Application of hydrological model to acidified watersheds: A study on Mersey River and Moosepit Brook,Nova Scotia

A hydrological model has been applied to Mersey River and Moosepit Brook watersheds, Nova Scotia. The computed hydrograph and snow water equivalent, sulfate in the snowpack and DOC are reasonably good agreement with observed data. Contrasts have also been made on the calibrated model coefficients for the different watersheds. An attempt to relate them to the geology and soil characteristics has led to realistic estimation of the soil contact times.     

概念性土壤侵蚀模型的建立及在紫色土小流域的应用

概念性土壤侵蚀模型在描述流域基本过程的同时对参数要求较低,现有概念性模型中计算产沙所需参数主要靠律定或借鉴经验值。该文介绍了1个无需流域出口产沙量长序列观测资料来律定且能适用于研究流域的概念性土壤侵蚀模型。模型中引入了分布式水文模型WetSpa Extension作为水文模块,结合流域内试验小区上建立的流量—产沙量经验关系计算侵蚀量,再结合泥沙输移比构建起产沙模块。通过在紫色土地区小流域的应用表明,模型能够得到较合理的流域出口产流量、产沙量以及侵蚀率的空间分布等模拟结果,在没有试验小区的邻近流域地区也具有推广性,且能作为评价水保措施效益的有力工具。该概念性模型对于流域出口泥沙资料稀少的地区具有很高的应用价值和协助流域管理的 潜力。     

黄河流域陕西片土壤侵蚀预报模型研究

以气候、地质、地形、植被及人类活动 5类因素中的 6个因子为预报因子 ,以陕西黄河流域水蚀区内 5大类型区中 3 3条小流域的实验观测资料和实地调查资料及有关科研单位的研究成果为基础 ,建立了适用于该区域的土壤侵蚀预报模型。据运用该模型对本区域内 4条小流域水土保持遥感普查成果和建模所用 3 3条小流域土壤侵蚀模数进行验证 ,证明该模型具有较高的精度 ,可以在陕西黄河流域水蚀区及条件相近的其他地区推广应用     

The role of integrated watershed management on soil-health in northern Ethiopia

ABSTRACT

Integrated watershed management (IWSM) technologies have been implemented around the world, including in the northern highlands of Ethiopia during the last few decades. However, their role in improving soil-health along different geological formations is not well studied. This study was, thus, aimed at quantifying the impact of IWSM on soil-health under dolerite and sandstone geological formations. Twelve soil samples were taken from two watersheds with IWSM and another 12 soil samples from two watersheds without IWSM at 30?cm soil depth. Physical, chemical, and biological properties of these soil samples were then analysed in a laboratory. Soil moisture content, Soil organic matter, total nitrogen, available phosphorus (Pav) and arbuscular mycorrhizal fungi spore density of soils were significantly high in watersheds with IWSM as compared to watersheds without IWSM. Although insignificant, total porosity, cation exchange capacity, Exchangeable bases and micronutrients also had higher mean value on watersheds with IWSM practices than watersheds without. Thus, this study reviled that an introduction of these IWSM practices has a positive impact in improving soil-health. Moreover, IWSM practices implemented on dolerite geological formation showed a higher impact on soil-health as compared to management practices implemented on sandstone geological formation.     

Modeling the impacts of soil management practices on runoff, sediment yield, maize productivity, and soil organic carbon using APEX

