Fine Sediment (fine + sediment)

Distribution by Scientific Domains

Selected Abstracts

A field-based microcosm method to assess the effects of polluted urban stream sediments on aquatic macroinvertebrates

Vincent Pettigrove
Abstract A method using field-based microcosms was developed to determine the effects of contaminated sediments on aquatic macroinvertebrates. Fine sediments from nonpolluted, moderately polluted, and severely polluted bodies of water were placed in microcosms positioned within the littoral zone of a nonpolluted wetland near Melbourne (Victoria, Australia). In three experiments, 47 taxa, including 18 Chironomidae, 6 taxa from other Diptera families, and 7 Hemiptera taxa, colonized the microcosms, mostly via eggs deposited by flying adults. The effects of sediment type on the presence and abundance of common taxa were considered statistically. Pollution levels in sediments (indexed either by a principal components analysis or by the concentration of zinc, the predominant metal) resulted in reduced occurrence and abundance of eight taxa but had no effect on another five taxa. These findings were validated with an extensive field database for the distribution of macroinvertebrates and associated concentrations of zinc in sediments from streams and wetlands in the Melbourne region. The occurrence of eight taxa and the abundance of two taxa varied at similar zinc concentrations in sediments from both the microcosms and the field. Patterns for another two species did not match the microcosm results, but these groups contained multiple species with potentially diverse responses. The present results suggest that contaminant levels in sediments probably have a direct effect on the occurrence and abundance of macroinvertebrates in bodies of water in urban areas. The microcosm method can be used to gather information regarding the effects of sediment quality on macroinvertebrates in lentic habitats, particularly for indigenous species that cannot be easily reared or tested in laboratory conditions. Because almost all macroinvertebrates in microcosms develop from eggs, the most sensitive life stages (i.e., first and second instars) are exposed to polluted sediments. [source]

Sediment transport in a highly regulated fluvial system during two consecutive floods (lower Ebro River, NE Iberian Peninsula)

Damia Vericat
Abstract The transfer of sediment through a highly regulated large fluvial system (lower Ebro River) was analysed during two consecutive floods by means of sediment sampling. Suspended sediment and bedload transport were measured upstream and downstream of large reservoirs. The dams substantially altered flood timing, particularly the peaks, which were advanced downstream from the dams for flood control purposes. The suspended sediment yield upstream from the dams was 1 700 000 tonnes, which represented nearly 99 per cent of the total solid yield. The mean concentrations were close to 0·5 g l,1. The sediment yield downstream from the dams was an order of magnitude lower (173 000 tonnes), showing a mean concentration of 0·05 g l,1. The dams captured up to 95 per cent of the fine sediment carried in suspension in the river channel, preventing it from reaching the lowermost reaches of the river and the delta plain. Total bedload transport upstream from the dams was estimated to be about 25 000 tonnes, only 1·5 per cent of the total load. The median bedload rate was 100 gms,1. Below the dams, the river carried 178 000 tonnes, around 51 per cent of the total load, at a mean rate of 250 g ms,1. The results of sediment transport upstream and downstream from the large dams illustrate the magnitude of the sediment deficit in the lower Ebro River. The river mobilized a total of 350 000 tonnes in the downstream reaches, which were not replaced by sediment from upstream. Therefore, sediment was necessarily entrained from the riverbed and channel banks, causing a mean incision of 33 mm over the 27 km long study reach, altogether a significant step towards the long-term degradation of the lower Ebro River. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Impact of wastewater discharge on the channel morphology of ephemeral streams

Marwan A. Hassan
Abstract The impact of wastewater flow on the channel bed morphology was evaluated in four ephemeral streams in Israel and the Palestinian Territories: Nahal Og, Nahal Kidron, Nahal Qeult and Nahal Hebron. Channel changes before, during and after the halting of wastewater flow were monitored. The wastewater flow causes a shift from a dry ephemeral channel with intermittent floods to a continuous flow pattern similar to that of humid areas. Within a few months, nutrient-rich wastewater flow leads to rapid development of vegetation along channel and bars. The colonization of part of the active channel by vegetation increases flow resistance as well as bank and bed stability, and limits sediment availability from bars and other sediment stores along the channels. In some cases the established vegetation covers the entire channel width and halts the transport of bed material along the channel. During low and medium size flood events, bars remain stable and the vegetation intact. Extreme events destroy the vegetation and activate the bars. The wastewater flow results in the development of new small bars, which are usually destroyed by flood flows. Due to the vegetation establishment, the active channel width decreases by up to 700 per cent. The deposition of fine sediment and organic material changed the sediment texture within the stable bar surface and the whole bed surface texture in Nahal Hebron. The recovery of Nahal Og after the halting of the wastewater flow was relatively fast; within two flood seasons the channel almost returned to pre-wastewater characteristics. The results of the study could be used to indicate what would happen if wastewater flows were introduced along natural desert streams. Also, the results could be used to predict the consequences of vegetation removal as a result of human intervention within the active channel of humid streams. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Competition for food between Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) over different substrate types

