The Influence of Physical Habitat,Pyrethroids, and Metals on Benthic Community Condition in an Urban and Residential Stream in California

This study was designed to characterize benthic communities and physical habitat in both an urban (Kirker Creek) and residential (Pleasant Grove Creek) stream in California in late spring of 2006 and 2007. Concurrent water quality evaluations, physical sediment parameters, pyrethroids, bulk metals, and SEM/AVS ratios were also measured during both years of this study. The relationship of various benthic metrics to physical habitat metrics, pyrethroids, and metals was evaluated for each stream using stepwise multiple linear regressions with both years combined for each stream, as well as both years and both streams combined, to increase the statistical power for determining significant relationships. Physical habitat was determined to be poor in each stream during both years of sampling. More than 100 benthic taxa were reported annually for both streams based on 2006 and 2007 sampling. A significant result from the stepwise regression analysis combining data for 2 years across both streams is that when habitat metrics and to a lesser degree metals are considered in the statistical models pyrethroids do not display any significant relationships to the benthic metrics. In summary, it is apparent from this analysis that the health of benthic communities in both streams is primarily affected by habitat metrics.     

Lag in Stream Channel Adjustment to Livestock Exclosure, White Mountains, California

Livestock have been excluded from riparian zones along many streams in western North America in an effort to restore aquatic and riparian habitat degraded by livestock grazing. Within these exclosures, channel adjustment to elimination of grazing pressure may lag behind plant recovery because of the time required to deposit sediment along the vegetated banks of the stream channel. Moreover, unless grazing is eliminated from the watershed, the channel within the exclosure must still accommodate increased runoff and sediment loads from upstream. This hydrologic regime may prevent a return to predisturbance channel morphology. Cross sections of the North Fork Cottonwood Creek in the White Mountains of California showed no significant difference in channel width within and downstream of a 24-year-old exclosure, despite a lush growth of stream bank vegetation that gives the impression of a narrower channel within the exclosure.     

Simulated environmental effects of wetland restoration scenarios in a typical Canadian prairie watershed

Wetland conservation and restoration contribute to improved watershed functions through providing both water quantity benefits in terms of flood attenuation and water quality benefits such as retention of sediment and nutrients. However, it is important to quantify these environmental benefits for informed decision making. This study uses a “hydrologic equivalent wetland” concept in the Soil and Water Assessment Tool to examine the effects of various wetland restoration scenarios on stream flow and sediment at a watershed scale. The modeling system was applied to the 25,139 ha Broughton’s Creek watershed in western Manitoba in Canada. As a representative prairie watershed, the Broughton’s Creek watershed experienced historic wetland losses from 2,998 ha in 1968 to 2,379 ha in 2005. Modeling results showed that if wetlands in the Broughton’s Creek watershed can be restored to the 1968 level, the peak discharge and average sediment loading can be reduced by 23.4 and 16.9%, respectively at the watershed outlet. Based on wetland and stream drainage areas estimated by the model and empirical nutrient export coefficients, the corresponding water quality benefits in terms of reductions in total phosphorus and nitrogen loadings were estimated at 23.4%. The modeling results are helpful for designing effective watershed restoration strategies in the Broughton’s Creek watershed. The developed methodology can be also applied to other study areas for examining the environmental effects of wetland restoration scenarios.     

Analysis of chlordane-impacted streams using chironomid pupal exuviae (Diptera: Chironomidae)

A method of rapidly assessing streams and rivers using chironomid pupal exuviae was tested on a chlordane-impacted stream near St. Louis, Missouri. Various concentrations of chlordane were found in sediments of Grand Glaize Creek, most likely resulting from soil runoff around housing and business developments throughout the stream's course. Chironomid pupal exuviae and sediment samples were collected concurrently from Grand Glaize Creek on two separate occasions, once in 1988 and again in 1990. Cluster analysis of samples at sites, based on the percent abundances of taxa within habitats and by subfamilies, produced two distinct clusters; one grouping samples with lower chlordane concentrations and the other grouping samples with higher chlordane concentrations. Further analysis showed a trend towards lower percent abundances of taxa living in depositional and transitional/depositional zones (Chironominae and some Tanypodinae) at the higher chlordane site, while the lower chlordane sites had lower percent abundances of taxa within erosional and erosional/transitional zones (Orthocladiinae and some Tanypodinae). These findings support the hypothesis that taxa living in close association to fine organic sediments will be exposed to higher concentrations of chlordane in the stream and more negatively affected than taxa feeding and living in habitats removed from chlordane-bound sediments. Comparisons from the present study were made to related studies revealing similar patterns among the Chironomidae.     

