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1.
In this article we evaluate the potential use of Cladonia foliacea tissue N content, C:N ratio, and phosphomonoesterase (PME) activity as biomarkers of N deposition by means of a field experiment. In order to do this, we continuously added NH4NO3 to a semi-arid shrubland at four rates: 0, 10, 20 and 50 kg N ha−1 yr−1 starting in October 2007. Tissue N content and C:N ratios, considered as N stress indicators, significantly increased and decreased, respectively, after 1.5 years. The response found suggests N saturation above 20 kg N ha−1 yr−1. After 2.5 years, extracellular PME activity increased with 20 kg N ha−1 yr−1 and this was attributed to an induced nutritional (N to P) imbalance. Above this threshold, PME significantly decreased as a consequence of the physiological stress caused by extra N. Effects on PME were dependent on the soil properties (pH and Ca and Mg availability) experienced by C. foliacea. PME response suggests a critical load of ∼26.4 kg N ha−1 yr−1 (20 kg N ha−1 yr−1 + background) for this lichen. Further tissue chemistry and PME evaluations in C. foliacea and soil surveys conducted along wide N deposition gradients will confirm the potential use of this species as a biomonitor of N pollution and the importance of soil properties on its ability to respond to atmospheric reactive N.  相似文献   

2.
Trace metals and polycyclic aromatic hydrocarbons (PAH) were analyzed in sediment cores from three central Alberta lakes to determine the contributions of local coal-fired power plants to contaminant loadings. In Wabamun Lake, with four power plants built since 1950 within a 35-km radius, sediment concentrations of mercury, copper, lead, arsenic and selenium have increased by 1.2- to 4-fold. Trace metal enrichments were less pronounced in Lac Ste. Anne and Pigeon Lake, situated 20 km north and 70 km south of Wabamun Lake, respectively. Total Hg flux to Wabamun Lake sediments (21–32μg m−2 yr−1) has increased 6-fold since 1950, compared to 2- and 1.5-fold increases in Lac Ste. Anne and Pigeon Lake, respectively, since circa 1900. Total PAH flux to surface sediments was 730–1100μg m−2 yr−1 in Wabamun Lake, 290–420μg m−2 yr−1 in Lac Ste. Anne, and 140–240μg m−2 yr−1 in Pigeon Lake. Without adoption of pollution-abatement technology that compensates for increases in generating capacity, continued expansion of coal-burning industry in Alberta will result in increased contaminant deposition, primarily from local sources.  相似文献   

3.
《Geomorphology》1988,1(2):143-160
A soil chronosequence was examined on landslide scars of different ages in the Taranaki hill country. This area, underlain by Tertiary silty sandstone, was deforested 90 years ago. Sequential aerial photographs, historical terrestrial photographs and documented erosion events were used to date landslide scars formed since forest removal and establish age control for the chronosequence.Soil depth increased with landslide age and was used as an index of soil formation. Mean soil depth increased from 5 cm on 15 year old scars to 20 cm on 82 year old scars. Measures soil depths were attributed to rafted soil, colluvium and bedrock weathering. A chronofunction was derived by regressing mean soil depth against the logarithm of known scar age. Similarly, a second chronofunction was derived by excluding depths of rafted soil from the calculation of mean soil depth to describe soil accumulation on exposed bedrock within the landslide scar. This chronofunction showed a better correlation (r2 = 0.92 compared with r2 = 0.79) and can give an estimate of the age of other landslide scars to within ±27% for ages up to 90 years.The rate of soil depth increase averaged 3.5 mm yr−1 over the first 40 years after slipping but dropped to 1.2 mm yr−1 over the following 50 years. The logarithmic chronofunction suggests that the rate of soil formation further decreases beyond 90 years. Soil formation is primarily a result of bedrock weathering and accumulation of colluvium derived from surface fragmentation of exposed bedrock and crumbling scar margins.  相似文献   

