Soil erosion rates in tropical villages: A case study from Lake Victoria Basin, Uganda

In an effort to pinpoint the sources of sediment pollution in Lake Victoria, the contribution of sediment from compounds, landing sites, unpaved roads and footpaths is determined in the catchment of Nabera Bay and Kafunda Bay at the northern shore of Lake Victoria in southern Uganda. The volume of soil loss is determined in 36 compounds, 1 school and 1 landing site by comparing the original and current soil surface. The original soil surface is reconstructed using botanical and man-made datable objects. The soil loss rates are calculated by dividing the eroded soil volume by the age of the oldest datable object. Considering all compounds and landing sites in the study area, the average soil loss rate in compounds amounts to 107 Mg ha^? 1 year^? 1 (per unit compound) and to 207 Mg ha^? 1 year^? 1 per unit landing site. The soil loss from footpaths and unpaved roads is calculated by multiplying the total length of footpaths and unpaved roads with the average width and soil loss depth. The mean soil loss rate on footpaths is 34 Mg ha^? 1 year^? 1 and on unpaved roads equals 35 Mg ha^? 1 year^? 1. Compounds, landing sites, footpaths and unpaved roads occupy a small fraction of the study area (2.2%), but contribute disproportionately to the total soil loss (i.e. 85%) in the study area. It is concluded that compounds, landing sites, footpaths and unpaved roads are very significant sources of sediment pollution to Lake Victoria. This needs to be considered when designing strategies to reduce sediment production in the area.     

草被减流减沙效应及其力学机制分析

 利用人工模拟降雨试验,定量研究不同降雨强度下20°坡面草地的减流减沙效应,探讨草被坡面固土作用的力学机制。结果表明:在45、87和127mm/h降雨强度下,草地坡面土壤的平均入渗率是裸地坡面入渗率的2.1～4.2倍;与裸地相比,草地径流流速减少77.3%～79.8%,径流量减少51.9%～99.1%,产沙量减少93.6%～99.2%;从力学角度分析坡面土壤颗粒的受力情况,建立的坡面产沙量与径流切应力的关系模型可用于草被坡面土壤流失量预测;试验条件下,草地临界径流切应力值为2.857N/m2,裸地临界径流切应力值为0.861N/m2,坡面产沙量随径流切应力的增大而增大。研究结果对定量评价草被减流减沙作用和深化土壤侵蚀力学过程有一定的参考意义。     

草被覆盖度对坡面流水力学参数的影响及其减沙效应

为研究坡面生物措施减蚀作用,利用试验土槽和放水冲刷方法,探讨不同流量、覆盖度条件下坡面流水力学参数的特征,以及草被拦沙效应。结果表明,有草被覆盖的坡面薄层流的流态基本上呈过渡流和紊流;坡面流的弗劳德数与雷诺数分别为0.27～2.04和326～1538,阻力系数为8.30～16.29,且随着流量的增加,草被覆盖度对这些参数的影响减弱;与裸坡相比,30%和70%覆盖度坡面水流平均流速降低25%和47%,草被具有显著的减沙效应,但随着流量的加大,草被对坡面流的阻滞作用呈下降趋势。     

