Abstract
The HSPF model was modified to improve the growth-temperature formulation of phytoplankton and used to simulate Chl-a concentrations at the outlet of the Seom River watershed in Korea from 2025 to 2050 under four climate change scenarios: RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5. The mean and median Chl-a concentrations increased by 5–10% and 23–29%, respectively, and the number of algal outbreak cases per year (defined as a day with Chl-a concentration ≥100 µg/L) decreased by 31–88% relative to the current values (2011–2015). Among the climate change scenarios, RCP 2.6 (stringent) showed the largest number of algal outbreak cases, mainly because of the largest yearly variability of precipitation and TP load. For each climate change scenario, three nutrient load reduction scenarios were in the HSPF simulation, and their efficiencies in reducing algal blooms were determined. Nonpoint source reduction in TP and TN from urban land, agricultural land, and grassland by 50% (S1) and controlling the effluent TP concentration of wastewater treatment plants (WWTPs) to 0.1 mg/L (S2) decreased algal outbreaks by 20–58% and 44–100%, respectively. The combination of effluent TP control of WWTPs during summer and S1 was the most effective management scenario; it could almost completely prevent algal outbreaks. This study demonstrates the cost effectiveness of using a season-based pollutant management strategy for controlling algal blooms.
Highlights
Degradation of water quality by harmful algal blooms (HABs) is a major global environmental issue [1,2]
The study area was the Seom River watershed in South Korea (Figure 1), which has an area of 1473 km2 and a total population of 380,000 [31]
Concentrations of the nitrogen species in streams were generally higher during winter seasons, owing to the efficiency of biological nitrogen removal from wastewater treatment plants (WWTPs) being lower at lower temperatures [48]
Summary
Degradation of water quality by harmful algal blooms (HABs) is a major global environmental issue [1,2]. Future climate changes will possibly be characterized by higher surface air temperature and precipitation variability, which would potentially increase nutrient loads and primary productivity in surface water bodies [4,5,6]. A higher rainfall intensity and longer dry periods resulting from climate changes can increase nutrient inputs to water bodies, potentially promoting algal growth [8,9,10,11]. Phosphorus and nitrogen are the two important nutrients regulating eutrophication and algal growth along with climatic factors such as precipitation, temperature, and solar radiation [12,13]. Phosphorus is the critical limiting nutrient for algal growth in inland waters, since the molar ratio between nitrogen and phosphorus (N/P ratio)
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