Community metabolism in a deep (stratified) tropical reservoir during a period of high water-level fluctuations

Abstract

As long as lakes and reservoirs are an important component of the global carbon cycle, monitoring of their metabolism is required, especially in the tropics. In particular, the response of deep reservoirs to water-level fluctuations (WLF) is an understudied field. Here, we study community metabolism through oxygen dynamics in a deep monomictic reservoir where high WLF (~10 m) have recently occurred. Simultaneous monitoring of environmental variables and zooplankton dynamics was used to assess the effects of WLF on the metabolism of the eutrophic Valle de Bravo (VB) reservoir, where cyanobacteria blooms are frequent. Mean gross primary production (Pg) was high (2.2 g C m−2 day−1), but temporal variation of Pg was low except for a drastic reduction during circulation attributed to zooplankton grazing. The trophogenic layer showed net autotrophy on an annual basis, but turned to net heterotrophy during mixing, and furthermore when the whole water-column oxygen balance was calculated, considering the aphotic respiration (Raphotic). The high total respiration resulting (3.1 g C m−2 day−1) is considered to be partly due to mixing enhanced by WLF. Net ecosystem production was equivalent to a net export of 3.4 mg CO2 m−2 day−1 to the atmosphere. Low water levels are posed to intensify boundary-mixing events driven by the wind during the stratification in VB. Long-term monitoring showed changes in the planktonic community and a strong silicon decrease that matched with low water-level periods. The effects of low water-level on metabolism and planktonic community in VB suggest that water-level manipulation could be a useful management tool to promote phytoplankton groups other than cyanobacteria.

Effects of Seasonal Thermal Stratification on the Functional Diversity and Composition of the Microbial Community in a Drinking Water Reservoir

“…Cyanobacteria bloomed at the surface water in August, and had an obvious vertical gradient in the water, as reported in other aquatic ecosystems [53]. Moreover, it is suggested that the blooms of Cyanobacteria are favored by the lack of mixing in the water body by Valdespino-Castillo et al [46]. Additionally, both Chlorobi and Chloroflexi were detected, with a higher abundance in the hypolimnion than in the epilimnion, and were dynamically affected by stratification.…”

“…Habitat heterogeneity was considered to play an important role in the determination of microbial community structure [20,25,45]. It is suggested that thermal conditions were the main factor affecting community metabolism and structure by altering hydrodynamic processes, water movement, and mixing events in the water bodies during the annual stratified period [46]. Thus, in this study, it appeared that the dramatic shifts in DO and water temperature among different layers were the main direction indices for the differences in the bacterial communities.…”

Key differences between lakes and reservoirs modify climate signals: A case for a new conceptual model

“…Reservoir management for fish production may also be disproportionately important in tropical systems. Since most freshwater fish production comes from the tropics, management of these systems often includes introduction of new species adapted to the reservoir environment, stocking, and management of fishing effort (van Zwieten et al 2011). Our proposed conceptual model is thus likely to differ for tropical ecosystems; however, more research is needed to formulate specific hypotheses about differential fates of E and m in these systems (Fig.…”

On the successful use of a simplified model to simulate the succession of toxic cyanobacteria in a hypereutrophic reservoir with a highly fluctuating water level

“…Water level fluctuations, caused by monsoonal climate and artificial drawdown can alter the hydrological conditions and influence light and nutrient availability, influencing phytoplankton succession (Tian et al 2015). The decrease in water level can indirectly affect the physical-chemical and biological characteristics of freshwater bodies, mainly through mixing enhancement (Valdespino-Castillo et al 2014). Extreme decreases in reservoir water level can affect the thermal structure of the water column (Zohary and Ostrovsky 2011).…”

“…Many reservoirs are characterized by frequent fluctuations in their water level (Wantzen et al, 2008). These fluctuations affect phytoplankton biomass and species composition through their effect on mixing processes, biogeochemical processes, oxygen dynamics, and underwater light climate (Naselli-Flores and Barone, 1997;Valdespino-Castillo et al, 2014). Their amplitude and frequency are modified by climate change because of changes in the occurrence of drought and heavy rainfall episodes (Callieri et al, 2014).…”