LAGUNA DE ROCHA

Northern part of the lagoon
with Spartina marsh in the background

Photo.
Photo: R.Sommaruga


A. LOCATION

  • Rocha municipality, Uruguay.
  • 34:33-34:41S, 54:12-54:22W; ca. 0 m above sea level.

B. DESCRIPTION

    Uruguay has several coastal lagoons in the southeastern and eastern part of the country. Many of them, including Laguna de Rocha, are comprised in the Biosphere Reserve designated by Man and the Biosphere Program (MAB) of UNESCO.
    Like most recent lagoons, Laguna de Rocha was formed through the rise of sea level during the last 6,000-8,000 years. It is separated from the Atlantic Ocean by a sand bar, which is sometimes opened by wave action and thixotropy as well as artificially. The intrusion of salt water during open-bar periods produces a clear gradient of salinity that controls physical and chemical water parameters. There are five inflowing rivers, of which the Arroyo Rocha (average flux 13.4 m3 sec-1) and the Las Conchas are the most important. This lagoon is known for its production of fish, crab, shrimp and molluscs harvested by fisherman families living on its southern shore.
    The Limnology Department, Faculty of Sciences, Univ. de la Republica, has been studying the lagoon system since 1986 and is currently constructing a limnology station which is expected to serve also as an operative centre for researches on other coastal lagoons.

C. PHYSICAL DIMENSIONS (1)

    Surface area [km2] 72
    Volume [km3] 0.04
    Maximum depth [m] 1.4
    Mean depth [m] 0.6
    Catchment area [km2] 1,312

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL
  • Bathymetric map: Fig. SAM-09-01.
D2 CLIMATIC (2)
  • Climatic data at Rocha city, 1951-1980
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    Mean temp. [deg C] 21.5 21.3 19.9 16.4 13.7 11.2 10.9 11.2 12.6 14.8 17.4 20.2 15.9
    Precipitation [mm] 98 102 87 81 78 97 96 102 109 92 70 61 1,073
  • Solar radiation (1979-1984): 14.3 MJ m-2 day-1.

    Fig. SAM-09-01
    Bathymetric map [m](Q).

  • Water temperature [deg C](2)
    Mean value for all stations, 1987
    Depth [m] Jan Feb*1 Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S*2 25.1 25.0 22.8 18.3 12.5 - 12.9 8.9 15.6 18.7 25.4 18.6
    *1 1988. *2 Surface.
  • Freezing period: None.
  • Mixing type: Polymictic.

