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1.
Geomorphological controls and catchment sediment characteristics control the formation of floodplains and affect their capacity to sequester carbon. Organic carbon stored in floodplains is typically a product of pedogenic development between periods of mineral sediment deposition. However, in organically-dominated upland catchments with a high sediment load, eroded particulate organics may also be fluvially deposited with potential for storage and/or oxidation. Understanding the redistribution of terrestrial carbon laterally, beyond the bounds of river channels is important, especially in eroding peatland systems where fluvial particulate organic carbon exports are often assumed to be oxidised. Floodplains have the potential to be both carbon cycling hotspots and areas of sequestration. Understanding of the interaction of carbon cycling and the sediment cascade through floodplain systems is limited. This paper examines the formation of highly organic floodplains downstream of heavily eroded peatlands in the Peak District, UK. Reconstruction of the history of the floodplains suggests that they have formed in response to periods of erosion of organic soils upstream. We present a novel approach to calculating a carbon stock within a floodplain, using XRF and radiograph data recorded during Itrax core scanning of sediment cores. This carbon stock is extrapolated to the catchment scale, to assess the importance of these floodplains in the storage and cycling of organic carbon in this area. The carbon stock estimate for the floodplains across the contributing catchments is between 3482-13460 tonnes, equating on an annualised basis to 0.8-4.5% of the modern-day POC flux. Radiocarbon analyses of bulk organic matter in floodplain sediments revealed that a substantial proportion of organic carbon was associated with re-deposited peat and has been used as a tool for organic matter source determination. The average age of these samples (3010 years BP) is substantially older than Infrared Stimulated Luminesence dating which demonstrated that the floodplains formed between 430 and 1060 years ago. Our data suggest that floodplains are an integral part of eroding peatland systems, acting as both significant stores of aged and eroded organic carbon and as hotspots of carbon turnover. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

2.
We draw on published studies of floodplain organic carbon storage, wildfire-related effects on floodplains in temperate and high latitudes, and case studies to propose a conceptual model of the effects of wildfire on floodplain organic carbon storage in relation to climate and valley geometry. Soil organic carbon typically constitutes the largest carbon stock in floodplains in fire-prone regions, although downed wood can contain significant organic carbon. We focus on the influence of wildfire on soil organic carbon and downed wood as opposed to standing vegetation to emphasize the geomorphic influences resulting from wildfire on floodplain organic carbon stocks. The net effect of wildfire varies depending on site-specific characteristics including climate and valley geometry. Wildfire is likely to reduce carbon stock in steep, confined valley segments because increased water and sediment yields following fire create net floodplain erosion. The net effect of fire in partly confined valleys depends on site-specific interactions among floodplain aggradation and erosion, and, in high-latitude regions, permafrost degradation. In unconfined valleys in temperate latitudes, wildfire is likely to slightly increase floodplain organic carbon stock as a result of floodplain aggradation and wood deposition. In unconfined valleys in high latitudes underlain by permafrost, wildfire is likely in the short-term to significantly decrease floodplain organic carbon via permafrost degradation and reduce organic-layer thickness. Permafrost degradation reduces floodplain erosional resistance, leading to enhanced stream bank erosion and greater carbon fluxes into channels. The implications of warming climate and increased wildfires for floodplain organic carbon stock thus vary. Increasing wildfire extent, frequency, and severity may result in significant redistribution of organic carbon from floodplains to the atmosphere via combustion in all environments examined here, as well as redistribution from upper to lower portions of watersheds in the temperate zone and from floodplains to the oceans via riverine transport in the high-latitudes. © 2019 John Wiley & Sons, Ltd.  相似文献   

