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Abstracts are not presented with Editorials. --SFEWS Editors

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.

Ferrihydrite and a vernadite-like mineral, in samples collected from the riverbeds and floodplains of the river draining the largest mining-contaminated site in the United States (the Clark Fork River Superfund Complex), have been studied with transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis. These poorly crystalline minerals are environmentally important in this system because contaminant heavy metals (As, Cu, Pb, and/or Zn) are always associated with them. Both two- and six-line ferrihydrite have been identified with selected area electron diffraction. For the vernadite-like mineral, the two d values observed are approximately between 0.1 and 0.2 A larger than those reported tier vernadite, the Mn hydrous oxide that is thought to have a birnessite-like structure, but which is disordered in the layer stacking direction. In several field specimens, the ferrihydrite and vernadite-like minerals are intimately mixed on the nanoscale, but they also occur separately. It is suggested that the vernadite-like mineral, found separately, is produced biogenically by Mn-oxidizing bacteria, whereas the same mineral associated with ferrihydrite is produced abiotitally via the heterogeneous oxidation of [Mn.sup.2+.sub.aq] initially on ferrihydrite surfaces. Evidence from this study demonstrates that the vernadite like mineral sorbs considerably more toxic metals than does ferrihydrite, demonstrating that it may be a good candidate for application to heavy-metal sorption in permeable reactive barriers.

The rates of change in hyporheic microbial communities in response to heavy-metal contamination were determined and group-level differences in resiliency in response to heavy metals were assessed. Studies indicate that hyporheic microbial communities are sensitive and useful indicator of heavy-metal contamination in streams.

The impact of dam removal on the ice regime of northern rivers has largely been ignored in the recent push for removal of dams to restore or improve aquatic habitat. However, dam removal may have significant impacts on the ice regime and has resulted in increased frequency and severity of downstream jams. Lowering of water levels in impoundments containing sediment deposits may result in more frequent or longer duration ice-induced scour and erosion of bed and bank material. Ice-related adverse impacts associated with dam removal can be mitigated through ice control measures. This paper presents a brief overview of the evolution of the typical ice regime, followed by a discussion of potential impacts resulting from dam removal. Examples of the impact of dam removal on riverine ice regime are presented, including two case studies in which dam removal has required the later construction of ice control structures. Recommendations are made for supplemental studies, when dam removal is considered in ice-affected rivers. CE Database keywords: Dams; Ice; Cold regions; Rivers.

This study offers data on the behavior of dimethylselenide (DMSe) in soil.

A study aimed at investigating the rates of selenium volatilization, particularly in wetland systems, is presented. Water samples from Benton Lake, MT are examined to determine their natural selenium volatilization. It was found out that selenium volatilization happened in water, sediment, and wetland plants. It was noted that algae and high-selenium sediment register a higher rate of selenium volatilization than watermilfoil and low-selenium sediment. It is believed that efforts in removing selenium in wetland systems can benefit from natural selenium volatilization process.

Selenium is a leading contaminant of natural water systems especially lakes and reservoirs. Bioaccumulation of selenium in organisms living in these waters poses serious harm to fish and waterfowl. The movement and toxicity of selenium depend on its oxidation states, which are mediated by microbes. Selenium fractionation studies at a wetland ecosystem separated major selenium species biogeochemical cycling. Selenium is removed from the water as the microbes oxidize selenate to elemental selenium.

Diel cycling of trace metals is controlled by photoreduction and pH-dependent adsorption-desorption processes. Trace metals are highly abundant in bed and flood plain sediments in upper Clark Fork River, MT. Hourly sampling of samples from the river identified several major and trace elements. Analytical methods reveal diel variation in dissolved manganese and zinc, and acid-soluble particulate aluminum, iron, manganese, copper and zinc. The elements are present in higher concentrations at night due to increased total suspended matter at night. This increase is accompanied by increased pH and dissolved oxygen.

A method for modeling the downstream dispersion of metal anomalies based on dilution mixing of anomalous and tributary sediments can help quantify the extent of metal contamination in rivers and to set realistic remediation goals. Quantification is made possible by allowing calculation of the dispersion curves of metals in stream sediments both before and after mining. Quantification of any anthropogenic exaggeration of an anomaly is also allowed. The model is designed to provide accurate approximations of natural and exaggerated dispersion trains.

The geochemical characteristics of the hyporheic zone in the bed sediment of Silver Bow Creek in Montana were investigated using a unique, in situ technique. The results indicated that the thickness of the hyporheic zone was due to the 96:4 mixing ratio of surface water to contaminated ground water. It is suggested that the hyporheic zone acts as a sink for metals and that there is a significant degree of metal loading to the bed sediment.

Research has been conducted on relationship between hyporheic microbial community structure and fluvially deposited heavy metal concentration in river sediments. The authors describe the study of this relationship carried out via the use of denaturing gradient gel electrophoresis, 16S rRNA gene phylogenetic analysis, quantitative PCR and phospholipid fatty acid analysis.