EZEQUIEL RAMOS MEXIA RESERVOIR

A view from the lakeside

Photo.
Photo: A.Mariazzi


A. LOCATION

  • Rio Negro Province, Argentina.
  • 39:50S, 66:20W; 381 m above sea level.

B. DESCRIPTION (Q)

    Ezequiel Ramos Mexia Reservoir is a man-made lake in the Southern Andean Range, about 600 km away from Bahia Blanca. The lake was formed in 1972 by the damming of Limay River, which flows out from Lake Nahuel Huapi. The Limay Valley is formed by the 10-30 m thick layer of well-graded pebbles mixed with 30% of sand. The stratigraphic structure of the lake district consists of three kinds of sediments; a) Cretaceous sediments emerging continuously on both sides of the reservoir, b) Cenozoic sediments of conglomerates of variable sandy and clayey matrix, and c) recent sediments of fine to very fine sands forming dunes up to 7 m high on the northeastern side of the reservoir.
    The lake water is soft, neutral to slightly alkaline, basically bicarbonate- calcic. The chlorophyll concentration and primary production are relatively low because of the low concentrations of nutrients (inorganic nitrogen and total phosphorus) and the short residence time. Therefore, the reservoir may be classified as an oligo-mesotrophic lake.

C. PHYSICAL DIMENSIONS (Q)

    Surface area [km2] 816
    Volume [km3] 20.2
    Maximum depth [m] 60
    Mean depth [m] 24.7
    Water level Regulated
    Length of shoreline [km] 346
    Residence time [yr] 1
    Catchment area [km2] 24,420

D. PHYSIOGRAPHIC FEATURES (Q)

D1 GEOGRAPHICAL
  • Sketch map: Fig. SAM-03-0l.
  • Names of main islands: None.
  • Number of outflowing rivers and channels (name): 1 (R. Negro).

    Fig. SAM-03-01
    Sketch map of the lake system.

D2 CLIMATIC
  • Water temperature: Fig. SAM-03-02.

    Fig. SAM-03-02
    Spatial-time distribution of water temperature [deg C].

  • Mixing type: Monomictic.

E. LAKE WATER QUALITY (Q)

E1 TRANSPARENCY

    Fig. SAM-03-03
    Seasonal trend of transparency [m] and relative light transmission [%].

E3 SS [mg l-1]
    57.8 (52.1-69.5).
E4 DO

    Fig. SAM-03-04
    Spatial-time distribution of DO [mg l-1].

E6 CHLOROPHYLL CONCENTRATION

    Fig. SAM-03-05
    Spatial-time distribution of Chlorophyll a [micro g l-1].

E7 NITROGEN CONCENTRATION
  • NH4-N [micro g l-1]: 10.
  • NO3-N [micro g l-1]: 10 (10-50).
  • NO2-N [micro g l-1]: 10.
E8 PHOSPHORUS CONCENTRATION
  • PO4-P [micro g l-1]: 5 (5-47).
  • Total-P [micro g l-1]: 10 (5-53).

F. BIOLOGICAL FEATURES (Q)

F1 FLORA
  • Phytoplankton
    Anabaena circinalis, Pandorina morum, Eudorina elegans, Binuclearia eriensis, Cyclotella stelligera, Melosira italica, M. granulata, M. granulata var. angustissima f. spiralis, Dinobryon divergens, Gymnodinium sp.
F3 PRIMARY PRODUCTION RATE

    Fig. SAM-03-06
    Vertical distribution of primary production [mg C m-3 h-1].

F4 BIOMASS

    Fig SAM-03-07
    Monthly fluctuation of phytoplankton density.

    Fig. SAM-03-08
    Vertical distribution of phytoplankton density.


G. SOCIO-ECONOMIC CONDITIONS

G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE (Q)
  • Secondary and tertiary industries: None.
  • Number of domestic animals in the catchment area: None.
G3 POPULATION IN THE CATCHMENT AREA (Q)
    Population Population density [km-2] Major cities (population)
    Rural 2,000 None
    Total 2,000 0.08 (One small village)

H. LAKE UTILIZATION

H1 LAKE UTILIZATION (Q)
    Sources of water, navigation and transportation, sightseeing and tourism, recreation (swimming and sport-fishing) and fisheries.
H2 THE LAKE AS WATER RESOURCES
    1987
    Use rate
    Domestic Negligible
    Irrigation Negligible
    Industrial Negligible
    Power plant l,200 MW

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS

I1 ENHANCED SILTATION (Q)
  • Extent of damage: Not serious.
I2 TOXIC CONTAMINATION (Q)
  • Present status: Not detected.
I3 EUTROPHICATION (Q)
  • Nuisance caused by eutrophication: None.
    Mean values and ranges of annual variation of nitrogen and phosphorus concentration in affluents [micro g l-1]
    Affluent Collon Cura River Limay River (Alicura) Limay River (Pantanito)
    Avg. Range Avg. Range Avg. Range
    PO4-P 5 - 5 - 5 -
    Total P 17 5-34 8 5-11 9 5-11
    NO3-N 10 - 10 - 10 -
    NO2-N 10 - 10 - 10 -
    NH4-N 10 - 10 - 10 -
I4 ACIDIFICATION (Q)
  • Extent of damage: None.

J. WASTEWATER TREATMENTS

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA (Q)
    b) No sources of significant pollution.
J3 SANITARY FACILITIES AND SEWERAGE (Q)
  • Wastewater treatment systems
    One small-scale domestic wastewater treatment plant.

K. IMPROVEMENT WORKS IN THE LAKE (Q)

    None.

L. DEVELOPMENT PLANS (Q)

    None.

N. SOURCES OF DATA

  1. Questionnaire filled by Dr. A. Mariazzi, Facultad de Ciencias Naturales y Museo, Instituto de Limnologia, La Plata, Argentina.