Southern California is a highly populated region with developed watersheds. Thus there is increased risk of pollution reaching coastal waters and estuaries: more runoff reaches marine environments in urbanized areas, and there is year-round influx of treated wastewater effluent entering a system typically exposed to freshwater during the rainy season. A major limitation of current methods of freshwater and nutrient measurement is the samples are discrete. Therefore an integrative way to quantify terrestrial inputs to marine communities is necessary. The green macroalga Enteromorpha intestinalis has the potential to be an indicator of water quality. This alga is tolerant of a variety of environmental conditions and responds to decreased salinity and increased nutrient supply on the cellular level.

The focus of this project is to quantify the response of E. intestinalis to factors associated with terrestrial influx of freshwater and nutrients in order to assess its usefulness as a bioindicator. We will measure tissue water content and potassium concentration to examine short-term effects of reduced salinity, and nutrient content (nitrate, ammonium) of tissue and water to see how salinity decrease, temperature change and light availability affect nutrient uptake. Labeled nitrogen (15N) will be used to determine the preferred form of nitrogen (nitrate, ammonium) taken up. Finally, the natural abundance of stable isotopes (5N/'4 N) will be used to determine where the nutrients available to the algae come from (sewage, terrestrial or marine derived).

The benefits from the results of this research include understanding how short-term environmental changes affect macroalgae, and learning about nutrient uptake and which sources of nutrients are most utilized by algae in the field. With these data we can begin development of a biological indicator to measure runoff in marine and estuarine environments, thus providing an inexpensive, easy way to measure water quality in areas subject to runoff influence.