5:15 PM - 6:45 PM
[MIS14-P02] Fluctuations of dissolved iron and dissolved organic carbon in stream water in peridotite watersheds
Keywords:peridotite, sedimentary rock, Mt. Apoi, forested watershed, stream discharge
Supply of dissolved iron (DI) from terrestrial river is an important factor to control production of marine ecosystems. However, differences in the concentration of DI among rivers and seasons remains unknown points, hindering our understanding of runoff process of DI. Iron generally forms complex with organic matter and runs off as DI. Therefore, observation with linking run off process of DI to that of organic matter dynamics is important. In addition, relating to the discharge permits detailed understanding of runoff process of DI. Geology is the one of the major factors controlling biogeochemical processes. Peridotite is formed by appearing mantle from deep in the earth without alternation, rich in magnesium and iron. Mt. Apoi in Hokkaido has a unique characteristic worldwide because all over the mountain is formed with peridotite. Furthermore, supply of substances to coastal area would be directly influenced by dynamics of substances in forested area because the forested area is located near the coast, thus here is appropriate place to consider the linkage between forest and coastal ecosystems. This study aimed to clarify the fluctuations of concentrations of DI and dissolved organic carbon (DOC) in stream water and relationship between the two solutes in each season at steams in peridotite watersheds and non-peridotite watersheds.
We collected stream water monthly at streams in peridotite watersheds in Mt. Apoi and adjacent sedimentary rock watersheds in Samani Town, Hokkaido in 2012-2014. We conducted intensive observation at the four streams in the peridotite and sedimentary rock watersheds by collecting stream water continuously with 4 hours interval in the rainfall event in March, July, August, October, and December, and measured water level continuously using water gauge and calculated stream discharge. We stored the water at 4 oC after the filtration using glass fiber filter (GF/F, 47mm). We analyzed DI and DOC using inductively coupled plasma optical emission spectrometry and total organic carbon analyzer, respectively.
Average DI concentration of each stream ranged between 0.005-0.21 mg L-1 and higher in streams in peridotite watershed. Stream discharge was lower in streams in peridotite watersheds during base flow, but higher than those in sedimentary rock watersheds in flood events. It was considered that the discharge responds rapidly to the rainfall event because rainfall does not penetrate underground deeply and contribution of surface flow is high in peridotite watersheds. DI and DOC concentrations increased dramatically at the peak of the discharge, then decreased gradually with decreasing discharge. Both DI and DOC concentrations were higher in the streams in peridotite watersheds and reached to 1.81 mg L-1 and 17.0 mg L-1, respectively, in flood event in October. In contrast, in flood event in August, maximum concentration of DI was 1.05 mg L-1 despite high concentration of DOC (34.0 mg L-1). Relationship between DI and DOC concentrations of entirely period was unclear, however they correlated positively in each season, indicating that iron coordinates with DOC and runs off. On the other hand, DI/DOC ratio differed among season as it was high in October and December and low in March and August. We speculated that low DI concentration despite high DOC concentration in August attributed to high ratio of easy decomposable fraction of DOC during summer season. In March, fluctuation of DI concentration was completely low although DOC concentration changes. These results showed that DI and DOC concentrations in stream water were high in peridotite watersheds compared to non-peridotite watersheds, suggesting that accumulation of organic matter and discharge property in addition to its iron-rich characteristics promote runoff of DI in peridotite watersheds.
We collected stream water monthly at streams in peridotite watersheds in Mt. Apoi and adjacent sedimentary rock watersheds in Samani Town, Hokkaido in 2012-2014. We conducted intensive observation at the four streams in the peridotite and sedimentary rock watersheds by collecting stream water continuously with 4 hours interval in the rainfall event in March, July, August, October, and December, and measured water level continuously using water gauge and calculated stream discharge. We stored the water at 4 oC after the filtration using glass fiber filter (GF/F, 47mm). We analyzed DI and DOC using inductively coupled plasma optical emission spectrometry and total organic carbon analyzer, respectively.
Average DI concentration of each stream ranged between 0.005-0.21 mg L-1 and higher in streams in peridotite watershed. Stream discharge was lower in streams in peridotite watersheds during base flow, but higher than those in sedimentary rock watersheds in flood events. It was considered that the discharge responds rapidly to the rainfall event because rainfall does not penetrate underground deeply and contribution of surface flow is high in peridotite watersheds. DI and DOC concentrations increased dramatically at the peak of the discharge, then decreased gradually with decreasing discharge. Both DI and DOC concentrations were higher in the streams in peridotite watersheds and reached to 1.81 mg L-1 and 17.0 mg L-1, respectively, in flood event in October. In contrast, in flood event in August, maximum concentration of DI was 1.05 mg L-1 despite high concentration of DOC (34.0 mg L-1). Relationship between DI and DOC concentrations of entirely period was unclear, however they correlated positively in each season, indicating that iron coordinates with DOC and runs off. On the other hand, DI/DOC ratio differed among season as it was high in October and December and low in March and August. We speculated that low DI concentration despite high DOC concentration in August attributed to high ratio of easy decomposable fraction of DOC during summer season. In March, fluctuation of DI concentration was completely low although DOC concentration changes. These results showed that DI and DOC concentrations in stream water were high in peridotite watersheds compared to non-peridotite watersheds, suggesting that accumulation of organic matter and discharge property in addition to its iron-rich characteristics promote runoff of DI in peridotite watersheds.