Implications of Genome Alterations in Chironomus bernensis Klȍtzli (Diptera) for Assessment of Trace Metal Pollution in Two Bulgarian Rivers

This study assesses the effect of sediment contaminants as indicated by the measurement of trace metal levels in two large Bulgarian rivers (river Maritsa and a tributary and the river Chaya) on the genome of the abundant chironomid species Chironomus bernensis Klȍtzli. Six trace metals: Cd, Cr, Cu, Mn, Pb and Zn were analysed in the sediments plus the overlying water. The polytene chromosomes of C. bernensis were very sensitive to the pollutants on the basis of numerous somatic chromosome alterations. Two biomarkers based on the degree of somatic structural chromosome alterations—the somatic and cytogenetic indices were applied. Both indices are a sensitive and reproducible approach for assessing the genotoxic effect of contaminants in the sediments. The somatic index from the differentially contaminated sites varied from 1.93 to 2.61, indicating the sensitivity of the C. bernensis genome to anthropogenic stress. The cytogenetic index revealed a high level of pollution in the rivers with a score between 0.27 and 0.37 (<0.5 indicates ‘highly polluted’). The genome of C. bernensis responded to the trace metal pollution by the appearance of a ‘B’ chromosome in between 4.4% and 7.1% of the individuals and detected for the first time in this species. Pollution also induced a heterozygous state in one of the Nucleolar Organizers in up to 3% of the sampled populations. The sensitivity of the C. bernensis genome shows that this species is a good candidate for detecting the presence of genotoxic compounds in freshwater and assessing their genotoxic effects. Copyright © 2015 John Wiley & Sons, Ltd.     

Bioassessment of contaminant transport and distribution in aquatic ecosystems by chemical analysis of burrowing mayflies (Hexagenia)

Burrowing mayfly nymphs (Ephemeroptera) inhabit and ingest fine-grained sediments and detritus that may be enriched with metals and persistent organic compounds. The burrowing nymphs can externally adsorb and internally assimilate these contaminants, providing a link for the food chain transfer of potentially toxic substances from sediments to organisms in higher trophic levels. The emergent adults are short-lived and do not feed, thus their gut contents do not contribute greatly to their total contaminant burden. These characteristics make Hexagenia spp. and certain other burrowing mayflies useful for assessing ecosystem contamination. General protocols are presented for the collection, processing and analysis of emergent mayflies to assess the spatial distribution and bioaccumulation of sediment-associated contaminants in aquatic ecosystems. Two essential components of this bioassessment approach are a network of on-site volunteers with the materials and instructions needed to correctly collect and store samples and quality assurance procedures to estimate the accuracy of chemical analyses. The utility of this approach is demonstrated with an example of its application to the Upper Mississippi River (USA). Determination of cadmium, mercury and polychlorinated biphenyl congeners in emergent Hexagenia bilineata from a 1250km reach of this river revealed (1) several source areas of contaminants and (2) distinct patterns in the bioaccumulation (and apparent sediment-associated transport) of each residue on both small and large spatial scales.     

Distribution of Pb, As, Cd, Sn and Hg in soil, sediment and surface water of the tropical river watershed, Terengganu (Malaysia)

Hydrogeochemistry and distribution of Pb, As, Cd, Sn and Hg in soils (n = 53), sediments (n = 42) and surface waters (n = 51) of the tropical Terengganu River basin, northeast coast of Peninsular Malaysia, were investigated. The order of abundance of the elements in soils followed granite > metasedimentary > Quaternary deposit ? volcanic with slight enrichment as compared to the upper continental crust. Both soils and sediments registered the order of concentration of Pb > Sn > As ? Cd ? Hg with an enrichment factor (EF) < 6 for sediments indicating slight enrichment representing the regional background and less likely due to the anthropogenic activity related input. SEM analysis revealed the presence of Malayaite (CaSnOSiO₄) explaining elevated Sn concentration (up to ∼34 mg/kg; 3 times the upper continental crust) in soils. Soil Pb distribution showed the geology as the primary control.Dissolved concentrations of As showed an increasing and Cd decreasing with distance from upstream to downstream along the river flow path. Lake surface waters registered 16 times higher Cd concentrations (average ∼ 14.21 μg/L) than the river waters, but lake sediments registered lower Cd concentration than the river sediments (average ∼ 0.45 mg/kg) revealing Eh, pH and TDS control. Dissolved average Hg concentration (∼0.04 μg/L) was measured to be lower than the tropical river waters from the Central Africa river, but higher than the Mekong and the Amazon Rivers.     

