共查询到20条相似文献,搜索用时 234 毫秒
1.
Soil carbon sequestration plays an essential role in mitigating CO 2 increases and the global greenhouse effect. This paper calculates soil organic carbon (SOC) storage changes during the course
of industrialization and urbanization in Yangtze Delta region, China, based on the data of the second national soil survey
(1982–1985) and the regional geochemical survey (2002–2005), with the help of remote sensing images acquired in periods of
1980, 2000, 2005. The results show that soils in the top 0–20 and 0–100 cm depth in this region demonstrate the carbon sink
effect from the early 1980s to the early 2000s. The SOC storage in 0–20 cm depth has resulted in increase from 213.70 to 238.65 Tg,
which corresponds to the SOC density increase from 2.94 ± 1.08 to 3.28 ± 0.92 kg m −2, and mean carbon sequestration storage and rate are 1.25 Tg a −1, 17.14 g m −2 a −1, respectively. The SOC storage in 0–100 cm depth has resulted in increase from 690.26 to 792.65 Tg, which corresponds to
the SOC density increase from 9.48 ± 4.22 to 10.89 ± 3.42 kg m −2, and mean carbon sequestration storage and rate are 5.12 Tg a −1, 70.32 g m −2 a −1, respectively. Urban area in Yangtze Delta region, China, increased more than 3,000 km 2 and the urban growth patterns circled the central city region in the past 20 years. The SOC densities in 0–20 cm depth decrease
gradually along urban–suburban–countryside and the urban topsoil is slightly enriched with SOC. Compared to the data of the
second national soil survey in the early 1980s, the mean SOC density in urban area increased by 0.76 kg m 2, or up 25.85% in the past 20 years. With the characteristics of SOC storage changes offered, land-use changes, farming system
transition and ecological city construction are mainly attributed to SOC storage increases. Because of lower SOC content in
this region, it is assumed that the carbon sink effect will go on in the future through improved soil management. 相似文献
2.
Shenzhen, located in South China has experienced rapid urbanization over the past three decades. This paper focuses on the
urban sprawl integrating remote sensing and geographic information systems (GIS). The overlay of the urban area maps for two
adjacent study years was used to generate the sprawl categories map. The three main sprawl categories of infilling sprawl,
edge-expansion sprawl and outlying sprawl were calculated and analyzed in regard to their distribution and change throughout
different counties during the study years. The result showed that the urban area in the study region had increased dramatically
from 19.55 km 2 in 1979 to 894.31 km 2 in 2005. The urban area centroids over the six study years transferred from southwest to northeast from 1979 to 2005. Among
the study counties, the patterns of sprawl categories were markedly distinctive over different study periods. From 1979 to
2005, Shenzhen’s chief spread was outlying sprawl. Bao’an experienced the maximum sprawl within the three study counties.
The findings show that studying urban sprawl can provide a method of monitoring urban area change, which, in turn, gives us
a clearer perspective of urban sprawl patterns over a longer period of time. This would prove invaluable to those researchers
such as land and urban planners. 相似文献
3.
利用多目标区域地球化学调查的实测数据,估算了吉林中西部地区表层土壤的有机碳密度和储量.结果表明,在不同深度的分布层次上,表层(0~0.2m)土壤对有机碳的积累较弱,SOC储量占到全层(0~1.8m)储量的23.8%,中上层(0~1.Om)储量则占到全层储量的95.7%.从上壤类型看,表层SOC密度较高的有暗棕壤(636... 相似文献
4.
