Methane pools within the Glacial Lake Agassiz Peatlands (GLAP) and their response to climatic change.

Abstract:

Global warming may destabilize the carbon pool in northern peatlands but it remains uncertain how climatic patterns regulate the transformation of solid-phase peat into greenhouse gases. Here we present a 43-year record of changes in the pore water chemistry from a major peat basin in northern Minnesota. These data indicate that methane production and its transient storage within bogs and fens is finely tuned to climatically driven flow systems on multiple time scales. The peak zones for methanogenesis were apparently limited to the uppermost peat strata during a dry climatic period (1965-1983) when shallow recharge systems prevailed across the GLAP. The shift to a moister climate after 1990 strengthened downward transport systems across the region greatly expanding the vertical suppy of labile root exudates and the peak production zones for methanogenesis in peat profiles. Large methane pools accumulated within the GLAP from 1990 through 2008. Dissolved methane concentrations were 2-to-4 times greater within the deeper peat (1-4 m) than above and were generally higher within bog landforms than in sedge fens. The size of these methane pools varied in response to seasonal and interannual climatic oscillations that apparently affected emission rates via ebullition (from deep peat) and wicking through plant stoma (from the rhizosphere). However, methane pools remained relatively stable during this period, except for a large change between 1990 and 1991. One remaining element of uncertainty concerns the transformation of dissolved methane to free-phase bubbles, which can represent 10-20% of peat volume in the GLAP. Nevertheless, methane profiles from the GLAP indicate that the entire peat profile can function as an incubator for methane depending on the prevailing climate regime and downward transport of labile carbon substrates.