Pore Water Concentrations of Nitrogen From N-Addition Plots in an Alberta Peatland, 2011-2015

Development of the oil sands has led to increasing atmospheric N
deposition, with values as high as 17 kg N
ha -1 yr -1 ;
regional background levels <2 kg N ha -1 yr -1 . Bogs, being ombrotrophic, may be
especially susceptible to increasing N deposition. To examine
responses to N deposition, over five years, we experimentally applied
N (as NH 4 NO 3 ) to a bog
near Mariana Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N
ha -1 yr -1 , plus
controls (no water or N addition). We collected surface pore water
from all plots several times a year throughout the 5 year experiment.
Porewater NH 4 + -N,
NO 3 - -N, and DON
concentrations were unaffected by N input in any of the five years
(rmANOVA; p = 0.44, 0.37, and 0.82, respectively). We hypothesized
that as N deposition increases to a level that exceeds the capacity of
the bog vegetation to take up N, net N mineralization in surface peat
would be inhibited by higher
NH 4 + -N availability,
net nitrification would be stimulated by higher
NH 4 + -N availability,
and concentrations of DIN in porewater at the top of the water table
would increase, as DIN bypasses interception by the ground layer
vegetation. None of these hypotheses was supported with nitrogen being
immediately taken up by vegetation. It is unclear if longer term study
would reveal similar responses.

油砂（oil sands）开发导致大气氮沉降持续升高，最高值可达17 kg N ha⁻¹ yr⁻¹；区域背景氮沉降水平则低于2 kg N ha⁻¹ yr⁻¹。
雨养型泥炭沼泽（ombrotrophic bog）作为仅依赖大气降水获取养分的湿地生态系统，对氮沉降增加的敏感性尤为突出。
为探究沼泽生态系统对氮沉降的响应，我们在为期5年的实验中，向加拿大阿尔伯塔省马里亚纳湖附近的一处泥炭沼泽施加硝酸铵（NH₄NO₃）溶液，施氮梯度设置为0、5、10、15、20、25 kg N ha⁻¹ yr⁻¹，另设对照组（不添加水与氮素）。
在整个5年实验周期内，我们每年多次采集所有样地的地表孔隙水。
经重复测量方差分析（rmANOVA）检验，5年间各处理组的孔隙水铵态氮（NH₄⁺-N）、硝态氮（NO₃⁻-N）与溶解有机氮（Dissolved Organic Nitrogen, DON）浓度均未受到施氮输入的显著影响（对应p值分别为0.44、0.37和0.82）。
我们曾提出如下假说：当氮沉降水平超过沼泽植被的氮吸收容量时，表层泥炭的净氮矿化作用会因更高的铵态氮有效性受到抑制，净硝化作用会因铵态氮水平升高得到促进，同时由于溶解态无机氮（Dissolved Inorganic Nitrogen, DIN）绕过地表植被的截留作用，地下水位表层的孔隙水中溶解态无机氮浓度将出现上升。
但所有假说均未得到实验支持，植被可直接快速吸收施加的氮素。
目前尚不清楚延长实验周期是否会观测到相似的响应结果。