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1.
为揭示太湖流域降雨和湖水酸根阴离子长期变化特征及环境意义,通过历史数据收集和采样分析,对太湖流域降雨和湖水中的SO42-、NO3-变化特征和来源进行了研究.结果表明：自1990s以来太湖流域降雨中SO42-呈显著下降趋势,年平均下降率为0.28 mg/（L·a）;NO3-浓度却呈显著上升趋势,年平均增长率为0.05 mg/（L·a）,降雨中氮污染呈现加重的趋势.与之相反,湖水中SO42-呈显著上升趋势,年平均增长率为1.24 mg/（L·a）;NO3-浓度却呈显著下降趋势,年平均下降率为0.02 mg/（L·a）.30年以来,太湖水体SO42-/NO3-比值不断升高,远高于降水SO42-/NO3-比值.研究认为：流域SO2排放引起的酸沉降是湖水SO42-浓度增长的最重要原因,但氮氧化物排放并未引起湖水NO3-浓度升高,说明太湖流域对大气沉降的氮氧化物有滞留作用,而太湖水体是流域大气沉降硫酸盐的重要汇.综合治理太湖流域酸性物质排放对防止太湖水体酸化和治理富营养化都具有重要意义.  相似文献   

2.
通过模拟沙湖沉积物-水系统,以沙湖原水氟离子（F-）浓度为1倍浓度（0.69 mg/L）,设置0.5倍浓度、1倍浓度、1倍浓度灭菌、2倍浓度和4倍浓度共5个实验组,探究不同上覆水F-浓度背景下沙湖沉积物中F-的迁移.结果表明,沉积物F-的释放量随上覆水F-浓度的增加而呈下降的趋势,其中2倍和4倍浓度组的沉积物由释放F-转变为吸附F-.碱性水体有利于沉积物F-的释放,即随着pH增大,F-释放量也会增加.微生物的Beta多样性层次聚类分析表明,F-会抑制Paenisporosarcina与Thiobacillus的相对丰度,但对Fusibacter的生命活动具有促进作用.根据各浓度组间优势菌属相对丰度与环境因子的冗余分析可得,Acinetobacter、Thiobacillus相对丰度与pH呈负相关;Fusibacter相对丰度与F-浓度呈显著正相关,而Thiobacillus的相对丰度则与F-表现出弱负相关.通过对各浓度组中重要离子的分析发现,0.5倍组和4倍组中F-的迁移受Ca2+、HCO3-和SO42-浓度影响较大;相关性分析表明0.5倍浓度组的Ca2+、HCO3-浓度与F-浓度呈极显著正相关,而4倍组中F-浓度和Ca2+、HCO3-浓度呈负相关,SO42-浓度和F-浓度的相关性则是0.5倍组呈负相关,4倍组呈极显著正相关.本文在不同上覆水F-浓度背景下全面探究了沙湖沉积物中F-释放和迁移机理,为沙湖及其他含氟地表水的氟污染防治提供理论支持.  相似文献   

