Multi-scale effects of hydrological and landscape variables on macrophyte richness and composition in British lakes

Abstract

Macrophytes are an integral component of lake littoral zones and play an irreplaceable role in maintaining the ecological balance of wetlands. Recent research has highlighted the role of lake-scale environmental factors (or “filters”) and catchment- and/or landscape-scale processes in explaining variation in macrophyte communities across different scales. In this work, the effects of land-use and connectivity on macrophyte communities were explored at two contrasting spatial scales (i.e. local catchment scale and topographic catchment scale). At the local catchment scale, the results revealed strong scale-dependency. The effects of land use on macrophyte richness were most apparent at fine spatial scales (within 0.5 to 1 km) and significantly outweighed the importance of hydrology. In terms of growth form composition, the effects of hydrological connectivity were stronger than those of land use, with the greatest effect observed at an intermediate distance (~ 5 km) from the lake. The study on the hydrologically-connected lake pairs indicated that environmental filters were more influential in explaining species turnover than lake connectivity. Interestingly, geographical connectivity explained more of the variability in species turnover than hydrological connectivity. Moreover, the relative importance of environmental filters and lake connectivity to species turnover was very sensitive to the degree of human disturbance. The multi-scale interaction analyses indicated the effect of lake alkalinity on macrophyte composition is strongly influenced by catchment scale variables including hydrological features and land use intensity. The turnover in macrophyte composition in response to variability in alkalinity was stronger in catchments with low lake and stream density and weaker in catchments with a more highly developed hydrological network. Lake abiotic variables were found to have more influence on macrophyte composition in lowland catchments with a higher intensity of human disturbance. Moreover, the catchment-scale factors promoting the establishment of different communities were found to vary between catchments depending on lake type, the degree of environmental heterogeneity and hydrological connectivity.