High-resolution freshwater dissolved calcium and pH data layers for Canada and the United States.

Freshwater ecosystems are biologically important habitats that provide many ecosystem services. Calcium concentration and pH are two key variables that are linked to multiple chemical processes in these environments, influence the biology of organisms from diverse taxa, and can be important factors affecting the distribution of native and non-native species. However, it can be challenging to obtain high-resolution data for these variables at regional and national scales. To address this data gap, water quality data for lakes and rivers in Canada and the continental USA were compiled and used to generate high-resolution (10 × 10 km) interpolated raster layers, after comparing multiple spatial interpolation approaches. This is the first time that such data have been made available at this scale and resolution, providing a valuable resource for research, including projects evaluating risks from environmental change, pollution, and invasive species. This will aid the development of conservation and management strategies for these vital habitats.

Changes in infaunal assemblage structure influence nutrient fluxes in sediment enriched by mussel biodeposition.

Although many studies have described the influence of bivalve aquaculture on the benthic environment, effects on benthic functional diversity are poorly known, as are links with ecosystem processes. We investigated the response of a benthic ecosystem in terms of taxonomic and functional diversity (infauna >500 µm), biogeochemical indicators (organic matter content, redox potential, sulfides level, bacteria) and metabolism (nutrient fluxes), subjected to various levels of mussel biodeposition as a general model of organic enrichment. Results show that local benthic conditions may recover fairly quickly depending on environmental conditions whereas modifications of the benthic community structure persist over a longer time scale with an impact on benthic ecosystem functioning. Fauna-mediated oxidation of the sediment likely increased nitrogen recycling through nitrification whereas binding and release of phosphorus to the water column seems to be driven by more complex processes. Results highlight the importance of species identity (ecological traits) on biogeochemical cycling and solute exchange across the sediment-water interface, with implications for the ecological functioning of exploited areas.

Relationship between propagule pressure and colonization pressure in invasion ecology: a test with ships' ballast.

Increasing empirical evidence indicates the number of released individuals (i.e. propagule pressure) and number of released species (i.e. colonization pressure) are key determinants of the number of species that successfully invade new habitats. In view of these relationships, and the possibility that ships transport whole communities of organisms, we collected 333 ballast water and sediment samples to investigate the relationship between propagule and colonization pressure for a variety of diverse taxonomic groups (diatoms, dinoflagellates and invertebrates). We also reviewed the scientific literature to compare the number of species transported by ships to those reported in nature. Here, we show that even though ships transport nearly entire local communities, a strong relationship between propagule and colonization pressure exists only for dinoflagellates. Our study provides evidence that colonization pressure of invertebrates and diatoms may fluctuate widely irrespective of propagule pressure. We suggest that the lack of correspondence is explained by reduced uptake of invertebrates into the transport vector and the sensitivity of invertebrates and diatoms to selective pressures during transportation. Selection during transportation is initially evident through decreases in propagule pressure, followed by decreased colonization pressure in the most sensitive taxa.