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Title (Primary) Continuous in-stream assimilatory nitrate uptake from high-frequency sensor measurements
Author Rode, M.; Halbedel, S.; Anis, M.R.; Borchardt, D.; Weitere, M.;
Journal Environmental Science & Technology
Year 2016
Department ASAM; FLOEK;
Volume 50
Issue 11
Language englisch;
POF III (all) T31;
UFZ wide themes RU2;
Abstract Recently developed in situ NO_3^- 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 multi-parameter sensor measurements to relate assimilatory NO_3^- 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 (45km²) revealed a strong correlation between assimilatory NO_3^- 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 NO_3^- uptake rates (Ua) were 7.4 times higher in the agricultural stream reach (mean 78.3 mgNm-2d-1, max 270 mgNm-2d-1) than in the forest stream reach (mean 10.7 mgNm-2d-1, max 97.5 mgNm-2d-1). Nitrate uptake velocities (Vf,a) tended to decrease with increasing nitrate concentrations for periods with high light availability. Percentage daily assimilatory NO_3^- uptake peaked at 47.4 % of the daily NO_3^- loading input to the stream network across the entire watershed, whereas the percentage yearly assimilatory NO_3^- uptake was 9.0% of nitrogen loading to the stream network. This a maximum because uptake can be revered by mineralization processes. The percentage yearly assimilatory NO_3^- uptake was lower in the forest dominated upstream subwatershed (4.8%) than in the lower agriculture dominated subwatershed (13.4%).
ID 17451
Persistent UFZ Identifier http://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=17451
Rode, M., Halbedel, S., Anis, M.R., Borchardt, D., Weitere, M. (2016):
Continuous in-stream assimilatory nitrate uptake from high-frequency sensor measurements
Environ. Sci. Technol. 50 (11), 5685 - 5694