3.
Downed large wood (LW) in floodplains provides habitat and nutrients for diverse organisms, influences hydraulics and sedimentation during overbank flows, and affects channel form and lateral migration. Very few studies, however, have quantified LW volumes in floodplains that are unaltered by human disturbance. We compare LW volumes in relatively unaltered floodplains of semiarid boreal lowland, subtropical lowland, and semiarid temperate mountain rivers in the United States. Average volumes of downed LW are 42.3 m3 ha?1, 50.4 m3 ha?1, and 116.3 m3 ha?1 in the semiarid boreal, subtropical, and semiarid temperate sites, respectively. Observed patterns support the hypothesis that the largest downed LW volumes occur in the semiarid temperate mountain sites, which is likely linked to a combination of moderate‐to‐high net primary productivity, temperature‐limited decomposition rates, and resulting slow wood turnover time. Floodplain LW volumes differ among vegetation types within the semiarid boreal and semiarid temperate mountain regions, reflecting differences in species composition. Lateral channel migration and flooding influence vegetation communities in the semiarid boreal sites, which in turn influences floodplain LW loads. Other forms of disturbance such as fires, insect infestations, and blowdowns can increase LW volumes in the semiarid boreal and semiarid temperate mountain sites, where rates of wood decay are relatively slow compared with the subtropical lowland sites. Although sediment is the largest floodplain carbon reservoir, floodplain LW stores substantial amounts of organic carbon and can influence floodplain sediment storage. In our study sites, floodplain LW volumes are lower than those in adjacent channels, but are higher than those in upland (i.e. non‐floodplain) forests. Given the important ecological and physical effects of floodplain LW, efforts to add LW to river corridors as part of restoration activities, and the need to quantify carbon stocks within river corridors, we urge others to quantify floodplain and instream LW volumes in diverse environments. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

4.
Arsenic-contaminated mine tailings that were discharged into Whitewood Creek at Lead, South Dakota, from 1876 to 1978, were deposited along the floodplains of Whitewood Creek and the Belle Fourche River. The resulting arsenic-contaminated floodplain deposit consists mostly of overbank sediments and filled abandoned meanders along White-wood Creek, and overbank and point-bar sediments along the Belle Fourche River. Arsenic concentrations of the contaminated sediments indicate the degree of dilution of mine tailings by uncontaminated alluvium. About 13 per cent of the 110 × 106 Mg of mine tailings that were discharged at Lead were deposited along the Whitewood Creek floodplain. Deposition of mine tailings near the mouth of Whitewood Creek was augmented by an engineered structure. About 29 per cent of the mine tailings delivered by Whitewood Creek were deposited along the Belle Fourche River floodplain. About 60 per cent of that sediment is contained in overbank deposits. Deposition along a segment of the Belle Fourche River was augmented by rapid channel migration. The proportions of contaminated sediment stored along Whitewood Creek and the Belle Fourche River are consistent with sediment storage along the floodplains of perennial streams in other, similar sized watersheds.  相似文献   

5.
Recent studies of sediment delivery and budgets in the United States indicate that upland erosion rates at a given time may not explain contemporaneous sediment yields from a drainage basin. This suggests temporal discontinuities in sediment delivery associated with hillslope and channel storage processes. Integration of sediment production, storage and transport is essential to understand sediment routing in basins. We analysed each process chronologically using aerial photographs, monitoring data of sediment movement and annual tree-rings, and then compared estimated temporal changes in sediment production from hillslopes, floodplain disturbance areas and sediment transport in river channels. Toeslopes, floodplains and alluvial fans together contained 59 per cent of sediment eroded from uplands over the last 30 years. Monitoring results of riverbed changes showed that the volume of stored sediment on floodplains decreased exponentially with succeeding floods. The age distribution of floodplain deposits reflected the disturbance history of a river channel, and followed an exponential decrease with age. The results of this study may have important implications for sediment control plans for watersheds in steep regions.  相似文献   

6.
Rivers are dynamic components of the terrestrial carbon cycle and provide important functions in ecosystem processes. Although rivers act as conveyers of carbon to the oceans, rivers also retain carbon within riparian ecosystems along floodplains, with potential for long‐term (> 102 years) storage. Research in ecosystem processing emphasizes the importance of organic carbon (OC) in river systems, and estimates of OC fluxes in terrestrial freshwater systems indicate that a significant portion of terrestrial carbon is stored within river networks. Studies have examined soil OC on floodplains, but research that examines the potential mechanistic controls on OC storage in riparian ecosystems and floodplains is more limited. We emphasize three primary OC reservoirs within fluvial systems: (1) standing riparian biomass; (2) dead biomass as large wood (LW) in the stream and on the floodplain; (3) OC on and beneath the floodplain surface, including litter, humus, and soil organic carbon (SOC). This review focuses on studies that have framed research questions and results in the context of OC retention, accumulation and storage within the three primary pools along riparian ecosystems. In this paper, we (i) discuss the various reservoirs for OC storage in riparian ecosystems, (ii) discuss physical conditions that facilitate carbon retention and storage in riparian ecosystems, (iii) provide a synthesis of published OC storage in riparian ecosystems, (iv) present a conceptual model of the conditions that favor OC storage in riparian ecosystems, (v) briefly discuss human impacts on OC storage in riparian ecosystems, and (vi) highlight current knowledge gaps. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

