|Priorities for Water Resources Allocation (NRI)|
Centre for Tropical Coastal Management Studies, Department of Mar¡ine Sciences and Coastal Management, University of Newcastle upon Tyne
Summary: Development which is focused on single uses of a system may lead to resource use conflicts, foreclose on other options and result in suboptimal and non-sustainable use. To justify multiple-use management, full economic analysis incorporating values of non-marketed on-site and off-site goods and services of ecosystems are required. Multi-disciplinary research is needed to assign such values. Water-borne interdependence of coastal ecosystems make it difficult to isolate areas for management purposes. Alterations to water (and associated suspended sediment, dissolved nutrient, etc.) flows within or between systems are generally detrimental to existing ecosystems. The water connections do however make it theoretically possible for protected areas to generate benefits over extensive areas. However, there are few data to support such a contention and the scientific basis for establishing marine reserves needs to be evaluated critically. The implications of rising sea level for coastal areas have been much discussed recently but in coastal developing countries, including low-lying atoll states which are extremely vulnerable, it appears that coastal management problems generated by burgeoning populations and ill-conceived coastal developments are the most important issues at present.
Three major challenges to those involved in coastal zone or coastal resources management are: (a) implementing the concept of multiple-use management of systems to derive long-term sustainable benefits for the maximum number of people; (b) recognising the problems of waterborne interdependence of coastal ecosystems and in special cases making use of this interdependence; and (c) dealing with the problems of trying to manage such dynamic systems and the likely exacerbation of these problems by predicted sea-level rise as a result of global warming. In the limited time available I would like to consider very briefly a few aspects of these challenges and identify a few areas where research might be directed.
Management of the coastal zone has tended to be piecemeal (project, sector, or single-use orientated) but coastal systems have a high level of interdependence, largely because of the water which links them. Development or management focused on single uses or activities often has negative impacts on other potential or actual uses of a system, may lead to resource use conflicts and generally results in suboptimal use of the system. As an example of a coastal ecosystem which may be optimally exploited by sustainable multiple-use management I will look at mangroves. Coral reefs or seagrass beds might equally well be used as examples.
Mangroves are an example of an ecosystem which has suffered particularly badly from development with 55% of original area reported lost in the Afrotropical realm and 58% in the Indonesian realm in 1986 (World Resources Institute, 1990). This has stemmed both from a sectoral approach to resource management and a failure to recognise the multiplicity of goods and services provided by mangroves. The 'Mangrove Area Management Handbook' (Hamilton and Snedaker, 1984) lists over 70 direct and indirect products and services provided by mangroves. Examples include: timber for construction, firewood, charcoal, medicinal compounds, alcohol, honey, shellfish, nursery and feeding grounds for finfish and shrimp, control of coastal erosion, protection of inland areas from storm surges and wind damage, and protection of offshore systems such as coral reefs from excessive nutrients and sediments from inland agriculture. Despite these multiple uses, and perhaps because most of the uses are on an artisanal scale and thus contribute to the local subsistence economy rather than national commercial interests, mangroves have in the past been regarded as 'wastelands' ripe for sectoral development by forestry, aquacultural or agricultural sectors. Sustainable mangrove forestry requires careful management and does not necessarily exclude other uses. On the other hand, wholesale conversion to fish or shrimp ponds, to salt production, or to rice paddies forecloses on other use options and may cause loss of valuable services such as coastal protection (e.g. in Java where a protective mangrove fringe is seldom left) and provision of shrimp and finfish nursery areas to sustain local capture fisheries.
An analytical framework for assessing the economics of preservation, multiple use ('utilisation') or conversion to single use (or destruction) of mangroves have been discussed in detail by Hamilton and Snedaker (1984). Figure 1 shows the relation between location (on-site/off-site) and type of mangrove goods and services (marketed/non-marketed) and traditional economic analysis. There are still uncertainties and difficulties in the valuation of quadrants 2, 3 and 4 which need to be resolved and are discussed below.