A. Dieterich
Abstract,,, Food consumption by Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) was studied in single and mixed-species treatments in the laboratory, where alternative food resources, chironomids and zooplankton, were offered simultaneously. The effects of structural complexity, which was represented by substrate grain size, and of feeding level on food consumption were analysed. Across all experiments, the outcome of competition between perch and ruffe depended on food abundance and on the structural complexity of the environment. Perch and ruffe both changed their food consumption in the presence of a heterospecific competitor. With high food supply, perch consumed more benthic food than ruffe. With low food supply, the consumption of perch decreased strongly, while that of ruffe remained high on fine sediment. Under all conditions tested, the mechanism of competition appeared to be of interference rather than of exploitative nature. It is suggested that with decreasing lake productivity caused by re-oligotrophication, habitat shifts of both species will occur, which will alleviate interspecific competition. Ruffe will forage over fine sediment and perch over coarse sediment, whereby both species will achieve the highest foraging efficiency under conditions of low food supply. Resumen 1. Hemos estudiado el consumo alimenticio de Perca fluviatilis L. y Gymnocephalus cernuus (L.) en condiciones de laboratorio. Bajo tratamientos de especies individuales y mezcladas, les ofrecimos, simultáneamente, varios recursos alimenticios alternativos (quironómidos y zooplancton). 2. Analizamos los efectos de la complejidad estructural - representada por el tamaño del sustrato (arena, grava, y guijo) - y del nivel alimenticio, sobre el consumo alimenticio. Pusimos especial atención a la potencial influencia de competidores hetero-específicos sobre los patrones alimenticios de ambas especies, tanto en términos cualitativos como cuantitativos. Además, dado que en un futuro cercano una menor productividad general en lagos debida a re-oligotrofia, probablemente aumente la competición por el alimento en muchos lagos donde ambas especies co-existen, los experimentos se llevaron a cabo bajo niveles de abastecimiento alimenticio alto y bajo. 3. En los experimentos, la aparición de competencia entre P. fluviatilis y G. cernuus dependió de la abundancia del alimento y de la complejidad estructural del ambiente. El consumo de quironómidos por P. fluviatilis dependió del tipo de sustrato a niveles altos de abastecimiento alimenticio pero no a niveles bajos, mientras que en G. cernuus observamos lo contrario. 4. Ambas especies cambiaron el consumo alimenticio en presencia de un competidor hetero-específico. A altos niveles de abastecimiento alimenticio, P. fluviatilis consumió más bentos que G. cernuus. A niveles bajos, el consumo de P. fluviatilis decreció substancialmente mientras que el de G. cernuus permaneció alto en sedimento fino. Bajo todas las condiciones experimentales analizadas, los mecanismos de competición parecieron ser de interferencia más que de naturaleza explotativa. 5. Finalmente, presentamos un escenario sobre como P. fluviatilis y G. cernuus pueden competir por alimento bentónico en lagos con variado sustrato de fondo. Sugerimos que a altos niveles de abastecimiento alimenticio, G. cernuus forrajee más sobre arena y grava mientras que P. fluviatilis puede utilizar todos los sustratos disponibles. Al decrecer el abastecimiento alimenticio por re-oligotrofia, pueden producirse cambios en el hábitat de ambas especies que minimizarán la competencia inter-específica. G. cernuus forrajeará básicamente sobre sedimento fino, allá donde sea claramente superior a P. fluviatilis. Esta última especie forrajeará predominantemente sobre sedimento más grueso donde se enfrentará a competencia intra- e inter-específica. A través de estos cambios de hábitat, ambas especies podrían alcanzar la mayor eficiencia de forrajeo bajo condiciones de bajo abastecimiento alimenticio. [source]

