Enhanced hyporheic exchange flow around woody debris does not increase nitrate reduction in a sandy streambed
Enhanced hyporheic exchange flow around woody debris does not increase nitrate reduction in a sandy streambed
复制标题
DOI：
10.1007/s10533-017-0401-2
复制
发表时间：
2017-12
期刊：
影响因子：
4
通讯作者：
F. Shelley;M. Klaar;S. Krause;M. Trimmer
中科院分区：
文献类型：
--
作者：
F. Shelley;M. Klaar;S. Krause;M. Trimmer
人类活动造成的淡水氮污染是一个严重的问题。虽然河床是已知的衰减硝酸盐，它是不知道，如果大型木质残体（LWD）可以通过增强潜流交换和河床停留时间增加这种生态系统服务。一年多来，我们监测了地表水和孔隙水化学在200个点沿着一个约50米的范围内的低地桑迪流与三个天然随钻测井结构。我们直接injected 15 N-硝酸盐在108个位置内的顶部1.5米的河床定量原位反硝化，厌氧氨氧化和异化硝酸盐还原为氨，平均而言，分别贡献了85%，10%和5%的总硝酸盐还原。总硝酸盐还原活性范围为0至16 µM h− 1，在河床顶部30 cm处最高。深度，环境硝酸盐和水的停留时间解释了44%的硝酸盐还原观察到的变化，最快的速度与缓慢的流动和浅的深度。在秋季，当河流在暴涨，硝酸盐还原（原位和实验室措施）增强周围的LWD与非木本地区相比，但这是没有看到在春季和夏季。总体而言，有没有显着的影响，随钻测井对硝酸盐还原率在周围河床沉积物，但较高的孔隙水硝酸盐浓度和较短的停留时间，接近随钻测井，表明增强输送地表水进入河床下的高流量。当潜流交换太强时，由于短的流动路径和相关的高氧浓度，总体硝酸盐还原被抑制。
Anthropogenic nitrogen pollution is a critical problem in freshwaters. Although riverbeds are known to attenuate nitrate, it is not known if large woody debris (LWD) can increase this ecosystem service through enhanced hyporheic exchange and streambed residence time. Over a year, we monitored the surface water and pore water chemistry at 200 points along a ~ 50 m reach of a lowland sandy stream with three natural LWD structures. We directly injected15N-nitrate at 108 locations within the top 1.5 m of the streambed to quantify in situ denitrification, anammox and dissimilatory nitrate reduction to ammonia, which, on average, contributed 85, 10 and 5% of total nitrate reduction, respectively. Total nitrate reducing activity ranged from 0 to 16 µM h−1and was highest in the top 30 cm of the stream bed. Depth, ambient nitrate and water residence time explained 44% of the observed variation in nitrate reduction; fastest rates were associated with slow flow and shallow depths. In autumn, when the river was in spate, nitrate reduction (in situ and laboratory measures) was enhanced around the LWD compared with non-woody areas, but this was not seen in the spring and summer. Overall, there was no significant effect of LWD on nitrate reduction rates in surrounding streambed sediments, but higher pore water nitrate concentrations and shorter residence times, close to LWD, indicated enhanced delivery of surface water into the streambed under high flow. When hyporheic exchange is too strong, overall nitrate reduction is inhibited due to short flow-paths and associated high oxygen concentrations.