Essays on Groundwater

Abstracts are not presented with Editorials. --SFEWS Editor

Time-courses in the retention of food material in the bivalves \u3cem\u3ePotamocorbula amurensis\u3c/em\u3e and \u3cem\u3eMacoma balthica\u3c/em\u3e: significance to the absorption of carbon and chromium

Time courses for ingestion, retention and release via feces of microbial food was investigated using 2 bivalves with different feeding strategies, Potamocorbula amurensis, and Macoma balthica. The results showed 2 pathways for the uptake of food material in these clams. The first is represented by an initial label pulse in the feces. The second pathway operates over longer time periods. Inert 51Cr-labeled beads were used to determine time frames for these pathways. The first pathway, involving extracellular digestion and intestinal uptake, is relatively inefficient in the digestion of bacterial cells by P. amurensis but more efficient in M. balthica. The second pathway involving intracellular digestion within the digestive gland of both clams, was highly efficient in absorbing bacterial carbon, and was responsible for most chromium uptake. Differences in the overall retention of microbial 51Cr and 14C relate not to gut passage times but to the processing and release strategies of the food material by these 2 clams

Humic and fulvic acids: sink or source in the availability of metals to the marine bivalves \u3cem\u3eMacoma balthica\u3c/em\u3e and \u3cem\u3ePotamocorbula amurensis\u3c/em\u3e?

Humic acids (HA) and fulvic acids (FA) are common forms of organic matter in marine sediments, and are routinely ingested by deposit- and suspension-feeding animals. These compounds may be a sink for metals, implying that once metals are bound to humic substances they are no longer available to food webs. A series of experiments was conducted to quantitatively examine this premise using 2 estuarine bivalves from San Francisco Bay, USA: the suspension feeder Potarnocorbula arnurensis and the facultative deposit feeder Macoma balthica. HA and FA, isolated from marine sediments, were bound as organic coatings to either hydrous ferric oxides (HFO) or silica particles. Cd and Cr(III) were adsorbed to the organic coatings or directly to uncoated HFO and silica particles. Pulse-chase laboratory feeding experiments using 109Cd and 51Cr(III) were then conducted to determine absorption efficiencies of Cd and Cr for individual specimens using each of the particle types. The results demonstrated that: (1) absorption of Cr(III) from all types of non-living particles was consistently low (\u3c 11%). Ingested Cd showed greater bioavailability than Cr(III), perhaps due to differences in metal chemistry. (2) Bivalves absorbed Cd bound to uncoated HFO or silica particles (i.e. with no HA or FA present). (3) The presence of organic coatings on particles reduced Cd bioavailability compared with uncoated particles. (4) Both geochemical and biological conditions affected the food chain transfer of Cd. The data suggest that in marine systems inorganic and organic-coated particles are predominantly a sink for Cr in sediments. In the transfer of Cd to consumer animals, inorganic particles and humic substances can act as a link (although not a highly efficient one) under oxidized conditions

The role of bacterial exopolymer and suspended bacteria in the nutrition of the deposit-feeding clam, Macoma balthica

Potential nutritional contributions of bacterial exopolymer and suspended bacteria to the detritus feeding estuarine clam, Macoma balthica, were examined separately in laboratory 14C labelling experiments. Significant removal and assimilation of suspended bacteria by M. balthica was observed within two days, although the low clearance rates suggested planktonic bacteria may not be among its major food sources. Sediment-bound and dissolved bacterial exopolymer did not appear to be directly metabolized by M. balthica, as evidenced by the 1–2 week lag in 14C uptake into clam tissue

Challenges Facing the Sacramento–San Joaquin Delta: Complex, Chaotic, or Simply Cantankerous?

Freshwater is a scarce and precious resource in California; its overall value is being made clear by the current severe drought. The Sacramento–San Joaquin Delta is a critical node in a complex water supply system that extends throughout much of the western U.S. wherein demand is exceeding supply. The Delta also underpins a major component of the U.S. economy, helps feed a substantial part of the country, is a unique and valuable ecological resource, and is a place with a rich cultural heritage. Sustaining the Delta is a problem that manifests itself in many dimensions including the physical structure of the Delta, the conflicting demands for water, changing water quality, rapidly evolving ecological character, and high institutional complexity. The problems of the California Delta are increasingly complex, sometimes chaotic, and always contentious. There is general agreement that current management will sustain neither the Delta ecosystem nor high-quality water exports, as required under the Delta Reform Act, so there is a renewed urgency to address all dimensions of the problem aggressively. Sustainable management of the Delta ecosystem and California’s highly variable water supply, in the face of global climate change, will require bold political decisions that include adjustments to the infrastructure but give equal emphasis to chronic overuse and misuse of water, promote enhanced efficiency of water use, and facilitate new initiatives for ecosystem recovery. This new approach will need to be underpinned by collaborative science that supports ongoing evaluation and re-adjustment of actions. Problems like the Delta are formally “wicked" problems that cannot be “solved” in the traditional sense, but they can be managed with appropriate knowledge and flexible institutions. Where possible, it is advisable to approach major actions incrementally, with an eye toward avoiding catastrophic unexpected outcomes. Collaborative analyses of risks and benefits that consider all dimensions of the problem are essential. Difficult as the problems are, California has the tools and the intellectual resources to manage the Delta problem and achieve the twin goals of a reliable water supply and an ecologically diverse Delta ecosystem

