环境流理论进展述评

本文回顾了环境流评价方法从简单的水文公式到水文变化生态限度方法(ELOHA)的发展历程。讨论了环境流的理论要点,如自然水流与径流调节水流的区别;水文情势改变-生态响应关系以及水生态系统阈值等问题。文章还评论了环境流方法应用的若干问题,包括生态需水概念;技术文件中引用国外文献的完整性和准确性;加强数值模型研究和软件开发;推行适应性管理策略。     

Including environmental flow requirements as part of real‐time water resource management

South African water resources legislation requires that environmental flow requirements are included as part of water resource management. An operational management method is presented that relies upon simulating natural flow conditions based on inputs of near real‐time observations of rainfall and a set of operating rules. The operating rules define the reservoir releases and water use supply curtailments that ensure downstream environmental flow objectives will be met. The focus is on managing the variability of continuous low flows, while a suitable method for managing event‐based high flow releases remains elusive. The main limitation to the successful implementation of the low flow approach is the lack of legislated control over run‐of‐river water abstractions. While this limitation is expected to be overcome, as the provisions of new legislation are implemented, water managers may still lack the capacity to exercise the necessary controls over abstraction. There is no reason why the method could not be applied outside South Africa, given compatibility in the definition of environmental flow requirements. Copyright © 2008 John Wiley & Sons, Ltd.     

Flow regimes in coastal California steelhead trout streams: Spatiotemporal patterns in magnitude,duration and timing

The magnitude, timing and duration of precipitation events can vary considerably across spatial and temporal scales. In lotic ecosystems, such differences in precipitation patterns can strongly influence water availability, which in turn affects the population dynamics of stream biota. Connectivity flow thresholds were developed for the movement of juvenile steelhead trout using hydraulic modelling for 37 coastal California streams. Spatial patterns in magnitude, and spatiotemporal patterns in duration and timing of flows meeting threshold levels were analysed using long‐term flow gaging data. Flow thresholds for the movement of juvenile steelhead through riffle sites varied from 0.06 (San Luisito Creek, Elder Creek) to 0.82 (Redwood Creek) cms (cubic meters per second). Flow thresholds increased positively with mean bankfull width, indicating that more water is required for fish movement in wider streams. Precipitation was a dominant driver of flow duration, with flows meeting thresholds longer in wetter regions of the state when compared with drier regions. On the rising limb of the hydrograph, the onset of meeting flow thresholds was influenced by stream width, with thresholds being met earlier in wider streams when compared with narrower streams. On the receding limb of the hydrograph, flow threshold timing was influenced by precipitation, with flows remaining above the threshold later in wetter regions when compared with drier regions. Based on these findings, we recommend that the management of aquatic resources for a broad range of objectives consider regional scales that account for local patterns in precipitation, channel form and prevailing water year conditions to accommodate California's wide spatiotemporal diversity of water availability.     

Operationalizing the allocation of environmental flows: A U.K. perspective on Baxter's Schedule

Early attempts to gauge streams were used by George Baxter in 1961 to propose a pioneering scheme for deriving and allocating water for what today may be recognized as environmental flows in the United Kingdom, but the approach was not accepted into practice. A fundamental concern was the quality of river flow data. Stream gauging was advanced by the 1963 Water Resources Act, and prior to this, the allocation of water resources to compensation flows below dams was based on the basic principle of one third of the reliable yield, estimated using rainfall data. Despite the increased availability of river flow data since the 1970s, it is suggested that low‐flow data quality has severely constrained the management and allocation of water resources and remains so today. Today, pressures and demands on water resources are increasing, but the accuracy of low‐flow measurement is still hindering the operational determination and implementation of environmentally robust, seasonally variable environmental flows. Successful river regulation and restoration relate to a complex suite of public policy questions and given uncertainty over the quality of low‐flow data, transparent, pragmatic decisions about societal allocations of water need to be made.     

A REGIONAL CLASSIFICATION OF UNREGULATED STREAM FLOWS: SPATIAL RESOLUTION AND HIERARCHICAL FRAMEWORKS

River regulation has resulted in substantial losses in habitat connectivity, biodiversity and ecosystem services. River managers are faced with a growing need to protect the key aspects of the natural flow regime. A practical approach to providing environmental flow standards is to create a regional framework by classifying unregulated streams into groups of similar hydrologic properties, which represent natural flow regime targets. Because spatial resolution can influence the structure of regional datasets, it may be advantageous to relate datasets created at different scales in order to establish hierarchical structure and to understand how the relative importance of variables change with regard to scale. The purpose of this study was to classify unregulated streams within an eight‐state region into groups in order to provide environmental flow standards for managers and to relate that dataset to frameworks created at larger scales. Using USGS daily stream gauge information, we used 66 hydrologic statistics to classify 292 streams in groups of similar hydrologic properties. We isolated six flow classes in a sub‐region of the Southeastern US that ranged from extremely stable to highly variable to intermittent. We developed classification trees to reduce the number of hydrologic variables for future classifications. By comparing flow classes in our study to those of the entire US, we found that hierarchical structure did exist and that the divergence of flow classes will largely depend on the spatial resolution. Copyright © 2011 John Wiley & Sons, Ltd.     