Simulation models are increasingly used to analyze the impact of agricultural management at the watershed-scale. In this study, the Agricultural Policy/Environmental eXtender (APEX) model was tested using long-term (1976–1995) data from two watersheds (W2 and W3) at the USDA Deep Loess Research Station near Treynor, Iowa. The two watersheds were cropped with continuous corn (Zea mays L.) and managed with conventional-tillage at W2 (34.4 ha) and ridge-till at W3 (43.3 ha). The monthly runoff and sediment yield were calibrated for the two watersheds during 1976–1987 by adjusting the curve numbers, curve number index coefficient, RUSLE C factor exponential residue and height coefficients, and erosion control practice factor for grassed waterways. Soil organic carbon values in the top 0.15 m soil layer were calibrated for the two watersheds in 1984 by adjusting the microbial decay rate coefficient. Model validation was conducted from 1988 to 1995. The calibrated model was able to reasonably replicate the monthly and yearly surface runoff and sediment yield for both watersheds for the validation period, with Nash–Sutcliffe efficiencies (EF) larger than 0.62 except for the EF of 0.41 for monthly sediment yield comparison at W3. The errors between the predicted and observed means were all within ±6% for runoff and sediment yield; predicted soil organic carbon in the 0.15 m soils in 1994 were within 10% of the observed values for both watersheds. The percentage error between the predicted and observed average corn grain yields was −5.3% at W2 and −2.7% at W3 during the 20-year simulation period. Scenario analyses were also conducted to assess the benefits of ridge-till over conventional-tillage. Over the 20 years, the predicted benefit of ridge-till versus conventional-tillage on surface runoff reduction was 36% in W2 and 39% in W3, and about 82–86% sediment yield reduction in both watersheds. The cumulative soil organic carbon losses from sediment were reduced about 63–67%. The long-term benefit of ridge-till over conventional-tillage was also quantified as a minimum corn grain yield increase of 3.8%. The results of this study indicate that APEX has the ability to predict differences between the two tillage systems. The modeling approach can be extended to other watersheds to examine the impacts of different tillage systems.     

小流域水土流失治理优先度的评价与应用

中国水土流失防治任务仍然繁重,有计划分批次实施水土流失治理是现阶段条件下的必然选择,优先治理小流域识别是其首要解决的一项基础工作,然而目前相关成果较为缺乏,难以支撑小流域水土流失治理智能决策和精准施策。在当前大力推进智慧水土保持背景下,积极探索优先治理小流域识别方法非常迫切,对于科学、合理、高效促进水土流失治理工作具有重要意义。该研究立足于小流域自然禀赋条件,以中国水土流失重点区域——三峡库区秭归县为例,坚持科学性和可操作性相结合原则,以水土流失“减量和降级”双重目标和治理效益最大化需求为导向,综合水土流失面积和土壤侵蚀强度两个维度,提出小流域水土流失治理优先度定义及定量评价方法,为识别优先治理小流域提供科学依据和技术支撑。结果显示,秭归县2021年现状水土保持率为69.12%,远期（2050年）水土保持率为81.74%,总体提升12.62个百分点。秭归县2021年全域土壤侵蚀模数现状为758.50 t/(km²·a),最小可能土壤侵蚀模数为408.71 t/(km²·a),总体下降比例达46%。秭归县大部分区域均具有较大的水土保持率提升潜力和土壤侵蚀控制度,可完全治理和可降级的水土流失地块分布较为广泛,尤其在县域中西部的小流域存在较大的水土流失面积消减和土壤侵蚀强度降级空间。秭归县各小流域水土流失治理优先度的空间分布总体呈现中部高,东部和南部相对较低的分布格局,全县治理优先度大于0.6的小流域占总全县小流域的11.76%。通过典型县应用,该研究提出的小流域治理优先度涵盖了水土流失面积和土壤侵蚀强度两个维度,能更为全面满足小流域水土流失“减量和降级”双重目标和和治理效益最大化需求,直观反映了水土流失面积消减空间和土壤侵蚀强度降级空间的目标和相对大小,对支撑小流域治理决策更加准确、科学,治理优先度评价方法不仅可行,且易操作。     

Prediction of soil and water conservation structure impacts on runoff and erosion processes using SWAT model in the northern Ethiopian highlands

Purpose

Land degradation due to soil erosion is a serious threat to the highlands of Ethiopia. Various soil and water conservation (SWC) strategies have been in use to tackle soil erosion. However, the effectiveness of SWC measures on runoff dynamics and sediment load in terms of their medium- and short-term effects has not been sufficiently studied.

