The Intersection of Wastewater Treatment Plants and Threatened and Endangered Species in California, USA Watersheds

Abstract

A changing climate and often unregulated water extractions have exposed over 2 billion people to water stress worldwide. While water managers have explored a portfolio of options to reduce this stress, supply augmentation through reuse of treated municipal wastewater is becoming increasingly attractive. Wastewater treatment plants protect water quality and prevent sewage from contaminating waterways. Increasingly, this resource is utilized for numerous human (e.g., irrigation, drinking water, groundwater recharge) and conservation (e.g., stream and river recharge) needs in water stressed regions. To understand the role treated municipal wastewater plays in impacting conservation objectives we identified the intersection of wastewater treatment plant locations and occurrences of threatened and endangered (T&E) species in California and compared the permitted contribution of effluent to baseflow quantities of the receiving waterbody to assess the degree to which changes in effluent could affect instream waterbodies. We found a positive correlation between the presence of treatment plants and T&E species in California watersheds—a quarter of species have 100% of their range in watersheds with at least one treatment plant. This correlation is greatest for species associated with terraces and riparian habitat, followed by aquatic habitat and aquatic emergent vegetation. One‐third of watersheds in our analysis can receive most of their cumulative watershed baseflow from effluent and are characterized by dense urbanization or agriculture. Our analysis demonstrates that the fates of T&E species and effluent are interconnected in ways important for water policy, suggesting that species conservation goals should be considered when making decisions about effluent reuse.

An analysis of threats to endangered animal taxa in California's freshwater systems

“…The freshwater habitat types were categorized to reflect aquatic floodplain habitat classifications (Cassady et al, 2023): 'aquatic habitat', meaning the taxon is submerged in water for at least some portion of its life cycle (e.g., fish and amphibians); aquatic vegetation (e.g., wetlands); riparian vegetation; terraces (e.g., alluvial fans); and vernal pools. The dominant habitat association for each taxon was determined by reviewing resource agency management plans, federal and State species reviews and reputable natural history websites.…”

“…To examine the types and number of threats with impacts on freshwater biodiversity, E&T taxa were classified according to their relationship with floodplain habitat types. The non-freshwater taxa in the threat analysis served as points of comparison to understand better the pervasiveness of threats across the State and those typically associated with freshwater ecosystems (Cassady et al, 2023). The assessment was confined to taxa listed by the federal Endangered Species Act or California Endangered Species Acts (ESA and CESA, respectively) because (i) these taxa are imperilled and exposed to a range of threats, (ii) they are generally sufficiently studied to have a uniform set of data and sources and (iii) they are conservation targets and therefore would be the greatest beneficiaries of water management decisions.…”