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Tailwater recovery system (TWR) sediment quality in Mississippi, USA, was evaluated seasonally within the storage reservoir and drainage ditch system from 2016 to 2019 for pesticide contamination, effects and bioavailability to Hyalella azteca (Saussure). Sediment bioassays (28-day) measured H. azteca survival and growth and tissue residue risks from sediment pesticide exposure. Sediment pesticide contamination comprised six current-use herbicides, three current-use insecticides, three legacy insecticides and one metabolite (p,p'-DDE). Sediment clomazone, bifenthrin and ΣDDT concentrations were greatest in drainage ditch sites during summer and fall. H. azteca tissue pesticide residues comprised three current-use herbicides and insecticides, as well as two legacy insecticides. Tissue residue clomazone, Ζ-cypermethrin and ΣDDT concentrations were greatest in drainage ditch sites during fall and winter. H. azteca survival and growth varied seasonally and spatially with lowest survival during fall and winter and lowest survival in the storage reservoir relative to drainage ditch sites during winter. Growth decreased during winter and spring with lowest growth in drainage ditches relative to the storage reservoir during spring. Patterns of associated survival and growth with tissue pesticide residues indicate increased risk during fall in TWR and where system water flows mobilise sediment pesticides increasing the risk of ecological impairment. [ABSTRACT FROM AUTHOR]

Abstract: Excessive phosphorus loading from fertilizers in agriculture results in enriched runoff and downstream aquatic system eutrophication. This study evaluated phosphorus dynamics in agricultural drainage ditches across eight sites within the Lower Mississippi Alluvial Valley (LMAV). The objective of the study was to examine the capacity of drainage ditches across the LMAV to sorb P. Spatially and temporally, all drainage ditch sediments had very low immediately bioavailable phosphorus (Pw), and a very low degree of phosphorus saturation (DPS<20%) throughout the LMAV. Phosphorus binding energy (K) (0.34–0.60L/mg) and P sorption maxima (17.8–26.6L/mg) were low, with very little variation in space and time. Using these metrics, drainage ditches sampled within the LMAV could be described as P sinks, capable of sorbing varying degrees of P seasonally as a result to changes in the Fe-P pool. Sorption, however, will likely be low due to low P sorption maxima and low binding energies. These results will help in P management within primary aquatic systems (such as drainage ditches) within the agricultural landscape and enhance P mitigation strategies at the source, prior to runoff reaching downstream aquatic systems. [Copyright &y& Elsevier]

This article discusses how agricultural drainage drainage ditches mitigate phosphorus loads in the watershed of north Mississippi. Total inorganic phosphorus concentrations were measured under no-till cotton for natural and variable rainfall conditions. According to the authors, throughout the year, ditches alternated between being a sink and source for dissolved inorganic phosphorus and particulate phosphorus concentrations. They concluded that agricultural drainage ditches exhibit a fair potential for phosphorus mitigation. They recommend future work on controlled drainage to improve mitigation capacity.

Ditch systems in Northeast Arkansas drain excess water from Mississippi Delta fields and transport water into larger streams. This conveyance system is part of the larger Mississippi River drainage basin that feeds sediment and nutrients into the Gulf of Mexico. These ditch systems can be an important component of ecosystem services for managing water quality because of their ability to settle sediment and sequester nutrients from field runoff. Vegetation is an important characteristic of these systems that influences sediment and nutrient values. This study investigated the impact of vegetation on water quality in agricultural ditches. Ten sites across two HUC-8 watersheds in Northeast Arkansas were measured weekly for three years to monitor pH, dissolved oxygen, conductivity, flow, turbidity, total suspended solids, total and dissolved nutrients, and chlorophyll a. Bed and bank vegetative coverage were qualitatively characterized at each site. Contaminant loading comparisons report an upstream - downstream increase in loading for all water quality variables, with few exceptions. Sites were then grouped based on vegetation coverage characteristics. Those with greater bed and bank vegetative coverage had reduced loading values compared to sites with less bed and bank coverage across many of the measured parameters. Additionally, many sediment and nutrient parameters were higher in the non-production season compared to the production season despite similar precipitation and discharge across the year, suggesting a need for non-production season control measures. This study helps to understand the important in-stream processes that potentially improve water quality on a regional basis. • A new method was used to assess riparian coverage qualitatively and quantitatively. • Greater plant coverage sites tended to have lower sediment and nutrient loading. • Overall, sediment and nutrient loading were greater in the non-production season. • Cropping system could affect non-production season water quality. [ABSTRACT FROM AUTHOR]

• We examined how rainfall characteristics impacted NO 3 – N concentrations in a tailwater recovery ditch. • Rainfall events were grouped into four classes by using the k -means clustering method. • NO 3 – N concentrations were strongly dependent on duration of rainfall events. • NO 3 – N concentrations were also strongly dependent on the characteristics of next-to-last rainfall events. • Rainfall characteristics have significant implications on the operation and management of TWR ditches. Rainfall characteristics can be a major factor influencing the ability of best management practices to reduce nutrient loss from agricultural lands to receiving waterbodies. The goal of this study was to examine how rainfall characteristics impacted NO 3 – N concentrations in a tailwater recovery (TWR) ditch implemented at a farm within the Porter Bayou watershed in Mississippi, USA. We used a methodology that correlates rainfall characteristics (i.e., a combination of variables such as depth, intensity, frequency, duration, and antecedent hydrological conditions before water sampling) and NO 3 – N levels measured in the ditch. Subsequently, a hierarchical clustering approach was implemented to classify rainfall events in the context of the NO 3 – N concentrations. Results indicate that NO 3 – N concentrations observed in the ditch were strongly dependent on antecedent hydrological conditions within the study area, specifically on the (1) duration of rainfall events before sampling and (2) characteristics of next-to-last rainfall events that occurred prior to sampling. Combined variables of total rainfall depth and frequency showed that rainfall classes I and III were likely to have the most impact on in-ditch NO 3 – N concentration. Effects of class I rainfall events on NO 3 – N levels appear to be magnified under higher depth, intensity, duration, and a shorter time before next-to-last rainfall events. Also, the influence of class III rainfall events on NO 3 – N concentrations in the ditch was driven mainly by high-frequency, low magnitude, and dry antecedent conditions. Results suggest that during periods with frequent, consecutive rainfall events, the nutrient reduction potential of TWR ditches may be reduced. Data can be used to improve management of TWR ditches with more frequent pumping when possible, to increase retention times, particularly during the spring and late fall periods. [ABSTRACT FROM AUTHOR]