Effects of catchment and riparian landscape setting on water chemistry and seasonal evolution of water quality in the upper Han River basin, China.

Six-year (2005-2010) evolution of water chemistry (Cl(-), NO(3)(-), SO(4)(2-), HCO(3)(-), Na(+), K(+), Ca(2+) and Mg(2+)) 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(-), SO(4)(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(-), NO(3)(-), SO(4)(2)), Na(+), K(+) and Ca(2+) 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.