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

Abstract

Valle de Bravo (VB) is a tropical reservoir located (19°21 0 30@ N, 100°11 0 00@ W) in the highlands of Mexico. The reservoir is daily swept by strong (7.4 m s À1 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 lmol l À1 mean) in the epilimnion, but reached up to 60 lmol l À1 in the hypolimnion. Soluble reactive phosphorous had a mean of 0.28 lmol l À1 in the epilimnion and a mean of 1.25 lmol l À1 in the hypolimnion. Nitrate exhibited maxima (up to 21 lmol l À1 ) during mixing, and also in the metalimnion (2 lmol l À1 ) 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 lg l À1 ), and high during stratification (mean 21 lg l À1 ), when blooms (up to 88 lg l À1 ) 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 À1 ) and boundary mixing, enhancing the productivity during the stratification period in this tropical reservoir.

The impact of anthropogenic pollution on limnological characteristics of a subtropical highland reservoir “Lago de Guadalupe”, Mexico

“…These changes are typical for warm monomictic water bodies as reported by Hutchinson and Loffler (1956) and by Tundisi (1994), but differ from the warm polymictic thermal cycle reported by Lewis Jr (1983) for other lakes at LG's latitude with similar depths. Nevertheless, the warm monomictic cycle of LG is consistent with the thermal cycle described by Merino-Ibarra et al (2007) for Valle de Bravo reservoir, located at 1780 m a.s.l., 106 km SW from LG. Similar thermal and oxygen profiles in the water column were observed by Vazquez et al (2004) in a tropical lake with an average water temperature higher than LG (21 to 26…”

“…Algal blooms occurred frequently over the stratification period and can be seen as an additional eutrophication indicator. The same observations were made at the Valle de Bravo reservoir (Merino-Ibarra et al, 2007), at Lake Lago de Chapala (Lind and Davalos-Lind, 2002), and at Lake Lago de Patzcuaro (Berlanga-Robles et al, 2002), all of which are located in sub-tropical areas of Mexico. This study confirms that cultural eutrophication is a major problem in several Mexican water reservoirs.…”

Thermal structure and response to long‐term climatic changes in Lake Qiandaohu, a deep subtropical reservoir in China

“…Furthermore, turbidity usually peaks in the thermocline region, which is closely related to the location of the maximum density gradient, so low turbulence stabilizes the sediments in the vertical water column (Elçi 2008). As a result, the degradation of water quality in the summer resulting from thermal stratification has been observed in many reservoirs and lakes around the world (Elçi 2008;Merino-Ibarra et al 2008;Wilhelm and Adrian 2008).…”

Tropical cyanobacterial blooms: a review of prevalence, problem taxa, toxins and influencing environmental factors

“…Since that incident some studies have been carried out on several reservoirs in South and Central America documenting blooms and progenitor species (Díaz-Pardo et al, 1998;Lind and Davalos-Lind, 2002;Ramirez et al, 2002;Bittencourt-Oliveira et al, 2005;Frias et al, 2006;Merino-Ibarra et al, 2007;Berry and Lind, 2010;Vasconcelos et al, 2010;Rejmánková et al, 2011). A review by Dorr et al (2010) revealed that there has been increased cyanobacterial bloom occurrence in water bodies in South America requiring better methods for screening and testing of cyanobacterial toxins.…”