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Karl Ramjohn
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Restoration of Degraded Tropical Agricultural Land
« Thread started on: Sep 21st, 2008, 2:37pm » |
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ASSESSMENT OF THE POSSIBILITIES OF FRESHWATER ECOSYSTEM RESTORATION AND MANAGEMENT AT DEGRADED AGRICULTURAL SITE AT CARONI (1975) LTD RICE SCHEME
INTRODUCTION
The west coast of Trinidad has traditionally been the focus of human and economic activities, resulting from a number of historical perspectives related to physical conditions and resource distribution on the western side of the island. The Caroni River Basin, particularly the Caroni Swamp and associated floodplain, has been subjected to a number of anthropogenic perturbations: agriculture, urbanisation, industry and residential development. Agricultural impacts increased in scale and intensity around 1920 when the hydrological functions of the swamp and floodplain were completely redefined in an attempt to facilitate rice cultivation (Bacon 1990). This had significant environmental impacts, changing the ecological character of the system.
The Scarlet Ibis (Eudocimus ruber), a national symbol of Trinidad & Tobago has been recorded as utilising the wetland habitats throughout the west coast (ffrench 1980). The Ibis appears not to have established breeding colonies at the Caroni wetland for almost 30 years. They use the mangrove forest for roosting only, feeding on the coastal mudflats and marshes (Erwin 1984). A number of explanations have been proposed for this observation, including loss of freshwater marsh sites, which nesting Ibises used as a food source throughout the 1950's and 1960's (ffrench 1966).
The only freshwater sites in the vicinity of the Caroni Swamp are located east of the Uriah Butler Highway (UBH), currently under rice cultivation. As noted by Bildstein (1990), the Ibises do not appear to fly across the highway to feed at these sites. This possibly indicates a lack of prey for adult foragers, although a number of other species (particularly herons) are observed feeding at the rice paddies. It is believed that Trinidad's current population of Scarlet Ibises migrate to coastal wetlands in South America (such as the Orinoco Delta) to establish breeding colonies (ffrench 1984).
The purpose of this paper is to:
i. Investigate the possibility of restoring freshwater ecosystem functions at a site of degraded or otherwise unproductive agricultural land east of the UBH, and
ii. Propose methods which enhance the sustainability of food production systems adjacent to the swamp, allowing useful component extraction (rice) while maintaining biodiversity and providing enhancement options for the national heritage of Trinidad & Tobago
Note that it is assumed that feasible engineering options exist for the maintenance of an adequate supply of freshwater for a managed ecosystem.
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Karl Ramjohn
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Re: Restoration of Degraded Tropical Agricultural
« Reply #1 on: Sep 21st, 2008, 4:08pm » |
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SITE CHARACTERISATION
Site Visit
A site visit was paid to the Caroni (1975) Ltd Rice Scheme on February 18, 1999. This food production system is located on the southwestern floodplain of the Caroni River, east of the swamp. The site visit served the purpose of:
i. Obtaining a general overview of site characteristics, to assist in the inventory of resources, and
ii. Assist in defining the objectives of management and sustainable restoration options and strategies.
Site Selection
The specific site selected (~60 acres) is in the western portion of the rice scheme, close to the UBH. The site was prepared for rice cultivation approximately 15 years ago. However, it was determined to be inappropriate and subsequently abandoned. The site is not under food production use; it can be regarded as degraded agricultural land as a result of past intervention (including sugar cane monoculture). The site, as a restoration unit, cannot be managed in isolation. As discussed by Christensen et al. (1996), the structure and functions established at the management site will be affected by the status and processes of surrounding systems and landscapes. As such, in this site characterisation and subsequent proposal and management plan, spatial and temporal trends in adjacent agro-ecosystems and the wider Caroni River Basin must be taken into consideration.
Physical Environment
The physical resources of the site, defined by hydrological, climatological and geomorphic characteristics are the major forcing functions which will influence the overall viability and success of the project. It is in this context that the "enduring features" of the site environment are discussed.
