富氧-缺氧过程对氧气分布及交换过程影响

为考察底层水体不同的氧动态对水土界面氧气交换过程影响,采用Unisence的微电极测试系统考察底层水体不同的复氧-缺氧环境(物理微曝空气供氧、添加过氧化剂的化学供氧及物理微曝氮气)中,沉积物-水界面氧气的分布及其传输机制,并评估不同富氧与厌氧过程对表层沉积物有机碳的矿化过程的影响.结果表明水体处极度厌氧状况,控制溶解氧分布和交换的水底扩散边界层(DBL)厚度明显变薄(一般在0.2~0.4mm)且溶解氧衰变相对较缓.但底层水体溶解氧丰富甚至处于过饱和状态, DBL层的厚度(一般在0.4~0.7mm)相对较厚且氧气变化迅速 (P<0.05).增加水体氧气供给的条件下,水体与沉积物间溶解氧交换过程加快,溶解氧交换通量由(4.87±0.92)增加至(5.31±0.66 )及(17.14±3.15 ) mmol O2/(m2·d)交换速率,最高提升252%,温度升高氧气交换速率可增加15%,温度效应明显.

Influence of anaerobic and aerobic processes on bottom oxygen dynamic and exchange process across sediment- water interface

To quantify impacts of oxygen distribution dynamic on exchange process between surface sediment and overlying water, we employed O2 penetrating microelectrode system (Unisence Ltd., Denmark) to obtain multiple high resolution microprofiles of in-situ O2, calculated O2 exchange rate using Fick First Law. Besides, we also investigated the influence of anaerobic and aerobic processes (microaeration air bubbles, microaeration nitrogen bubbles, injection CaO2 suspension into surface sediments) on mineralization of soil organic matter. In the present study, the results showed that diffusive boundary layer (DBL) thickness containing significant chemical gradients, which greatly limited oxygen exchange between bottom water and topsoil, is dependent on oxygen levels in the benthic overlying water. In anaerobic conditions by means of nitrogen microbubbles, DBL ranged from 0.2 to 0.4millimeters in thickness. However, DBL thickness increased dramatically between 0.4~0.7mm (P<0.05) compared to treatments with bubbling air or injection CaO2 suspension into surface sediments. Also, O2 exchange was accelerated in the case of enough oxygen supply. O2 benthic diffusive flux were (5.31±0.66) and (17.14±3.15) mmol O2/(m2·d) in bubbling air treatment, injection CaO2 suspension into surface sediments, increased by 9% and 250% in relation to (4.87±0.92) mmol O2/(m2·d) in control, respectively. An obvious tendency for increasing O2exchange was observed with temperature rise.