Abstract:
MaduruOya reservoir was constructed in 1983 under the Accelerated Mahaweli Program. The
dam is located in North Central province and the reservoir extends to Eastern province and Uva
provinces (between 7º 32' 42" to 7º 39' 57" North latitude and 81º 11' 35" to 81º 12' 21" East
longitude). It is reported that high amount of nutrients and other chemical residues accumulate
in water of the reservoir due to heavy use of agrochemicals in the catchment area. Fifteen
locations were selected for sub-surface water sampling and analysis from February to July in
2016. Temperature, pH, Dissolved Oxygen (DO), Electrical Conductivity (EC) and Turbidity
were measured in-situ. Ammonical nitrogen, nitrate nitrogen, nitrite nitrogen, dissolved
phosphate, and other chemical parameters such as alkalinity and hardness were also assessed.
Water temperature of the reservoir varied from 29.7 ͦ C to 36 ͦ C while pH value was from 6.8 to
9.5. DO value was from 3.3 ppm to 9.4 ppm. EC varied from 94 μS cm-1 to 200 μS cm-1 and
turbidity of water fluctuated from 0.96 NTU to 49.4 NTU. Ammonical nitrogen varied from
0.001 ppm to 0.652 ppm. Nitrite Nitrogen was from 0.001 ppm to 0.905 ppm and Nitrate
Nitrogen was detected from 0.001 ppm to 1.131 ppm. The highest phosphate concentration was
detected as 0.468 ppm near the dam site of the reservoir in July. Total hardness was from 21ppm
to 68 ppm and alkalinity varied from 15 ppm to 190 ppm. The highest pH was recorded in June
near the dam site of the reservoir and exceed the WHO standards for drinking water. The
maximum nitrate and nitrite concentrations were recorded in June at the middle of reservoir and
maximum ammoniacal nitrogen was also recorded in June and it was at the dam site. High
accumulation of nutrients can lead to eutrophication in the reservoir and it causes the spreading
of toxin producing algal species such as Microcystis affecting the ecosystem health and human
livelihood.
