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1.
Over the past 150 years, major land use changes have occurred in the Stemple Creek Watershed in northern California that have caused erosion to move soils from the upland to the flood plain, stream channels, and the bay. The purpose of this study is to document the recent (1954 to present) sediment deposition patterns in the flood plain area adjacent to Stemple Creek using the 137Cesium technique. Sediment deposition ranged from 0.26 to 1.84 cm year−1 for the period from 1964 to 2002 with an average of 0.85±0.41 cm year−1. Sediment deposition rates were higher for the 1954 to 1964 period with a range of 0.31–3.50 cm year−1 and an average of 1.29±1.04 cm year−1. These data indicate that sediment deposition in the flood plain has decreased since the middle 1950s, probably related to reduction in row crop agriculture and an increase in pasturelands. This study shows that the flood plains in the Stemple Creek Watershed are a significant sink for the soils being eroded from the upland area. Given the significance of the flood plain for trapping eroded materials before they reach the stream channels or the bay, efforts need to be made to manage these flood plain areas to insure that they do not change and become a source rather than a sink for eroded materials as improved management practices on the upland areas reduce sediment input to the flood plain.  相似文献   

2.
The natural abundance15N/14N method was used to estimate the influence of silvicultural and P fertilization treatments on N accretion, N2fixation and N partitioning among tissues in a mature mesquiteProsopis glandulosavar.glandulosastand in Texas. The silvicultural treatments consisted of understory removal, herbicide treatment of brushy resprouts, thinning trees to single stems and 100 kg ha−1P fertilization. The trees had a mean basal diameter of 17·8 cm with 8 to 35 cm range. The stand was slow growing with the increase in dry matter ranging from 0·465 Mg ha−1year−1to 0·701 Mg ha−1year−1for the 8 years after the treatments were applied. N accretion after 8 years ranged from 3·1 kg ha−1year−1to 4·4 kg ha−1year−1.Due to the range in δ15N of the leaves, twigs, branches and trunk, we used the weighted (by biomass) average δ15N per tree in calculations of the percent N derived from N2fixation (%Ndfa). There was considerable variability in δ15N of the reference plants, i.e. from 3·3 to 5·9. In contrast there was low variability in the background δ15N of nearby soils (7·0±1·0). As the total above-ground biomass δ15N of a grass grown outside the influence of mesquite (7·8±0·58) had the same δ15N as the soil (7·5±1·0), we used the grass outside the influence of mesquite and the weighted tree mean δ15N to calculate % of N derived from N2fixation.The decrease in intraspecific competition by thinning multistemed trees to single stemmed trees was the only treatment that significantly (p= 0·0001) increased growth. Interspecific competition, i.e. understory removal, did not increase growth. There were no significant differences in total N production or N fixation among treatment means. The most striking result was the highly positive correlation between tree δ15N and total N per tree and biomass per tree (R2= 0·90,F= 164·4, df. = 18, mean square error (MSE) = 0·155,p= 0·0001). This implies that the younger trees colonizing infertile soils relied more heavily on N2fixation than larger trees which accumulated 1200 kg ha−1more N under their canopies. The percentage N derived from N2fixation ranged from 63 to 73% in the various treatments. Despite the high percentage of N derived from N2fixation, the N2fixation of the stand was very low, i.e. 1·98 to 2·80 kg N ha−1year−1, due to the low growth of the stand. We believe that comparisons of the whole tree weighted δ15N to background soil δ15N provides a more reasonable approach to estimate % N2fixation than comparisons of leaves of fixers and reference plants.  相似文献   

3.
Factors affecting temporal and spatial variations of growth were studied in cirio, a succulent often surpassing 10 m in height. Measurements were obtained for intervals of 3–93 years at 14 sites in Baja California. Height tended to be asymptotic but total plant length (i.e. including all succulent stems) increased in linear relation to trunk diameter. Growth in length showed an overall average of 4·6 cm year−1 but ranged from 0·3–16·7 cm year−1 (annualized from data for intervals >34 year). Most of the variation was among individuals, but some differences between sites were also significant. Growth was clearly and strongly related to size only for individuals less than 1 m in height. Repeated measures on the same individuals showed that the autocorrelation of growth was about 0·8 between intervals of 3 or more years. Differences among individuals were related to physiographic position, the presence of caliche and the density of neighboring plants, which together explained 43% of the variation. We discuss the implications of these results for age estimates, indicators of site quality and studies of similar plants.  相似文献   