Atmospheric Qualities: Climate
The Caroni River Basin is located in the Caroni Hydrometric Area in northwestern Trinidad, and experiences an average annual rainfall 1500 - 1780 mm (WASA 1990, Adams 1977). Generally, 80-90% of rainfall occurs in the wet season (June to December). Winds are predominantly from the east to northeast, with higher wind speeds in the dry season. Long-term data (1961-1990) supplied by the Meteorological Services Division (Ministry of Public Utilities) indicates that average temperatures (and relative humidity) within the Caroni Basin range from 25.7 °C (79.8%) in the dry season to 26.1 °C (84.4%) in the wet season. The study site can be regarded as a subsidised solar-powered ecosystem. Average daily sunshine in the Caroni Basin (1986-95) ranges from 8.3 to 6.8 hours per day in the dry and wet seasons, respectively (CSO 1997). Extreme climatic events (such as tropical storms and hurricanes) can have large-scale unpredictable impacts on a restoration project. Although the necessary conditions for tropical cyclone development are a regular feature of tropical oceans in the hurricane season, the annual variation in activity is large, probably related to a number of global and regional factors (Ramnanan 1993). Trinidad is considered to be slightly south of the hurricane belt (Blume 1974). Since 1861, one hurricane affected Trinidad's southwest peninsula (1933) and the study area was affected by tropical storm Fran in 1990.
Land Surface Qualities: Soils
The study site is located on the alluvial plain of the Caroni River Basin. As noted by Hardy (1981), the swamp and the area immediately east of the UBH have "deep hydromorphic soils", comprising mainly the Bejucal clays, which is described as a "soil of the flat land" with impeded drainage. Similar types of soils have been recorded for most of the other coastal wetlands in Trinidad including South Oropouche, Roussillac and Nariva. The wider study area has been subjected to intensive agriculture for a number of years. In the case of rice cultivation, physical manipulation includes topographic modification, substrate disturbance, compaction, ploughing, mud-rolling and forced (static) inundation. Although the proposed restoration site has not been under cultivation for more than 15 years, land preparation was previously done, altering the ecological character of the soil.
Hydrology
As discussed by Bedford (1996) landscape hydrological characteristics are the pivotal determinants of the structure, features and location of wetland ecosystems. Significant anthropogenic alterations have changed the hydrology of the Rice Scheme, now characterised by a network of drainage and irrigation canals. Inundation of selected sites is forced via embankments and bunds. Surface freshwater is no longer able to flow in a uniform sheet to the swamp (as it would have done prior to 1920). The proposed restoration site is a brackish marsh, surrounded by freshwater rice paddies.
Ecological Character
The Caroni (1975) Ltd Rice Scheme is a restructured and simplified ecosystem, intensively managed to sustain its major function of component extraction (food production). It is an artificially solar-powered ecosystem, characterised by a (net) unidirectional flow of energy and nutrients. The species diversity is low, with a poorly organised community structure, i.e., underdeveloped internal self-regulation (high entropy). A low biomass is supported per unit energy flow, the system characterised by a short, simple life-cycle. To maintain the functions of the system, fertilisers are required (either natural organic or chemically designed). This increases the potential for deterioration in water quality (nutrification) of surrounding systems. The soil quality also decreases. The paddies are characterised by a monoculture of exotic species (rice). Inundation assists in weed control; however, some species adapt including exotics ("red rice") and native (cat-tail and sedges). Exotic species (mainly Guinea Grass) grow on the bunds. Some selective herbicides are applied during the cropping cycle.
The reduction in diversity (large monocultural "islands") tends to encourage the dispersal and colonization by pest species, including caterpillars, insect-hoppers and paddy-bugs. These are managed through the use of pesticides. Some fungicides are also applied. The chemicals are sprayed directly onto the fields, increasing the potential for non-target areas and species (including the natural predators of the pests) being affected. There is also the possibility of bio-magnification impacts on the trophic flows in surrounding ecosystems. The drainage canals are inhabited by Cascadura (native) and Tilapia (exotic), which are commercially/recreationally harvested. There is also evidence of Caimans. The proposed restoration site is characterised by a "monoculture" of brackish-adapted species, predominantly sedges. The ecological character of the site is directly affected by the adjacent rice paddies, and indirectly by landscape level activities.
Human Environment
Inclusion of residents and resource users of the site in the planning and implementation process improves the probability of success, and conforms with the aims of sustainable development. There are no human habitations in the immediate vicinity of the Rice Scheme. The closest regulated settlement is Caroni Village, just north of the rice paddies, on the south bank of the Caroni River. At the proposed restoration site, the closest village is the Bamboo #3 Settlement, on the north bank of the Caroni River. This is a poorly regulated settlement on the wetland margin with little infrastructure, which however contains a major shopping complex. Strictly, there are no "local area" residents at the proposed restoration site. However, the canals adjacent to the site are used for fishing and recreation, with the resource users most likely from the surrounding settlements. In 1995, average monthly income in the Caroni Administrative Area was $1,600 with a median of $1,200, somewhat lower than the national average of $1,800 and median of $1,400 (CSO 1997). The closest municipality, the city of Port-of-Spain had, in the same period, an average monthly income of $2,000 with a median of $1,700. These socio-economic factors in Caroni are likely to encourage natural resource use as a means of supplementing incomes.
