Richard E. Lizotte

Nutrient mitigation capacity in Mississippi Delta, USA drainage ditches

Eutrophication and hypoxia within aquatic systems are a serious international concern. Various management practices have been proposed to help alleviate nutrient loads transported to the Gulf of Mexico and other high-profile aquatic systems. The current study examined the nutrient mitigation capacity of a vegetated (V) and non-vegetated (NV) agricultural drainage ditch of similar size and landform in the Mississippi Delta. While no statistically significant differences in ammonium, nitrate, or dissolved inorganic phosphorus mitigation between the two ditches existed, there were significant differences in total inorganic phosphorus percent load reductions (V: 36% +/- 4; NV: 71% +/- 4). However, both agricultural drainage ditches were able to mitigate nutrients, thus reducing the load reaching downstream aquatic receiving systems. Further studies examining ecosystem dynamics within drainage ditches such as sediment and plant nutrient partitioning, as well as microbial processes involved, are needed to provide a better understanding of natural nutrient variability, seasonality and flux.

Inundation influences on bioavailability of phosphorus in managed wetland sediments in agricultural landscapes.

Agricultural runoff carries high nutrient loads to receiving waters, contributing to eutrophication. Managed wetlands can be used in integrated management efforts to intercept nutrients before they enter downstream aquatic systems, but detailed information regarding sorption and desorption of P by wetland sediments during typical inundation cycles is lacking. This study seeks to quantify and elucidate how inundation of wetland sediments affects bioavailability of P and contributions of P to downstream systems. A managed wetland cell in Tunica County, Mississippi was subjected to a simulated agricultural runoff event and was monitored for bioavailable phosphorus (water-extractable P [P], Fe-P, and Al-P) of wetland sediments and water level during the runoff event and for 130 d afterward. Inundation varied longitudinally within the wetland, with data supporting significant temporal relationships between inundation and P desorption. Concentrations of P were significantly higher at the site that exhibited variable hydroperiods (100 m) as compared with sites under consistent inundation. This suggests that sites that are inundated for longer periods of time desorb less P immediately to the environment than sites that have periodic or ephemeral inundation. Concentrations of iron oxalate and NaOH-P were significantly higher at the least inundated site as compared with all other sites (F = 5.43; = 0.001) irrespective of time. These results support the hypothesis that increased hydraulic residence time decreases the bioavailability of P in wetland sediments receiving agricultural runoff. This finding suggests that the restoration of wetlands in the mid-southern United States may be hydrologically managed to improve P retention.

An assessment of the ecological effects of a C9--11 linear alcohol ethoxylate surfactant in stream mesocosm experiments

The responses of stream mesocosm communities to a linear alcohol ethoxylate (LAE) surfactant were studied to (i) assess the relationship between laboratory and field-scale tests; (ii) develop NOECs for responding taxa; and (iii) provide data to develop an aquatic risk assessment for alcohol ethoxylates. The LAE was a mixture of C9--11 linear alcohols with an average of six ethylene oxide (EO) units per mole of alcohol. Twelve stream mesocosms were used to test the effects of five concentrations of the LAE on periphyton, aquatic macrophytes, invertebrates and fish during a 30-day exposure. Vascular plants were unaffected at 11.4 mg L−1, the highest surfactant concentration tested, but various periphyton parameters were altered at lower concentrations. The effects on periphyton were attributed to grazing by resident invertebrates. Invertebrate densities were affected at LAE concentrations above 2.0 mg L−1. Fathead minnows were particularly sensitive to LAE with a NOEC of 0.73 mg L−1 for egg production and larval survival. Bluegill were less sensitive than fathead minnows, with a NOEC for survival and growth of 5.7 mg L−1. The stream mesocosm results for fish and invertebrates were similar to those obtained using laboratory single-species tests

Mitigating agrichemicals from an artificial runoff event using a managed riverine wetland

We examined the mitigation efficiency of a managed riverine wetland amended with a mixture of suspended sediment, two nutrients (nitrogen and phosphorus), and three pesticides (atrazine, metolachlor, and permethrin) during a simulated agricultural runoff event. Hydrologic management of the 500 m-long, 25 m-wide riverine wetland was done by adding weirs at both ends. The agrichemical mixture was amended to the wetland at the upstream weir simulating a four-hour, ~1cm rainfall event from a 16ha agricultural field. Water samples (1L) were collected every 30 min within the first 4h, then every 4h until 48 h, and again on days 5, 7, 14, 21, and 28 post-amendment at distances of 0m, 10 m, 40 m, 300 m and 500 m from the amendment point within the wetland for suspended solids, nutrient, and pesticide analyses. Peak sediment, nutrient, and pesticide concentrations occurred within 3 h of amendment at 0m, 10 m, 40 m, and 300 m downstream and showed rapid attenuation of agrichemicals from the water column with 79-98%, 42-98%, and 63-98% decrease in concentrations of sediments, nutrients, and pesticides, respectively, within 48 h. By day 28, all amendments were near or below pre-amendment concentrations. Water samples at 500 m showed no changes in sediment or nutrient concentrations; pesticide concentrations peaked within 48 h but at ≤11% of upstream peak concentrations and had dissipated by day 28. Managed riverine wetlands≥1 ha and with hydraulic residence times of days to weeks can efficiently trap agricultural runoff during moderate (1cm) late-spring and early-summer rainfall events, mitigating impacts to receiving rivers.