Hiatal shell concentrations, sequence analysis, and sealevel history of a Pleistocene coastal alluvial fan, Punta Chueca, Sonora

Richly fossiliferous marine sediments exposed along the Sonoran coastline of the Gulf of California near Punta Chueca provide an excellent setting in which to test (a) the strength of the association of skeletal concentrations with sedimentary hiatuses, (b) the utility of taphonomic evidence for reconstructing detailed histories of those non-depositional episodes, and thus (c) the largely unexploited potential of skeletal concentrations in the identification and interpretation of lithologically obscure unconformities and condensed sequences in shallow marine deposits. Sequence analysis based on discontinuity surfaces is possible in the complex, alluvial fan-to-shallow marine transition at Punta Chueca despite rapid facies changes. Progradation of depositional sequences that contain cobbles reworked from older terrace deposits indicates accumulation during a fall in eustatic sea level. The supratidal to subtidal conglomerates and sands contain a variety of predominantly molluscan shell concentrations that, on the basis of postmortem histories of shells, formed during periods of low net sedimentation (i.e. depositional hiatuses); the majority of these shell beds lie along discontinuity surfaces identified by independent physical stratigraphic evidence. Although not all discontinuity surfaces in the terrace are paved by shell material. and not all relative concentrations of shells indicate distinct discontinuities, the strength of the association between skeletal concentrations and stratigraphic hiatuses reveals the high degree of control on fossil occurrence by sedimentation rates, and indicates that skeletal concentrations can provide good clues to stratigraphically significant surfaces. Moreover, the detailed dynamics of non-depositional episodes are reliably revealed by taphonomic analysis of the associated fossil assemblages, improving interpretations of non-depositional episodes in local sedimentary history.     

Effects of sediment loads on the fish and invertebrates of a Sierra Nevada river, California

This study examined the effects of sedimentloadings from an abandoned hydraulic miningsite on potential trout spawning gravels, largeaquatic macroinvertebrates, and fish growth,survival and reproduction in the South YubaRiver (Nevada County) California. Effects ofsediment loadings, which are transported to theSouth Yuba River via Humbug Creek, wereinvestigated by comparing data from sites onthe South Yuba River upstream and downstream ofHumbug Creek. The study did not find anydeleterious effects of sediment loadings onfish survival and reproduction (based onsnorkel survey data), or large aquaticmacroinvertebrate populations. In addition,the lack of a significant difference in thepercentage of 0.30 to 3.35 mm material insubstrate samples suggests that sediment loadsare not affecting trout spawning gravels. Incontrast, Sacramento pikeminnow(Ptychocheilus grandis) growth appears to beaffected by both water temperatures andsediment loadings. Downstream of Humbug Creek,growth during the first year was significantlyfaster, based on calculated standard lengths atthe age 1 annulus, but condition factor wassignificantly lower than above Humbug Creek.     

