Effect of the in-stream processes on spatial distribution of stream nitrate concentration in the meso-scale headwater catchment
Abstract
The spatial distributions of major ion concentrations of streamwater have been investigated in the meso-scale headwater catchment in the mountainous area of central Japan since 2001. The observed results showed that the spatial variability of specific discharge and solute concentrations increases with decrease of stream order and sub-catchment area, and there is a certain catchment scale where the variability become minimum. In a case of the forested catchment called Fudoji located in the central Japan, the catchment scale where the variability became minimum was ~100 ha for the conservative solute such as SiO2, Na+, and Cl- . On the other hand, although the variability of stream NO3- concentration was largest at the most upstream headwaters, the variability became minimum at the upper point of the stream than that of the conservative solute did. The converged concentration for NO3- was nearly zero, while that for the conservative solutes were in-between maximum and minimum concentration. Moreover, there was a remarkable difference in the seasonal variations of stream NO3- concentration between upstream and down stream portion. The NO3- concentration in the downstream part had clear bimodal seasonal variation with peaks in February-March and August-September, while that in upstream part had circannian seasonal variations reaching highest in summer to early fall. These two facts suggest that the NO3- in stream water removed by some in-stream biogeochemical reaction. It can be hypothesized that the biological uptake including utilization by benthic algae and/or denitrification in hyporheic zone acted to remove the stream NO3- in the early summer (late April to July). This bimodal seasonal variation of the stream NO3- concentration was significant in the 4 th and higher order streams, and its catchment area was more than 100 ha. This indicated that the 4 th order stream or 100 ha can be the critical scale for this catchment at which the controlling factor of the seasonal pattern changed from the hillslope hydrology and biogeochemistry to the in-stream biological reaction.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2006
- Bibcode:
- 2006AGUSM.H42A..03O
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0793;
- 1615;
- 4805;
- 4912);
- 1804 Catchment;
- 1813 Eco-hydrology;
- 1845 Limnology (0458;
- 4239;
- 4942);
- 1860 Streamflow