South America
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LAGO DE VALENCIA (LAKE VALENCIA)
A view from the lakeside hill
Photo: A.Infante
A. LOCATION
- Aragua and Carabobo, Venezuela.
- 10:05-10:16N, 67:35-67:52W; 405 m above sea level.
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B. DESCRIPTION
Lake Valencia is the largest natural freshwater lake of Venezuela. It is located in the central-north part of the country, which is the most densely populated. Lake Valencia lies on an east-west tectonic depression between two ranges of mountains: Cordillera de la Costa on the north and the Serrania del Interior in the south. The graben originated probably at the end of the Tertiary. As it developed, flowing waters of river Valencia were dammed and the lake was first established in the late Pliocene. Peeters (1968) recognizes four different evolutionary periods for Lake Valencia. They are related to the alternation of humid and dry climate. Thirteen thousand years ago the lake basin was probably dry (Bradbury, et al., 1981). The lake drained into a tributary of Orinoco River until the beginning of the 18th century. However, due to a negative water balance the level of the lake declined very fast (7.5 m yr-1, Bockh, 1956). The lake became endorheic about 250 years ago, when the discharge level (427 m) was exceeded due to desiccation. Intensive human intervention of the watershed and a reduction of groundwater flow have been mentioned for causing that rapid decline of the lake level. A minimum was achieved in 1976 (400.8 m above sea level). However, the lake level has recovered to 405 m with water provided from another watershed for urban consumption. Incoming untreated wastewater from domestic, agricultural and industrial activities of about 2 million people contribute to eutrophication, contamination and salinization of the lake. The use of the lake as water source for domestic activities and for irrigation is restricted by the high salt content (electric conductivity ca. 2000 micro mhos cm-1). Commercial fishing and recreation are also very limited by the precarious sanitary conditions of the water. Permanent algal blooms, high fish mortality, stench, etc. prevent the practice of aquatic sports and tourism (Q, 1, 2, 3).
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C. PHYSICAL DIMENSIONS (4)
| Surface area [km2] |
350 |
| Volume [km3] |
6.3 |
| Maximum depth [m] |
39 |
| Mean depth [m] |
18 |
| Water level |
Unregulated |
| Length of shoreline [km] |
117 |
| Residence time [yr] |
* |
| Catchment area [km2] |
2,646 |
* No surface outflow (endorheic).
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D. PHYSIOGRAPHIC FEATURES
D1 GEOGRAPHICAL (Q)
- Bathymetric map:
Fig. SAM-05-0l.
- Names of main islands
Isla Burro (0.05 km2), I. Otama (0.015 km2), I. Caiguire (0.007 km2), I. El Horno (0.002 km2), I. El Zorro (0.0016 km2) and Bagre (0.0012 km2).
- Number of outflowing rivers and channels (name):
None.
D2 CLIMATIC (4, 5)
- Climatic data at Maracay, 1979-1980
|
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
Ann. |
| Mean temp. [deg C] |
23.9 |
24.3 |
25.4 |
26.1 |
25.8 |
24.5 |
23.7 |
24.1 |
24.4 |
24.7 |
24.6 |
24.7 |
24.7 |
| Precipitation [mm] |
4 |
6 |
7 |
75 |
130 |
163 |
161 |
202 |
139 |
90 |
51 |
18 |
1,046 |
- Number of hours of bright sunshine:
2,847 hr yr-1.
- Solar radiation:
17.3 MJ m-2 day-1.
Fig. SAM-05-01
Bathymetric map (Q).
- Water temperature [deg C]
Deepest point, 1976-1978
| Depth [m] |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| 0.1* |
25.9 |
25.7 |
25.9 |
26.7 |
27.3 |
28.0 |
26.6 |
28.8 |
28.2 |
28.5 |
28.2 |
27.5 |
| 5 |
25.8 |
25.6 |
25.8 |
26.6 |
27.1 |
27.7 |
26.4 |
28.2 |
27.8 |
27.8 |
27.6 |
27.4 |
| 10 |
25.7 |
25.4 |
25.6 |
26.5 |
26.9 |
27.7 |
26.4 |
27.5 |
27.7 |
27.7 |
27.5 |
27.0 |
| 15 |
25.6 |
25.4 |
25.5 |
26.3 |
26.6 |
27.4 |
26.3 |
27.3 |
27.5 |
27.5 |
27.4 |
26.9 |
| 20 |
25.6 |
25.4 |
25.4 |
26.0 |
26.4 |
27.2 |
26.2 |
27.0 |
27.1 |
27.4 |
27.2 |
26.9 |
| 25 |
25.6 |
25.3 |
25.3 |
25.8 |
26.4 |
27.0 |
26.0 |
26.8 |
26.8 |
27.0 |
27.0 |
26.9 |
| 30 |
25.6 |
25.3 |
25.3 |
25.8 |
26.0 |
26.8 |
25.9 |
26.5 |
26.7 |
26.8 |
26.9 |
26.9 |
* Surface.
