Tracing Hydrologic Pathways Using Chloride at the Panola Mountain Research Watershed,Georgia, USA

An analysis of chloride (Cl-) concentrations and fluxes at the 41 ha Panola Mountain Research Watershed indicates that Cl- may be used effectively to differentiate "new" and "old" water flow through the hillslope and their respective contributions to streamwater. Rainfall and throughfall, the "new" water inputs, are marked by low Cl- concentrations (<15 µeq L-1). Stormwater moves rapidly to depth along preferred pathways in a deciduous forest hillslope, as evidenced by low Cl- concentrations (<20 µeq L-1) in mobile soil water from zero-tension stainless-steel pan lysimeters. "Old" waters, matrix soil waters and groundwater, typically have high Cl- concentrations (>30 µeq L-1). Timing of soil water transport is not sufficiently rapid to suggest that soil water from this hillslope site (20 m from the stream) contributes to streamwater during individual rainstorms. The source of streamflow, therefore, must be a combination of channel interception, overland flow and soil water from near-channel areas, and runoff from a 3 ha bedrock outcrop in the headwaters. Groundwater contribution to streamflow was estimated using Cl- concentrations of throughfall and groundwater as the two end members for a two-component hydrograph separation. For the study period, groundwater contributed 79% of the streamflow and from 1985 to 1995, contributed 75% of the streamflow. Rainfall was the source of 45% of the Cl- flux from the watershed in the long term; the remaining Cl- is hypothesized to be derived from dry deposition, consistent with the enrichment noted for throughfall. At peak flow during individual rainstorms, "new" water can contribute 95% of the runoff.     

Episodic acidification of a coastal plain stream in Virginia

This study investigates the episodic acidification of Reedy Creek, a wetland-influenced coastal plain stream near Richmond, Virginia. Primary objectives of the study were to quantify the episodic variability of acid-base chemistry in Reedy Creek, to examine the seasonal variability in episodic response and to explain the hydrological and geochemical factors that contribute to episodic acidification. Chemical response was similar in each of the seven storms examined, however, the ranges in concentrations observed were commonly greater in summer/fall storms than in winter/spring storms. An increase in SO _inf4 ^sup2? concentration with discharge was observed during all storms and peak concentration occurred at or near peak flow. Small increases in Mg²⁺, Ca²⁺, K⁺ concentrations and dissolved organic carbon (DOC) were observed during most storms. At the same time, ANC, Na⁺ and Cl^? concentrations usually decreased with increasing discharge. In summer/fall storms, the absolute increase in SO _inf4 ^sup2? concentration was one-third to 15 times the increase observed in winter/spring storms; the decrease in ANC during summer/fall storms was usually within the range of the decrease observed in winter/spring storms. In contrast, the decrease in Na⁺ and Cl^? concentrations during winter/spring storms was much greater than that observed during summer/fall storms. Data show that while base flow anion deficit was higher in summer/fall than in winter/spring, anion deficit decreased during most summer/fall storms. In contrast, base flow anion deficit was lower in spring and winter, but increased during winter/spring storms. Increased SO _inf4 ^sup2? concentration was the main cause of episodic acidification during storms at Reedy Creek, but increased anion deficit indicates organic acids may contribute to episodic acidification during winter/spring storms. Changes in SO _inf4 ^sup2? concentration coincident with the hydrograph rise indicate quick routing of water through the watershed. Saturation overland flow appears to be the likely mechanism by which solutes are transported to the stream during storm flow.     

