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 two 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 N and 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 one week, showing a high potential for N remediation in these wetlands.This article is protected by copyright. All rights reserved

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Wetland impoundments are constructed for recreational and conservational purposes. Here, the water level can be carefully controlled, producing ideal conditions for aquatic plant growth to support migratory birds or other management goals. These wetlands also perform a critical function of nutrient assimilation, with the capability to protect downstream waters from eutrophication. Understanding how the structural characteristics of wetlands are related to this functional capacity within shallow impoundments will help inform management practices to improve overall wetland function. We characterized 18 waterfowl impoundments surrounding the Great Salt Lake, Utah, USA. Wetland assimilation of nitrogen (N) and phosphorus (P) was estimated at each wetland by controlled nutrient addition within mesocosms. In addition, wetland condition was assessed using a multimetric index (MMI), an indicator of the biological quality of the wetlands. We found that N assimilation was inversely correlated with water depth and positively correlated with soil % clay and total iron. Phosphorus assimilation was related to dissolved oxygen, aluminum, and N and P concentrations within the water column and soil. Nutrient assimilation did not differ among wetlands rated as poor, fair, and good by the MMI.