Two-stage Ditch Research Articles

Managing nitrate-nitrogen in the intensively drained upper Mississippi River Basin, USA under uncertainty: a perennial path forward.

The upper Mississippi River basin has been identified as the most significant contributor of excessive nutrients to the hypoxic zone in the Gulf of Mexico. The land-use changes from an internally drained prairie-wetland complex to an intensively managed corn-soybean production system drained by subsurface tile drainage system in the north-central Iowa and south-central Minnesota are the primary cause of nutrient loads into the Mississippi River and many other environmental stresses. The present study summarizes the water-quality degradation from land-use change and offers a fuzzy logic-based decision support for assessing degree of suitability of the four recommended perennial plant options for managing water and nitrate-nitrogen export. These options are designed based on landscape position that currently fails to produce high yielding row crops and scale: (1) marginal upland depressions for water storage by planting deep-rooted perennial grasses and fast-growing woody poplar, willow, and alder in poorly drained swales; (2) saturated buffers and/or subtle changes in landscape slope for draining high nitrate-nitrogen subsurface (through multi-species phytoremediation treatment buffers or strips of perennial vegetation); (3) two-stage ditches with linear floodplains planted with perennial grasses; and (4) riparian and in-channel ecologically engineered trees, shrubs, and grasses to better connect meander belt width to frequent peak stream flows at larger scales. When applied throughout a typical (Des Moines Lobe Till) DMLT watershed, each option can have positive cumulative environmental effects. Fuzzy logic enhanced the precision in watershed decision-making by incorporating the uncertainty associated with factors like cost effectiveness, nitrate reduction potential, water quality improvement, and level of acceptance.

Catchment controls of denitrification and nitrous oxide production rates in headwater remediated agricultural streams

Heavily modified headwater streams and open ditches carry high nitrogen loads from agricultural soils that sustain eutrophication and poor water quality in downstream aquatic ecosystems. To remediate agricultural streams and reduce the export of nitrate (NO3−), phosphorus and suspended sediments, two-stage ditches with constructed floodplains can be implemented as countermeasures. By extending hydrological connectivity between the stream channel and riparian corridor within constructed floodplains, these remediated ditches enhance the removal of NO3− via the microbial denitrification process. Ten remediated ditches were paired with upstream trapezoidal ditches in Sweden across different soils and land uses to measure the capacity for denitrification and nitrous oxide (N2O) production and yields under denitrifying conditions in stream and floodplain sediments. To examine the controls for denitrification, water quality was monitored monthly and flow discharge continuously along reaches. Floodplain sediments accounted for 33 % of total denitrification capacity of remediated ditches, primarily controlled by inundation and stream NO3− concentrations. Despite reductions in flow-weighted NO3− concentrations along reaches, NO3− removal in remediated ditches via denitrification can be masked by inputs of NO3−-rich groundwaters, typical of intensively managed agricultural landscapes. Although N2O production rates were 50 % lower in floodplains compared to the stream, remediated ditches emitted more N2O than conventional trapezoidal ditches. Higher denitrification rates and reductions of N2O proportions were predicted by catchments with loamy soils, higher proportions of agricultural land use and lower floodplain elevations. For realizing enhanced NO3− removal from floodplains and avoiding increased N2O emissions, soil type, land use and the design of floodplains need to be considered when implementing remediated streams. Further, we stress the need for assessing the impact of stream remediation in the context of broader catchment processes, to determine the overall potential for improving water quality.

Effects of Two-Stage Ditch and Natural Floodplains on Sediment Processes Driven by Different Hydrological Conditions

The two-stage ditch is a river restoration technique that aims at improving the sediment regime and lateral channel connectivity by recreating a small floodplain alongside a stream reach. This study aimed to analyze the efficiency of a two-stage ditch in improving the stream sediment structure and functions under different hydrological conditions (baseflow, post-bankfull, post-flood). Stream sediments were collected in channel sections adjacent to the two-stage ditch, adjacent to a natural floodplain along channelized reaches without inundation areas. Grain sizes, organic matter content and phosphorous (P) fractions were analyzed along with functional parameters (benthic respiration rate and P adsorption capacity, EPC0). The reach at the two-stage ditch showed no changes in sediment texture and stocks, while the floodplain reach showed higher fines and organic matter content under all hydrological conditions. The sediments in degraded reaches were more likely to be P sources, while they were more in equilibrium with the water column next to the natural floodplains and the two-stage ditch. Only functional parameters allowed for assessing the restoration effects on improving the sediment stability and functionality. Due to its sensitivity, the use of P adsorption capacity is recommended in future studies aiming at evaluating the response of river sediments to restoration measures under different hydrological conditions.

