Prediction of macrophyte distribution: The role of natural versus anthropogenic physical disturbances

Abstract

Questions: Do natural and anthropogenic physical disturbances equally affect the distribution of aquatic plant communities? Can hydrodynamic and geomorphological features be used to predict the establishment of macrophyte communities at the shoreline scale? Locations: Two large, shallow lakes, southwest France.Methods: Based on field observations (vegetation occurrence and anthropogenic modifications of the shore) and data generated by a geographic information system (wave exposure, wave-induced sediment re-suspension, slope and land cover), we defined sites and community groups using cluster and indicator species analyses. The groups were then analysed by means of a statistical classifier (Random Forest). These different steps in data treatment enabled us to characterize the importance of each physical factor in determining macrophyte occurrence and distribution. As a result, a predictive map to forecast aquatic plant distribution at the shoreline scale was obtained.Results: Anthropogenic disturbances were less important parameters than natural physical variables in structuring the distribution of lakeshore macrophytes. Within natural factors, wave-induced sediment re-suspension and slope had the most impact; nevertheless, the presence of swimming areas seemed to have a strong impact on aquatic habitats, being correlated with the total absence of aquatic vegetation.The predictive map obtained through the model spatially defined the position and occurrence of suitable sites for the settlement of both invasive and rare and endangered species. Conclusions: In this study, natural disturbances play a major role in structuring aquatic plant distribution over physical anthropogenic factors. The model contributes to improving knowledge on plant communities with respect to local hydrodynamic and morphological features of lakeshores. Furthermore, the model provides a predictive map as a useful tool for the management of aquatic vegetation in temperate shallow lakes. K E Y W O R D S aquatic weeds, distribution model, hydromorphological alteration, isoetids, lakeshore zone, softwater lakes, variable importance, vegetation management, wave action 396 | Applied Vegetation Science BERTRIN ET al.

Invasive Aquatic Plants as Ecosystem Engineers in an Oligo-Mesotrophic Shallow Lake

“…Macrophyte community is here mainly composed by isoetids ( Lobelia dortmanna L., Littorella uniflora (L.) Asch. and Isoetes boryana Durieu) together with some species of charophytes (Bertrin et al, 2018). This community is recognized to reduce carbon benthic fluxes and to contribute to sediment oxygenation through radial oxygen loss.…”

“…Global changes, such as the increase of water temperature, the modifications of lakeshore for anthropic activities and the unintentional introduction of plant fragments may favor the spread of exotic aquatic plants (Gillard et al, 2017; Bertrin et al, 2018). The settlement of invasive species, and the massive developed biomass, has been recently recognized to strongly influence biodiversity (Hussner et al, 2009; Strayer, 2010).…”

Influence of historical landscape on aquatic plant diversity

“…Macrophyte surveys were made in all lakes along the total perimeter of each lake, which had been divided into 100 m-long sectors (Bertrin et al, 2018). All aquatic, amphibious and helophytic plants visible to the naked eye were considered as macrophytes.…”

“…Macrophyte communities are also known to be strongly influenced by water chemical composition (e.g. nutrient concentrations, Bornette & Puijalon, 2011) as well as by the morphological characteristics of lakes (Bertrin et al, 2018). Indeed, the higher diversity of lake macrophytes is usually found in littoral zones (Schmieder, 2004;Strayer & Findlay, 2010) whose characteristics (e.g.…”

“…Indeed, the higher diversity of lake macrophytes is usually found in littoral zones (Schmieder, 2004;Strayer & Findlay, 2010) whose characteristics (e.g. area, depth, wave exposure, shore slope) have a subsequent large impact on its taxonomic diversity and composition (Azzella, Rosati, Iberite, Bolpagni, & Blasi, 2014;Bertrin et al, 2018;Chambers, 1987). Therefore, as lake macrophyte communities are known to be influenced by numerous factors including water composition, morphological characteristics and land use in the surrounding landscape, we expect an influence of trophic level, lake morphometry and recent land use on macrophyte diversity structure.…”