SEDIMENT RESUSPENSION AND DRAWDOWN IN A WATER SUPPLY RESERVOIR1

ABSTRACT: The magnitudes and patterns of sediment resuspension are assessed in Cannonsville Reservoir, New York, to quantify and characterize this internal source of sediment. The assessment is based on analyses of sediment trap collections from 10 sites over the spring to fall interval of two years. Temporal and spatial patterns in sediment deposition are demonstrated to be driven by resuspension/redeposition processes. Sediment that had been resuspended and redeposited represented 80 to 96 percent, on average, of the depositing solids collected along the main axis of the lake. About 90 percent of the redeposited sediment was inorganic. Increased resuspension caused by drawdown of the reservoir surface and fall turnover resulted in 10 to 50‐fold increases in deposition rates compared to levels observed when the reservoir was full and strongly thermally stratified. Elevated levels of redeposition from resuspension in the reservoir have been driven by both higher water column concentrations of suspended solids and settling velocities. Recurring longitudinal and lateral gradients in resuspension are delineated, establishing that resuspended solids are transported from the riverine to the lacustrine zone and from near‐shore to pelagic areas. Resuspension is demonstrated to cause increases in inanimate particle (tripton) concentrations. Higher tripton levels have been observed in years with greater drawdown. Water quality impacts of the resuspension phenomenon are considered.     

STREAM ASSESSMENTS USING BIOTIC INDICES: RESPONSES TO PHYSICOCHEMICAL VARIABLES1

ABSTRACT: Responses of the Wyoming Stream Integrity Index (WSII), a regionally calibrated multimetric index, were investigated in relation to background elevational changes in water quality and habitat conditions versus accelerated anthropogenic degradation at the watershed scale. Assessments were conducted for three rivers in southeast Wyoming: the Little Medicine Bow River, the Medicine Bow River, and Rock Creek. Pearson correlation coefficients and regression models related “core metrics” and index scores to elevational gradients of physicochemical variables. Velocity, substrate, and weighted habitat values were positively correlated to index scores, while suspended solids was negatively correlated. The exclusive dependence of index scores on physical variables specifies the type of environmental gradients the WSII is most robust in detecting. The individual “core metrics” Plecoptera taxa, Trichoptera taxa, percent Trichoptera without Hydropsychidae, and percent noninsects appeared most sensitive to physical changes and were thus driving associations between index scores and physical variables. Despite strong correlations with physical variables, anomalies existed where habitat conditions were good, unknown stressors existed, or gradients were naturally occurring despite “Poor” index scores (i.e., degraded stream conditions). Such findings illustrate the influence of regional variability on biotic indices and the importance of identifying sufficient reference and impaired stream reaches used to develop and calibrate multimetric indices relying on reference conditions.     

Distribution Pattern of Benthic Invertebrate Communities in Traunsee (Austria) in Relation to Industrial Tailings and Trophy

Traunsee, an oligotrophic Alpine lake, has suffered from inputsof industrial tailings (soda- and salt-mining industries) forseveral decades. The effects of the industrial sludges on thespatial distribution of the littoral and profundal invertebratefauna was investigated along three transects at five dates. Inthe littoral zone, no negative impacts were found. A distinctgradient in faunal composition and diversity was, however,observed along a profundal transect relative to the distance fromthe waste emission. Near the industrial input, the enhanced pH,the substrate instability, and the poor sediment quality forsubstrate- and deposit-feeders were the main factors that loweror prohibit colonization of the industrial sludges. Along atransitional zone between the waste emission and the deepestbasin, recolonization was delayed, but did occur as soon aslayers of a few mm natural sediment seal the sludge. Mobile,epibenthic organisms are the first to settle these areas, whereasrecolonization by tube-building oligochaetes and chironomidsrequires thicker sealings of the industrial sludges. Differencesin the abundance of benthic invertebrates at different profundalsites were not only related to the waste emission, but also tothe influence of the main tributary, the River Traun. Theenhanced availability of allochthonous organic matter wasprobably responsible for high densities of tubificids near theinlet in the South of Traunsee. Moreover, a higher proportion oftolerant oligochaete and ostracod species in the lower profundaloutside the influence of the industrial tailings was interpretedas reflecting the increased trophy of Traunsee in the 1970s,which forced sensitive species to shift to the upper profundalwhen the oxygen climate deteriorated.     