沟床草被对干热河谷冲沟产沙特性影响的野外模拟试验

金沙江干热河谷冲沟极为发育,水土流失强烈,严重威胁着该区的生态安全和社会经济发展。为探明植被影响径流过程、促进沟床稳定的机理,该研究采用野外放水冲刷试验,研究分析了沟床草被带长度对径流产输沙过程和特征的影响,旨在探明沟床草被影响下径流含沙量和输沙率时空变化规律。结果表明:1)增大草被带长度可有效降低冲沟径流泥沙含量,改变径流泥沙含量的时空分布特征。泥沙含量在时间上呈指数递减趋势,在冲沟径流运动方向上呈增大趋势。沟床草被带越长,泥沙含量在时间上波动性越弱,递减趋势越明显;随沟床草被带长度的增大,径流泥沙含量在沟床径流运动方向上的增大趋势有减缓现象;此外,当草被带长度增加到8 m以后,进一步增加草被带长度对减小径流泥沙含量效果不显著,而对照小区和4 m草被带小区泥沙含量均显著高于草被带长度≥8 m的小区,说明8 m草被带是降低径流泥沙含量的较好配置长度;2)沟床草被带对径流输沙率有减小作用。当草被带长度8 m时,径流输沙率高于草被带8 m的小区,且在时间上呈先增大后急剧减小而后趋于稳定的变化趋势。当草被带长度≥8 m时,径流输沙率在时间上表现出微弱的降低趋势。试验冲沟径流输沙率均值在空间上沿径流运动方向自冲沟上游至其下游表现出增大趋势,但草被带长度对输沙率在冲沟径流运动方向上的增大过程有较大影响。该研究为植被措施控制冲沟侵蚀提供理论依据。     

氧化势影响下的滇池沉积物孔隙水磷浓度变化

The sediment redox potential was raised in the laboratory to estimate reduction of internal available phosphorus loads, such as soluble reactive phosphorus （SRP） and total phosphorus （TP）, as well as the main elements of sediment extracts in Dianchi Lake. Several strongly reducing substances in sediments, which mainly originated from anaerobic decomposition of primary producer residues, were responsible for the lower redox potential. In a range of -400 to 200 mV raising the redox potential of sediments decreased TP and SRP in interstitial water. Redox potentials exceeding 320 mV caused increases in TP, whereas SRP maintained a relatively constant minimum level. The concentrations of Al, Fe, Ca^2＋, Mg^2＋, K^＋, Na^＋ and S in interstitial water were also related to the redox potential of sediments, suggesting that the mechanism for redox potential to regulate the concentration of phosphorus in interstitial water was complex.     

Runoff sediment particle sizes associated with soil erosion in the Lake Tahoe Basin,USA

Runoff sediment from disturbed soils in the Lake Tahoe Basin has resulted in light scattering, accumulation of nutrients, and subsequent loss in lake clarity. Little quantified information about erosion rates and runoff particle‐size distributions (PSDs) exists for determining stream and lake loading associated with land management. Building on previous studies using rainfall simulation (RS) techniques for quantifying infiltration, runoff, and erosion rates, we determine the dependence and significance of runoff sediment PSDs and sediment yield (SY, or erodibility) on slope and compare these relationships between erosion control treatments (e.g., mulch covers, compost, or woodchip incorporation, plantings) with bare and undisturbed, or ‘native’ forest soils. We used simulated rainfall rates of 60–100 mm h⁻¹ applied over replicated 0·64 m² plots. Measured parameters included time to runoff (s), infiltration and runoff rates (mm h⁻¹), SY (g mm⁻¹ runoff), and average sediment concentration (SC, g L⁻¹) as well as PSDs in runoff samples. In terms of significant relationships, granitic soils had larger particle sizes than volcanic soils in bulk soil and runoff samples. Consequently, runoff rates, SCs, and SYs were greater from bare volcanic as compared to that from bare granitic soils at similar slopes. Generally, runoff rates increased with increasing slope on bare soils, while infiltration rates decreased. Similarly, SY increased with slope for both soil types, though SYs from volcanic soils are three to four times larger than that from granitic soils. As SY increased, smaller particle sizes are observed in runoff for all soil conditions and particle sizes decreased with increasing slope. Copyright © 2008 John Wiley & Sons, Ltd.     

