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1.
A combination of field measurements, modelling and laboratory experiments was used to evaluate the potential impact of sediment resuspension on phosphorus (P) dynamics. The study was carried out in two adjacent shallow coastal lakes (Lake Honda and Lake Nueva) which, due to their geographic proximity (only 200 m apart), are subject to equal meteorological forcing and represent ideal systems to study how morphometry and sediment properties relate to wind events. The focusing factors (a measure of the fluxes of sediment into the water column through resuspension) estimated by comparing settling fluxes measured in surface sediment traps with those measured in bottom traps, were significantly larger (approximately 34% larger) in Lake Honda (LH; 1.18) than in Lake Nueva (LN; 0.88). Our model estimates of resuspension fluxes (E) were also ca. 40% larger in LH than in LN, in agreement with the observed focusing factors. The larger resuspension fluxes encountered in LH, in comparison with LN, can mainly be explained by differences in lake morphometry. Still, they could arise from differences in grain size distribution or in benthic algae concentration encountered in the lake sediments. By means of adsorption experiments in the laboratory, we show that resuspension events will have different effects on P-dynamics in LH and LN. While the resuspended material from LH tends to adsorb phosphate (PO4 3−), removing it from the water column, in LN the resuspended sediments tend to increase the availability of PO4 3− in solution. These differences arise from (1) higher concentrations of PO4 3− in water in LH compared to LN; and (2) larger PO4 3−adsorption capacity of the LH sediments as a result of the more abundant iron oxyhydroxides and clay.  相似文献   

2.
沉水植物和螺类都是水生生态系统的重要组成部分,两者的牧食关系也是水生食物网中重要的一环,而不同的基质类型可能会影响两者的生长和改变沉水植物对螺类牧食的防御策略.以耳萝卜螺（Radix auricularia）和苦草（Vallisneria spiralis）为对象,研究基质类型、螺类牧食对沉水植物的生长及防御策略的影响,以及基质类型及沉水植物对螺类生长和生理特征的影响.研究发现,螺类牧食和基质类型对苦草生长和元素特征具有显著的影响,存在螺类牧食时,泥沙基质和沙基质苦草的相对生长速率显著降低,泥沙、沙和泥基质苦草地上生物量分别减少了67.74%、58.58%和17.84%,根冠比分别升高了177.51%、217.23%和1.44%;且泥沙基质中苦草的叶片数显著低于无牧食组.不同基质类型下,牧食对苦草总碳含量无显著影响,但泥和泥沙组中,螺类牧食使苦草的总氮含量均显著降低,碳氮比均显著升高;沙基质下,螺类牧食使苦草总酚含量显著降低.基质类型对螺类的形态特征（除壳宽外）、生长及元素含量均无显著影响.总体来看,基质类型对耳萝卜螺牧食和苦草防御策略具有一定程度的影响,但对螺类的生长及元素特征基本无影响.本研究可以为牧食理论的研究提供基础数据支持,也可为沉水植被恢复、水生生态系统稳定提供参考,但基质类型对螺草牧食关系的长期影响,仍需进一步深入研究.  相似文献   

3.
The relative significance of primary and secondary suspended sediment sources has been identified in a small (15 km2) agricultural catchment through the application of a linear unmixing model using mineral magnetic, geochemical and radionuclide signatures of fine sediments. Roads appear to be important as a secondary source of suspended sediment and in the conveyance of topsoils to the river channel. Roads also alter the source signatures of sediment in transport, especially that derived from agricultural topsoils. Modelling suggests that c. 30% of the suspended sediment collected from suspended sediment traps in the River Leadon were derived from, or transported via, roads. Relative contributions from primary sources of c. 43% and c. 27% were estimated from a combined (subsoil and channel bank) subsurface source, and a combined (arable and grassland) topsoil source, respectively. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

