Case study on the efficacy of a lanthanum-enriched clay (Phoslock®) in controlling eutrophication in Lake Het Groene Eiland (The Netherlands)

Lake Het Groene Eiland was created in the beginning of 2008 by construction of dikes for isolating it from the surrounding 220-ha water body. This so-called claustrum of 5 ha was treated using lanthanum-modified clay (Phoslock®) to control eutrophication and mitigate cyanobacterial nuisance. Cyanobacteria chlorophyll-a were significantly lower in the claustrum than those in the reference water body, where a massive bloom developed in summer, 2008. However, PO4-P and TP did not statistically differ in these two waters. TN and NO3-N were significantly lower in the claustrum, where dense submerged macrophytes beds developed. Lanthanum concentrations were elevated after the applications of the modified clay in the claustrum, but filterable lanthanum dropped rapidly below the Dutch standard of 10.1 μg l−1. During winter, dozens of Canada geese resided at the claustrum. Geese droppings contained an average of 2 mg PO4-P g−1 dry weight and 12 mg NH3-N g−1 dry weight and might present a growing source of nutrients to the water. Constructing the claustrum enabled unrestricted bathing in subsequent three summers, as no swimming bans had to be issued due to cyanobacteria blooms. However, the role of the modified clay in this positive outcome remains unclear, and longevity of the measures questionable.

Disturbance and diversity at two spatial scales

The spatial scale of disturbance is a factor potentially influencing the relationship between disturbance and diversity. There has been discussion on whether disturbances that affect local communities and create a mosaic of patches in different successional stages have the same effect on diversity as regional disturbances that affect the whole landscape. In a microcosm experiment with metacommunities of aquatic protists, we compared the effect of local and regional disturbances on the disturbance–diversity relationship. Local disturbances destroyed entire local communities of the metacommunity and required reimmigration from neighboring communities, while regional disturbances affected the whole metacommunity but left part of each local community intact. Both disturbance types led to a negative relationship between disturbance intensity and Shannon diversity. With strong local disturbance, this decrease in diversity was due to species loss, while strong regional disturbance had no effect on species richness but reduced the evenness of the community. Growth rate appeared to be the most important trait for survival after strong local disturbance and dominance after strong regional disturbance. The pattern of the disturbance–diversity relationship was similar for both local and regional diversity. Although local disturbances at least temporally increased beta diversity by creating a mosaic of differently disturbed patches, this high dissimilarity did not result in regional diversity being increased relative to local diversity. The disturbance–diversity relationship was negative for both scales of diversity. The flat competitive hierarchy and absence of a trade-off between competition and colonization ability are a likely explanation for this pattern

The role of the freshwater shrimp atyaephyra desmarestii in leaf litter breakdown in streams

This version does not correspond to the published one. To access the final version go to: http://www.springerlink.com/content/a31518u452m03286/In aquatic ecosystems, microorganisms and invertebrates provide critical links between plant detritus and higher trophic levels. Atyaephyra desmarestii is an omnivorous decapod that inhabits freshwaters and exhibits high tolerance to temperature oscillations and high ability to colonize new habitats. Although A. desmarestii is able to ingest a variety of foods, few studies have been conducted to elucidate the role of this freshwater shrimp on detritus breakdown in streams. In this study, A. desmarestii was allowed to feed on conditioned or unconditioned alder and eucalyptus leaves in microcosms with or without access to its fecal pellets. At the end of the experiment, total body length of the animals was measured, and the remaining leaves and fecal pellets were used for dry mass quantification and assessment of bacterial and fungal diversity by denaturing gradient gel electrophoresis (DGGE). Cluster analyses of DGGE fingerprints indicated that the major differences in microbial communities on leaves were between leaf types, while on fecal pellets were between conditioned and unconditioned leaves. However, the consumption rate by the shrimp did not differ between leaf types, and was significantly higher on leaves conditioned by microorganisms and in treatments without access to feces. In treatments without access to feces, the production of feces and fine particulate organic matter was also significantly higher for conditioned leaves. Overall, our results support the feeding plasticity of A. desmarestii and its potential role in plant litter breakdown in streams. This might have implications for maintaining stream ecosystem functioning, particularly if more vulnerable shredders decline.The Portuguese Foundation for the Science and Technology supported S. Duarte (SFRH/BPD/47574/2008

Seasonal changes in caddis larvae assemblages in river-floodplain habitats along a hydrological connectivity gradient

Contains fulltext : 117225.pdf (preprint version ) (Open Access