from which to improve the connections between watershed scale risks and the potential use of natural infrastructure practices to reduce these risks.

Streambank erosion is an important source of sediment to river systems but is difficult to quantify at watershed scales. In this study, high-resolution Light Detection and Ranging (LiDAR) measurements collected from 2009 and 2020 were used to quantify the difference in land surface elevation that occurred along the fourth and fifth-order streams in Old Mans Creek watershed in southeast Iowa. Study objectives were to quantify the volume of streambank sediment erosion and deposition occurring along the river systems and compare net channel erosion to watershed sediment export. Results indicated that streambank erosion and deposition along the fourth and fifth-order channels totaled nearly 720,000 m3 and 148,000 m3, respectively, over the 11-year study period. Five times more streambank erosion occurred than deposition, and the difference between the two totals (net sediment erosion) comprised 77% of the sediment export from the watershed. The contribution of streambank sediment to basin export, along with estimates of mean annual streambank recession derived from the analyses, were consistent with results reported in other studies of streambank erosion. The LiDAR differencing methodology was able to identify areas of both sediment erosion and deposition occurring in the stream channels and quantify the net difference, which is related to watershed-scale sediment export.

The US state of Iowa has experienced profound historical changes in its streamflow and baseflow. While several studies have noted increasing baseflow and baseflow index (BFI) values throughout the 20th century, analyses quantifying BFI trends in recent years or exploring spatial differences in watersheds marked by varying land use and geologic properties have not been conducted. This study calculated annual values for BFI (and several other hydrologic metrics) using flow records from 42 Iowa stream gauges containing at least 50 years of uninterrupted measurements. While BFI overwhelmingly rose throughout the mid-1900s, circa 1990 it began to level off. In some areas of Iowa (e.g., the southwest), BFI has continued to rise over the past 30 years—albeit at a slower rate; in other regions, it has become stationary or declined. One site failed to follow this trend (Walnut Cr), the only basin to experience large-scale urbanization. Furthermore, BFI demonstrated a strong negative correlation to streamflow flashiness, indicating that rising baseflow has also made Iowa streams less dynamic. BFI was largely independent of overall streamflow. These results may suggest the increased influence of conservation practices and the diminishing impacts of tile drainage on the delivery of water to Iowa’s rivers.

Flood control reservoirs in the U.S. Midwest intercept riverine nitrate‑nitrogen (NO3-N) transport from agricultural watersheds and are known to reduce mass loads as water flows through them. In this study, we conducted six comprehensive boat surveys over a two-year period to evaluate spatial patterns of NO3-N concentration reductions occurring within the delta environment of Lake Red Rock reservoir in south-central Iowa. Surface water NO3-N concentrations were mapped over a distance of 26,000 to 36,000 m within the main channel and off-channel delta areas using a boat-mounted Nitratax sensor. Concurrent with the boat surveys, groundwater quality conditions were assessed by installing and sampling five shallow monitoring wells. During the six surveys, background reservoir NO3-N concentrations ranged from 3.3 to 10.8 mg/L. Higher and more uniform concentrations were observed in the connected flowing channels compared to NO3-N concentrations in off-channel coves, bays, and side channels, which were approximately 2 to 6 mg/L lower. Shallow groundwater was shown to be highly anoxic and contain nearly non-detectable levels of NO3-N. Denitrification is hypothesized to be the main process reducing NO3-N within the off-channel areas and in shallow groundwater, and reductions occurring in these areas are contributing to reservoir-wide N reductions. Overall, the study highlights significant spatial patterns in NO3-N concentrations that can develop within deltas of typical Midwestern flood-control reservoirs. Future work can focus on evaluating seasonal patterns of reductions in off-channels and groundwater with an eye toward developing strategies for capitalizing on these delta environments to decrease the export of NO3-N from agricultural watersheds.

Vulnerability assessments are frequently used to guide land use and resource planning efforts in groundwater-dependent regions. However, many readily available methodologies are not particularly useful to assess pollution risks to aquifers in specific hydrogeologic settings. In this study, aquifer vulnerability was evaluated in Black Hawk County, Iowa (USA), using an index-based approach conceptually aligned with traditional methodologies focused on groundwater resistance through overlying sedimentary layers. Incorporating elements of groundwater recharge, travel time to the uppermost used aquifer, pollution risk and groundwater use, the enhanced aquifer vulnerability index (AVI) method revealed spatial variability in vulnerability at local and regional scales within the county. Increased aquifer vulnerability was evident within the Cedar River floodplain and other minor floodplain areas where there is greater recharge, shorter vertical groundwater travel times, the presence of point and nonpoint pollution sources, and increased water use. In upland regions underlain by unoxidized till, bedrock aquifers are largely protected from pollution, whereas in areas where the bedrock surface is relatively shallow, the protection of unoxidized till is missing and aquifer vulnerability to contamination is higher. Groundwater use reflected by incorporating 10-year capture zones into the index model identified zones where water supply aquifers are at greater risk from point and nonpoint source contamination. Overall, the new methodology adapts and greatly expands on the traditional AVI approach and can be adopted in other regions as applicable. Users are able to modify and adapt the index-based groundwater vulnerability schemes to better account for localized patterns and location-specific use and pollution risks.

