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1.
Effects of plant rhizosphere on mercury methylation in sediments   总被引:1,自引:0,他引:1  

Purpose  

This research investigates the effects of different plant species on Hg methylation rates, examines the difference in mercury (Hg) methylation rates in the plant rhizospheres, and shows the trend in methylmercury (MeHg) content of sediment in the Second Songhua River (SSR) of China, thereby providing the basis for estimating the ecological risk of this area.  相似文献   

2.
The annual river discharges and suspended sediment loads into the Yellow River Delta show a declining tendency with some distinct fluctuations over the last 50 years. The decrease of river discharge and suspended sediment load and the change in the river channel must influence the evolution of the Yellow River Delta. During this period several new river mouths formed via channel switch at the river delta, and the old watercourse was gradually abandoned. Recently, in years with very low annual suspended load, erosion of land area has been recorded for the delta. The aims of this work are (1) to determine what is the critical suspended sediment load needed in order to maintain the land balance of the Yellow River Delta for two periods before and after 1976 (the last time the channel shifted), and (2) to examine the variation in the channel geometry and gradient in response to changes in suspended sediment load and delta area at the river mouth. In order to estimate these critical values, we used statistical method to analyze the relationships between land area increment, and suspended sediment load and channel geometry. In order to examine the variation in the channel geometry, the channel cross-sections of the Q1 and Q6 were compared. The results show that to maintain the land area balance between 1953 and 1973, when the river mouth was the Diaokouhe, the critical annual suspended sediment load entering the delta was 4.21  108 tonnes/a. After the main channel switched to Qingshuigou in 1976, the critical value to maintain the Qingshuigou mouth between 1976 and 1997 was 1.51  108 tonnes/a. To maintain the land area balance for the entire Yellow River Delta between 1976 and 1997 the critical suspended sediment load was 3.18  108 tonnes/a. The annual mean channel thalweg elevation and channel gradient at the river delta increase with increasing land area increment at the Qingshuigou mouth. The critical channel gradient at the channel reach between cross sections Q1 and Q6 is 0.000095. The channel has narrowed during the time period from 1976 to 1997. Also, lateral channel migration has decreased remarkably, resulting in enhanced hydraulic efficiency of the deltaic channel and artificial levees. This channel geometry evolution was influenced by river adjustment and human activities. These results are of importance for the management of the lower Yellow River channel and the delta. Future water diversion or river damming should consider the balance between suspended sediment delivery and delta growth.  相似文献   

3.
The purpose of this study is to describe the history of sediment deposition that has been occurring for several decades along the margins of the Kushiro Mire, into which the Kuchoro River drains. The dendrogeomorphic technique was used to examine an even-aged forest and adventitious roots to assess short-term (20 years) deposition rates and the frequency of heavy rainfall events. For medium- (40 years) and long-term (100 years) deposition rates, radiochronological analyses using 137Cs and 210Pb were also conducted. Several instances of high deposition rates caused by flooding events during the last 20 years were identified from the analysis of adventitious roots. The average sedimentation rate from 1963 to the present, estimated from the 137Cs study, is over 1.3 cm/year. Using the 210Pb dating method, based on a CFCS model which considered the organic matter content appropriate to wetland sediment, three deposition rates in the last 60 years were estimated: 2.0 cm/year from 1981 to 2000, 8.9 cm/year from 1975 to 1981, and 0.14 cm/year from 1939 to 1975. The analysis of environmental radionuclides indicated that the greatest sedimentation rates occurred in the years 1975 to 1981, when the Kuchoro River was extensively channelized and flood and/or precipitation events occurred. This suggests that land-use development and channelization introduced a large amount of sediment into the marginal areas of wetland through the drainage system and this was deposited on top of the peat soil.  相似文献   

4.

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   

5.

