LAGO YPACARAI

An aerial view of the ahole lake

Photo.
Photo: K.Nomura


A. LOCATION

  • Cordillera and Central, Paraguay.
  • 25:14-25:22S, 57:17-57:22W; 64.1 m above sea level.


B. DESCRIPTION

    Lake Ypacarai is a shallow and swampy natural lake located some 30 km east of Asuncion, the capital of Paraguay. It has a surface area of approximately 60 km2 and a maximum depth of 3 m. The catchment basin of 833 km2 is largely covered by pastures and crop fields.
    There are some 20 inflowing tributaries of various sizes, while only one river, Rio Slado, drains the lake joining the Paraguay River at about 20 km downstream. An extensive area of wetlands with luxuriant growth of emergent and submerged plants develops near the lake's outlet and maintains the lake water level effectively within a narrow range of fluctuation.
    Since natural water bodies are particularly valuable for this flat inland country, Lake Ypacarai district offers one of the best sites for tourism and outdoor recreation in Paraguay, with abundant facilities for visitors and summer houses around the lake. The lake water is also used for drinking water supply and irrigation.
    The lake has recently suffered from progressive eutrophication owing to the nutrient discharge from surrounding crop fields, livestock farms, residential areas, deforested lands and large-scale land development. An international multi-disciplinary research project has been launched since 1987 by the national government to cope with this problem (Q, 1).

C. PHYSICAL DIMENSIONS (Q)

Surface area [km2] 60 Volume [km3] 0.115 Maximum depth [m] 3.0 Mean depth [m] 2.0 Water level Unregulated Normal range of annual water level fluctuation [m] 0.2 Length of shoreline [km] ca. 40 Residence time [yr] 0.2* Catchment area [km2] 833 * 81 days.

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL
  • Bathymetric map: Fig. SAM-08-01.
  • Names of main islands: None.
  • Number of outflowing rivers and channels (name): 1 (Rio Slado).
D2 CLIMATIC
  • Climatic data at Asuncion

    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    Mean temp. [deg C]*1 27.6 27.1 25.8 22.9 20.3 18.0 18.4 18.7 20.7 23.5 25.2 26.8 22.9
    Precipitation [mm]*2 161 146 143 159 118 74 47 54 82 125 146 141 1,396
    *1 1965-1988. *2 1950-1988.
  • Number of hours of bright sunshine: 2,530 hr yr-1.

    Fig. SAM-08-01
    Bathymetric map (1).

    Fig. SAM-08-02
    Depth profiles of the lake (1).

  • Water temperature [deg C]

    San Bernardino, March-August 1988
    Depth [m] Mar Apr May Jun Jul Aug
    S* 28.4 23.7 19.4 16.1 15.5 18.5
    * Surface.
  • Mixing type: Monomictic. Occasionally polymictic.

E. LAKE WATER QUALITY (2)

E1 TRANSPARENCY [m]
    Lake centre, February-September 1984
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    - 0.08 0.08 0.15 0.07 0.07 0.08 0.06 0.15 - - -
E2 pH
    Lake centre, February-August 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* - 8.7 7.3 6.8 7.0 7.1 7.4 6.0 6.8 - - -
    * Surface.
E3 SS [mg l-1]
    Lake centre, February-August 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* - - 74.4 - - 77.0 33.1 69.1 - - - -
    * Surface.
E4 DO [mg l-1]
    Lake centre, February-August 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* - 6.0 7.5 7.5 6.8 8.4 - 8.9 8.6 - - -
    * Surface.
E5 COD [mg l-1]
    Determined by K2Cr2O7 method.
    Lake centre, February-August 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* - 10.3 12.7 12.3 12.4 15.7 12.0 15.5 - - - -
    * Surface.
E7 NITROGEN CONCENTRATION
  • Total-N [mg l-1]
    Lake centre, February-August 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* - NSD 0.582 0.653 0.724 0.888 0.702 0.654 - - - -
    * Surface.
E8 PHOSPHORUS CONCENTRATION
  • Total-P [mg l-1]
    Lake centre, February-August 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* - 0.230 0.273 0.148 0.295 0.276 0.259 0.268 - - - -
    * Surface.

F. BIOLOGICAL FEATURES (Q)

F1 FLORA
  • Emerged macrophytes
    Typha sp., Scirpus sp., Pontenderia rotundifolia, Philodendron undulatum.
  • Floating macrophytes
    Hydrocleys nymphoides, Hydromystria sp., Nymphoides sp.
  • Submerged macrophytes: Cabomba sp.
  • Phytoplankton
    Anabaena spiroides, Oscillatoria tenuis, Phormidium tenue, Melosira granulata, M. granulata f. spiralis, M. granulata var., Ankistrodesmus falcatus.
F2 FAUNA
  • Zooplankton
    Keratell valga, K. americana, K. cochlearis, Daphnia sp., Bosmina longirostris, Bosmina sp., Diaptomus sp.
  • Benthos
    Hirudinea sp., Hexagenia sp., Dero cooperi, Ablabesmyia sp., Micropsectra sp., Microtendipes sp., Paratendipes sp., Polypedilum sp., Procladius sp., Pseudochironomus sp., Pheotanytarsus (?) sp., Tanypus sp.

