Iodine in groundwater of the North China Plain: Spatial patterns and hydrogeochemical processes of enrichment

Abstract

The North China Plain (NCP), with an area of 139,238km2, has concurrent occurrence of high-iodine (>150μg/L) and low-iodine (<10μg/L) groundwater regions that frequently result in iodine excess or deficiency disorders. The spatial distribution of iodine was delineated based on 6098 groundwater samples obtained through the “National Groundwater Quality Investigation and Assessment Program (2006–2010)” by the China Geological Survey. Of those, 4390 samples were from shallower depths (<100–150m) and 1708 were from deeper depths (>100–150m). In the piedmont alluvial fan and alluvial–pluvial plain along the northern and western margins of the NCP, groundwater iodine concentrations were low at both shallow and deep depths. Extensive areas in the flood plain adjacent to the Yellow River and the Haihe River and in the coastal plain had high-iodine groundwater, although the patterns were more patchy for the shallower depths than for the deeper depths. Cones of groundwater depression in the NCP were extensive due to excessive pumping of groundwater, and in turn, may contribute to complex spatial patterns of iodine distribution in the eastern NCP. Principal component analysis of hydrogeochemistry of 46 shallow and 48 deep groundwater samples (representative of the entire dataset) identified three factors (sea water, carbonate mineral dissolution and decomposition of organic matter) to account for 86.8% variance in 9 hydrogeochemical parameters. Decomposition of organic matter is the leading cause for high-iodine in groundwater, with sea water influence more important in the shallow groundwater than in the deep groundwater.