科研之友
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摘要
Human activities have increased the availability and distribution of dissolved inorganic N (DIN) in the biosphere. Streams can remove some of this excess DIN, but in-stream uptake pathways of NO3- and NH4+ can be sensitive to the concentration of DIN. DIN uptake kinetics (i.e., changes in uptake in response to changes in concentration) are used to predict how streams will respond to increased DIN. This concentration-uptake relationship is unclear for NH4+ because of complex interactions governing uptake, including the influence of dissimilatory processes (i.e., nitrification) on total uptake. We used sequential pulse additions of NO3- and NH4+ to investigate DIN uptake in 3 subalpine streams in Rocky Mountain National Park, Colorado, USA. Mass removal rates (U; mu g m(-2) min(-1)) of NO3- were higher than NH4+, but NH4+ had greater uptake rate relative to concentration (vf; mm/ min). We used a new method of estimating nitrification that accounts for concomitant NH4+ uptake and found that 7 to 19% of the NH4+ added was nitrified immediately. We used the Tracer Additions for Spiraling Curve Characterization (TASCC) method to quantify ambient spiraling parameters and to parameterize kinetic models for NH4+ by following changes in whole-reach uptake in response to short-term NH4+ additions. Relationships between NH4+ concentration and v(f) were consistent within, but not among, streams. The relationship between v(f) and NH4+ concentration followed an efficiency-loss model for 2 streams, in which vf decreased exponentially with NH4+ concentration. v(f) increased with NH4+ concentration in 1 stream on 2 separate occasions. Different NH4+ uptake kinetics across streams indicate site-specific variation in processes controlling uptake and that some streams may accommodate increasing NH4+ concentrations by increasing uptake.
- 出版日期2017-3
