Assessment of detachment and sediment transport capacity of runoff by field experiments on a silt loam soil   总被引：2，自引：0，他引：2  

W. Schiettecatte  K. Verbist  D. Gabriels 《地球表面变化过程与地形》2008,33(8):1302-1314

The detachment capacity (D_c) and transport capacity (T_c) of overland flow are important variables in the assessment of soil erosion. They determine respectively the lower and upper limit of sediment transport by runoff and therefore control detachment and deposition pro‐cesses. In this study, the detachment and transport capacity of runoff was investigated by rainfall simulations and overland flow experiments on small field plots. On the bare field plots, it was found that T_c was strongly related to total runoff discharge. This was also observed for the plots covered by maize residues, but T_c was less due to the lower runoff velocity. A simple regression equation was derived to estimate T_c for both bare and covered soil. Comparing our observations with T_c equations mentioned in the literature revealed that T_c equations based on laboratory experiments overestimated, on average, our measurements. Although T_c can be assessed more easily in laboratory experiments, the applicability of the results to field conditions remains questionable. Detachment by runoff was also related to total runoff discharge. The D_c values were, however, 4–50 times smaller than the T_c at corresponding high and low runoff discharge. This indicates that detachment by runoff constitutes only part of the transported sediment. Interrill erosion supplies an important additional amount of sediment. In this study, however, only sealed soils were considered. In the case of freshly tilled, loose soils, the D_c of runoff may be larger, resulting in a larger contribution to the total soil loss. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Biogeochemical study of a coccolithophore bloom in the northern Bay of Biscay (NE Atlantic Ocean) in June 2004     

J. Harlay  A.V. Borges  C. Van Der Zee  B. Delille  R.H.M. Godoi  L.-S. Schiettecatte  N. Roevros  K. Aerts  P.-E. Lapernat  L. Rebreanu  S. Groom  M.-H. Daro  R. Van Grieken  L. Chou 《Progress in Oceanography》2010,86(3-4):317-336

The present paper synthesizes data obtained during a multidisciplinary cruise carried out in June 2004 at the continental margin of the northern Bay of Biscay. The data-set allows to describe the different stages of a coccolithophore bloom dominated by Emiliania huxleyi. The cruise was carried out after the main spring phytoplankton bloom that started in mid-April and peaked in mid-May. Consequently, low phosphate (PO₄ < 0.2 μM) and silicate (DSi < 2.0 μM) concentrations, low partial pressure of carbon dioxide (pCO₂) and high calcite saturation degree in surface waters combined with thermal stratification, probably favoured the blooming of coccolithophores. During the period of the year our cruise was carried out, internal tides induce enhanced vertical mixing at the continental shelf break leading to the injection of inorganic nutrients to surface waters that probably trigger the bloom. The bloom developed as the water-column stratified and as the water mass was advected over the continental shelf, following the general residual circulation in the area. The most developed phase of the bloom was sampled in a remote sensed high reflectance (HR) patch over the continental shelf that was characterized by low chlorophyll-a (Chl-a) concentration in surface waters (<1.0 μg L^?1), high particulate inorganic carbon (PIC) concentration (～8 μmol L^?1) and coccolithophore abundance up to 57 × 10⁶ cells L^?1. Transparent exopolymer particles (TEP) concentrations ranged between 15 and 75 μg C L^?1 and carbon content of TEP represented up to 26% of the particulate organic carbon (POC; maximum concentration of 15.5 μmol L^?1 in the upper 40 m). Integrated primary production (PP) ranged between 210 and 680 mg C m^?2 d^?1 and integrated calcification (CAL) ranged between 14 and 140 mg C m^?2 d^?1, within the range of PP and CAL values previously reported during coccolithophore blooms in open and shelf waters of the North Atlantic Ocean. Bacterial protein production (BPP) measurements in surface waters (0.3–0.7 μg C L^?1 h^?1) were much higher than those reported during early phases of coccolithophore blooms in natural conditions, but similar to those during peak and declining coocolithophorid blooms reported in mesocosms. Total alkalinity anomalies with respect to conservative mixing (ΔTA) down to ?49 μmol kg^?1 are consistent with the occurrence of biogenic precipitation of calcite, while pCO₂ remained 15–107 μatm lower than atmospheric equilibrium (372 μatm). The correlation between ΔTA and pCO₂ suggested that pCO₂ increased in part due to calcification, but this increase was insufficient to overcome the background under-saturation of CO₂. This is related to the biogeochemical history of the water masses due to net carbon fixation by the successive phytoplankton blooms in the area prior to the cruise, hence, the investigated area remained a sink for atmospheric CO₂ despite calcification.  相似文献   

