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1.
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   

2.
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   

3.
The majority of Scottish upland soils are particularly sensitive to acid deposition because of their low weathering rates. The compositions of the exchangeable base cations of such soils in the United Kingdom are dominated by sea salt inputs rather than by mineral weathering inputs of base cations. Catchments with low mineral weathering rates are also those particularly susceptible to freshwater acidification. Therefore, catchments exhibiting a high sea salt effect should also exhibit the most acid waters under base flow and storm flow conditions. A field evaluation study based on 61 catchments in NE Scotland has shown that this is indeed the case. River water pH under both base flow and high flow conditions is correlated stronhly with the relative contribution of Na+ to the sum of Ca2+, Mg2+ and Na+. From these results, an attempt is being made to produce a quantitative signature of weathering for the soils within the catchment upstream of the sampling point. Representative soil samples from the LFH, AE, B and C horizons and on 4 different parent materials have been obtained from the surrounding catchments to validate the above results for associated soil solutions. Sampling took place on upland moorland podzols under Calluna vulgaris. Tension lysimeters were used to sample the soil solutions so that their chemistry could be compared with that of the relevant river water.  相似文献   

4.
Ion mass and H+ budgets were calculated for three pristine forested catchments using bulk deposition, throughfall and runoff data. The catchments have different soil and forest type characteristics. A forest canopy filtering factor for each catchment was estimated for base cations, H+, Cl? and SO 4 2? by taking into account the specific filtering abilities of different stands based on the throughfall quality and the distribution of forest types. Output fluxes from the catchments were calculated from the quality and quantity of the runoff water. Deposition, weathering, ion exchange, retention and biological accumulation processes were taken into account to calculate catchment H+ budgets, and the ratio between external (anthropogenic) and internal H+ sources. In general, output exceeded input for Na+, K+, Ca2+, Mg2+, HCO 3 ? (if present) and A? (organic anions), whereas retention was observed in the case of H+, NH 4 + , NO 3 ? and SO 4 2? . The range in the annual input of H+ was 22.8–26.3 meq m?2 yr?1, and in the annual output, 0.3–3.9 meq m?2 yr?1. Compared with some forested sites located in high acid deposition areas in southern Scandinavia, Scotland and Canada, the catchments receive rather moderate loads of acidic deposition. The consumption of H+ was dominated by base cation exchange plus weathering reactions (41–79 %), and by the retention of SO 4 2? (17–49 %). The maximum net retention of SO 4 2? was 87% in the HietajÄrvi 2 catchment, having the highest proportion of peatlands. Nitrogen transformations played a rather minor role in the H+ budgets. The ratio between external and internal H+ sources (excluding net base cation uptake by forests) varied between 0.74 and 2.62, depending on catchment characteristics and acidic deposition loads. The impact of the acidic deposition was most evident for the southern Valkeakotinen catchment, where the anthropogenic acidification has been documented also by palaeolimnological methods.  相似文献   

5.
The release of base cations from chemical weathering is the fundamental process by which base cations lost through leaching or biological uptake are replenished. Soils with a high content of easily weatherable minerals will, in general, be readily able to neutralise incoming acidity and satisfy biological requirements through this supply of base cations from weathering. Conversely those soils with a low content of such minerals will be unable to buffer acid inputs or meet biological demands and will be vulnerable to acidification. It is evident therefore that an accurate estimate of the rate of chemical weathering is a prerequisite for any assessment of ecosystem sensitivity to acidification. The principal methods by which these calculations are made can be grouped into those based on element depletion in soil horizons calculated against a conservative element reference, catchment fluxes, laboratory studies and the use of mathematical models which utilise data from each of these sources. A review of the published data has been undertaken to determine if a systematic variation in weathering rates can be observed for a range of parent materials and/or methods used. Variations of 0.03–0.8 keq ha?1yr?1 for K+, 0.0–1.0 keq ha?1yr?1 for Na+, 0.01–1.39 keq ha?1yr?1 for Mg2+ and 0.0–5.8 keq ha?1yr?1 for Ca2+ were found. In general individual cation weathering rates determined from catchment fluxes, and also the model MAGIC, are dominated by Ca2+, with Mg2+ being the next most significant release rate. However it has not been possible to determine any other systematic variations due to the limited number of sites where weathering rate has been determined by more than one method.  相似文献   