4.
The migration of a small slipfaceless dome dune close to the northern edge of the Namib Sand Sea has been measured by topographic survey. The dune dimensions are 45-m wide and 1-m high with a volume of 551 m3 that has been calculated as the difference between the dune's surface elevation and an interdune surface extrapolated from measurements around the edge of the dune. The migration direction, 64°, and distance moved, 90 m, are measured against stakes set out in 1976. The dune has moved about 90 m between 1976 and 1999. This is an average linear migration rate of around 4 m year−1, and is equivalent to an annual sand transport rate of about 1.2 tonnes m−1 year−1. The calculated total potential sand flow in this part of the Namib Desert is 119 tonnes m−1 year−1, and the resultant potential sand flow is 63 tonnes m−1 year−1. The dune migration is therefore about 1% of the total potential sandflow and 2% of the resultant indicating that dune migration is only a small part of total potential sand transport. The results suggest that small slipfaceless dome dunes are very inefficient at trapping sand, and that winds blowing across the interdune in this area are undersaturated with sand.  相似文献   

5.
The northern coastal part of Korinthia prefecture can be characterized as an agrotourism center that has grown and urbanized rapidly. The area is formed of recent unconsolidated material consisting of sands, pebbles, breccias and fine clay to silty sand deposits. These deposits host the main aquifer system of the area, which depends on groundwater as a water resource. Groundwater is the main source for irrigation in the area. A total water volume of 29.2×106–34.3×106 m3 yr−1 was estimated to recharge the aquifer system from direct infiltration of rainfall, streambed infiltration, irrigation return, artificial recharge via flood irrigation and lateral subsurface inflows. The present annual abstraction ranges between 39.2×106 and 44.6×106 m3 yr−1. Groundwater abstraction in dry years exceeds renewable freshwater resources by more than 38%. Approximately 79% of the total abstraction is consumed for agriculture supply. Water balance in the coastal aquifer system is in disequilibrium; a deficit, which ranges from 4.9×106 to 15.4×106 m3 yr−1 exists. The safe yield of the coastal aquifer system has been estimated at 37.1×106 m3 yr−1 for normal hydrological year and 32×106 m3 yr−1 for severely dry hydrological year. The total abstraction is greater than the recharge and the safe yield of the aquifer. The aquifer system has shown signs of depletion, seawater intrusion and quality contamination. The integrated water resources management, securing water in the future, should include measures that augment groundwater budget in the coastal aquifer of the study area.  相似文献   

6.
We have investigated secondary influences on the noble gas budget in rim and interior pairs of three Martian meteorites from Antarctica: the lherzolitic shergottites Y000027 and Y000097, and the nakhlite Y000593. Three factors have been found to influence the original Martian noble gas budget: shock metamorphic overprint, cosmic irradiation, and terrestrial weathering. The 3He/4He ratio of the shergottites is between 0.189 and 0.217, which indicates almost complete loss of radiogenic 4He. This is expected from the high shock pressure observed in the shergottite samples. The concentration of 4He in these shergottite samples ranges from 33.8 to 39.4 × 10−8 ccSTP/g. 22Ne in the shergottites is on the order of 14 × 10−9 ccSTP/g. The nakhlite has 800 × 10−8 ccSTP/g 4He and 26 × 10−9 ccSTP/g 22Ne. An indication for solar cosmic ray contribution to the neon budget can be found in the shergottites. As Y000027 and Y000097 are reported to be paired we conclude the cosmic ray exposure (CRE) age T(3+21) of this shergottite to be 4.41 ± 0.54 Ma. For the nakhlite Y000593 T(3+21) is 11.8 ± 0.3 Ma. Heavy noble gas concentrations show large differences between rim and interior samples with the rim samples having 1.3–2.9, 1.7–38, and 1.4–20 times as much 36Ar, 84Kr, and 132Xe, respectively. The enrichment of heavy noble gases in the rim samples indicates severe terrestrial contamination. The relation between 129Xe/132Xe and 84Kr/132Xe in the rim samples shows that the incorporation mechanism caused elemental fractionation of Kr and Xe to the extent that in the Y000027 shergottite samples any Martian signature is completely masked by terrestrial contamination, if the total is taken. Only the 1400 °C steps show clear evidence for Martian atmosphere. The Y000593 nakhlite interior sample, on the other hand, shows low 84Kr/132Xe in relation to 129Xe/132Xe, which is characteristic for fractionated Martian atmosphere observed in nakhlites.  相似文献   