Using cosmogenic beryllium,7 as a tracer in sediment budget investigations

W. H. Blake
Recent advances in the use of the environmental radionuclides caesium,137 and unsupported lead,210 to quantify medium, and longer,term rates of erosion and sediment accumulation have proved of considerable value in catchment sediment budget investigations. However, there remains a need to explore the potential for using other shorter,lived radionuclides to provide evidence of sediment mobilisation, transport and storage over shorter timescales and particularly for individual events. This contribution reports the results of a study aimed at exploring the potential for using beryllium,7 (7Be, t½= 53.3 days) to meet this requirement. The study investigated the use of 7Be as a sediment tracer in three key components of the sediment budget, namely, soil erosion and sediment mobilisation from slopes, the transport, storage and remobilisation of fine sediment in river channels and overbank deposition on river floodplains. The results presented clearly demonstrate the potential for using 7Be to obtain information on short,term and event,based sediment redistribution rates for use in catchment sediment budget investigations. [source]

Suspended-sediment sources in an urban watershed, Northeast Branch Anacostia River, Maryland

Olivia H. Devereux
Abstract Fine sediment sources were characterized by chemical composition in an urban watershed, the Northeast Branch Anacostia River, which drains to the Chesapeake Bay. Concentrations of 63 elements and two radionuclides were measured in possible land-based sediment sources and suspended sediment collected from the water column at the watershed outlet during storm events. These tracer concentrations were used to determine the relative quantity of suspended sediment contributed by each source. Although this is an urbanized watershed, there was not a distinct urban signature that can be evaluated except for the contributions from road surfaces. We identified the sources of fine sediment by both physiographic province (Piedmont and Coastal Plain) and source locale (streambanks, upland and street residue) by using different sets of elemental tracers. The Piedmont contributed the majority of the fine sediment for seven of the eight measured storms. The streambanks contributed the greatest quantity of fine sediment when evaluated by source locale. Street residue contributed 13% of the total suspended sediment on average and was the source most concentrated in anthropogenically enriched elements. Combining results from the source locale and physiographic province analyses, most fine sediment in the Northeast Branch watershed is derived from streambanks that contain sediment eroded from the Piedmont physiographic province of the watershed. Sediment fingerprinting analyses are most useful when longer term evaluations of sediment erosion and storage are also available from streambank-erosion measurements, sediment budget and other methods. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Changes in hydrology and erosion over a transition from grassland to shrubland

Laura Turnbull
Abstract The degradation of grasslands is a common problem across semi-arid areas worldwide. Over the last 150 years, much of the south-western United States has experienced significant land degradation, with desert grasslands becoming dominated by shrubs and concurrent changes in runoff and erosion which are thought to propagate further the process of degradation. Plot-based experiments to determine how spatio-temporal characteristics of soil moisture, runoff and erosion change over a transition from grassland to shrubland were carried out at four sites over a transition from black grama (Bouteloua eriopoda) grassland to creosotebush (Larrea tridentata) shrubland at the Sevilleta NWR LTER site in New Mexico. Each site consisted of a 10 × 30 m bounded runoff plot and adjacent characterization plots with nested sampling points where soil moisture content was measured. Results show distinct spatio-temporal variations in soil moisture content, which are due to the net effect of processes operating at multiple spatial and temporal scales, such as plant uptake of water at local scales versus the redistribution of water during runoff events at the hillslope scale. There is an overall increase in runoff and erosion over the transition from grassland to shrubland, which is likely to be associated with an increase in connectivity of bare, runoff-generating areas, although these increases do not appear to follow a linear trajectory. Erosion rates increased over the transition from grassland to shrubland, likely related in part to changes in runoff characteristics and the increased capacity of the runoff to detach, entrain and transport sediment. Over all plots, fine material was preferentially eroded which has potential implications for nutrient cycling since nutrients tend to be associated with fine sediment. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Sediment infiltration traps: their use to monitor salmonid spawning habitat in headwater tributaries of the Cascapédia River, Québec

André E. Zimmermann
Abstract Sediment infiltration can clog salmon nests and reduce egg survival. As a countermeasure, environmental managers often deploy infiltration traps to monitor sediment infiltration. Traps provide a repeatable means of measuring infiltration and enable comparisons to be made between sites. Results from infiltration rates measured with traps have also been used to estimate infilling rates into salmon nests. Application of these data is questionable, as the composition of the bed and the amount of fine sediment within the bed is known to affect infiltration rates. Thus, infiltration rates measured with infiltration traps may differ from the infiltration rates occurring in redd and riffle gravels. To examine how relationships between sediment infiltration rates varied between four watersheds, we continuously monitored suspended sediment transport, shear stress and infiltration rates at four sites over 5 months. We also compared infiltration rates measured with infiltration traps with changes in the hydraulic conductivity and subsurface grain size distribution of adjacent artificially constructed salmon nests and natural riffle gravels. Among the four watersheds, clear differences in sediment infiltration rates were observed. The differences correlated with the subsurface silt content but no strong relationship existed between land-use or basin physiography/geology. Despite observing an average of 30 kg m,2 of sediment finer than 2 mm being deposited in the infiltration traps during the study, no change in redd or riffle substrate was observed. If the deposition rates measured with the traps reflect the processes in redds, enough sediment would have been deposited to inhibit egg emergence. However, no reduction in egg survival to the eyed stage was observed. In summary, our results show that infiltration traps with clean gravels can be used to detect intersite differences in sediment transport regimes. Extrapolations of sediment infiltration rates measured with such collectors to estimate infiltration rates in redds or riffles is, however, flawed. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Heavy metal concentrations during storm events in a rehabilitated industrialized catchment