6.
As a means of assessing the relative contributions of watershed (terrestrial) and in-lake processes to overall lake/watershed alkalinity budgets, alkalinity production rates for watersheds and low alkalinity lakes were compiled from the literature and compared. Based on net alkalinity production data, derived using wet or bulk deposition data, mean and median alkalinity production for 20 watersheds in North America and Europe were 89 and 69 meq m?2 yr?1 (range 20 to 235 meq m?2 yr?1). For a subset of 10 watersheds with dry deposition data, terrestrial alkalinity production neutralized an additional 35 meq m?2 yr?1 of acidic deposition. For 11 lakes, mean and median in-lake alkalinity generation were 99 and 88 meq m?2 yr?1 (range 22 to 240 meq m?2 yr?1). Analysis of data indicates that for the low alkalinity systems described here, areal alkalinity production rates for watersheds and lakes are approximately equal. This relationship suggests that watershed area to lake area ratio can be used as a convenient estimator of the relative importance of watershed and in-lake sources of alkalinity for drainage lake systems. For precipitation-dominated seepage lakes and other systems where hydrology limits soil-water contact, hydrologic flow paths and residence times can be of overriding importance in determining alkalinity sources. For regions dominated by drainage lakes with high watershed area to lake area ratios (such as the Northeastern U.S.), however, alkalinity budgets are dominated by watershed processes. Omission of in-lake alkalinity consideration for most lakes in such regions would have little impact on computed alkalinity budgets or on predicted response to changes in acidic deposition loadings.  相似文献   

7.
Abstract. The approximate time-scales for serious lowering of the base status of acidic upland soils in northeast Scotland have been based on assessments of geochemical weathering rates in two upland catchments. Periods of 1100 and 12000 years are obtained for soils evolved primarily from granite and quartz-biotite-norite respectively. Factors regulating the rate of removal of base cations in drainage water are discussed, to elucidate those which significantly influence long-term rates of soil acidification. The relationship between base cation leaching and river water acidity is briefly considered.  相似文献   

8.
The soil acidification model SAFE was modified to calculate historical changes in geochemistry and runoff since the last glaciation ended at the Lake Gårdsjön F1 catchment 12 000 B.P. Changes in runoff pH and ANC, soil weathering rate, soil mineralogy, soil texture and base saturation was also calculated. The changes in mineralogy compared favorable to data. Modeled historic weathering rates were slightly higher than data suggest, while present weathering rate was somewhat to low, 37 mmolc m?2 yr?1. The weathering rate was very high immediately after the last glaciation, and decreased as the smaller particles were consumed by weathering. The calculated runoff pH follows the pattern of the paleo-inferred pH. SAFE suggests a natural depletion of base cations in the C-layer.  相似文献   

9.
To calculate critical acid loads or to predict elementconcentrations in the soil solution, information on weatheringrates is essential. Several studies have taken place in theNetherlands to obtain weathering rates for non-calcareous sandysoils. Recently information on weathering rates in less vulnerable loess and clay soils have become available. However,up to now no system is available to estimate weathering rates ona regional scale by relating them to regionally available soilproperties.To obtain weathering rates of loess and clay soils on a regionalscale for the Netherlands, the applicability of a statisticalregression model and the process based PROFILE model have beenevaluated. Both models were calibrated on a set of laboratoryexperiments. To evaluate their predictive power, both methodswere validated on a number of sites for which field weatheringrates were available.Predictions with the statistical model, for the individual basecations, were generally within a factor 2 of the calculatedhistorical weathering rates, except for Ca, which wasoverestimated, by a factor 3 to 4. PROFILE stronglyoverestimated all weathering rates using both standard parameters and in particular after calibration on the laboratoryrates. However, PROFILE predicted weathering rates of the loesssoils quite good after calibration on historical weatheringrates, indicating that the downscaling procedure used in PROFILEto translate laboratory to field weathering rates is inadequatefor the considered soils.The statistical model was applied to predict weathering rates,for the Netherlands on a 1 × 1 km grid scale. Weathering rates at the present pH values in forested loess and clay soilsranged from 135 to 6000 molc ha-1 a-1 in loesssoils and from 100 to 1750 molc ha-1 a-1 in claysoils.  相似文献   

