ABSTRACT. The high density of animal production in southeastern Coastal

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N onpoint source (NPS) pollution of streams and groundwater is a major concern in the USA. To assess NPS problems, water quality demonstration projects have been implemented to accelerate the adoption of improved management practices that can reduce NPS pollution. These water quality projects require methods to measure or monitor the associated improvements in water quality in groundwater and stream water. Monitoring methods in streams involve collecting water samples at periodic intervals and determining changes over time. The collection of these samples of stream water may include simple periodic grab sampling, statistical and probability driven grab sampling techniques, regular time monitoring of the samples, or sampling based on stream flow or stage. In addition to the water samples taken, flow measurements are needed to relate the concentrations of nutrients to a mass loading of nutrients exported or removed from the watershed over time. Previous research has looked at various methods for sampling streams to determine flow-weighted nutrient concentrations and their corresponding loads. Humenik et al. (1980) implemented a probability sampling scheme to quantify rural water quality on a watershed basis in North Carolina. They sampled streams using grab samples and averaged two samples per sampling site in a 28-day period or approximately 26 samples per year. They found that the probability sampling technique produced adequate results for the purposes of their monitoring objectives for state NPS water quality plans. Bliven et al. (1980) used both grab and automated sampling techniques in the Piedmont of Virginia and the Coastal Plain of North Carolina. They found runoff concentrations were only marginally greater than base flow concentrations and that loadings were highly correlated to flow. Shih et al. (1994) studied the accuracy of nutrient load calculations using time-composite sampling. They found that when flow and phosphorus concentrations were positively correlated, computations using the timecomposite methods underestimated the load and vice-versa. Tremwel et al. (1996) developed a program to geometrically sample incremental runoff volumes from ephemeral streams and ditches. They compared this method with standard flow proportional sampling techniques. The geometrically incremental volume sampling technique samples rising hydrograph limbs frequently and falling limbs less frequently. Rekolainen et al. (1991) evaluated the accuracy and precision of annual phosphorus load estimates from two agricultural basins in Finland. Sampling methods that summed the products of regularly sampled flows and concentrations produced the best precision, but the best accuracy was achieved using a method based on multiplying annual flow by flow-weighted annual mean

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