Comparison of Streambed Sediment and Aquatic Biota as Media for Characterizing Trace Elements and Organochlorine Compounds in the Willamette Basin, Oregon

During 1992–93, 27 organochlorine compounds (pesticides plus total PCB) and 17 trace elements were analyzed in bed sediment and aquatic biota from 20 stream sites in the Willamette Basin as part of the U.S. Geological Survey's National Water-Quality Assessment Program. Data from each medium were compared to evaluate their relative effectiveness for assessing occurrence (broadly defined as documentation of important concentrations) of these constituents. Except for Cd, Hg, Se, and Ag, trace element concentrations generally were higher in bed sediment than in biota. Conversely, although frequencies of detection for organochlorine compounds in biota were only slightly greater than in bed sediment, actual concentrations in biota (normalized to lipid) were as much as 19 times those in sediment (normalized to organic carbon). Sculpin (Cottus spp.) and Asiatic clams (Corbicula fluminea), found at 14 and 7 sites, respectively, were the most widespread taxa collected during the study. Concentrations of trace elements, particularly As and Cu, were typically greater in Asiatic clams than in sculpin. In contrast, almost half of the organochlorine compounds analyzed were found in sculpin, but only DDT and its degradation products were detected in Asiatic clams; this may be related to the lipid content of sculpin, which was about three times higher than for clams. Thus, the medium of choice for assessing occurrence depends largely on the constituent(s) of interest.     

Habitat Conditions and Correlations of Sediment Quality Triad Indicators in Delaware Bay

This paper summarizes sampling results from NOAA's National Status and Trends (NS&T) Program for marine environmental quality in Delaware Bay. A stratified-random design was used to determine the spatial extent of sediment contamination and toxicity in Delaware Bay from offshore stations in the coastal zone, the lower estuary, the upper estuary, the fresh/salt mixing zone, and tidal fresh areas. Sediment samples were taken for chemical analyses of major classes of environmental contaminants, a suite of toxicity bioassays, and benthic macrofaunal community assessment to identify patterns of resident species. The tidal-fresh areas and portions of the mixing zone of the study area were heavily contaminated. Contaminant concentrations were frequently above the 90th percentile of EMAP Virginian Province levels. PAHs in the sediment were higher than previously documented, with a major component of PAHs being pyrogenic in origin. Bioassay results were highly variable. Toxicity and contaminant levels were correlated when aggregated into indices, but were only marginally correlated with benthic community impacts. High and low abundance stations were found in all zones. Most of the tidal fresh stations were dominated by pollution tolerant species. Species diversity and abundance were generally lowest in the fresh/salt mixing zone.     

Initial Adjustments Within a New River Channel: Interactions Between Fluvial Processes, Colonizing Vegetation, and Bank Profile Development

A conceptual model of the morphological development of the riparian margins of newly cut river channels is presented, suggesting early feedbacks between vegetation growth and bank form. To test the model, observations of long and cross profiles, bank sediment and seed deposition, and bank vegetation development were collected over the first 2 years of river flows through a reach of the River Cole, West Midlands, UK. The newly created channel had a sinuous planform and varying asymmetric trapezoidal cross section in sympathy with the planform. No imposed bedforms or bank reseeding were included in the design. Over the 2 years, development of bedforms was rapid, with bed sediment sorting and bank profile adjustment occurring more steadily and progressively. Six classes of bank profile were identified by the end of the study period, illustrating close associations with sediment aggradation, vegetation colonization, and growth patterns. Vegetation colonization of the banks was seeded predominantly from local sources during the summer and from hydrochory (transport by the river) during the winter. Colonizing vegetation on the riverbanks appeared to act as a significant propagule source by the second summer and as an increasingly important roughness element, trapping both propagules and sediment, within the second year and providing early feedback into bank evolution. As a result, the time required for riparian margin development in the conceptual model was found to be considerably longer than observed in the study river. In addition, the role of surface wash/bank failure in modifying the bank profile and transporting seeds onto the upper bank face during the first year of bank development was found to be important in initiating rapid bank vegetation colonization and surface stabilization. This set of processes had not been incorporated in the initial conceptual model. In relation to channel restoration, this research illustrates that in small temperate rivers of modest energy the provision of an initial, sinuous corridor is sufficient to induce rapid development of fluvial features and vegetation cover without the need to construct bed forms or to seed the banks.     

The Reshaping of Conventional Farming: A North American Perspective

Debates over the future of agriculture in North Americaestablish a dialectical opposition between conventional,industrial agriculture and alternative, sustainable agriculture.This opposition has roots that extend back to the 18th century inthe United States, but the debate has taken a number ofsurprising turns in the 20th century. Originally articulated as aphilosophy of the left, industrial agriculture has utilitarianmoral foundations. In the US and Canada, the articulation of analternative to industrial agriculture has drawn upon threecentral themes: the belief that agriculture is, in some way, tiedto democracy; the belief that complex bureaucratic organizationsare inherently opposed to human interests; and the belief thatthe family farms characteristic of 19th century North Americatend to produce people of superior moral character. It has proveddifficult to weave these themes into a coherent vision ofagriculture for the 21st century. Often, risk and health-basedconcerns are the basis for public criticism of conventionalagriculture, but these do not conflict with the utilitarianorientation of the industrial model, and are easily incorporatedinto it. If there is to be a philosophical debate over the futureof agriculture, we must find some way to rehabilitate thequasi-Aristotelean view of agriculture that emerges from thethree critical themes noted above.     

