Energy flows in the coffee plantations of Costa Rica: from traditional to modern systems (1935–2010)

Regional Environmental Change - This article addresses energy flows in the coffee agro-ecosystems of Costa Rica within the context of the socio-ecological transition, between 1935 and 2010,...     

Biomonitoring heavy metals in estuaries: a field comparison of two brown algae species inhabiting upper estuarine reaches

Biomonitoring dissolved heavy metals within estuaries,particularly at their upper reaches, frequently has to relyon several biomonitors; rarely a single species thrives allalong the salinity gradient. To properly do so, it must beestablished whether those biomonitors actually accumulateheavy metals alike. In this study, two brown seaweeds fromthe upper section of three NW Spain estuaries – the widely-known Fucus vesiculosus and the estuarine Fucusceranoides – were compared as metal biomonitors. Bothspecies were collected at five locations where they eithercoexist or live close to each other and their heavy metalcontent (Cu, Cr, Mn, Zn, Fe, Al) was measured. Analyseswere appropriately replicated for each species x locationcombination to allow a statistically reliable detection ofdifferences in bioaccumulation, with particular emphasis onthe magnitude of interspecific differences. The lack of significant differences for Cu, Mn, and Zncontents in F. ceranoides and F. vesiculosussupports the feasibility of their joint use to monitorthese metals along the estuaries. Conversely, F.ceranoides concentrated significantly higher levels of Cr,Fe, and Al than F. vesiculosus and hence combiningdata for both fucoids to monitor these elements seemsimpractical. The correlation of species differencestogether with a similar Al:Fe ratio in both weed tissue andsediment suggest that Cr, Fe, and Al tissue-burdens mightbe considerably biased by sediment retained on the surfaceof the weed. Parallel analyses of Al and/or Fe in seaweedsand sediments could serve to keep track of thisinterference and may help to combine data from both fucoidsfor monitoring elements like Cr.     

Mercury sorption to sediments: dependence on grain size, dissolved organic carbon, and suspended bacteria

A combination of laboratory scale derived correlations and measurements of grain size distribution, DOC (dissolved organic carbon) concentration, and density of suspended bacteria promises to be useful in estimating Hg(II) sorption in heterogeneous streambeds and groundwater environments. This was found by shaking intact sediment and fractions thereof (<63-2000mum) with solutions of HgCl(2) (1.0-10.0ngml(-1)). The intact sediment was also shaken with the Hg(II) solutions separately in presence of DOC (6.5-90.2mugml(-1)) or brought in contact with suspensions of a strain of groundwater bacteria (2x10(4)-2x10(6)cellsml(-1)). Hg(II) sorption was rather weak and positively correlated with the grain size, and the sorption coefficient (K(d)) varied between about 300 and 600mlg(-1). By using the relative surface areas of the fractions, K(d) for the intact sediment was back calculated with 2% deviation. K(d) was negatively correlated with the concentration of DOC and positively correlated with the number of bacteria. A multiple regression showed that K(d) was significantly more influenced by the number of bacteria than by the grain size. The findings imply that common DOC concentrations in groundwater and streambeds, 5-20mugml(-1), will halve the K(d) obtained from standard sorption assays of Hg(II), and that K(d) will almost double when the cell numbers are doubled at densities that are common in aquifers. The findings suggest that simultaneous measurements of surface areas of sediment particles, DOC concentrations, and bacterial numbers are useful to predict spatial variation of Hg(II) sorption in aquifers and sandy sediments.