Soil inorganic carbon (SIC) and organic carbon (SOC) levels can change with forest development, however, concurrent changes in soil carbon balance and their functional differences in regulating soil properties are unclear. Here, SIC, SOC, and other physicochemical properties of soil (N, alkali-hydrolyzed N, effective Si, electrical conductivity, pH, and bulk density) in 49 chronosequence plots of larch plantation forests were evaluated, by analyzing the concurrent changes in SIC and SOC storage during growth of plantation and the functional difference of these levels in maintaining soil sustainability. These soils had characteristically high SOC (15.34 kg m ?2) and low SIC storage (83.38 g m ?2 on average). Further, 28 of 30 linear regressions between SIC and SOC storage and larch growth parameters (age, tree size, and biomass density) were not statistically significant ( p > 0.05). However, significant changes were observed in ratios of SIC and SOC with these growth parameters (between 0–40 cm and 40–80 cm, respectively; p < 0.05). These results were more useful for determining the changes in SIC and SOC vertical distribution than changes in storage. Moreover, larch growth generally decreased SIC and increased SOC. Linear correlation and multiple-regression analysis showed that the SIC influences soil acidity, whereas SOC affects soil nitrogen. This clearly indicates that larch growth could result in divergent changes in SIC and SOC levels, particularly in their vertical distribution; further, changes in SIC and SOC may variably affect soil physicochemical properties. 相似文献
5.
The dynamics of desertification in the Horqin Sandy Land between 2000 and 2005 were analyzed using Landsat TM/ETM images and
the data-processing function of geographical information software. The results showed that the extent of desertified land
decreased at a rate of slightly more than 0.1 km 2 year −1, from 22,423.1 km 2 in 2000 to 22,422.4 km 2 in 2005, indicating that desertification has been controlled in this area and that desert areas may be approaching a steady
state. The dynamics of desertification differed among land types. Desertification decreased most obviously in areas of previous
desert land. The area in which desertification was ameliorated was higher than the area that underwent further degradation,
but non-desertified land (113.3 km 2) deteriorated at a rate of 22.7 km 2 year −1 during this period. This significant change requires careful attention by managers in the study area. 相似文献
6.
Kathmandu Valley aquifer in central Nepal is continuously under stress since the commencement of mechanized extraction of
groundwater resources in early 1970s. Many wells have been drilled in shallow and deep aquifers of the valley; and numerous
studies have been made in last four decades to understand the aquifers. However, up-to-date information on well inventory,
water extraction, water quality and overall situation of groundwater environment are not yet known in the absence of institutional
responsibility in groundwater management. This study attempts to evaluate current state of the groundwater environment considering
natural and social system together; to better understand origin of stresses, their state, expected impact and responses made/needed
to restore healthy groundwater environment. The analysis reveals increasing population density (3,150–4,680 persons/km 2), urbanization (increase in urban population from 0.61 to 1.29 million) and increasing number of hotels due to tourism (23–62
hotels) during a decade are acting as driving forces to exceed groundwater extraction over recharge (extraction = 21.56 and
recharge = 9.6 million-cubic meter-a-year), decrease in groundwater levels (13–33 m during 1980–2000 and 1.38–7.5 m during
2000–2008), decline in well yield (4.97–36.17 l/s during mid-1980s to 1998) and deterioration in water quality. In the absence
of immediate management intervention with institutional responsibility for groundwater development, regulation and knowledgebase
management (i.e. to facilitate collection, integration and dissemination of knowledge); situation of groundwater environment
are expected to deteriorate further. Groundwater modeling approach may help to suggest appropriate management intervention
under current and expected future conditions. 相似文献
7.
Associated with the rapid urbanization and industrialization, most of the urban parks and recreational areas in Shanghai are
built close to major roads or industrial areas, where they are subject to many potential pollution source, including automobile
exhaust and factory emissions. Urban dusts, containing many toxic heavy metals such as Pb, Cr, Cd, Hg and As, are one of main
contributors for environmental pollution. In this study, 261 dust samples were collected from two different localities (streets
and parks) in the urban area of Shanghai, China. Pb and Cr concentrations of all samples were determined by atomic adsorption
spectrophotometer analyzer, and Cd, As and Hg concentrations in 74 samples by atomic fluorescence spectroscopy. The mean concentrations
of Pb, Cr, Cd, As and Hg are 287, 157, 1.24, 8.73 and 0.16 mg kg −1, respectively. Each heavy metal shows a wide range of concentration values. In comparison with heavy metal background values
of soil in Shanghai, urban dusts have elevated metal concentrations as a whole, except those of As. The concentrations of
Pb, Cr, Cd, As and Hg are 11.3, 2.1, 10.3, 0.997, 1.7 times of the soil background values, respectively. Compared with the
global mean concentrations, Cr concentration in urban dusts is slightly higher. Pb, Cr and Hg show normal distribution after
logarithmic transformation. Pb, Cr, Cd, As and Hg have second-order variation trends of the spatial distribution. The spatial
distribution features of five toxic heavy metals, in general, illustrate relatively high levels within the regions of the
inner-city ring highway and southwestern Shanghai. Cr and Cd are higher in Baoshan industrial park and the shipbuilding industries
regions. The order of environmental risk is Pb > Cd > Cr > Hg > As. Pb and Cd have the highest risk for environment pollution
and human health among the five metals. The pollutant sources of toxic heavy metals in Shanghai urban dusts are preliminarily
concluded as follows: As may have mainly a natural source. Burning of coal has become the main source of Hg pollution. Pb,
Cr and Cd have three sources, traffic, building construction, and weathering corrosion of building materials. 相似文献
8.
