In-situ Determination Of Dissolved Fe(?) And S(-?) In Sediment Pore Water With An Integrated Measurement System

As an important site and medium for material exchange between sediment and overlying water,sediment pore water contains many key elements that are closely related to biogeochemical cycles and biological activities.Among those elements,the most important ones are iron and sulfur.Iron plays key roles in the processes of plant respiration,nitrogen fixation and photosynthesis,and sulfur is involved in synthesis of proteins and vitamins.In sediment pore water,the two elements mainly exist as reduced forms,namely Fe(II)and S(-II).The conventional method for their determination is the ex-situ analysis,in which the sediment samples or collected chemicals are taken back to the laboratory for measurement.The most major drawback of the method is that the oxidation of Fe(II)and S(-II)may happen during sampling,transportation and processing.Therefore,in-situ analysis methods that integrate concentrating,sampling and determination on site are necessary and important for the study of iron and sulfur in sediment pore water.However,the in-situ analytical methods and applications reported so far are still limited to in-situ concentrating or laboratory tests,and there is no true in-situ analysis method for on-site measurement.Focusing on solving the problems remained in the existing methods,this study established an in-situ method and sensor system for determination of dissolved Fe(II)and S(-II)in sediment pore water.The system could integrate color developing,concentrating and recording during sampling,and minimize environmental impact and human interference that may occur during sampling,transportation,preserving and handling.The main research contents and results are as follows:(1)A home-made concentrating device with a transparent holder consisted of a polyacrylamide diffusive gel,and a polyacrylamide gel impregnated C18 and ferrozine as the concentrating phase.A sample plate with several concentrating devices and a digital video camera were assembled into an integrated sensor system for the in-situ determination of dissolved Fe(II)in the sediment pore water.The relationship of the diffusion coefficient of polyacrylamide gel,the concentrating amount,and the grayscale intensity of colored concentrating phase were analyzed and used to establish a series of quantitative equations,which are different from the classical DGT's and suitable for this research method.The parameters of the method were optimized,and the effects of salinity on the concentrating performance and the accuracy and precision of the method were examined.The method was successfully applied to the in-situ determination of dissolved Fe(II)in sediment pore water in the reservoir of Xiang'an campus of Xiamen University and in the Zini mangrove reserve of Fujian Province.The results showed that the proposed method could meet the requirements of semi-quantitative and even quantitative measurement of Fe(II)in sediment pore water.(2)Based on the above work,the concentrating device and in-situ sensor system were improved.A AgI-acrylamide gel was used as the concentrating phase,and a polyacrylamide diffusion gel was assembled into an integrated sensor system for the in-situ determination of the dissolved S(-II)in sediment pore water.A group of quantitative equations were established and the method parameters were optimized.The effect of salinity and the accuracy and precision of the method were examined.The method was applied in the reservoir of Xiang'an campus of Xiamen University and the Zini mangrove reserve of Fujian Province for in-situ determination of dissolved S(-?)in sediment pore water.The results showed that the proposed method could be used for the semi-quantitative and even quantitative determination of S(-II)in sediment pore water.