Inch/Pound to SI Multiply By To obtain Length millimeter (mm) 0.039 inch (in.) mile (mi) 1.609 kilometer (km) Area square mile (mi 2) 2.590 square kilometer (km 2) Volume gallon (gal) 3.785 liter (L) liter (L) 0.26417 gallon (gal) Flow cubic foot per second (ft 3 /s) 0.02832 cubic meter per second (m 3 /s) SI to Inch/Pound Multiply By To obtain Length millimeter (mm) 0.03937 inch (in.) Volume liter (L) 0.2642 gallon (gal) Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:°F = (1.8×°C)+32 Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25 °C).

Hydrology (streamflow and stage) and water quality (suspended sediment, total nitrogen [N], ammonia [NH 3 ], total Kjeldahl N, nitrate plus nitrite [NO 3 + NO 2 ], and total phosphorus [TP]) were monitored in two small agricultural drainages in northwestern Mississippi to document changes in water quality that coincided with the implementation of best management practices (BMPs) in upstream drainages. Using an event-based data set and bootstrapping techniques, we tested for difference and equivalence in median event concentration and differences in concentration-streamflow (C-Q) relationships between an early and late period at each site, where most of the major BMP implementation occurred during the early period. Results for Bee Lake Tributary were inconclusive. Using 95% confidence intervals, none of the constituents were statistically different or equivalent for median event concentrations between the periods, indicating a lack of evidence to determine whether water quality had changed or stayed the same, and only TP had a significantly higher C-Q intercept during the late period. At Lake Washington Tributary, more than half the constituents had a significantly different median, slope, or intercept between periods, indicating a 35% or more decrease in event concentration following a period of intense BMP implementation. These mixed results could be due to a variety of differences between the sites including the type and timing of BMP implementation, production practices, and crop types. We also used the monitoring data to generate synthetic data and performed a simulation-based power analysis to explore the ability to detect change under 25 scenarios of sampled event counts and hypothetical percentage changes. The simulation-based power analysis indicated that natural variability in event concentration and flow hindered our ability to detect change. The results from this study can be used to guide future decisions pertaining to monitoring efforts in small agricultural drainage basins in the Mississippi Alluvial Plain.

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