,- SAIDAD UNITED NATIONS CRA
SFOTHEAMERICANPEOPE O N DAION UNEP WCMC N WWF WRI
Watershed Analysis for the Mesoamerican Reef
This document provides a brief overview of a hydrologic analysis implemented by the World Resources
Institute (WRI) as part of the International Coral Reef Action Network (ICRAN) Mesoamerican Reef
(MAR) partnership. The objective of the analysis was to quantify the impact of human alteration of the
landscape on land-based threats to the MAR to inform land-use planning, agricultural policy and practice,
conservation priority setting, and coastal threat mitigation efforts.
Over a two year period, WRI collaborated with
many partners in the region to evaluate sediment'
and nutrients coming from land in over 400
watersheds that discharge along the MAR. The
analysis evaluates the amount of sediment and
nutrients (nitrogen and phosphorous) coming
from each plot of land; the amount of eroded
sediment and nutrients reaching the river mouth
(coastal discharge point); and the amount of
sediment reaching the reef.
In addition, the analysis provides estimates of H/
the increase in sediment and nutrient delivery-
resulting from human activities, and predictions
of future sediment and nutrient delivery (in.
2025) given varying land-use scenarios. This
analysis is the first of this scope and level of ,-
detail for the MAR region. O ua
Dulce y a
Dull ^ (Aguan 0
The results provide a preliminary overview of Motagua Ulua
regional patterns of sediment and nutrient runoff ." "- v Patuca
and delivery, and indicate how human alteration .............
of the landscape can influence these patterns. =__ _.. ......I.
To ensure that the project's results and analytical methods support action in the region, WRI makes the
underlying data, analytical method, and modeling tools publicly available, and has conducted training
sessions with users in the region. Based on this training, regional users can implement more detailed,
focused analyses for smaller areas, calibrating them to local conditions.
All data used in the analysis and all model results, accompanied by metadata, are provided on the data
CD, Watershed Analysis for the Mesoamerican Reef WRI/ICRAN MAR project, 2006. The data CD
provides a summary report in English and Spanish describing the analysis method and results, as well as
digital maps of key results.
Shared by Mexico, Belize, Guatemala, and Honduras, the Mesoamerican Reef (MAR), stretches over
1,000 km, and is the largest continuous reef in the Western Hemisphere. Alteration of the natural
landscape for development, road construction, or agriculture can have adverse impacts on coral reefs
through increased delivery of sediment, nutrients, and other pollutants to coastal waters. Threats from
land clearing are higher in areas of steep slope, intense precipitation, and more erodible soils.
Appropriate land-use practices in erosion-prone areas are essential for
watershed management to minimize the transport of sediment,
nutrients, and other pollutants to coral reefs. In the Mesoamerican
region, over 300,000 hectares of land is allocated to banana, oil palm,
sugar cane, citrus, and pineapple crop production. Eroded sediments
and fertilizer and pesticide residues used by farms drain through rivers
and streams and enter coastal waters along the Mesoamerican reef.
As part of the ICRAN MAR project, the World Resources Institute
(WRI) partnered with UNEP-World Conservation Monitoring
Centre (WCMC) and the World Wildlife Fund (WWF) to provide
comprehensive watershed analysis to complement the ICRAN MAR
project's activities on Sustainable Fisheries and Sustainable Tourism.
The ICRAN MAR watershed analysis was developed to produce information and tools for examining the
potential impact of different land use and development options in the region and the associated impacts on
water quality on the MAR. The project objectives are to:
O Link patterns of land use within watersheds to the impacts at coral
reefs, and identify reefs at greatest risk of degradation;
Identify watersheds most vulnerable to erosion and those which
contribute the most sediment and pollution to coastal waters; .....