7.
River floodplains act as sinks for fine‐sediment and sediment‐associated contaminants. Increasing recognition of their environmental importance has necessitated a need for an improved understanding of the fate and residence times of overbank sediment deposits over a broad range of timescales. Most existing investigations have focused on medium‐term accretion rates, which represents net deposition from multiple flood events over several decades. In contrast, the fate of recently‐deposited sediment during subsequent overbank events has received only limited attention. This paper presents a novel tracing‐technique for documenting the remobilization of recent overbank sediment on river floodplains during subsequent inundation events, using the artificial radionuclides, caesium‐134 (134Cs) and cobalt‐60 (60Co). The investigation was conducted within floodplains of the Rivers Taw and Culm in Devon, UK. Small quantities of fine‐sediment (< 63 µm dia.), pre‐labelled with known activities of either 134Cs or 60Co, were deposited at 15 locations across each floodplain. Surface inventories, measured before and after three consecutive flood events, were used to estimate sediment loss (in g m–2). Significant reductions provided evidence of the remobilization of the labelled sediment by inundating floodwaters. Spatial variations in remobilization were related to localized topography. Sediment remobilized during the first two events for the River Taw floodplain were equivalent to 63 · 8% and 11 · 9%, respectively, of the original mass. Equivalent values for the River Culm floodplain were 49 · 6% and 12 · 5%, respectively, of the original mass. Sediment loss during the third event proved too small to be attributed to remobilization by overbank floodwaters. After the third event, a mean of 22 · 5% and 35 · 2% of the original mass remained on the Taw and Culm floodplains, respectively. These results provide evidence of the storage of the remaining sediment. The findings highlight the importance of remobilization of recently‐deposited sediment on river floodplains during subsequent overbank events and demonstrate the potential of the tracing‐technique. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
Erosion, sediment transportation and accumulation in rivers   总被引：8，自引：5，他引：3  
The present paper analyses the interrelation between erosion, sediment transportation and accumulation proposed by N. I. Makkaveyev （1908-1983） and its further development in modem studies of river channel processes in Russia. Spatio-temporal linkages between erosion and accumulation are defined considering channel processes at different scales - river longitudinal profile, channel morphological patterns, alluvial bedforms （bars, dunes） and individual sediment particles. Relations between river geomorphic activity, flow transportation capacity and sediment budgets are established （sediment input and output; channel bed erosion and sediment entrainment into flow - termination of sediment transport and its deposition）. Channel planforms, floodplain segments separated by the latter and alluvial channel bedforms are shown to be geomorphic expressions of sediment transport process at different spatial and temporal scales. This paper is dedicated to the 100th anniversary of N. I. Makkaveyev, Professor of the Moscow State University, author of the book ＂River channel and erosion in its basin＂ （1955）. That book is regarded in Russia as the pioneering work which initiated the complex hydrological and geographical studies of channel processes and laid a basis for the theory of unified fluvial erosion-accumulation process.  相似文献   

9.
Downed large wood on floodplains creates similar geomorphic and ecological effects as wood in the active channel, but has been the subject of fewer geomorphic studies. I propose floodplain large wood process domains that are distinguished based on recruitment source at the reach to river-length scale. Wood recruited to the floodplain can be autochthonous (individual or mass recruitment from floodplain forest), fluvially transported, or transported from adjacent hillslopes via mass movements that come down the valley side slopes or down the main channel. Fluvially transported wood can be further distinguished as being deposited: within the channel and subsequently accreted to the floodplain; marginal to the channel; on the floodplain during overbank flow; or on tributary fans. The mechanism of wood recruitment to a floodplain influences the spatial distribution of the wood across the floodplain and the proportion of wood pieces within jams, which in turn influences geomorphic and ecological effects of the floodplain wood. Using published studies of floodplain wood load for unmanaged river corridors, I hypothesize that the climate-controlled balance between forest primary productivity and decay rates of downed wood is the first-order control on floodplain large wood loads. Disturbance regime and wood recruitment mechanism are second-order controls on wood load and primary controls on the spatial distribution of large wood. Understanding of floodplain large wood can be applied to quantifying the effect of large wood on river corridors; river restoration; paleoenvironmental inferences; and estimation of organic carbon stock in river corridors. © 2019 John Wiley & Sons, Ltd.  相似文献   