Water quality response to the Angora Fire, Lake Tahoe, California

The Angora Fire (summer of 2007) was the largest and most severe wildfire in recent history within the Lake Tahoe basin of the Sierra Nevada. To determine the watershed response and to assess the potential for downstream impacts of nutrient and sediment delivery to Lake Tahoe, we monitored the post-fire hydrology and stream water chemistry for 2 years at four locations along the length of Angora Creek, a perennial stream draining the burned watershed. When compared with unburned streams, the hydrology of Angora Creek indicated an earlier and faster melting of the spring snowpack. Peak stream water concentrations of total N (TN) and ammonium occurred within the burned area, whereas peak concentrations of nitrate (NO₃ ^?), total P, soluble reactive P, total suspended solids, turbidity, electrical conductivity (EC), and dissolved organic C occurred below the burned area. In comparison to pre-fire data, TN, NO₃ ^?, TP, total dissolved P, EC, and turbidity increased following the fire, particularly in the wetter second year. Yields for subwatershed areas suggest that the burned urban subwatershed was the largest source of nutrients and sediments, whereas the wet meadow subwatershed downstream of the burned area retained materials. Erosion control efforts, below-average annual precipitation and the timing of its arrival (absence of summer and fall rainstorms), and the existence of a wet meadow below the burned watershed likely reduced the negative impacts that would have been expected from such a severe wildfire.     

Effects of experimentally enhanced flows on fishes of a small Texas (U.S.A.) stream: assessing the impact of interbasin transfer

1. Completion of a large interbasin water transfer system in northern Texas (U.S.A.) provided the opportunity to test the effects of pre-planned, experimental increases (≈×30) in flow on the fish fauna of a small, low-gradient, natural stream that was included as part of the conveyance system. Water from Lake Texoma (Red River basin) was pumped via a 16-km pipeline to the headwaters of Sister Grove Creek (Trinity River basin), which then carried the donor water 50 km downstream to Lake Lavon.
2. Baseline (pre-transfer) data on the composition of fish assemblages at seven stations on the creek or at its confluence with the receiving reservoir were collected monthly for 3 years, and similar data were collected for 2 years during and after trial flows of Lake Texoma water to Sister Grove Creek. We also documented fish abundance at five creek stations immediately before and after three trial flow periods of 10–14 days each in summer and autumn.
3. Multivariate analysis of all routine monthly samples over the 5-year pre- and post-transfer period showed moderate changes in the fish fauna of the creek after initiation of the trial flows. Samples taken within a week before and after the artificial high flows showed little overall change in abundance of individual fish species, but at some stations the quantitative or qualitative change in composition of the local assemblage was substantial.
4. The trial flows lasted 2 weeks or less. Long-term effects of water transfer on the fish fauna of Sister Grove Creek can only be determined after the conveyance system goes into normal operation, with periods of artificial flow of longer duration.     

Effects of experimentally enhanced flows on fishes of a small Texas (U.S.A.) stream: assessing the impact of interbasin transfer

1. Completion of a large interbasin water transfer system in northern Texas (U.S.A.) provided the opportunity to test the effects of pre-planned, experimental increases (≈×30) in flow on the fish fauna of a small, low-gradient, natural stream that was included as part of the conveyance system. Water from Lake Texoma (Red River basin) was pumped via a 16-km pipeline to the headwaters of Sister Grove Creek (Trinity River basin), which then carried the donor water 50 km downstream to Lake Lavon.
2. Baseline (pre-transfer) data on the composition of fish assemblages at seven stations on the creek or at its confluence with the receiving reservoir were collected monthly for 3 years, and similar data were collected for 2 years during and after trial flows of Lake Texoma water to Sister Grove Creek. We also documented fish abundance at five creek stations immediately before and after three trial flow periods of 10–14 days each in summer and autumn.
3. Multivariate analysis of all routine monthly samples over the 5-year pre- and post-transfer period showed moderate changes in the fish fauna of the creek after initiation of the trial flows. Samples taken within a week before and after the artificial high flows showed little overall change in abundance of individual fish species, but at some stations the quantitative or qualitative change in composition of the local assemblage was substantial.
4. The trial flows lasted 2 weeks or less. Long-term effects of water transfer on the fish fauna of Sister Grove Creek can only be determined after the conveyance system goes into normal operation, with periods of artificial flow of longer duration.     

Benthic macroinvertebrate community structure, function and production with respect to habitat type, reach and drainage basin in the southern Appalachians (U.S.A.)

