Stream Bed Sediments Research Articles

Lithology‐controlled evolution of stream bed sediment and basin‐scale sediment yields in adjacent mountain watersheds, Idaho, USA

AbstractThe composition, grain‐size, and flux of stream sediment evolve downstream in response to variations in basin‐scale sediment delivery, channel network structure, and diminution during transport. Here, we document downstream changes in lithology and grain size within two adjacent ~300 km2 catchments in the northern Rocky Mountains, USA, which drain differing mixtures of soft and resistant rock types, and where measured sediment yields differ two‐fold. We use a simple erosion–abrasion mass balance model to predict the downstream evolution of sediment flux and composition using a Monte Carlo approach constrained by measured sediment flux. Results show that the downstream evolution of the bed sediment composition is predictably related to changes in underlying geology, influencing the proportion of sediment carried as bedload or suspended load. In the Big Wood basin, particle abrasion reduces the proportion of fine‐grained sedimentary and volcanic rocks, depressing bedload in favor of suspended load. Reduced bedload transport leads to stronger bed armoring, and coarse granitic rocks are concentrated in the stream bed. By contrast, in the North Fork Big Lost basin, bedload yields are three times higher, the stream bed is less armored, and bed sediment becomes dominated by durable quartzitic sandstones. For both basins, the geology‐based mass balance model can reproduce within ~5% root‐mean‐square error the composition of the bed substrate using realistic erosion and abrasion parameters. As bed sediment evolves downstream, bedload fluxes increase and decrease as a function of the abrasion parameter and the frequency and size of tributary junctions, while suspended load increases steadily. Variable erosion and abrasion rates produce conditions of variable bed‐material transport rates that are sensitive to the distribution of lithologies and channel network structure, and, provided sufficient diversity in bedrock geology, measurements of bed sediment composition allow for an assessment of sediment source areas and yield using a simple modeling approach. Copyright © 2016 John Wiley & Sons, Ltd.

Fractions and Release Risk of Phosphorus in Surface Sediments of Three Headwater Streams with Different Styles of Water Supply

From May to September 2015, seasonal sediment samples were collected from three headwater streams and ditches which were discharged from sewage plant tail water, food processing wastewater and agricultural drainage-groundwater seepage, respectively, in Hefei, Chaohu Lake basin. The stream-bed sediments were analyzed for phosphorus fractions. The risk assessment on phosphorus release from sediments was conducted using the phosphorus sorption index (PSI), degree of phosphorus saturation (DPS) and the phosphorus release risk index (ERI). Moreover, nonparametric tests method was used to explore the difference among the three studied streams and ditches. Study results showed that:1 Guanzhenhe Distributary and Taochong Stream were seriously damaged by phosphorus pollution both in waters and stream-bed sediment, and the phosphorus pollution levels could be arranged in the order of Guanzhenhe Distributary >Taochong Stream >Modian Stream. The mean content of total phosphorus (TP) in sediments in Guanzhenhe Distributary was 1376.95 mg·kg-1, which was 2.94 and 1.91 times as high as those of Modian Stream and Taochong Stream, respectively. 2 Significant differences and different sort orders in contents of phosphorus fractions were found for each of the three streams. 3 Obvious seasonal variations existed in PSI for the three streams, and all the sampling points in the same stream had similar changing law, namely, the maximum content emerged in autumn, followed by winter, and the minimum occurred in spring or summer. 4 The same conclusions were drawn in phosphorus release risk according to the PSI, DPS and ERI, and the risk ranked as follows:Guanzhenhe Distributary >Taochong Stream >Modian Stream. 5 According to the difference analysis, significant differences existed in almost all of the indexes among the three streams.