10.
H. Marttila  B. Kløve 《水文研究》2014,28(17):4756-4765
Lowland catchments in Finland are intensively managed, promoting erosion and sedimentation that negatively affects aquatic environments. This study quantified fine‐grained bed sediment in the main channel and upstream headwaters of the River Sanginjoki (399.93 km2) catchment, Northern Finland, using remobilization sediment sampling during the ice‐free period (May 2010–December 2011). Average bed sediment storage in river was 1332 g m?2. Storage and seasonal variations were greater in small headwater areas (total bed sediment storage mean 1527 g m?2, range 122–6700 g m?2 at individual sites; storage of organic sediment: mean 414 g m?2, range 27–3159 g m?2) than in the main channel (total bed sediment storage: mean 1137 g m?2, range 61–4945 g m?2); storage of organic sediment: mean 329 g m?2, range 13–1938 g m?2). Average reach‐specific bed sediment storage increased from downstream to upstream tributaries. In main channel reaches, mean specific storage was 8.73 t km?1, and mean specific storage of organic sediment 2.45 t km?1, whereas in tributaries, it was 126.94 and 34.05 t km?1, respectively. Total fine‐grained bed sediment storage averaged 563 t in the main channel and 6831 t in the catchment. The proportion of mean organic matter at individual sites was 15–47% and organic carbon 4–455 g C m?2, with both being highest in small headwater tributaries. Main channel bed sediment storage comprised 52% of mean annual suspended sediment flux and stored organic carbon comprised 7% of mean annual total organic carbon load. This indicates the importance of small headwater brooks for temporary within‐catchment storage of bed sediment and organic carbon and the significance of fine‐grained sediment stored in channels for the suspended sediment budget of boreal lowland rivers. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

11.
Intertidal habitats provide numerous ecosystem services, including the sequestration and storage of carbon, a topic of great recent interest owing to land‐cover transitions and climate change. Mangrove forests and seagrass meadows form a continuum of intertidal habitats, alongside unvegetated mudflats and sandbars, however, studies that consider carbon stocks across these spatially‐linked, threatened ecosystems are limited world‐wide. This paper presents the results of a field‐based carbon stock assessment of aboveground, belowground and sediment organic carbon stock to a depth of 1 m at Chek Jawa, Singapore. It is the first study of ecosystem carbon stocks of both vegetated and unvegetated intertidal habitats in the tropics. Ecosystem carbon stocks were 497 Mg C ha‐1 in the mangrove forest and 138 Mg C ha‐1 in the seagrass meadow. Sediment organic carbon stock dominated the total storage in both habitats, constituting 62% and >99% in the mangrove forest and seagrass meadow, respectively. In the adjacent mudflat and sandbars, which had no vegetative components, sediment organic carbon stock ranged from 124–143 Mg C ha‐1, suggesting that unvegetated habitats have a carbon storage role on the same order of importance as seagrass meadows. This study reinforces the importance of sediment in carbon storage within the intertidal ecosystem, and demonstrates the need to consider unvegetated habitats in intertidal ‘blue carbon’ stock assessments. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