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Karl Ramjohn
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Re: Restoration of Degraded Tropical Agricultural
« Reply #2 on: Sep 21st, 2008, 6:05pm » |
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RESTORATION PROPOSAL
Introduction
Restoration ecology has been described as the experimental formation of living communities, by reconstituting ecosystems to restore original biodiversity, adding to the productivity of agriculture and forestry, and assisting in making ecology a more predictive science (Wilson 1989). The pre-disturbance species composition of the former herbaceous freshwater wetlands east of the Caroni Swamp is uncertain (Bildstein 1990). During the documented years (1954-1970) of Scarlet Ibis nesting and breeding, the ecological character was maintained by a man-made embankment. As such, the overall aim of this project is not necessarily to re-establish the exact pre-disturbance ecosystem, but to restore functional equivalence to the systems previously utilised by the Ibises.
Restoration Goal
The goal of this project is to improve the sustainability of food production systems. The intention is to increase the productivity of the site (by allowing multiple-use stewardship), conserve biodiversity, provide a basis for economic activity (e.g., eco-tourism) and supply other goods, services and attributes. One of the aims is also to possibly provide a freshwater site for utilisation by the Scarlet Ibis. The Ibis, a national symbol since 1962 is considered to be one of the Country's charismatic species of note (EMA 1997). As such, the project can assist in providing a template for the identification of "Environmentally Sensitive Species" and "Environmentally Sensitive Areas", one of the mandates of the EMA. It will also aim to involve residents of surrounding communities and site resource users (e.g., fishermen and conservationists) in a meaningful way. As such, the project envisages a reduction in environmental costs associated with the Rice Scheme, and the provision of benefits by assisting in maintaining the set of options available to future generations.
Restoration Materials: Source and Reference Wetland
As a result of agriculture on the landward side of most coastal wetlands in Trinidad, it appears that no freshwater sites of sufficient size or integrity exist on the west coast (Bacon 1993, James et al. 1986) to provide restoration materials for this project. The Nariva Swamp, on Trinidad's east coast is the only site with large functional remnants of freshwater marshes. This is the Country's only site listed by the Ramsar Bureau as a "Wetland of International Importance".
Apart from providing freshwater flora and fauna for use in site colonisation, Nariva can also be used as a "reference wetland" to assist in evaluation of the project. Based on Brinson & Rheinhardt (1996), the advantages of using a reference wetland for this project include:
i. Assist in defining explicit and practical goals, through identification of reference standards, from data that typifies a self-sustaining freshwater site.
ii. Providing a template for restoration design and implementation, and
iii. Providing a framework for adaptive management from which changes to the overall plan can be made.
Implementation and Management
Restoration can be regarded as a managed ecological succession, particularly in degraded agro-ecosystems in which exotic species and other stressors impede the system's potential for natural succession or self-restoration. As such, any restoration project requires high levels of inputs, including energy, water, labour (including specialist technical input) and colonising species.
The intensive management is intended for the short-term (to accelerate the process). The level of management will be inversely proportional to the succession stage. When ecological function and biodiversity have sufficiently re-established, management will return to minimal, concerned mainly with monitoring, research and general ecological security. An appropriate balance between active and passive management will be established, relevant to the stage of the project.
Stressor Abatement: Hydrological Function Restoration
The first act of the intensive management stage is to remove the stressors from the system. In this case, the fundamental stressor is brackish water intrusion. The feasibility of the engineering mechanism to return the site to freshwater conditions at a temporally suitable scale for this project, is assumed. The site will no longer present conditions that support brackish species. The fundamental forcing functions will be restored, simultaneously creating conditions that no longer support the brackish water. However, it may be necessary to remove the stressor-species residues from the site.
