Sam Testa

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.

Large Woody Debris Structures for Incised Channel Rehabilitation

Described is a project intended to restore habitats along 2 km of a sand bed stream severely damaged by channel incision. Structural measures are limited to placement of large woody debris and planting switchgrasses and woody vegetation. Assessment of pre-project channel stability and design of large woody debris structures are described. If successful, this approach will offer significant cost savings over traditional approaches involving stone bank protection structures.

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.

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 (

Use of acoustic Doppler current profilers to describe velocity distributions at the reach scale

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Nitrogen and phosphorus levels in the Yazoo River Basin, Mississippi

X¯k day−1 = 0.007–0.011) and riparian species (

Conservation Management in Cotton Production: Long-Term Soil Biological, Chemical, and Physical Changes

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