Impact of 2016 intense drought to small tropical reservoir: An early onset and late recovery experience in Timah Tasoh, Malaysia

This study investigates the hydrological drought impact during the extreme 2016 El-Nino to small tropical reservoir of Timah Tasoh, in Perlis, Malaysia. Small tropical reservoirs are important freshwater supplier due to its economic & strategic factors including (i) closer distance to inhabitants and agriculture footprints, (ii) easy access to the resource, and (iii) cheaper cost of water pipelines system. In theory, small tropical lakes or reservoirs are facing higher risk to drought compared to the bigger ones. However, detail information and evidence are required for site specific drought adaptation in the future especially the onset and offset of the drought at specific hydrometeorological and dam scale. Prior to that, a case study was conducted in one of the small-sized and shallow reservoirs of Timah Tasoh, Perlis to analyze the impact. The larger Pedu reservoir was selected as control site. Both reservoirs were having identical hydro-climatic characteristics (seasonality of rainfall). The observation on the rainfall and reservoir level data indicated that the small sized reservoir (Timah Tasoh) tends to dry about 2 months faster (reached dam critical level) and recover 1 month late compared to the normal dry season. In comparison with the Pedu reservoir, the drought onset and offset in Timah Tasoh was earlier and late respectively although the rainfall pattern is typical. The total impacted drying days for Timah Tasoh is 197 days compared to 78 days of Pedu (about 3 months longer). The findings indicate that the 2016 extreme drought impacted the Timah Tasoh small reservoir where they would suffer longer dry season and experienced slower recovery compared to the bigger Pedu reservoir. The outcome of this investigation signifies that the early drought onset monitoring should be implemented for the small sized reservoirs to take appropriate mitigation and preventive measures in adapting to the intense drought.

Seasonal variation of Microcystis aeruginosa and factors related to blooms in a deep warm monomictic lake in Mexico

The occurrence of cyanobacterial blooms has increased globally over the last decades, with the combined effect of climate change and eutrophication as its main drivers. The seasonal dynamic of cyanobacterial blooms is a well-known phenomenon in lakes and reservoirs in temperate zones. Nevertheless, in the tropics, most studies have been performed in shallow and artificial lakes; therefore, the seasonal dynamic of cyanobacterial blooms in deep and eutrophic tropical lakes is still under research. We studied the seasonal variation of the phytoplankton community and the factors associated with Microcystis aeruginosa blooms along the water column of Lake Alberca de Tacámbaro, a warm monomictic crater lake located in Mexico, during 2018 and 2019. According to previous studies performed in 2006 and 2010, this lake was mesotrophic-eutrophic, with Chlorophyta and Bacillariophyta as the dominant groups of the phytoplankton community. During 2018 and 2019, the lake was eutrophic and occasionally, hypertrophic, a phenomenon likely associated with the increase of farmland area around the lake. The dominant species was M. aeruginosa, forming blooms from the surface to 10 m depth in winter, in the hypolimnion in spring and summer, and along the full water column in autumn. These findings suggest that M. aeruginosa in Lake Alberca de Tacámbaro displays seasonal and spatial population dynamics. Total phosphorus, dissolved inorganic nitrogen, water temperature and photosynthetically active radiation were the environmental factors related to M. aeruginosa blooms. Our results suggest that the changes in the structure of the phytoplankton community through time, and M. aeruginosa blooms in Lake Alberca de Tacámbaro, are mainly related to changes in land use from forest to farmland in areas adjacent to the lake, which promoted its eutrophication in the last years through runoffs. Comparative studies with other deep and eutrophic lakes will allow us to gain a deeper understanding of the dynamic of cyanobacterial blooms in natural and artificial water reservoirs strongly stressed by human activities.

Aquatic reservoir of Vibrio cholerae in an African Great Lake assessed by large scale plankton sampling and ultrasensitive molecular methods

The significance of large tropical lakes as environmental reservoirs of Vibrio cholerae in cholera endemic countries has yet to be established. By combining large scale plankton sampling, microbial culture and ultrasensitive molecular methods, namely Droplet Digital PCR (ddPCR) and targeted genomics, the presence of Vibrio cholerae was investigated in a 96,600 L volume of surface water collected on a 322 nautical mile (596 km) transect in Lake Tanganyika. V. cholerae was detected and identified in a large area of the lake. In contrast, toxigenic strains of V. cholerae O1 or O139 were not detected in plankton samples possibly in relation to environmental conditions of the lake ecosystem, namely very low salinity compared to marine brackish and coastal environments. This represents to our knowledge, the largest environmental study to determine the role of tropical lakes as a reservoir of V. cholerae.

Climate change drives widespread shifts in lake thermal habitat

Lake surfaces are warming worldwide, raising concerns about lake organism responses to thermal habitat changes. Species may cope with temperature increases by shifting their seasonality or their depth to track suitable thermal habitats, but these responses may be constrained by ecological interactions, life histories or limiting resources. Here we use 32 million temperature measurements from 139 lakes to quantify thermal habitat change (percentage of non-overlap) and assess how this change is exacerbated by potential habitat constraints. Long-term temperature change resulted in an average 6.2% non-overlap between thermal habitats in baseline (1978–1995) and recent (1996–2013) time periods, with non-overlap increasing to 19.4% on average when habitats were restricted by season and depth. Tropical lakes exhibited substantially higher thermal non-overlap compared with lakes at other latitudes. Lakes with high thermal habitat change coincided with those having numerous endemic species, suggesting that conservation actions should consider thermal habitat change to preserve lake biodiversity.

Highest Composition Dissimilarity among Phytoplankton Communities at Intermediate Environmental Distances across High-Altitude Tropical Lakes

Tropical high-altitude lakes are vital freshwater ecosystems for the functioning and dynamics of tropical high-altitude wetlands called páramos, found at over 3300 m above sea level. They play a major role in the hydrogeological cycle and provide important hydrological services such as water storage, and yet they are understudied. Describing the patterns and processes of community composition in these lakes is required to better understand the consequences of their degradation by human activities. In this study we tested the geographical and environmental components of distance–decay relationships in the phytoplankton structure across 24 tropical high-altitude lakes from Southern Ecuador. Phytoplankton composition at the phyla level showed high among-lake variation in the tropical high-altitude lakes from Tres Lagunas. We found no links, however, between the geographic distance and phytoplankton composition. On the contrary, we observed some environmentally related patterns of community structure like redox potential, altitude, water temperature, and total phosphorus. The absence of support for the distance–decay relationship observed here can result from a conjunction of local niche-based effects and dispersal limitations. Phytoplankton community composition in the Tres Lagunas system or any other ecosystem may be jointly regulated by niche-based and neutral forces that still need to be explored. Despite not proving a mechanistic explanation for the observed patterns of community structure, we hope our findings provide understanding of these vulnerable and vital ecosystems. More studies in tropical high-altitude lakes are urgently required.