Getting into hot water: Water quality in tropical lakes in relation to their utilisation

Abstract

Over-exploitation of tropical lakes and reservoirs (‘lakes’) causes water quality problems that occur as a result of competing socio-economic demands and the presence of feedback loops within the system that exacerbate the situation. We review well documented case studies from Brazil, India, Indonesia, Kenya, Malaysia and Mexico to examine the effect that changes in water quality and quantity have had on the utilisation of these tropical lakes. By comparing the different approaches used to improve their sustainable management, we have found that nutrient enrichment is one of the most important and widespread water quality problems, causing adverse effects such as algal blooms, nuisance levels of aquatic plants, low oxygen levels and elevated greenhouse gas emissions. These effects restrict the use of these lakes for water supply, fisheries, recreation, tourism and wildlife. We conclude that tropical lakes require better management, urgently, to restore the ecosystem services that they deliver to man and nature. However, to be effective, the development of sustainable management programmes needs to be underpinned by reliable scientific evidence and the results of extensive stakeholder engagement activities. We note that, currently, there is little information available on how tropical lakes respond to management interventions that can be used to guide these activities. Further research is needed to address this knowledge gap.

Vertical Boundary Mixing Events during Stratification Govern Heat and Nutrient Dynamics in Windy Tropical Lakes with High Water-Level Fluctuations: A Long-Term (2001-2018) Study

“…A cascade of ecosystemic processes are potentially affected by boundary mixing and vertical nutrient transport, as has been addressed broadly in the literature [45][46][47][48][49][50]. Understanding the relationships between temperature and vertical transport is key to model emergent ecosystem functions in a warmer world [18]. Previous reports of oxygen dynamics in VB and plankton community composition have been correlated with WLF and boundary mixing, and comprise indirect evidence consistent with the nutrient transport results presented here.…”

“…Altogether, the multiple consequences of WLF in windy tropical lakes such as VB can alter both the ecology of the lake and its suitability for a sustained water exploitation by the main users. The effects we have here identified should be accounted for by water managers [18], who could outweigh them against the particular needs of water distribution that may require affecting the water level of reservoirs and lakes.…”

“…Because important WLF have been occurring in VB in the past two decades, their study on the long-term can contribute to the understanding of their effects on mixing and biogeochemical processes and to better manage deep monomictic lakes and reservoirs in order to cope with their eutrophication, which is an urgent management issue [18]. We have been monitoring this lake for over 18 years, and here we report on the variability of temperature distributions in the water column of this lake with a strong diurnal wind regime, and use the hypolimnetic temperature increase rates observed during each of the stratification periods to calculate the water mass mixing between layers of each stratification cycle.…”

“…These calculations yield estimates of the magnitude of vertical mixing, the coefficient of vertical eddy diffusivity (Kz) and the vertical nutrient entrainment into the epilimnetic zone. The temporal variability of these fluxes is analyzed to assess the effects of water level fluctuations (WLF) on the intensity of this water mixing and nutrient entrainment, which in turn have important ecological effects and implications that should be considered for the urgent and adequate management of tropical lakes and reservoirs [18].…”

Vertical Boundary Mixing Events during Stratification Govern Heat and Nutrient Dynamics in a Windy Tropical Reservoir Lake with Important Water-Level Fluctuations: A Long-Term (2001–2021) Study

“…As important WLFs have been occurring in VB in the past two decades, their long-term study can contribute to the understanding of their effects on mixing and biogeochemical processes. Such an understanding can be useful to cope with the eutrophication of deep monomictic lakes and reservoirs, which is an urgent management issue [18]. We monitored this reservoir lake for over 21 years, and in this study, we (1) report on the variability of temperature distributions in the water column of the windy reservoir lake of VB and (2) used the hypolimnetic temperature increase rates observed during each of the stratification periods to calculate the vertical mixing, the coefficient of vertical eddy diffusivity (Kz), and the vertical nutrient entrainment into the epilimnetic zone for each stratification of 2001-2021.…”