Threats to the coastal zone
This article presents an introduction to threats to the coastal zone that result from human activities and pressures. It discusses generic modifications to coastal ecosystems in relation to specific human activities and introduces the various threats resulting from poorly managed activities.
- 1 Climate change
- 2 Fisheries
- 3 Water quality/pollution
- 4 Land use and coastal defences
- 5 Land-sea flows
- 6 Recreation and tourism
- 7 Coastal hazards
- 8 Threats to biodiversity
- 9 Conclusion
- 10 Related articles
- 11 References
- 12 Further reading
A study by Halpern et al. (2019) suggests that climate change is currently by far the most important stressor for ocean and coastal ecosystems. In this study the cumulative impact of 14 stressors related to human activities (including climate change, fishing, land-based pressures, and other commercial activities) on 21 different marine ecosystems globally was estimated for each of eleven years spanning 2003–2013. The increase of the estimated cumulative impact for the global ocean was estimated to be due for more than 90% to increasing sea surface temperature and acidity and the increase of the estimated cumulative impact for the coastal zones was estimated to be due for more than 80% to increasing sea surface temperature and sea level. Other results regarding threats resulting from climate change are dealt with elsewhere in the Coastal Wiki, see the page Climate change and the links and references therein.
The reader is referred to the separate pages Effects of fisheries on marine biodiversity and Mariculture. These articles discuss how and why ecosystems are at risk, while the human demand of resources from the sea is increasing, particularly in coastal areas.
The separate pages Coastal pollution and impacts and Possible consequences of eutrophication discuss the way in which coastal and estuarine ecosystems have been, and still are, heavily influenced by anthropogenic pollution throughout the world. Examples of environmental issues include the enrichment of enclosed waters with organic matter leading to eutrophication and pollution by industrial chemicals and oil.
Land use and coastal defences
Land use and human populations
Some 40% of the world’s human population live not far from the coast, within about 100 kilometers of the shore . This means that about 3 billion people rely to some extent on coastal and marine ecosystems, habitats and resources for food, building materials, building sites, and agricultural and recreational areas, while utilising coastal areas as a dumping ground for sewage, garbage, and toxic wastes. The pressure on the living and non-living resources of the coastal zone is expected to further increase, due to growing urbanization, industrialization, and transportation. This section considers physical structures and land use modification in the coastal zone, and anticipated future developments (e.g. off-shore airports, wind-energy parks, land reclamation, etc.), due to an increase in human demography and increased use of coastal areas. The tremendous population increase puts a heavy burden on the coastal zone requiring careful management. The obvious global demand for proper guidelines to cope with these increasing pressures presents the science community with a major challenge, namely to supply scientific information on possible solutions, and on the predicted effects of the different measures. There is a need for systemic studies of the ecosystems associated with large coastal urban agglomerations. Growth in the so-called mega-cities adds to a tendency of people to concentrate in the coastal zone, see the article Coastal cities and sea level rise. Clearly, this extends the range of impacts on the marine environment beyond traditional sewage and waste, adding things like increased risk of disasters, excessive noise levels and thermal.
Some of the increases in human population numbers are temporary and are due to seasonal migration. Some can be significant as for example in the Mediterranean coastal zone, which has a population of about 130 million swelling to 230 million for most of the summer, increasing transportation and pollution problems. See also the articles Impacts originating from the tourism sector and Impact of tourism in coastal areas: Need of sustainable tourism strategy.
Coastal industries and constructions
Industrial development has altered, disturbed and destroyed coastal ecosystems, including sensitive habitats. Many important industrial centres are situated on estuaries and in the vicinity of urban areas and ports. Main industrial activities affecting coastal areas include iron ore smelting and processing, chemical and petrochemical industry (oil and gas storage and refining), paper mills, vehicle factories, ship building, power plants (coal, oil gas, nuclear energy) and food processing (including fish). Numerous pipelines, data and energy cables buried in the seabed create problems for other users (bottom trawl fisheries, marine aggregate extraction). Construction engineering activities often cause permanent destruction of habitats or decrease and fragmentation of habitats, due to land claim, coastal protection, extraction of bottom material, dumping and disposal.