Adapt tools to forecast potential trends, evaluate different policy or V. ..
development options, and facilitate improved land management = S.::i=
within the region;
" Use the results of the models and diagnostic tools to help educate
and encourage key stakeholders to adopt a suite of "better
management practices" to reduce impacts on the coastal and
The watershed project includes analytical components looking at land cover change and associated
impacts on runoff, erosion, and sediment and pollutant delivery to and transport within coastal waters. It
also includes on-the-ground activities with agricultural businesses to implement better management
practices. Many local partners were consulted on modeling methods, for data input and evaluation, and on
agricultural management practices. Three ICRAN partners collaborated on this effort:
o UNEP-WCMC developed land cover change scenarios and provided data sets as input to the
o WRI implemented the watershed delineation and hydrologic analysis for the MAR region,
performed analysis of vulnerability to erosion, and coordinated the circulation modeling along the
SWWF led the work with agri-business (banana, pineapple, citrus and sugar) to implement better
management practices, focused on reducing the presence of pesticides in the MAR marine
environment and controlling soil erosion from major commercial agricultural sectors.
Overview of the Methodology
In collaboration with partners in the MAR region, WRI:
O Implemented a watershed delineation for all land areas draining along the Mesoamerican reef;
O Implemented a hydrologic analysis using the Nonpoint-Source Pollution and Erosion Comparison
Tool (N-SPECT) model to examine sources of sediment and nutrients from this entire drainage
area, as well as the delivery of sediment and nutrients to coastal waters;
o Applied this hydrologic analysis tool to examine sediment and nutrient delivery for several land
cover scenarios (current land cover, original or "natural" land cover, and three scenarios of land
cover in 2025 scenario data provided by UNEP-WCMC);
O Provided outputs of the hydrologic analysis as inputs to a circulation model implemented by the
University of Miami to examine sediment transport along the MAR; and
Collaborated with partners on calibration and validation of model results.
This hydrologic analysis serves to integrate a wide range of data, and adapt modeling tools for an
innovative, region-wide analysis for the MAR. The region-wide results should be considered preliminary
and indicative of the overall pattern and magnitude of erosion and nutrient and sediment delivery across
the region. An important aspect of the project is to provide these modeling tools to partners in the MAR
region so that they might apply them at higher resolution to produce more detailed results for smaller
areas within the MAR region. This approach will allow for refinement and better calibration of the model
to local circumstances within the region.
The origin of sediments and nutrients reaching the --
o Of the 400 watersheds in the MAR region, the *,
Ulua watershed in Honduras was found to be the
largest contributor of sediment, nitrogen, and ...
phosphorous. Other large rivers found to be
significant contributors of sediment and nutrients
are the Patuca (in Honduras), Motagua (in
Guatemala and Honduras), Aguan (in Honduras), -..':
Dulce (in Guatemala), Belize River (in Belize), ;
and Tinto o Negro (in Honduras). .,
The origin of sediments and nutrients reaching the MAR:
o Most of the sediment and nutrients delivered by watersheds
along the MAR originate in Honduras. It is estimated that
over 80% of sediment and over half of all nutrients (both
nitrogen and phosphorous) originate in Honduras.
o Guatemala was identified as a source of about one-sixth of
all sediments and about one-quarter of all nitrogen and
phosphorous entering coastal waters along the MAR.
o The modeling suggests that compared to the other countries,
relatively minor percentages of the regional sediment load
come from Belize and Mexico. Belize contributes between
10-15% of nutrients and Mexico is estimated to contribute
about 5%of the nutrients from all modeled watersheds. The
estimate for Mexico is probably an underestimate, as the
contribution of underground rivers is not included in this
Runoff, erosion, and nutrient delivery to coastal waters are
o As a result of human alteration of the landscape, runoff and
associated river discharge at river mouths has nearly
doubled; sediment delivery at river mouths has increased by
a factor of 20; nitrogen delivery has increased by a factor of
3, and phosphorous delivery by a factor of 7. (Ratios are
based on model results for current (2003/04) land cover and
on hypothetical natural (unaltered) land cover.)
The potential impacts of development and land-use paths are
o Under land-use scenarios which favor free markets and little
policy regarding the environment, nutrient delivery is likely
to increase by about 10% by 2025, while sediment delivery
might increase by 13% or more.
o If environmental policies that favor sustainable development
are implemented, nutrient and sediment delivery are likely to
be reduced by at least 5% from current levels, fostering
recovery of degraded corals.
o Implementation of better agricultural management practices
will yield additional reductions in sediment and nutrient
delivery beyond those evaluated in this study, which has
focused on the effect of changes in land cover.