THE WATER BALANCE OF AN AGRICULTURAL CATCHMENT III THE WATER BALANCE

The catchment of the Kingston Brook has an area of 57 km², mainly under pasture (56%) and arable crops (36%). Changes of soil water content, measured with a neutron probe from April 1969 to March 1973, were analysed to determine evaporation (summer only) and drainage. From measurements of rainfall and runoff, supplemented by Penman estimates of evaporation (in winter), water storage is estimated month by month. Annual mean values (mm) were: rainfall (559), evaporation (398), runoff (157). During the summer, the measured decrease in soil water storage contributed ca 100 mm to evaporation and drainage and there is evidence of delayed recharge (about 30 mm) during the winter. A linear relation between annual rainfall and annual runoff is interpreted in terms of (i) a fixed catchment storage (125 mm); (ii) a small and nearly constant winter evaporation (ca 49mm); (iii) summer evaporation of 125 mm from storage plus a constant fraction (0.57) of contemporary precipitation. Summer evaporation was restricted by the supply of rain in every year from 1969 to 1976. By estimation, 500 mm of summer rain is needed to maintain potential evaporation, and the deficit at which actual evaporation falls below the potential rate was about 40 mm. Replacing the pasture by cereals would increase runoff by about 10% because of the shorter growing season.     

不同土壤容重条件下水分亏缺对作物生长和水分利用的影响

为探究不同土壤容重和不同程度水分亏缺条件下冬小麦-夏玉米生长指标及产量的变化。采用桶栽土培法,分别设置3种土壤容重(1.2,1.4,1.6 g/cm^3)和3个土壤水分控制下限(低水分50%田间持水量、中水分60%田间持水量和高水分70%田间持水量),研究不同土壤容重和水分亏缺对冬小麦—夏玉米根系、生长指标、耗水量、产量和水分利用的影响。结果表明:随水分亏缺程度的加剧,冬小麦和夏玉米生长指标、生物量、耗水量和产量均呈降低趋势。随土壤容重增加,冬小麦生物量和产量呈先升高再降低的趋势,冬小麦耗水量和水分利用效率呈降低趋势;而夏玉米产量、耗水量和水分利用效率均呈降低趋势。试验中,1.4,1.2 g/cm^3分别为冬小麦和夏玉米生长的最适土壤容重。土壤容重与水分处理互作对夏玉米株高、耗水量和水分利用效率有极显著影响,而对冬小麦和夏玉米生物量及产量无显著影响。研究结果可为黄淮海地区作物绿色增产增效及水土资源高效利用提供理论参考。     

Acidity neutralization mechanism in a forested watershed in Central Japan

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).     

Temporal variation in the surface-water chemistry of a blanket bog on Dartmoor, southwest England: analysis of 5 years' data

Blanket‐bog peats, mapped as the Winter Hill and Crowdy associations by the Soil Survey of England and Wales, are an oceanic manifestation of the ombrotrophic ‘raised‐bog’ (Hochmoor) peats that cover large tracts in the boreal zone of the northern hemisphere. This paper examines monthly analyses from 1992 to 1997 of major ions and other variables from an upland blanket bog in southwest England in relation to seasonality, rainfall, and the chemical composition of rainwater. Average ionic composition of surface water (and peat) integrates variable atmospheric solute inputs over the years. The dominant ions in the surface water, Na⁺ and Cl^–, showed only weak seasonality, but divalent cations a stronger seasonal pattern with a summer maximum. Mean pH ranged from c. 4.4 in February to c. 4.2 in August. Changes in concentration of different cations were closely interlinked by cation exchange. The anion deficit, accounted for by anionic groups on the dissolved organic matter, was strongly seasonal with a summer maximum, as was optical absorbance at 320 nm. Nitrate and NH₄⁺ were both at much smaller concentrations than in rain. Nitrate exceeded 1 μmol l^?1 only during cold periods in winter, mainly following drought in the summer of 1995; NH₄⁺ reached a few μmol l^?1 only in summer. There was evidence of net retention of S by the peat in wet sites and during wet periods, and of net release of SO₄^2– (and acidity) under dry conditions. The 1995 summer drought and ensuing dry year in 1996 had marked and persistent effects on pH, apparent ion deficit (DEF), SO₄^2–, the divalent cations and Fe.     

