干旱区生态环境知识资源中心

1 Landsat imagery was used to map the distribution of 127 raised bogs in northwestern Minnesota. Bogs collectively cover 1236 km(2) (16% of the study area) despite the relatively dry regional climate and periodic droughts.

2 The physical, chemical, and biotic properties of these bogs have no apparent relationship to the westward climatic gradient indicating a high degree of buffering from changes in moisture stress.

3 Most bogs are located where groundwater discharge moderates moisture losses to the atmosphere and may decouple bogs from a direct climatic control. Bogs are also consistently related to physiographic features, such as drainage divides, interfluves of tributary streams, and beach ridges that constrain the surface and groundwater hydrology.

4 During droughts groundwater moves upward through the peat column toward the depressed water table, which is located 1-2 m below the peat surface. During moist periods, however, water-table mounds within these bogs drive surface water downward deflecting the deeper upwardly moving groundwater laterally to the bog margins.

5 Such short-term reversals in flow have little effect on the pore-water chemistry of major cations, which reflect the predominant downward flow over the past decade. Several chemical species, however, behave nonconservatively and respond more directly to climatic change.

6 Discharge zones for groundwater seem to be an essential prerequisite for bog formation in arid regions. Feat accumulation should be most rapid over discharge zones, which can maintain water table mounds, even during droughts Once a peat mound has formed, its higher water table will drive local recharge cells, which isolate the vegetation from groundwater and facilitate the development of a raised bog.