The Investigation of ‘Water Bloom’ in the Downstream of the Han River

The first outbreak of ‘water bloom' in the downstream of the Han River during the spring of 1992 was investigated, and the characteristics and causes of this phenomenon and the possible countermeasures and control suggestions were analyzed and discussed. It was found that the rapid proliferation of diatom (with density of more than 10 7/L), mainly the cyclotella meneghiniana, is the basic characteristic as well as the direct cause of the ‘water bloom'. By examining the relative changes of hydrological factors, such as water temperature, water flow and flow velocity, and water quality factors, such as pH, DO, chromaticity and COD Mn , the concepts of ‘sensitivity factor' (or indicating factor) and ‘precaution value' for the Han River were proposed.