Ecological Processes and Species Restoration
This will require physical manipulation, restoring the physical processes of the site that will facilitate ecological successions, including topography, soil attributes, nutrient and water relations. The aim is to prepare the ecosystem for the re-introduction of species. As the processes and interactions are rehabilitated, the integrity of the functions will increase, as will the ecosystem's ability to support increasing numbers and diversity of components. Due to a lack of appropriate in-situ colonisers, species will be "imported" from a remote wetland location. As noted, the source of the wetland materials will be the Nariva Swamp. Appendix A summarises the development of a freshwater marsh, based on this wetland. Applications of fertilisers may be necessary at this stage.
Ecosystem development is a dynamic process, and as such, the project will be managed such that it is implemented in stages. Appendix B summarises a model of ecological successions, showing trends that may be expected during the stages of ecosystem development for this project. As a result of the continued persistence of some of the stressors in adjacent agro-ecosystems, and the fragile state of the system during its developmental stages, measures must be taken to protect the system. This can be achieved by buffer zone placement. The exact nature of the buffer zone will be modified depending on the progress of the development stage.
Socio-economic Factors
The implementation and management will require inputs from more than simply managers and scientists. Political will is a pre-condition, and success is more likely if resource users and the public at large are involved. In this particular case, threats to the Scarlet Ibis, a national symbol, must be given a crucial role in public education and political lobbying. This in itself implies difficulty, in the context of the need for international cooperation in migratory avifauna resource management. There have been a number of conflicts between Trinidad & Tobago and Venezuela regarding the shared management of the Gulf of Paria, which may be regarded as a sensitive transboundary resource. The lack of control regarding impacts on the locally resident Ibises in their breeding colonies in the western Gulf of Paria must be emphasised in public discourse. A project of this nature will have a high economic cost, for implementation and management, and as such, the benefits must be made tangible as far as possible, to achieve required support and commitment.
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Karl Ramjohn
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Re: Restoration of Degraded Tropical Agricultural
« Reply #3 on: Sep 21st, 2008, 7:14pm » |
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UNCERTAINTY: MONITORING, EVALUATION & RESEARCH
Wetland restoration technology is still an experimental science, particularly in the tropics. There is always uncertainty associated with attempts to create “natural” ecosystems. Despite extensive scientific evidence and comprehensive modelling applied to a created ecosystem, there is always the possibility for unexpected outcomes, or even failure for a “useful” wetland to become established. There is the possibility that an ecologically functional, but previously non-existent (locally) species assemblage will develop, and contaminate more-natural native wetland ecosystems.
The trends in succession for this restoration project will be monitored at appropriate intervals and where undesirable trends are observed, adaptive management will be implemented. For a sub-tropical system, Streever et al. (1996) recommended routine monitoring and reporting of hydrologic conditions and vegetation once a year for at least 3 years following implementation. In the assessment of unexpected outcomes, the dynamic nature of all ecosystems, and the provisional nature of current ecological models and understanding must be taken into account in trying to identify a desirable steady-state for the restored ecosystem.
Criteria for assessing wetland restoration success should include
• Sustainability – can the created system perpetuate itself with minimal management?
• Does the system resist invasion by exotic species?
• Does it show expected productivity and normal cycling of energy and nutrients?
• Has the expected hydrological cycling and water quality been achieved?
• Is the interaction with humans sustainable? Is there a perception of displacement or exclusion by the project?
• Is there sufficient commitment to the project?
• Does it support a variety of uses, in this case food production, conservation of biodiversity and heritage/recreation?
CONCLUSIONS
• Since 1995, sustainable development has become an explicitly stated policy in Trinidad & Tobago, as mandated by the Environmental Management Act.
• Traditional food production systems were unsustainable, leading to large areas of abandoned “ruinate” land.
• Ecological restoration is one means whereby some of this land can be brought back to productive use, by restoring the ecological functions and biodiversity
• Restoration can be used as a means of enhancing the sustainability of food production systems, by encouraging multiple land-use, as well as maintaining the option of returning a restored site to agricultural use, thus reducing the pressure on undisturbed land
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Karl Ramjohn
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Re: Restoration of Degraded Tropical Agricultural
« Reply #4 on: Sep 21st, 2008, 11:36pm » |
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Based on:
Ramjohn, Karl. Assessment of the Possibilities of Freshwater Ecosystem Restoration and Management at Degraded Agricultural Site at Caroni (1975) Ltd Rice Scheme. Tropical Environment Research & Management Center, Trinidad & Tobago. March 1999.