Optimization of River Water Quality Surveys by Multivariate Analysis of Physicochemical,Bacteriological and Ecotoxicological Data

This study aims to optimize the water quality monitoring of a polluted watercourse (Leça River, Portugal) through the principal component analysis (PCA) and cluster analysis (CA). These statistical methodologies were applied to physicochemical, bacteriological and ecotoxicological data (with the marine bacterium Vibrio fischeri and the green alga Chlorella vulgaris) obtained with the analysis of water samples monthly collected at seven monitoring sites and during five campaigns (February, May, June, August, and September 2006). The results of some variables were assigned to water quality classes according to national guidelines. Chemical and bacteriological quality data led to classify Leça River water quality as “bad” or “very bad”. PCA and CA identified monitoring sites with similar pollution pattern, giving to site 1 (located in the upstream stretch of the river) a distinct feature from all other sampling sites downstream. Ecotoxicity results corroborated this classification thus revealing differences in space and time. The present study includes not only physical, chemical and bacteriological but also ecotoxicological parameters, which broadens new perspectives in river water characterization. Moreover, the application of PCA and CA is very useful to optimize water quality monitoring networks, defining the minimum number of sites and their location. Thus, these tools can support appropriate management decisions.     

The Niagara River mussel biomonitoring program (Elliptio complanata): 1983-2009

The Ontario Ministry of the Environment has monitored the concentrations of contaminants in mussel (Elliptio complanata) tissue and bottom sediments at sites in the Niagara River since 1983 to describe the general contamination of the river and identify contaminant sources. More recently, the data have been used to document the effectiveness of remedial actions implemented at identified sources along the river. Results from Canadian sites and five U.S. sites at which remedial actions have been implemented [Bloody Run Creek (Hyde Park Hazardous Waste Site); Gill Creek; Occidental Chemical Company (Buffalo Avenue Plant); 102nd Street Hazardous Waste Site; and Pettit Flume Cove] are discussed. p,p′-DDE, PCBs and dioxins were the only contaminants detected at Canadian sites at concentrations probably representative of background. Results from the five sites showed the effectiveness of implemented remedial actions in reducing the flow of contaminants to the river ranged between very effective (Gill Creek: PCBs; and 102nd Street, CBs) to no effect (Bloody Run Creek: PCBs, CBs, and dioxins). Remedial actions at the Pettit Flume Cove (for dioxins/furans) initially appeared to be effective, but were subsequently shown to have missed a source to the cove. The effectiveness of the actions taken at these sites in improving contaminant conditions in the Niagara River since the 1980s as demonstrated by our mussel and sediment results is corroborated by the data from other fish and water quality monitoring programs. Additional remedial efforts are still required at these sites and other known sources of contaminants to the river.     

Morphological Deformities in Chironomus (Chironomidae: Diptera) Larvae as Indicators of Pollution in Lake Winnebago,Wisconsin

Lake Winnebago, a large, shallow lake in east-central Wisconsin, supports substantial populations of several different chironomid species (the larvae of which inhabit bottom sediments) and has been the repository of substantial amounts of lead from non-point sources. Larval morphological characters, in particular mouthpart deformities, have been used in other systems as sensitive, but non-specific, indicators of anthropogenic pollution. Forty-eight percent of the lake fly (Chironomus spp.) larvae collected from Lake Winnebago had either a deformed mentum or a deformed mandible. That level of deformities is taken as strong evidence of polluted bottom sediments. Lake Winnebago sediments were found to contain approximately 50 ppm lead. In laboratory experiments, Chironomus pallidivittatus larvae were cultured in Lake Winnebago sediments supplemented with different concentrations of lead as high as 20,000 ppm. Less than 10% of the larvae in those experiments had either a deformed mentum or a deformed mandible. These results suggest that lead alone is unlikely to be the cause of the high levels of deformities seen in the Chironomus spp. larvae collected from the Lake Winnebago sediments.     

