CHANGES IN THE QUANTITY AND QUALITY OF DOC DURING STORM EVENTS AS A FUNCTION OF LAND COVER

Two major anthropogenic effects to the Earth of recent concern are an increase in the amount of ultraviolet radiation (UVR) reaching Earth's surface due to a reduction in the ozone layer and climate change causing greater intensity storms. The increase in UVR may damage aquatic organisms whose primary defense is the presence of naturally occurring UV-attenuating substances such as dissolved organic carbon (DOC) within their ecosystems. The degree of UVR attenuation by DOC within a stream is a function of both the quantity of DOC and the quality of the DOC, which is a function of its source. This research takes an in-depth look at how DOC quantity and quality change in streams during storm events and the role of watershed landcover.

Stream samples were collected every 12 hours for baseflow and every hour during major storm events using ISCO© automated samplers for two small low order streams located in Eastern Pennsylvania. The primary difference between these two watersheds is landcover, with one watershed dominated by agricultural land and the other primarily forested. Fluorescence index (FI) values for the forested site ranged from 1.50 to 1.68 while the agricultural site had values that ranged from 1.47 to 1.76. Both sites exhibited changes in DOC quality during the storm events, indicating varying contributions from algal-derived DOC (FI values of 1.9) and terrestrial-derived DOC (FI values of 1.4). For both sites, DOC concentration showed a direct relationship with stream stage, with the highest concentrations coinciding with peak flow. Following both storms, the concentration of DOC returned to baseflow values in the forested site in contrast to the agricultural site, where DOC concentration returned to a value lower than baseflow conditions. The FI, however, returns to baseflow values following the storm. This is an indication of a decrease in the available pool of DOC within the stream channel of the agricultural watershed during the course of a storm, but not a change in the source of DOC.