Export Of Organic Carbon From A Minimally Developed SouthernNew England Watershed

Abstract

The Pawcatuck River Watershed (797 km2), located on the border between Rhode Island (80%) and Connecticut, is unusual for a southern New England coastal area because sixty-five percent of it remains undeveloped, including over 30% classified as protected natural habitat. The Pawcatuck River (47 km long) drains this watershed until it meets tidal waters in Westerly, R.I. Population increase in the river watershed of over one hundred-percent in the last thirty years, combined with increasing freshwater withdrawal, is potentially degrading water quality. As part of a larger study of nutrient and sediment exports from the watershed, we measured concentrations of dissolved (DOC) and particulate (>0.45 pm) organic carbon (POC) approximately weekly since December 2001. Our sampling site corresponds with that used for water discharge measurements by the United States Geological Survey (USGS) since 1941. The USGS also obtained total organic carbon measurements at varying intervals (monthly, bimonthly and quarterly) at this station from 1976 to the present, allowing us to put our results in a historical context. This is particularly useful because the sampling period of our study corresponds with the most severe drought in over one hundred years. Export of total organic carbon (TOC) displayed a strong linear relationship with water discharge and amounted to 2.8 g C m-2 yl. Approximately 80% of the total carbon flux was in the form of DOC. The relationship between TOC flux and water discharge has not changed significantly over the twenty-five year period of record despite development and extreme drought.