Effect of dam on iron species distribution and transformation in riparian zones

Abstract

The redox cycle of Fe(II)/Fe(III) species in riparian zones mediates a wide range of biogeochemical processes. Most rivers in the world have been changed by dams, but the effect of dams on the distribution and transformation of Fe species in riparian zones is poorly understood. This study investigated the spatial distribution and seasonal transformation of Fe species in a riparian zone that was impacted by a dam in the Han River, which is the largest branch of the Yangtze River. Results show that dam changed the distribution pattern of solid Fe species in the riparian zone. For example, the dam resulted in a higher content of total Fe in the upstream riparian zone than downstream. The dam operation resulted in a more rapid carbonate-associated Fe(II) oxidation and crystalline Fe oxide reduction in the upstream riparian zone than in the downstream zone. These influences were attributed to variations in sediment lithology and hydrodynamic process. In the upstream zone, the dam resulted in the deposition of iron-rich fine particles and the intrusion of river water that contained O2 and dissolved organic carbon into the aquifer. In the downstream zone, the dam resulted in fine particle erosion and groundwater discharge. This study revealed the significant role of dams in Fe species distribution and transformation and in Fe-related biogeochemical processes in riparian zones.