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1.

Purpose

Determining the dynamics of silicon in lakes, one of the essential nutrients for diatoms, is valuable for understanding aquatic environmental problems. The dissolved silicon (DSi) and biogenic silicon (BSi) budgets in Lake Kasumigaura, a shallow eutrophic lake in Japan, during the last three decades were assessed based on the analysis of dated sediment cores and a water quality database.

Materials and methods

Sediment cores (100?cm long) were taken at the center of Lake Kasumigaura in 2005, 2007, and 2009 and at two other sites in 2007. BSi contents of the dated sediments were determined by wet alkaline digestion. The net sedimentation rates of BSi were defined as the difference between the DSi load from inflowing rivers and the DSi and BSi loads from the outflow of the lake, calculated using DSi concentrations and diatom abundances in the lake from 1980 to 2007 and DSi concentrations of the inflowing rivers during 1994, 2007, and 2009. The gross sedimentation rates of BSi were estimated by multiplying BSi concentrations in lake water by the diatom sinking rate reported by previous studies.

Results and discussion

Budgetary calculations based on the database showed that 60?C70?% of DSi inputs from the inflowing rivers during the 27?years could ultimately be accumulated as diatom frustules in bottom sediments in the lake. The sediment analysis revealed that the amount of BSi accumulated in the lake from 1980 to 2007 was 2.0?C2.6?×?1011?g, similar to the amount based on the database of 1.3?C2.4?×?1011?g. Although the gross sedimentation rates of BSi likely increased, the net sedimentation rates of BSi decreased significantly from 6?C10?×?109?g?year?1 in the 1980s to 2?C6?×?109?g?year?1 in the 2000s, suggesting a fast recycling of BSi in recent years caused by an increase in sediment resuspension and regeneration.

Conclusions

The sediment core information and the water quality database can be used for calculating the long-term silicon budgets in Lake Kasumigaura. An increase in the DSi release rates was identified, which is consistent with recent sediment resuspension. Comparing the sediment core information with the database suggests the long-term dissolution of sediment BSi; however, analysis of the BSi content in sediment cores representing a much longer time period is needed to confirm this.  相似文献   

2.
A model has been developed that relates the cation denudation rate (CDR) of a watershed (the rate that cations derived from chemical weathering are carried off by runoff), the atmospheric load of excess SO4, and the pH of the river. Chemical and discharge data for rivers in Nova Scotia and Newfoundland were used to develop and test the model, which is based upon the common major ion chemistry of soft surface waters, and may be expressed by three statements: (1) CDR (meq m?2 yr?1) ? Excess SO4 ?? load (meq m?2 yr?1) = HCO3 ? (meq m?2 yr?1), (2) HCO3 ? (meq m?2 yr?1)/Runoff (m3 m?2 yr?1) = HCO3 ? (meq m?3), (3) pH = pK + \(pP_{CO_2 } \) ? pHCO3 ?. The model in concentration form applies well to lakes. A detailed analysis of the data for the Isle aux Morts River, Newfoundland, is presented, showing that the CDR varies throughout the year, affected by both discharge and seasonal pattern.  相似文献   

3.

Purpose

The Turvo/Grande drainage basin (TGDB), located in the northwestern region of S?o Paulo state, covers an area of 15,983?km2. The region is typically regarded as agricultural by the S?o Paulo State Environmental Agency, but the industrial area is expanding, and some studies have shown that metal concentrations in water can be higher than the values regulated by Brazilian law. Therefore, the aim of this study was to assess the role of sediments as a source or a sink of metals for drainage basin management.

Materials and methods

Interstitial water from different sediment depths (0?C42?cm) and the sediment?Cwater interface and sediment core samples were collected in February and July 2010 from the Preto, Turvo, and Grande rivers. Quantification of Cr, Cu, Fe, Mn, Ni, and Pb in these samples was performed by graphite furnace or flame atomic absorption spectrometry. Metal diffusive flux estimation from sediment into the overlying water was calculated by Fick??s First Law of Diffusion.

Results and discussion

The fluxes of all metals for the three rivers were positive, indicating diffusion into the overlying water. Ni and Pb showed the lowest diffusive fluxes, which ranged from 2.4 to 3,978???g?m?2?day?1 for Ni and from ?0.1 to 1,597???g?m?2?day?1 for Pb. In turn, Cu and Cr were subject to the largest transfer to water, especially in the dry season (Cr, 4.5?C7,673???g?m?2?day?1; Cu, 1.3?C14,145???g?m?2?day?1). The Preto River (urban area) showed smaller fluxes than the Grande River (agricultural area), and the values of the latter were higher than those found in other impacted areas of the world.

