Title: Reefs at risk in the Caribbean, threats to coral reefs from land-based sources of pollution
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Title: Reefs at risk in the Caribbean, threats to coral reefs from land-based sources of pollution
Physical Description: Book
Language: English
Creator: World Resources Institute
Publisher: World Resources Institute
Place of Publication: Washington, D.C.
Copyright Date: 2008
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Bibliographic ID: UF00095909
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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WAESE-AE SOURCES OF; SEDMN AND PO11T


tormwater runoff and erosion are natural environmental
processes. However, human activities that alter the land-
scape can increase both runoff and erosion, and ultimately
result in increased delivery of sediment and pollutants to coastal
ecosystems far removed from the converted lands. Conversion of
land from forest and other natural land cover types to agriculture
typically increases runoff (due to decreased infiltration), and exposes
more soil to erosion. The runoff from lands converted to agricultural
usage will also transport other pollutants, such as excess nutrients
(especially nitrogen and phosphorus) from fertilizers, and toxic com-
pounds found in herbicides and pesticides. In addition, conversion of
land to urban or industrial use (urbanization), which is widespread
in the region, results in increased river-borne pollution from industri-
al and domestic waste with significant negative impacts on coral
reef ecosystems.
The effects of land use change are also exacerbated by natural dis-
turbances, such as hurricanes. Altered land use compounded the
effects of Hurricane Mitch in 1998 causing massive loads of sedi-
ment-laden water to flow out on to the Mesoamerican Barrier Reef
System (MBRS).









Pollution and erosion from land-clearing activities
far inland contribute to reef sedimentation


SEDIMENT Increased sediment delivery to coastal waters is a key stress on coastal ecosys-
tems. Increased sedimentation can cause a variety of negative impacts on coral reefs, including
screening out light needed for photosynthesis, scouring of coral by sand and sediments, poor
survival of juvenile coral due to loss of suitable substrate, and the direct smothering of coral in
cases of extreme sedimentation.

NUTRIENTS Elevated nutrient in coastal waters promotes increased algal growth on coral
reefs, and can result in algal blooms, changes in the aquatic community structure, decreased
biological diversity, and fish kills.

TOXIC SUBSTANCES Heavy metals, petroleum hydrocarbons (much of which comes from runoff
of motor oil and other wastes from roads), and other toxic materials are a cause for concern
because of their poisonous effects on aquatic life, and because their accumulation in the tis-
sues of fish and shellfish can be harmful to human health.











atersheds are critical units for analysis since they link land areas with their point of dis-
charge to the sea. A watershed is the area of land that drains water, sediment and other
pollutants to a common outlet along the coastline. In this analysis we try to capture the
influence of the primary factors that affect erosion: land cover type, slope, soil characteristics,
and precipitation. These relative erosion estimates are summarized by watershed. As not all ero-
sion makes its way to the river mouth, sediment delivery ratios (based on watershed size) were
applied in order to estimate relative sediment delivery at the river mouth. Sediment plumes were
estimated based on the relative sediment delivery and distance from each river mouth. By over-
laying sediment plumes with the location of coral reefs, we are able to estimate the degree of
threat to coral reefs from watershed-based sediment and pollution. (See map below.)

The value of this approach
This approach permits patterns of land use within watersheds to be linked with sources of sedi-
ment transport and delivery to coral reefs, enabling those reefs at greatest risk to be identified.
Maintaining healthy coral reef ecosystems and their associated biodiversity depends on applying This Landsat image of the northwest of Puerto
appropriate land-use practices in critical watersheds to ensure that the impact of sediment, Rico, taken in January 2003, clearly shows sed-
nutrients, and other pollutants on the coral reef system is minimized. Using this approach, it is iment laden plumes dispersing along the coast
possible to identify those areas that will be particularly sensitive to development or land use
changes, and facilitate the prioritization of watersheds to ensure that the best practices are
developed in areas where land use change is most threatening to the health of coral reefs.








Bermuda ESTIMATED THREAT LEVEL
S Unite States ee Low
SMedium
High
[W Country boundaries
JShelf area
<30 metres
30 to 200 meters
>200 metres


Gulf of Mexico
SI Bahamas Atlantic
Ocean

STurks and Caicos



L Virgin Islands

M o Puerto Rico I
Q Eastern
Guatemala Caribbean Threat from water-
Honduras S e a shed-based sources
was identified as
f-. particularly high in
Nicaragua / the Southwestern
N *.4 ,,, J V "- -. . .Caribbean, in the
,' / 'Trinidad & Bay of Honduras,
S---" Tobago and off many of the
00 0 lO L KOhigh islands in the
1 o Kanama Colombia Venezuela Greater and Lesser
Reefs at Risk in the Caribbean, WRI, 2004 Ia I Antilles.







