A semi-enclosed river-mouth bay (Kojima Bay) and the artificial lake within it (Kojima Lake) were studied to examine their nutrient storage and export processes and characteristics. The aim of this study was to perform mass balance analysis using long-term monitoring and historical accumulation data of phosphorus (P) via ²¹⁰Pb measurements of accumulated sediment. The results are then compared with data based on analysis of P concentrations in core samples to delineate input and output nutrient fluxes in a semi-enclosed bay and an artificial lake, in order to evaluate if the lake sediment is a source or sink of P during the transportation process from the river to the bay. From 1980 to 2008, total P flux into the lake is 3520 tons. The lake sediment phosphorus retention estimated by the model (383 tons) was lower than that obtained by multiplying the average total P concentration in sediment samples by the sediment accumulation rate (1288 tons), possibly indicating that recycling from sediments deposited before 1980 contributed to the recent P cycle. The implication for these data is that the severe eutrophication of the lake in the 1970s led to greatly elevated P levels. The inner artificial lake had a significant amount of trapped P, and the production of diatoms increased in response to P enrichment in lake water, an initial sign of eutrophication. The modeled annual P flux into the lake sediments decreased from ~ 15 g m⁻² yr⁻¹ (a flux into the sediment) in 1980 to negative values (a flux out of sediment) by 2008. The decreasing trend of nutrients accumulating in lake sediments suggests the lake is slowly recovering from eutrophication, especially since the 1990s.

中文翻译：

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富含养分的沉积物中的沉积物磷循环与沉积物磷库和释放的关系

对半封闭的河口湾（小岛湾）及其内的人工湖（小岛湖）进行了研究，以研究其养分储存，输出过程和特征。这项研究的目的是通过长期监测和通过²¹⁰的磷（P）的历史积累数据进行质量平衡分析沉积物的铅含量测量。然后将结果与基于核心样品中P浓度分析的数据进行比较，以描述半封闭海湾和人工湖中的输入和输出养分通量，以便评估湖底沉积物是P的源还是汇。从河流到海湾的运输过程。从1980年到2008年，流入湖泊的磷总量为3520吨。该模型估算的湖泊沉积物磷保留量（383吨）低于沉积物样品中的平均总P浓度乘以沉积物积累速率（1288吨）所获得的值，这可能表明1980年前沉积物中沉积物的再循环导致了该过程。最近的P周期。这些数据的含义是，1970年代该湖的严重富营养化导致磷水平大大升高。内部人工湖中有大量的磷被捕集，硅藻的产生响应于湖水中磷的富集而增加，这是富营养化的最初迹象。进入湖泊沉积物的模拟年P通量从〜15 g m下降1980年的⁻²  yr ^-1（流入沉积物的通量）到2008年降至负值（流出沉积物的通量）。湖泊沉积物中积累的养分减少的趋势表明湖泊正在从富营养化中缓慢恢复，尤其是自1990年代以来。