Characterizing relationships among fecal indicator bacteria, microbial source tracking markers, and associated waterborne pathogen occurrence in stream water and sediments in a mixed land use watershed

Bed sediments of streams and rivers may store high concentrations of fecal indicator bacteria (FIB) and pathogens. Due to resuspension events, these contaminants can be mobilized into the water column and affect overall water quality. Other bacterial indicators such as microbial source tracking (MST) markers, developed to determine potential sources of fecal contamination, can also be resuspended from bed sediments. The primary objective of this study was to predict occurrence of waterborne pathogens in water and streambed sediments using a simple statistical model that includes traditionally measured FIB, environmental parameters and source allocation, using MST markers as predictor variables. Synoptic sampling events were conducted during baseflow conditions downstream from agricultural (AG), forested (FORS), and wastewater pollution control plant (WPCP) land uses. Concentrations of FIB and MST markers were measured in water and sediments, along with occurrences of the enteric pathogens Campylobacter, Listeria and Salmonella, and the virulence gene that carries Shiga toxin, stx2. Pathogens were detected in water more often than in underlying sediments. Shiga toxin was significantly related to land use, with concentrations of the ruminant marker selected as an independent variable that could correctly classify 76% and 64% of observed Shiga toxin occurrences in water and sediment, respectively. FIB concentrations and water quality parameters were also selected as independent variables that correctly classified Shiga toxin occurrences in water and sediment (54%–87%), and Salmonella occurrences in water (96%). Relationships between pathogens and indicator variables were generally inconsistent and no single indicator adequately described occurrence of all pathogens. Because of inconsistent relationships between individual pathogens and FIB/MST markers, incorporating a combination of FIB, water quality measurements, and MST markers may be the best way to assess microbial water quality in mixed land use systems.

Heterogeneity in leaf litter decomposition in a temporary Mediterranean stream during flow fragmentation

In temporary Mediterranean streams, flow fragmentation during summer droughts originates an ephemeral mosaic of terrestrial and aquatic habitat types. The heterogeneity of habitat types implies a particular ecosystem functioning in temporary streams that is still poorly understood. We assessed the initial phases of leaf litter decomposition in selected habitat types: running waters, isolated pools and moist and dry streambed sediments. We used coarse-mesh litter bags containing Populus nigra leaves to examine decomposition rates, microbial biomass, macroinvertebrate abundance and dissolved organic carbon (DOC) release rates in each habitat type over an 11-day period in late summer. We detected faster decomposition rates in aquatic (running waters and isolated pools) than in terrestrial habitats (moist and dry streambed sediments). Under aquatic conditions, decomposition was characterized by intense leaching and early microbial colonization, which swiftly started to decompose litter. Microbial colonization in isolated pools was primarily dominated by bacteria, whereas in running waters fungal biomass predominated. Under terrestrial conditions, leaves were most often affected by abiotic processes that resulted in small mass losses. We found a substantial decrease in DOC release rates in both aquatic habitats within the first days of the study, whereas DOC release rates remained relatively stable in the moist and dry sediments. This suggests that leaves play different roles as a DOC source during and after flow fragmentation. Overall, our results revealed that leaf decomposition is heterogeneous during flow fragmentation, which has implications related to DOC utilization that should be considered in future regional carbon budgets.

Preliminary assessment of pseudo-total and bioavailable metals in depth in the sediment of Luíz Rau stream in Novo Hamburgo (RS).

The Luíz Rau stream is one of the main streams of Novo Hamburgo. In the stream industrial effluents are released from various sectors, from paint and adhesive industries, metallurgy and leather industry, besides receiving a large amount of domestic sewage. The emissions of these pollutants contribute to decrease water and sediment quality. Within this context, this study evaluated the conditions of the Luíz Rau stream bed sediments, with the determination of the metals like cadmium, lead, chromium and nickel, in depth. To perform the evaluation three points were chosen for sampling along the stream course. The sampling sites were identified as Point A, in Roselândia district and this corresponds to one of the springs and therefore considered as reference value, Point B, in Santo Afonso district being a midpoint of the stream, and Point C also located in Santo Afonso district, near the outfall in Rio dos Sinos river. Cadmium was not detected in any point. At the A and C points chromium was the metal observed in higher concentration in the sediment, up to 45.14 mg kg(-1) concentration. In the B point, the metal that was observed in the highest amount was nickel in the concentration of 20.69 mg kg(-1).

The legacy of lead (Pb) in fluvial bed sediments of an urban drainage basin, Oahu, Hawaii.