4.
Glacier Benito is a temperate outlet glacier on the west side of the North Patagonian Icefield. Rates of thinning and ablation were obtained using data collected by the British Joint Services Expedition in 1972/73 and subsequent data collected in 2007 and 2011. Ice‐front recession rates were based on dendrochronological dating for the terminal moraines and aerial and satellite imagery of the ice front in 1944, 1998 and 2002. Between the first Benito survey in 1973 and 2007, the lower glacier thinned by nearly 150 m at an average rate of 4.3 m yr?1 with the rate increasing to 6.1 m yr?1 between 2007 and 2011, a 28.7% increase during the latter period. Increases in ice movement and ablation were negligible: ice movement for 1973 and 2007 averaged 0.45 m day?1 and ablation averaged 0.05 m day?1. Ice front recession along the glacier's centre line from 1886 to 2002 was approximately 1860 m. Retreat rates between 1886 and 1944 averaged 8.9 m yr?1. Thereafter glacier asymmetry makes measurement along the glacier centre line unrepresentative of areal change until 1998 when symmetry was restored; retreat between 1944 and 1998 was 15.4 m yr?1. From 1998 to 2002 the rate increased dramatically to 127.2 m yr?1. Recession from the southern end of Benito's terminal moraine in the 1850s supports an early date for initial retreat of the Icefield's glaciers.  相似文献   

5.
The main objective of our study was to provide consistent information on land cover changes between the years 1990 and 2010 for the Cerrado and Caatinga Brazilian seasonal biomes. These areas have been overlooked in terms of land cover change assessment if compared with efforts in monitoring the Amazon rain forest. For each of the target years (1990, 2000 and 2010) land cover information was obtained through an object-based classification approach for 243 sample units (10  km × 10  km size), using (E)TM Landsat images systematically located at each full degree confluence of latitude and longitude. The images were automatically pre-processed, segmented and labelled according to the following legend: Tree Cover (TC), Tree Cover Mosaic (TCM), Other Wooded Land (OWL), Other Land Cover (OLC) and Water (W). Our results indicate the Cerrado and Caatinga biomes lost (gross loss) respectively 265,595 km2 and 89,656 km2 of natural vegetation (TC + OWL) between 1990 and 2010. In the same period, these areas also experienced gain of TC and OWL. By 2010, the percentage of natural vegetation cover remaining in the Cerrado was 47% and in the Caatinga 63%. The annual (net) rate of natural vegetation cover loss in the Cerrado slowed down from −0.79% yr−1 to −0.44% yr−1 from the 1990s to the 2000s, while in the Caatinga for the same periods the rate increased from −0.19% yr−1 to −0.44% yr−1. In summary, these Brazilian biomes experienced both loss and gains of Tree Cover and Other Wooded Land; however a continued net loss of natural vegetation was observed for both biomes between 1990 and 2010. The average annual rate of change in this period was higher in the Cerrado (−0.6% yr−1) than in the Caatinga (−0.3% yr−1).  相似文献   

6.
《Geomorphology》2004,57(1-2):117-127
Detailed wind tunnel tests were conducted to examine the fetch effect of a sandy surface on a sand cloud blowing over it. The results suggest that the fetch length of a sandy surface has a significant effect on both the vertical flux profile and total horizontal flux. The sand flux over a sandy surface increases with height in the very near surface layer, but then decays exponentially. In agreement with the widely accepted conclusion, the decay function can be expressed by q=aexp(−h/b), where q is the sand flux at height h. Coefficient a that tends to increase with wind speed implies the influence of wind, while coefficient b that defines the relative decay rate shows the influence of both the fetch and wind. The relative decay rate increases with fetch when the fetch length is short, then becomes constant when the fetch reaches a certain length. The threshold fetch length over which the relative decay rate keeps constant increases with wind speed. The average saltation height generally increases with fetch. Both the relative decay rate and average saltation height show that the fetch effect on the flux profile becomes more significant when the wind speed increases. The total sand transport equation for the total fetch can be expressed by Q=C(1−Ut/U)2U3(ρ/g), where Q is the total sand transport rate, U and Ut are the wind velocity and threshold wind velocity at the centerline height of the wind tunnel, respectively, g is gravitational acceleration, ρ is the density of air, and C is a proportionality coefficient that increases with the fetch length, implying that the total sand flux increases with the fetch length.  相似文献   

