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Stream Sediments (stream + sediment)
Selected AbstractsBenthic organic carbon influences denitrification in streams with high nitrate concentrationFRESHWATER BIOLOGY, Issue 7 2007CLAY P. ARANGO Summary 1. Anthropogenic activities have increased reactive nitrogen availability, and now many streams carry large nitrate loads to coastal ecosystems. Denitrification is potentially an important nitrogen sink, but few studies have investigated the influence of benthic organic carbon on denitrification in nitrate-rich streams. 2. Using the acetylene-block assay, we measured denitrification rates associated with benthic substrata having different proportions of organic matter in agricultural streams in two states in the mid-west of the U.S.A., Illinois and Michigan. 3. In Illinois, benthic organic matter varied little between seasons (5.9,7.0% of stream sediment), but nitrate concentrations were high in summer (>10 mg N L,1) and low (<0.5 mg N L,1) in autumn. Across all seasons and streams, the rate of denitrification ranged from 0.01 to 4.77 ,g N g,1 DM h,1 and was positively related to stream-water nitrate concentration. Within each stream, denitrification was positively related to benthic organic matter only when nitrate concentration exceeded published half-saturation constants. 4. In Michigan, streams had high nitrate concentrations and diverse benthic substrata which varied from 0.7 to 72.7% organic matter. Denitrification rate ranged from 0.12 to 11.06 ,g N g,1 DM h,1 and was positively related to the proportion of organic matter in each substratum. 5. Taken together, these results indicate that benthic organic carbon may play an important role in stream nitrogen cycling by stimulating denitrification when nitrate concentrations are high. [source] Regional Spatial Modeling of Topsoil GeochemistryBIOMETRICS, Issue 1 2009C. A. Calder Summary Geographic information about the levels of toxics in environmental media is commonly used in regional environmental health studies when direct measurements of personal exposure is limited or unavailable. In this article, we propose a statistical framework for analyzing the spatial distribution of topsoil geochemical properties, including the concentrations of various toxicants. Due to the small-scale heterogeneity of most geochemical topsoil processes, direct measurements of the processes themselves only provide highly localized information; it is thus financially prohibitive to study the spatial patterns of these processes across a large region using traditional geostatistical analyses of point-referenced topsoil data. Instead, it is standard practice to assess geochemical patterns at a regional scale using point-referenced measurements collected in stream sediment because, unlike topsoil data, individual stream sediment geochemical measurements are representative of the surrounding area. We propose a novel multiscale soils (MSS) model that formally synthesizes data collected in topsoil and stream sediment and allows the richer stream sediment information to inform about the topsoil process, which in environmental health studies is typically more relevant. Our model accommodates the small-scale heterogeneity of topsoil geochemical processes by modeling spatial dependence at an aggregate resolution corresponding to hydrologically similar regions known as watersheds. We present an analysis of the levels of arsenic, a toxic heavy metal, in topsoil across the midwestern United States using the MSS model and show that this model has better predictive abilities than alternative approaches using more conventional statistical models for point-referenced spatial data. [source] Potential for 4- n -nonylphenol biodegradation in stream sedimentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008Paul M. Bradley Abstract The potential for in situ biodegradation of 4-nonylphenol (4-NP) was investigated in three hydrologically distinct streams impacted by wastewater treatment plants (WWTPs) in the United States. Microcosms were prepared with sediments from each site and amended with [U-ring- 14C]4- n -nonylphenol (4- n -NP) as a model test substrate. Microcosms prepared with sediment collected upstream of the WWTP outfalls and incubated under oxic conditions showed rapid and complete mineralization of [U-ring- 14C]4-n-NP to 14CO2 in all three systems. In contrast, no mineralization of [U-ring- 14C]4- n -NP was observed in these sediments under anoxic (methanogenic) conditions. The initial linear rate of [U-ring- 14C]4- n -NP mineralization in sediments from upstream and downstream of the respective WWTP outfalls was inversely correlated with the biochemical oxygen demand (BOD) of the streambed sediments. These results suggest that the net supply of dissolved oxygen to streambed sediments is a key determinant of the rate and extent of 4-NP biodegradation in stream systems. In the stream systems considered by the present study, dissolved oxygen concentrations in the overlying water column (8,10 mg/L) and in the bed sediment pore water (1,3 mg/L at a depth of 10 cm below the sediment,water interface) were consistent with active in situ 4-NP biodegradation. These results suggest WWTP procedures that maximize the delivery of dissolved oxygen while minimizing the release of BOD to stream receptors favor efficient biodegradation of 4-NP contaminants in wastewater-impacted stream environments. [source] A field-based microcosm method to assess the effects of polluted urban stream sediments on aquatic macroinvertebratesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2005Vincent 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] Degradation and sorption of selected organophosphate and carbamate insecticides in urban stream sedimentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2004Svetlana Bondarenko Abstract Monitorings studies show that urban surface streams in the United States are commonly contaminated with pesticides, and contamination by organophosphates and carbamates is of particular concern because of their aquatic toxicity. The degradation and sorption of four common organophosphate and carbamate insecticides were studied in urban creek sediments from southern California, USA. In sediment, malathion was quickly degraded under either aerobic or anaerobic conditions, with a half-life (t1/2) <3 d. Diazinon and chlorpyrifos were moderately persistent under aerobic conditions (t1/2 = 14,24 d). However, persistence of chlorpyrifos increased significantly under anaerobic conditions, and t1/2 was prolonged to 58 to 223 d. The greatest effect of redox potential was found with carbaryl. Although rapid dissipation occurred under aerobic conditions (t1/2 = 1.8,4.9 d), carbaryl became virtually nondegradable under anaerobic conditions (t1/2 = 125,746 d). The sorption coefficient consistently increased with time for all pesticides, and chlorpyrifos displayed greater sorption potential than the other pesticides. This study indicates that pesticides in sediment may become less available with time because of increased sorption, and pesticide persistence in sediment may vary greatly among compounds and with redox conditions. Under anaerobic conditions, long persistence may occur even for nonpersistent compounds. [source] Interregional comparisons of sediment microbial respiration in streamsFRESHWATER BIOLOGY, Issue 2 2000B. H. Hill Summary 1The rate of microbial respiration on fine-grained stream sediments was measured at 371 first to fourth-order streams in the Central Appalachian region (Maryland, Pennsylvania, Virginia, and West Virginia), Southern Rocky Mountains (Colorado), and California's Central Valley in 1994 and 1995. 2Study streams were randomly selected from the United States Environmental Protection Agency's (USEPA) River Reach File (RF3) using the sample design developed by USEPA's Environmental Monitoring and Assessment Program (EMAP). 3Respiration rate ranged from 0 to 0.621 g O2 g -1 AFDM h -1 in Central Appalachian streams, 0-0.254 g O2 g -1 AFDM h -1 in Rocky Mountain streams, and 0-0.436 g O2 g -1 AFDM h -1 in Central Valley streams. 4Respiration was significantly lower in Southern Rocky Mountain streams and in cold water streams (< 15 °C) of the Central Appalachians. 5Within a defined index period, respiration was not significantly different between years, and was significantly correlated with stream temperature and chemistry (DOC, total N, total P, K, Cl, and alkalinity). 6The uniformity of respiration estimates among the three study regions suggests that sediment microbial respiration may be collected at any number of scales above the site-level for reliable prediction of respiration patterns at larger spatial scales. [source] Major and trace element provenance signatures in stream sediments from the Kando River, San'in district, southwest JapanISLAND ARC, Issue 2 2006Edwin Ortiz Abstract Basement rocks in the catchment of the Kando River in southwest Japan can be divided into two main groups. Paleogene to Cretaceous felsic granitoids and volcanic rocks dominate in the upstream section, and more mafic, mostly Miocene volcanic and volcaniclastic rocks occur in the downstream reaches. Geochemically distinctive Mount Sambe adakitic volcanic products also crop out in the west. X-ray fluorescence analyses of major elements and 14 trace elements were made of two size fractions (<180 and 180,2000 µm) from 86 stream sediments collected within the catchment, to examine contrasts in composition between the fractions as a result of sorting and varying source lithotype. The <180 µm fractions are depleted in SiO2 and enriched in most other major and trace elements relative to the 180,2000 µm fractions. Na2O, K2O, Ba, Rb and Sr are either depleted relative to the 180,2000 µm fractions, or show little contrast in abundance. Sediments from granitoid-dominated catchments are distinguished by greater K2O, Th, Rb, Ba and Nb than those derived from the Miocene volcanic rocks. Granitoid-derived <180 µm fractions are also enriched in Zr, Ce and Y. Sediments derived from the Miocene volcanic rocks generally contain greater TiO2, Fe2O3*, Sc, V, MgO and P2O5, reflecting their more mafic source. Sediments containing Sambe volcanic rocks in their source are marked by higher Sr, CaO, Na2O and lower Y, reflecting an adakitic signature that persists into the lower main channel, where compositions become less variable as the bedload is homogenized. Normalization against source averages shows that compositions of the 180,2000 µm fractions are less fractionated from their parents than are the <180 µm fractions, which are enriched for some elements. Contrast between the size fractions is greatest for the granitoid-derived sediments. Weathering indices of the sediments are relatively low, indicating source weathering is moderate, and typical of temperate climates. Some zircon concentration has occurred in granitoid-derived <180 µm fractions relative to 180,2000 µm counterparts, but Th/Sc and Zr/Sc ratios overall closely reflect both provenance and homogenization in the lower reaches. [source] | ||||||||||