Evaluation of nutrient impact from river to coastal biogeochemical systems as an aspect from material transport processes

我们在北海道、本州中部和四国地区的几个地点调查了河流径流的生物地球化学作用，并评估了这些河流水对处理海洋碳循环的沿海生物生产的贡献。通过对德胜河、阿部河、新堂河和岛曼托河的地球化学观测，包括营养物和同位素分析，我们发现了以下结果：(1) Tokachi河对DIN和DIP的养分负荷分别为1.3 mol/m^2/yr和0.009 mol/m^2/yr。(2)这些营养物的光合作用速率可达8.4 molC/m^2/yr，其N/P和Si/N比值可能有利于硅藻的生产。(3)强降水的零星事件对氮的影响较大，可能相当于年平均输送通量的8%。(4)融雪季节的河流排放可提供沿海生物生产所需养分的30 ~ 40%，而颗粒有机碳的固碳量不到1 / 10，PON氮的固氮量不到1 / 2。(5)静冈县一级河流氮含量相对较低，范围为27 ~ 98 μM，而二级河流氮含量较高，范围为82 ~ 504 mM，且差异较大。磷、硅酸盐浓度分别在0.21 ~ 9.2 μM和109 ~ 413 μM之间，反映了流域面积、土地利用方式和文明程度等当地环境条件的差异。

We have investigated biogeochemical role of river runoff at several locations in Hokkaido, Central Honshu and Shikoku districts and have evaluated the contribution of these river water for the coastal biological production that is dealing with the marine carbon cycling. Based on geochemical observations including nutrient and isotopic analyses at Tokachi river, Abe river, Niyodo river, and Shimanto river, we found following results. (1) Nutrient loadings from Tokachi river were estimated as 1.3 and 0.009 mol/m^2/yr for DIN, and DIP, respectively. (2) These nutrient discharge can have dealings with 8.4 molC/m^2/yr as photosynthesis and may benefit for diatom production by their N/P and Si/N ratios. (3) Sporadic events with heavy precipitation can supply large effect mainly for nitrogen which provides potentially corresponding to 8% DIN supply of mean annual transport flux. (4) River discharge in the snow melting season would supply 30 to 40% of nutrient needed for coastal biological production, on the other hand particulate organic carbon make for less than one tenth of carbon fixation and less than a half of PON nitrogen. (5) The first class rivers in Shizuoka prefecture tend to have relatively lower nitrogen content ranging from 27 to 98 μM, but those in the second class rivers showed higher concentrations ranging from 82 to 504 mM and even wide variations. The phosphate and silicate concentrations are ranging from 0.21 to 9.2 μM and from 109 to 413 μM, respectively, reflecting difference of local environmental conditions such as water shed area, land utilization pattern and degree of civilizations.