W. H. Blake
Abstract Water quality data collected on a fortnightly or monthly basis are inadequate for assessment and modelling of many water quality problems as storm event samples are underrepresented or missed. This paper examines the stormflow dynamics of heavy metals (Pb, Cu, Cd and Zn) in the Nant-y-Fendrod stream, South Wales, which has been affected by 250 years of metal smelting, followed by 35 years of landscape rehabilitation measures. For storm events of contrasting (very dry and very wet) antecedent conditions in May 2000 and February 2001, respectively, temporal changes in streamwater heavy metal concentrations above and below an in-line flood detention lake are analysed. At the upstream site, peaks in total metal concentration were recorded on the rising limb for Pb (0·150 mg l,1) and Cu (0·038 mg l,1) but on the falling limb for Zn (1·660 mg l,1) and Cd (0·006 mg l,1) in the summer 2000 storm event, yielding clockwise and anticlockwise hysteretic loops respectively. In contrast, metal concentrations, although high throughout the winter storm event, were diluted somewhat during the storm peak itself. The Pb and Cu appear to be supplied by quickflow processes and transported in close association with fine sediment, whereas Zn and Cd are delivered to the channel and lake by slower subsurface seepage in dissolved form. In the winter 2001 event, antecedent soil moisture and shallow groundwater levels were anomalously high and seepage sources of dissolved metals dominated. Downstream of the lake, Pb and Cu levels and suspended sediment were high in the summer storm, but low in the winter storm, suggesting retention with deposition of fine sediment in the lake during the latter. In the winter storm, Zn and Cd levels were higher downstream than upstream of the lake, perhaps because of additional seepage inputs from the surrounding slopes, which failed to have an impact during summer. An understanding of the complex interplay of antecedent soil moisture and the dynamics of subsurface seepage pathways in relation to the three-dimensional distribution of sources is important in modelling heavy metal fluxes and levels in contaminated urban catchments. Copyright © 2003 John Wiley & Sons, Ltd. [source]

The importance of measuring biotic and abiotic factors in the lower egg pocket to predict coho salmon egg survival

C. B. Meyer
Based on results from simulated redds of coho salmon Oncorhynchus kisutch, the amount of fine sediment <0·5 mm in the lower half of the egg pocket, rather than the entire egg pocket of the redd, was a strong predictor of egg survival to hatching ( r2 = 0·62). The relationship was much stronger than observed in other studies, which typically ignore egg pocket structure. Abundance of a fish egg-eating worm, Haplotaxis ichthyophagous, an oligochaete that may have been attracted to fine sediment and dead eggs in the egg pocket, was also associated with a decrease in egg survival. The worm, however, accounted for little of the variance in survival compared to fine sediment. Only 10% fine sediment (<0·5 mm) in the lower pocket was required to decrease survival from 100 to 5%. Other abiotic factors had weaker (gravel permeability) or non-existent (dissolved oxygen) correlations with survival. [source]


Jonathan W. Long
ABSTRACT: To prioritize sites for riparian restoration, resource managers need to understand how recovery processes vary within landscapes. Complex relationships between watershed conditions and riparian development make it difficult to predict the outcomes of restoration treatments in the semiarid Southwest. Large floods in 1993 scoured riparian areas in the Carrizo watershed on the White Mountain Apache Reservation in east-central Arizona. We evaluated recovery at three of these sites using repeated photographs and measurements of channel cross sections and stream-side vegetation along permanent transects. The sites were mapped as lying on the same soil type, had similar streamside vegetative communities, and were similarly treated through livestock exclusion and supplemental seeding. However, the sites and individual reaches within the sites followed strikingly different development paths. Dramatic recovery occurred at a perennial reach where cover of emergent wetland plants increased from 4.7 percent (standard error = 0.8 percent) in October 1995 to 55.5 percent (standard error = 2.7 percent) in September 2001. At several other reaches, geologic and hydro geomorphic characteristics of the sites limited inputs of fine sediment or surface water, resulting in modest or negligible increases in emergent cover. Recovery efforts for highly valued marshlands in this region should prioritize perennial reaches in low gradient valleys where salty sediments are abundant. [source]

