Anthropogenic Carrion Subsidy and Herbicide Glyphosate Depressed Leaf-Litter Breakdown: Effects on Environmental Health in Streams

Terrestrial leaf-litter (LL) inputs impose great bottom-up effects on freshwater ecosystems by fueling detritus-based food webs, affecting macroinvertebrate and microbial communities, and influencing ecosystem functioning. However, increasing intensive anthropogenic activities including the inputs of herbicide glyphosate disturb the breakdown of LL in streams. In this study, an anthropogenic carrion subsidy (chicken meat) and glyphosate (a stressor) were used to investigate their individual and combined effects on LL breakdown in urban streams and forest streams in China. We found that: 1) carrion subsidy decreased LL breakdown rate in both urban and forest streams and increased total and predator richness in forest streams, the reduced LL breakdown rates may be attributed to the foraging shift of macroinvertebrates from LL to carrion subsidy; 2) glyphosate depressed LL breakdown rate in forest but not in urban streams, the reduced LL breakdown rate may be caused by the negative effects on microbes; 3) forest streams showed significantly higher LL breakdown rates in both coarse and fine mesh bags than urban streams which were induced by the high dissolved oxygen (DO) and collector-gatherer richness. Our results provide evidence that LL breakdown in streams is sensitive to inputs of anthropogenic carrion subsidy and glyphosate through the impacts on macroinvertebrates and microbes, respectively. Furthermore, this study underscores the importance of local macroinvertebrate and microbial communities when assessing the responses of stream ecosystem functioning and macroinvertebrate communities to multiple stressors, as the individual and combined effects of stressors can be site-specific in streams with different physical characteristics and biological communities.