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| Titel |
Is headwater chemistry predictable from downstream observations? |
| VerfasserIn |
J. Temnerud, J. Fölster, I. Buffam, H. Laudon, M. Erlandsson, K. Bishop |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023371
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| Zusammenfassung |
| The length of all perennial streams in Sweden is estimated at 530 000 km, with 78% of the
stream length having catchment areas under 2 km2. There is an interest in assessing the
quality and sensitivity of these headwaters, but small streams (catchment size < 2 km2)
usually have larger chemical and hydrological variation than larger streams. This study tests
the hypothesis that downstream monitoring data can be used to predict the distribution of
chemistry in headwaters.
Data from 17 Swedish synoptic catchment surveys was used, covering 4 degrees of
latitude. Samples were taken between 2000 and 2008, at different times of the year including
all seasons and one snow melt episode. The median size of the catchments at the outlets was
72 km2 (range 36-127 km2), and the median number of headwater streams surveyed in each
catchment was 28 (range 14-55), with an average catchment size of 0.57 km2 (range 0.03-2
km2). All catchments consist mainly of forest (>80%), with forest mostly coniferous
dominated by Norway spruce (Picea abies). Mires and small lakes make up most of the
remaining parts of the catchments, which have only minimal developed or agricultural areas.
The water chemistry parameters analysed were pH, total organic carbon (TOC) and acid
neutralizing capacity (ANC).
Correlations between the outlets and their headwaters were evaluated, both for the median
chemistry and the variability, here expressed as the interquartile range (IQR = 75th-percentile
minus 25th-percentile). The highest correlation between the outlet and headwaters was found
for ANC (r2 = 0.94 for the median and r2 = 0.75 for the IQR, both p < 0.001),
followed by TOC (r2 = 0.43, p < 0.05, and r2 = 0.15, p = 0.07, respectively). Using
all pH data no significant correlations were observed. Omitting the spring flood
synoptic data from the evaluation the biologically important pH had a similarly strong
correlation between outlet pH and median headwater pH (r2 = 0.60, p < 0.001) but still
no correlation with IQR. All correlations were positive, i.e. higher values at the
outlet were associated both with higher median values as well as higher variability
(IQR).
There was also a pattern of changing chemistry with distance downstream in most
catchments. Median TOC was higher in headwaters than at the outlets, while ANC and pH
were lower in headwaters, compared to the outlets. The proportionality between headwaters
and outlet was such that the headwater median was 59% of the outlet ANC, 89% of outlet pH
and 134% of the outlet TOC.
These preliminary results suggest that downstream chemistry will provide a
valuable tool in characterizing the range of chemistry experienced in the headwater
streams which make up the bulk of any stream network. Current lines of research
include further evaluating whether GIS information on amount of lakes, mires etc. in
these systems could improve the prediction of headwater chemistry parameters, and
make it possible to advance from describing the distribution to assessing specific
streams. |
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