Abstract
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.
Highlights
Kulekhani Multipurpose Reservoir is located at ~1500 m above the sea level, in between the latitudes 27.683N and 27.584N, and longitudes 85.305E and 85.040E in Kulekhani watershed area, Central Nepal (Figure 1) [1] [2]
Among the twelve genera of phytoplankton, Synedra (34.85%) was most dominant phytoplankton followed by Melosira (24.56%), and Fragilaria (0.475%) was the rarest genera followed by Amphora (1.09%)
The investigation of water quality and planktons’ community composition showed that the Kulekhani Multipurpose Reservoir is low to moderately polluted, and the water is suitable for the growth and development of aquatic organisms as well as for the fish culture
Summary
Kulekhani Multipurpose Reservoir is located at ~1500 m above the sea level, in between the latitudes 27.683N and 27.584N, and longitudes 85.305E and 85.040E in Kulekhani watershed area, Central Nepal (Figure 1) [1] [2]. The reservoir was constructed in 1981 by impounding Kulekhani River water behind a 114 m high dam, with a capacity of 73.3 million m3 live volume [3]. It receives water as well as a large amount of sediments and nutrients from 126 km of watershed (largely agricultural land with elevation between 1534 - 2621 m above the sea level) [1]. In addition to the seasonal power generation, the reservoir water is extensively used for fish farming, as a cage culture, throughout the year [6] This cage fish farming is one of the major sources of economy for people living near the Kulekhani Reservoir, especially for a significant number of people among the ~500 households displaced by the construction of the reservoir in 1981 [7]. Such daily and seasonal water uses and water level fluctuations depend on the hydroelectric power demand of the country, higher during high demand season (summer) and time of the day (evening) [4] [8]
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