Diapositiva 1

IBE
Instituto de
Biología
Experimental
Main problems of reservoirs in
North – Central Venezuela
Ernesto J. González
Universidad Central de Venezuela
Introduction
A great number of reservoirs have been built in Venezuela, which serve for
diverse purposes: drinking and industrial water supplies, irrigation, flood control,
recreation and hydroelectric power production.
However, their misuse and human activities in their basins have generated
several problems, among them:
* Fish culture without a previous limnological evaluation.
* Pollution with agrochemicals and biocides.
* Eutrophication.
The aim of this study was to identify the main problems of reservoirs located in
North-Central Venezuela.
Studied reservoirs
Caribbean Sea
N
La Mariposa
La Pereza
Agua Fría
Quebrada Seca
Taguaza
Lagartijo
Guanapito
Tierra Blanca
Pao-Cachinche
Camatagua
90 km
Reservoir locations in Venezuela
Cities and populations that receive drinking water from the studied reservoirs:
Camatagua, La Mariposa, La Pereza, Lagartijo, Quebrada Seca, Taguaza
• Caracas and its metropolitan area (~ 4,000,000 inhabitants)
Pao-Cachinche
• Valencia (1,225,000 inhabitants)
• Maracay (568,000 inhabitants)
• San Carlos (66,000 inhabitants)
Agua Fría
• Los Teques (172,000 inhabitants)
Tierra Blanca
• San Juan de Los Morros (85,000 inhabitants)
Guanapito
• Altagracia de Orituco (44,000 inhabitants)
Climatic periods in North – Central Venezuela:
• Rainy season (May – October)
• Dry season (November – April)
Main threats and human impacts are as follow:
Agua Fría reservoir
Ultraoligotrophic, used for drinking water supply.
Threats and anthropogenic impacts: Low; reservoir is located in a protected area.
However, high water demand produces decrease in water level and exposure of
submerged vegetation which produces their decomposition and nutrient release.
Lagartijo reservoir
Oligotrophic, used for drinking water supply and recreation.
Exotic fishes: Caquetaia krausii.
Threats and anthropogenic impacts: The water body is affected by high water level
fluctuations during the year due to the high water demand from the Caracas City.
Due to the fact that the water demand is greater than the reservoir capacity, the
hydrological company decided to pump water from the Tuy River, which receives high
industrial and waste water discharges. Before pumping to the reservoir, the water is
submitted to sedimentation and chlorination processes. The treated water is after
introduced to the reservoir near to its uptake point, where it is pumped to the Tuy
System; due to this reason, water quality is affected locally, but does not in a
significant way in the rest of the water body.
Taguaza reservoir
Ultraoligotrophic, used for drinking water supply.
Threats and anthropogenic impacts: This reservoir is located in a protected area, and
there are no human activities in its basin.
Tierra Blanca reservoir
Oligo-mesotrophic, used for drinking water supply and recreation.
Threats and anthropogenic impacts: Reservoir is located in a semi-protected area,
with little human influence. This artificial lake is affected by high water level
fluctuations, and due to its small area and volume, any impact could be rapidly
reflected in the water quality. Fish stocking was unsuccessful, and ichthyofauna is
basically composed by 3 species at now.
Guanapito reservoir
Mesotrophic, used for drinking water supply and irrigation.
Exotic fishes: Bryconops giacopinii, C. krausii
Threats and anthropogenic impacts: Adjacent areas of the reservoir are used for
extensive livestock, fruit culture and horticulture, which directly supply fertilizers
(mainly nitrates) and biocides to the water body through runoff and through its
tributaries. Pumped water has no good quality, because it comes from the anoxic
strata.
Camatagua reservoir
Mesotrophic, used for drinking water supply, irrigation, flood control and recreation.
Threats and anthropogenic impacts: Reservoir receives waste water from surrounding
small populations. In the vicinity of the water body, extensive livestock is practiced .