Materials and methods

A study was conducted in 2011 to 2015 in the Gumara-Maksegnit watershed to study the impacts of SWC structures on runoff and soil erosion processes using the soil and water analysis tool (SWAT) model. The study was conducted in two adjacent watersheds where in one of the watersheds, SWC structures were constructed (treated watershed (TW)) in 2011, while the other watershed was a reference watershed without SWC structures (untreated watershed (UW)). For both watersheds, separate SWAT and SWAT-CUP (SWAT calibration and uncertainty procedure) projects were set up for daily runoff and sediment yield. The SWAT-CUP program was applied to optimize the parameters of the SWAT using daily observed runoff and sediment yield data.

Results and discussion

The runoff simulations indicated that SWAT can reproduce the hydrological regime for both watersheds. The daily runoff calibration (2011–2013) results for the TW and UW showed good correlation between the predicted and the observed data (R ²?=?0.78 for the TW and R ²?=?0.77 for the UW). The validation (2014–2015) results also showed good correlation with R ² values of 0.72 and 0.70 for the TW and UW, respectively. However, sediment yield calibration and validation results showed modest correlation between the predicted and observed sediment yields with R ² values of 0.65 and 0.69 for the TW and UW for the calibration and R ² values of 0.55 and 0.65 for the TW and UW for the validation, respectively.

Conclusions

The model results indicated that SWC structures considerably reduced soil loss by as much as 25–38% in the TW. The study demonstrated that SWAT performed well for both watersheds and can be a potential instrument for upscaling and assessing the impact of SWC structures on sediment loads in the highlands of Ethiopia.

     

An Empirical Model for Estimating Remediation Costs at Contaminated Sites

A model for estimating the remediation costs at contaminated sites is developed, in which the predictor variable is a composite of surface, subsurface, and contaminant risk factors. Calibration of the model is performed at 83 sites in an urbanized watershed with diverse surface geology in southeastern Michigan. These test sites exhibited different extents of contamination, including some where only soil was contaminated, and others where soil and groundwater were contaminated. The model was then applied to 79 sites with multiple contamination extents within different watersheds in North America, Europe, Australia, and Africa. The results indicate a very high correlation between the estimated and actual remediation costs at these sites. This model thus has the potential for providing reliable estimates of remediation costs across a broad array of soil and groundwater contamination scenarios, including dense nonaqueous phase liquid (DNAPL) contamination in sandy soil and lead in clay soil.     

红壤丘陵区不同植被覆盖阈值小流域时空分布规律

植被覆盖度是反映土壤侵蚀状况的关键指标,实施植被恢复是防治小流域土壤侵蚀的重要措施,但小流域植被覆盖度到底恢复到多少才能有效控制土壤侵蚀尚不清楚。基于土壤侵蚀治理的小流域植被覆盖度阈值效应,对红壤丘陵区33 157个小流域2000—2015年植被覆盖度的时空变化进行了分析,评估不同植被覆盖阈值小流域时空分布规律与格局,以期精准制定小流域土壤侵蚀治理方式与对策。结果表明：(1) 2000—2015年,84%的小流域植被覆盖呈不断增加趋势,植被覆盖下降的小流域占15%,植被覆盖度基本不变的小流域仅有1%;(2)植被覆盖小于40%(低阈值带)的小流域占比小且相对稳定(3%～7%),说明大规模人工治理小流域土壤侵蚀的局面已扭转,但耕地依然是重点关注的对象;(3)植被覆盖位于40%～80%(过渡带)的小流域占比一直最高(超过83%),应采取以“自然恢复为主,人工修复为辅”的治理方式,重点关注土地利用结构和植被结构的优化配置;(4)植被覆盖大于80%(高阈值带)的小流域占比从2010年前的1%～2%上升到2015年的14%,可见具有自我修复植被覆盖条件的小流域显著增加,实施自然恢复(如封禁)是高阈...     