The present study combined remote sensing with geographical information system (GIS) technology to interpret Landsat TM images
from 1996 to 2000 and establish a land cover database for the Hexi Corridor of China’s Gansu Province. The areas of sand and
dust emission and trends in their change were extracted by analyzing the database, with the following results: In 2000, the
source area for sand and dust storms totaled nearly 170,000 km 2, accounting for 75.1% of the study region. The emission area decreases from as much as 70,000 km 2 in winter and spring to around 58,000 km 2 in summer and autumn, accounting for 41.1 and 34.1% of the source area, respectively. During the 4 years of the study period,
the emission area decreased by nearly 57 km 2 in winter and spring (a 0.1% change); however, the vulnerability of the land surface to wind erosion increased in ca. 190 km 2 and decreased in ca. 102 km 2. Although the area of dust emission decreased from 1996 to 2000, the area vulnerable to wind erosion increased by ca. 87 km 2, and the increased number of sand and dust storm days in the region between 2000 and 2003 appears to be correlated with this
increase. 相似文献
9.
Water quality in less-developed countries is often subject to substantial degradation, but is rarely studied in a systematic way. The concentration and flux of major ions, carbon, nitrogen, silicon, and trace metals in the heavily urbanized Bagmati River within Kathmandu Valley, Nepal, are reported. The concentrations of all chemical species increased with distance downstream with the exceptions of protons and nitrate, and showed strong relationships with population density adjacent to the river. Total dissolved nitrogen (TDN), dominated by NH 4, was found in high concentrations along the Bagmati drainage system. The export of dissolved organic carbon (DOC) and TDN were 23 and 33 tons km ?2 year ?1, respectively, at the outlet point of the Kathmandu Valley, much higher than in relatively undeveloped watersheds. The cationic and silica fluxes were 106 and 18 tons km ?2 year ?1 at the outlet of the Bagmati within Kathmandu Valley, and 36 and 32 tons km ?2 year ?1 from the relatively pristine headwater area. The difference between headwaters and the urban site suggests that the apparent weathering flux is three times higher than the actual weathering rate in the heavily urbanized Bagmati basin. Fluxes of cations and silica are above the world average, as well as fluxes from densely populated North American and European watersheds. End-member composition of anthropogenic sources like sewage or agricultural runoff is needed to understand the drivers of this high rate of apparent weathering. 相似文献
11.
Rispana River flows through the heart of Dehradun, the capital city of Uttarakhand State, India. Uttarakhand had separated from Uttar Pradesh State in the year 2000; since then, Dehradun City has witnessed numerous changes. Both urban sprawl and densification were noticed, with around a 32% increase in population. The city had faced recurrent high runoff and urban flood situations in these last 2 decades. Therefore, the study was conducted to detect the change in land use/land cover (LULC), especially urbanization, through remote sensing data; and later to determine the impacts of such changes on the Rispana watershed hydrology. The LULC maps for the year 2003 and the 2017 were generated through supervised classification technique using the Landsat Series satellite datasets. The LULC change analysis depicted that mainly the urban settlement class increased with significant area among other classes from the year 2003–2017. It was noticed that majorly agriculture and fallow land (8.18 km2, which is 13.52% of total watershed area) converted to urban, increasing the impervious area. Almost all the municipal wards, falling in the Rispana watershed, showed urbanization during the said period, with an increase of as high as 71%. The change in LULC or effect of urbanization on the hydrological response of the watershed was assessed using the most widely used Natural Resources Conservation Services Curve Number method. It was noticed that the area under moderated runoff potential (approx. 10.23 km2) steeply increased during the lean season, whereas, high runoff potential zones (5 km2) increased significantly under wet season. Therefore, it was concluded that an increase in impervious surface resulted in high runoff generation. Further, such LULC change along with climate might lead to high runoff within the watershed, which the present storm drainage network could not withstand. The situation generally led to urban floods and affected urban dwellers regularly. Therefore, it is critical to assess the hydrological impacts of LULC change for land use planning and water resource management. Furthermore, under the smart city project, the local government has various plans to improve present infrastructure; therefore, it becomes necessary to incorporate such observations in the policies. 相似文献
12.
