Document Detail

Seasonal changes in the character and nitrogen content of dissolved organic matter in an alpine/subalpine headwater catchment.
MedLine Citation:
PMID:  12805880     Owner:  NLM     Status:  MEDLINE    
We are studying the chemical quality of dissolved organic nitrogen (DON) in a high-elevation watershed in the Colorado Front Range. Samples were collected over the 2000 snowmelt runoff season at two sites across an alpine/subalpine ecotone to understand how the transition between the lightly vegetated alpine and forested reaches of the catchment influences the chemical character of DON. Samples were analyzed approximately weekly for dissolved organic material (DOM) content and chemical character. A subset of samples was analyzed for the elemental content of fulvic and hydrophilic acids. Concentrations of DON at both sites were highest in the spring at the initiation of snowmelt, decreased during snowmelt, and increased again during the late summer and fall. In contrast, concentrations of dissolved organic carbon (DOC) peaked on the ascending limb of the hydrograph and declined to seasonal minima on the descending limb of the hydrograph. The ratio of DOC:DON showed a seasonal shift at both sites with high values (40 to 55) during peak runoff in early summer and lower values (15 to 25) during low flows late in the runoff season. These results indicate that there was a seasonal change in the relative N content of DOM at both sites. Chemical fractionation of DOC showed that there were temporal and longitudinal changes in the chemical character of DOC. At the alpine site, the fulvic acid content of DOC decreased from 57% in June to 35% in September. The change in fulvic acid was less pronounced at the forested site, from 66% in June to 54% in September. Elemental analysis of fulvic and hydrophilic acids indicated that hydrophilic acids were N rich compared to fulvic acids. Additionally, fulvic and hydrophilic acids isolated at the alpine site had a lower C:N ratio than those isolated at the forested site. Similarly, the C:N ratio of organic acids at both sites was lower in September than in June during peak runoff. These differences appear to be a result of changes in both DOM precursor material and hydrologic flowpaths. Using C:N ratios of fulvic and hydrophilic acids, we estimate that nonhumic material carried between 54 to 73% of the organic N in surface water at the alpine site and 44 to 58% of the organic N in surface water at the subalpine site.
E W Hood; M W Williams
Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2001-10-30
Journal Detail:
Title:  TheScientificWorldJournal     Volume:  1 Suppl 2     ISSN:  1537-744X     ISO Abbreviation:  ScientificWorldJournal     Publication Date:  2001 Oct 
Date Detail:
Created Date:  2003-06-13     Completed Date:  2004-05-27     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  101131163     Medline TA:  ScientificWorldJournal     Country:  United States    
Other Details:
Languages:  eng     Pagination:  556-63     Citation Subset:  IM    
Departmetn of Geography and Institute for Arctic and Alpine REsearch, University of Colorado, Boulder 80309-0450, USA.
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MeSH Terms
Benzopyrans / metabolism
Carbon / metabolism
Chemical Fractionation
Environmental Monitoring / methods
Nitrogen / metabolism*
Organic Chemicals / chemistry*,  metabolism*
Soil / analysis
Water Movements
Water Supply / analysis
Reg. No./Substance:
0/Benzopyrans; 0/Organic Chemicals; 0/Soil; 479-66-3/fulvic acid; 7440-44-0/Carbon; 7727-37-9/Nitrogen

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