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1.
Compared to benthic and water-column invertebrate assemblages, considerably less is known about terrestrial arthropods inhabiting estuarine wetlands despite their importance to tidal wetland biodiversity and productivity. We also need to know more about how human modification of estuaries, including efforts to restore estuarine wetlands, affects these assemblages. To address this knowledge gap, we assembled data from multiple studies on terrestrial arthropod assemblages from 87 intertidal wetland sites in 13 estuaries along the west coast of North America. Arthropods were sampled between 1998 and 2013 with fallout traps deployed in wetlands for 1 to 3 days at a time. We describe patterns in the abundance and taxonomic composition of terrestrial arthropods and evaluate the relative ability of natural and anthropogenic factors to explain variation in abundance and composition. Arthropod abundance was highly variable. Vegetation assemblage, precipitation, and temperature best explained variation in arthropod abundance, while river discharge, latitude, and developed and agricultural land cover surrounding sampling sites were less important. Arthropod abundance rapidly achieved levels of reference wetlands after the restoration of tidal influence to leveed wetlands, regardless of surrounding land cover. However, arthropod assemblage composition was affected by the amount of developed land cover as well as restoration age. These results suggest that restoration of tidal influence to leveed wetlands can rapidly restore some components of estuarine wetland ecosystems but that recovery of other components will take longer and may depend on the extent of anthropogenic modification in the surrounding landscape.  相似文献   

2.
The restoration of tidal wetland and seagrass systems has the potential for significant greenhouse gas benefits, but project-level accounting procedures have not been available at an international scale. In this paper, we describe the Verified Carbon Standard Methodology for Tidal Wetland and Seagrass Restoration, which provides greenhouse gas accounting procedures for marsh, mangrove, tidal forested wetland, and seagrasses systems across a diversity of geomorphic conditions and restoration techniques. We discuss and critique the essential science and policy elements of the methodology and underlying knowledge gaps. We developed a method for estimating mineral-protected (recalcitrant) allochthonous carbon in tidal wetland systems using field-collected soils data and literature-derived default values of the recalcitrant carbon that accompanies mineral deposition. We provided default values for methane emissions from polyhaline soils but did not provide default values for freshwater, oligohaline, and mesohaline soils due to high variability of emissions in these systems. Additional topics covered are soil carbon sequestration default values, soil carbon fate following erosion, avoided losses in organic and mineral soils, nitrous oxide emissions, soil profile sampling methods, sample size, prescribed fire, additionality, and leakage. Knowledge gaps that limit the application of the methodology include the estimation of CH4 emissions from fresh and brackish tidal wetlands, lack of validation of our approach for the estimation of recalcitrant allochthonous carbon, understanding of carbon oxidation rates following drainage of mineral tidal wetland soils, estimation of the effects of prescribed fire on soil carbon stocks, and the analysis of additionality for projects outside of the USA.  相似文献   

3.
Tidal marsh (re)creation on formerly embanked land is increasingly executed along estuaries and coasts in Europe and the USA, either by restoring complete or by reduced tidal exchange. Ecosystem functioning and services are largely affected by the hydro-geomorphologic development of these areas. For natural marshes, the latter is known to be steered by feedbacks between tidal inundation and sediment accretion, allowing marshes to reach and maintain an equilibrium elevation relative to the mean sea level. However, for marsh restoration sites, these feedbacks may be disturbed depending on the restoration design. This was investigated by comparing the inundation-elevation change feedbacks in a natural versus restoration site with reduced tidal exchange in the Scheldt estuary (Belgium). This study analyzes long-term (9 years) datasets on elevation change and tidal inundation properties to disentangle the different mechanisms behind this elevation-inundation feedback. Moreover, subsequent changes in sediment properties that may affect this feedback were explored. In the restoration area with reduced tidal exchange, we found a different elevation-inundation feedback than on natural marshes, which is a positive feedback on initially high sites (i.e., sediment accretion leads to increasing inundation, hence causing accelerating sediment accretion rates) and a gradual silting up of the whole area. Furthermore, there is evidence for the presence of a relict consolidated sediment layer. Consequently, shallow subsidence is less likely to occur. Although short-term ecological development of the tidal marsh was not impeded, long-term habitat development may be affected by the differences in hydro-geomorphological interactions. An increase of inundation frequency on the initially high sites may cause inhibition of habitat succession or even reversed succession. Over time, the climax state of the restoration area may be different compared to natural marshes. Moreover, sediment-related ecosystem services, such as nutrient and carbon burial, may be positively influenced because of continuing sedimentation, although flood water storage potential will decrease with increasing elevation. Depending on the restoration goals, ecosystem trajectories and delivery of ecosystem services can be controlled by adaptive management of the tidal volume entering the restoration area.  相似文献   