The Yangtze River is the China’s longest river and the third-longest river in the world. The river’s source region in the
Qinghai-Tibet Plateau is especially sensitive to global environmental change because of its high elevation and cold environment.
Under the influence of global warming, aeolian desertified land has expanded rapidly in this area. To assess the trends in
aeolian desertification from 1975 to 2005, remote-sensing and GIS technology were used to monitor the extent of aeolian desertification
in 1975, 1990, 2000, and 2005. The data sources included Landsat multi-spectral scanner images acquired in 1975, Enhanced
Thematic Mapper (ETM+) images acquired in 2000, and Thematic Mapper (TM) images acquired in 1990 and 2005. Images recorded
between June and October were selected, when vegetation grew well, because aeolian desertified land was more easily recognized
during this period. Thematic maps, including land use and geomorphologic maps, were used as supplementary data. Aeolian desertification
maps (1:100000) were produced for each year from the Landsat images through visual interpretation. The area of aeolian desertified
land increased by 2,678.43 km 2 from 1975 to 2005, accounting for 8.8% of the total area of aeolian desertified land in 1975, an increase of 89.28 km 2 a −1. Increasing mean annual temperature and the combination of a dry, cold, and windy climate in winter and spring were mainly
responsible for the expansion of desertified land. 相似文献
13.
Land subsidence has been affecting Tianjin for the past 50 years. It leads to comprehensive detrimental effects on society,
the economy and natural environment. Overpumping of groundwater is the main cause. In 2008, the maximum cumulative subsidence
reached 3.22 m and the total affected area nearly 8,000 km 2. The subsidence reached its most critical state in the early 1980s when it occurred at a rate as high as 110 mm/year. At
the same time, groundwater extraction had also reached a maximum of 1,200 million m 3. By importing the Luan River to Tianjin and restricting exploitation of groundwater, hydraulic heads gradually recovered
after 1986 in all aquifers, and this has continued to the present in the second aquifer. The subsidence rate in urban areas
dropped to 10–15 mm/year. The area of groundwater extraction expanded to the suburban area with economic growth in the 1990s,
and it was shifted to the third and fourth aquifers. At present, with a subsidence rate of 30–40 mm/year, four new suburban
subsidence centers have been formed. Several measures were adopted to mitigate and prevent land subsidence disasters. These
included restricting groundwater exploitation, groundwater injection, prohibiting use in the specific zone, a pricing policy
for water resources, advocating water-saving technology, and strict enforcement of groundwater laws. Although the subsidence
area is still increasing slowly, the subsidence rate is being controlled. 相似文献
14.
The central and highest area of Mt. Prokletije (Albanian Alps) is situated in northern Albania and eastern Montenegro (at 42°30′N). The highest peak is Maja e Jezerces (2694 m). Detailed geomorphological mapping was used to reconstruct the positions of former glaciers. The longest Ropojana glacier had a length of 12.5 km and surface of 20 km 2; others include Valbona Glacier (9.5 km, 10.5 km 2), Grbaja Glacier (5 km, 6.7 km 2) and Bogićevica Glacier (6 km, 6.9 km 2). Three series of moraines can be distinguished: the lowest at an average altitude of 990 m (average ELA 1750 m), the middle series at 1350 m (ELA 1942 m), and the highest at 1900 m (ELA 2123 m). As no advanced dating methods have yet been used to provide a numerical chronological framework for these features, hypotheses are made based on the comparison with the advanced studies of other similar mountains in the Mediterranean region. The moraines of the first stage (lowest series) correspond to one of pre-LGM glaciations (Middle or even Early Würmian), the second stage moraines probably correspond to LGM, and the third stage could be attributed to Younger Dryas. The mapping included a number of inactive and active rock glaciers, as well as three small active glaciers (surface 5 ha and less), at 1980–2100 m altitude, in the area close to Maja e Jezerces. 相似文献
15.
