Physical and chemical limnology of a wind-swept tropical highland reservoir

Valle de Bravo (VB) is a tropical reservoir located (19°21′30″ N, 100°11′00″ W) in the highlands of Mexico. The reservoir is daily swept by strong (7.4 m s−1 mean speed) diurnal (12:00–19:00 h) winds that blow along its two main arms. As expected from its fetch (6.9 km) and its depth (21.1 m mean), the reservoir behaves as a warm monomictic water body. During 2001, VB was stratified from February to October, and well mixed from November to January. Its mean temperature was 19.9°C; the maximum found was 23.8°C in the epilimnion, while a minimum of 17.8°C was registered during mixing. VB exhibited a thermal regime similar to other water bodies of the Mexican tropical highlands, except for a steady increase of its hypolimnetic temperature during stratification, which is attributed to entrainment of epilimnetic water into the hypolimnion. During stratification, the hypolimnion was anoxic, while the whole water column remained under-saturated (60%) during mixing. The flushing time is 2.2 years. Mineralization and total alkalinity are low, which allows strong changes in pH. Ammonia remained low (2.4 μmol l−1 mean) in the epilimnion, but reached up to 60 μmol l−1 in the hypolimnion. Soluble reactive phosphorous had a mean of 0.28 μmol l−1 in the epilimnion and a mean of 1.25 μmol l−1 in the hypolimnion. Nitrate exhibited maxima (up to 21 μmol l−1) during mixing, and also in the metalimnion (2 μmol l−1) during stratification. Low dissolved inorganic nitrogen indicated nitrogen limitation during stratification. Eutrophication is an emerging problem in VB, where cyanobacteria dominate during stratification. At VB chlorophyll a is low during mixing (mean of 9 μg l−1), and high during stratification (mean 21 μg l−1), when blooms (up to 88 μg l−1) are frequent. This pattern is similar to that found in other eutrophic tropical water bodies. We propose that in VB the wind regime causes vertical displacements of the thermocline (0.58–1.10 m hr−1) and boundary mixing, enhancing the productivity during the stratification period in this tropical reservoir.

[1]  G. F. Humphrey,et al.  New spectrophotometric equations for determining chlorophylls a, b, c1 and c2 in higher plants, algae and natural phytoplankton , 1975 .

[2]  L. Solórzano.  DETERMINATION OF AMMONIA IN NATURAL WATERS BY THE PHENOLHYPOCHLORITE METHOD 1 1 This research was fully supported by U.S. Atomic Energy Commission Contract No. ATS (11‐1) GEN 10, P.A. 20. , 1969 .

[3]  T. Parsons,et al.  A manual of sea water analysis , 1960 .

[4]  Water column stratification and its implications in the tropical warm monomictic Lake Alchichica, Puebla, Mexico , 2000 .

[5]  Ilia Ostrovsky,et al.  Seiche-induced mixing: Its impact on lake productivity , 1996 .

[6]  E. González,et al.  Physical and chemical features of a tropical hypertrophic reservoir permanently stratified , 2004, Hydrobiologia.

[7]  J. Alcocer,et al.  WIND-DRIVEN UPWELLING INDICATED BY HIDROLOGICAL VARIABILITY IN A TROPICAL EUTROPHIED RESERVOIR, VALLE DE BRAVO, MEXICO , 2003 .

[8]  A. E. Greenberg,et al.  Standard methods for the examination of water and wastewater : supplement to the sixteenth edition , 1988 .

[9]  D. G. Davis.  Chronopotentiometry of uranium(iv) , 1962 .

[10]  h-sas-i-ahlgren.  Lake restoration by reduction of nutrient loading: Expectations, experiences, extrapolations , 1989 .

[11]  F. Schiemer,et al.  Perspectives in tropical limnology. , 1996 .

[12]  M. Oliva,et al.  Phytoplankton dynamics in a deep, tropical, hyposaline lake , 2001, Hydrobiologia.

[13]  S. Davies,et al.  Environmental changes in the Zirahuén Basin, Michoacán, Mexico, during the last 1000 years , 2004 .

[14]  J. P. Riley,et al.  A modified single solution method for the determination of phosphate in natural waters , 1962 .

[15]  S. Montenegro-Guillén.  Limnological perspective of Lake Xolotlán (Managua): The PLALM , 1991, Hydrobiological Bulletin.

[16]  E. González,et al.  Características físicas y químicas del embalse Agua Fría (Parque Nacional Macarao, Estado Miranda, Venezuela) , 2004 .

[17]  John Melak.  Ecological Dynamics of Tropical Inland Waters. , 2000 .

[18]  H. Salas,et al.  A simplified phosphorus trophic state model for warm-water tropical lakes , 1991 .

[19]  R. Wetzel.  Limnology: Lake and River Ecosystems , 1975 .

[20]  M. Dokulil,et al.  Cyanobacterial dominance in lakes , 2000, Hydrobiologia.

[21]  Vera Istvanovics,et al.  Temporal changes in biomass specific photosynthesis during the summer: regulation by environmental factors and the importance of phytoplankton succession , 1992, Hydrobiologia.

[22]  S. MacIntyre,et al.  Nutrient fluxes from upwelling and enhanced turbulence at the top of the pycnocline in Mono Lake, California , 2001, Hydrobiologia.

[23]  Abraham Lerman,et al.  Lakes--chemistry, geology, physics , 1978 .

[24]  C. Jiménez-Sierra,et al.  Some limnological features of three lakes from Mexican neotropics , 1996, Hydrobiologia.

[25]  V. Olvera-Viascán,et al.  Aquatic ecology and management assessment in Valle de Bravo reservoir and its watershed , 1998 .

[26]  W. M. Lewis.  A Revised Classification of Lakes Based on Mixing , 1983 .

[27]  Ralph Smith,et al.  Limnology—Inland water ecosystems , 2002, Journal of the North American Benthological Society.

[28]  C. Mortimer.  Strategies for Coupling data Collection and Analysis with Dynamic Modelling of lake Motions , 1979 .

[29]  G. Vilaclara,et al.  Comparative description of crater-lakes basic chemistry in Puebla State, Mexico , 1993 .

[30]  Colin S. Reynolds,et al.  Non-determinism to probability, or N : P in the community ecology of phytoplankton : Nutrient ratios , 1999 .

[31]  W. Lewis.  Tropical lakes: how latitude makes a difference , 2002 .