Organic versus anthropogenic acidity in tributaries of the kejimkujik watersheds in Western Nova Scotia

Dilute waters (Ca = 0.3 to 0.8 mg L^?1) respond by depressed pH levels throughout the year to existing atmospheric wet deposition of sulphate (20 kg ha^?1yr^?1).This occurs in southwest Nova Scotia particularly during the cold, wet season when runoff is high. Colored waters of similar Ca levels receiving runoff from peaty catchments exhibit pH values one unit lower (4.7 to 4.1) than those of catchments of similar Ca levels but free from peat deposits (pH > 5.3). In colored streams sulphate and organic anions show opposing cyclic patterns while the negative gran alkalinity is the near mirror image of sulphate. Sulphate anion peaks during the high spring discharge when the organic anion concentration is lowest. Sulphate suddenly drops during the summer months during periods of high evapotranspiration, low water table and runoff, when the concentration of organic anions is highest. Both Al and Fe follow cyclic patterns similar to that of the organic anions while H⁺ reflects that of the sulphate anion. Hydrogen ion concentration is always higher than that of sulphate in very colored waters, particularly during the summer months when organic anion concentrations are very high. Analysis of data in the tributaries in the Kejimkujik watersheds indicates that while considerable organic acidity is present in colored waters, anthropogenic sulphate further increases the free acidity of these waters, particularly at times of high discharge.     

Factors affecting snowmelt streamwater chemistry in the black forest (West Germany)

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.     

Are ion exchange processes important in controlling the cation chemistry of soil- and runoff waters ?

Soil- and stream water elemental concentrations from a subcatchment in the Lake Gårdsjön area have been used to evaluate the importance of ion exchange processes on the transport of cations to aquatic ecosystems. The importance of cation exchange processes in the upper organic and upper B soil horizons was demonstrated using lysimeter water data from a recharge area and soil water flow simulated with SOIL model during winter rain events with high sea-salt concentration. The importance of the hydrological conditions, such as water flow and water pathway, silicate weathering and the ion exchange of Al with H⁺ on the streambed materials in controlling cation concentrations in soil and stream waters are also discussed. With the SAFE model, the contribution of cations from ion exchange by depletion of base cations from the exchange matrixes compared to from weathering was also assessed. SAFE calculations indicate that the release rate of base cation by ion exchange to runoff water has decreased since 1945 and is very low, approx. 0.1 keq/ha per year, at present time as a result of soil acidification due to S and N inputs.     

四川凉山州孙水河流域近60年来径流趋势特征分析

基于流域出口孙水关水文站流量资料,采用统计分析、趋势分析和突变分析等方法,分析了孙水河流域近60年来的径流分布特征和变化趋势;定量研究了降水和人类活动对径流变化的影响。结果表明:(1)流域年均流量年际变化较小,整体上呈现明显但不显著的下降趋势,以每年0.1163m3/s的速率递减,其中流量于1997年发生了增加突变。(2)流域径流年内分布较为不均,主要集中在夏秋两季;四季流量变化中春冬两季下降趋势显著,分别以每年0.0288,0.0709m3/s的速率递减;而夏秋两季下降趋势较平缓。其中流量在1995年夏天发生了增加突变。(3)人类活动和降水变化是影响孙水河流域流量减少的主要原因,不同阶段二者对流量影响程度不同。其中1975年后流域流量减少主要由人类活动引起,影响率最高达89.16%。研究成果可为研究流域产流规律服务,并为西南山区防洪防旱、水资源利用开发等提供可靠依据。     