Reclamation of salt marshes and mangroves has taken place for centuries almost everywhere in estuaries, intertidal bays and inlets throughout the world. The main impacts on marine ecosystems are: disturbance and removal of benthic organisms, damage to spawning areas for fish, alteration of the seabed, destabilisation of shallow banks and increased erosion. Severe beach erosion is a problem shared by many countries. The threat from industry and tourism infrastructure is still acute even if local and regional management plans help by slowing down the rate of construction. In several countries (e.g. Japan, Singapore, Hongkong and Dubai) artificial islands are built in the sea for urban extension, tourist resorts and airports. Changes to the shoreline have been extensive in recent decades and threats from rising sea levels and sinking landmasses have required the development of new coastal management strategies. For example, water storage schemes and managed retreat schemes along coastlines have been proposed and enacted as soft-engineering works, for dealing with long-term problems in an environmentally friendly and sustainable way (see also Climate adaptation policies for the coastal zone).
Dredging and dumping at sea
Dredging mainly causes physical disturbance and may result in the redistribution of contaminants through desorption from fine sediments. Offshore sand mining for beach nourishment and land reclamation and aggregate extraction for the construction industry causes temporary disturbance of benthic communities and in some cases permanent loss of habitats. Contaminants can be resuspended and remobilised from sediments and create new entries in the food web. Any increase in suspended matter will impede growth of filter feeding organisms (bivalves) and alter the burial capacity of benthos. It is well established that changes in substrate quality are synonymous to changes in the structure of benthic communities
The bulk of material disposed in the sea comes from dredging of navigation channels. Sewage sludge dumping increases the fallout of organic material and associated contaminants to the seafloor. It can contribute to eutrophication in coastal waters, see What causes eutrophication? and other links in this article.
Marine litter is derived from land-based and marine sources. It is found in large quantities on the coastal seabed, floating in the water column and on the shore. It is brought to the sea by rivers but originates also from activities at sea such as shipping, fishing and mariculture or recreation and tourism. About 80% of the material is plastic which is hardly degradable and provokes smothering. Entangling and drowning of biota (birds, mammals) may happen and inflict physical injury to animals (turtles) or even an obstruction of digestive system after ingestion of plastic objects. Once in the food-web, plastics release toxic substances. Containers or all sorts (bottles, boxes) will host alien species and help in the transportation of invasive species, see the article Non-native species invasions for an introduction to this topic.
River runoff and load
Flow of fresh water and entrained materials to the coastal zone has been grossly altered by human activities. In some arid regions where freshwater is diverted for irrigation, the discharge to the coastal zone has diminished to a small fraction of the natural flow. In other regions the issue is management of water, as the seasonal pattern of discharge has been greatly modified. Either water loss or alteration of the seasonality of discharge can have major impact on coastal ecosystems. Human activities have also altered the patterns of sediment discharge. In some regions increased soil erosion has occurred associated with human land use (especially agriculture) and has led to increases in sediment delivery. However, in most cases an overriding effect has been increased trapping of sediments in water reservoirs. Thus, some regions experience artificially elevated sediment discharge, whereas many others experience severe diminution. Either change can be detrimental to ecosystems acclimated to receive a particular level of sediment load. For example, severe erosion without sediment replacement may occur in systems poised to receive high sediment loads. For several large deltas such as the Nile and Colorado River deltas the sediment discharge to the coastal zone has diminished by more than 90% compared to the natural situation. By contrast, ecosystems such as coral reefs are generally acclimated to low sediment discharge, and large amounts of sediments can bury or otherwise damage reefs.
Human activities have generally led to increased discharges of pollutants which affect water quality. Some countries have done better than others in effectively regulating and controlling these discharges.
