Land Cover Changes in Caroni Swamp in Trinidad

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  • Land Cover Changes in the Caroni Swamp, Trinidad

    from 1942-2007

    Prepared by

    Rahanna A. Juman

    Wetlands Ecologist

    and

    Deanesh Ramsewak

    Remote Sensing Officer

    July 2011

  • ii

  • iii

    All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or

    transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise,

    except as permitted by the Copyright Act of Trinidad and Tobago No. 8 of 1997, without the prior

    permission of the publisher. IMA encourages the fair use of this document and proper citation is requested.

  • i

    ABSTRACT

    Caroni Swamp, the largest mangrove dominated wetland in Trinidad and Tobago, has

    been impacted by human activities since the early 1900s. This study examines the

    change in land cover and land use from 1942-2007. Remote sensing technology and

    geographic information systems (GIS) together with extensive field surveys in 2004 and

    2005 were used to demarcate the boundary of the wetland as well as the various land use

    and land cover classes. Land cover maps for were produced for 1942, 1957, 1986, 1994,

    2003 and 2007 from aerial photos and satellite imagery. Caroni Swamp occupied

    approximately 21.7 km of the Gulf of Paria coastline, extending from the Beetham and

    Churchill Roosevelt Highways in the north to the Chandernagore River in the South. In

    2005, the wetland was estimated at 9,648.4 ha inclusive of the WASA Sewage Treatment

    Plant, Beetham Landfill and the El Socorro Industrial Estate.

    Major hydrological alteration in this wetland in the 1920s resulted in large freshwater

    marsh and rice fields. From 1942 to 1957, marshland and agriculture cover increased,

    but after this period there was a decline in both due to salt water intrusion and freshwater

    diversion. Although mangrove forest was cleared for built development, it coverage has

    consistently increased in the Swamp from 1957, with the exception of 2003 when there

    was a slight decrease by less than 100 ha. Natural wetland communities (mangrove,

    marsh and open water) increased from 1942-2003, but declined in 2007, as built

    development more than doubled. The report provides spatial coverage, and quantified

    land cover from 1942-2007. It also identifies reasons for the changes in land cover and

    uses.

  • ii

    ACKNOWLEDGEMENT

    The authors wish to acknowledge the following individuals who have contributed to this

    study: Suresh Sookbir, Neal OConnor, Lamani Patino, Jonathan Gomez, Al Small,

    Addison Titus, Marc Bejai, Sarah Hosein, Jillian St. Bernard, Kahlil Hassanali, Adam

    Jehu and Ramesh Gayah.

  • iii

    TABLE OF CONTENT

    Page No.

    1.0 INTRODUCTION ... 1

    2.0 GOAL AND OBJECTIVES ... 7

    3.0 METHODOLOGY .. 8

    4.0 RESULTS .... 10

    5.0 DISCUSSION .. 24

    6.0 REFERENCES 32

  • iv

    LIST OF FIGURES

    Page No.

    Figure 1: Location of Caroni Swamp, Trinidad 2

    Figure 2: Map of the major rivers in the Caroni River Basin .. 3

    Figure 3: Land cover in the Caroni River Basin in 2003-2004 5

    Figure 4: Land cover map of Caroni Swamp as determined

    using 2003 aerial photography . 11

    Figure 5: Land cover map in the Caroni Swamp in 1942 and 1957 . 13

    Figure 6: Land cover map in the Caroni Swamp in 1957 and 1986 . 15

    Figure 7: Land cover map in the Caroni Swamp in 1986 and 1994 . 17

    Figure 8: Land cover map in the Caroni Swamp 1994-2003 18

    Figure 9: Land Cover map in the Caroni Swamp 2003-2007 .. 21

    Figure 10: Chart showing mangrove, marsh and agriculture coverage

    from 1042-2007 . 23

    Figure 11: Map showing channels within the Caroni Swamp

    Ramsar site .. 28

    Figure 12: Map of Caroni Ramsar Site showing privately owned lands .. 31

  • v

    LIST OF TABLES

    Page No.