4.
Tidal wetlands play an important role with respect to climate change because of both their sensitivity to sea-level rise and their ability to sequester carbon dioxide from the atmosphere. Policy-based interest in carbon sequestration has increased recently, and wetland restoration projects have potential for carbon credits through soil carbon sequestration. We measured sediment accretion, mineral and organic matter accumulation, and carbon sequestration rates using 137Cs and 210Pb downcore distributions at six natural tidal wetlands in the San Francisco Bay Estuary. The accretion rates were, in general, 0.2?C0.5?cm?year?1, indicating that local wetlands are keeping pace with recent rates of sea-level rise. Mineral accumulation rates were higher in salt marshes and at low-marsh stations within individual sites. The average carbon sequestration rate based on 210Pb dating was 79?g?C?m?2?year?1, with slightly higher rates based on 137Cs dating. There was little difference in the sequestration rates among sites or across stations within sites, indicating that a single carbon sequestration rate could be used for crediting tidal wetland restoration projects within the Estuary.  相似文献   

5.
Spatially varying water-level regimes are a factor controlling estuarine and tidal-fluvial wetland vegetation patterns. As described in Part I, water levels in the Lower Columbia River and estuary (LCRE) are influenced by tides, river flow, hydropower operations, and coastal processes. In Part II, regression models based on tidal theory are used to quantify the role of these processes in determining water levels in the mainstem river and floodplain wetlands, and to provide 21-year inundation hindcasts. Analyses are conducted at 19 LCRE mainstem channel stations and 23 tidally exposed floodplain wetland stations. Sum exceedance values (SEVs) are used to compare wetland hydrologic regimes at different locations on the river floodplain. A new predictive tool is introduced and validated, the potential SEV (pSEV), which can reduce the need for extensive new data collection in wetland restoration planning. Models of water levels and inundation frequency distinguish four zones encompassing eight reaches. The system zones are the wave- and current-dominated Entrance to river kilometer (rkm) 5; the Estuary (rkm-5 to 87), comprised of a lower reach with salinity, the energy minimum (where the turbidity maximum normally occurs), and an upper estuary reach without salinity; the Tidal River (rkm-87 to 229), with lower, middle, and upper reaches in which river flow becomes increasingly dominant over tides in determining water levels; and the steep and weakly tidal Cascade (rkm-229 to 234) immediately downstream from Bonneville Dam. The same zonation is seen in the water levels of floodplain stations, with considerable modification of tidal properties. The system zones and reaches defined here reflect geological features and their boundaries are congruent with five wetland vegetation zones.  相似文献   

6.
An integrated marsh management (IMM) project in an urbanized watershed on Long Island, New York, USA, aimed to mitigate salt marsh degradation and to reduce mosquito production by an innovative combination of restoration and open marsh water management methods. The grid ditch network at two treatment marshes was replaced with naturalized tidal channels and ponds. Effects of the hydrologic alterations were monitored utilizing a before–after–control–impact approach. The treatment marshes experienced a number of beneficial outcomes including a fourfold reduction in the invasive Phragmites australis and increased native vegetation cover in the most degraded portions of the marsh, increased abundance and diversity of marsh killifish and estuarine nekton species, higher shorebird and waterfowl densities, and increased avian species diversity. The successful implementation of IMM concept led to improved marsh health and diminished mosquito production. Therefore, this study may serve as a template for similar large-scale integrated salt marsh restoration projects.  相似文献   

7.
The eastern oyster, Crassostrea virginica, is a prominent ecosystem engineer, whose reefs exhibit strikingly consistent morphologies at multiple spatial scales throughout its North American range. These distinct morphologies are thought to form by interactions of nascent reef structures with hydrodynamics. We carried out two field studies to determine if historical reef configurations applied in a restoration context would improve reef persistence and restoration outcomes. We collected seabed and water column observations across constructed reefs of three orientations representative of those found historically throughout the oyster’s range: parallel or perpendicular to tidal currents or circular. Areas adjacent to reefs were sites of fine sediment trapping, with lower flow velocities, evidence of particle settling, and more fine sediments on the seabed relative to off-reef reference sites. The water column above the reef crest exhibited higher acoustic backscatter, higher flow velocities, and larger particles in suspension, consistent with local erosion of flocculated fine sediment from the reef crest. Perpendicular reefs produced conditions that were more conducive to reef persistence and improved oyster performance, including high flow velocities and enhanced resuspension of sediments from the reef, compared to parallel or circular reefs. Particle trapping in areas between reefs has the potential to inhibit reef growth between existing reef structures, providing support for hypotheses of landscape-scale reef pattern formation. Oyster reef restoration efforts can benefit from this improved understanding of biophysical interactions arising from reef orientation that contribute to sediment dynamics on constructed oyster reefs.  相似文献   

