The aquatic benthic food webs: The determinants of periphyton biofilms in a diversion canal and its upstream reservoir

Abstract

Excessive accumulation of periphyton biofilms could cause a series of environmental problems in the South-to-North Water Diversion (SNWD) Canal. To better understand the determinants of periphyton biofilms, we applied generalized linear models (GLMs) and structural equation modelling (SEM) to compare and quantify the relative importance of multiple factors on the periphyton biofilm biomasses in the SNWD Canal and its upstream Danjiangkou Reservoir. The excessive accumulation of periphyton biofilms in the SNWD Canal was obviously higher than that of the reservoir. Our data indicate that water temperature is the most important abiotic factor for explaining the biofilm biomass. Biotic factors for explaining the biofilm biomasses are quite different in the two ecosystems. Evidence from GLMs and SEM shows that prawns (Macrobrachium nipponense) have a significant negative direct effect on the reservoir biofilm biomass, while gobies (Rhinogobius giurinus) have a significant positive indirect effect via molluscs on the canal biofilm biomass. The Bayesian mixing models from stable isotope data also verify that biofilms are a major component of the reservoir prawn diets (72.5 ± 1.9%). However, in the canal, biofilms are the major component of the canal mollusc diets (70.2 ± 19.8%), and a rather high proportional contribution of molluscs is found for the goby diets (67.4 ± 8.0%). These results suggest the main paths of benthic food chains in the two ecosystems. In this study, we reveal the determinants of periphyton biofilm accumulation, which may provide useful information for biomanipulation in the SNWD and its upstream reservoir.