Sediment in Lake Soyang, South Korea : as Integrating Archive of Catchment Processes and Potential Effect on Lake Water Quality and Methane Gas Ebullition Kim, Kiyong1, Kim, Bomchul2, Knorr, Klaus-Holger3, and Stefan, Peiffer1   1Department of Hydrology, University of Bayrueth, Bayreuth, Germany 2Department of Environmental Science, Kangwon National University, Chuncheon, Korea 3Institute for Landscape Ecology, University of Muenster, Muenster, Germany Photo of Lake Soyang

Background Lake Water Quality Impact on Land use changes Lake Sediment Formation Watershed Activities Monsoon Climate Effect Land use changes Causing runoff Tillage Flushing effect Fertilizer overuse Impact on Lake Water Quality

Background Sediment controls lake water quality under certain condition in monsoon climate area

Study Site – Lake Soyang Agricultural area, Heaan dendrictic shape Metropolitan city, Seoul (Map source and lake inforamtion : Bomchul Kim et al., 2001 & Jai-Ku Kim et al., 2007)

Sampling Location and Frequency Samples Sampling time Lake water Every month By depth Stream water Inflow streams Lake sediment Before & after monsoon season Core & grab samples Gas sample Before monsoon Bubble type in water

Results – Precipitation in Watershed Gentle summer monsoon climate Intensive summer monsoon climate 100mm/day (Source : www. wamis.go.kr)

High amount of nutrients and OMs Results – Lake Water Oxygen depletion in hypolimnion with thermal stratification in summer Mixing period in winter season High amount of nutrients and OMs Oxygen depletion in bottom water

Results – ORP, pH and DIP pH, ORP and DIP Sediment Porewater ORP : -130 ~ -80mV Under this conditions, the concentration of Fe(II) and Mn(II) rises and, further sulfate begins to be reduced The phosphate concentration in the porewater was higher in top sediment than bottom water layer

Results – Lake Water Detached Fe from Lake Soyang watershed transport to the lake water body especially during summer monsoon season after intensive rainfall event

Results – Lake Water Mn concentration in bottom water layer is the highest during summer monsoon season as same as Fe Mn and Fe can be used as electron acceptors faster than sulfate reduction (Robert G. Wetzel, 2001)

Results – Porewater 2012. Sep. 2012. June In sediments, Fe oxides are reduced by two mechanisms: (1) microbial dissimilatory Fe reduction as terminal electron acceptors in respiration (2) chemically by sulfides formed in microbial sulfate reduction (Canfield et al., 2005; Lovley, 1991)

Results – Sediment We thought high amount of pyrite (Fe2S2) is deposited after sulfate reduction process

Results – Gas ebullition Buoy (Jari T. Huttunen et al., 2001) Gas bubble sampler

Results – Gas ebullition Site Total gas volume (ml hour-1) Ebullition (g C m -2 yr -1) 1 7.5 16.19 2 416.7 1261.61 3 6.7 8.63 4 15.0 29.08 Source Lake Area (ha) Ebullition (mg C m -2 yr -1) Bastviken et al., 2004 Brown 32.9 1428 Crampton 25.8 841 East Long 2.3 2649 Hummingbird 0.8 1152 Morris 5.9 16284 North Gate 0.3 896 Paul 1.7 2680 Roach 45.0 4452 Huttunen et al., 2003 Postilampi 3.0 6750 Tuesday 407.0 983 Casper et al., 2004 Ward 1.0 54312

Conclusions Fe, Mn input from watershed to Lake Soyang control phosphate release from sediment into water layer . Significant amount of methane emission occurs from the lake into atmosphere in the form of ebullition Intensive and well-organized field work is required for elucidating lake bottom sediment processes

Thanks to … TERRECO project and people University of Bayreuth, Hydrology department people Kangwon National University, Prof. Bomchul Kim and Environmental Ecology laboratory people

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