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1.
Although there have been recent significant gains in our understanding of mercury (Hg) cycling in aquatic environments, few studies have addressed Hg cycling on a watershed scale. In particular, attention to Hg species transfer between watershed components (upland soils, groundwater, wetlands, streams, and lakes) has been lacking. This study describes spatial and temporal distributions of total Hg and MeHg among watershed components of the Allequash Creek watershed (northern Wisconsin, USA). Substantial increases in total Hg and MeHg were observed as groundwater discharged through peat to form springs that flow into the stream, or rivulets that drain across the surface of the wetland. This increase was concomitant with increases in DOC. During fall, when the Allequash Creek wetland released a substantial amount of DOC to the stream, a 2–3 fold increase in total Hg concentrations was observed along the entire length of the stream. Methylmercury, however, did not show a similar response. Substantial variability was observed in total Hg (0.9 to 6.3) and MeHg (<0.02 to 0.33) concentrations during synoptic surveys of the entire creek. For the Allequash Creek watershed, the contributing groundwater basin is about 50% larger than the topographic drainage basin. Total Hg concentrations in groundwater, the area of the groundwater basin, and annual stream flow data give a watershed-yield rate of 1.2 mg/km2/d, which equates to a retention rate of 96%. The calculated MeHg yield rate for the wetland area is 0.6 to 1.5 mg/km2/d, a value that is 3–6 fold greater than the atmospheric deposition rate.  相似文献   

2.
2000年以来宁夏引黄灌区引水量不断下降,为探究引水量下降对农田退水污染的影响,以银北灌区为研究对象,选择灌区两条典型排水沟——银新沟和第五排水沟,揭示其退水量与污染来源年内分布规律,基于水文统计分析方法探讨灌溉期水质氨氮和总磷的演变及其污染负荷年际变化特征,分析引水量下降对灌区农田退水污染的影响。结果表明:排水沟流量过程与引水过程具有很好的一致性,且农田退水污染主要发生在灌溉期;引水量减少以来,银新沟和第五排水沟退水量显著下降,灌溉期水质有所改善,与2004年以前相比,银新沟农田氨氮、总磷污染负荷消减率分别为35.3%和41.7%,第五排水沟相应为71.2%和63.7%。两沟农田污染负荷与退水量间存在较为显著的正相关。分析得出控制灌区引水量,实施农业节水对防治农田退水污染具有积极作用。  相似文献   

3.

Purpose

Fine-grained sediment is an important pollutant in streams and estuaries, including the Chesapeake Bay in the USA. The objective of this study was to determine the sources of fine-grained sediment using the sediment fingerprinting approach in the Linganore Creek watershed, a tributary to the Chesapeake Bay.

Materials and methods

The sediment fingerprinting approach was used in the agricultural and forested, 147-km2 Linganore Creek watershed, Maryland from 1 August 2008 to 31 December 2010 to determine the relative percentage contribution from different potential sources of fine-grained sediment. Fine-grained suspended sediment samples (<63 μm) were collected during storm events in Linganore Creek using an automatic sampler and manual isokinetic samplers. Source samples were collected from 40 stream bank sites, 24 agricultural (cropland and pasture) sites, and 19 forested sites. Suspended sediment and source samples were analyzed for elements and stable isotopes.

Results and discussion

Results of sediment fingerprinting for 194 samples collected in 36 separate storm events indicate that stream banks contributed 53% of the annual fine-grained suspended sediment load, agriculture contributed 44%, and forests contributed 3%. Peak flows and sediment loads of the storms correlate to stream bank erosion. The highest peak flows occurred in the winter and, along with freeze–thaw activity, contributed to winter months showing the highest rate of stream bank erosion. Peak flow was negatively correlated to sediment sources from agricultural lands which had the greatest contribution in non-winter months. Caution should be observed when trying to interpret the relation between sediment sources and individual storms using the sediment fingerprinting approach. Because the sediment fingerprinting results from individual storms may not include the temporal aspects of the sourced sediment, sediment that is in storage from previous events, remobilized and sampled during the current event, will reflect previous storm characteristics. Stream bank sediment is delivered directly to the channel during an event, whereas the delivery of upland sediment to the stream is lower due to storage on hillslopes and/or in channels, sediment from stream banks are more likely to be related to the characteristics of the sampled storm event.

