Abstract
Six-year (2005–2010) evolution of water chemistry (Cl−, NO3 −, SO4 2−, HCO3 −, Na+, K+, Ca2+ and Mg2+) and their interactions with morphological properties (i.e., slope and area), land cover, and hydrological seasonality were examined to identify controlling factors and processes governing patterns of stream water quality in the upper Han River, China. Correlation analysis and stepwise multiple regression models revealed significant correlations between ions (i.e., Cl−, SO4 2−, Na+ and K+) and land cover (i.e., vegetation and bare land) over the entire catchment in both high- and low-flow periods, and in the buffer zone the correlation was much more stronger in the low-flow period. Catchment with steeper slope (>15°) was negatively correlated with major ions, largely due to multicollinearity of basin characteristics. Land cover within the buffer zone explained slightly less of major elements than at catchment scale in the rainy season, whereas in the dry season, land cover along the river networks in particular this within 100 m riparian zone much better explained major elements rather than this over the entire catchment. Anthropogenic land uses (i.e., urban and agriculture) however could not explain water chemical variables, albeit EC, TDS, anthropogenic markers (Cl−, NO3 −, SO4 2), Na+, K+ and Ca2+ significantly increased during 2005–2010, which was corroborated by principal component analyses (PCA) that indicated anthropogenic inputs. Observations demonstrated much higher solute concentrations in the industrial-polluted river. Our results suggested that seasonal evolution of water quality in combined with spatial analysis at multiple scales should be a vital part of identifying the controls on spatio-temporal patterns of water quality.
Highlights
The geochemical study of water major ions reveals the character of water-rock interactions and other various natural and anthropogenic processes in the drainage basin and plays an important role in understanding stream mineralogy/petrology, as well as chemical weathering rates and associating CO2 consumption, which are greatly affected by meteoric water and land coverage [1,2,3,4,5,6]
Our results demonstrated that similar variables in the rainy season and more variables in the dry season could be predictable by landscape setting within varied buffer zone (Tables 5 and 6), indicating the interactive influence of hydrological routing/landscape overriding land cover [13],[15]
Our results demonstrated that the Pearson R/adjusted R2 decreased as the width of buffer zone increases from 100 m to 500 m (Tables 2, 3, 5 and 6) [23], indicating that the 100 m riparian zone could effectively explain major elements in the Han River
Summary
The geochemical study of water major ions reveals the character of water-rock interactions and other various natural (i.e., evaporation and precipitation) and anthropogenic processes in the drainage basin and plays an important role in understanding stream mineralogy/petrology, as well as chemical weathering rates and associating CO2 consumption, which are greatly affected by meteoric water and land coverage [1,2,3,4,5,6]. Numerous studies have related landscape to water quality especially nutrients using empirical techniques such as correlation analysis and stepwise multiple linear regression models [7], [12,13,14,15], and indicated that basin physical characteristics such as land use types, morphological characteristics and local geology substantially influence the hydrology and water variables, and mediate fluvial chemical compositions [10], [16], [17] Their relative impacts on water chemistry depend on geographical scale (e.g., local, regional, national, continental and global) and sampling factors (e.g., random versus geostatistical; high versus low density). The relative influences of land cover in catchment vs riparian zone and diverse riparian land cover on water quality are mixed (cf. [10], [13], [14])
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