The study of fluvial bed sediments is essential for deciphering the impact of anthropogenic activities on water quality and drainage basin integrity. In this study, a systematic sampling design was employed to characterize the spatial variation of lead (Pb) concentrations in bed sediment of urban streams in the Palolo drainage basin, southeastern Oahu, Hawaii. Potentially bioavailable Pb was assessed with a dilute 0.5 N HCl extraction of the <63 μm grain-size fraction from the upper bed sediment layer of 169 samples from Palolo, Pukele, and Waiomao streams. Contamination of bed sediments was associated with the direct transport of legacy Pb from the leaded gasoline era to stream channels via a dense network of storm drains linked to road surfaces throughout the basin. The Palolo Stream had the highest median Pb concentration (134 mg/kg), and the greatest road and storm drain densities, the greatest population, and the most vehicle numbers. Lower median Pb concentrations were associated with the less impacted Pukele Stream (24 mg/kg), and Waiomao Stream (7 mg/kg). The median Pb enrichment ratio values followed the sequence of Palolo (68) > Pukele (19) > Waiomao (8). Comparisons to sediment quality guidelines and potential toxicity estimates using a logistic regression model (LRM) indicated a significant potential risk of Palolo Stream bed sediments to bottom-dwelling organisms.

Microbial Transport, Retention, and Inactivation in Streams: A Combined Experimental and Stochastic Modeling Approach.

Long-term survival of pathogenic microorganisms in streams enables long-distance disease transmission. In order to manage water-borne diseases more effectively we need to better predict how microbes behave in freshwater systems, particularly how they are transported downstream in rivers. Microbes continuously immobilize and resuspend during downstream transport owing to a variety of processes including gravitational settling, attachment to in-stream structures such as submerged macrophytes, and hyporheic exchange and filtration within underlying sediments. We developed a stochastic model to describe these microbial transport and retention processes in rivers that also accounts for microbial inactivation. We used the model to assess the transport, retention, and inactivation of Escherichia coli in a small stream and the underlying streambed sediments as measured from multitracer injection experiments. The results demonstrate that the combination of laboratory experiments on sediment cores, stream reach-scale tracer experiments, and multiscale stochastic modeling improves assessment of microbial transport in streams. This study (1) demonstrates new observations of microbial dynamics in streams with improved data quality than prior studies, (2) advances a stochastic modeling framework to include microbial inactivation processes that we observed to be important in these streams, and (3) synthesizes new and existing data to evaluate seasonal dynamics.

Marcellus and mercury: Assessing potential impacts of unconventional natural gas extraction on aquatic ecosystems in northwestern Pennsylvania

Mercury (Hg) is a persistent element in the environment that has the ability to bioaccumulate and biomagnify up the food chain with potentially harmful effects on ecosystems and human health. Twenty-four streams remotely located in forested watersheds in northwestern PA containing naturally reproducing Salvelinus fontinalis (brook trout), were targeted to gain a better understanding of how Marcellus shale natural gas exploration may be impacting water quality, aquatic biodiversity, and Hg bioaccumulation in aquatic ecosystems. During the summer of 2012, stream water, stream bed sediments, aquatic mosses, macroinvertebrates, crayfish, brook trout, and microbial samples were collected. All streams either had experienced hydraulic fracturing (fracked, n = 14) or not yet experienced hydraulic fracturing (non-fracked, n = 10) within their watersheds at the time of sampling. Analysis of watershed characteristics (GIS) for fracked vs non-fracked sites showed no significant differences (P > 0.05), justifying comparisons between groups. Results showed significantly higher dissolved total mercury (FTHg) in stream water (P = 0.007), lower pH (P = 0.033), and higher dissolved organic matter (P = 0.001) at fracked sites. Total mercury (THg) concentrations in crayfish (P = 0.01), macroinvertebrates (P = 0.089), and predatory macroinvertebrates (P = 0.039) were observed to be higher for fracked sites. A number of positive correlations between amount of well pads within a watershed and THg in crayfish (r = 0.76, P < 0.001), THg in predatory macroinvertebrates (r = 0.71, P < 0.001), and THg in brook trout (r = 0.52, P < 0.01) were observed. Stream-water microbial communities within the Deltaproteobacteria also shared a positive correlation with FTHg and to the number of well pads, while stream pH (r = −0.71, P < 0.001), fish biodiversity (r = −0.60, P = 0.02), and macroinvertebrate taxa richness (r = −0.60, P = 0.01) were negatively correlated with the number of well pads within a watershed. Further investigation is needed to better elucidate relationships and pathways of observed differences in stream water chemistry, biodiversity, and Hg bioaccumulation, however, initial findings suggest Marcellus shale natural gas exploration is having an effect on aquatic ecosystems.

