Nutrient removal and loading rate analysis of Louisiana forested wetlands assimilating treated municipal effluent

Abstract

The relationship between nutrient removal and loading rate was examined using data from five forested wetlands in Louisiana that have received secondarily treated effluent from 3 to 60 years. Loading rates ranged from 0.65 to 26.80 g/m(2)/yr for total nitrogen and 0.18 to 8.96 g/m(2)/yr for total phosphorus. At loading rates below 20 g/m(2)/yr, total nitrogen concentrations in surface waters of Louisiana forested wetlands were reduced to background concentrations (i.e., < or =3 mg/l). Similarly, at loading rates below 2 g/m(2)/yr, total phosphorus concentrations were also generally reduced to background concentrations (i.e., < or =1 mg/l). These data demonstrate that freshwater forested wetlands can reduce nutrient concentrations in treated effluent to background concentrations present in relatively undisturbed wetlands. An understanding of the relationship between loading rates and nutrient removal in natural wetlands is important, particularly in Louisiana where discharges of fresh water are being used in ecosystem restoration.