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1.
Comparison of conceptual landscape metrics to define hillslope-scale sediment delivery ratio 总被引：5，自引：0，他引：5
The aim of this study was to evaluate four metrics to define the spatially variable (regionalised) hillslope sediment delivery ratio (HSDR). A catchment model that accounted for gully and streambank erosion and floodplain deposition was used to isolate the effects of hillslope gross erosion and hillslope delivery from other landscape processes. The analysis was carried out at the subcatchment (~ 40 km2) and the cell scale (400 m2) in the Avon-Richardson catchment (3300 km2), south-east Australia. The four landscape metrics selected for the study were based on sediment travel time, sediment transport capacity, flux connectivity, and residence time. Model configurations with spatially-constant or regionalised HSDR were calibrated against sediment yield measured at five gauging stations. The impact of using regionalised HSDR was evaluated in terms of improved model performance against measured sediment yields in a nested monitoring network, the complexity and data requirements of the metric, and the resulting spatial relationship between hillslope erosion and landscape factors in the catchment and along hillslope transects. The introduction of a regionalised HSDR generally improved model predictions of specific sediment yields at the subcatchment scale, increasing model efficiency from 0.48 to > 0.6 in the best cases. However, the introduction of regionalised HSDR metrics at the cell scale did not improve model performance. The flux connectivity was the most promising metric because it showed the largest improvement in predicting specific sediment yields, was easy to implement, was scale-independent and its formulation was consistent with sedimentological connectivity concepts. These properties make the flux connectivity metric preferable for applications to catchments where climatic conditions can be considered homogeneous, i.e. in small-medium sized basins (up to approximately 3000 km2 for Australian conditions, with the Avon-Richardson catchment being at the upper boundary). The residence time metric improved model assessment of sediment yields and enabled accounting for climatic variability on sediment delivery, but at the cost of greater complexity and data requirements; this metric might be more suitable for application in catchments with important climatic gradients, i.e. large basins and at the regional scale. The application of a regionalised HSDR metric did not increase data or computational requirements substantially, and is recommended to improve assessment of hillslope erosion in empirical, semi-lumped erosion modelling applications. However, more research is needed to assess the quality of spatial patterns of erosion depicted by the different landscape metrics. 相似文献
2.
Knowledge of fluvial sediment supply to the coastal sediment budget is important for the assessment of the impacts on coastal stability. Such knowledge is valuable for designing coastal engineering schemes and the development of shoreline management planning policies. It also facilitates understanding of the connection between rivers in the hinterland and adjoining coastal systems. Ghana's coast has many fluvial sediment sources and this paper provides the first quantitative assessments of their contributions to the coastal sediment budget. The methods use largely existing data and attempt to cover all of Ghana's significant coastal rivers. Initially work was hindered by insufficient direct measured data. However, the problem was overcome by the application of a regression approach, which provides an estimated sediment yield for non-gauged rivers based on data from gauged rivers with similar characteristics. The regression approach was effective because a regional coherence in behaviour was determined between those rivers, where direct measured data were available. The results of the assessment revealed that Ghana's coast is dissected by many south-draining rivers, stream and lagoons. These rivers, streams and lagoons supply significant amounts of sediment to coastal lowlands and therefore contribute importantly to beaches. Anthropogenic impoundment of fluvial sediment, especially the Akosombo dam on the Volta River, has reduced the total fluvial sediment input to the coast from about 71 × 106 m3/a before 1964 (pre-Akosombo dam) to about 7 × 106 m3/a at present (post-Akosombo dam). This sharp reduction threatened the stability of the east coast and prompted an expensive ($83 million) defence scheme to be implemented to protect 8.4 km-long coastline at Keta. Sections of Ghana's coast are closely connected to the hinterland through the fluvial sediment input from local rivers. Therefore, development in the hinterland that alters the fluvial sediment input from those local rivers could have significant effects on the coast. There is the need, therefore, to ensure that catchment management plans and coastal management plans are integrated or interconnected. 相似文献
3.
