Carbon loss by water erosion in drylands: implications from a study of vegetation change in the south‐west USA          下载免费PDF全文

R. E. Brazier  L. Turnbull  J. Wainwright  R. Bol 《水文研究》2014,28(4):2212-2222

Soil organic carbon (SOC) is an important component of the global carbon cycle yet is rarely quantified adequately in terms of its spatial variability resulting from losses of SOC due to erosion by water. Furthermore, in drylands, little is known about the effect of widespread vegetation change on changes in SOC stores and the potential for water erosion to redistribute SOC around the landscape especially during high‐magnitude run‐off events (flash floods). This study assesses the change in SOC stores across a shrub‐encroachment gradient in the Chihuahuan Desert of the south‐west USA. A robust estimate of SOC storage in surface soils is presented, indicating that more SOC is stored beneath vegetation than in bare soil areas. In addition, the change in SOC storage over a shrub‐encroachment gradient is shown to be nonlinear and highly variable within each vegetation type. Over the gradient of vegetation change, the heterogeneity of SOC increases, and newer carbon from C₃ plants becomes dominant. This increase in the heterogeneity of SOC is related to an increase in water erosion and SOC loss from inter‐shrub areas, which is self‐reinforcing. Shrub‐dominated drylands lose more than three times as much SOC as their grass counterparts. The implications of this study are twofold: (1) quantifying the effects of vegetation change on carbon loss via water erosion and the highly variable effects of land degradation on soil carbon stocks is critical. (2) If landscape‐scale understanding of carbon loss by water erosion in drylands is required, studies must characterize the heterogeneity of ecosystem structure and its effects on ecosystem function across ecotones subject to vegetation change. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Decoupling of nutrient and grazer impacts on a benthic estuarine diatom assemblage     

Anna R. Armitage  Vanessa L. Gonzalez  Peggy Fong   《Estuarine, Coastal and Shelf Science》2009,84(3):375-380

Strong interactions between top-down (consumptive) and bottom-up (resource supply) trophic factors occur in many aquatic communities, but these forces can act independently in some microphytobenthic communities. Within benthic estuarine diatom assemblages, the dynamics of these interactions and how they vary with abiotic environmental conditions are not well understood. We conducted a field experiment at two sites with varying habitat characteristics to investigate the interactive effects of grazers and nutrients on benthic estuarine diatoms. We crossed snail (Cerithidea californica) and nutrient (nitrogen and phosphorus) addition treatments in enclosures on a restored tidal sandflat and a reference tidal mudflat in Mugu Lagoon, southern California. We repeated the study in summer 2000 and spring 2001 to assess temporal variation in the interactions. Snails caused a large decrease in diatom relative abundance and biomass (estimated as surface area); nutrients increased diatom abundance but did not alter diatom biomass. Snails and nutrients both reduced average diatom length, although the nutrient effect was weaker and temporally variable, occurring in the reference mudflat in the spring. There were few interactions between snail and nutrient addition treatments, suggesting that links between top-down and bottom-up forces on the diatom community were weak. There were no consistent differences in diatom assemblage characteristics between the two study sites, despite marked differences in sediment grain size and other abiotic characteristics between the sites. The strong diatom response to herbivores and weaker responses to enrichment differed from the previous studies where cyanobacteria increased in response to nutrient enrichment, further dissolving the “black box” perception of microphytobenthic communities.  相似文献   

Spatial and temporal changes in estuarine water quality during a post-flood hypoxic event     

Vanessa N.L. Wong  Scott G. Johnston  Richard T. Bush  Leigh A. Sullivan  Christina Clay  Edward D. Burton  Peter G. Slavich 《Estuarine, Coastal and Shelf Science》2010

A major fish kill occurred in the Richmond River estuary in January 2008 due to oxygen depletion following extensive overbank flooding. This paper examines spatial and temporal changes in the chemistry of main channel waters, thereby identifying the primary sources of deoxygenating water. Over 40 km of the mid- to lower estuary main channel was deoxygenated within seven days of the flood peak. Hypoxia was confined to downstream of the confluences with mid-estuary backswamp basins and occurred during the later phase of the flood recession. Water chemistry at key locations in the estuary indicated elevated concentrations of redox sensitive species associated with acid sulfate soils (ASS) during the hypoxic period. Peak concentrations of Fe²⁺ up to 18.2 μmol L⁻¹, dissolved Mn up to 4.3 μmol L⁻¹, chemical oxygen demand (COD) up to 2052 μmol L⁻¹, dissolved organic carbon (DOC) up to 960 μmol L⁻¹ and elemental S⁰ up to 4.7 μmol L⁻¹ were found in the backswamp discharge confluences and mid-estuary main channel locations. The geochemical signature of main channel floodwaters identifies anaerobic decomposition of floodplain vegetation in ASS backswamps as a primary process leading to generation of hypoxic waters. The transport of these hypoxic floodwaters to the estuary has been accelerated and prolonged by extensive floodplain drainage, thereby enhancing the magnitude and duration of estuarine deoxygenation.  相似文献   