Conclusions

Stream banks and agricultural lands are both important sources of fine-grained sediment in the Linganore Creek watershed. Peak flows and sediment loads for the 36 storms show a significant relation to sediment sources from stream bank erosion. Attempting to link upland sediment sources to flow and seasonal characteristics is difficult since much of the upland sediment eroded in an event goes into storage. By averaging sediment sources over several storms, it may be possible to determine not only the sediment sources that are directly contributed during the current event but also sediment from previous events that was in storage and remobilized.  相似文献   

4.

Purpose

The aims of the study were to evaluate the effect of combined sewer overflows (CSO) and storm water drains (SWD) on metal bioavailability in small urban streams in Prague and to evaluate levels of metals in water, sediment, and macroinvertebrates. The following working hypotheses were adopted: (a) sites dominantly affected by SWD are less polluted by metals, and (b) sites dominantly affected by SWD have higher bioavailability of metals.

Materials and methods

Physical and chemical parameters (pH, conductivity, NO3-N, NH4-N, COD, alkalinity, and water hardness) and concentrations of the metals Cu, Zn, Pb, Ni, and Cr were determined in samples of water and sediment at five to six sites on four target streams—Záti?ský Creek, Ko?íkovský Creek, Boti? Creek, and Rokytka Creek—three to five times per year during the period 2002–2004. The sites from all studied creeks were categorized into five groups according to the prevailing type of urban drainage impact. Macroinvertebrates were sampled and analyzed for metals at each site for a period of 1 month. The concentration patterns of metals were interpreted by partition coefficient (Kd), hazard quotient (HQ), cumulative criterion unit (CCU), and biota sediment accumulation factor (BSAF).

Results and discussion

Concentrations of metals in water as well as in sediment at sites receiving water from SWD were lower than at sites where creeks receive water from CSO, except for Pb. Concentrations of Cu, Zn, and Pb in sediment were higher at sites affected by CSO. Concentrations of metals in aquatic macroinvertebrates, expressed as BSAF, indicated higher values at sites affected by SWD. Frequencies of high BSAF (>1) were lower in CSO compared to SWD. This finding was explained by (a) a decrease of pH on SWD sites compared to the increase of pH on CSO sites during rain events, (b) a greater resuspension of sediment at SWD sites during rain events, and (c) an abundance of organic matter in CSO available for sorption of metals and a corresponding reduction of their bioavailability.

Conclusions

In the study area, the type of urban drainage affects the bioavailability of metals—while SWD increase metal bioavailability, CSO cause its decrease. The sediments in SWD sites do not indicate risk to the benthic community according to the applied environmental quality standards. Water and sediment in creeks affected by SWD are less polluted by metals. Both working hypotheses were therefore supported.
  相似文献   

5.
The purpose of this study was to determine the impacts of regional historical uranium mining activities within sediments of the Bowman?CHaley reservoir of southwestern North Dakota. The extent of anthropogenic-influenced watershed impacts were quantified through the determination of sediment metals concentrations and metal enrichment factors to evaluate the potential of geochemically influenced As and U remobilization within the reservoir sediments. Sediment cores were collected and analyzed for total metal concentrations at five locations within the reservoir: Spring Creek delta, Alkali Creek delta, two locations within the North Fork of the Grand River confluence, and adjacent to the reservoir outfall. Pearson-moment correlations were used to establish inter-core metal correlations, while sediment enrichment factors were determined relative to background concentrations. Enrichment factor results suggest all sampling sites are classified as minor to moderately enriched for As and U. Metal behavior for the three reservoir inlets indicated similar metal loading sources and post-depositional behavior, while metals migration within the vicinity of the reservoir outlet appear to be controlled by geochemical and/or physical processes. For the reservoir outlet, As and U normalized to Al suggest the occurrence of vertical migration of As, while surface-bound U remobilization was apparent within the water column immediately above the sediments. Elevated U was found within the Spring Creek inlet, and appear attributed to historical uranium processing operations located in Griffin, North Dakota. While the reservoir As and U sediment concentrations may be considered low, their presence appears directly attributed to historical uranium mining activities within the Bowman?CHaley reservoir watershed.  相似文献   