Conclusions

The diffusive fluxes indicate that sediments from the TGDB act as a source of metals for the water column, with increased export of metals, particularly Cr and Ni, from the sediment into the overlying water during the dry season.  相似文献   

4.

Purpose

Wildfires represent one of the major natural disturbances within forested landscapes and have potential implications for the quality and function of downstream aquatic ecosystems. This study aimed to determine if a wildfire in a mountainous, forested watershed in British Columbia, Canada, caused a change in the dominant sediment source in the immediate 1?C2?years following the wildfire, and if the sediment sources changed over the medium term (3?C7?years) as the landscape recovered.

Materials and methods

Source materials (surface soil, subsurface soil and channel bank material) and fluvial (suspended and channel bed) sediment samples were collected over the period 2004 to 2010 from a watershed burnt by a wildfire in 2003, and from an adjacent watershed that was not impacted by the fire. Samples were analysed for the fallout radionuclides (FRNs) caesium-137 (137Cs) and unsupported lead-210 (210Pbun). An unmixing model was used to calculate the relative source contributions of the fluvial sediment samples.

Results and discussion

137Cs and 210Pbun were concentrated in the upper layers of surface soils in both watersheds and were statistically different to concentrations in subsurface and channel bank material. In the burnt watershed, FRN concentrations were greatest in the ash layer. Sediment sources as determined by the unmixing model were 100?% subsurface/channel bank material in the unburnt watershed, while in the burnt watershed 8.5?±?2.5?% was derived from surface soils. In both watersheds, there were no major changes in the relative contributions from surface soil and from subsurface/channel bank material over the period 2004 to 2010. Thus, while the wildfire did cause a change in sediment sources, it was fairly subtle and did not conform to the effects following wildfire described for other studies in contrasting environments, which typically document a major increase in hillslope contributions relative to channel bank sources.

Conclusions

There was a limited response in terms of fine-grained sediment sources (and also sediment fluxes) in the burnt watershed. The reason for this muted response to a severe wildfire is likely to be the lack of precipitation, especially winter precipitation and the associated snowmelt, in the first year following the wildfire. Thus while the landscape was primed for erosion and sediment transport, the lack of a driving force meant that there was a limited immediate post-fire sediment response.  相似文献   

5.

Purpose

Approximately 74 % of agricultural soils in Tunisia are affected by water erosion, leading to the siltation of numerous human-made reservoirs and therefore a loss of water storage capacity. The objective of this study was to propose a methodology for estimating the relative contributions of gully/channel bank erosion and surface topsoil erosion to the sediment accumulated in small reservoirs.

Materials and methods

We tested an approach based on the sediment fingerprinting technique for sediments collected from a reservoir (which has been in operation since 1994) at the outlet of a catchment (Kamech, 2.63 km2). Sampling concentrated on the soil surface (in both cropland and grassland), gullies and channel banks. A total of 17 sediment cores were collected along a longitudinal transect of the Kamech reservoir to investigate the origin of the sediment throughout the reservoir. Radionuclides (particularly caesium-137, 137Cs) and nutrients (total phosphorus, total nitrogen and total organic carbon (TOC)) were analysed as potential tracers.

Results and discussion

The applications of a mixing model with 137Cs alone or 137Cs and TOC provided very similar results: The dominant source of sediment was surface erosion, which was responsible for 80 % of the total erosion within the Kamech catchment. Additionally, we showed that the analysis of a single composite core provided information on the sediment origin that was consistent with the analysis of all sediment layers in the core. We demonstrated the importance of the core sampling location within the reservoir for obtaining reliable information regarding sediment sources and the dominant erosion processes.