Quantifying denitrification following floodplain restoration via the two-stage ditch in an agricultural watershed

In agricultural streams, constructed floodplains have been shown to expand bioreactive surface area and enhance nitrate (NO3−-N) removal via microbial denitrification, thereby reducing export to downstream ecosystems. At the Shatto Ditch Watershed (Indiana, USA), 0.6 km of two-stage ditch was constructed at the watershed outlet in 2007, while an additional 3.7 and 2.7 km were constructed in 2017 and 2018, respectively. We quantified denitrification following floodplain construction using experimental incubations of stream sediments and floodplain soils from Spring 2017 to Spring 2019. We measured dissolved dinitrogen gas (N2) concentrations using membrane inlet mass spectrometry (MIMS) and found that denitrification on unconsolidated stream sediments was minimally impacted by stream dredging during two-stage construction in 2017 and 2018. In contrast, even one year after the 2017 construction, denitrification on floodplain soils fell below detection limits; we finally observed measurable rates in Spring 2019. As predicted, stream sediment denitrification was driven by water column NO3−-N concentration, while organic matter limited denitrification on floodplain soils. Floodplains constructed via the two-stage ditch can increase NO3−-N removal by >20% in agricultural watersheds, representing an effective ecological engineering solution to combat downstream eutrophication. However, our results also show that denitrification on floodplain soils may take longer to recover from construction-related activities as organic matter builds up more slowly over time. As such, lags in the recovery or enhancement of ecosystem function are important to consider when documenting restoration success.

Seasonal evaluation of biotic and abiotic factors suggests phosphorus retention in constructed floodplains in three agricultural streams

Floodplain restoration constructed via the two-stage ditch in agricultural streams has the potential to enhance nutrient retention and prevent the eutrophication of downstream ecosystems. Identifying the role of biotic and abiotic factors influencing soluble reactive phosphorus (SRP) retention in floodplains is of interest given that changing redox conditions associated with floodplain inundation can result in a release of geochemically sorbed SRP to the water column. In three agricultural waterways (Indiana, USA), we conducted seasonal measurements of a suite of biogeochemical pools (total P, bioavailable P and Fe) and processes (SRP flux and microbial respiration) from multiple floodplain transects, along with their adjacent stream sediments, to determine the role of biotic and abiotic processes on floodplain SRP retention or release. Across floodplain soils, organic matter explained a significant amount of variation in soil respiration, and SRP flux from the water column to the floodplain soils was driven by the molar ratio of Fe: P, with values >6 indicating potential SRP sorption due to increased available sorption sites. We developed a mass balance model at a single site to relate seasonal floodplain processes with water column SRP export, above and below the study reach, using measurements in this study combined with data from the literature. Grab sample data suggest that the reach retained 26% of incoming SRP, which the mass balance model attributed to seasonal synergy between plant assimilation in spring and summer (removing P from floodplain soils) and abiotic P sorption during winter and spring inundation (adding SRP to the floodplain). Retention of SRP was higher in floodplain soils compared to stream sediments based on the modeled SRP budget. Thus, we suggest that these constructed floodplains will maximize SRP retention from the water column if they inundate regularly, have floodplain soils with Fe:P > 3–6, and that promote sustained plant life.

Promoting adoption of two-stage agricultural drainage ditches: A change agent perspective.

Adoption of innovations, including adoption of conservation practices, is a topic of extensive scholarly enterprise. The diffusion of innovations literature has often examined the characteristics of three sets of variables: the adopter, the change agent, and the innovation. This literature clearly establishes the crucial role of change agents in promoting an innovation. However, what we don’t know is what makes change agents want to promote a particular innovation. In this study, change agents’ perceptions of the attributes of two-stage drainage ditches, an innovative agricultural drainage ditch design, are examined in order to understand what affects their willingness to promote them. Diffusion of innovation theory provides the conceptual grounding as well as the theoretical motivation for this study. The data for this study come from semi-structured interviews with 17 change agents. Results suggest that change agents perceive the relative advantage associated with two-stage ditches to be low, and that two-stage ditches might be perceived by potential adopters to be incompatible with the prevalent sociocultural beliefs about drainage ditch management. Results also indicate that change agents’ perceptions of environmental benefits of adopting two-stage ditches affects their willingness to promote them. Results are more broadly informative about promoting conservation practices, and is relevant for both academicians and practitioners.