3.
新疆艾比湖干涸湖底不同景观单元蒸发盐分布与变化特征   总被引：2，自引：0，他引：2  
盐尘暴是由干旱、半干旱区尾闾湖干涸湖底及其附近盐质荒漠风蚀所导致的一种灾害性极强的天气现象.盐尘主要来自风蚀过程中干涸湖底盐分的释放.由于干涸湖底不同的植被覆盖状况,导致风蚀过程中盐分损失不同.为了解风蚀过程中不同景观单元下盐分分布与变化特征,选择艾比湖干涸湖底自然状态下典型的6种景观单元(胡杨林带(Landscape 1,简写为L1)、乔本结合带(L2)、草本结合带(L3)、芦苇荒漠带(L4)、梭梭荒漠带(L5)、无植被覆盖(L6)),于2011年6月初和10月初2次采集沉积物样品,运用方差分析方法,研究各个景观单元下盐分的分布与季节变化特征.结果表明:1)2次采样不同景观单元0~30 cm和30~60 cm处阳离子Na+、K+、Mg2+含量均存在显著差异,其中Na+含量存在极显著差异且含量最高,而不同景观单元0~30 cm和30~60 cm处阴离子Cl-、SO42-含量均存在显著差异,CO32-、HCO3-含量甚微;2)干涸湖底沉积物的主要盐分类型是NaCl,其次是CaSO4,其它盐分含量较小,且不同景观单元相同深度沉积物盐分含量存在显著差异.无论是盐分离子组成还是含量,L5均最高,其次是L6,而L2均最低.随着深度的增加,不同景观单元沉积物中的盐分含量均呈现降低的趋势.随着时间变化,景观单元L2、L3、L4、L5、L6盐分含量有不同程度的增加,而L1盐分含量减少;3)在小尺度范围内,局地气候条件相对均一,地下水矿化度、地下水埋深及沉积物性质差别不大,不同景观类型是影响盐分表聚的主要因素.  相似文献   

4.
本研究在太湖梅梁湾采集沉积柱,采用一种自制的毫米级柱状沉积物自动垂向分层切割装置对表层50 mm沉积物进行垂向切割(间隔2 mm),结合高通量测序技术分析沉积物中细菌群落的毫米级垂向分布;同时采用毫米级高分辨透析技术和薄膜扩散梯度技术(DGT)分析溶解态和DGT可获取态铵态氮(NH4+-N)、硝态氮(NO3--N)、Fe、P的垂向分布特征。结果显示,沉积物中细菌群落与溶解态和DGT可获取态氮铁磷浓度在垂向上呈现显著的异质性。细菌硝酸盐还原主要发生在-16～0 mm沉积物深度,这可能导致了溶解态和DGT可获取态NO3--N含量在该沉积物深度的明显减少。细菌铁还原主要分布在-32～-18 mm沉积物深度,细菌硫酸盐还原主要分布在-50～-34 mm的沉积物深度;细菌硫酸盐还原是导致沉积物溶解态和DGT可获取态铁磷浓度从-32 mm随沉积物的深度增加而显著增加的主要原因。本研究加深了对富营养化湖泊沉积物中细菌影响氮磷在垂向上迁移转化的认识。  相似文献   

5.
Exchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH < 3). To identify links between groundwater‐lake exchange rates and acid neutralization processes in the sediments, exchange rates were quantified and related to pore‐water pH, sulfate and iron concentrations as well as sulfate reduction rates within the sediment. Seepage rates measured with seepage meters (?2.5 to 5.8 L m‐2 d‐1) were in reasonable agreement with rates inverted from modeled chloride profiles (?1.8 to 8.1 L m‐2 d‐1). Large‐scale exchange patterns were defined by the (hydro)geologic setting but superimposed by smaller scale variations caused by variability in sediment texture. Sites characterized by groundwater upwelling (flow into the lake) and sites where flow alternated between upwelling and downwelling were identified. Observed chloride profiles at the alternating sites reflected the transient flow regime. Seepage direction, as well as seepage rate, were found to influence pH, sulfate and iron profiles and the associated sulfate reduction rates. Under alternating conditions proton‐consuming processes, for example, sulfate reduction, were slowed. In the uppermost layer of the sediment (max. 5 cm), sulfate reduction rates were significantly higher at upwelling (>330 nmol g‐1 d‐1) compared to alternating sites (<220 nmol g‐1 d‐1). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

