AbstractIn January and February 2009, a series of water samples were collected from streams on Byers Peninsula. These samples were analysed for major elements and δ¹⁸O to determine the role of lithology and landscape position on stream geochemistry, and to understand better the hydrology (i.e. residence time of water) of these systems. Precipitation chemistry is enriched in Na⁺, as are the streams located close to the coast. Streams originating from inland locations have much higher percentages of Ca²⁺. In contrast, Mg²⁺ varied little, though streams that are in greater contact with volcanic-derived soils have slightly higher concentrations. Anion percentages varied greatly between streams with SO₄^2- ranging from 5% to 45% of the anion composition. Dissolved Si concentrations as high as 141 μM were observed. All these data suggest that active chemical weathering is occurring in this region. A time series over 13 days at one stream showed little variation in major element geochemistry. The δ¹⁸O of precipitation samples collected over this same period varied by ∼10‰ while the majority of stream samples varied less than ∼1.5‰. These data indicate that the stream waters represent mixtures of precipitation events, melting snow and water from the subsurface that had gained solutes through chemical weathering.