Investigating Temporal Variation of Water Quality and Benthic Macroinvertebrates in Taudaha Lake, Kathmandu, Nepal

Taudaha Lake is one of the important wetlands in Nepal, as it provides critical habitats for thousands of migratory birds and fishes. Despite being a critically important water body, there is a lack of detail chemical and biological studies on this lake. The present study investigates the effects of seasonal water quality variations in distribution and abundance of macroinvertebrates in Taudaha Lake, during four different seasons in 2006. The results indicate that all the water quality parameters, except secchi depth, and total alkalinity, significantly varied among seasons. The gross primary productivity of the lake also significantly varied among the seasons, with highest primary production during summer (3.92 ± 0.18 gC/m3/day) and lowest during spring (2.44 ± 0.67 gC/m3/day). A total of 2166 individual benthic macroinvertebrates from 10 families and 7 orders were collected during the study period. Unlike water quality parameters, the macroinvertebrate species composition did not vary significantly among the seasons. The results suggested that the change in lake water quality did not have significant impacts on community metrics such as species diversity, species richness, and species evenness.

Evaluation of Spatial-Temporal Variations of Water Quality and Plankton Assemblages and Its Relationship to Water Use in Kulekhani Multipurpose Reservoir, Nepal

Spatial and temporal variation in planktons and water quality parameters were investigated in order to determine the effects of seasonal water use on reservoir water quality and planktons’ diversity in Kulekhani Multipurpose Reservoir, Nepal. This study also focuses on interactions among various water quality parameters with planktons and how such interactions can affect the second major utility, the fish farming in the reservoir. The analyses of seasonal water samples collected from three different sampling locations in the reservoir showed that select water quality parameters varied significantly (P < 0.05) with sampling seasons (transparency: 30 - 250 cm, pH: 7 - 7.5, alkalinity: 30 - 120 mg/L, DO: 6 - 11.5 mg/L, CO2: 0.1 - 1.1 mg/L) and sampling locations (phosphate: 0.1 - 0.25 mg/L, nitrate 0.01 - 0.19 mg/L) in the reservoir. Three groups of zooplankton and four classes of phytoplankton, respectively with eleven and twelve genera, were identified and quantified in the reservoir. Among them, Cyclops, Asplanchana, and Keratella were most dominant zooplanktons while Synedra, Melosira and Peridinum were the most dominant phytoplankton in the reservoir water. The abundance of select zooplanktons (Cyclops, Keratella, Polyanthra), and phytoplankton (Navicula, Melosira, Amphora, Chroococcus, Staurastrum, Scendesmus) showed significant interaction between sampling sites and sampling seasons, while the other varied only with sampling seasons and/or sites. These results showed that seasonal water level fluctuations, along with the variation of water quality parameters, change the abundance and diversity of planktons’ in the reservoir. Such changes can negatively impact the fish in cage culture, affecting the livelihood of people extensively relying on these fish farming.

CFD analysis for mixing performance of different types of household biodigesters

Household biodigesters are self-mixing anaerobic digesters used mostly in rural areas of developing countries as a reliable source of clean cooking energy.For an efficient anaerobic digestion process,the mixing of slurry inside the digester is regarded as one of the most important parameters.In this study,the mixing of slurry in three different designs of household digesters,namely the fixed-dome digester(GGC 2047 model),plug-flow digester and prefabricated plastic digester,are investigated and compared using compu-tational fluid dynamics.A 3D transient simulation is performed using a multiphase volume of fluid(VOF)model in Ansys^(■)Fluent release 16.0.The rheological properties of the feedstock are considered identical for all three digesters.The volume of the plug-flow and prefabricated plastic digesters is designed to be 1 m^(3) while the volume of the GGC 2047 digester was 6 m^(3) as the standard size of the household digester.The regions inside the digester where the velocity of slurry is<0.02 m/s are regarded as dead zones and the obtained results were analysed and compared using velocity patterns and dead-zone formation.It is found that the prefabricated plastic digester model has a relatively higher percentage of dead volume(74.6%)and the plug-flow digester has the lowest per-centage(54%)of dead volume among digesters that were compared in this study.The study will serve as the basis for designers and researchers to improve the design of household digesters for better mixing performances.