- Freezing period:
None.
- Mixing type:
Monomictic.
- Notes on water mixing and thermocline formation
The lake becomes thermally stratified from March to November (rainy season) and isothermal between December and February (dry season). Winds and nocturnal convection contribute to daily mixing of the upper layer (5-15 m). Two or more thermoclines are usually recognizable during the stratification period.
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E. LAKE WATER QUALITY
E1 TRANSPARENCY [m](5)
Lake centre, 1976-1978
| Depth [m] |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
|
2.20 |
1.90 |
1.70 |
1.85 |
1.45 |
1.55 |
1.60 |
1.25 |
1.85 |
1.55 |
1.77 |
1.45 |
E2 pH (5)
Lake centre, 1976-1978
| Depth [m] |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| 0 |
8.9 |
9.0 |
9.0 |
8.8 |
9.0 |
9.0 |
9.1 |
9.1 |
9.1 |
9.0 |
9.0 |
9.0 |
| 5 |
8.9 |
8.9 |
9.0 |
8.8 |
9.0 |
9.0 |
9.1 |
9.1 |
9.1 |
9.0 |
9.1 |
9.0 |
| 10 |
8.9 |
8.9 |
9.0 |
8.8 |
9.0 |
9.0 |
9.1 |
9.0 |
9.1 |
9.0 |
9.1 |
8.9 |
| 15 |
8.9 |
8.9 |
9.0 |
8.8 |
9.0 |
8.9 |
9.1 |
9.0 |
9.0 |
8.9 |
9.1 |
8.9 |
| 20 |
8.9 |
8.9 |
9.0 |
8.8 |
9.0 |
8.9 |
9.0 |
9.0 |
9.0 |
8.9 |
9.0 |
8.9 |
| 25 |
8.9 |
8.9 |
8.9 |
8.8 |
9.0 |
8.9 |
8.9 |
8.9 |
8.9 |
8.7 |
8.7 |
8.8 |
E4 DO [mg l-1](5)
Lake centre, 1976-1978
| Depth [m] |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| 0 |
6.0 |
6.6 |
6.8 |
6.1 |
7.7 |
6.5 |
6.7 |
8.5 |
6.8 |
6.6 |
6.0 |
4.2 |
| 5 |
5.5 |
6.3 |
6.6 |
6.4 |
6.6 |
6.4 |
6.2 |
8.1 |
6.5 |
6.6 |
5.9 |
3.4 |
| 10 |
5.3 |
6.0 |
6.3 |
5.4 |
5.6 |
5.2 |
5.3 |
5.8 |
5.9 |
4.3 |
4.4 |
2.4 |
| 15 |
5.2 |
5.6 |
5.0 |
3.8 |
4.2 |
3.1 |
4.4 |
4.0 |
2.9 |
2.9 |
3.4 |
1.5 |
| 20 |
5.2 |
5.3 |
4.4 |
2.0 |
3.0 |
1.7 |
1.8 |
2.6 |
0.8 |
1.2 |
1.1 |
1.1 |
| 25 |
5.2 |
5.2 |
4.0 |
1.3 |
1.7 |
0 |
0 |
0 |
0 |
0 |
0 |
1.0 |
E6 CHLOROPHYLL CONCENTRATION (7)
Chlorophyll a [micro g l-1] : 40.
E7 NITROGEN CONCENTRATION (Q)
Lake centre, 1977-1981
| Depth [m] |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| 0-5 |
.112 |
.075 |
.025 |
.012 |
.005 |
.001 |
.013 |
.017 |
.001 |
.008 |
.021 |
.146 |
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F. BIOLOGICAL FEATURES
F1 FLORA (5, 10, 11, 12, 13, 14, 15)
- Emerged macrophytes:
Typha sp.
- Floating macrophytes
Eichhornia crassipes, Pistia stratiotes, Nymphaea spp.
- Submerged macrophytes:
Najas marina, N. guadalupensis, Potamogeton sp.
- Phytoplankton
Microcystis aeruginosa, Oscillatoria limnetica, Anabaena spiroides, Lyngbia limnetica, Melosira granulata, Nitzschia pales, Thalassiosira guillardi, Chlorella vulgaris, Scenedesmus acuminatus, Staurastrum leutkemuelleri.