8.
湿陷性黄土地区岩土工程往往涉及大量挖方填方工程，极易引发一系列的地面沉降和植被破坏问题。本文基于SBAS-InSAR技术结合遥感数据处理对延安新区平山造城工后地面沉降及植被恢复特征进行了分析。首先，通过目视解译及DEM提取，获取工程基本特征；随后，基于SBAS-InSAR技术对新区工后地面沉降进行探测；最后，利用遥感提取新区的NDVI时序数据。结果表明:(1)延安新区建筑工程建设滞后挖填方工程约2a，填方区域沿着原始地形的沟谷展布，挖填方体最大厚度均超过90m；(2)延安新区主要沉降区为填方区域，2017~2018年最大沉降速率达45mm ·a-1，主要建筑工程所处的挖方区无明显地面沉降，工程边坡大多处于稳定状态；(3)延安新区2013~2015年NDVI平均值增长230%，2015~2018年增长50%，植被恢复明显。延安新区平山造城工程的规划建设合理的规避了地面沉降及缓解了生态环境恶化，研究成果可为类似工程建设提供科学参考依据。  相似文献   

9.
Inundation patterns and plant establishment were observed in a riparian wetland mitigation project following predictions made by a dynamic water budget model. The model combined field measurements of hydrologic variables, historical weather observations, and digital elevation data in a geographic information system. It identified one excavation among four candidates as most likely to thrive in a harsh environment with periodic drought and extreme water level fluctuations. Observed, pulsing inundation patterns are consistent with predictions made by the model. Numerous native species, many found on site, were planted in the excavation; more than half of them survived a year-long period of observation with months of no standing water. The most successful species were graminoids (especially Cyperus acuminatus), a forb (Eclipta prostrata), and herbs (especially Hibiscus laevis and Polygonum densiflorum) capable of extracting soil moisture during prolonged dry spells.  相似文献   

10.
Coastal and inland waters are continuing to decline in many parts of the world despite major efforts made to restore them. This is due in part to the inadequate role that ecological science has played in shaping restoration efforts. A significant amount of fundamental ecological knowledge dealing with issues such as system dynamics, state changes, context-dependency of ecological response, and diversity is both under-used by managers and practitioners and under-developed by ecologists for use in real-world applications. Some of the science that is being ‘used’ has not been adequately tested. Thus, restoration ecology as a science and ecological restoration as a practice are in need of reform. I identify five ways in which our ecological knowledge should be influencing restoration to a far greater extent than at present including a need to: shift the focus to restoration of process and identification of the limiting factors instead of structures and single species, add ecological insurance to all projects, identify a probabilistic range of possible outcomes instead of a reference condition, expand the spatial scale of efforts, and apply hierarchical approaches to prioritization. Prominent examples of restoration methods or approaches that are commonly used despite little evidence to support their efficacy are highlighted such as the use of only structural enhancements to restore biodiversity. There are also major gaps in scientific knowledge that are of immediate need to policy makers, managers, and restoration practitioners including: predictive frameworks to guide the restoration of ecological processes, identification of social-ecological feedbacks that constrain ecosystem recovery and data to support decisions of where and how to implement restoration projects to achieve the largest gains. I encourage ecologists to respond to the demand for their scientific input so that restoration can shift from an engineering-driven process to a more sustainable enterprise that fully integrates ecological processes and social science methods.  相似文献   

