首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The sensitivity of catchments to acidification is often assessed by calculation of weathering rates for comparison of the rates of release of base cations with the measured acidic inputs. Methods of calculation of weathering rates include (1) long-term rates from elemental depletion in soil profiles; (2) current rates from input-output budgets; (3) strontium isotope ratios to modify current rates for calcium; (4) modelling using PROFILE or MAGIC; (5) laboratory experimental methods. Not all these methods can be applied in any one situation and when more than one method can be used, there are often discrepancies in the resulting figures. Comparison of long-term and current rates with acidic inputs are often consistent with the known acidification status of some Scottish catchments, but in others it is often difficult to establish a relationship. In some catchments where acidification only occurs under high-flow conditions, for example, long-term rates (12–24 meq m?2a?1) are an order of magnitude lower than current rates (185–340 meq m?2a?1). In seven Scottish catchments on four rock types, weathering rates calculated by PROFILE are of the same order of magnitude as long-term rates calculated for the same soil profiles. Current rates, on the other hand, are always higher than the long-term rates, sometimes by a factor as high as 22, and although this could indicate that release of base cations from these soils has increased in recent times, possibly due to anthropogenic inputs, the comparisons may not be valid.  相似文献   

2.
To investigate the weathering rates of different soil parent materials which occur in Scotland, a study has been undertaken in which detailed soil mineralogy has been used to calculate base cation release. To calculate base cation release, this data, and supplementary soil chemistry and physical attribute data, have provided the input to the PROFILE model. The model is a multi-layer, steady state, deterministic model in which the soil is represented by a series of mixed tank reactors, each of which has the mineralogical, physical and chemical attributes measured for individual soil horizons. The major parent materials from which Scottish soils have developed are glacial till, derived from acid to basic igneous rocks, schist and other metamorphic types, Lower Palaeozoic greywackes and shales, Old Red Sandstone sediments, Carboniferous sediments and Permo-Trias sediments. For each of the parent materials, three soil profiles were analysed and used with the PROFILE model. The base cation release rates, calculated for these parent materials in the top 50cm of the soil profile, varies between 0.2 and 3.2 keq/ha/yr, although, for a given parent material, the range was usually quite small. In general, these results compare very favourably with those suggested for the calculation of critical loads using an empirical approach proposed at Skokloster. In comparison with current rates of deposition, this suggests many of these soils are being acidified and that for many soil-plant combinations, the critical load may be exceeded.  相似文献   

3.
Weathering in an upland granitic till catchment receiving an intermediate level of acidic deposition has been studied by chemical and mineralogical analyses of soil profiles and chemical analysis of precipitation and streamwater. Long-term weathering rates for base cations calculated from analyses of soil profile horizons using Zr as an internal, immobile, index element are similar for alpine podzols and peaty podzols and are 2–3 meq.m–2.a–1 for Ca and Mg, and 10–11 meq.m–2.a–1 for K and Na. The high loss of Na is associated with the weathering of oligoclase, particularly in the coarse sand fraction. Loss of K is related to weathering of K-feldspar and micas. Current weathering rates for base cations calculated from input-output budgets are higher than long-term rates by factors of 12, 8 and 3 for Ca, Mg and Na, but lower by a factor of 7 for K probably due to biomass uptake. The higher current overall loss of base cations may be due to increased rates of weathering in recent times but this is not conclusive as there are large uncertainties inherent in both methods of estimation.  相似文献   

4.
Critical loads of acid deposition are exceeded in parts of the Southern Uplands of Scotland where base saturation in the topmost mineral horizons in many soils developed on greywackes and shales is <10%. Long-term weathering rates calculated by the elemental depletion method from nine soil profiles across a 200 km transect indicate losses of base cations in the range 4–31 meq m?2a?1. In every profile the most depleted base cation is Mg which is directly related to the weathering of chlorite which is often present at the 20–40% level in basal horizons but is often completely weathered out in E horizons. The second most depleted base cation is usually K, and this is clearly related to the weathering of mica to a vermiculitic mineral which, in the clay fractions, contains polymeric hydroxyaluminium in the interlamellar space if the soil pH is >4.3. The base cation least depleted is Ca and this is in sharp contrast to current weathering rates calculated from input-output budgets where Ca is the main base cation being exported. This discrepancy may be due to a contribution to the output from easily soluble Ca-bearing minerals (e.g. calcite) in narrow veins and fractures in the bedrock.  相似文献   