Incorporation of environmental flows in water allocation in Texas

An institutional framework and supporting water availability modelling capabilities are presented for integrating ecological needs into water resources management. Concepts illustrated by the Texas experience are relevant worldwide. Environmental flow standards with subsistence, base, in-bank pulse and over-bank flow components are established through a legislatively mandated process by stakeholder committees and science teams working in collaboration with government agencies. The flow standards incorporate ecosystem needs into water allocation and associated water availability modelling. Recognizing the complexities of defining and preserving environmental stream flows, expedited present action is combined with an adaptive management process for future improvements.     

Predicting the natural flow regime: models for assessing hydrological alteration in streams

Understanding the extent to which natural streamflow characteristics have been altered is an important consideration for ecological assessments of streams. Assessing hydrologic condition requires that we quantify the attributes of the flow regime that would be expected in the absence of anthropogenic modifications. The objective of this study was to evaluate whether selected streamflow characteristics could be predicted at regional and national scales using geospatial data. Long‐term, gaged river basins distributed throughout the contiguous US that had streamflow characteristics representing least disturbed or near pristine conditions were identified. Thirteen metrics of the magnitude, frequency, duration, timing and rate of change of streamflow were calculated using a 20–50 year period of record for each site. We used random forests (RF), a robust statistical modelling approach, to develop models that predicted the value for each streamflow metric using natural watershed characteristics. We compared the performance (i.e. bias and precision) of national‐ and regional‐scale predictive models to that of models based on landscape classifications, including major river basins, ecoregions and hydrologic landscape regions (HLR). For all hydrologic metrics, landscape stratification models produced estimates that were less biased and more precise than a null model that accounted for no natural variability. Predictive models at the national and regional scale performed equally well, and substantially improved predictions of all hydrologic metrics relative to landscape stratification models. Prediction error rates ranged from 15 to 40%, but were ≤25% for most metrics. We selected three gaged, non‐reference sites to illustrate how predictive models could be used to assess hydrologic condition. These examples show how the models accurately estimate pre‐disturbance conditions and are sensitive to changes in streamflow variability associated with long‐term land‐use change. We also demonstrate how the models can be applied to predict expected natural flow characteristics at ungaged sites. Copyright © 2009 John Wiley & Sons, Ltd.     

Invertebrate response to impacts of water diversion and flow regulation in high‐altitude tropical streams

Water supply systems are critical infrastructure that provides food and energy security for developed societies. The operation of reservoirs (flow regulation) and water intakes (water diversion) has known negative impacts on aquatic ecosystems; however, quantification of ecological impacts and examination of these two types of flow alteration remain a developing area of research. We investigated the individual and combined impact of flow regulation and water diversion on stream ecosystem integrity, the freshwater macroinvertebrate community, and the population structure of flow‐sensitive insects. For 2 years, we monitored quarterly discharge, physical and chemical stream conditions, and benthic invertebrates of four high‐altitude tropical streams that are part of the water supply system of Quito, Ecuador. Flow regulation caused a loss of the hydrological seasonality of these streams, including a decrease in stream depth and biotic quality. Water diversion caused a decrease in dissolved oxygen and overall ecosystem integrity. Freshwater invertebrate density and richness decreased as a result of water diversion and flow regulation. The combined flow alteration in these streams decreased the density of nymphal stages of the widely distributed mayfly Andesiops peruvianus. Given the societal needs for food and energy security, water management for diversion (e.g., irrigation) and in‐line storage practices (e.g., hydroelectric dams) are anticipated to increase. This research suggests that the negative environmental impacts of flow alteration could be mitigated with discharge releases designed to approximate the natural hydrologic regime of undisturbed streams.     

