Continuous Dissolved Oxygen Measurements and Modelling Metabolism in Peatland Streams

Stream water dissolved oxygen was monitored in a 3.2km(2) moorland headwater catchment in the Scottish Highlands. The stream consists of three 1(st) order headwaters and a 2(nd) order main stem. The stream network is fringed by peat soils with no riparian trees, though dwarf shrubs provide shading in the lower catchment. Dissolved oxygen (DO) is regulated by the balance between atmospheric re-aeration and the metabolic processes of photosynthesis and respiration. DO was continuously measured for >1 year and the data used to calibrate a mass balance model, to estimate primary production, respiration and re-aeration for a 1(st) order site and in the 2(nd) order main stem. Results showed that the stream was always heterotrophic at both sites. Sites were most heterotrophic in the summer reflecting higher levels of stream metabolism. The 1(st) order stream appeared more heterotrophic which was consistent with the evident greater biomass of macrophytes in the 2(nd) order stream, with resulting higher primary productivity. Comparison between respiration, primary production, re-aeration and potential physical controls revealed only weak relationships. However, the most basic model parameters (e.g. the parameter linking light and photosynthesis) controlling ecosystem processes resulted in significant differences between the sites which seem related to the stream channel geometry.