During the dry season, about 90% of the water flowing into the LA River is treated wastewater discharged from wastewater treatment plants.

AGU: Many of California’s threatened species live in reused water — for better or worse

From the American Geophysical Union

In the parched west, reusing water is a must. But scientists are still working to understand how reused, treated municipal waste water might impact the environments it’s released into. This water can have negative impacts, such as eutrophication, but can also provide new flow for spots where water had been diverted or dried up long ago. While many studies have explored the impact of reused water on water quality, fewer have examined its impacts on flora and fauna.

A new study maps out California’s watersheds and how much of their water is reused. The researchers found that about one-third of all watersheds get most of their base flow water from treated water. These watersheds are typically densely populated or used for agriculture, such as the Los Angeles Basin, the Inland and Central Valleys, and the San Francisco Bay region.

The researchers then checked to see how many threatened or endangered animal species of a wide variety are present in the watersheds. They found that one-quarter of these species had 100% of their range in watersheds with at least one water treatment plant.

Localized, species-specific research will be necessary to discern the impacts, positive or negative, of the presence and chemical composition of reused water on different species and watersheds. This study lays the groundwork for those investigations, pinpointing the most heavily impacted watersheds and coupling that with species distributions.

The intersection of wastewater treatment plants and threatened and endangered species in California, USA watersheds

Authors: Anna CassadyKurt AndersonKurt SchwabeHelen Regan

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 emergent vegetation and habitat. 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.

Access the article at AGU’s Water Resources Research (open access).

Print Friendly, PDF & Email