Actually, is the biggest water reserve for the Caracas City. In recent years, it suffered a
significant volume diminution, affecting water supply to Caracas. This change could be
attributed to the human activities in the basin (mainly deforestation), and probably, due
to the change in the rainy pattern in this region. Water level remained, from 2001 to
2004, more than 20 m below of its normal operation level, generating a rationing
program in the drinking water supply for the Caracas City.
La Mariposa reservoir
Hypertrophic, used for drinking water supply and recreation.
Exotic fishes: Oreochromis mossambicus
Threats and anthropogenic impacts: Reservoir suffers high and frequent level fluctuations
due to the high water demand from Caracas and water pumping from Camatagua and
Lagartijo reservoirs. Its basin is highly impacted and eroded, which directly contribute with
a lot of nutrients and sediments to the water body.
Recently, an overgrowth of the water hyacinth Eichhornia crassipes has covered 10% of
the reservoir. Mechanical harvesting is used to control this macrophyte now.
La Pereza reservoir
Eutrophic, used for drinking water supply and recreation.
Threats and anthropogenic impacts: Reservoir is surrounded by highly eroded hills, in
which pig farms and bovine and horse livestock are settled; nutrients from these
activities freely reach to the reservoir waters. In addition, residual water from a
galvanic factory runs freely through the reservoir basin.
Quebrada Seca reservoir
Hypertrophic, used for drinking water supply.
Threats and anthropogenic impacts: This water body is not protected. Its basin is
highly impacted by human activities, with rural settlements around the water body
which do not have any sewage collector. This reservoir is filled with untreated water
from the Tuy River, which is highly polluted with industrial and waste waters.
Pao-Cachinche reservoir
Hypertrophic, used for drinking water supply, irrigation and recreation.
Threats and anthropogenic impacts: Tributaries transport untreated waste water from
the Valencia City, and waste water from poultry and pig farms. Thus, tributaries
introduce high level of nutrients into the reservoir. Cyanobacteria blooms are common
during the rainy season period.
In November 2001 the process of artificial destratification of the reservoir started,
which effectively controlled the eutrophication effects after one year of continuous
operation.
However, in November 2005, due to the increase of the water level in Lake Valencia,
one of its tributary, the Cabriales stream, was deviated to the Pao stream basin,
through the Paito stream. The high organic load contained in the Cabriales stream had
again caused the oxygen depletion in the water column of the reservoir, and reverted
benefits obtained after the artificial destratification.
Other regulatory standards
• Decree 996 (1972): Established a protected area around the Pao-Cachinche reservoir,
in which anthropogenic activities are forbidden. However, this regulation is not
accomplished and its basin is highly affected by anthropogenic activities.
• Decree 883 (1995): Among other regulations, established maximal limits allowed for
phosphorus and nitrogen concentrations in the waste waters: 10,000 µg/l for total
phosphorus, 40,000 µg/l for total nitrogen and 10,000 µg/l for nitrates + nitrites; these
limits are high in extreme and therefore, do not contribute to enhance or protect the water
quality of the reservoirs.
• On the other
Seca reservoir
process of their
area and there
mesotrophic.
hand, Camatagua, Guanapito, La Mariposa, La Pereza and Quebrada
basins lack protection, and this fact is reflected in the eutrophication
waters. Tierra Blanca is partially protected (is located in a semi-protected
is a restricted access for people); therefore, its trophic state is oligo-
Conclusions
• The Venezuelan Government has had an institutional and juridical weakness in
relation to the administration of natural resources, which has permitted the degradation
of important water sources.
• Thus, the trophic state of each reservoir is a consequence of the human activities in
their basins.
• The protection of the water quality must be based on the basin management and not
just on the reservoir management.
• This management must include: Protection of the reservoir basins and regulation
policies of anthropogenic activities inside them; regulatory standards that really control
the waste water discharges and their nutrient and organic load; and permanent
monitoring of water quality of the reservoirs and their tributaries.
• The Academies of Sciences can contribute with these aspects by stimulation of
research and cooperation among scientific and government institutions, in order to
propose and apply adequate management policies for conservation of the water
resources.
• Recently, the Venezuelan Academy of Sciences designated a person who will
conform the National Water Committee for the country.