Use of landscape and land use parameters for classification and characterization of watersheds in the mid-Atlantic across five physiographic provinces

The Atlantic Slope Consortium (ASC) is a project designed to develop and test a set of indicators in coastal systems that are ecologically appropriate, economically reasonable, and relevant to society. The suite of indicators will produce integrated assessments of the condition, health and sustainability of aquatic ecosystems based on ecological and socioeconomic information compiled at the scale of estuarine segments and small watersheds. The research mandate of the ASC project is the following:

Using a universe of watersheds, covering a range of social choices, we ask two questions:

• ? How “good” can the environment be, given those social choices?
• ? What is the intellectual model of condition within those choices, i.e., what are the causes of condition and what are the steps for improvement?

As a basis for compiling ecological indicators, a watershed classification system was required for the experimental design. The goal was to develop approximately five categories of watersheds for each physiographic province, utilizing landscape and land use parameters that would be predictive of aquatic resource condition. All 14-digit Hydrologic Unit Code (HUC) watersheds in the Mid-Atlantic region would then be classified according to the regime. Five parameters were utilized for the classification: three land cover categories, consisting of forested, agricultural, and urban, median slope or median elevation, and total variance of land covers in 1-km-radius circles positioned on all stream convergence points in a specified 14-digit?HUC watershed. Cluster analysis utilizing these five parameters resulted in approximately five well-defined watershed classes per physiographic province. The distribution of all watersheds in the Mid-Atlantic region across these categories provides a unique report on the probable condition of watersheds in the region.     

The rate and extent of deforestation in watersheds of the southwestern Amazon basin.

The rate and extent of deforestation determine the timing and magnitude of disturbance to both terrestrial and aquatic ecosystems. Rapid change can lead to transient impacts to hydrology and biogeochemistry, while complete and permanent conversion to other land uses can lead to chronic changes. A large population of watershed boundaries (N=4788) and a time series of Landsat TM imagery (1975-1999) in the southwestern Amazon Basin showed that even small watersheds (2.5-15 km2) were deforested relatively slowly over 7-21 years. Less than 1% of all small watersheds were more than 50% cleared in a single year, and clearing rates averaged 5.6%/yr during active clearing. A large proportion (26%) of the small watersheds had a cumulative deforestation extent of more than 75%. The cumulative deforestation extent was highly spatially autocorrelated up to a 100-150 km lag due to the geometry of the agricultural zone and road network, so watersheds as large as approximately 40000 km2 were more than 50% deforested by 1999. The rate of deforestation had minimal spatial autocorrelation beyond a lag of approximately 30 km, and the mean rate decreased rapidly with increasing area. Approximately 85% of the cleared area remained in pasture, so deforestation in watersheds of Rond?nia was a relatively slow, permanent, and complete transition to pasture, rather than a rapid, transient, and partial cutting with regrowth. Given the observed landcover transitions, the regional stream biogeochemical response is likely to resemble the chronic changes observed in streams draining established pastures, rather than a temporary pulse from slash-and-burn.     

Effects of Urbanization on the Distribution and Abundance of Amphibians and Invasive Species in Southern California Streams

Abstract:  Urbanization negatively affects natural ecosystems in many ways, and aquatic systems in particular. Urbanization is also cited as one of the potential contributors to recent dramatic declines in amphibian populations. From 2000 to 2002 we determined the distribution and abundance of native amphibians and exotic predators and characterized stream habitat and invertebrate communities in 35 streams in an urbanized landscape north of Los Angeles (U.S.A.). We measured watershed development as the percentage of area within each watershed occupied by urban land uses. Streams in more developed watersheds often had exotic crayfish ( Procambarus clarkii ) and fish, and had fewer native species such as California newts ( Taricha torosa ) and California treefrogs ( Hyla cadaverina ). These effects seemed particularly evident above 8% development, a result coincident with other urban stream studies that show negative impacts beginning at 10–15% urbanization. For Pacific treefrogs ( H. regilla ), the most widespread native amphibian, abundance was lower in the presence of exotic crayfish, although direct urbanization effects were not found. Benthic macroinvertebrate communities were also less diverse in urban streams, especially for sensitive species. Faunal community changes in urban streams may be related to changes in physical stream habitat, such as fewer pool and more run habitats and increased water depth and flow, leading to more permanent streams. Variation in stream permanence was particularly evident in 2002, a dry year when many natural streams were dry but urban streams were relatively unchanged. Urbanization has significantly altered stream habitat in this region and may enhance invasion by exotic species and negatively affect diversity and abundance of native amphibians.     

