Relationship Between Flow Regime and Aquatic Macroinvertebrate Abundance in Headwater Streams in the Piedmont Region of North Carolina

Abstract

Approximately 85% of the area of watersheds in the Piedmont Region of North Carolina are drained by headwater streams. Headwater streams may also serve as sources or sinks for sediments, nutrients, and biota hence their importance on a watershed scale. Water depth data was collected from eight first order headwater streams for 18 months. In addition, macroinvertebrates were sampled from the study streams three times a year. Hydrographs, created from the water depths collected for each study stream, were analyzed to determine periods of lower and higher hydrologic flow in the stream channels. Based on the hydrographs it was determined that near the end of the growing season, some sub-reaches of the stream channel may cease to flow whereas others exhibit lower levels of water. Conversely, after the growing season, water depths in streams will increase. Four different statistical models were used to characterize the effect that water depths in the headwater streams have on macroinvertebrate abundance. The four models used in the analysis were a full mixed effects model, a reduced model with the stream type variable, a reduced model without the stream type variable and a reduced model with a minimum water depth term. Both the reduced model without the stream type variable and the minimum water depth model were chosen as models that better fit the data. These models indicated that water depths may affect general macroinvertebrate abundance in the study streams. An additional objective of this study was to evaluate the North Carolina Division of Water Quality (NCDWQ) Stream Classification Method for identifying the origins of intermittent and perennial streams. Results from statistical analysis indicated that the NCDWQ's Stream Classification Method is an effective tool for distinguishing stream types (ephemeral, intermittent, and perennial).