Quantitative Assessment of the Intertidal Environment of Kuwait II: Controlling Factors

Multivariate analysis of variance, canonical correlation and canonical discriminate analysis were performed on environmental data collected from the Kuwaiti intertidal zone to determine the statistical relationships between the sediment, chemical, biological, spatial and temporal variables. The quantitative analysis showed that the sediment type was the paramount factor influencing the distribution and composition of the intertidal benthic fauna. The muddy, sandy and rocky shores support three distinct faunal communities. The seasonal variation in the benthic fauna community was not statistically significant but variation in biological data due to differences in transect location and tidal level were significant. This spatial variation has been attributed to differences in sediment and substrate types. The physico-chemical parameters were found to correlate positively with the mud content of the sediments but were unimportant in the overall composition of the intertidal fauna. This paper complements the results reported in Al Bakriet al. (1997–Part I) in establishing a valuable benchmark for assessing environmental impacts and for developing sustainable coastal zone management in Kuwait. The integrated approach outlined here could be adopted to develop a sound basis for the protection and management of coastal environments and resources in similar areas.     

DETRITUS ABUNDANCE AND BENTHIC INVERTEBRATE CATCH IN ARTIFICIAL SUBSTRATE SAMPLES FROM MOUNTAIN STREAMS1

ABSTRACT: Artificial substrates were designed using rock filled polyethylene bags which were perforated with holes. The substrates trapped waterborne sediment and detritus which enhanced microhabitat complexity. Colonization was compared in side-by-side tests with multiple plate samplers in mountain streams ranging from second to seventh order. After 41 days the bag samples contained more sediment and detritus and more animals than did multiple plates. Plastic bags exceeded multiple plate samples by a factor of nearly 8 for individuals and 1.5 for taxa expressed as numbers/sampler. Although detritus amounts differed significantly between samplers, catch composition was similar in habitat preference and functional groups. Most taxa were “lotic erosional” or “lotic erosional-depositional” detritivores. The plastic bags better represented the streambed fauna judged by their greater similarity to dip net samples. Bag samplers had 4.5 × the colonization area of multiple plates, hence would be expected to support more species. Catch/m² of colonization area was not significantly different between samplers. Functionally the plastic bags act as detritus retention devices, offering a diverse, highly dynamic microhabitat for colonization. Results are interpretable in terms of research on microdistribution of stream benthos and the river continuum model. This study supports the conclusion that stream benthos abundance and diversity are related to the amount of detritus. Maximum diversity and numbers of individuals occurred in samples from third and fourth order streams. Grazers reached peak abundances in the same streams where the continuum model predicts P>R Shredders reached maximum abundances in third and fourth order streams where the riparian canopy was greatest. Predator abundance changed little with stream size. Although bag samples required more sorting time, the samplers are catch effective, inexpensive, and adaptable.     

EFFECTS OF SPATIAL ORIENTATION OF MULTIPLE PLATE ARTIFICIAL SUBSTRATES ON INVERTEBRATE COLONIZATION1

ABSTRACT: Jumbo multiple plate samplers were suspended in a river at 0.3 and 1 m depth in one of three orientations: interplate spaces closed to downwelling light and open to flow, open to light and flow, or open to light and closed to flow. Mean numbers of colonizing taxa and individuals were not significantly different among orientations after eight weeks of submergence. All variables tested decreased significantly with depth. Mean number of taxa, number of individuals (1 m only), and insect diversity decreased between samplings at four and eight weeks for samplers that were closed to light and open to flow. All orientations, depths, and durations had one-half to two-thirds of the total taxa. Colonization was affected by location in the river and position on sampler suspension equipment. The results indicate lack of orientation effects on colonization or high variability that obscured such effects. The sampler suspension equipment possibly increased among-sampler variability by forming artificial snag habitats, and interplate light and flow conditions at different orientations may not have been sufficiently distinct to elicit different biological responses. Individual samplers provided diverse microhabitats regardless of orientation, but it would be prudent to include orientation among the variables considered in use of multiple plate samplers.     

