Creation of a multi-metric index for describing the environmental integrity of Austin-area lakes

Introduction The City of Austin’s Watershed Protection Department strives to protect the water quality in Austin area watersheds. Austin creeks have been monitored for years through the Environmental The Austin Lake Index (ALI) was designed to provide a yearly assessment of the environmental integrity of Lake Austin, Lady Bird Lake, and Lake Long. Sub-indices used to compute the ALI include representative measures of water quality, sediment quality, habitat quality, diversity/cover/% exotic aquatic vegetation, aquatic life health, and degree of eutrophication. The water quality and sediment indices are reliable metrics also used in Environmental Integrity Index (EII) calculations for Austin streams. The calculations of habitat and aquatic life scores from the EII were modified to better explain the biological integrity of the lentic (lake) rather than lotic (stream) habitat. The aquatic vegetation sub-index and the eutrophication sub-index use survey data describing measures of the plant and algal communities on each lake. Samples are collected throughout the year at several locations within each lake in order to obtain a more accurate representation of the lake in a given year. First year results of the Austin Lake Index did not show differences in the overall health of each lake. The individual subindices showed much greater variability between the lakes. Lake Austin obtained the highest score in the water quality sub-index. Sediment, habitat, and aquatic vegetation sub-indices were highest in Lake Long, while the aquatic life and eutrophication subindices were highest in Lady Bird Lake. The Austin Lake Index was developed from the local data available for Lake Austin, Lady Bird Lake and Lake Long; therefore, it should provide the City a comprehensive regional assessment tool for detection and communication of environmental change in these lakes. It should also allow for prioritization of water quality needs on each lake and provide an easily understood representation of each lake to the general public.