Spatial and seasonal variations in δ13C AND δ15N of particulate organic matter in a dam‐controlled subtropical river

Alteration of stream flow by artificial dams has been observed to be a significant factor for river water environmental changes. Therefore, understanding the biogeochemical processes occurring in the dam‐controlled rivers is important for water resource management. In this paper, δ¹³C and δ¹⁵N signatures of particulate organic matter (POM) in a dam‐controlled subtropical river, Beijiang River, in south China are reported for their spatial and seasonal distributions. POM affected by reservoirs is lighter in δ¹³C and heavier in δ¹⁵N relative to unaffected POM. In April, POM δ¹³C and δ¹⁵N values show less spatial variation in the mainstem, and suggest relatively greater contributions of terrestrial organic matter (OM) to POM. This could be related to the onset of summer monsoon that caused an abrupt increase in terrestrial input to the river by the monsoon‐induced enhancement of rainfall and runoff. In August and December, however, POM isotopic values for the sites affected by the Feilaixia dam reservoir in the middle of the river show marked changes, suggesting aquatic plankton proliferation in the reservoir during the times. Upstream from the reservoirs, POM isotopes are seasonally less varied and suggest mainly terrestrial origin. However, the isotopic signals of aquatic plankton proliferation in the reservoir in August and December is imprinted on the POM isotopic compositions downstream the reservoir, indicating far‐reaching influences of the reservoir on the downstream water environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Field and Laboratory Studies of Environmental Carcinogenesis in Niagara River Fish

Combined field and laboratory studies were carried out to assess the possible role of contaminated bottom sediments to neoplastic disease in fish from eastern Lake Erie and the upper Niagara River. Correlations between sediment polycyclic hydrocarbons, neoplasms in feral fish, and the induction of neoplasms in bullheads (Ictalurus nebulosus) by exposure to extracts of polluted sediment support the hypothesis that some fish neoplasms result from exposure to carcinogenic chemicals present in the fishes environment.     

Colorado river benthic ecology in Grand Canyon,Arizona, USA: dam,tributary and geomorphological influences

The serial discontinuity concept (SDC; Ward and Stanford, in Ecology of River Systems, 1983) predicts that recovery of large regulated rivers over distance downstream from a dam is limited by relative tributary size; however, channel geomorphology may also influence the recovery process. We examined the spatial variation in water quality, benthic composition and ash-free dry standing biomass (AFDM) among the bedrock-defined geomorphological reaches in three turbidity segments of the Colorado River between Glen Canyon Dam and Diamond Creek, Arizona, including most of the Grand Canyon. This 387-km long study area supported virtually no Ephemeroptera, Plecoptera or Trichoptera, probably because cold, stenothermic, hypolimnetic releases limited maximum aestival warming to 17·1°C. The benthos displayed abrupt, physically related decreases in AFDM over distance from the dam and in the varial zone. The 26-km long clear water segment between the dam and the Paria River supported a depauperate Cladophora glomerata/epiphyte/chironomid/Gammarus lacustris/lumbricine/Physella sp. assemblage, and ooze-dwelling oligochaetes. This segment contained 6·9% of the aquatic habitat below the 140 m³/s (normal minimum) discharge stage of the Colorado River study area, but supported 63·5% of the benthic primary producer AFDM and 87% of the benthic consumer AFDM in the entire study area. Turbidity increased and light penetration decreased immediately downstream from the confluence of the small, turbid Paria River, and further downstream from the Little Colorado River confluence. The benthos downstream from the Paria River was abruptly replaced by an Oscillatoria/Simuliium assemblage with a mean AFDM of <0·12 g C/m². Dam-related effects on water clarity, varial flow and water temperature overrode geomorphological influences on habitat availability. These results generally support the SDC, in that recovery of the benthos did not take place over distance in this large river ecosystem; however, geomorphological differences in substratum availability between reaches mediated dam and tributary effects on water clarity and benthic AFDM. Interactions between flow regulation and geomorphology produce a pattern of circuitous recovery of some physical river ecosystem characteristics over distance from the dam, but not of the benthos. Improving discharge management for endangered native fish populations requires detailed understanding of existing and potential benthic development, and trophic interactions, throughout the geomorphological reaches and turbidity segments in this river. © 1997 John Wiley & Sons, Ltd.     

