Showing papers in "Environmental Management in 1990"

Physical habitat template of lotic systems: Recovery in the context of historical pattern of spatiotemporal heterogeneity

Abstract: Spatial and temporal environmental heterogeneity in lotic ecosystems can be quantitatively described and identified with characteristic levels of ecological organization. The long-term pattern of physicochemical variability in conjunction with the complexity and stability of the substratum establishes a physical habitat template that theoretically influences which combinations of behavioral, physiological and life history characteristics constitute appropriate “ecological strategies” for persistence in the habitat. The combination of strategies employed will constrain ecological response to and recovery from disturbance. Physical habitat templates and associated ecological attributes differ geographically because of biogeoclimatic processes that constrain lotic habitat structure and stability and that influence physicochemical variability and disturbance patterns (frequency, magnitude, and predictability). Theoretical considerations and empirical studies suggest that recovery from natural and anthropogenic disturbance also will vary among lotic systems, depending on historical temporal variability regime, degree of habitat heterogeneity, and spatial scale of the perturbation. Characterization of physical habitat templates and associated ecological dynamics along gradients of natural disturbance would provide a geographic framework for predicting recovery from anthropogenic disturbance for individual streams. Description of lotic environmental templates at the appropriate spatial and temporal scale is therefore desirable to test theoretical expectations of biotic recovery rate from disturbance and to guide selection of appropriate reference study sites for monitoring impacts of anthropogenic disturbance. Historical streamflow data, coupled with stream-specific thermal and substratum-geomorphologic characteristics, are suggested as minimum elements needed to characterize physical templates of lotic systems.

Role of Refugia in Recovery from Disturbances: Modern Fragmented and Disconnected River Systems

Abstract: Habitats or environmental factors that convey spatial and temporal resistance and/or resilience to biotic communities that have been impacted by biophysical disturbances may be called refugia. Most refugia in rivers are characterized by extensive coupling of the main channel with adjacent streamside forests, floodplain features, and groundwater. These habitats operate at different spatial scales, from localized particles, to channel units such as pools and riffles, to reaches and longer sections, and at the basin level. A spatial hierarchy of different physical components of a drainage network is proposed to provide a context for different refugia. Examples of refugia operating at different spatial scales, such as pools, large woody debris, floodplains, below dams, and catchment basins are discussed. We hope that the geomorphic context proposed for examining refugia habitats will assist in the conservation of pristine areas and attributes of river systems and also allow a better understanding of rehabilitation needs in rivers that have been extensively altered.

Overview of case studies on recovery of aquatic systems from disturbance

Abstract: An extensive review of the published literature identified more than 150 case studies in which some aspect of resilience in freshwater systems was reported. Approximately 79% of systems studied were lotic and the remainder lentic. Most of the stressor types were chemical with DDT (N=29) and rotenone (N=15) the most common. The most common nonchemical stressors were logging activity (N=16), flooding (N=8), dredging (N=3), and drought (N=7). The variety of endpoints to which recovery could be measured ranged from sparse data for phytoplankton (N=13), periphyton (N=6), and macrophytes (N=8) to relatively more data for fish (N=412) and macroinvertebrates (N=698). Unfortunately the same characteristics were rarely measured consistently among sites. For example, with respect to fish, more than 30 different species were studied and recovery was measured in many ways, most commonly on the basis of: (1) first reappearance of the species, (2) return time of predisturbance densities, and (3) return time of predisturbance average individual size. Based on these criteria, all systems in these studies seem to be resilient to most disturbances with most recovery times being less than three years. Exceptions included when (1) the disturbance resulted in physical alteration of the existing habitat, (2) residual pollutants remained in the system, or (3) the system was isolated and recolonization was suppressed.