    Table 1: Land cover and plant communities in the Caroni

    Swamp in 2003 10

    Table 2: Land cover and plant communities in the Caroni Swamp

    1942-2007 14

    Table 3: Land cover of natural wetland types in the Caroni Swamp

    1942-2007 23

    LIST OF PLATES

    Plate 1: The straightened Caroni River and mangrove dieback

    observed on the southern side . 19

    Plate 2: Narrow cut that connects the Caroni river to the Blue River .. 20

    Plate 3: Red mangroves extending into marshland dominated

    by sedges (Eleocharis sp.) in the Caroni Swamp . 22

    Plate 4: Infilling of marshland along the Uriah Butler

    Highway for built development .. 22

  • 1

    1.0 INTRODUCTION

    Human transformation of land to yield goods and services represents the most substantial

    changes to ecosystems worldwide (Millennium Ecosystems Assessment, 2005; Worm et

    al., 2006). Material demands of production and human consumption alter land use and

    land cover, biodiversity, and hydro-systems locally to regionally; and waste discharge

    affects local to global biogeochemical cycles and climate (Grimm et al. 2008). While it

    is more difficult to quantify alterations to marine ecosystems, changes are substantial as

    about 60% of the world population lives within 100 km of the ocean (Vitousek et al.,

    1997). Coastal wetlands that mediate interactions between land and sea have been altered

    over large areas; approximately 50% of mangrove ecosystem globally have been

    transformed or destroyed by human activities (World Resource Institute, 1996).

    Trinidad and Tobago, like other Small Islands Developing States (SIDS), has a small land

    mass, high population density and concentrated economic activities along the coast which

    makes it more vulnerable to environmental disasters. SIDS river basins are generally of

    comparatively small size because of the predominance of island areas, and thus, impacts

    are characterized by a short response time from basin development activities to coastal

    responses as compared to the larger basins of South America (Kjerfve, 2002). In almost

    all Caribbean watersheds, population growth has overwhelmed any attempt to implement

    rational coastal management. In Trinidad and Tobago for instance, the population has

    almost doubled from 600,000 in 1950 to 1.2 million in 2000 (CSO, 2000) with

    approximately 70% living on the west coast of Trinidad.

    The Caroni River Basin, the hydrometric area that encompasses the Caroni Swamp is

    situated in the northwestern section of Trinidad and covers about 883.4 km2, equivalent

    to 22% of the land surface area of the island (Figure 1) (Juman et al., 2002). The Caroni

    and associated Rivers discharge into the Caroni Swamp, the largest mangrove forest in

    Trinidad and Tobago (Juman et al., 2010). The swamp is important economically for

    oyster and fish harvesting, for hunting and for ecotourism. Major commercial fisheries

    are based on demersal stock in the adjacent eastern Gulf of Paria.

  • 2

    Figure 1: Location of Caroni Swamp, Trinidad

    The Caroni River, which is the largest river in Trinidad, drains the Northern and Central

    Ranges to the west and has a catchment area of about 600 km2 (Juman et al., 2002). The

    major part of the Caroni River water supply comes from perennial tributaries of the

    Northern and Central Ranges. Twelve rivers flow into the Caroni Swamp on its northern

    side from the Northern Range, and six rivers flow in from the southern side from the

    Caroni Plain and the northern side of the Central Range (Juman et al., 2002) (Figure 2).

  • 3

    Figure 2: Map of the major rivers in the Caroni River Basin

    The gently sloping foothills of the northern and central ranges and the non-flood prone

    areas of the Caroni floodplain are used extensively for built development, both industrial

    and residential. The Caroni River Basin represents the most populated part of the

  • 4

    country, housing 33% of the national population (CSO, 1995). The area has a population

    density of 439 persons km-2

    which is higher than the national average. The river basin

    contains some of the most fertile land in the country (Brown et al., 1966). Increased

    competition for lands in the flatter areas of the basin has led to built development on the

    fertile lowlands, encroachment into the wetland area and additional development on

    steeper slopes. Figure 3 is a land cover map for the Caroni Basin based on data collected

    during 2003-2004.

    Caroni Swamp is situated southwest of the capital, Port of Spain. It is the second largest

    wetland in Trinidad after Nariva Swamp and consists of mangrove and herbaceous marsh

    interrupted by numerous channels and lagoons (Bacon, 1993). This swamp was altered in

    the 1920s under the Cipriani Reclamation Scheme which was initiated to facilitate rice

    cultivation. The scheme involved hydrological alterations to the swamp; the North South

    Drain was excavated, 10 eastwest channels were cut to join the NS drain, two tide

    exclusion sluices were constructed, 7 east-west canals on the south side of the Blue River

    were cut to increase water circulation and 2 embankments were built (Bacon, 1970).

