Lake budgetary study on nutrients in water and sediment : Long-term change in sediment nutrients, nutrient budget, and modeling of sediments

水质没有改善，在日本的许多湖泊，无论明显的流入负荷减少，因此，沉积物-水交换的营养物质被怀疑是原因，但其对湖泊营养动态的长期影响还没有澄清。2005-2007年，在霞浦湖、Suwa湖、Kizaki湖和Shinji湖多次采集沉积物柱状样，测定了营养盐（P、N、C）、多环芳烃（PAHs）、Pb-210_ex、Cs-137等的垂直剖面，估算了几十年来物质沉积速率和营养盐积累的变化，并计算了营养盐收支.入湖河口处的沉积速率较高，在强降雨过程中沉积速率出现多个峰值.在霞浦湖，沉积物中几种TP含量的释放可以解释实验室估算的TP释放速率和夏季湖水TP浓度的增加;沉积物TP浓度在河口附近观察到降低，但在湖中心没有观察到，可能是由于再沉积.苏瓦湖沉积物中TP含量明显降低，这几乎可以解释夏季湖水TP含量增加的原因.如果能够准确估算沉积面积，20多年来沉积物中TP的累积量几乎相当于霞浦湖和须和湖TP收支的残差之和。2003年和2007年TP垂直剖面的差异高估了营养盐沉积速率，可能是由于沉积物测年分辨率较低.多环芳烃的垂直剖面也被确定为沉积物中讨论的长期变化，他们的变化与流域发展。从沉积物物理性质变化的角度分析了霞浦湖最近浊度的增加。

Water quality has not improved in many lakes in Japan, regardless of the apparent inflow load reduction; thus, sediment-water exchange of nutrients was suspected to be the reason, but its long-term influence on lake nutrient dynamics has not clarified. Sediment cores were taken in Lakes Kasumigaura, Suwa, Kizaki and Shinji several times during 2005-2007; then, vertical profiles of nutrients (P, N, C), PAHs, Pb-210_ex, Cs-137, etc. were determined to estimate the changes in mass sedimentation rates and nutrient accumulation during several decades and nutrient budget was calculated.1. Mass sedimentation rates were higher at inflow river mouths in the lakes and several peaks of sedimentation rates were observed during heavy rainfall events.2. In Lake Kasumigaura, release of several of TP contents in sediments could account for TP release rates estimated by laboratory experiment and increase of lake water TP concentration in summer; the decrease in sediment TP concentration was observed near river mouth, but not observed at the center of the lake, probably due to redeposit.3. Apparent decrease of TP contents in sediments, which could nearly account for the increase in lake water TP during summer, was observed in Lake Suwa.4. The TP accumulation in sediments for more than 20 years corresponded nearly to the sum residuals of TP budget in Lakes Kasumigaura and Suwa if we could estimate the accurate depositional area. Nutrient sedimentation rates were overestimated for the difference in TP vertical profiles between 2003 and 2007, probably due to low resolution of sediment dating.5. PAHs vertical profiles were also determined for the sediments to discuss the long-them change in change in relation to watershed development. The recent increase in turbidity in Lake Kasumigaura was analyzed from the view of the change in physical properties of sediments.