Influence of integrated watershed-scale agricultural conservation practices on lake water quality

Watershed-scale management efforts to improve conservation of water resources in agricultural watersheds depend upon the effectiveness of integrated multiple agricultural best management practices (BMPs). To more comprehensively assess the effectiveness of combined BMPs on water quality requires large-scale, long-term (>10 year) studies measuring key water quality parameters. One such suite of critical water quality parameters includes water clarity, total suspended solids (TSS), and total dissolved solids (TDS). To address this, Beasley Lake, a 25 ha (62 ac) oxbow lake located in a 915 ha (2,261 ac) watershed of intensive row crop agricultural activity, was studied. The lake was sediment impaired when monitoring was initiated in 1995 and was a candidate to assess the effectiveness of watershed-wide BMPs on lake water clarity (as Secchi depth), TSS concentrations, and TDS. A variety of BMPs within row crop fields, at field edges throughout the watershed, and enrollment of 112 ha (277 ac) into the Conservation Reserve Program (CRP) between 1997 to 2006 focused on reducing soil erosion and concomitant sediment runoff. Selected parameters were measured approximately biweekly from 1996 to 2009. During this 14-year period, changes in row crop management and BMP implementations and alterations were observed and recorded in conjunction with targeted water quality parameters. While annual improvement in water quality occurred, distinct seasonal effects were noticeable. Observed changes in water clarity and TSS concentrations were greatest during spring and least in winter in association with increased BMPs, vegetated buffer strips west of the lake, and CRP north of the lake. Observed decreases in TDS concentrations were greatest during summer and fall in association with implemented CRP north of the lake. Reductions in spring TSS by >60% often directly increased spring water clarity by >100%. Results of this study indicate clear improvement in lake water quality with watershed-wide implementation of integrated multiple agricultural BMPs, and these improvements, manifested most strongly during spring, will assist to promote a healthy, sustainable lake ecosystem.

Influence of varying nutrient and pesticide mixtures on abatement efficiency using a vegetated free water surface constructed wetland mesocosm

The nutrient and pesticide abatement efficiency of varying mixtures was examined in a vegetated free water surface constructed wetland. Three different agricultural chemical pollutant mixture conditions were assessed: nutrients only (N and P); pesticides only (atrazine, S-metolachlor and permethrin); and a mixture of nutrients and pesticides. With nutrients only, 672 h nutrient mitigation of 77–91% total phosphorous (TP) and 74–98% total nitrogen (TN) was associated with distance from the injection point and rainfall, whereas with nutrient and pesticide mixtures, 672 h nutrient mitigation of 11–71% TP and 84–98% TN were associated with distance and time. With pesticides only, 672 h pesticide mitigation of 50–99% was associated with distance and time, whereas with nutrients and pesticide mixtures, 672 h pesticide mitigation of 48–99% was associated primarily with distance. Dissipation half-lives were 2–10 times greater for P and 1.5–5 times greater for N when pesticides were present. Pesticide dissipation half-lives showed no clear differences with or without nutrients. While vegetated free water surface constructed wetlands can be effective best management practice tools to trap and abate agricultural run-off during rainfall events, efficiencies can be affected by different types of complex pollutant mixtures and wetland design and implementation should accommodate varying efficiencies.

Sediment quality assessment of Beasley Lake: bioaccumulation and effects of pesticides in Hyalella azteca

Beasley Lake is a Conservation Effects Assessment Program (CEAP) watershed in the intensively cultivated Mississippi Delta, USA. Lake sediment quality at three sites was evaluated in 2004 and 2008 for biological impairment and uptake (animal tissue pesticide residues) from 14 pesticides and three metabolites using Hyalella azteca (Saussure). Eleven pesticides and three metabolites were detected in sediment among the three sites in 2004 and all 17 compounds examined were detected among the three sites in 2008, with the herbicide atrazine having the greatest concentrations. Twenty-eight-day H. azteca survival and growth (mg w/w) indicated no survival effects at any site for either year, but growth impairment occurred in H. azteca exposed to sediments in 2004, whereas growth enhancement occurred in H. azteca exposed to sediments at one site in 2008. Pesticides observed in animal tissue pesticide residues occurred more frequently and in greater concentrations in 2004 compared with 2008. Thirteen pesticides were detected in animal tissue pesticide residues in 2004, with chlorpyrifos occurring in the greatest concentrations, and six pesticides were detected in 2008, with p,p′-DDT occurring in the greatest concentrations. H. azteca tissue pesticide residues of seven pesticides, two herbicides, three insecticides, one insecticide metabolite, and p,p′-DDT, were associated with growth.

