An autobiotic wetland phosphorus model

Constructed and natural wetlands are capable of absorbing new phosphorus loadings, and in appropriate circumstances can provide a low cost alternative to chemical and biological treatment. Phosphorus (P) interacts strongly with wetland soils and biota, which provide both short term and sustainable long term storage of this nutrient. Soil sorption may provide initial removal, but this partly reversible storage eventually becomes saturated. Uptake by biota, including bacteria, algae, and duckweed, as well as macrophytes, forms an initial removal mechanism. Cycling through growth, death and decomposition returns most of the biotic uptake: but an important residual contributes to long term accretion in newly formed sediments and soils. Despite the apparent complexity of these several removal mechanisms, data analysis shows that relatively simple equations can describe the sustainable processes. Previous global first order removal rates characterize the sustainable removal, but do not incorporate any biotic features. This paper presents an autobiotic model, based upon cycling through the biomass compartments, and calibrates it to data from 17 years of operation of the Houghton Lake, MI treatment wetland. This model replaces a first order concentration-based rate with a first order biomass-based rate. When coupled with mass balances, it describes the spatial distribution of both biomass and P concentrations, as well as the evolution of the new standing crop. (C) 1997 Elsevier Science B.V.