12.
We use field measurements and airborne LiDAR data to quantify the potential effects of valley geometry and large wood on channel erosional and depositional response to a large flood (estimated 150-year recurrence interval) in 2011 along a mountain stream. Topographic data along 3 km of Biscuit Brook in the Catskill Mountains, New York, USA reveal repeated downstream alternations between steep, narrow bedrock reaches and alluvial reaches that retain large wood, with wood loads as high as 1261 m3 ha−1. We hypothesized that, within alluvial reaches, geomorphic response to the flood, in the form of changes in bed elevation, net volume of sediment eroded or aggraded, and grain size, correlates with wood load. We hypothesized that greater wood load corresponds to lower modelled average velocity and less channel-bed erosion during the flood, and finer median bed grain size and a lower gradation coefficient of bed sediment. The results partly support this hypothesis. Wood results in lower reach-average modelled velocity for the 2011 flood, but the magnitude of change in channel-bed elevation after the 2011 flood among alluvial and bedrock reaches does not correlate with wood load. Wood load does correlate with changes in sediment volume and bed substrate, with finer grain size and smaller sediment gradation in reaches with more wood. The proportion of wood in jams is a stronger predictor of bed grain-size characteristics than is total wood load. We also see evidence of a threshold: greater wood load correlates with channel aggradation at wood loads exceeding approximately 200 m3 ha−1. In this mountain stream, abundant large wood in channel reaches with alluvial substrate creates lower velocity that results in finer bed material and, when wood load exceeds a threshold, reach scale increases in aggradation. This suggests that reintroducing small amounts of wood or one logjam for river restoration will have limited geomorphic effects. © 2020 John Wiley & Sons, Ltd.  相似文献   

13.
Floodplains are vital components of river ecosystems and play an important role in carbon cycling and storage at catchment and global scales. For efficient river management and conservation, it is critical to understand the functional role of spatiotemporally complex and dynamic habitat mosaics of river floodplains. Unfortunately, the fundamental understanding of mineralization and carbon flux patterns across complex floodplains is still fragmentary. In this study, respiratory potential (i.e., electron transport system activity [ETSA]) was quantified seasonally across different aquatic and terrestrial habitats (wetted channels, gravel bars, islands, riparian forests, and grasslands) of 2 Alpine floodplains differing in climate, altitude, discharge, flow alteration intensity, and land use (So?a [natural flow regime, 12% grassland area] and Urbach [mean annual discharge reduction by 30% due to water abstraction, 69% grassland area]). In situ respiration (R) was measured, and ETSA–R ratios were calculated to examine differences in exploitation intensity of the overall respiratory capacity among floodplain habitats and seasons. ETSA and R provided potential and actual estimates, respectively, of organic matter mineralization in the different floodplain habitats. Hierarchical linear regression across habitat types showed that organic matter, grain sizes <0.063 mm, and water content were the most important predictors of ETSA in both floodplains, and grain sizes 2–0.063 and >8 mm were also highly important for the So?a floodplain. The combination of ETSA and R measurements conducted in contrasting floodplains increased our understanding of the relationships between floodplain habitat heterogeneity, organic matter mineralization and human impacts, that is, structural–functional linkages in floodplains. These data are integral towards predicting changes in floodplain function in response to environmental alterations from increasing human pressures and environmental change.  相似文献   

14.
Flow regulation and water diversion for irrigation have considerably impacted the exchange of surface water between the Murray River and its floodplains. However, the way in which river regulation has impacted groundwater–surface water interactions is not completely understood, especially in regards to the salinization and accompanying vegetation dieback currently occurring in many of the floodplains. Groundwater–surface water interactions were studied over a 2 year period in the riparian area of a large floodplain (Hattah–Kulkyne, Victoria) using a combination of piezometric surface monitoring and environmental tracers (Cl−, δ2H, and δ18O). Despite being located in a local and regional groundwater discharge zone, the Murray River is a losing stream under low flow conditions at Hattah–Kulkyne. The discharge zone for local groundwater, regional groundwater and bank recharge is in the floodplain within ∼1 km of the river and is probably driven by high rates of transpiration by the riparian Eucalyptus camaldulensis woodland. Environmental tracers data suggest that the origin of groundwater is principally bank recharge in the riparian zone and a combination of diffuse rainfall recharge and localized floodwater recharge elsewhere in the floodplain. Although the Murray River was losing under low flows, bank discharge occurred during some flood recession periods. The way in which the water table responded to changes in river level was a function of the type of stream bank present, with point bars providing a better connection to the alluvial aquifer than the more common clay‐lined banks. Understanding the spatial variability in the hydraulic connection with the river channel and in vertical recharge following inundations will be critical to design effective salinity remediation strategies for large semi‐arid floodplains. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

