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| Titel |
Nitrogen concentrations in a small Mediterranean stream: 1. Nitrate 2. Ammonium |
| VerfasserIn |
A. Butturini, F. Sabater |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 6, no. 3 ; Nr. 6, no. 3, S.539-550 |
| Datensatznummer |
250003570
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| Publikation (Nr.) |
 copernicus.org/hess-6-539-2002.pdf |
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| Zusammenfassung |
| The
importance of storm frequency as well as the groundwater and hyporheic inputs on
nitrate (NO3-N) and ammonium (NH4-N) levels in stream
water were studied in a small perennial Mediterranean catchment, Riera Major, in
northeast Spain. NO3-N concentrations ranged from 0.15 to 1.9 mg l-1.
Discharge explained 47% of the annual NO3-N concentration variance,
but this percentage increased to 97% when single floods were analysed. The rate
of change in nitrate concentration with respect to flow, ΔNO3-N/ΔQ,
ranged widely from 0 to 20 μg NO3-N s l-2. The
ΔNO3-N/ΔQ
values fitted to a non linear model with respect to the storm flow magnitude
(ΔQ) (r2=0.48, d.f.=22, P<0.01). High
values of ΔNO3-N/ΔQ occurred at intermediate
ΔQ values, whereas low ΔNO3-N/ΔQ
values occurred during severe storms (ΔQ > 400 l s-1).
N3-N concentrations exhibit
anticlockwise hysteresis patterns with changing flow and the patterns observed
for autumnal and winter storms indicated that groundwater was the main N3-N
source for stream and hyporheic water. At baseflow, NO3-N
concentration in groundwater was higher (t=4.75, d.f.=29, P>0.001) and
co-varied with concentrations in the stream (r=0.91, d.f.=28, P<0.001). In
contrast, NO3-N concentration in hyporheic water was identical to
that in stream water. The role of the hyporheic zone as source or sink for
ammonium was studied hyporheic was studied comparing its concentrations in
stream and hyporheic zone before and after a major storm occurred in October
1994 that removed particulate organic matter stored in sediments. Results showed
high ammonium concentrations (75±28 s.d. μg NH4-N l-1)
before the storm flow in the hyporheic zone. After the storm, the ammonium
concentration in the hyporheic dropped by 80%
(13.6±8 μg N4-N l-1)
and approached to the level found in stream water
(11±8 μg NH4-N l-1)
indicating that indisturbed hyporheic sediments act as a source for ammonium.
After the storm, the ammonium concentrations in the stream, hyporheic and
groundwater zones were very similar suggesting that stream ammonium
concentrations are sustained mainly by input from groundwater. The present study
provides evidence that storm flow magnitude is an important source of
variability of nitrate concentration and fluxes in Mediterranean streams
subjected to an irregular precipitation regime with prolonged dry periods. |
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