10.
Critical loads of nutrient and acidifying nitrogen, as well as of sulphur and acidity, were derived for various ecosystems in China using the steady state mass balance (SSMB) equations. The weathering rates of major soils necessary for applying SSMB were calculated through the PROFILE model on the basis of mineralogical data from experimental analysis. The growth uptakes of nitrogen and base cations were also derived by multiplying the annual increases in biomass with the element contents of the vegetation. Using a geographical information system (GIS), 1°(latitude)×1°(longitude) critical load maps of China with different percentiles were compiled. Results indicate that low critical loads of S (< 0.5 keq·ha?1·a?1) occurred predominately in southwest and northeast China, and the critical loads of southeast China were intermediate and in the range of 0.5～1.0 keq·ha?1·a?1. In addition, the critical loads of N were very low for desert ecosystems in northwest China and high for agricultural ecosystems in east China. Among the ecosystems with intermediate critical load of N, coniferous forests may be more sensitive to N deposition than broad-leaf forests and temperate steppes.  相似文献   

11.
Manipulations with whole catchments were initiated in Norway in 1983 (RAIN project Reversing Acidification In Norway) to obtain direct experimental evidence relating to the reversibility of soil and water acidification, rate of change, and the relative roles of sulfur and nitrogen. We present here results for soil and runoff chemistry during 8 years of acid addition at Sogndal, a pristine acid-sensitive site in central Norway characterized by gneissic bedrock, thin and patchy soils, and alpine vegetation. Catchment SOG2 receives 100 meq m?2 yr?1 H2SO4, catchment SOG4 receives a 1∶1 mixture of H2SO4 and HNO3, while catchments SOG1 and SOG3 serve as untreated controls. Acid is applied to the snowpack in April and in 5 portions of 11 mm of pH 3.2 acidified lakewater during the snowfree period. The 8-years of acid addition have caused major changes in runoff chemistry. Concentrations of sulfate and base cations have increased while acid neutralizing capacity (ANC) has decreased. Henriksen's F-factor (change in concentration of non-marine Ca+Mg divided by change in concentration of non-marine SO4) is about 0.35, but is expected to decrease as soil acidification proceeds. Runoff is acidic, aluminum-rich, and toxic to fish and other aquatic organisms. Repeated soil sampling indicates no dramatic trends related to treatment. Year-to-year variations are large, and mask changes expected. The input-output budgets indicate that over the 8-yr period Ca has been depleted by about 5% of the total soil pool of exchangeable Ca. The observed trends are consistent with response predicted by MAGIC, a process-oriented model of soil and water acidification. The gradual increase in nitrate flux from catchment SOG4 may be the first indication of ‘nitrogen saturation’ induced simply by increasing nitrogen deposition.  相似文献   

12.
Acidic precipitation, wet or frozen precipitation with a H+ concentration greater than 2.5 μeq l?1, is a significant air pollution problem in the United States. The chief anions accounting for the H+ in rainfall are nitrate and sulfate. Agricultural systems may derive greater net nutritional benefits from increasing inputs of acidic rain than do forest systems when soils alone are considered. Agricultural soils may benefit because of the high N and S requirements of agricultural plants. Detrimental effects to forest soils may result if atmospheric H+ inputs significantly add to or exceed H+ production by soils. Acidification of fresh waters of southern Scandinavia, southwestern Scotland, southeastern Canada, and northeastern United States is caused by acid deposition. Areas of these regions in which this acidification occurs have in common, highly acidic precipitation with volume weighted mean annual H+ concentrations of 25 μeq l?1 or higher and slow weathering of granitic or precambrian bedrock with thin soils deficient in minerals which would provide buffer capacity. Biological effects of acidification of fresh waters are detectable below pH 6.0. As lake and stream pH levels decrease below pH 6.0, many species of plants, invertebrates, and vertebrates are progressively eliminated. Generally, fisheries are severely impacted below pH 5.0 and are completely destroyed below pH 4.8. At the present time studies documenting effects of acidic precipitation on terrestrial vegetation are insufficient to establish an air quality standard. It must be demonstrated that current levels of precipitation acidity alone significantly injure terrestrial vegetation. For aquatic ecosystems, current research indicates that establishing a maximum permissible value for the volume weighted annual H+ concentration of precipitation at 25 μeq l?1 may protect the most sensitive areas from permanent lake acidification. Such a standard would probably protect other systems as well.  相似文献   

