Human impacts on the stream-groundwater exchange zone

Active exchanges of water and dissolved material between the stream and groundwater in many porous sand- and gravel-bed rivers create a dynamic ecotone called the hyporheic zone. Because it lies between two heavily exploited freshwater resources—rivers and groundwater—the hyporheic zone is vulnerable to impacts coming to it through both of these habitats. This review focuses on the direct and indirect effects of human activity on ecosystem functions of the hyporheic zone. River regulation, mining, agriculture, urban, and industrial activities all have the potential to impair interstitial bacterial and invertebrate biota and disrupt the hydrological connections between the hyporheic zone and stream, groundwater, riparian, and floodplain ecosystems. Until recently, our scientific ignorance of hyporheic processes has perhaps excused the inclusion of this ecotone in river management policy. However, this no longer is the case as we become increasingly aware of the central role that the hyporheic zone plays in the maintenance of water quality and as a habitat and refuge for fauna. To fully understand the impacts of human activity on the hyporheic zone, river managers need to work with scientists to conduct long-term studies over large stretches of river. River rehabilitation and protection strategies need to prevent the degradation of linkages between the hyporheic zone and surrounding habitats while ensuring that it remains isolated from toxicants. Strategies that prevent anthropogenic restriction of exchanges may include the periodic release of environmental flows to flush silt and reoxygenate sediments, maintenance of riparian buffers, effective land use practices, and suitable groundwater and surface water extraction policies.     

Quantitative Assessment of Agricultural Runoff and Soil Erosion Using Mathematical Modeling: Applications in the Mediterranean Region

Three mathematical models, the runoff curve number equation, the universal soil loss equation, and the mass response functions, were evaluated for predicting nonpoint source nutrient loading from agricultural watersheds of the Mediterranean region. These methodologies were applied to a catchment, the gulf of Gera Basin, that is a typical terrestrial ecosystem of the islands of the Aegean archipelago. The calibration of the model parameters was based on data from experimental plots from which edge-of-field losses of sediment, water runoff, and nutrients were measured. Special emphasis was given to the transport of dissolved and solid-phase nutrients from their sources in the farmers' fields to the outlet of the watershed in order to estimate respective attenuation rates. It was found that nonpoint nutrient loading due to surface losses was high during winter, the contribution being between 50% and 80% of the total annual nutrient losses from the terrestrial ecosystem. The good fit between simulated and experimental data supports the view that these modeling procedures should be considered as reliable and effective methodological tools in Mediterranean areas for evaluating potential control measures, such as management practices for soil and water conservation and changes in land uses, aimed at diminishing soil loss and nutrient delivery to surface waters. Furthermore, the modifications of the general mathematical formulations and the experimental values of the model parameters provided by the study can be used in further application of these methodologies in watersheds with similar characteristics.     

Comparative Influence of Forest Management and Habitat Structural Factors on the Abundances of Hollow-Nesting Bird Species in Subtropical Australian Eucalypt Forest

We examined the impact of single-tree selective logging and fuel reduction burns on the abundance of hollow-nesting bird species at a regional scale in southeastern Queensland, Australia. Data were collected on species abundance and habitat structure of dry sclerophyll production forest at 36 sites with known logging and fire histories. Sixteen bird species were recorded with most being resident, territorial, obligate hollow nesters that used hollows that were either small (<10 cm diameter) or very large (>18 cm diameter). Species densities were typically low, but combinations of two forest management and three habitat structural variables influenced the abundances of eight bird species in different and sometimes conflicting ways. The results suggest that habitat tree management for biodiversity in production forests cannot depend upon habitat structural characteristics alone. Management histories appear to have independent influence (on some bird species) that are distinguishable from their impacts on habitat structure per se. Rather than managing to maximize species abundances to maintain biodiversity, we may be better off managing to avoid extinctions of populations by identifying thresholds of acceptable fluctuations in populations of not only hollow-nesting birds but other forest dependent wildlife relative to scientifically valid forest management and habitat structural surrogates.     

A GIS/Simulation Framework for Assessing Change in Water Yield over Large Spatial Scales

Recent legislation to initiate vegetation management in the Central Sierra hydrologic region of California includes a focus on corresponding changes in water yield. This served as the impetus for developing a combined geographic information system (GIS) and simulation assessment framework. Using the existing vegetation density condition, together with proposed rules for thinning to reduce fire risk, a set of simulation model inputs were generated for examining the impact of the thinning scenario on water yield. The approach allows results to be expressed as the mean and standard deviation of change in water yield for each 1-km² map cell that is thinned. Values for groups of cells are aggregated for typical watershed units using area-weighted averaging. Wet, dry, and average precipitation years were simulated over a large region. Where snow plays an important role in hydrologic processes, the simulated change in water yield was less than 0.5% of expected annual runoff for a typical watershed. Such small changes would be undetectable in the field using conventional stream flow analysis. These results suggest that use of water yield increases to help justify forest-thinning activities or offset their cost will be difficult.     