5.
The project Comprehensive Control and Demonstration for Acid Deposition in Liuzbou area is a national key project in the 8th Five-year-plan, and the study on critical loads will provide scientific and quantitative accordance for formulating control strategy. In this paper, critical loads of acid deposition to soil in Lirzhou area, China, were calculated using the Steady State Mass Balance method (SMB and PROFILE) and dynamic modeling methods(MAGIC), based on data obtained from field investigations and physiochemical properties measured through experiments such as the organic content, cation exchange capacity, base saturation, sulfate adsorption capacity, gibbsite coefficient, biomass base cation uptake and selectivity coefficient for cations. Weathering rates necessary to calculate soil chemistry in applying SMB and MAGIC model were determined by computation with PROFILE using independent geophysical properties such as soil texture and mineralogy as the input data, or by the total soil base cation content correlation. The results have shown that the critical loads of acidity in this area are in the range of 0.7–6.0 keq ha–1 yr–1, indicating sulfur deposition should be cut down by 50–90 percent of the present level. The upper soil layer is the most sensitive. The maximum allowable deposition loading of this area is also presented in the paper.  相似文献   

6.
The magnetic properties and magnetic mineralogy of a weathering sequence of soils developed on basalt parent material from eastern China, were studied by rock magnetism, X-ray diffraction and soil chemical analyses to establish the connection between mineral magnetic properties and pedogenic development in a subtropical region. The magnetic susceptibility of soils formed on basalt varied greatly and did not increase with the degree of pedogenic development. The frequency-dependent susceptibility (χfd) values of soils ranged from 1.0 to 11.1% and increased with the pedogenic development. Highly significant linear relationship was found between the frequency-dependent susceptibility and the Fed content (R2 = 0.683) and Fed/Fet ratio (R2 = 0.780) in soils, indicating that pedogenic SP ferrimagnetic grains were associated with enrichment of the secondary iron oxide minerals in the weathering process of soil. Rock magnetism analysis showed that the major magnetic carriers in the weakly weathered soil profiles are magnetite and/or maghemite, and the highly developed soil profiles are generally enriched in magnetite/maghemite grains of pedogenic origin and the magnetically hard haematite, indicating that the magnetic component was transformed from a ferrimagnetic phase (magnetite) to antiferromagnetic phase (hematite) during pedogenic development. Results indicated that some of the magnetic parameters of soils, in this case χfd, can be useful for pedogenic comparisons and age correlations in the weathering sequence of soil. It is thus suggested that multiparameter rock magnetic investigations represent a more powerful approach for pedogenesis.  相似文献   

7.
Determining weathering rates of soils in China   总被引：2，自引：0，他引：2  
As an important parameter for critical load calculation and soil acidification simulation, weathering rates of soils in China were studied using different methods of calculation. The approaches used were the mass balance approach, the soil mineralogical classification, the total analysis correlation, the PROFILE model, the MAGIC model and a simulated leaching experiment. Since chemical weathering of secondary minerals usually plays a much more important role in neutralizing the long-term acidification of soils in China than that of parent material, soil mineralogy rather than parent rock/material type, which is regarded as the most suitable factor representing weathering rates in Europe, should be adopted as the basis for soil classification. The weathering rate assigned to each soil should also be corrected when the effect of temperature is considered. Due to the variation in experimental conditions, the weathering rates of soils from laboratory experiment may be difficult to compare with field determined rates, and should be adjusted by pH and percolation rate. The comparison of various methods in this study shows that the weathering rates of soils estimated by the PROFILE model coincide well with those from other independent methods such as the dynamic modeling by MAGIC and the modified leaching experiment. The weathering rates were very low (usually lower than 1.0 kEq·ha−1·year−1) for Allites (including Latosol, Lateritic Red Earth, Red Earth, Yellow Earth and Yellow-Brown Earth) in south China and Silalsols (consisting of Dark Brown Forest Soil, Black Soil and Podzolic Soil) in northeast China, and very high for Alpine Soils, Desert Soils and Pedocals in west China. The content of weatherable minerals in soil is the most important factor in determining the spatial distribution of weathering rate in China, while the difference in temperature may be the reason why the weathering rate of soil in northeast China was lower than that in southeast China.  相似文献   