Postfire Logging in Riparian Areas

Abstract:  We reviewed the behavior of wildfire in riparian zones, primarily in the western United States, and the potential ecological consequences of postfire logging. Fire behavior in riparian zones is complex, but many aquatic and riparian organisms exhibit a suite of adaptations that allow relatively rapid recovery after fire. Unless constrained by other factors, fish tend to rebound relatively quickly, usually within a decade after a wildfire. Additionally, fire and subsequent erosion events contribute wood and coarse sediment that can create and maintain productive aquatic habitats over time. The potential effects of postfire logging in riparian areas depend on the landscape context and disturbance history of a site; however, available evidence suggests two key management implications: (1) fire in riparian areas creates conditions that may not require intervention to sustain the long-term productivity of the aquatic network and (2) protection of burned riparian areas gives priority to what is left rather than what is removed. Research is needed to determine how postfire logging in riparian areas has affected the spread of invasive species and the vulnerability of upland forests to insect and disease outbreaks and how postfire logging will affect the frequency and behavior of future fires. The effectiveness of using postfire logging to restore desired riparian structure and function is therefore unproven, but such projects are gaining interest with the departure of forest conditions from those that existed prior to timber harvest, fire suppression, and climate change. In the absence of reliable information about the potential consequence of postfire timber harvest, we conclude that providing postfire riparian zones with the same environmental protections they received before they burned is justified ecologically. Without a commitment to monitor management experiments, the effects of postfire riparian logging will remain unknown and highly contentious.     

Scale Perspectives on Avian Diversity in Western Riparian Ecosystems

Conservation of riparian vegetation in western North America has, in part, emphasized providing habitats for a locally diverse avifauna. Site diversity, especially relative to the number of species present, is generally high within riparian avifaunas. Between-habitat diversity changes across a watershed, with riparian species assemblages differing most from upland assemblages at the highest and lowest elevations. This pattern can be attributed to enhanced avian movements within the riparian vegetation. The corridors for bird movements, in turn, facilitate faunal mixing on a broader scale, influencing regional diversity within landscapes. Riparian ecosystems are viewed as connectors of forests across fragmented landscapes. In western settings, however, they are highly linearized forests transecting watersheds between upland associations of high elevations and very different associations at lower elevations. Regionally, riparian vegetation represents linear islands that are internally both floristically and faunistically dynamic rather than mere bridges of homogeneous vegetation in landscape networks. The significance of riparian vegetation as habitat for western birds has been defined primarily at the local level. Conservation activities favoring site diversity are short-sighted, however, and could have severe consequences for unique elements of riparian avifaunas. Conservation actions must evaluate how local activities alter potential dispersal opportunities for ecological-generalist versus riparian-obligate species. Maintaining the character and integrity of riparian avifaunas requires planning from regional and continental perspectives.     

Terrestrial Reserve Networks Do Not Adequately Represent Aquatic Ecosystems

Abstract: Protected areas are a cornerstone of conservation and have been designed largely around terrestrial features. Freshwater species and ecosystems are highly imperiled, but the effectiveness of existing protected areas in representing freshwater features is poorly known. Using the inland waters of Michigan as a test case, we quantified the coverage of four key freshwater features (wetlands, riparian zones, groundwater recharge, rare species) within conservation lands and compared these with representation of terrestrial features. Wetlands were included within protected areas more often than expected by chance, but riparian zones were underrepresented across all (GAP 1–3) protected lands, particularly for headwater streams and large rivers. Nevertheless, within strictly protected lands (GAP 1–2), riparian zones were highly represented because of the contribution of the national Wild and Scenic Rivers Program. Representation of areas of groundwater recharge was generally proportional to area of the reserve network within watersheds, although a recharge hotspot associated with some of Michigan's most valued rivers is almost entirely unprotected. Species representation in protected areas differed significantly among obligate aquatic, wetland, and terrestrial species, with representation generally highest for terrestrial species and lowest for aquatic species. Our results illustrate the need to further evaluate and address the representation of freshwater features within protected areas and the value of broadening gap analysis and other protected‐areas assessments to include key ecosystem processes that are requisite to long‐term conservation of species and ecosystems. We conclude that terrestrially oriented protected‐area networks provide a weak safety net for aquatic features, which means complementary planning and management for both freshwater and terrestrial conservation targets is needed.     

