Marine Atlas: Maximizing Benefits for Fiji
FROM RIDGE TO REEF: WATERSHED ASSESSMENT Healthy reefs depend on clean rivers, which in turn depend on intact healthy catchments. To maintain healthy coastal and marine ecosystems, Fiji must ensure that sustainable management practices are in place from ridge to reef.
In Fiji, agriculture—especially sugarcane farming, cattle grazing and logging—are the major sources of sedimentation and nutrient-loading. Even after logging activities have ended, logging roads con- tinue to bleed sediments for over a decade. Sed- iments are therefore likely to seep into adjacent marine and freshwater ecosystems, particularly in higher rainfall areas, for long, continuous periods. In addition, the burning of grasslands, also par- ticularly in higher rainfall areas, for cattle grazing or sugar cane plantations, for example, greatly contributes to erosion within watersheds. The map shows, the percentage of water- shed-based pollution and the percentage of pollution affecting reef units. Watershed based pollution is highest in eastern Viti Levu (up to 10 per cent), mainly due to high rainfall and logging. Watershed pollution is generally a reflection of the level of erosion due to biophysical conditions (e.g. soil, rainfall, slope, level of development), with its impact relative to the importance of the adjacent reef systems. Critical watersheds important for reef conservation are mostly found along the northeast coast of Viti Levu (Ra Province), the south-east- ern coast of Vanua Levu (Bua Province), and the western and north-central coast of Vanua Levu (Macuata Province). However, all watersheds in Fiji should be well-managed in order to sustain local freshwater and marine fisheries, maintain clean water and reduce flood damage. To this end, erosion mitigation practices should be implemented in all watersheds. Key actions include closing unused logging roads and their subsequent revegetation, building erosion berms, particularly on stream crossings, and reforesting stream sides. Logging code practices should also be adhered to more strictly, since these intend to prevent logging on slopes and along streams. The Wildlife Conservation Society (WCS) recommends that logging should be entirely prohibited in critical watersheds, particularly those that are adjacent to reefs with high conservation value or that have forests with high conservation value. Watersheds
in southern Bua Province, Macuata Province and Ra Province should remain unlogged. Taveuni and Kadavu, both well-forested islands, should also prohibit logging as their broader ecosystems, from ridgetops to reefs, are largely intact. Coordinating the use and management of land and water, from source to sea, offers solutions to tackle water pollution. By implementing actions in river basins and along coasts, ecosystem ser- vices can be supported and riparian and coastal livelihoods improved. The Pacific Ridge to Reef (R2R) programme, which is funded by the Global Environment Facility, follows this approach and includes Fiji and 13 other Pacific Islands countries. The programme aims to preserve biodiversity and ecosystem services, sequester carbon, improve climate resilience and sustain livelihoods through a ridge-to-reef management of priority water catch- ments on Fiji’s two main islands. Selected priority catchments include Ba River, Tuva River and Waidi- na River/Rewa Delta on Viti Levu and Labasa River, Vunivia River and Tunuloa district on Vanua Levu. As the graphic shows, it is only by addressing veg- etation and soil upslope that rivers and ultimately reefs can stay clean and healthy, sustaining their fish population. To maintain its marine values, Fiji must consider its ridges through to its reefs.
As the previous chapters show, everything is connect- ed to the ocean, though this connection does not end at the shore. On the contrary, activities on land have a big influence on adjacent and downstream coastal and marine ecosystems. It is therefore important to follow water from its source to the sea, from ridge to reef. Based on this, the term “watershed” should be used, since this is refers to the catchment area where precipitation (rain) collects and drains into a common outlet, such as a river or bay.
Illustration of a drainage basin. The dashed line is the watershed’s main water divide.
Altered watersheds degrade reef and freshwa- ter ecosystems primarily through increasing the amount of sediments and nutrients well beyond natural levels, as shown in the previous chapter. Sediments smother and shade out corals and other invertebrates, while higher levels of nutri- ents cause an imbalance in ecosystems that often results in blooms of algae. Sedimentation and nu- trient-loading are known to reduce fish abundance, species diversity and coral cover in nearshore reef ecosystems. Although corals can survive heavy sedimentation events for short periods, longer-term stress induced by extended periods of low-level sedimentation causes significant damage to reef ecosystems.
To maintain its healthy coastal and marine ecosystems Fiji has to implement sustainable management practices from ridge to reef.
Sugarcane farming is a major source of sedimentation and nutrient-loading on Fiji’s reefs.
MAXIMIZING BENEFITS FOR FIJI
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