NUTRIENT TRAPPING EFFICIENCY OF A SMALL SEDIMENT DETENTION RESERVOIR

Weekly measurements of water quality parameters were taken over a 5 year period from four sites in Morris Pond, a 1.09 ha reservoir in the loess hills of Mississippi's Goodwin Creek drainage basin. Catchment of the 30 year old reservoir, constructed for flood and sediment control, consisted of 17.8 ha of permanent pasture and 14.6 ha of cultivated and mixed-cover land. Inflow in winter and spring increased reservoir concentrations of phosphorus (from nondetectable to 1 mg/l), nitrate-nitrogen (from nondetectable to 1 mg/l), and suspended sediments (from 30 to > 300 mg/l). Storm-related inflow was the driving force behind short-term limnological and water quality cycles in Morris Pond. Multiple chlorophyll peaks indicated rapid phytoplankton response to runoff-related nutrient loading in this shallow (2.5 m normal max. depth) reservoir. Chlorophyll a ranged from < 10 mg/m3 in winter to < 100 mg/m3 in summer. Nutrient and suspended sediment concentrations in inflow were significantly correlated (P < 0.001) with precipitation and storm runoff and were significantly (P < 0.05) higher than normal seasonal pond concentrations. Nutrient trapping efficiency during storms averaged above 70% for phosphorus and nitrogen compounds flushed into the pond. This buffering capability of agricultural impoundments makes them excellent tools for managing intensive agricultural runoff and downstream water quality. © 1990.