Urbanization and nutrient retention in freshwater riparian wetlands.

Urbanization can degrade water quality and alter watershed hydrology, with profound effects on the structure and function of both riparian wetlands (RWs) and aquatic ecosystems downstream. We used freshwater RWs in Fairfax County, Virginia, USA, as a model system to examine: (1) the effects of increasing urbanization (indexed by the percentage of impervious surface cover [%ISC] in the surrounding watershed) on nitrogen (N) and phosphorus (P) concentrations in surface soils and plant tissues, soil P saturation, and soil iron (Fe) chemistry; and (2) relationships between RW soil and plant nutrient chemistries vs. the physical and biotic integrity of adjacent streams. Soil total P and NaOH-extractable P (representing P bound to aluminum [Al] and Fe hydrous oxides) varied significantly but nonlinearly with % ISC (r2 = 0.69 and 0.57, respectively); a similar pattern was found for soil P saturation but not for soil total N. Relationships were best described by second-order polynomial equations. Riparian wetlands appear to receive greater P loads in moderately (8.6-13.3% ISC) than in highly (25.1-29.1% ISC) urbanized watersheds. These observations are consistent with alterations in watershed hydrology that occur with increasing urbanization, directing water and nutrient flows away from natural RWs. Significant increases in total and crystalline soil Fe (r2 = 0.57 and 0.53, respectively) and decreases in relative soil Fe crystallinity with increasing %ISC suggest the mobilization and deposition of terrestrial sediments in RWs, likely due to construction activities in the surrounding watershed. Increases in RW plant tissue nutrient concentrations and %ISC in the surrounding watershed were negatively correlated with standard indices of the physical and biotic integrity of adjacent streams. In combination, these data suggest that nutrient and sediment inputs associated with urbanization and storm-water management are important variables that affect wetland ecosystem services, such as water quality improvement, in urbanizing landscapes.     

Development and application of multi-proxy indices of land use change for riparian soils in southern New England, USA

Understanding the effects of land use on riparian systems is dependent upon the development of methodologies to recognize changes in sedimentation related to shifts in land use. Land use trends in southern New England consist of shifts from forested precolonial conditions, to colonial and agrarian land uses, and toward modern industrial-urban landscapes. The goals of this study were to develop a set of stratigraphic indices that reflect these land use periods and to illustrate their applications. Twenty-four riparian sites from first- and second-order watersheds were chosen for study. Soil morphological features, such as buried surface horizons (layers), were useful to identify periods of watershed instability. The presence of human artifacts and increases in heavy metal concentration above background levels, were also effective indicators of industrial-urban land use periods. Increases and peak abundance of non-arboreal weed pollen (Ambrosia) were identified as stratigraphic markers indicative of agricultural land uses. Twelve 14C dates from riparian soils indicated that the rise in non-arboreal pollen corresponds to the start of regional deforestation (AD 1749 +/- 56 cal yr; mean +/- 2 SD) and peak non-arboreal pollen concentration corresponds to maximum agricultural land use (AD 1820 +/- 51 cal yr). These indices were applied to elucidate the impact of land use on riparian sedimentation and soil carbon (C) dynamics. This analysis indicated that the majority of sediment and soil organic carbon (SOC) stored in regional riparian soils is of postcolonial origins. Mean net sedimentation rates increased -100-fold during postcolonial time periods, and net SOC sequestration rates showed an approximate 200-fold increase since precolonial times. These results suggest that headwater riparian zones have acted as an effective sink for alluvial sediment and SOC associated with postcolonial land use.     

Headwater riparian forest-floor invertebrate communities associated with alternative forest management practices.