    The Reclamation Scheme was officially abandoned in 1954 by which time the canals and

    embankments were already in a state of disrepair (Bacon, 1970). Further flood protection

    works which began in the 1950s and the construction of the Caroni Arena Dam has

    resulted in an overall reduction of freshwater inflow into the Caroni Swamp (Phelps,

    1997). This has reduced freshwater storage in the wetland and caused salinity levels to

    increase. In addition to saltwater penetration, the Caroni Swamp receives water polluted

    with sewage, wastewater from industry and agriculture run-off (Phelps, 1997).

  • 5

    Figure 3: Land cover in the Caroni River Basin in 2003-2004

    In the 1970s, the eastern borders of the Caroni Swamp between the North-South

    Embankment and the Uriah Butler Highway were predominantly freshwater herbaceous

    wetland (Bacon, 1970) This area know by local residents as the Reeds was largely an

    artifact of embankment work carried out under the Cipriani Drainage Scheme (Bacon,

    1970). Bacon (1970) hypothesized that there was likely to have been a large lagoon,

  • 6

    bordered by freshwater marsh along the eastern border of the wetland. Distributary

    patterns and water movements were altered by the drainage work, leading to

    impoundment of land run-off to the east and influencing the location and extent of

    colonization by freshwater species. As the tide exclusion banks deteriorated in the late

    1960s, the wetland began to revert to its former structure (Bacon, 1970). Ramcharan et

    al., (1982) produced a vegetation map for Caroni Swamp, but the legend is difficult to

    decipher.

    Between 1922 and 1985, more than 500 ha of mangrove forest were lost for the

    construction of roads, WASA sewage ponds, landfill, and as a results of dredging to

    widen the river (Gerald, 1985). In 2001, the IMA detected from satellite imagery large

    areas of mangrove dieback in the Caroni Swamp. The total area of mangrove die-off

    detected was estimated at 170 ha, and this is within the Caroni Swamp Forest Reserve,

    which was proclaimed in 1936. More recently, private landowners have cleared wetland

    and there is encroachment on the eastern boundary from unregulated housing (squatting).

    The management of this wetland has become very challenging since most of the impacts

    on the wetland emanate from outside its boundaries and there are issues of land tenure.

    The Caroni Swamp has been impacted by human activities within the catchment areas

    and within its borders. The plant communities have changed over time. This study

    examines the changes in land cover and land use from 1942-2007 based upon aerial

    photography and satellite imagery.

  • 7

    2.0 PROJECT GOAL AND OBJECTIVES

    The goal of this study was to investigate land use and cover changes in Caroni Swamp

    from 1942 to 2007. The specific objectives were:

    1. To map the historical and up-to-date areal extent and physical features

    of the Caroni Swamp using Remote Sensing and GIS tools.

    2. To characterize the plant communities within the Caroni Swamp and map

    their spatial extent and distribution.

    3. To determine spatial changes in the plant community and identify the

    human impacts on the ecology of the swamp.

  • 8

    3.0 METHODOLOGY

    A literature search was conducted to obtain information on the Caroni River Basin and the

    associated Caroni Swamp. Documentation was sought primarily from the libraries of the

    following agencies:

    Institute of Marine Affairs

    University of the West Indies

    Wildlife Section, Forestry Division, Ministry of Public Utilities and the

    Environment

    Environmental Management Authority

    Land and Water Development Division, Ministry of Agriculture, Lands and

    Marine Resources

    The boundaries of Caroni Swamp were defined using physical and biological

    characteristics: topography, hydrology, and vegetation type. Extensive ground-truthing

    surveys were conducted between November 2004 and April 2005 using 2003 aerial

    photography to delineate the boundary of the wetland. Additional surveys were

    conducted in October 2008 and February 2009 using IKONOS satellite imagery (2007).

    Areal cover was determined using maps and aerial and satellite imagery relevant to the

    study area. Data obtained included the following:

    1:25 000 Topographic Map Sheets (Nos. 23, 24, 33 & 34)

    1:50 000 Aerial Photographs (1942)

    1:12 500 Aerial Photographs (1957)

    1:10 000 Aerial Photographs (1986)

    1:12 500 Aerial Photographs (1994)

    1: 25 000 Aerial Photographs (2003)

    Landsat Imagery (Aug 2001)

    2007 IKONOS Imagery

  • 9

    Aerial photographs were geo-referenced and registered in the Naparima Datum UTM

    Projection to be compatible with the Topographic map sheets. For each epoch, aerial

    photographs were mosaicked to produce a seamless data layer. The satellite images (as

    well as other data layers) were also registered in the Naparima Datum to ensure spatial

    correspondence.

