[Temporal and Spatial Variations in the Conductivity in Different Media in Taihu Lake, China].

Conductivity is an important parameter for characterizing dissolved solids and salinity in water, and is also one of the routinely measured parameters in water quality monitoring. To reveal temporal and spatial variations in conductivity in different media in Taihu Lake, historical data (1980-2009) were collected and field monitoring data (2009-2018) were analyzed. The results indicated that water conductivity in Taihu Lake has shown a significant increasing trend over the past 40 years and diverged in 1996-1997. Conductivity values increased from (239.43±70.60)μS·cm in the period 1980-1996 to(477.31±23.47)μS·cm in the present day, with an average annual increase of 10.40 μS·(cm·a). Spatially, the conductivity of water in the northwest part of the lake was significantly higher than the southeast part. These changes in conductivity are dominated by changes in major ions, and the contribution of nitrogen was essentially negligible. Human activities in the basin have been the main factors causing changes in water conductivity. In addition, conductivity is significantly affected by seasonal runoff. Compared with the water, the conductivity of the surface sediments and pore water (0-10 cm) in the northwest part of the lake were lower than in the southeast part, while this trend was opposite in the deeper sediments (>10 cm). The conductivity of the sediment and pore water were no different between surface (0-10 cm) and deeper (>10 cm) sediments in the northwest lake, while these were higher in the surface sediments in the southeast part of the lake. Sediment conductivity was positively correlated with organic matter (<0.01) and was negatively correlated with pH (<0.05). This indicated that organic matter promotes the activation and migration of metal ions, which are more activated under acidic conditions. We found that conductivity in the surface sediments and pore water (0-10 cm) were significantly positively correlated with conductivity in the overlying water (<0.01). In contrast, the conductivity of overlying water was not correlated with the conductivity of deeper sediments and pore water (>10 cm). These patterns indicated that surface sediments and pore water have a significant effect on the conductivity of overlying waters. In addition, there was a significant positive correlation between the conductivity of sediment and pore water (<0.01) within the entire sedimentary section (0-50 cm), indicating efficiency ion-exchange between the two. The interaction between sediment and pore water was generally stronger than their interaction with the overlying water.