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1.
Salt marsh elevation and geomorphic stability depends on mineral sedimentation. Many Mediterranean-climate salt marshes along southern California, USA coast import sediment during El Niño storm events, but sediment fluxes and mechanisms during dry weather are potentially important for marsh stability. We calculated tidal creek sediment fluxes within a highly modified, sediment-starved, 1.5-km2 salt marsh (Seal Beach) and a less modified 1-km2 marsh (Mugu) with fluvial sediment supply. We measured salt marsh plain suspended sediment concentration and vertical accretion using single stage samplers and marker horizons. At Seal Beach, a 2014 storm yielded 39 and 28 g/s mean sediment fluxes and imported 12,000 and 8800 kg in a western and eastern channel. Western channel storm imports offset 8700 kg exported during 2 months of dry weather, while eastern channel storm imports augmented 9200 kg imported during dry weather. During the storm at Mugu, suspended sediment concentrations on the marsh plain increased by a factor of four; accretion was 1–2 mm near creek levees. An exceptionally high tide sequence yielded 4.4 g/s mean sediment flux, importing 1700 kg: 20 % of Mugu’s dry weather fluxes. Overall, low sediment fluxes were observed, suggesting that these salt marshes are geomorphically stable during dry weather conditions. Results suggest storms and high lunar tides may play large roles, importing sediment and maintaining dry weather sediment flux balances for southern California salt marshes. However, under future climate change and sea level rise scenarios, results suggest that balanced sediment fluxes lead to marsh elevational instability based on estimated mineral sediment deficits.  相似文献   

2.
The objective of this study was to assess the lake sediment budget of land use changes using the Universal Soil Loss Equation (USLE), sediment delivery ratio (SDR), and trap efficiency (TE). The geographic information system was combined with the USLE to estimate the soil erosion of the Lake Asan watershed. Spatial data for each of the USLE factors were obtained from the land use, soil, and 1/25,000 scale digital contour maps. Landsat-5 TM images were selected for analyzing soil erosion changes due to land use changes. The sediment yield to Lake Asan was estimated using the SDR and TE. The estimated sediment budget was compared with observed data from the Lake Asan watershed between 1974 and 2003. The total estimated annual mean sediment budgets from Lake Asan in 1986, 1992, and 2000 were 0.267, 0.301, and 0.339 × 106 ton, respectively, with an average of 0.302 × 106 ton. The average measured sediment budget was 3.15 × 106 ton year?1. The average estimated value shows reasonable agreement with the observed sediment balance. The average estimated and measured sediment budgets contain uncertainties due to both the methods and the approach used by the observers. The simulated results indicated that soil erosion in the Lake Asan watershed increased at a rate of approximately 2 % per year from 1986 to 2000 due to land use change. This study may be useful for managers to identify reservoir rehabilitation management methods for stable irrigation water supply.  相似文献   

3.
Interactions between catchment variables and sediment transport processes in rivers are complex, and sediment transport behaviour during high‐flow events is not well documented. This paper presents an investigation into sediment transport processes in a short‐duration, high‐discharge event in the Burdekin River, a large sand‐ and gravel‐bed river in the monsoon‐ and cyclone‐influenced, semi‐arid tropics of north Queensland. The Burdekin's discharge is highly variable and strongly seasonal, with a recorded maximum of 40 400 m3 s?1. Sediment was sampled systematically across an 800 m wide, 12 m deep and straight reach using Helley‐Smith bedload and US P‐61 suspended sediment samplers over 16 days of a 29‐day discharge event in February and March 2000 (peak 11 155 m3 s?1). About 3·7 × 106 tonnes of suspended sediment and 3 × 105 tonnes of bedload are estimated to have been transported past the sample site during the flow event. The sediment load was predominantly supply limited. Wash load included clay, silt and very fine sand. The concentration of suspended bed material (including very coarse sand) varied with bedload transport rate, discharge and height above the bed. Bedload transport rate and changes in channel shape were greatest several days after peak discharge. Comparison between these data and sparse published data from other events on this river shows that the control on sediment load varies between supply limited and hydraulically limited transport, and that antecedent weather is an important control on suspended sediment concentration. Neither the empirical relationships widely used to estimate suspended sediment concentrations and bedload (e.g. Ackers & White, 1973) nor observations of sediment transport characteristics in ephemeral streams (e.g. Reid & Frostick, 1987) are directly applicable to this river.  相似文献   

