CAN WE USE NUTRIENT CONCENTRATIONS DURING BASEFLOW CONDITIONS TO MANAGE NONPOINT SOURCE POLLUTION AND PRIORITIZE SUBWATERSHEDS FOR MANAGEMENT OPTIONS?

The lack of observed changes in water quality at the larger watershed scale (i.e., HUC 8 and larger) has prompted state and federal agencies to focus on smaller watersheds (e.g., HUC 12 and smaller), requiring some scheme to prioritize where to invest financial resources and implement conservation practices. The approaches to assess water resources and priotize watersheds has often involved the use of complex watershed models, predicting nutrient concentrations and loads. The reality is that this watershed models are often calibrated and validated at a scale much larger than what is needed to prioritize smaller watersheds. The question posed by this presentaion - can we use stream nutrient concentrations during base flow conditions to prioritize smaller watersheds? The premise is based on three observations: (1) that stream nutrients concentrations are positively correlated to human development (urban and agriculture) within the watershed, (2) nutrient concentrations during base flow and storm events are related, and (3) these land uses also results in increased runoff and likely nutrient loads from the landscape. Given these observations, we will use threshold relationships between stream nutrient concentrations and various watershed metrics to present a decision tree to target smaller watersheds for conservation practices and funding. The preliminary anlaysis shows that streams in select eco-regions have a tendency to have greater nutrient concentrations during base flow conditions with these criteria:

• Less than 50% forested area within the catchment and riparian buffer,
• More than 40% pasture within the riparian buffer,
• More than 0.006 poultry houses per hectare within the catchment, and
• a stream density which exceeds 0.008 meters per hectare

Water resource managers could use these criteria to prioritize smaller watersheds, and the watersheds that meet multiple criteria would even be a higher priority for the implementation of conservation practices and funding opportunities through state and federal programs.