Spring Distribution and Abundance of Larval Fishes in the St. Marys River,With a Note on Potential Effects of Freighter Traffic on Survival of Eggs and Larvae

Larval fishes were collected at seven transects in the St. Marys River from late April to late May, 1985, to determine potential effects of extending the winter navigation season on spawning success and survival. Larval lake herring (Coregonus artedii) 8 to 25 mm occurred in densities of 0 to 1,450 larvae/1,000 m³ and were most commonly found in shallow water (1 to 2 m). Most lake herring hatching occurred during late April to early May, the first 3 wk after ice break-up, but there was no distinct hatching peak. Lake whitefish (C. clupeaformis) larvae, 12 to 23 mm, with densities of 0 to 600/1,000 m³, were most common at 1 m being collected at all transects, except the transect in the Edison Hydropower Canal which passes Lake Superior water into the river. Densities of the two coregonine species were similar to densities observed in important nursery areas of Lake Huron. However, the contribution of lake herring to the river population is not known. Burbot (Lota lota) larvae were common temporally and spatially, with higher abundances in the channel. Yellow perch (Perca flavescens) and rainbow smelt (Osmerus mordax) larvae were absent in April and early May, and abundant in late May. Lake herring, lake white-fish, and burbot have the greatest probability of being affected by the proposed extension of the navigation season through resuspension of sediments, dislodgment of eggs, and premature emergence of larvae.     

Risk assessment of heavy metal contamination in Danube sediments from Hungary

The aim of the current research is to establish a suitable Environmental Risk Assessment (ERA) scheme for Danube sediments in Hungary by determining contaminants' concentrations by chemical analysis and by assessing their ecotoxicological effects. Seventeen sedimentation sites were identified, mainly upstream of Budapest, between river kilometres 1811 and 1586. The heavy metal contents and basic properties of sediments were determined. Excess heavy metal content was used to characterize the extent of heavy metal contamination. Direct contact biotests were developed for testing the toxic effect of contaminated sediments. Ecotoxicological effects were measured by three bacterial tests and one plant bioassay. Effect Concentrations were determined by the inhibition of the bioluminescence of Photobacterium phosphoreum. The resultant inhibition of different partial toxic effects was characterized by Cu equivalent. Chemical and ecotoxicological results were studied together, making it possible to characterize the extent of the pollution and its biological effects at the same time. It was concluded that combined chemical and ecotoxicological characterization of contaminated sediments may serve as a strong basis for assessing the site-specific risk of heavy metal pollution.     

Aquatic macroinvertebrate assemblages of two contrasting floodplains: The rhǒne and ain rivers,France

