Estimation of greenhouse gas emissions of a tropical reservoir in Colombia

Tropical reservoirs are generally flooded in soils with a high content of organic matter. This, combined with high temperatures, favors the generation of carbon dioxide (CO2) and methane (CH4) by biological degradation, contributing to the impact on climate change. A tropical reservoir in Colombia was monitored for 7 years in the pre-fill, fill and post-fill stages, for the last of these during the day and night. Emissions from diffusive fluxes at the surface of the water were measured using a floating static chamber, while inverted funnel methodology was used to measure the fluxes by bubbling. The samples collected in the field were analyzed in the laboratory using a gas chromatograph with a mass detector. The results showed average emissions of 70,892.51 ± 41,079.16-ton CO2eq/year for pre-filling; 178,254.53 ± 105,838.01-ton CO2eq/year for filling; and 466,946.57-ton CO2eq/year for post-filling (for 5 years), concluding that the weather conditions and the filling percentage (Area surface and volume) had an impact on the generation of greenhouse gases at filling and post-filling stages, as did the organic matter present in the area of influence of the sampling point. Higher greenhouse gas emissions were found during the day compared to the results at night, indicating that temperature affects these processes, especially in tropical reservoirs. This study, currently unique in Colombia, will allow directing efforts towards mitigating the impacts of greenhouse gas emissions in tropical reservoirs.

Uncertainty assessment of open water evaporation measurements: case study in a tropical reservoir in Brazil

<p>The Brazilian semiarid region covers about 1 million km² and is characterised by irregular rainfall and high potential evaporation (above 2000 mm per year of water loss). To overcome the lack of water, the population depends on man-made reservoirs, which are the main source of water during the dry season (8 months of the year). In the federal state of Ceará there is on average one dam every 5 km, totalling more than 20,000. It is, therefore, noteworthy how the accurate estimation of evaporation would improve the management of scarce water resources. Moreover, climate change scenarios predict impacts on water availability in this region and better accuracy in evaporation assessments are fundamental to foster such simulations, which itself works at an intra-day time resolution. We suggest the most precise measurements possible, close to the lake and preferably on top of the water body. We used between October-December 2019 two direct measurement sensors in floating pans on the reservoir. A newly developed one based on the echo sounder principle and a standard differential pressure meter. Both show that at the reservoir more than 6 mm evaporate per day on average in the dry period. Uncertainty analyses for a single measurement show good performance of the acoustic sensor (± 0.11 mm) compared to the standard sensor (± 0.6 mm), sensitive enough to record the daily course of evaporation. The field measurements show 3.7% of uncertainty comparing the acoustic sensor with the standard pressuremeter. The minimum number of measurements with the acoustic sensor to obtain such uncertainty is 307. In this case, for 1h step, the uncertainty is 1.1%. The wave movement caused by wind influences the quality and frequency of the measurement. These results serve as a basis for future approaches to assess spatial variation of evaporation and wind on the lake. This might highlight the minimal number of instruments needed to solve the issue of spatial variability of evaporation.</p>

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.

Investigating the toxicity of tropical reservoir sediments using the Allium test

Water pollution is a global environmental issue, and aquatic sediments are important compartments that might act as sinks or sources of contaminants. Once in the environment, inorganic contaminants such as metals can cause cytogenotoxic effects that damage genetic material and harm the aquatic community. Biological assays such as the Allium test can be used to investigate potential cytogenotoxicity of contaminated sediments based on the alterations of cell cycle indexes and chromosomal aberration frequencies. Therefore, we aimed to assess the toxicity of sediments from four Brazilian reservoirs using the Allium test. Sediments were sampled and elutriates were prepared in a simulating sediment resuspension in the water column. The Allium test was applied to the elutriates, and the metals copper, chromium, cadmium, lead, zinc, and iron were quantified. The elutriates derived from reservoir sediments were able to reduce the mitotic and anaphase index, increase the prophase and metaphase index, and boost chromosomal aberrations compared to the negative control. The cytogenotoxic effects observed may be linked to the presence of copper, zinc, and iron. Therefore, our results showed that the Allium test was a sensitive tool for warning the occurrence of genotoxic contaminants in sediment elutriates from four Brazilian reservoirs.

Human Health Risks Assessment of Some Heavy Metals in Oreochromis niloticus from a Tropical Reservoir

This study evaluated the human health risks of Mn, Fe, Zn, Cu, Cd, Pb, Cr, Co and Ni in Oreochromis niloticus inhabiting Agodi reservoir in Ibadan, Nigeria. The metals’ concentrations were determined with atomic absorption spectrophotometer. Carcinogenic and non-carcinogenic risk of consumers from the intake of metals in the fish was evaluated by Health Risk Index (HRI), Health quotient (HQ) Target Hazard Quotient (THQ) and Target cancer risk (TR). The metal concentrations in the fish were below the recommended limit by Environmental Protection Agencies. HRI and HQ of each examined metal was greater than one, indicating that there was potential noncarcinogenic health risk associated with the consumption of the fish. However, the THQ and TR were less than one. This indicated that Oreochromis niloticus will not pose any immediate carcinogenic threat to its consumers. It is therefore recommended that only eco-friendly activities should be permitted in/around aquatic ecosystems especially Agodi reservoir in order to keep contaminants below safety limit.