Scientist and policy-maker response types and times in suburban watersheds

Differences between scientist and policy-maker response types and times, or the “how” and “when” of action, constrain effective water resource management in suburbanizing watersheds. Policy-makers are often rushed to find a single policy that can be applied across an entire, homogeneous, geopolitical region, whereas scientists undertake multiyear research projects to appreciate the complex interactions occurring within heterogeneous catchments. As a result, watershed management is often practiced with science and policy out of synch. Meanwhile, development pressures in suburban watersheds create changes in the social and physical fabric and pose a moving target for science and policy. Recent and anticipated advances in the scientific understanding of urbanized catchment hydrology and pollutant transport suggest that management should become increasingly sensitive to spatial heterogeneities in watershed features, such as soil types, terrain slopes, and seasonal watertable profiles. Toward this end, policy-makers should encourage funding scientific research that characterizes the impacts of these watershed heterogeneities within a geopolitical zoning and development framework.     

长江流域生态环境的意义及生态功能区段的划分

中国加入WTO之后,中国经济进一步与国际市场接轨,融入世界经济体系,机遇和挑战同在。欧美各国近年大力推行的环境标志产品认证,对第三世界商品质量设置入关的环境门槛。长江产业带作为世界最大的内河产业带和制造业基地,现在世界通行的环境管理认证体系和环境标志产品的认证,对长江流域产业尤其是外贸出口产业有长远而深刻的影响。这种认证制度,一方面对我出口商品设置了新的障碍,另一方面又将环境保护压力直接施加到企业。重视流域生态环境将从政府行为、公民压力扩展到企业行动,由于流域生态环境的负荷愈来愈重,流域生态环境的自我调节和恢复功能大幅下降,引起了日益严重的流域性生态安全问题。根据长江流域生态环境特征、不同的生态功能及存在的主要生态安全问题,将长江流域划性生态安全问题。根据长江流域生态环境特征、不同的生态功能及存在的主要生态安全问题,将长江流域划分成以下五个不同的生态功能区段,即长江源地区、金少江段（直门达至宜宾）、长江上游段（宜宾至宜昌）、长江中游段（宜昌至湖口段）、长江下游段（湖口至入海口）。针对不同区段主要的生态安全问题,应因地制宜采取相应的防范和整治措施。为保护与恢复生态功能服务。     

Management of an Agroecosystem

Agroecosystems (AESs) are autotrophic ecosystems managed by man. The goal of the management is to obtain the maximum possible amount of high-quality agricultural products while preserving agricultural resources, primarily the soils and biodiversity. The main components of the management of AES structures and functions, including primary and secondary biological production, the ratio between the energy flows in the plant–man and plant–livestock–man food chains, the efficiency of energy transfer in the plant–livestock link, and conservation of agricultural resources, are considered.     

Explaining Agricultural Expansion, Resource Booms and Growth in Latin America

The following paper examines the main factors determining long-run agricultural land expansion in Latin America compared to other tropical regions. Given the importance of natural resource-based sectors for most economies in Latin America, the impact of price-induced "resource booms" on economic growth in the region is explored. In addition, the paper examines whether there is an inherent "boom and bust" pattern of economic development associated with agricultural land expansion in Latin America, and the extent to which economic policies in the region exacerbate this problem. The paper concludes by examining the role of targeted policies in alleviating the structural obstacles to Latin American agricultural and economic development.     

涝渍地暗管排水示范工程建设有关问题研究

结合中日专项技术合作四湖项目的具体实践,指出了暗管工程规划中排水调查的内容和重点,就如何评判暗管排水的必要性和确定暗管设计排水量进行了探讨,分析了暗管排水与规划单元排灌系统的关系。排水调查是农田基本建设实施过程中不可缺少的一个环节,就涝渍地治理改造而言,调查的重点是要弄清排水不良的原因和取得解决问题的基础资料。为了制定符合实际的农田排水规划实施方案,可从土壤类型、土壤承载力、降雨后地表积水状况、土壤透水性和地下水位等对规划单元内的农田是否需要暗管排水作出判断。对水田而言,在田面水排除后,领先暗管要排除地表残留水和过剩的土壤重力水,据此决定暗管设计排水量。对于旱田,渗入土壤中以重力水存在的过乘水需要通过暗管排除,据此决定暗管设计排水量。暗管工程适于江河中下游地势低洼、排水不良的农田,当明排不能有效地降低地下水位满足作物生长时,有必要采取暗管排水。     

Using Decision Analysis to Choose Phosphorus Targets for Lake Erie

Lake Erie water quality has improved dramatically since the degraded conditions of the 1960s. Additional gains could be made, but at the expense of further investment and reductions in fishery productivity. In facing such cross-jurisdictional issues, natural resource managers in Canada and the United States must grapple with conflicting objectives and important uncertainties, while considering the priorities of the public that live in the basin. The techniques and tools of decision analysis have been used successfully to deal with such decision problems in a range of environmental settings, but infrequently in the Great Lakes. The objective of this paper is to illustrate how such techniques might be brought to bear on an important, real decision currently facing Lake Erie resource managers and stakeholders: the choice of new phosphorus loading targets for the lake. The heart of our approach is a systematic elicitation of stakeholder preferences and an investigation of the degree to which different phosphorus-loading policies might satisfy ecosystem objectives. Results show that there are potential benefits to changing the historical policy of reducing phosphorus loads in Lake Erie.