A multi-method approach for the characterization of urban stream quality and algal dynamics

The health of streams decreases due to land development and urbanization. Setting and enforcing limitations on physiochemical inputs into streams can help preserve stream quality; however, because of inconsistencies in studies that relate physiochemical stream conditions to biological conditions, it is unclear what management actions are needed to correct impairments due to algae. Failure to consider the highly variable nature of physiochemical stream conditions may be obscuring the relationships between algal dynamics and the physiochemical conditions. Compounded with this issue, traditional algal biomass measurements exclude site history and do not accurately account for algal cell loss. This study developed new methods to address these two major issues. The first method, high-resolution physiochemical sampling, was used to quantify the dynamics of biologically relevant stream parameters at headwater streams in Southern California. The second method, an in-situ algal bioassay, was developed to determine a watershed-specific measure of algal response to stream conditions that is independent of site history or cell loss.;We found variation on small scales both temporally (over a 24-hour period) and spatially (over distances of a few meters) that was as large as the seasonal variation. Using the averages from the diel sampling (as compared to single measurements) increased the amount of variability described in a multiple regression analysis of algal biomass to light, phosphate, and nitrate from 65% to 91%. For the algal bioassay, we isolated a non-nitrogen fixing blue-green alga from the Malibu Creek Watershed, determined the dose-response relationships of that culture to relevant stream conditions, and generated a simple multiplicative model for algal response. The algal bioassay had a strong, repeatable linear correlation to the model in both laboratory and field tests. This bioassay demonstrated that the simple multiplicative model used in this study provided a repeatable relationship between stream conditions and algal growth. If both high-resolution sampling and this algal bioassay are used to supplement traditional stream monitoring stream studies will be begin to account for much of the spatiotemporal variability that is typically ignored.