Research On Nitrogen Variation During Water Supply And Characteristics Of Ammonia Nitrogen Adsorption And Desorption Of Sediments In Dongchang Lake

The research of nitrogen pollution and migration and transformation of nitrogenforms is a hotspot in lakes, and it is also the main problem in control theeutrophication of lakes. Urban shallow lakes have the unique characteristics incomparison with the deep-water lakes, and nitrogen migration and transformation ismore complicated in its water and sediments. Dongchang Lake is a typical artificialurban shallow lake in the north of China, the research of nitrogen migration andtransformation rules and ammonia nitrogen adsorption-desorption characteristics ofsediments can provide some reference for controlling the eutrophication of artificialshallow lakes.The Dongchang Lake was selected as the research object in this paper, themigration and transformation rules of dissolved nitrogen and particulate nitrogenduring the Yellow River water supply was monitored, the content and characteristicsof different forms of nitrogen in the surface sediments were analyzed by the chemicalsequential extraction methods. And the role of different nitrogen forms in the nitrogencycle of the interface of sediments and water was discussed. The influence of differentfactors such as granularity, organic matter, hydrodynamic disturbance and differentclay minerals on the behaviour of ammonia nitrogen adsorption-desorption insediments was also studied by simulation experiments. The main research results andconclusions are as follows:(1) The Yellow River water supply, which had high content of pollutants andsuspended sediments, had a great influence on the nitrogen existing forms in waterand sediments. The total nitrogen (TN) and chemical oxygen demand (COD) is themain pollutants in Dongchang Lake. The content of both is basically higher than thequality standards of V water, the whole water presents a tendency of eutrophication. The water supply had a great influence on lake zones near the water inlet, themigration and transformation of different nitrogen forms was mainly affected by theexogenous water supply, adsorption of particulate matters and the function ofnitrifying bacteria, ammonifying bacteria. The influence of ammonia nitrogen bysuspended sediments of the Yellow River was biggest. The suspended sedimentsplayed an importantly positive role in the migration and transformation of nitrogenand reducing the nitrogen pollution load.(2) The content of transferable nitrogen is high, then the probability of lakeeutrophication caused by internal nitrogen release in sediments is bigger. The contentof total transferable nitrogen (TTN) is between214.01~440.47mg/kg, the percentageof TTN/TN is between18.86%~59.20%. The content of TTN inⅠand Ⅲ lake zonesis higher than other lake zones, because the two lake zones are more closer to thewater inlet, then sediments are influenced perennially by the Yellow River water.(3) There are big differences on the characteristics of different nitrogen exisitingforms and their abilities of participating in the nitrogen cycle. The rate of contributionof different nitrogen forms to TTN is in turn strong oxidant extractable form(SOEF-N)> weak acid extractable form (WAEF-N)> strong alkali extractable form(SAEF-N)> ion exchangeable form (IEF-N), IEF-N will be most easily release intothe water, it is the largest contributor to the eutrophication of lakes, and its sources aremore related with iron-manganese oxides. SAEF-N and SOEF-N may have the sameouter origin. The granularity and organic matter of the sediments have a greatinfluence on the content and distribution of different nitrogen forms. Theuntransferable nitrogen is mostly preserved in the fine silt (0.004~0.032mm).(4) The abilities of ammonia adsorption and fixation in sediments are increasedas the increase of organic, the decrease of the granularity and a certain degree ofdisturbance. The component and content of clay minerals have a remarkable influenceon the behaviour of ammonia adsorption-desorption in sediments, and the abilities ofammonia adsorption and fixation in sediments are increased as the increase of contentof clay minerals. Sediments doped zeolite have the biggest abilities to adsorb and fixammonia, and sediments doped kaoline have the smallest abilities. This is due to their unique structural characteristics and properties.(5) The three adsorption-desorption model fitting revealed that Freundlich modelis the optimum model to describe the behavior of ammonia adsorption-desorption insediments. And the parameter KFcan better reflect the abilities of ammonia adsorptionin sediments.