Respiration-photosynthesis balance of terrestrial aquatic ecosystems, Ottawa area, Canada

Rivers link terrestrial and marine biospheres by transporting carbon from l and to ocean and by exchanging CO2 with the atmosphere. In an attempt to qu antify the aquatic carbon cycle, we developed a technique based on carbon i sotopic composition of dissolved inorganic carbon (delta C-13(DIC)) and oxy gen isotopic composition of dissolved oxygen (delta O-18(DO)). The approach was tested on selected boreal ecosystems in the Ottawa area, Canada: Meech Lake; the Ottawa River; and Green Creek, the latter dewatering the Mer Ble ue bog. The three ecosystems were monitored for 1 yr and the calculated aqu atic respiration/photosynthesis ratios in general fell within the 1 to 3.5 ranges. The ecosystems were respiration dominated year-round, despite incre ased photosynthetic rates during the warm season, a development that was ap parently matched by a comparable enhancement in respiration rates. The year -round predominance of respiration over photosynthesis supports the results of earlier studies, showing that boreal aquatic ecosystems, particularly t he lakes, are not solely dissipation pathways for soil-generated CO2 introd uced into surficial water bodies by groundwater input. To fuel this year-ro und "excess" respiration, the steady state balance consideration demands th at the ecosystem must have a continuous supply of allochthonous reduced car bon. Copyright (C) 2000 Elsevier Science Ltd.