4.
Increasing sediment loads entering the Lake Tanganyika ecosystem are hastening the need for improved understanding of the linkages between catchment characteristics and influent sediment transport and loading. Sediment loads of two catchments at the southern end of the lake were estimated for October 1998–December 1999, and catchment characteristics determined using GIS. It was found that both sediment yields and loads were higher from the catchment of the Lunzua River (19.8 t km?2 and 20,114 t, respectively) compared with that of the Kalambo (4.1 t km?2 and 12,197 t) in 1999. These differences were both attributed to the smaller size and higher road density of the Lunzua catchment, and suggest that previous recommendations regarding the positioning of underwater lake reserves fail to take into account the low sediment retention capacity of small mountainous rivers. Differences between the study rivers in the transport of suspended sediments, organic matter, and bedload sediments into the lake were also found, the latter determined by the novel application of the 'McLaren Model'.  相似文献   

5.
Soil losses and siltation of the hydrological system (watershed–dam) of K’sob were obtained using direct and indirect methods. The Wadi K’sob watershed of 1,484 km2, average slope of 0.14, and average elevation of 1,060 m is located in a semiarid climate. The average annual rainfall is 341 mm and the mean annual water discharge is 0.89 m3/s. Data from the Medjez gauging station located 6 km upstream of the dam, are the daily liquid flow and instantaneous concentrations of suspended sediments. Over a time period from 1973 to 2010, the relationship between water and sediment discharges is quantified by the equation: Q s?=?5.6 Q 1.31. Thus, in view of the availability data on a daily scale, the assessment of soil erodibility of the K’sob watershed was used to estimate specific soil losses of 203 t?km?2?year?1or 301,000 t eroded annually from the K’sob basin. The bathymetric measurements of the sediment volumes deposited in the K’sob dam, has quantified the annual siltation of 0.8 hm3, corresponding to an average erodibility of the K’sob watershed of 809 t?km?2?year?1. However, when adding the volume of sediment removed by the dredging operation and de-silting by the valves during heavy floods, the value of soil losses is 2,780 t?km?2?year?1. The indirect assessment of soil erodibility of the basin was obtained by applying two models: the quantitative geomorphological analysis (QGA) and PISA model (prediction of silting in the artificial reservoirs, in Italian: Previsioni dell’Interimento nei Serbatoi Artificiali) using physical and climatic factors in the watershed. The obtained results by QGA method underestimate specific soil losses of 524 t?km?2?year?1. The PISA model gives a value of 2,915 t?km?2?year?1, which is close to the value obtained by bathymetric measurements. This study concludes that PISA model is most suitable to estimate soil loss and siltation of the K’sob hydrological system.  相似文献   

6.
The experiment was conducted to ascertain net production and consumption rates of 15NH4 + and 15NO3 ? for water and sediment in a wetland. This was done using 15N isotope pool dilution methodology under ambient and elevated atmospheric CO2 concentrations in experimental riparian wetlands to obtain the gross N transformation rates. The 15N budget for sediment was also estimated. The results suggested that the differences in high proportion of 15N concentration in the overlying water body under elevated CO2 could be attributed to the low production and high consumption rates of 15NH4 + in sediment. The elevated CO2 effect on production and consumption of NH4 + decreased by 144 % (P = 0.014) and increased by 153 % (P = 0.009), respectively. Thereby, 15NH4 + production rates are negatively related with 15NO3 ? consumption rates and this accounted for the decreases in net 15NO3 ? consumption under CO2 enrichment in the wetland sediment by 11 % (P = 0.528). Therefore, 15NO3 ? production and consumption rates may strongly depend on NH4 + production. Inorganic 15N and total 15N exported from sediment to overlying water body by the effect of CO2 were 41 % (P = 0.071) and 18 % (P = 0.000), respectively. Therefore, low net 15NH4 + production and high 15NH4 + consumption rates under elevated CO2 may partly explain the significant reduction of N from the sediment.  相似文献   