巢湖沉积物磷的形态及其与间隙水磷的关系

采用磷形态的连续提取法,研究了巢湖沉积物中磷的地球化学形态及间隙水中总溶解性磷（DTP）、可溶性磷酸盐（DIP）、可溶性有机磷（DOP）含量的垂向分布特征。结果表明,西湖区的沉积物总磷含量明显高于东湖区。表层沉积物中活性磷含量占总磷的44％-81％,金属氧化物结合态磷（NaOH—P）作为活性磷的主要存在形式,在西湖区含量比例达到47％-60％,对磷释放起重要贡献;磷形态剖面表明,西湖区的金属氧化物结合态磷、可还原态磷（BD—P）含量高于东湖区。金属氧化物结合态磷、可还原态磷、钙结合态磷（HCl-P）受人类活动影响较大,有机磷（Org—P）受外源磷污染影响很小;BD—P、NaOH—P随深度增加而减小,说明巢湖近期磷负荷有增加的趋势;DTP、DIP、DOP在水-沉积物界面的浓度梯度反映它们有自间隙水向上覆水扩散的趋势;巢湖间隙水不同形态磷与BD—P、NaOH—P显著相关（α=0．01）。这项研究可为巢湖内源污染和富营养化的控制与治理提供理论参考。     

Laboratory assessment of the workable range of soils in the tropical zone of Veracruz, Mexico

Information on workability limits is highly valuable at the farm level to help the farmer in deciding when and possibly how to carry out tillage. On higher levels (e.g. on regional scale) this knowledge will form a basis for obtaining guidelines with respect to required number of tractors, equipment etc. and so help in planning and policy making. Data of this kind are often lacking. The study reported here is the laboratory component of research carried out in the tropical area of Veracruz, Mexico. In this study, laboratory methods to determine workability limits were assessed for a typical clay and loam soil. For the dry workability limit (where energy for producing specifically sized aggregates is the decisive factor), the drop test was applied. Results in terms of soil moisture tension at the point of lowest energy expenditure were comparable with the field results, although energy levels were different. For the determination of the wet workability limit (WWL), an air permeability test and a compression test were used. Both tests yielded limits that were very close to the ones determined in the field. The compressibility test allows the assessment of other soil characteristics such as prediction of modification of pF curve and aeration properties under compressive forces. For field or farm scale, workability limits can be obtained from representative areas and then used in combination with water balance models to determine the number of workable days under a certain weather (rainfall) regime. The applicability on a regional scale is as yet more difficult, soil physical information from soil maps is usually not sufficient to allow reliable interpretations. The use of existing pedo-transfer functions to obtain input for models to predict workable days did not produce satisfactory results.     

金鸡湖与尚湖中微生物数量及群落特征的研究

对苏州地区金鸡湖与尚湖水体中的微生物数量及种群组成的研究表明，异养细菌数金鸡湖比尚湖高，分别为1．7－26万个／mL和500－80000 个／mL，高峰期出现在10月份；放线菌和霉菌数量较少，金鸡湖为0－19个／mL和0－7个／mL，尚湖为1－25个／mL和0－37个／mL。从大肠菌群数看，金鸡湖明显高于尚湖，分别为350－16000个／L和20－250个／L， 表明金鸡湖接纳生活污水和施肥养鱼对大肠菌群数的升高至关重要；金鸡湖和尚湖水体 中分别检测出8个和9个属的异养细菌，优势菌分别为弧菌属、气单胞菌属、芽孢杆菌属和不动杆菌属、假单胞菌属、芽孢杆菌属。     

鄱阳湖区典型堤防不同植草护坡产流产沙特征试验研究

[目的]对鄱阳湖区典型堤防不同植草护坡产流产沙特征进行试验研究,为该区植草护坡草种筛选以及护坡技术构建提供一定的科学依据。[方法]采用人工模拟降雨的手段,利用水土流失移动监测车选取鄱阳湖区典型堤防——九江市永修县九合联圩为研究对象,对裸露坡面(BL)、自然恢复坡面(NRS)、狗牙根护坡坡面(CDS)、中华结缕草护坡坡面(ZSS)和假俭草护坡坡面(EOS)等5种护坡模式进行了水土流失监测,量化不同护坡模式的水土保持效益。[结果]裸地具有最短的初始产流时间和最大的径流流速,植草后能较大幅度延长初始产流时间,降低径流流速,并且假俭草坡面减缓坡面流速的效果最为明显。20 mm/h雨强下,4种植草坡面与裸露坡面之间的径流系数没有明显差异,但是随着雨强的增大,植草坡面对径流的抑制作用就越来越明显。各处理土壤流失量均随着雨强增大而增大。[结论]植草护坡能有效减少堤防土壤流失量,并且堤防植草护坡的减沙效益在大雨强下表现得更为明显。     

