3.4 Eutrophication of reservoir water quality
Through using the TLI method to derive the TLI ( Σ ) value of each
reservoir, we found that the eutrophication level of Huanglishu
Reservoir was the most serious during the three years, followed by Shahe
Reservoir, and optimal for Chengxi Reservoir. The highest value of TLI(
Σ ) in the Huanglishu Reservoir was 52.38 and the lowest value was
40.40, the water body was medium nutrition most of the time, but there
existed three periods of time when the TLI( Σ ) was greater than 50,
which was in the mild eutrophication status. This result indicates that
the water quality of the Huanglishu Reservoir has been mildly polluted.
The eutrophication evaluation results of the water body in Shahe
Reservoir are similar to the Huanglishu Reservoir, with the fluctuation
range of TLI( Σ ) from 40.96 to 51.29, and the water quality evaluation
level is mild eutrophication only in October 2020, and the TLI( Σ )
tends to be close to 50 in most of the other periods, which is on the
edge of the medium nutrient water quality. The TLI ( Σ ) value of
Chengxi Reservoir was always below 50, which did not reach the criterion
of mild eutrophication, and the qualitative evaluation of the water body
was good, the results indicated that the water body of the reservoir was
lightly polluted. As a whole, the water quality class of Huanglishu
Reservoir and Shahe Reservoir reached Class III, whereas Chengxi
Reservoir was always maintained at Class II (Fig. 3 and Table 1).