7.
Tidally driven flows, waves, and suspended sediment concentrations were monitored seasonally within a Zostera marina seagrass (eelgrass) meadow located in a shallow (1–2 m depth) coastal bay. Eelgrass meadows were found to reduce velocities approximately 60 % in the summer and 40 % in the winter compared to an adjacent unvegetated site. Additionally, the seagrass meadow served to dampen wave heights for all seasons except during winter when seagrass meadow development was at a minimum. Although wave heights were attenuated across the meadow, orbital motions caused by waves were able to effectively penetrate through the canopy, inducing wave-enhanced bottom shear stress (τ b ). Within the seagrass meadow, τ b was greater than the critical stress threshold (=0.04 Pa) necessary to induce sediment suspension 80–85 % of the sampling period in the winter and spring, but only 55 % of the time in the summer. At the unvegetated site, τ b was above the critical threshold greater than 90 % of the time across all seasons. During low seagrass coverage in the winter, near-bed turbulence levels were enhanced, likely caused by stem–wake interaction with the sparse canopy. Reduction in τ b within the seagrass meadow during the summer correlated to a 60 % reduction in suspended sediment concentrations but in winter, suspended sediment was enhanced compared to the unvegetated site. With minimal seagrass coverage, τ b and wave statistics were similar to unvegetated regions; however, during high seagrass coverage, sediment stabilization increased light availability for photosynthesis and created a positive feedback for seagrass growth.  相似文献   

8.
Concentrations of lead (Pb) in domestic water and blood plasma in the Olya and Al-Batha regions of Riyadh City, Saudi Arabia were correlated (r 2?=?0.03, p?<?0.0072 and r 2?=?0.37, p?<?0.00092, respectively). Greater concentrations of Pb in domestic water of Olya and Al-Batha (0.0119 and 0.03 mg/l, respectively) were greater than concentrations of Pb in bottled water and was also greater than the concentration of 0.01 mg Pb/l recommended by both the World Health Organization US Environmental Protection Agency (USEPA). In Al-Batha, 52.2 % of the population had concentrations of Pb in blood that exceeded 10 μg Pb/dl, which is the concentration used by USEPA to classify people as being at risk from effects of Pb. In Al-Batha, 17.5 and 22.5 % of the population exceeded 20–40 and >40 μg Pb/dl, respectively. In Olya, 37 and 10 % of the population had concentrations of Pb in blood that exceeded 10 and 20–40 μg Pb/dl, respectively, while none of the concentrations of PB exceeded 40 μg Pb/dl.  相似文献   

9.
The authors investigate the hydrological and geochemical characteristics of the Jamari (30430 km2) and Jiparana (60350 km2) river basins (Amazonia), during the period 1978–1984. A spectral analysis of Fourier is applied to time series of mean monthly river discharges, in order to assess the contribution (7 to 8%) of the surface runoff to the total river flow. The mean annual runoff coefficient calculated for the Jiparana river basin (36%), is higher than for the Jamari (32%), and this coefficient increases during the study period, only for the Jiparana. The total specific suspended sediment discharge calculated for both rivers shows the same value 13 t/km2/y, and the estimated suspended sediment concentration in the surface runoff is slightly superior for the Jiparana river (0.3 g/l) than for the Jamari one (0.2 g/l). The river suspended sediments are mainly composed of kaolinite, quartz and feldspar, but the Jiparana is more enriched in quartz. For both rivers, the dominant clay mineral is the kaolinite which is in agreement with the rock weathering type determined for both basins using the Tardy's weathering index: the monosiallitisation. The total chemical erosion rate calculated after correction for the atmospheric inputs (ions and CO2), is higher for the Jiparana (10.11 t/km2/y) than for the Jamari river basin (7.75 t/km2/y). These values are lower than the mechanical denudation rate calculated previously for both river basins.  相似文献   