F2 FAUNA (5, 10, 11, 12, 13, 14, 15)
- Zooplankton
Rotaria rotatoria, Liliferotrocha subtilis, Epiphanes macrourus, Brachionus calyciflorus, Keratella americana, Anuraeopsis navicula, Lepadella patella, Lecane bulla, Lindia torulosa, Trichocerca pusilla.
- Benthos
Less than 10 m depth (Campsurus sp., Goeldichironomus amazonicus, Coelotanypus scapularis, Ablabesmyia monilis, Limnodrilus hoffmeisteri, Planaria sp.): Deeper areas (Chaoborus (Samomyia) brasiliensis).
- Fish
Sarotherodon mossambicus, Petenia kraussii, Symbranchus marmoratus, Rhamdia quelen, Loricarichthys typus, Hypostomus plecostomus, Poecilia sphenops, Hoplias malabaricus, Geophagus surinamensis, Xenomelaniris venezuelae.
- Supplementary notes on the biota
Xenomelaniris venezuelae is an endemic atherinid of Lake Valencia.
F3 PRIMARY PRODUCTION RATE (4, Q)
|
Jul 1974 [mg C m-3 hr-1] |
Nov 1987 [mg C m-2 day-1] |
| Net production |
285*1 |
2,148 |
| Dark respiration |
- |
432*2 |
| Gross production |
330 |
- |
*1 0 m. *2 0-10 m.
F4 BIOMASS (14, 16)
- Zooplankton* [mg m-3]
Notodiaptomus venezolanus: 12,883.
Mesocyclops crassus: 17,739.
Keratella americana: 1,373.
Brachionus calyciflorus: 11,415.
Chaoborus sp: 36,833.
*Annual mean value of standing crop.
- Benthos* [g m-2]
Campsurus sp: 0.48.
Chironomidae: 0.05.
Chaoborus brasiliensis: 0.10.
Limnodrilus hoffmeisteri: 0.04.
Planaria sp: 0.03.
*Annual mean value of standing crop.
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G. SOCIO-ECONOMIC CONDITIONS
G1 LAND USE IN THE CATCHMENT AREA (17)
1983
|
Area [km2] |
[%] |
| Natural landscape |
| - Woody vegetation |
583 |
22.0 |
| - Herbaceous vegetation |
1,213 |
45.9 |
| Agricultural land |
| - Crop field |
530 |
20.0 |
| - Pasture land |
170 |
6.4 |
| Residential area |
150 |
5.7 |
| Total |
2,646 |
100.0 |
- Main types of woody vegetation
Mainly secondary vegetation; dominant species belong to Leguminosae (Platymiscium sp., Pterocarpus podocarpus, Prosopis juliflora, Pithecolobium saman) and others (Capparis sp., Bulnesia arborea, B. simaruba).
- Main types of herbaceous vegetation
Agave sp., Lippia origanoides, Dodonacea viscosa, Aloe vera and in drier places cactaceous vegetation (Opuntia and Mamillaria).
- Types of the other important vegetation
The transition zone around the lake (Sterculia apelata, Erythrina sp., Ceiba pentrandra, Pithecolobium saman).
- Main kinds of crops
Sugar cane, vegetables, fruit tree (citrus, banana, mango), tobacco, cotton, maize.
- Levels of fertilizer application on crop fields:
Heavy.
- Trends of change in land use
It is a recent trend for the development of settlement areas at the cost of agriculture land.
G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE (18)
1981
|
No.of persons engaged |
Main products or major industries |
| Primary industry |
77,700 |
Sugar cane, fruits, vegetables, cattle |
| Secondary industry |
230,700 |
Food, chemical, dairy, metallurgy |
| Tertiary industry |
339.400 |
Bank activities, government activities |
- Numbers of domestic animals in the catchment area Cattle 6,000, swine 97,500, poultry 311,200.
G3 POPULATION IN THE CATCHMENT AREA (8)
1981
|
Population |
Population density [km-2] |
Major cities (population) |
| Urban |
1,559.483 |
473 |
Valencia, Maracay, La Victoria, |
| Rural |
60,261 |
18 |
Villa de Cura, Mariara, San Joaquin, Guigue, Magdaleno |
| Total |
1,619,744 |
492 |
|
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H. LAKE UTILIZATION (Q)
H1 LAKE UTILIZATION
No direct utilization of the lake water.
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I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS
I1 ENHANCED SILTATION (Q)
- Extent of damage:
Serious.