    The data layers were imported into a GIS for mapping, change detection and analysis.

    Features mapped and assessed for changes over time include the following:

    Extent and size of the wetland system (based on a set of criteria)

    Mangrove and other vegetation types

    Agricultural areas

    Water channels

    Land use (agriculture, urban, recreation, grazing, waste etc.)

    The major plant communities (natural and agricultural) within the system were identified,

    and classified following the classification for Caribbean wetlands provided by Bacon

    (1993). Data collected was compared to past studies (Bacon, 1970; Bissessar, 1998). The

    status of the mangrove swamp was investigated, and impacts identified.

  • 10

    4.0 RESULTS

    Caroni Swamp Boundary

    The boundary of Caroni Swamp as delineated in 2005 using 2003 aerial photography

    (1: 25,000) is shown in Figure 4. The wetland boundary is contiguous, hydrologically

    connected and below the 25 ft (7.5 m) contour. Caroni Swamp was estimated at

    9,648.4 ha inclusive of the WASA Sewage Treatment Plant, Beetham Landfill and the El

    Socorro Industrial Estate. It occupied approximately 21.7 km of the Gulf of Paria

    coastline, extending from the Beetham and Churchill Roosevelt Highways in the north to

    the Chandernagore River in the South (Figure 4).

    The land-cover and plant communities within the Swamp in 2003 are provided in

    Table 1. The mangrove forest was the dominant plant community occupying about 45 %

    of the wetland area (Figure 4). It occupied the western side of the wetland where

    conditions were brackish to marine. Marsh lands and rice fields were the other main

    plant communities. Rice fields accounted for 1,279 ha of the agriculture lands

    Table 1: Land cover and plant communities in the Caroni Swamp in 2003

    Land Cover Class Area (ha)

    Mangrove 4,343.1

    Marsh 1,836.6

    Pond and open water 536.3

    Mangrove die-back 110.7

    Backfilled area 38.0

    Agriculture 2,289.2

    Built Development 346.4

    Total 9,648.4

  • 11

    Figure 4: Land cover map of Caroni Swamp as determined using 2003 aerial photography

  • 12

    Caroni Swamp has experienced land cover / land use changes dating back to the early

    1900s. In 1942, a larger portion of the swamp was covered with marsh vegetation and

    agriculture (primarily rice cultivation) and the mangrove forest extended north to the

    Railway which is presently the Priority Bus Route (Figure 5; Table 2). The Beetham

    Gardens community and Highway, the WASA Sewage Treatment Plant, the Beetham

    Landfill did not exist. Construction of the ChurchillRoosevelt Highway began in

    December 1941 and was completed in March 1942, however it did not extend far west

    into the Caroni Swamp.

    By 1957, there was a large increase in agriculture (> 600 ha), and slight increases in built

    development and marsh vegetation (Table 2). There was a small decrease in mangrove

    coverage as more (East-West) drains were cut and pond and open water areas increased.

    While the agriculture land expanded on the eastern edge of the swamp taking up marsh

    area, agriculture land on the northern edge reverted to marsh, and mangrove area on the

    southeastern edge was colonized by marshes (Figure 5). By 1957, the Churchill

    Roosevelt Highway extended north to the Eastern Main Road in Barataria. Construction

    of the Princess Margaret Highway began and was completed by 1958 (Figure 5). It was

    extended and later renamed the Uriah Butler Highway in 1988.

    There were major changes in the Caroni Swamp between 1957 and 1986. Within those

    29 years, more than 500 ha of mangroves were cleared for the Construction of the

    Beetham Landfill, WASA Sewage Treatment Plant, Beetham Highway and from

    widening the Caroni River (Figure 6). However, mangrove coverage increased in the

    swamp by 523 ha as mangrove trees expanded into marshland. Therefore, more than

    1000 ha of mangroves spread into marshland while approximately 500 ha were cleared

    on the northern edge.