Headwater streams and their riparian zones are a common, yet poorly understood, component of Pacific Northwest, USA, landscapes. We describe the ecological importance of headwater stream riparian zones as habitat for forest-floor invertebrate communities and assess how alternative management strategies for riparian zones may impact these communities. We compared community composition of forest-floor invertebrates at increasing distances along trans-riparian (stream edge to upslope) transects in mature forests, clearcuts, and riparian buffers of approximately 30-m width with upslope clearcuts. Invertebrates were collected using pitfall traps in five replicate blocks of three treatments each in the Willamette National Forest, Oregon, USA. We measured microclimate and microhabitat variables at pitfall locations. Despite strong elevation and block effects on community composition, community analyses revealed a distinct "riparian" invertebrate community within 1 m of the stream edge in mature forest treatments, which was strongly related to cool, humid microclimate conditions. Invertebrate community composition in buffer treatments was far more similar to that of mature forests than to clearcuts; a pattern mirrored by microclimate. These results suggest that, within our study sites, forest-floor invertebrate distributions are strongly associated with microclimate and that riparian buffers of approximately 30-m width do provide habitat for many riparian and forest species. Riparian reserves may serve as effective forest refugia and/or dispersal corridors for invertebrates and other taxa, and their incorporation into watershed management plans likely will contribute to meeting persistence and connectivity objectives.     

Light-mediated thresholds in stream-water nutrient composition in a river network

The elemental composition of solutes transported by rivers reflects combined influences of surrounding watersheds and transformations within stream networks, yet comparatively little is known about downstream changes in effects of watershed loading vs. in-channel processes. In the forested watershed of a river under a mediterranean hydrologic regime, we examined the influence of longitudinal changes in environmental conditions on water-column nutrient composition during summer base flow across a network of sites ranging from strongly heterotrophic headwater streams to larger, more autotrophic sites downstream. Small streams (0.1-10 km2 watershed area) had longitudinally similar nutrient concentration and composition with low (approximately 2) dissolved nitrogen (N) to phosphorus (P) ratios. Abrupt deviations from this pattern were observed in larger streams with watershed areas > 100 km2 where insolation and algal abundance and production rapidly increased. Downstream, phosphorus and silica concentrations decreased by > 50% compared to headwater streams, and dissolved organic carbon and nitrogen increased by approximately 3-6 times. Decreasing dissolved P and increasing dissolved N raised stream-water N:P to 46 at the most downstream sites, suggesting a transition from N limitation in headwaters to potential P limitation in larger channels. We hypothesize that these changes were mediated by increasing algal photosynthesis and N fixation by benthic algal assemblages, which, in response to increasing light availability, strongly altered stream-water nutrient concentration and stoichiometry in larger streams and rivers.     

Riparian shading and groundwater enhance growth potential for smallmouth bass in Ozark streams.

Moderation of stream temperatures by riparian shading and groundwater are known to promote growth and survival of salmonid fishes, but effects of riparian shade and groundwater on to be growth of warmwater stream fishes are poorly understood or assumed to be negligible. We used stream temperature models to relate shading from riparian vegetation and groundwater inflow to summer water temperatures in Missouri Ozark streams and evaluated effects of summer water temperatures on smallmouth bass, Micropterus dolomieu, growth using a bioenergetics model. Bioenergetics model simulations revealed that adult smallmouth bass in non-spring-fed streams have lower growth potential during summer than fish in spring-fed streams, are subject to mass loss when stream temperatures exceed 27 degrees C, and will likely exhibit greater interannual variation in growth during summer if all growth-influencing factors, other than temperature, are identical between the two stream types. Temperature models indicated that increased riparian shading will expand the longitudinal extent of thermal habitat capable of supporting adult smallmouth bass growth in spring-fed stream reaches when mean daily air temperatures exceed 27 degrees C. Optimum growth temperature (22 degrees C) will be present only in spring-fed streams under these conditions. Potential for increasing shade through riparian restoration is greatest for streams <5 m wide and along north-south reaches of larger streams. However, temperature models also indicated that restoring riparian shading to maximum levels throughout a watershed would increase the total stream mileage capable of supporting positive growth of adult smallmouth bass by only 1-6% when air temperatures are at or near average summer maxima; increases in suitable thermal habitat would be greatest in watersheds with higher spring densities. Riparian management for maintenance or restoration of the thermal habitat of adult smallmouth bass during summer should be focused in areas strongly influenced by groundwater. Restoring riparian shading along spring-fed warmwater streams will likely benefit adult smallmouth bass growth and may ultimately influence population sizes.     

