Fecal Bacteria, Nutrients, Chlorophyll, and Dissolved Oxygen in a Constructed Habitat Wetland Receiving Treated Municipal Effluent and River Water

Abstract

ABSTRACT The Eagle Bluffs Conservation Area (Eagle Bluffs) in central Missouri includes about 400 ha of floodable pools and channels managed as seasonal or permanent habitat wetlands using treated municipal effluent from the Columbia Wastewater Treatment Wetland. Effluent, which is used year around, provides about half the annual water input and is supplemented during waterfowl migrations by pumping from the adjacent Missouri River. Infiltration rates are high (≈900 cm yr−1) because of high soil permeability. Water quality of inflows and selected pools and channels on Eagle Bluffs has been monitored since wetland flooding began in 1994 because of concerns about possible negative effects of wastewater and interest in the dynamics of nutrients and algal biomass in the system. Compared to river water, effluent typically had high concentrations of fecal bacteria, chloride, dissolved phosphorus, and dissolved nitrogen, especially ammonia-N. In the water Distribution Channel (DC) and terminal wetland pools of Eagle Bluffs fecal bacteria decline rapidly and are usually within the range suitable for human water contact (<200 cells 100 mL−1). Phosphorus and nitrogen concentrations vary with the relative inputs of effluent and river water and in situ losses. On the basis of comparison with chloride concentrations, over half of incoming phosphorus and nitrogen are lost from surface water to sediments, plant uptake or denitrification. Nutrient losses from the large proportion of water lost to infiltration are not known. Chlorophyll concentrations in the DC and wetland pools exceeded 100 μg L−1 in 35% of observations, but chlorophyll and organic matter concentrations on Eagle Bluffs are similar to those in Missouri River oxbow lakes with much lower nutrient inputs. Ammonia concentration frequently exceed USEPA acute and chronic toxicity criteria, but fish seem to thrive on Eagle Bluffs. Overall, negative effects of effluent use seem minimal with respect to intended uses of the habitat wetland, but effects of infiltrating effluent on subsurface drinking water supplies are still in question.