Abstract
Understanding hydrological processes controlling stream chemistry and quantifying solute concentrations over time is crucial for estimating future alterations of water quality due to land use or climate change impacts, as well as for setting preventive or remedial actions. In the current study, soluble sodium (Na+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+) concentrations and loads were assessed in waters from two small catchments located at different distances to the sea (9 km Valiñas and 30 km Abelar) in NW Spain from 2003 to 2016. Solute concentrations were determined using spectrometric techniques, while streamflow data were employed for estimating loads. Moreover, concentration-discharge relations were calculated for each solute and catchment. The average concentrations of soluble Na+, K+, Ca2+ and Mg2+ were, respectively, 16.5, 2.6, 7.9 and 4.1 mg L−1 in Valiñas, and 8.2, 0.9, 2.9 and 3.4 mg L−1 in Abelar, although variability among samplings was high. The four soluble ions showed a dilution pattern in Valiñas, whereas in Abelar Na+ tended to a chemostatic behavior and K+ and Ca2+ were positively related to streamflow. In conclusion, the dominant processes controlling these relationships are local and depend on catchment characteristics such as land use (including slurry applications in Abelar), distance to the sea, and vegetation cover.
Highlights
Peri-urban catchments are characterized by a wide range of land uses, including agriculture, forestry and recreation, that impact on water quality [1,2]
Rock weathering and solute transport are linked to hydrology in watersheds and this coupling is reflected in the relationships between stream discharge and solute concentrations [8]
According to the criteria proposed by Herdon et al [44], limiting chemostatic behavior as −0.1 < b < 0, the C-Q curves observed in the current study indicated that the concentrations of Na+, Mg2+ and Ca2+ in Abelar followed a chemostatic behavior, which is usually attributed to homogeneous and uniform distribution of elements in a given catchment or, alternatively, to temporal stability of flow paths [3,8,43]
Summary
Peri-urban catchments are characterized by a wide range of land uses, including agriculture, forestry and recreation, that impact on water quality [1,2]. Solute concentrations in water depend on catchment characteristics such as climatology, topography, land use, size and bedrock nature [3,4]. In this context, understanding the hydrological processes that control stream chemistry, as well as the sources of chemical inputs, is highly relevant for estimating how changing climate and future land use may affect the chemistry of water bodies [5]. The three main behaviors–enrichment or removal (i.e. positive slope), chemostatic (i.e. near-zero slope) and dilution (i.e. negative slope)–can be the consequence of mechanisms controlling the runoff formation and the transport processes [4,11]
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