1. Benthic macroinvertebrates were sampled for 1 year to assess functional and taxonomic differences in invertebrate biomass and production with respect to habitat types, reaches and catchments in Wine Spring Basin, western North Carolina. Quantitative samples were collected from depositional, cobble-riffle and bedrock outcrop habitats at four stream reaches (two headwater sites, one second order, and one third order). Other measures included physical parameters, periphyton and organic matter standing crops. Invertebrate data from the Wine Spring catchment were also compared with data from another catchment (Ball Creek) within the same region. 2. The three habitat types had different current velocities and mean substratum particle sizes; both measures were greatest in bedrock outcrop habitats and lowest in depositional habitats. Organic matter standing crops, invertebrate functional group productivity and biomass also differed significantly with respect to habitat type. Cobble-riffle areas had the lowest standing crops of organic matter, invertebrate productivity and biomass. 3. Both invertebrate communities and organic matter standing crops differed significantly between the two headwater reaches. First- to third-order reaches differed in taxonomic composition at the genus level, yet had similar relative functional group productivity and biomass. 4. Annual mean invertebrate biomass and secondary production were greater in the Wine Spring Basin than in Ball Creek. Sites in both the Wine Spring and Ball Creek catchments, however, exhibited similar functional group distributions per habitat type. 5. Local geomorphology and related physical parameters influenced the structure of invertebrate functional group composition, and the distribution of organic matter standing crops. Furthermore, comparison of community structure in Wine Spring with that in Ball Creek suggested that taxonomic composition was more related to catchment-specific parameters (e.g. thermal regime, evolutionary history) than stream size.     

Total Mercury Concentrations in Lake and Streams Sediments Related to Wet-Area Coverage and Geogenic Sources within Upslope Basins

Total mercury concentrations (THg) in lake and stream sediments generally decrease with wet-area coverage (A_W) per upslope basin area (A_B). This was determined by delineating the wet-area component of 12,653 basins above as many sediment-sampling locations of the Geological Survey of Canada. These locations represent four climate regions (maritime, boreal, arctic, alpine) comprising six stream and six lake study areas. The dependence of sediment THg on A_W/A_B was examined by dividing the 0 < A_W/A_B < 1 range into 40 equal segments, and obtaining the mean sediment THg value for each segment. The results were evaluated by way of regression analysis using the following equation: mean sediment THg = a (1 ? A_W/A_B)^b + c A_W/A_B, with a, b and c as area-specific coefficients. The “a” and “c” coefficients could – in part – be inferred from bedrock type, annual atmospheric Hg deposition, and mean monthly air temperatures, and mean annual precipitation. Both “a” and “c” increased with increasing atmospheric Hg deposition for lake sediments. For stream sediments, only “a” did so. The geogenic influence on the THg variations per study area was addressed through multiple regression analyses, using sediment concentrations of other heavy elements and organic matter as independent variables.     

Retention of suspended sediment and phosphorus on a freshwater delta, South Lake Tahoe, California

The Upper Truckee River and Trout Creek, two major tributaries inflowing to Lake Tahoe, join to form what was historically the largest wetland in the Sierra Nevada mountain range that separates California and Nevada (USA). In the 1950s the delta floodplain of the Upper Truckee River was greatly reduced in area (38%) by urban development and the diversion of the river into a single excavated channel. Conversely, Trout Creek still flows through a wide marsh system with significant overbank flooding before entering Lake Tahoe. This study hypothesized that river channel reaches that are not incised within the delta floodplain retain more sediment and nutrients as a result of greater floodplain connectivity, compared to more incised and excavated reaches. Suspended sediment (SS) and total phosphorus (TP) load data from the delta formed by the Upper Truckee River and Trout Creek were collected using flow stage sensors, turbidometers and depth-integrated samples. During the spring snowmelt flow events monitored in 2003, SS load was reduced by 13–41% for the Upper Truckee River and by 68–90% for Trout Creek. Similar reductions in TP load were observed: 13–32% for the Upper Truckee River and 61–84% for Trout Creek. Monitoring of Trout Creek indicated a reduction in load per unit volume of 20–34% in a moderately incised reach versus a reduction of 51–77% in a non-incised marsh reach containing lagoons, braided channels and backwater areas created by a beaver dam. Smaller particle sizes, <10 μm, were retained in the lower marsh reach with similar efficiencies as larger particle sizes. If retention rates from the Trout Creek portion of the marsh are applied to the Upper Truckee River, sediment loading to Lake Tahoe for 2003 would have been reduced by 917 tons of SS.     