BENTHIC COMMUNITY RESPONSES TO WATER REMOVAL IN TROPICAL MOUNTAIN STREAMS

Mountain streams that originally supported Hawaiian cultural practices have been diverted for development, agriculture and tourism for over 150 years. Habitat characteristics and benthic macroinvertebrate community responses to water withdrawal were studied in four West Maui Mountain watersheds. We compared riffle and cascade habitats upstream and downstream of the highest‐elevation diversion in each stream and further compared streams to understand variation among watersheds. Riffles were shallow areas with moderate flow, whereas cascades had high‐velocity water flowing over boulders and were separated into torrenticolous (submerged) and amphibious (splash zones on adjacent exposed rock) microhabitats. Among streams, downstream discharge was reduced by 84–99%, flow velocity was four times greater upstream, and depth was 50% lower downstream. There was a significant 44% reduction in downstream macroinvertebrate density (t = 3.261, df = 136, p = 0.0014); however, density did not significantly differ among streams (F = 1.95, df = 3, p = 0.125). Habitat‐corrected density, based on total available habitat area, indicated significantly greater proportions of native taxa in amphibious microhabitats compared with riffle and torrenticolous habitats. Non‐native Chironomidae and Trichoptera (Cheumatopsyche sp. and Hydroptila sp.) were dominant (>95%) and ubiquitous in riffles, whereas native Limonia sp. dominated (30%) amphibious microhabitats. Macroinvertebrate community structure varied among streams, sites and microhabitats, indicating inconsistent response to water withdrawal, dependent upon watershed size and microhabitat conditions. Our findings contribute to water management and restoration efforts focused on conservation of native species and habitat integrity in tropical streams worldwide. Copyright © 2013 John Wiley & Sons, Ltd.     

Application of nitrogen and phosphorus criteria for streams in agricultural landscapes

Efforts to control eutrophication of water resources in agriculturally dominated ecosystems have focused on managing on-farm activities to reduce nutrient loss; however, another management measure for improving water quality is adoption of environmental performance criteria (or 'outcome-based standards'). Here, we review approaches for setting environmental quality criteria for nutrients, summarize approaches developed in Canada for setting 'ideal' and 'achievable' nutrient criteria for streams in agricultural watersheds, and consider how such criteria could be applied. As part of a 'National Agri-Environmental Standards Initiative', the Government of Canada committed to the development of non-regulatory environmental performance standards that establish total P (TP) and total N (TN) concentrations to protect ecological condition of agricultural streams. Application of four approaches for defining ideal standards using only chemistry data resulted in values for TP and TN spanning a relatively narrow range of concentrations within a given ecoregion. Cross-calibration of these chemically derived standards with information on biological condition resulted in recommendations for TP and TN that would likely protect aquatic life from adverse effects of eutrophication. Non-point source water quality modelling was then conducted in a specific watershed to estimate achievable standards, i.e. chemical conditions that could be attained using currently available and recommended management practices. Our research showed that, taken together, short-term achievable standards and ultimate ideal standards could be used to set policy targets that should, if realized, lower N and P concentrations in Canadian agricultural streams and improve biotic condition.     

汾河水环境容量计算及特征分析

根据汾河水质状况,以及该河段各功能区水质管理目标,选取一维水质数学模型与合适的参数,计算得到了1994年～2006年最枯月平均流量不同保证率下该河段的水环境承载能力,为汾河水资源保护和管理提供了科学依据.     

Using an economic framework to inform management of environmental entitlements

There is much in the scientific literature dealing with methods to determine environmental water requirements in streams. However, most of these methods are suited to long‐term water resource planning and setting regulatory targets. In Australia, the environment is now recognized as a legitimate user of water with its own water entitlement. With this in mind, and in the context of a water market, transparent decisions need to be made as to how best to utilize environmental water reserves on yearly, monthly or even daily basis. Environmental water managers must identify priority flow components and environmental assets. This will call for information on environmental water requirements to be presented in a manner that informs operational decisions. This paper proposes that describing environmental requirements as a function relating to different flow levels, a relationship named here as an environmental response curve, is an important first step in making transparent decisions to achieve the best outcome from limited environmental entitlements. The environmental response curves allow the marginal benefit of water (or value of each additional ML) to the environment to be understood. This allows environmental recommendations to be more readily translated into operational rules. This is not a new environmental flows methodology. The contribution of this paper is representing existing data to allow operational decisions. This paper provides a possible way forward in representing environmental demands for operation of environmental water and highlights areas where our current knowledge falls short. Copyright © 2009 John Wiley & Sons, Ltd.     