4.
粒度组分是影响黄土震陷的重要因素之一.通过采集新疆艾其沟泥火山泥质碎屑喷出样品和泥火山发育区域出露的沉积剖面泥质碎屑样品,利用激光粒度分析测试的实验方法对样品进行粒度测试,分别对样品中值(Md)、均值(Mz)、标准偏差(σφ)、偏度(SK1)、峰度(KG)等粒度参数进行分析.研究结果显示:艾其沟泥火山泥质沉积物粒度组分...  相似文献   

5.
Particle selectivity plays an important role in clarifying sediment transport processes in vegetative filter strips (VFS). 10-m long grass strips at slopes of 5° and 15° were subjected to a series of sediment-laden inflows experiments with different particle sizes to investigate the sediment transport and its response to overland flow hydraulics. The inflow sediments came from local soil, river-bed sand, and mixed, with median particle size d50 of 39.9, 207.9 and 77.4 μm, respectively. Three independent repeated experiments were carried for each treatment. The results show that when the sediment trapping lasted for a certain length of time, the re-entrainment of some small-sized particles was greater than the deposition; that is, net loss occurred, which was not erosion of the original soil. Net loss of particles is mainly determined by the particle diameter. The coarser the inflow sediment particles and/or the steeper the slope, the coarser the particles can be net lost. Deposited sediment causes the VFS bed surface to become smooth and hydraulic resistance decrease exponentially. Unit stream power P is more suitable than shear stress τ of overland flow to be used to describe the process of sediment particle transport in VFS. The relationship between P and d50 of outflow sediment is very consistent with the form of power function with a constant term. These results are helpful to understand the physical process of sediment transport on vegetation hillslopes.  相似文献   

6.
为探究重污染底泥对沉水植物繁殖体萌发和幼苗生长影响,以苦草（Vallisneria natans）种子和黑藻（Hydrilla verticillata）冬芽为研究对象,以轻污染底泥为对照组,通过室内模拟实验研究了重污染底泥对两种繁殖体萌发和幼苗生长、生理特性的影响。实验结果表明,与轻污染底泥相比,重污染底泥对苦草种子萌发和幼苗生长无显著影响。黑藻冬芽萌发和幼苗地上部生物量在两组间没有显著差异,但重污染底泥组幼苗的地下部生物量显著高于轻污染底泥组,其地上部和地下部生物量比值由7.06±0.38下降至2.97±0.08。此外,苦草和黑藻幼苗受到重污染底泥胁迫表现出不同的生理响应。苦草幼苗叶片的类胡萝卜素含量显著减少,可溶性糖和蛋白含量分别降低11.56%、24.10%,根系活力也明显受到抑制,仅为（34.93±3.28） mg/（g·h）;黑藻幼苗生理响应与苦草略有不同,其叶片的叶绿素a、b含量显著增加,根系活力降低44.29%,可溶性糖和蛋白含量在轻污染组和重污染组之间无显著差异。由此可见,重污染底泥对苦草种子和黑藻冬芽的萌发影响不显著,但会明显影响幼苗的生长发育和生理特性,研究结果为...  相似文献   

7.
The potential for humic substances to serve as a terminal electron acceptor in microbial respiration and to function as an electron shuttle between Fe(III)-reducing microorganisms and insoluble Fe(III) oxides was investigated. The Fe(III)-reducing microorganism Geobacter metallireducens conserved energy to support growth from electron transport to humics as evidenced by continued oxidation of acetate to carbon dioxide after as many as nine transfers in a medium with acetate as the electron donor and soil humic acids as the electron acceptor. Growth of G. metallireducens with poorly crystalline Fe(III) oxide as the electron acceptor was greatly stimulated by the addition of as little as 100 μM of the humics analog, anthraquinone-2,6-disulfonate. Other quinones investigated, including lawsone, menadione, and anthraquinone-2-sulfonate, also stimulated Fe(III) oxide reduction. A wide phylogenetic diversity of microorganisms capable of Fe(III) reduction were also able to transfer electrons to humics. Microorganisms which can not reduce Fe(III) could not reduce humics. Humics stimulated the reduction of structural Fe(III) in clay and the crystalline Fe(III) forms, goethite and hematite. These results demonstrate that electron shuttling between Fe(III)-reducing microorganisms and Fe(III) via humics not only accelerates the microbial reduction of poorly crystalline Fe(III) oxide, but also can facilitate the reduction of Fe(III) forms that are not typically reduced by microorganisms in the absence of humics. Addition of humic substances to enhance electron shuttling between Fe(III)-reducing microorganisms and Fe(III) oxides may be a useful strategy to stimulate the remediation of soils and sediments contaminated with organic or metal pollutants.  相似文献   