Kamaleldin M. Hassan James B. Swinehart Roy F. Spalding 《Journal of Paleolimnology》1997,18(2):121-130
Profiles of percent carbon and nitrogen, carbon/nitrogen (C/N) ratios and stable carbon (13C), and nitrogen (15N) isotopic ratios in organic matter from an 11.6 m core were used to reconstruct environments of deposition in the Swan Lake basin during the past 5300 YBP. The upper 6.5 m consisted of gyttja containing variable amounts of reddish brown-colored fine organic matter and calcium carbonate. It was followed by a 0.5 m sandy silt, which was followed by a 3.6 m reduced layer characterized by large quantities of black organic plant remains, sapropel, and then by another sapropel layer consisting mainly of well-sorted sapropelic sand with relatively low organic matter content. The C- and N-contents in the organic matter in the sediment profile ranged from 0.5 to 23% and from 0.02 to 2%, respectively. Carbon content were positively correlated to both N and clay content while carbon content was negatively correlated to sand content. Two major environmental phases in Swan Lake were apparent from large differences in the C and N data of the sediment organic matter. These include the sapropel (marsh) stage that stretched from approximately 5330 to 3930 YBP, and the following gyttja (open water stage). During the sapropel marsh plants identified in a previous pollen study as cattails and sedges proliferated and produced copious amounts of well-preserved organic matter. C/N ratios, 13C values, and 15N values in the sapropel were significantly different from those that characterized organic matter in the gyttja. During the gyttja 13C values indicated that deep primary producers have dominated lake biomass. By utilizing bicarbonate as their C-source, the accumulating biomass became relatively enriched 13C values. The presence of high sediment CaCO3 contents indicated more alkaline and deeper water conditions prevailed during the gyttja. Further refinement of the data suggested that each major phase initially contained an identifiable transition stage. During the sapropelic (initial marsh stage) which occurred before 5330 YBP, sand content gradually decreased as organic matter increased. As reflected by high C/N ratios and slightly enriched 13C values, these sands appear to have contained sufficient permeability to promote partial mineralization of accumulated organic-N containing compounds. A short initial gyttja transition period from about 3930–3830 YBP occurred in which the sediment silt content was anomalously high relative that measured in the surrounding layers. The silt content suggests that this turbid transition layer can not be completely explained by sediment mixing via bioturbation. The silts appeared to have been associated with the sharp climate change that resulted in higher water-table conditions during the gyttja stage. 相似文献
4.
The paper presents the sediment budget of the Isábena basin, a highly dynamic 445-km2 catchment located in the Central Pyrenees that is patched by highly erodible areas (i.e., badlands). The budget for the period 2007-2009 is constructed following a methodology that allows the interpolation of intermittent measurements of suspended sediment concentrations and enables a subsequent calculation of sediment loads. Data allow specification of the contribution of each subbasin to the water and sediment yield in the catchment outlet. Mean annual sediment load was 235,000 t y− 1. Specific sediment yield reached 2000 t km− 2 y− 1, a value that indicates very high sedimentary activity, especially in the case of Villacarli and Lascuarre subcatchments, were most badlands are located. The specific sediment yield obtained for the entire Isábena is 527 t km− 2 y− 1, a high value for such a mesoscale basin. Results show that a small part of the area (i.e., 1%) controls most of the catchment's gross sediment contribution. Sediment delivery ratio (ratio between sediment input from primary sources and basin export) has been estimated at around 90%, while in-channel storage represents the 5% of the annual load on average. The high connectivity between sediment sources (i.e., badlands) and transfer paths (i.e., streamcourses) exacerbates the influence of the local sediment production on the catchment's sediment yield, a quite unusual fact for a basin of this scale. 相似文献
5.