7.
Shallow basins in the savannas of Peten, Guatemala filled with water after 305±55 BP (calibrated age+1430–1660 AD). Aguadas Chimaj and Chilonche possess dilute waters and iron-rich, clayey sediments that are poor in Ca and Mg, reflecting the highly weathered nature of riparian soils. Low 210Pb flux rates to Chimaj (0.085 pCi cm-2 yr-1) and Chilonche (0.134 pCi cm-2 yr-1) are attributed to low 222Rn emission rates from the nearby Caribbean Sea. Mean sediment accumulation rates in Chimaj and Chilonche for the past 150 years are 0.015 g cm-2 yr-1 and 0.047 g cm-2 yr-1 respectively. Forest expansion after 305 BP is documented in pollen profiles from the small aguadas and larger Lake Oquevix. Regional reforestation postdates the 9th century Classic Maya collapse and coincides with indigenous depopulation that was a consequence of European intrusion that began in the early 1500s. The timing of forest regrowth indicates the importance of historical anthropogenic factors in controlling Peten's vegetation. Nevertheless, other sedimentological lines of evidence (e.g. lithology, algal remains and charcoal particles) suggest that changing climate and/or local hydrology may have played a role in the reforestation process.  相似文献   

8.
Palaeovariations of the atmospheric 210Pb flux in Northeast China (Long Gang area, Jilin province), quantified by high resolution 210Pb measurements on seasonally laminated sediments of Lake Sihailongwan are presented on decadal scale. The mean flux of unsupported 210Pb between 1790 and 1970 for the centre of the lake basin is 517 Bq m−2 yr−1 with maximum deviations between −23% and +27% of this value. Flux rates above this average were found between 1783 and 1813, around 1836, and between 1860 and 1901. The mean 210Pbexc flux rates derived were clearly lower around 1821, 1908, 1930, and 1953. The 210Pbexc flux reached its minimum of 344 Bq m−2 yr−1 during the period 1977–1982. The atmospheric flux of unsupported 210Pb is correlated with the precipitation frequency during the summer monsoon and shows coinciding variability with geochemical proxies that document the groundwater inflow into the lake. Al2O3-rich dust of remote provenance scavenged by wet-deposition in the rainy season is the major carrier of the atmospheric 210Pbexc flux.  相似文献   

9.
Two experiments were conducted in southern Kordofan State to determine the influence of Acacia senegal L., Balanites aegyptiaca L. and Azadirachta indica L. on millet (Pennisetum typhoides) yield, soil quality and to monitor decomposition and nutrients release from tree litters. Yield under A. indica (174.83 kg ha−1) and B. aegyptiaca (173.09 kg ha−1) were significantly higher than the control (121.43 kg ha−1). The lowest yield (111.04 kg ha−1) was recorded under A. senegal. Straw dry matter under B. aegyptiaca (1161.5 kg ha−1) and A. indica (857.8 kg ha−1) was significantly higher than both under A. senegal (321.8 kg ha−1) and the control (454.8 kg ha−1). Trees varied in their capacity to induce changes in soil properties whereas effects on soil N were not substantial. A. indica had a decomposition rate (0.6283 week−1) 2.0 times higher than that of B. aegyptiaca (0.2057 week−1) and A. senegal (0.267 week−1). The highest rate of P and K release from A. indica and B. aegyptiaca litters has resulted in significant accumulation in the soil indicating these tree litters are potential sources for these elements. The capacity of trees to improve soil fertility could offer an alternative management system for improved cultivation of field crops.  相似文献   

10.
Biofuels are considered as a climate-friendly energy alternative. However, their environmental sustainability is increasingly debated because of land competition with food production, negative carbon balances and impacts on biodiversity. Arid and semi-arid lands have been proposed as a more sustainable alternative without such impacts. In that context this paper evaluates the carbon balance of potential land conversion to Jatropha cultivation, biofuel production and use in arid and semi-arid areas. This evaluation includes the calculation of carbon debt created by these land conversions and calculation of the minimum Jatropha yield necessary to repay the respective carbon debts within 15 or 30 years.The carbon debts caused by conversion of arid and semi-arid lands to Jatropha vary largely as a function of the biomass carbon stocks of the land use types in these regions. Based on global ecosystem carbon mapping, cultivated lands and marginal areas (sparse shrubs, herbaceous and bare areas) show to have similar biomass carbon stocks (on average 4–8 t C ha−1) and together cover a total of 1.79 billion ha. Conversion of these lands might not cause a carbon debt, but still might have a negative impact on other sustainability dimensions (e.g. biodiversity or socio-economics). Jatropha establishment in shrubland (0.75 billion ha) would cause a carbon debt of 24–28 t C ha−1 on average (repayable within 30 year with yield of 3.5–3.9 t seed ha−1 yr−1). Land use change in the 1.15 billion ha of forested area under arid and semi-arid climates could cause a carbon debt between 70 and 118 t C ha−1. This debt requires 8.6–13.9 t seed production ha−1 yr−1 for repayment within 30 years. If repayment is required within 15 years, the necessary minimum yields almost double. Considering that 5 t seed ha−1 yr−1 is the current maximum Jatropha yield, conversion of forests cannot be repaid within one human generation. Repayment of carbon debt from shrubland conversions in 30 years is challenging, but feasible. Repayment in 15 year is currently not attainable.Based on this analysis the paper discusses the carbon mitigation potential of biofuels in arid and semi-arid environments.  相似文献   