Conclusions

The dominance of surface erosion processes indicates that conservation farming practices are required to mitigate erosion in the agricultural Kamech catchment. Based on the results from 17 sediment cores, guidelines regarding the number and location of sampling cores to be collected for sediment fingerprinting are proposed. We showed that the collection of two cores limited the sediment source apportionment uncertainty due to the core sampling scheme to <10 %.  相似文献   

6.
在黔中喀斯特高原农林复合生态系统峰丛谷地小流域,利用137Cs和磁化率双指纹因子对碳酸盐岩表层土壤(坡地和坝地)、深层土壤(沟道和洞穴/裂隙)以及碎屑岩夹层岩屑3类来源开展指纹特征分析,通过多元混合模型对流域暴雨过程侵蚀悬移质泥沙进行指纹复合示踪,并计算小流域地表及地下出口输出泥沙的主要来源及相对贡献率。结果表明:137Cs和磁化率在碳酸盐岩表层土壤、深层土壤以及碎屑岩夹层岩屑3类来源存在显著差异,流域内表层土壤、深层土壤和碎屑岩夹层岩屑的137Cs和磁化率平均含量分别为3.39 Bq/kg和310.07×10-8 m^3/kg、0.50 Bq/kg和180.69×10-8 m^3/kg、0 Bq/kg和7.02×10-8 m^3/kg。表层土壤、深层土壤和碎屑岩夹层岩屑对流域地表出口泥沙的相对贡献分别为16.2%,4.3%和79.5%,拟合优度为99.97%;表层土壤、深层土壤和碎屑岩夹层岩屑对流域地下出口泥沙的相对贡献分别为<0.1%,37.9%和62.1%,拟合优度为83.80%。喀斯特流域泥沙来源区别于其他碎屑岩流域具有的特点为:(1)碳酸盐岩风化表层土壤来源少,对河流泥沙贡献小,主要贡献于地表河流。(2)无论流域地表出口还是地下出口,河流泥沙来源主要为流域中碳酸盐岩所夹的少量(地面物质组成<10%)的碎屑岩夹层岩屑。(3)深层土壤略有贡献,地下河流贡献比例高于地表河流。另外,137Cs和磁化率可作为双指纹示踪物较好地示踪喀斯特小流域地表、地下河流泥沙来源和确定相对贡献率。  相似文献   

7.
Specific activity of tritium (3H) in precipitation and specific activity of 137Cs in ground-level air were monitored at three locations in Belgrade (Meteorological Station of Belgrade at Zeleno Brdo (ZB), Meteorological Station Usek (USEK), and Vin?a Institute of Nuclear Sciences (VINS)). Data presented cover the period 1985?C1997 for 137Cs for all locations and 1985?C2009 (ZB), 1988?C1997 (USEK), and 1988?C2009 (VINS) for 3H. Concentrations of 3H in precipitation have been determined using electrolytic enrichment and liquid scintillation spectrometer LKB-Wallac 1219 RackBeta. The activity of 137Cs in air was determined on an HPGe detector (Canberra, relative efficiency 23?%). 3H concentrations in precipitation ranged from 0.40?±?0.08 to 74.6?±?5.2?Bq?l?1 decreasing with distance from the nuclear facilities. Significantly higher tritium levels were measured in samples in VINS compared with those from an off-site location. The observed seasonal variations of tritium concentration indicate the stratospheric source of tritium. Increases in activity concentration of 137Cs in the atmosphere were observed after the nuclear plant accident at Chernobyl in April 1986. The concentrations obtained for 137Cs in 1986 were compared with the integrated air concentrations of 137Cs in the region. The increases of 137Cs air concentrations in 1987 and 1988 were attributed to local resuspensions from the ground. Since 1989, the activity level before the accident has been obtained. The average monthly concentrations of 137Cs in ground-level air were shown spread maximum in spring?Csummer period and pronounced maximum during winter. The obtained results were statistically analyzed, i.e., the following parameters were determined: tritium deposition, monthly activities of 3H and 137Cs, seasonal indices, radionuclide loading indices, and linear correlation coefficients.  相似文献   

8.
Zhang  Kexin  Li  Guosheng  Pan  Shaoming  Qian  Xiaoqing  Liu  Zhiyong  Xu  Yihong  Hao  Yongpei 《Journal of Soils and Sediments》2019,19(1):491-500
Purpose

Currently, the distribution characteristics and transport processes of the radionuclides 137Cs and 239?+?240Pu in the sediments of estuaries are still a controversial issue. Thus, in the present study, we investigated the distribution characteristics, sources and migration path of 137Cs and 239?+?240Pu in sediment cores of the Liao River estuary (LRE), China, and evaluated the relative contributions of the Pacific Proving Grounds (PPG) and riverine sources of Pu for the sediments in this area. We used 137Cs and Pu isotopes for dating the sediments and estimated the sedimentation rates by the two radionuclides in the LRE.