渭河下游河流输沙需水量计算 总被引：8，自引：1，他引：7
基于对河流输沙运动特性的分析,认为最小河流输沙需水量是当河流输沙基本上处于冲淤平衡状态时输送单位重量的泥沙所需要的水的体积,通过河段进口即上游断面水流挟沙力 (Su*) 与含沙量 (Su) 比较,分Su ≤ Su*和Su > Su*两种情况,分别建立了最小河段输沙需水量的计算方法。并应用该方法对渭河下游输沙需水量做了计算。计算的空间尺度为渭河下游的咸阳、临潼、华县三个断面,时间尺度为四个代表年的年内月均需水量,分p = 25% (1963年)、p = 50% (1990年)、p = 75% (1982年)、p = 90% (1979年)。计算结果分析表明：渭河各断面汛期月均输沙需水量大于非汛期月均输沙需水量。相较而言,在不同代表年的汛期和非汛期,从咸阳断面至华县断面输沙需水量在增加。在丰水年 (p = 25%),渭河下游咸阳、临潼、华县等3个断面年输沙需水量分别为63.67亿m3、97.95亿m3和103.25亿m3;在平水年 (p = 50%),渭河下游咸阳、临潼、华县等3个断面年输沙需水量分别为49.71亿m3、83.27亿m3和85.08亿m3;在枯水年 (p = 75%),渭河下游咸阳、临潼、华县等3个断面年输沙需水量分别为30.17亿m3、55.14亿m3和65.32亿m3;在特枯水年 (p = 90%),渭河下游咸阳、临潼、华县等3个断面年输沙需水量分别为23.96亿m3、37.91亿m3和38.92亿m3。由丰水年到枯水年,渭河下游各断面年输沙需水量变小。 相似文献
6.
Benjamin M. Rau Dale W. Johnson Bruce A. Roundy Richard F. Miller Todd G. Caldwell Annmarie Lucchesi 《Journal of Arid Environments》2011,75(9):827-835
Vegetation changes associated with climate shifts and anthropogenic disturbance can have major impacts on biogeochemical cycling and soils. Much of the Great Basin, U.S. is currently dominated by sagebrush (Artemisia tridentate (Rydb.) Boivin) ecosystems. Sagebrush ecosystems are increasingly influenced by pinyon (Pinus monophylla Torr. & Frém and Pinus edulis Engelm.) and juniper (Juniperus osteosperma Torr. and Juniperus occidentalis Hook.) expansion. Some scientists and policy makers believe that increasing woodland cover in the intermountain western U.S. offers the possibility of increased organic carbon (OC) storage on the landscape; however, little is currently known about the distribution of OC on these landscapes, or the role that nitrogen (N) plays in OC retention. We quantified the relationship between tree cover, belowground OC, and total below ground N in expansion woodlands at 13 sites in Utah, Oregon, Idaho, California, and Nevada, USA. One hundred and twenty nine soil cores were taken using a mechanically driven diamond tipped core drill to a depth of 90 cm. Soil, coarse fragments, and coarse roots were analyzed for OC and total N. Woodland expansion influenced the vertical distribution of root OC by increasing 15-30 cm root OC by 2.6 Mg ha−1 and root N by 0.04 Mg ha−1. Root OC and N increased through the entire profile by 3.8 and 0.06 Mg ha−1 respectively. Woodland expansion influenced the vertical distribution of soil OC by increasing surface soil (0-15 cm) OC by 2.2 Mg ha−1. Woodland expansion also caused a 1.3 Mg ha−1 decrease in coarse fragment associated OC from 75-90 cm. Our data suggests that woodland expansion into sagebrush ecosystems has limited potential to store additional belowground OC, and must be weighed against the risk of increased wildfire and exotic grass invasion. 相似文献
7.
长江口盐沼土壤有机质更新特征的滩面趋势 总被引：9，自引：0，他引：9
通过对长江口崇明东滩高潮滩、中潮滩以及光滩柱状样的有机元素(C、N)含量与碳稳定同位素组成(δ13C)、粒度组成等的测定,研究盐沼土壤有机质更新特征及其滩面趋势.结果表明,长江口盐沼土壤POC-δ13C相关特征与山地土壤剖面上部土层的基本类似,盐沼土壤有机质主要源于长江流域表层土壤,有机质年龄不足100年.不同高程柱样TN-C/N、POC-TIC与POC-δ13C关系特征表明盐沼土壤有机质更新程度普遍较低,有机质更新特征呈明显的滩面变化趋势.光滩有机质基本反映沉积母质特征,更新程度极低;中、高潮滩有机质更新作用已经发生,随着滩面演变,处于不同更新阶段的有机质组分混杂程度提高.盐沼滩面过程塑造垂向沉积层序,层序中独特的沙、泥纹层构造导致物质上下运移困难,有机质更新作用受到抑制.盐沼滩面过程直接影响有机质的累积与更新,对于有机质更新的时空特征具有显著制约. 相似文献
8.
