Modelling the impact of historical land uses on surface-water quality using groundwater flow and solute-transport models

Groundwater age, and its influence on contemporary water chemistry, needs to be accurately described to quantify the temporally varying impacts of land use on water quality. The time lags between solute inputs at the land surface and impacts on stream chemistry can be an important factor for managing land use in regional watersheds. Our approach uses a modified groundwater flow code to simulate reverse groundwater flow, regional flow and the solute‐transport model where a unit concentration of a conservative solute serves as a proxy for groundwater age. Solute‐contour lines represent groundwater travel time, which can then be coupled with Geographic Information System analyses to examine the relationship between water quality and historical land‐use patterns. The reverse flow and solute modelling produced a reasonable distribution of groundwater travel times across the watershed, given the hydrology of the system. These groundwater flow paths would be unexpected if surface topography or even surface hydrology were used to predict groundwater movement. Approximately 70% of the watershed has a groundwater lag of ≤30 years. When the temporal lags for individual drainage areas within the watershed are compared, flush times vary dramatically. This variability is related both to the size of the sourceshed and its geology. The influence of a particular land use on stream chemistry changes depending on the time scale considered, and also depending on the sourceshed in question as a result of landscape diversity. The results suggest that land‐use management practices to reduce solute loading to a watershed might not result in water‐quality improvements for many years, especially if implemented on land far from streams. The influence of long groundwater flow paths that integrate past and current land uses must be considered in the interpretation of land‐use effects on surface‐water quality.     

Influences of land use/cover on water quality in the upper and middle reaches of River Njoro, Kenya

Data from 10 sampling sites along the River Njoro are used to examine the contribution of nutrients from upstream land uses draining each of the sampling sites. The data also are used to assess whether both the proportion of land uses and the size of the subwatersheds account for the variability in water quality in the River Njoro watershed. Geographical Information System analysis was used to determine the spatial distribution of land‐cover types and subwatersheds contributing run‐off to the sampling sites in the River Njoro. Standard Digital Elevation Model‐based routines were used to establish the watershed area contributing run‐off to each sampling site. Water and sediment samples were collected for chemical analysis, and the nutrient levels were related to the upstream land‐use types and the size of the subwatersheds. The mid‐stream portion of the River Njoro (near Egerton University) accounts for the highest nutrient contributions. The percentage contribution is magnified by additions from industrial, human settlements and agricultural land uses around the University. There is a significant decrease in nutrient levels downstream, however, indicating natural purification as the river flows through an area of large‐scale farming with intense, well‐preserved riparian and in‐stream vegetation. Steep slopes of the land upstream of Egerton University enhance erosion and nutrient losses from those subwatersheds. Mixed small‐scale agricultural and bare lands contribute over 55% of the phosphorus load to the upper and mid‐reaches of the River Njoro. The size of the subwatershed accounts for about 53% of the variability in the soluble phosphorus in the river. The land‐use subwatershed proportions are important for characterizing and modelling water quality in the River Njoro watershed. Upland land uses are as important as near‐stream land uses. We suggest that conservation of intact riparian corridor along the river and its tributaries contributes significantly to natural purification processes and recovery of the ecological integrity of the River Njoro ecosystem.     

Land‐use effects on water quality of a first‐order stream in the Ozark Highlands,mid‐southern United States

