Small-scale chemical and isotopic variability of hydrological pathways in a mountain lake catchment.

• Catchment transforms chemical and isotopic signals of precipitation. • Water flow redistribution in weathered rocks determines elements transport. • Isotopic stratification in the lake reflected the location of the subsurface inlets. • Water transit time impact water composition of surface and subsurface flows. Understanding water flow paths and chemical inputs from the catchment to downstream water bodies is essential for determining sensitivity and response of water resources to climatic, land use and environmental changes. Multivariate analysis of hydrochemical data and estimation of water balance using chloride as a chemical tracer, and oxygen and hydrogen stable isotopes in water as physical tracers were applied to explore surface and subsurface hydrological pathways of water, organic and inorganic solutes in the unmanaged mountain catchment of Plešné Lake (Czech Republic). Nitrate 18O and 15N data were used to support hydrochemical data and hydrological pathways identification. Our results showed that even small variations of water transit time had an important influence on chemical composition in surface and subsurface flows. Water flowing through the subsurface weathered granite had mean transit time of about 11 months and a higher content of geogenic ions due to longer contact with bedrock materials. In contrast, surface flows with a transit time of about 5 months had higher concentrations of dissolved organic carbon, total phosphorus and organic nitrogen due to a higher proportion of water originating from the upper, organic-rich soil horizon. Stratification of oxygen isotopes in the water column of the lake were related to subsurface inlets into the lake. Our results were used to describe the transformation of chemical and isotopic signals by surface and subsurface hydrological pathways in the sensitive headwater catchment. [ABSTRACT FROM AUTHOR]