7.
Monthly samples of riverine water were collected and analyzed for the concentrations of major ions (Ca2+, Mg2+, K+, Na+, HCO3−, SO42−, Cl−, NO3−), dissolved silicon, and total dissolved solids (TDS) at Wuzhou hydrological station located between the middle and lower reaches of the Xijiang River (XJR) from March 2005 to April 2006. More frequent sampling and analysis were carried out during the catastrophic flooding in June 2005. Stoichiometric analysis was applied for tracing sources of major ions and estimating CO2 consumption from the chemical weathering of rocks. The results demonstrate that the chemical weathering of carbonate and silicate rocks within the drainage basin is the main source of the dissolved chemical substances in the XJR. Some 81.20% of the riverine cations originated from the chemical weathering processes induced by carbonic acid, 11.32% by sulfuric acid, and the other 7.48% from the dissolution of gypsum and precipitates of sea salts within the drainage basin. The CO2 flux consumed by the rock chemical weathering within the XJR basin is 2.37 × 1011 mol y− 1, of which 0.64 × 1011 mol y− 1 results from silicate rock chemical weathering, and 1.73 × 1011 mol y− 1 results from carbonate rock chemical weathering. The CO2 consumption comprises 0.38 × 1011 mol during the 9-d catastrophic flooding. The CO2 consumption from rock chemical weathering in humid subtropical zones regulates atmospheric CO2 level and constitutes a significant part of the global carbon budget. The carbon sink potential of rock chemical weathering processes in the humid subtropical zones deserves extra attention.  相似文献   

8.
At the beginning of December 2003, one of the biggest floods for at least 150 yr was recorded on the Rhone River. In the lower part of the river, the peak flood reached 11,000 m3 s−1. The geomorphological and radioecological consequences of such an event were investigated downstream all the nuclear installations by using measured and calculated fluxes and the total export of suspended sediment and associated 137Cs. Results pointed out the major role played by large floods in the annual suspended sediment load, as 3.70 × 106 tons of silts, 0.85 × 106 tons of sands, and 0.84 × 106 tons of clays were transferred towards the coastal environment. Nevertheless, these solid loads were found to be lower than those expected as regards the liquid discharge reached during this event and suggested that previous floods that occurred on the river and on its main tributaries during the last decade have probably led to the removal of available sediment from the channels and their banks. Besides, the 137Cs activity measured within the suspended load was estimated at 14.9 ± 0.4 Bq kg−1, which is a level characteristic of the suspended sediments from the Rhone catchment area and demonstrated that nuclear installations located along the Rhone valley did not significantly contribute to any increase in 137Cs activity in the water during the flood. The total 137Cs particulate export amounted to 77 ± 17 GBq and was mainly associated with the silt fraction that contributes to around 70% of the total 137Cs export.  相似文献   

9.
The profile distribution of total, diethylene triamine penta-acetic acid (DTPA)- and 0·1 HCl-extractable Fe and Mn were determined in 12 pedons formed on three contiguous sand dunes in the semi-arid savanna of Nigeria. The total Fe and Mn contents varied from 100 to 3750 and 40 to 11,375 μg g−1, respectively. Values of 0·1 HCl-extractable Fe and Mn varied from 8·0 to 123 and 1·5 to 43·5 μg g−1, respectively. The corresponding values of DTPA-extractable Fe and Mn were 4·5 to 16·0 and 1·0 to 38·8 μg g−1. Total Fe and Mn correlated significantly with clay in nearly all the dunes (p≤ 0·01) but were not significantly correlated with organic matter. The 0·1 HCl-extractable Mn had a positive significant correlation with soil pH (r= 0·58*) in Illela dunes but a negative significant correlation with pH in the Sangiwa dunes (r= −0·75***). The values of extractable Fe and Mn in the sand dune soils are above the critical limits reported in other literature, thus deficiencies of these micronutrients do not pose a problem to crop production in the study area.  相似文献   