Relict sand dredging for beach nourishment in the central Tyrrhenian Sea (Italy): effects on benthic assemblages

Barbara La Porta
Abstract The aim of this study is to analyse the effects in space and time of relict sand-dredging activities on macrobenthic assemblages, in an area situated offshore Montalto di Castro (central Tyrrhenian Sea, Italy), and to analyse the recolonisation processes of macrobenthos in the dredged areas. The area in question is characterised by relict sand deposits (Holocenic paleo-beaches), used for beach nourishment along the Latium coast. The effects of sand extraction on benthic assemblages were investigated before, during and after three dredging operations. The sites analysed are located within the dredged areas (inside stations) and in neighbouring, not dredged, areas (outside stations). The results showed that the impact of sand extraction was confined to the dredged stations and to the areas in proximity to the dredged areas. During dredging activities, the structure of benthic assemblages within the impacted stations was characterised by low species richness and diversity. Both the direct removal of sediment and the re-suspension and consequent deposition of fine sediment affected benthic assemblages of the impacted stations. A few months after the dredgings, a recolonisation process was still observed at all the impacted stations. A gradual recolonisation process was observed at those stations affected by only one dredging, whereas a different recolonisation was observed at those stations affected by two dredgings over time. This study suggests that differences of re-colonisation processes of benthic assemblages are related to the intensity of dredging operations in terms of dredging frequency. [source]

The influence of sediment type on the aggregative response of oystercatchers, Haematopus ostralegus, searching for cockles, Cerastoderma edule

OIKOS, Issue 1 2000
Ian Johnstone
Models that describe the dispersion patterns of predators between a series of patches that vary in prey density frequently assume that predators, in the absence of interference, will aggregate in patches with the highest prey density, at any point in time. This assumption has important implications for patterns of prey mortality, and the extent to which prey mortality is density dependent. In natural predator-prey systems, it is likely that environmental factors interact with spatial variation in prey density to influence the aggregative response of predators. We show data consistent with this idea on a population of overwintering oystercatchers foraging on cockles. There was no evidence that birds aggregated in patches with the highest biomass density of cockles. The biomass density of cockles was highest in muddy patches at the start of winter, and birds aggregated in patches that switched from being muddy at the start of winter to being sandy at some point during the winter. We argue that sediment type influences foraging costs experienced by the birds, so birds avoid feeding in muddy patches unless the fine sediment is removed from a patch, as happens during winter storms. When this happens a high biomass density of cockles suddenly becomes available and the birds aggregate in such patches. The rate of biomass loss was greatest in patches used intensively by birds for feeding, suggesting that the birds' aggregative response influences cockle mortality. We discuss the implications of our results for ideal free models. [source]

Effects of tidal flat reclamation on sediment quality and hypoxia in Isahaya Bay

Yoshikuni Hodoki
Abstract 1.Ariake Bay, which is located in western Japan, has a large tidal range (>6 m) and a vast tidal flat (200 km2). In the early 1990s, the government-managed Isahaya Reclamation Project began in the western part of Ariake Bay. A 16-km2 area of tidal flat in the inner part of Isahaya Bay was destroyed through reclamation and separated from the sea by a dyke, which created land and a freshwater reservoir. 2.Since the initiation of the project, fishery yields around Isahaya Bay have dramatically decreased. The objective of this study was to clarify the relationship between the work associated with the Isahaya Reclamation Project and the recent environmental deterioration in Ariake Bay, with references to present sediment thickness and organic matter content, and hypoxic water distributions in Isahaya Bay. 3.The organic matter load from the reservoir has increased since the initiation of the reclamation project and has been associated with a thick layer of fine sediment at the bottom of Isahaya Bay. The thickness of fine sediment and the total organic carbon content were higher in Isahaya Bay than in the freshwater reservoir. 4.Based on measurements in August 2001, hypoxic water spread widely in and around Isahaya Bay; the lowest dissolved oxygen (DO) concentration (0.53 mg L,1) was observed just outside the dyke. An analysis based on a two-layered box model using data obtained in August 2001 showed that the DO consumption rate in the bottom layer was high (0.61 mg O2 L,1 day,1), and that 22,41% of the total organic carbon load needed to induce the hypoxic water was derived from the reclamation area. 5.Our findings strongly suggest that enclosed seas may suffer from eutrophic and hypoxic conditions because of their low seawater-exchange rate. A comprehensive conservation programme and environmental assessment including physical and material transport processes in the system is needed to manage the environment of the enclosed sea. Copyright © 2005 John Wiley & Sons, Ltd. [source]