11.
This study evaluated the use by fish of restored tidal wetlands and identified links between fish species composition and habitat characteristics. We compared the attributes of natural and constructed channel habitats in Sweetwater Marsh National Wildlife Refuge, San Diego Bay, California, by using fish monitoring data to explore the relationships between channel environmental characteristics and fish species composition. Fishes were sampled annually for 8 yr (1989–1996) at eight sampling sites, four in constructed marshes and four in natural marshes, using beach seines and blocking nets. We also measured channel habitat characteristics, including channel hydrology (stream order), width and maximum depth, bank slope, water quality (DO, temperature, salinity), and sediment composition. Fish colonization was rapid in constructed channels, and there was no obvious relationship between channel age and species richness or density. Total richness and total density did not differ significantly between constructed and natural channels, although California killifish (Fundulus parvipinnis) were found in significantly higher densities in constructed channels. Multivariate analyses showed fish assemblage composition was related to channel habitat characteristics, suggesting a channel’s physical properties were more important in determining fish use than its restoration status. This relationship highlights the importance of designing restoration projects with natural hydrologic features and choosing proper assessment criteria in order to avoid misleading interpretations of constructed channel success. We recommend that future projects be designed to mimic natural marsh hydrogeomorphology and diversity more closely, the assessment process utilize better estimates of fish habitat function (e.g., individual and community-based species trends, residence time, feeding, growth) and reference site choice, and experimental research be further incorporated into the restoration process.  相似文献   

12.
Wetlands are commonly assessed for ecological condition and biological integrity using a three-tiered framework of landscape-scale assessment, rapid assessment protocols, and intensive biological and physiochemical measurements. However, increased inundation resulting from accelerated sea level rise (SLR) is negatively impacting tidal marsh ecosystem functions for US Northeast coastal wetlands, yet relative vulnerability to this stressor is not incorporated in condition assessments. This article assesses tools available to measure coastal wetland vulnerability to SLR, including measurements made as part of traditional rapid condition assessments (e.g., vegetation communities, soil strength), field and remote sensing-based measurements of elevation, VDatum, and Sea Level Affecting Marshes Model (SLAMM) model outputs. A vulnerability metric that incorporates these tools was calibrated and validated using recent rates of marsh vegetation losses (1972–2011) as a surrogate for future vulnerability. The metric includes complementary measures of elevation capital, including the percentage of high vs. low marsh vegetation, Spartina alterniflora height, elevation measurements, and SLAMM outputs that collectively explained 62% of the variability in recent rates of marsh vegetation loss. Stepwise regression revealed that all three elements (elevation, vegetation measures, and SLAMM outputs) explained significant and largely unique components of vulnerability to SLR, with the greatest level of overlap found between SLAMM outputs and elevation metrics. While soil strength varied predictably with habitat zone, it did not contribute significantly to the vulnerability metric. Despite the importance of determining wetland elevation above key tidal datums of mean sea level and mean high water, we caution that VDatum was found to perform poorly in back-barrier estuaries. This factor makes it difficult to compare elevation capital among marshes that differ in tidal range and poses accuracy problems for broad-scale modeling efforts that require accurate tidal datums. Given the pervasive pattern of coastal wetland drowning occurring in the Northeastern USA and elsewhere, we advocate that compilation of regional data on marsh habitats and vulnerability to SLR is crucial as it permits agencies to target adaptation to sites based on their vulnerability or mixture of habitats, it helps match sites to appropriate interventions, and it provides a broader regional context to site-specific management actions. Without such data, adaptation actions may be implemented where action is not necessary and to the disadvantage of vulnerable sites where opportunities for successful adaptation will be missed.  相似文献   

13.
Estuary evolution is investigated using the hydrodynamic and sediment transport model, Delft3D, to study the response of a dammed tidal basin to restored tidal processes. The development of decadal (10-year) morphological simulations of the restored estuary required simplifying several data inputs and implementing a time-scale acceleration technique. An innovative river sediment discharge schematization was developed that connected sediment discharge to morphological change in the estuary. Mud erodibility parameters were determined from laboratory analysis of sediment cores from the modern lakebed and statistical refinement with a Bayes network of the probability of occurrence. The changing estuary morphology appears to have a dominant impact on the physical habitat (substrate, inundation frequency, mean salinity, and salinity range). The numerical model provides a tool to compare the functions of the historical estuary and possible future alternatives for a restored estuary. Sensitivity of the morphological model to sediment types and erodibility parameters was also examined. A conceptual model covering morphology and indicators of physical habitat for three phases of estuary evolution during restoration is presented that could be applied to estuarine systems that are severely out of equilibrium.  相似文献   