    Marshland coverage decreased considerably by more than 500 ha. Besides marsh being

    over grown by mangroves, marsh on the northern end of the wetland was also cleared for

    the El Soccoro Industrial Estate. At the same time, some agriculture land was left to lie

    fallow and reverted to marsh. Agriculture decreased considerable by 413 ha; some lands

  • 13

    Figure 5: Land cover map in the Caroni Swamp in 1942 and 1957

  • 14

    Table 2: Land cover and plant communities in the Caroni Swamp 1942-2007

    Land Cover Class AREA (hectares)

    1942 1957 1986 1994 2003 2007

    Mangrove 3575.9 3560.5 4083.5 4444.3 4343.1 4681.1

    Marsh 1535.8 1693.0 1155.1 1162.4 1836.6 1012.6

    Pond /open water 156.8 337.0 783.0 612.1 536.3 676.3

    Agriculture 3086.0 3724.7 3311.3 2603.6 2289.2 2692.5

    Built Development 6.9 55.8 215.2 363.4 346.4 842.1

    Highway 8.0 18.5 44.3 89.5 75.4 82.4

    Railway

    Mangrove die-back

    17.7

    18.7

    NA

    NA

    NA

    NA

    NA

    NA

    NA

    110.7

    NA

    12.1

    Back fill

    Solid Waste Land fill

    NA

    NA

    NA

    NA

    NA

    47.5

    NA

    68.5

    38.0

    72.6

    NA

    73.7

    NA Not applicable

  • 15

    Figure 6: Land cover map in the Caroni Swamp in 1957 and 1986

  • 16

    reverted to marshland and others were converted into built development. Built

    development increased by 159 ha.

    Between 1986 and 1994, mangrove forest continued to expand and increased in coverage

    by 361 ha (Figure 7). Mangrove forest continued to spread eastward into marshland, as

    well as in the northwestern side around the sewage ponds and landfill. Ponds and open

    water areas were overgrown by mangroves and they decreased by 170 ha. Dredged spoilt

    that was dropped at the mouth of the Caroni River, was also colonized by mangroves.

    Although marshlands were lost to mangrove, marsh coverage in the swamp increased

    slightly by 6 ha, as some agriculture lands reverted to marsh, and the WASA sewage

    ponds were covered with marsh vegetation. Agriculture decreased considerably in the

    swamp during this period by more than 700 ha. Built development increased by 148.2 ha

    as new developments were built along the fringes of the Uriah Butler Highway on land

    that was previously used for agriculture.

    By 2003, the agricultural land on the northeastern side of the wetland, and between

    Caroni and Blue Rivers, west of the Uriah Butler Highway had reverted to marshland

    (Figure 8). Between 1994 and 2003, marshland increased by 674.2 ha while agricultural

    land decreased by 314 ha (Figure 8). Open water areas within the mangrove swamp

    decreased by about 75 ha and these areas were occupied by marsh vegetation (Figure 8).

    Marsh vegetation also occupied areas that were once built up as built development

    decreased by 14 .1 ha.

    During this same period (1994-2003), the Caroni River was straightened and widened,

    and mangroves along the banks were cleared. An island was created and an area of dead

    mangrove approximately 110.7 ha was observed south of the Caroni River (Plate 1).

    Overall, mangrove coverage decreased by 101.2 ha, even though mangrove dieback

    accounted for 110.7 ha. This indicates that there were about 9.5 ha of new growth.

    Mangrove continued to extend into marshes on the eastern side of the wetland, west of

    the Uriah Butler Highway.

  • 17

    Figure 7: Land cover map in the Caroni Swamp in 1986 and 1994

  • 18

    Figure 8: Land cover map in the Caroni Swamp 1994-2003

  • 19

    Plate 1: The straightened Caroni River and mangrove dieback observed on the southern side (Photo by R. Karim)

  • 20

    Between 2003 and 2007, mangrove coverage increased by 338 ha, built development

    more than doubled (increased from 346.4 to 842.1 ha), and agricultural land increased by

    403.3 ha (Figure 9). The area of mangrove dieback observed in 2003 had re-grown,

    however some new dieback was observed further east on the southern side of the Caroni

    River. Although not shown in Figure 9, a narrow cut was made connecting the Caroni

    River to the Blue River (Plate 2); this is close to the area where the die-off is seen (Figure

    9).