Seawater intrusion was observed in China’s coastal aquifers as early as 1960s. At present, it covers an area of more than
2,000 km 2 in China. In 2002, the seawater intrusion area was increased to 1773.6 km 2 in Shandong Province, China, and it is continuing to extend in the coastal area of Laizhou Bay. In order to study the characteristic
of the seawater intrusion and the pattern of the saltwater/freshwater interface, we set the China’s first three-dimensional
seawater intrusion observation network in Longkou City of Shandong Province in 1989. In order to control the development of
the seawater intrusion, in 1995, a continuous underground concrete wall, by the method of high-pressure jet grouting, was
constructed in the downstream plain area of the Huangshuihe river in Longkou City. The average depth of the 5,842 m long concrete
wall is 26.7 m, and the maxim depth is 41 m. It forms a coastal underground reservoir with the total storage capacity of about
5,359 × 10 4 m 3. In the past 10 years, the reservoir obtained great economic benefit, social benefit and ecosystem benefit. 相似文献
16.
Landsat enhanced thematic mapper imagery (ETM) of 2002 and aerial photography of 1955, combined with published charts and
field observations were used to interpret coastal changes in the zone between Kitchener drain and Damietta spit in the northeastern
Nile delta, previously recognized as a vulnerable zone to the effects of any sea level rise resulting from global warming.
The interpretation resulted in recognition of several changes in nine identified geomorphological land types: beach and coastal
flat, coastal dunes, agricultural deltaic land, sabkhas, fish farms, Manzala lagoon, saltpans, marshes and urban centers.
Reclamation of vast areas of the coastal dunes and of Manzala lagoon added about 420 km2 to the agricultural deltaic land.
About 48 km2 of backshore flats, marshes, salt pans and Manzala lagoon have been converted to productive fish farms. The main
urban centers have expanded; nearly 12.1 km 2 have been added to their areas, and new urban centers (Damietta harbor and the New Damietta city) with total area reach of
~35.3 km 2 have been constructed at the expense of vast areas of Manzala lagoon, coastal dunes, and backshore flats. As a consequence
of human activities, the size of Manzala lagoon has been reduced to more than 65%. Shoreline changes have been determined
from beach profile survey (1990–2000), and comparison of 1955 aerial photographs and ETM satellite image of 2002 reveal alongshore
patterns of erosion versus accretion. The short-term rate of shoreline retreat (1990–2000) has increased in the downdrift
side of Damietta harbor (≃14 m/year), whereas areas of accretion exist within the embayment of Gamasa and in the shadow of
Ras El Bar detached breakwaters system, with a maximum shoreline advance of ~15 m/year. A sandy spit, 12 km long, has developed
southeast of Damietta promontory. These erosion/accretion patterns denote the natural processes of wave-induced longshore
currents and sediment transport, in addition, the impact of man-made coastal protection structures. 相似文献
17.