8.
The PROFILE model is used extensively in the European Critical Loads programme as an aid to international negotiations on SO2 emission abatement. PROFILE calculates the rates of cation release by mineral weathering and it then uses these data to calculate soil solution and runoff chemistry. No independent assessment of the underlying assumptions and data in the model has been published and this paper reports such an assessment. The rate equations, which are the key to the PROFILE model require rate coefficients and constants. These have been derived from the literature but more work is required to produce a consistent set of constants. Manipulation of these rates to take into account the exposed reactive surface area of the minerals is fraught with problems. Calculation of exposed mineral surface area from soil textural data results in under-estimates and the requirement to determine the surface area fraction of the different minerals in the soil to be known is extremely difficult if not impossible. Further uncertainty is introduced by adjustment of the rates to take into account temperature differences and by the use of a default mineralogy which is compositionally unrealistic. Despite its flaws PROFILE usually predicts similar weathering rates to other methods of calculation. It is argued that the unrealistic constraints imposed by the use of the surface area equation may be responsible for limiting calculated weathering rate to a fixed range which coincides with characteristically determined values for weathering rates.  相似文献   

9.
The distribution of red and black soil (Xeralfs–Xerolls) associations in the Monarto area (South Australia) is complex and their genesis either being derived from a uniform parent material or a lithologic discontinuity is not known. The objectives of this study were (i) to assess Zr- and Ti-bearing grains as minerals resistant to chemical weathering prior to employing Zr and Ti in determining parent material uniformity, and (ii) to confirm whether pedological processes or a lithologic discontinuity may be responsible for the textural contrast within the red and black soil profiles. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) were used to study chemical weathering and elemental composition of surfaces of Zr- and Ti-bearing grains. X-ray fluorescence (XRF) analysis was used to determine elemental concentrations in various soil fractions. Results showed that Zr-bearing grains consisted of only zircon having smooth clean surfaces, which are characteristic of a mineral resistant to chemical weathering. EDAX spectra confirmed that Zr was a specific element to represent zircon, suggesting its reliability to be used in assessing parent material uniformity. On the other hand, Ti derived not only from minerals (rutile/anatase) resistant but also from minerals (ilmenite/pseudorutile, biotite) susceptible to chemical weathering. This limited the usefulness of Ti as an index mineral for soil development studies. Except for Zr:Ti ratio, all other indicators of parent material uniformity, i.e., depth distribution curves of Zr and Y in various fractions and Y:Zr ratio showed no considerable inflection and variation with depth in a Xeralf (red soil). This indicated the Xeralf derived from a uniform parent material (mica schists), thereby texture contrast within a profile is due to pedological processes. On the other hand, depth distribution curves showed clear inflection and variation in Xerolls (black soils), indicating soils developed from lithologic discontinuities, so different trends in particle size fractions between 0–48 cm for MA5 and 0–59 cm for MA3 profiles compared to the underlying layers are due to parent material differences and not pedogenesis. The presence of complex red and black soil association in the landscape is attributed to the difference in parent materials, where the red soil developed from mica schist and the black soils from calcareous deposits.  相似文献   

10.
Ten soil colloids were obtained from three kinds of Fe-rich (> 50 g kg− 1) subtropical soil parent materials (Basalt, Sandshale, and Quaternary Period Red Earth) collected in nine sites in Guangdong of China. Effect of the Fe-rich soil colloids and adding Fe(II) and oxalic acid on reductive dechlorination transformation of pentachlorophenol (PCP) were studied on colloids interfaces of reaction suspension. Mineralogical properties and specific surface area of the soil colloids were characterized by X-ray powder diffraction and Brunauer-Emmett-Teller (BET) methods, respectively. A series of reductive experiments were designed to determine PCP transformation and chloride ion release, and to calculate rate constant (k values) of pseudo first-order kinetics. Our results showed that reductive transformation of PCP occurred with k values from 0.007 to 0.057 d− 1, and relevant chloride was released in the suspension of the ten soil colloids. Soil colloid developed from Basalt presented higher transformation rates (0.040-0.057 d− 1) than that from Sandshale (0.007-0.033 d− 1) and Quaternary Period red earth (0.012 d− 1). Two paddy soil colloids developed from Sandshale (0.032-0.033 d− 1) were more active than other three Sandshale soil colloids (0.007-0.011 d− 1). The k values were significantly and positively correlated to the BET surface area (P < 0.01, n = 10). Addition of oxalic acid (0.022-0.231 d− 1) or Fe(II) (0.029-0.256 d− 1) into suspension of soil colloids gave arise to increase by 1.2-9.4 times in the k values. The release of chloride ion was simultaneously elevated. The enhancement of oxalic acid or Fe(II) on reductive transformation of PCP was attributed to increase of surface-bound Fe(II), which possess high reductive reactivity. The k values adding 1.0 mM oxalic acid were significantly and positively correlated to BET surface area and soil pH (P < 0.01), while k values adding 1.0 mM Fe(II) were related to total Fe (P < 0.001). The results may give new insight to understand the contribution of PCP abiotic reductive transformation in subtropical and tropical soils, and also in permeable reactive barriers.  相似文献   

