Estuarine coastal and shelf science pdf collection
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- Estuarine, Coastal and Shelf Science
- Field observations in a small subtropical estuary during and after a rainstorm event
- Estuarine, Coastal and Shelf Science — Template for authors
Estuarine, Coastal and Shelf Science
A short summary of this paper. Estuarine, coastal and marine ecosystem restoration: Confusing management and science — A revision of concepts. Introduction to recovery terminology and conceptsThere is an increasing need to remedy long-standing adverse effects of human activities on estuarine, coastal and marine ecosystems.
While there is an extensive body of literature, terminology and experience relating to terrestrial and freshwater systems e. Perrow and Davy, a,b , it is only recently that such experience has been gained for the coastal and estuarine systems e.
Fonseca et al. Furthermore, given the difficulties of determining the level of change in open marine areas and the scale of the change, very little practical restoration has been carried out for open marine systems Hawkins et al. Bradshaw emphasises the terms restoration, rehabilitation, remediation and reclamation from a terrestrial viewpoint and so it is necessary to translate these terms to the estuarine, coastal and marine environments.
In particular this includes the recovery or re-attainment, by natural active or passive means, of the physical, chemical and biological environments. However, although some aspects are well understood for the marine and estuarine environments, such as sedimente hydrography relationships and poor sediment quality following pollution, other aspects such as the effects of species reintroductions and the determination of viable population sizes are more difficult in open, dynamic marine systems cf.
The need for habitat restoration in coastal areas, especially those subjected to intensive agriculture, urbanisation and tourism, has increased because of a large historical loss and alteration of habitats and therefore adverse ecological impacts Madgwick and Jones, Table 1. Because of this, there are now many schemes which purport to be restoration, especially in North America, Europe and Australia where there is both the legislation which requires it and financial ability to carry it out Ruiz-Jaen and Aide, ;French, The large number of schemes and studies, however, has led to a detailed but sometimes confusing semantics of restoration with an inconsistent, conflicting and sometimes overlapping application and interpretation of the terms 'corroborating the jargon' according to Simenstad et al.
In addition, the further understanding of these terms, approaches and their application requires many fundamental questions to be answered Table 1. The term recovery implies that a system will return to a previous condition after being in a degraded or disrupted one, which is often interpreted as being in poor ecological health. This condition can be evaluated and communicated in different terms, depending upon the questions being asked; studies can examine fundamental ecological processes; they can seek to examine community function, possibly in response to human activities; or they can seek to inform questions on how various ecosystem services are affected by human and ecosystem interactions.
These different approaches are not mutually exclusive e data collected in support of one objective should be applicable elsewhere as long as common language and a conceptual framework linking the various levels of information have been developed. In every case, however, the return to the original state will be with active recovery or without passive recovery human intervention, analogous to medical treatment Hawkins et al.
The recovery may occur naturally but of course may be speededup with intervention implying that recovery will occur in the system once the stressor is removed; it can be encouraged by management actions or is the response to management actions.
If recovery is truly successful then the community established will be similar in species composition, population density and size and biomass structure to that previously present or present at a comparable unimpacted, unaffected site e.
Emu Ltd. The ecosystem goods and services provided and its carrying capacity will have been recovered or been regained to the pre-impact state. Despite this, it is questioned whether the original state can ever be achieved even if it is known ; it is more likely that the recovery will be evaluated using single or sets of structural, functional or socio-economic indicators of recovery, which may or may not return to pre-impact states, whether known or not.
Ecological recovery of a disturbed habitat depends upon several biological factors, such as the sources and transport of propagules, which may require management to effect or enhance the natural processes Pratt, Similarly, long-lived and poorly dispersing target species may need particular management through re-introduction Associated British Ports Research and Consultancy Ltd. As such, newly restored wetlands may have to be inoculated with biota from similar aquatic ecosystems to ensure effective colonisation Pratt, , unless the created site is adjacent to established sites and where opportunity exists for exchange and transport of natural propagules Associated British Ports Research and Consultancy Ltd.
What the human uses are for the system and the demands on the system, and are these compatible with natural ecological structure and functioning? Can the stressors be stopped, mitigated or compensated; and if so will the system recover on its own or require some degree of intervention? Is the system to be restored to a pristine state or merely fit-for-purpose?
Are there some human impacts which are unavoidable? What are the human impacts against a background of natural and wider change, such as global climate change? Passive recoveryRecovery will occur in ecosystems once stressors have been removed but this depends on properties allowing them to either absorb change or attain an improved structure and functioning.