- Supplementary notes
Although no measurements of siltation have been done in Lake Valencia, the problem is evident. Extensive areas of land in the catchment area have been deforested and burned. Frequent landslides on the mountains where tributaries originate have produced recently catastrophic floods.
I2 TOXIC CONTAMINATION (19, 20, 21)
- Present status:
Serious.
- Main contaminants, their concentrations and sources
| Name of contaminant | Concentration [ppm]*1 | Main source |
|---|
| Water*2 [mg l-1] |
Bottom mud*3 [mg*5 kg-1] |
Fish*4 [mg*6 kg-1] |
| Ni |
0.10 |
68 |
- |
Industrial |
| Pb |
0.04-0.05 |
134 |
- |
Industrial |
| Zn |
0.02-0.05 |
139 |
- |
Industrial |
| Cu |
0.02-0.05 |
44 |
- |
Industrial |
| Hg |
0.02-0.07 |
0.224 |
0.153 |
Industrial |
| Cd |
- |
2.9 |
- |
Industrial |
| Cr |
- |
82 |
- |
Industrial |
*1 At 40 sampling points scattered over the lake.
*2 1982.
*3 1983.
*4 Petenia kraussii (muscle), 1981.
*5 Dry wt.
*6 Wet wt.
- Food safety standards or tolerance limits for toxic contaminant residue
In general, limits recommended by the World Health Organization are accepted.
- Supplementary notes
The highest concentrations of metals in sediments are obtained at the entrance of affluents receiving wastewaters from the cities Valencia and Maracay. Higher concentrations of Hg, Cd, Cr and Pb were measured in fish (muscle) captured at the northern part of the lake, where the influence of large human concentrations and industrial activities is more direct.
I3 EUTROPHICATION (4, 5, 22)
- Nuisance caused by eutrophication
Unusual algal bloom: Microcystis aeruginosa, Synechocystis aquatilis, Lyngbia limnetica.
Harms to fishery products: All kinds of fish (fish mortality at the beginning of the circulation period every year). Toxicant: H2S.
- Nitrogen and phosphorus loadings to the lake [g m-2 yr-1]
| Sources |
Total |
| T-N |
20 |
| T-P |
7.6 |
- Supplementary notes
Human activities are increasing very fast around Lake Valencia and eutrophication has intensified during the last years. P-loading has increased from 1.4 g P m-2 yr-1 in 1974 to 7.6 g m-2 yr-1 in 1983. Hitherto, no significant countermeasures have been implemented.
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J. WASTEWATER TREATMENTS
J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA
(e) Severe pollution with no wastewater treatment (Q).
J2 APPROXIMATE PERCENTAGE DISTRIBUTION OF POLLUTANT LOADS (18)
|
[%] |
| Non-point sources |
17 |
| Point sources |
| - Municipal |
34 |
| - Industrial |
49 |
| Total |
100 |
J3 SANITARY FACILITIES AND SEWERAGE (Q)
- Percentage of municipal population in the catchment area provided with adequate sanitary facilities (on-site treatment systems) or public sewerage:
70.
- Industrial wastewater treatment systems:
163 (total number of highly contaminant industries: 378).
- Supplementary notes
A project for environmental recovery of Lake Valencia and its catchment area has been developed and will be carried out by the Ministery of Environment and Natural Resources (MARNR) and financed by the Interamerican Bank for Development. At least three sewage treatment systems are planned for Lake Valencia and should be functioning in the near future.
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M. LEGISLATIVE AND INSTITUTIONAL MEASURES FOR UPGRADING LAKE ENVIRONMENTS
M1 NATIONAL AND LOCAL LAWS CONCERNED (23)
- Names of the laws (the year of legislation)
- Organic Law for Environment (1976)
- Ordinance for Classification of Waterbodies According to Its Use (1978)
- Resolution No. 304 (1979)
- Resolution No.85 (1979) about use, conservation and improvement of the catchment area of Lake Valencia
- Responsible authorities
- Ministery of Environment and Natural Resources
- Ministery of Environment and Natural Resources
- Presidency of the Republic
- Ministery of Environment and Natural Resources
- Main items of control
- Natural resources
- Waterbodies of the country
- Water treatment
- Control of urban and industrial development in the catchment area of Lake Valencia
- Supplementary notes
Legal controls are only theoretical. Laws are constantly violated. Public protests are not considered by responsible authorities. Limnological investigations carried out by universities and other institutes are not considered.
