Catchment topography and distribution of electron donors for denitrification control stream NO3- concentration in the Lake Hachiro watershed, Akita, Japan
Abstract
Topography and distribution of electron donors for denitrification in a catchment can control stream NO3- concentration. We examined the linkages between topography, distribution of electron donors and the importance of denitrification as a nitrate removal mechanism in headwater streams in the Lake Hachiro watershed (LHW) at Akita prefecture, Japan. Study sites are 35 headwater streams (0.07-16.9 km2) in the LHW. Streamwater in each catchment was sampled nine times for two years. Stream sediments which can represent a surface soil and geology in a catchment were collected from a top 5 cm of a streambed for a measurement of denitrification potential (DP) and electron donors (water soluble organic carbon, WESOC; easily oxidizable sulfide, EOS). Dissolved nitrous oxide (dN2O) concentration in streamwater was also measured. Topographic index (TI) in each catchment was calculated using 10 m-grid digital elevation model using GIS. Stream NO3- concentrations among catchments had a large spatial variability ranging from 0.06 to 0.52 mg N L-1 and were negatively correlated with TI significantly (r = 0.56, p < 0.01, n = 35), indicated NO3- was removed in a gentle-slope catchment. Sediment DP and dN2O concentration were positively correlated with TI, supporting that denitrification was a dominant mechanism of NO3- removal in such catchments. The WSOC content in the sediment, the primary predictor of denitrification rates, increased with TI and affected sediment DP, significantly. Stream NO3- concentrations tended to decrease with increasing of stream SO42- concentrations and log(EOS) contents in the sediments, indicating sulfur denitrification could occur in the catchments, although the distribution of log(EOS) was independent of TI. Multiple regression analysis showed TI, sediment DP, and log(EOS) content in the sediment affected concentration of stream NO3- significantly. This study demonstrated that catchment's topography and distribution of electron donors evaluated from river sediments affected catchment's denitrification, resulting in variation of stream NO3- concentration.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.B43F0466H
- Keywords:
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- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0448 BIOGEOSCIENCES / Geomicrobiology;
- 0469 BIOGEOSCIENCES / Nitrogen cycling;
- 0488 BIOGEOSCIENCES / Sulfur cycling