Multiyear Links between Water Chemistry, Algal Chlorophyll, Drought-Flood Regime, and Nutrient Enrichment in a Morphologically Complex Reservoir

Abstract

This investigation targeted the largest morphologically complex reservoir (Soyang) in South Korea during 1992–2013. It is a prominent source of domestic water supply, irrigation, flood control, and hydroelectric power generation. Therefore, this investigation focused on regional- to global-scale applications. We revealed the empirical links between chlorophyll (Chl-a) and total nitrogen (TN) and total phosphorus (TP), the impact of the monsoon regime on nutrients, and flood and drought regime. Further, we investigated the trophic status dynamics, tendencies of water chemistry factors, and valuation of zonal water chemistry by the application of a modified multimetric water pollution index (WPI). The physicochemical indicators illustrated significant disparities among the Lacustrine (Lz), Transition (Tz), and Riverine (Rz) zones. The solid contents (TSS) displayed a significant increase in the lake zones in the order of Lz (4.58 ± 13.7 mg/L), Tz (6.16 ± 16.2 mg/L), and Rz (7.38 ± 18.9 mg/L). However, TP and allied chemical species revealed an inverse relationship with the TN:TP ambient ratios. Nevertheless, Chl-a displayed sharp interzonal fluctuations from the Lz (2.90 ± 3.29 µg/L) to Tz (4.61 ± 4.98 µg/L). The seasonal deviations, however, exposed divergent heterogeneities among the TSS, TN, TP, and Chl-a. The regression plot between the observed and predicted Chl-a in the Soyang reservoir displayed a very strong relationship (R2 = 0.997). The seasonal and interannual variations of trophic status displayed a higher impact of precipitation, particularly in the case of TP and Chl-a. The flood years indicated phosphorus limitations, while drought years alluded to the non-algal light limitations (biogenic turbidity). Water temperature (WT), dissolved oxygen (DO), biological oxygen demand (BOD), TSS, TP, and Chl-a displayed decreasing trends in the ambient water. In contrast, pH, chemical oxygen demand (COD), electrical conductivity (EC), and TN displayed increasing tendencies by the application Mann–Kendall trend analysis. The WPI outcomes designated Lz with excellent water quality while Tz an Rz indicated good water quality. It also indicated impending sedimentation tendencies in the Rz. In conclusion, our findings indicated fluctuating rainfall patterns (drought and flood conditions) that significantly impacted the Soyang reservoir water quality, flood and drought severity, and trophic status of the reservoir. This study highlights the requirements of further studies to substantiate the drought and flood dynamics and their impacts on nutrients and overall water quality status.

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

“…A consistent rise of chemical contaminants in lentic water bodies must pose grave threats to the water resource’s intended usages, which in this case is mostly for drinking [ 2 , 6 ]. The results indicated a growing influx of oxygen-demanding chemicals generated by the various anthropic and geochemical processes in the reservoir basin [ 8 ]. The annual TSS showed a mixed response to high and low inflows mediated by intensive precipitation.…”

“…The flood years mostly indicated an increase in the nutrient-contributing parameters, while drought years displayed a decline. It could be inferred that the lower rainfall intensity could have helped in the reduction of nutrient-rich inflows that could be potentially linked to the lower production of the sestonic CHL-a [ 8 , 51 ]. However, according to Brasil et al [ 20 ], the reduction in reservoir water level (reduced inflow of water currents) favors the production of cyanobacterial blooms that could be linked to higher algal productivity.…”

“…The water quality fluctuations become even critical high flows [ 55 , 56 ]. Frequent and severe high and low flow conditions may negatively influence the WRT, stable movement of nutrients, aquatic biodiversity, and damage to costly installations [ 8 ]. Therefore, high and flow investigations are more appropriate in DR owing to their frequent and broader use.…”

“…Large freshwater reserves are indispensable for viable urban populations, environmental health, sustainable economic growth, and greater strategic importance as they provide drinking and irrigation water, recreation, catch fisheries, transportation, hydroelectric power generation, and flood control [ 1 , 2 , 3 ]. However, under the increasing anthropic stressors, reservoirs at the global scale are facing water quality degradation under the combined influence of climate change [ 4 ], urbanization [ 5 ], and agriculture [ 6 ], land use [ 7 ], precipitation, and river discharge [ 8 ], topography, and surface geology [ 9 ].…”

Linking fish and crustacean taxonomic composition with seasonal contrasts in the soft-bottom intertidal zone

“…The biodiversity and its distribution patterns are conspicuous in the tropical regions and manifested in the seasonal variations of the population and community structures of the intertidal organisms (Nicolaidou et al, 2006b;Equbal et al, 2018). Monsoon patterns equally influence the freshwater and marine biodiversity (Atique and An, 2018;Hara et al, 2020;Atique et al, 2020b;Haque et al, 2020). Tropical estuarine ecosystems are dependable indicators of environmental change (Dauvin, 2007); therefore, species composition and structure are the sensitive community features that modify in reaction to habitat level changes (Post et al, 2006;Lefrere et al, 2015;Atique and An, 2020).…”