Groundwater discharge into the coastal waters
Although not as obvious as river discharge, continental ground waters also discharge directly into the sea. Like surface water, groundwater flows down-gradient. Therefore, groundwater flows directly into the ocean wherever a coastal aquifer is connected to the sea. Furthermore, artesian aquifers can extend for considerable distances from the shore, underneath the continental shelf. In some cases, these deeper aquifers may have fractures or other breaches in the overlying confining layers, allowing groundwater to flow into the sea. If polluted, groundwater flow into the sea will contribute to marine pollution. See for further details the article Submarine groundwater discharge and its influence on the coastal environment.
Seawater intrusion into the coastal aquifer
Conversely, seawater intrusion in the coastal aquifer causes salinisation of fertile soil in low-lying parts of the inland coastal zone. These areas can therefore become unsuitable for agriculture, especially in arid regions, with considerable social and economic consequences. Coastal areas can also become less suitable for habitation due to upwelling of brackish water and salinisation of drinking water wells. These issues are exacerbated by climate change, on the one hand as a result of more frequent and longer dry periods and, on the other hand, as a result of sea level rise, which strengthens the salt water intrusion into the coastal aquifer. For further details on this topic, see the article Groundwater management in low-lying coastal zones.
Recreation and tourism
Coastal areas provide recreation opportunities for local people and for tourists who travel at present the whole world. Tourism causes pressures on coastal ecosystems by excessive influx of visitors. People movements rely on transportation systems which range from pathways for walkers to landing strips for airports. These movements contribute to the wandering of pests, construction and building with associated pollution and eutrophication and disposal of litter and other waste in tourist areas. The paradox is that, most often, tourism will disturb and threaten local populations and wildlife and their habitats, which attracted them to the area in the first instance.
Beaches, swimming, recreational boating
Beaches are important areas for tourism. However, the increasing population and standard of living push many areas beyond their sustainable limits, both from a tourism and environmental point of view. In beach tourism there are clear feedback mechanisms: nice beaches attract people, and too many tourists on the beach decrease the attractiveness. Tourism, a major source of income for many coastal communities, can have major effects on coastal environments unless the scale and type of activities are controlled. Biodiversity reduction, resource depletion, and human health problems may result from the accumulated environmental effects. Setting maxima to tourist numbers is a proper managerial measure, however, once these maxima are reached, pressure to relax the restrictions increase. Clear definitions of maxima, and scientifically adopted calculation methods are still lacking.
Recreational boating increases with the increasing standard of living, and in some countries harbours and marinas built primarily for recreational use by small boats may disturb more of the coastal zone than commercial and industrial use. The environmental impacts of marinas and small harbours depend on site location, design, construction methods, and 'house-keeping'. Careful site planning can help avoid or minimize many of the impacts.
Seabirds and marine mammals, particularly cetaceans, offer excellent opportunities for ecotourism in many parts of the world. Seabird colonies and seal rookeries are spectacular and increasingly popular places to visit. In many places around the world, whale watching trips are organized or specific advice is given by tourism organisations as to where and how whales can be observed from headlands and coastal promontories. This rapidly growing interest for ecotourism has been reason for concern. Subsequently, codes of ethics and best practice guidelines for ecotourism have been published and most of the major tourism organisations have formally declared to follow such guidelines. This topic is further developed in Impact of tourism in coastal areas: Need of sustainable tourism strategy.
The coastlines of many countries face high risks of damage from certain types of natural disasters. A major concern is death and property loss by winds and flooding by hurricanes or cyclones. Along many densely populated coastlines, the risks of natural disasters are being increased by population growth and unmanaged development projects, including residential urban development. Coastal natural disasters cut across all economic sectors. Wind or water damage from a cyclone (hurricane), flooding by tsunami, wreckage from an earthquake, or coastal erosion from storms can affect tourism, fishing, port operations, public works, transportation, housing and industry. For a more extensive discussion, see the article Shoreline management.
