Véronique Rosset

Is eutrophication really a major impairment for small waterbody biodiversity

Eutrophication remains a major stress for freshwater biodiversity. Its deleterious consequences on biodiversity are well documented for large waterbodies. However, the impact of eutrophication may differ in smaller waterbodies, such as ponds and small lakes, which generally support naturally high levels of nutrients in lowlands. Furthermore, this response could depend on the scale considered, from local (individual waterbody, alpha diversity) to regional (the network of waterbodies, gamma diversity). It is also unclear whether the richness of threatened species responds in the same way as the richness of the whole assemblage. The present study investigates local- and regional-scale consequences of eutrophication on taxonomic richness (all taxa) and conservation value (threatened taxa) in temperate lowland small waterbodies. Five taxonomic groups were investigated: macrophytes, gastropods, water beetles, adult dragonflies and amphibians, in a set of natural waterbodies and a set of enriched waterbodies covering a large nutrient gradient from mesotrophic to hypertrophic conditions. Globally, our study did not reveal consistent, systematic responses to eutrophication. For macrophytes, the richness and conservation value suffered from eutrophication at both local and regional scales. In contrast, for amphibians and gastropods, eutrophication did not impair biodiversity at the local nor the regional scale. Dragonflies and water beetles showed intermediate situations, with an impairment by eutrophication varying according to the type of waterbodies considered. At the regional scale, each trophic status, even the nutrient richest, brought an original contribution to biodiversity. Synthesis and applications. The management of eutrophication for small lowland waterbodies has to be considered differently than for lakes. For an individual waterbody (the local scale), nutrient enrichment is not necessarily a major impairment and its impact depends on the taxonomic group considered. Conversely, at the landscape scale, eutrophication is a major pressure on small waterbody biodiversity, especially because nutrient-rich small waterbodies are dominant in the landscape. Therefore, conservation efforts should integrate the notion of pond regional networks or ‘pondscapes’, where the regional biodiversity is supported by a mosaic of trophic conditions, and promote the presence of less rich waterbodies.

Invertebrate Communities of Alpine Ponds

Alpine ponds are small standing water bodies situated in mountainous regions at or above tree line. Hydrology is driven by snow and ice with harsh conditions comparable to that in shallow water bodies at high latitudes. Invertebrate communities are less diverse than at low altitudes and often dominated by “cold stenotherms” with arctic/boreal-alpine distributions. The unique assemblages in alpine ponds (many regional endemics) are of special conservation value. Species composition and diversity vary among basins of different size, substrate types, and permanence. Clusters of alpine ponds are excellent habitats for studying metacommunity dynamics and patterns of regional diversity. Alpine ponds are sentinel systems for, and especially vulnerable to, the effects of regional (e.g., acid precipitation) and global (climate change) human impacts.

Alien aquatic plants in wetlands of a large European city (Geneva, Switzerland): from diagnosis to risk assessment

Wetlands often form an important component in the urban matrix, where they are largely disseminated. Despite the abundance of these urban waterbodies, little is known about the spread of alien aquatic plant species in cities. Ponds are frequent in urban parks and domestic gardens where terrestrial alien plant species are common. Therefore, urban ponds are likely to support many aquatic alien species which might disperse to the natural environment. To investigate this potential, we collected data from 178 ponds in a large European city (Geneva, Switzerland), across an urbanization gradient. 17% (23 taxa) of the aquatic flora appears to be non-native, including five species at high risk of invasion. A large proportion of the waterbodies (43%) supported at least one alien taxa. Through the development of a risk assessment tool, the “Geneva-Aquatic Weed Risk Assessment system”, a risk map was created which revealed several alien species hotspots situated in the urban environment, but also in rural areas, including in protected wetlands. This risk mapping included the dispersal potential distance of species around these risk hotspots, and showed that most areas of dispersal seem to be relatively small. Ponds are target sites for deliberate introduction but they tend to be hydrologically isolated in the urban matrix, and these ‘islands’ therefore present a relative low risk of a wider dissemination of alien species. This risk is nevertheless expected to sharply increase in future. Introduction by humans is likely to be the main source of new alien aquatic plants, and so management should primarily aim to prevent the introduction of these species. Sites supporting alien species should also be monitored and, if possible, the species presenting a risk should be eradicated. Sites supporting alien species should also be monitored and, if possible, the species presenting a risk eradicated.

Local diversity of macroinvertebrates in alpine ponds as an indicator of global change: a Gastropod case-study

Anthropogenic global change is a potential threat for biodiversity worldwide. lncreasing temperatures are responsible for numerous shifts in species distributions and abundances that may lead to species-level extinctions (THOMAS et al. 2004). Regional diversity can be particularly threatened, as demonstrated in the Alps (THEURILLAT & GuiSAN 2001). Furthermore, the local diversity (e.g. ecosystem species richness) is also likely to be significantly impacted. Such consequences at the local scale are insufficiently documented, especially for areas where temperature increases are expected to be important. This is the case for high altitude regions, like the Swiss Alps, where temperature increases are predicted to be particularly high (BRADLEY et al. 2004). Ponds may play a central role in such local assessments, not only because of their small size and simple community structure (oE MEESTER et al. 2005), but also because oftheir sensitivity to physical environment changes. Aquatic macroinvertebrates are good bioindicators oftemperature changes (HoDKINsoN & JAcKSON 2005). Among them, the passive dispersers, like gastropods, are good sentinels of pond biodiversity changes because o f their complete dependency on aquatic habitats and their weak colonization ability. W e evaluated the potential response ofthe local biodiversity to global change in alpine and subalpine ponds in the Swiss Alps by modelling the changes in gastropod species richness according to 7 different global change scenarios.