The Cordillera Blanca, located in the central zone of the Andes Mountains in Peru, has shown a retreat in its glaciers. This paper presents a trend analysis of the glacier area over the groups of Nevados Caullaraju-Pastoruri from 1975 to 2010 using Landsat-5 Thematic Mapper (TM) imagery. In the case of the Nevados Pastoruri/Tuco, the study period was extended back to 1957 by using an aerial photograph taken that year. The extent of clean glacier ice was estimated using Normalized Difference Snow Index (NDSI) thresholds. Moreover, the estimation of debris-covered glacier ice was retrieved by means of a decision tree classification method using NDSI, Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST). Area estimations derived from Landsat imagery were compared to the glacier ground-truth data in 1975 and 2010. Results show a statistically significant (p < 0.05) decreasing trend over the whole study area. Total glacier area decreased at a rate of 4.5 km 2 per decade from 1975 to 2010, with a total loss of 22.5 km 2 (58%). Lower decreasing rates were found for the period 1987–2010: 3.5 km 2 per decade with a total loss of 7.7 km 2 (32.5%). In the case of the Nevados Pastoruri/Tuco, decreasing rates of clean ice extent were constant for the periods 1957–2010, 1975–2010 and 1987–2010, with values close to 1.4 km 2 per decade and a total loss between 1957 and 2010 estimated at about 5 km 2 (54%). This work shows an evident area decrease in the Caullaraju-Pastoruri tropical glaciers, which needs to be included in a future hydrological scenario of local adaptability and water management. 相似文献
18.
A fully distributed, physically-based hydrologic modeling system, MIKE SHE, was used in this study to investigate whole-watershed
hydrologic response to land use changes within the Gyeongancheon watershed in Korea. A grid of 200 × 200 m was established
to represent spatial variations in geology, soil, and land use. Initial model performance was evaluated by comparing observed
and simulated streamflow from 1988 to 1991. Results indicated that the calibrated MIKE SHE model was able to predict streamflow
well during the calibration and validation periods. Proportional changes in five classes of land use within the watershed
were derived from multi-temporal Landsat TM imageries taken in 1980, 1990 and 2000. These imageries revealed that the watershed
experienced conversion of approximately 10% non-urban area to urban area between 1980 and 2000. The calibrated MIKE SHE model
was then programmed to repeatedly analyze an artificial dataset under the various land use proportions identified in the Landsat
TM imageries. The analysis was made to quantitatively assess the impact of land use changes (predominantly urbanization) on
watershed hydrology. There were increases in total runoff (5.5%) and overland flow (24.8%) as a response to the land use change. 相似文献
19.
Agricultural (Ap, A p-horizon, 0–20 cm) and grazing land soil samples (Gr, 0–10 cm) were collected from a large part of Europe (33 countries, 5.6 million km 2) at an average density of 1 sample site/2500 km 2. The resulting more than 2 × 2000 soil samples were air dried, sieved to <2 mm and analysed for their Hg concentrations following an aqua regia extraction. Median concentrations for Hg are 0.030 mg/kg (range: <0.003–1.56 mg/kg) for the Ap samples and 0.035 mg/kg (range: <0.003–3.12 mg/kg) for the Gr samples. Only 5 Ap and 10 Gr samples returned Hg concentrations above 1 mg/kg. In the geochemical maps the continental-scale distribution of the element is clearly dominated by geology. Climate exerts an important influence. Mercury accumulates in those areas of northern Europe where a wet and cold climate favours the build-up of soil organic material. Typical anthropogenic sources like coal-fired power plants, waste incinerators, chlor-alkali plants, metal smelters and urban agglomerations are hardly visible at continental scales but can have a major impact at the local-scale. 相似文献
20.
Soil organic carbon (SOC) is one of the key components for assessing soil quality. Meanwhile, the changes in the stocks SOC may have large potential impact on global climate. It is increasingly important to estimate the SOC stock precisely and to investigate its variability. In this study, Yangjuangou watershed was selected to investigate the SOC distribution under different land uses. We found that SOC concentration decreased with increasing soil depth under all land uses and was significantly different across the vertical soil profile ( P < 0.01). However, considering effect of land use on SOC, it is only significant ( P < 0.01) in the topsoil (0-5 cm) layer. This indicated that land use has a large effect on the stocks of SOC in the surface soil. The stratification ratio of SOC > 1.2 may mean that soil quality is improving. The order of the SOC density (0-30 cm) under different land uses is forestland > orchard land > grassland > immature forestland > terraced cropland. The SOC stock is found to be as large as 2.67 × 10 3 t (0-30 cm) in this watershed. Considering time effect of restoration, the slope cropland just abandoned is more efficient for SOC accumulation than trees planted in the semi-arid hilly loess area. 相似文献
|