A hierarchical framework for stream habitat classification: Viewing streams in a watershed context

Environmental Management - Classification of streams and stream habitats is useful for research involving establishment of monitoring stations, determination of local impacts of land-use practices,...     

Utility of laboratory streams for ecosystem toxicity studies

Laboratory stream microcosms have been used to study transport, fate, and effects of toxic substances in stream ecosystems. Several general concerns exist in utilizing laboratory streams in this way. We summarize some of the most important and difficult of these problems and endeavor to provide theoretical understanding, evaluation, and empirical approaches necessary for making laboratory stream ecosystem studies more useful in solving problems of toxic substance behavior in natural stream ecosystems. Well-designed laboratory streams and other microcosms are complex dynamic systems that can contribute to our understanding of the behavior of toxic substances. But such systems are far too complex and dynamic to be employed as bioassay, monitoring, or predictive tools, as individual organisms have been.     

Compartmentalization of metals within the diverse colloidal matrices comprising activated sludge microbial flocs

Activated sludge floc from a wastewater treatment system was characterized, with regard to principal structural, chemical, and microbiological components and properties, in relation to contaminant-colloid associations and settling. Multiscale analytical microscopies, in conjunction with multimethod sample preparations, were used correlatively to characterize diverse colloidal matrices within microbial floc. Transmission electron microscopy, in conjunction with energy dispersive spectroscopy (EDS), revealed specific associations of contaminant heavy metals with individual bacterial cells and with extracellular polymeric substances (EPS). Floc structure was mapped from the level of gross morphology down to the nano-scale, and flocs were described with respect to settling properties, size, shape, density, porosity, bound water content, and EPS chemical composition; gross surface properties were also measured for correlation with principal floc features. Compartmentalization results based on 171 EDS analyses and representative high-resolution images showed that nano-scale agglomerations of (i) silver (100%) and (ii) zinc (91%) were confined almost entirely to EPS matrices while (iii) Pb (100%) was confined to intracellular granules and (iv) aluminum was partitioned between EPS matrices (41%) and intracellular matrices (59%). The results suggest that engineered changes in microbial physiology and/or in macromolecular EPS composition may influence metal removal efficiencies.     

Values Associated with Management of Yellowstone Cutthroat Trout in Yellowstone National Park

Recent emphasis on a holistic view of natural systems and their management is associated with a growing appreciation of the role of human values in these systems. In the past, resource management has been perceived as a dichotomy between extraction (harvest) and nonconsumptive use, but this appears to be an oversimplified view of natural-cultural systems. The recreational fishery for Yellowstone cutthroat trout ( Oncorhynchus clarki bouvieri ) in Yellowstone National Park is an example of the effects of management on a natural-cultural system. Although angler harvest has been drastically reduced or prohibited, the recreational value of Yellowstone cutthroat trout estimated by angling factors (such as landing rate or size) ranks above that of all other sport species in Yellowstone National Park. To maintain an indigenous fishery resource of this quality with hatchery propagation is not economically or technically feasible. Nonconsumptive uses of the Yellowstone cutthroat trout including fish-watching and intangible values, such as existence demand, provide additional support for protection of wild Yellowstone cutthroat trout populations. A management strategy that reduces resource extraction has provided a means to sustain a quality recreational fishery while enhancing values associated with the protection of natural systems.     

Hydrodynamic treatment of wastewater effluent flocs for improved disinfection

Hydrodynamic forces generated by an orifice plate under low pressure were examined as a means of disrupting flocs, in order to improve disinfection of treated wastewater effluents. Changes in cavitation conditions were found to have little impact on the extent of particle breakage in this experimental setup. The rate of strain (flow rate divided by the hole radius cubed), however, was found to be the best predictor of floc breakage. Floc breakage was not affected by changes in floc concentration, but was very sensitive to differences between flocs collected from different sources. Larger flocs (90 to 106 microm) were broken apart to a greater extent than smaller ones (53 to 63 microm). Hydrodynamic treatment decreased the viability of bacteria associated with large flocs, and also increased the ultraviolet dose response by up to one log unit (i.e., a factor of ten). Subjecting final effluent wastewaters to hydrodynamic treatment, therefore, provides a treatment strategy for conditions in which the presence of flocs limits the level of disinfection that can be achieved.