Rainfall-induced runoff from exposed streambed sediments: an important source of water pollution.

When surface water levels decline, exposed streambed sediments can be mobilized and washed into the water course when subjected to erosive rainfall. In this study, rainfall simulations were conducted over exposed sediments along stream banks at four distinct locations in an agriculturally dominated river basin with the objective of quantifying the potential for contaminant loading from these often overlooked runoff source areas. At each location, simulations were performed at three different sites. Nitrogen, phosphorus, sediment, fecal indicator bacteria, pathogenic bacteria, and microbial source tracking (MST) markers were examined in both prerainfall sediments and rainfall-induced runoff water. Runoff generation and sediment mobilization occurred quickly (10-150 s) after rainfall initiation. Temporal trends in runoff concentrations were highly variable within and between locations. Total runoff event loads were considered large for many pollutants considered. For instance, the maximum observed total phosphorus runoff load was on the order of 1.5 kg ha. Results also demonstrate that runoff from exposed sediments can be a source of pathogenic bacteria. spp. and spp. were present in runoff from one and three locations, respectively. Ruminant MST markers were also present in runoff from two locations, one of which hosted pasturing cattle with stream access. Overall, this study demonstrated that rainfall-induced runoff from exposed streambed sediments can be an important source of surface water pollution.

Using radiometric fingerprinting and phosphorus to elucidate sediment transport dynamics in an agricultural watershed

AbstractThe major goals of this study were to determine stream bed sediment erosion/deposition rates, sediment age, percent ‘new’ sediment, and suspended sediment origin during two storm events of contrasting magnitudes (11.9 mm over 5 h and 58.9 mm over 39 h) using fallout radionuclides (excess lead 210 – 210Pbxs and beryllium 7 – 7Be) and link the nature and type of sediment source contributions to potential phosphorus (P) off‐site transport. The study was conducted in cropland‐dominated and mixed land use subwatersheds in the non‐glaciated Pleasant Valley watershed (50 km2) in South Central Wisconsin. Fine sediment deposition and erosion rates on stream beds varied from 0.76 to 119.29 mg cm−2 day−1 (at sites near the watershed outlet) and 1.72 to 7.72 mg cm−2 day−1 (at sites in the headwaters), respectively, during the two storm events. The suspended sediment age ranged from 123 ± 12 to 234 ± 33 days during the smaller storm event; however, older sediment was more prevalent (p = 0.037) in the streams during the larger event with suspended sediment age ranging from 226 ± 9 to 322 ± 114 days. During the small and large storm event, percent new sediment in suspended sediment ranged from 5.3 ± 2.1 to 21.0 ± 2.9% and 5.3 ± 2.7 to 6.7 ± 5.7%, respectively. In the cropland‐dominated subwatershed, upland soils were the major source of suspended sediment, whereas in the mixed land use subwatershed, both uplands and stream banks had relatively similar contributions to suspended sediment. In‐stream (suspended and bed) sediment P levels ranged from 703 ± 193 to 963 ± 84 mg kg−1 during the two storm events. The P concentrations in suspended and bed sediment were reflective of the dominant sediment source (upland or stream bank or mixed). Overall, sediment transport dynamics showed significant variability between subwatersheds of different land use characteristics during two contrasting storm events. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Effects of a small-scale, abandoned gold mine on the geochemistry of fine stream-bed and floodplain sediments in the Horsefly River watershed, British Columbia, Canada

