 |
| Titel |
Numerical modeling of the nitrogen retention and turnover at the surface-subsurface interface of riffle-pool sequences |
| VerfasserIn |
T. Kebede Gurmessa, D. Borchardt, M. Rode |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250021458
|
|
|
|
|
|
| Zusammenfassung |
| Quantification of the retention and turnover of constituents in the hyporheic zone of rivers
and streams is very challenging as a result of complex physical and biogeochemical
processes. There is a tremendous potential of using processes based numerical models to
advance our understanding of hyporheic processes. The presentation aims at the calibration
and validation procedure for the NH4 and NO3 profiles at various section of a reach and
specification of parameters of major significance among large number of parameters involved
in the modeling procedure. A case study was conducted on a riffle-pool sequence
of the river Lahn, Germany. Using the hydrodynamic TELEMAC2D model, the
surface water profile was calibrated. The groundwater flow model, MODFLOW
with its reaction module RT3D, was used for the analysis in the subsurface. The
first order reaction module was coded for NH4-NO3-N2 conversion process. The
water surface elevation data from the hydrodynamic model is integrated into the
subsurface flow and reactive transport model. The measured concentration profile (over
depth), at various points of River Lahn were calibrated and parameter sensitivity
analysis were performed. The model is found to be highly sensitive to hydraulic
conductivity, reaction parameters, specific storage, and longitudinal dispersivity;
moderately sensitive to conductance; and slightly sensitive to specific yield and
molecular dispersion coefficient. It was found that the beginning of the riffle is the
location of the highest concentration gradient. The locations of highest hydraulic
gradient as a result of morphological change (riffle), is the location of the highest
water exchange and nitrogen transformation. In spite of uncertainties involved in the
process-based models (data, parameters, and model structure) valuable conclusions can
be made towards focused theoretical and experimental studies for new process
understating. There is a need to improve the process based numerical models in a more
sophisticated manner by stronger coupling of the surface and subsurface process,
with due consideration the difficulties in data acquisition and parameter estimation. |
|
|
|
|
|
|