Assessing the effects of lateral hydrological connectivity alteration on freshwater ecosystems: A meta-analysis

Abstract

The alteration of lateral hydrological connectivity (LHC) is among the major causes of decline in biodiversity and ecosystem functioning and services in river-floodplain ecosystems. Yet, the effects of LHC alteration on aquatic ecosystems have not been rigorously tested and synthesized. Here, we conducted a literature review and meta-analysis to provide a global synthesis of the effects of LHC alteration on aquatic ecosystems, and to test the effectiveness of indicators for bioassessment. In our review we found that the effects of LHC alteration were disproportionally documented in terms of geographic distribution and research subject. Most studies were conducted in Europe and America on the biodiversity and abundance of macroinvertebrates and fish. In our meta-analysis, we compared effect sizes between pairs of three LHC levels, i.e. disconnected, moderately connected, and highly connected. We found that only a limited number of water quality indicators (e.g. chlorophyll a, total phosphorus, conductivity, and dissolved oxygen) and biological community indicators (e.g. fish species richness, and zooplankton abundance) showed significant differences between LHC levels. The responses of these indicators to LHC alteration differed, and sometimes in opposing directions. We found out responsive indicators and their response trends, which could not only facilitate effective biomonitoring and bioassessment with regard to engineering and restoration of LHC, but also provide scientific underpinnings of the understanding of trade-offs among the indicators. We identified knowledge gaps and provided recommendations on how to fill these gaps, which included investigating rarely documented regions, developing new indicators, and quantifying mechanistic links between LHC and ecosystem functioning and services.