Materials and methods

Seven sediment samples were collected using a box corer from the Liao River estuarine wetland and tidal flat in the LRE in October 2012 and April 2015, respectively. The activities of 137Cs in the various samples were determined by γ spectrometry using HP-Ge detectors with 60% relative counting efficiency. Approximately 2–5 g of sediment were spiked with 242Pu (ca. 1 mBq) as a chemical yield tracer for Pu isotopic analysis at the School of Radiation Medicine and Protection, Soochow University. The measurement of Pu isotopes (239Pu, 240Pu, 242Pu) was performed by a sector field ICP-MS. In order to quantitatively differentiate the relative proportions of global fallout and PPG, we employed a two-end member mixing model to estimate their contributions.

Results and discussion

The average values of 137Cs, 239?+?240Pu activity concentrations, and 240Pu/239Pu atom ratios in the surface sediment samples of the LRE were 6.727?±?0.251 mBq g?1, 0.294?±?0.024 mBq g?1, and 0.188?±?0.049 (1σ), respectively. The average 240Pu/239Pu atom ratios ranged from 0.180?±?0.034 to 0.199?±?0.021 in sediment cores from the east and west sides of the LRE. For core LT-2 values for 137Cs and 239?+?240Pu concentrations were from below the detection limit: 3.380?±?0.414 and 0.036?±?0.007 to 0.105?±?0.007 mBq g?1. The mean 240Pu/239Pu atom ratio 0.217?±?0.050 (1σ) in sediment core LT-2 lies between the global fallout and PPG close-in fallout.

Conclusions

We found that atmospheric fallout is the main source of Pu in sediment cores from the east and west sides of the LRE. For core LT-2, atmospheric fallout and riverine input (~?73.4%) are the major sources of Pu with the source of the rest of Pu (~?26.6%) attributed to the PPG via the Tsushima Warm Current and the coastal water of the East China Sea. The sedimentation rates (means 0.62–0.8 cm year?1) estimated by the two radionuclides were in good agreement and without any statistically significant difference.

  相似文献   

9.

Purpose

Almost 20 nuclear reactors are situated along the Rh?ne valley, representing Europe??s largest concentration of nuclear power plants. The fate of suspended sediments and natural and artificial particle-bound radionuclides in relation to extreme hydrological events was assessed at the lower course of the Rh?ne River, which provides the main source of water and sediment inputs to the northwestern Mediterranean Sea.

Materials and methods

We sampled water at a high frequency over the period 2001?C2008 and measured suspended particulate matter (SPM) loads and particle-bound natural and artificial radionuclide concentrations at the SORA observatory station in Arles, France. We monitored various hydrological events (either natural or anthropogenic origin) and characterize their influence on concentrations and fluxes.

Results and discussion

The relationship between SPM concentration and the very wide range of water discharges did not differ significantly from previous periods, indicating no significant shift in the average sediment delivery over the last 20?years. Unexpected hydrological events of anthropogenic origin, in particular those associated with flushing of reservoirs that are generally not captured by sampling strategies, were recorded and were shown to transfer significant additional sediment and associated contaminants towards the marine environment. Concentrations of anthropogenic radionuclides associated with sediment (i.e., 137Cs, 60Co, 54Mn, 110mAg, and Pu isotopes) varied over two to three orders of magnitude during periods of low and moderate flow due to variations in the liquid release from nuclear facilities. Except for Pu isotopes, the concentrations of the various particle-bound radionuclides generally showed a decreasing trend with increasing discharge, revealing the geochemical or anthropogenic background values, and providing a useful flood fingerprint for this large fluvial system before its entry into the marine environment.

Conclusions

Our approach produced key data on the level and fate of suspended solids and radionuclide concentrations during flood events occurring in a large river system that could be contaminated by chronic or accidental radioactive releases. These results are of fundamental importance for further interpretations of sediment dynamics at the river mouth.  相似文献   

10.

Purpose

Rice-paddy-dominated watersheds in eastern China are intensively cultivated, and lands with two crops receive as much as 550–600 kg?ha–1?year–1 of nitrogen (N), mainly through the addition of N-based fertilizers. However, stream N concentrations have been found to be relatively low. Waterways in the watersheds are assumed to be effective “sinks” for N, minimizing its downstream movement. We directly measured net sediment denitrification rates in three types of waterways (ponds, streams/rivers, and a reservoir) and determined the key factors that control net sediment denitrification. Such information is essential for evaluating the impact of the agricultural N cycle on the quality of surface water.