10.
Encroachment of the shrub Prosopis glandulosa Torr. (honey mesquite) into semi-arid grasslands is a serious concern in the south-western United States, yet little is known about the long-term dynamics of the invasion process. We used ten high-resolution aerial and satellite images taken from 1936 to 1996 to track the population dynamics and spatial pattern of all P. glandulosa greater than 2 m in diameter on a 75 ha area in southern New Mexico.Shrub cover and patch numbers increased from 1936 to the 1970s, then stabilized at 43% cover and 83 patches ha−1. Individual patches were extremely persistent: 95% of the area occupied by shrub patches in 1936 was still occupied in 1996. Recruitment into the 2 m size class was more variable: 0·6–5·2% year−1 (mean 0·8% year−1). Patch-shape complexity increased from 1936 to 1983 as adjacent shrubs merged, and then declined as those clusters filled in and became rounder. Spatial pattern of shrubs showed a distinct trend over time: strongly clustered in 1936 at lag distances up to 250 m, then random arrangement at all scales, and by 1983 pattern was regular at lag distances greater than 100 m. There was no clear relationship with precipitation.The use of remote sensing imagery allowed us to examine one site over time, and revealed patterns in population dynamics and spatial pattern that would not have been visible otherwise. Comparison of field estimates collected in 2001 with 1996 image data suggest that the canopy cover estimates were accurate, but shrub densities were seriously underestimated in the satellite photographs, which do not show shrubs smaller than 2 m diameter. As long as limitations of the imagery are understood, these methods can be applied over a larger and more heterogeneous area to examine environmental correlates of invasion success.  相似文献   

11.
Although in the last decades gully erosion has been a thriving research field, few studies have specifically addressed the contribution and location of sidewall erosion processes in gullies. In this paper, sidewall erosion in some large gullies in a Mediterranean area (Anoia-Penedès, NE Spain) is mapped and assessed for two time intervals (1975–1995 and 1995–2002), using detailed digital elevation models derived from aerial photographs at a scale of 1:5000 to 1:7000. Logistic regression analysis is applied to compute the probability of occurrence of gully sidewall erosion from terrain variables. The results confirm the complex nature of sidewall processes, whose intensity is most probably related to rainfall characteristics. Prolonged wet soil conditions in the period 1995–2002, together with the large and high-intensity rainfall of an extreme event occurred on 10th June 2000, help to explain the different sediment production rates: 16±0.4 Mg ha−1 year−1 in 1975–1995 and 83±6.3 Mg ha−1 year−1 in 1995–2002. The logistic regression analysis revealed that gully-wall slope angle was the main factor controlling gully sidewall failure. In gully walls with high slope angles, tension crack development is the main process promoting wall collapse. The application of the logistic regression model showed a high overall accuracy (87%) but over 50% of commission and omission errors for the class of interest (sidewall erosion), in agreement with the variance explained by the model.  相似文献   

12.
The objective of this study is to outline how the ground-water quality is affected by geological factors, soil characteristics and subsurface structure. The results of 25 ground-water samples, and 30 soil samples of which 10 soil samples analysed chemically provide the basis of this study. Procedures to interpret water quality data are based on a combined use of the traditional graphical methods, ratios of Na+/Cl−and Ca2+/Mg2+, multivariate geostatistical methods and computation of the saturation indices (SI) of minerals. The results of soil analyses show that the grain size ranges from very coarse sand to clayey loams, and from well sorted and extremely poorly sorted. The soil salinity increases in old alluvial plains and decreases in the dissected wadis of limestone plateaux, while vertical distribution decreases with depth. It is found that the ground-water is supersaturated with respect to calcite and dolomite, and undersaturated with respect to gypsum. Calculated values of PCO2for the ground-water samples range from 2×10−4to 7×10−3with a mean value of 3×10−3(atm.). This indicates that the ground-water becomes charged with CO2during infiltration processes.  相似文献   

13.
Three-week old soybean (Glycine max) plants were subjected to a factorial combination of four regimes of soil matric water potential (ψm=−0·03, −0·5, −1·0 and −1·5 MPa), two levels of supplementary Zn (O and 20 mgl−1) and two levels of foliar IAA application (O and 10 mgl−1). Under control conditions (no Zn, no IAA), increasing soil drying progressively retarded shoot and root growth (length and dry mass production), reduced leaf relative water content (RWC) and decreased the contents of chlorophyll (Chl) and shoot soluble sugars (SS), but increased soluble sugar content of roots and lowered osmotic water potential of shoots and roots (osmotic adjustment). Total free amino acid (TAA) content increased in shoots but decreased in roots whereas contents of soluble proteins (SP) decreased in shoots and roots. The effect of water stress was statistically significant (p<0·05) and had a major effect (as indicated by η2values) on leaf RWC, shoot and root dry masses and osmotic potential. Supplementary Zn improved root growth at all levels of stress and shoot growth under severe stress. Improvement of growth was positively correlated with the internal tissue Zn concentrations (r=0·91 and 0·86 for shoot and 0·94 and 0·82 for root length and dry mass respectively). Exogenous IAA raised (p<0·05) RWC, Chl, DM (slightly), root SS, and SP, whereas shoot TAA was lowered. Effects on root TAA and shoot SS were more complex: they were lowered at zero stress and raised under severe stress. IAA and Zn in combination had additive effects on Chl, growth and osmotic potential, but their combined effects on SP and TAA were more complex. It is concluded that the treatment of soybean plants grown under conditions of low soil water potentials and Zn deficiency with Zn and IAA solutions counteracted the deleterious effects of stress, especially at high stress levels, and helped stressed plants to grow successfully under these adverse unfavourable conditions.  相似文献   