人工毛竹林生态水文过程对气候变化的响应

为揭示生态水文过程与气候变化的关系,以广西猫儿山典型流域人工毛竹林为研究对象,利用Hydrus-1D模型模拟了毛竹林土壤水分及其他水文要素,在此基础上,针对设定的不同气候变化情景,分析了人工毛竹林对气候变化的响应。结果表明:Hydrus-1D模型可满足人工毛竹林生态水文分析,人工毛竹林蒸散发量占总降水量的28.40%,径流以基流为主。在不同气候变化情景下,气温升幅控制蒸发和蒸腾的增幅,且冬季增幅大于夏季增幅。径流对降水变化更敏感,降水变化会更多地影响夏季径流,而气温则更易影响冬季径流。降水对夏季土壤储水量影响大于冬季,气温则更多地影响冬季土壤储水量。气温降水耦合情况下,土壤储水量对降水减少气温升高时敏感性最明显,总体表现为冬季土壤储水量更易受影响。研究结果可为区域生态规划、水资源开发利用等提供参考依据。     

Characterization of hydrophobic acid fractions in water-soluble organic matter in Dystric Cambisol and in a stream in a small forested watershed: Seasonal and vertical variations in chemical properties

Abstract

Chemical properties of hydrophobic acid (HoA) fractions in water-soluble organic matter in soil and water are concerned with its interactions with mineral soil surfaces and organic pollutants. In 2004 we examined the seasonal and vertical changes in chemical properties of the HoA fraction in a Cambisol profile and compared these properties with those in the HoA fraction of an adjacent stream (aquatic humic substances) in a temperate forested watershed using high performance size exclusion chromatography (HPSEC) and ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The HoA fractions from Oi, Oe/Oa, A and B horizon soils in summer had lower O-alkyl C proportions than those recorded in samples in other seasons. The proportions of aromatic C in HoA fractions from A and B horizons were highest in summer. These seasonal variations were less significant than variations with soil depth. O-alkyl C proportions in HoA fractions decreased with increasing soil depth from the Oi to the A horizon. The HoA fractions from the B horizon showed a higher alkyl C proportion than samples from other horizons in winter and spring. These changes with soil depth from the Oi to A horizons might result from selective utilization of carbohydrate carbon by microorganisms, whereas those in the B horizon may result from sorption to mineral surfaces. The HoA fractions in the stream were similar in relative molecular weight, distribution of each type of proton and carbon species in HoA fractions from the B horizon, whereas stream HoA fractions collected in summer would be derived from organic horizons. This indicated that vertical changes in the chemical properties of HoA fractions in soil and pathways of water to the stream would largely affect the chemical properties of HoA fractions in the stream.     

放水冲刷对红壤坡面侵蚀过程及溶质迁移特征的影响研究

坡面薄层水流侵蚀不仅造成土壤养分流失,土壤质量恶化,同时对水体污染等环境问题造成一定影响。为了分析上方来水流量对红壤坡面径流侵蚀过程中泥沙的迁移规律及土壤溶质运移特征的影响,本试验利用室内放水冲刷试验,采用3个不同上方来水流量（10 L min-1、15 L min-1、20 L min-1）对第四纪黏土发育红壤坡面径流侵蚀过程中坡面径流泥沙和径流中非吸附性离子（Br-）迁移过程进行了研究。结果表明：不同上方来水条件下,放水初期产流量迅速增大,后期趋于稳定,累积径流量与产流时间成显著的线性关系,10 L min-1、15 L min-1、20 L min-1三种上方来水流量下累积径流量分别为263.2 L、295.1 L、291.04 L;上方来水流量越大,薄层径流冲刷作用越强烈,径流含沙量随时间变化波动越剧烈,累积泥沙量随产流时间呈幂函数变化,15 L min-1、20 L min-1流量下累积泥沙量分别为10 L min-1流量下累积泥沙量的1.42倍、4.25倍;径流Br-浓度随产流时间呈幂函数衰减,反映了土壤溶质随径流迁移量变化主要受水流与土壤接触时间和作用程度的影响。研究表明放水冲刷对土壤侵蚀及溶质运移有重要作用,试验结果对有效预测与控制红壤坡面侵蚀及养分流失具有重要实际意义。     

Hydrochemical modelling of a stream dominated by organic acids and organically bound aluminium

