Stream microbial communities and ecosystem functioning show complex responses to multiple stressors in wastewater.
Francis J Burdon1,2, Yaohui Bai3, Marta Reyes1
1Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
Global Change Biology
|September 4, 2020
Summary
Wastewater treatment plants (WWTPs) release micropollutants (MPs) and microbes into freshwater, altering ecosystems. While warming and nutrients boost decomposition, MPs negatively impact microbial communities and ecosystem services.
Area of Science:
- Environmental Science
- Ecotoxicology
- Macroecology
Background:
- Urbanization significantly impacts freshwater ecosystems, with wastewater treatment plants (WWTPs) being a major source of pollution.
- WWTPs release micropollutants (MPs) and antibiotic-resistant microbes, potentially affecting biodiversity and ecosystem services.
- Understanding the combined effects of multiple stressors from WW is crucial for freshwater ecosystem management.
Purpose of the Study:
- To investigate the effects of wastewater (WW) on microbial communities and organic-matter processing.
- To determine how different components of WW (warming, nutrients, MPs, microbes) interact to influence ecosystem functioning.
- To assess the ecological consequences of WW inputs on freshwater ecosystems.
Main Methods:
- Mensurative field experiments sampling 60 locations in 20 Swiss streams above and below WWTPs.
- Flume experiments to test the effects of diluted WW on microbial processes.
- Laboratory experiments including standardized decomposition assays and next-generation sequencing of microbial communities.
- Transplant experiments to evaluate the role of WW-borne microbes.
Main Results:
- WW inputs positively influenced microbial respiration and decomposition rates through warming and nutrient enrichment.
- WW decreased the activation energy of decomposition, indicating a temperature-dependent "slowing" of the process.
- Microbial community structure below WWTPs showed altered composition, reduced richness, and negative MP influences.
- Nutrient enrichment masked negative MP effects in diluted WW, while WW-borne microbes enhanced decomposition rates.
- Increased respiration below WWTPs may lead to greater carbon evasion, while MPs may alter ecological scaling relationships.
Conclusions:
- Wastewater exerts complex, multiple-stressor effects on freshwater ecosystems, influencing microbial communities and organic-matter processing.
- WWTP effluents can lead to ecosystem "disservices" such as increased carbon evasion.
- Toxic MP effects necessitate integrating ecotoxicological and macroecological perspectives to understand fundamental ecological changes.
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