The behavior of specific sediment yield in different grain size fractions in the tributaries of the middle Yellow River as influenced by eolian and fluvial processes

Jiongxin Xu
Abstract Based on data from 35 stations on the tributaries of the Yellow River, annual specific sediment yield (Ys) in eight grain size fractions has been related to basin-averaged annual sand,dust storm days (Dss) and annual precipitation (Pm) to reveal the influence of eolian and fluvial processes on specific sediment yield in different grain size fractions. The results show that Ys in fine grain size fractions has the highest values in the areas dominated by the coupled wind,water process. From these areas to those dominated by the eolian process or to those dominated by the fluvial process, Ys tends to decrease. For relatively coarse grain size fractions, Ys has monotonic variation, i.e. with the increase in Dss or the decrease in Pm, Ys increases. This indicates that the sediment producing behavior for fine sediments is different from that for relatively coarse sediments. The results all show that Ys for relatively coarse sediments depends on the eolian process more than on the fluvial process, and the coarser the sediment fractions the stronger the dependence of the Ys on the eolian process. The Ys,Dss and Ys,Pm curves for fine grain size fractions show some peaks and the fitted straight lines for Ys,Dss and Ys,Pm relationships for relatively coarse grain size fractions show some breaks. Almost all these break points may be regarded as thresholds. These thresholds are all located in the areas dominated by the coupled wind,water process, indicating that these areas are sensitive for erosion and sediment production, to which more attention should be given for the purpose of erosion and sediment control. A number of regression equations were established, based which the effect of rainfall, sand,dust storms and surface material grain size on specific sediment yield can be assessed. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Impacts of nonpoint inputs from potato farming on populations of slimy sculpin (Cottus cognatus)

Michelle A. Gray
Abstract The potential influence of agricultural activity, particularly potato cultivation, on slimy sculpin populations (Cottus cognatus) was examined at 19 rivers of New Brunswick, Canada. Comparisons with forested streams resulted in differences in fish density, size, and reproductive performance. Young-of-the-year (YOY) sculpin were present only at two of 11 agricultural sites, though they were present at all nine forested sites. Sediment deposition was greatest at agricultural sites, with increased fine sediments deposited. Larger, coarse sands were deposited at two sites with active forest operations. Temperature had a stronger correlation than sedimentation with sculpin size and density in the agricultural region. Agricultural catchments were warmer than in forested catchments (median = 16.0 and 13.3°C, respectively). Body size of slimy sculpin was correlated positively and YOY densities correlated negatively with temperature, and sites with temperatures ,25°C were devoid of YOY sculpin. Our data indicate there is a significant effect of temperature on slimy sculpin populations in rivers of potato farming areas, highlighting the importance of examining indirect factors when investigating possible impacts of nonpoint source agricultural inputs. Indirect factors such as sediment deposition and temperature need to be considered in order to discriminate accurately the chronic impacts of agricultural chemicals on fish populations. [source]

Geomorphology and fish assemblages in a Piedmont river basin, U.S.A.

D. M. Walters
Summary 1.,We investigated linkages between fishes and fluvial geomorphology in 31 wadeable streams in the Etowah River basin in northern Georgia, U.S.A. Streams were stratified into three catchment sizes of approximately 15, 50 and 100 km2, and fishes and geomorphology were sampled at the reach scale (i.e. 20,40 times stream width). 2.,Non-metric multidimensional scaling (NMDS) identified 85% of the among-site variation in fish assemblage structure and identified strong patterns in species composition across sites. Assemblages shifted from domination by centrarchids, and other pool species that spawn in fine sediments and have generalised food preferences, to darter-cyprinid-redhorse sucker complexes that inhabit riffles and runs, feed primarily on invertebrates, and spawn on coarser stream beds. 3.,Richness and density were correlated with basin area, a measure of stream size, but species composition was best predicted (i.e. |r| between 0.60,0.82) by reach-level geomorphic variables (stream slope, bed texture, bed mobility and tractive force) that were unrelated to stream size. Stream slope was the dominant factor controlling stream habitat. Low slope streams had smaller bed particles, more fines in riffles, lower tractive force and greater bed mobility compared with high slope streams. 4.,Our results contrast with the ,River Continuum Concept' which argues that stream assemblages vary predictably along stream size gradients. Our findings support the ,Process Domains Concept', which argues that local-scale geomorphic processes determine the stream habitat and disturbance regimes that influence stream communities. [source]