13.
A model has been developed that relates the cation denudation rate (CDR) of a watershed (the rate that cations derived from chemical weathering are carried off by runoff), the atmospheric load of excess SO4, and the pH of the river. Chemical and discharge data for rivers in Nova Scotia and Newfoundland were used to develop and test the model, which is based upon the common major ion chemistry of soft surface waters, and may be expressed by three statements: (1) CDR (meq m?2 yr?1) ? Excess SO4 ?? load (meq m?2 yr?1) = HCO3 ? (meq m?2 yr?1), (2) HCO3 ? (meq m?2 yr?1)/Runoff (m3 m?2 yr?1) = HCO3 ? (meq m?3), (3) pH = pK + \(pP_{CO_2 } \) ? pHCO3 ?. The model in concentration form applies well to lakes. A detailed analysis of the data for the Isle aux Morts River, Newfoundland, is presented, showing that the CDR varies throughout the year, affected by both discharge and seasonal pattern.  相似文献   

14.
Sulphur deposition has diminished by about half during the last decade. For Sweden consistent estimates of total deposition are available for 1991, and 1994–97. Based on these estimates and using GIS the deposition for large drainage areas during one decade are calculated. These values are compared with the measured S transport in rivers covering about 85% of the Swedish territory, thus enabling the construction of a S budget for Sweden. The majority of the drainage areas have a net loss of S, which can be attributed to desorption of S in the soil. During the period of high deposition in the 1980:s (>60 meq m?2 yr?1 in southern Sweden) S was adsorbed, and retarded acidification. There still seems to be some S-adsorption in the northern parts of the country, where the deposition is less (now <20 meq m?2 yr?1).  相似文献   

15.
Site conditions such as parent material, soils, but also vegetation cover and elevation explain the varying snowmelt streamwater chemistry in the Black Forest. The results are derived from multiple statistical analysis of a regional survey of 104 small mountain streams in the first phase of snowmelt in spring 1984. Cluster analysis classifies the snowmelt streams into three groups which are clearly linked to bedrock geology. Factor analysis finds podsolization, weathering and mineralization processes in the soils of the catchments to have most impact even under snowmelt conditions. There is no evidence that acidic atmospheric deposition directly affects the acidity of the investigated streams. However, the deposition rates are low compared to certain other regions in Central Europe. In areas with podsolic soils the organic soil layer plays a key role in the acidity and mobilization of Al and heavy metals. This is shown in the high correlations between pH, DOC, UV-extinction, color and metal concentrations. Because the concentrations of DOC are low (<10 mg.L?1) and an anion deficit cannot be found, it is assumed that water acidity is not caused by dissolved humic acids, but by cations exchanged in the organic layer of acidic soils. Streamwater chemistry in areas with brown earth soil types is mainly affected by leaching of basic cations in the mineral soil horizons and mineral weathering.  相似文献   

16.
Mn biogeochemistry was studied from 1994 to 2003 in a small forested catchment in the central Czech Republic using the watershed mass balance approach together with measurements of internal stores and fluxes. Mn inputs in bulk deposition were relatively constant during a period of sharply decreasing acidic deposition, suggesting that the Mn source was terrestrial, and not from fossil fuel combustion. Mn inputs in bulk deposition and Mn supplied by weathering each averaged 13 mg m?2 year?1 (26 mg m?2 year?1 total input), whereas Mn export in streamwater and groundwater averaged 43 mg m?2 year?1. Thus an additional Mn source is needed to account for 17 mg m?2 year?1. Internal fluxes and pools of Mn were significantly greater than annual inputs and outputs. Throughfall Mn flux was 70 mg m?2 year?1, litterfall Mn flux was 103 mg m?2 year?1, and Mn net uptake by vegetation was 62 mg m?2 year?1. Large pools of labile or potentially labile Mn were present in biomass and surficial soil horizons. Small leakages from these large pools likely supply the additional Mn needed to close the watershed mass balance. This leakage may reflect an adjustment of the ecosystem to recent changes in atmospheric acidity.  相似文献   