8.
模拟湖泊系统构建了"沉积物-水-苦草(Vallisneria natans)"系统,应用磷脂脂肪酸(PLFAs)法测定在沉水植物苦草不同生长时期沉积物表层微生物群落结构的变化,探讨沉水植物对沉积物中的微生物群落结构的影响.结果表明,从苦草生长初期到旺盛期再到衰亡期,沉积物中有机质含量先下降后上升;总磷、有机磷、无机磷分别下降了8.97%、7.81%、10.28%;沉积物微生物的活性与总磷呈极显著负相关,在苦草生长初期和旺盛期,实验组的沉积物微生物活性大于对照组,而在衰亡期对照组的沉积物微生物活性略高于实验组;不同时期沉积物中微生物群落结构发生了明显变化,组成结构差异显著,微生物组成中细菌占主要成分(占微生物总量的76%~84%);细菌中革兰氏阳性菌占主要优势,且革兰氏阳性菌百分含量随苦草生长呈上升趋势,革兰氏阴性菌呈下降趋势;真菌的百分含量呈上升趋势.  相似文献   

9.
Estimates of suspended sediment yield over the past 800 years have been derived from a whole-basin study of lake sediments in Llyn Geirionydd, North Wales. Magnetic and physical sediment properties were used to correlate a suite of cores to a master chronology based on 210Pb and 14C dates. The sources of sediment within the catchment were identified by comparing the magnetic and heavy metal properties of sediments, soils, and stream sediments. Mean suspended sediment yields range from 6 to 18 t km?2 yr?1 with high yields in the periods 1765-1830 and 1903-1985 corresponding to mining activities in the catchment. The impact of earlier deforestation, agricultural expansion, or climatic change on sediment yields is low, although there is evidence that agricultural activities increased levels of peak stream discharge. Afforestation in the 20th century does not appear to have significantly increased sediment yield. Sediment sources have remained fairly constant through time; they appear to be widespread and dominated by stream channel sides rather than point sources, except during the mining phases when spoil material has dominated the sediment load. Sediment loads to the lake today are still dominated by sediment derived from unvegetated spoil heaps.  相似文献   

10.
The transport of sediment from six small (0.2 to 17.6 km2) headwater catchments is described. The catchments under investigation were located in relation to predominant lithological deposits within the Cretaceous rock succession; two of the areas were underlain by (Weald) clay, two by sandstone (Ashdown Sand and Tunbridge Wells Sand) and two by chalk. The climate of the region under investigation is temperate, with an average annual precipitation (850 mm) in excess of potential evapotranspiration (450 mm). The transport of suspended material from within the catchments was examined by collecting samples of the water-sediment mixture draining the areas, using hand held depth-integrating and permanently installed stage sampling systems. The results of the regularly maintained sampling programme, over a two-year period, are described. Attempts were made to both measure and compute bed load transport. Suspended sediment concentrations are compared between catchments and related to hydrological characteristics. The nature of the material in transit is examined. Sediment rating curves are derived for each of the headwater catchments, defining the relationship in the form y = Axb (where y = suspended sediment concentration (mg/1) and x = water discharge (m3/s)). Annual rating curves are used to derive annual suspended sediment loads by combination with water discharge data, using a log-incremental computerized approach. Multiple regression techniques have been used to examine annual loads in terms of hydrological and morphological characteristics of the headwater catchments. Based on the field information available, a generalized model for the relationship between suspended sediment concentration and water discharge is described. Finally, the derived annual loads from the headwater catchments are combined with both limited observations from the larger Sussex rivers and data available for other catchment investigations in the British Isles, to produce a series of prediction equations for catchment yield under temperate climatic conditions.  相似文献   