三峡水库干流消落带泥沙沉积影响因素

为揭示三峡水库消落带不同自然环境因素对泥沙沉积过程的影响及判别人类活动的干扰程度,采用原位观测方法,对三峡水库干流消落带的泥沙沉积量及其潜在影响因素(消落带微地形、河流水文泥沙条件、消落带土壤侵蚀、消落带植被状况和人类活动)展开调查、分析和量化测算,并利用典型相关分析和方差分析,研究不同因素对泥沙沉积量的影响.结果表明:1)库尾江津—涪陵河段以人类活动的影响最为剧烈,自然环境因素与泥沙沉积量均无显著关系.2)库中涪陵—奉节河段以消落带地形特征中的坡度和高程影响较为明显,二者与泥沙沉积量的相关程度分别为-0.508和-0.714;坡度越小,泥沙沉积越多;高程越低,消落带被含沙水流淹没的时间越长,泥沙沉积量也越多.3)库首奉节-秭归段则以坡度的影响为主,其与泥沙沉积量的相关程度为-0.517,坡度越小,泥沙沉积越多,不同高程间的泥沙沉积量并无太大差异.研究说明,三峡水库干流消落带泥沙沉积影响因素主要包括消落带坡度、高程、河流水沙条件和人类活动4种,植被盖度对消落带泥沙沉积过程没有影响,4种因素的影响范围存在较明显的空间变异性.     

利用TM影像分析巢湖悬沙分布及其原因

悬浮泥沙是重要的水质参数之一,其大小直接影响水体透明度、浑浊度、水色等光学性质及水生生态条件,其含量及其动态变化对该区的水下地貌的发展及冲淤变化等具有非常重要的影响。以巢湖为例,利用TM影像分析了巢湖泥沙的空间分布情况,指出巢湖泥沙的来源主要是各入湖河流携带的泥沙,其次是岸坡崩塌物形成的,并结合流域环境背景分析其原因,为巢湖的航道治理、湖区清淤提供了科学依据;最后提出了巢湖水质保护的对策。     

基于CSLE-TLSD耦合模型的近40年洞庭湖流域土壤侵蚀时空分异及归因分析

为了精确模拟洞庭湖流域土壤侵蚀动态过程并定量评估其影响因素贡献,在中国水土流失方程(CSLE)的基础上耦合泥沙输送限制模型(TLSD),实现对土壤分离-搬运-沉积全动态过程分析。在此基础上,采用趋势分析和地理探测器方法探究洞庭湖流域1980-2020年土壤侵蚀时空分异特征与影响机制。结果表明:(1)CSLE-TLSD耦合模型在各水文站的年输沙量模拟值和实测值拟合结果较好(R²=0.56);(2)1980-2020年洞庭湖流域年均土壤侵蚀模数为5.09 t/(hm²·a),侵蚀模数和面积在整体上均呈下降趋势,其中侵蚀显著改善区域占流域总面积的22.60%,而显著加剧区域仅占2.69%;(3)年侵蚀总量以2005年为突变点,呈现出先下降后上升的趋势;(4)2005年前后导致土壤侵蚀变化的主导因子从地类变化转变为年降雨量变化。综上,洞庭湖流域土壤侵蚀总体呈现侵蚀面积收缩、局地恶化的趋势,其中极端降雨事件和经果林开发是侵蚀加剧的主要原因。     

