Dynamics of dissolved organic carbon in forested and disturbed catchments, Westland, New Zealand: 2. Larry River

Dissolved organic carbon (DOC) dynamics were investigated in three small wetland catchments: one covered by a scrub forest and the other two cleared, V‐bladed, and planted with pine, 1 and 4 years before sampling. Over a 4‐month sampling period, DOC concentrations averaged 1.4, 20.9, 47.1, 46.0, and 45.7 mg/L in precipitation, throughfall, stemflow, surface soil water, and subsoil water, respectively, in the scrub forest catchment. DOC concentration in the stream draining the catchment averaged 43.4 mg/L, reflecting the inability of the Larry River subsoils to adsorb DOC and the pathways taken by water. In 1986, discharge‐weighted DOC concentrations in the streams ranged from 29.9 mg/L in the catchment disturbed 4 years before sampling to 35.0 mg/L in the recently disturbed catchment and 37.9 mg/L in the catchment covered by scrub forest. DOC export from the catchments in 1986 was estimated to be 30.6, 43.8, and 41.7 g m −2 yr −1 , suggesting that disturbance had a minor effect on DOC export. The role of the high DOC concentrations on the chemistry of the stream water was revealed by a large anion deficit, an average anion deficit:DOC relationship of 5.7 meq/g, and an annual export of acidity of 184–263 meq m −2 yr −1 . Within‐storm sampling showed that pH and DOC were related inversely and base titration suggested acid dissociation constants ( p K a ) ranging from 4.4 to 4.9.