6.
Small‐scale heterogeneities and large changes in hydraulic gradient over short distances can create preferential groundwater flow paths that discharge to lakes. A 170 m2 grid within an area of springs and seeps along the shore of Shingobee Lake, Minnesota, was intensively instrumented to characterize groundwater‐lake interaction within underlying organic‐rich soil and sandy glacial sediments. Seepage meters in the lake and piezometer nests, installed at depths of 0·5 and 1·0 m below the ground surface and lakebed, were used to estimate groundwater flow. Statistical analysis of hydraulic conductivity estimated from slug tests indicated a range from 21 to 4·8 × 10?3 m day?1 and small spatial correlation. Although hydraulic gradients are overall upward and toward the lake, surface water that flows onto an area about 2 m onshore results in downward flow and localized recharge. Most flow occurred within 3 m of the shore through more permeable pathways. Seepage meter and Darcy law estimates of groundwater discharge agreed well within error limits. In the small area examined, discharge decreases irregularly with distance into the lake, indicating that sediment heterogeneity plays an important role in the distribution of groundwater discharge. Temperature gradients showed some relationship to discharge, but neither temperature profiles nor specific electrical conductance could provide a more convenient method to map groundwater–lake interaction. These results suggest that site‐specific data may be needed to evaluate local water budget and to protect the water quality and quantity of discharge‐dominated lakes. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

7.
湖泊沉积物储存着长时期的流域环境信息,是百年尺度湖泊环境演变研究的高分辨率记录器。本文通过210Pbex、137Cs组合定年法,分析放射性核素剖面特征,研究沉积速率时空变化规律,并解析沉积物粒度指示的环境信息,揭示百年尺度湖泊沉积环境演变。结果表明:洞庭湖210 Pbex剖面分布呈现多段衰变型、混合—衰变—平衡型、衰变—本底型和无沉积型4种类型。3大湖体200 cm的沉积深度对应的年代跨度为127～162年,构建了洞庭湖沉积物深度—年代关系。洞庭湖平均质量沉积速率为1.47～3.11 g/(cm2·a),整体上呈现南洞庭湖>西洞庭湖>东洞庭湖的空间特征;自1900年后,质量沉积速率增加了3～7倍,呈时序增加趋势。沉积年代上,沉积物粒度特征表明洞庭湖沉积环境呈3个阶段2个过渡期的演变特征,与同时期区域内毁林开荒、水利建设、植树造林等人为活动有较好的对应关系,说明近百年来人为活动是洞庭湖泥沙沉积的重要因素。本研究结果可为强化湖泊及其流域生态环境保护...  相似文献   

8.
Study of interactions between surface-water and pore-water in lakes is complicated due to spatio-temporal heterogeneities in flow condition across the sediment–water interface. In this study, seasonal hypersaline Maharlu Lake was investigated by collecting surface-water and pore-water samples from four nests of multilevel piezometers installed at different distances from the inflow of rivers to the lake. The hydraulic heads in the piezometers as well as vertical profiles of Mg+2, Na/Cl, and Br/Cl were used to investigate both hydraulic and geochemical interactions between surface-water and pore-water in the lake. Depletion of lake surface water and pore water with respect to B, Br, Li+, K+, Mg2+ and the absence of Mg-K chlorides and sulphates in the lake bed sediments is probably due to leakage of highly evaporated residual brine from the lake. Hydraulic gradients in the multilevel piezometric nests indicate that a general downward flow from surface-water to pore-water occurs across sediment–water interface. Vertical profiles of Br/Cl, Mg2+, and Na/Cl showed that the maximum flow rate was more than 1 m/yr close to the mouth of the inflowing rivers. The downward vertical flow was limited in the area far from the inflowing rivers due to the presence of an impermeable confining halite layer which interrupts the hydraulic connection between shallow pore water (less than 50 cm deep) and deeper zones. The hydraulic and geochemical interactions between surface-water and pore-water across sediment–water interface in the Maharlu Lake are of interest to find out the fate of pollutants and their distribution in the lake.  相似文献   