An existing hydrogeochemical model, the Birkenes model (BIM), has been extended to include production of dissolved organic carbon (DOC) in the soil/water system and its chemical interactions with H⁺ and A1³⁺. The model has been calibrated and verified using precipitation and runoff data from the Svartberget catchment in northern Sweden. The catchment is impacted by moderate amounts of sulphur deposition (6 kg S ha^?1 a^?1; the stream is high in DOC (7–35 mg L^?1) and experiences episodically low pH-values (～4.0). The refined BIM is able to simulate the main variations in major chemical components of the stream water (H⁺, Ca²⁺, Mg²⁺, Al_i, Al₀, Cl^?, SO₄ ^?2 and DOC), as well as stream discharge and ¹⁸O, while Na⁺ is not well reproduced. Although very simplified relationships are used for the chemical interactions between DOC and H⁺ and aluminium, the model shows that these interactions are essential to stream acidity and aluminiumspecies content. Some of the model parameters are poorly determined by calibration with runoff data only. Soil and soil water investigations may contribute to the evaluation and development of the model structure and the representation of chemical processes. Further improvements of the model should emphasize DOC-production/absorption, detailed studies on DOC chemical behaviour and hydrological structure.     

RZWQM模拟小麦 玉米轮作系统氮素运移及损失特征

本文以位于华北平原的河北省农林科学院大河试验站冬小麦-夏玉米轮作系统为研究对象,应用RZWQM(Root Zone Water Quality Model)模型对华北地区2010年冬小麦-夏玉米的1个轮作周期内土壤剖面水分和剖面硝态氮累积、作物产量、硝态氮淋失以及氨挥发进行模型模拟。本文利用并通过RZWQM模型在不同梯度施肥情况下讨论了施肥量对小麦-玉米轮作体系中硝态氮淋溶和氨挥发特性,并尝试通过拟合出的回归曲线来确定施氮量和硝态氮淋失和氨挥发之间的关系。设置冬小麦-夏玉米轮作周期施纯氮量分别为575 kg-hm-2(N3)、400 kg-hm-2(N2)、215 kg-hm-2(N1)和0 kg-hm-2(N0)4个处理,应用轮作周期中玉米数据进行模型参数率定,应用小麦进行模型参数的验证。结果表明:模型的玉米率定以及小麦验证的过程中结果偏差均在可接受范围内,剖面水分率定均方误差(RMSE)最高为0.019 cm3-cm-3,平均相对误差(MRE)最高为15.98%;剖面硝态氮累积验证结果 RMSE平均值为4.580 mg-kg-1,MRE平均值为52.63%。在模型验证的小麦-玉米季土壤基础上,硝态氮淋溶和氮挥发都与施氮量呈一定线性相关关系。综上结论,本试验结果能较好地模拟华北地区土壤剖面水分、硝态氮积累,以及施氮量对土壤硝态氮淋失和氨挥发的影响,为预测和估算土壤适宜施氮量提供了便捷可靠的方法。但RZWQM模型验证参数过程还需要进一步的校正与完善。     

Catchment-Scale Variation in the Nitrate Concentrations of Groundwater Seeps in the Catskill Mountains,New York,U.S.A.

Forested headwater streams in the Catskill Mountains of New York show significant among-catchment variability in mean annual nitrate (NO₃ ^-) concentrations. Large contributions from deep groundwater with high NO₃ ^-concentrations have been invoked to explain high NO₃ ^-concentrations in stream water during the growing season. To determine whether variable contributions of groundwater couldexplain among-catchment differences in streamwater, we measuredNO₃ ^- concentrations in 58 groundwater seeps distributed across six catchments known to have different annual average streamwater concentrations. Seeps were identified based on release from bedrock fractures and beddingplanes and had consistently lower temperatures than adjacentstreamwaters. Nitrate concentrations in seeps ranged from neardetection limits (0.005 mg NO₃ ^--N/L) to 0.75 mg NO₃ ^--N/L. Within individual catchments, groundwaterresidence time does not seem to strongly affect NO₃ ^-concentrations because in three out of four catchments therewere non-significant correlations between seep silica (SiO₂) concentrations, a proxy for residence time, andseep NO₃ ^- concentrations. Across catchments, therewas a significant but weak negative relationship betweenNO₃ ^- and SiO₂ concentrations. The large rangein NO₃ ^- concentrations of seeps across catchmentssuggests: 1) the principal process generating among-catchmentdifferences in streamwater NO₃ ^- concentrations mustinfluence water before it enters the groundwater flow system and 2) this process must act at large spatial scales becauseamong-catchment variability is much greater than intra-catchmentvariability. Differences in the quantity of groundwater contribution to stream baseflow are not sufficient to account for differences in streamwater NO₃ ^- concentrationsamong catchments in the Catskill Mountains.     

