Guiding principles for the development and application of solid-phase phosphorus adsorbents for freshwater ecosystems

While a diverse array of phosphorus (P)-adsorbent materials is currently available for application to freshwater aquatic systems, selection of the most appropriate P-adsorbents remains problematic. In particular, there has to be a close correspondence between attributes of the P-adsorbent, its field performance, and the management goals for treatment. These management goals may vary from a rapid reduction in dissolved P to address seasonal enrichments from internal loading, targeting external fluxes due to anthropogenic sources, or long term inactivation of internal P inventories contained within bottom sediments. It also remains a challenge to develop new methods and materials that are ecologically benign and cost-effective. We draw on evidence in the literature and the authors’ personal experiences in the field, to summarise the attributes of a range of P-adsorbent materials. We offer 'guiding principles' to support practical use of existing materials and outline key development needs for new materials

Effects of Ca(OH)(2) additions on phytoplankton communities under ice cover in eutrophic hardwater lakes

The effects of Ca(OH)(2) treatment during the open-water season on phytoplankton communities under ice cover were examined for up to three winters (Nov. Apr.) in three eutrophic hardwater lakes in central Alberta. Phytoplankton communities were compared between treated and untreated lakes, and between pre- and posttreatment periods within a treatment lake. In all study lakes, phytoplankton biomass tended to be high at ice-on, decrease after November, and remain low (< 2mg/L) from January to early March, when light conditions and water temperatures were also low. After late March to early April, phytoplankton biomass started to increase exponentially because of higher light conditions and water temperature. Most phytoplankton species that were common under ice also occurred during the open-water season. Although phytoplankton species composition was diverse under ice, the biomass of most species, except for flagellates, did not increase before mid-March. Species composition and biomass of some phytoplankton groups varied without clear trends among winters in treated and untreated lakes. Therefore, Ca(OH)(2) treatment during the open-water season did not appear to affect winter phytoplankton communities

The relevance of size parameters as indicators of fishery exploitation in two West African reservoirs

Fish communities living within the artificial reservoirs of Manantali and Selingue in Mali are compared after the monitoring of small-scale fishery landings over 13 months (May 2002-June 2003). The fishing pressure constitutes the main difference of these two similar reservoirs. The effects of fishing on the structure of the fish communities are analyzed by using fish size spectra and derived indicators. In Selingue Reservoir, the fishing gears mostly target smaller species (mean length of 165 mm) than in Manantali Reservoir (mean length of 210 mm). Unlike in Selingue, the size structure does not change between seasons in Manantali. In Selingue, fishing practices that target the fish recruitment of the year constitute a structuring factor of the fish sizes observed in the catches. In spite of similar values of the slopes of the global fish communities' size spectra between the two reservoirs, they clearly display an intense exploitation at Selingue. Then, size-based spectra indicators represent a potential tool for assessing the impact of fishing on fish communities in small-scale fisheries