11.
Knowledge of sediment exports from continental areas is essential for estimating denudation rates and biogeochemical cycles. However, the estimation of current sediment fluxes to the sea is often limited by the availability and quality of sediment discharge data. This study aims to quantify the relative contributions of French rivers to the sediment discharge to the ocean. Sediment fluxes were assessed using the French river quality database, which is characterized by a low temporal resolution but long‐term measurement periods. An improved rating curve approach (IRCA) using daily discharge data, which allows the estimation of mean annual sediment loads from infrequent sediment concentration data, was used to calculate sediment fluxes. The resulting mean annual sediment loads show that French rivers export c. 16.21 Mt yr‐1 of sediments to the sea. Among the 88 defined French rivers flowing to the sea, the four largest basins (Loire, Rhone, Garonne and Seine) export 13.2 Mt yr‐1, which corresponds to 81.3% of total exports. No relationship was found between the mass of exported sediment and the size of the drainage basins. This is due to the variety of river basin typologies among these rivers, including lowland rivers in temperate climates, such as the Seine on the one hand and rivers draining mountainous areas in Alpine/Mediterranean areas on the other hand, such as the Rhone. The latter contributes 60% to the total sediment export for France while its drainage area is only 19% of the total area considered. Differences between the river basins considered are also shown by temporal indicators describing the duration of the exports, which may be linked with sediment production processes over drained areas. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

12.
This study investigated the influence of the regional flow on the streambed vertical hydraulic conductivity (Kv) within the hyporheic zone in three stream reaches of the Weihe River in July 2016. The streambed Kv with two connected depths was investigated at each test reach. Based on the sediment characteristics, the three test reaches could be divided into three categories: a sandy streambed without continuous silt and clay layer, a sandy streambed with continuous silt and clay layer, and a silt–clay streambed. The results demonstrate that the streambed Kv mainly decreases with the depth at the sandy streambed (without continuous silt and clay layer) and increases with the depth at the other two test reaches. At the sandy streambed (with continuous silt and clay layer) where streambed Kv mainly decreases with the depth, the regional upward flux can suspend fine particles and enhance the pore spacing, resulting in the elevated Kv in the upper sediment layers. At another sandy streambed, the continuous silt and clay layer is the main factor that influences the vertical distribution of fine particles and streambed Kv. An increase in streambed Kv with the depth at the silt/clay streambed is attributed to the regional downward movement of water within the sediments that may lead to more fine particles deposited in the pores in the upper sediment layers. The streambed Kv is very close to the bank in the sandy streambed without continuous silt and clay layer and the channel centre in the other two test reaches. Differences in grain size distribution of the sediments at each test reach exercise a strong controlling influence on the streambed Kv. This study promotes the understanding of dynamics influencing the interactions between groundwater and surface water and provides guidelines to scientific water resources management for rivers.  相似文献   

13.
Organic carbon (OC) is easily enriched in sediment particles of different sizes due to aggregate breakdown and selective transport for sheet erosion. However, the transport of aggregate-associated OC has not been thoroughly investigated. To address this issue, 27 simulated rainfall experiments were conducted in a 1 m × 0.35 m box on slope gradients of 15°, 10°, and 15°and under three rainfall intensities of 45 mm h−1, 90 mm h−1 and 120 mm h−1. The results showed that OC was obviously enriched in sediment particles of different sizes under sheet erosion. The soil organic carbon (SOC) concentrations of each aggregate size class in sediments were different from those in the original soil, especially when the rainfall intensity or slope was sufficiently low, such as 45 mm h–1 or 5°, respectively. Under a slope of 5°, the SOC enrichment ratios (ERocs) of small macroaggregates and microaggregates were high but decreased over time. As rainfall intensity increased, OC became enriched in increasingly fine sediment particles. Under a rainfall intensity of 45 mm h–1, the ERocs of the different aggregate size classes were always high throughout the entire erosion process. Under a rainfall intensity of > 45 mm h–1 and slope of > 5°, the ERocs of the different aggregate size classes were close to 1.0, especially those of clay and silt. Therefore, the high ERocs in sediments resulted from the first transport of effective clay. Among total SOC loss, the proportion of OC loss caused by the transport of microaggregates and silt plus clay-sized particles was greater than 50%. We also found that low stream power and low water depth were two requirements for the high ERocs in aggregates. Stream power was closely related to sediment particle distribution. Flow velocity was significantly and positively related to the percentage of OC-enriched macroaggregates in the sediments (P > 0.01). Our study will provide important information for understanding the fate of SOC and building physical-based SOC transport models. © 2019 John Wiley & Sons, Ltd.  相似文献   