Figure 1 Relationship between location and valuation of goods and services derived from mangroves
The Asian Wetland Bureau indicates that in Malaysia mangrove systems contribute some $ 800 million to the national economy in terms of the marine fisheries they sustain. Martosubroto and Naamin (1977) show a correlation between shrimp catch and area of mangrove swamp remaining in various parts of Indonesia. In Fiji approximately 60% of commercially important coastal fishes are either caught or spend part of their life-cycle within mangrove areas. Lindall (1973) estimated that in Florida 80% of all marine species of commercial or recreational value are dependent upon mangrove estuarine areas for part of their life-cycle. However, Thollot (1992) working in New Caledonia pointed out that most reef fish juveniles found in mangroves also occur in other coastal habitats. As in many other areas of coastal management the scientific evidence for the importance of mangroves to both finfish and shrimp fisheries is somewhat equivocal and qualitative. Few scientists doubt their importance as nursery and feeding areas to many marine species but questions remain as to (a) which marine species absolutely require mangroves to complete their life-cycles and maintain populations, and (b) how much mangrove is necessary to sustain capture fisheries deemed dependent on them.
Similarly the storm-protection role of mangroves appears generally accepted. For example, areas where mangroves have been destroyed in Bangladesh appear to suffer greater damage and loss of life than those where the mangroves survive and provide some protection of areas inland, but again little quantitative information seems to be available which would allow monetary values to be placed on this service. There are difficulties in that the value of the service will depend on the value of the land being protected, and if the adjacent land is developed the value of the mangrove area as building land may increase so that it becomes cost-effective to destroy it and also construct sea defences. Leaving a belt of mangroves to stabilise and protect coastlines which are being developed is generally considered sensible, but the relative effectiveness of belts of different thicknesses under different climate regimes does not yet appear to have been modelled. Coastal managers need such information or at least some guidelines on which to base decision making.
In summary , the optimal use of an ecosystem is likely to be through multiple-use management (i.e. utilisation of the full range of goods and services provided in a sustainable way). This is likely to provide least social disruption, greater equity, and greatest long-term economic benefits to society and it does not foreclose other options for use at a later date. However, it may not be seen as 'development' by politicians and is unlikely to be attractive financially to commercial interests wishing to exploit the resource base for single uses. At present multiple-use management is perhaps more of a concept than a reality but a powerful one which can be used to draw attention to the alternatives to wholesale conversion or destruction. Multi-disciplinary research still needs to be done to attach figures to the economic value of non-marketed on-site and off-site goods and services provided by ecosystems. There is a case for more direct involvement of economists with scientists and engineers in such research.
The ebb and flow of the tides, longshore currents, wave action, land drainage, surface runoff and riverine outflows act to link coastal ecosystems such as mangroves, beaches, marshes, seagrass beds, estuaries and coral reefs both with themselves and with distant areas such as upland watersheds. This intimate linking of coastal systems by water has important implications with respect to management. These implications may make management more difficult. Two examples are:
· It is difficult to isolate areas for management purposes, thus external factors or activities outside of a manager's control can render his local efforts futile. This should be borne in mind when boundaries are assigned to managed areas.
· Significant alterations to water flows within or between systems are generally detrimental.
An example of the encroachment of external influences can be seen in one of the largest mangrove reserves in the world, the Everglades of Florida where c. 100 000 ha of mangrove are protected. Elevated phosphorus levels released in drainage waters from agricultural areas to the north are causing changes in plant and wildlife communities within the National Park (Maltby, 1991) and there is also some concern about pesticide levels. Similarly, the character of the Indus delta which used to prograde at about 30 m per year has been so altered by upstream barrages and damming for irrigation purposes that it is no longer a suitable habitat for most of the mangrove species which once grew there luxuriantly. Freshwater flow has been drastically reduced and sediment discharges are about one quarter of what they were and still decreasing. External factors have changed the character of the coastal habitat so that it can no longer support the ecosystems it once did and productivity of the whole delta area is declining. Eastern Mediterranean fisheries and the future of the Nile delta have similarly been markedly affected by building of the Aswan High Dam hundreds of miles inland.
