Study On The Assessment Methods Of The Red Tide Caused By Ships' Ballast Water In Dalian Port

With increasing expansion of international trade, ballast water become one of the main methods to transmit invasive pest as shipping industry plays an important role in the world trade. The ballast water is obtained from the ports of departure and its near areas and the native red tide organisms were easily carried in the ships and transported to the port of destination. Due to the invasive characteristics of these organisms, it is a possibility that they become HABs(harmful algal blooms) when the ballast water are discharged and into the new environment. The problems caused by red tide threaten human health and ecosystems and are detrimental to economic development. Thus it is urgent to establish a rational system of risk assessment to face the challenge and reduce the hazard of biological invasion.According to the investigation of 12 sites in the waters of Dalian port, related information about physical and chemical factors of this water were obtained and the species composition and cell abundance of plankton were discussed and analyzed, which provide the information for the following assessment.This paper discusses risk assessment methods and models from two aspects. Researching and assessing the risk assessment system of red tide organisms introduced by ships ballast water in Dalian port. First, risks of invasive organisms by ships ballast water were identified through the literatures and analysis of survey data in Dalian port and potential risk were found. After study and analysis, a three-layer (target layer, criteria layer and index layer) risk assessment indexes system were established, in which the weight value was determined by analytical hierarchy process and membership degree was determined by fuzzy comprehensive assessment method. Finally, the risk of introduction of invasive red tide organisms by ballast water was valued by figures through weighted sum using the principle of score and the risk levels of red tide organisms by ships' ballast water was obtained. By using the decisive factors which affected the abundance of phytoplankton in Bohai Bay, this work established a multi-variant regression equation based on the monitoring data of environmental factors in Dalian port. Multi-variant regression equation is essential to predict the red tides thus to prevent the potential damages and reduce the economic loss.By the combination of the risk assessment of red tide and the forecast of HABs, the risk assessment system of red tide organisms introduced by ships ballast water in Dalian port was analyzed and the risk level was determined to be moderate; the establishment of forecast model of red tide provides useful information for relevant departments.