10.
Erosion potential method (EPM) and Modified Pacific Southwest Interagency Committee (MPSIAC) are two empirical models for estimating soil erosion and sediment delivery. These models use a relatively simple formulation, but they are still applied in various areas with different environmental conditions. However, evaluation of their efficiency is challenging. Accordingly, the main purpose of this study is investigating the performance of EPM and MPSIAC in estimating soil erosion and sediment yield using sediment rating curve (SRC) methods. Talar watershed in Iran was selected as the study area and suspended sediment load (SSL) of two Shirgah–Talar and Valikbon stations were used to assess the output of the models. Remote sensing and geographic information system were utilized in implementing the models. The estimated sediment yield values by the models were evaluated using the results of least square error regression and quantile regression (QR) SRC methods. Then, sediment yield values were obtained from 20-year discharge data (1992–2011). Despite the high uncertainty of QR results, the annual sediment delivery values of the models were achieved in an acceptable range. The most likely (with a probability of 0.5) average annual SSL values were between 713?×?103 and 840?×?103 ton for Shirgah–Talar station. Those values for Valikbon station were between 3142?×?101 and 3702?×?101. Moreover, the estimated average sediment yield in Shirgah–Talar station using MPSIAC and EPM were 591392 and 514054 ton/year, respectively. Those values for Valikbon station were 51881 and 27449 ton/year. Then, the results proved the better performance of MPSIAC in estimating SSL in the study area compared with EPM.  相似文献   

11.
In this paper, sediment texture, clay mineral composition, and δ 18O data on Globigerinoides ruber of a sediment core collected from a water depth of 250 m near Landfall Island, Bay of Bengal, is presented to understand paleoenvironmental shifts during the Mid–Late Holocene period. From the sediment core, five organic carbon-rich samples were radiocarbon dated and the reservoir-corrected ages range from 6,078 to 1,658 years BP. The marine sediment core is represented dominantly by clayey silt with incursions of coarser components that occur around 6,000, 5,400, and 3,400 years BP. The sedimentation of the coarser detritus is due to strengthened southwest monsoon (SWM) since 6,500 to 5,400 years BP. Clay minerals are represented by smectite, illite, kaolinite, and chlorite in varying amounts. High kaolinite content and K/C ratio indicate intense SWM and strong bedrock weathering from the hinterland (~6,500–5,400 years BP). Incidence of smectite (48.82 to 25.09 %) and chlorite/illite (C/I) ratio (0.56 to 0.28) indicate an overall weakened southwest monsoon since 6,000 to 2,000 years BP with a brief incursion of extremely reduced SWM around 4,400 to 4,200 years BP. This is corroborated with the oxygen isotope on G. ruber that reveals a significant shift in the isotopic values ~4,300 years BP (?3.39?‰), indicating weakening in SWM. Subsequently, fluctuations in the intensity of SWM are observed since 2,000 years to present.  相似文献   

