Warming, food web simplification and surface runoff pollution additively reduce the functioning of shallow freshwater ecosystems

Global declines in biodiversity are driving food web simplification, which threatens the functioning of freshwater ecosystems. These impacts are strongly affected by climatic and anthropogenic stressors, which further reduces biodiversity. However, how these stressors operate in concert to alter ecosystem functioning is still poorly understood. Here, we used 48 large-scale field mesocosms to test how the individual and combined effects of warming, surface runoff pollution (SRP), and food web simplification (FWS) affect the functioning of standing waters. We found that warming and pollution significantly altered primary producer community composition in simplified food webs by reducing the production of submerged macrophytes, with the associated reduction in shading increasing the growth of periphyton. Warming also suppressed the growth of submerged macrophytes, particularly M. spicatum. SRP (inorganic particles, organic matter and nutrients) stimulated filamentous algal (FLA) growth, as macrophytes provided suitable growth surfaces and the algae had stronger competition ability than macrophytes with pulse nutrient released into water. We further calculated the temporal stability of each primary producer group and found it decreased for macrophytes in the simplified food web treatments, while stability of FLA increased under SRP. Our findings demonstrate that when faced with an increasing range of global environmental stressors, which is often the case in natural ecosystems, shallow freshwaters lose functioning as the system shifts away from submerged macrophytes and towards benthic algal dominance. Our study provide a mechanistic basis for conservation strategies aimed at preserving shallow freshwater ecosystem functions.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Peiyu Zhang, Institute of Hydrobiology, Chinese Academy of Sciences (zhangpeiyu@ihb.ac.cn)

Authors:

Peiyu Zhang, Institute of Hydrobiology, Chinese Academy of Sciences  (zhangpeiyu@ihb.ac.cn)