    Plate 2: Narrow cut that connects the Caroni River to the Blue River

    During the same period marshland decreased by 824 ha and open water area decreased by

    140 ha. Mangrove forest extended further east overgrowing marshlands (Plate 3), and

    filled in some of the open water/ pond. The marsh areas observed on the western side of

    the swamp among the mangroves in 2003 have either been overgrown with mangroves or

    have reverted to open water areas. Marshland has also been converted into built

    development and agriculture lands. Built development continues to encroach upon

    marshland along the Uriah Butler Highway (Plate 4).

  • 21

    Figure 9: Land Cover map in the Caroni Swamp 2003-2007

  • 22

    Plate 3: Red mangroves extending into marshland dominated by sedges (Eleocharis sp) in the

    Caroni Swamp

    Plate 4: Infilling of marshland along the Uriah Butler Highway for built development

  • 23

    Mangrove forest is the major vegetation community in the Caroni Swamp. This ecotype

    has increased considerable from 1957 to 2007 (Figure 10). In the 65 years span of this

    study (1942-2007), mangrove coverage in the swamp has increased by 1105 ha while

    marshland has decreased by 523 ha, agriculture has decreased by 393.5 ha, and built

    development within the swamp has increased by 835 ha. The solid waste landfill has

    increased in size since its construction from 47.5 ha in 1986 to 73.7 ha in 2007 (Table 2).

    Figure 10: Chart showing mangrove, marsh and agriculture coverage from 1942-2007

    Generally, the natural wetland communities (mangrove, marshes and open water/ pond)

    increased between 1942 and 2003, as agriculture lands reverted to marsh and mangrove

    colonized mudflats and dredge spoilt on the seaward side. However between 2003 and

    2007, natural wetland coverage declined by about 346 ha as built developed and

    agriculture lands increased (Table 3).

    Table 3: Land cover of natural wetland types in the Caroni Swamp 1942-2007

    Wetland class Year

    1942 1957 1986 1994 2003 2007

    Mangrove 3575.9 3560.5 4083.5 4444.3 4343.1 4681.1

    Marsh 1535.8 1693.0 1155.1 1162.4 1836.6 1012.6

    Open-water/ pond 156.8 337.0 783 612.1 536.3 676.3

    Total 5,268.5 5,590.5 6,021.6 6,218.8 6,716.0 6,370.0

  • 24

    5.0 DISCUSSION

    Wetlands were once considered wastelands which would better serve nations when filled

    for built development or drained for agriculture (Field, 1995). This perception is

    changing as research conducted during the past four decades have highlighted the values

    of wetlands and the services they provide. The Millennium Ecosystem Assessment

    (2005) classified wetland services as provisioning (food, water and fuel), regulating

    (erosion, flood control, climate regulation), cultural and supporting (tourism and

    recreation), and has acknowledged their tremendous economic benefits (Blumenfield et

    al., 2009). Yet, wetland coverage worldwide continues to decline to accommodate

    growing populations.

    Knowledge of the wetlands current and past extent, condition and uses is essential for

    managers, policy and decision makers. This can help them to make effective

    management interventions, so as to maintain and if necessary, restore ecosystem services.

    This study examined the land-use / land cover changes that occurred in the Caroni

    Swamp from 1942-2007 using remote sensing and GIS technology. The 2003 aerial

    photographs were extensively ground-truthed and the different land use/land cover types

    classified. These classifications were used as a guide to visual interpretation in order to

    map the land cover in earlier imagery.

    The first documented alteration to Caroni Swamp was under the Cipriani Reclamation

    Scheme during 1921-1922; although aerial photography prior to, and during this period

    were not available to confirm changes. The original drainage pattern in the Swamp was

    modified to reclaim the eastern section of the Swamp for agriculture, specifically rice

    cultivation, and to improve drainage from the swamp to the coast (Bacon, 1970; Phelps,

    1997). This involved the:

    i. excavation of the North-South Drain, construction of an embankment and

    installation of two sluice gates to isolate the reclaimed area from tidal movement;

  • 25

    ii. division of the reclaimed areas into polders with embankments founded on

    mangrove mat and divided into 9 East-West drainage channels that discharges

    into the N-S Drain;

    iii. construction of an East-West channel west of the N-S embankment to intercept

    the natural watercourses running from northeast to southwest in the Swamp and

    link them to the Blue River;

    iv. construction of 7 east-west canals on the south side of the Blue River to increase

    water circulation;

    v. construction of a Cipriani Canal linking the Caroni River to the Blue River near

    the coast;

    vi. construction of flood relief channel south of the Caroni River, and parallel to it;

    vii. installation of a pumping station at the northern end of the N-S Drain for drainage

    of reclaimed area.