6.
The spatial variability in chemical composition of water and sediments along Snow Fork, a stream draining 70 km2 of southeastern Ohio, was investigated under low-flow conditions. The stream is affected by acid mine drainage (AMD) beginning atEssex Mine, an abandoned mine opening, and extending 23 km downstream to the confluence with Monday Creek. Volumetric discharge and changes in stream water and sediment metalconcentrations were examined to identify chemical interactionsand processes controlling the transport and fate of metalcontaminants. The stream loses water to the groundwater system insome sections. The water loss probably occurs through fracturesconnecting the stream to underlying underground coal mines. Massbalance (loading) and mineral saturation index calculations wereused to identify metal sources and sinks. Dissolved metal loadingincreases downstream along the length of Snow Fork, despite theprecipitation of metals as hydroxides in the streambed,indicating multiple groundwater sources of AMD along the flowpath. Relatively high dissolved metal concentrations and lowsediment metal concentrations occur where the pH is low,indicating that local sediment-water interaction dominates masstransfer between sediments and water. Calculated mineralsaturation indexes indicate that aluminum and iron hydroxidesprecipitate in some stream segments and dissolve in others. X-raydiffractograms of sediments show two distinct mineral groups.Amorphous or weakly crystalline minerals dominate one group foundnear the stream headwaters near the underground mine. Crystallinemineral phases dominate the sediments downstream. Thesediffractograms contain the primary peaks for quartz, kaoliniteand illite all of which constitute the local sandstones, shalesor underclay. Peaks of amorphous phases of iron and manganese,if present, are obscured. The implications of these findings arethat the transport of metals in sediments may be as important asdissolved metal transport in estimating the overall stream load,particularly if downstream sources of AMD may remobilize metalsfrom soluble precipitates.  相似文献   

7.
The attenuation of residual industrial loads of chloride (Cl-) and total ammonia (T-NH3) from Solvay waste bedsto Ninemile Creek, New York, and downstream polluted Onondaga Lake, is characterized and quantified based on fourteen years ofmonitoring following closure of a soda ash manufacturing facility. Concentrations of these constituents were monitored atleast bi-weekly at two sites on Ninemile Creek that bound the waste bed inputs, and at the mouths of the two other major tributaries to the lake, to quantify inputs from the industrial deposits and to place these residual loads in the perspective of contributions to total lake loading. Variations in the concentrations of these constituents in Ninemile Creek downstreamof the industrial inputs within individual years are well represented by a dilution model; i.e., linearity of concentrationversus inverse stream flow. A relatively uniform ratio of T-NH3 to Cl- has been maintained in the residual loading, about 0.42 g T-NH3 per kg Cl-. Substantial decreases (～40%) in loading of these constituents fromthe waste beds to Ninemile Creek over the post-closure period are documented through shifts in the dilution model. As a result,the contribution of this source to the total lake loading has decreased from ～45% to <30%. The estimated total residual Cl- load received from the waste beds since closure of the industry (～1 million metric tons) corresponds to ～1.6 yr of the full operating load of the industry before closure. The time required to reach a Cl- concentration goal for Ninemile Creek is considered, based onprojections of the post-closure trend.  相似文献   