Average Annual Soil Erosion
I ,. /'
wb4n m1 sq kmn)
Average Annual Nitrogen
Source by Sub-basin
..~d ~II"' ~1'
Average Annual Phosphorous
Source by Sub-basin
r 00- 500
M S W"O
. ', .... ..
Conclusion from the Analysis
Policy action is needed to address the contributions from agricultural lands.
Most of the sediment and nutrients delivered to the MAR from watersheds in the region come from
agricultural lands in Honduras and Guatemala. The contributions of Belize and Mexico are substantially
less, but still pose a threat along their coasts. Promising initiatives to decrease pollution within the region
are underway, including: sustainable forestry management and integrated watershed management in
Guatemala; improved land use planning, reforestation and soil conservation programs in Honduras; and
similar initiatives in Belize and Mexico. These important efforts need public support, recognition, and
Results can help identify areas in need of
better agricultural management.
This analysis identified vulnerable areas
where conversion to an erosive land use
should be avoided, or where converted
conservation practices should be
implemented. It also identified areas with eas',s
high erosion and nutrient runoff, where better ': .
1i. Vulr.eatil? :I ;Mrd in a r:'sr
agricultural management practices should be :*rv '
targeted. Em ma.,
Policies that support sustainable 1i
development can reduce sediment and
As evidenced by our findings, land-use
planning, integrated watershed management,
and other policies that support sustainable
development can help to lessen erosion and
pollution runoff, thereby decreasing sediment
and nutrients reaching the MAR.
More detailed modeling is needed to create
more accurate information at higher *.
Regional-scale analyses are useful for providing an overview and for prioritizing areas in which action is
needed. However, local analyses provide more detailed and accurate information that policymakers need
in order to target their interventions. The tools provided on the data CD, Watershed Analysis for the
Mesoamerican Reef (WRI/ICRAN MAR project, 2006), allow users to perform more detailed analyses of
sediment and nutrient delivery within smaller areas in the MAR region, such as at the watershed level.
More specifically, the model can be applied to individual watersheds or groups of watersheds using data
provided or with the user's own data. More detailed local modeling will improve the accuracy of the
results, by using higher resolution data on slopes and land cover, and by calibrating the model to local
soils and precipitation regimes.
It would be valuable to extend the current analysis to include the effect of improved agricultural
management practices on erosion and pollutant runoff Such an extension would require detailed
information on how each practice influences erosion rates and pollutant runoff Once such information is
available, it should be possible to use the model to evaluate reductions by treating each management
intervention on each land cover type as a unique category with specific erosion and pollutant runoff
characteristics. For example, citrus groves with cover crops planted to reduce erosion might be treated as
a separate category.
Analyses such as these can help to evaluate progress in reducing land-based sources of threat.
A number of national initiatives, as well as donor-funded regional initiatives, seek to reduce or mitigate
threats to the MAR. This analysis can help these initiatives to estimate their progress by giving them the
information they need to ensure they are moving in the right direction.
Transnational natural resource management can be strongly supported by analyses such as these.
To mitigate and reduce the land-based threats to the MAR, constructive regional cooperation among a
variety of stakeholders is necessary. Examples include the multilateral cooperation agreements among the
four countries involved in this analysis, and agreements between the agriculture and tourism sectors and
civil society groups. This tool works across borders and sectors, creating information that allows
productive discussion on threat origins and potential mitigation measures.
By sponsoring technical training (see right) and
other activities, the International Coral Reef
Action Network (ICRAN) collaboration will
continue to support the application of analysis
results and modeling tools in the region. For
information on future ICRAN activities, visit
The full paper and all high resolution maps
are available on the CD, which is available
through ICRAN MAR and WRI.
For questions or comments about this analysis please contact:
Lauretta Burke, Senior Associate
Zachary Sugg, Research Associate
zS'I '-- \\ i .org
World Resources Institute
10 G St. NE,
Washington, DC 20002
Tel: +1 (202) 729-7600
Fax: +1(202) 729-7798
Liza Karina Agudelo, Coordinator
ICRAN-Mesoamerican Reef Alliance
Princess Margaret Drive
Belize City, Belize