Purpose

A thorough understanding of mechanisms controlling sedimentation and erosion is vital for a proper assessment of the effectiveness of delta restoration. Only few field-based studies have been undertaken in freshwater tidal wetlands. Furthermore, studies that measured sediment deposition in newly created wetlands are also sparse. This paper aims to identify the factors controlling the sediment trapping of two newly created freshwater tidal wetlands.

Materials and methods

Two recently re-opened polder areas in the Biesbosch, The Netherlands are used as study area. Field measurements of water levels, flow velocities, and turbidity at both the in- and outlet of the areas were carried out to determine the sediment budgets and trapping efficiencies under varying conditions of river discharge, tide, and wind in the period 2014–2016.

Results and discussion

Short-term sediment fluxes of the two study areas varied due to river discharge, tide, and wind. A positive sediment budget and trapping efficiency was found for the first study area, which has a continuing supply of river water and sediment. Sediment was lost from the second study area which lies further from the river and had a lower sediment supply. The daily sediment budget is positively related to upstream river discharge, and in general, export takes place during ebb and import during flood. However, strong wind events overrule this pattern, and trapping efficiencies decrease for increasing wind strengths at mid-range river discharges and for the highest river discharges due to increased shear stress.

Conclusions

Delta restoration, based on sedimentation to compensate for sea-level rise and soil subsidence, could only be effective when there is a sufficient supply of water and sediment. Management to enhance the trapping efficiency of the incoming sediment should focus on directing sufficient river flow into the wetland, ensuring the supply of water and sediment within the system during a tidal cycle, creating sufficiently large residence time of water within the polder areas for sediment settling, and decreasing wave shear stress by the establishment of vegetation or topographic irregularities.
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6.

Purpose

This study used multi-element signatures of stream sediments to assess both natural and human-induced impact on fluvial system in the River Neretva delta receiving environment over time. The river basin actually comprises several sub-catchments, and the geochemical features of major elements, trace metals radiometric and mineralogical characterisation of river bed sediments were used to assist the interpretation of the environment of deposition and its subsequent modifications caused by various anthropogenic pressures within the river basin.

Materials and methods

Five sites were chosen for sediment sampling at key locations within the study area with assumed undisturbed, continuous sedimentation process. At each of the sites, three representative cores were taken by scuba divers. Sample sites were selected in order to reflect the influence of different sub-catchments they belong to and the land-use pattern of the surrounding area. Samples were analysed for pH, redox-potential, granulometry, mineralogy, thermogravimetry, major and trace element concentrations and radionuclide activities. The univariate and multivariate statistics were applied. The geochemical normalisation of data was done using Al, the procedure based on calculation of the regression line of the metal on the normaliser followed by testing the ratios metal/normaliser on all data-points.

Results and discussion

All studied sediments are classified as silt, ranging from clayey silt to silt and sandy silt. Mineralogically, the sediments were dominated by carbonates and quartz. The chemical contaminant data are generally of good quality, mostly below guideline levels. Sedimentation rates were estimated using vertical distribution of 137Cs activities. Normalisation of TMs done by using Al shows strong R 2 adj values for the regressions of Al and V, Al and Cr, and Al and Ni. However, Al cannot fairly explain the fluctuation of the concentrations of Cd, Cu, Pb and Zn in sediment cores from all of the sampling sites. Generally, inorganic scavengers such as clay minerals followed by Fe and Mn oxides and S (pyrite and gypsum) seem to be dominant factors controlling TMs in studied sediments.

Conclusions

Although the River Neretva delta occupies a rather small area, the geochemical features of major and trace elements and 137Cs activities show complex sediment provenances. Each of the sampling sites reflect exactly different effects of anthropogenic intervention that particularly refer to the changes in river morphology and ecology, along with the altered flow regimes within the catchment on sediment loads and quality.
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7.

