Epiphyton dependency of macrophyte biomass in shallow reservoirs and implications for water transparency

The competition between macrophytes and epiphyton in shallow lakes can be a crucial factor in a regime shift, between the macrophyte-dominated, clear-water state and the phytoplankton-dominated, turbid state. To investigate the effects of macrophyte maximum growth rate (Mmgr) and epiphyton maximum growth rate (Emgr) on the growth of macrophytes using a mathematical model, the integrated Water Quality Model and modified Submerged Aquatic Vegetation Model were tested in two shallow reservoirs; the Yuqiao Reservoir (China) and the Jankovac Reservoir (Croatia). A sensitivity analysis was applied to assess macrophyte biomass changes. In the Yuqiao Reservoir, macrophyte biomass decreased in relation to the increase of Emgr, while in the Jankovac Reservoir, a positive correlation was found when Emgr was below 0.1 d−1, and a negative correlation showed when Emgr was in the range of 0.1-0.4 d−1. We also tested the influence of different pairs of Mmgr and Emgr on the macrophyte biomass. The present study introduced a method to analyse the competition between macrophytes and epiphyton for phosphorus-limited shallow reservoirs. Our study proposes a macrophyte model that might serve as a useful tool to help maintain water transparency in similar shallow lakes.