Arsenic in the environment

Arsenic, long synonymous in people's mind with poison exhibits a varied, fascinating and dynamic biogeochemistry. Chemically and biologically reactive, its chemical form, or speciation, changes with slight variations in chemical or biological conditions. Depending upon the extent to which any arsenic containing system is dominated by physical/chemical or biological process, the forms of arsenic may change between the various in organic and methylated species, and may alter rapidly with varying conditions. Early research revolved around the formulation of pigments, and later in the development of effective medicines. Later still, thanks due to its long history as a poison, arsenic was included in numerous agricultural practices, mainly as a herbicide or pesticide. It has also seen service in the rather more specialised field of chemical warfare, and still poses threats as a result of improper disposal. Much of the recent research has focused on the identification of previously unknown organoarsenic species found in estuarine and marine waters. This work is building up an understanding of the biological pathways involved in the biochemical cycling of arsenic. Little work has been carried out with respect to the cycling of arsenic in freshwaters in comparison to that in marine and estuarine waters. Similarly, there has been less work performed on the speciation of arsenic in freshwater sediment interstitial waters, than there has on marine sediments, or intertidal sediments. The characterisation of arsenic in dynamic porewater poses a set of unusual and difficult problems, not the least being the procurement of representative, discrete samples. A number of potential sampling methods are reviewed, and variations on the thin film gel sampling technique are drought to provide perhaps the best option, although this will depend upon the type of intertidal sediment being investigated, and the information sought. It may be impossible to propose a general model of arsenic cycling either at a local scale or at a global level. This is of course due to the great diversity in ecosystems, each having different controls over arsenic speciation, and containing different biological communities. Once a given system has been described, the patterns of arsenic speciation (both spatially and temporally) are explainable, and potential impacts can be identified, but (hey cannot be transferred to another system. The continuing accumulation of information regarding arsenic speciation in different systems is helping in the unravelling of the larger global arsenic cycle. Such an understanding can only be a benefit in the development of safe and efficient remediation schemes for contaminated soil and aquatic systems

Temperature effects on periphyton, epiphyton and epipelon under a nitrogen pulse in low-nutrient experimental freshwater lakes

The ongoing global climate change involves not only increased temperatures but may also produce more frequent extreme events, such as severe rainfall that could trigger a pulse of nutrients to lakes. In shallow lakes, this may affect primary producers through a number of direct and indirect mechanisms. We conducted a six-month mesocosm experiment to elucidate how periphyton (on inert substrata), epiphyton and epipelon biomass responded to a nitrogen (N) pulse, an approximately tenfold enrichment of the NO3-pool, under three contrasting warming scenarios: ambient temperature and ca. +3°C and ca. +4.5°C elevated temperatures (hereafter T1, T2 and T3). After the N pulse, we found a higher periphyton biomass at elevated than at ambient temperatures but no change in epiphyton biomass. Epipelon biomass was lower in T3 than in T1. Both periphyton and epiphyton biomasses correlated negatively with snail biomass, while epiphyton biomass correlated positively with light. Different responses to higher temperatures under short-term extreme nutrient loading conditions may be attributed to differences in the access to nutrient sources and light. Our data suggest that the biomass of periphyton in oligotrophic clear-water lakes will increase significantly under conditions exhibiting short-term extreme nutrient loading in a warmer climate.Fil: Cao, Yu. University Aarhus; Dinamarca. Chinese Academy of Sciences; República de ChinaFil: Olsen, Saara. Sino-danish Centre For Education And Research (sdc); China. University Aarhus; DinamarcaFil: Gutierrez, Marìa Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Brucet, Sandra. Institucio Catalana de Recerca I Estudis Avancats; . University Aarhus; Dinamarca. Universitat de Vic;Fil: Davidson, Thomas A.. University Aarhus; DinamarcaFil: Li, Wei. Chinese Academy of Sciences; República de China. Sino-danish Centre For Education And Research (sdc); ChinaFil: Lauridsen, Torben L.. University Aarhus; Dinamarca. Sino-danish Centre For Education And Research (sdc); ChinaFil: Søndergaard, Martin. University Aarhus; DinamarcaFil: Jeppesen, Erik. University Aarhus; Dinamarca. Sino-danish Centre For Education And Research (sdc); Chin