12.
Pore water solutes increase to depths of up to six meters in unsaturated 10 kyr-old glacial outwash sediments in the Trout Lake Basin of northern Wisconsin, USA. After correction for evapotranspiration, these increases reflect weathering gradients produced from plagioclase, calc-magnesium pyroxenes, and amphiboles. In spite of relatively abundant K-feldspar, solute K and Rb reflect negative gradients produced by nutrient plant uptake and cycling. Weathering rates are calculated from solute gradients (b solute), hydraulic fluxes (q h ), volumetric BET surface areas (S v ), and mineral-specific stoichiometric coefficients (β) such that $ R_{\text{solute}} = \frac{{q_{h} }}{{b_{\text{solute}} \beta {\kern 1pt} {\kern 1pt} S_{v} }} $ Average plagioclase weathering rates (R plag = 1.6–3.1 × 10?15 mol m?2 s?1) bracket rates calculated for other Quaternary glaciated landscapes. Deeper soil pore waters are as chemically concentrated as underlying groundwaters which, based on hydrologic analyses, have traveled distances up to several kilometers over transient times of hundreds of years. Pore water recharge essentially sets solute compositions close to thermodynamic saturation, thus limiting additional weathering potential along these ground water flow paths. Solid-state elemental and mineral gradients, unlike solute gradients, are essentially invariant with soil depth, reflecting low weathering intensities produced over the relatively short geologic time since sediment deposition. A spreadsheet calculator reproduces modest mass loses from such profiles and indicates that present-day weathering is kinetically and not saturation/transport controlled.  相似文献   

13.
Field measurements conducted 4 years after the construction of a new portion of the Weixi?CShangri-La road in Yunnan, China, reveal that unprecedented rates of mass wasting occurred along the road with much of this sediment directly impacting the headwaters of the Mekong River. Landslide erosion (including dry ravel) exceeded 33,000 t ha?1 year?1 along the most severely eroded sections of the road and averaged more than 9,600 t ha?1 year?1 along the surveyed 23.5 km of road; these values are the highest ever reported for road-related landslides. While surface erosion was only about 7% of the total erosion from the road, it is still more than an order of magnitude higher than typical surface erosion rates from disturbed lands in Southeast Asia. Combined landslide and surface erosion from this road delivered an estimated 19 times more sediment to the river than the remaining 99.6% of the contributing catchment. These sediment inputs are aggrading local channels, promoting downstream sediment transport, degrading aquatic habitat, and creating the possibility for a future debris flood or hyperconcentrated flow.  相似文献   

14.
Recent (past 100 years) sedimentary processes in the highly dynamic Gulf of Batabano (Cuba, Caribbean Sea) were investigated through the analyses of environmental radionuclides (e.g., 210Pb, 226Ra, 137Cs, 239,240Pu, and 14C) in nine sediment cores. We evaluated the mean mass accumulation rates (MARs) and the surface mixed layers (SMLs) in each sediment core. Based on these results, three sedimentary environments were identified in the study region. In the central zone, the sediments were mainly composed of carbonate transported from the southern area and showed elevated mass accumulation rates (MAR, 0.11–0.23 g cm?2 year?1) and relatively deep surface mixed layers (SML, 14–16 cm). The southwestern zone was characterized by lower MAR (0.05–0.08 g cm?2 year?1) and thinner SML (7–8 cm). In both areas, the long sediment mixing times in the SMLs (of 45–61 years) smoothed out the sedimentary records. The coastline sedimentary environments were characterized by higher MAR (0.30–0.57 g cm?2 year?1) and the sedimentary records displayed clear signatures of extreme climatic events such as the intensive rains in 1999 reported for La Coloma and the hurricanes Lili and Isodore in 2002. Our study shows that the application of the 210Pb sediment dating method in dynamic costal zones is a challenging task but still may provide important information regarding sedimentation and mixing processes in the ecosystem.  相似文献   

15.
A workflow is described to estimate specific storage (S s) and hydraulic conductivity (K) from a profile of vibrating wire piezometers embedded into a regional aquitard in Australia. The loading efficiency, compressibility and S s were estimated from pore pressure response to atmospheric pressure changes, and K was estimated from the earliest part of the measurement record following grouting. Results indicate that S s and K were, respectively, 8.8?×?10?6 to 1.2?×?10?5 m?1 and 2?×?10?12 m s?1 for a claystone/siltstone, and 4.3?×?10?6 to 9.6?×?10?6 m?1 and 1?×?10?12 to 5?×?10?12 m s?1 for a thick mudstone. K estimates from the pore pressure response are within one order of magnitude when compared to direct measurement in a laboratory and inverse modelled flux rates determined from natural tracer profiles. Further analysis of the evolution and longevity of the properties of borehole grout (e.g. thermal and chemical effects) may help refine the estimation of formation hydraulic properties using this workflow. However, the convergence of K values illustrates the benefit of multiple lines of evidence to support aquitard characterization. An additional benefit of in situ pore pressure measurement is the generation of long-term data to constrain groundwater flow models, which provides a link between laboratory scale data and the formation scale.  相似文献   

