HYDROLOGIC AND WATER-QUALITY RESPONSE OF FORESTED AND AGRICULTURAL LANDS DURING THE 1999 EXTREME WEATHER CONDITIONS IN EASTERN NORTH CAROLINA

Abstract

This study evaluated hydrologic and water-quality data collected on a coastal-plain research watershed duringa series of hurricanes and tropical storms that hit coastal North Carolina in 1999, including hurricanes Dennis, Floyd, andIrene. During September and October 1999, the research watershed received approximately 555 mm of rainfall associatedwith hurricanes. This was the wettest such period in a 49-year historical weather record (1951-1999). Prior to the hurricanes,the watershed experienced a dry late winter, spring, and summer (565 cm for Feb.-Aug.). This was the third driest such periodin the 49-year record. Maximum daily flow rates measured across the research watershed were greater during hurricane Floydthan for any other time in a four-year (1996-1999) study of the watershed. Daily flows observed for an agriculturalsubwatershed were generally greater than for a forested subwatershed throughout the study, and during the hurricanes of1999. Daily nutrient loads measured across the research watershed were greater during hurricane Floyd than for any othertime in the study. In general, the two-month period of hurricanes produced total nitrogen and total phosphorus loads nearlyequal to average loads for an entire year. Total annual nitrogen export from an agricultural subwatershed was 18 kg/ha in1999, with 11 kg/ha (61%) lost during September and October. Total annual nitrogen export from a forested subwatershedwas 15 kg/ha in 1999, with 10 kg/ha (67%) lost during September and October. The nitrogen export observed in the forestedsubwatershed was high compared to other forested areas, likely due to the highly permeable organic soils in the watershed.Total annual phosphorus export from an agricultural subwatershed was 0.9 kg/ha in 1999, with 0.7 kg/ha (78%) lost duringthe hurricanes/tropical storms. Total annual phosphorus load from a forested subwatershed was 0.1 kg/ha in 1999, with 74%of the load exported during the months of September and October. Hurricanes and floods occur with some regularity in NorthCarolina, but the effects are infrequently documented. This study provides information that will contribute to greaterunderstanding of how watersheds respond to these events.