11.
Base cation (BC) concentrations of rain, throughfall, percolation from leaf litter, and soil solution were periodically measured in two forests: Kannondai (red pine stand on volcanic soil) and Yasato (deciduous stands on granitic soil). Calculation of a BC budget gave the rate of BC release from soils; the BCs originated from mineral weathering and cation exchange. Weathering rates under field conditions were estimated from the Sr isotope ratios (87Sr/86Sr) of water and soil samples. Isotope ratios decreased in the order rain > throughfall > percolation > soil solution. Clay and silt had extremely high isotope ratios; this suggests that the sandy fraction, whose isotope ratio was smaller than that of the soil solution, was the main contributor to mineral weathering. Estimated BC weathering rates (kmolc·ha?1y?1) were 1.16 for Ca and 0.57 for Mg at Kannondai, and 0.82 for Ca and 0.51 for Mg at Yasato. The unexpected high weathering rate of granitic soil in Yasao was due to the wide coverage of the original parent material by volcanic ash. The contribution of cation exchange derived by subtraction was a little smaller than the weathering rates and was similar to the values estimated from a dynamic model that we developed.  相似文献   

12.
Simplified steady state mass balance model for critical load (CL) estimation was applied to a test area in Japan to evaluate applicability of the model. Three different criteria for acidification limits (1: [Al3+]<0.2 eq.=">–3, 2: Al/BC<1.0 mol=">–1, 3:Al depletion criterion) were used. Mean values and spatial distribution patterns of CL values calculated by these criteria were extremely different from each other. The first criterion produced much higher CL than the second criterion in the Japanese condition with high annual precipitation. Improvements including definition of the criterion were considered necessary. As quantitative data of the base cation weathering rate (BCw) was lacking, the rate was specified based on surface geology and the soil type of each site. To evaluate uncertainty of BCw used for CL calculation, ion content and particle-size distribution were measured for the soils collected from the test area, and BCw was estimated with PROFILE model based on these measurements. It appeared that BCw estimates by surface geology were adequate as a mean value, but they had uncertainty of about 50% of the average values due to variability of ion contents within the same surface geology group.  相似文献   

13.
The importance of bioturbation as an agent of soil and geomorphological change is well known but few observations have been made of spatial and temporal variations in bioturbation rates. We quantified variations in surface bioturbation by ants (particularly Aphaenogaster longiceps) and vertebrates in the sandstone terrain of the Blue Mountains, southeast Australia. Following wildfire during the period late 2001–early 2002, we monitored thirty-three 5 m2 plots positioned in six different slope units and in two catchments affected by different wildfire severities. Measurements were made seasonally for six years. Overall, mean rates of ant mounding and surface scraping by vertebrates were similar (246 ± 339 g m− 2 yr− 1 and 274 ± 179 g m− 2 yr− 1, respectively). However, rates varied substantially according to slope unit, showing a marked maximum for both ant mounding and total bioturbation on footslopes. Possible reasons for this spatial variation are discussed. A complex response to various soil and ecological factors such as soil texture, soil moisture and vegetation patterns is the most likely explanation. Associated estimates of topsoil (0–30 cm depth) turnover times, based on ant mounding rates alone, ranged from 300 to 100,000 years for different slope units. In contrast to previous findings, wildfire severity did not seem to affect bioturbation, possibly because of ant survival in deep nests and spatial patchiness of fire severity. There was likewise no clear link between temporal changes in bioturbation and fire severity; high rates in the first two years after wildfire were followed by lower rates for all burn severity types. There was also seasonal variability that was not directly related to rainfall. The results substantiate the importance of bioturbation in modifying soil characteristics and influencing soil erosion, especially following a major disturbance event like wildfire.  相似文献   