14.
本文对甘南大夏河流域现存的生态环境问题进行了识别与诊断,对其生态问题成因进行了剖析,提出了相应的修复措施。研究显示,矿山环境破坏、草地退化沙化、水土流失、湿地萎缩和生物多样性减少是甘南大夏河流域目前主要的生态环境问题。针对这些主要问题,基于山水林田湖草沙一体化生态修复理念,划分了三个生态修复单元,确立了自然恢复、保护保育、辅助再生、生态重塑四种生态修复模式,提出了以水源涵养为核心的区域生态保护与修复策略,重点布设与实施矿山生态修复、草原生态保护修复、小流域生态保护修复、湿地和生物多样性保护修复、生态环境监测预警与评价系统等五大生态保护与修复工程。该研究可为甘南大夏河流域生态保护与修复提供借鉴与参考。  相似文献   

15.
中国水文循环与水体研究进展   总被引：7，自引：0，他引：7       下载免费PDF全文
根据2002-2005年中国公开发表的关于水科学研究的论文及国家重大攻关项目和国家自然科学基金项目的科研报告,综述了近年来中国在水文循环诸要素如降水、径流、蒸发,水文模型,河流与泥沙、湖泊、沼泽与湿地、冰川与冻土以及地下水与土壤水等方面研究取得的主要成果和进展.  相似文献   

16.
Through their physiological effects on ion, oxygen, and carbon balance, respectively, salinity, sulfide, and prolonged flooding combine to constrain the invasion and spread ofPhragmites in tidal wetlands. Initial sites of vigorous invasion by seed germination and growth from rhizome fragments appear limited to sections of marsh where salinity is <10‰, sulfide concentrations are less than 0.1 mM, and flooding frequency is less than 10%. In polyhaline tidal wetlands the invasion sites include the upland fringe and some high marsh creek banks. The zones of potential invasion tend to be larger in marshes occupying lower-salinity portions of estuaries and in marshes that have been altered hydrologically. Owing to clonal integration and a positive feedback loop of growth-induced modification of edaphic soil conditions, however, a greater total area of wetland is susceptible toPhragmites expansion away from sites of establishment. Mature clones have been reported growing in different marshes with salinity up to 45‰, sulfide concentration up to 1.75 mM, and flooding frequency up to 100%. ForPhragmites establishment and expansion in tidal marshes, windows of opportunity open with microtopographic enhancement of subsurface drainage patterns, marsh-wide depression of flooding and salinity regimes, and variation in sea level driven by global warming and lunar nodal cycles. To avoidPhragmites monocultures, tidal wetland creation, restoration, and management must be considered within the context of these different scales of plant-environment interaction.  相似文献   

17.
Functional trajectory models were used to assess the restoration of ecological functions in two transplanted eelgrass (Zostera marina L.) beds compared to three natural, reference beds in the Great Bay Estuary, New Hamsphire. Functional trajectory models describe the development of ecological functions over time in restored habitats relative to levels of function in natural habitats. We present the first application of trajectory models to transplanted seagrass and evaluate the utility of these models as a tool for assessing seagrass restoration. The project was an analysis of 9 yr of monitoring data, the longest monitoring of transplanted eelgrass to date. We used trajectory models to assess the time course of development of functions in transplanted beds by evaluating statistical trends, and to determine functional equivalence, defined as the time when functions in a transplanted bed reach an asymptote and are no more than 1 standard deviation below the reference mean. The functions modeled included primary production, 3-dimensional habitat structure, faunal use, and sediment filtering and trapping. Measured proxies for primary production and habitat structure increased logistically (sigmoidally) with time, reaching functional equivalence after 3 yr. In transplanted beds, trends in habitat use by infaunal invertebrates and fish were logarithmic, and values were functionally equivalent 2–4 yr after transplanting. We saw no trend in sediment filtering and trapping capacity of transplanted eelgrass over the 9 yr. Measures of function in both reference and transplanted beds fluctuated due to natural and anthropogenic disturbances. After reaching equivalence, measures of function in transplanted beds tracked those in reference beds, exhibiting long-term persistence and rebounding from disturbances similarly to reference beds. Trajectory models can illustrate the time course of eelgrass bed development, aiding the design of monitoring programs and the evaluation of ecological functional equivalence in seagrass restoration projects.  相似文献   

