A GIS approach of aquatic plant spatial heterogeneity in relation to sediment and depth gradients, Lake Geneva, Switzerland

A georeferenced database was constructed for a section of the littoral zone of Lake Geneva in order to investigate aquatic plant spatial heterogeneity at a community level, by exploring the relationships between species distribution and: (i) depth and sediment characteristics; and (ii) plant traits. This database includes information layers on vegetation, sediment and bathymetry. Vegetation was mapped from a digital photo interpretation coupled with field observation of species distribution and cover index. An abundance index was calculated for each species by multiplying the surface area of each stand by the species relative percentage and its cover index. Bathymetry was established from echosounder profiles and sediment maps were obtained from point interpolation between sediment core samples. Measured sediment characteristics include texture, nutrient and organic matter contents. Multiple regression models were developed in a related article (Lehmann et al., 1997) in order to estimate species biomass and maximum shoot length from depth and sediment characteristics. These models are applied in this article between the corresponding GIS layers to give a spatial estimation of these plant traits for three species of Potamogeton. Macrophyte stands, wherein a given species was dominant at more than 80%, were selected by a spatial selection together with the underlying depth and sediment characteristics and the estimated plant traits. When compared, P. lucens L. appeared to have the best competitive ability in relation to the observed plant traits, but it was dominated by a species more tolerant to wave disturbance in shallower depth ( P. pectinatus L.) and a species more tolerant to the stress of light attenuation and nutrient availability in deeper sites ( P. perfoliatus L.).