Studies on morphological regime conditions of bi-modal grain size rivers: Challenges and new insights for freshwater pearl mussel habitats

Freshwater pearl mussels have high ecological demands on their habitat. For natural reproduction and distribution, they need a colmation-free porespace in the substrate and sufficient host fish for their parasitic stage of life. In Austria, river alterations and anthropogenic activities in the catchments are causing habitat degradation for both, the freshwater pearl mussel Margaritifera margaritifera and its host fish Salmo trutta. Due to the lack of reference stretches, sediment transport and sediment deposition in the main channel cannot be measured directly. In (semi-) natural river sections as well as in sections with anthropogenically caused over-width of the river bed, however, it can be observed that the river itself forms a two-stage ditch within a few years. This study examines the deposits of those rivers and describes hydraulic and sedimentological processes influencing the geometry within the main channel below bankfull stage. A possible correlation between the mean annual discharge and the instream geometry could be determined. A simple formula is given as a recommendation for action, which can be used for pre-dimensioning of channel geometry below the bankfull stage in case of river restoration of freshwater pearl mussel habitats. This equation also allows authorities to review planning services for ecologically negative interventions and to recommend a method of implementing measures below bankfull stage.

Lateral distribution of sediment and phosphorus in a two-stage ditch with partial emergent vegetation on the floodplain.

Two-stage channels are effective drainage facilities because they can decrease soil erosion and nutrient loss effectively. The lateral distribution of streamwise velocity in two-stage channels has been substantially studied. However, knowledge about the lateral distribution of sediment and phosphorus in two-stage channels with emergent vegetation on the floodplain are limited. In this work, flume experiments were conducted to investigate the relationship between current and transport of sediment and phosphorus. Results show that lateral distributions of total suspended sediment (TSS), particulate phosphorus (PP), and dissolved phosphorus (DP) are affected by the lateral variation of streamwise velocity, i.e., larger TSS and DP were found in the main channel, while larger PP appeared in the floodplain. Besides, theoretical models for the lateral distribution of TSS and DP were presented. Three models were adopted to predict the depth-averaged streamwise velocity, and corresponding results have been used to predict the TSS and DP. Comparisons indicated that with a high-precision velocity model, the newly presented analytical models can give satisfied predictions of the lateral distributions of TSS and DP.

Hydrologic Extremes and Legacy Sources Can Override Efforts to Mitigate Nutrient and Sediment Losses at the Catchment Scale.

Combating eutrophication requires changes in land and water management in agricultural catchments and implementation of mitigation measures to reduce phosphorus (P), nitrogen (N) and suspended sediment (SS) losses. To date, such mitigation measures have been built in many agricultural catchments, but there is a lack of studies evaluating their effectiveness. Here we evaluated the effectiveness of mitigation measures in a clay soil-dominated headwater catchment by combining the evaluation of long-term and high-frequency data with punctual measurements upstream and downstream of three mitigation measures: lime-filter drains, a two-stage ditch, and a sedimentation pond. Long-term hydrochemical data at the catchment outlet showed a significant decrease in P (-15%) and SS (-28%) and an increase in nitrate nitrogen (NO-N, +13%) concentrations. High-frequency (hourly) measurements with a wet-chemistry analyzer (total and reactive P) and optical sensor (NO-N and SS) showed that the catchment is an abundant source of nutrients and sediments and that their transport is exacerbated by prolonged drought and resuspension of stream sediments during storm events. Lime-filter drains showed a decrease in SS by 76% and total P by 80% and an increase in NO-N by 45% compared with traditional drains, potentially indicating pollution swapping. The effectiveness of two-stage ditch and sedimentation pond was less evident and depended on the prevalent hydrometeorological conditions that drove the resuspension of bed sediments and associated sediment-bound P transport. These results suggest that increased frequency of prolonged drought due to changing weather patterns and resuspension of SS and sediment-bound P during storm events can override the generally positive effect of mitigation measures.

Twenty Years of Riparian Zone Research (1997-2017): Where to Next?