Urban and agricultural land uses can alter the natural hydrologic conditions of streams and rivers and often degrade water quality. In the Ozark Highlands of the mid‐southern United States, the climate, topography, soil properties, karst limestone geology, agricultural practices and rapid urbanization make water quality of particular concern due to the increased potential for water quality degradation by contaminant leaching to groundwater and runoff to surface waters. The objective of this study was to evaluate the effects of season (i.e. dry/cool and wet/warm) and riparian land use (i.e. urban, grazed pasture, ungrazed pasture, wetland, cultivated agriculture and grassland) on surface water quality in a first‐order stream within a diverse agricultural watershed in the Ozark Highlands. Water samples were collected twice a month within each land use during base‐flow conditions from October 2006 through October 2007. Samples were also collected periodically during storm‐flow conditions from October 2006 through December 2007. The greatest in‐stream pH was adjacent to the grazed pasture. In‐stream NO₃‐N concentrations were greatest adjacent to the cultivated agriculture and grassland during the dry/cool season (i.e. October 2006 to March 2007) and averaged 2.67 mg L^?1. In‐stream soluble reactive P (SRP) concentrations were greatest adjacent to the grassland during the wet/warm season (i.e. April 2007 to October 2007) and averaged 0.81 mg L^?1. Concentrations of SRP, K, Mg and Zn were greater during storm‐ than base‐flow conditions and in‐stream As concentrations frequently exceeded 0.01 mg L^?1. Discharge and in‐stream NH₄‐N concentrations were unaffected by land use or season and averaged 0.003 m³ s^?1 and 0.10 mg L^?1, respectively, across all land uses and seasons. Results of this study clearly demonstrate the significant effect of adjacent land use on in‐stream water quality of a first‐order stream in a diverse agricultural watershed and highlight the importance of managing upstream land use in order to regulate downstream water quality. Copyright © 2010 John Wiley & Sons, Ltd.     

强人类活动平原地区河网提取中的流路强化方法

我国北方强人类活动平原地区的水资源问题越来越严峻,基于分布式水文模型的水循环模拟是流域水资源研究的基础,其中基于DEM的河网水系提取是基础环节。平原地区由于沟谷发育不明显,且人工河道和沟渠众多,流域汇流结构支离破碎,常用的河网提取模型往往很难得到正确的结果。本文借助已有的主要干流数字化河网水系,提出了流路强化处理方法,用于对平原地区的DEM进行预处理,经过处理后的DEM输入河网提取模型,可以得到流路正确、且河网密度更精细的河网水系拓扑结构,为分布式水文模型的高精度水文单元划分奠定基础。该方法在强人类活动干扰的典型流域——海河流域进行了应用,对比了流路强化处理前后的河网提取结果,表明该方法是一种方便、快捷、高效的处理方法。     

Identifying Temperature Thresholds Associated with Fish Community Changes in British Columbia,Canada, to Support Identification of Temperature Sensitive Streams

We collected fish samples and measured physical habitat characteristics, including summer stream temperatures, at 156 sites in 50 tributary streams in two sampling areas (Upper Fraser and Thompson Rivers) in British Columbia, Canada. Additional watershed characteristics were derived from GIS coverages of watershed, hydrological and climatic variables. Maximum weekly average temperature (MWAT), computed as an index of summer thermal regime, ranged from 10 to 23 °C. High values of MWAT were associated with large, warm, low relief watersheds with a high lake influence. Measures of community similarity suggested that the fish community changed most rapidly through a lower transition zone at an MWAT of about 12 °C and an upper transition zone at an MWAT of about 19 °C. These results were confirmed using existing fisheries inventory data combined with predictions of MWAT from a landscape‐scale regression model for the Thompson River watershed. For headwater sites in the Chilcotin River watershed (which drains into the middle Fraser River), the relative dominance of bull trout versus rainbow trout (based on inventory data) decreased with increasing predicted MWAT although the distinction was not as clear as for the Thompson River sites. The fish communities in these watersheds can be characterized in terms of very cold water (bull trout and some cold water species), cold water (salmonids and sculpins) and cool water (minnows and some cold water salmonids). The two transition zones (ca 12 and 19 °C) can be used to identify thresholds where small changes in stream temperature can be expected to lead to large changes in fish communities. Such clear, quantifiable thresholds are critical components of a management strategy designed to identify and protect vulnerable fish communities in streams where poor land use practices, alone or in combination with climatic change, can lead to changes in stream temperatures. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of land use on channel geometry and sediment distribution in gravel mantled bedrock streams,Illinois River watershed,Arkansas

Headwater stream morphology is a direct reflection of watershed characteristics and therefore can inform our understanding of anthropogenic influence on channel geometry and sediment dynamics. Little knowledge of the geomorphology of headwater streams in the Ozark Plateaus region of northwest Arkansas exists. The Illinois River watershed, in northwest Arkansas, is of critical interest within the region because of land use changes in the headwaters due to rapid population growth. A mixture of forest and agricultural (open pasture and poultry houses) land use dominates the watershed, but urban areas are rapidly expanding. These land use types: forest, agriculture and urban are an effective proxy for increasing anthropogenic disturbance. Analysis of longitudinal profile, cross‐section and sediment distribution in streams from each land use type shows a strong trend of increasing slope and channel cross‐sectional area with a greater degree of anthropogenic disturbance. Additionally, urban streams are characterized by the presence of exposed bedrock in the stream bed, while agricultural and forested streams are gravel mantled. These data have important implications for current and future stream management policies and practices regionally. Copyright © 2010 John Wiley & Sons, Ltd.     