Tropical cyclones (hurricanes) form over the warm oceans (at least 26o C) mainly over the western parts where no cold currents exist. Apart from wind and rain, a major impact is from the associated storm surge and storm waves. These have been responsible for major loss of life particularly in low lying densely populated coastal areas such as Bangladesh or China. Tsunamis are quite a different phenomenon and are often associated with subsea earth movements. However, their speed and height can cause extensive coastal destruction with little warning and some distance from their origin (see: Tsunami). Further details can be found in Extreme storms and Natural causes of coastal erosion.
Threats to biodiversity
The composition and structure of the fauna, flora and habitats of coastal seas has been changing at an unusual rate in the last few decades, due to changes in the global climate, invasive species and an increase in human activities. The unusual rapid rate of change, rather than the nature of the change itself, is the reason for the deterioration of many environments; over the last 50 years the rate and extent of this deterioration has been unprecedented, as were the consequences on biological diversity. The term biodiversity is used by the Convention on Biological Diversity (1992) to refer to all aspects of variability evident within the living world, including diversity within and between individuals, populations, species, communities, and ecosystems. The term is commonly used loosely to refer to all species and habitats in some given area, or even on the Earth overall. In fact, it relates to environmental attributes, often species or species groups, which can be sampled and whose modification is supposed to reflect a change of biological diversity (see Measurements of biodiversity)).
What primarily matters, is the capacity of ecosystems to fulfil their role within the biosphere. The notion of functional diversity is useful in that it provides insight into the resilience of ecosystems and how changes affect them. There are many causes to losses of marine biodiversity, especially in the coastal waters of industrialised countries. The most drastic loss is habitat destruction through the erection of engineering and drainage works, which disturb the physical integrity of coastal and marine systems, as the habitat itself is changed to a point where the ecosystem loses its identity and fulfils a completely different function as before. Poor fisheries management, including the uncontrolled exploitation of corals and molluscs and the by-catch of large numbers of non-target species in fisheries is another important aspect of the detrimental exploitation of marine living resources. This is further illustrated in the article Effects of fisheries on marine biodiversity. The underlying cause is the lack of an integrated approach to coastal zone management, leading to impoverished functioning. As a consequence, the productivity of fisheries and such important ecosystems such as mangroves and coral reefs has been depressed, with detrimental impact on local human communities. In general, estuaries and salt marshes, mudflats, mangrove forests, and sea grass beds (such as posidinia) near cities and towns are severely degraded worldwide with many species being threatened. The increasingly observed worldwide bleaching of corals could lead to massive ecological changes for coral reefs and other marine ecosystems. See also Marine Biodiversity and Threats to Coral Reefs: the Effects of Chemical Pollution.
Living organisms play an essential role in biogeochemical cycles through coastal systems. They are themselves vulnerable to rapid changes which take place in the coastal zone due to anthropogenic activities, but changes in the structure of populations of organisms will in turn affect the geochemistry of the habitat, to a point where such cycles might become dysfunctional. The consequences of such changes taking place in coastal ecosystems may have consequences at global level leading to an unbalance in fluxes of energy and minerals at the interface between land and sea. The dynamics of such systems are very high and complex meaning that conservation is not just concerned with fixing the coastline to its physical actual limits, fighting erosion and sea level rise. Because coastal systems are alive, they are able to cope with changes of any sorts, but what counts is more the rate of change than the nature of the change. What makes the anthropocene unique is the rapidity of changes inflicted by humans to natural systems. Threats of all sorts from human activities onto ecosystems are now well documented but action remains difficult and uncertain because of a lack of understanding of the scale and of the speed of observed changes. Notably, the variability of natural systems is difficult to include in any political reasoning which relies on the certainty of statements for decision making. Through improving the scientific understanding of the performance of coastal ecosystems in terms of fluxes of energy and matter in relation to human impacts, integrated coastal management should become more able to predict the effects of measures taken and find adapted responses to fast evolving demands from society.
- Integrated Coastal Zone Management (ICZM)
- Pressures, impacts and policy responses in European coastal zones
- Coastal pollution and impacts
- Effects of fisheries on marine biodiversity
- Coastal cities and sea level rise
- Human causes of coastal erosion
- Resilience and resistance
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