COMPARISON OF SELENIUM BIOACCUMULATION IN THE CLAMS CORBICULA FLUMINEA AND POTAMOCORBULA AMURENSIS: A BIOENERGETIC MODELING APPROACH

rate) were compared between two bivalves, Corbicula fluminea and Potamocorbula amurensis. The effects of salinity and tem-perature on these kinetic parameters for both clam species also were evaluated. The Asiatic clam, C. fluminea, more efficiently assimilated Se associated with algae (66–87%) than Se associated with oxic sediments (20–37%). However, no consistent difference was found between Se assimilation efficiencies from both food types (19–60%) for P. amurensis. The temperature and salinity had a minor influence on the Se assimilation from ingested food. However, the effects of temperature and salinity were more evident in the uptake from dissolved sources. The influx rate of Se(IV) increased by threefold with the increase of temperature from 5 to 218C for C. fluminea. The increase of salinity from 4 to 20 psu decreased the uptake rate constant (ku) of Se in P. amurensis from 0.011 to 0.005 L/g/h, whereas salinity change (0–8 psu) had a negligible effect on the Se influx rate of C. fluminea. The Se influx rate of P. amurensis decreased by half with the 3.5-fold increase in tissue dry weight. The rate constant of loss was greater for P. amurensis (0.029/d at 8 psu) than for C. fluminea (0.014/d at 0 psu and 0.01/d at 8 psu). A bioenergetic model suggests that dietary uptake is the dominant pathway for Se bioaccumulation in the two clams in San Francisco Bay and that interspecies differences in Se bioaccumulation can be explained by differences in food ingestion rates

Characterisation of carbon nanotubes in the context of toxicity studies

Nanotechnology has the potential to revolutionise our futures, but has also prompted concerns about the possibility that nanomaterials may harm humans or the biosphere. The unique properties of nanoparticles, that give them novel size dependent functionalities, may also have the potential to cause harm. Discrepancies in existing human health and environmental studies have shown the importance of good quality, well-characterized reference nanomaterials for toxicological studies

Genetic susceptibility of intervertebral disc degeneration among young Finnish adults

<p>Abstract</p> <p>Background</p> <p>Disc degeneration (DD) is a common condition that progresses with aging. Although the events leading to DD are not well understood, a significant genetic influence has been found. This study was undertaken to assess the association between relevant candidate gene polymorphisms and moderate DD in a well-defined and characterized cohort of young adults. Focusing on young age can be valuable in determining genetic predisposition to DD.</p> <p>Methods</p> <p>We investigated the associations of existing candidate genes for DD among 538 young adults with a mean age of 19 belonging to the 1986 Northern Finland Birth Cohort. Nineteen single nucleotide polymorphisms (SNP) in 16 genes were genotyped. We evaluated lumbar DD using the modified Pfirrmann classification and a 1.5-T magnetic resonance scanner for imaging.</p> <p>Results</p> <p>Of the 538 individuals studied, 46% had no degeneration, while 54% had DD and 51% of these had moderate DD. The risk of DD was significantly higher in subjects with an allele G of <it>IL6 </it>SNPs rs1800795 (OR 1.45, 95% CI 1.07-1.96) and rs1800797 (OR 1.37, 95% CI 1.02-1.85) in the additive inheritance model. The role of <it>IL6 </it>was further supported by the haplotype analysis, which resulted in an association between the GGG haplotype (SNPs rs1800797, rs1800796 and rs1800795) and DD with an OR of 1.51 (95% CI 1.11-2.04). In addition, we observed an association between DD and two other polymorphisms, <it>SKT </it>rs16924573 (OR 0.27 95% CI 0.07-0.96) and <it>CILP </it>rs2073711 in women (OR 2.04, 95% CI 1.07-3.89).</p> <p>Conclusion</p> <p>Our results indicate that <it>IL6</it>, <it>SKT </it>and <it>CILP </it>are involved in the etiology of DD among young adults.</p

San Francisco Estuary and Watershed Science: Next Steps

Abstracts are not presented with Editorials. -SFEWS Editor