Changes in Water Quality in Key Locations of the Four Rivers

Due to the implementation of Comprehensive Water Quality Management Measures in 1996, Comprehensive Water Quality Improvement Measures on the Four Major Rivers (1998-2005) and Master Plan for Water Environment Management (2006-2015), BOD (Biological Oxygen Demand) levels in public waters has improved largely. However, COD (Chemical Oxygen Demand) levels show either slight or unsatisfactory improvement when compared to BOD due to the inflow of non-degradable organic pollutants from nonpoint source (NPS) pollution and the increased use of chemical compounds. Moreover, with the algal bloom and decay, Total Phosphorus (TP) concentration, the limiting factor of organic productivity, also increased.

The targets of water environment quality by 2015 were set as follows - (1) to achieve ‘good’ water quality (BOD less than 3 mg/ℓ) in over 98 of total 115 mid-watershed regions at rivers and (2) to improve the water quality in 46 out of total 49 lakes, which are mainly used as drinking water sources, by reducing COD below 4mg/ℓ. As a result, by 2015, 85% of mid-watersheds and 94% of major lakes in the country will reach good water quality.

Annual Change in Water Quality in Key Locatin (lakes) of the Four Rivers

Results of the ‘Survey and Evaluation of Aquatic Ecosystem Health’

Since 2007, the survey on aquatic ecosystem has been proceeding at the four major rivers and other main rivers on following parameters - attached algae, fish, benthic macro-invertebrates, inhabitation/waterside environment, and organism's habitat. The ecological health status is evaluated and categorized as  four different grades (Optimum, Fair, Average, and Poor) by using quantified composite index. In 2012, the aquatic ecosystem was assessed at 960 locations (segments) countrywide. The results showed that the proportion of grade ‘Fair’ or 'Optimum' for benthic macroinvertebrates and inhabitation/riparian environment was high, whereas it appeared low for attached algae and fish.


Last modified : 2013-10-28 18:43

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