Purpose  

Since 2005, freshwater fish contamination by polychlorobiphenyls (PCBs), polychlorodibenzodioxins, and polychlorodibenzofurans has been assessed in the Rhone River basin (France). A large database of surface sediment contamination by PCBs is also available, opening the way to the study of biota-to-sediment accumulation factor (BSAF) distribution throughout this basin. The ultimate goal of the study was to determine a sediment quality guideline (SQG) corresponding to the regulatory fish consumption limit.  相似文献   

8.

Purpose

The geochemical compositions of sediments from three sectors in Trincomalee Bay (Koddiyar Bay, Thambalagam Bay and the Inner Harbour) in Sri Lanka were examined to determine fluvial and marine contributions and the effects of sorting and heavy mineral concentration. The present environmental status of the bay was also assessed.

Materials and methods

Forty-nine sediment samples were collected from Trincomalee Bay and analysed by X-ray fluorescence, yielding data for the major elements and 17 trace elements. Mean grain size and sorting were also measured. Data were compared with the compositions of sediments from the lower Mahaweli River, which supplies most of the clastic detritus to Trincomalee Bay.

Results and discussion

Sediments in the three sectors differ significantly in chemical composition, according to position relative to the Mahaweli River delta source, depositional environment, heavy mineral concentration and marine influences. According to accepted sediment quality guidelines, some As contamination may have occurred in the Inner Harbour and Thambalagam Bay and Cr contamination in all three sectors.

Conclusions

Proximal Koddiyar Bay sediments compare closely with Mahaweli River bedload. Although the clastic component in the more distal Thambalagam Bay and the Inner Harbour is also derived from the Mahaweli River, compositions are modified significantly by marine contributions. High concentrations of elements including Ti, Zr, Ce, Nb and Y in NW Koddiyar Bay are consistent with heavy mineral concentration by winnowing in high-energy zones. Some decoupling of Fe–Ti- and Zr-bearing heavy mineral assemblages may occur within the bay. Al-normalized metal enrichment factors and contour maps show that apparent contamination by As and Cr is spurious and is caused by locally high background levels from Mahaweli River detritus. This illustrates the importance of establishing local background levels of elements during environmental studies.  相似文献   

9.
Background, Aim and Scope  Past and present management of the Ebro catchment have altered water, sediment and nutrient fluxes of the lower Ebro River and its delta. The construction of the Mequinensa and Riba-Roja dams during the 1960s disrupted the sediment transport continuity. As a result, the lower Ebro River and its delta are facing a reduction in sediment delivery which is estimated to be up to 99% of its original yield (about 3 × 107 t/yr). Consequently, about 45% of the emerged delta will be under the mean sea level by 2100 due to subsidence and sea level rise, whereas the delta coast is retreating at a rate of several meters per year in the mouth area. This paper aims to establish the basis for a sediment management plan directed to offset the effects of the sediment delivery deficit of the Ebro delta. Main Features  A new management plan named ‘Integrated Plan for the Protection of the Ebro Delta’ (PIPDE) is being presently elaborated in order to develop sustainable management of the Ebro River and delta through an integrated management of water, sediment and habitats, in order to achieve European Union (EU) Water Framework Directive (WFD) requirements. Among other aspects, the plan aims to restore the sediment flux of the lower Ebro River by means of both the removal of the sediment trapped behind the dams and the transport of the sediment downstream of the reservoirs to the river mouth and delta plain. Results  Preliminary studies show that the ‘flushing flood’ method has lower costs and is the most adapted method to transfer the sediments retained into the Riba-Roja dam. The required sediment load to stop coastal retreat in the mouth area and to compensate relative sea level rise represents 10 times the present suspended load (0.021 g/l), but is 10 times lower than the total volume of sediment delivered to the sea under natural conditions. Sediment delivery to the delta plain can be accomplished through the rice irrigation system, a method used prior to dam construction. Discussion  Problems of achieving a sustainable management of water and sediment are mostly linked to reservoir management. Technical problems associated with by-passing sediments through the reservoirs can be solved through operational and structural changes. Benefits of sediment flow recovery are multiple, including maintenance of the reservoir capacity, possible decline of invasive species, reduction of elevation loss and coastal retreat in the delta. Conclusions  The partial restoration of sediment fluxes in the lower Ebro River and its delta is technically feasible and environmentally desirable, but further detailed studies need to be carried out before the plan can be implemented. Perspectives  Overall, the sustainability of the lower Ebro River and delta can only be guaranteed by the implementation of a new reservoir management concept where the ecological and morphological values, as well as the economical and social values, have to be taken into consideration.  相似文献   

10.

