Developing vegetation metrics for the assessment of beneficial uses of impounded wetlands surrounding Great Salt Lake, Utah, USA

摘要

Many wetlands around Farmington Bay of Great Salt Lake are managed waterfowl habitat by means of impounding the flow at the terminus of the Jordan River. The majority of the Jordan River flow is comprised of the secondary-treated effluent of several municipal waste water treatment plants (WWTP), resulting in elevated phosphorus concentrations. This study was initiated to determine whether the assimilative capacity for phosphorus of the impounded wetlands had been exceeded, resulting in a negative impact to the submerged aquatic vegetation (SAV) in the wetlands. The majority of the SAV is sago pondweed and western fineleaf pondweed (Stuckenia pectinata and S. filiformis ssp. occidentalis, respectively), highly preferred food items for waterfowl. Utah Department of Environmental Quality had identified support for waterfowl and shorebirds and the aquatic life in their food chain as the primary beneficial use of these wetlands, and thus, loss or degradation of Stuckenia prior to waterfowl fall staging and migration may constitute a loss of this important beneficial use. Therefore, Utah needs vegetation metrics what will indicate relative health of a wetland with respect to the abundance, density and health of the SAV and the level of nutrient loading it receives. The primary goal of this ongoing study is to develop wetland assessment methods that will be used to establish water quality standards and methods for Clean Water Act 305(b)/303(d) assessments-one of the first attempts by any state of the U.S. to set wetland water quality standards through development of site-specific assessment protocols. To develop metrics that describe the relationship between nutrient gradients and biological responses, we are 1) testing potentially useful parameters for their utility in assessing wetland condition; and 2) refining condition metrics that will identify thresholds of significant change (impairment) that can be attributed to nutrients. This paper presents the first of several potentially useful vegetation metrics. Our analyses showed that percent areal cover of SAV in nutrient enriched wetlands senesced 62-84% from July through November whereas the vegetation in a non-impacted reference wetland remained stable. The fall senescence occurs at a time when migratory waterfowl rely on submerged aquatic vegetation (SAV) for sustenance.