Collapse of riparian poplar forests downstream from dams in western prairies: Probable causes and prospects for mitigation

Abstract: Although historically abundant, the riparian poplar forests of the western prairies are now endangered as a result of the damming and diversion of rivers in this region Recent reports have described substantial declines of riparian poplar forests downstream from dams in Alberta, Canada; Montana, North Dakota, Wyoming, Colorado, and Arizona, USA The present report analyzes the forest and hydrological conditions reported previously in order to clarify the causes of the downstream forest decline Dams were found to contribute to forest failure by (1) reducing downstream flows and/or (2) altering flow patterns to attenuate spring flooding and/or stabilize summer flows Reduced flows are reported to induce drought stress, which is particularly lethal to seedlings and very old poplars The artificial moderation of spring flooding may inhibit the formation of seedbeds essential for seedling replenishment Increased river valley development involving cattle grazing, agricultural clearing, and direct harvesting of trees also contributes to forest failure Potential methods for mitigating the impacts of dams on downstream forests include downstream flow schedules that (1) retain occasional spring flooding, (2) taper off rather than abruptly drop downstream flow, and (3) provide adequate flows throughout the summer Poplar forest stabilization and recovery can be further promoted by fencing to protect trees from livestock grazing and trampling, or artificial site preparation such as cultivation or scarification to encourage poplar regeneration

Recovery of lotic communities and ecosystems from disturbance: a narrative review of case studies

Abstract: We present a narrative account of case studies of the recovery of flowing water systems from disturbance, focusing on the investigators' conclusions about recovery time and the factors contributing to recovery. We restrict our attention to case studies in which the recovery of some biological property of the system has been examined, excluding those that deal only with physical or chemical properties. Although natural processes and rates of recovery are emphasized, studies of reclamation or restoration of damaged ecosystems are included where they contribute to an understanding of recovery processes. For the majority of studies examined, the systems recovered quite rapidly. The most commonly cited reasons for short recovery times were: (1) life history characteristics that allowed rapid recolonization and repopulation of the affected areas, (2) the availability and accessibility of unaffected up-stream and downstream areas and internal refugia to serve as sources of organisms for repopulation, (3) the high flushing rates of lotic systems that allowed them to quickly dilute or replace polluted waters, and (4) the fact that lotic systems are naturally subjected to a variety of disturbances and the biota have evolved life history characteristics that favor flexibility or adaptability. In general, longer recovery times were observed in disturbances, such as channelization, that resulted in alterations to physical conditions. This review also indicates that much of our knowledge of recovery in lotic ecosystems is fragmented and uncoordinated. In addition to establishing the bounds of recovery time, our review identifies some research gaps that need to be filled.

Environmental variation, life history attributes, and community structure in stream fishes: Implications for environmental management and assessment

Abstract: Fishes in midwestern streams of the United States experience strong upstream—downstream gradients in natural environmental variability. Upstream fishes experience greater temporal variability in physical—chemical conditions than downstream fishes, particularly in intermittent streams. Associated with these changes in environmental variability, basic changes occur in life history attributes and temporal variation in community structure of stream fishes. As a whole, upstream species have a shorter life-span, smaller body size, and earlier sexual maturity than downstream species. Descriptive studies also suggest upstream species exhibit more rapid recolonization after severe physical disturbance than downstream species, and fish community structure is temporally more variable in upstream than downstream areas. These longitudinal differences in life history characteristics suggest that upstream fish communities will exhibit more rapid recovery from severe anthropogenic disturbances than downstream fish communities. The greater temporal variability of fish community structure in upstream areas also suggests it will be more difficult in upstream than downstream areas to use fish-based indices to distinguish whether subtle changes in environmental quality are due to natural or anthropogenic disturbances. Long-term monitoring of fishes throughout drainage basins is critically needed to establish more precisely the natural range of variation in community structure. Such monitoring will allow regulatory agencies to distinguish, with greater confidence, the influence of anthropogenic disturbances on stream fishes from the influence of natural environmental variation.

