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EVALUATION OF SAMPLING FREQUENCIES REQUIRED TO ESTIMATE NUTRIENT AND SUSPENDED SEDIMENT LOADS IN LARGE RIVERS
Citation:
Rowe, G. L. AND T Flum. EVALUATION OF SAMPLING FREQUENCIES REQUIRED TO ESTIMATE NUTRIENT AND SUSPENDED SEDIMENT LOADS IN LARGE RIVERS. Presented at Society of Environmental Toxicology and Chemistry, Nashville, TN, November 12-16, 2000.
Impact/Purpose:
The purpose of this research project is to provide methods, tools and guidance to Regions, States and Tribes to support the TMDL program. This research will investigate new measurement methods and models to link stressors to biological responses and will use existing data and knowledge to develop strategies to determine the causes of biological impairment in rivers and streams. Research will be performed across multiple spatial scales, site, subwatershed, watershed, basin, ecoregion and regional/state.
Description:
Nutrients and suspended sediments in streams and large rivers are two major issues facing state and federal agencies. Accurate estimates of nutrient and sediment loads are needed to assess a variety of important water-quality issues including total maximum daily loads, aquatic ecosystem response and hypoxia in the Gulf of Mexico. Despite work by U.S. Geological Survey's National Water-Quality Assessment (NAWQA) program, questions remain concerning sampling frequency required to accurately estimate loads of nutrients and suspended sediments. A preliminary effort to determine appropriate sampling frequencies for estimating loads of nutrients and suspended sediments in a large river was made jointly by NERL and the Great and Little Miami River Basins NAWQA unit. Water samples were collected hourly with an automatic sampler at a single station on the Great Miami River just upstream from the confluence with the Ohio River. The GreAt Miami River was selected because available data indicate it has one of the highest yields of nutrients per unit area among watersheds contributing to the Gulf of Mexico. Hourly samples were composited into daily samples and analyzed for nitrate, ammonia, total phosphorus (TP), total Kjeldahl nitrogen (TKN) and suspended sediments (SS). For the period 9/99 to 4/00 ammonia concentrations ranged from 0.01 to 0.39 mg/L-1, nitrate from 0.10 to 8.35 mg/L-1, TP from 0.07 to 0.94 mg/L-1, TKN from 0.22 to 1.32 mg/L-1 and SS from 2.25 to 487 gm/L-1. Spring planting and feritlizer applications have begun and increased concentrations of nutrients and suspended sediment are expected. Analysis of availlable data indicates that loads estimated on the basis of monthly or bimonthly samples were as much as 30% less than loads estimated from daily composite samples.