A Study On Water-bloom And Self-purification In Small-scaled Urban Scenery Water

With fast development of eco-construction, more and more small-scaled urban scenery water-bodies appear in the city. The characteristics of small-scaled scenery water bodies, such as shallow depth, small area and distributed scale, result in poor ability to disturbance-resistance. Therefore, the water-bodies are easy to become entrophic and even "water-blooms" can happen, not only influencing the landscape water body appreciation value, but also polluting environment, increasing environmental risk. It is important to study urban small-scaled scenery water-body's natural change and the self-purification.This thesis chooses a small-scaled landscape water-body located in the former Chengdu World Garden. This water body had been there for a number of years with limited exchanges with outside water. The "red-water-bloom" phenomenon happened several times during January 2006 to March 2007, followed by some other "water-bloom" phenomena. The process of water change in color and other features was reported for a period of over one year. Investigations ruled out chemical pollution but extrinsic conditions caused red water bloom. Data, including water temperature, pH, NH3-N, TN, TP, DO, turbidity, etc. were collected from 19 January 2006 to 22 September 2006. Preliminary conclusions are listed below: (1) There are periodic variation tendency in the water-body: "fish death—red-water-bloom—Microcystis-water-bloom—green duckweed—fishdeath—red-water-bloom ".(2)The "red-water-bloom" is caused by a large quantity of reproduction ofTZ-S bacteria, which is a kind of size 2×5～10μm, rod-shaped, withpositive G⁺ reflection. Due to various constraints, the bacterium was notidentified.(3) The main factors that cause changes in water quality and leaded water-bloom are TN, pH and TP. Water-bloom will occur when water temperature is low in winter and the lowest water temperature for water-bloom is 7.8℃, 2.2℃lower than that reported elsewhere (10℃);(4) The study water has strong ability of self-purification. The average removal rate of NH₃-N, TN and TP was 68.69%, 65.58%, 64.95%, and the average add rate of DO was 235.84%, respectively.