Mining is known to be a major source of metal contamination for fluvial systems worldwide. Monitoring and understanding the effects on downstream water and sediment quality is essential for its management and to mitigate against detrimental environmental impacts. This study aimed to examine the effects of the small-scale, abandoned, hydraulic Black Creek gold mine on the geochemical content of fine (&lt;63 μm) stream bed and floodplain sediment in the Horsefly watershed (British Columbia, Canada), which is a part of the Quesnel River basin. Concentrations of As, Cd, Se and Zn were determined byaqua regiadigestion and the modified BCR (European Community Bureau of Reference) sequential extraction procedure followed by inductively coupled plasma-optical emission spectroscopy or inductively coupled plasma-mass spectrometry. Age-depth models for the floodplain cores were constructed using excess Pb-210 and Cs-137 activity concentration profiles. The results show that the mine caused local As contamination of the Horsefly River floodplain sediment during the first years of operation, but at present the contamination is mainly contained in the Black Creek. Present-day and recent concentrations of Cd, Se and Zn in the Horsefly River are elevated and this is probably derived from other upstream mining activities. The spatial and temporal changes in heavymetal concentrations suggest a slight, but not particularly widespread, mining effect on the finesediment geochemistry in the Horsefly River system.

Geochemical mapping of Pb- and Zn-contaminated streambed sediments in southwest Missouri, USA

Purpose Four locations in southwest Missouri, USA, purportedly contaminated with mining wastes, Joplin, Aurora, Springfield, and the James River, were investigated for lead and zinc content using spatial distribution and statistical analyses. Lead (Pb) and zinc (Zn) concentrations in streambed sediment samples were compared spatially against a regional background concentration map to determine both the contamination level and dispersion of these metals.

Distribution and persistence of Escherichia coli and Enterococci in stream bed and bank sediments from two urban streams in Houston, TX

The purpose of this research was to determine if Escherichia coli and enterococci in streambed and bank sediments from two urban bayous, Buffalo Bayou and White Oak Bayou, in Houston, TX, USA are a significant source of the chronically high levels of these bacteria in the overlying water. The watersheds of the bayous lie within highly urbanized areas of Greater Houston and there is primary recreational contact with the public. Extensive sampling of the watersheds was conducted from 2008 to 2010. Both fecal indicator bacteria were found at ≥104MPNgdry wt.−1 concentrations in the upper 1cm of sediment cores with declines by orders of magnitude at 15 and 30cm sediment horizons and in some cases 60cm, but, nonetheless, indicating that they can remain viable even at depth. No interannual variation was observed. And, there was no correlation with percent organic matter, however there was moderate correlation (R2=0.12; p=0.001) of E. coli with sediment moisture. In sediments, most E. coli and enterococci in Buffalo Bayou (76%) and White Oak Bayou (87.5%) were associated with fine sand grains (60 to 250μm). In the water column, E. coli was associated, in roughly equal percentages, with particle sizes <10, 10–25, 25–63, and ≥63μm (21.9, 25.6, 30.4, and 32.9%, respectively). Enterococci were mostly attached to particle sizes in the ranges of 10–25μm (36.0%) and 25–63μm (31.1%) as well as ≥63μm (37.7%) (p=0.0001). Fingerprinting of E. coli isolates from both bayous with Rep-PCR and the BOX A1R primer was used to demonstrate translocation of sediments from the upper to lower watersheds.

Diversification of stream invertebrate communities by large wood

Summary To evaluate the effects of large wood (LW) on benthic habitats and macroinvertebrates in sand‐bed lowland rivers, we compared invertebrate communities recorded on four pieces of LW (12 samples in total) and around them (60 samples) with those in four control sites in the same river (four samples). Mean flow velocity was 32% lower in the channel areas surrounding the LW than in control sites, while median sediment grain size was 50% higher, and the organic matter content of the riverbed sediments was 287% higher. At the same time, habitat conditions showed threefold to 1000‐fold increases in variance for five key abiotic habitat descriptors in the surrounding channel extending at least 60 cm upstream and 160 cm downstream of the LW. Three habitat patches typically occurred around the LW pieces: scouring pools, sand bars and accumulations of organic matter. These patches were colonised by distinctive invertebrate communities (e.g. accumulations of organic matter and gravel hosted 15 and 2 indicator taxa, respectively) that overall harboured 110% more taxa and exhibited a 168% higher diversity than control sites. The LW itself contributed only a small fraction to these increases, exhibiting a 15% increase in taxa richness and a 21% increase in species diversity compared to the control sites. The diversification of benthic invertebrate communities colonising streambed sediments around LW could be directly linked to the much more heterogeneous habitat conditions recorded there. Thus, local additions of large wood within river restoration programmes have the potential to promote the establishment of diverse invertebrate communities in extended areas of a river channel.

