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The influence of epipsammic biofilm developed on riverbed sediment on the sorption, uptake, mobility and transformation of As was studied. Native biofilm was incubated on sediment samples at microcosm level. Once the biofilm had developed, 500 µg L As was spiked in two systems designated BAS and BASP, without P and with equimolar As:P concentration ratio, respectively, and compared with identical control (sterilized) systems (CAS and CASP). The evolution and speciation of arsenic (As) concentrations in the overlying water were followed during two additional weeks. The biofilm enhanced removal of As from the water up to 91 % of its initial concentration, while only ~70 % removal was attained in CAS. Presence of equimolar P concentration enhanced the amount of As removal up to 97 % in BASP, but had no effect in CASP. In the systems with biofilm, As was mostly (~97 %) in As form, whilst As only accounted for ~1 % of total aqueous As. The organic species, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), represented 0.6 and 0.7 % of total As, respectively. In contrast, in the systems devoid of biofilm, As accounted for up to 39 % of aqueous As, whereas methylated aqueous species were negligible. The distribution of As in the biofilm showed that ~71 % of the retained As was extracellular, most (>99.5 %) in the form of As. Volatile As forms were only detected in the systems incorporating biofilm. It is concluded that biofilm covering sediments increases As retention, inhibits reduction of As to As and methylates inorganic As, thus playing a key role in the biogeochemistry of As in river environments. [ABSTRACT FROM AUTHOR]

In this study, five cores of the Anllóns River bed sediments were analyzed in order to evaluate the downcore and downstream variations in their chemical composition. The first step was the evaluation of the metal distribution in the bulk (<2 mm) and fine fractions (<63 μm). The analysis revealed that most of the metals followed the same trend in both fractions, although the fine fraction presented usually higher concentrations. However, the concentration of both fractions tended to equalize with increasing contamination. No general increase was observed in the metal concentrations toward the surface which could be attributed to recent anthropogenic contributions. Instead, the distributions were homogeneous or peaked at various depths downcore. The most important historical feature was observed at the mouth of the river, at 96-cm depth, corresponding to the end of the eighteenth century. Upcore increased metal concentrations in parallel with increased fine fraction occurred from this depth, which were attributed to a bridge construction and consequent changes in sediment dynamics. As the metal concentrations can be influenced by variations in texture or other sediment characteristics, the second step was to evaluate the efficiency of several normalized indexes in the assessment of the degree of contamination, by calculating the enrichment factor (EF), the geoaccumulation index ( I) and the pollution load index (PLI). The EFs obtained were <10, thus revealing little anthropogenic inputs to the basin. The I produced higher values when compared with the EFs. Instead of absolute EF or I absolute values, the use of cumulative probability plots allowed identifying more accurately potential outliers indicating contamination. Only one population was identified for Zn and Pb, with a reduced number of outliers at the highest concentrations for Pb. As shown, a more complex plot with the outliers identified at C4 and C5. Finally, the PLI allowed determining the absence of a significant contamination in the bed sediments. The bioavailable and non-geogenic fractions contribute up to a 90% of the total concentrations in the case of As and Cu, and showed similar (dissimilar) profiles in comparison with total metals. Also, the quality guidelines were surpassed, so the high solubility of As, Zn, Pb and Ni in the sediments revealed the need to monitor the bed sediment quality of the Anllóns River. [ABSTRACT FROM AUTHOR]

Phytopigment estimation has a considerable interest in the evaluation of freshwater bodies’ quality, because it takes into account the synergistic effect of nutrients like phosphorus or nitrogen on algal growth producing eutrophication. Furthermore, their increasing concentration constitutes the first step in the formation of biofilms on the surface sediments, adding a new and very important element to the dynamic nature of the surface sediments. In this study the distribution of phytoplankton—in terms of chlorophyll- a, chlorophyll- b, phaeophytin- a, phaeophytin- b, total carotenoids, total chlorophyll, and total phaeophytin—was evaluated in river bed sediments. Samples collected at sites with low levels of nutrients (P,N) and metal concentrations showed lower phytopigment concentrations than those collected at the sampling sites affected by sources of pollution. Phytoplankton concentrations were directly and highly related to the organic matter concentrations—in particular to the humic fraction—as well as to the total nitrogen (N), total phosphorus ( PT) and available phosphorus ( PA) concentrations in sediments. In addition, phytoplankton also correlates positively with Cu, Zn, Fe and Al extracted in oxalate, being Cu the variable that most influences the phytopigment growth. These are essential metals for the metabolism of the phytoplankton, so therefore the increase in metal concentrations can increase algal growth, unless they reach toxic levels. [ABSTRACT FROM AUTHOR]

The Anllóns basin (NW Spain) has been included in the Natura 2000 Network and declared as Site of Community Importance. The main contamination problems of the basin come from a former gold mine and from agricultural activities, which influence the quality of the sediment–water system. Phosphorus (P) enrichment in the bed sediments was evaluated by analyzing P in the pore waters, in the surface bed sediments, and in the vertical sediment profiles, including both total and bioavailable forms. Two granulometric fractions (<2 mm and <63 μm) were evaluated. Pore waters, bed sediments, and vertical profiles showed high percentages of the bioavailable P fraction with respect to the total P content, which evidences the potential risk of pollution which suppose the bed sediments of the Anllóns River. The vertical profiles showed P enrichment in the superficial layers, which could be the consequence of the increased use of fertilizers in the last decades. With regards to the granulometric distributions, the <63 μm showed, in general, higher P concentrations than the <2 mm fraction. However, at the sampling points most heavily contaminated, the concentration of both fractions becomes similar, thus indicating that, at these sites, the coatings formed over sands can retain important P concentrations in the bed sediments. [ABSTRACT FROM AUTHOR]

The arsenic bioavailability in the bed sediments from the Anllóns River (NW Spain) has been assessed by using several analytical approaches. A six-step sequential fractionation was compared to three general availability tests: the Toxicity Characteristic Leaching Procedure (TCLP) extraction, which estimates the leaching potential of As and its effect on the survival of microorganisms ( Vibrio fischeri), an extraction with 1 M HCl extraction, which estimates the bioavailability to higher plants, and a physiologically based extraction test (PBET), which estimates the bioavailability to superior animals. Arsenic was found to be mainly associated to the least mobile fractions: bound to Fe-Al oxides and in the residual phase. Among the three single extractants considered, the PBET extracted the highest As concentrations (1–11% of the total As). The TCLP extracts showed toxicity to Vibrio fischeri whereas for the plants evaluated, aqueous extracts did not show adverse effects. [ABSTRACT FROM AUTHOR]

Two methods of environmental toxicological tests were compared and applied to bed sediments of the Anllóns River: the standardized toxicological test based on inhibition of luminescence employing Vibrio fischeri, and a phytotoxicity test, using garden cress ( Lepidium sativum L. ), water cress ( Nasturtium officinalis L. ) and annual rye-grass ( Lolium multiflorum L. ) seeds. In addition, TCLP and HCl extracts were evaluated. The inhibition of luminescence test showed more sensitivity to toxicants than phytotoxicity assays, and no significant correlations were found between them. On the other hand, TCLP metal concentrations (Fe, Al, Zn, Pb, As) were lower than HCl concentrations, but seemed to represent more accurately the phytoavailability of metals to plants. [ABSTRACT FROM AUTHOR]