8.
Nutrient (C, N and P) and metal (Cr, Cu, Ni, Pb and Zn) content and dynamics of suspended and channel bed sediments were analysed within the rural Attert River basin (Luxembourg). This basin is representative of the main physiographic characteristics of the country, where there is currently little information available on the composition and dynamics of fluvial sediment. Stream bed fine-grained sediment samples (n?=?139) collected during low flow conditions and time-integrated suspended sediment samples (n?=?183) collected during storm runoff events (October 2005 to April 2008) in seven nested basins ranging from 0.45 to 247?km2 were analysed. Nutrient and metal spatial patterns, temporal trends and the relationship between their content and storm runoff characteristics (e.g. maximum discharge and sediment concentration) were assessed. Results showed a high spatial and temporal variability, mainly associated with basin characteristics and local inputs. Higher values of total C were measured in the highly forested basins located in the northern part of the Attert River basin, whereas the highest values of total P were mainly associated with material coming from grassland and with the inflow of wastewater treatment plants (i.e. higher values of total P were measured in the southern part of the basin). The abundance of metals, not only in suspended but also in channel bed sediments, was generally as follows: Zn > Cr > Ni > Pb > Cu. Both nutrient and metal concentrations were at a maximum at the beginning of the wet season, after having been accumulated during the summer. These values tended to decrease during autumn and winter due to sediment mobilisation, and a higher flow capacity to transport coarser particle fractions from the sources. In general, concentrations of nutrients and metals on suspended sediment were negatively correlated with antecedent precipitation, total precipitation, total specific discharge and maximum discharge, which has been previously associated to a ??dilution?? effect during storm runoff events. Results show that both sediment sources and hydrologic events play an important role on the spatial and temporal variability of sediment-associated nutrient and metal contents.  相似文献   

9.
Reimer Herrmann 《CATENA》1981,8(2):171-189
The load of 3.4-benzopyrene in storm drains of an urban watershed is linked to the load of suspended sediments because of the high partition coefficient. The strong influence of the antecedant weather conditions on 3.4-benzopyrene washoff indicates a 'supply limiting watershed' (SUTHERLAND 1978). After strong antecedant rainfall and low flow rates of the storm under consideration the concentrations of 3.4-benzopyrene in rainfall and storm run-off are not significantly different from each other. Compared with a wateshed with an old combined sewer system, which can be described as ‘transport limiting’, a higher washoff intensity is needed to result in the same 3.4-benzopyrene load.  相似文献   

10.
The Hg accumulation in sedimentary environments of a mangrove ecosystem in Sepetiba Bay, SE Brazil, was investigated. These environments include sediments of a mangrove forest, the main tidal creek that drains the forest, and the bare seaward-edge mud flat adjacent to forest and tidal creek. Maximum Hg concentration peaks in sediments from the mud flat (184 ng g-1), tidal creek (98 ng g-1), and mangrove forest (60 ng g-1) correspond to enrichment factors of 6.1, 3.3, and 2.0 above the estimated average background level, respectively. Average inventories of Hg excess (background-corrected) concentrations were substantiallydifferent between environments, decreasing from mud flat sediments (5.2 mg m-2) to creek sediments (3.3 mg m-2)to mangrove forest sediments (0.9 mg m-2). Mercury concentration profiles indicated a consistently higher accumulation of Hg in surface layers of mud flat and tidal creeksediments, whereas mangrove forest sediments showed a higher Hgaccumulation in root-rich subsurface layers, in agreement with an enrichment of Fe and organic matter contents. While Hg distribution in mud flat and tidal creek sediments appears to belargely affected by contamination, its distribution in mangrove forest substrate appears to be greatly affected by root-sedimentinteractions. Mercury levels in the study site were comparable tothose observed in coastal sediments under moderate Hg contamination at local and regional scales. Results indicate thatsedimentary environments surrounding the mangrove forest retain most of the anthropogenic Hg reaching the ecosystem. Since tidal waters have been previously demonstrated as the main source of metals to the site, it is suggested that the Hg retention in mudflat sediments precede and may avoid a higher Hg accumulation inlandward environments.  相似文献   