This paper examines the evolution of Pagham Harbour, southern England following storm-induced breaching of a protective barrier in AD 1910. Stratigraphic studies of sediments collected from intertidal areas show the presence of a distinct stratigraphic horizon in the northeast of Pagham Harbour at ca. 0 to +1.0 m ordnance datum (OD). Radiometric data indicate that this horizon is a ‘reclamation surface’ formed after land claim in AD 1846. Following marine flooding in AD 1910, sediment has accreted relatively rapidly (at a broadly constant rate of between 4 and 8 mm a−1), wave and/or tidal energy have decreased and extensive marshes have developed. An asymptotic reduction in sediment accretion rate through time, as predicted in various theoretical models of salt marsh accretion, is not observed. Over the entire Pagham Harbour area, the period between AD 1948 and AD 1986 has seen an average marsh loss of 0.0087 km2 a−1, which is relatively small in comparison with other more exposed sites in the local area. Historically breached sites such as Pagham Harbour are common around European coasts, and these provide important natural laboratories within which the medium-term (decadal to centennial) coastal response to barrier breaching, and to managed-realignment coastal protection schemes, can be assessed. 相似文献
9.
The spatial relationship between topography and rock uplift patterns in asymmetric mountain ranges was investigated using a stream erosion model in which the asymmetric rock uplift was given and erosion rates were proportional to the m-th power of the drainage area and the n-th power of the channel gradient. The model conditions were simple, and thus the effects of horizontal rock movement, diffusional processes, and erosion thresholds were neglected, and spatially uniform precipitation, lithology, and vegetation were assumed. In asymmetric mountain ranges, under realistic exponent conditions (m < n) and the above assumptions, the surface erosion rate is faster on the steeper side and slower on the gentler side. The topographic axis migrates away from the rock uplift axis toward the center of the mountain range owing to the contrast in erosion rates. This migration continues until the erosion is balanced with rock uplift. In a dynamic steady state, the topographic pattern is independent of the rock uplift rate as indicated by an analytical solution, and is prescribed by the rock uplift pattern and the exponents m and n. As the asymmetry of the rock uplift pattern increases, the topographic axis migrates a greater distance. The location of the topographic axis is related to the location of the rock uplift axis by a simple logarithmic function, for a wide range of m and n. The fit of the numerical results and the logarithmic function is particularly good when m = 0.5 and n = 1.0. If the rock uplift pattern in asymmetric mountain ranges is known, the value of n − 5m/4 can be constrained based on the logarithmic relation, assuming a dynamic steady state. On the other hand, if the value of n − 5m/4 is known in an asymmetric mountain range, the rock uplift pattern can be estimated directly from the topography. This relation was applied to the Suzuka Range in central Japan, and the value of n − 5m/4 was estimated for an assumed reverse fault motion. 相似文献
10.
Christian Christiansen Troels Aagaard Jesper Bartholdy Merete Christiansen Jørgen Nielsen Niels Nielsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):107-126
Average sea-level rise in the northern part of the Danish Wadden Sea has been 1.3 mm a?1 during the last 100 years but during the last 25 years a rise of 4.2 mm a?1 was observed. Concurrent with the recent sea-level rise the Skallingen barrier spit has migrated landward by 3–5 m a?1. Long term sediment budgets for each of the morphological units involved in the migration are reviewed (e.g. onshore in the shore face +90.000 m3 a?1, longshore -641.000 m3 a?1, foredunes +65,000 m3 a?1, overwash fan including shorenormal dunes +11,000 m3 a?1, spit terminus -96,000 m3 a?1, tidal flat + 10,000 m3 a?1 and backbarrier salt marsh +33,000 m3 a?1) and used to establish the relative importance of sediment transport processes involved in barrier migration. Strong interannual variations exist in the long term budget making evaluation of barrier behaviour based on short term measurements doubtful. In a cross shore sense the barrier spit is accreting in spite of the sea level rise. This is specially pronounced at an active overwash fan. However, due to substantial sediment losses to longshore transport the barrier, gets narrower and shorter during its transgressive behaviour. This may indicate that preservation of barriers in the geological record during rapid sea level rise is promoted when sediment loss to longshore transport is insignificant. 相似文献
11.
