A Study on Trophic State in Lakes of Dong Da District, Hanoi

Abstract

One of approaches to assessing the water quality of lakes is to look at their primary
production or trophic state. Protecting water quality of urban lakes from eutrophication is an
important task of all governments. This study presents an analysis of the trophic state of lakes in
Dong Da district, Hanoi. The tropic states of the lakes were characterized using the Carlson TSI
and the Chlorophyll-a concentrations and referenced with the thresholds of US. The deviations of
the Secchi depth and total phosphorus indices from the Chlorophyll-a index were used to identify
limiting factors affecting to the tropic state of the lakes. It comes to a conclusion that most of the
lakes in study area were hypereutrophic or eutrophic in August 2017 and eutrophic or oligotropic
in March 2017. It also reveals that phosphorus was not a limited factor for algal biomass while
other factors such as nitrogen showed certain effects. The time plot method suggested that
transparency was dominated by non-algal factors such as color and size,of suspended substances/
particles, whereas the difference plot method revealed that large particles were dominated in the
studied lakes. Consequently, further studies should be done to find out the real causes of the lakes’
eutrophication.
Keywords

Tropic state, lake, time pots, different pots

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