9.
Williams Lake, Minnesota is a closed‐basin lake that is a flow‐through system with respect to ground water. Ground‐water input represents half of the annual water input and most of the chemical input to the lake. Chemical budgets indicate that the lake is a sink for calcium, yet surficial sediments contain little calcium carbonate. Sediment pore‐water samplers (peepers) were used to characterize solute fluxes at the lake‐water–ground‐water interface in the littoral zone and resolve the apparent disparity between the chemical budget and sediment data. Pore‐water depth profiles of the stable isotopes δ18O and δ2H were non‐linear where ground water seeped into the lake, with a sharp transition from lake‐water values to ground‐water values in the top 10 cm of sediment. These data indicate that advective inflow to the lake is the primary mechanism for solute flux from ground water. Linear interstitial velocities determined from δ2H profiles (316 to 528 cm/yr) were consistent with velocities determined independently from water budget data and sediment porosity (366 cm/yr). Stable isotope profiles were generally linear where water flowed out of the lake into ground water. However, calcium profiles were not linear in the same area and varied in response to input of calcium carbonate from the littoral zone and subsequent dissolution. The comparison of pore‐water calcium profiles to pore‐water stable isotope profiles indicate calcium is not conservative. Based on the previous understanding that 40–50 % of the calcium in Williams Lake is retained, the pore‐water profiles indicate aquatic plants in the littoral zone are recycling the retained portion of calcium. The difference between the pore‐water depth profiles of calcium and δ18O and δ2H demonstrate the importance of using stable isotopes to evaluate flow direction and source through the lake‐water–ground‐water interface and evaluate mechanisms controlling the chemical balance of lakes. Published in 2003 by John Wiley & Sons, Ltd.  相似文献   

10.
A combination of field measurements, modelling and laboratory experiments was used to evaluate the potential impact of sediment resuspension on phosphorus (P) dynamics. The study was carried out in two adjacent shallow coastal lakes (Lake Honda and Lake Nueva) which, due to their geographic proximity (only 200 m apart), are subject to equal meteorological forcing and represent ideal systems to study how morphometry and sediment properties relate to wind events. The focusing factors (a measure of the fluxes of sediment into the water column through resuspension) estimated by comparing settling fluxes measured in surface sediment traps with those measured in bottom traps, were significantly larger (approximately 34% larger) in Lake Honda (LH; 1.18) than in Lake Nueva (LN; 0.88). Our model estimates of resuspension fluxes (E) were also ca. 40% larger in LH than in LN, in agreement with the observed focusing factors. The larger resuspension fluxes encountered in LH, in comparison with LN, can mainly be explained by differences in lake morphometry. Still, they could arise from differences in grain size distribution or in benthic algae concentration encountered in the lake sediments. By means of adsorption experiments in the laboratory, we show that resuspension events will have different effects on P-dynamics in LH and LN. While the resuspended material from LH tends to adsorb phosphate (PO4 3−), removing it from the water column, in LN the resuspended sediments tend to increase the availability of PO4 3− in solution. These differences arise from (1) higher concentrations of PO4 3− in water in LH compared to LN; and (2) larger PO4 3−adsorption capacity of the LH sediments as a result of the more abundant iron oxyhydroxides and clay.  相似文献   

11.
Porewater profiles often are used to identify and quantify important biogeochemical processes occurring in lake sediments. In this study, multiple porewater profiles were obtained from two eutrophic Swiss lakes using porewater equilibrators (peepers) in order to examine spatial and seasonal trends in biogeochemical processes. Variability in profile shapes and concentrations was small on spatial scales of a few meters, but the uncertainty in calculated diffusive fluxes across the sediment surface was, on average, 35%. Focusing of Fe and Mn oxides toward the lake center resulted in systematic increases in porewater concentrations and diffusive fluxes of Fe2+ and Mn2+ with increasing water depth; these fluxes are postulated to be regulated by the pH-dependent dissolution of reduced-metal phases. Despite higher concentrations of inorganic carbon, NH 4 + , Si and P in pelagic compared to littoral sites, diffusive fluxes of these substances across the sediment surface increased only slightly or not at all with increasing water depth. Porewater profiles did reveal temporal changes in Fe2+, Mn2+, Ca2+ and Mg2+ that were an indirect result of the large, seasonal changes in seston deposition, but no clear seasonal variations were found in diffusive fluxes of nutrients across the sediment surface. The intense mineralization occurring at the sediment surface was not reflected in the porewater profiles nor in the calculated diffusive fluxes. Calculated diffusive fluxes across the sediment surface resulted from decomposition occurring primarily in the top 5–7 cm of sediment. Diffusive fluxes from this subsurface mineralization were equal to the solute release from mineralization occurring at the sediment-water interface. Buried organic matter acts as a memory of previous lake conditons; it will require at least a decade before reductions in nutrient inputs to lakes fully reduce the diffusive fluxes into the lake from the buried reservoir of organic matter.  相似文献   