Disturbance and recovery of large floodplain rivers

Abstract: Disturbance in a river-floodplain system is defined as an unpredictable event that disrupts structure or function at the ecosystem, community, or population level. Disturbance can result in species replacements or losses, or shifts of ecosystems from one persistent condition to another. A disturbance can be a discrete event or a graded change in a controlling factor that eventually exceeds a critical threshold. The annual flood is the major driving variable that facilitates lateral exchanges of nutrients, organic matter, and organisms. The annual flood is not normally considered a disturbance unless its timing or magnitude is “atypical.” The record flood of 1973 had little effect on the biota at a long-term study site on the Mississippi River, but the absence of a flood during the 1976–1977 Midwestern drought caused short- and long-term changes. Body burdens of contaminants increased temporarily in key species, because of increased concentration resulting from reduced dilution. Reduced runoff and sediment input improved light penetration and increased the depth at which aquatic macrophytes could grow. Developing plant beds exerted a high degree of biotic control and were able to persist, despite the resumption of normal floods and turbidity in subsequent years. In contrast to the discrete event that disturbed the Mississippi River, a major confluent, the Illinois River, has been degraded by a gradual increase in sediment input and sediment resuspension. From 1958 to 1961 formerly productive backwaters and lakes along a 320-km reach of the Illinois River changed from clear, vegetated areas to turbid, barren basins. The change to a system largely controlled by abiotic factors was rapid and the degraded condition persists. Traditional approaches to experimental design are poorly suited for detecting control mechanisms and for determining the critical thresholds in large river-floodplains. Large river-floodplain systems cannot be manipulated or sampled as easily as small streams, and greater use should be made of man-made or natural disturbances and environmental restoration as opportunistic experiments to measure thresholds and monitor the recovery process.

Assessing ecological risk on a regional scale

Abstract: Society needs a quantitative and systematic way to estimate and compare the impacts of environmental problems that affect large geographic areas. This paper presents an approach for regional risk assessment that combines regional assessment methods and landscape ecology theory with an existing framework for ecological risk assessment. Risk assessment evaluates the effects of an environmental change on a valued natural resource and interprets the significance of those effects in light of the uncertainties identified in each component of the assessment process. Unique and important issues for regional risk assessment are emphasized; these include the definition of the disturbance scenario, the assessment boundary definition, and the spatial heterogeneity of the landscape.

Disturbance regimes, resilience, and recovery of animal communities and habitats in lotic ecosystems

Abstract: Disturbance regime is a critical organizing feature of stream communities and ecosystems. The position of a given reach in the river basin and the sediment type within that reach are two key determinants of the frequency and intensity of flow-induced disturbances. We distinguish between predictable and unpredictable events and suggest that predictable discharge events are not disturbances. We relate the dynamics of recovery from disturbance (i.e., resilience) to disturbance regime (i.e., the disturbance history of the site). The most frequently and predictably disturbed sites can be expected to demonstrate the highest resilience. Spatial scale is an important dimension of community structure, dynamics, and recovery from disturbance. We compare the effects on small patches (⩽1 m2) to the effects of large reaches at the river basin level. At small scales, sediment movements and scour are major factors affecting the distribution of populations of aquatic insects or algae. At larger scales, we must deal with channel formation, bank erosion, and interactions with the riparian zone that will affect all taxa and processes. Our understanding of stream ecosystem recovery rests on our grasp of the historical, spatial, and temporal background of contemporary disturbance events.

Recovery of lotic macroinvertebrate communities from disturbance

Abstract: Ecosystem disturbances produce changes in macrobenthic community structure (abundances, biomass, and production) that persist for a few weeks to many decades. Examples of disturbances with extremely long-term effects on benthic communities include contamination by persistent toxic agents, physical changes in habitats, and altered energy inputs. Stream size, retention, and local geomorphology may ameliorate the influence of disturbances on invertebrates. Disturbances can alter food webs and may select for favorable genotypes (e.g., insecticidal resistance). Introductions of pesticides into lotic ecosystems, which do not result in major physical changes within habitats, illustrate several factors that influence invertebrate recovery time from disturbance. These include: (1) magnitude of original contamination, toxicity, and extent of continued use; (2) spatial scale of the disturbance; (3) persistence of the pesticide; (4) timing of the contamination in relation to the life history stages of the organisms; (5) vagility of populations influenced by pesticides; and (6) position within the drainage network. The ability of macroinvertebrates to recolonize denuded stream habitats may vary greatly depending on regional life histories, dispersal abilities, and position within the stream network (e.g., headwaters vs larger rivers). Although downstream drift is the most frequently cited mechanism of invertebrate recolonization following disturbance in middle- and larger-order streams, evidence is presented that shows aerial recolonization to be potentially important in headwater streams. There is an apparent stochastic element operating for aerial recolonization, depending on the timing of disturbance and flight periods of various taxa. Available evidence indicates that recolonization of invertebrate taxa without an aerial adult stage requires longer periods of time than for those that possess winged, terrestrial adult stages (i.e., most insects). Innovative, manipulative experiments are needed in order to address recolonization mechanisms of animals inhabiting streams that differ in size, latitude, disturbance frequency and magnitude, as well as the potential influence of early colonists on successional sequences of species following disturbance.