半干旱黄土区自然恢复与人工造林恢复植被群落对比研究

为研究半干旱黄土区高效植被恢复途径,选取陕西省吴起县境内的合沟封禁流域和柴沟人工造林流域为研究区,在两流域内,沿顺坡和横坡方向,选择一系列20 m×20 m的样地,各组成2条样带。在每个样地内的对角线交点和对角线四分之一处选取5个样方进行植被调查,草本样方和乔灌样方的尺寸分别为1 m×1 m和5 m×5 m。共获得草本样方185个、乔灌木样方80个,其中,合沟封禁流域105个,均为草本样方,柴沟人工造林流域草本样方与乔灌样方各80个。运用植物生态学和植物群落学方法,调查各样方内的植物种类、株数、株高、盖度、地上生物量以及树木基茎、树高、冠幅等植被群落特征指标,并在此基础上对两流域的植被群落特征进行对比分析。结果表明：（1）两流域的植被种类共61种,其中柴沟人工造林流域46种,合沟封禁流域51种,共存物种36种;（2）经过10年生态恢复,柴沟人工造林流域已形成乔-灌-草群落,合沟封禁流域仍为草本群落,且两流域草本群落均以铁杆蒿（Artemisia sacrorum Ledeb.）和茭蒿（Artemisiagiraldii Pamp.）为主要建群种;（3）柴沟人工造林流域的植被盖度、平均高、生物量均明显高于合沟封禁流域的相应指标。两流域植物群落Simpson指数和Shannon-Weiner指数差异较小,Sorensen指数为0.742,主要草本植物种的指标差异不显著。以上特征反映出,在半干旱黄土区,适宜的人工造林可加速该区植被恢复的进程。     

Forest to reclaimed mine land use change leads to altered ecosystem structure and function.

The United States' use of coal results in many environmental alterations. In the Appalachian coal belt region, one widespread alteration is conversion of forest to reclaimed mineland. The goal of this study was to quantify the changes to ecosystem structure and function associated with a conversion from forest to reclaimed mine grassland by comparing a small watershed containing a 15-year-old reclaimed mine with a forested, reference watershed in western Maryland. Major differences were apparent between the two watersheds in terms of biogeochemistry. Total C, N, and P pools were all substantially lower at the mined site, mainly due to the removal of woody biomass but also, in the case of P, to reductions in soil pools. Mineral soil C, N, and P pools were 96%, 79%, and 69% of native soils, respectively. Although annual runoff from the watersheds was similar, the mined watershed exhibited taller, narrower storm peaks as a result of a higher soil bulk density and decreased infiltration rates. Stream export of N was much lower in the mined watershed due to lower net nitrification rates and nitrate concentrations in soil. However, stream export of sediment and P and summer stream temperature were much higher. Stream leaf decomposition was reduced and macroinvertebrate community structure was altered as a result of these changes to the stream environment. This land use change leads to substantial, long-term changes in ecosystem capital and function.     

Introduced trout sever trophic connections in watersheds: consequences for a declining amphibian