Purpose

The importance of bank erosion was quantified during three periods (October 2006–April 2007, May 2007–April 2008 and May 2008–April 2009) in the 486 km2 catchment area of River Odense, Denmark. A catchment sediment budget was established including other sediment sources such as tile drains and surface runoff, in-channel and overbank sinks and storage and the resulting bed load and suspended sediment load exported from the catchment.

Material and methods

Bank erosion and sedimentation were measured using ca. 3,000 erosion pins established in 180 pin plots, each consisting of three vertical lines of pins. Thirty-six representative reaches, each with a length of 100 m, were selected by a stratified random procedure in GIS. Bed load and suspended sediment export from the catchment were measured using a bed load sampler and from continuous measurements of turbidity at the outlet gauging station.

Results and discussion

The gross sediment input from bank erosion during the three study periods amounted to 21,100–25,200 t in the River Odense catchment, which is considerably higher than the estimated input of sediment from tile drains and surface runoff, which amounted to 220–500 t and 0–100 t, respectively. The measured bed load (20–490 t) was five to 60 times lower than the suspended sediment export from the catchment (1,240–2,620 t) during the three study periods, with the largest difference occurring in the driest year. Sediment sinks and storage were of high importance for the catchment sediment budget as the measured in-channel storage of sediment on stream banks was as high as 16,200–20,100 t, and the overbank sediment sink was estimated at 360–3,100 t.

Conclusions

Bank erosion was the dominant sediment source (90–94 %) in the River Odense catchment during the three study years. In-channel and overbank sediment sinks and storage dominated the sediment budget as 79–94 % of the sediment input from all sources was not exported from the catchment during the three study years. Such a large attenuation of sediment in river channels and on floodplains is extremely important for fluvial habitats and ecology. Moreover, it has strong implications for attempts to document changes in sediment export following implementation of mitigation measures.  相似文献   

11.

Purpose  

The primitive recycling of electronic waste (e-waste) in developing countries is causing serious environmental pollution. The objective of this study was to determine the contamination and toxicity of surface sediment of Nanguan River, which runs through the e-waste recycling area of Taizhou, East China.  相似文献   

12.

Purpose  

This research aims to investigate: (1) the evolutional sequence of erosion of cohesive sediments entering the Athabasca River, (2) the influence of consolidation/biostabilization time on bed sediment stability, and (3) the implication of these results on contaminant transport within the Athabasca River.  相似文献   

13.

Purpose

In this paper, a novel modeling approach is applied to assess the unique transport characteristics of hydrophobic (bitumen containing) cohesive sediment for the Ells River, AB, Canada. The modeling offers a new way of treating the transport and fate of fine sediment in rivers and points to the importance of including a sediment entrapment process in the modeling of the Ells River sediment dynamics.

Materials and methods

The modeling approach involves combining two existing models (RIVFLOC and MOBED). Using fine sediment transport parameters derived from laboratory flume experiments (e.g., settling velocity of sediment as a function of floc size and the critical shear stresses for deposition) and the calculated flow field from the MOBED model (using field survey data such as, cross-sectional geometry, river slope, grain size of bed material, and discharge), the RIVFLOC model is used to predict the transport characteristics (including entrapment) of the hydrophobic Ells River sediment.