The Ohalo II prehistoric camp (19.5 Ky): New evidence for environmental and tectonic changes at the Sea of Galilee

Shmuel Belitzky
Combined archaeological data, shore surveys, and aerial photos of submerged sediments in the Sea of Galilee provide new insights into environmental and tectonic events, their dating, and their impact on the Ohalo II prehistoric camp (ca. 19,500 yr B.P.) and its surroundings. The Ohalo II waterlogged campsite contains excellently preserved brush hut remains and other in situ features, all embedded in late Pleistocene lacustrine strata. The findings indicate relatively short occupation of the site, not more than months or several years at a time. The high quality in situ preservation of delicate organic materials, as well as the short occupation period, suggests a quick and gentle burial by fine sediments. The evident fast submergence (water level rise of the Sea of Galilee) could have been the result of climatic fluctuations towards the end of the last glaciation and/or small-scale tectonic subsidence. The site is located on a tectonic block formed in the western fault belt of the Dead Sea Rift. We present new evidence of post-occupational folding of the late Pleistocene strata and recent tilting and faulting. A westward tectonic tilt may have caused the blockage of the old Jordan River outlet after A. D. 1106. Excellent preservation of the fault traces to the east of the site is attributed to the young age of the displacement on the fault. The last displacement apparently post-dates the blockage of the old Jordan River. © 2002 Wiley Periodicals, Inc. [source]

Electron Transport System (ETS) Activity in Alder Leaf Litter in Two Contrasting Headwater Streams

Tadeusz Fleituch
Abstract Decomposition rates, carbon and nitrogen concentrations and respiration electron transport (ETS) activity in alder leaf litter were examined by bag exposition method in two contrasting 2nd order streams. Oberer Seebach, Austria (alpine, limestone, karstic) and Goscibia, Poland (sub mountain, flysh) contrasted in catchment geology, channel hydrology, thermal regime and water chemistry. Despite differences in water temperature, the breakdown rates did not show statistical differences. However, the C:N ratio in alder leaf litter varied significantly between two sites. The potential ETS activity was significantly higher in the colder Goscibia and weakly related to stream thermal regimes. The effect of temperature on ETS of alder leaves was not the dominating factor. It was masked by variation of other factors like stream chemistry and the contribution of fine sediments, which are related to stream morphology and channel hydrology. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Sediment preferences and size-specific distribution of young-of-the-year Pacific halibut in an Alaska nursery

A. W. Stoner
A combination of laboratory experiments and field surveys was used to test the hypotheses that responses to sediments change with fish size and that sediment grain-size is the predominant environmental factor affecting small-scale distribution in young-of-the-year (yoy) Pacific halibut Hippoglossus stenolepis. Laboratory tests showed that the smallest fish (31,40 mm LT) chose fine sediments (muddy and fine sands), fish 51,70 mm had high selectivity (primarily medium sand), and the largest fish (80,150 mm) were not selective although they avoided the largest grain-sizes (pebbles and granules). Sediment preferences were correlated with size-dependent burial capabilities. Beam trawl collections were made over a 6 year period in Kachemak Bay, Alaska, to examine the distribution of yoy Pacific halibut (14,120 mm LT) using small size classes (e.g. 10 mm intervals). Canonical correlation analysis showed that the per cent of sand in the sediment was a highly significant variable for all but one size and date combination. Catch per unit of effort (CPUE) for newly settled fish (<30 mm LT) was highest on very fine sand, fish 41,80 mm were most abundant on fine sand, and the largest yoy fish (81,120 mm) were abundant over a range of sediments from fine sand to mud. Except for the smallest fish, Pacific halibut in the field were associated with sediments somewhat finer than predicted from the laboratory experiments; however, virtually all were captured where they could bury easily. The ability of flatfish to bury and shelter in sediment is related to fish size; consequently, habitat associations shift rapidly during the first year of life. Habitat models for yoy flatfishes should consider size-dependent shifts in capabilities and preferences. [source]

Bed Stability and Sedimentation Associated With Human Disturbances in Pacific Northwest Streams,