11.
A sedimentary record of human disturbance from Lake Miragoane,Haiti   总被引：1，自引：0，他引：1  
Lake Miragoane, Haiti is one of the largest, natural freshwater lakes in the Caribbean (A=7.06 km2, zmax=41.0 m, conductivity = 350 S cm–1). Lake waters are dominated by calcium and bicarbonate ions. The lake was thermally stratified, and oxygen profiles were clinograde during summer visits in 1983 and 1985. A 72-cm mud-water interface core was taken near the center of the lake and dated with 210Pb. The local 210Pb fallout rate is low (0.09 pCi cm–2 yr–1), about 20% of the global average. Bulk sedimentation rates ranged from 0.008 to 0.030 g cm–2 yr–1 during the past 130 years (0–8 cm depth). Sediment geochemistry and pollen have been analyzed in the topmost 58 cm of the section. Tentative ages were assigned to the core by extrapolation of 210Pb dates. According to this preliminary chronology, the bottom part of the core (58–30 cm) records pre-Columbian sedimentation (1000–500 B.P.) and contains pollen evidence of intact, dry and mesic forest. Pre-Columbian deposits are rich in organic matter (x = 30%) and relatively poor in carbonates (x = 15% as CO2). The top 30 cm of the core preserve the record since European contact (500 B.P. to present). Pollen data reveal two episodes of deforestation following European arrival. Consequent soil erosion is documented by a decrease in organic matter content (x = 15%) and an increase in carbonates (x = 27% as CO2). Surficial sediments reflect the widespread deforestation and soil loss that characterize the watershed today.  相似文献   

12.
The well‐constrained seismic stratigraphy of the offshore Canterbury basin provides the opportunity to investigate long‐term changes in sediment supply related to the formation of a transpressive plate boundary (Alpine Fault). Reconstructions of the relative motion of the Australian and Pacific plates reveal divergence in the central Southern Alps prior to ～20.1 Ma (chron 6o), followed by increasing average rates of convergence, with a marked increase after ～6 Ma (late Miocene). A strike–slip component existed prior to 33.5 Ma (chron 13o) and perhaps as early as Eocene (45 Ma). However, rapid strike–slip motion (>30 mm yr?1) began at ～20.1 Ma (chron 6o). Since ～20.1 Ma there has been no significant change in the strike–slip component of relative plate motion. Sedimentation rates are calculated from individual sequence volumes that are then summed to represent sequence groups covering the same time periods as the tectonic reconstructions. Rates are relatively high (>22 mm yr?1), from 15 to ～11.5 Ma (sequence group 1). Rates decrease to a minimum (<15 mm yr?1) during the ～11.5–6 Ma interval (sequence group 2), followed by increased rates during the periods of ～6–2.6 Ma (21 mm yr?1; group 3) and 2.6–0 Ma (～25 mm yr?1; group 4). Good agreement between sedimentation and tectonic convergence rates in sequence groups 2–4 indicates that tectonism has been the dominant control on sediment supply to the Canterbury basin since ～11.5 Ma. In particular, high sedimentation rates of 21 and ～25 mm yr?1 in groups 3 and 4, respectively, may reflect increased plate convergence and uplift at the Southern Alps at ～6 Ma. The early‐middle Miocene (～15–11.5 Ma) high sedimentation rate (22 mm yr?1) correlates with low convergence rates (～2 mm yr?1) and is mainly a response to global climatic and eustatic forcing.  相似文献   

