Thursday, May 29, 2008 - 3:45 PM
618

Relating benthic algal biomass to stream nutrients using hierarchical lineal models

Christian Parker and Yangdong Pan. Environmental Sciences and Resources, Portland State University, PO Box 751, Portland, OR 97201

The relationships between benthic algal biomass (e.g., Chlorophyll a) and nutrients in streams over a large geographic region remain elusive. Coarse-level variables such as climate and geology may likely contribute to the spatial variability of algal responses to nutrients in streams. We explore the use of HLM to identify major factors at different scales which could account for variability of algal responses to nutrients. We used data collected for the EPA Western EMAP program. A total of 1089 and 376 stream reaches were used to calibrate and validate the models respictively. Sites were grouped at a number of scales ranging in size from watershed to state. Unconditional (intercept only) models were first checked to evaluate the usefullness of grouping the data. Predictions from a one variable (total nitrogen) random coefficient HLM models were then compared to ordinary least squares (OLS) models. Analysis found that groups accounted for as much as 16% of the variability in chlorophyll a (Ecoregion level 3). Preliminary findings indicate that grouping results in a slight increase in predictive ability using simple models of stream chlorophyll a conditional on total nitrogen.


Web Page: Hierarchical linear models, periphyton WEMAP