Spatial variability in sediment phosphorus characteristics along a hydrological gradient upstream of Lake Rotorua, New Zealand

This study examined particulate phosphorus (PP) characteristics of terrestrial, stream bed and lake bed sediments along a common hydrological pathway. The objective was to quantify spatial variability of PP in the catchment of a eutrophic lake, Rotorua (New Zealand). Median total phosphorus (TP; dry weight) concentration in sediments (‘terrestrial’) deposited from overland flow on farmland in the upper stream catchment was high (2,157 mg kg−1), greatly exceeding that of stream bed sediments (212 mg kg−1; Waiteti Stream) which exhibited downstream decline in TP concentrations. Lake bed sediments were enriched in TP (median = 2,661 mg kg−1) with relatively low Fe:P and Al:P mass ratios. Sequential extraction of three PP fractions showed that the mean proportion of HCl-extracted P (Ca-bound, denoting the refractory fraction) in extracted P was higher in terrestrial sediments (17 %) than stream bed sediments (4 %). Accordingly, TP concentrations of terrestrial sediments were highly (p < 0.01) correlated with Ca (R = 0.89), whereas TP was most closely correlated with Al (R = 0.83) in the stream bed sediments. Nonetheless, the majority of sequentially extracted P in both terrestrial and stream bed sediments comprised fractions (bicarbonate dithionate- and NaOH-extractable) that are potentially bioavailable in Lake Rotorua. Furthermore, phosphate buffering experiments indicated that terrestrial sediments desorbed P to be a source of PO4–P to receiving waters, whereas stream bed sediments buffered PO4–P concentrations in stream water. Such quantification of landscape-scale variability in PP characteristics can support strategic management of TP loading to the lake.

New empirical relationship between grain size distribution and hydraulic conductivity for ephemeral streambed sediments

Grain size distribution, porosity, and hydraulic conductivity were determined for 39 sediment samples collected from ephemeral streams (wadis) in western Saudi Arabia. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations commonly used to estimate hydraulic conductivity from grain size analyses. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly with the measured hydraulic conductivity values. Modifications of the empirical equations, including changes to special coefficients and statistical offsets, were made to produce modified equations that considerably improved the hydraulic conductivity estimates from grain size data for wadi sediments. The Chapuis, Hazen, Kozeny, Slichter, Terzaghi, and Barr equations produced the best correlations, but still had relatively high predictive errors. The Chapius equation was modified for wadi sediments by incorporating mud percentage and the standard deviation (in phi units) into a new equation that reduced the predicted hydraulic conductivity error to ±14.1 m/day. The equation is best applied to ephemeral stream samples that have hydraulic conductive values greater than 2 m/day.

Colonization dynamics of ciliate morphotypes modified by shifting sandy sediments

Sandy stream-bed sediments colonized by a diverse ciliate community are subject to various disturbance regimes. In microcosms, we investigated the effect of sediment shifting on the colonization dynamics of 3 ciliate morphotypes differing in morphology, behavior and feeding strategy. The dynamics of the ciliate morphotypes inhabiting sediment pore water and overlying water were observed at 3 sediment shifting frequencies: (1) stable sediments, (2) periodically shifting sediments such as migrating ripples, and (3) continuously shifting sediments as occurring during scour events of the uppermost sediment. Sediment shifting significantly affected the abundance and growth rate of the ciliate morphotypes. The free-swimming filter feeder Dexiostoma campylum was vulnerable to washout by sediment shifting since significantly higher numbers occurred in the overlying water than in pore water. Abundance of D. campylum only increased in pore water of stable sediments. On the contrary, the vagile grasper feeder Chilodonella uncinata and the sessile filter feeder Vorticella convallaria had positive growth rates and successfully colonized sediments that shifted periodically and continuously. Thus, the spatio-temporal pattern of sediment dynamics acts as an essential factor of impact on the structure, distribution and function of ciliate communities in sand-bed streams.