鄱阳湖流域降雨侵蚀力变化及其对入湖悬移质输沙量的影响

鄱阳湖是中国最大的淡水湖,揭示流域降雨侵蚀力时空演变及其对入湖泥沙的影响对科学指导流域生态保护与修复、促进流域生态文明高质量发展具有重要意义。基于鄱阳湖流域63个气象站1961—2017年逐日降雨量和鄱阳湖五河入湖悬移质输沙量（以下简称输沙量）年数据,采用Mann—Kendall非参数检验、双累积曲线、线性回归等方法,分析了流域降雨侵蚀力和入湖输沙量动态过程,定量评估了降雨侵蚀力变化和人类活动对入湖输沙量的影响。结果表明：鄱阳湖流域平均降雨侵蚀力为10 034.1（MJ·mm）/（hm²·h）,介于6 738.8~12 734.8（MJ·mm）/（hm²·h）,呈西南地区低、东北地区高的空间分布格局;降雨侵蚀力年际间呈不显著的上升趋势（P>0.05）,在21世纪10年代最大,20世纪60年代最小。鄱阳湖入湖年均总输沙量1 183.3×10⁴ t,呈极显著下降趋势（P<0.01）,在20世纪70年代最大,21世纪00年代最小。入湖总输沙量和赣江、信江及修水输沙量分别在1992年、1999年后发生趋势性减少（P<0.01）。以输沙量突变前的时段为基准期,突变年份后人类活动和降雨侵蚀力变化对入湖总输沙量变化的影响程度分别为-138.1%和38.1%;对赣江入湖输沙量变化的影响程度分别为-125.8%和25.8%;对信江入湖输沙量变化的影响程度分别为-121.3%和21.3%;对修水入湖输沙量变化的影响程度分别为-141.4%和41.4%。近60年降雨侵蚀力变化表现为增加入湖输沙量,而人类活动（水库建设、水土保持和采砂活动）是鄱阳湖入湖输沙量减少的主要原因。     

广西桂林漓江滨岸带植被对地表产流产沙的影响

降雨及其产生的地表径流是造成水土流失的主要原因之一,水土流失所带来的河床抬高、水质污染等环境问题亟待解决.本文通过广西桂林漓江滨岸带内建立的7个试验小区,在汛期内观测自然降水条件下各小区的产流产沙情况,研究漓江滨岸带内植被对地表产流产沙的影响,从而为漓江水土流失防治以及面源污染治理等问题提供参考.结果表明:1)植被覆盖能显著拦截坡面径流、沉积泥沙,且植被盖度愈高拦截效果愈显著;2)在草本覆盖处理中,狗尾草植被覆盖处理截流减沙效果较其他几种草本植物覆盖处理好,可作为漓江滨岸带裸露退化区域优先选择的植物种;3)纯草本植物配置的植被带截流减沙效果优于草灌相结合配置的植被带;4)地表径流量、产沙量与降雨量、降雨强度之间在P＜0.01水平上显著正相关,径流量与产沙量之间存在密切的线性关系.由此,采用增加裸坡坡面植被覆盖、选择狗尾草作为漓江快速绿化的草种、坡面上部建立截留措施等方式,可有效减轻坡面水土流失,缓解由水土流失带来的面源污染等问题.     

滇池底泥中氮素空间分布异质性分析

采用传统统计与地统计学相结合的方法,对滇池底泥0-5,5-10,10-20 cm中的全氮、有机氮、铵态氮进行了空间变异特征研究.结果表明,3层底泥中不同形态氮的空间变异性均较大.结构性因素对0-5 cm底泥中全氮影响比较大,而随机性因素和结构性因素对0-5 cm和10-20 cm这两层底泥中的铵态氮以及10-20 cm中的3种形态氮的影响相近.从整个滇池来看,3层底泥中3种形态氮的含量均呈现自北向南递减,各种形态氮均在湖泊中心出现较深颜色的斑块,说明底泥氮有向湖泊中间沉积的趋势.同时随着深度的增加,3种形态氮在空间分布的颜色深浅是0-5 cm>5-10 cm>10-20 cm,可见底泥中氮的累积逐年增加,滇池污染有加重的倾向.     

