NUTRIENT LOADING PATTERNS ON AN AGRICULTURALLY IMPACTED STREAM SYSTEM OVER THREE SUMMERS

Spruce Creek and Warrior's Mark Run were studied from 2002 to 2004 to determine the effects of agricultural nutrient loading on water quality. These two streams are part of the Spruce Creek watershed, which contains both the state's premier trout fishery and largest Concentrated Animal Feeding Operation.

The summers of ‘02, ‘03, and ‘04 represent different hydrologic conditions of the Spruce Creek watershed. The summer of ‘02 is typified by drought conditions and an overall decline in discharge, the summer of ‘03 is characterized by rainy conditions and variable discharge, and the summer of ‘04 is characterized as a combination of the hydrologic conditions of ‘02 and ‘03.

Patterns in the nitrate concentrations behaved similarly during ‘03 and the start of ‘04, and similarly during ‘02 and the end of ‘04. During ‘03 and ‘04, increases in discharge created a decrease in nitrate concentration. This indicates that nitrate dilution occurs during discharge events. But during ‘02 and ‘04, decreases in discharge created small increases in nitrate concentration.

The patterns in the phosphate concentrations are more complex than those of the nitrates. Phosphate concentrations are related to discharge, but each summer shows a different pattern in relation to concentration and discharge.

Increases in discharge also caused large increases in turbidity during ‘03 and the start of ‘04. This increase in turbidity occurred along side a great increase of phosphate and nitrate concentrations. This correlation implies that increases in turbidity will increase nitrate and phosphate concentrations due to nutrients in sediments washed off of farming fields.

The headwaters of Warrior’s Mark Run were sampled during the summer of ‘04 and analyzed for nutrient concentrations. Phosphate concentrations for the headwater samples were comparable to concentrations found along the rest of the stream, indicating a source of phosphate that affects the water before agriculture is prevalent in the area. This source is likely the stream's underlying bedrock. Nitrate concentrations at the headwaters are effectively zero, whereas the concentrations downstream are much higher. This increase in nitrate concentration points to an important source of nitrate downstream from the headwaters of Warrior’s Mark Run, which could be an agricultural source.