15.
Stratigraphy is a fundamental component of floodplain heterogeneity and hydraulic conductivity and connectivity of alluvial aquifers, which affect hydrologic processes such as groundwater flow and hyporheic exchange. Watershed-scale hydrological models commonly simplify the sedimentology and stratigraphy of floodplains, neglecting natural floodplain heterogeneity and anisotropy. This study, conducted in the upper reach of the East River in the East River Basin, Colorado, USA, combines point-, meander-, and floodplain-scale data to determine key features of alluvial aquifers important for estimating hydrologic processes. We compare stratigraphy of two meanders with disparate geometries to explore floodplain heterogeneity and connectivity controls on flow and transport. Meander shape, orientation, and internal stratigraphy affected residence time estimates of laterally exchanged hyporheic water. Although the two meanders share a sediment source, vegetation, and climate, their divergent river migration histories resulted in contrasting meander hydrofacies. In turn, the extent and orientation of these elements controlled the effective hydraulic conductivity and, ultimately, estimates of groundwater transport and hyporheic residence times. Additionally, the meanders’ orientation relative to the valley gradient impacted the hydraulic gradient across the meanders—a key control of groundwater velocity. Lastly, we combine our field data with remotely sensed data and introduce a potential approach to estimate key hydrostratigraphic packages across floodplains. Prospective applications include contaminant transport studies, hyporheic models, and watershed models. © 2019 John Wiley & Sons, Ltd.  相似文献   

16.
Lake sedimentation has a fundamental impact on lake lifetime. In this paper, we show how sensitive calculation of the latter is to the quality of data available and assumptions made during analysis. Based on the collection of a large new dataset, we quantify the sediment masses (1) mobilized on the hillslopes draining towards Lake Tana (Ethiopia), (2) stored in the floodplains, (3) transported into the lake, (4) deposited in the lake and (5) delivered out from the lake so as to establish a sediment budget. In 2012–2013, suspended sediment concentration (SSC) and discharge measurements were made at 13 monitoring stations, including two lake outlets. Altogether, 4635 SSC samples were collected and sediment rating curves that account for land cover conditions and rainfall seasonality were established for the 11 river stations, and mean monthly SSC was calculated for the outlets. Effects of the floodplain on rivers' sediment yield (SY) were investigated using measurements at both sides of the floodplains. SY from ungauged rivers was assessed using a model that includes catchment area and rainfall, whereas bedload and direct sediment input from lake shores were estimated. As a result, the gross annual SY was c. 39.55 (± 0.15) Mt, dominantly from Gilgel Abay and Gumara Rivers. The 2.57 (± 0.17) Mt sediment deposited in floodplains indicate that the floodplains serve as an important sediment sink. Moreover, annually c. 1.09 Mt of sediment leaves the lake through the two outlets. Annual sediment deposition in the lake was c. 36.97 (± 0.22) Mt and organic matter accumulation was 2.15 Mt, with a mean sediment trapping efficiency of 97%. Furthermore, SSC and SY are generally higher at the beginning of the rainy season because soils in cultivated fields are bare and loose due to frequent ploughing and seedbed preparation. Later in the season, increased crop and vegetation cover lead to a decrease in sediment production. Based on the established sediment budget with average rainfall, the lifetime of Lake Tana was estimated as 764 to 1032 years, which is shorter than what was anticipated in earlier studies. The sedimentation rate of Lake Tana (11.7 ± 0.1 kg m?2 yr?1) is in line with the sedimentation rates of larger lakes in the world, like Lake Dongting and Lake Kivu. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

17.
Floodplains are depositional features of riverine landscapes that display complex sedimentation patterns that are amenable to multi‐scale approaches. We examined sedimentation in the Lower Balonne floodplain, Queensland, Australia, at three different spatial scales: the channel (103 km), floodplain process zone (10 km) and geomorphic unit (102 m) scales, and compared scale‐related patterns evident from stratigraphy with those evident from quantitative multivariate analysis. Three stratigraphic sequences were found in the Lower Balonne floodplain: generally fining upward, episodic fining upward, and mud‐dominated. Stratigraphical analysis revealed the detailed character of sedimentary sequences embedded within the scale patterns derived from multivariate analysis. Multivariate statistical analyses of a range of textural and geochemical data revealed different patterns of floodplain sedimentation at each scale. At the channel scale, sediment texture and geochemistry were more heterogeneous in the Culgoa River than in Briarie Creek. At the floodplain process zone scale clear patterns of sediment texture and geochemistry were observed along the upper, mid and lower floodplain process zones of Briarie Creek, but not along the Culgoa River. At the geomorphic unit scale, clear patterns of sediment texture and geochemistry were observed among the bank, buried channel and flat floodplain units of the Culgoa River, but were not as clear in Briarie Creek. Recognition of rivers as hierarchically organized systems is an emerging paradigm in river science. Our study supports this paradigm by demonstrating that different sedimentation patterns occur at different scales to reveal a hierarchically organized floodplain environment. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