Flood-mitigation reservoirs have long been known to impact pollutant transport by retaining or removing incoming sediment and nutrients. However, historical reductions in these systems have rarely been well quantified. In this study, we used water quality data to estimate inputs and outputs of total suspended solids (TSS), two phosphorus (P) forms, and three nitrogen (N) forms in three Iowa reservoirs (Coralville, Red Rock, and Saylorville). We also explored the influence of reservoir residence times on removal rates. Annual residence times were largely consistent across the basins, ranging from roughly 6 to 100 days (mean of 19 days). Between 2001 to 2023, most TSS (similar to 80%) entering the reservoirs was retained. This sedimentation corresponded to average volume losses in the reservoirs' normal storage pools of 0.37%-0.85%/year. About 40% of P and 12% of N were likewise reduced-driven mainly by decreases in particulate P and nitrate. Residence time appeared unrelated to removal rates of TSS and particulate nutrient forms, but longer residence times coincided with increased nitrate loss. Reservoir impact on statewide nutrient export was significant, with loads in Iowa's major rivers being reduced by 9.8% (for P) and 4.7% (for N) due to reservoir capture. These findings suggest that reservoir operators may be able to facilitate further nitrate removal by lengthening storage durations without incurring additional sedimentation or generating other nutrient forms.

Phosphorus (P) is a problematic waterborne pollutant, and considerable efforts have been taken to monitor its presence and transport in locales struggling with eutrophication. Most historical P datasets consist of intermittent grab samples, necessitating the construction of surrogacy models to explore P at high resolutions. In Iowa, models using historical data to relate turbidity to particulate P (PartP) have successfully been created. However, it is unknown how comprehensively historical datasets reflect Iowa’s hydrologic conditions and how well these models perform during flows not well represented within the existing data. In this study, we analyzed historical P datasets from 16 major Iowa rivers to determine how well they captured the rivers’ full range of streamflow conditions. While these datasets contained sufficient samples during low and average flows, they typically under-sampled high flows—containing few values above the 85–95th percentiles. Therefore, we collected new data in each river during wet conditions, with ~300 samples taken from 2021 to 2024. These new sampling results largely aligned with the existing surrogacy models and slightly improved model performance, suggesting that utilizing turbidity to predict PartP is appropriate in nearly all streamflow conditions. These findings may prove consequential for robustly modeling PartP due to its dynamic nature and disproportionately high transport during wet weather events.

Phosphorus (P) is a widespread waterborne pollutant that impairs many waterbodies. However, it is challenging to measure directly, and much research has been dedicated to developing surrogacy models that can repeatedly predict its concentration. Optimal approaches for modeling strategies are often unclear and depend upon local P dynamics and the availability of financial and technical resources. This study presents a schema for developing P surrogacy models at a statewide scale (16 major rivers in Iowa, USA). Specifically, we examined the relationship between particulate phosphorus (Part P) and orthophosphate (OP) and explored the viability of eight potential surrogates in predicting their concentrations using multiple linear regression and power regression methods. We also investigated similarities between surrogate models for Part P and total suspended solids (TSS). At all sites, OP and Part P were not strongly correlated (mean R = 0.20±0.17). Many instances were observed where samples had high concentrations of one form but not the other. Modeling results demonstrated that turbidity was consistently the best predictor (t-statistics > 10) of Part P, and adding other surrogates alongside turbidity did little to improve model performance. No surrogates proved useful in estimating OP. Viable power regression models were created using turbidity to predict Part P (mean R2 = 0.69±0.12). These models had a nonlinear form where Part P concentrations leveled off as waters became exceptionally turbid. This contrasted with TSS, which maintained a strong linear relationship across all turbidity levels. Turbidity-based models show promise in quantifying statewide P levels, as they enable high-resolution and real-time Part P estimates.