12.
淮北临涣矿采煤沉陷区不同水体水化学特征及其影响因素   总被引：3，自引：0，他引：3  
为研究淮北临涣矿采煤沉陷区不同水体的补给水源及溶质来源,在现场调查的基础上,系统采集丰水期、平水期、枯水期沉陷区积水、地表河水和浅层地下水样进行测试分析,采用Piper三线图、Gibbs图和因子分析方法,对不同水体水化学特征及其影响因素进行讨论.结果表明:地表水水体总溶解性固体(TDS)质量浓度表现为枯水期丰水期平水期,浅层地下水表现为枯水期平水期丰水期,地表水TDS质量浓度明显高于浅层地下水.地表水中主要阴阳离子为Na~+、Cl~-和SO_4~(2-),水化学类型主要为SO_4~(2-)-Cl~--Na~+型;浅层地下水离子以HCO_3~-、Ca~(2+)和Mg~(2+)为主,表现为HCO_3~--Ca~(2+)-Mg~(2+)型.结合Gibbs图和因子分析可知,地表水受蒸发作用、地表径流以及采煤活动等因素影响,浅层地下水在一定程度上体现出大气降水和地表水补给的特点,受岩石风化作用影响较为明显.  相似文献   

13.
Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, Stot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S4O62−+S5O62−+S6O62−=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO2/H2S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant 34S fractionation (ΔSO4–Se of 20‰), probably the result of SO2 disproportionation in or below the lake. The lake waters show strong enrichments in 18O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern.  相似文献   

14.
巴丹吉林沙漠湖泊水化学空间分布特征   总被引：7，自引：2，他引：5  
通过对巴丹吉林沙漠腹地拐子湖-地质公园一线51个湖泊水,8个泉水,12个井水及1个雨水水样的水化学成分分析,初步探讨了沙漠湖泊水化学分布特征及其影响因素.结果表明由东南边缘至腹地湖泊总体上依次呈硫酸盐型-碳酸盐型-氯化物型分布.东南边缘以Na+、Cl-、SO24-为主的湖泊因矿化度分异,形成Ca2+、Mg2+含量不同的三种亚型,其中高矿化度的Na-Cl-(SO4)型湖泊在腹地湖泊群中也有出现,表现出地理上的不连续分布;边缘若干湖泊受局部地理环境的影响水离子多含Na+、Cl-、CO32-+HCO3-.综合分析表明湖泊水化学型的空间分异与区域气候差异和气候变化有关,湖水直接或间接地接受当地降水补给,但不排除外源地下水补给对其有一定贡献.通过对比不同时段部分沙漠湖泊水化学特征发现近十年以来腹地湖泊补给源或受气候干暖化影响使其水化学特性较边缘湖泊的变化大.  相似文献   

