Research On The Causes Of Low Dissolved Oxygen In The Downstream Of Minjiang River

Dissolved oxygen is an important environment factor to maintain the dynamic balance of water ecological environment, is also the necessary conditions for the survival of a large number of aquatic organisms. Study and master the change of the dissolved oxygen content in water, is great significance for water environmental protection and maintain the water ecological balance. In recent years, according to the monitoring data of dissolved oxygen from the downstream of minjiang segments of huangtian thou farmland county town to river "meixi river" into the mouth of water, often appear the phenomenon of low dissolved oxygen. On the basis of comparing various functions related to water quality model, this study selected QUAL2K water quality model for simulating minjiang downstream the change trend of dissolved oxygen, and considering the change of water quality of BOD5, and other indicators, to explore the causes of low dissolved oxygen, and further research Suggestions are put forward.Research adopted in 2006,2009 and 2011, the three year period water quality data, in September 7 monitoring cross section in the downstream of minjiang water quality on the basis of status evaluation, the use of the downstream of minjiang and shuikou reservoir hydrologic data, based on the choice of the parameter in huangtian to chief gaps of QUAL2K model is established, and its application to the analysis of the dissolved oxygen changes. Combined with 9 month are 2011 water quality monitoring data, hydraulic parameters, pollutants and meteorological data application model, the study found that the main pollutants concentration under the condition of relatively stable, part of the content of dissolved oxygen reduced obviously, this kind of phenomenon and the river was correlated fish breeding density is higher.This study gets the following conclusion:(1)The two indicators of BOD5 and ammonia nitrogen,which has important influence on water dissolved oxygen changes, the simulated values is close to the measured values along the river. That shows that there is no obvious change basically in pollutant degradation characteristics of the river in the study, and there is no obvious change of dissolved oxygen in the water consumption compared with previous did not change significantly;(2)QUAL2K model in consideration of factors such as contamination, sediment, phytoplankton and bacteria in the aquatic dissolved oxygen consumption by simulated values in the study area (huangtian to river "meixi river" into mouth section) in the upper than monitoring measured values, the region also exist in actual situation of dissolved oxygen consumption of other water bodies.(3)Together with the present situation of minjiang downstream shuikou reservoir area breeding, the dissolved oxygen concentration in river analysis study found that the consumption of dissolved oxygen in water is due to the region caused by fish farming. For dissolved oxygen balance of payment in the study area in September 2011 after analysis found that a lot of dissolved oxygen consumption and aquaculture, is closely related to fish farming.Analysis get the following conclusions:â‘ Regional income mainly get through the atmosphere of dissolved oxygen water after oxygen;â‘¡The spending of dissolved oxygen degradation is mainly composed of breathing, bacteria, sediment oxygen consumption and photosynthesis of phytoplankton of four parts;â‘¢The cages fish farming total dissolved oxygen consumption accounted for 46.4% of atmospheric oxygen compound.Through the study, we found that what due to aquaculture the shuikou reservoir downstream dissolved oxygen is history on the low side, this will affect the downstream of minjiang degradation efficiency of pollutants and, in turn, affects the downstream water quality and ecosystem of the downstream of minjiang unpredictable potential impact. So we suggest to make a reasonable plan of shuikou reservoir aquaculture, and to determine its reasonable breeding capacity.Under the premise that ensure the downstream of minjiang water quality standards, make it meets the requirements of reservoir fisheries sustainable development.