Phosphorus (P) plays an integral part in Iowa’s economic and environmental activities through its role as an essential nutrient and waterborne pollutant. However, the amount of phosphorus transported through these activities has not been well quantified. This study estimates the annual mass of P entering and exiting Iowa’s landscape from 1998 to 2022 through seven transport pathways. Four input pathways (fertilizer application, manure production, industrial sources, and human sources) and three output pathways (harvesting, livestock grazing, and stream export) were quantified using various agricultural, economic, and water quality datasets. We also estimated the total mass of P present in the top 0.61 m layer of Iowa’s landscape using results from a statewide soil sampling survey. The harvest component was the largest, with annual values consistently above 200 million kg. This was followed by the fertilizer and manure components, with annual values near 100 million kg. The other components were much smaller; the mean grazing and stream export values were 15 and 19 million kg, respectively, and human and industrial sources were less than 4 million kg. Stream export was the most dynamic pathway, with the largest coefficient of variation (0.59). The net P budget (inputs–outputs) was negative in 20 of the 25 years assessed, indicating that Iowa typically runs a P deficit. A trend analysis revealed that the manure, human, industry, and harvesting components increased across the 1998–2022 period while the grazing component decreased. The mass of P in Iowa’s top layer of soil was 81.5 billion kg—orders of magnitude larger than any individual budget component. This analysis provides a new perspective on P transport pathways in Iowa and may help inform policymakers as they make decisions on the many activities involving P.

Floodplains constitute a vital and integrated component of the riverine network ensuring the connectivity and continuity of the river with the upland watershed areas. However, the sediment trapping efficiency of floodplains has not been well investigated. The purpose of this experimental study was to evaluate the functionality of floodplains to act as either sources or sinks for fine sediments and sediment-bound nutrients (e.g., total phosphorus) during floods of various return periods. Thus, we hypothesized that (i) soil texture, in terms of topsoil erodibility and (ii) the magnitude of the incoming flood, in terms of the applied shear stress, are the two key parameters govern river floodplains' ability to store or release fine sediments and total phosphorus, during major flood conditions. Topsoil erodibility experiments were coupled with site-specific flood inundation maps to estimate the eroded fine sediment mass and the total phosphorus release rates per unit area per unit time of each flood condition considered. Results suggested that the floodplain soils of the upstream reaches act as net sources, the floodplains of the midstream reaches have a dual functionality; during low magnitude flood events (up to 10-year return periods), they act as net sinks, while during higher flood events, they act as sources; and the floodplains of the downstream reaches largely act as sinks. This study results are applicable for watershed managers to identify floodplain areas vulnerable to erosion and sources of nutrient pollution.

Riverine sampling of pollutants is commonly used to understand pollutants' transport pathways, relationships with hydrology, and overall presence in a waterbody. However, temporal gaps between sample collection introduce errors to these efforts, and guidance prescribing sampling frequency remains sparse. The magnitude of error often depends on a contaminant's transport mechanisms and local hydrologic conditions, making the creation of comprehensive sampling guidance difficult. This study analyzed a unique dataset that measured 18 analytes, including pesticides, nutrients, and pathogens, in three Iowa rivers for 90 consecutive days (May 4-August 1, 2000). This dataset provided a novel opportunity to relate pollutants to local hydrology and quantify errors associated with recurring sampling. Pesticide concentrations followed the spring flush phenomenon, where values were greatest during high streamflow in May and June but often depleted by July. Fecal coliform and total phosphorus (TP) also coincided with high flow, but unlike pesticides, their concentrations never diminished. Nitrate exhibited more complex behavior; concentrations were diluted during high flows and then increased as streamflow receded. Autocorrelations were significant for nitrate and atrazine in larger rivers but negligible for fecal coliform and TP. Loads were calculated for four pollutants with minimal non-detects (atrazine, fecal coliform, nitrate, and TP). We simulated intermittent sampling by selecting evenly spaced subsets of measured values to estimate loads, which were compared to the loads calculated using every daily sample to quantify error. This method typically overestimated nitrate loads but underestimated other pollutants, and errors often decreased in larger watersheds. Nitrate generally had the lowest error, while fecal coliform had the highest. We used these results to approximate the sampling frequency needed to bind errors within a certain threshold.

The Upper Mississippi Information System (UMIS) is a cyberinfrastructure framework designed to support large-scale real-time water quality data integration, analysis, and visualization for the Upper Mississippi River Basin (UMRB). UMIS is intended to directly address three of the Grand Challenges for Engineering including: 1) understanding access to clean drinking water, 2) management of the nitrogen cycle, and 3) engineering the tools of scientific discovery. The UMIS is designed to provide significant immediate and long-term impacts including a central platform for data access, integration, discovery, and adoption of cyberinfrastructure tools and services. The UMIS demonstrates that public data aggregators and central repositories can provide important services to anyone interested in water quality research or education. In addition, working across multiple scales (e.g., state, region, county, or watershed) allows researchers to understand broad and narrow effects of water quality strategies. Exploration of data across these scales encourages the development of problem-based research questions that can eventually provide feedback to public policies.