Dissimilatory nitrate reduction in the coastal area

钏路沼泽是日本最大的沼泽，1980年成为日本第一个在拉姆萨尔公约下注册的湿地。最近的报告表明，由于土地利用的变化，钏路沼泽的养分负荷增加。在Kushiro泥沼两个测点采集了深度约1.5m的土壤样品，测量了土壤中溶解无机氮（DIN、NO_3^-、NO_2^-、NH_4^+）、溶解有机碳（DOC）和各类微生物活性的垂直剖面。我们在较深的土壤中发现了NO_3^-和DOC的积累。反硝化活性在较浅的土壤中最高，随着深度的增加而急剧下降，而荧光indiacetate水解和β-葡萄糖苷酶、酸性磷酸酶和木糖糖苷酶活性在较深的土壤中较高。我们还在DOC中检测到腐殖质样物质。这些结果表明，湿地土壤中的DOC不能作为反硝化的基质，导致深层土壤的反硝化作用受到抑制。此外，由于土壤温度较低，深层的反硝化活性很低。因此，氮素对沼泽的输入导致了深层土壤中NO_3^-的大量积累。这将最终通过增加富营养化和酸化等影响改变沼泽生态系统。

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.