Study on structure of environmental problems in an inner bay from viewpoint of long-term change of watershed, estuary and ocean. -Arase study in Hamana Lake

(i)通过柑橘园区的河水中观察到高浓度的氮和磷。随着施肥量的增加，土壤中磷、铵含量有增加的趋势。磷负荷，特别是颗粒态磷，随降雨量的增加而增加。年养分负荷估计。(ii)伊诺哈纳湖和滨名湖之间的水交换取决于风力。河道水流和磷的垂向分布都具有明显的双层结构，有利于水和物质（养分）的交换。通过建立箱形模型，定量地讨论了沃茨和磷的流动和收支。(iii)根据50年的长期观测数据和模拟结果，提出了富营养化和缺氧发生的几种原因。在1980年以前，码头的建设使水交换更好，因此水质得到改善。然而，自1980年以来，水质一直在恶化。这项研究表明，其中一个原因是水温升高。(iv)A采用自适应网格加密方法建立了数值模拟方法，并将其应用于滨名湖浅水区。验证了该方法的有效性。(v)对猪花湖和滨名湖周边柑橘园施肥后养分负荷的长期变化进行了估算。自20世纪70年代中期以来，由于猪花湖周围施肥量的减少和滨名湖周围果园面积的减少，氮负荷一直在下降。(vi)自1993年以来，在滨名湖北方地区经常观察到蛤苗。这被认为是由于建造内码头增加了水交换率。它还导致了食用蛤类贝类的增加

(i) High nitrogen and phosphate concentrations were observed in the river water through the citrus orchard area. The phosphate and ammonium concentrations have increasing trends with the application of fertilizer. The phosphorus loads, especially particulate phosphorus, increase with rain. Annual nutrient loads are estimated.(ii) Water exchange between Inohana and Hamana Lakes is dependent upon wind forcing. Both of the flow in the channel and vertical distribution of phosphorus have distinct two-layer structures, which contribute to the exchanges of water and material(nutrient)strongly. By developing a box model, the flows and budgets of waters and phosphorus are quantitatively discussed.(iii) From the long-term field data for 50 years and simulation results, several causes of entrophication and hypoxia occurrances were suggested. Prior to 1980, jetties construction made the water exchange better, as a result the water quality was improved. However, the water quality has been worse since 1980. This study suggests that one of the cause for it is the increase in water temperature.(iv)A numerical simulation method was developed using the adaptive mesh refinement method and applied to the shallow water region in Hamana Lake. The effectiveness of the method was confirmed.(v) Long-term changes of nutrient loads from the fertilization in citrus orchards around Inohana and Hamana lakes were estimated. Since mid-1970s, nitrogen load has been decreasing due to decrease in fertilization quantity around Inohana Lake and due to decrease in area of orchard around Hamana Lake.(vi) Since 1993, the clam spat has been frequently observed in northern area of Hamana Lake. This is considered due to increase in water exchange rate by constructing the inner jetties. It also induced increase of clam-eating shellfish