Assemblage stability in stream fishes: A review

Abstract: We quantified the stability of nine stream fish assemblages by calculating coefficients of variation of population size for assemblage members. Coefficients of variation were high and averaged over 96%; indicating that most assemblages were quite variable. Coefficient of variation (CV) estimates were not significantly affected by: (1) years of study, (2) mean abundance, (3) familial classification, or (4) mean interval between collections. We also detected minor regional differences in CVs. The high variability exhibited by many stream fish assemblages suggests that it may be difficult to detect the effects of anthropogenic disturbances using population data alone. Consequently, we urge managers to exercise caution in the evaluation of the effects of these disturbances. More long-term studies of the ecological characteristics of undisturbed stream fish assemblages are needed to provide a benchmark against which disturbed systems can be compared.

Endpoints for regional ecological risk assessments

Abstract: Ecological risk assessments must have clearly defined endpoints that are socially and biologically relevant, accessible to prediction and measurement, and susceptible to the hazard being assessmed. Most ecological assessments do not have such endpoints, in part because the endpoints of toxicity tests or other measurements of effects are used as assessment endpoints. This article distinguishes assessment and measurement endpoints in terms of their roles in risk assessments and explains how the criteria for their selection differ. It then presents critical discussions of possible assessment and measurement endpoints for regional ecological risk assessments. Finally, the article explains how endpoint selection is affected by the goal of the assessment. Generic goals for regional risk assessment include explanation of observed regional effects, evaluation of an action with regional implications, and evaluation of the state of a region. Currently, population level assessment endpoints such as abundance and range are the most generally useful. For higher levels (ecosystems and regions), data are generally not available and the validity of models has not been demonstrated, and for lower level effects (physiological, and organismal) are not relevant. However, landscape descriptors, material export, and other regional-scale measurement end-points show promise for regional assessments.

The meaning and ethics of sustainability

Abstract: Some have argued that the meaning of sustainability varies according to context, forcing us to be as explicit as possible when defining our terms. An argument is offered that disputes this conclusion by maintaining that it is not the meaning of sustainability that changes with respect to context, but rather our understanding of the context itself. This is frequently apparent in contradictions that arise when conceiving each context in terms of sustainability. If this argument is correct, then we should be concerned not with the “meaning” of sustainability but rather the implications of sustainability as they affect the status quo. And in order to do this we must be prepared to answer the question: Why is sustainability desirable? This approach is illustrated through a preliminary conceptual and ethical analysis of ecologically sustainable development.

Indicators of Ecosystem Recovery

Abstract: Assessment of ecological changes relative to disturbance, either natural or human-induced, confronts a fundamental problem. Ecosystems are complex, variable, and diverse in nature; consequently, the need for simplification to essential features that would characterize ecosystems adequately is generally acknowledged. Yet there is no firm prescription for what to measure in order to describe the response and recovery of ecosystems to stress. Initial focus is provided by identifying relevant ecological endpoints, i.e., ecological changes of particular relevance to humans. Furthermore, we suggest generic purposes and criteria to be considered in making choices of ecological indicators that relate to those endpoints. Suites of indicators, with variety of purposes, are required to assess response and recovery of most ecosystems and most stresses. We suggest that measures of certain ecosystem processes may provide special insight on the early stages of recovery; the use of functional indicators as complimentary to other biotic indicators is highlighted in an extended example for lotic ecosystems.

