%0 Journal Article
%A Rode, Michael
%A Halbedel née Angelstein, Susanne
%A Anis, Muhammad Rehan
%A Borchardt, Dietrich
%A Weitere, Markus
%D 2016
%T Continuous
In-Stream Assimilatory Nitrate Uptake from
High-Frequency Sensor Measurements
%U https://acs.figshare.com/articles/journal_contribution/Continuous_In-Stream_Assimilatory_Nitrate_Uptake_from_High-Frequency_Sensor_Measurements/3395251
%R 10.1021/acs.est.6b00943.s001
%2 https://acs.figshare.com/ndownloader/files/5304670
%K assimilatory
%K r 2
%K GPP
%K multiparameter sensor measurements
%K stream network
%K Nitrate uptake velocities
%K mg
%K 15 min data
%X Recently
developed in situ NO3– sensors provide new opportunities
to measure changes in stream concentration at high temporal frequencies
that historically have not been feasible. In this study, we used multiparameter
sensor measurements to relate assimilatory NO3– uptake to metabolic
rates and calculate continuous uptake rates for two stream reaches
and a whole stream network. Two years of continuous 15 min data from
a forest and agricultural reach of the Selke river (456 km2) revealed a strong correlation between assimilatory NO3– uptake
and growth primary production (GPP) for the forest (r2 = 0.72) and agricultural (r2 = 0.56) stream reach. The slopes of these regressions were in agreement
with predicted assimilatory N-uptake based on additional metabolic
data. Mean yearly assimilatory NO3– uptake rates (Ua) were
7.4 times higher in the agricultural stream reach (mean 78.3 mg N
m–2 d–1, max 270 mg N m–2 d–1) than in the forest stream reach (mean 10.7
mg N m–2 d–1, max 97.5 mg N m–2 d–1). Nitrate uptake velocities
(Vf,a) tended to decrease with increasing
nitrate concentrations for periods with high light availability. Percentage
daily assimilatory NO3– uptake peaked at 47.4% of the daily
NO3– loading input to the stream network across the entire watershed,
whereas the percentage yearly assimilatory NO3– uptake was 9.0% of nitrogen
loading to the stream network. This is a maximum because uptake can
be revered by mineralization processes. The percentage yearly assimilatory
NO3– uptake was lower in the forest-dominated upstream subwatershed (4.8%)
than in the lower agriculture dominated subwatershed (13.4%).
%I ACS Publications