Dissolved inorganic and organic carbon in moorland and forest streams: Plynlimon, Mid-Wales

Abstract

Information on dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations and fluxes is presented for streams draining a matrix of acid moorland, conifer forested and harvested areas of Plynlimon, Mid-Wales. The results show six features. 1. (1) pCO 2 levels average 2.25 times the atmospheric value at 10 −3.15 for all the streams; excluding outlier points, 95% of the data lie in the range 0.2–5.4 times the atmospheric value. Although data scatter is high, the pCO 2 levels tend to increase with decreasing pH. The flow-weighted pCO 2 levels average 2.5 times the atmospheric value at 10 −3.1. 2. (2) Flow weighted average DIC and DOC concentrations are similar for all the main streams, at about 55.1 μM DIC 1 −1 (range 46.9–60.8) and at about 143 μM DOC 1 −1 (range 121–159), respectively. 3. (3) The DIC and DOC fluxes are similar for the main streams, at about 12.4 kg DIC ha −1 year −1 (range 11.5–15.6) and at about 32.7 kg DOC ha −1 year −1 (range 25.8–37.2), respectively. 4. (4) DOC makes up about 72% of the total dissolved carbon concentration/flux in the main streams, and undissociated carbonic acid contributes more than 87% to the total DIC. 5. (5) Deforestation leads to an increase in the DOC concentration and flux of about 29%; this increase persists for several years after felling. 6. (6) There is a statistically insignificant change in the concentration and flux for DIC, and pCO 2, with deforestation. However, the main streams contain lower bicarbonate concentrations under baseflow conditions during and for the first few years after felling.