16.
This paper reports the presence of a metastable mixture of Fe(II), O2, superoxide and hydrogen peroxide in sediment pore water in organic carbon-rich sediments in Spartina alterniflora-dominated salt marsh systems. Field measurements at two different estuarine sites in South Carolina (one heavily urbanized and a protected research reserve) showed a broad region of reactive oxygen species (ROS) production more than 15 cm below the sediment surface within and immediately adjacent to the rhizospheres of S. alterniflora. Dissolved Fe(II) was positively correlated with hydrogen peroxide indicating a possible abiotic pathway to ROS production (r 2 = 0.94). The null hypothesis was tested that Fe(II) inventories were maintained by protective ligands and thus unreactive with respect to O2 consumption and ROS production. The addition of an Fe-binding ligand, DTPA, resulted in rapid decline of ROS in pore water, indicating that Fe(II) was labile. The half-life of superoxide under the measured solution conditions was calculated and found to be less than a second. The combination of high lability and persistent ROS was interpreted to indicate a high rate of Fe(II) and O2 supply to the pore water. The 224Ra/228Th disequilibrium was measured to determine the potential for advective mass transfer of dissolved oxygen via pore water exchange. The estimated pore water exchange of 54 L m?2 day?1 was significant but could not support the measured production of ROS alone, the direct exchange of O2 from the S. alterniflora root system may have contributed significantly to ROS production in the sediments.  相似文献   

17.
Riverine sediment load, a reflection of basin erosion and sediment yield, is influenced by both climatic and human factors. Complex interaction between various factors within a basin dampens and counteracts the forces that drive sediment variations. The gross human impact index and the index estimation method have both been proposed to reflect the impacts of human activities on soil erosion and sediment yield. Sediment load and daily rainfall data from 1955 to 2010 in the upper Yangtze basin, and in the Wu, Jialing, Min and Jinsha subbasins, were collected to assess the human versus climatic impacts on sediment yield. From 1955 to 2010, the average annual runoff in the study area was 428.2 billion m3, and the average annual suspended sediment load was approximately 0.43 billion t. There was a critical point in 1984, 1985, 1991, 1993 and 1999 when the sediment load decreased in the Wu, Jialing, upper Yangtze, Min and Jinsha river, respectively. The annual regional rainfall erosivities in the upper Yangtze basin in most years ranged between 2,500 and 3,500 MJ mm hm?2 h?1 year?1 and fluctuated around 3,000 MJ mm hm?2 h?1 year?1 with a small coefficient of variation of 0.11. In the Jinsha subbasin, the index indicated that increasing rainfall erosivity could not account for the reduction in riverine sediment load and that anthropogenic erosion-control measures played a key role. The index values for the Min, Jialing and Wu subbasins ranged from 76 to 97 % and for the upper Yangtze basin is 95 %, demonstrating the joint effects of precipitation and human activities in all basins, with erosion-controlling measures playing a major role in sediment load reduction.  相似文献   

18.
Thirty two cores were collected from Lake Geneva sediments along one longitudinal and eight transverse profiles. Rates of sedimentation determined by137Cs vary from 0.01 to 1.86 g cm−2 y−1. The average deposition rates in coastal and slope areas amounts to 0.37 g cm−2 y−1 in the Upper Lake (Grand Lac) and 0.12 g cm−2 y−1 in the Lower Lake (Petit Lac). In the deep basins, average rates of 0.13 and 0.05 g cm−2 y−1 were found for the Grand Lac and Petit Lac, respectively. The estimated mass of sediment deposited yearly outside of the principal deltas and turbidity current depositional areas is about 1.0 million tons (about 13% of the estimated total river load). One turbidite is clearly identified in the deepest, central lake area. There is little variation of surface sediment texture (mean grain size about 8–9μm) with the exception of delta areas. Since the beginning of the twentieth century, both carbonate and organic matter have increased as a result of lake eutrophication.  相似文献   