Since 1974, flow releases from Long Draw Reservoir have increased annual peak flows on La Poudre Pass Creek, Colorado, from ~ 5.6 m3/s to > 8.4 m3/s. The creek drains 61 km2 and channel morphology varies from step-pool to pool-riffle. Comparison of five channel reaches along the creek to channel reaches along neighboring rivers without flow regulation indicates that channel width has increased by as much as a factor of three along La Poudre Pass Creek. Width-to-depth ratio has also increased, the bed material in step-pool channel reaches has coarsened, and residual pool volumes have increased in pool-riffle channel reaches. Pool-riffle channel reaches have undergone the greatest change in response to flow augmentation. Although discharge has increased consistently for all five channel reaches, morphologic response varies in relation to gradient and channel morphology, making it impractical to precisely predict a priori the magnitude of channel response to flow augmentation. 相似文献
12.
以20世纪50年代中期以来崇明岛东部盐沼6个钻孔潮坪层段为研究对象,根据柱样粒度特征、碳/氮元素含量、有机碳稳定同位素组成（δ13C）和C/N比,结合长江入海泥沙通量的变化,研究20世纪50年代中期以来崇明岛东部盐沼发育与长江入海泥沙的响应关系。结果表明：长江入海泥沙通量及组成是20世纪50年代中期以来崇明岛东部盐沼物质粗细变化的主控因素;崇明岛东部盐沼沉积物δ13C与C/N比的相关程度、有机质含量与各粒径区间颗粒含量的相关性在不同时期均存在差异;20世纪60年代,长江入海泥沙量达到顶峰,流域不同侵蚀区域的泥沙相互混合,有机质含量与各粒径区间颗粒含量的相关性及δ13C与C/N比的相关程度均很差;20世纪90年代以来,崇明岛东部地区进行了高强度的围垦活动,δ13C与C/N比的相关程度下降。这表明20世纪50-80年代崇明岛东部盐沼发育受长江入海泥沙控制,20世纪90年代以来崇明岛东部盐沼发育除受长江入海泥沙控制外,还受围垦等人类活动的显著影响。 相似文献
13.
The influence of landsliding on sediment supply and channel change in a steep mountain catchment 总被引：4，自引：1，他引：3
Peter Schuerch Alexander L. Densmore Brian W. McArdell Peter Molnar 《Geomorphology》2006,78(3-4):222-235
Rates of sediment supply by landsliding to an alluvial channel in a small catchment in central Switzerland were estimated over an 11-month study period. Fluvial sediment transport in the channel is independently monitored at the upstream and downstream ends of the study reach, yielding a unique opportunity to quantitatively compare the volume of sediment supplied to the channel with the volume in fluvial transport. Landslide-derived sediment discharge to the channel was greatest during the winter and spring months, while most of the fluvial sediment transport occurred during short, intense summer storms. Approximately 98 m3 of sediment was delivered directly to the study reach by landsliding, 80 m3 was transported into the reach from upstream, and 70 m3 was transported out of the reach. Thus, there was a net accumulation of 100 m3 of sediment during the 11-month study. Decadal-scale channel aggradation was independently assessed by comparing channel longitudinal profiles in 1993 and 2004. During this 11-year period, a total of 1500 m3 of sediment has accumulated in the study reach. Aggradation has occurred largely in two broad zones that correspond with both the locations of major landslide complexes and reaches of high channel slope, indicating that hillslope sediment input left an imprint on the morphology of the channel bed that appears to be stable over at least decadal time scales. 相似文献
14.
We used 210Pb-dated sediment cores from wetlands and Blue Cypress Lake, in the Upper St. Johns River Basin (USJRB), Florida, USA, to measure historical accumulation rates of bulk sediment, total carbon (C), total nitrogen (N), and total phosphorus (P). Marsh cores displayed similar stratigraphies with respect to physical properties and nutrient content. Wetland sediments typically contained > 900 mg organic matter (OM) g–1 dry mass, > 500 mg C g–1, and 30–40 mg N g–1. OM, C, and N concentrations were slightly lower in uppermost sediments of most cores, but displayed no strong stratigraphic trends. Total P concentrations were relatively low in bottommost deposits (0.01–0.11 mg g–1), but ranged from 0.38–2.67 mg g–1 in surface sediments. The mean sediment accretion rate in the marsh since ~ 1900, 0.33 ± 0.05 cm yr–1, was calculated from ten 210Pb-dated cores. All sites displayed increases in accumulation rates of bulk sediment, C, N, and P since the early part of the 20th century. These trends are attributed to recent hydrologic modifications in the basin combined with high nutrient loading from agricultural, residential, and urban sources. 相似文献
15.