14.
Bedrock surfaces in the Ouachita Mountains, Arkansas, exposed by spillway construction and which had not previously been subjected to surface weathering environments, developed 15–20 cm thick soil covers in less than three decades. All open bedrock joints showed evidence of weathering and biological activity. Rock surfaces and fragments also showed evidence of significant weathering alteration. The results suggest a soil production function whereby weathering and increases in thickness are initially rapid. The rapid initial rate (5 to 10 mm year− 1) is facilitated by a weathering-favorable regional climate, local topography favoring moisture and sediment accumulation, and aggressive vegetation colonization. The ages of the trees on the bedrock benches suggests that a short period (< 10 years) of pedogenic site preparation is necessary before trees can become established. Initial chemical weathering within newly-exposed rock fractures in resistant sandstone strata and chemical weathering of weak shale layers, coupled with accumulation of organic and mineral debris in fractures and microtopographic depressions facilitates plant establishment, which accelerates local weathering rates.  相似文献   

15.
The island of Milos (Greece), part of the South Aegean volcanic arc with a typical Mediterranean climate, is covered with volcanic deposits of different ages. The objective of this study was to investigate the physicochemical and mineralogical properties of the soils developing on these volcanic deposits and their classification. Samples were taken from seven locations of soil on different parent material and of different ages. There were substantial differences in their particle size distribution, with sand ranging from 19% to 92%, silt from 3.5% to 50%, and clay from 5% to 46%. Organic matter content was low (< 2.0%). The soil pH ranged from 5.6 to 8.0. In two of the profiles, CaCO3 equivalents of 1.4% to 24.6% were found and a calcic horizon identified. The cation exchange capacity (CEC) and specific surface area (SSA) varied between profiles ranging from 3 cmol(+) kg− 1 to 47 cmol(+) kg− 1 and 30 m2 g− 1 to 380 m2 g− 1, respectively. The soils exhibited high base saturation. The amounts of Al, Fe and Si extracted with ammonium oxalate (Αlo, Feo and Sio) were particularly low (< 0.1%, < 0.17%, and < 0.1%, respectively) which demonstrates the absence of amorphous clay-silicate minerals (allophane). Fe extracted with dithionite citrate bicarbonate — DCB (Fed) was greater than Feo sharing the dominance of crystalline Fe oxides. Al and Si extracted with hot 0.5 M NaOH (Al2Ο3NaOH and SiΟ2NaOH) and with Τiron-C6H4Na2O8S2, (Al2Ο3Τ and SiΟ2Τ). SiΟ2NaOH and SiΟ2Τ were particularly high (mean values 3.4% and 4.5%, respectively), showing that amorphous silica was present. The clay fraction of the soil was dominated by the presence of 2:1 (vermiculite and smectite) and 1:1 (kaolinite) clay-silicates. Alo+ 1/2Feo was low (< 0.18%), while the P-retention in most soils was less than 15%. These soils do not exhibit andic properties and hence cannot be classified as Andisols. The silica saturation index (ISS) may be used for these soils to describe a pedogenetic environment rich in Si which favours the formation of pedogenic amorphous silica. The climate is the major determinant of the evolution of these soils.  相似文献   

16.
Based on the enclosed chamber method, soil respiration measurements of Leymus chinensis populations with four planting densities (30, 60, 90 and 120 plants/0.25 m2) and blank control were made from July 31 to November 24, 2003. In terms of soil respiration rates of L. chinensis populations with four planting densities and their corresponding root biomass, linear regressive equations between soil respiration rates and dry root weights were obtained at different observation times. Thus, soil respiration rates attributed to soil microbial activity could be estimated by extrapolating the regressive equations to zero root biomass. The soil microbial respiration rates of L. chinensis populations during the growing season ranged from 52.08 to 256.35 mg CO2 m−2 h−1. Soil microbial respiration rates in blank control plots were also observed directly, ranging from 65.00 to 267.40 mg CO2 m−2 h−1. The difference of soil microbial respiration rates between the inferred and the observed methods ranged from −26.09 to 9.35 mg CO2 m−2 h−1. Some assumptions associated with these two approaches were not completely valid, which might result in this discrepancy. However, these two methods' application could provide new insights into separating root respiration from soil microbial respiration. The root respiration rates of L. chinensis populations with four planting densities could be estimated based on measured soil respiration rates, soil microbial respiration rates and corresponding mean dry root weight, and the highest values appeared at the early stage, then dropped off rapidly and tended to be constant after September 10. The mean proportions of soil respiration rates of L. chinensis populations attributable to the inferred and the observed root respiration rates were 36.8% (ranging from 9.7 to 52.9%) and 30.0% (ranging from 5.8 to 41.2%), respectively. Although root respiration rates of L. chinensis populations declined rapidly, the proportion of root respiration to soil respiration still increased gradually with the increase of root biomass.  相似文献   

