# Algal growth dynamics in drinking water reservoir and the driving force

### Abstract

After the water flow into the reservoir from the river, as the hydrology characteristic changes, including water resitence time increasing, water transparecny increasing etc., the reservoir will facillate algal growth; at the same time, the water quality problems become a threaten to dringking water safety, such as algal bloom as well as taste&odor compounds produced by cyanobacteria. In the present study, long term investigation on water quality and phytoplankton community was performed in two important source water—Miyun Reservoir and Yanghe Reservoir; according to the data collected, the seasonal and spatial dynamic distributions of phytoplankton community were analized; moreover, the competetion and succession of two harmful cyanobacteria—Microcystis sp. and Oscillatoria sp. associated with taste&odor problem in Miyun Reservoir was discussed; additionally, a model describing the mechamism of light shaping on algal cells under light-limitted condition was constructed.

Type
Publication
In PhD Thesis in University of Chinese Academy of Sciences.

Rapid detection method of Anabaena associated with odorous compound based on qPCR in freshwater system: Geosmin has often been associated with off-flavor problems in drinking water with Anabaena sp. as the major producer. Rapid on-site detection of geosmin-producers as well as geosmin is important for a timely management response to potential off-flavor events. In this study, quantitative polymerase chain reaction (qPCR) methods were developed to detect the levels of Anabaena sp. and geosmin, respectively, by designing two PCR primer sets to quantify the rpoC1 gene (ARG) and geosmin synthase one (GSG) in Anabaena sp. in freshwater systems. The ARG density determined by qPCR assay is highly related to microscopic cell count ($r^2 = 0.726$, p < 0.001), and the limit of detection (LOD) and limit of quantification (LOQ) of the qPCR method were 0.02 pg and 0.2 pg of DNA, respectively. At the same time，the relationship between geosmin concentrations measured by gas chromatography-mass spectrometry (GC–MS) and GSG copies was also established ($r^2 = 0.742$, p < 0.001) with similar LOD and LOQ values. Using the two qPCR protocols, we succeeded in measuring different levels of ARG and GSG copies in different freshwater systems with high incidence environmental substrata and diverse ecological condi- tions, showing that the methods developed could be applied for environmental monitoring. Moreover, comparing to the microscopic count and GC–MS analytical methods, the qPCR methods can reduce the time-to-results from several days to a few hours and require considerably less traditional algal identification and taxonomic expertise.

1. Spatial and temporal variations of algal populations associated with odorous compounds in drinking water reservoirs: Spatial variations in phytoplankton community within a large mesotrophic reservoir (Miyun Reservoir, North China) was investigated in relation to variations in physico-chemical properties, nutrient concentrations, temperature and light conditions over a 5 months period in 2009. The dynamics of phytoplankton community was represented by the dominance of cyanobacteria through summer and fall, following with a short term dominance of chlorophyta in late fall, and a relatively high abundance of diatom in October; on the other hand, maximum phytoplankton biomass was recorded in the north shallow region of Miyun Reservoir with a higher nutrients level. Particular attention was paid to the impacts of environmental conditions on the growth of two cyanobacteria genera, the toxin producing Microcystis and the taste & odor producing Oscillatoria. Microcystis biomass was in general greatly affected by water temperature and mixing depth/local water depth ($z_{mix}$/$z_{max}$) ratio in this reservoir, while the Oscillatoria biomass in the surface and middle layers was greatly affected by TDP, and that in the bottom layer was related with the secchi depth/local water depth (SD/zmax) ratio. Abundant Oscillatoria biomass was observed only in late September when Microcystis biomass decreased and allowed sufficient light went through.

2. A study of phytoplankton community succession: cell morphologic response to natural light availability: This study attempted to reveal the effect of solar radiation fluctuation on the dynamics of phytoplankton communities expressed as cell morphology in enclosed water bodies with sufficient nutrients. A model was established to describe the responses of phytoplankton morphology to natural light availability with underwater climate and mixing process in the water column considered. Based on the data collected from the eutrophicated Yanghe Reservoir, the model was derived as $V = 37.92\lambda$ $\varphi_p$ ($r^2 = 0.673$, p < 0.01), where $\lambda$ is a function of solar elevation angle (θ) and mixing/euphotic depth ratio ($z_{mix}/z_{eu}) in water, and$\varphi_p$(cellular projected area) could reflect the cell’s light-harvesting potential. Post analysis of the model results revealed that species with large φp and flattening index (f, obtained by model results and could reflect the cell’s energy requirement) in general have advantages in spring and winter when underwater light availability is low; by contrast, those with small$\varphi_p$and f have advantages in summer. Such variations are mainly due to the cell’s energy balance: larger$\varphi_p\$ and f meaning that the cells could harvest more light energy and consumed less, allowing them to be selected under low light availability; and vice versa. We thus concluded that the driver of phytoplankton community succession may be the seasonal fluctuation of solar radiation in eutrophicated water bodies.

##### Ming Su
###### Associate Professor of Environmental Engneering

My research interest is water quality problems in drinking water bodies, with a focus on harmful algal blooms and associated taste & odor problems.