15.
Between 1989 and 1998 the small eutrophic stratified Lake Belau was investigated intensively and multidisciplinarily. This article is a short, comprehensive summary and re‐evaluation of the hydrochemistry of the lake, with focus on nitrogen and phosphorus. In several aspects the lake can be regarded as a typical example of the glacial north German lakes. The 1960's and 1970's are characterised by heavy nutrient inputs and fast eutrophication. During the last two decades the external nutrient load, especially the phosphorus load into Lake Belau was significantly reduced. But phosphorus‐rich sediments and large areas with summerly anoxic sediment surface conditions cause intensive release of phosphorus from older deeper sediment layers. Annual budgets reveal that despite an average sediment accumulation of 3 mm a?1 the lake has lost its function as net phosphorus sink and it is very likely that internal eutrophication by the sediments will keep the lake in its eutrophic state during the next decades. Despite that, monthly budgets of five vertical layers show that the main phosphorus supplier for the phosphorus depleted epilimnion during summer is the creek Alte Schwentine. The annual nitrogen budget indicates groundwater and interflow water as well as atmospheric input as additional important nitrogen sources. 36% (98 μmol m ?2 h?1 N) of all nitrogen input is lost to atmosphere mainly due to denitrification. The example of a heavy storm shows that about 10% of the annual nitrogen loss to the atmosphere can take place during a single day and in form of ammonia. The storm further made obvious that these unpredictable events can have strong impact on nutrient cycling and ecology in Lake Belau and the lake can become an unexpected nutrient source for downstream systems.  相似文献   

16.
Processes controlling the nitrogen (N) exchange between water and sediment in eutrophic Lake Sempach were studied using three different independent methods: benthic flux chambers, interstitial water data and hypolimnetic mass balances. The sediments released NH 4 + (1.1–16.1 mmoles m–2 d–1), NO 2 - (0.1–0.4 mmoles m–2 d–1) and dissolved organic N (<0.25 mmoles m–2 d–1). A net NO 3 - consumption (2.4–11.1 mmoles m–2 d–1) related to the NO 3 - concentrations in the overlying water was observed in all benthic chamber experiments. The flux of the reactive species NO 3 - and NH 4 + was found to depend on hydrodynamic conditions in the water overlying the sediment. For this reason, benthic chambers overestimated the fluxes of inorganic N compared to the other methods. Thus, in short-term flux chamber experiments the sediment may either become a sink or a source for inorganic N depending on the O2 concentration in the water overlying the sediment and the stirring rate. As demonstrated with a15NO 3 - experiment, nitrate-ammonification accounted for less than 12% of the total NO 3 - consumption. After six years of artificial oxygenation in Lake Sempach, a decrease in hypolimnetic total inorganic nitrogen (TIN) was observed in the last two years. The occurrence of dense mats of H2S-oxidizingBeggiatoa sp. indicated micro-aerobic conditions at the sediment surface. Under these conditions, a shorter distance between the ecological niches of nitrifying and denitrifying bacteria, and therefore a faster NO 3 - -transport, can possibly explain the lowering of TIN by enhanced net denitrification.  相似文献   

17.
The heterogeneous nature of both groundwater discharge to a lake (inflow) and nitrate concentrations in groundwater can lead to significant errors in calculations of nutrient loading. Therefore, an integrated approach, combining groundwater flow and transport modelling with observed nitrate and ammonium groundwater concentrations, was used to estimate nitrate loading from a catchment via groundwater to an oligotrophic flow‐through lake (Lake Hampen, Denmark). The transport model was calibrated against three vertical nitrate profiles from multi‐level wells and 17 shallow wells bordering a crop field near the lake. Nitrate concentrations in groundwater discharging to the lake from the crop field were on average 70 times higher than in groundwater from forested areas. The crop field was responsible for 96% of the total nitrate loading (16.2 t NO3/year) to the lake even though the field only covered 4.5% of the catchment area. Consequently, a small change in land use in the catchment will have a large effect on the lake nutrient balance and possible lake restoration. The study is the first known attempt to estimate the decrease of nitrate loading via groundwater to a seepage lake when an identified catchment source (a crop field) is removed.  相似文献   

