Development of local pollution tolerance and multimetric indices responsive to urbanization in central Texas, USA

Urbanization of watersheds is an important driver of ecological degradation and necessitates development of robust monitoring programs to track ecosystem alterations toward protection and restoration of essential ecosystem services. Stream biological population metrics and pollution tolerance indices (PTIs) are frequently used to assess condition, but many PTI values are not tailored to the ecoregion in which they are being applied. Therefore, we developed novel stressor-specific tolerance values and metrics for benthic macroinvertebrates and diatoms to more accurately assess ecological integrity of streams in a rapidly urbanizing region of central Texas, USA. We used 23 y of monitoring data to establish taxa optima and tolerance values relative to impervious cover, specific conductance, total N, and total P to derive new metrics. We compared the strength of the relationships between the selected stressors and 1) previously used, globally common metrics and 2) our newly created metrics. We observed higher correlation coefficients between our created metrics with the Austin region’s stressor gradient. After combining the metrics into macroinvertebrate- and diatom-specific multimetric indices (MMIs), the observed effect size delineating reference from anthropogenically degraded sites were 2 to 4× larger relative to other common MMIs and indices. Our analysis has generated a powerful new set of metrics by using the empirical responses of biological communities to anthropogenic stressors in the Austin area. Our analytical process is transferable to entities seeking to establish localized metrics or to improve the resolution of biological MMIs to stressors of interest for better system characterizations.