11.
This study was conducted to characterize the heavy metal contamination in the soils of peach orchards irrigated with water from Nilüfer creek, which is heavily polluted by industrial and municipal wastes. Twenty-one peach orchards with 3 different cultivars in 7 orchards each located along Nilüfer creek were monitored in the experiment. To determine levels of pollution, soils and aboveground parts of the trees were sampled and analyzed for iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), cobalt (Co), nickel (Ni), chromium (Cr), lead (Pb), and cadmium (Cd). Total amounts of Ni and Cr were found to be at the excessive levels in soils. Extractable Ni concentration decreased with increasing pH and CaCO3 content in soils. Leaf metal contents were generally at tolerable levels, but Ni and Pb accumulated to toxic levels in different parts of the fruit (flesh and peel). Except for Fe and Ni, plant concentrations of the metals did not correlate with their total and DTPA-extractable concentrations in the soils. There was no significant difference among the cultivars in accumulation of heavy metals.  相似文献   

12.
Concentrations of Cl, total ammonia (TNH3), NO3 plus NO2, total P (TP), and soluble reactive P (SRP) were measured at two sites, located 5 km apart, on Ninemile Creek, New York, for a period of more than 8 mo. The sites bound the most recently formed Solvay waste beds, associated with the production of soda ash, that adjoin the creek. Concentrations of Cl and T-NH3 increased on average by factors of 16.1 and 7.6, respectively, over the monitored stream reach. The estimated average loadings of these materials to the stream over this reach were 2.3 × 105 and 1.2 × 102 kg d?1, respectively. These inputs are attributable to the Solvay waste beds. The loading of Cl from this source has not changed significantly over a 4 yr period since the closure of the soda ash manufacturing facility. This is the single largest source of Cl, and the second largest source of T-NH3, to polluted Onondaga Lake. Profiles of Cl in the lake indicated that at times the creek inflow plunges to subsurface layers as a result of its elevated density. This is at least in part a result of the creek's ionic enrichment. The concentration of SRP decreased by a factor of 2.0 on average over the study reach, probably due to adsorption to the CaCO3 deposits that cover the stream bed in this area. However, the TP load from the creek to the lake is not significantly affected by this phenomenon.  相似文献   

13.
Estuarine systems adjacent to urban areas are at risk of contamination by contaminants from anthropogenic sources, such as heavy metals. We anticipated that the sediments of the Swan River estuary, which runs through metropolitan Perth in Western Australia, would show metal contamination related to industrialization and inputs of stormwater. Total Cu, Pb and Cd concentrations, and Cu, Pb, Cr and Zn inoperationally-defined fractions, were determined inseparate sampling exercises in near-shore sediments ofthe upper Swan River estuary.Total metal concentrations in sediments were not high (maximum values of 297 mg kg-1 for Cu, 184 mg kg-1 for Pb and 0.9 mg kg-1 for Cd) when compared with Australian environmental assessmentguidelines for soils. On the basis of linear regressions between sediment metal concentrations andphysicochemical properties of the sediments (pH, organic carbon, particle size distribution), no single parameter could explain the variation in metal concentrations for all metals. Sediment organic carbon content was positively correlated with Cu concentration; Cu concentrations also increased significantly with increasing clay content anddecreasing sand content. Pb concentrations showed a significant increase with increasing sediment pH, and were approximately three-fold higher in sediments adjacent to stormwater drain outfalls than in sediments remote from drains; no such effect was observed for Cu or Cd. No effect of distance downstream was observed. Sequential extraction of sediments showed that most of the metals were in relatively immobile forms, for example bound to Feoxides, or only extractable by aqua regia. The enhanced concentrations of Pb near stormwater outfalls suggest that vehicle-derived Pb may be an important contributor of Pb to the estuary.  相似文献   

14.
While the presence of fecal indicator bacteria such as Escherichia coli in urban stormwater has been widely documented, their occurrence and persistence in sediments are not as well understood. Recent investigations suggest that E. coli can accumulate in drainage basin sediments and act as a fecal bacterial reservoir within a watershed. We investigate the prevalence of E. coli populations in a tidal creek stormwater catchment and examine their interaction with overlying stormwater under wet and dry weather conditions. Two rain events are sampled more intensively with samples collected prior to, during, and after rainfall to profile bacteria in each matrix throughout a storm. Results of profile sampling and estimates of sediment resuspension provide evidence for E. coli accumulation during dry conditions and entrainment in overlying waters during storm conditions. Profile results suggest the occurrence of steady-state E. coli populations in drainage basin sediments.  相似文献   

