PAIRED WATERSHED APPROACH TO MODELING THE QUANTITY AND SOURCES OF DISSOLVED ORGANIC CARBON AND MAJOR CATIONS IN STREAM WATER DURING STORMFLOW AND BASEFLOW

Continued depletion in the stratospheric ozone hole has spurred research to understand the effect increased ultraviolet (UV) radiation would have on aquatic life. As one of the major UV-attenuating substances occurring naturally in water, dissolved organic carbon (DOC) and the factors influencing its natural fluxes from small headwater streams are important for understanding the effects of additional UV radiation on low order streams. Two low order streams and their watersheds in close proximity to each other in Eastern Pennsylvania were paired together in this study. These two watersheds differ mainly in land use and land cover; one watershed is predominately agriculture while the other is primarily forest. They were paired together to answer the question of whether the quantity and timing of DOC and major cations in streams differs during storm events between forested and agricultural watersheds and whether the contribution of DOC from throughfall directly into the stream surface is measurable in the stream water during stormflow.

Samples of precipitation, canopy throughfall, stormflow and baseflow in each of the watersheds collected during a 1.5 year period were analyzed for absorbance, fluorescence, total organic carbon and major cation concentrations in addition to in-stream monitoring of pH, DO, conductivity and turbidity and temperature. Results indicate differences in the timing of the hydrograph peak between a primarily agricultural watershed and a forested watershed. There is generally a higher DOC signal in the forested precipitation samples, which is a possible indication that there is a flux of DOC seen early in the hydrograph coming purely from throughfall of canopy overhanging or near the stream channel. CDOM a320 tends to rise faster and peak higher in the agricultural site than in the forested site, indicating a greater flux of DOC in the agricultural site. In addition to having a slower recovery time for base level specific conductance, the forested site usually has lower maximum values of peak absorbance. This is evidence of differences in the quantity between allochthonous and autochthonous sources of DOC. Future work will involve more detailed analyses of the samples collected for cations as well as determining the influence of canopy cover in each watershed.