These properties include recoverability, resilience and adaptation but also carrying capacity as an indication of the overall desired state of the system. RecoverabilityRecoverability can be defined as 'the ability of a habitat, community or individual or individual colony of species to redress damage sustained as a result of an external factor' MarLIN Glossary, It is an inherent property of the ecosystem in that certain ecosystems may have a greater potential for recovering from stress than others; for example, a mobile subtidal sandbank whose physical and biological structures created by a high-energy regime will have greater recoverability than more stable areas to anthropogenic causes of change such as beam-trawling or aggregate extraction Collie et al.
Resilience is most simply defined as 'the ability of an ecosystem to return to its original state after being disturbed' MarLIN Glossary, or 'how fast the variables return to equilibrium following perturbation' Pimm, ; though this may also be termed 'robustness' Loreau et al. Ecosystems may be regarded as being in stability states Bengtsson et al. Tett et al. Costanza et al. This feature can also be interpreted as redundancy in the system, for example, if the system is sufficiently complex it is unlikely that the loss of one or two species will cause a change in the system from having one set of characteristics, such as feeding trophic structure, to another.
The latter, regarded as a cascade effect Kaiser et al. Furthermore, the structure and complexity of food webs centre on connectance the number of links between species and the length of food chains, amongst others Dunne et al. These properties of food webs change with scale, diversity and complexity, and this is particularly the case with estuarine, coastal and marine food webs which have large numbers of opportunist and generalist feeders Elliott and Hemingway, In particular, highly connected communities tend to be more robust resilient to species loss than low connected communities and so perhaps estuarine and marine communities have a greater structural robustness than other ecosystems Dunne et al.
As an inherent, fundamental property, all ecosystems are resilient but to differing degrees and a more specialised and less variable ecosystem may have a lower resilience than a naturally highly variable one. Similarly, the amount of resilience a system possesses relates to the degree of disturbance required to fundamentally disrupt the system causing a large-scale change to another state controlled by a different set of processes Gunderson, ;Bengtsson et al. In turn, reduced resilience increases the vulnerability of a system to smaller disturbances that could previously have been absorbed.
However, even in the absence of disturbance, gradually changing conditions e. The Resilience Alliance, ; Kaiser et al. Because of these aspects, it is suggested here that resilience and recoverability are synonymous so only the former is required. The paths of decline and recovery of systems are regarded as trajectories or performance curves which although conceptually valid have not been defined quantitatively.
Any attempt at restoration thus requires either an active or passive approach in which the habitat is made, respectively, to re-trace or re-traces without intervention the trajectory of decline.
Aronson and Le Floc'h refer to three different options for recovery: restoration by reactivating or allowing to be reactivated natural processes including species re-introductions; rehabilitation, a short-term management measure to attain a specific ecosystem attribute, goods or service; and reallocation where over the long-term new trajectories produce new ecosystems and uses.
The conceptual model of Tett et al. Following the removal of the stress, the system will recover although not necessarily along the same trajectory of decline, the difference being termed hysteresis which differs with types of system and stressor. They then implied that more stress was needed to be removed to make the system recover, a feature they called resilience. Given the above discussion, we have revised their conceptual model to indicate that systems do not necessarily recover their former state and also that their ability to recover is termed resilience Fig.
For a given structural or functional parameter which only defines one aspect of the multidimensional definition of ecosystem health, status and function , resistance can be defined as the amount of a given pressure that can be applied without a deterioration in status as defined by a specific measure.
As a pressure is removed, Type I Hysteresis represents the lag in recovery; status may not improve for some time after the pressure is removed. Given time, though, status may recover, although it may not return to original levels.
Resilience can thus be defined as the degree of recovery, based upon a given measure, compared to the original status e complete resilience results in a return to the original level, partial resilience is a return to some lower or higher level, with Type II Hysteresis being the difference between the two.
Whilst the definition of resilience in Fig. Thus, we conclude that Fig. Because ecosystem status is defined by a multidimensional set of variables, an understanding of the interplay is required between various ecosystem parameters to an overall definition and management of ecosystem ''health'', status, function, and services.
Then, if restoration, remediation or recovery does not result in a return to reference conditions, ecosystems can be evaluated over space or time in terms of their functional characteristics, or their ability to provide valued ecosystem services. Within such a conceptual framework, habitat degradation, management and recovery can be addressed using a variety of indicators. Despite this, empirical evidence for this model is still required for the marine environment in order to determine the precise patterns, sequence, magnitude and repercussions of these changes.
The fact that these subtly different and often interchangeable uses of the terms resistance and resilience are seen throughout the literature suggests that they should be used with care, and always with a clear statement of their meaning in the given context. AdaptationAdaptation can generally be defined as the ability to alter something for a new use but ecologically it refers to the processes or coping strategies to be used by communities to increase their resilience or decrease their vulnerability to ecosystem changes.