Variability of the gas transfer velocity of CO<Subscript>2</Subscript> in a macrotidal estuary (the Scheldt)   总被引：1，自引：0，他引：1  

Alberto?Vieira?BorgesEmail author  Jean-Pierre?Vanderborght  Laure-Sophie?Schiettecatte  Frédéric?Gazeau  Sarah?Ferrón-Smith  Bruno?Delille  Michel?Frankignoulle 《Estuaries and Coasts》2004,27(4):593-603

We report a large set of 295 interfacial carbon dioxide (CO₂) flux measurements obtained in the Scheldt estuary in November 2002 and April 2003, using the floating chamber method. From concomitant measurements of the air-water CO₂ gradient, we computed the gas transfer velocity of CO₂. The gas transfer velocity is well correlated to wind speed and a simple linear regression function gives the most consistent fit to the data. Based on water current measurements, we estimated the contribution of water current induced turbulence to the gas transfer velocity, using the conceptual relationship of O'Connor and Dobbins (1958). This allowed us to construct an empirical relationship to compute the gas transfer velocity of CO₂ that accounts for the contribution of wind and water current. Based on this relationship, the spatial and temporal variability of the gas transfer velocity in the Scheldt estuary was investigated. Water currents contribute significantly to the gas transfer velocity, but the spatial and temporal variability (from daily to seasonal scales) is mainly related to wind speed variability.  相似文献   

Planktonic and whole system metabolism in a nutrient-rich estuary (the Scheldt estuary)     

Frédéric Gazeau  Jean-Pierre Gattuso  Jack J. Middelburg  Natacha Brion  Laure-Sophie Schiettecatte  Michel Frankignoulle  Alberto Vieira Borges 《Estuaries and Coasts》2005,28(6):868-883

Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the 1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m⁻² d⁻¹) decreasing seaward (22–37 mmol C m⁻² d⁻¹). A significant decrease of NIT was observed with regard to previous investigations although this process still represents up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time in the estuary with values ranging from −300 to 165 mmol C m⁻² d⁻¹. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published benthic metabolic rates. A NEP of −39±8 mmol C m⁻² d⁻¹ was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m⁻² d⁻¹) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear.  相似文献   

Influence of age, sex and body condition on zinc, copper, cadmium and metallothioneins in common guillemots (Uria aalge) stranded at the Belgian coast.     

V Debacker  L S Schiettecatte  T Jauniaux  J M Bouquegneau 《Marine environmental research》2001,52(5):427-444

The common guillemots, Uria aalge, found stranded at the Belgian coast, display high levels of Cu in both liver and kidneys. The condition index of the animals, defined as the ratio of liver to kidneys mass (Wenzel & Adelung, 1996, The suitability of oiled Guillemots (Uria aalge) as monitoring organisms for geographical comparisons of trace element contaminants. Archives of Environmental Contamination and Toxicology, 31, 368-377), influences both the metal concentration and its binding to metallothioneins (MT): the lower the condition index, the more emaciated the animals, and the higher the total Cu concentration and the concentration of Cu bound to MT. In less robust individuals, our results suggest that Cu could displace Zn from MT, rendering the Zn ions available to induce a new MT synthesis. Sex-related effects also emerged as significantly higher hepatic MT as well as Cu- and Zn-MT concentrations were found in emaciated male guillemots compared to females. In both organs, Cd concentrations remained low and typically demonstrated an age-dependent renal accumulation, with no noticeable effect of the condition index. As a whole, these results suggest that, for guillemots found stranded at the Belgian coast. Cu binding to hepatic and renal MT could function as a protective mechanism, rendering the metal ions unavailable to exert any cytotoxic activity.  相似文献   