Results and discussion

The application of the connected RIVFLOC and MOBED models, demonstrated the unique hydrophobic sediment dynamics of the Ells River. The model showed no deposition (in the classical sense) of the hydrophobic sediment as the bed shear stresses, even at base flow, are well above the critical bed shear for deposition (flocculation is shown to occur, but its impact on settling is negligible given the high shear stresses). However, the model showed the possibility of fine sediment ingression into the river bed (interstitial voids) due to the entrapment process which is known to occur at bed shear stresses well above the critical shear stress for deposition.

Conclusions

The salient features of RIVFLOC and MOBED models and their applications for understanding the transport and fate of unique hydrophobic fine sediments are presented. The models are shown to be useful for the understanding and projection of flow characteristics and sediment dynamics (including entrapment), and will be of benefit for the adaptive management of riverine monitoring programs given various flow scenarios including extreme events and climate change.
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14.

Purpose  

Even though sediments may represent a reservoir for antimicrobial agents, little is known about the persistence of these molecules over time or their accumulation. In this study, six antimicrobial agents, oxolinic acid, flumequine, nalidixic acid, norfloxacin, sulphamethoxazole and trimethoprim, were investigated in a sediment core from the Seine River. This work aimed to (1) measure antimicrobial agent contamination levels in the sediment and identify their origins, (2) obtain information on the persistence of these compounds in sediment over long periods (>4 years) and (3) show the existence of a historical record in sediment of river contamination by antimicrobial agents.  相似文献   

15.
River floodplains have been recognised as important sinks for storing suspended sediment and associated contaminants mobilised from the upstream catchment. However, information on contemporary rates of overbank sedimentation is difficult to obtain using conventional methods. Measurements of the 137Cs content of floodplain sediments provide an alternative approach to obtaining; estimates of medium-term rates (ca. 40 years) of overbank sediment deposition. The 137Cs approach requires only a single site visit and minimum sample preparation. Furthermore, it is capable of providing information on spatial patterns of sediment deposition on floodplains, which is needed to improve our understanding of the processes involved in overbank flow and sediment deposition. This paper reviews the basis for using 137Cs measurements in floodplain sedimentation studies and presents improved procedures for interpreting 137Cs profiles in floodplain sediments and for obtaining estimates of sedimentation rates from single measurements of the total. 137Cs inventories of bulk sediment cores. The results obtained from a case study undertaken on the floodplain of the River Stour, Dorset, UK, are presented.  相似文献   

16.

Purpose  

This study aims to understand better the relationship between measured soil loss rates due to sheet and rill erosion (SL), predicted SL rates and measured catchment sediment yields (SY) in Europe.  相似文献   

17.

Purpose

Few studies have described the bacterial community structures of turbid rivers. In this paper, the characteristics of the bacterial community in the water and surface sediment of the Yellow River, China, the largest turbid river in the world, were studied.

Materials and methods

Water and sediment samples were collected from six sites along the river. Bacterial community composition was determined using the 16S ribosomal RNA (rRNA) gene clone library technique. The relationship between environmental parameters and bacterial diversity was analyzed.

Results and discussion

A total of 1,131 gene sequences were obtained and clustered into 639 operational taxonomic units (at the 97 % identity level), with Proteobacteria as the predominant phylum. The Shannon index for water samples ranged from 3.39 to 4.40 and was generally higher than that in other rivers; this was probably due to the high suspended particulate sediment (SPS) concentration in the Yellow River, which can provide more habitats for both aerobic and anaerobic bacteria. Also, the bacterial diversity of the water samples was slightly higher than that of the surface sediment samples. The bacterial diversity of water increased along the river in the downstream direction, while there was no trend for the sediment. Redundancy analysis indicated that pH, dissolved organic carbon (DOC), and SPS were the main factors controlling the water bacterial community in the Yellow River, and pH, nitrate–nitrogen, and water content were the main factors for the surface sediment bacterial community.

Conclusions

This study indicated that the bacterial diversity of the Yellow River is generally higher than that in other rivers, suggesting that SPS plays an important role in regulating bacterial diversity and community structure in aquatic environments.  相似文献   

18.

