Peat depth as a control on moss water availability under evaporative stress

Abstract

Northern peatlands are a vital component of the global carbon cycle, containing large stores of soil organic carbon and acting as a long‐term carbon sink. Moss productivity is an important factor in determining whether these wetlands will retain this function under future climatic conditions. Research on unsaturated water flow in peatlands, which controls moss productivity during periods of evaporative stress, has focused on relatively deep bog systems. However, shallower peatlands and marginal connective wetlands can be essential components of many landscape mosaics. In order to better understand factors influencing moss productivity, water balance simulations using HYDRUS‐1D were run for different soil profile depths, compositions, and antecedent moisture conditions. Our results demonstrate a bimodal distribution of peatland realizations, either primarily conserving water by limiting evapotranspiration or maximizing moss productivity. For sustained periods of evaporative stress, both deep water storage and a shallow initial water table delay the onset of high vegetative stress, thus maximizing moss productivity. A total depth of sand and peat of 0.8 m is identified as the threshold above which increasing peat depth has no effect on changing vegetative stress response. In contrast, wetlands with shallow peat deposits (less than 0.5 m thick) are least able to buffer prolonged periods of evaporation due to limited labile water storage and will thus quickly experience vegetative stress and so limit evaporation and conserve water. With a predicted increase in the frequency and size of rain events in continental North America, the moss productivity of shallow wetland systems may increase, but also greater moisture availability will increase the likelihood they remain as wetlands in a changing climate.

Estimating Peatland Water Table Depth and Net Ecosystem Exchange: A Comparison between Satellite and Airborne Imagery

“…The vertical profile of Sphagnum is a dense canopy with spaces and dead hyaline cells of the leaves and branches providing the mechanism for the retention of capillary water above the water table [28]. Lowering of the WT decreases the soil water pressure [60], increasing the possibility of desiccation of the mosses thus resulting in a loss of productivity and carbon sequestration [61]. Substantial lowering of the WT through draining accelerates the decomposition process in the peat and releases of CO 2 to the atmosphere [62].…”

“…Instead, the BRDF effects constitute a higher reflectivity perpendicular to the illumination angle at low view angles (similar to illumination conditions found at high latitudes). The BRDF properties of vascular plant canopies are primarily characterized by a hotspot, a peak in reflectance when the sun is directly behind the sensor [61]. At the ecosystem scale, BRDF is a complex process, influenced not only by crown size, density, and spacing between crowns, but also the background soil BRDF, which for peatlands is the moss canopy.…”

Opportunistic wetland formation on reconstructed landforms in a sub-humid climate: influence of site and landscape-scale factors

“…Several large circular wetlands span flat tops or terraces, often perched above groundwater (Unpublished data, CA Mendoza), where low relief and smaller contributing areas severely limit proportional contribution from adjacent non-wetland areas. These wetlands occur in large endorheic pans where fine-texture and poor drainage potential promotes frequent surface saturation, shallow water tables and soil anoxia precluding water intolerant forest vegetation, even in sub-humid climates (Rodriguez-Iturbe et al 2007;Dixon et al 2017). Gently sloping wetland areas (typically swamps) provide lateral runoff to the adjacent shallow center depression, and internal distribution of water appears to dominate the hydrology and contributes to the complexity in forms of these wetlands.…”

“…However, regional runoff studies show limited runoff from forest ecosystems while peatland wetland land covers are water source areas on the Boreal Plains (Devito et al 2017). Formation of isolated wetlands perched above regional water tables by confining layers of clay, calcrete, or bedrock and lacking ground water or surface runoff inputs, have been observed in water-limiting arid (Melly et al 2017) and sub-humid Boreal Plains climates (Devito et al 2005;Hokanson et al 2016), highlighting the possibility of autogenic and internal soil-atmosphere interactions in initial wetland development (Waddington et al 2015;Dixon et al 2017).…”

“…If internal feedback mechanisms enable formation, wetlands may form on both topographic highs and lows, in extended flat areas or gentle depressions with limited runoff sources, and where low soil permeability and storage potential combine with poor drainage to enable frequent and rapid soil saturation after precipitation events (Atkinson and Cairns 1994;Schoeneberger and Wysocki 2005;Dixon et al 2017). This can promote wetland soil development and vegetation types and structures with low evapotranspiration rates (Winter 1988;Rodriguez-Iturbe et al 2007) while also impeding terrestrialization by forest species (Bates et al 1998).…”