Connectivity and Variability: Metrics for Riverine Floodplain Backwater Rehabilitation

Stream Restorat Approaches, Anal Geophysical Mon This paper is not s Published in 2011 10.1029/2010GM The importance of floodplain aquatic habitats that are seasonally or periodically connected to the main channel (backwaters) within lowland riverine ecosystems is well established. However, backwaters are becoming rare as development is transforming floodplain landscapes. Therefore, rehabilitation, protection, and management of riverine backwaters are becoming increasingly common, with annual expenditures in the millions of dollars. Even with the increasing number of projects, general criteria for selecting restoration goals and evaluating project outcomes are lacking. To address this need, Kondolf et al. (2006) proposed an approach for evaluating river restorations that is based on assigning a position to the system in a four-dimensional space that represents hydrologic temporal variability on one axis and connectivity in the three spatial dimensions on the remaining three axes. Use of the Kondolf approach for evaluating restoration of a backwater adjacent to a medium-sized river in northern Mississippi is presented as a case study, in which nearby degraded and less impacted backwaters were used as references. The restoration project resulted in a reduction in main-channel connectivity and lower levels of variability for the treated backwater. Additional responses to treatment included increased summer water depth, moderation of severe diurnal water quality fluctuations, and reductions in concentrations of solids, nutrients, and chlorophyll a. Fish species richness, numbers, and biomass were unchanged following rehabilitation, but trophic structure shifted away from omnivorous species and toward predators. Ecological services provided by floodplain riverine backwaters may be enhanced by modest management measures, but regaining and maintaining connectivity with adjacent ecological functional patches remains difficult.

Water Quality from Oxbow Lakes within the Mississippi Delta Management Systems Evaluation Area

Objectives of this paper were to examine and document pre-management water quality conditions on three oxbow lakes and resulting changes following the implementation of Best Management Practices within the Mississippi Delta Management Systems Evaluation Area (MSEA). Aquatic habitats have declined worldwide over the last decade. This decline can be attributed to the draining and clearing of these habitat areas for other agricultural uses. Non-point source pollution associated with agricultural runoff has also contributed to the decline in aquatic habitats. The Mississippi Delta MSEA is a competitive agricultural systems-based research project designed to address the problems associated with non-point source pollutants. This project is unique among MSEA projects because of its location in the Mississippi River alluvial plain and its strong ecological research component. Experimental design of the Mississippi Delta MSEA called for the development of structural and cultural treatments to reduce sediment and associated pollutants entering watershed oxbow lakes. Three watersheds within the project were selected and developed with different levels of best management practices (BMPs). Changes in lake water quality and fisheries characteristics were used as measures of management success. Analyses of water quality prior to the implementation of BMPs indicated lakes that were stressed and ecologically damaged due to excessive in-flowing sediments. Significant improvements in water quality were realized through the use of cultural and structural BMPs. Sediments were decreased 34 to 59%, while Secchi visibility and chlorophyll generally increased. The most dramatic improvements in water quality occurred in the two watersheds that featured cultural practices and combinations of cultural and structural practices, respectively. Reducing suspended sediment concentrations in these oxbow lakes resulted in conditions favorable for phytoplankton production. Increases in phytoplankton production resulted in increased chlorophyll concentrations and higher concentrations of dissolved oxygen, leading to improved secondary productivity. Results further indicated that cultural BMPS may play the more vital role in improving lake water quality and may be needed in addition to structural measures to ensure improved water quality in oxbow lakes receiving agricultural runoff.

Breakdown rates and associated nutrient cycling vary between novel crop-derived and natural riparian detritus in aquatic agroecosystems

Freshwater ecosystem function within agricultural landscapes may be altered by differences in processing of organic matter (OM) detritus entering freshwater habitats. We compared litter breakdown rates between crop residues; maize, cotton and soybean, and native riparian species: willow oak, American sycamore and cottonwood from inundated remnant river meander channels located within the Lower Mississippi River Basin (LMRB). Litter breakdown varied among the six species with the highest and lowest breakdown rates represented by crop (