The study examines the relationship between floodplain aquatic macroinvertebrates and sector-scale parameters such as geomorphology and history of regulation. The assemblages of six groups of invertebrates (Molluscs, Crustaceans, Ephemeroptera, Odonata, Trichoptera, and Coleoptera) were compared in various types of former channels from two contrasting but adjacent floodplain sectors: (1) the Jons sector of the Rhǒne River where successive meandering and braiding phases has left diversified fluvial forms in the landscape but where the main river is now embanked, and (2) the unregulated Ain River sector where the river is still actively meandering, although this process is being slowed by incision. The results demonstrate little difference in faunal composition between the two sectors but a significant difference in faunal structure. In the Rhǒne floodplain, there was a clear distinction between the faunal assemblages together with a high taxa richness at the scale of the sector (dominance of the beta diversity). In the Ain floodplain, the faunal assemblages were overlapping and the taxa richness was high at the sample scale (alpha diversity). Sector-scale spatial patterns of the faunal assemblages along former channels were also distinct: between-channel heterogeneity dominated in the Rhǒne, whereas within-channel heterogeneity dominated on the Ain. These results stress the influence of geomorphological and historical determinants on the floodplain communities and, conversely, the relevance of macroinvertebrate assemblages for the assessment, at the landscape scale, of aquatic systems within the floodplains.     

An Investigation of the Impacts of Agricultural Runoff on the Water Quality and Aquatic Organisms in a Lowveld Sand River System in Southeast Zimbabwe

In this research we examined the hypothesis that agricultural pollution is a key determinant of variability in nutrients concentrations and benthic fauna in a semi-arid tropical lowveld region of southeast Zimbabwe. Water quality was monitored in the river water column and river bottom sediments at a time when dissolved oxygen concentration was thought to be very low during the winter period in the rivers passing through low input agricultural sections and intensive commercial agricultural sections. The surveys used established chemical methods and biological methods. Benthic fauna assemblages were used to complement chemical cases of nutrient loading at localities chosen for sampling. Unpolluted control sites were not significantly different (t test, p < 0.05) from polluted sites in levels in mean values of dissolved oxygen, conductivity, total dissolved solids and mean density (no.m²) of benthic invertebrates in May. Significant differences (t test, p < 0.05) were not found in mean values of calcium, magnesium, potassium, total nitrogen, nitrate nitrogen, ammonia nitrogen and total phosphorous in river bottom sediments in May and August. These data certainly do not support the notion that the Runde River is severely polluted by the upstream agricultural activities and the hypothesis that agricultural runoff is a key determinant of water quality is rejected. As the data suggests the Runde River may be receiving moderate nutrient pollution. The positive effects of moderate eutrophication on fish catch and the trade-off in pollution implied here needs to be addressed by appropriate agricultural and environmental policies that relate to water pollution and land use.     

The effects on fish spawning and management implications of impoundment water releases in an intermittent South African river

The potamodromous smallscale redfin minnow (Pseudobarbus asper) spawned in the riffle areas of the regulated Groot River, the major tributary of the Gamtoos River system, during controlled releases of water from Beervlei Dam. Water had been released at irregular intervals from this flood control dam solely for irrigating agricultural lands. Flushing flows removed accumulated salts from riverine pools and were followed by reduced flows which initiated spawning of the minnow species. Developing embryos of P. asper were found in the riffle zone of the main river channel during the water releases. Ripe-running males were located under the boulders in the riffles. Several developing embryos of Labeo umbratus were found with the P. asper eggs. Very little is known about the effects of man-made alterations to the river flow regime on the reproductive activity of fishes in the majority of South African river systems. The agriculturally based flooding regime at Beervlei may have increased the recruitment of the redfin minnow species. Water management must give cognizance to the biological and environmental requirements within the regulated river systems. Water release strategies from Beervlei Dam should include instream flow decisions based on the requirements of the aquatic environment as well as for agriculture.     