Ubiquity and persistence of Escherichia coli in a Midwestern coastal stream

Dunes Creek, a small Lake Michigan coastal stream that drains sandy aquifers and wetlands of Indiana Dunes, has chronically elevated Escherichia coli levels along the bathing beach near its outfall. This study sought to understand the sources of E. coli in Dunes Creek's central branch. A systematic survey of random and fixed sampling points of water and sediment was conducted over 3 years. E. coli concentrations in Dunes Creek and beach water were significantly correlated. Weekly monitoring at 14 stations during 1999 and 2000 indicated chronic loading of E. coli throughout the stream. Significant correlations between E. coli numbers in stream water and stream sediment, submerged sediment and margin, and margin and 1 m from shore were found. Median E. coli counts were highest in stream sediments, followed by bank sediments, sediments along spring margins, stream water, and isolated pools; in forest soils, E. coli counts were more variable and relatively lower. Sediment moisture was significantly correlated with E. coli counts. Direct fecal input inadequately explains the widespread and consistent occurrence of E. coli in the Dunes Creek watershed; long-term survival or multiplication or both seem likely. The authors conclude that (i) E. coli is ubiquitous and persistent throughout the Dunes Creek basin, (ii) E. coli occurrence and distribution in riparian sediments help account for the continuous loading of the bacteria in Dunes Creek, and (iii) ditching of the stream, increased drainage, and subsequent loss of wetlands may account for the chronically high E. coli levels observed.     

Miocene invertebrate trace fossils from a braided river environment,western Nebraska,U.S.A

Lower Miocene cross-stratified sands of the Gering and Monroe Creek Formations exposed on Scotts Bluff National Monument in western Nebraska, U.S.A., were deposited by migrating sand bars in a braided river system similar to the modern Platte River in eastern Nebraska and, like the Platte, contain local lenses of parallel stratified sediment that accumulated in ponded areas of abandoned channels. During times of low discharge, broad areas of river bar sands and abandoned channel sediments were subaerially exposed on the Miocene river plain. These sediments, like those exposed in the Platte River today, were subjected to burrowing by insects and other animals.Trace fossils in Lower Miocene braided river deposits are: vertical shelter burrows, horizontal deposit-feeding burrows, bioturbated layers, and vertical passageways between bioturbated layers. The burrows are cylindrical to sub-cylindrical in cross-section, internally meniscate or massive, generally non-branching, and smooth walled. Shelter burrows are similar in shape and size to recent burrows dug by beetles in river sediment for protection from day-time temperatures, to pass the night, and to hibernate. The shelter burrows, deposit-feeding burrows, and vertical passageways in the Lower Miocene sediments occur in four distinct “populations” with modal diameters of 1–2, 3–4, 7–8, and 10–12 mm. The occurrence of both vertical and horizontal burrows in all four “populations” suggests that they could have been made by the same insect. “Populations” with modal diameters of 1–2, 3–4, and 7–8 mm also occur in modern Platte River sediment and are made by tiger-beetle larvae (3–4 mm) and heterocerid (1–2 mm) beetles. Miocene shelter burrows, deposit-feeding burrows, bioturbated layers, and vertical passageways, therefore, could have been formed by different types of beetles, and/or larval instars and adults of the same beetle species.     

Linking fish trait responses to in‐stream habitat in reconstructed valley‐plugged stream reaches of the Coastal Plain,U.S.A.