The objective of this study was to assess the contribution of the major soil/sediment surfaces in the Southern Aral Sea Basin to the dust generation potential of this region. Eight crusts and soils/sediments from seven sites, representative of these surfaces, were sampled in the field and their major characteristics (particle size distribution, organic carbon content, carbonate content, salt content and composition) that are related to dust generation, were determined. The PM10 and PM2·5 dust generation potential of the materials was determined in the laboratory using the Lubbock Dust Generation, Analysis and Sampling System (LDGASS). The highest amount of PM10 dust (579·3 mg.m−3) was generated from the Takyr crust material. The lowest by one Solonchak salt crust material (39·6 mg.m−3). Salt crusts from the desiccated Aral Sea bottom generated intermediate amounts of dust.The experimental results indicate that the Takyrs and Takyr-like soils, that occupy over 1 million ha in the Southern Aral Sea Basin, constitute the surfaces with the highest potential for being the source for the severe dust storms of the area. Second to the Takyr soils, the Solonchaks and Solonchak-like soils, also with an extent of over 1 million ha, contribute highly saline dust. To these must be added a large, as yet uncharted, proportion of the approximately 4 million ha of exposed sea bed, that exhibit Solonchak-like characteristics. 相似文献
16.
Retrieval of small-relief marsh morphology from Terrestrial Laser Scanner, optimal spatial filtering, and laser return intensity 总被引：1，自引：0，他引：1
Marshes are ubiquitous landforms in estuaries and lagoons, where important hydrological, morphological and ecological processes take place. These areas attenuate sea action on the coast and act as sediment trapping zones. Due to their ecosystem functions and effects on coastal stabilization, marshes are crucial structures in tidal environments, both biologically and geomorphologically, and are fundamental elements in wetland restoration and coastal realignment schemes. The spatially-distributed study of the geomorphology of intertidal areas using remotely-sensed digital terrain models remains problematic, owing to their small relief, often of the order of a few tens of centimetres, and to the presence of short and dense vegetation, which strongly reduces the number of resolvable ground returns. Here, we use high-resolution Terrestrial Laser Scanning ( 200 returns/m2) to retrieve a high-resolution and high-accuracy Digital Terrain Model within a tidal marsh in the Venice lagoon. To this aim we apply a new filtering scheme to Terrestrial Laser Scanner data which selects the lowest values within moving windows, whose optimal size is determined with the aid of a limited number of ancillary Differential GPS data in order to maximize resolution while ensuring the identification of true ground returns. The accuracy of the filtered data is further refined using classifications of the intensity of the returns to extract additional information on the surface (ground or canopy) originating the returning laser beam. Validations against about 200 reference Differential GPS ground elevation observations indicates that the best separation of canopy and ground signals is obtained using a low-pass filter with window size of the order of 1 m and the maximum likelihood classifier to further refine the detection of ground returns. In this case the average estimation error is about 1 cm (slight overestimation of ground elevation), while its standard deviation is about 3 cm. Our approach allows the separation of laser returns coming from the low marsh vegetation from those coming from the marsh surface. The overall result is a new observation technique producing Digital Terrain and Digital Surface Models in areas with very small relief, which is shown to provide unprecedented high-resolution and high-accuracy characterizations of marsh morphology. 相似文献
17.
