The effect of anthropogenic disturbance on the hydrochemical characteristics of riparian wetlands at the Middle Ebro River (NE Spain) |
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Authors: | Alvaro Cabezas Mercedes Garcia Belinda Gallardo Eduardo Gonzalez Maria Gonzalez-Sanchis Francisco A Comin |
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Institution: | 1.Pyrenean Institute of Ecology-Spanish Research Council, IPE-CSIC,Zaragoza,Spain |
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Abstract: | In natural systems, the chemistry of floodplain waters is a function of the source of the water, which is influenced by geomorphic
features of riparian wetlands. However, anthropogenic disturbances may alter both geomorphic features and the natural balance
of water mixing in the floodplain. The aim of this study was to classify riparian wetlands and characterize their water characteristics
in one reach of the Middle Ebro River to assess the hydrochemical functioning of the system. In order to accomplish that goal,
water samples were collected at 40 sampling sites during low-water conditions and two floods of different magnitude. Moreover,
geomorphic characteristics of riparian wetlands were also analyzed to interpret the results at broader spatio-temporal scales.
Three group of wetlands were identified using multivariate ordination: (1) major and secondary channels highly connected to
the river by surface water, containing weakly ionized water with high nitrate levels during floods; (2) secondary channels
and artificial ponds located in riparian forests near the river, most of which were affected by river seepage during the examined
events. This type of sites had high major ions concentrations and elevated spatial variability with respect to nutrient concentrations
during floods; (3) Siltated oxbow lakes, whose hydrogeochemical features seemed to be unaffected by factors related to river
fluctuations. Total dissolved solids, major ion (sulfate, chloride, sodium, calcium, magnesium, and potassium) and nutrient
(nitrate, ammonium and organic nitrogen, and phosphate) depended upon the relationships between surface and subsurface water
flows. Seasonal changes and geomorphic characterization indicated that a strong functional dependence of floodplain wetlands
close to the main river channel is established, whereas most of the floodplain area remains disconnected from river dynamics.
Moreover, the effect of nitrate-enriched agricultural runoff seems to affect water quality and hydrochemical gradients of
the system. Based on our results, we propose different types of actions for the management of the Ebro River flow to ensure
a more natural ecological functioning of its floodplains.
Handling editor: P. Viaroli |
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Keywords: | Hydrogeochemistry Floodplain Riparian wetlands Ebro Alluvial aquifer Riverscape |
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