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| Titel |
Scale effects of nitrate sinks and sources in stream networks |
| VerfasserIn |
Tobias Schuetz, Markus Weiler, Chantal Gascuel-Odoux |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093648
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| Publikation (Nr.) |
 EGU/EGU2014-8564.pdf |
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| Zusammenfassung |
| Increasing N-fertilizer applications in agricultural catchments are considered as one of the
major sources for dissolved nitrate-nitrogen (NO3-N) in surface water. While NO3-N
mobilization pathways depend on catchment’s pedological and hydrogeological
characteristics and its runoff generation processes, in-stream retention and removal
processes depend on local/reach-scale conditions such as weather, discharge, channel
morphology, vegetation, shading or hyporheic exchange and others. However, knowledge
is still limited to scale up locally observable retention and removal processes to
larger stream networks to understand the spatial and temporal dynamics of in-stream
NO3-N concentrations. Relevant processes to consider explicitly are the effects
of “hot spots”, dominant NO3-N sources (e.g. sub-catchments, “critical source
areas”) or specific NO3-N sinks (e.g. riparian wetlands and stream reaches with high
biogeochemical activity). We studied these processes in a 1.7 km2 agricultural headwater
catchment, where distinct locations of groundwater inflow (a dense artificial drainage
network) and a predominantly impervious streambed allowed separating mixing and
dilution processes as well as in-stream retention and removal processes. During two
summer seasons we conducted a set (25) of stream network wide (stream water
and drainage water) synoptic sampling campaigns including climate parameters,
discharge, channel geomorphology, vegetation, stream water chemistry and physical
water parameters (dissolved oxygen concentration, water temperatures, electrical
conductivity, pH). Analyzing these data sets we were able to determine a) time variant
NO3-N concentrations and loads for all sub-catchments (sources), b) time variant
in-stream removal rates for all stream reaches (sinks) and c) the hierarchical order of all
contributing NO3-N sinks and sources and their time variant influence on total
NO3-N export. Climate parameters, discharge, channel geomorphology, vegetation,
stream water chemistry and physical water parameters were then used to identify
controls of in-stream removal processes. The strongest correlations with NO3-N
in-stream removal rates were found for stream water temperatures, vegetation density
and shading. We developed a data-driven mixing-and-removal model to directly
quantify the spatial scaling effects on the reproducibility of observed in-stream NO3-N
concentration patterns. The position of the largest sinks and sources in the stream
network is the major control, due the local impacts on the relationship between
discharge, concentration and load. The upstream positions of sources control the
efficiency of downstream sinks by regulating in-stream NO3-N availability, while the
upstream positions of sinks have an impact on downstream mixing and dilution
processes. Understanding the interplay of NO3-N sinks and sources in stream networks
will contribute to a better description of NO3-N export and retention processes
even for catchments with a more diffuse occurrence of NO3-N sinks and sources. |
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