BLACK WILLOW CUTTING SURVIVAL IN STREAMBANK PLANTINGS,SOUTHEASTERN UNITED STATES1

Field studies were conducted on black willow (Salix nigra) cuttings planted for riparian zone restoration along Harland Creek, Twentymile Creek, and Little Topashaw Creek in Mississippi, USA. Planted cuttings were 2.5 to 3 m long and had base diameters of 2.5 to 7.5 cm. Streams were unstable, deeply incised sand bed channels with eroding banks 1 to 6 m high. Soil texture, redox potential (Eh), depth to water table, and willow survival were monitored for two to three years after planting. While many factors influence willow cuttings at restoration sites, soil texture and moisture are key to plant success. In these studies, plant survival and growth were best for cuttings planted in soils with less than 40 percent silt‐clay content and a water table 0.5 m to 1.0 m below the soil surface during the growing season. These conditions produced soil Eh greater than approximately 200 mV and were most often observed 1 to 2 m higher than the bank toe. These findings suggest criteria useful for preplanting site evaluations. Additional evidence suggests that preplanting soaking enhances performance of black willow cuttings. Additional factors (channel erosion, herbivory by beaver, and competition from exotics) may control performance over periods longer than two to three years.     

REASSEMBLING HETCH HETCHY: WATER SUPPLY WITHOUT O'SHAUGHNESSY DAM1

The Hetch Hetchy System provides San Francisco with most of its water supply. O'Shaughnessy Dam is one component of this system, providing approximately 25 percent of water storage for the Hetch Hetchy System and none of its conveyance. Removing O'Shaughnessy Dam has gained interest for restoring Hetch Hetchy Valley. The water supply feasibility of removing O'Shaughnessy Dam is analyzed by examining alternative water storage and delivery operations for San Francisco using an economic engineering optimization model. This model ignores institutional and political constraints and has perfect hydrologic foresight to explore water supply possibilities through reoperation of other existing reservoirs. The economic benefits of O'Shaughnessy Dam and its alternatives are measured in terms of the quantity of water supplied to San Francisco and agricultural water users, water treatment costs, and hydropower generation. Results suggest there could be little water scarcity if O'Shaughnessy Dam were to be removed, although removal would be costly due to additional water treatment costs and lost hydropower generation.     

"平退"工程与洞庭湖区湿地生态保护

从考察洞庭湖湿地生态特征入手,探讨了"平退"工程对洞庭湖区湿地生态环境的影响,认为通过"平退"防洪标准较低或影响江湖行蓄洪水的洲滩民垸以扩大江湖槽蓄来提高江湖调蓄洪水的能力,"平退"工程不但不会破坏湖区湿地生态环境,反而会使湖洲草滩及候鸟等越冬环境得到稳定和改善.同时,提出了保护洞庭湖湿地的相关对策.     

STREAM HEALTH RANKINGS PREDICTED BY SATELLITE DERIVED LAND COVER METRICS1

ABSTRACT: Land cover and land use change have long been known to influence the chemical, physical, and biological characteristics of streams. This study makes use of land cover maps derived from fine resolution satellite imagery and an extensive stream quality dataset to determine the relationship between small watershed health rankings and land cover composition and configuration. Landscape metrics were derived from digital impervious surface area (ISA), tree cover (percent), and agricultural crop maps within Montgomery County, Maryland. Watershed rankings were developed by state and county collaborators (MD‐DNR and MCDEP) using extensive biological and chemical measurements. In stepwise logistic regression models the factors accounting for the most variation in stream health ranking were the percent ISA, followed by the percent of tree cover. Riparian buffer zone tree cover was also a significant predictor. Of the metrics that considered the spatial configuration of the landscape, a contagion index and the percent of ISA in the flow path from the ISA to the stream were also found to be significant predictors of stream health. Despite limited ability to characterize landscape configuration or narrow riparian buffer zone vegetation with coarser resolution imagery (from Landsat), model results were not significantly different from those based on the use of fine‐resolution ISA information, suggesting that broader area applications of the approach are possible. The results indicate that management practices designed to improve stream water quality should focus on the amount of ISA and tree cover in both the watershed and within the buffer zone.     