18.
Relationships between the surface area and age of alluvial deposits were used to estimate the residence time of alluvium in the 2205 km2 Waipaoa River basin, New Zealand. The contemporary Waipaoa River is an efficient transporter of sediment to the continental shelf, but the basin has been characterized by rapid channel and valley aggradation in the historic period, and by extensive mid‐ to late Holocene alluvial storage in the lower reaches. The area‐weighted mean age of alluvial deposits in the lower part of the river basin is ～4400 yr. These deposits comprise terrace remnants isolated by downcutting, and Holocene to Recent sediments that are potentially remobilizable by the modern river. Even though the amount of storage is small relative to downstream transport, the majority of the potentially remobilizable alluvium is likely to remain in storage for >100 yr, and its half‐life (time for 50 per cent removal) is >2000 yr. Within the confines of the flfloodplain, the apparent ‘loss’ of older deposits is due primarily to burial, but losses of the most recent deposits are due almost entirely to remobilization (30–40 per cent), with the remainder preserved in the alluvial record for at least 104 yr. Most of this sediment is likely to remain in storage until there is a shift to a degradational state. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
This study provides the first detailed estimate of riverine organic carbon fluxes in British rivers, as well as highlighting major gaps in organic carbon data in national archives. Existing data on organic carbon and suspended solids concentrations collected between 1989 and 1993, during routine monitoring by the River Purification Boards (RPBs) in Scotland and the National River Authorities (NRAs) in England and Wales, were used with annual mean flows to estimate fluxes of dissolved and particulate organic carbon (DOC and POC) in British rivers. Riverine DOC exports during 1993 varied from 7·7–103·5 kg ha−1 year−1, with a median flux of 31·9 kg ha−1 year−1 in the 85 rivers for which data were available. There was a trend for DOC fluxes to increase from the south and east to the north and west. A predictive model based on mean soil carbon storage in 17 catchments, together with regional precipitation totals, explained 94% of the variation in the riverine DOC exports in 1993. This model was used to predict riverine DOC fluxes in regions where no organic carbon data were available. Calculated and predicted fluxes were combined to produce an estimate for exports of DOC to tidal waters in British rivers during 1993 of 0·68±0·07 Mt. Of this total, rivers in Scotland accounted for 53%, England 38% and Wales 9%. Scottish blanket peats would appear to be the largest single source of DOC exports in British rivers. An additional 0·20 Mt of organic carbon were estimated to have been exported in particulate form in 1993, approximately two–thirds of which was contributed by English rivers. It is suggested that riverine losses of organic carbon have the potential to affect the long-term dynamics of terrestrial organic carbon pools in Britain and that rivers may regulate increases in soil carbon pools brought about by climate change. © 1997 by John Wiley & Sons, Ltd.  相似文献   

20.
We analyzed variation of channel–floodplain suspended sediment exchange along a 140 km reach of the lower Amazon River for two decades (1995–2014). Daily sediment fluxes were determined by combining measured and estimated surface sediment concentrations with river–floodplain water exchanges computed with a two‐dimensional hydraulic model. The average annual inflow to the floodplain was 4088 ± 2017 Gg yr?1 and the outflow was 2251 ± 471 Gg yr?1, respectively. Prediction of average sediment accretion rate was twice the estimate from a previous study of this same reach and more than an order of magnitude lower than an estimate from an earlier regional scale study. The amount of water routed through the floodplain, which is sensitive to levee topography and increases exponentially with river discharge, was the main factor controlling the variation in total annual sediment inflow. Besides floodplain routing, the total annual sediment export depended on the increase in sediment concentration in lakes during floodplain drainage. The recent increasing amplitude of the Amazon River annual flood over two decades has caused a substantial shift in water and sediment river–floodplain exchanges. In the second decade (2005–2014), as the frequency of extreme floods increased, annual sediment inflow increased by 81% and net storage increased by 317% in relation to the previous decade (1995–2004). Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

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