Threats to the coastal zone
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This article provides a review of human activities and the threats to the coastal zone that are created as a result of these 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.
In this section on Living resources we will look at how and why ecosystems are at risk, despite the fact that humans are increasingly dependant on resources from the sea, particularly in coastal areas.
Water quality/pollution discusses the way in which coastal and estuarine ecosystems have been, and still are, heavily influenced by the human species through pollution and habitat loss throughout the world. Examples of environmental issues include the enrichment of enclosed waters with organic matter leading to eutrophication, pollution by chemicals such as oil, and sedimentation due to land-based activities or sea level rise due to the global change.
Land use and coastal defences
Land use and human populations
Some 60% of the world’s human population live close to the coast, within about 100 kilometers of the shore. This means that about 3.5 billion people rely heavily on coastal and marine ecosystems, habitats and resources for food, building materials, building sites, and agricultural and recreational areas and use coastal areas as a dumping ground for sewage, garbage, and toxic wastes. This proportion is expected to increase, along with growing urbanization, industrialization, and transportation, putting even greater pressure on the living and non-living resources of the coastal ocean. 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 anyway. 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 pollution.
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.
Coastal industries and constructions
Industrial development has altered, disturbed, and destroyed costal 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 metal smelting and processing, chemical, petrochemical (oil and gas storage and refining), paper mills, vehicle factories, ship building, power plants (coal, oil gas, nuclear energy), and food processing (including fish). Data and energy cables are numerous with similar effects to pipelines which are submerged in the seabed. This creates problems for other users (bottom trawl fisheries, marine aggregate extraction). Construction engineering activities very often cause permanent destruction of habitats or decreases in habitat size and their fragmentation, due to land claim, coastal protection, extraction of bottom material, dumping and disposal.
Habitat infilling, in particular 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 sites as spawning areas for fish, alteration of seabed profiles, increase in instability of shallow banks and an increase in 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. The construction of artificial islands is now well developed in Japan and in the Southern North Sea, for instance in the Netherlands for the installation of a future airport. This is a highly political issue. Changes to the shoreline have been extensive in recent decades and threats from rising sea levels and sinking landmasses have required new strategies to be developed. For example, water storage schemes and managed retreat schemes along coastlines have been proposed and enacted as soft-engineering works as environmentally friendly and sustainable methods of dealing with long-term problems.
Dredging and dumping at sea
Dredging mainly causes physical disturbance and may result in the redistribution of contamination through release from the sediment. Contaminants might be resuspended and remobilised from sediments and create new entries in food webs. Any increase in suspended matter will impede growth of filter feeding organisms (bivalves) and alter the burial capacity of benthos. It is well known that changes in substrate quality are synonymous to changes in the structure of benthic communities.
The bulk of material eligible for dumping at sea comes from dredging operations from navigation channels, material removed in coastal engineering projects, beach nourishment, and reclamation and coastal marsh preservation. Sewage sludge dumping increases the fallout of organic material and associated contaminants to the seafloor. It can contribute to eutrophication in naturally nutrient rich coastal waters.
Marine litter is derived from land-based and marine sources. It is found in large quantities on coastal seabed, floating in the water column and on the shore. It originates from many diverse activities such as shipping, fishing and mariculture or recreation and tourism. About 80% of the material is plastic which is non-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.
River runoff and loadcoastal zone has been grossly altered by human activities. In some arid regions, such as the Nile (Egypt) and Colorado (Mexico), where freshwater on land is a major resource limiting human activities, discharge has diminished to 10% or less of natural flow. In other regions the issue is management of water, with the seasonal pattern of discharge having 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. Although increased erosion has occurred associated with human land use (especially agriculture) and has led to increases in sediment delivery, a confounding effect has been increased trapping of sediments in water reservoirs. Thus, some regions experience artificially elevated sediment discharge; others experience severe diminution of discharge. To an ecosystem acclimated to receive a particular level of sediment load, either change can be detrimental. For example, severe erosion without sediment replacement may occur in systems (such as the Colorado River delta) poised to receive high sediment loads. 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 an increase discharges of pollutants which affect water quality. Some countries have done better than others in effectively regulating and controlling the discharges.
Groundwater discharge into the coastal zone
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 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.
Recreation and tourism
Coastal areas provide recreation opportunities for local people and for tourists who travel the whole world. Tourism cause 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. Such movements at the planetary level mean 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 to their sustainable limits, both from a tourism and environmental point of view. In beach tourism there are clear feed back 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 necessary.
With the increasing standard of living, the recreational boating increases, 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.
The coastlines of many countries face high risks of damage from certain types of natural disasters. The major concern is death and property loss by winds and waters of 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), inundation by tsunami (see: Waves#tsunami), wreckage from an earthquake, or coastal erosion from storms can affect tourism, fishing, port operations, public works, transportation, housing and industry.
Tropical cyclones (hurricanes) form over the warm oceans (at least 26o C) mainly over the western parts where no cold currents exist. Apart from the 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 associated with sub sea earth movements. However, their speed and height can cause extensive coastal destruction with little warning and some distance from their origin.
Threats to Biodiversityinvasive 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.
What is important 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 industrialized countries. Direct habitat destruction through the erection of engineering and drainage works which disturb the physical integrity of coastal and marine systems is the most drastic, as the habitat itself is changed to a point where the ecosystem looses 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 due to 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, and local human communities are suffering. In general, estuaries and salt marshes, mangrove forests, and sea grass beds near cities and towns are severely degraded worldwide with many species being threaten. The increasingly observed worldwide bleaching of corals could lead to massive ecological changes for coral reefs and other marine ecosystems.
Living organisms are an essential link in the turnover of biogeochemical cycles through costal 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 costal 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 coast line to its physical actual limits, fighting erosion and sea level rise. Because costal 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.
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