Stream chemistry impacts of conifer harvesting in welsh catchments

Hydrochemical data have been collected for between 6 and 9 years from forest harvesting experiments in small catchments (>10 ha) at Plynlimon and Beddgelert, Wales, UK. Felling resulted in rapid increases in NO ₃ ^? and K⁺ concentrations at both sites. A maximum of 3.2 mg N L^?1 was observed at Plynlimon about one year after the start of felling. Concentrations declined to control stream values (0.5 mg N L^?1) after 5 years. At Beddgelert, NO ₃ ^? concentrations in the manipulated catchments remained above those in the unfelled control catchment for three years, before declining below control values. The NO ₃ ^? pulse was related to increased rates of mineralization and nitrification in the soil after felling. The initial increase in K⁺ concentration after felling at Plynlimon was followed by a slow decline, but concentrations were still above those in the control stream after 5 years. From 4 to 8 years after felling at Beddgelert, K⁺ concentrations fell below and then generally remained lower than control values. The NO ₃ ^? pulse after felling at Plynlimon sustained inorganic anion concentrations above those in the control stream for the first 18 months after felling. As the NO ₃ ^? pulse declined, inorganic anion concentrations decreased to below those in the control stream about 4 years after felling. At Beddgelert, the smaller increase in NO ₃ ^? concentrations had less of an effect on inorganic anion concentrations which decreased after felling relative to values in the control stream. The increase in NO ₃ ^? was associated with temporary streamwater acidification in the felled catchments due to the increased rates of nitrification and nitrate leaching. At Plynlimon, streamwater filterable Al concentrations declined after felling, but controls on Al behaviour are complex and not explained by simple equilibrium relationships with Al(OH)₃ or by variations in inorganic anion concentrations. At Beddgelert, felling had no effect on stream water filterable Al concentrations. Felling at Plynlimon led to a large reduction in streamwater Cl^?, Na⁺ and SO ₄ ^2? concentrations. At Beddgelert reductions in SO ₄ ^2? and ‘sea salt’ ion concentrations were less clear, reflecting the smaller proportions of the catchments which were harvested. Felling had no deleterious effects on water quality, apart from a temporary slight further decline in stream pH at Beddgelert. Increases in NO ₃ ^? concentrations were short-lived and concentrations were well below drinking water standards. Filterable Al concentrations were already higher than statutory standards, but were not increased or decreased through felling.     

T-M水量平衡模型在流域产流计算中的应用

[目的]旨在通过研究流域各月度产水量,对水资源管理和农业灌溉用水调度进行指导。[方法]以锦阳川流域为研究对象,运用遥感(remote sensing,RS)和地理信息系统(geographic information system,GIS)提取和处理空间土地利用、土壤及数字高程模型数据,结合降雨、气温及不同植物的根深数据,采用Thornthwaite and Mather(T—M)模型计算了水分亏缺与剩余,土壤水分补给与利用的周期及月度产流量。[结果]研究区2011年平水年全年总径流量为281.0mm,在1,3—4,6和10月,存在水分亏缺及土壤水分利用,面积加权的水分亏缺值为5.8mm;2月,11—12月降水对土壤水分进行补给;5和7—9月,存在水分剩余,面积加权的剩余值为286.2mm。丰水年(25%)、平水年(50%)和枯水年(75%)多年平均产水量分别为8.3×107,4.8×107及2.2×107 m3。[结论]研究区在丰水年(25%)的2,7—11月,平水年(50%)的2—3,7—9月和枯水年(75%)的12—2,7—9月存在水分剩余。     