    After this hydrological work, the eastern section of the swamp was isolated by the

    embankment and salinity was gradually lowered so that it was possible to begin

    agriculture activities.

    During 1940-1955, the government had developed two areas for rice cultivation; the

    Caroni Irrigation Scheme; east and west of the Uriah Butler Highway and the Caroni

    Savannah Scheme which occupied the same area reclaimed under the Cipriani Scheme.

    Agriculture had increased by 639 hectares from 1942-1957 (Table 2). In the interest of

    agriculture, the Uriah Butler Highway (formerly Princess Margaret Highway) was

    constructed to connect the Churchill Roosevelt Highway to the Southern Main Road at

    Chaguanas. The highway partially blocked the free flow of flood waters of the Caroni

    River arriving from the east; thereafter drainage in the swamp could take place only

    through culverts and under the bridges provided integrally with the new highway (Phelps,

    1997).

  • 26

    In 1942, a larger portion of the Caroni Swamp was covered with marsh as well as

    agriculture (Figure 5). Bacon (1970) provided a detailed description of this freshwater

    marsh community referred to as the Reeds by locals since it comprised extensive tracts

    of sedges and grasses. Beard (1946) and Bacon (1970) postulated that the construction of

    the tidal exclusion embankments along the western side of the N-S drain may have led to

    the development of the marshland, therefore this section of the swamp may have

    developed artificially. In the 1942 image, the mangrove forest was found mainly west of

    the N-S embankment, except in the south along the banks of the Madame Espagnole

    River. The mangrove also extended north to the Railway (Figure 5).

    The Cipriani Reclamation scheme was officially abandoned in 1954, by which time the

    N-S embankments and the enclosing polder embankments were already in a state of

    disrepair, allowing saline water to enter the reclaimed area once again (Bacon, 1970).

    The new swamp drainage channel constructed under the Scheme provided a conduit for

    saline water to enter (Phelps, 1997). In the 1957 image, mangroves had started to grow

    into the marsh area (Figure 5) and rice cultivation had expanded.

    In the 1950s, government also implemented the first flood protection scheme for the

    Caroni River Basin as built development within the Basin increased (Phelps, 1997). The

    Caroni River was widened and deepened, and flood embankments constructed. The flow

    capacity of the Caroni River downstream of the Uriah Butler Highway increased

    substantially by widening and deepening the River and dredging the mouth. The breach

    in the embankment at the N-S drain was repaired in the 1966, and this eliminated

    freshwater flow into the Swamp from the Caroni River.

    The freshwater supply to the southern section of the Swamp by the Guayamare and

    Cunupia Rivers was cut off when the joint flow of these rivers were directed solely to the

    Madame Espagnole by sealing the eastern end of the lower section of the Guayamare

    (Phelps, 1997) (Figure 11). The quantity of freshwater flowing in the Swamp decreased

    consistently through this drainage work as well as the irrigation scheme for agriculture.

  • 27

    Freshwater was diverted from the Caroni River to the Guayamare River to provide an

    irrigation supply to the Caroni rice projects.

    Freshwater diversion and saltwater encroachment have changed the Reed plant

    community (Bacon et al., 1997; Bissessar, 1998). This has now been replaced by

    mangroves, open saline water bodies, and by saline marshes, dominated by sedges,

    Eleocharis spp. and the fern Acrostichum aureum. The spread of mangroves into the

    eastern marshland has been rapid over the past four decades (Figures 6-9). These

    marshes may eventually be replaced by mangrove forest.

    Prior to the 1960s, the major changes to Caroni Swamp were hydrological in nature;

    channels were cut, embankments were built, water was diverted away from the wetland,

    and the Caroni River was dredged and widened. Conduits were constructed to drain the

    wetland, and these same conduits carried saline water upstream when the embankment

    fell into disrepair in the 1950s (Figure 11). Highways (Churchill Roosevelt and Uriah

    Butler) were constructed and this also impeded the flow of the rivers into the wetland.

    There were minor changes in the natural wetland communities (Table 3), while

    agricultural land increased and built development started.