Philip R. Kaufmann
Abstract:, To evaluate anthropogenic sedimentation in United States (U.S.) Pacific Northwest coastal streams, we applied an index of relative bed stability (LRBS*) to summer low flow survey data collected using the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program field methods in a probability sample of 101 wadeable stream reaches. LRBS* is the log of the ratio of bed surface geometric mean particle diameter (Dgm) to critical diameter (D*cbf) at bankfull flow, based on a modified Shield's criterion for incipient motion. We used a formulation of LRBS* that explicitly accounts for reductions in bed shear stress that result from channel form roughness due to pools and wood. LRBS* ranged from ,1.9 to +0.5 in streams within the lower quartile of human riparian and basin disturbance, and was substantially lower (,4.2 to ,1.1) in streams within the upper quartile of human disturbance. Modeling results suggest that the expected range of LRBS* in streams without human disturbances in this region might be generally between ,0.7 and +0.5 in either sedimentary or volcanic lithology. However, streams draining relatively soft, erodible sedimentary lithology showed greater reductions in LRBS* associated with disturbance than did those having harder, more resistant volcanic (basalt) lithology with similar levels of basin and riparian disturbance. At any given level of disturbance, smaller streams had lower LRBS* than those with larger drainages. In sedimentary lithology (sandstone and siltstone), high-gradient streams had higher LRBS* than did low-gradient streams of the same size and level of human disturbance. High gradient streams in volcanic lithology, in contrast, had lower LRBS* than low-gradient streams of similar size and disturbance. Correlations between Dgm and land disturbance were stronger than those observed between D*cbf and land disturbance. This pattern suggests that land use has augmented sediment supplies and increased streambed fine sediments in the most disturbed streams. However, we also show evidence that some of the apparent reductions in LRBS*, particularly in steep streams draining small volcanic drainages, may have resulted in part from anthropogenic increases in bed shear stress. The synoptic survey methods and designs we use appear adequate to evaluate regional patterns in bed stability and sedimentation and their general relationship to human disturbances. More precise field measurements of channel slope, cross-section geometry, and bed surface particle size would be required to use LRBS* in applications requiring a higher degree of accuracy and precision, such as site-specific assessments at individual streams. [source]

Adaptation of reef and mangrove sponges to stress: evidence for ecological speciation exemplified by Chondrilla caribensis new species (Demospongiae, Chondrosida)

Klaus Rützler
Abstract Sponges (Porifera) in mangroves have adapted to a wide range of environmental parameters except for extended periods of exposure to freshwater or air. Many marine mangrove islands are located in the shallow backwaters of coral reefs in Belize and elsewhere in the Caribbean and have a mean tidal range of only 15 cm. They are densely populated by sponges, mostly attached to subtidal red-mangrove stilt roots and peat banks lining tidal channels. Some species are endemic to mangroves, others are immigrants from nearby reefs. Mangrove endemics endure environmental hardships, such as occasional exposure to air during spring tides, temperature and salinity extremes, fine sediments, even burial in detritus. Reef immigrants into mangroves enjoy protection from spongivores that do not stray into the swamp but they eventually succumb to environmental stress. There is evidence exemplified by the common demosponge Chondrilla aff. nucula, that sponges flourishing in both mangrove and reef habitats may develop separate ecologically specialized and reproductively isolated populations. Such processes can lead to genetic modifications and thus serve as mechanisms for ecological speciation. Because Chondrilla nucula Schmidt was first described from the Mediterranean Sea, it was long suspected that the western Atlantic population may be a separate species. New morphological and molecular evidence prompt us to describe it under a new name, Chondrilla caribensis, with two ecological forms, forma caribensis from mangroves and lagoons, and forma hermatypica from open reefs. [source]

The conservation of unionid mussels in Louisiana rivers: diversity, assemblage composition and substrate use

Kenneth M. Brown
Abstract 1.,To aid in their conservation, unionid mussel assemblages were surveyed in three relatively unstudied rivers in south-eastern Louisiana. 2.,Although total species richness varied among rivers, species diversity (as estimated both by Shannon-Weaver H, and rank-abundance curves) was fairly similar. 3.,Assemblage composition varied among the rivers, with the West Pearl River having the most dissimilar group of species. The endangered inflated heel splitter, Potamilus inflatus, was found only in the lower Amite River. 4.,The most common species had size distributions skewed towards larger individuals, but small individuals were collected (including the inflated heel splitter), indicating successful recruitment. 5.,Mussels were more common in silt than in sand or gravel, perhaps because fine sediments are more stable through time in these river systems. 6.,The greatest threat to these assemblages is gravel mining in the upper reaches of the rivers. At the present time only rivers with endangered species, or that have been declared scenic rivers, have any protection from gravel mining. Copyright © 2001 John Wiley & Sons, Ltd. [source]