FLOODPLAIN MANAGEMENT NEEDS PECULIAR TO ARID CLIMATES1

ABSTRACT: Many practices followed uniformly nationwide in the federal flood control and floodplain management programs are inappropriate or even counter productive in the arid Utah climate. An analysis of the 130-year Utah flood history, the structural and nonstructural flood programs in the state, and local perceptions obtained by field visits and interviews in 35 Utah communities revealed a number of such inefficiencies. Since flood flows dissipate quickly when they emerge from mountain watersheds onto desert lowlands, risks are concentrated near the apex of alluvial fans, include hazard from mud as well as water flow, and are compounded by canal interception of flood waters. Because of variation in the area flooded from one event to the next, floodplain mapping has tended to show risks too high in mapped areas and too low outside. Traditional channelization carries floods downstream past where they would dissipate naturally. The federal government needs to become more active in developing better flood hazard delineation and structural and nonstructural designs for arid areas. State government can help by providing a forum where communities can exchange experiences, reviewing structural designs prepared by local government, and providing local communities with technical expertise for dealing with federal agencies.     

Stream renovation: An alternative to channelization

Channelization is one of the most common solutions to urban drainage problems, despite the fact that channelized streams are frequently morphologically unstable, biologically unproductive, and aesthetically displeasing. There is increasing empirical and theoretical evidence to suggest that channelization may be counterproductive unless channels are designed to prevent the bank erosion and channel silting that often accompanies stream dredging. Many of the detrimental effects of channelization can be avoided, with little compromise in channel efficiency, by employing channel design guidelines that do not destroy the hydraulic and morphologic equilibria that natural streams possess. These guidelines include minimal straightening; promoting bank stability by leaving trees, minimizing channel reshaping, and employing bank stabilization techniques; and, emulating the morphology of natural stream channels. This approach, called stream restoration or stream renovation, is being successfully employed to reduce flooding and control erosion and sedimentation problems on streams in Charlotte, North Carolina.     

Shorebird fauna changes of a small tropical estuary following habitat alteration: Biological and political impacts of environmental restoration

Numbers of shorebirds visiting the Paiko Lagoon Wildlife Sanctuary, a small tropical estuary located on Oahu, Hawaii, are compared before and after environmental restoration of the lagoon. An attempt is made to examine both the biological impacts and policy implications of the project. The biological results indicate that shorebird abundance did not increase following restoration. On the other hand, public perceptions regarding the ecological value of the lagoon suggest that in spite of a lack of biological benefit to shorebirds, the lagoon was perceived by the public, particularly local residents, as being more ecologically valuable because it had been aesthetically improved. The discussion focuses on the interplay between scientific and non-scientific factors in natural resource decision making.     

古尔班通古特沙漠公路扰动带植被恢复研究

古尔班通古特沙漠区域伴随多条沙漠公路的修筑，公路沿线形成了生态扰动带（包括施工扰动带和运营扰动带）。它使地表空气流场改变、地表覆被剥离、风沙源出现、地表径流过程受阻、地表水分重分配以及生境隔离。野外考察和样品分析表明，扰动带的植被恢复取决于消面稳定性、降水的地表分配、时间、地下水位、种源和风场等因素，并初步总结出如下规律：①草方格内部表面沙层的有机质随时间逐渐增多；②草方格固沙措施加速了植被恢复的速度；③迎风坡自然覆沙，种子易于着床和萌发；④路肩上形成长营养期的中生植物，边坡形成旱生植物，路边优动带内的植被恢复情况因水分条件而变化；⑤植被恢复与时间成正比，演替过程为：短命植物、三芒草→蒿类→梭梭或白梭梭。最后提出改进草方格沙障的材料、增加土壤的有机质含量、使用干水、适时播种等恢复措施。     

AN INTEGRATIVE APPROACH TOWARDS UNDERSTANDING ECOLOGICAL RESPONSES TO DAM REMOVAL: THE MANATAWNY CREEK STUDY1

ABSTRACT: Dam removal has been proposed as an effective method of river restoration, but few integrative studies have examined ecological responses to the removal of dams. In 1999, we initiated an interdisciplinary study to determine ecological responses to the removal of a 2 m high dam on lower Manatawny Creek in southeastern Pennsylvania. We used an integrative monitoring program to assess the physical, chemical, and biological responses to dam removal. Following removal in 2000, increased sediment transport has led to major changes in channel form in the former impoundment and downstream reaches. Water quality did not change markedly following removal, probably because of the impoundment's short hydraulic residence time (less than two hours at base flow) and infrequent temperature stratification. When the impoundment was converted to a free flowing reach, the composition of the benthic macroinvertebrate and fish assemblages in this portion of Manatawny Creek shifted dramatically from lentic to lotic taxa. Some fish species inhabiting the free flowing reach downstream from the dam were negatively affected by large scale sediment transport and habitat alteration following dam removal, but this appears to be a short term response. Based on our observations and experiences in this study, we provide a list of issues to evaluate when considering future dam removals.