The effects of caffeine-laden wastewater effluent on linked stream and riparian food webs
Wastewater effluent is being discharged into streams globally. Caffeine is one of the most frequent and highly concentrated contaminants found in this effluent. Data regarding effects of caffeine on individual species is beginning to accumulate but effects on species interactions, food webs, and aquatic-terrestrial linkages are largely unknown. Caffeine-mediated changes in aquatic ecosystems could cascade into neighboring riparian ecosystems, via changes in fluxes and quality of emergent insects.
To begin examining these possible effects, we compared samples up and downstream of wastewater inputs in three locations within the Portage River watershed, a tributary of Lake Erie in western Ohio. Specifically, we examined both water quality and benthic macro-invertebrates. To supplement this comparison, we took water quality measurements at nine additional sites in this watershed.
We found considerably and consistently high concentrations of caffeine at all sampling sites. We suggest that this could indicate a saturation of caffeine contamination throughout the watershed. Members of seven orders of arthropod were present in the benthic invertebrate samples from these sites. However, we found very similar communities when comparing upstream sites with downstream sites. No significant differences in diversity, richness, or abundance were found. Considering the uniformly high concentrations of caffeine, the lack of a difference in the biotic community is unsurprising. In the future, we plan to make comparisons to low-caffeine reference sites, gain larger sample sizes, and examine potential responses of particular components of both aquatic and riparian food webs.