Materials and methods

The pond–stream–reservoir continuum was sampled every 2 months at nine sites in an agricultural watershed between November 2010 and December 2011. Net sediment N2 fluxes/net sediment denitrification rates were determined by membrane inlet mass spectrometry and the N2/Ar technique. A suite of parameters known to influence denitrification were also measured.

Results and discussion

Net denitrification rates ranged between 28.2?±?18.2 and 674.3?±?314.5 μmol N2–N?m–2?h–1 for the streams, 23.7?±?23.9 and 121.2?±?38.7 μmol N2–N?m–2?h–1 for the ponds, and 41.8?±?17.7 and 239.3?±?49.8 μmol N2–N?m–2?h–1 for the reservoir. The mean net denitrification rate of the stream sites (173.2?±?248.4 μmol N2–N?m–2?h–1) was significantly higher (p?<?0.001) than that of the pond sites (48.3?±?44.5 μmol N2–N?m–2?h–1), and the three types of waterways all had significantly higher (p?<?0.01) mean net denitrification rates in summer than in other seasons. Linear regression and linear mixed effect model analysis showed that nitrate (NO3 ?–N) concentration in surface water was the primary controlling factor for net sediment denitrification, followed by water temperature. Using monitoring data on NO3 ?–N concentrations and temperature of the surface water of waterways and an established linear mixed effect model, total N removed through net sediment denitrification in the pond–stream–reservoir continuum was estimated at 46.8?±?24.0 t?year–1 from July 2007 to June 2009, which was comparable with earlier estimates based on the mass balance method (34.3?±?12.7 t?year–1), and accounted for 83.4 % of the total aquatic N. However, the total aquatic N was only 4.4 % of the total N input to the watershed, and thus most of the surplus N in the watershed was likely to be either denitrified or stored in soil.

Conclusions

High doses of N in a rice-paddy-dominated watershed did not lead to high stream N concentrations due to limited input of N into waterways and the high efficiency of waterways in removing N through denitrification.  相似文献   

11.

Purpose

The science of sediment fingerprinting has been evolving rapidly over the past decade and is well poised to improve our understanding, not only of sediment sources, but also the routing of sediment through watersheds. Here, we discuss channel–floodplain processes that may convolute or modify the sediment fingerprinting signature of alluvial bank/floodplain sources and explore the use of nonconservative tracers for differentiating sediment derived from surface soil erosion from that of near-channel fluvial erosion.

Materials and methods

We use a mathematical model to demonstrate the theoretical effects of channel–floodplain exchange on conservative and nonconservative tracers. Then, we present flow, sediment gauging data, and geochemical measurements of long- (meteoric beryllium-10, 10Be) and short-lived (excess lead-210 and cesium-137, 210Pbex and 137Cs, respectively) radionuclide tracers from two study locations: one above, and the other below, a rapidly incising knick zone within the Maple River watershed, southern Minnesota.

Results and discussion

We demonstrate that measurements of 10Be, 210Pbex, and 137Cs associated with suspended sediment can be used to distinguish between the three primary sediment sources (agricultural uplands, bluffs, and banks) and estimate channel–floodplain exchange. We observe how the sediment sources systematically vary by location and change over the course of a single storm hydrograph. While sediment dynamics for any given event are not necessarily indicative of longer-term trends, the results are consistent with our geomorphic understanding of the system and longer-term observations of sediment dynamics. We advocate for future sediment fingerprinting studies to develop a geomorphic rationale to explain the distribution of the fingerprinting properties for any given study area, with the intent of developing a more generalizable, process-based fingerprinting approach.

Conclusions

We show that measurements of conservative and nonconservative tracers (e.g., long- and short-lived radionuclides) can provide spatially integrated, yet temporally discrete, insights to constrain sediment sources and channel–floodplain exchange at the river network-scale. Fingerprinting that utilizes nonconservative tracers requires that the nonconservative behavior is predictable and verifiable.  相似文献   