Riparian vegetation instream flow requirements: a case study from a diverted stream in the eastern Sierra Nevada, California, USA.

Abstract: A methodology is described that allows determination of instream flow requirements for maintenance of riparian trees. Tree-ring data revealed strong relationships between tree growth and stream flow volume for riparian species at Rush Creek, an alluvial stream within an arid setting; these relationships allowed development of models that predict growth rates from hydrologic variables. The models can be used to assess instream flow requirements under the assumption that certain levels of growth are necessary to maintain the population. There is a critical need for development and use of instream flow methodologies for riparian vegetation, since present methodologies focus on needs of aquatic animals (e.g., fish) and may underestimate needs of the entire riparian ecosystem.

Recovery of lotic periphyton communities after disturbance

Abstract: Periphyton communities represent potentially excellent candidates for assessing the recovery of lotic ecosystems after disturbance. These communities are ubiquitous, relatively easy to sample and measure (in terms of total community biomass), have short generation times, and may influence the recovery rates of higher trophic levels. The first section of this article analyzes how site availability, species availability, and differential species performance influence periphyton successional dynamics. This background information provides a foundation for understanding how periphytic organisms respond after a disturbance. The second section of this article analyzes how periphyton communities respond to four different types of disturbance (flood events, desiccation, organic nutrient enrichment, and toxic metal exposure). Although data are limited, it is concluded that the fast growth rates and short generation times of periphytic organisms, coupled with their flexible life history strategies and good dispersal ability, allow lotic periphyton communities to recover relatively quickly after a disturbance. In addition, disturbance type and severity, local environmental conditions, and site-specific factors also will influence recovery rates.

Birth of a megaproject: political economy of flood control in Bangladesh

Abstract: A major flood control initiative has been launched in Bangladesh under the coordination of the World Bank. The bank's five-year Action Plan is intended to initiate a long-term investment program, the specifics of which remain to be determined. Long-term proposals under consideration include the construction of massive embankments along the great rivers of the Bangladesh delta. The wisdom of such a “structural solution” to Bangladesh's flood problems can be questioned on economic, environmental, and technical grounds. Regrettably, the decision-making process has not encouraged wide debate on these questions.

Recovery processes in lotic ecosystems: Limits of successional theory

Abstract: The concept of succession has a distinguished history in general ecology and has been applied to stream ecosystems with some success. Succession in streams is largely secondary, follows initial floristics models, and occurs through a variety of mechanisms. The process is moderately predictable but is highly influenced by “climatic” factors, particularly nutrient chemistry. In desert streams, succession does not result in a climax state. While evidence is slim, succession may not be a significant process in streams of certain types or in certain regions.

Fire hazards at the urban-wildland interface: What the public expects

Abstract: Urban-wildland issues have become among the most contentious and problematic issues for forest managers. Using data drawn from surveys conducted by the authors and others, this article discusses how public knowledge and perceptions of fire policies and fire hazards change over time, the kinds of policy responses homeowners prefer as a way of preventing fire hazards at the urban-wildland interface, and how citizens view their own obligations as participants in interface issues. These data show that public attitudes toward fire have changed significantly over the past two decades and that educating the public about fire and the managers' use of fire can have positive effects on behavior. Yet, modifying the individual's behavior in regard to interface fire risks must also deal with important issues of individual incentives, the distribution of costs, and unanticipated policy impacts.

A regional framework for establishing recovery criteria

Abstract: Effective assessments of aquatic ecosystem recovery require ecologically sound endpoints against which progress can be measured. Site-by-site assessments of end points and potential recovery trajectories are impractical for water resource agencies. Because of the natural variation among ecosystems, applying a single set of criteria nationwide is not appropriate either. This article demonstrates the use of a regional framework for stratifying natural variation and for determining realistic biological criteria. A map of ecoregions, drawn from landscape characteristics, formed the framework for three statewide case studies and three separate studies at the river basin scale. Statewide studies of Arkansas, Ohio, and Oregon, USA, streams demonstrated patterns in fish assemblages corresponding to ecoregions. The river basin study in Oregon revealed a distinct change at the ecoregion boundary; those in Ohio and Montana demonstrated the value of regional reference sites for assessing recovery. Ecoregions can be used to facilitate the application of ecological theory and to set recovery criteria for various regions of states or of the country. Such a framework provides an important alternative between site-specific and national approaches for assessing recovery rates and conditions.