G. SOCIO-ECONOMIC CONDITIONS (Q)

G1 LAND USE IN THE CATCHMENT AREA
    1988
    Area [km2] [%]
    Natural landscape
    - Woody vegetation 117.7 14.1
    - Herbaceous vegetation 35.3 4.3
    - Swamp 2.2 0.3
    Agricultural land
    - Crop field 240.5 28.9
    - Pasture land 302.0 36.2
    Residential area 135.2 16.2
    Total 833.0 100
  • Main kinds of crops: Cotton, cassava, sugar cane, vegetables.
  • Levels of fertilizer application on crop fields: Light.
  • Trends of change in land use in recent years
    Deforestation, cultivation and urbanization have rapidly proceeded in the western part of the catchment area.
G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE
    No.of persons engaged No. of establishments Main products or major industries
    Primary industry
    - Crop production 3,000 4
    - Animal husbandry 50 4
    Secondary industry - - Vegetable oil refinery, butchery, sausage, noodle, juice
  • Number of domestic animals in the catchment area
    Cattle 61,100, sheep 1,800, swine 14,600, horses, goat, donkey and mule.
G3 POPULATION IN THE CATCHMENT AREA
    1982
    Population Population density [km-2] Major cities
    Total 207,326 249 Aregua, Capiata, Itaugua, Lugue, San Lovenzo, Ypacarai, San Bernardino, Pirayu

H. LAKE UTILIZATION (Q)

H1 LAKE UTILIZATION
    Source of water, sightseeing and tourism and recreation (swimming and yachting).
H2 THE LAKE AS WATER RESOURCE
    1987
    Use rate [m3 day-1]
    Domestic 700 (winter)
    2,000 (summer)

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS (Q)

I1 ENHANCED SILTATION
  • Extent of damage: Serious.
  • Supplementary notes
    Lake water is always turbid with suspended silt and clay derived from roads and cultivated lands. Therefore, purification process for potable water takes time.
I2 TOXIC CONTAMINATION
  • Present status: Detected but no minute data.
  • Main contaminants
    1988 Name of Concentration [ppm] in contaminant Water T-Fe 0.38 T-Mn 0.017
  • Environmental quality standards for contamination in the lake
    Under consideration.
I3 EUTROPHICATION
  • Nuisance caused by eutrophication
    Unusual algal bloom (Anabaena, Microcystis).
  • Nitrogen and phosphorus loadings to the lake [kg day-1]
    1988 Sources Industrial & Domestic Agricultural Total T-N 652 1,426 2,078 T-P 120 712 832
  • Supplementary notes
    Trends of eutrophication in recent years are not clarified due to the lack of monitoring of water quality in the lake and rivers, though monthly observations of certain water quality items were made in 1982 and 1984. Countermeasures for water quality degradation are still under consideration.

J. WASTEWATER TREATMENTS

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA
    e) Severe pollution with little wastewater treatment.
J2 APPROXIMATE PERCENTAGE DISTRIBUTION OF POLLUTANT LOADS (3)
    Point source [%] Non-point source [kg yr-1]
    Domestic Industrial Domestic animal and siltation
    COD 52 44 9,800,000
    T-N 78 15 370,000
    T-P 65 30 94,000
    SS - - 20,000,000
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: 98.6%.
  • Percentage of rural population with adequate sanitary facilities (on-site
    treatment systems): 97.4%.
  • Municipal wastewater treatment systems
    No. of tertiary treatment systems: 0. No. of secondary treatment systems: 0. No. of primary treatment systems: 1. No. of other types: 0.
  • Industrial wastewater treatment systems
    No. of industrial wastewater treatment systems: 2-4 (oxidation pond).

K. IMPROVEMENT WORKS IN THE LAKE (Q)

None.

L. DEVELOPMENT PLANS (Q)

Under consideration.

M. LEGISLATIVE AND INSTITUTIONAL MEASURES FOR UPGRADING LAKE ENVIRONMENTS (Q)

M1 NATIONAL AND LOCAL LAWS CONCERNED
  • Names of the laws (the year of legislation)
    1. Sanitation Act (Law No. 836)(1980)
    2. Presidential Ordinance No. 18831 (1986)
  • Responsible authorities
    1. Ministry of Public Health and Social Welfare
  • Main items of control: Not yet decided.
M2 INSTITUTIONAL MEASURES
  1. National Environmental Sanitation Service, Asuncion
M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES
  1. National Institute for Technology and Standards, Asuncion
  2. Institute of Basic Science, Asuncion National University

N. SOURCES OF DATA

  1. Questionnaire filled by Mr. K. Nomura, Shiga Prefectural Institute of Public Health and Environmental Science, Otsu, Japan.
  2. Nomura, K. Personal communication.
  3. After Estudio Limnologico del Lago Ypacarai by ICB, Univ. Nac. Asuncion.
  4. Nakajima, K. (1990) The study on water pollution control plan for the Lake Ypacarai and its basin. Water Pollution Research (Suishitsu Odaku Kenkyu), 13(7): 20-23 (in Japanese).