12.
The Esk estuary is approximately 10 km from the marine outfall fromBritish Nuclear Fuels plc (BNFL) Sellafield Site and saltmarshes here havereceived significant quantities of radionuclides as reported in many studiessince 1975. These studies have concentrated on the inventory ofradionuclides in the estuary, but they have not addressed the continualreworking of radionuclides from these deposits. A detailed investigation ofboth the concentration of 137Cs in the surface 10 cm and gammaair-kerma dose rates has been made where 120 determinations were made in agrid over 14600 m2 of saltmarsh. The surface microtopographyis shown to be important for the continuing deposition of contaminatedsediments to the saltmarsh surface. This study has concentrated on thedevelopment and the possible application of sediment traps made fromAstroturf (an artificial grass). They were deployed at three sites whichwere representative of the major saltmarsh units in the estuary. The trapswere used to investigate the mobile sediments during a single tide, for aweek, and for a month. The Astroturf provided a reasonable analogue for thesaltmarsh surface and was arranged such that the radionuclide concentrationof the trapped sediment was measured directly by gamma spectrometry. Sediment deposition rates of between 30 and 240 g m-2d-1 were determined for the study sites, and these wereconsistent with earlier studies. Measurement of the radionuclideconcentration of the deposited sediment showed the addition of between 90and 750 Bq 317Cs m-2 d-1 and 200and 1400 Bq 241Am m-2 d-1. At thedepositional sites over the saltmarsh this would represent an annualaddition of about 90 kBq m-2 of 137Cs and 180kBq m-2 of 241Am.  相似文献   

13.

Purpose

Many drainage basins are terminal recipients of hydrophobic contaminants such as pesticides. To minimize adverse effects of the contaminated sediments on wildlife, it is important to understand sediment contamination patterns. This study was conducted at the Salton Sea, which is a heavily polluted large lake in southern California, USA, with the purpose to identify areas with minimal contamination so as to support species conservation.

Materials and methods

We investigated the horizontal and vertical distribution of 14 organochlorine pesticides (OCPs) and 12 currently used pesticides (CUPs) in playas at locations near the drainage outfalls. The data were subjected to spatial analysis using Kriging interpolation and converted to contour maps. Statistical comparisons were made among different areas, between different sediment depths, and between air-exposed and submerged sediments.

Results and discussion

Various OCPs were found near two drainage inlets, with mean concentrations of 6?C30???g?kg?1 in air-exposed sediments and 3?C18???g?kg?1 in submerged sediments. Chlordane (detected frequency, DF?=?77?%) and DDT derivatives (DF?=?100?%) were among the most frequently detected OCP. Significantly higher concentrations were found in air-exposed sediments than in submerged sediments, and in subsurface sediments than in surface sediments (P?<?0.01), suggesting historical deposition and burial. Sediments at many locations exceeded the threshold levels for DDE. A total of seven CUPs were detected with the maximum ??CUPs concentration of up to 27???g?kg?1. Bifenthrin was the dominant CUP contaminant, representing more than 60?% of ??CUPs for most samples with the highest concentration of 26???g?kg?1.

Conclusions

Findings from this study provide a snapshot of the spatial distribution in both horizontal and vertical directions of hydrophobic pesticides in a drainage-dominated lake, and such information and the method of investigation may be used for identifying areas of minimal contamination as alternative habitats for this and other impacted lakes.  相似文献   

14.
The Fukushima Daiichi nuclear power plant accident caused radioactive pollution in northeastern Honshu Island, Japan. This study examined the influence of snowmelt and rainfall on soil erosion processes and siltation of small lakes in Miyagi Prefecture (150 km northwest of the power plant). Two sets of slopes and lakes, respectively in pasture and forest catchments, were examined. Snowpack thickness, soil infiltration, surface runoff volume, soil and sediment physicochemical properties, Cs concentration of precipitation, meltwater, and rainwater, and lake siltation rates were determined. The total radioactive Cs content in precipitation was 0.7–7.4 BqˑL−1 and was below the Japanese standard (10 BqˑL−1). Total radioactive Cs was at the allowable level in water flowing down the pasture catchment slope (0.1–9.2 BqˑL−1) during snowmelt and rainfall, as well as in pasture (0.9–8.8 BqˑL−1) and forest (0.7–5.2 BqˑL−1) catchment lake water. There was no soil erosion (surface runoff) in the forest catchment. Soil losses in the pasture catchment were 23 due to rainfall and 9 kg ha−1 yr−1 following spring snowmelt. After snowmelt, a 0.5 and 0.2 mm thick layer of silt was deposited in pasture and forest catchment lakes, respectively, and 1.4 and 0.6 mm were deposited during the rainfall period. Average siltation rates were 1.9 and 0.8 mmˑyr−1 for pasture and forest catchment lakes, respectively. The upper layer of lake bottom sediments is represented mainly by silt fractions (2–50 μm), with high organic matter (4.0–5.7%) and radiocesium (1100–1600 kgˑha−1) contents.  相似文献   

15.