For example, reducing freshwater flow into an estuary will reduce the brackish euryhaline component of the fauna and increase the marine stenohaline component. While individual species may not adapt to the changed salinities, the new community adapted to the new situation may function in the same way as the original one.
Thus, for example, an increased estuarine salinity will change a community from being dominated by the euryhaline ragworm, Hediste diversicolor, to one dominated by the more marine catworm, Nephtys hombergi, but the system still maintains its functioning Dr D. McLusky, University of Stirling, Scotland, pers. Similarly, a community may be regarded as having adapted to changing conditions if, through temperature regime change due to climate change, warmer water species migrate into an area and colder ones migrate out of it see Laffoley et al.
This, however, changes the focus of the definition of recovery to a stressor from that of a given population structure to that of ecosystem function, as is reflected in the discussion of Fig. Whilst the community above will be considered to be adapting successfully within an ecological context, regulatory contexts that focus primarily on structural indicators may not deal effectively with such adaptations.
Simenstad et al. Carrying capacity was formerly and more usually used as an ecological concept but more appropriately it is considered here in terms of both environmental and societal demands, i. Baretta-Bekker et al. In relation to commercial stocks, Cohen gives five further definitions: population size at which the standing stock of animals is maximal, population size at which the steady yield of animals is maximal, animal population size being at that for maximal plants, the size of a harvested population that belongs to a sole owner, and the population size of an open access resource.
MacLeod and Cooper suggest that it is exceeded when population mortality exceeds recruitment because of environmental limitations a stressor that a particular ecosystem can withstand before the ecological value is unacceptably affected e a definition more widely adopted in fisheries science. However, they also acknowledge the difficulty of defining ecological value and unacceptable change e again implying a value judgement regarding what is acceptable change against a reference condition see below.
Hence, until recently, estuarine ecological carrying capacity related to resources principally food and space available for use, a concept used more for wading birds than other organisms see, e. Stillman et al. Measures of both habitat quality and resource quantity are therefore needed to determine the population supported by an area although, in the particular case of over-wintering bird populations, factors at their polar breeding sites away from temperate coasts will also have an influence.
Where a resource such as food or space is limiting, it can be assumed that carrying capacity for birds is reached when one bird has to leave a site after the arrival of another Dr J.
However, the development of competitive interference between birds has indicated that food resource competition alone cannot be used for determining carrying capacity as it underestimates the demands for space by birds Stillman et al. This feature has recently been determined for the schemes designed to compensate for the loss of wetlands caused by the construction of the Cardiff Bay Barrage Dr J.
Although the above indicates the ecological nature of carrying capacity, here we also recommend including societal aspects such as the ability of an area to support a given human activity.
For example, a well-mixed, high-energy area may have a high carrying capacity to absorb organic wastes without adverse effects being detected.
Field observations in a small subtropical estuary during and after a rainstorm event
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Estuarine, Coastal and Shelf Science — Template for authors
C Corresponding author. Email: mdolbeth ci. Climate extremes, such as drought and floods, are increasing and should be considered in ecosystem management plans. The effects of an extreme drought were studied in two estuaries of the Iberian coast, Minho and Mondego, by exploring fish recruitment, growth and production over four years. The two estuaries are located within an area with transitional climate, and differ considerably in size, availability of freshwater wetlands and freshwater inflow.
Estuarine, Coastal and Shelf Science
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As humans continue to influence the quantity, timing, and quality of freshwater input to estuaries, it is becoming increasingly common for policies to be enacted that mandate the establishment of freshwater inflow criteria that will serve to preserve and protect estuarine ecosystems. This paper reviews the scientific literature describing how changes in freshwater inflow affect estuaries, proposes a conceptual model that explores the roles of scientists, citizens, politicians, and managers in the management of freshwater inflow to estuaries, and uses the model to explore the ways in which freshwater inflow is managed in a variety of estuaries. The scientific review is organized to provide an overview of the connections between freshwater inflow in terms of the quantity, quality, and timing of water delivery , estuarine conditions such as salinity and concentrations of dissolved and particulate material , and estuarine resources such as the distribution and abundance of organisms , and to highlight our understanding of the causative mechanisms that underlie the relationships among these variables. The premise of the conceptual model is that the goal of estuarine freshwater inflow policy is to protect those resources and functions that we as a society value in estuaries, and that management measures use scientific information about the relationships among inflow, conditions, and resources to establish inflow standards that can meet this goal. The management approach can be inflow-based flow is kept within some prescribed bounds under the assumption that taking too much away is bad for the resources , condition-based inflow standards are set in order to maintain specified conditions in the estuary , or resource-based inflow standards are set based on the requirements of specific resources , but each of these is carried out by regulating inflow. This model is used as a framework to describe the development of freshwater inflow criteria for estuaries in Texas, Florida, and California. This is a preview of subscription content, access via your institution.