Reconnaissance of Pharmaceuticals and Wastewater Indicators in Streambed Sediments of the Lower Columbia River Basin, Oregon and Washington

AbstractOne by‐product of advances in modern chemistry is the accumulation of synthetic chemicals in the natural environment. These compounds include contaminants of emerging concern (CECs), some of which are endocrine disrupting compounds (EDCs) that can have detrimental reproductive effects. The role of sediments in accumulating these types of chemicals and acting as a source of exposure for aquatic organisms is not well understood. Here we present a small‐scale reconnaissance of CECs in bed sediments of the lower Columbia River and several tributaries and urban streams. Surficial bed sediment samples were collected from the Columbia River, the Willamette River, the Tualatin River, and several small urban creeks in Oregon. Thirty‐nine compounds were detected at concentrations ranging from &lt;1 to &gt;1,000 ng [g sediment]−1 dry weight basis. Concentrations and frequencies of detection were higher in tributaries and small urban creeks than in the Columbia River mainstem, suggesting a higher risk of exposure to aquatic life in lower order streams. Ten known or suspected EDCs were detected during the study. At least one EDC was detected at 21 of 23 sites sampled; several EDCs were detected in sediment from most sites. This study is the first to document the occurrence of a large suite of CECs in the sediments of the Columbia River basin. A better understanding of the role of sediment in the fate and effects of emerging contaminants is needed.

Re-suspension of bed sediment in a small stream – results from two flushing experiments

Abstract. Streams draining small watersheds often exhibit multiple peaking sedigraphs associated with single peaking hydrographs. The process reasons of the multiple sediment peaks are not fully understood but they may be related to the activation of different sediment sources such as the stream bed itself, where deposited sediments from previous events may be available for resuspension. To understand resuspension of stream bed sediments at the reach scale we artificially flooded the small stream of the HOAL Petzenkirchen catchment in Austria by pumping sediment-free water into the stream. Two short floods were produced and flow, sediment and bromide concentrations were measured at three sites with high temporal resolution. Hydrologically, the two flood events were almost identical. The peak flows decreased from 57 to 7.9 L s−1 and the flow volumes decreased from 17 to 11.3 m2 along the 590 m reach of the stream. However, a considerably smaller sediment load was resuspended and transported during the second flood due to depletion of stream bed sediments. The exception was the middle section of the stream, where more sediment was transported during the second flood event which can be explained by differences between flow velocity and wave celerity and the resulting displacement of sediments within the stream. The results indicate that the first peak of the sedigraphs of natural events in this stream is indeed caused by the resuspension of stream bed sediments, accounting for up to six percent of the total sediment load depending on total flow volume.

Bacterial Community Composition and Extracellular Enzyme Activity in Temperate Streambed Sediment during Drying and Rewetting

Droughts are among the most important disturbance events for stream ecosystems; they not only affect stream hydrology but also the stream biota. Although desiccation of streams is common in Mediterranean regions, phases of dryness in headwaters have been observed more often and for longer periods in extended temperate regions, including Central Europe, reflecting global climate change and enhanced water withdrawal. The effects of desiccation and rewetting on the bacterial community composition and extracellular enzyme activity, a key process in the carbon flow of streams and rivers, were investigated in a typical Central European stream, the Breitenbach (Hesse, Germany). Wet streambed sediment is an important habitat in streams. It was sampled and exposed in the laboratory to different drying scenarios (fast, intermediate, slow) for 13 weeks, followed by rewetting of the sediment from the fast drying scenario via a sediment core perfusion technique for 2 weeks. Bacterial community structure was analyzed using CARD-FISH and TGGE, and extracellular enzyme activity was assessed using fluorogenic model substrates. During desiccation the bacterial community composition shifted toward composition in soil, exhibiting increasing proportions of Actinobacteria and Alphaproteobacteria and decreasing proportions of Bacteroidetes and Betaproteobacteria. Simultaneously the activities of extracellular enzymes decreased, most pronounced with aminopeptidases and less pronounced with enzymes involved in the degradation of polymeric carbohydrates. After rewetting, the general ecosystem functioning, with respect to extracellular enzyme activity, recovered after 10 to 14 days. However, the bacterial community composition had not yet achieved its original composition as in unaffected sediments within this time. Thus, whether the bacterial community eventually recovers completely after these events remains unknown. Perhaps this community undergoes permanent changes, especially after harsh desiccation, followed by loss of the specialized functions of specific groups of bacteria.