QUANTIFICATION OF ACTINIDE MIGRATION PATHWAYS AT ROCKY FLATS,COLORADO1

ABSTRACT: Migration of plutonium, americium, and uranium (actinides) in the environment at the Rocky Flats Environmental Technology Site (RFETS) is the subject of ongoing studies to develop effective strategies for cleanup and regulatory closure of the Department of Energy facility. The Actinide Migration Evaluation pathway analysis quantified actinide transport processes to validate a qualitative conceptual model of environmental actinide transport. Major actinide transport mechanisms evaluated include surface water, ground water, airborne, and biological pathways. Relative quantities of actinide movement via different pathways were compared in terms of actinide loads delivered off the RFETS, using a combination of monitoring data, predictive transport models and results from historic RFETS studies. Results indicate air and surface water constitute the dominant transport mechanisms for plutonium and americium. In ground water, shallow alluvial flow is a limited pathway for plutonium and americium because of the low aqueous solubility of these actinides and their tendency to sorb to soil. However, localized flow in shallow alluvium is a more significant pathway for uranium movement, because of the relatively higher solubility of uranium (VI) species, though isotopic ratios indicate much of the uranium is from natural sources. Biological transport of actinides by mammals, birds, fish, and arthropods is small compared to the other pathways.     

Simulated Responses of a Forest-Interior Bird Population to Forest Management Options in Central Hardwood Forests of the United States

I used estimates of carrying capacity, survival, fecundity, and edge effects to simulate the responses of a forest-interior bird population to selection cutting clearcutting, and no timber harvest. I also modeled population sensitivity to changes in fecundity, survival, K , and edge relationships. Because model parameters are based on scant data, results should he regarded as hypotheses to be further investigated or measures of the relative impact or sensitivity (given model assumptions). Simulated population size was greater with no timber harvest than with clearcutting and greater with clearcutting than with group selection when edge effects were included in the model. Without edge effects, population levels were only slightly lower under group selection than under no timber harvest, and greater than clearcutting. Edge effects had only a small impact on population levels under clearcutting. Clearcut size did not have much effect on population levels, but longer and shorter rotation ages resulted in higher and lower population levels, respectively. The model was very sensitive to declines in mean fecundity and survival, suggesting that factors affecting mean demographic rates could be more important than local edge effects. Some methods of timber harvest may be compatible with the conservation of forest-interior birds, but better demographic data and information on habitat suitability of selectively cut forests and young even-aged stands is needed to adequately evaluate management options.     

Distribution and abundance of choanoflagellates (Acanthoecidae) in the coastal cold ocean of Newfoundland, Canada

Water samples from six bays were taken over a 5-year period (1988 to 1992) to determine the distribution and abundance of loricate choanoflagellates in coastal Newfoundland, and to assess the impact that these organisms might have on this cold ocean food web. Scanning electron microscopy was used to study the morphology of these flagellates, allowing us to identify 11 species of loricate choanoflagellates. Parvicorbicula socialis (Meunier) Deflandre was the most abundant species (80 × 10³ cells l⁻¹), particularly during the spring diatom bloom. Single-cell species, such as Bicosta spini fera (Throndsen) Leadbeater and Calliacantha natans (Grontved) Leadbeater, were found more commonly after the spring diatom bloom in the summer months. Many of the single-cell choanoflagellates were attached to bacteria-rich microaggregates and debris in the water column and in unpoisoned sediment traps. The P. socialis cell flux was calculated to be 5.3 × 10⁶ cells m⁻² d⁻¹ in late May sediment traps. P. socialis in the upper 100 m of the water column was removing 0.3% of the standing crop of bacteria each day (April/May), and the equivalent of 7.4% of the daily bacterial production over the water column. Diel studies of P. socialis in Conception Bay suggest that the sharp decline in population numbers observed in midnight samples may be related to the high number of grazing zooplankton observed during the same period. Pelagic tunicate and zooplankton fecal pellets were found to contain large numbers of choanoflagellate costae, thus providing a direct link from the microbial loop to the macrozooplankton. Received: 17 March 1997 / Accepted: 9 May 1997     

Measurement of filtration rates by infaunal bivalves in a recirculating flume

A flume system and protocol for measuring the filtration rate of infaunal bivalves is described. Assemblages of multi-sized clams, at natural densities and in normal filter-feeding positions, removed phytoplankton suspended in a unidirectional flow of water. The free-stream velocity and friction velocity of the flow, and bottom roughness height were similar to those in natural estuarine waters. Continuous variations in phytoplankton (Chroomonas salinay) cell density were used to measure the filtration rate of the suspension-feeding clam Potamocorbula amurensis for periods of 2 to 28 h. Filtration rates of P. amurensis varied from 100 to 580 liters (gd)^-1 over a free-stream velocity range of 9 to 25 cm s^-1. Phytoplankton loss rates were usually constant throughout the experiments. Our results suggest that suspension-feeding by infaunal bivalves is sensitive to flow velocity.