Purpose

In lake restoration, the redox sensitivity of iron (Fe)?Cphosphorus (P) compounds has been regarded as detrimental for a sustainable increase in sedimentary P retention since developing low redox potentials release Fe-bound P. Thus, Fe salts alone have rarely been used successfully to inactivate sediment P, and there are no studies on the long-term effects of in-lake Fe applications on P retention. Here, we analyzed for how long, and how efficiently, a single and continuous Fe application can affect the P budget of lakes.

Materials and methods

Two aerated lakes in Berlin, Germany were compared: Lake Tegel (TEG) experienced a continuous Fe supply via its tributaries, while Lake Gro?-Glienicke (GGS) was treated once with Fe in the winter of 1992/1993. By controlling the operation of aerators, their effectiveness on P exchange at the sediment?Cwater interface (non-aerated vs. aerated) was directly compared in spring and autumn between 2008 and 2010. The amount of P controllable by aeration (P control) was experimentally determined by non-aerated vs. aerated sediment cores (at 10 and 16?°C). Core stratigraphy of Fe was observed by high-resolution ??X-ray fluorescence analysis.

Results and discussion

In TEG, the mobility of Fe was limited due to its sulfidic fixation, and thus Fe only accumulated slightly at the sediment surface (Fe/P ratio, ??3). P control corresponded to only 4?% of the P content of the lake and 18?% of P loading. Hence, aeration only slightly influenced trophy-relevant epilimnetic P. In GGS, the single Fe application still ensures a high P binding ability of sediment since Fe relocated towards the surface (Fe/P ratio, ??7). P control corresponded to 38?% of the P content of the lake and 74?% of annual P loading. Thus, the P release is not relevant for the P supply to the epilimnion since with the lake??s overturn P is co-precipitated by the hypolimnetically accumulated Fe.

Conclusions

When external P loading is sufficiently reduced, as in GGS, amendments to Fe precipitants can increase sediment P retention in a redox-dependent manner over the long term. Thus, the redox-dependent mobility of Fe should no longer be regarded as a disadvantage of Fe-containing precipitants. To compensate for co-precipitation and complexation of Fe with sediment organic matter, a high Fe dosage (??200?g?m?2) is needed.  相似文献   

16.

Purpose

The aim of this work was to develop a comprehensive fluvial suspended sediment budget for a large regulated river, the lower River Ebro (NE Spain).

Materials and methods

The sediment loads of the Ebro mainstem and its main tributaries were estimated from continuous records of water discharge and turbidity (appropriately transformed to suspended sediment concentrations). Records were obtained at ten monitoring sections during the relatively dry 2008–2011 period.

Results and discussion

The sediment load estimated for the River Ebro upstream of the Mequinenza Reservoir is remarkable (i.e. mean suspended load of 0.6?×?106?t?year?1), despite the fact that the site is already affected by a sediment deficit due to upstream reservoirs. Further downstream, and owing to their humid characteristics, the contribution of the Pyrenean tributaries (Segre and Cinca Rivers) is much larger compared with their Iberian Massif counterparts (Matarranya and Algars Rivers), with sediment loads of 0.49?×?106 and 2,260 t, respectively. The suspended sediment load trapped in the Mequinenza-Ribarroja-Flix Dam Complex for the study period was estimated at 2.3?×?106?t. Below the dams, the sediment load was reduced by 95 % but increased gradually in a downstream direction due to the erosion processes that clear water (i.e. very low sediment concentrations) flood flows exert on the river bed and banks and the episodic contribution from ephemeral tributaries.

Conclusions

Reservoirs have reduced the overall sediment load and the natural variability of flow and sediment transport in the River Ebro. In addition, the sediment budget revealed that floods were not the only drivers of the sediment dynamics in the lower Ebro. For instance, the particular location of the monitoring sections showed that episodic contributions from small tributaries alter the general sediment load of the river during certain torrential events.  相似文献   

17.
Radiation protection planning in urban areas after a radioactive fallout requires knowledge of decontamination caused by storm water transport. This report elucidates the transport of 137Cs from a roof and three storm sewers in Uppsala during the first rainfall after those, on 29–30 April 1986, causing the Chernobyl contamination. Runoff and concentration Of 137Cs in storm water were determined with an accuracy of 10 to 15%. The origin of storm water was determined from its content of 18O. Surface contamination was measured on 3 July 1986. Total fallout was 25 kBq m?2. During the rainfall on 11 May, 4 kBq m?2 were transported from the roof and approximately 1 kBq m?2 from the sewered areas. From 30 April to 4 July there was a decontamination of 13 to 20 kBq m?2. Measurements from another project showed that the fallout rain events washed off 10 to 16 kBq m?2. The wash-off by the small rainfall on 11 May constituted one third of the remaining decontamination occurring up until 4 July. The transport of 137Cs during the 11 May event increased when the runoff increased, but was less efficient as the event proceeded. The relations between 137Cs concentrations and runoff implied that the wash-off of 137Cs in Uppsala was totally dominated by that bound to particles.  相似文献   

