Seasonal Stratification Characteristics of Vertical Profiles and Water Quality of Lake Lugu in Southwest China

Abstract

According to the vertical section monitoring data of Lake Lugu water temperature (WT), electrical conductivity (EC), dissolved oxygen (DO), pH and chlorophyll-a (Chl-a) parameters in January (winter), April (spring), July (summer), and October (autumn) in 2015, the vertical stratification structure of WT and the null seasonality of water chemistry were analyzed. The relationship between the seasonal variation of WT stratification and the spatial and temporal distribution of EC, pH, DO and Chl-a was explored. The relationship between EC and WT was found for the epilimnion, thermocline and hypolimnion. The results of the study showed that: (1) The Lake Lugu water body shows obvious thermal stratification in spring, summer and autumn. In winter, the WT is close to isothermal condition in the vertical direction; in summer, the thermocline is located at 10–25 m water depth; while in autumn, the thermocline moves down to 20–30 m. (2) The Hypolimnion WT was maintained at 9.5 °C~10 °C, which is consistent with the annual mean temperature of Lake Lugu, indicating that the hypolimnion water column is stable and relatively constant, and reflects the annual mean temperature of the lake. The thermally stratified structure has some influence on the changes of EC, DO, pH and Chl-a, resulting in the obvious stratification of EC, DO and pH in the water body. (3) Especially in summer, when the temperature increased, the thermal stratification phenomenon was significant, and DO and pH peaked in thermocline, with a decreasing trend from the peak upward and downward, and the hypolimnion was in an anoxic state and the pH value was small. Although chlorophyll a remained low below thermocline and was not high overall, there was a sudden increase in the surface layer, which should be highly warned to prevent a large algal bloom or even a localized outbreak in Lake Lugu. (4) There is a simple linear function between EC and WT in both vertical section and Epilimnion, thermocline and hypolimnion, which proves that Lake Lugu is still influenced by natural climate and maintains natural water state, and is a typical warm single mixed type of lake. (5) It is suggested to strengthen water quality monitoring, grasp its change pattern and influence factors, and take scientific measures to prevent huge pressure on the closed ecological environment of Lake Lugu, and provide scientific basis for the protection of high-quality freshwater lakes in the plateau.

Water Quality of Lake Erhai in Southwest China and Its Projected Status in the near Future

“…Concentrations began to decline in November and remained low from December to March of the following year. The seasonal variation of water quality in Lake Erhai is consistent with the research results of other scholars in plateau lakes [28][29][30]. As shown in Figure 6, the concentration of COD Mn at all monitoring sites met the standard in all months, while the concentrations of TP and TN at some monitoring sites exceeded the standard in some months.…”

Seasonal Water Quality Changes and the Eutrophication of Lake Yilong in Southwest China

“…In winter, due to the disappearance of thermocline in shallow lakes, the exchange capacity of water bodies is enhanced, and surface water and bottom water show the same properties. In addition, the monitoring shows that there is no temperature stratification phenomenon in lake Yilong, which is significantly different from other deep-water bodies in Yunnan-Guizhou Plateau, such as Lake Lugu [38] and Lake Yangzong [39].…”

Assessment of Stoplog Gates’ Operational Effectiveness for Improving Discharged-Water Temperatures during the Thermal Stratification Period in a Reservoir

“…Continuous monitoring of water temperature has the advantage of providing realtime and accurate information on the changes in the water-temperature-structure process, in contrast to empirical formulas, physical tests, and numerical models [18,19]. With recent advancements in temperature-sensor accuracy, long-distance transmission, and high-frequency monitoring technologies, water-temperature monitoring in reservoir areas and rivers downstream of dams has become more widespread [15,[19][20][21][22]. The use of hourly and daily monitoring data enables a more realistic and accurate reflection of the reservoir's thermal-change process [16,23,24].…”