Estimating resource costs of compliance with EU WFD ecological status requirements at the river basin scale     

Niels Riegels  Roar Jensen  Lisa Bensasson  Stella Banou  Flemming Møller  Peter Bauer-Gottwein 《Journal of Hydrology》2011,396(3-4):197-214

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Landslide impact on organic carbon cycling in a temperate montane forest     

Robert G. Hilton  Patrick Meunier  Niels Hovius  Peter J. Bellingham  Albert Galy 《地球表面变化过程与地形》2011,36(12):1670-1679

In humid, forested mountain belts, bedrock landslides can harvest organic carbon from above ground biomass and soil (OC_modern) while acting to refresh the landscape surface and turnover forest ecosystems. Here the impact of landslides on organic carbon cycling in 13 river catchments spanning the length of the western Southern Alps, New Zealand is assessed over four decades. Spatial and temporal landslide maps are combined with the observed distribution and measured variability of hillslope OC_modern stocks. On average, it is estimated that landslides mobilized 7.6 ± 2.9 tC km^?2 yr^?1 of OC_modern, ~30% of which was delivered to river channels. Comparison with published estimates of OC_modern export in river suspended load suggests additional erosion of OC_modern by small, shallow landslides or overland flow in catchments. The exported OC_modern may contribute to geological carbon sequestration if buried in sedimentary deposits. Landslides may have also contributed to carbon sequestration over shorter timescales (<100 years). 5.4 ± 3.0 tC km^?2 yr^?1 of the eroded OC_modern was retained on hillslopes, representing a net‐carbon sink following re‐vegetation of scar surfaces. In addition, it was found that landslides caused rapid turnover of the landscape, with rates of 0.3% of the surface area per decade. High rates of net ecosystem productivity were measured in this forest of 94 ± 11 tC km^?2 yr^?1, which is consistent with rapid landscape turnover suppressing ecosystem retrogression. Landslide‐OC_modern yields and rates of turnover vary between river catchments and appear to be controlled by gradients in climate (precipitation) and geomorphology (rock exhumation rate, topographic slope). Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Comparing biodiversity between protected savanna and adjacent non-protected farmland in the southern Kalahari     

Bernd Wasiolka  Niels Blaum 《Journal of Arid Environments》2011,75(9):836-841

In this study we investigated the effect of different land use options (wildlife versus livestock) on species richness of plants and reptiles in the protected Kgalagadi Transfrontier Park (KTP) versus adjacent non-protected farmland within the same savanna habitat type (Aoub dune veld) in the southern Kalahari, South Africa. Our results show that both plant and reptile species richness as well as plant cover and reptile abundance was significantly higher in the protected KTP than in the non-protected farmland. The higher proportion of shrub but lower proportions of perennial grass cover, herb cover, and herb species richness in the farmland can be explained by higher stocking rates and the differences in feeding behaviour between native wild ungulates (e.g. Antidorcas marsupialis, Oryx gazella) and livestock (mainly sheep). The reptile’s prey availability and microhabitats (perennial grass tussocks and rodent burrows) for thermoregulation and protection against predators were significantly lower in the farmland. To conclude, our results clearly show that long term effects of different land use options (wildlife in protected KTP versus extensive livestock production in the non-protected farmland) even within the same habitat type have led to significant changes in vegetation composition, availability of microhabitat structures and in the reptile community.  相似文献   

Numerical runout simulation of debris avalanches in the Faroe Islands, North Atlantic Ocean   总被引：1，自引：1，他引：0  

Mads-Peter J Dahl  Peter Gauer  Bjørn G Kalsnes  Lis E Mortensen  Niels H Jensen  Anita Veihe 《Landslides》2013,10(5):623-631

The Faroe Islands in the North Atlantic Ocean are susceptible to flow-type landslides in coarse-grained highly organic colluvium. Following several hazardous debris avalanche events, research work has been initiated to quantify landslide risk. A central task in this work is to predict landslide runout behavior. From numerical simulation of four debris avalanches, this study provides a first screening of which rheology and appertaining input parameters best predict runout behavior of debris avalanches in the Faroe Islands. Three rheologies (frictional, Voellmy, and Bingham) are selected and used for individual back analysis of the events in the numerical models BING and DAN3D. A best fit rheology is selected from comparing predicted and observed landslide runout behavior. General back analysis to identify the optimal input parameters for the chosen rheology is performed by cross validation, where each debris avalanche is modeled with input parameters from the three other events. Optimal input parameters are found from the model run producing the most accurate runout length and velocity. The Bingham is selected as the best fit rheology, a result differing from similar studies of coarse-grained landslides. A reason for why particularly the frictional rheology proves unsuitable is its tendency to produce too long runout lengths of the low-weight runout material, a result showing important limitations for using the frictional rheology in DAN3D. Optimal Bingham input parameters are τ _y ?=?980 Pa and μ _b ?=?117 Pa/s. However, future studies performed in 2D models are needed for precise parameterization before results can be used for landslide risk assessment.  相似文献   

A demonstration of the importance of bedload transport for fluvial bedrock erosion and knickpoint propagation     

