Evaluation of nutrient assimilative capacity in waterfowl impoundments: The role of environmental stressors.

The effectiveness of wetlands in sequestering nutrients and improving water quality relies on a suite of abiotic and biotic conditions. To more fully understand the restraints on nutrient removal, especially salinity and plant cover, we created field-scale mesocosms and monitored nutrient sequestration with nutrient additions and isotopic pool dilutions over 2 years in two wetlands near the Great Salt Lake in Utah. Surprisingly, we found no differences in nutrient removal with plant removal, increased salinity, and altered ambient nutrient concentrations, suggesting functional redundancy in associated primary producers. When submerged aquatic vegetation was removed, chlorophyll α concentration (0.1-9.0 µg/L) increased while nitrogen (N) and phosphorus (P) assimilation remained the same as phytoplankton occupied the open niche space. We did find ammonium concentrations to be inversely related to nitrate assimilation-as the ammonium concentration increased, nitrate assimilation decreased, suggesting preferential uptake of ammonium. Last, in our high N and P treatment mesocosms, the nitrate dramatically declined from 43.9 mg/L to background levels (<0.1 mg/L) within 1 week, showing a high potential for N remediation in these wetlands.