Introduction
Eutrophication produces an excess of algae and macrophytes
in water bodies that can cause certain water use
problems: taste and odor problems in water supplies,
corrosion of hydroelectric equipment and upsets
of different water treatment processes due to the
reduction of the dissolved oxygen content, accumulation
of ammonia in the water column and re-suspension
of certain metals (Fe, Mn) from the sediments under
anaerobic conditions.
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In eutrophied reservoirs, the
high level of organic substances combined with the application
of chlorine for drinking water supplies can generate
substances potentially harmful to health. Toxins produced
by cyanobacteria can also be a health concern.
CEPIS/PAHO Actions
Considering the implications of the above for the use
of lakes and reservoirs in the Region of Latin America
and the Caribbean, the Pan American Center for Sanitary
Engineering and Environmental Sciences (CEPIS), specialized
center of the Division of Health and Environment (HEP)
of the Pan American Health Organization/World Health
Organization (PAHO/WHO) convened a regional meeting
in December 1981, in Sao Paulo, Brazil, to analyze methodologies
for the evaluation of eutrophication and its inclusion
in the planning process.
At this meeting the then available simplified models,
developed with data from predominantly temperate lakes,
were reviewed and it was concluded that due to the fundamental
differences between temperate and warm-water tropical
lakes, these temperate lake models were not applicable
to the majority of water bodies of the Region. The Regional
Program for the Development of Simplified Methodologies
for the Evaluation of Eutrophication in Warm-Water Tropical
Lakes was then initiated.
Objectives
A minimum data collection program to obtain the necessary
data was agreed upon and the overall goals of the action
plan were established as follows:
- The establishment of a tropic
state classification system for warm-water tropical
lakes.
- The development of simplified
methodologies for the evaluation of the eutrophication
in warm-water tropical lakes.
- The development of a reliable
simplified mathematical model to be applied in the
management of lakes and in the planning of future
reservoirs.
Results
Subsequent regional meetings were held in Brasilia,
Brazil (1983), Guadalajara, Mexico (1985); San Juan,
Puerto Rico (1987) and Caracas, Venezuela (1990), in
which additional countries and data were incorporated
into the Regional Action Plan. In 1990, 16 countries/states
of the Region were participating, providing data from
about 39 lakes and reservoirs.
The product of the first stage completed in 1990, was
a tool for planning future reservoirs and estimating
corrective measures to remediate eutrophication problems
through the control of macronutrients.
In 1996, data from 8 additional lakes and reservoirs
from Colombia and Brazil were added to the 39 original
data utilized to develop the simplified mathematical
model and no significant modification of the original
model resulted.
The second stage of the program proposes the assessment
of the impact of nutrient control systems. Case studies
were proposed for La Plata Lake (Puerto Rico) for non-point
sources and Paranoa Reservoir (Brasilia) and Barra Bonita
Reservoir (Sao Paulo) for point sources. The impact
on the water quality of these warm-water tropical reservoirs
would be evaluated through intensive surveys conducted
before and after implementing control systems. It is
estimated that such an evaluation would require monitoring
for three to five years. To date, this second stage
has not been initiated.
Products
•
SALAS, H. & MARTINO, P. (1990). Metodologías
simplificadas para la evaluación de eutroficacion
en lagos cálidos tropicales. Programa Regional
CEPIS/HEP/PAHO 1981-1990. CEPIS, Lima (Spanish only).
•
SALAS, H. & MARTINO, P. (1991). A simplified phosphorus
trophic state model for warm-water tropical lakes. Water
Resources, 25(3): 341-350. (English only).
Available Mathematical Models
•
LACAT
Simplified water quality mathematical model for the
evaluation of trophic
states and the management of macro-nutrients in warm
water tropical
lakes/reservoirs. The model is user-friendly. Developed
by CEPIS (1990).
•
CLARK
Mathematical model for the calculation of tributary
nutrient loadings to lakes
based on tributary field data. The model is user-friendly.
Developed by
Sonzogny, W.C. et al. (1978). Great Lakes Tributary
Loadings, EPA and U.S.
Task D. Committee.
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