The Effect of Wildfire on Soil Mercury Concentrations in Southern California Watersheds

Mercury (Hg) stored in vegetation and soils is known to be released to the atmosphere during wildfires, increasing atmospheric stores and altering terrestrial budgets. Increased erosion and transport of sediments is well-documented in burned watersheds, both immediately post-fire and as the watershed recovers; however, understanding post-fire mobilization of soil Hg within burned watersheds remains elusive. The goal of the current study is to better understand the impact of wildfire on soil-bound Hg during the immediate post-fire period as well as during recovery, in order to assess the potential for sediment-driven transport to and within surface waters in burned watersheds. Soils were collected from three southern California watersheds of similar vegetation and soil characteristics that experienced wildfire. Sampling in one of these watersheds was extended for several seasons (1.5 years) in order to investigate temporal changes in soil Hg concentrations. Laboratory analysis included bulk soil total Hg concentrations and total organic carbon of burned and unburned samples. Soils were also fractionated into a subset of grain sizes with analysis of Hg on each fraction. Low Hg concentrations were observed in surface soils immediately post-fire. Accumulation of Hg coincident with moderate vegetative recovery was observed in the burned surface soils 1 year following the fire, and mobilization was also noted during the second winter (rainy) season. Hg concentrations were highest in the fine-grained fraction of unburned soils; however, in the burned soils, the distribution of soil-bound Hg was less influenced by grain size. The accelerated accumulation of Hg observed in the burned soils, along with the elevated risk of erosion, could result in increased delivery of organic- or particulate-bound Hg to surface waters in post-fire systems.     

黄土丘陵沟壑区小流域土壤侵蚀及其预报模型研究

在小流域内建立人工径流试验小区和自然坡面径流试验小区,观测天然降雨条件下的土壤侵蚀现象、土壤侵蚀量和小流域出口治沟骨干工程的淤积量,并对小流域土壤侵蚀进行了分类。在特别界定小流域"坡面侵蚀"、"沟道侵蚀"和沟道"重力侵蚀"词语含义的基础上,建立起坡面侵蚀模数和沟道侵蚀模数的预报模型。该侵蚀预报模型具有较高的精度,适用于年降雨量为430mm左右的黄土丘陵沟壑区。     

川中不同类型小流域土壤侵蚀特征分析

以川中小流域为研究对象,2004年第5期小流域竣工验收报告为基础数据,以流域土地利用方式面积比例为指标进行聚类,将小流域分为不同类型,然后分别建立以不同类型小流域的土壤侵蚀量为因变量,用地面积为自变量的多元线性回归方程。从而比较区域内部小流域之间的差异,分析不同类型小流域的土壤侵蚀特征,以期更有针对性地为小流域综合治理提供理论和实际依据。研究表明:（1）根据其主要土地利用方式,研究区小流域分为4类;（2）不同类型小流域,水土流失主要及最大来源、侵蚀模数等特征有显著差异。     

Tillage methods and soil and water conservation in southern Brazil

The intensive tillage systems adopted in southern Brazil have accelerated soil erosion, depleted plant-available nutrients and reduced crop productivity. These effects are better perceived in terms of farmer's land use and soil management techniques, i.e. animal- or machine-powered equipment through high and low aptitude land use classification systems. However, these tillage systems coexist together at the level of agricultural watersheds and are not compatible for continuous and sustainable agriculture. This article proposes a methodology for using agricultural watersheds as planning units for integrated soil conservation plans. This methodology is based on considerations of the farmer's socioeconomic conditions, land aptitude and other biophysical factors. The proposed methodology envisages a continuous and intensive land use for sustained production.     

Soil–landscape relationships at the lower reaches of a watershed at Bear Creek near Oak Ridge,Tennessee