M2 INSTITUTIONAL MEASURES (Q)
- Ministery of Environment and Natural Resources, Caracas, 1978
M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES (Q)
- Universidad Central de Venezuela, Escuela de Biologia, Laboratorio de Limnologia, Caracas
- Universidad de Carabobo, Facultad de Ingenieria, Oficina de Estudios Ambientales, Edo, Carabobo
- Ministerio del Ambiente y de los Recursos Naturales Renovables, Direccion de Investigacion del Amhiente, Caracas
- Instituto Venezolano de Investigaciones Cientificas, Departamento de Ecologia, Edo, Miranda
N. SOURCES OF DATA
Questionnaire filled by Dr. A. Infante, Apartado 47106, Chaguaramos, Caracas 1041, Venezuela.
- Peeters, L. (1968) Origen y Evolucion de la Cuenca del Lago de Valencia, Venezuela. Instituto para la Conservacion del Lago de Valencia, 66 pp.
- Bradbury, J. P., Leyden, B., Salgado-Labouriau, M., Lewis, W. M., Schubert, C., Binford, M. W., Frey, D. G., Whitehead, D. R. & Weibezahn, F. H. (1981) Science, 214 (4527): 1299-1305.
- Bockh, A. (1956) El Desecamiento del Lago de Valencia. Fundacion Eugenio Mendoza, Caracas, 246 pp.
- Lewis, W. M. & Weibezahn, F. H. (1976) Arch. Hydrobiol. Suppl., 50 (2/3): 145-207.
- Infante, A. (1980a) El Zooplancton del Lago de Valencia. Informe Tacnico CONICIT, Proyecto 51-0612, 203 pp.
- Colmenares, B. & Urosa, G. (1987) 0pciones de Sistemas de Tratamiento para Mejorar la Calidad del Aqua del Lago de Valencia. Trabajo Especial de Grado, Universidad Catolica Andres Bello, Caracas.
- Levine, 5. & Lewis, W. M. (1984) Limnol. 0ceanogr., 29 (4): 887-893.
- Lewis, W. M. (1986) Hydrobiologia, 138: 189-203.
- Lewis, W. M. & Weibezahn, F. H. (1983) Venezolana, 34: 345-349.
- Chardon, C. & Crist, R. (1971) El Lago, 5: 422-424.
- Infante, A. (1979) Venezolana, 30: 224-233.
- Infante, A. (1980b) Venezolana, 31: 593-603.
- Infante, A. (1980c) Venezolana, 31: 30-47.
- Solabarrieta, M. E. & Weibezahn, F. H. (1980) Venezolana,31: 247-274.
- Infante, 0. (1984) Contribucion al Estudio de los Peces del Lago de Valencia. Trabajo de Ascenso, Escuela de Biologia, Universidad Central, Caracas.
- Saunders, J. F. (1980) The Role of Predation as a Mechanism for Controlling Planktonic Herbivore Populations in Lake Valencia, Venezuela. Ph. D. Thesis. University of Colorado, USA, 140 pp.
- Ewel, J., Madriz, A. & Tosi, J. (1976) Zonas de Vida de Venezuela, 2a. ed. Ministerio de Agricultura y Cria, Venezuela, 270 pp.
- M. A. R. N. R. (1986a) Planes Estadales de 0rdenacion del Territorio. Estados Aragua y Carabobo. Informe Tecnico.
- M. A. R. N. R. (1982) Estudio Integral Sobre la Contaminacion del Lago de Valencia. Bioensayos eon Algas del Lago de Valencia. I. Bioensayos in Vitro. Serie Informes Cientificos, 70 pp.
- Losada, A., Giraud, J. & Fermin, Y. (1984) Distribucion de Metales Potencialmente Contaminantes en el Sedimento del Lago de Valencia. Tesis de Grado, Escuela de Quimeca, Universidad Central, Caracas, 147 pp.
- Esaa, M. E. & Goncalves, O. (1981) Determinacion de los Niveles de Mercurio Total en dos Especies de Peces, Petenia kraussii Steindachner 1678 y Sarotherodon mossambicus (Peters 1852)(0steichthyes, Perciformes, Cichlidae) del Lago de Valencia, Venezuela. Tesis de Grado, Escuela de Biologia, Universidad Central, Caracas, 123 pp.
- Torres, M. & Torres, J. (1983) Balance de Nutrientes Sobre el Lago de Valencia. En: Criterios de Calidad Ambiental: Residuos Liquidos, Solidos y Gaseosos. Asociacion Venezolana de Ingenieria Sanitaria y Ambiental (eds.), Caracas.
- M. A. R. N. R. (1986) Exposicion de Motivos y Proyectos de Ley de Credito Publico para el Financiamiento del Programa de Saneamiento Ambiental e Integral de la Cuence del Lago de Valencia. DGSP0A-DPRH.
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