Mississippi State University

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Evaluating changes in diversity and functional gene abundance of denitrifying microbe communities to nutrient concentrations in run-off following the implementation of low-grade weirs in agricultural drainage systems

Robert Kröger

Research Associate:  Beth Poganski

This study aims to evaluate the composition of microbial communities involved in key processes of denitrification following physiochemical changes introduced by low-grade weir implementation. Investigations of functional genes involved in denitrification via quantitative polymerase-chain reaction (qPCR) will include those encoding for subunits of nitrate reductase (nirK, nirS) and nitrous oxide (nosZ). These functional genes will also be used to determine community diversity using terminal restriction fragment length polymorphism analysis (T-RFLP). Understanding how low-grade weirs alter drainage environments in such a way that impacts microbial community structure and function, and subsequent nutrient transformations, will advance engineering and remediation strategies. Understanding the impacts of low-grade weirs on nutrient reduction capacities will also provide a greater understanding of how to improve nutrient management strategies to reduce Gulf of Mexico hypoxia.

Project Objectives
Traditional agricultural drainage practices in the MRB are limited by the following: 1) innovative practices for management of water resources have traditionally not been supported by quantifiable data, 2) effects of water management strategies have not addressed potential impacts on microbial communities, and 3) current management strategies fail to integrate strategies to conserve water, food, and habitat resources simultaneously. The overall objective of this study is to determine mechanisms of action by which variable frequency and spatial patterns of controlled drainage structures alter drainage ditch environments. Objectives will specifically focus on environmental changes at the microbial scale to foster NO3--N reductions through denitrification in effluent throughout a drainage ditch, with aims to develop limiting resources to adapt current management practices. Four specific objectives will be addressed. Objective 1) Quantify the effects of low-grade weir frequency and spatial arrangement on nutrient reduction efficiencies of agriculture runoff using field-based experimental designs. Objective 2) Determine patterns of denitrifying microbe community spatial distributions within an agricultural drainage system fitted with low-grade weirs by measuring abundance and composition of communities. Objective 3) Determine the effects of low-grade weirs on spatial patterns of denitrifying microbe community abundance and composition in agricultural drainage ditches. Objective 4) Integrate nutrient reduction data, soil carbon and nitrogen availability, and microbial community analyses water to determine conditions that enhance denitrifying microbe communities, to be utilized in the adaptation of current management strategies.

Gulf of Mexico Research

Completed Projects