18.
Chesapeake Bay tidal wetlands are experiencing a broad-scale, aggressive invasion by the non-native, clonal grass Phragmites australis. The grass is often managed with herbicides in efforts to restore native plant communities and wildlife habitat. Management efforts, however, can act as a disturbance, resulting in increased light availability, potentially fostering reinvasion from soil seedbanks. If native vegetation establishes quickly from seedbanks, the site should have greater resiliency against invasion, while disturbed sites where native plants do not rapidly establish may be rapidly colonized by P. australis. We surveyed the soil seedbank of three vegetation cover types in five Chesapeake Bay subestuaries: areas where P. australis had been removed, where P. australis was left intact, and with native, reference vegetation. We determined the total germination, the proportion of the seedbank that was attributable to invasive species, the richness, the functional diversity, and the overall composition of the seedbanks in each of the cover types (i.e., plots). After 2 years of herbicide treatment in the P. australis removal plots, vegetation cover type impacted the total germination or the proportion of invasive species in the seedbank. In contrast, we also found that seedbank functional composition in tidal brackish wetlands was not influenced by vegetation cover type in most cases. Instead, plots within a subestuary had similar seedbank functional composition across the years and were composed of diverse functional groups. Based on these findings, we conclude that plant community recovery following P. australis removal is not seed-limited, and any lack of native vegetation recruitment is likely the result of yet-to-be-determined abiotic factors. These diverse seedbanks could lead to resilient wetland communities that could resist invasions. However, due to the prevalence of undesirable species in the seedbank, passive revegetation following invasive plant removal may speed up their re-establishment. The need for active revegetation will need to be assessed on a case-by-case basis to ensure restoration goals are achieved.  相似文献   

19.
潮滩剖面形态与泥沙分选研究进展   总被引：1，自引：0，他引：1       下载免费PDF全文
潮滩剖面形态与多组分泥沙分选是海岸动力学与河口、海岸地貌学的重要研究内容,对保持生物多样性、研究沉积历史和沿海工程评估等具有重要的实际意义。从现场观测、理论解析和数值模拟等方面,归纳了在潮滩剖面形态特征与多组分泥沙分选方面研究的主要进展。回顾了潮滩剖面形态分别在潮流和波浪主导下的经典理论解析解,剖析了包括潮流、波浪泥沙来源及特性等主要影响因子以及植被、海平面上升、围垦工程等其他影响因子对潮滩剖面形态水平向、垂向泥沙分选过程的作用机理,同时提出了考虑水动力、生物作用、人类活动等多因子耦合作用下潮滩演变研究以及定量化预测方向的若干亟待解决的科学问题。  相似文献   

20.
Inactive deltas are more extensive than active deltas in most deltaic landscapes; thus, the subsurface generally is dominated by mineral sediments that rapidly accreted at different times, whereas the landscape at any one time generally is dominated by ephemeral emergent wetlands that are slowly accreting via vegetative growth. Subsidence is slow enough in most deltas that emergent wetlands, although ephemeral, can persist for millennia but accelerating global sea level rise probably will slow wetland creation in active deltas and accelerate the loss of existing wetlands in inactive deltas this century worldwide. A recent publication created confusion regarding the effects of river management on coastal Louisiana, where spatially variable subsidence is great enough in some areas to mimic extremely rapid sea level rise. I show how integrating Successional Ecology with the Delta Lobe Cycle, and correcting some omissions and errors in recent publications, clarifies the effects of river management in coastal Louisiana and provides a framework for predicting deltaic landscape dynamics worldwide. Successional Ecology provides a framework for understanding changes in natural and managed environments worldwide, whereas the Delta Lobe Cycle provides a framework for understanding river-dominated deltas worldwide. Sediment diversions are a form of river management that removes artificial barriers to river flow and are designed to mimic hydrologic conditions during the active delta stage of the Delta Lobe Cycle by focusing rapid mineral sedimentation in open water and thus creating new emergent wetlands. Freshwater diversions are another form of river management that also removes artificial barriers to river flow but are designed to mimic hydrologic conditions during the inactive stages of the Delta Lobe Cycle by reducing salinity stress over large areas of emergent wetlands and thus promoting marsh vertical accretion via vegetative growth. The Delta Lobe Cycle and both types of river diversions also create salinity gradients that simultaneously increase the sensitivity of emergent wetlands to disturbance while increasing the ability of emergent wetlands to recover from disturbance. Freshwater diversions only slow the loss of existing wetlands because the natural Delta Lobe Cycle, artificial channels that increase salinity stress, artificial ridges that increase flooding stress, and repeated disturbances eventually will cause vertical accretion via vegetative growth to become inadequate. Formally integrating these concepts might advance research and restoration in deltaic landscapes worldwide especially in the majority of deltas where inactive deltas are more extensive than active deltas.  相似文献   

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