The watersheds at Bear Creek, Oak Ridge, TN, have similar soil–landscape relationships. The lower reaches of many of these watersheds consist of headwater riparian wetlands situated between sloping non-wetland upland zones. The objectives of this study are to examine the effects of (i) slope and geomorphic processes, (ii) human impacts, and (iii) particular characteristics of soils and saprolite that may effect drainage and water movement in the wetlands and adjacent landscapes in one of these watersheds. A transect was run from west to east in a hydrological monitored area at the lower reaches of a watershed on Bear Creek. This transect extended from a steep side slope position across a floodplain, a terrace, and a shoulder slope. On the upland positions of the Nolichucky Shale, mass wasting, overland flow and soil creep currently inhibit soil formation on the steep side slope position where a Typic Dystrudept is present, while soil stability on the shoulder slope has resulted in the formation of a well-developed Typic Hapludult. In these soils, argillic horizons occur above C horizons on less sloping gradients in comparison to steeper slopes, which have Bw horizons over Cr (saprolite) material. A riparian wetland area occupies the floodplain section, where a Typic Endoaquept is characterized by poorly drained conditions that led to the development of redoximorphic features (mottling), gleying, organic matter accumulation, and minimal development of subsurface horizons. A thin colluvial deposit overlies a thick well developed Aquic Hapludalf that formed in alluvial sediments on the terrace position. The colluvial deposit from the adjacent shoulder slope is thought to result from soil creep and anthropogenic erosion caused by past cultivation practices. Runoff from the adjacent sloping landscape and groundwater from the adjacent wetland area perhaps contribute to the somewhat poorly drained conditions of this profile. Perched watertables occur in upland positions due to dense saprolite and clay plugging in the shallow zones of the saprolite. However, no redoximorphic features are observed in the soil on the side slope due to high runoff. Remnants of the underlying shale saprolite, which occur as small discolored zones resembling mottles, are also present. The soils in the study have a CEC of <10 cmol kg⁻¹, silt loam textures and Fe_d values of 0.5–4.3%. These soils are also mainly acidic and low in total carbon.     

内蒙古十大孔兑西柳沟流域土壤侵蚀及水土保持措施调查

[目的]内蒙古十大孔兑地区属黄河中上游多沙粗沙区和生态脆弱区,对该区典型流域西柳沟的土壤侵蚀进行实地调查,分析流域土壤侵蚀特征及成因,为该区水土流失防治提供科学依据。[方法]于2022年9月19—26日和2023年6月21—26日沿X640解柴线(解家营—柴沟堡)和G109京拉线(北京—拉萨)2条公路分别布设15个调查点和14个集水区,对调查点及集水区植被、土壤、土壤侵蚀特征和水土保持措施等进行调查。[结果]流域内草地片蚀较为严重,耕地侵蚀不严重,沟谷内裸地风蚀较为严重。上游黄土高原丘陵区沟蚀严重,且溯源侵蚀、下切侵蚀及沟岸扩张未停止,伴随较为严重的重力侵蚀。中游风沙区以风水复合侵蚀为主,大幅增加了流域的产沙总量。流域内道路建设及边坡开挖等人为扰动进一步加剧了侵蚀风险。径流泥沙含量测定结果验证了流域泥沙的主要来源为上游地区。流域内水土保持措施以植被措施及工程措施为主,虽已起到一定水土保持作用,但由于形式单一而未能发挥理想效果。[结论]西柳沟短历时高强度的降雨特点叠加下层砒砂岩土壤条件共同加剧了该区土壤侵蚀,经济发展压力下的人类活动扰动加剧了生态风险,当地政府亟需持续增加水土保持投入,提...     

Watershed-scale assessment of soil quality in the loess hills of southwest Iowa

Soil quality is a concept that integrates soil biological, chemical and physical factors into a framework for soil resource evaluation. Conventional tillage practices can result in a loss of soil organic matter and decreased soil quality. The potential for soil quality degradation with tillage may vary depending upon landscape position and the spatial distribution of critical soil properties. Information on how to accurately integrate soil spatial information across fields, landscapes and watersheds is lacking in the literature. The primary objective of this study was to evaluate the long-term effect of conventional and ridge-tillage on soil quality in three small watersheds at the Deep Loess Research Station near the town of Treynor in southwest Iowa. Soil types included Monona silt loams in summit positions, Ida or Dow silt loams in backslope positions, and Napier or Kennebec silt loams in footslope positions. We removed surface soil cores from transects placed along topographic gradients in each watershed and quantified total soil organic C (SOC), total soil N (TN), particulate organic matter C (POM-C) and N (POM-N), microbial biomass C (MB-C), N mineralization potential (PMIN-N), nitrate N, extractable P and K, pH, water-stable macroaggregates (WSA), and bulk density (BD). We used terrain analysis methods to group the data into landform element classes to evaluate the effect of topographic position on soil quality. Results indicate that soil quality is higher under long-term ridge-tillage compared with conventional tillage. Soil quality differences were consistently documented among the three watersheds by: (1) quantification of soil indicator variables, (2) calculation of soil quality index values, and (3) comparison of indicator variable and index results with independent assessments of soil function endpoints (i.e. sediment loss, water partitioning at the soil surface, and crop yield). Soil quality differences under ridge-till were found specifically for the backslope and shoulder landform elements, suggesting that soil quality increases on these landform elements are responsible for higher watershed-scale soil quality in the ridge-tilled watershed.     

