DIEL PATTERNS IN DISSOLVED ORGANIC MATTER IN A FORESTED HEADWATER CATCHMENT IN MARYLAND

Patterns of water quality parameters such as dissolved organic carbon (DOC) and nitrate-N caused by biotic and abiotic processes in a watershed are vital to understanding intrinsic biological and hydrological controls within a stream. Seasonal and annual fluctuations of organic matter have been studied extensively in varying types of watersheds; however, there are only a few studies focusing on the short-term patterns of DOC and nitrate that occur over a 24-hour period. This study investigates the nature of diel patterns of dissolved organic matter (DOM) and the potential variables that influence the concentration and composition of organic matter in a forested watershed. Closely analyzing these trends may allow us to predict how streams will respond to changing conditions, such as climate change.

Baseflow samples were collected hourly for 72 hours from 4 sites within a 79 ha forested, headwater catchment in the Piedmont Region of Maryland. Additionally, in stream UV and fluorescence sensors measured temperature, pH, conductivity, turbidity, nitrate-N, DOC, dissolved oxygen, and fluorescence of dissolved organic matter every 15-30 minutes. Subhourly measurements of discharge and groundwater elevation were also collected. Grab samples were analyzed for major cations and anions, DOC, and excitation-emission matrices- an indicator of DOM quality.

The results of this study suggest that during the data collection time period, DOC and nitrate-N concentrations did not exhibit as strong of a diel pattern as dissolved oxygen, which showed a consistent diel pattern at all 4 sites. Conversely, data from earlier months indicate that DOC and nitrate-N diel patterns may be stronger during dry periods, indicating potential for future investigation and interpretations.