    Beyond, the 1950s there were major land cover/ land use changes in the Caroni Swamp.

    The mangrove forest on the northern side of the Caroni River was reclaimed for the

    construction of the Beetham landfill, WASA sewage treatment plant and ponds, and the

    Beetham Gardens. Built development expanded along the fringes of the wetland and

    while agriculture land reverted to marshes, marsh lands were overgrown by mangroves

    (Figure 9). In 2007, there was a small increase in agriculture land ( 400 ha), which had

    consistently declined form 1957-2003.

  • 28

    Figure 11: Map showing channels within the Caroni Swamp Ramsar site

  • 29

    The Caroni River Basin has also experienced extensive land-use/land cover changes

    within the past few decades and this has serious consequences for the Caroni Swamp, the

    receiving environment for the land-based runoff. In addition to saltwater penetration,

    Caroni Swamp receives sediment laden water polluted with sewage, wastewater from

    industry and agriculture run-off (Donawa, 1976; Deonarine 1980, Siung-Chang, 1987;

    Phelps, 1997; IMA 1999; IMA (unpublished). This has affected the quality of the habitat,

    and the shellfish harvested in the swamp. For instance there was a country-wide ban on

    mangrove oyster (Crassostrea rhizophorae) in 1992 because of the threat of cholera.

    Fish kills and mangrove dieback seem to be a regular occurrence in Caroni Swamp

    (Bacon, 1970; Siung-Chang, 1987; IMA unpublished). Major mangrove die-off events

    were reported by Bacon (1970) and observed in 2001 Landsat Imagery. In 2001, 170 ha

    of mangroves were recorded and although the cause of the die-off was undetermined, it

    coincided with the widening, deepening and straightening of the Caroni River, the raising

    of the southern bank (IMA, unpublished) and hypersaline conditions. Interstitial salinity

    in the dead area was recorded at 82.

    Frequent hydrological work in the Caroni Swamp to mitigate flooding in the associated

    catchment have negatively impacted on the health of the mangroves, since channels are

    widened and dredged, mangrove trees are removed, and the dredge spoilt placed on the

    bank inhibits the natural flushing of the system. Mangrove productivity is a function of

    water turnover in the forest (Pool et al., 1975); reduced tidal flushing results in higher

    soil salinity (Cintrn et al., 1978; Santos et al., 1997), decrease in nutrients and/ or the

    accumulation of toxic substances such as hydrogen sulphide (Nickerson and Thibodeau,

    1985). Mangroves have an optimum salinity range for maximum growth; at extreme

    level mangrove species suffer damage and even mortality (FAO, 1994).

    Management of Caroni Swamp

    In 1936, approximately 2,833 ha of Caroni Swamp were proclaimed a Forest Reserve. In

    1953, a further 136 ha were designated a Wildlife Sanctuary for breeding Scarlet Ibises,

    and this was later extended to 200 ha (Bacon & Ffrench, 1972). Fishing, oyster

  • 30

    collecting and hunting had been permitted in all areas except the Wildlife Sanctuary, but

    in 1987 the major part of Caroni Swamp, south of the Blue River, was declared a

    Prohibited Area (Forests Act, Chap 66:01) and these activities became prohibited. Only

    licensed tour guides were allowed to take tours into the Prohibited Area.

    In 2005, the Caroni Swamp was declared a Ramsar Site, a wetland of international

    importance, as it is an essential habitat for numerous commercial species, as well as rare

    and endangered species (Figure 11). Within the Ramsar site boundary, there are privately

    owned land (Figure 12) and development of these lands especially along the Uriah

    Highway would further encroach on the wetland communities. The Forestry Division is

    the government agency with responsibility for managing the Caroni Swamp and while

    they provide game wardens to patrol the swamp to discourage poaching, there is no

    comprehensive management plan for the conservation and restoration of this wetland.

  • 31

    Figure 12: Map of Caroni Ramsar Site showing privately owned lands

  • 32

    6.0 REFERENCES

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    Central Statistical Office, Trinidad and Tobago, 68 pp.

    Bacon, P. R. 1993 Mangroves in the Lesser Antilles, Jamaica and Trinidad and Tobago.

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    International Tropical Timber Organization/ International Society of

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    Bacon, P. R., Bissessar, V. and Cuffy, G., 1997. Study of the Feasibility of Marsh

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