15.
The loads and sources of heavy metals (Cd, Co, Cu, Mn, Mo, Ni, Pb, V, and Zn) in the midstream of Tama River were evaluated on the basis of their chemical analyses in ordinary and stormwater runoff from July 2007 to November 2008. Tama River is one of the three major rivers flowing into Tokyo Bay. The total annual water discharges differed largely for 2007 and 2008, depending on the scales of typhoon rainfalls and other heavy rainfalls in each year. The concentrations of the metals other than Mo in the river did not change markedly at a flow rate of less than approximately 200 m3 s?1, but at higher flow rates, the concentrations of all the metals increased linearly with the increase in the log of flow rate (r 2?=?0.94–0.99). The annual loads of heavy metals for 2007 and 2008 were estimated using regression equations between the above parameters and the hourly flow rate data for each year. For the metals other than Mo, the contribution of the loads at higher flow rates (>200 m3 s?1) was much larger than that at lower flow rates (<200 m3 s?1), showing the importance of the particulate loads (primarily crustal materials) during storm runoff following typhoon rainfalls and other heavy rainfalls. In contrast, the loads of Mo at lower flow rates accounted for major portions (56–78%) of the total loads, because of a relatively small contribution of particulate load during storm runoff. The contribution of the loads of Mo, Zn, Cd, Cu, and Ni at lower flow rates to the annual loads was larger than that of other metals. It was found that the concentrations of these metals in ordinary runoff are strongly affected by the discharge of treated water from sewage treatment plants which are located along the catchment. Thus, treated water from sewage treatment plants may be the primary source contributing to the present pollution of Mo, Zn, Cd, Cu, and Ni in Tokyo Bay.  相似文献   

16.
In the Pocone district, Brazil, Hg distribution was studied in a small watershed which drains tailings from a 10 yr old gold mining operation. Heavy regional rains are responsible for continuous weathering, thereby making it possible to transport Hg into the ecologically important Pantanal area. Mercury concentrations in creek sediments range from < 0.02 to 0.18 mg. kg?1. The highest concentrations occur close to the tailings deposit. Mercury concentrations in the water were always below the detection limit of the analytical method used (<0.04 µg. L?1). Suspended matter samples collected before, during and after a storm, showed a Hg peak value of 0.61 mg kg?1. about 30 min after the event. Dissolved Hg concentration still fell below the detection limit. Among the biota, molluscs accumulated moderately high concentrations of Hg, while macrophytes and fish did not. Mercury concentrations in molluscs were dependent on size, with larger animals presenting higher Hg concentration. We conclude that Hg present in the tailings shows low mobility and that its eventual transport into the drainage system is dependent on the erosion of fine material from the wastes during rains, resulting in a restricted contamination of the area and low Hg concentration in the biota.  相似文献   

17.
An important component of monitoring pollution of urban road-deposited sediment (RDS) is an understanding of the temporal variability in its composition and physical characteristics. This study set out to determine what the monthly variability in metal concentrations, organic matter content, grain-size and grain-size fraction metal-loadings are in inner city sites in Manchester, northwest England. The results show that there is significant temporal variability in metal (Pb, Zn, Fe, Mn) concentration in RDS from inner city Manchester. There was no significant temporal variability in grain-size characteristics or organic matter content, indicting that these metal variations were the result of variation in sources and accumulation processes. Pb and Zn displayed local variability, suggesting local controls on variability, whereas Fe and Mn displayed consistent variability across all sites, suggesting a common, larger-scale control on variability. The finest grain-size fraction (<63 μm) contained the highest Pb, Cu and Zn concentrations, but for the case of Fe and Mn, the coarser fractions (>300 μm) commonly contained the highest concentrations, again suggesting differing controls. For all metals, due to the weight percent dominance of the coarser fractions, the dominant loading of metals is in the coarser fractions. This has implications on management strategies, via street sweeping and the subsequent waste disposal, and on the modelling of the input of RDS and associated metals into surface waterways. The recognition of significant temporal variability of metal concentrations in RDS, independent of grain-size changes, implies that the monitoring of urban road sediment pollution will require not just consideration of spatial variability, but the design of schemes that will capture temporal variability also.  相似文献   