18.
This paper presents the results of using the 137Cs technique to assess soil erosion rates of both sloping cultivated land and flat terraces in the Upper Yangtze River Basin, China. The study was carried out on eighteen sloping cultivated fields and four flat terrace fields in eight counties and cities over the eastern part of the basin. The 137Cs-reference inventory ranged from 620.5 to 2573.2 Bq/m2. For the 18 sloping cultivated fields, the average 137Cs inventory over a field ranged from 204.9 to 1847.7 Bq/m2, which accounts for 15–77% of the local 137Cs reference inventory, and the average water erosion rate ranged from 758 to 9854 t/km2 per year, with erosion rates of <1000 t/km2 per year in two fields; 1000–5000 t/km2 per year in eight fields; and >5000 t/km2 per year in eight fields. It is apparent that most of the sloping cultivated fields suffer severe or very severe soil erosion. For the four terrace fields under this study, the average 137Cs inventory over a field ranged between 915.8 and 2675.4 Bq/m2, which accounts for 97–104% of the local 137Cs reference inventory. However, water erosion is very slight on the terrace fields and little soil is lost from the terraces. The study also indicated that the severity of soil erosion is strongly related to soil texture and slope gradient.  相似文献   

19.

Purpose

Quantifying suspended sediment fluxes and dynamics across mountains, and identifying the origin of sediment in severely eroded areas, are of primary importance for the management of water resources. This contribution aims to generalise previous results from suspended sediment fingerprinting obtained during 2007?C2009 in a mesoscale Alpine catchment (the Bléone River; 905?km2) in France, and to assess variability in sediment sources throughout the second half of the twentieth century.

Materials and methods

Sediment fingerprinting, based on elemental geochemistry and radionuclide measurements, was conducted on a sediment core collected in an alluvial floodplain at the basin outlet. This technique was combined with hydro-sedimentary time-series to reconstruct the origin of suspended sediment deposited at this location over the last 50?years.

Results and discussion

Interpretation of sedimentation based on historical hydrological databases corroborates core dating obtained with 137Cs and 210Pbxs activity measurements. Black marls and (marly) limestone sources provided the main fraction of sediment throughout the sequence (40 and 22?%, respectively). However, we also found evidence for the occurrence of major floods carrying large quantities of sediment originating from Quaternary deposits and conglomerates (25 and 16?%, respectively). The variability of sediment sources throughout the sequence may reflect the spatial variability of rainfall within the catchment, which in turn reflects its origin. However, the relatively homogeneous sediment composition throughout the sequence confirms that core-derived information is representative of widespread flood events.

Conclusions

These results are consistent with those obtained in previous studies. They also outline the need to take into account the entire grain size range of fine sediment in order to provide an overall picture of sediment sources and transfers within highly erosive catchments. This study also emphasizes the importance of using archival data to validate the results of sediment fingerprinting studies conducted during short contemporary monitoring programmes, and to extend fingerprinting of sediment sources over longer time-scales which include large and widespread floods.  相似文献   

20.
The concentrations of various radionuclides have been measured in the incoming water, the outgoing water and the sludge from the sewage treatment plant serving the town of Lund in southern Sweden. The mean residence time for the water in the plant is 1 to 2 days, whereas for the sludge it is 3 to 4 weeks. Variations in the residence time, which may influence the efficiency of the plant, are related to the season of the year and the load on the plant. Measurements show that for 7Be, 51Cr, 134Cs, and 137Cs between 37 and 56% of the incoming activity leaves the plant with the sludge. For 106Ru and 131I these figures lie between 6 and 14%. The deposition of 7Be has been measured at Lund and the relation between the deposition on the ground (Bq m?2) and the activity concentration in the sludge (Bq kg?1 dry weight) has been studied and found to by relatively constant at ?(0.8 ±0.2) kg m?2. In measurements on sewage sludge, the detection limit for deposition of 7Be on the ground is around 16 Bq m?2.  相似文献   

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