17.
A total of 26 soft-water, seepage lakes in the Northern Highlands (NH) of Wisconsin (N =16) and the Upper Peninsula (UP) of Michigan (N=10) were sampled four times between early May and mid October 1984 as part of the ‘PIRLA’ Project (Paleolimnological Investigations of Recent Lake Acidification). Because of low antecedent recharge of the local water-table, this ‘summer’ interval likely featured minimal groundwater inputs (<2 cm over lake surface) to most of these seepage lakes. Based on this hydrogeologic relationship, and on regional deposition data, I evaluated short-term net epilimnetic (June–August) and whole-lake (May–October) sediment-water exchange of ANC, base cations, acid oxy-anions, Al, DOC and silicic acid in these lakes using a simplified mass balance algorithm. Silica, nitrate and ammonium were all efficiently retained in these seepage lakes. The assimilation of NO3 ? (19±4 meq m?2) slightly exceeded assimilation of NH4 + (16±4), resulting in a net internal ANC production of only +3 meq m?2 over 161 d between early May and mid October 1984. Over this same interval ANC production resulting from lacustrine S retention averaged +35±8 meq m?2 in the NH, but was too variable to be statistically significant (+21±21 meq m?2) in the UP. Epilimnetic S retentions in mid summer were more comparable (21±4 in NH; 14±5 meq m?2 in UP). McNearney Lake (UP) illustrates how high sulfate, linked to low alkalinity, high Al, low P, and low productivity, can become a negative correlate of lacustrine S retention. Temporal changes in base cations in the 26 lakes were generally small and erratic compared with uncertainties in deposition inputs and analytical errors, rendering estimates of related ANC production inconclusive. Even small analytical biases can be critical when designing and interpreting lake monitoring studies.  相似文献   

18.
Immobile element-based weathering estimation methods assume that Zr (or Ti) is an immobile element, and that weathering rates of other elements can be estimated according to the enrichment of Zr in weathered horizons relative to an unweathered parent material. This approach was used to estimate base cation weathering rates for 33 soil profiles on acid-sensitive terrain in north-eastern Alberta. Zirconium generally showed enrichment within the rooting zone, but the deepest (subsoil) samples were not always associated with the lowest Zr concentrations. Weathering rates estimated with the Zr depletion and Pedological Mass Balance (PMB) methods were generally low (ranges: 0-51 and 0-58 mmolc m− 2 yr− 1, respectively); however, low base cation oxide concentrations and heterogeneity within soil profiles complicated weathering rate calculations and net base cation gains were calculated for several (six) sites. Evaluation of the Zr depletion and PMB weathering estimates against those calculated with the process-oriented PROFILE model at a subset (n = 9) of the sites indicated the estimates were poorly related, with PROFILE rates typically being higher. The effects-based emissions management strategy for acid precursors in this region requires spatial coverage of soil properties (including weathering rates) across a large area, but the apparent limitations associated with the immobile element based methods in this region: identifying representative parent soils and deriving weathering rate estimates comparable to more robust methods are arguments against their candidacy for future use.  相似文献   

19.
The contributions of cation exchange and mineral weathering to the neutralization of acidity in the Jingahata watershed in central Japan were estimated through a laboratory weathering experiment and runoff chemistry measurements. The laboratory experiment was conducted in a stirred-flow reactor for a whole soil sample collected from the C horizon in the watershed. The concentration ratios of base cations (Ca2+, Mg2+, K+ and Na+) to Si (BC/Si) released during the steady-state stage of the laboratory experiment were in good agreement with the ratios of the net flux of base cations to the flux of Si in the streamwater (BC N ET/Si L).This result suggests that the acidity in the watershed is neutralized primarily by mineral weathering without causing a net loss of base cations from exchange sites. The alkalinity/acidity balance estimated for the watershed shows that the total weathering rate of base cations is approximately 3.26 keq ha?1 yr?1. Weathering of plagioclase (An41) contributes 83% of the total weathering rate. The dominant acidity source is CO2 released within the soil horizons, accounting for roughly 85% of the total acidity flux (3.20 keq ha?1 yr?1). This high internal production of acidity suppresses the relative importance of atmospheric acidity inputs (0.3 keq ha?1 yr?1).  相似文献   

20.
The relation between soil acidification and element cycling   总被引：2，自引：0，他引：2  
Controversy about the contribution of acidic deposition to soil acidification partly arises from different concepts of soil acidification. Differentiating between actual and potential soil acidification has proved to be appropriate for properly identifying and quantifying the natural and anthropogenic sources of protons. Actual soil acidification is primarily manifested by leaching of cations from the soil, regulated by the mobility of major anions. Leaching of HCO3 ? and RCOO? occurs naturally whereas leaching of NO3 ? and SO4 2? is mainly caused by land use in agricultural soils and by acidic deposition in forest soils. Potential soil acidification is primarily due to accumulation of atmospherically derived N and S. This potential acid threat is partly realized by mineralization processes after the removal of vegetation.  相似文献   

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