A comprehensive index for stream depletion in coupled human-water systems

Intensive land use and land cover (LULC) change along with the gradually increasing effects of climate change have made streams both hydrologically and ecologically vulnerable to depletion. Since stream depletion has a direct impact on human and ecological water use with socioeconomic and ecological consequences, it is imperative to manage streams to keep them in a healthy state. In this study, we developed a stream depletion potential index (SDPI) based on the concept of a coupled human-water system (CHWS) operating at simultaneous, interacting scales, and we tested its applicability to watersheds across South Korea. Eight indicators - precipitation, dry days, effective basin area, stream water usage, return flow, groundwater usage, impervious area, and environmental flow supplied by dams - were identified as the key variables for the SDPI. We adopted the Structural Equation Model (SEM) to estimate the weights of the identified indicators based on their causal relationships. Furthermore, we applied three different weighting schemes for urban, rural, and intermediate areas to make the index more effective and applicable to watershed LULC. The spatial distribution of the SDPI results indicated that the western Han River, the central and southern Nak-Dong River and some parts of the southwestern region of the Korean peninsula are prone to stream depletion from several different causes. The SDPI, by predicting changing streamflow characteristics, can be used by policy makers and stakeholders to determine a safe yield for both human and environmental stream use without causing a long-term decline of water availability.     

Stream Temperature Impacts Because of Changes in Air Temperature,Land Cover and Stream Discharge: Navarro River Watershed,California, USA

Stream temperatures are critically important to aquatic ecology, especially cold‐water fish such as salmonids. Stream temperatures are influenced by multiple factors, including local climate, solar radiation on the stream channel, stream discharge volume and groundwater contributions. The Heat Source hydrodynamic and thermodynamic numerical model was used to evaluate temperatures in three stream reaches in the Navarro River watershed, California, USA. The model was calibrated and validated for summer 2015 conditions and then applied to scenarios that address changes in air temperatures, riparian forest cover and stream discharge. Modelling results indicate that stream temperatures are sensitive to changes in air temperatures and riparian forest cover and that higher discharge volume mitigates those impacts. Modelled stream maximum weekly average temperatures (MWAT) increased by 1.5–2.3°C in response to an air temperature increases of 3.5°C under low flow conditions (drought) but by only 0.9–2.0°C under moderate flow. Complete removal of riparian forest in a large‐scale forest fire would increase MWAT by 2.2–5.9°C in low discharges and by 1.0–4.4°C under moderate discharge. Riparian zone reforestation would decrease MWATs by less than 0.8°C, a modest change reflecting high existing shade on the modelled stream reaches. Comparison of identical climate and land cover change scenarios under low and moderate discharge conditions reveals that efforts to conserve stream discharge volume could be an effective mechanism to mitigate stream temperature increases. Copyright © 2016 John Wiley & Sons, Ltd.     

基于古河道变迁的廊坊东沽港地面沉降影响因素研究

通过搜集河北平原东沽港镇工程地质及水文地质资料,开展工程地质、水文地质、环境地质调查,利用物探、钻探、水准测量等技术手段进行勘查,并对地面沉降现状及危害进行跟踪调查,系统研究了东沽港镇地面沉降影响因素。结果表明:①研究区位于第四系古河道变迁带,具有物质松散、抗压性弱、沉陷性大的特点,在地下水位变化过程中,受砂层饱和自重、地下水下渗及其孔隙水压力差等影响,古河床与河漫滩易出现错动裂缝。②研究区地面沉降主要的外部因素是浅层地下水位下降,是引起地面沉降的动力;主要的内部因素是地层沉积差异,为地面不均匀沉降提供了物质基础;次要因素是深层地下水位变化、地质构造活动和人为回填池、塘等。研究区地面沉降影响因素的研究成果为河北平原地面沉降研究及防治提供理论依据。     

