Action: Change effluent treatments of domestic and urban waste water
- We found no evidence for the effects on bats of changing effluent treatments of domestic and urban waste water discharged into rivers. One replicated, site comparison study in the UK found that foraging activity over filter bed sewage treatment works was higher than activity over active sludge systems.
'No evidence' for an action means we have not yet found any studies that directly and quantitatively tested this action during our systematic journal and report searches. Therefore we have been unable to assess whether or not the action is effective or has any harmful impacts. Please get in touch if you know of such a study for this action.
Organic pollution occurs when treated sewage effluents containing organic compounds are discharged into rivers affecting plant growth and the number and diversity of insects. Riparian habitats are important for foraging bats and changes in water quality may have positive effects for some species, and negative effects for others (Vaughan et al. 1996, Kalcounis-Rüppell et al. 2007, Abbott et al. 2009).
We found evidence that filter sewage bed treatment works can provide foraging habitat for bats. However, the results must be treated with caution as a subsequent study found that insects above these filter beds were contaminated with endocrine disrupting chemicals that may have adverse effects on bats feeding on them (Park et al. 2009).
Abbott I.M., Sleeman D.P. & Harrison S. (2009) Bat activity affected by sewage effluent in Irish rivers. Biological Conservation, 142, 2904–2914.
Kalcounis-Rüppell M.C., Payne V., Huff S.R. & Boyko A. (2007) Effects of wastewater treatment plant effluent on bat foraging ecology in an urban stream system. Biological Conservation, 138, 120–130.
Park K. J., Müller C. T., Markman S., Swinscow-Hall O., Pascoe D. & Buchanan K. L. (2009) Detection of endocrine disrupting chemicals in aerial invertebrates at sewage treatment works. Chemosphere, 77, 1459–1464.
Vaughan N., Jones G. & Harris S. (1996) Effects of sewage effluent on the activity of bats (Chiroptera: Vespertilionidae) foraging along rivers. Biological Conservation, 78, 337–343.
Supporting evidence from individual studies
In a replicated, site comparison study between June and August 2003 at 30 sewage treatment works in central and southern Scotland, UK (Park & Cristinacce 2006) significantly higher activity of Pipistrellus spp. was recorded over percolating filter beds than over activated sludge systems (average 15 vs. 4 bat passes/15 min respectively). Foraging activity of Pipistrellus spp. over filter beds was comparable to that at nearby foraging habitat along river banks, whereas foraging activity over activated sludge sites was lower. At filter beds, waste water is sprayed over inert filter material creating a microbial film which supports high insect numbers. In activated sludge systems, sewage and bacterial sludge are mixed together creating an unfavourable habitat for insects. Insect biomass was found to be significantly higher at filter beds. Bat activity was recorded with bat detectors at three points per site for 15 minutes each after dusk, and insects were assessed using suction traps for two hours after dusk at each site. Myotis spp. were also detected at both types of treatment works but numbers were too low for analysis.