Interruptions or disturbances to water flows take the form of dams, barrages, jetties, breakwaters, causeways, roads, groynes, canals, etc. Such structures often upset delicate balances among coastal systems. Alteration in salinities in mangrove areas as a result of solid causeway construction can lead to mangrove death as has occurred in parts of the Yucatan for example, while changes in hydrological conditions in lagoonal areas such as that caused by dams or canalisation can lead to reduced productivity and damage to fisheries (e.g. Iguape-Paranagua lagoon system in Brazil). Solid causeways built between atoll islands in Addu Atoll in the Maldives have exacerbated erosional problems by blocking sediment transport from outer reef flats to the lagoon-side of islands. This has led to sediment build-up on the outside of the blocked channel and accelerated erosion of beaches primarily on the lagoon-side, driven by long shore currents (Kenchington, 1985). Various other examples of the consequences of disturbing sediment transport along beaches and engineering solutions to the problems created are discussed by Hayes (1985).
On the positive side is the implication that protected areas or reserves may have effects over quite wide areas. Thus relatively small circumscribed mangrove or coral reef reserve areas may, for example, sustain fisheries over extensive areas by, on the one hand, providing nursery grounds and, on the other, maintaining adult spawning stocks in the face of heavy fishing pressure elsewhere. The idea is seductive and it is perhaps easier politically and administratively to designate restricted marine reserve areas and control access and use of these than to enforce other management measures over wider areas. Whatever the reasons, such areas are currently in vogue as management options with strong support form the conservation lobby. As usual the science is lagging behind but recent work looking at the fishery implications of marine reserves clearly indicates significant increase in numbers and average size of commercially important fish in reserve areas compared to unprotected areas where fishing pressure is significant (Bohnsack et al., 1992; Roberts and Polunin, 1991). In the Sumilon Island reserve in Philippines, loss of reserve status in one year led to a quartering of the stocks of the main group of fish being exploited (Caesionidae). Numbers recovered a few years after reserve status was re-established (Russ, 1992). There is some evidence that fishermen catch more in the vicinity of reserve areas that in areas distant from them but quantitative evidence of: the range of effects; the percentage of a habitat which needs to be preserved for benefits to be observed; and the level of fishing pressure required outside of protected areas for them to be likely to have any noticeable effect on recruitment, is lacking. Russ (1992) suggests that the proposed closing of 5% of the Great Barrier Reef and 20% of the US South Atlantic shelf to line fishing is likely to have benefits in terms of enhanced larval supply. Such options are unlikely to be available in many developing countries closely dependent on these resources for protein.
Coastal dynamics, anthropogenic disturbances and rising sea level
Coasts are very dynamic systems with vast amounts of energy being dissipated at the land-sea interface. The predicted acceleration in the rate of rise of global mean sea level from about 1.2 mm/year to a 'best guess' of 4.5 mm/year (recently revised downwards from 6 mm/year, Wigley and Raper, 1992) under the IPCC 'Business-as-Usual' scenario (Warrick and Oerlemans, 1990) and possible increases in storm power and/or frequency are likely to make coastal areas more dynamic and unstable and put much infrastructure at risk of inundation. Human society requires various structures to be sited on the coast for reasons of transport, availability of sea water or estuarine water for cooling or waste disposal, recreation (hotels, holiday homes), access to coastal resources, etc. Because of the dynamic nature of the majority of coasts and the static nature of the structures, this often creates problems. Interestingly, while rising sea level is perceived as a major problem with vast economic costs in sea defence or relocation in the next century for developed countries, most developing nations appear more concerned with immediate coastal management problems.
Among countries particularly at risk in the face of rising sea level are low-lying atoll states such as Tuvalu and Kiribati in the Pacific and the Maldives in the Indian Ocean. Since President Gayoom of the Maldives has helped instigate much debate on sea-level rise both in the UN and in the Commonwealth Secretariat, I thought it might be useful to look at the problems facing his country, dubbed as one of the 'first-to-go' by the popular press.