Riparian zones have been used for water quality management with respect to NO in subsurface flow and total P (TP), sediments, and pesticides in overland flow for decades. Only recently has the fate and transport of soluble reactive P (SRP), Hg, emerging contaminants, and greenhouse gas (GHG) fluxes (NO, CO, and CH) been examined in riparian zones. Overall, riparian zones are efficient at reducing emerging contaminants in subsurface flow and only function as hot spots of methylmercury production in the landscape when dominated by Hg-rich wet organic soils. However, riparian zones do not provide consistent benefits with respect to SRP removal or GHG emissions. Although most existing riparian models almost exclusively focus on NO removal, recent developments in riparian models demonstrate the potential for using easily accessible digital environmental datasets to simulate and scale up riparian functions beyond NO removal to include SRP, TP, and GHG dynamics. To further inform integrated watershed management efforts, more research should be conducted on how various practices, including stream restoration, subsurface drainage, two-stage ditches, beaver dam analogues, denitrification bioreactors and permeable reactive barriers, artificial wetlands, and short-rotation forestry crops affect riparian water and air quality functions. Riparian zone benefits should be discussed not only with respect to water and air quality, but also in terms of recreation, habitat for wildlife, and other ecosystem services. More research is needed to fully address potential water quality or air quality tradeoffs associated with riparian zone management in a multicontaminant-multiuse landscape context.

Habitat Improvements and Fish Community Response Associated with an Agricultural Two‐Stage Ditch in Mower County, Minnesota

AbstractWater quality and stream habitat in agricultural watersheds are under greater scrutiny as hydrologic pathways are altered to increase crop production. Ditches have been traditionally constructed to remove water from agricultural lands. Little attention has been placed on alternative ditch designs that are more stable and provide greater habitat diversity for wildlife and aquatic species. In 2009, 1.89 km of a conventional drainage ditch in Mower County, Minnesota, was converted to a two‐stage ditch (TSD) with small, adjacent floodplains to mimic a natural system. Cross section surveys, conducted pre‐ and post‐construction, generally indicate a stable channel with minor adjustments over time. Vegetation surveys showed differences in species composition and biomass between the slopes and the benches, with changes ongoing. Longitudinal surveys demonstrated a 12‐fold increase in depth variability. Fish habitat quality improved with well‐sorted gravel riffles and deeper pool habitat. The biological response to improved habitat quality was investigated using a Fish Index of Biological Integrity (FIBI). Our results show higher FIBI scores post‐construction with scores more similar to natural streams. In summary, the TSD demonstrated improvements in riparian and instream habitat quality and fish communities, which showed greater fish species richness, higher percentages of gravel spawning fish, and better FIBI scores. This type of management tool could benefit ditches in other regions where gradient and geology allow.

Restored floodplains enhance denitrification compared to naturalized floodplains in agricultural streams

Predicted changes in the timing and magnitude of storms have the potential to amplify water quality challenges associated with agricultural runoff. In agricultural streams of the Midwestern US, floodplain restoration has the potential to enhance inorganic nitrogen (N) removal by increasing the bioreactive surface area for microbially-mediated denitrification. The restoration of inset floodplains via construction of the two-stage ditch increases denitrification compared to channelized systems, however, little is known about how denitrification on restored floodplains compares to those formed naturally when stream channel management lapses. We used sacrificial microcosm incubations and membrane-inlet mass spectrometry (MIMS) to compare denitrification rates in floodplain soils collected along transects in both naturalized and restored floodplains; longitudinal transects spanned two zones in the active floodplain (near-stream, NS vs. middle, MID) and a third zone that reflected upland conditions in the riparian buffer strip (UP). Denitrification rates were 35–49% higher in the restored, inset floodplains compared to naturalized floodplains. Variation in denitrification rates were primarily explained by soil organic matter (OM) and OM was > 20% higher in restored floodplains than naturalized, highlighting the contrasts between stable, constructed floodplains with heterogeneous, depositional bars typical of naturalizing channels. Consequently, restored inset floodplains could remove > 70% more N than the naturalized floodplains during similar storm inundation events.