Island biogeographical theory: Can it be used to predict lotic recovery rates?

Abstract: Classic island biogeographic theory predicts that equilibrium will be reached when immigration and extinction rates are equal. These rates are modified by number of species in source area, number of intermediate islands, distance to recipient island, and size of intermediate islands. This general model has been variously modified and proposed to be a stochastic process with minimal competitive interaction or heavily deterministic. Predictive models of recovery (regardless of the end point chosen) have been based on the appropriateness of the MacArthur-Wilson models. Because disturbance frequency, severity, and intensity vary in their effect on community dynamics, we propose that disturbance levels should first be defined before evaluating the applicability of island biogeographical theory. Thus, we suggest a classification system of four disturbance levels based on recovery patterns by primary and secondary succession and faunal organization by primary (invasion of vacant areas) and secondary (remnant of previous community remains) processes. Level 1A disturbances completely destroy communities with no upstream or downstream sources of colonizers, while some component of near surface interstitial or hyporheic flora and fauna survive level 1B disturbances. Recovery has been reported to take from five years to longer than 25 years, when most invading colonists do not have an aerial form. Level 2 disturbances destroy the communities but leave upstream and downstream colonization sources (level 2A) and, sometimes, a hyporheic pool of colonizers (level 2B). Recovery studies have indicated primary succession and faunal structuring patterns (2A) with recovery times of 90–400 days or secondary succession and faunal structuring patterns (2B) with recovery times of 40–250 days. Level 3 disturbances result in reduction in species abundance and diversity along a stream reach; level 4 disturbances result in reduction of abundance and diversity in discrete patches. Both disturbance types lead to secondary succession and secondary faunal organization. Recovery rates can be quite rapid, varying from less than 10 days to 100 or more days. We suggest that island biogeographical models seem appropriate to recovery by secondary processes after level 3 and 4 disturbances, where competition may be an important organizing factor, while models of numerical abundance and resource tracking are probably of better use where community development is by primary succession (levels 1 and 2). Development of predictive recovery models requires research that addresses a number of fundamental questions. These include the role of hydrologic patterns on colonization dynamics, the role of nonaerial colonizers in recovery from level 1 disturbances, and assessment of the impact of changes in the order of invasion by colonizers of varying energetic efficiencies. Finally, we must be able to assemble these data and determine whether information that guides community organization at one level of disturbance can provide insights into colonization dynamics at other levels.

A proposal to conserve black-footed ferrets and the prairie dog ecosystem

Abstract: Prairie dogs (Cynomys spp.) have been poisoned throughout this century because of grazing competition with livestock. Recent evidence showed these early claims were exaggerated, but animal control was already entrenched in government policy. As a result, ongoing government subsidized poisoning has reduced prairie dogs to about 2% of their former distribution. The reduction of prairie dogs diminished species diversity in the arid grasslands of North America, including the potential extinction of the black-footed ferret (Mustela nigripes). Cost-benefit analysis revealed that poisoning costs more than any grazing benefits accrued. This analysis did not consider the long-term costs of reversing ecosystem degradation, the intangible value of biological diversity as a public benefit, or the depletion of biotic resources as a loss of actual or potential wealth. The government presently finances the poisoning policy and the preservation of endangered species like the black-footed ferret, two apparently conflicting programs. We, therefore, propose an integrated management plan that considers both interests. We propose that federal monies allocated to the poisoning program be converted into a rebate for ranchers who manage livestock while preserving the prairie dog community. This would redirect funds and personnel already allocated to prairie dog eradication to an incentive for ranchers who manage for livestock and wildlife. Livestock interests and grassland biotic diversity would both benefit.