17.
Although information regarding the spatial variability of soil respiration is important for understanding carbon cycling and developing a suitable sampling design for estimating average soil respiration, it remains relatively understudied compared to temporal changes. In this study, soil respiration was measured at 35 locations by season on a slope of Japanese cedar forest in order to examine temporal changes in the spatial distribution of soil respiration. Spatial variability of soil respiration varied between seasons, with the highest coefficient variation in winter (42%) and lowest in summer (26%). Semivariogram analysis and kriged maps revealed different patterns of spatial distribution in each season. Factors affecting the spatial variability were relief index (autumn), soil hardness of the A layer (winter), soil hardness at 50 cm depth (spring) and the altitude and relief index (summer). Annual soil respiration (average: 39 mol m−2 y−1) varied from 26 mol m−2 y−1 to 55 mol m−2 y−1 between the 35 locations and was higher in the upper part of the slope and lower in the lower part. The average Q10 value was 2.3, varying from 1.3 to 3.0 among the locations. These findings suggest that insufficient information on the spatial variability of soil respiration and imbalanced sampling could bias estimates of current and future carbon budgets.  相似文献   

18.
Biochemical characterization of urban soil profiles from Stuttgart, Germany   总被引：1，自引：0，他引：1  
The knowledge of biochemical properties of urban soils can help to understand nutrient cycling in urban areas and provide a database for urban soil management. Soil samples were taken from 10 soil profiles in the city of Stuttgart, Germany, differing in land use—from an essentially undisturbed garden area to highly disturbed high-density and railway areas. A variety of soil biotic (microbial biomass, enzyme activities) and abiotic properties (total organic C, elemental C, total N) were measured up to 1.9 m depth. Soil organic matter was frequently enriched in the subsoil. Microbial biomass in the top horizons ranged from 0.17 to 1.64 g C kg−1, and from 0.01 to 0.30 g N kg−1, respectively. The deepest soil horizon at 170-190 cm, however, contained 0.12 g C kg−1 and 0.05 kg N kg−1 in the microbial biomass. In general, arylsulphatase and urease activity decreased with depth but in three profiles potentially mineralizable N in the deepest horizons was higher than in soil layers directly overlying. In deeply modified urban soils, subsoil beside topsoil properties have to be included in the evaluation of soil quality. This knowledge is essential because consumption of natural soils for housing and traffic has to be reduced by promoting inner city densification.  相似文献   

19.
In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the 137Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m− 2). All the sampling sites were eroded and 137Cs inventories varied widely (between 245 and 3670 Bq m− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha− 1 yr− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha− 1 yr− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha− 1 yr− 1 and reaching a maximum of 48.8 t ha− 1 yr− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha− 1 yr− 1) to 25° (40. 8 t ha− 1 yr− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha− 1 yr− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha− 1 yr− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area.  相似文献   

20.
The impact of land-use change on soil nitrogen (N) transformations was investigated in adjacent native forest (NF), 53 y-old first rotation (1R) and 5 y-old second rotation (2R) hoop pine (Araucaia cunninghamii) plantations. The 15N isotope dilution method was used to quantify gross rates of N transformations in aerobic and anaerobic laboratory incubations. Results showed that the land-use change had a significant impact on the soil N transformations. Gross ammonification rates in the aerobic incubation ranged between 0.62 and 1.78 mg N kg−1 d−1, while gross nitrification rates ranged between 2.1 and 6.6 mg N kg−1 d−1. Gross ammonification rates were significantly lower in the NF and the 1R soils than in the 2R soils, however gross nitrification rates were significantly higher in the NF soils than in the plantation soils. The greater rates of gross nitrification found in the NF soil compared to the plantation soils, were related to lower soil C:N ratios (i.e. more labile soil N under NF). Nitrification was found to be the dominant soil N transformation process in the contrasting forest ecosystems. This might be attributed to certain site conditions which may favour the nitrifying community, such as the dry climate and tree species. There was some evidence to suggest that heterotrophic nitrifiers may undertake a significant portion of nitrification.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号