Valley‐plug formation is a challenging consequence of stream channelization especially in physiographic regions with highly erodible soils. Upstream channel degradation and incision results in accelerated sediment delivery processes wherein downstream aggradation decreases stream power and creates sand‐clogged channels. Channel reconstruction is now meeting hydrogeomorphic goals related to valley‐plug remediation, yet there exists a need to understand how this practice also facilitates ecological restoration. We evaluated fish trait response to in‐stream habitat conditions in channelized, recently restored, and “least‐disturbed” reference reaches of Coastal Plain streams in West Tennessee. Restored reaches were ecologically similar to channelized reaches, having higher proportions of nest‐guarding omnivores that were correlated with higher percentages of pool habitats and lower wetted width:depth ratios compared to reference reaches. Reference reaches had higher proportions of fast‐water dwelling and specialized insectivores that were correlated with high abundance of large woody debris, high‐wetted width:depth ratios, and low percentages of pool habitats. We conclude that in‐stream habitats in reconstructed channels have yet to promote reach‐scale ecological restoration relative to fish assemblage organization because trait‐habitat associations were not similar to reference conditions. However, our results lend to the development of ecological restoration targets that can be incorporated in future channel reconstruction projects in valley‐plugged, channelized streams of the Coastal Plain.     

Pyrethroid resistance and mechanisms of resistance in field strains of Helicoverpa armigera (Lepidoptera: Noctuidae)

Pyrethroid resistance was found in 54 field strains of Helicoverpa armigera collected between 1995 and 1999 from 23 districts in seven states of India. LD50 values of the field strains ranged from 0.06 to 72.2 microg/larva with slopes of 0.5-3.1. Resistance was highest in regions where pyrethroid use was frequent (four to eight applications per season). Resistance to deltamethrin was exceptionally high with resistance ratios of 13,570 and 27,160 in two strains collected during February 1998 in central India. Resistance to cypermethrin, fenvalerate and cyhalothrin also was high with resistance ratios of >1,000 in four strains collected from central and southern India. Resistance ratios were below 100 in >50% of the strains tested. Pyrethroid resistance was high in strains collected from the districts in Andhra Pradesh where a majority of the cotton farmer suicide cases in India were reported. Resistance to pyrethroids appeared to have increased over 1995-1998 in most of the areas surveyed. Studies carried out through estimation of detoxification enzyme activity and synergists indicated that enhanced cytochrome p450 and esterase activities were probably important mechanisms for pyrethroid resistance in field strains. Pyrethroid nerve insensitivity also was found to be a major mechanism in some parts of the country where the use of pyrethroids was high. The information presented illustrates the importance of proper insect management programs to avoid the consequences associated with improper insecticide use.     

The impact of an industrially contaminated lake on heavy metal levels in its effluent stream

Levels of cadmium and zinc in various components of Williamson Ditch (an industrially contaminated stream flowing into Palestine Lake), Trimble Creek (a stream draining Palestine Lake) and the Tippecance River (a river receiving Trimble Creek) were determined. Water, sediment, plant, fish and clam samples were analyzed for cadmium and zinc content by atomic absorption spectrophotometry. Unweighted mean metal concentrations in Trimble Creek were the following: water, 51 µg Zn/1 and 4.2 µg Cd/1; sediment, 592 µg Zn/g and 48.8,µg Cd/g; plants, 375 µm Zn/g and 7.91 µg Cd/g; fish, 145 µg Zn/g and 6.02 µg Cd/g. These concentrations were generally lower than those found in Williamson Ditch and higher than those found in the Tippecanoe River or background levels previously reported for other aquatic ecosystems.     

Relationship between genotoxicity,mutagenicity, and fish community structure in a contaminated stream

