Dissimilatory nitrate reduction in the coastal area

钏路沼泽是日本最大的沼泽，1980年是日本第一个根据《拉姆萨尔公约》登记的湿地。最近的报告表明，由于土地利用的变化，营养物负荷增加到钏路沼泽。在钏路沼泽的两个采样点采集了约1.5m深度的土壤样品，测定了溶解无机氮（DIN ; NO_3^-，NO_2^-，NH_4^+）、溶解有机碳（DOC）和各种类型的微生物活性的垂直剖面。NO_3^-和DOC在土壤深层有一定的积累。反硝化活性在较浅的土壤中最高，并随深度急剧下降，而更高水平的荧光素二乙酸酯水解和β-葡萄糖苷酶，酸性磷酸酶，木糖苷酶的酶活性被发现在较深的层。我们还检测到腐殖类物质作为DOC的组成部分。这些结果表明，DOC在湿地土壤中不能被用作反硝化的基质，导致反硝化作用被抑制在更深的土壤。此外，由于土壤温度较低，深层土壤的酸化活性很低。因此，氮输入沼泽导致NO_3^-在深层土壤中大量积累。这将最终改变沼泽生态系统的影响，如增加富营养化和酸化。

Kushiro Mire is the largest mire in Japan and in 1980 was the first wetland in Japan registered under the Ramsar Convention. Recent reports indicate an increase in nutrient loading into Kushiro Mire from changes in land use. We measured vertical profiles of dissolved inorganic nitrogen (DIN ; NO_3^-, NO_2^-, NH_4^+), dissolved organic carbon (DOC), and various types of microbial activity in soil samples collected to approximately 1.5m depth at two sites in Kushiro Mire. We found an accumulation of NO_3^- and DOC in the deeper soil. Denitrifying activity was highest in the shallower soils, and decreased drastically with depth, whereas higher levels of fluoresceindiacetate hydrolysis and β-glucosidase, acid phosphatase, and xylosidase enzyme activity were found in the deeper layers. We also detected humic-like substances as components of the DOC. These results suggest that the DOC in the wetland soil cannot be used as a substrate for denitrification, causing denitrification to be suppressed in the deeper soil. In addition, denitrifying activity would be very low in the deeper layers due to low soil temperature. As a result, nitrogen inputs to the Mire have resulted in a large accumulation of NO_3^- in the deeper soil. This will eventually change the mire ecosystem through effects such as increased eutrophication and acidification.