Lack of theoretical basis for predicting rate and pathways of recovery

Abstract: An inadequate basis for precisely predicting the outcome of lotic ecosystem recovery, whether due to unaided natural processes or management techniques or both, exists because: (1) the field of ecology has not yet matured as a rigorous predictive science; (2) the precise sequence of events, including climatic occurrences, affecting the recovery process may be unique events and thus rarely or never repeated; and (3) even when attempts are made to control the recolonization process through introduction of species, etc., the interaction of these species may not follow deterministic models. Although this symposium focuses on lotic ecosystems, such systems are influenced strongly by exports from the surrounding land mass and, under certain circumstances, this may be the overriding influence on the recovery process; therefore, unless the boundary conditions are determined realistically, the recovery process may not follow desirable pathways. Despite the lack of a robust theoretical support base for lotic ecosystem recovery, some remarkable and rapid recoveries have occurred to either a close approximation of the original condition or to a condition ecologically superior to the damaged condition. In some cases, the recovery was due entirely to natural processes and, in others, often followed relatively straightforward management practices. There is evidence indicating that lotic ecosystem restoration is both cost effective and likely to produce satisfying results relatively rapidly. It is both fortunate that this is the case, since society is likely to support such efforts when the results have been extraordinarily successful, and unfortunate since restoration ecology needs a predictive capability.

Comparison of vesicular-arbuscular mycorrhizae in plants from disturbed and adjacent undisturbed regions of a coastal salt marsh in Clinton, Connecticut, USA

Abstract: Roots of salt marsh plant speciesSpartina alterniflora, S. patens, Distichlis spicata, and others were examined for the presence of vesicular-arbuscular mycorrhizal (VAM) fungi. Samples were taken from introduced planted material in a salt marsh restoration project and from native material in adjacent marsh areas along the Indian River, Clinton, Connecticut, USA. After ten years the replanted area still has sites devoid of vegetation. The salt marsh plants introduced there were devoid of VAM fungi, while high marsh species from the adjacent undisturbed region showed consistent infection, leading the authors to suggest that VAM fungal infection of planting stocks may be a factor in the success of marsh restoration.

Ecotoxicological effects assessment in the Netherlands: Recent developments

Abstract: In a recently published annex to the National Environmental Policy Plan of the Netherlands (1989), attention was paid to ecotoxicological effects assessment. The proposed procedure was based on the advice of the Health Council of the Netherlands (1989) on risk assessment of toxic chemicals for ecosystems. The various extrapolation methods described by the Health Council are critically discussed in this paper. The extrapolation method of Van Straalen and Denneman (1989) is evaluated for eight chemicals and 11 aquatic species. Conclusions are drawn about the quality and quantity of the ecotoxicological data needed for aquatic effects assessment. For the soil—a compartment that is often at risk—ecotoxicological effects assessment is not possible because suitable ecotoxicological test methods still have to be developed.

Application of Ecological Theory to Determining Recovery Potential of Disturbed Lotic Ecosystems: Research Needs and Priorities

Abstract: This article summarizes the views of aquatic scientists who gathered to assess the ability of stream ecosystem theory to predict recovery from disturbance. Two views of disturbance were evident: a discrete removal of organisms vs an unusual deviation from normal. These were perceived as applying to different scales and/or objectives. Long-term information is required from both points of view to define recovery. Recovery also may be defined in different ways, but it is clear that recovery has both spatial and temporal components, and includes both physical and biological processes. Consensus was very strong that a major role (and challenge) for theory lies in the understanding of spatial aspects, temporal scales, coupling of physics and biology, and the interaction of these features in recovery processes. Some progress is evident in the articles of this volume, but among the topics identified as critical for further theoretical contributions were: homogeneous vs heterogeneous distribution of disturbance, local extent of disturbance relative to a regional context, critical vs noncritical patches (size and location) of disturbance at different spatial scales and temporal frequencies, delineation of reversible and nonreversible processes, and physical and biological constraints on the time frame for recovery. Such concepts need attention across different types of lotic ecosystems. Thus, there was strong consensus that a national monitoring system of representative lotic ecosystems within ecological regions be established. The purpose of this monitoring system would be to acquire long-term data on natural variability, to establish viable indicators of spatial and temporal aspects of recovery, and to develop and test emerging theoretical developments.