13.
Shrubs play an important role in water-limited agro-silvo-pastoral systems by providing shelter and forage for livestock, for erosion control, to maintain biodiversity, diversifying the landscape, and above all, facilitating the regeneration of trees. Furthermore, the carbon sink capacity of shrubs could also help to mitigate the effects of climate change since they constitute a high proportion of total plant biomass. The contribution of two common extensive native shrub species (Cistus ladanifer L. and Retama sphaerocarpa (L.) Boiss.) to the carbon pool of Iberian dehesas (Mediterranean agro-silvo-pastoral systems) is analyzed through biomass models developed at both individual (biovolume depending) and community level (height and cover depending).The total amount of carbon stored in these shrubs, including above- and belowground biomass, ranges from 1.8 to 11.2 Mg C ha−1 (mean 6.8 Mg C ha−1) for communities of C. ladanifer and from 2.6 to 8.6 Mg C ha−1 (mean 4.5 Mg C ha−1) for R. sphaerocarpa. These quantities account for over 20–30% of the total plant biomass in the system. The potential for carbon sequestration of these shrubs in the studied system ranges 0.10–1.32 Mg C ha−1 year−1 and 0.25–1.25 Mg C ha−1 year−1 for the C. ladanifer and R. sphaerocarpa communities' respectively.  相似文献   

14.
Annual above-ground net primary production (ANPP), evapotranspiration (ET) and water use efficiency (WUE) of rangeland have the potential to provide an objective basis for establishing pricing for ecosystem services. To provide estimates of ANPP, we surveyed the biomass, estimated ET and prepared a water use efficiency for dwarf shrublands and arid savanna in the Riemvasmaak Rural Area, Northern Cape, South Africa. The annual production fraction was surveyed in 33 MODIS 1 km2 pixels and the results regressed against the MODIS fPAR product. This regression model was used to predict the standing green biomass (kg DM ha−1) for 2009 (dry year). Using an approach which combines potential evapotranspiration (ET0) and the MODIS fPAR product, we estimated actual evapotranspiration (ETa). These two models (greening standing biomass and ETa) were used to calculate the annual WUE for 2009. WUE was 1.6 kg DM mm−1 ha−1 yr−1. This value may be used to provide an estimate of ANPP in the absence of direct measurements of biomass and to provide a comparison of the water use efficiency of this rangeland with other rangeland types.  相似文献   

15.
《Polar Science》2014,8(3):218-231
To investigate the dynamics and environmental drivers of CO2 flux through the winter snowpack in a dwarf bamboo ecosystem (Hokkaido, northeast Japan), we constructed an automated sampling system to measured CO2 concentrations at five different levels in the snowpack, from the base to the upper snow surface. Using a gas diffusion approach, we estimated an average apparent soil CO2 flux of 0.26 μmol m−2 s−1 during the snow season (December–April); temporally, the CO2 flux increased until mid-snow season, but showed no clear trend thereafter; late-season snow-melting events resulted in rapid decreases in apparent CO2 flux values. Air temperature and subnivean CO2 flux exhibited a positive linear relationship. After eliminating the effects of wind pumping, we estimated the actual soil CO2 flux (0.41 μmol m−2 s−1) to be 54% larger than the apparent flux. This study provides new constraints on snow-season carbon emissions in a dwarf bamboo ecosystem in northeast Asia.  相似文献   

16.
The soil dilution plate method was used to examine spatiotemporal changes in microfungal communities inhabiting the playa and interdune areas in the western Negev Desert, Israel. Soil samples were collected from the 0–50 cm depth at 10 cm intervals at both habitats during the wet and dry seasons of 2010. Forty-six species belonging to 31 genera were identified, 14 and 12 species were common to both habitats during the wet and dry seasons. The colony-forming units (CFUs) ranged from 75 to 4875 and from 500 to 6925 CFU g−1 dry soil at the playa and interdune, respectively. More diverse species and higher microfungal density were recorded during the wet season compared to the dry season at both habitats, and the microfungal communities inhabiting the playa were characterized by lower species diversity and CFU compared with the interdune regardless of soil depth and sampling season. With the increase in soil depth, decreasing trends were found in both species diversity and CFU throughout the study period, especially in the playa soils. Generally, Cladosporium cladosporioides, Alternaria alternata, Ulocladium atrum, and Fusarium spp. were widespread at the playa with high relative abundance, as were Penicillium and Aspergillus spp. at both habitats.  相似文献   