18.
Most tidal creeks in North Carolina are closed or partially closed to shellfishing. These creeks often remain closed due to the inability to determine sources of fecal pollution. This study was designed for intensive fecal coliform monitoring of Futch Creek, N.C., to try and determine sources(s) of fecal pollution. Futch Creek is a mildly polluted tidal creek, with marginal levels of fecal coliforms and could potentially be reopened. Problems in interpreting levels of fecal coliforms and pollution risks are two fold and were extremely pronounced in this study. First, several environmental factors have been shown to influence levels of fecal coliforms. Therefore, effects of temperature, salinity, tidal cycles, and rain events on fecal coliform counts were examined. There were higher fecal coliform levels in the warmer temperatures. There was a strong inverse relationship with salinity, with highest fecal coliform counts in the 10–14 g L-1 range for both the mFC and mTEC counts with no apparent source of pollution. This trend was also observed in three other tidal creeks. Tidal cycles did affect fecal coliform counts with substantially higher counts during low tide and appeared to be more important than rain events. It is apparent that when evaluating several stations in a creek, samples must be taken during the same tidal cycle stage in order to have comparative data. Counts obtained using the mTEC method were consistently higher than mFC counts in all salinity ranges. Basic taxonomic tests were performed on fecal coliforms isolated from three salinity regimes: 0 g L-1, 10–14 g L-1, and 23–26 g L-1. The mFC method in the 10–14 g L-1 (45%) and 23–26 g L-1 (70%) salinity range had the highest incidence of false-positive counts (non E. coli). The mTEC method also had the highest incidence of false-positive counts in the 23–26 g L-1 (27%) and 10–14 g L-1 (24%), none as high as the mFC method. Therefore, the mTEC method appears to be the better of the two but is still not an ideal approach.  相似文献   

19.
Due to the episodic nature of rainfall and the high dissolved metal concentrations in the acid sulfate soil catchment of Clothiers Creek (NSW, Australia), active treatment was considered more appropriate than passive treatment. Alkaline reagents were added to oxidised shallow drains to remove acidities ranging from 438 to 1,837 mg/L CaCO3. A fine limestone slurry was produced from the pounding together of limestone rock fragments within a rotating drum and, on addition to drain waters, was found to remove acidity to varying degrees of effectiveness (from 12 to 100%). The efficiency decreased as the pH of the water approached neutrality due to calcite saturation and the slow reaction rate of limestone at high pH. Hydrated lime powder was also mixed with drain water in the rotating drum though most mixing occurred once the slurry entered the drain where efficiencies ranging from 67 to 89% were observed. A powdered mixture of MgCO3 and CaCO3 was only 11% effective in treatment of the drainage water due to the slow rate of reaction of MgCO3. Whilst the active treatment system was capable of treating a large acidity flux (particularly using hydrated lime) it required regular addition of reagent and the dosing of hydrated lime was particularly difficult to control. Future designs of this active treatment system should be automated to prevent adverse aquatic impacts due to overdosing.  相似文献   

20.
Soil profiles were examined, described and sampled by horizons in various geomorphic positions along a transect originating at the Coniston smelter and extending in a southeasterly direction for approximately 12 km. The samples were then analyzed to determine particle-size distribution, pH, organic carbon and five heavy metals.Within the study area, elevated levels of nickel, copper and iron were found with maximum total concentrations of 1.2, 0.97 and 20.0%, respectively. Manganese and zinc did not occur in above-normal concentrations. The pH values of the soils were depressed with levels as low as 2.4.Near the smelter, erosion from soils on slopes has transferred materials into lower lying areas, thereby rearranging the areal distribution of nickel, copper and iron. Although the surface soil horizons along the entire transect have above-normal concentrations of these elements, only within the eroded area is there marked variability in their vertical distribution.  相似文献   

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