Visual interpretation of satellite imagery for monitoring floods in Bangladesh

Abstract: This article presents the methods and results of visual interpretation of NOAA AVHRR imagery for mapping flood areas in Bangladesh. Color composites of channels 1 and 2 for 18 August 1987 and 10, 15, and 24 September 1988 were interpreted visually for delineating flood boundaries. On such imagery flood areas appear in dark tones and are separated from land (light tones) owing to the absorption of near infrared by water and its reflectance by land and non-waterbodies. Visual interpretation was aided by the use of ground information, such as physiographic and river maps, previous flood maps, newspaper reports, and other published and unpublished documents on the 1987 and 1988 floods. Interpreted flood areas on selected images ranged from 31% to 43% of the total area of Bangladesh. Visual interpretation overestimated flood areas by 5%–10%, compared to the digitally analyzed data. The main advantage of visual analysis lies in the cost effectiveness of AVHRR photographic products, which make them more accessible than the digital image analysis of computer-compatible tapes.

An inventory of wetland impoundments in the coastal zone of Louisiana, USA: Historical trends

Abstract: We inventoried wetland impoundments in the Louisiana, USA, coastal zone from the late 1900s to 1985. Historically, impoundment of wetlands for reclamation resulted in direct wetland loss after levees (dikes) failed and the impounded area was permanently flooded, reverting not to wetland, but to open-water habitat. A current management approach is to surround wetlands by levees and water control structures, a practice termed semi-impoundment marsh management. The purpose of this semi-impoundment is to retard saltwater intrusion and reduce water level fluctuations in an attempt to reduce wetland loss, which is a serious problem in coastal Louisiana. In order to quantify the total impounded area, we used historic data and high-altitude infrared photography to map coastal impoundments. Our goal was to produce a documented inventory of wetlands intentionally impounded by levees in the coastal zone of Louisiana in order to provide a benchmark for further research.

Economic sustainability and the preservation of environmental assets

Abstract: The core requirement of sustainability is that current economic activities should not result in an excessive burden on future generations. This criterion is general enough to imply different decision rules for the preservation of environmental assets. Neoclassical economics does not have a sustainability criterion for environmental assets independent of the intertemporal efficiency criterion, which allocates environmental and man-made capital based on projected monetary benefits and costs. This criterion is examined in terms of the feasibility of valuing the benefits of environmental assets, the substitution possibilities between natural and man-made capital, and the ethical grounds for using efficiency as the sole determinant of the allocation of environmental assets. An alternative ecological sustainability criterion is the preservation of safe minimum levels of environmental assets in physical terms rather than the dollar value of a composite of natural and man-made capital. Safe minimum standards for environmental assets constrain the efficiency criterion in order to ensure the sustainability of economic systems. It is argued that the ecological approach to sustainability should limit the economic approach for decisions involving the allocation of environmental assets.

Vegetation dynamics in impounded marshes along the Indian River Lagoon, Florida, USA.

Abstract: Data are presented on the vegetation dynamics of two impounded marshes along the Indian River Lagoon, in east-central Florida, USA. Vegetation in one of the marshes (IRC 12) was totally eliminated by overflooding and by hypersaline conditions (salinities over 100 ppt) that developed there in 1979 after the culvert connecting the marsh with the lagoon was closed. Over 20% recovery of the herbaceous halophytesSalicornia virginica, S. bigelovii, andBatis maritima was observed at that site after the culvert was reopened in 1982, but total cover in the marsh remains well below the original 75%. No recovery of mangroves was observed at this site. The second site (SLC 24), while remaining isolated from the lagoon during much of the study, did not suffer the complete elimination of vegetation experienced at the first site. At this location, mangroves increased in cover and frequency with a concomitant decrease in herbaceous halophytes.