14.
The world fallout of caesium-137 (137Cs) associated with nuclear weapons testing during the 1950s and 1960s has provided a valuable man-made tracer for studies of soil erosion and sediment delivery. But relatively few researchers have used it to estimate wind erosion. In this paper, the137Cs technique is introduced into the study of wind erosion and its modern processes in the Qinghai-Tibet Plateau. Two137Cs reference inventories of 982·11 and 2376·04 Bq m−2was established preliminarily, which distribute in the south and mid-north parts of the study area respectively. By analysing the patterns of137Cs depth profiles from sampling sites, the aeolian processes of erosion and deposition along nearly 40 years has been revealed, i.e. the shrub coppice dunes(S1) and semi-fixed dunefields (S3) had experienced the alternation of erosion and deposition, while the grasslands (S4, S6 and S7) and dry farmlands (S5) suffered erosion only. By using the137Cs model, the average wind erosion rates for shrub coppice dune (S1), semi-fixed dunefields (S3), dry farmlands (S5) and grasslands (S4, S6 and S7) were estimated to be 84·14, 69·43, 30·68 and 21·84 tha−1a−1respectively, and for the whole Plateau, averaging 47·59 ha−1a−1which can be regarded as the medium erosion standard. These results derived from137Cs for the first time have significant implications for the further research of wind erosion and desertification control in the Qinghai-Tibet Plateau.  相似文献   

15.
Chemical and environmental isotope study of precipitation in Syria   总被引：1，自引：0，他引：1  
Waters from a network of rainfall collection covering nine meteorological stations distributed mainly in the western part of Syria have been assayed using chemical and environmental isotope techniques for a period of 5 months from Dec 1989 to Apr 1990. The chemistry of rain waters falling over the mountainous stations shows a low solute concentration (20–105 mg−1/L) compared with those falling over the coastal and anterior stations (50–210 mg−1/L). The rain waters are generally characterized by a high deuterium excess (d = 19 ‰) compared with that of typical global meteoric waters (d = 10 ‰). The estimated deuterium excess is lower than that for the eastern Mediterranean meteoric waters (d = 22 ‰). The altitude effect is shown up by a depletion of heavy stable isotopes of about −0·23 ‰ and −1·65 ‰ per 100 m elevation of δ18O and δD, respectively. The spatial distribution pattern of tritium contents shows a gradual build up with increasing distance from the Syrian coast. The weighted mean tritium content in rain waters falling over the country is estimated to amount to 9·5 tritium units (TU) during the period of observation.  相似文献   

16.
Over-abstraction of groundwater is one concern of the Badia Research and Development Programme. The upper aquifer of the Azraq basin forms the largest resource of good-quality water, but current abstraction exceeds both average recharge and the safe yield of the aquifer, which is over-exploited. Although there has been no deterioration in water quality and only minor drawdown, the springs at Azraq have dried up, with severe, undesirable environmental impacts. Total abstraction of 20 × 106 m3 yr−1 appears to be sustainable and would allow some springflow, but this leaves a shortfall of 40 × 106 m3 yr−1 for domestic supply and agriculture.  相似文献   

17.
The selective use by cattle of range resources in the Sahel was assessed in terms of quantity and nutritional quality of the herbage grazed and diet selected. Peak standing crop was 1951 kg ha−1dry matter (DM) with 47·9 kg nitrogen (N) ha−1and 7·4 kg phosphorus (P) ha−1. Esophageally fistulated cattle diets were consistently (p<0·05) higher in N, P and organic matter digestibility (OMD) than the herbage grazed. Cattle consumed 48% of the mean annual herbage production. The results indicate grazing ruminants select a higher quality diet from Sahelian rangelands than can be predicted on the basis of pasture evaluation alone. Therefore, the foraging behaviour of the animals needs to be considered in the evaluation of Sahelian rangelands for animal production.  相似文献   

