Effects Of Tubificid Bioturbation On Distribution Of PH, DO And PCO₂in A Water/Sediment System Studyed On Planar Optodes

Natural sediment plays the role as an important part of natural water environment, animportant sink and source of environmental pollutants, and an arena for manybottom-dwelling creatures. pH, DO and pCO2are not only the main parameters whichrepresented the biogeochemical characteristics of natural water and sediments, but also thelimiting factors of microorganisms and benthos in sediments. pH, DO and pCO2near thewater/sediment interface can greatly reflect various biogeochemical changes there.Restricted by detection means, we are lack of full understanding of sedimentmicrostructure and in-situ, high-resolution two-dimensional distribution changes of pH,DO and pCO2caused by bioturbation.In this study, tubificids were employed as bioturbators. Natural sediment, theenvironmental sample, was collected from the South Lake in Changchun. Based on theplanar optode, we monitored two-dimensional distributions of pH, DO and pCO2in thesimulated water/sediment microcosm with the presence of bioturbation, investiga ted thevariability and interaction of pH, DO and pCO2in water/sediment system and explored therelationship between variation of pH, DO and pCO2and the release and existing forms ofpollutants in sediment.As the results showed, the pH, DO and pCO2plane sensor prepared by the existing andimproved methods presented good fluorescence properties and short response time withstrong reversibility and stability. When applying to a homogenized water/sedimentsimulated system, the sensor depicted visual two-dimensional distributions in verticalprofile which were basically consistent with microelectrode measurements in pH and DO,just like that with determinator measurements in pCO2.pH, DO and pCO2plane sensor were combined and applied to a simulatedwater/sediment microcosm with the presence of bioturbation for14days of continuousmonitoring. The monitoring results indicated that vertical gradients of pH, DO and pCO2 near the water/sediment interface had greatly decreased from the start. In the sediment, pH,DO and pCO2changed from the surface downward to the deep, gradually showing arelative trend of high pH, DO and low pCO2in surface sediment with low pH, DO and highpCO2in deep sediment. Finally, pH, DO and pCO2in the overlying water, surface sediment,and even in the whole system tended to be uniform. The higher tubifex density led to themore uniform pH, DO and pCO2distributions in the water/sediment system, the faster DOincreasing, lower pCO2in the sediment and the deeper low pCO2diffusion layer. Thechanges of pH, DO and pCO2appeared as a complex and multidimensional process withsynthetic action of bioirrigation, resuspension, transportation and mixing, the tubificidmetabolism, life activities of microorganism in addition with mutual influence amongpH, DO and pCO2. With the increase of tubifex density, disturbance of tubifex nearwater/sediment interface and from surface sediments to the deep tended to be strong, whichspeeded up the process of synthetic action to the water/sediment system with tubificidbioturbation.