Spatiotemporal Distribution of Algae and Characteristics of Algal Abundance in Lake Okjung, Korea

Abstract

Objectives The objective of this study was to identify the water quality parameters and environmental factors that control the growth and distribution of phytoplankton in Lake Okjung by analyzing water quality and meteorological data using various statistical analysis methods. Methods Water samples collected from the lake between May and November, 2017 were analyzed for various water quality parameters following the Standard Methods for Water Quality Analysis. Identification and quantification of phytoplankton species from the lake were conducted manually under the microscope. Meteorological data of the lake watershed were also collected and analyzed in combination with water quality and phytoplankton data using various statistical analysis methods. Correlation analysis and multivariable statistical methods were applied to identify the parameters that influenced the distribution of phytoplankton in the lake. Results and Discussion While the concentration of particulate matter was elevated in July and August presumably due to concentrated precipitation in the summer, total phosphorus concentration appeared to be controlled by fertilizer application associated with agricultural activities in the area, which was evidenced by the higher concentrations in May and September. Comparison of total nitrogen and total phosphorus data indicated that 76 samples out of 81 showed N/P ratios higher than 17 indicating that Lake Okjung was in a phosphorus-limited condition during the study period. Calculation of Korea Trophic State Index (TSIko) showed that the lake is generally in mesotrophic or oligotrophic conditions. The phytoplankton community was dominated by chlorophyte (50%), diatoms (25%), and cyanobacteria (9.6%) in terms of the number of species, and the highest cell concentrations were observed in the area where Oknyeodong-cheon, one of the tributaries, joins the lake. Principal component analysis identified 4 components that explained 74.6% of the total variance of the data with PC1, PC2, PC3, and PC4 explaining 40.4%, 14.9%, 11.3%, and 8.0%, respectively. These components were attributed to biogeochemical change induced by growth of phytoplankton in response to meteorological fluctuation, inflow of phosphorus from regional agricultural activities and its impact on phytoplankton growth, physical change of the lake water caused by concentrated precipitation in the summer, and environmental changes causing growth of cyanobacteria in the summer. Conclusions Lake Okjung was in P-limited conditions and the distribution of phytoplankton appeared to be controlled by seasonal variation of meteorological conditions and input of nutrients, especially phosphorus from the 2 main tributaries, Oknyeodong-cheon and Seomjin river. Although seasonal distribution of precipitation did not cause a significant increase in phosphorus concentration in the lake, proper management of pollution sources in the watershed of the 2 tributaries seem to be important in controlling algal bloom formation as severely concentrated rainfall in the area has the potential to produce eutrophic conditions in the lake and trigger explosive growth of phytoplankton. Key words: Lake Okjung, Algae, Statistical Analysis, Nutrients, Seomjin River Dam