Catchment-scale weathering fluxes in the Southern Alps, New Zealand

Abstract

The dissolved and suspended sediment flux in a small headwater in the Southern Alps, New Zealand over a 16-month period showed that mass transferred as dissolved load (91 t km−2 a−1) is a significant flux relative to the suspended sediment flux (210 t km−2 a−1). Export of dissolved load occurs mostly under baseflow, with 268 t being transported over 10 discrete events, relative to a total load of 1171 t over the experimental observation period; which is equivalent to 23% of the ionic flux occurring during event flow. Storm events contribute 2420 t of suspended sediment, accounting for 90% of the total suspended sediment flux. The chemical weathering flux was 43% of the physical weathering flux, and much higher than previous estimates of 1–9% for the Southern Alps. Such a high relative rate of chemical weathering is unlikely to be indicative of the full Southern Alps extent, but suggests that in some regions of the eastern Southern Alps mass loss via chemical weathering may be a significant portion of overall flux. During storm events, temporal exhaustion of sediment occurred and inferred limited sediment source production, rather than limited connectivity with the hillslope environment. Similar supply-limitation is expressed in the ionic flux, where rainfall events do not usually express hysteretic behaviour, and event flow is dominated by a simple dilution recession.