Carbon sink potential of eutrophic lake sediments: a reconstruction of the potntial in lakes Nakaumi and Shinji during the last about four hundred years

利用表层沉积物和沉积物岩心研究了中海湖和真地湖富营养化湖泊沉积物近百年和数百年来的碳汇潜力。中川湖南部和中部1cm表层沉积物TOC （total organic carbon）含量较高，腐泥含量约为3.6~4.0%。这些值是AD1997以来的常量。除东部地区外，所有样品TOC含量均呈腐泥状，较高，约为3.5~4.3%。这些TOC值在近5年内没有变化。根据C/N比值（7-9）和py-GC-MS分析，两湖有机质来源均以浮游植物为主。在AD1800 ~ 1900年间，中海和真地沉积物岩心TOC含量均较低，约为1%，AD1900年后TOC含量从1%急剧上升至4%。初步分析AD2003数据表明，表层沉积物中TOC含量大于3.5%与H2S （ppm）呈良好的正相关关系，即H2S (ppm) = 13.9 * TOC (%) - 52.1 （TOC>3.5%）。2013年4 ~ 5月，中海东北部大气CO2浓度较低，平均约为360 ppm，这可能与浮游植物的春季开花有关。白天和夜间的二氧化碳浓度差异令人印象深刻，高达80ppm。根据Kanai et al.,（1998,2002）报道的沉积速率，L. Nakaumi和Shinji表层沉积物的平均ocar分别为7.0 mgC/cm2/y和4.0 mgC/cm2/y。因此，L. Nakaumi和Shinji的潜在碳汇分别约为6,000吨/年和3,200吨/年。小冰期50 ~ 25 cm（1770 ~ 1890年），L. Nakaumi沉积物TOC含量低约1%，30 ~ 20cm（1830 ~ 1890年），L. Shinji沉积物TOC含量低约0.7%，ocar值分别为2000和1300 tonC/y。这些在凉爽气候下的低值约为目前潜能值的三分之一。这些微咸湖泊的特点是对气候变化的快速反应碳汇。少

Carbon sink potential of eutrophic lake sediments from lakes Nakaumi and Shinji was studied for recent and several hundred years environments using surface sediments and sediment cores.TOC (total organic carbon) contents of southern and central L. Nakaumi showed high sapropelic about 3.6~4.0% in the 1cm surface sediments. These values are constant from AD1997. TOC contents of all samples from L. Shinji showed also sapropelic and high about 3.5~4.3% except for eastern part. These TOC values in L. Shinji are not changed during the last 5 years. According to the result of C/N ratio (7-9) and py-GC-MS, origin of organic matter in both lakes is supposed to be predominant phyto-plankton. Sediment cores showed low TOC contents about 1% between AD1800 and 1900 in both L. Nakaumi and Shinji and TOC contents drastically increased from 1% to 4% after AD1900. Analysis of AD2003 data by our preliminary research indicates that TOC contents over 3.5% of surface sediments have a good positive correlat … More ion with H2S (ppm), showing an equation: H2S (ppm) = 13.9 * TOC (%) - 52.1 (TOC>3.5%). Atmospheric CO2 concentration on the northeastern Nakaumi was low about 360 ppm in average (April to May, 2013), which could depend on spring blooming of phyto-plankton. Impressive difference of the CO2 concentration between daytime and nighttime was up to 80 ppm. Average OCARs in the surface sediments of L. Nakaumi and Shinji are 7.0 mgC/cm2/y and 4.0 mgC/cm2/y，respectively based on the sedimentation rate reported by Kanai et al., (1998, 2002). As a result, L. Nakaumi and Shinji have a potential carbon sink of about 6,000 tonC/y and 3,200 tonC/y, respectively. Low OCARs of the cored sediments with low TOC about 1% in L. Nakaumi during 50-25 cm (1770-1890) and TOC about 0.7% in L. Shinji during 30-20cm (1830-1890), i.e. Little Ice Age, suggested 2,000 tonC/y and 1,300 tonC/y, respectively. These low values during cool climate are about one - third of the present potential. These brackish lakes are characterized as a quick response carbon sink for climate change. Less