Study of
Nutrients (Nitrogen and Phosphorous) in Phewa Lake Sediments
Introduction
Lakes are sensitive to increase in nutrient concentration. Normally,
urban lakes are more prone to nutrient loading and eutrophication caused by
watershed development. The lake sediment acts as a sink as well as source of
nutrients for lake water. The nutrients concentration in the bed sediments has
substantial influence on the trophic status of lake. Thus, regular monitoring
of nutrient concentration in the lake sediment is essential.
Tropic structure of Phewa
lake has changed from oligotrophic to mesoeutrophic and then to eutrophic from
1973 to 1986 and till now (Heyojoo & Takhacche, 2014; Shrestha &
Janauer, 2001). Hydrological and sediment transport dynamics in Phewa lake
watershed is being altered by modification in natural landscape. Accumulation
of sediments from tributaries , creeks, and the sewage inlet from hotels in
Phewa Lake has reduced both effective depth and surface area of the lake, which
eventually reduces the effective life of the lake (Balla & Sthapit, 1998;
Gurung et al., 2007). This shows
lakes of Nepal are at risk.
Nitrogen and Phosphorous are
essential nutrients for growth of plants but excess amount of those nutrients
will result in depletion of dissolved oxygen (DO). If the amount of DO
decreases resulting less or no concentration of it in water, then lake is
considered as dead lake. Also, it is said that the concentration of nutrients
in lake is normally 10 times the concentration in water (Havens et al., 2001).
In lake, nutrients are flushed out through outlet as well as from sinking in
sediments. Therefore, sediments are the source of internal loading of nutrients
into water. For this reason, it is necessary to study nutrients of water along
with sediments to prevent the lake from being dead lake.
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