Trophic linkages between terrestrial and aquatic ecosystems are increasingly recognized as important yet poorly known features of food webs. Here we describe research to understand the dynamics of lake food webs in relation to a native riparian amphibian and its interaction with introduced trout. The mountain yellow-legged frog Rana muscosa is endemic to alpine watersheds of the Sierra Nevada Mountains and the Transverse Ranges of California, but it has declined to a small fraction of its historical distribution and abundance. Although remaining frogs and introduced trout feed in different habitats of alpine lakes, our stable-isotope analyses clearly show that the same resource base of benthic invertebrates sustains their growth. During one period, insect emergence from naturally fishless lakes was nearly 20-fold higher compared to adjacent lakes with trout, showing that fish reduce availability of aquatic prey to amphibious and terrestrial consumers. Although trout cannot prey on adult frogs due to gape limitation, foraging post-metamorphic frogs are 10 times more abundant in the absence of trout, suggesting an important role for competition for prey by trout in highly unproductive alpine watersheds. Most Sierran lakes contain fish, and those that do not are usually small isolated ponds; in our study, these two lake types supported the lowest densities of post-metamorphic frogs, and these frogs were less reliant on local, benthic sources of productivity. Since Rana muscosa was formerly the most abundant vertebrate in the Sierra Nevada, the reduction in energy flow from lake benthos to this consumer due to fish introductions may have had negative consequences for its numerous terrestrial predators, many of which have also declined. We suggest that disruptions of trophic connections between aquatic and terrestrial food webs are an important but poorly understood consequence of fish introduction to many thousands of montane lakes and streams worldwide and may contribute to declines of native consumers in riparian habitats.     

Salmon, wildlife, and wine: marine-derived nutrients in human-dominated ecosystems of central California.

Pacific salmon transfer large quantities of marine-derived nutrients to adjacent forest ecosystems with profound effects on plant and wildlife production. We investigated this process for two highly modified California wine country rivers, one with consistent salmon runs (Mokelumne River) and one without (Calaveras River). Mokelumne River Chinook salmon transported biomass and N comparable to Pacific Northwest salmon streams. Calaveras River levels were much less. Scavenger numbers correlated with salmon carcass counts over time on the Mokelumne River but not the Calaveras River. Likewise, salmon carcasses were consumed significantly faster on the Mokelumne River. Native riparian vegetation as well as cultivated wine grapes adjacent to Mokelumne River spawning sites received 18-25% of foliar N from marine sources, significantly higher than vegetation along the Calaveras River. These data suggest that robust salmon runs continue to provide important ecological services with high economic value, even in impaired watersheds. Loss of Pacific salmon can not only negatively affect stream and riparian ecosystem function, but can also affect local economies where agriculture and salmon streams coexist.     

Structural equation-based latent growth curve modeling of watershed attribute-regulated stream sensitivity to reduced acidic deposition

Little information is available about the effects of watershed attributes on long-term stream chemical responses to reduced acidic deposition. Long-term chemical data (1980-2006) for 21 stream sites from the Appalachian Mountain region and data of 8 watershed attributes of the corresponding watersheds were analyzed to study such effects. Latent growth curve modeling (LGM), a structural equation modeling (SEM) approach, was conducted to quantify stream sensitivity to reduced acidic deposition in the region, and to model the initial chemical conditions (intercepts) and changing rates (slopes) in three time periods: 1980s, 1990s, and 2000s. The modeled chemical trends were generally consistent with those trends which were detected by trend analyses in a previous study. Watershed attributes including area, mean elevation, percentage of developed land, percentage of grassland, percentages of shale and sandstone, percentage of barren land, and percentage of soil type Gilpin-Upshur-Vandalia (GUV) were found to affect stream sensitivity to the reduced acidic deposition with their importance in the respective order. The stream sensitivity in turn regulated streams’ chemical initial conditions and their changing rates in the studied watersheds. This innovative application of LGM for modeling long-term chemical trends advanced our understanding of the role of watershed attributes in regulating streams’ responses to reduced acidic deposition. This approach can be applied for evaluating streams’ responses to acidic deposition in other regions and, more broadly, for studying causal effects on long-term behaviors in other ecological and environmental science subjects.     

Aquatic ecological health assessment of Shaying River Basin based on indices of physico-chemistry and aquatic organisms北大核心CSCD

