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.     

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.     

无毒防污涂料表面底栖硅藻附着评价的实验方法

在实验室培养了底栖硅藻目标附着生物,利用显微镜、图像处理技术等实验研究了底栖硅藻在低表面能无毒防污涂层上的附着面积分数,并测定了附着底栖硅藻的叶绿素a值。研究结果表明,文中提出的海洋生物附着评价实验方法科学有效,并且附着底栖硅藻的叶绿素a值与其在无毒防污涂层上的附着面积分数成反比。     

The Sensitivity and Adaptation of Ecosystems to the Disturbances: A Case Study in Northeastern Estonia

The study focused on the problem of the response and adaptation of an ecosystem to natural fire in case of greenhouse warming. The palaeoecological approach was used and reconstructions were made for timeca 6000 years ago, when the human impact in the studied area was absent or very weak and the summer temperatures were about 2.4 degrees higher than at the present time. The palaeoreconstructions were compliled using the charcoal, pollen and diatoms data from the sediments of a northeast Estonian lake. The results show that forest fires influenced the biota of the lake mainly through evapotranspiration and the accompanying erosional changes. The impacts of the fire directly to the lake ecosystem were short-term and the primary diatom association was restored after 10–15 years. The pollen influx was influenced by the fires mainly through the changes in the openness of the landscape and the composition of the pollen spectra was restored over a period of 50–60 years. The data demonstrate the high ability of the studied ecosystem to adapt to the impact of natural fires in the climatic environment comparable with that predicted for the future.     

三峡库区蓄水期长江口底栖生物数量动态分析

三峡库区蓄水期于2004年在长江口区进行季节性(2、5、8、11月)综合调查.结果表明,该水域出现底栖生物种类依序为2月127种,5月为114种,8月和11月分别为83种和97种.在种类组成中,以多毛类占首位(42～70种)、其次软体类17～32种.甲壳类和棘皮类较少.底栖生物优势种有15种,其优势度(D2)值以多毛类丝异须虫(0.27～0.36)和小头虫(0.18～0.26)明显高于其他种类.底栖生物的平均总生物量以2月和5月较高,分别为19.7g/m2和23.4 g/m2.在生物量组成中,以软体类最高为5.6～12.2 g/m2.底栖生物的平均总密度以5月和11月最高,分别为623.0个/ m2和781.7个/m2.在生物密度组成中,多毛类的密度居首位(194.8～625.6个/ m2).底栖生物多样性指数(H')值最高为2月(2.94)和5月(2.76).生物种类丰度指数(D)值以2月较高为1.34.各月的生物种类均匀度指数(J)值均不足1.通过调查分析,长江口外水域及口北少数站的底栖生物量和密度,仍保持高于河口附近测站的分布格局.     

Deformity frequencies of benthic marine diatoms associated with contaminated sediments in Hong Kong

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Testing Bioassessment Metrics: Macroinvertebrate, Sculpin, and Salmonid Responses to Stream Habitat, Sediment, and Metals

The purpose of this article is to report on the testing of responses of multimetric macroinvertebrate and habitat indices to common disturbances to streams: stream habitat alteration, excessive sediment, and elevated metals concentrations. Seven macroinvertebrate community metrics were combined into a macroinvertebrate biotic index (MBI), and 11 channel morphology, riparian, and substrate features were combined into a habitat index. Indices were evaluated by comparing the habitat results to fish population surveys and comparing the macroinvertebrate results to habitat ratings, percent fine sediments measured by Wolman pebble counts, and copper concentrations. Macroinvertebrate scores decreased with increasing percentages of fine sediments measured either across the bankfull or instream channel widths. Macroinvertebrate scores decreased with increasing copper. One metric, richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa, was more responsive to both copper and sediment than was the multimetric MBI. Habitat scores corresponded well with the age class structure of salmonids, but not with that of benthic sculpins. Both salmonid and sculpin age classes declined with increasing percentages of fine sediments. The decline was graded with the sculpin age classes, whether fine sediments were measured across the instream or bankfull channel, whereas salmonids consistently responded only to the instream fine sediments.