Is eutrophication really a major impairment for small waterbody biodiversity?

Abstract

Summary1. 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. 2. 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. 3. 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. 4. 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.

Intense ranchland management tips the balance of regional and local factors affecting wetland community structure

“…Soil nutrients also affected wetland communities, likely as a result of direct effects on vegetation (Bloom, 1985) and indirect effects on vertebrates. Eutrophication is well known to reduce diversity, although the effect varies among taxa (Keddy, 2010;Kneitel and Lessin, 2010;Rosset et al, 2014). Moreover, eutrophication can facilitate introduced species where background nutrient levels were previously low (Káplová et al, 2010), as in the sandy soils of MAERC.…”

“…non-point source pollution) on aquatic communities. Different taxa (e.g., plants and insects) should exhibit very different responses to anthropogenic disturbance and it is likely inadequate to expect results from one taxon to translate well to another (Rosset et al, 2014;Söderström et al, 2001;Zulka et al, 2014). For instance, ectothermic vertebrate composition was more sensitive to eutrophication among semi-natural wetlands than other taxa.…”

Review: Toward management of urban ponds for freshwater biodiversity

“…However, they may still support a rich biodiversity adapted to these conditions (Rosset et al. ). An excess of allochthonous inputs of nutrients can lead to a deterioration of habitat conditions which may only support a selection of resistant species (e.g., tolerant of anoxic conditions).…”

Assessing the ecological integrity of endorheic wetlands, with focus on Mediterranean temporary ponds

“…Aquatic plants respond directly (through competition for light and nutrients) or indirectly (through food web interactions) to changes in water quality. Especially eutrophication is a major stressor for aquatic biodiversity, and particularly for macrophytes, as shown by Rosset et al (2014). Bornette and Puijalon (2011) reviewed the different responses to abiotic factors of aquatic plants in freshwater habitats.…”

“…Additionally, ponds within one single region are often characterized by different communities and environmental characteristics and contribute therefore to high beta-diversity in space Angeler et al, 2008), which makes it difficult to find general indicator species. Therefore, conserving and monitoring networks of temporary ponds instead of focussing on single ponds was suggested to be more accurate and efficient (Gómez-Rodríguez et al, 2009;Rhazi et al, 2012;Rosset et al, 2014).…”