With a variety of ecosystem services, river ecosystem plays an important role in the process of human society development. On the other hand, health condition of most aquatic ecosystems is seriously threatened by human activities. Restoring and maintaining a healthy ecosystem has already become a vital goal of river management. As a basis of river management, river health assessment is therefore particularly important. Based on indices of physics, chemistry and aquatic organisms, this research tried to establish a comprehensive evaluation system of aquatic ecological health suitable for the situation of Shaying River Basin. The system included 6 factors including riparian zone, river morphology, nutrients, oxygen balance, periphyton and benthic macroinvertebrates, which were defined into 19 indices reflecting the aquatic ecological health from different aspects. The assessment results indicated that the health condition of overall basin was normal, varying among different parts of the region, with Shahe River, Lihe River and Beiru River in the upper part sub-healthy, and Jialu River in the same part sub-sick. The middle region was generally in normal or sub-sick level; the health condition of the lower part was comparatively better due to a good condition. Within the indices, the nutrients and benthic macroinvertebrates were the major constraining factors to the health condition of Shaying River Basin for their poor health condition. The health conditions showed significant differences among the rivers (P < 0.01), with Jialu River being the worst. The result indicated that the aquatic ecological health of Shaying River Basin is affected by many factors, with urban and industrial sewage being the main ones, And that different protective measures should be employed for rivers of different conditions. The result can provide theoretical basis for the ecological restoration of Shaying River Basin and reasonable exploitation and conservation of the water resource of the whole Huaihe River Basin.     

生态恢复对退化河岸植物群落的作用 ——以重庆九龙外滩河岸带生态恢复为例

河岸带是陆地生态系统与水生生态系统之间的过渡地带,受人类干扰的威胁较大.长江是流经重庆都市区的主要河流,主城区两江四岸部分河岸硬化,河岸生态功能退化或丧失,生物多样性降低.本文以重庆主城区九龙外滩的河岸带为研究区域,通过调查,采用Ward最小方差法对植物群落类型进行划分,比较了生态恢复区域和自然区域的植物群落特征及优势...     

A model examining hierarchical wetland networks for watershed stormwater management

There is increasing awareness that solutions to degraded quality and excessive quantity of stormwater and resulting impacts on downstream water bodies may require a watershed approach to management rather that the incremental approach that is now common. Examination of low-relief watersheds characteristic of the southeastern coastal plain reveals common hierarchical patterns of surface water convergence that may be emulated in developed watersheds to enhance the efficacy of peak-flow attenuation and pollutant removal. A dynamic systems model was developed to compare stormwater management using a hierarchical network of treatment wetlands with the standard incremental approach wherein treatment systems are designed considering only site-level effluent criteria. The model simulates watershed hydrology, suspended sediment transport and phosphorus removal and transformation. Results indicate that watershed planning of stormwater collection and treatment systems using hierarchical networks can greatly enhance overall effectiveness (annual retention improvements of 31% for flow, 36% for sediment and 27% for phosphorus) with respect to an equal area of uniformly sized wetlands. Further, network proportions can be adjusted to specific runoff characteristics. Distinct roles were observed for each wetland size class: small headwater wetlands effectively removed sediment, medium-sized mid-reach wetlands retained phosphorus, while large wetlands primarily stored and attenuated long-period hydrologic flows.     

The importance of fires and floods on tree ages along mountainous gravel-bed streams.

This paper examines the commonly accepted assumption in the riparian literature that areas adjacent to streams do not burn. Using time-since-fire distributions, derived from stand-origin maps for a watershed in the front ranges of the Canadian Rocky Mountains, we found that the areas adjacent to streams and the whole study watershed have similar fire frequencies. In addition, the relative importance of fires and floods is regulated by a change in channel morphology associated with the creation of bars. The results demonstrate that fires solely control tree establishment along straight streams without bars, while the influence of floods is observed at the onset of lateral- and point-bar formation. This occurs because bars are formed in-channel and require smaller discharges in order to be flooded, compared to higher terraces. Consequently, bars are the only surfaces being flooded more frequently than they are being burned. Thus, overall the results indicate that, on this watershed, areas adjacent to streams are not less likely to burn than the uplands, except for lateral and point bars. The generality of these results to other systems should be tested as they have important implications for current forest ecological definition of "riparian zones," which typically include all fluvially derived landforms, from the channel banks to the terraces. Indeed, this study suggests that along smaller, headwater, gravel-bed mountain watersheds, the forests found on terraces are only influenced by fire and not fluvial processes and should therefore not be included in the riparian zone, while the forests on bars are the only surfaces currently being influenced by fluvial processes. Such a change in definition has implications for both ecologists and forest managers aiming to protect areas along streams as they now must take into account the effects of two disturbances on these small gravel-bed streams.