Chemical and biological trends associated with acidic atmospheric deposition in the Rhode River watershed and estuary

The Rhode River estuarine/watershed system is a tributary of Chesapeake Bay located on the inner Atlantic Coastal Plain. Its soils are fine sandy loams. Bulk precipitation pH in the spring season declined from 4.95 in 1974 to 3.82 in 1981 and was 4.03 in 1985. The changes in pH of a forested primary stream were more related to changes in bulk precipitation pH than were the changes in pH of agricultural streams, reflecting the importance of other major terrestrial sources of acidity on agricultural systems. Surges in acidity and dissolved total Al concentration in primary (first order) streams reached extremes of pH 3.2 and 300 μg Al L^?1. Higher order streams were observed to have surges in acidity with pH minima below 5.0. Surges in acidity ocurred during accelerated groundwater percolation following storm events and did not coincide with surface runoff or snowmelt. One of the reasons why groundwater is more acidic than surface runoff is that the vegetation exchanges H30 ⁺ for alkaline cations in the soil and translocates these ions to the vegetational canopy. When it rains, subsequently, H₃0⁺ in the precipitation displace some of these alkaline cations from the canopy. The end result is that overland flow during storms is enriched in alkaline cations, while groundwater is enriched in H₃0⁺. Although the source of dissolved Al is dissolution of clay minerals with atomic ratios of Al to silicate of 1:l, 1:2, or 1:3, this ratio in stream water rapidly declined to 1:1200 due to loss of Al. On average, forest drainage was the most acidic, the highest in dissolved Al, and the lowest in Ca. Surges in acidity were most severe from pastureland, and next most severe from cropland. Total fluoride concentrations were high relative to Al from all three land uses. Rhode River spawning runs of Perca flavescens declined drastically from the early 1970s to essentially zero since 1981. Larval bioassays of acidity indicate negligible toxicity to Hyla crucifer, significant toxicity to Perca flavescens and drastic effects on Morone saxatilis at pH 5.0.     

Model Assessment of Cattle and Climate Impacts on Stream Fecal Coliform Pollution in the Salmon River Watershed, British Columbia, Canada

A bacterial water quality model (BWQM) was developed and used to evaluate the impacts of cattle farming and climate change on the stream fecal coliform pollution in the Salmon River watershed in south-central British Columbia, Canada. The accuracy of the model simulation was evaluated using the Nash-Sutcliffe coefficient of efficiency (COE). The BWQM simulated the observed field data well, with the values of the COE ranging from 0.76 to 0.78 for the stream flow, from 0.55 to 0.60 for the fecal coliform (FC) concentration, and from 0.85 to 0.89 for the FC loading. The BWQM captured more than 79%, 66%, and 90% variation of the daily stream flow, FC concentration, and FC loading, respectively. The BWQM predicts that between 70% and 80% of the FC were transferred from the cattle farm to the Salmon River through the snowmelt-caused surface runoff during late winter and early spring, with the balance 20% to 30% coming from the soil-lateral flow and the groundwater return flow. The model also indicates that the stream FC concentration is sensitive to the distance of the cattle farm to the Salmon River. The model scenario analysis reveals that the climate change, at an assumed 1??C increment of daily air temperature, results in an increase in the stream FC concentration in the spring, fall, and winter, but there is also a decrease in the summer. The increased air temperature also changes the seasonal pattern of the stream FC concentration. Rainfall can reduce the stream FC concentration and mitigate the impact of the increased air temperature on the stream FC concentration as long as it does not result in a surface runoff or flooding event.