Evaluating Change in Intermittent Streams Monitored by the Mississippi Delta Nutrient-Reduction Strategy Efforts: Successes and Challenges

Author(s): Hicks, M.

Evaluating the effectiveness of on-field implementation of agricultural best management practices (BMPs) to improve downstream water quality is a challenge due to seasonal and temporal fluctuations in streamflow and water chemistry and to the limited resources available to monitor these two variables. Yet consistent monitoring and evaluation of collected data is the ideal way to document water-quality changes. In 2010, the U.S. Geological Survey began monitoring in several small drainages in northwestern Mississippi as part of nutrient-reduction strategy efforts in the Mississippi Delta. Various BMPs were implemented to reduce sediment and nutrient runoff in the drainages. Water quality and streamflow were monitored for 5-10 years and data were evaluated and then correlated with observed changes in BMPs. Data analysis progressed in a two-step approach. First, exploratory analyses were completed to evaluate the general hydrologic and water-quality conditions of each site. Then, inferential analyses including tests of differences and equivalences were completed using bootstrapping or an assumed distribution based on the available data. Finally, a power analysis was completed to evaluate the minimum detectable change in water quality possible based on the collected data and to determine the ideal number of samples that need to be collected in the future for similar studies. An example of these data-analysis results will be presented for an intermittent tributary that drains into Bee Lake. This particular tributary has had several BMPs installed over the study period. The results of the analysis and “lessons learned” during monitoring, summarized as successes and challenges presented by this approach, will provide relevant information for forthcoming analyses and similar future studies in this area.

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