Modelling Primary Producers in Some Shallow Spanish Lakes

Abstract

Increased nutrient loading is regarded as one of the major causes of a shift from macrophyte to phytoplankton dominance in shallow lakes. This work investigates the responses of phytoplankton and epiphyton biomass, macrophytes and algal species assemblages along a trophic gradient in some shallow Mediterranean lakes. A unimodal response of epiphyton biomass to increasing phosphorus levels was observed, while phytoplankton developed exponentially and submerged aquatic plant coverage decreased. At TP levels above 100 μg L−1 (~30 μg-P L−1 by element) phytoplankton began to dominate over the other primary producers and led the system to a turbid state, mainly dominated by cyanobacteria. This could be regarded as a critical threshold to avoid algal turbid states, especially for shallow Mediterranean lakes. Macrophyte typology was also important in modulating this response. On average, the unimodal maximum of epiphyton biomass was about 20 μg g−1 of macrophyte dry weight and hydrophytes had higher epiphytic biomass than helophytes. The coverage of submerged aquatic vegetation was not related to the epiphytic and phytoplanktonic biomass, but to the distribution of their species. Further studies on epiphyton-plant ecology are needed, especially for specific aquatic macrophyte conservation and lake management.