17.
Remarkably high rates of sedimentation (up to nearly 60 kg m−2 yr−1) are documented for offshore areas of Freefight Lake, a deep, hypersaline, meromictic lake in the northern Great Plains of Canada. Most material in the offshore sediment traps consists of soluble and suparingly soluble endogenic salts. Deposition of allogenic sediment is minor. The observed high sedimentation rates are in response to several mechanism: (i) freeseout precipitation of salts from the mixolimnion; (ii) redistribution of shallow water endogenic precipitates by turbidity flows and interflow processes; and (iii) precipitation of salts from within the monimolimnion Because the bottom water mass of the lake is essentially isothermal and isochemical, large scale temperature induced remobilization of these salts at or near the sediment-water interface is unlikely. Similarly, the morphology of the basin suggests that resuspension of bottom sediment by waves in the offshore areas of the basin is negligible. Although the sedimentation rates observed in Freefight Lake are extraordinarily high and considerably greater than other modern lacustrine sedimentation rates documented in the literature to date, the observed rates are entirely compatible with suggested accumulation rates of ancient evaporite sequences. Palliser Tringle Global Change Contribution Number 6.  相似文献   

18.
Environmental change in many tropical, alpine habitats remains poorly resolved due to an absence of proximate and sustained observations. In the Rwenzori Mountains of East Africa, glaciers have receded rapidly over the last century, and here we assess the impact of this recession through palaeolimnological analyses of a 45 cm sediment core (Buju3) from Lake Bujuku which is closest to the ice-fields and partly supplied by melt water in-flows. 210Pb and 137Cs suggest that Buju3 has an average sedimentation rate of 2.9 mm year−1 and the base of the core can be dated to 1864 ± 20 years. Contemporary diatom taxa found in the lake are dominated by Tabellaria flocculosa and Synedra spp., but also include Achnanthes minutissima and Fragilaria pinnata. However, the diatom flora for Buju3 is less diverse and dominated by small, tychoplanktonic species of Fragilaria. Over the period associated with glacial recession, organic carbon isotope analysis (δ13C) suggests a small but distinct increase in within-lake productivity, which increases in rate since the mid 1970s up to the present day, in line with a shift towards increased algal productivity (as highlighted by C/N ratios). However, the diatom and pollen records appear rather insensitive to changes in glacier recession since the late 19th century.  相似文献   

19.
Wetland vegetation is intimately related to floodplain inundations, which can be seriously affected by dam operation. Poyang Lake is the largest floodplain wetland in China and naturally connected with the Yangtze River and the Three Gorges Dam(TGD) upstream. To understand the potential impacts of TGD on Poyang Lake wetlands, we collected remote sensing imagery acquired during dry season from 1987 to 2020 and extracted vegetation coverage data in the Ganjiang Northern-branch Delta(GND) and the G...  相似文献   

20.
The chemistry of major cations (Mg2+, Ca2+, Na+, and K+) and anions (HCO3 −, SO4 2−, and Cl−) in the water of Lake Pumayum Co and its inflow river was studied, revealing the obvious ionic difference among various inflow rivers and the lake. The chemical type of the lake water was Mg2+-Ca2+-HCO3 −-SO4 2+, but the major ions of the main inflow rivers were Ca2+-Mg2+-HCO3 −. In the lake inlet of Jiaqu River, the main inflow river, there was significant variance of water chemistry within the depth less than 2 m. However, it was almost homogeneous at other area of the lake. Therefore, with the evidence of distribution of water chemistry and oxygen isotope of lake water, a conclusion can be outlined that Jiaqu River had a distinct effect on the hydrochemistry of the water on the submerged delta, whereas this is not the case for other rivers. The Gibbs plot revealed that the dominant mechanism responsible for controlling chemical compositions of the lake water was rocks weathering in the drainage area. Ion ratios and ternary plots further explored the main processes controlling the water chemistry of the catchment, i.e., carbonate weathering, pyrite weathering, and silicate weathering. The different hydrochemistry characteristics between river water and lake water may result from the CaCO3 precipitation. The findings will benefit the explanation of the environmental significance of carbonate in paleolimnological studies in the lake.  相似文献   

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