An empirical regression model of soluble phosphorus retention for small pristine streams evaluating tracer experiments

Abstract

Models of in-stream phosphorus retention either lack high spatial and temporal resolution, or need a high number of input parameters. We provide a simple new approach that deals with these deficits. Soluble reactive phosphorus (SRP) tracer studies based on the nutrient spiralling concept were evaluated to derive a simple model that explains SRP retention. SRP uptake length (SRP-S-w) was considered to be a measure of transient SRP storage and was transformed to load-weighted retention (R) using an exponential relationship. Stream order (so) and flow velocity (u) were considered as input parameters to explain SRP uptake length. Model validation showed significant correlation with measured uptake lengths. The model explained 46% of SRP retention, and simulated and measured retention were in the same order of magnitude. Our model may act in concert with emission models to account for lateral SRP sources within the catchment. Although our empirical model does not describe biological processes and is not a substitute for detailed biogeochemical studies, it provides an efficient tool to predict load-weighted soluble nutrient retention and nutrient transport to downstream systems and is applicable in most small pristine streams.