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. 2021 Mar 11;18(6):2871.
doi: 10.3390/ijerph18062871.

Long-Term Interannual and Seasonal Links between the Nutrient Regime, Sestonic Chlorophyll and Dominant Bluegreen Algae under the Varying Intensity of Monsoon Precipitation in a Drinking Water Reservoir

Ji Yoon Kim  1 , Usman Atique  1 , Md Mamun  1 , Kwang-Guk An  1
Affiliations

Long-Term Interannual and Seasonal Links between the Nutrient Regime, Sestonic Chlorophyll and Dominant Bluegreen Algae under the Varying Intensity of Monsoon Precipitation in a Drinking Water Reservoir

Ji Yoon Kim et al. Int J Environ Res Public Health. .

Abstract

Long-term variations in reservoir water chemistry could provide essential data in making sustainable water quality management decisions. Here, we analyzed the spatiotemporal variabilities of nutrients, sestonic chlorophyll-a (CHL-a), nutrient enrichment, dominant algal species, and overall chemical water health of the third-largest drinking water reservoir in South Korea during 2000-2020. Our results distinctly explained the strong influence of monsoon rainfall on spatial and annual water chemistry variations. We observed a consistent increase in the chemical oxygen demand alluding to organic matter pollutants, while a steady declining trend in the sestonic CHL-a. The long-term total phosphorus (TP) level showed a steady reduction from the riverine zone to the lacustrine area. However, a higher total coliform bacteria (TCB) was observed at the water intake tower sites. TP displayed a strong link to algal CHL-a and ambient nitrogen phosphorus ratios, suggesting a robust phosphorus-limitation state. The severe phosphorus-limitation was also corroborated by the findings of trophic state index deviation. The high and low flow dynamics exhibited the strong influence of intensive rainfall carrying many nutrients and sediments and flushing out the sestonic CHL-a. Successive eutrophic conditions prevailed along with dominating blue-green algae species (Microcystis and Anabaena). We observed a strong positive correlation (r = 0.62) between water temperature and CHL-a and between total suspended solids and TP (r = 0.65). The multi-metric water pollution index characterized the overall water quality as 'good' at all the study sites. In conclusion, the long-term spatiotemporal variabilities of the ecological functions based on the nutrient-CHL-a empirical models are regulated mainly by the intensive monsoon precipitation. The drinking water could become hazardous under the recurrent eutrophication events and chemical degradations due to uncontrolled and untreated inflow of sewage and wastewater treatment plant effluents. Therefore, we strongly advocate stringent criteria to mitigate phosphorus and organic pollutant influx for sustainable management of Daecheong Reservoir.

Keywords: Daecheong Reservoir; algal blooms; drinking water; high flow; long-term water quality; nutrients; sewage pollution.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure A1
Figure A1
Comparison between the blue-green algae species, nutrients, water temperature and non-algal light attention coefficient (Kna) during 2015–2020 at the IT2, i.e., Site 5.
Figure 1
Figure 1
Study area map showing the sampling sites of the Daecheong Reservoir. S1 and S2: riverine zone (Rz); S3: transitional zone (Tz); S6: Lacustrine zone (Lz); S4 (IT1) and S5 (IT2): intake tower of drinking water.
Figure 2
Figure 2
Inter-annual variation of salient water quality parameters. TP: total phosphorus, TN: total nitrogen, BOD: biological oxygen demand, COD: chemical oxygen demand, TSS: total suspended solids, EC: Electrical conductivity, SD: Secchi depth, CHL-a: chlorophyll-a. The blue curve line indicated the total rainfall (TRF) while the red lines indicate means.
Figure 3
Figure 3
Spatial variations of water quality parameters at the reservoir zones and water intake towers. TP: total phosphorus, TN: total nitrogen, BOD: biological oxygen demand, COD: chemical oxygen demand, TSS: total suspended solids, CHL-a: chlorophyll-a, TCB: total coliform bacteria, SD: Secchi depth. For site identification, please refer to Figure 1.
Figure 4
Figure 4
Monthly variations of selected water quality parameters during the high (2011) and low (2015) flow years. TP: total phosphorus, TSS: total suspended solids, TN: total nitrogen, EC: electrical conductivity, CHL-a: chlorophyll-a, BOD: biological oxygen demand, SD: Secchi depth, TCB: total coliform bacteria.
Figure 5
Figure 5
Pearson correlation analysis on water quality parameters during 2000–2020. WT: water temperature, pH: hydrogen ion concentration, EC: electrical conductivity, DO: dissolved oxygen, TSS: total suspended solids, BOD: biological oxygen demand, COD: chemical oxygen demand, TN: total nitrogen, TP: total phosphorus, TDN: total dissolved nitrogen, NH4-N: ammonium-nitrogen, NO3-N: nitrate-nitrogen, TDP: total dissolved phosphate, PO4-P: phosphate, CHL: chlorophyll, TCB: total coliform bacteria, SD: Secchi depth, IF: inflow, OF: outflow, WRT: water residence time. The graphs’ color scale is explained as red color range showing negative while blue color range positive correlation.
Figure 6
Figure 6
Empirical relationships between chlorophyll-a, nutrients, and their ambient ratios. CHL-a: chlorophyll-a; TP: total phosphorus; TN: total nitrogen; TDN: total dissolved nitrogen; TDP: total dissolved phosphorus; NO3-N: nitrate-nitrogen; and PO4-P: phosphate.
Figure 7
Figure 7
Determination of limiting nutrient based on empirical modeling on the TN:TP ratios, TP, and TN. TP: total phosphorus; TN: total nitrogen.
Figure 8
Figure 8
Empirical links between water transparency (SD), nutrients. TP: total phosphorus; TN: total nitrogen; suspended solids (TSS), and chlorophyll-a (CHL-a) in Daecheong Reservoir during 2000–2020.
Figure 9
Figure 9
Dynamics of nutrients, algal chlorophyll-a, and organic pollutant ratios in longitudinal zones of Daecheong Reservoir. TN: total nitrogen; TP: total phosphorus; CHL-a: chlorophyll-a; BOD: biological oxygen demand; COD: chemical oxygen demand; Rz: riverine zone; Tz: transitional zone; Lz: Lacustrine zone; IT1 and IT2: intake tower of drinking water 1 and 2; red lines in the box indicate mean values.
Figure 10
Figure 10
Trophic state index (a) and its deviation (b) based on TP, CHL-a and SD of Daecheong Reservoir. TP: total phosphorus; CHL-a: Chlorophyll-a; SD: Secchi depth; Rz: riverine zone; Tz: transitional zone; Lz: Lacustrine zone; IT1 and IT2: intake tower of drinking water 1 and 2; red lines in the box indicate mean values.
Figure 10
Figure 10
Trophic state index (a) and its deviation (b) based on TP, CHL-a and SD of Daecheong Reservoir. TP: total phosphorus; CHL-a: Chlorophyll-a; SD: Secchi depth; Rz: riverine zone; Tz: transitional zone; Lz: Lacustrine zone; IT1 and IT2: intake tower of drinking water 1 and 2; red lines in the box indicate mean values.
Figure 11
Figure 11
Relationship between the algal blooms of four blue-green algae species, nutrients, ambient ratios, water temperature, and algal CHL-a during 2015–2020.
Figure 12
Figure 12
Path diagram of water quality parameters for principal component analysis.
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