Effects of Road Crossings on Habitat Connectivity for Stream‐Resident Fish

Road crossings can act as barriers to the movement of stream fishes, resulting in habitat fragmentation, reduced population resilience to environmental disturbance and higher risks of extinction. Strategic barrier removal has the potential to improve connectivity in stream networks, but managers lack a consistent framework for determining which projects will most benefit target species. The objective of this study is to develop a method for identifying and prioritizing action on road crossings in order to restore stream network connectivity. We demonstrate the method using a case study from the Pine‐Popple watershed in Wisconsin. First, we propose a new metric for quantifying stream connectivity status for stream‐resident fish. The metric quantifies the individual and cumulative effects of barriers on reach and watershed level connectivity, while accounting for natural barriers, distance‐based dispersal limitations and variation in habitat type and quality. We conducted a comprehensive field survey of road crossings in the watershed to identify barriers and estimate replacement costs. Of the 190 surveyed road crossings, 74% were determined to be barriers to the movement of at least one species or life stage of fish, primarily due to high water velocity, low water depth or outlet drops. The results of the barrier removal prioritization show that initial projects targeted for mitigation create much greater improvements in connectivity per unit cost than later projects. Benefit–cost curves from this type of analysis can be used to evaluate potential projects within and among watersheds and minimize overall expenditures for specified restoration targets. Copyright © 2014 John Wiley & Sons, Ltd.     

Exploring market-based environmental policy for groundwater management and ecosystem protection for the Great Lakes region: Lessons learned

The Great Lakes–St. Lawrence River Basin Water Resources Compact (the Compact) was created to protect future water supplies and aquatic ecosystems in the Great Lakes. The Compact requires the eight Great Lakes state to regulate, among other things, large withdrawals of groundwater and surface water so that they do not negatively affect stream flows and ecosystems within the Great Lakes Basin. Thus, the Compact raises the possibility of increased restrictions on groundwater withdrawals in many locations throughout the Great Lakes region. However, restricting withdrawals is likely to encounter opposition from water users when such restrictions are viewed as an infringement on existing water use rights and/or as negatively impacting local economic development. Such conflicts could hinder effective implementation of state and regional water policy. This paper explores the application of a market-based environmental management tool called “Conservation Credit Offsets Trading (CCOT)” that could facilitate allocation of groundwater withdrawals, and develops a framework for guiding the implementation of CCOT within the context of a groundwater permitting system. Using a watershed in southwestern Michigan, this study demonstrates how bio-physical information and input from various local stakeholders were combined to aid groundwater policy designed to achieve the objective of no net (adverse) impact on stream ecosystems. By allowing flexibility through trading of conservation credit offsets, this groundwater policy tool appears to be more politically acceptable than traditional, less flexible, regulations. The results and discussion provide useful lessons learned with relevance to other areas in the Great Lakes Basin.     

Evaluation of irrigation canal networks to assess stream connectivity in a watershed

We used digital data sets, aerial photos and direct field observations in a geographical information system to evaluate the stream habitat in an Idaho watershed affected by agriculture. We found that the scale of the digital data sets affected the outcome of the assessment due to the presence of dewatered stream channels in the drainage. We analysed the spatial configuration of irrigation canals in the watershed to determine if the contemporary stream network connectivity could be attributed to human‐ caused or to natural hydrological processes. Many irrigation canals were significantly longer than would have been expected if these canals were constructed to capture water from the closest portion of the abandoned stream channels. Our findings provide evidence that some of these tributary streams had reaches that were likely ephemeral or intermittent at the time of canal construction. Our approach for assessing stream and irrigation network connectivity in pastoral and agricultural lands should aid managers in prioritizing the effective and appropriate reconnection efforts. Published in 2008 by John Wiley & Sons, Ltd.     

