Linking Stream Water Phosphorus to Ecological Endpoints in Ozark Headwater Streams.

Phosphorus (P) is a key limiting nutrient of freshwater eutrophication, a major impairment to designated uses in the U.S. Efforts have focused on reducing nutrient and sediment losses from agricultural lands with the objective of improving water quality. While measures are available to reduce edge-of-field losses, water quality improvements at a larger, watershed scale have not always occurred.

Stream water numeric criteria developed for Illinois River Watershed (IRW) of 0.037 mg total P L^-1, was based on the frequency distribution of flow-weighted P in undeveloped rivers. However, a recent independent review stated that the US EPA stressor-response approach is the most appropriate, scientifically based method for developing numeric nutrient criteria, as long as it used in conjunction with a ‘weight-of-evidence’ approach. Thus, it is essential that algal-response characteristics be determined as a function of in-stream P sources and processing to provide the needed ‘weight-of-evidence’ data for IRW streams. The objectives of this study were to examine the relationship fluvial P sources and algal biomass accumulation.

A mesocosm experiment was conducted which simulated the release of P during baseflow from sediment deposited in a stream. Periphyton biomass (as chlorophyll-a) was determined after 8 days after tiles inoculated in IRW stream were equilibrated with soils of varying P levels in 700 mL water. As expected, there was a positive linear relationship between the Mehlich-3 P content of stream sediment and stream P (R²=0.99) as well as biofilm chlorophyll-a (R²=0.75).

A mesocosm experiment was conducted which simulated the release of P during baseflow from sediment deposited in a stream. Periphyton biomass (as chlorophyll-a) was determined after 7 days after tiles inoculated in IRW stream were equilibrated with soils of varying P levels in 700 mL water. As expected, there was a positive linear relationship between the Mehlich-3 P content of stream sediment and stream P (R²=0.99) as well as biofilm chlorophyll-a (R²=0.75).