The influence of demonstration sites and field days on adoption of conservation practices

For more than 100 years, demonstrations have been used by university extension programs and other conservation professionals to increase knowledge, awareness, and adoption of agricultural practices and technologies. However, there has been no systematic, empirical examination of the effect demonstrations have on adoption of agricultural innovations nor conservation practices. We examined the relationship between producer attendance at demonstration sites and field days of four conservation practices and the subsequent adoption of these practices using a mail survey (<i>n</i> = 513) and in-person interviews (<i>n</i> = 24) with agricultural producers in three regions of Indiana. Results show that there is a significant, moderate relationship between attendance and adoption of cover crops, nutrient management, and filter strips and a significant, weak relationship for two-stage ditches. Interviews with agricultural producers suggest that cover crop demonstration sites and field days allow for learning about practices from persons outside their regular social and professional network and provide tailored advice that allow producers to understand what to consider when making a decision to adopt a conservation practice. Results indicate that demonstration sites and field days do influence adoption of conservation practices; however, data do not control for the probability that those who attend are more likely to adopt regardless of attendance.

Management Practices Used in Agricultural Drainage Ditches to Reduce Gulf of Mexico Hypoxia.

Agricultural non-point sources of nutrients and sediments have caused eutrophication and other water quality issues in aquatic and marine ecosystems, such as the annual occurrence of hypoxia in the Gulf of Mexico. Management practices have been implemented adjacent to and in agricultural drainage ditches to promote their wetland characteristics and functions, including reduction of nitrogen, phosphorus, and sediment losses downstream. This review: (1) summarized studies examining changes in nutrient and total suspended solid concentrations and loads associated with management practices in drainage ditches (i.e., riser and slotted pipes, two-stage ditches, vegetated ditches, low-grade weirs, and organic carbon amendments) with emphasis on the Lower Mississippi Alluvial Valley, (2) quantified management system effects on nutrient and total suspended solid concentrations and loads and, (3) identified information gaps regarding water quality associated with these management practices and research needs in this area. In general, management practices used in drainage ditches at times reduced losses of total suspended solids, N, and P. However, management practices were often ineffective during storm events that were uncommon and intense in duration and volume, although these types of events could increase in frequency and intensity with climate change. Studies on combined effects of management practices on drainage ditch water quality, along with research towards improved nutrient and sediment reduction efficiency during intense storm events are urgently needed.

Impact of a two-stage ditch on channel water quality

A two-stage ditch involves modifications of a conventional, trapezoidal drainage ditch to better replicate the features of a natural stream through the addition of adjacent floodplains or benches. Previous research in Indiana and Ohio has shown that two-stage ditches offer the potential to reduce sediment load and extend the interaction time between water, bench vegetation, and bench soil allowing larger uptake of nutrients by the vegetation and increasing the denitrification rates. A two-stage ditch was constructed that drains an area of approximately 267ha of farmland used for corn and soybean production. Discharge, nitrate-N (NO3), total phosphorus (TP), soluble reactive phosphorus (SRP) and total suspended sediment (TSS) were monitored in the two-stage ditch and a control reach immediately upstream. The two-stage ditch was found to significantly decrease TP, SRP and TSS concentrations and loads. Although the two-stage ditch decreased NO3 concentrations significantly, it did not have a significant impact on NO3 loads. More specifically, the two-stage ditch reduced the loads of TP by 40%, SRP by 11% and TSS by 22–40% depending on the stage of vegetation establishment on its floodplain benches, compared to an increase in load of 78%, 2% and 1%, respectively in the control reach.

Modeling nutrient removal using watershed-scale implementation of the two-stage ditch

Western Lake Erie Basin (WLEB) is the most intensively farmed region of the Great Lakes. Because of the flat topography and poorly-drained soils many farmers rely on drainage management practices (e.g., subsurface tile drainage, ditch channelization) to maintain productive agriculture. However, these practices also facilitate the delivery of excess nutrients and sediments to Lake Erie, which have been linked to recurring harmful algal blooms (HABs) and associated environmental degradation. Implementation of inset floodplains in formerly channelized waterways via the two-stage ditch can improve water quality but the efficacy has been tested using only implementation in short reaches. Watershed models are critical tools for assessing watershed-scale implementation and as such can guide effective management. We evaluated the effectiveness of the two-stage ditch in improving water quality in the River Raisin Watershed (RRW), a major subbasin in the WLEB, combining empirical measurements for nutrient reductions from two-stage ditches across the Midwest with output from a Soil Water Assessment Tool (SWAT) model. We modeled two-stage implementation in 25, 50, and 100% of headwater reaches in the RRW, and found that the practice could reduce total annual NO3−-N export by 2, 5 and 10%, respectively. The two-stage was even more effective at reducing total phosphorus (TP) export, which was reduced by 12, 20 and 31%, respectively. Compared to other conservation practices, nutrient reduction efficiency for the two-stage ditch was good, both in terms of percent load reduction and cost, but watershed-scale adoption will be required in order to achieve significant nutrient reductions as called for by policymakers.