Purpose

A monitoring investigation undertaken along the River Ibach, northwest Switzerland over the winter 2012/2013, found that riparian areas recently supporting the invasive plant Himalayan Balsam (HB) recorded significantly higher erosion rates than nearby uninvaded areas. This communication sythesises the latest findings about the influence of HB on sedimentation processes, again, from the Ibach, but also from a second river system in southwest UK.

Materials and methods

Erosion pins, a micro-profile bridge and a digital caliper were used to measure changes in soil surface profile (SSP) at selected riparian areas supporting HB plants along both rivers. Values were statistically compared against equivalent data recorded from nearby reference areas supporting mixed perennial vegetation. A comparison of source and sediment geochemistry was also undertaken on soil from HB-invaded and uninvaded floodplain areas along the Ibach, to assess the potential for identifying the extent to which either group acts as a sediment source.

Results and discussion

Erosion pin data indicate that soil loss from HB-colonised areas was significantly greater than soil loss from reference areas in two out of the four periods at the River Ibach site, and in two out of three measurement periods at the River Taw site. Colonisation of new HB sites may initially occur by hydrochorous processes, but HB plants may increase colonisation potential by trapping additional fine sediment and organic matter, including viable HB seeds. Geochemical results from the Ibach suggest that high inputs of suspended sediment originate from sources close to the river channel, but HB-invaded floodplain sources have geochemical properties that are most similar to suspended river sediment.

Conclusions

The findings from both rivers led us to rethink our original hypothesis; that HB promotes soil erosion, to an amended hypothesis in which HB may be associated with areas where high erosion is sometimes recorded. Whilst initial colonisation may be due to hydrochorous processes, as HB becomes increasingly established, the displacement of perennial vegetation increases the risk of erosion during the winter period when live HB plants are absent. Preliminary geochemical findings of floodplain soils supporting different vegetation types along the Ibach tentatively suggest that at least some material originating from HB sites may enter the watercourse.
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19.

Purpose  

The impact of wildfire on (a) slope hydrological processes, (b) soil erodibility, and (c) post-fire hillslope sediment and phosphorus (P; dissolved and particulate) yields are quantified for natural forest areas of the burned Evrotas River basin, Peloponnese, Greece. Further, the geochemical partitioning of P in burned and unburned sediment is evaluated by sequential extraction to assess potential bioavailability of particulate P (PP) in downstream aquatic ecosystems.  相似文献   

20.

Purpose

Investigations of geochemical characteristics of sediments of the Zrmanja River estuary were done in order to determine the natural and anthropogenic factors influencing sediment composition in this area. For that purpose, spatial and temporal distribution of major and trace elements in the sediments and surrounding soils was studied.

Materials and methods

Sediment and soil samples, including one marl sample, were collected at 28 locations. All samples were subjected to total digestion and subsequently analysed by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) for total concentration of 20 elements (Ag, Al, As, Be, Ca, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Rb, Sb, Sn, Sr, Ti and Y). Obtained concentrations and their normalized counterparts were used for assessment of factors influencing sedimentation in the study area.

Results and discussion

The results of the analysis showed that the composition of sediments of the Zrmanja River estuary is primarily determined by the composition of bedrock, existing hydrodynamic conditions and the relative isolation of the studied basin. Nevertheless, anthropogenic influences were observed as well. The composition of the Zrmanja River sediments reflects the impact of the ex-alumina factory “Jadral” and transfer by wind of the material from its immediate surroundings to the water system of the Zrmanja River. In addition, sedimentation in the Zrmanja River was found to be influenced by the construction of reservoirs and the HE “Velebit”, hydroelectric power plant located in the Zrmanja watershed.

Conclusions

The geochemical composition of recent sediments of the Zrmanja River estuary is controlled primarily by natural factors, although the influence of anthropogenic activities is also evident.
  相似文献   

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