Kristen L. Cook  Jens M. Turowski  Niels Hovius 《地球表面变化过程与地形》2013,38(7):683-695

We provide field evidence for the role of bedload in driving fluvial incision and knickpoint propagation. Using aerial photographs, field surveys, and hydrological data, we constrain the incision history of a bedrock gorge 1200 m long and up to 20 m deep cut by Da'an River in western Taiwan. This reach of the river experienced 10 m of uplift during the 1999 Chi‐Chi earthquake. For five years following the earthquake, bedload was prevented from entering the uplift zone, the knickpoint was static and little incision took place. Bedload transport across the uplift zone resumed in 2004, initiating extremely rapid incision, with 620 m of knickpoint propagation and up to 20 m of downcutting by 2008. This change highlights the relative inefficiency of suspended sediment and the dominant role of bedload as a tool for fluvial erosion and knickpoint propagation. Once bedload tools became available, knickpoint propagation was influenced by geological structure, lithology, and drainage organization. In particular, a change in dip of the sandstone beds at the site caused a decrease of knickpoint propagation velocity. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

En fluvisol i Sydsjælland     

Cand. Agro. Niels J. Christoffersen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):79-84

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Making a living in the cocoa frontier,Western Ghana: Diversifying incomes in a cocoa economy     

Michael Helt Knudsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):29-44

Geografisk Tidsskrift, Danish Journal of Geography 107(2):29–44, 2007

The literature on livelihoods in rural Africa has for the past decade documented and discussed the growing importance of non-farm income for rural livelihoods and often linked this to an increasing divorce of rural livelihoods from farming and land. This paper challenges the view that the increasing importance of income earned on non-farm activities is a direct expression of processes of deagrari-anisation. Drawing on empirical evidence from recent research in the Ghanaian cocoa frontier, the paper shows that a growing importance of income from non-farm activities is evident, but that incomefrom cocoa is still the determining factor for most households' income and thereby for the demand for non-farm goods and investment in the non-farm sector. By identifying two overall factors explaining the level of income diversification, the paper questions how generally applicable processes of deagrarianisation are in the Ghanaian case. Firstly, the actual crop cultivated and its price and marketing possibilities are of great importance for a farmer's choice to engage and stay in the agricultural sector or to diversify into non-farm activities. Secondly, different dynamics are evident between settlements dominated by either migrant or indigenous households, mainly due to unequal access to land. The paper argues that what on a general scale may look like processes of deagrarianisation during the last decade to a large extent can be explained by migrants without access to land who engage full-time in the nonfarm sector and by cocoa farmers diversifying their incomes, but not leaving a deteriorated agriculture.  相似文献   

The use of salinity contrast for density difference compensation to improve the thermal recovery efficiency in high-temperature aquifer thermal energy storage systems     

Jan H. van Lopik  Niels Hartog  Willem Jan Zaadnoordijk 《Hydrogeology Journal》2016,24(5):1255-1271

The efficiency of heat recovery in high-temperature (>60 °C) aquifer thermal energy storage (HT-ATES) systems is limited due to the buoyancy of the injected hot water. This study investigates the potential to improve the efficiency through compensation of the density difference by increased salinity of the injected hot water for a single injection-recovery well scheme. The proposed method was tested through numerical modeling with SEAWATv4, considering seasonal HT-ATES with four consecutive injection-storage-recovery cycles. Recovery efficiencies for the consecutive cycles were investigated for six cases with three simulated scenarios: (a) regular HT-ATES, (b) HT-ATES with density difference compensation using saline water, and (c) theoretical regular HT-ATES without free thermal convection. For the reference case, in which 80 °C water was injected into a high-permeability aquifer, regular HT-ATES had an efficiency of 0.40 after four consecutive recovery cycles. The density difference compensation method resulted in an efficiency of 0.69, approximating the theoretical case (0.76). Sensitivity analysis showed that the net efficiency increase by using the density difference compensation method instead of regular HT-ATES is greater for higher aquifer hydraulic conductivity, larger temperature difference between injection water and ambient groundwater, smaller injection volume, and larger aquifer thickness. This means that density difference compensation allows the application of HT-ATES in thicker, more permeable aquifers and with larger temperatures than would be considered for regular HT-ATES systems.  相似文献   

The geography of urban greenhouse gas emissions in Asia: A regional analysis     

Peter J. Marcotullio  Andrea Sarzynski  Jochen Albrecht  Niels Schulz 《Global Environmental Change》2012,22(4):944-958

This paper aims to advance two objectives: (1) identify and explore greenhouse gas emissions from urban areas in Asia at the regional level; and (2) explore covariates of urban greenhouse gas emissions. We use the Emissions Database for Global Atmospheric Research estimates for carbon dioxide, methane, nitrous oxide, and sulfur hexafluoride from 14 source activities for the year 2000, which are allocated on a 1/10° global grid. We extract emissions for 3535 urban extents all with populations over 50,000, accounting for approximately 91% of the region's urban population. We use regression analysis to associate emissions with urban area and growth, economic, and biophysical characteristics. Our findings suggest that urban areas account for between 30 and 38% of total anthropogenic greenhouse gas emissions for the region and that emission per capita averages from urban areas are lower than those at the national level. Important covariates for total urban greenhouse gas emissions include population size, density and growth rate, income per capita, development status and elevation. This is a first and preliminary assessment of regional baseline trends using these data and this top-down analysis.  相似文献   

Environmental reconstructions of Eemian Stage interglacial marine records in the Lower Vistula area,southern Baltic Sea     

Karen Luise Knudsen  Hui Jiang  Philip L. Gibbard  Peter Kristensen  Marit‐Solveig Seidenkrantz  Zofia Janczyk‐Kopikowa  Leszek Marks 《Boreas: An International Journal of Quaternary Research》2012,41(2):209-234

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