地边截水地物对黑土区小流域坡长因子计算的影响

[目的]研究地边截水地物对黑土区小流域坡长因子(L)和土壤侵蚀速率(A)的影响,为提高该地区的土壤侵蚀预报精度提供依据。[方法]选取2个小流域,结合野外调查和DEM分析,比较不考虑与考虑地边截水地物情况下的L。[结果]如果不考虑地边截水地物,L平均被高估18%,A平均被高估31%。[结论]在计算黑土区小流域土壤侵蚀速率时,有必要考虑地边截水地物。在其他因素相同的情况下,坡度越大,横坡分布的地边截水地物的间距越小,越要考虑地边截水地物。     

基于水土流失风险的流域景观格局识别方法研究

运用"源、汇"景观理论,利用洛伦兹曲线,考虑了植被覆盖因素,基于景观坡度指数,构建了景观空间负荷对比指数,定量分析了丹江流域9个子流域的景观空间格局。结果表明:丹江流域北部各子流域主要以水土流失的"源"景观为主,景观坡度指数大,空间负荷指数小,水土流失风险大;流域南部各子流域上游以"汇"景观为主,坡度指数大,中下游以"源"景观为主,景观空间分布不均衡,存在一定的水土流失风险。     

基于集对分析模型的水土保持工程效益后评价研究

[目的]建立一个科学合理的水土保持效益后评价指标体系对水土保持工程进行效益评价,为小流域的生态治理提供科学后评估依据。[方法]综合分析小流域水土保持工程特性和影响水土保持工程效益的关键因素,识别和选取水土保持工程效益后评价的13项关键指标,建立小流域工程效益后评价指标体系,运用层次分析法和熵值法改进评价指标的权重,结合评价指标数据和指标评价标准应用改进的集对分析模型开展工程效益后评价研究。[结果]改进的集对分析模型结果表明,评价指标体系中水保效益、生态效益、社会效益,流域水土保持工程效益评价总体处于2级水平,流域治理的成效显著、可供开发的空间和潜力较大。[结论]该方法是一种有效地针对小流域的水土保持工程效益评价的新方法。在构建水土保持工程效益后评价指标体系的基础上,将该方法运用到水土保持工程效益后评价中,基本达到了预期的研究目的。     

Comparison of Acid Neutralization by Chemical Weathering Between Acidified and Non-Acidified Watersheds

In eastern Asia, emission of acid materials and acid depositionwill increase with industrialization in future, and freshwatersin Japan are likely to become acidified. In this article, anevaluation method for acid-neutralization by chemical weatheringwas applied to one acidified watershed in U.S.A. and three non-acidified watersheds in Japan, and effect of hydrogeochemicalproperties on chemical weathering and stream water chemistry wasdiscussed. In three non-acidified watersheds in Japan, arealchemical weathering rates of primary minerals are much largerthan those observed in U.S.A. Watersheds in both countries showno difference in mineralogy, while the soil thickness (weatheredprofile) in watersheds is contrastive between acidified and non-acidified watersheds. Therefore, it is concluded that acidity is neutralized by chemical weathering of primary minerals in thick weathered profiles in Japanese watershed. In non-acidified Japanese watersheds which has the smallest acid-neutralization capacity in three observed watersheds, stream water will not acidify even if the acid deposition increases asmuch as two or three times the observed level. From the viewpoint of Japan's nationwide streamwater chemistry, more than 90% of the watersheds have far greater acid-neutralization capacities than this watershed, and will not be acidified even in cases where the acid deposition increase as much as two or three fold.