19.
The effects of fish farm activities on sediment biogeochemistry were investigated in Loch Creran (Western Scotland) from March to October 2006. Sediment oxygen uptake rates (SOU) were estimated along an organic matter gradient generated from an Atlantic salmon farm using a combination of in situ techniques: microelectrodes, planar optode and benthic chamber incubations. Sulphide (H2S) and pH distributions in sediment porewater were also measured using in situ microelectrodes, and dissolved inorganic carbon (DIC) fluxes were measured in situ using benthic chambers. Relationships between benthic fluxes, vertical distribution of oxidants and reduced compounds in the sediment were examined as well as bacterial abundance and biomass. Seasonal variations in SOU were relatively low and mainly driven by seasonal temperature variations. The effect of the fish farm on sediment oxygen uptake rate was clearly identified by higher total and diffusive oxygen uptake rates (TOU and DOU, respectively) on impacted stations (TOU: 70 ± 25 mmol O2 m?2 day?1; DOU: 70 ± 32 mmol O2 m?2 day?1 recalculated at the summer temperature), compared with the reference station (TOU: 28.3 ± 5.5 mmol O2 m?2 day?1; DOU: 21.5 ± 4.5 mmol O2 m?2 day?1). At the impacted stations, planar optode images displayed high centimetre scale heterogeneity in oxygen distribution underlining the control of oxygen dynamics by small-scale processes. The organic carbon enrichment led to enhanced sulphate reduction as demonstrated by large vertical H2S concentration gradients in the porewater (from 0 to 1,000 μM in the top 3 cm) at the most impacted site. The impact on ecosystem functions such as bioirrigation was evidenced by a decreasing TOU/DOU ratio, from 1.7 in the non-impacted sediments to 1 in the impacted zone. This trend was related to a shift in the macrofaunal assemblage and an increase in sediment bacterial population. The turnover time of the organic load of the sediment was estimated to be over 6 years.  相似文献   

20.
Fine sediment inputs can alter estuarine ecosystem structure and function. However, natural variations in the processes that regulate sediment transport make it difficult to predict their fate. In this study, sediments were sampled at different times (2011–2012) from 45 points across intertidal sandflat transects in three New Zealand estuaries (Whitford, Whangamata, and Kawhia) encompassing a wide range in mud (≤63 μm) content (0–56 %) and macrofaunal community structure. Using a core-based erosion measurement device (EROMES), we calculated three distinct measures of sediment erosion potential: erosion threshold (? c ; N m?2), erosion rate (ER; g m?2 s?1), and change in erosion rate with increasing bed shear stress (m e ; g N?1 s?1). Collectively, these measures characterized surface (? c and ER) and sub-surface (m e ) erosion. Benthic macrofauna were grouped by functional traits (size and motility) and data pooled across estuaries to determine relationships between abiotic (mud content, mean grain size) and biotic (benthic macrofauna, microbial biomass) variables and erosion measures. Results indicated that small bioturbating macrofauna (predominantly freely motile species <5 mm in size) destabilized surface sediments, explaining 23 % of the variation in ? c (p ≤ 0.01) and 59 % of the variation in ER (p ≤ 0.01). Alternatively, mud content and mean grain size cumulatively explained 61 % of the variation in m e (p ≤ 0.01), where increasing mud and grain size stabilized sub-surface sediments. These results highlight that the importance of biotic and abiotic predictors vary with erosion stage and that functional group classifications are a useful way to determine the impact of benthic macrofauna on sediment erodibility across communities with different species composition.  相似文献   

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