AN EVALUATION OF THE RELATIVE QUALITY OF DIKE POOLS FOR BENTHIC MACROINVERTEBRATES IN THE LOWER MISSOURI RIVER,USA

A habitat‐based aquatic macroinvertebrate study was initiated in the Lower Missouri River to evaluate relative quality and biological condition of dike pool habitats. Water‐quality and sediment‐quality parameters and macroinvertebrate assemblage structure were measured from depositional substrates at 18 sites. Sediment porewater was analysed for ammonia, sulphide, pH and oxidation–reduction potential. Whole sediments were analysed for particle‐size distribution, organic carbon and contaminants. Field water‐quality parameters were measured at subsurface and at the sediment–water interface. Pool area adjacent and downstream from each dike was estimated from aerial photography. Macroinvertebrate biotic condition scores were determined by integrating the following indicator response metrics: % of Ephemeroptera (mayflies), % of Oligochaeta worms, Shannon Diversity Index and total taxa richness. Regression models were developed for predicting macroinvertebrate scores based on individual water‐quality and sediment‐quality variables and a water/sediment‐quality score that integrated all variables. Macroinvertebrate scores generated significant determination coefficients with dike pool area (R² = 0.56), oxidation–reduction potential (R² = 0.81) and water/sediment‐quality score (R² = 0.71). Dissolved oxygen saturation, oxidation–reduction potential and total ammonia in sediment porewater were most important in explaining variation in macroinvertebrate scores. The best two‐variable regression models included dike pool size + the water/sediment‐quality score (R² = 0.84) and dike pool size + oxidation–reduction potential (R² = 0.93). Results indicate that dike pool size and chemistry of sediments and overlying water can be used to evaluate dike pool quality and identify environmental conditions necessary for optimizing diversity and productivity of important aquatic macroinvertebrates. A combination of these variables could be utilized for measuring the success of habitat enhancement activities currently being implemented in this system. Published in 2011 by John Wiley & Sons, Ltd.     

大汶河污染现状及其治理措施

阐述大汶河污染对南水北调东线工程水质的危害 ,分析大汶河主要的污染来源。为实现大汶河水质控制目标 ,必须从管理措施和工程措施两方面着手 ,即提高认识 ,深化改革 ,以法治污 ;从末端治理转为源头治理 ;建设好污水处理厂 ,集中处理城市污水 ;治理河道污泥 ;发展生态农业 ,治理面源污染 ;划定大汶河水生态环境保护区。     

Evidence of Lake Whitefish Spawning in the Detroit River: Implications for Habitat and Population Recovery

Historic reports imply that the lower Detroit River was once a prolific spawning area for lake whitefish (Coregonus clupeaformis) prior to the construction of the Livingstone shipping channel in 1911. Large numbers of lake whitefish migrated into the river in fall where they spawned on expansive limestone bedrock and gravel bars. Lake whitefish were harvested in the river during this time by commercial fisheries and for fish culture operations. The last reported landing of lake whitefish from the Detroit River was in 1925. Loss of suitable spawning habitat during the construction of the shipping channels as well as the effects of over-fishing, sea lamprey (Petromyzon marinus) predation, loss of riparian wetlands, and other perturbations to riverine habitat are associated with the disappearance of lake whitefish spawning runs. Because lake whitefish are recovering in Lake Erie with substantial spawning occurring in the western basin, we suspected they may once again be using the Detroit River to spawn. We sampled in the Detroit River for lake whitefish adults and eggs in late fall of 2005 and for lake whitefish eggs and fish larvae in 2006 to assess the extent of reproduction in the river. A spawning-ready male lake whitefish was collected in gillnets and several dozen viable lake whitefish eggs were collected with a pump in the Detroit River in November and December 2005. No lake whitefish eggs were found at lower river sites in March of 2006, but viable lake whitefish eggs were found at Belle Isle in the upper river in early April. Several hundred lake whitefish larvae were collected in the river during March through early May 2006. Peak larval densities (30 fish/1,000 m³ of water) were observed during the week of 3 April. Because high numbers of lake whitefish larvae were collected from mid-and downstream sample sites in the river, we believe that production of lake whitefish in the Detroit River may be a substantial contribution to the lake whitefish population in Lake Erie.     