Mechanisms controlling the air–sea flux in the North Sea     

A.E.F. Prowe  Helmuth Thomas  Johannes Ptsch  Wilfried Kühn  Yann Bozec  Laure-Sophie Schiettecatte  Alberto V. Borges  Hein J.W. de Baar 《Continental Shelf Research》2009,29(15):1801-1808

The mechanisms driving the air–sea exchange of carbon dioxide (CO₂) in the North Sea are investigated using the three-dimensional coupled physical–biogeochemical model ECOHAM (ECOlogical-model, HAMburg). We validate our simulations using field data for the years 2001–2002 and identify the controls of the air–sea CO₂ flux for two locations representative for the North Sea's biogeochemical provinces. In the seasonally stratified northern region, net CO₂ uptake is high () due to high net community production (NCP) in the surface water. Overflow production releasing semi-labile dissolved organic carbon needs to be considered for a realistic simulation of the low dissolved inorganic carbon (DIC) concentrations observed during summer. This biologically driven carbon drawdown outcompetes the temperature-driven rise in CO₂ partial pressure (pCO₂) during the productive season. In contrast, the permanently mixed southern region is a weak net CO₂ source (). NCP is generally low except for the spring bloom because remineralization parallels primary production. Here, the pCO₂ appears to be controlled by temperature.  相似文献   

Nitrogen and carbon cycling in the North Sea and exchange with the North Atlantic—A model study,Part II: Carbon budget and fluxes     

Wilfried Kühn  Johannes Pätsch  Helmuth Thomas  Alberto V. Borges  Laure-Sophie Schiettecatte  Yann Bozec  A.E. Friederike Prowe 《Continental Shelf Research》2010

The 3-d coupled physical–biogeochemical model ECOHAM (version 3) was applied to the Northwest-European Shelf (47°41′–63°53′N, 15°5′W–13°55′E) for the years 1993–1996. Carbon fluxes were calculated for the years 1995 and 1996 for the inner shelf region, the North Sea (511,725 km²). This period was chosen because it corresponds to a shift from a very high winter-time North Atlantic Oscillation Index (NAOI) in 1994/1995, to an extremely low one in 1995/1996, with consequences for the North Sea physics and biogeochemistry. During the first half of 1996, the observed mean SST was about 1 °C lower than in 1995; in the southern part of the North Sea the difference was even larger (up to 3 °C). Due to a different wind regime, the normally prevailing anti-clockwise circulation, as found in winter 1995, was replaced by more complicated circulation patterns in winter 1996. Decreased precipitation over the drainage area of the continental rivers led to a reduction in the total (inorganic and organic) riverine carbon load to the North Sea from 476 Gmol C yr⁻¹ in 1995 to 340 Gmol C yr⁻¹ in 1996. In addition, the North Sea took up 503 Gmol C yr⁻¹ of CO₂ from the atmosphere. According to our calculations, the North Sea was a sink for atmospheric CO₂, at a rate of 0.98 mol C m⁻² yr⁻¹, for both years. The North Sea is divided into two sub-systems: the shallow southern North Sea (SNS; 190,765 km²) and the deeper northern North Sea (NNS; 320,960 km²). According to our findings the SNS is a net-autotrophic system (net ecosystem production NEP>0) but released CO₂ to the atmosphere: 159 Gmol C yr⁻¹ in 1995 and 59 Gmol C yr⁻¹ in 1996. There, the temperature-driven release of CO₂ outcompetes the biological CO₂ drawdown. In the NNS, where respiratory processes prevail (NEP<0), 662 and 562 Gmol C yr⁻¹ were taken up from the atmosphere in 1995 and 1996, respectively. Stratification separates the productive, upper layer from the deeper layers of the water column where respiration/remineralization takes place. Duration and stability of the stratification are determined by the meteorological conditions, in relation to the NAO. Our results suggest that this mechanism controlling the nutrient supply to the upper layer in the northern and central North Sea has a larger impact on the carbon fluxes than changes in lateral transport due to NAOI variations. The North Sea as a whole imports organic carbon and exports inorganic carbon across the outer boundaries, and was found to be net-heterotrophic, more markedly in 1996 than in 1995.  相似文献