Field Observation of Different Wind‐Induced Basin‐Scale Current Field Dynamics in a Large, Polymictic, Eutrophic Lake

Abstract

Basin-scale current fields are fundamental to determining the environmental characteristics and ecological attributes of large polymictic lakes. However, little is known concerning the effects of different winds on the currents and further on ecological systems of these lakes. Therefore, synchronous meteorological and hydrological data were collected from Lake Taihu (China) during summer 2015. Time series analysis and stress calculations conducted to elucidate the basin-scale current field revealed frequent occurrence of a bilayer current mode, comprising a wind-driven surface current and bottom compensation current, under low or medium wind conditions. The main forcings of the lake currents are seasonal winds related to the East Asian monsoon, and the lake-land thermal contrast wind with 24-hr periodicity causes marked diurnal fluctuation. Inflows, outflows, the Coriolis force, and bottom frictional stress also make important contributions to the bilayer current mode, and weak temperature stratification can stabilize this mode. However, as wind speed increases, wind-driven surface currents can develop downward to form uniform currents throughout the water depth, and water temperature stratification is destroyed during typhoon-affected periods. During such short-term strong wind events, the current structure mainly adopts a monolayer current mode and the incidence of the bilayer current mode decreases substantially. The monolayer current mode causes a clockwise circulation and a basin-scale temporary oscillation with~80-hr periodicity. The influences of the monsoon and lake-land thermal contrast wind on lake currents were masked by the pulse-like strong winds. Both modes can contribute to persistent cyanobacterial blooms in the northwest of Lake Taihu.Plain Language Summary Large lake currents profoundly influence the lake environmental characteristics and ecological attributes. However, little is known concerning about the current distribution in response to the different wind fields. Therefore, synchronous meteorological and hydrological data were observed in Lake Taihu during the summer of 2015. It was found that a bilayer current mode was frequently observed under condition of low wind speed. This current mode comprised a wind-driven surface current and bottom opposite compensation current. The main driving forces were the seasonal winds related to the East Asian monsoon and land-lake thermal contrast wind, inflow-outflow, the Coriolis force, and bottom frictional stress. A weak temperature stratification can stabilize this mode. However, wind-driven surface currents could develop downward trends with greater wind speeds to form uniform currents throughout the entire water column and the water temperature stratification was destroyed during typhoon-affected periods. During the monolayer current period, a clockwise circulation and a basin-scale temporary oscillation with a periodicity of~80 hr were observed. Both modes can contribute the persistent cyanobacterial blooms in the northwest region of Lake Taihu.

Extreme Climate Anomalies Enhancing Cyanobacterial Blooms in Eutrophic Lake Taihu, China

“…The measurements were started in 2008 and terminated near the end of 2016 due to equipment failure. Although we have only one site with near‐bottom DO observation for exploring the relationship between cyanobacterial bloom and DO depletion, this location is right in bloom prevailing zone (Wu et al., 2018).…”

“…The measurements were started in 2008 and terminated near the end of 2016 due to equipment failure. Although we have only one site with near-bottom DO observation for exploring the relationship between cyanobacterial bloom and DO depletion, this location is right in bloom prevailing zone (Wu et al, 2018 Riverine input of nutrients in Lake Taihu is a dominant fraction of external loading (Zhai et al, 2020). Riverine loadings of nitrogen and phosphorus have been measured since 2006 by Taihu Basin Authority, Ministry of Water Resources of China, based on observations of flow rate and nutrient concentration of ca.…”

Reconsideration of winds, wind waves, and turbulence in simulating wind-driven currents of shallow lakes in the Wave-current Coupled Model (WCCM) version 1.0

“…southeast-east winds prevail from April to August, while north-northwest winds dominate in the other months. The basin-scale hydrodynamics is mainly determined by winds rather than inflow-outflow (Li et al, 2011;Wu et al, 2018;Zhao et al, 2012). Except temporary small vertical water temperature gradient, Lake Taihu is mixed evenly along water depth because of frequent disturbance of winds (Wu et al, 2018).…”

“…The basin-scale hydrodynamics is mainly determined by winds rather than inflow-outflow (Li et al, 2011;Wu et al, 2018;Zhao et al, 2012). Except temporary small vertical water temperature gradient, Lake Taihu is mixed evenly along water depth because of frequent disturbance of winds (Wu et al, 2018). Several numerical models have been used to simulate the wind-driven currents and their influence on the ecological processes in Lake Taihu (Feng et al, 2018;Han, et al, 2019;Li et al, 2015;Zhao et al, 2012), but the hydrodynamic part of these models was not evaluated using the process-based field observation.…”

Sulfur Development in the Water-Sediment System of the Algae Accumulation Embay Area in Lake Taihu

“…It is a typical large and shallow eutrophic lake with an algal bloom area that can engulf 75% of the lake during blooming seasons [38]. The northwestern area is the primary area for algae accumulation because of the serious pollution from the inflowing rivers and surrounding cities and the influence of the East Asian monsoon [38,39]. Lake Taihu is a drinking water source for the surrounding cities, including Wuxi and Suzhou.…”