Nitrogen and phosphorus dynamics during runoff events over a transition from grassland to shrubland in the south‐western United States     

Laura Turnbull  John Wainwright  Richard E. Brazier 《水文研究》2011,25(1):1-17

During the last 150 years, land degradation across the semi‐arid grasslands of the south‐western United States has been associated with an increase in runoff and erosion. Concurrent with this increase in runoff and erosion is a loss of nitrogen (N) and phosphorus (P), which are plant‐essential nutrients. This study investigates the runoff‐driven redistribution and loss of dissolved and particulate‐bound N and P that occurs during natural runoff events over a trajectory of degradation, from grassland to degraded shrubland, in central New Mexico. Runoff‐driven nutrient dynamics were monitored at four stages over a transition from grassland to shrubland, for naturally occurring rainfall events over 10 × 30 m bounded runoff plots. Results show that particulate‐bound forms of N and P are responsible for most of N and P lost from the plots due to erosion occurring during runoff events. Results suggest that for high‐magnitude rainfall events, the output of N and P from the plots may greatly exceed the amount input into the plots, particularly over shrub‐dominated plots where erosion rates are higher. As these results only become apparent when monitoring these processes over larger hillslope plots, it is important to recognize that processes of nutrient cycling related to the islands of fertility hypothesis may have previously been overstated when observed only at smaller spatial scales. Thus, the progressive degradation of semi‐arid grassland ecosystems across the south‐western United States and other semi‐arid ecosystems worldwide has the potential to affect N and P cycling significantly through an increase in nutrient redistribution and loss in runoff. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Beaver dams attenuate flow: A multi-site study     

Alan Puttock  Hugh A. Graham  Josie Ashe  David J. Luscombe  Richard E. Brazier 《水文研究》2021,35(2):e14017

Beavers can profoundly alter riparian environments, most conspicuously by creating dams and wetlands. Eurasian beaver (Castor fiber) populations are increasing and it has been suggested they could play a role in the provision of multiple ecosystem services, including natural flood management. Research at different scales, in contrasting ecosystems is required to establish to what extent beavers can impact on flood regimes. Therefore, this study determines whether flow regimes and flow responses to storm events were altered following the building of beaver dams and whether a flow attenuation effect could be significantly attributed to beaver activity. Four sites were monitored where beavers have been reintroduced in England. Continuous monitoring of hydrology, before and after beaver impacts, was undertaken on streams where beavers built sequences of dams. Stream orders ranged from 2nd to 4th, in both agricultural and forest-dominated catchments. Analysis of >1000 storm events, across four sites showed an overall trend of reduced total stormflow, increased peak rainfall to peak flow lag times and reduced peak flows, all suggesting flow attenuation, following beaver impacts. Additionally, reduced high flow to low flow ratios indicated that flow regimes were overall becoming less “flashy” following beaver reintroduction. Statistical analysis, showed the effect of beaver to be statistically significant in reducing peak flows with estimated overall reductions in peak flows from −0.359 to −0.065 m³ s⁻¹ across sites. Analysis showed spatial and temporal variability in the hydrological response to beaver between sites, depending on the level of impact and seasonality. Critically, the effect of beavers in reducing peak flows persists for the largest storms monitored, showing that even in wet conditions, beaver dams can attenuate average flood flows by up to ca. 60%. This research indicates that beavers could play a role in delivering natural flood management.  相似文献   

Geoarchaeological evidence of a Chola‐period tsunami from an ancient port at Kaveripattinam on the southeastern coast of India     

C.P. Rajendran  Kusala Rajendran  S. Srinivasalu  Vanessa Andrade  P. Aravazhi  Jaishri Sanwal 《Geoarchaeology》2011,26(6):867-887

