Hydrotransport-Oriented Zn, Cu, and Pb Behavior Assessment and Source Identification in the River Network of a Historically Mined Area in the Hokuroku Basin, Northeast Japan

Abstract

Aquatic ecosystems continuously receive potentially hazardous heavy metals from natural and anthropogenic sources. Focusing on the origin of heavy metals, this study aims to estimate the load contribution of tributaries from individual watershed and human drainage and to dissect the source of heavy metals, as commonly required for environmental impact assessment. Using integrated water dynamics, Geographic Information System (GIS), and chemical analysis, we identified and evaluated the heavy metal sources of the Kosaka river system in Hokuroku basin, which is a historically mined area in Northeast Japan, both in the high-water and low-water seasons. The migration and diffusion behaviors of heavy metals along with hydro-transport were analyzed, and the effects of mining activities on regional water quality both in the high-water and low-water seasons were clarified. The results indicate that Zn pollution was obvious in the Kosaka River network, especially in the downstream area. The spatial heterogeneity of heavy metal outflows from tributary watersheds was obvious, and the variations had strong correlations with mine site locations. The heavy metal flows in the mainstream increased sharply in the vicinity downstream of the Kosaka refinery drainage outlets. Compared to the low-water season, the influences of human drainage were slighter in high-water season, with lower contribution rates due to the dilution effect of the greater water discharge. Downscale sampling is effective to identify pollutant sources in regional basins.

Assessment of heavy metal pollution and ecological risk in river water and sediments in a historically metal mined watershed, Northeast Japan

“…Compared to mine drainage, the diffusional heavy metals are more difficult to capture, and the water quality reflects not only its origin but also what it encounters along its flow path (Lu et al, 2019). In this study, downscale sampling method was carried out according to watershed segmentation, taking water samples from tributaries which flow into the mainstream.…”

“…1) (Kitazono & Ueno, 2003;Sato et al, 1974;Urabe & Marumo, 1991). The whole Kosaka River watershed was divided into several selfgoverned sub-watershed polygons (Lu et al, 2019). The climate of the study area is subfrigid and humid, with four distinct seasons.…”

“…The tributary in sub-watershed 601 and its downstream polygon 612 exhibited a dramatic increase in the heavy metal outputs carried by suspended particles on rainy days. This area is located downstream of the Kosaka watershed and has a large amount of farmland (Lu et al, 2019). The surface material is easier to remove after rain erosion in sub-watersheds with frequent human disturbance, resulting in a high abundance of suspended particles in the water.…”

“…Naturally occurring rocks or soils with high heavy metal enrichment react with rainwater or groundwater, high heavy metal accumulation will generate in the sources to rivers, introduced naturally through the weathering of land covers (Lu et al, 2019). Furthermore, a variety of human activities, including mining, smelting and agricultural practices, have accelerated the weathering as well as released countless tons of trace elements into the environment.…”

“…These mining legacies continue to influence the geochemical cycle of the watershed, and large amounts of heavy metals have been released into the river system (Gozzard et al, 2011;Valencia-Avellan et al, 2017). Compared to point mine drainage, diffusive nonpoint sources are more difficult to identify and remediate and therefore deserve greater attention (Gozzard et al, 2011;Lu et al, 2019). Little information is available on heavy metals in river water and sediments in the Kosaka watershed of Hokuroku District.…”