Comparison of stream nutrient conditions in a subtropical lowland watershed to EPA suggested criteria
Nutrients such as nitrogen, phosphorus and organic carbon are essential to the health and diversity of stream ecosystems. However, excess nutrients can cause eutrophication, resulting in overgrowth of aquatic plants and decline of the ecosystem diversity. A paired-watershed study was initiated in a subtropical forested watershed within the Ouachita River Basin in Louisiana to identify stream nutrient conditions with respect to the U.S. Environmental Protection Agency (EPA) suggested criteria, and to examine changes in nutrient levels following timber harvesting operations with and without BMP implementation. Nutrient concentrations were measured in both storm runoff and monthly stream water samples collected at 11 sites in the headwater streams. Water samples were analyzed for total and dissolved phosphorus, nitrite, nitrate, ammonia, total Kjeldahl nitrogen, along with total and dissolved organic and inorganic carbon. The preliminary results show that the low-order streams in these watersheds frequently exceeded the suggested nitrogen criteria before any harvesting activities were initiated. Average nitrite/nitrate at all monitoring sites (0.172 - 0.410 mgL-1) was significantly higher than EPA’s recommended level (0.067 mg L-1), especially during rainstorm events and warmer months. Total phosphorus varied from 0.028 mg L-1 - 0.104 mg L-1, which were within the EPA recommendation levels. Total organic carbon showed high levels in both monthly and storm water samples at most of the monitoring sites.