Further Resources:
> http://tropicalenv.conforums.com/index.cgi?board=manmade03&action=display&num=1218399006
> http://tropicalenv.conforums.com/index.cgi?board=landuse01&action=display&num=1218483973
> http://tropicalenv.conforums.com/index.cgi?board=manmade01&action=display&num=1216323960
REFERENCES
Adams, C.D. 1977. Caroni River Basin Study Appendices: Terrestrial Ecology. Water & Sewerage Authority, Republic of Trinidad & Tobago; 89 pp.
Bacon, P.R. 1978. Flora and Fauna of the Caribbean: An Introduction to the Ecology of the West Indies. Key Caribbean Publications; 319 pp.
Bacon, P.R. 1990. Extracts from a Field Guide to the Caroni Swamp, Trinidad. Department of Life Sciences, University of the West Indies, St. Augustine; 16 pp.
Bacon, P.R. 1993. Mangrove in the Lesser Antilles, Jamaica and Trinidad & TobagoConservation and Sustainable Utilisation of Mangrove Forests in Latin America and African Regions. Project PD114/90(F). International Tropical Timber Organisation; pp. 189-209
Bedford, B.L. 1996.The Need to Define Hydrologic Equivalence at the Landscape Level for Freshwater Wetland Mitigation. Ecological Applications 6(1):: 57-68
Bildstein, K.L. 1990.Status, Conservation and Management of the Scarlet Ibis, Eudocimus ruber, in the Caroni Swamp, Trinidad, West Indies.Biological Conservation 54:: 61-78
Blume, H. 1974. The Caribbean Islands. Longman Group; 464 pp.
Brinson, M.M. & Rheinhardt, R. 1996.The Role of Reference Wetlands in Functional Assessment and Mitigation. Ecological Applications 6(1):: 69-76
Christensen, N.L. (chair) et al. 1996. The Report of the Ecological Society of America Committee on the Scientific Basis for Ecosystem Management. Ecological Applications 6(3):: 665-691
CSO 1997. Annual Statistical Digest 1994-95. Central Statistical Office, Office of the Prime Minister, Republic of Trinidad & Tobago; 207 pp.
EMA 1997. Trinidad & Tobago: State of the Environment 1996 Report. Environmental Management Authority, Republic of Trinidad & Tobago; 93 pp.
Erwin, R.M. 1984.Conservation of Colonial Waterbirds in the Caribbean. Colonial Waterbirds 7:: 139-142
ffrench, R.P. 1966. The Utilisation of Mangroves by Birds in Trinidad Short Communications 108: 423-425
ffrench, R.P. 1980. A Guide to the Birds of Trinidad & Tobago. Asa Wright Nature Centre, Publication#1, Harrowood Books; 470 pp.
ffrench, R.P. 1984. The Scarlet Ibis in Trinidad Evaluation of the Wildlife Resources of Trinidad & Tobago. Ministry of Agriculture, Land & Marine Resources, Republic of Trinidad & Tobago
Hardy, F. 1981. "Soils" In Cooper, St.G.C. & Bacon, P.R. (eds) The Natural Resources of Trinidad & Tobago. Edward Arnold (UK); pp. 23-42
James, C., Nathai-Gyan, N. & Hislop, G. 1986. "Trinidad & Tobago" In Scott, D.A. & Carbonell, M. (eds) A Directory of Neotropical Wetlands. IUCN & IWRB; pp. 256-265
Ramnanan, H. 1993. The Annual Variability of Tropical Cyclone Activity in the North Atlantic-Caribbean Sea-Gulf of Mexico Basin. In Proc. Caribbean Conference on Natural Hazards: Volcanoes, Earthquakes, Windstorms, Floods. Seismic Research Unit & Department of Civil Engineering, University of the West Indies, St. Augustine. October 1993
Streever, W.J., Crisman, T.L. & Kiefer, J.H. 1996. "Constructing Freshwater Wetlands to Replace Impacted Natural Wetlands: A Subtropical Perspective" In Scheimer, F. & Boland, K.T. (eds) Perspectives in Tropical Limnology. SPB Academic Publishing; pp. 295-303
WASA 1990. Explanatory Notes: Hydrogeological Maps of Trinidad & Tobago. Water Resources Agency, Republic of Trinidad & Tobago; 19 pages & maps.
Wilson, E.O. 1989. "Conservation: The Next Hundred Years" In Western, D. & Pearl, M. (eds) Conservation for the Twenty-First Century. Oxford University Press; pp. 3-7
Zedler, J.B. 1996.Ecological Issues in Wetland Mitigation: An Introduction to the Forum. Ecological Applications 6(1):: 33-37
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