Moe Iplemenatio


Re ativ Erosion Potential
Low
MEXICO |
High
Caribbean











1. DERIVE RELATIVE EROSION POTENTIAL
We use a simplified version of the Revised Universal Soil Loss Equation
(RUSLE)1 in order to estimate likely erosion rates for each 1 kilometer reso-
lution grid cell. Information on slope, land cover type, precipitation, and soil
porosity were integrated to develop an indicator of relative erosion potential
(REP) for all land areas within the wider Caribbean.






F] Watershed boandares
i B | -ur.dar, ol iarn aria
drar rm tl.= MP P3.
M-a rdelA eero .or. p-4lem l
Low















3. CALCULATE EROSION INDICATORS BY WATERSHED
Two indicators of erosion for the watershed were calculated for each water-
shed mean relative erosion potential within the basin and total relative
erosion potential for the basin. This map shows which watersheds have the
highest mean erosion rates.


SI Wateshed boundaari
S/ Major rivers
Land Elevation (meters)
-I 500
501 -1000
1001 -1500
i 1501-2000
1 2001 -2500
2501-3000

] 4001 -5500









2. DELINEATE WATERSHED BOUNDARIES
Watershed boundaries were developed for the region based on a 1 kilometer
resolution elevation data set (DEM).2 At WRI the DEM was "filled" and rivers
and lakes were "burned" to improve the accuracy of the watersheds. This
resulted in a data set of more than 2,700 watersheds draining into the
Caribbean, with a minimum size of 35 km2





L_ Wateshed boundaries
SBomdary of land aea
draining onto the MBRS
//Major rivers
Relative sediment delivery
Low

/ High
Relative sediment cispersal
Low
it
High








4. CALCULATE SEDIMENT DELIVERY AT RIVER MOUTH AND DISPERSE SEDIMENT
An indicator of relative sediment delivery at the river mouth was estimated by
multiplying total relative potential erosion in the basin by the sediment delivery
ratio for the basin, which is a function of watershed size.' We estimated rela-
tive sediment plumes by dispersing sediment delivery from the river mouth
using a distance-based decay function.4


Notes
1 USDA. 1997. Predicting soil erosion by water: A guide to conservation planning with the revised universal soil loss equation (RUSLE). USDA Handbook 703.
2 US Geological Survey HYDR01K Digital Elevation Data Set (DEM), 2000
3 Sediment Delivery Ration (SDR) = 0.41 basin area (in sq.km) 0 (This factor comes from Thattai, D., B. Kjerfve, and W. D. Heyman. 2003. Hydrometeorology and variability of water discharge and sedi
ment load in the inner Gulf of Honduras, Western Caribbean. Journal of Hydrometeorology4(6):985-995.)
4 The plume function used a 10% reduction in sediment per km from the river mouth; Model results were calibrated based on available data on river discharge, sediment delivery, and observed impacts
to coral reefs. It should be noted that relative erosion rates and sediment delivery are being used as a proxy for both sediment and pollution delivery.






- 4STI 3SMEV EIOPMEN


he growing population and
expanding tourism in the region
drive the demand for the construc-
tion of new infrastructure in the coastal
zone. Coastal development can result in
direct or indirect pressures on coral reefs
from construction, sewage discharge and
poorly managed tourism.
In the analysis, we developed an indicator
of coastal development threat which incor-


pirates estimated pressure from sewage
discharge, urban runoff, construction, and
tourism development. Threats to reefs were
evaluated based on distance to cities,
ports, airports, and tourism centers. In
addition, "coastal population pressure" was
included in the analysis, as a function of
coastal population density, coastal popula-
tion growth, per capital GDP, and annual
tourism growth.


BACTERIA Untreated sewage can contains bacteria and other harmful pathogenic organ-
isms, which contaminates fish and shellfish and also detrimentally affects water quality
for recreational users.
NUTRIENTS The widespread discharge of untreated sewage is a major source of nutrients
entering coastal waters. Elevated nutrients in coastal waters promote increased algal
growth on coral reefs, and can result in algal blooms, changes in the aquatic community
structure, decreased biological diversity, and fish kills.
PHYSICAL IMPACT Coral reefs can be obliterated through the removal of coral substrate,
or by burying the reef under sediment.




Bermuda ESTIMATED THREAT LEVEL
United States 0 Low
Medium
0 High
S- Country boundaries
Shelf area
S \ <30 metres
30 to 200 meters
>200 metres


Threat from coastal
development is significant
in most of the Lesser and
Greater Antilles, along
parts of the Yucatan, the
Bay islands, and along
parts of Colombia's and
Venezuela's coasts.











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