18.
This paper addresses analysis of surface meteorological and hydrographic data collected along the transects Durban–India Bay, Antarctica (Track-1) and Prydz Bay–Mauritius (Track-2) during February–March 2007 as part of the International Polar Year project (IPY#70). Strong winds (>12 m s−1) resulted in enhanced turbulent heat loss north of 45°S. Whereas a highly stable marine atmospheric boundary layer (MABL) and strong winds facilitated the release of latent heat of condensation along Track-1, a highly unstable MABL and strong winds resulted in large turbulent heat loss from the sea surface along Track-2, in the 40–45°S belt. The northern and southern branches of Subantarctic Front on both tracks coalesce, while the Agulhas Retroflection Front (AF) and South Subtropical Front (SSTF) merge between 43° and 44°S on Track-2. The southern branch of the Polar Front (PF2) meanders 550 km southward towards the east. The Subtropical Surface Water, Central Water, and Mode Water are located north of 43.5°S, while the Subantarctic Surface Water, Antarctic Surface Water, Antarctic Intermediate Water, and Circumpolar Deep Water are encountered in the region of the Antarctic Circumpolar Current (ACC). Baroclinic transport relative to 1000 db reveals that the ACC is enhanced by 10 × 106 m3 s−1 eastward, and a four-fold increase in transport occurs south of the ACC. Nearly 50% of the ACC transport occurs in the 100–500 m slab. We discuss the effects of the feedback of AC and hydrological fronts on the MABL.  相似文献   

19.
A portable wind tunnel was used to test the contribution of biological and physical elements to overall soil aggregation on a soil dominated by biological soil crusts in south-eastern Australia. After moderate disturbance and simulated wind erosion, 90% of surface aggregates on the loamy soil and 76% on the sandy soil were dominated by biological elements (cryptogams). Lower levels of biological bonding were observed on the severely disturbed treatment. Linear regression indicated a significant positive relationship (r2=0·72) between biological soil crust cover and dry aggregation levels greater than 0·85mm. To maintain sediment transport below an erosion control target of 5gm−1s−1 for a 65kmh−1 wind at 10m height, a crust cover of approximately 20% is required. When a multiple regression model which sequentially fitted biological crust cover and dry aggregation greater than 0·85mm was applied to the data, dry aggregation accounted for more of the variation in sediment transport rate than biological crust cover. These data were used to develop a conceptual model which integrates crust cover and dry aggregation, and provides a useful framework within which to predict the likely impacts of changes in soil crust cover and aggregation.  相似文献   

20.
Granitic regolith, developed in the Boulder Creek catchment and adjacent areas, records a history of deep weathering, some of which may predate Quaternary time. Field and well-log measurements of weathering, chemical denudation and rates of erosion derived from 10Be cosmogenic radionuclide (CRN) data help to quantify rates of landscape change in the post-orogenic Rocky Mountains. The density of oxidized, fractured bedrock ranges from 2.7 to about 2.2 g cm− 3, saprolite and grus have densities between 2.0 and 1.8 g cm− 3, and 30 soil samples averaged 1.6 ± 0.2 g cm− 3. Highly weathered regolith in 540 wells averages 3.3 m thick, mean depth to bedrock in 1661 wells is 7 m, and the weathered thickness exceeds 10 m in relatively large local areas east of the late Pleistocene glacial limit. Thickness of regolith shows no simple relationship to rock type or structure, local slope, or distance from channels. Catchments in the vicinity of the Boulder Creek have an average CRN erosion rate of 2.2 ± 0.7 cm kyr− 1 for the past 10,000 to 40,000 yr. Annual losses of cations and SiO2 vary from about 2 to 5 g m− 2 over a runoff range of 10 to nearly 160 cm.Using measured rates in simple box models shows that if a substantial fraction of void space is created by volume expansion in the weathering rock materials, 7 m of weathered rock materials could form in as little as 230 kyr. If density loss results mainly from chemical denudation and some volume expansion, however, the same weathering profile would take > 1340 kyr to form. Rates of erosion measured by CRN could be balanced by the rate of soil formation from saprolite if the annual solute loss from soil is 2.0 g m− 2 and 70% of the density decrease from saprolite to grus and soil results from strain. Saprolite, however, forms from oxidized bedrock at a far slower rate and rates of saprolite formation cannot balance soil and grus losses to erosion. The zone of thick weathered regolith is likely an eroding relict landscape. The undulating surface marked by relatively low relief and tors is not literally a topographic surface of Eocene, Oligocene or Miocene age unless it was covered with deposits that were removed in Pliocene or Quaternary time.  相似文献   

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