14.
In 2007/08, a study was undertaken on the sediment dynamics in shallow Lake Markermeer (the Netherlands). Firstly, sediment characteristics were determined at 49 sites in the lake. Parameters such as median grain size and loss on ignition showed a spatial as well as water depth related pattern, indicating wind-induced sediment transport. Highly significant correlations were found between all sediment parameters. Lake Markermeer sediment dynamics were investigated in a sediment trap field survey at two permanent stations in the lake. Sediment yields, virtually all coming from sediment resuspension, were significantly correlated with average wind speeds, though periods of extreme winds also played a role. Sediment resuspension rates for Lake Markermeer were high, viz. on average ca. 1,000 g m−2 day−1. The highly dynamic nature of Lake Markermeer sediments must be due to the overall shallowness of the lake, together with its large surface area (dynamic ratio = [√(area)]/[average depth] = 7.5); wind-induced waves and currents will impact most of the lake’s sediment bed. Indeed, near-bed currents can easily reach values >10 cm/s. Measurements of the thickness of the settled “mud” layer, as well as 137Cs dating, showed that long-term deposition only takes place in the deeper SE area of the lake. Finally, lake sediment dynamics were investigated in preliminary laboratory experiments in a small “micro-flume”, applying increasing water currents onto five Lake Markermeer sediments. Sediment resuspension started off at 0.5–0.7 cm/s and showed a strongly exponential behaviour with respect to these currents.  相似文献   

15.
Water level, sediment heterogeneity, and plant density are important factors that determine plant growth, distribution, and community structure. In the present study, we investigated the effects of these factors on the growth and root characteristics of Carex brevicuspis. We conducted an outdoor experiment to monitor biomass accumulation and allocation, relative root distribution mass ratio, longest root length, and total N and P contents of C. brevicuspis plants. We used a factorial design with two water levels (0 cm and −15 cm relative to the soil surface, named high and low water level treatments, respectively), three sediment types (sand/clay sediment with 0–15 cm of sand and 15–30 cm of clay; mixed sediment with 0–30 cm mixture of sand and clay with 1:1 volumw ratio; and clay/sand sediment with 0–15 cm of clay and 15–30 cm of sand), and three plant densities (88 plants per m2, 354 plants per m2, and 708 plants per m2). Biomass accumulation decreased with increasing plant density and was significantly higher in the low water level and the clay/sand sediment than in the high water level and the other two sediment types. The shoot:root ratio was markedly higher in the high water level than in the low water level and decreased with increasing plant density; further, in the high water level, it was significantly lower in the sand/clay sediment than in the other two sediment types. The relative root distribution mass ratio was markedly higher in the high water level treatments than in the low water level treatments. Further, in the high water level treatments, the relative root distribution mass ratio increased with increasing plant density in the clay/sand sediment and was lower in the sand/clay sediment than in the other two sediment types. The longest root length was significantly lower in the high water level than in the low water level and increased with increasing plant density in the sand/clay sediment in the high water level. Total N content in the plants was influenced only by sediment type; on the other hand, total P content was markedly higher in the high water level than in the low water level. Our data indicate that growth of C. brevicuspis was limited by higher water level, higher density and sand/clay sediment. Plants can increase shoot:root ratio and develop shallow root system to acclimate to high water level and thus could adjust shoot:root ratio and root characteristics, e.g. decrease their shoot:root ratio and allocating more root and increasing root length to the nutrient rich layer to acclimate to conditions of higher density and sediment heterogeneity.  相似文献   