滇池流域建设用地景观格局与滇池水质关系分析

运用灰色关联度分析法,研究了高原湖滨区滇池流域建设用地的景观格局指数与滇池水体的TN,TP浓度变化之间的关系。结果表明,1988-2008年,滇池草海与外海TN,TP浓度呈不断上升的趋势;滇池流域建设用地斑块的团聚程度和整合性升高,建设用地斑块间距离变小,大面积的建设用地增多,且建设用地斑块形状趋于复杂,具有不规则的特征;滇池流域建设用地对水质的影响与其景观空间格局关系密切,特别是聚合度和面积加权的平均斑块分维数。要保证该地区迅速发展的城市化背景下的水环境安全,滇池流域土地利用调整的基本方向是在湖滨带地区,保留足够的生态用地,避免建设用地的过度整合及大面积建设用地的形成。     

论黔西北麻窝山岩溶盆地土壤堆积记录——兼答张信宝先生

针对张信宝先生用137Cs断代法计算黔西北麻窝山岩溶盆地土壤沉积速率,以及对谢良胜等研究成果提出的质疑,笔者从黔西北麻窝山岩溶盆地环境现状、环境演变、土壤堆积、137Cs活度等方面进行论述。认为:易地堆积土壤来源的不确定性导致土壤层中137Cs来源复杂,不能根据其峰值确定沉积年代,但可以作为定性判定土壤侵蚀强度的依据;在资料匮乏和无测站数据时,沉积量测量法是盆地型喀斯特山区土壤侵蚀计算的有效方法;麻窝山特殊的环境地质条件为喀斯特石漠化系统研究提供理想场所。     

太湖流域农村生活污水处理技术模式调查和分析——以江苏省为例

通过对太湖流域农村生活污水处理技术模式的调查研究,选取4种典型处理技术:DSP-SH(Anaerobic-Anoxic-Oxic,A~2/O)生物脱氮除磷技术、Hy Wat海沃特复合生物滤池技术、膜生物反应技术(Membrane Bio-Reactor,MBR)以及活性污泥法(Sequencing Batch Reactor Activated Sludge,SBR)进行分析比较。结果表明:除Hy Wat海沃特复合生物滤池技术处理效果基本达标外,DSP-SH(A~2/O)技术、SBR技术以及MBR技术对氮、磷去除效果较差,均未稳定达到一级B标准,需定期加药提高去除率。4种污水处理技术的投资及占地面积均较低,DSP-SH(A~2/O)和Hy Wat海沃特复合生物滤池技术的操作管理和后续维护均比较方便;MBR技术污水处理效果好,但运行费用较高,适用于经济较发达或对出水要求较高的地区;SBR技术运行方便灵活且费用适中,适用于受地形、占地面积限制的农村集中居住地。只有因地制宜地选用水处理技术模式,并结合稳定有效的资金投入和管理维护机制,才能保障农村生活污水处理达到预期目标。     

鄱阳湖-赣江各支入湖段沉积物中微塑料分布及其组成特征

微塑料作为一种新型污染物已受到全球的广泛关注。以鄱阳湖南矶山、赣江北支、赣江中支和赣江南支入湖段为研究区,湖泊湿地沉积物为研究对象,对不同区域不同水期沉积物进行采样,利用浮选分离法对沉积物中的微塑料进行分离,进一步进行微塑料分布特征及其组成研究。结果表明,四个区域沉积物中微塑料丰度由高到低依次为赣江中支、赣江南支、南矶山、赣江北支,其中赣江中支微塑料丰度达到1 936±89 ind·kg~(–1)。四个区域不同水期沉积物中微塑料丰度均表现为枯水期高于平水期高于丰水期。南矶山沉积物中微塑料以发泡类为主,赣江北支沉积物中微塑料以纤维类为主,赣江中支和赣江南支沉积物中微塑料以碎片类为主。南矶山沉积物中微塑料粒径以2～3 mm为主,赣江各大支流沉积物中微塑料均以1 mm为主。不同类型微塑料表面形貌特征相差很大,组成成分也不相同,主要为聚乙烯和聚丙烯。