Literature of the ancient Chola Dynasty (A.D. 9th–11th centuries) of South India and recent archaeological excavations allude to a sea flood that crippled the ancient port at Kaveripattinam, a trading hub for Southeast Asia, and probably affected the entire South Indian coast, analogous to the 2004 Indian Ocean tsunami impact. We present sedimentary evidence from an archaeological site to validate the textual references to this early medieval event. A sandy layer showing bed forms representing high‐energy conditions, possibly generated by a seaborne wave, was identified at the Kaveripattinam coast of Tamil Nadu, South India. Its sedimentary characteristics include hummocky cross‐stratification, convolute lamination with heavy minerals, rip‐up clasts, an erosional contact with the underlying mud bed, and a landward thinning geometry. Admixed with 1000‐year‐old Chola period artifacts, it provided an optically stimulated luminescence age of 1091 ± 66 yr and a thermoluminescence age of 993 ± 73 yr for the embedded pottery sherds. The dates of these proxies converge around 1000 yr B.P., correlative of an ancient tsunami reported from elsewhere along the Indian Ocean coasts. © 2011 Wiley Periodicals, Inc.  相似文献   

AN EXPERIMENT IN ADJUSTMENTS, USING SUPER-WIDE ANGLE PHOTOGRAPHY TAKEN FOR TOPOGRAPHIC MAPPING     

H. H. Brazier  D. Read 《The Photogrammetric Record》1970,6(35):452-458

The paper describes an experiment using three different methods for the production of control for topographic mapping from super-wide angle photography. The result showed that aerial triangulation by independent models observed on a Wild A9 would show economic advantages in cartographic effort required, control requirements, and accuracy attained in contouring. The experiment also indicated that great benefit in heighting accuracy is derived from the addition of tie strips flown at right angles to the main photographic cover at a suitable interval and that heights supplied by airborne profile recorder are not sufficiently accurate to be economically advantageous where close interval contours are a requirement.  相似文献   

Water Quality Improvements in Liverpool Docks: The Role of Filter Feeders in Algal and Nutrient Dynamics     

Stephen B.  Wilkinson  Weizhong  Zheng  Janette R.  Allen  Nicola J.  Fielding  Vanessa C.  Wanstall  George  Russell Stephen J.  Hawkins 《Marine Ecology》1996,17(1-3):197-211

Abstract. The redevelopment of disused docks around Liverpool into areas suitable for shops, offices, housing and recreational watersports has necessitated the maintenance of good water quality in these areas. The main source of water to the docks is the River Mersey, which contains high concentrations of nutrients, encouraging algal blooms - including potentially nuisance species - in the enclosed dock basins. Since 1988 an extensive monitoring programme has been run sampling the hydrography, plankton and benthos of the docks. During this period there has been an improvement in water quality, including a reduction in summer phytoplankton biomass and anoxic bottom water. There are strong indications that phytoplankton biomass has been severely reduced by the filter feeding of Mytifus edulis . Changes in the composition of the benthic community since 1988 suggest that the large population of M. edulis is now suffering from limited recruitment. The long-term development and stability of the system is discussed with reference to community succession and its link to ecosystem functioning.  相似文献   

Pathways of runoff and sediment transfer in small agricultural catchments     

C. Deasy  R. E. Brazier  A. L. Heathwaite  R. Hodgkinson 《水文研究》2009,23(9):1349-1358

Simultaneous field monitoring of runoff and suspended sediment loads from a 30 ha, artificially‐drained, mixed‐agricultural catchment in Herefordshire, UK indicates field drains are the dominant pathway for the transfer of runoff and sediment to the stream. Surface runoff pathways draining 6·2% of the catchment area transported around 1% of the catchment sediment load, while subsurface runoff in field drains draining 26·5% of the catchment transported around 24% of the sediment load. The explanations offered here for the dominance of drainflow—the spatial limitation of surface runoff generation and low hillslope‐stream connectivity of surface runoff compared with subsurface runoff—are also likely to apply to other artificially‐drained lowland agricultural catchments in the UK. These catchments are usually on poorly‐drained soils, and land management can have a considerable effect on the operation of runoff pathways and the transfer of sediment from hillslope to stream. As a result, subsurface inputs may also dominate sediment transfers in other underdrained catchments. The focus on sediment and pollutant losses via surface runoff pathways means that pollution inputs from subsurface, preferential pathways have been unfairly neglected, and it may be more important to focus on subsurface sediment and sediment‐associated pollution inputs for mitigation rather than inputs from surface pathways. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Is sediment delivery a fallacy? Reply     

Anthony J. Parsons  John Wainwright  Richard E. Brazier  D. Mark Powell 《地球表面变化过程与地形》2008,33(10):1630-1631

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