16.
This paper provides comprehensive evidence that sediment routing around pools is a key mechanism for pool‐riffle maintenance in sinuous upland gravel‐bed streams. The findings suggest that pools do not require a reversal in energy for them to scour out any accumulated sediments, if little or no sediments are fed into them. A combination of clast tracing using passive integrated transponder (PIT) tagging and bedload traps (positioned along the thalweg on the upstream riffle, pool entrance, pool exit and downstream riffle) are used to provide information on clast pathways and sediment sorting through a single pool‐riffle unit. Computational fluid dynamics (CFD) is also used to explore hydraulic variability and flow pathways. Clast tracing results provide a strong indication that clasts are not fed through pools, rather they are transported across point bar surfaces, or around bar edges (depending upon previous clast position, clast size, and event magnitude). Spatial variations in bedload transport were found throughout the pool‐riffle unit. The pool entrance bedload trap was often found to be empty, when the others had filled, further supporting the notion that little or no sediment was fed into the pool. The pool exit slope trap would occasionally fill with sediment, thought to be sourced from the eroding outer bank. CFD results demonstrate higher pool shear stresses (τ ≈ 140 N m–2) in a localized zone adjacent to an eroding outer bank, compared to the upstream and downstream riffles (τ ≈ 60 N m–2) at flows of 6 · 2 m3 s–1 (≈ 60% of the bankfull discharge) and above. There was marginal evidence for near‐bed velocity reversal. Near‐bed streamlines, produced from velocity vectors indicate that flow paths are diverted over the bar top rather than being fed through the thalweg. Some streamlines appear to brush the outer edge of the pool for the 4 · 9 m3 s–1 to 7 · 8 m3 s–1 (between 50 and 80% of the bankfull discharge) simulations, however complete avoidance was found for discharges greater than this. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

17.
The species composition of clostridial communities of the sediment in a polluted area of the Danube (South of Budapest, Háros‐Bay, Hungary) was investigated. The spore counts exceeded 700...800 CFU per gram (wet weight). 23 clostridial strains were identified by using API 20A anaerobe identification kits, another 20 physiological, biochemical, and ecological tests were also carried out. Results of numerical analysis showed that the clostridial community in the sediment of the Danube is composed of at least 4 different species. Members of C. perfringens, indicating to fecal contamination, C. subterminale and related bacteria were dominant in the examined area. All strains showed wide pH (5...9) and temperature (3...45°C) tolerance. They were able to grow on media containing significant amounts of lead (Pb2+), mercury (Hg2+), copper (Cu2+), and zinc (Zn2+). Strains of C. perfringens showed a wide range of degradative capacities (acid production from many different carbohydrates, gelatinase, lecithinase, lipase production, etc.).  相似文献   

18.
Chemical and mineralogical data are presented for a suite of 59 sediment samples collected from the P8 and Speedwell cave systems (and mineralogical data are presented for a further six surface sediments) in the Castleton karst catchment, Derbyshire, England. Sediments are grouped according to age and depositional environment and these groups show distinctive mineralogical and chemical characteristics. Clay mineralogy is effective at distinguishing different sediment sources for ancient and modern sediments which are derived from pre-Devensian tills and Devensian solifluction deposits, respectively. Major element chemistry reflects these differences in clay mineral content, while trace elements demonstrate the importance of abrasion of ore minerals in conduits in the aquifer which follow mineral veins, even under natural, pre-mining conditions. Clay minerals are confirmed as the host for uranium in uranium-rich ancient sediments. Consideration of organic carbon and hydrogen concentrations shows that plant material is the dominant source of organic material in the modern sediments. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

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