How cost-effective are cover crops, wetlands, and two-stage ditches for nitrogen removal in the Mississippi River Basin?

Abstract Excess nitrogen (N) causes numerous water quality problems, and in the upper Mississippi River Basin, much of the excess N results from landscape modifications necessary for row crop agriculture. Several conservation practices reduce N export, but cost estimates for these practices are often lacking, which can inhibit decisions by farmers and policy-makers. Many practices are eligible for cost-share funds from the United States Department of Agriculture (USDA) , but these programs do not usually cover the full cost, and so farmers need to be able to approximate their share of costs. In addition, cost estimates may help the USDA to set priorities and make programmatic decisions. We address lack of cost information by estimating the direct implementation costs and USDA program costs for three agricultural conservation practices: wetlands, cover crops, and two-stage ditches, over 10 and 50 year time horizons. We then compare these costs to the N removal effectiveness of each practice, in $ kg N−1 removed. Wetlands were the most cost-effective practice (in $ kg N−1 removed) over both time horizons. Over 50 years, the two-stage ditch ranked second in cost-effectiveness and cover crops were least cost-effective, while over 10 years, cover crops were second and two-stage ditches were least cost-effective. Finally, we note that these practices need not be used in isolation, but can be implemented simultaneously to maximize N removal. Overall, our analysis suggests that careful implementation can cost-effectively mitigate N pollution.

The Role of County Surveyors and County Drainage Boards in Addressing Water Quality.

Water quality problems stemming from the Midwestern U.S. agricultural landscape have been widely recognized and documented. The Midwestern state of Indiana contains tens of thousands of miles of regulated drains that represent biotic communities that comprise the headwaters of the state's many rivers and creeks. Traditional management, however, reduces these waterways to their most basic function as conveyances, ignoring their role in the ecosystem as hosts for biotic and abiotic processes that actively regulate the fate and transport of nutrients and farm chemicals. Novel techniques and practices such as the two-stage ditch, denitrifying bioreactor, and constructed wetlands represent promising alternatives to traditional management approaches, yet many of these tools remain underutilized. To date, conservation efforts and research have focused on increasing the voluntary adoption of practices among agricultural producers. Comparatively little attention has been paid to the roles of the drainage professionals responsible for the management of waterways and regulated drains. To address this gap, we draw on survey responses from 39 county surveyors and 85 drainage board members operating in Indiana. By examining the backgrounds, attitudes, and actions of these individuals, we consider their role in advocating and implementing novel conservation practices.

Estimation of Two-Stage Ditch Excavation Volume Using LiDAR Data

Estimation of Two-Stage Ditch Excavation Volume Using LiDAR Data

Preliminary Evidence of Sediment and Phosphorus Dynamics Behind Newly Installed Low-Grade Weirs in Agricultural Drainage Ditches

Low-grade weirs are innovative management strategies that control surface drainage, slow water velocities, and encourage sedimentation in agricultural drainage ditches. There is little information on how low-grade weirs perform in terms of short-term (0–12 months) sediment retention and associated phosphorus (P) dynamics. This study documents initial results of sediment and P dynamics of low-grade weirs in a drainage system that was built in a two-stage ditch design. Average sediment deposition did not differ significantly among sites (χ 2 = 2.42; P = 0.49); however, average water depths behind weir sites were significantly greater (28 ± 10 cm) than the comparison inflow site (6 ± 8 cm; χ 2 = 7.67; P = 0.05). Total P concentrations were not significantly different through time, or between sites, but there was a general trend of progressively higher total P retention moving downstream. Bioavailability ratios of P (i.e., the ratio of potentially bioavailable to non-bioavailable P fractions) were similar between all sites through time (χ 2 = 2.09; P = 0.55). The only variables correlated significantly with time were found at the inflow site, where water depth significantly decreased with corresponding increases in sediment/water column pH and bioavailability ratios. From best management practice installation to 12 months after construction, there was a lack of significant correlations with any measured variables behind weirs. However, the lack of correlation between variables suggests increasing the hydroperiod, reducing the ephemeral nature of the drainage ditch system, and prolonging inundation, improves conditions for P retention.