Principal Determinants of Aquatic Macrophyte Communities in Least-Impacted Small Shallow Lakes in France

Abstract

Small shallow lakes (SSL) support exceptionally high and original biodiversity, providing numerous ecosystem services. Their small size makes them especially sensitive to anthropic activities, which cause a shift to dysfunctional turbid states and induce loss of services and biodiversity. In this study we investigated the relationships between environmental factors and macrophyte communities. Macrophytes play a crucial role in maintaining functional clear states. Better understanding the factors determining the composition and richness of aquatic plant communities in least-impacted conditions may be useful to protect these shallow lakes. We inventoried macrophyte communities and collected chemical, climatic, and morphological data from 89 least-impacted SSL widely distributed in France. SSL were sampled across four climatic ecoregions, various geologies, and elevations. Hierarchical cluster analysis showed a clear separation of four macrophyte assemblages strongly associated with mineralization. Determinant factors identified by distance-based redundancy analysis (db-RDA) analysis were, in order of importance, geology, distance from source (DIS, a proxy for connectivity with river hydrosystems), surface area, climate, and hydroperiod (water permanency). Surprisingly, at a country-wide scale, climate and hydroperiod filter macrophyte composition weakly. Geology and DIS are the major determinants of community composition, whereas surface area determines floristic richness. DIS was identified as a determinant in freshwater lentic ecosystems for the first time.

A new method for monitoring macrophyte communities in small shallow lakes and ponds

“…Our results, from lowly to highly impacted SSLs, confirmed the key role of surface area, elevation, and distance from the source previously established on French lowimpacted SSLs (Labat et al 2021). The decrease in floristic richness above 1,000 m asl was probably due to an indirect effect of the short duration of the growing season, cold temperatures (Jones et al 2003), and maybe lower nutrient availability (Lacoul and Freedman 2005).…”

“…The distance from the source had an influence on the macrophyte community composition (Labat et al 2021). Moreover, higher DIS was often characterised by communities typical of natural eutrophic lakes including Magnopotamion or Hydrocharition alliances, whereas lower DIS was characterised by communities of oligotrophic to mesotrophic standing waters including Littorelletea uniflorae and/or the Isoeto-Nanojuncetea.…”

Assessment of Spatial and Vertical Variability of Water Quality: Case Study of a Polymictic Polish Lake

“…Shallow lakes are widespread worldwide. They are often subject to conservation policies [3] because of their susceptibility to eutrophication [4]. Shallow lakes do not stratify, so the water column is frequently mixed [5].…”