The nation is entirely low lying with no point of land much more than 500 m from the sea and with its human habitation, industry and vital infrastructure all within 0.8-2.0 m of mean sea level. The sandy islands, about 1300 of which make up the archipelago, undergo seasonable cycles of erosion and deposition with the changing monsoons which underlines the dynamic nature of the equilibrium which permits their existence. The dynamic nature and fragility of the islands is shown by historical records which indicate that some 50 islands have been wholly or partly washed away and 40 have suffered inundations, often repeatedly (Maniku, 1990). Accretion processes are also at work and about 50 islands are reported to have been joined by the build-up of sandbanks between them. In a recent swell wave incident which causes inundation and erosion at the capital island Male in April 1987 (and also played a large role in stimulating local concern about both the environment and sea-level rise), sediment was at the same time piled up on a submerged reef to create the island of Udhafushi in North Male Atoll. This island is now surrounded by a rapidly developing fringing reef and had vegetation on it in 1989. Two points I would like to stress are: (a) on these islands the dynamic' equilibrium is very delicate and little disturbance is required to generate coastal management problems, and (b) the only areas of Male inundated by the swell wave incident in 1987 were those which had been 'reclaimed' from the sea. To protect 1.52 km length of coast in front of a (60 ha reclaimed area, which lies on top of what was previously the ocean side lagoon and reef flat of the island, some US$ 14 million has been spent on detached breakwaters courtesy of the Japanese International Co-operation Agency.
The vertical growth of coral reefs which provide the main sea defence of the islands is considered likely to be able to keep up with a sea-level rise of 4-5 mm/year (Buddemeier and Smith, 1988). However, it is still not known at what rate biogenic sediments are generated on the reefs and thus it is unclear whether lagoons behind fringing reefs will get deeper and alter beach profiles or fill at the same rate as sea-level rises and maintain bead, profiles. Without such knowledge it is difficult to predict how vulnerable the islands will be to sea-level rise.
Although the Maldives are dearly at risk in a world of rising sea level, over the next 25 years it is dear that their major problems are ones of coastal management arising from coral quarrying, groundwater over-abstraction leading to salinisation, erosion due to solid causeway constructions between islands, and 'reclamation' (infilling of reef and lagoon areas) to increase land areas of over-populated islands. These local anthropogenic disturbances are of immediate concern although in the longer term they will make the Maldives more vulnerable to sea-level rise.
In a wide range of developing countries it seems that rates of anthropogenic degradation of coastal resources and the problems of how to manage these resources in the face of increasing use and increasing conflicts are seen as the critical problems beside which problems associated with global warming and sea-level rise are of little immediate significance.
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In respect to coastal reefs it was pointed out that the ODA has been extensively involved in helping with erosion and coral mining studies for the Maldives with over £1 million being spent. However, there is still disagreement between experts about causes and solutions. The traditional coral mining technique used in the Maldives is to trim off the top of the reef but the reef does not recover and a means of rehabilitation has not been identified. An alternative theory would be to take an uninhabited reef down by 10 m, providing 50 years' supply of aggregate and, being submerged, the coral would then rebuild. On the subject of mangroves it was pointed out that they are an ecological succession creating land. In the management of mangroves one has to consider the roles of a range of species and the challenge is to maintain the ecological succession. A comment was made on the Sundarbans mangrove forest in Bangladesh which is not very biodiverse, consisting of very specialised species yet it produces a wide range of products several of which have been valued in terms of cash and employment (such as prawns). Mangrove replanting schemes were reported from Maldives, Pakistan and Vietnam. A mangrove rehabilitation scheme in Pakistan is using different species from the original ones since salinity levels have changed; in Vietnam a successful mangrove replacement programme has resulted in increased supplies of fish in markets. The problems over the declining freshwater lenses in atolls was raised; these may be destroyed long before the atolls are submerged by rising sea level. In Male the freshwater lens is almost non-existent being at most only 5 m deep; this occurred mainly due to the installation of a freshwater sewage system. It was suggested that the value of the coastal protection works ($ 14 million to protect 60 ha of land in the case of Male) might reflect the protection value of mangrove or the original coral reef.