IMPACT OF WATERSHED URBANIZATION ON STREAM INSECT COMMUNITIES1

ABSTRACT: The impact of urbanization on stream insect communities was determined by sampling 22 sites in northern Virginia representing a range of human population densities. Watershed development had little effect on the total insect numbers (no./m²), but shifted the taxonomic composition markedly. Relative abundance of Diptera (mainly chironomids) increased at more highly urbanized sites, while most other insect orders including Ephemeroptera (mayflies), Coleoptera (bettles), Megaloptera (dobsonflies), and Plecoptera (stone-flies) decreased. Trichoptera (caddisfiles) exhibited a variable response. Genus diversity and richness (number of genera) were significantly higher in less urbanized streams. Two genera of chironomids were positively correlated with increased urbanization, while 14 other genera (scattered through several orders) were negatively related to human population density. Principal components analysis demonstrated a gradient from more urbanized to less urbanized stations based on generic and order level biological data. Results of this study indicate that watershed urbanization has a major impact on benthic insect communities even in the absence of point source discharges.     

BENTHIC INVERTEBRATE RESPONSE TO POLLUTION ABATEMENT: STRUCTURAL CHANGES AND FUNCTIONAL IMPLICATIONS1

We examined changes in certain structural and functional aspects of the benthic invertebrate community in the Penobscot River, Maine, between 1974 and 1981. During this period, two pulp and paper manufacturers and three municipalities spent an estimated $33 million to reduce point source effluents harmful to aquatic life. We developed a biotic index based on objectively derived pollution tolerance values for resident taxa. Analysis of the benthic invertebrate community indicated that substantial improvement in water quality had resulted from pollution abatement. We established a four-group water quality classification scheme based on biotic index ranges, and showed that every site that was not in the best water quality classification in 1974 improved its classification to a better water quality group in 1981, and that the sites in the best group did not change. Relative abundances of functional feeding groups also changed, as were predicted by the river continuum theory. The effluents had acted as a “reset mechanism” that shifted polluted areas from autotrophic to more heterotrophic conditions. The direction of the shift was reversed in response to abatement efforts. Functional analyses of energy dynamics could lead to a more ecologically sound classification of water quality.     

Derivation and Use of Sediment Quality Guidelines for Ecological Risk Assessment of Metals and Radionuclides Released to the Environment from Uranium Mining and Milling Activities in Canada

The Screening Level Concentration (SLC) approach was used to derive Lowest Effect Level (LEL) and Severe Effect Level (SEL) concentrations for nine metals (As, Cr, Cu, Pb, Mo, Ni, Se, U and V) and three radionuclides (²²⁶Ra, ²¹⁰Pb, and ²¹⁰Po) released to the aquatic environment during the mining and milling of uranium ore. This method was chosen because it allowed for the best use of the considerable historical and current data collected for diverse purposes in the uranium mining and milling regions of Canada (20,606 data points used in the analysis). Except for Cr, all the LELs derived in this study using the weighted method and published sediment quality guidelines (SQGs) were highly reliable (> 85%) in predicting sites unimpacted by uranium mining/milling defined as sites where reductions in the abundance and species richness of benthic invertebrate communities were < 20%. The derived SEL values and corresponding published SQGs (with the exception of Ni) were not reliable predictors (≤60%) of severe impacts on benthic invertebrate communities when severe impacts are defined as a reduction in abundance and species richness ≥40%. Most of the severely impacted sites had sediment contaminant concentrations well below the SEL values. It is concluded that LELs derived using the weighted method can reliably be used in ecological risk assessments as concentrations below which adverse effects on benthic invertebrate communities are not expected. In contrast, it is recommended that SELs not be used in assessments of uranium mining/milling activities as concentrations above which adverse effects are anticipated.     

APPLICATION OF BIOLOGICAL MEASURES FOR STREAM INTEGRITY ASSESSMENT IN SOUTH-EAST BRAZIL

The sensitivity of eleven metrics using macroinvertebrate assemblages were evaluated in an environmental gradient in a tropical river in south-east Brazil. Eight sites were sampled in an altitudinal range of 160–650 m.a.s.l. during 1999 (April and August) and 2000 (February). Four substrates were sampled at each site: riffle litter, pool litter, stony substrates and sediment. Correspondence Analysis indicated that assemblages were primarily more influenced by physical changes (like deforestation and erosion processes) than the water chemistry. The sensitivity of each metric was evaluated through the application of box-and-whisker plot method by its power to assess impairment (metrics should be able to discriminate reference sites from impaired sites) and natural variability (metrics should not discriminate two reference sites). Metrics that failed in at least one of the above premises were not considered as sensitive. In this study, the most sensitive metrics were Shannon index, BMWP-ASPT, %_EPT, and relative abundance of EPT to Chironomidae.