EVALUATING TRADEOFFS BETWEEN ENVIRONMENTAL FLOW PROTECTIONS AND AGRICULTURAL WATER SECURITY

River basin managers responsible for water allocation decisions are increasingly required to evaluate tradeoffs between environmental flow protections and human water security. However, the basin‐scale effects of environmental flow regulations on water users are not well understood, in part because analyses are complicated by the spatial and temporal variation in water availability, human demands, and ecosystem needs. Here, we examine alternative regional environmental flow policies and their effects on a distributed network of water users in a small (182 km²) river basin in coastal California. We use a hydrologic model to simulate water diversion operations under three policy scenarios and quantify potential impacts to bypass flows for adult migrating salmon and agricultural water storage. The results indicate that there are inherent tradeoffs between environmental flows and agricultural water security, with the most restrictive environmental policy associated with the greatest impacts to water users. Surprisingly, the moderate environmental flow policy had larger impacts to bypass flows than the unregulated management scenario, suggesting that ecological benefits of the moderate policy are small relative to the adverse effects on agricultural water users. Conflicts between environmental and human water needs were greatest in upper catchments (<2.5 km²), where flow protections caused the greatest reduction in water storage. Although natural supplies were adequate for meeting water needs in most years regardless of policy restrictions, potential for conflict between environmental flow protections and water security was evident in dry years. Therefore, strategies are particularly needed for drought‐year water management to ensure adequate environmental flows while reducing human water allocations in an equitable manner. Copyright © 2013 John Wiley & Sons, Ltd.     

环境流计算新方法:水文变化的生态限度法

水文变化的生态限度框架(ELOHA)是环境流理论最新成果。ELOHA要求对河流按照水文情势特征进行分类,相同类型河流的水文—生态关系具有相似性。ELOHA还要求对开发前后水文情势变化进行分析,计算现状水文条件与基准水文条件的偏离程度。ELOHA提出了水文情势变化预期生态响应的若干假定,总结了一套为建立水文—生态关系采用的生态指标。在建立大型水文和生物数据库的基础上,运用统计学方法拟合水文—生态函数关系。最后,各利益相关者对水文变化引起的生态风险进行评估,认定可以接受的生态风险水平,再依据水文—生态曲线,确定环境流标准。     

The influence of riparian shade on lowland stream water temperatures in southern England and their viability for brown trout

Suitable thermal conditions in streams are necessary for fish and predictions of future climate changes infer that water temperatures may regularly exceed tolerable ranges for key species. Riparian woodland is considered as a possible management tool for moderating future thermal conditions in streams for the benefit of fish communities. The spatial and temporal variation of stream water temperature was therefore investigated over 3 years in lowland rivers in the New Forest (southern England) to establish the suitability of the thermal regime for fish in relation to riparian shade in a warm water system. Riparian shade was found to have a marked influence on stream water temperature, particularly in terms of moderating diel temperature variation and limiting the number of days per year that maximum temperatures exceeded published thermal thresholds for brown trout. Expansion of riparian woodland offers potential to prevent water temperature exceeding incipient lethal limits for brown trout and other fish species. A relatively low level of shade (20–40%) was found to be effective in keeping summer temperatures below the incipient lethal limit for brown trout, but ca. 80% shade generally prevented water temperatures exceeding the range reported for optimum growth of brown trout. Higher levels of shade are likely to be necessary to protect temperature‐sensitive species from climate warming. © Crown copyright 2010.     

黄河重点河段水环境承载能力及其合理利用

在界定水环境承载能力内涵及其影响因素的基础上,结合黄河重点河段水资源特征、水环境和排污状况,分析黄河重点河段水环境承载能力的特点,提出以水功能区管理为依据、总量控制为手段、水污染防治为根本的思路,通过工程、非工程措施来提高黄河水环境承载能力,以达到保护黄河水资源,实现流域社会经济增长和水资源保护相协调的可持续发展目的。     

Critical Flow for Water Management in a Shallow Tidal River Based on Estuarine Residence Time

To support the development of protective water resources management strategies, a 3D hydrodynamic model was applied to the Little Manatee River (LMR) to evaluate the effects of reducing river flow and drought on the Estuarine Residence Time (ERT). ERT is an important indicator for estuarine environmental quality. The Little Manatee River is a small tidal river estuary with a yearly mean gaged freshwater inflow of 4.8 m³/s. The hydrodynamic model was calibrated and verified by using two continuous data sets for a six month period. Model simulations were conducted for 17 river inflow scenarios. Among the flow scenarios, 13 scenarios were within a flow range from 0.26 m³/s to 10 m³/s total freshwater inflow. A regression equation (R ² = 0.98) fitted by a power-law function was derived from analysis of the hydrodynamic modeling results to correlate model predicted ERT to total river inflow, though ERT can be predicted from gaged freshwater inflow as well. The study indicates that the estuarine residence time reaches 53.3 days under an extreme drought condition of 0.26 m³/s total inflow. When river inflow falls below the critical flow (4 m³/s or less), further flow reductions can cause the substantial increases of ERT by a factor of 2 to 10 times. This suggests that the management of flow reductions is particularly critical when total river flows are 4 m³/s or less if adverse impacts to the water quality and ecological characteristics of the Little Manatee River are to be avoided.