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| Titel |
Hydrological and erosion behaviour in two experimental agricultural watersheds in the centre of Navarra (Spain) |
| VerfasserIn |
J. Casalí, R. Gastesi, J. Álvarez-Mozos, J. Del Valle de Lersundi, R. Giménez, J. Díez, M. Goñi, U. Agirre, M. A. Campo, J. J. López |
| 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 |
250026111
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| Zusammenfassung |
| Two experimental watersheds, La Tejería and Latxaga, located in the central area of Navarra
and maintained by the regional government, were monitored for 12 years (1996-2008) with
the aim of assessing their hydrological and erosion behaviour, as well as the quality
of their water. In this work, an extensive and detailed analysis has been made of
these aspects on different time scales, from annual to per ten minutes, or per rain
event.
Both watersheds have a similar surface coverage (approx. 200 ha), geology, soils, climate
(a Mediterranean one with a mean annual temperature and precipitation of around 13º and
750 mm, respectively), and land use (cereal growing). However, their sediment production
records are very different. For instance, the total sediment evacuated in La Tejería ranged
between 390 Kg ha-1 (2000/01) and 5,609 Kg ha-1 (1996/97), whereas in Latxaga it only
varied between 48 Kg ha-1 (2002/03) and 1,386 Kg ha-1 (2006/07). Simulations made with
the EUROSEM model led to the assumption that this notable contrast in sediment
production was mainly due to the different general shape of the watersheds, along with
the unequal relief predominant in each of them. In another direction, the largest
amount of sediment was recorded during the winter, as, in that season, the soil is
usually bare and contains a high degree of moisture. The mean annual sediment
discharge in La Tejería was of 1,342.27±2,390.39 Kg ha-1, with 84% of the total
annual sediment being accumulated in wintertime. This figure was, again, much
more modest in Latxaga: 444.94±436.15 Kg ha-1 and 61% of the total annual
sediment.
With regard to water quality, the nitrate concentration values were also disparate in both
watersheds. In Latxaga, the nitrate concentration was of 31.22 ± 26.98 mg NO3 l-1, namely,
below human consumption tolerance and environmental values (50 mg NO3 l-1).
Conversely, in La Tejería, this concentration was notably higher, 93.89 ± 26.98 mg NO3 l-1,
thus, continuously throughout the year, exceeding the tolerance values cited. However,
the phosphate concentrations were similar in Latxaga and La Tejería: 0.236 ±
0.622 mg l-1 and 0.150 ± 0.495 mg l-1, respectively. These values are not so
high but, together with the presence of nitrogen, they could cause eutrophication
problems.
A more detailed analysis of the variations in the sediment-discharge in the time shows a
more complex dynamics, specific to each watershed, which is manifested through the
“hysteresis” phenomenon. The most frequent rain events normally presented a single peak
sediment discharge, which did not necessarily coincide with the hydrograph peak
(“clockwise” or “counter clockwise”); although double peak events (“figure of eight shape”)
have also been observed. No clear relationship between the time of year at which the event
occurred and the type of hysteresis was noted in La Tejería, but it was found in Latxaga,
where the clockwise hysteresis was predominant during the winter. On the other hand, only in
La Tejería and during the wintertime was a close relationship observed between
hydrological variables like: the present rainfall, the rainfall previous to the event
accumulated for 21 days, and the maximum flow value of the event with the total sediment
discharge.
The cross-correlation analysis showed a close correspondence between the runoff and the
previous day’s precipitation, but only during autumn and winter (r close to 0.6); this was not
so during spring and summer (r |
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