SMALL IS BEAUTIFUL? STATE OF THE DAMS AND MANAGEMENT IMPLICATIONS FOR THE FUTURE

Dams are a critical component of water infrastructure, providing services such as water supplies, recreational opportunities and flood control. At the same time, dams alter the flow regime of rivers and the biota that inhabit them. Large dams have been the subject of many studies because of their potentially significant impacts on stream hydrology and ecosystems. However, most dams are not large and consequently have received far less attention. Data for more than 5700 dams in New York State, USA located in 17 watersheds were used to develop watershed level metrics that relate the characteristics of the dams to the hydrology and demographics of each watershed. Metrics presented, stratified by watershed, include median structure age, density, dams per stream length, persons per dam, storage per drainage area, storage per person and percent high impact dams (high hazard and large). These metrics were used to perform a simple characterization of the 17 watersheds. Considerable regional differences in these parameters suggest varying management strategies in each watershed. A new era of river management has resulted in the removal of many dams, which is driven by the high cost of maintenance and state regulations. Copyright © 2013 John Wiley & Sons, Ltd.     

基于数字高程模型的流域变动等流时线方法

本文探讨了降雨的空间分布和地形对流域等流时线的影响，提出了变动等流时线的新方法，该方法避免了传统等流时线假设流速在全流域均匀分布的缺陷，并且同时考虑了地形和降雨空间分布不均匀性对流速的影响。本文利用数字地形分析技术从DEM数据中提取流域数字水系以及地形地貌等空间特征，在此基础上，对降雨进行空间插值，获得降雨的空间分布，综合考虑地形和降雨因素，推求流域变动等流时线，更进一步真实反映流域的产汇流机制。该方法应用于缺乏实测资料的小流域，应用结果表明基于数字水系推求的变动等流时线体现了地形和降雨的空间分布不均匀性对流域径流的综合影响。     

长江流域水系划分与河流分级初步研究

将推荐的水系划分与河流分级Horton法相结合,通过合理选取最小河流(流域)单元、科学制作河流树状图表,初步研究了长江流域(不含太湖水系)的河流分级。研究结果显示:①推荐将长江水系划分为干流水系与雅砻江、岷江、嘉陵江、乌江、洞庭湖、汉江、鄱阳湖、太湖8个支流水系;② 581条河流基本特性资料的收集、整理与分析表明长江流域河流的河长与流域面积约为0.5次方关系,选取流域面积不小于2 000 km²或河长不小于100 km的河流为最小河流(流域)单元,确定长江流域(不含太湖水系)河流总数为374条;③以岷江水系为例,精心制作了长江流域各水系的河流树状图表,树状图显示了河流隶属关系、分级数、河长、流域面积等特性;④长江流域(不含太湖水系)最高河流分级数为6级。按河流统计:6级1条(0.3%),5级3条(0.8%),4级6条(1.6%),3级14条(3.7%),2级71条(19.0%),1级279条(74.6%);按水系统计:岷江、嘉陵江、鄱阳湖为5级,干流、雅砻江、洞庭湖、汉江为4级,乌江为3级。     

城市河流综合征及其驱动因素

城市河流综合征的症状表现在河道形态和稳定性改变、水文情势的显著改变、河流养分和污染物浓度升高、生物多样性减少、敏感性物种减少、耐受性强的物种占据优势以及河流生态系统过程受影响等。造成城市河流综合征的原因复杂多样,驱动机制复杂且相互作用。对城市河流影响最为显著的因素是城市土地利用以及与之相关的地面硬化。要治理城市河流综合征问题,必须从流域尺度出发,减少城市地表径流和污染物的排放,还要采取生态治理的模式,并尽可能取得公众的理解和支持等。     

基于水库流域非点源防治的用地规划

水体富营养化的一个重要原因是非点源污染。相对于点源而言,非点源控制难度较大。试图从非点源防治的角度,采用线性规划模型进行流域用地规划。列举横岗水库流域的用地规划进行污源预测以及环境容量计量。具体思路如下:①预测流域污染物产生量;②计算流域内纳污水体环境容量,分配点源与非点源环境容量;③通过线性规划,确定各种土地利用类型的面积大小;④根据纳污水体位置以及用地现状,确定各种用地类型的相对位置。     

Effect of New Nag Hammadi Barrage on Groundwater and Drainage Conditions and Suggestion of Mitigation Measures

