Distribution Characteristics Of Phosphorus And Nitrogen In Surface Sediments Of The Dongjiang River And Its Tributaries In Huizhou And Capping Technology For Remediation

Dongjiang river is an important source of drinking water, which water quality is essential forthe security of water supply of HK Special Administrative Region and most cities in Guangdongprovince. In recent years, with the increase of population and development of economy, waterquality of Dongjiang tributaries has been seriously polluted by domestic sewage and industrialwaste water discharge of their riparian cities, which may influence the water quality of Dongjiangriver. Most pollutants cumulate in the sediments after flowing into river, therefore, contaminatedsediments become main internal pollution sources when external sources are controlled effectively.Consequently, internal and external pollution sources should be controlled simultaneously whenimproving the water quality. At present, levels of nitrogen and phosphorus content in sediments ofDongjiang river and its tributaries and their influence on overlying water has been rarely reported.So it is meaningful to know the content of nitrogen and phosphorus in sediment and distribution ofthese nutrients, discuss the migration and release rule of nitrogen and phosphorus, develope therepair technology of sediment to protect the Dongjiang river water quality and control endogenousdischarged into the river tributaries.In this paper, Dongjiang river （Huizhou section） and its tributaries is the main research object,of which the nitrogen and phosphorous content and temporal-spatial distribution characteristics isstudied. In addition, the release rule of sediments in high contaminated urban river and the repairtechnology, in-situ capping of contaminated sediments are also studied in the example of XinkaiRiver. The main conclusions are as follows:1、The research of water quality and sediments of Dongjiang river and its tributaries wasimplemented on March and August,2011. Different forms of phosphorous, TN and exchangeableNH4+-N were detected by SEDEX sequential extraction, persulfate digestion and Nessler’sreagent colorimetric. The distribution characteristics and contaminated degree of pollutants werestudied. The results are as follows:（1） TN, TP and NH₄⁺-N, COD content in the overlying water of Dongjiang river weresignificantly lower than Shuikou river and Xinkai river （p <0.05）. NH₄⁺-N of Dongjiang river wasâ…£grade of Environmental Quality Standards for Surface Water. TP、NH₄⁺-N in the sediment ofDongjiang river were unpolluted but TN was polluted. The sedimentary phosphorous and nitrogenof its tributaries were mild pollued. It showed that tributaries were main pollution sources toDongjiang river and their sedimentary phosphorous and nitrogen had potential risk to release.（2） The release of phosphorous and nitrogen in the sediment was depended on their forms. IP andechangeable NH₄⁺-N of tributaries were higher than Dongjiang river （p <0.05）. It showed thatbiological effectiveness and potential biological effectiveness of phosphorous and nitrogen in thesediment of tributaries were very high, and they might release with change of environment.2. Through laboratory simulation experiment, the impact of environmental factors, liketemperature, dissolved oxygen, disturbance and levels of nutrients on the the migration and releaserule of nitrogen and phosphorus has been studied. The rise of temperature will help the release andtranfomation of nutrients, among20℃and30℃,the release amount of phosphorous in thesediment increase with temperature,but nitrogen is not affected obviously. Anaerobic conditions is conducive to the release of Fe-P, Al-P and NH₄⁺-N. Overlying water aeration can improvedissolved oxygen content in the water and inhibit the release of phosphorus and nitrogen in thesediment. Disturbing in60r/min can inhibit the release of phosphorus, while promoting reaerationrate, ammoniation and nitrification. The decrease of nutrient levels in the overlying water canpromote the release of phosphorous and nitrogen, while having no impact on NH₄⁺-N. It showedthat increase of temperature and decrease of nutrient levels promoted the release of phosphorousbut had no impact on nitrogen; the release of phosphorous and nitrogen could be effectivelyinhibited by increasing the content of DO in the tributaries artificially.3. Through laboratory simulation experiment, choosing glass beads, river sand, zeolite, andvolcanic rock as materials, the inhibited effects of the release of phosphorous and nitrogen andinfluenced factors, flow condition, depth and partical size were studied,meanwhile materialshaving better inhibited effects were choosed.The result showed as follows:（1）River sand, zeolite, and volcanic rock had better inhibited effects on phosphorous andzeolite was best for NH₄⁺-N inhibition. So zeolite and volcanic rock were choosen as cappingmaterials.（2）When capped by zeolite, the inhibition effect of phosphorous release increasedsignificantly with the increase of capping depth（p <0.05）, which of NH₄⁺-N、NO-3-N and TN werenot significant changed （p>0.05）.And the inhibition effects of phosphorous and nitrogen releasewere not significant affected by particle size （p>0.05）.（3）When capped by volcanic rock, the inhibition effect of TP and NO-3-N were notsignificant affected by capping depth （p>0.05）, which of NH₄⁺-N and TN increased significantlywith increase of capping depth （p <0.01）. And partical size had no significant impact on theinhibition effect of TN, TP and NO3—N. However, the release flux of NH₄⁺-N was significantly（p <0.01） higher with particle size of3～5mm than less20mesh.（1）The motion condition of overlying water can effectively promote the release ofphosphorous and nitrogen in the sediment.（2）Capped by zeolite and volcanic rock, it showed that the motion condition of overlyingwater can effectively promote the release of phosphorous in the sediment, however had no impacton the release of NH₄⁺-N.（3） In conclution, sediment is the main internal pollution source and water quality ofDongjiang river are influenced by its tributaries. Hgher temperature, lower DO and levels ofnitruents are conductive to the release sedimentary phosphorous. The release of phosphorous andnitrogen could be effectively inhibited by increasing the content of DO in the tributariesartificially.The inhibited effect of zeolite is better than volcanic rock.