The Effect of Contaminated Sediments on Fecundity of the Brown Bullhead in Three Lake Erie Tributaries

Female brown bullhead (Ameiurus nebulosus) were collected from three Lake Erie tributaries (Ohio) from 8 to 25 May 1989, to determine the effects of contaminated sediments on reproductive potentials. Fish obtained from the Black and Cuyahoga rivers, which contain sediments with elevated concentrations of metals, PCBs, and PAHs, were compared with fish collected in Mud Brook, a tributary of the Huron River, which was selected as our reference site. Fecundity, egg diameter, fish length and weight, and the presence of external abnormalities were recorded for each fish. Brown bullhead from the contaminated sites were larger then those from the reference site and fecundity was significantly (P ≤ 0.05) different in all three river systems. Those from the most polluted river (Cuyahoga River) had the greatest number of eggs per individual female. The high frequency of external abnormalities observed on brown bullhead from the contaminated sites did not appear to have a detrimental influence on fecundity. These results suggest that fecundity of the brown bullhead was not adversely affected in ecosystems altered by the presence of contaminated sediments. Increased fecundity of the brown bullhead from impacted rivers may be the result of reduced competition for an abundant invertebrate food source and limited predation by other fish species whose numbers are largely depleted in these degraded systems.     

Statistical Distribution of Streambed Vertical Hydraulic Conductivity along the Platte River,Nebraska

Streambed vertical hydraulic conductivity (K _v ) plays an important role in understanding and quantifying the stream–aquifer interactions. While several researchers have discussed the spatial variability of streambed horizontal hydraulic conductivity or K _v at one or several close-located sites in a river, they did not develop any statistical distribution analysis of streambed K _v at distant sites along a large river. In this paper, the statistical distribution and spatial variation of streambed K _v at 18 test sites in a 300-km reach of the Platte River in Nebraska are presented. In-situ permeameter tests using the falling-head method were carried out to calculate the streambed K _v values. Fine-grained sediments transported by two tributaries, the Loup River and the Elkhorn River, to the Platte River appear to result in lower streambed K _v values downstream of the confluences between the Platte River and the tributaries. The streambed K _v values were found to be normally distributed at nearly each test site. When the correlated K _v values were eliminated from the grid sampling plots, the remaining independent sub-datasets of streambed K _v values were still in normal distribution at each test site. Furthermore, the combined streambed K _v values upstream of the first confluence between the Platte River and the Loup River was normally distributed, which may be due to the lack of tributaries in-between and thus streambed sediments were well distributed in this reach and belonged to a single population of hydraulic conductivity values. In contrast, the combined dataset of all measurements conducted downstream of this confluence was no longer in normal distribution, presumably as a result of the mixing of different sediment sources.     

Stable isotopes in zebra mussels as bioindicators of river–watershed linkages

Concerns about biodiversity and sustainability extend to many ecological systems, including large river systems that are highly modified by human activities. The Mississippi River is one such system that is currently regulated for navigational and flood control purposes, bears a large agricultural nutrient load, and has experienced rapid spread of the exotic zebra mussel, Dreissena polymorpha, since 1991. Human development of the extensive watershed system of the Mississippi River is ongoing and is expected to lead to further changes in river ecology. This study tested whether stable isotope compositions of the zebra mussel could help identify watershed and tributary loading of carbon (C), nitrogen (N), and sulphur (S) to the mainstem river. Zebra mussels were collected seasonally in the lower Mississippi River at Baton Rouge in 1997, and along most of the length of the river in a north–south transect from Minnesota to Louisiana during August 1998. Results showed substantial seasonal variations in C, N and S isotopic compositions of 2‰ or greater, but also that seasonal changes appeared regular and linked to changing watershed inputs and chemistry of the river water. Nitrate was the dominant N nutrient in the Mississippi River, but isotope analyses showed that food webs based on ammonium rather than nitrate were likely important for the zebra mussel. Results from the north–south transect followed expectations based on mixing of mainstem river water with tributaries that had different chemistries, so that local zones of influence were detectable in the combined CNS zebra mussel isotopes downstream of major tributary confluences for the Illinois, Missouri and Ohio Rivers. Overall, the study supports use of stable isotopes to help monitor watershed development and downstream effects on aquatic food webs. Copyright © 2003 John Wiley & Sons, Ltd.