E. LAKE WATER QUALITY (2)

E1 TRANSPARENCY [m]
    Secchi disc usually reaches bottom surface.
E2 pH
    Station 1, 1987
    Depth [m] Jan Feb*1 Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S*2 7.9 8.3 8.4 7.9 7.9 - 7.7 7.9 8.0 7.9 8.4 8.1
    *1 1988. *2 Surface.
    Station 8, 1987
    Depth [m] Jan Feb* Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 8.0 6.5 6.7 6.7 7.7 - 7.1 6.9 7.4 6.9 9.0 6.8
    * 1988.
E3 SS [mg l-1]
    Station 1, 1987
    Depth [m] Jan Feb*1 Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S*2 8.0 10.6 11.6 11.0 24.2 - 0.0 20.2 8.1 10.0 6.7 11.5
    *1 1988. *2 Surface.
    Station 8, 1987
    Depth [m] Jan Feb* Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 3.0 65.0 49.4 32.0 18.3 - 0.8 72.9 36.0 36.8 17.0 45.5
    * 1988.
E4 DO [mg l-1]
    Station 1, 1987
    Depth [m] Jan Feb*1 Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S*2 6.4 7.5 7.7 8.8 9.2 - 9.8 10.0 10.0 8.9 - 9.4
    *1 1988. *2 Surface.
    Station 8, 1987
    Depth [m] Jan Feb* Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 8.2 3.5 6.0 6.7 9.6 - 8.8 10.0 9.4 9.4 - 8.4
    * 1988.
E6 CHLOROPHYLL CONCENTRATION [micro g l-1](3)
    Station 1, December 1988-November 1989
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* 15.7 16.7 15.8 9.3 9.1 11.3 12.0 8.9 8.0 8.0 12.8 23.1
    *Surface.
    Station 8, December 1988-November 1989
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 12.9 14.3 11.0 21.1 6.2 8.8 14.7 13.2 10.9 16.1 24.3 56.1
E7 NITROGEN CONCENTRATION
  • NO3-N [mg l-1](2)
    Station 1, 1987
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* 0.10 - 0.36 0.10 0.17 - 0.14 0.19 - - - 0.17
    * Surface.
    Station 8, 1987
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 0.80 - 0.20 0.11 0.17 - 0.08 0.19 - - - 0.27
  • NH4-N [mg l-1](2)
    Station 1, 1987
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 0.05 - 0.00 0.19 0.04 - 0.15 0.03 - - - 0.03
    Station 8, 1987
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 0.03 - 0.35 1.32 0.01 - 0.04 0.04 - - - 0.27
E8 PHOSPHORUS CONCENTRATION (2)
  • Total-P [micro g l-1]
    Station 1, 1987
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S* 0 - 42 67 83 - 21 25 3 249 10 -
    * Surface.
    Station 8, 1987
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 199 - 63 226 74 - 46 27 35 151 80 -
E9 CHLORIDE CONCENTRATION (1)
  • Salinity [%]
    Station 1, 1987
    Depth [m] Jan Feb* Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S*2 9.0 7.5 13.7 27.7 15.3 - 7.4 8.0 19.2 5.8 8.5 7.0
    *1 1988. *2 Surface.
    Station 8, 1987
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S 0.0 1.0 0.0 0.2 2.7 - 1.0 0.0 1.3 3.0 0.0 0.0
    * 1988.

F. BIOLOGICAL FEATURES

    1987-1989
F1 FLORA
  • Emerged macrophytes (3)
    Scirpus californicus, Spartina montevidensis, Typha latifolia, Sagittaria montevidensis, Ludwigia peploides, L. gramineans.
  • Floating macrophytes: Eichhornia azurea (3).
  • Submerged macrophytes: Potamogeton sp. (3).
  • Phytoplankton (4)
    Melosira sp., Navicula sp., Diploneis sp., Amphiprora sp., Nitzchia sp., Cymbella sp., Stephanodiscus sp., Coscinodiscus sp., Peridinium sp., Oscillatoria sp., Aphanothece sp., Anabaena sp., Mallomonas sp., Spirogyra sp., Pandorina sp., Eudorina sp.
F2 FAUNA
  • Benthos (5)
    Erodona mactroides*, Heleobia australis, Laeonereis culveri, Nephtys fluviatilis, Heteromastus simi, Balanus improvisus, Tanais stanfordi, Dies fluminensis, Melita mangrovi, Amphitoe ramondi, Chasmagnatus granulata, Cyrtograpsus angulatus, Callinectes sapidus*, Palemonetes argentinus, Penaeus paulensis*.
    * Economically important.
  • Fish (1)
    Micropogonias furnieri*, Pogonias chromis*, Mugil spp., Paralichthys brasiliensis, Brevoortia sp.*
    * Economically important.
  • Supplementary notes on the biota (6)
    A very important population of Cygnus melancorhphus (black neck swan) exists in the lagoon. A maximum number of 7,066 individuals was found in 1986. Also important is Coscoroba coscoroba (endemic).
F3 PRIMARY PRODUCTION RATE
  • Phytoplankton gross production [mg C l-1 hr-1]
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    Station 1, December 1988-November 1989
    1.31 0.99 0.83 0.94 0.11 0.10 0.11 0.12 0.19 0.26 0.18 0.26
    Station 8, December 1988-November 1989
    1.02 0.99 0.78 0.63 0.03 0.07 0.09 0.11 0.19 0.11 0.12 0.07
F4 BIOMASS
  • Erodona mactroides [g (dry wt.) m-2]
    Stn. Winter Spring Summer Fall
    1 10.48 32.34 26.45 53.9
    8 12.99 45.95 59.57 37.8

