The flow-through bogs are inclined mires presenting a small channel or stream running through it, which water permits saturation and periodical flooding of the lateral-connected terrain, the development of vegetation, and consequently, peat formation. In the U.S.A., Chadde et al. (1998) characterize under “flow-through bog” one of the major mire forms of the northern Rocky Mountains (U.S.A.), which are fed by percolating runoffs and by rainfall channelizing through the mire. In Germany, Schumann and Joosten (2008) gave the name of “Spring-mire” to the ecosystems moisturized (moistened) by spring water on slopes and inclined areas. In South Africa, the concept of “channelled wetland” designs channelized ecosystems in valley bottoms (Ollis et al., 2013). Flow-through bogs in the chilean Patagonia, can be considered as a category integrating all the water sources (rainfall, lateral inputs, percolations and channel-flows) contained in these mentioned classifications. The peat level can even develop in the watercourse up to a height that covers and occupies the whole channel.
Current vegetation
Flow-through bogs are among the mires presenting the widest peat forming vegetation diversity, including Sphagnum species (Sp. magellanicum, Sp. fimbriatum), brown mosses (Dendroligotrichum dendroides, Dendroligotrichum squamosum), cushion plants (Astelia pumila, Donatia fascicularis), Carex species (C. magellanica, C. chillanensis), and other vascular plants such as Oreobolus obtusangulus, Drosera uniflora and Lepidothamnus fonkii, amongst others.
Hydrology
Although rainfall is the main hydrologic component in the coastal areas of Aysén, a particular type of small stream is what makes flow-through bogs hydrologically distinctive. Due to their inclination, these ecosystems exhibit the marks of major water dynamicity more than ecosystems with convexes or flat morphologies. Evidence of this is the major diversity of plant species, as is the different peat decomposition. In this way, depending on the rain or snow melting intensity, the intensity of the mire hydrological dynamicity will also be of influence (e.g. through periodical floods of the stream affecting the encompassing terrain with intervals of inundations and dryness, or through lateral flows and horizontal percolations influencing the edges of the mire), driving in this way different decomposition degrees and botanical peat types in these ecosystems. An average mire water level of 29±16 cmbs was registered, for flow through bogs in the Región Aysén. A simplified and stereotypical schema of a flow-through bog is shown as follows:
Substrate Types and Stratigraphy
Flow-through bogs are characterized by a very thin ombrogenic peat horizon, above geogenic peat horizons, or sometimes only geogenic peat horizons, lying directly over the bedrock of the slope, normally composed of coarse to fine sands. Depending on the current peat forming layer (if it is ombrogenic peat above geogenic peat, or only geogenic peat over the parent material), these ecosystems will be primary or secondary. The most common substrate types are amorphous peat and the geogenic substrate radicels peat. Among the ombrogenic peat types, the most common are Oreobolus peat, cushion plants peat and Sphagnum magellanicum peat. The typical median pH-value reaches 4.2±0.3, covering a spectrum from 3.7 to 4.6The degree of peat decomposition increased quickly below the superficial ombrogenic peat horizon showing that its current formation is periodically affected by water fluctuations in these mire types, inducing the decomposition of the peat in the overlying substrate. Furthermore, recently formed ombrogenic peat of Sp. magellanicum in mires of Aysén (Rodríguez, 2015) is characterized by a low bulk density (≤0.07 g cm3), whereby after intensive rainfall or floods, the available decomposed peat on the surface can be washed through percolation into the underlying horizons, increasing the presence of decomposed material on them. Additionally, although the superficial water fluctuations are the reason for the current mesotrophic conditions on the surface of flow-through bogs, it appears that the inputs of rain water via infiltration in these coast-mountainous ecosystems are intensive enough to reach the catotelm composed by amorphous and radicels peat, and induce oligotrophic conditions. For more information please review the document: Substrate types in mires of Aysén: a tool for their recognition.
References:
Chadde, S. W.; Shelly, J. S.; Bursik, R. J.; Moseley, R. K.; Evenden, A. G.; Mantas, M. et al. (1998): Peatlands on National Forests of the Northern Rocky Mountains: Ecology and Conservation. General Technical Report RMRS-GTR-11. Edited by Forest Service of the United States Department of Agriculture. Rocky Mountain Research Station. Utha, USA, 80 pp.
Schumann, M. and Joosten, H. (2008): Global Peatland Restoration. Manual. Institute of Botany and Landscape Ecology, Greifswald University. Greifswald, 68 pp.
Ollis, D.; Snaddon, K.; Job, N.; Mbona, N. (2013): Classification system for wetlands and other aquatic ecosystems in South Africa. User manual: inland systems (SANBI biodiversity series, 22), Pretoria: South African National Biodiversity Institute, 124 pp.