Source Apportionment Of Pollutants And Variation Analysis In Phytoplankton Compositions In The Pudu River

In high-bloom seasons in Dianchi Lake, a large amount of lacustrine Microcystis would be transported to the upper reaches of Pudu River(namely Tanglang River). Hence, blue-green algal blooms have been a frequent sight at the origin of the Tanglang River, which may cause many serious problems for river ecology as well as drinking water security. However, the spatial variations of the Microcystis abundance and the corresponding influencing factors are stil l unclear. In the case, it is difficult to estimate both the scope and extent of the influence of the Dianchi Lake on the Pudu River. In this work, a set of pollution source apportionment for large rivers was established. The method consisted of three steps: sampling station grouping, identification of key pollutants and source apportionment of key pollutants. The method was applied in the Pudu River(the Tanglang River, the lower Pudu River and three main tributaries) to analyse the source apportionments o f pollutants leading to eutrophication. The results showed that the Dianchi Lake had the most significant impact on the Tanglang River. In addition, it was the main contributor for the eutrophication in the Tanglang River, which made the Tanglang River obviously more spatial heterogenous in water quality and more eutrophic than other reaches.Two field observations were conducted in the mouth of the Dianchi Lake and the Tanglang River in June and September 2013, respectivel y. The results showed that the total abundance gradually decreased along the river downstream. However, the decrease rate in September was slower than that in June. The influence scope of the Dianchi Lake on the Tanglang River varied with time. The Microcystis colonies from the Dianchi Lake were gradually replaced by centric diatoms and chlorococalean green algae in the middle and lower reaches of the river. Considering that the nutrients were rich and the water temperature was suitable, the incident light was the only competition resource. In addition, the differences in adaptability of different algae to changing hydrodynamics explained the variations of phytoplankton abundances along the Tanglang River.Based on the analysis of field observations, a vertical competition model for light between Microcystis and Chlorella under different hydrodynamic turbulences was developed. The buoyancy regulation of the Microcystis with different colony sizes was incorporated into the competition model. According to the simulation results, it was found that the largest abundance of the Microcystis showed up below the water surface. On the surface, the Microcystis colonies would sink in the daytime and float upwards in the night, which would be more obvious in the calm water. The vertical self-migration of the competition algae determined the vertical distributions of populations in the calm water while the vertical turbulent diffusion determined the vertical distributions in the turbulent water. Therefore, the buoyant Microcystis floated upwards to have fully photosynthesis and dominated in the calm water. However, the faster-growing Chlorella dominated in the turbulent water because both the phytoplanktons were distributed uniformly over depth. In addition, the depth of water and the turbulent diffusion were chosed to describe the water. The competitive advantage pictures were drawn through numerous model simulations. They revealed that the toxic and buoyant Microcystis was suitable to live in the calm and deep aquatic environment while the sinking Chlorella was well adapted to the shallow water. None of them could survive in the turbulent and deep water. The dominant algae would shift according to the changes in the turbulent diffusion and the depth of water. Many reported cases including the phytoplankton composition variations in the Tanglang River confirmed that the competitive advantage pictures could predict the shift in the dominant phytoplankton when the hydrodynamics change.