Genotoxic responses (chromosomal damage, DNA strandbreakage) of redbreast sunfish (Lepomis auritis)populations exposed to industrial effluent andmutagenicity of the associated sediments weredetermined in order to compare them to changes incommunity structure. Data were collected from areference stream and East Fork Poplar Creek (EFPC), afirst-order stream which originates on the grounds ofthe Department of Energy Y-12 Plant at Oak Ridge, TN. This stream is contaminated with mercury, PCBs, andnumerous other compounds. Previous studies have shownthat sediment contaminant concentrations, as well asphysiological biomarker responses of the local fishpopulations, are highest at the headwaters of EFPC anddecrease with increasing distance from the DOEfacility as contaminant loading decreases. Chromosomal damage was measured by flow cytometry – asreflected by variation in cellular DNA content – andstrand breakage was determined by agarose gelelectrophoresis using blood as the source of DNA. Mutagenicity was determined by theSalmonella/microsome assay using organic solventextracts of sediment surface samples. Community levelresponses included community diversity and percentpollution-tolerant species. Biomarker responses andmutagenicity were found to be highest at theheadwaters of EFPC, and tended to decrease withincreasing distance from the effluent. In general,biomarker responses appeared to be correlated withmutagenicity of the sediment, and both of theserelated to fish community disturbance and level ofstream contamination. Because responses at severallevels of biological organization show similarpatterns of downstream effects, this suggests thatthere may be a causal relationship betweencontamination and biological effects.     

Abundance of Three Bacterial Populations in Selected Streams

The population sizes of three bacterial species, Acinetobacter calcoaceticus, Burkholderia cepacia, and Pseudomonas putida, were examined in water and sediment from nine streams in different parts of the United States using fluorescent in situ hybridization (FISH). Population sizes were determined from three sites (upstream, midstream, and downstream) in each stream to compare differences in the occurrence and distribution of the species within each stream and among streams. Physical and chemical variables measured reflected differences in environmental conditions among the streams. In the water, B. cepacia numbers were highest in the agricultural, Iowa stream. P. putida numbers were highest in the southern coastal plain streams, Black Creek (GA) and Meyers Branch (SC). Compared to the other two species, the abundance of A. calcoaceticus was similar in all the streams. In sediment, the greatest abundance of all three species was found in the Iowa stream, while the lowest was in Hugh White Creek (NC). Detrended correspondence analysis (DCA) explained 95.8% and 83.9% of the total variation in bacterial numbers in water and sediment of the streams, respectively. In sediments and water, B. cepacia numbers were related to nitrate concentrations. A. calcoaceticus in water clustered with several environmental variables (i.e., SRP, pH, and conductivity) but benthic populations were less well correlated with these variables. This study reveals the potential influence of various environmental conditions on different bacterial populations in stream communities.     

Benthic indicators of sediment quality associated with run-of-river reservoirs

Freshwater ecosystems have been fragmented by the construction of large numbers of dams. In addition to disruption of ecological continuity and physical disturbance downstream, accumulation of large amounts of sediment within run-of-river reservoirs constitutes a latent ecotoxic risk to aquatic communities. To date, run-of-river reservoirs and ecotoxic risks associated with contaminated sediment to the biodiversity and functioning of such systems are little studied. Therefore, the main objective of this study was to describe macroinvertebrate assemblages, and the functioning of these systems, and to propose indicators of sediment contamination to integrate in in-situ risk assessment methodology. To identify specific assemblages of run-of-river reservoirs, we first compared macroinvertebrate assemblages and their biotrait profiles (i.e. from a database of biological and ecological traits) in reservoirs (n = 6) and associated river sites (upstream and downstream of dams). Then, we compared responses of assemblages and biotrait profiles to sediment contamination of the banks and channels of reservoirs to select the most useful spatial scale to identify sediment contamination. Nineteen indicator taxa were observed to be specifically associated with channel habitats of reservoirs. Among these, the abundance of three taxa (Tanypodinae (Diptera), Ephemerella (Ephemeroptera) and Atherix (Diptera)) revealed the effect of metal sediment contamination. “Between-reservoirs” differences in their biotrait profile were found along the contamination gradient, with a shift of communities’ composition and functionality, and an increase in functional similarity. Many traits (response traits), for example “maximum size”, “transverse distribution”, “substrate preferences”, “saprobity”, “temperature”, “resistance forms”, and “locomotion”, were specifically linked to contamination of sediments by metals. This study indicates how sediment contamination can change the structural and functional composition of run-of-river reservoir assemblages. Indicator taxa and response traits identified in this study could improve current risk assessment methodology and potentially enable prediction of the risks of contaminated sediments stored in reservoirs in downstream ecosystems.