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4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Characterizing Peatland Microtopography Using Gradient and Microform-Based Approaches

Abstract Peatlands represent an important component of the global carbon cycle, storing 180–621 Gt of carbon (C). Small-scale spatial variations in elevation, frequently referred to as microtopography, influence ecological processes associated with the peatland C cycle, including Sphagnum photosynthesis and methane flux. Microtopography can be characterized with measures of topographic variability and by using conceptual classes (microforms) linked to function: most commonly hummocks and hollows. However, the criteria used to define these conceptual classes are often poorly described, if at all, and vary between studies. Such inconsistencies compel development of explicit quantitative methods to classify microforms. Furthermore, gradient-based characterizations that describe spatial variability without the use of microforms are lacking in the literature. Therefore, the objectives of this study were to (1) calculate peatland microtopographical elevation gradients and measures of spatial variability, (2) develop three microform classification methods intended for specific purposes, and (3) evaluate and contrast classification methods. Our results suggest that at spatial scales much larger than microforms, elevation distributions are unimodal and are well approximated with parametric probability density functions. Results from classifications were variable between methods and years and exhibited significant differences in mean hollow areal coverages of a raised ombrotrophic bog. Our results suggest that the conceptualization and classification of microforms can significantly influence microtopographic structural metrics. The three explicit methods for microform classification described here may be used and built upon for future applications.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Microtopography Matters: Belowground CH 4 Cycling Regulated by Differing Microbial Processes in Peatland Hummocks and Lawns

Water table depth and vegetation are key controls of methane (CH 4 ) emissions from peatlands. Microtopography integrates these factors into features called microforms. Microforms often differ in CH 4 emissions, but microform-dependent patterns of belowground CH 4 cycling remain less clearly resolved. Here, to investigate the impact of microtopography on belowground CH 4 cycling, we characterized depth profiles of the community composition and activity of CH 4 -cycling microbes using 16S rRNA amplicon sequencing, incubations, and measurements of porewater CH 4 concentration and isotopic composition from hummocks and lawns at Sallie's Fen in NH, USA. Geochemical proxies of methanogenesis and methanotrophy indicated that microforms differ in dominant microbial CH 4 cycling processes. Hummocks, where water table depth is lower, had higher porewater redox potential (Eh) and higher porewater δ 13 C-CH 4 values in the upper 30 cm than lawns, where water table depth is closer to the peat surface. Porewater δ 13 C-CH 4 and δD-CH 3 D values were highest at the surface of hummocks where the ratio of methanotrophs to methanogens was also greatest. These results suggest that belowground CH 4 cycling in hummocks is more strongly regulated by methanotrophy, while in lawns methanogenesis is more dominant. We also investigated controls of porewater CH 4 chemistry. The ratio of the relative abundance of methanotrophs to methanogens was the strongest predictor of porewater CH 4 concentration and δ 13 C-CH 4 , while vegetation composition had minimal influence. As microbial community composition was strongly influenced by redox conditions but not vegetation, we conclude that water table depth is a stronger control of belowground CH 4 cycling across microforms than vegetation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Examining the peatland shrubification-evapotranspiration feedback following multi-decadal water table manipulation

Northern peatlands are globally important long-term sinks of carbon due to their predominantly saturated conditions. However, these ecosystems are expected to become drier with climate change, potentially leading to shrubification. As such, the response of the shrubification–evapotranspiration (ET) feedback may be of critical importance to future peatland energy, water and carbon dynamics. Here we examined the effect of multi-decadal peatland water table (WT) alteration at three adjacent sites with increasing depth to WT (WET, INTermediate, and DRY). In order to better understand the WT–shrubification–ET feedback, we measured peatland vegetation composition, microtopography and ET partitioning, where ET was measured at the ecosystem, microform, and leaf level using eddy covariance (EC), chambers and porometry, respectively. Averaged across microforms and WT treatments, there was a difference in the median measured leaf resistance (r leaf ) between plant functional types ranging from 213 s m -1 for erect dwarf shrubs, 325 s m -1 for graminoids/sedges, and 520 s m -1 for prostrate dwarf shrubs. Scaled based on LAI, the low r leaf of erect dwarf shrubs dominated hummocks, where sites with a higher proportion of hummocks had lower median canopy resistance (r v ) of 141, 133 and 130 s m -1 at the WET, INT and DRY sites respectively. Nevertheless, ET was highest at the WET site and similar between the INT and DRY sites, with greater evaporation from the moss surface at the WET site. Porometry and EC data along with a three-source model were used to independently assess the evaporative contribution from the moss surface, which ranged from 17% to 40%. For moderate and persistent changes in WT from land-use or climate change, our results suggest vegetation succession is minimal, but the microtopographic development and the concomitant differences in LAI for the various plant functional types is key to understanding changes in total ET and partitioning.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1974

Telecommunications media for the delivery of educational programming

The technical characteristics of various telecommunications media are examined for incorporation into educational networks. FM radio, AM radio, and VHF and UHF television are considered along with computer-aided instruction. The application of iteration networks to library systems, and microform technology are discussed. The basic principles of the communications theory are outlined, and the operation of the PLATO 4 random access system is described.

Ballard, R.↗