长江口盐沼土壤有机质更新特征的滩面趋势 总被引：1，自引：0，他引：1
Characteristics and tidal flat trends of soil organic matter （SOM） turnover were studied for the Chongmingdongtan Salt Marsh in the Yangtze River estuary, based on analyses of stable carbon isotope composition （δ^13C）, grain sizes and contents of particulate organic carbon （POC）, total nitrogen （TN） and inorganic carbon （TIC） for three cores excavated from high tidal flat, middle tidal flat and bare flat. Results demonstrate that correlations between soil POC contents and δ^13C values of the salt marsh cores were similar to those between soil organic carbon （SOC） contents and δ^13C values of the upper soil layers of mountainous soil profiles with different altitudes. SOM of salt marsh was generally younger than 100 years, and originated mainly from topsoil erosions in catchments of the Yangtze River. Correlations of TN content with C/N ratio, POC content with TIC content and POC content with δ^13C values for the cores suggest that turnover degrees of SOM from the salt marsh are overall low, and trends of SOM turnover are clear from the bare flat to the high tidal flat. Bare flat samples show characteristics of original sediments, with minor SOM turnover. Turnover processes of SOM have occurred and are discernable in the high and middle tidal flats, and the mixing degrees of SOM compartments with different turnover rates increase with evolution of the muddy tidal flat. The exclusive strata structure of alternate muddy laminae and silty laminae originated from dynamic depositional processes on muddy tidal flat was a great obstacle to vertical migration of dissolved materials, and SOM turnover was then constrained. The muddy tidal flat processes exerted direct influences on sequestration and turnover of SOM in the salt marsh, and had great constraints on the spatial and temporal characteristics of SOM turnover of the Chongmingdongtan Salt Marsh in the Yangtze River estuary. 相似文献
18.
《Polar Science》2014,8(2):166-182
The larch forests on the permafrost in northeastern Mongolia are located at the southern limit of the Siberian taiga forest, which is one of the key regions for evaluating climate change effects and responses of the forest to climate change. We conducted long-term monitoring of seasonal and interannual variations in hydrometeorological elements, energy, and carbon exchange in a larch forest (48°15′24′′N, 106°51′3′′E, altitude: 1338 m) in northeastern Mongolia from 2010 to 2012. The annual air temperature and precipitation ranged from −0.13 °C to −1.2 °C and from 230 mm to 317 mm. The permafrost was found at a depth of 3 m. The dominant component of the energy budget was the sensible heat flux (H) from October to May (H/available energy [Ra] = 0.46; latent heat flux [LE]/Ra = 0.15), while it was the LE from June to September (H/Ra = 0.28, LE/Ra = 0.52). The annual net ecosystem exchange (NEE), gross primary production (GPP), and ecosystem respiration (RE) were −131 to −257 gC m−2 y−1, 681–703 gC m−2 y−1, and 423–571 gC m−2 y−1, respectively. There was a remarkable response of LE and NEE to both vapor pressure deficit and surface soil water content. 相似文献
19.
Supriyo Kumar Das Joyanto Routh Alakendra N. Roychoudhury J. Val Klump 《Journal of Paleolimnology》2008,39(3):349-360
We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and
total phosphorus (TP) as well as stable carbon and nitrogen isotopes (δ13C and δ15N) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater
lake in South Africa. Typical C/N (10–12), H/C ratios (≥1.7) and δ13Corganic values (−22 to −19‰) together with the increase in TOC concentration indicate elevated primary productivity in lower middle
(18–22 cm) and top (0–8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant,
rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent
with this, measured δ15Norganic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are
evident from the low δ15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼0) and high
TP (100–2,200 mg l−1) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter
pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation
in the upper mid-section (12–14 cm) of the core. 相似文献
20.
Michael Craghan 《Geomorphology》2005,69(1-4):57-75
The study area is a portion of a coastal community that is adjacent to a salt marsh and tidal creek. The developed area was built upon wetlands, and like the marsh, it floods during spring tides and strong coastal storms. Following floods, little visual evidence of sedimentation is in the built area, prompting the hypothesis that physical characteristics of coastal development limit sediment availability during floods and reduce deposition. Because the area floods from a tidal creek during the same events that lead to inundation of the adjacent high marsh, salt marshes are used as an analogue system for planning this research. Although salt marsh geomorphology is a starting point, people are endogenous actors at this site who influence geomorphic evolution by changing the flow of naturally occurring energy. Suspended sediment levels or deposition were measured during 10 flooding events. Water samples were collected from the tidal creek, at a catchbasin, at another location in the street, and in the Spartina patens marsh. Sediment is found to be delivered to the street in the same quantities and for the same duration as in the salt marsh. Suspended sediment levels are alike throughout the research area. The amount of sediment that accumulates following coastal floods was measured by placing samplers within the street and the marsh. Highly significant differences in sediment accumulation exist between the environments. After a flood event, much less sediment is deposited in the street than in the marsh. 相似文献