G. SOCIO-ECONOMIC CONDITIONS

G1 LAND USE IN THE CATCHMENT AREA
    1976
    Area [km2]* [%]
    Natural landscape
    - Woody vegetation 552 6.0
    Agricultural land
    - Crop field 215 2.4
    - Pasture land 8,385 91.6
    Total 9,153 100
    *Data based on the total area of Rocha municipality (10,551 km2).
  • Types of important forest vegetation
    Gallery forest along rivers and Eucalyptus sp. (non-native).
  • Main kinds of crops: Rice and maize.
G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE
  • Number of domestic animals in the catchment area
    Cattle 477,649, sheep 1,155,604.
G3 POPULATION IN THE CATCHMENT AREA (8)
    1985
    Population Population density [km-2] Major cities (population)
    Urban 56,200 Rocha (25,200)
    Rural 12,300
    Total 68,500 6.5

H. LAKE UTILIZATION (Q)

H1 LAKE UTILIZATION
    Sightseeing, tourism and fisheries.

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS (8)

I1 ENHANCED SILTATION
  • Extent of damage: None.
I2 TOXIC CONTAMINATION
  • Present status: No information but not suspected.
I4 ACIDIFICATION
  • Extent of damage: None.

J. WASTEWATER TREATMENTS

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA
    b) No sources of significant pollution.
J3 SANITARY FACILITIES AND SEWERAGE
  • Percentage of municipal population in the catchment area provided with adequate sanitary facilities (on-site treatment systems) or public sewerage:
    94.9%.

L. DEVELOPMENT PLANS

    Continuation of a highway crossing the southern part of the lagoon is planned for the next year (1991) and an ecological hotel will be built in the near future.

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. Law of water quality control (1979)
  • Responsible authorities
    1. National Office of Environmental Health
  • Main items of control
    1. Industrial and domestic wastewater effluents
M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES
  1. Department of Limnology, Faculty of Sciences, Univ. de la Republica

N. SOURCES OF DATA

  1. Questionnaire filled by Drs. L. W. Pintos and L. R. Sommaruga, Department of Limnology, Faculty of Sciences, Univ. de la Republica, Uruguay.
  2. Pintos, L. W., Sommaruga, L. R., Conde, D., de Leon, R. & Chalar, G. (1988) Antecedents and New Contributions to the Knowledge of Laguna de Rocha. Progress Report, Univ. de la Republica, Uruguay.
  3. Pintos, L. W., Sommaruga, L. R. Conde, D., de Leon R. & Chalar, G. (in preparation) Seasonal variation of physical and chemical parameters of Laguna de Rocha.
  4. De Leon, R. (in preparation) Primary productivity in two zones of Laguna de Rocha.
  5. ---. Personal communication.
  6. Pintos, W., Conde, D., de Leon, R., Cardezo, M. J., Jorcin, A. & Sommaruga, R. (in press) Some limnological characteristics of Laguna de Rocha (Uruguay). Rev. Bio. Bras.
  7. Vaz Ferreira, R., Rilla, F., Gambarotta, J. C., Arbella, E. & Skuk, G. (1987) Ornithologic importance of the East wetlands of Uruguay. III Neotropical Ornithol. Cong., Columbia.
  8. Jorcin, A. (1989) Ecological studies on Erodona mactroides (Daudin, 1801) of Laguna de Rocha. Graduate Thesis, Univ. de la Republica, Uruguay.
  9. General Office of Statistics (1986) Statistic Data Book of Uruguay. (All references in Spanish except for (5)).