18.
A geochemical survey carried out in November 1993 revealed that Lake Quilotoa was composed by a thin (14 m) oxic epilimnion overlying a 200 m-thick anoxic hypolimnion. Dissolved CO2 concentrations reached 1000 mg/kg in the lower stratum. Loss of CO2 from epilimnetic waters, followed by calcite precipitation and a consequent lowering in density, was the apparent cause of the stratification.The Cl, SO4 and HCO3 contents of Lake Quilotoa are intermediate between those of acid–SO4–Cl Crater lakes and those of neutral-HCO3 Crater lakes, indicating that Lake Quilotoa has a ‘memory’ of the inflow and absorption of HC1- and S-bearing volcanic (magmatic) gases. The Mg/Ca ratios of the lake waters are governed by dissolution of local volcanic rocks or magmas, but K/Na ratios were likely modified by precipitation of alunite, a typical mineral in acid–SO4–Cl Crater lakes.The constant concentrations of several conservative chemical species from lake surface to lake bottom suggest that physical, chemical and biological processes did not have enough time, after the last overturn, to cause significant changes in the contents of these chemical species. This lapse of time might be relatively large, but it cannot be established on the basis of available data. Besides, the lake may not be close to steady state. Mixing of Lake Quilotoa waters could presently be triggered by either cooling epilimnetic waters by 4°C or providing heat to hypolimnetic waters or by seismic activity.Although Quilotoa lake contains a huge amount of dissolved CO2 (3×1011 g), at present the risk of a dangerous limnic eruption seems to be nil even though some gas exsolution might occur if deep lake waters were brought to the surface. Carbon dioxide could build up to higher levels in deep waters than at present without any volcanic re-awakening, due to either a large inflow of relatively cool CO2-rich gases, or possibly a long interval between overturns. Periodical geochemical surveys of Lake Quilotoa are, therefore, recommended.  相似文献   

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20.
马松  魏榆  韩翠红  晏浩  刘再华  孙海龙  鲍乾 《湖泊科学》2021,33(6):1701-1713
为探究筑坝后不同水库物理、化学、生物过程对水化学和碳循环的影响,本研究对贵州三岔河流域的平寨水库、普定水库以及猫跳河流域的红枫湖水库进行研究,于2018年3月2019年1月分别在入库河流和库区采集了分层水样和沉降颗粒物,并探究水中主要离子及颗粒物通量的时空变化特征及其控制因素.结果表明,水体主要离子的主要来源受碳酸盐溶解影响,并且离子浓度受光合作用控制.红枫湖水库水体水化学类型为Ca-Mg-HCO3-SO4型,普定水库、平寨水库水化学类型均为Ca-HCO3-SO4.夏季藻类光合作用诱导碳酸盐沉淀导致水体表层Ca2+、HCO3-及溶解态Si浓度降低,其降低幅度分别为20.87%~44.25%、33.12%~51.18%、48.55%~96.34%.此外,藻类光合作用也影响C、N、Si等生源要素间的化学计量关系.Mg2+/Ca2+比值在水体垂向剖面上主要受碳酸钙沉淀的控制,而在不同水库之间则主要受流域岩性的控制.根据沉积物捕获器通量计算的平寨水库、普定水库、红枫湖水库夏季颗粒无机碳沉积通量分别为0.74、1.36、0.27 t/（km2·d）,而根据水体Ca2+浓度降低计算的通量分别为0.31~0.64、0.35~0.99、0.09~0.29 t/（km2·d）,根据水体HCO3-浓度降低计算的通量分别为0.30~0.65、0.29~1.26、0.12~0.33 t/（km2·d）.其红枫湖水库无机碳沉降通量的实测值与计算值接近,而平寨、普定水库实际沉降通量高于计算值,这可能是有外源输入导致.因此,利用水化学分层数据能对喀斯特水库中的无机碳沉降通量进行合理估算,并且能够得到较好的估算结果,从而指示碳循环的过程.  相似文献   

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