The government of Egypt has decided to construct a new barrage with hydropower facilities, 3.5 km downstream of the existing old one. The water levels in the head pond for the new barrage will be continuously maintained at a level with approximately 0.5 m higher than water level in the head pond of the existing one. To evaluate the effect of increasing the head pond water level on the groundwater and drainage, there is a need to enhancelinking reservoir and stream/aquifer system. Visual MODFLOW hasbeen used to simulate the surface water/groundwater interaction in the area of proposed new barrage. The model has been calibratedagainst the available historical groundwater levels for 25 observation wells based on the steady state conditions. Numerical modeling suggests that river stage is the primary control of rapid groundwater hydraulic head fluctuations in theaquifer system. At present the area at which the depth to groundwater table less than one meter is about 30 110 feddans (1 feddan = 4200 m²). This area will increase to be about40 610 feddans after the construction of the new barrage and increasing the head pond water level. The mitigation measures toovercome the effect of construction of the new barrage have been discussed and their costs have been estimated and evaluated. Increasing the efficiency of existing drainage system by maintenance/upgrading and constructing a new pump station is recommended.     

The Pros and Cons of Encouraging Shallow Groundwater Use through Controlled Drainage in a Salt-Impacted Irrigation Area

Encouraging shallow groundwater use through water table management or controlled drainage in irrigated areas can relief crop water stress under water shortage condition. But substituting fresh irrigation water with saline groundwater may speed up salinity buildup in the crop root zone, and consequently increase water use for salt leaching. With a proposed analytical model, this paper presents a case study demonstrating the effect of encouraging shallow groundwater use through controlled drainage on salt and water management in a semi-arid irrigation area in northwestern China. Based on the average rainfall condition, the model assumes that salt accumulates in the crop root zone due to irrigation and shallow groundwater use; till the average soil salinity reaches the crop tolerance level, leaching irrigation is performed and the drainage outlet is lowered to discharge the salt-laden leaching water. For the relatively salt tolerant crop–cotton in the study area, the predicted leaching cycle was as long as 751 days using the fresh water (with salinity of 0.5 g/L) irrigation only; it was shortened to 268 days when the water table depth was controlled at 2 m and 23% of the crop water requirement was contributed from the saline groundwater (with salinity of 4.43 g/L). The predicted leaching cycle was 140 days when the water table depth was controlled at 1.5 m and groundwater contribution was 41% of the crop water requirement; it was shortened to 119 days when the water table depth was controlled at 1.2 m and the groundwater contribution was 67% of the crop water requirements. So the benefit from encouraged shallow groundwater use through controlled drainage is obtained at the expense of shortened leaching cycle; but the shallow groundwater use by crops consists of a significant portion of crop water requirements, and the leaching cycle remains long enough to provide a time window for scheduled leaching in the off season of irrigation. Weighing the pros and cons of the encouraged shallow groundwater use may help plan irrigation and drainage practices to achieve higher water use efficiency in saline agricultural areas.     

Patterns of species richness and introduced species in native freshwater fish faunas of a Mediterranean‐type basin: the Guadiana River (southwest Iberian Peninsula)

In this study, we analysed the factors affecting species richness and introduced species component patterns in native fish faunas of 30 streams of the Middle Basin of the Guadiana River. From a principal component analysis and a stepwise multiple regression analysis performed on a data matrix composed of ten hydrological and biotic variables, we showed that: (1) fish species richness increased with stream length and watershed area, (2) the number of native species in a stream declined as channelizations and river regulation (constructions of dams) are higher, whereas introduced species increased in the same way, (3) the two main negative factors affecting native ichthyofaunas affected dissimilar ecological areas: channelizations, which depend on land‐use intensity of floodplain, mainly occurred in lower reaches of streams, but construction of dams mainly took place in upper sections of rivers, (4) the length of the remaining well‐preserved reaches in a stream appeared to be the only factor accurately predicting native fish species richness, and (5) native fish faunas of small isolated streams are more vulnerable to habitat alteration than those of large streams. Both isolation and fragmentation of populations were recorded, so the conservation status of native and highly endemic fish fauna of the study area is extreme. Protection of the few still extant, well‐preserved small streams and upper reaches, habitat restoration of channeled areas, and inclusion of the need for native fish fauna conservation in long‐term public planning of water use become a priority. Fish communities appear to be a sensitive indicator of biological monitoring to assess environmental degradation. Copyright © 2001 John Wiley & Sons, Ltd.