@article {2703,
	title = {Comparing and improving methods for reconstructing peatland water-table depth from testate amoebae},
	journal = {The Holocene},
	volume = {29},
	year = {2019},
	month = {Jan-08-2020},
	pages = {1350 - 1361},
	abstract = {Proxies that use changes in the composition of ecological communities to reconstruct temporal changes in an environmental covariate are commonly used in paleoclimatology and paleolimnology. Existing methods, such as weighted averaging and modern analog technique, relate compositional data to the covariate in very simple ways, and different methods are seldom compared systematically. We present a new Bayesian model that better represents the underlying data and the complexity in the relationships between species{\textquoteright} abundances and a paleoenvironmental covariate. Using testate amoeba{\textendash}based reconstructions of water-table depth as a test case, we systematically compare new and existing models in a cross-validation experiment on a large training dataset from North America. We then apply the different models to a new 7500-year record of testate amoeba assemblages from Caribou Bog in Maine and compare the resulting water-table depth reconstructions. We find that Bayesian models represent an improvement over existing methods in three key ways: more complete use of the underlying compositional data, full and meaningful treatment of uncertainty, and clear paths toward methodological improvements. Furthermore, we highlight how developing and systematically comparing methods lead to an improved understanding of the proxy system. This paper focuses on testate amoebae and water-table depth, but the framework and ideas are widely applicable to other proxies based on compositional data.},
	keywords = {Bayesian statistics, compositional data, Holocene, hydrology, North America, Northeast United States, Paleoclimate, peatlands, statistical methods, testate amoebae},
	issn = {0959-6836},
	doi = {10.1177/0959683619846969},
	url = {https://journals.sagepub.com/doi/10.1177/0959683619846969},
	author = {Nolan, Connor and Tipton, John and Booth, Robert K and Hooten, Mevin B and Jackson, Stephen T}
}
@article {2862,
	title = {A probabilistic method of assessing carbon accumulation rate at Imnavait Creek Peatland, Arctic Long Term Ecological Research Station, Alaska},
	journal = {Journal of Quaternary Science},
	volume = {32},
	year = {2017},
	month = {Jan-07-2017},
	pages = {579 - 586},
	abstract = {Arctic peatlands are an important part of the global carbon cycle, accumulating atmospheric carbon as organic matter since the Late glacial. Current methods for understanding the changing efficiency of the peatland carbon sink rely on peatlands with an undisturbed stratigraphy. Here we present a method of estimating primary carbon accumulation rate from a site where permafrost processes have either vertically or horizontally translocated nearby carbon-rich sediment out of stratigraphic order. Briefly, our new algorithm estimates the probability of the age of deposition of a random increment of sediment in the core. The method assumes that if sediment age is measured at even depth increments, dates are more likely to occur during intervals of higher accumulation rate and vice versa. Multiplying estimated sedimentation rate by measured carbon density yields carbon accumulation rate. We perform this analysis at the Imnavait Creek Peatland, near the Arctic Long Term Ecological Research network site at Toolik Lake, Alaska. Using classical radiocarbon age modeling, we find unreasonably high rates of carbon accumulation at various Holocene intervals. With our new method, we find accumulation rate changes that are in improved agreement within the context of other sites throughout Alaska and the rest of the Circum-Arctic region.},
	keywords = {carbon accumulation, Imnavait, peatlands, permafrost, radiocarbon, Toolik LTER},
	doi = {10.1002/jqs.2952},
	url = {https://onlinelibrary.wiley.com/doi/10.1002/jqs.2952},
	author = {Nichols, Jonathan E. and Peteet, Dorothy M. and Frolking, Steve and Karavias, John}
}
@article { ISI:000337285500012,
	title = {Organic matter transformation in the peat column at Marcell Experimental Forest: Humification and vertical stratification},
	journal = {JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES},
	volume = {119},
	number = {{4}},
	year = {2014},
	month = {APR 28},
	pages = {661-675},
	type = {Article},
	abstract = {We characterized peat decomposition at the Marcell Experimental Forest (MEF), Minnesota, USA, to a depth of 2m to ascertain the underlying chemical changes using Fourier transform infrared (FT IR) and C-13 nuclear magnetic resonance (NMR) spectroscopy) and related these changes to decomposition proxies C:N ratio, C-13 and N-15, bulk density, and water content. FT IR determined that peat humification increased rapidly between 30 and 75cm, indicating a highly reactive intermediate-depth zone consistent with changes in C:N ratio, C-13 and N-15, bulk density, and water content. Peat decomposition at the MEF, especially in the intermediate-depth zone, is mainly characterized by preferential utilization of O-alkyl-C, carboxyl-C, and other oxygenated functionalities with a concomitant increase in the abundance of alkyl- and nitrogen-containing compounds. Below 75cm, less change was observed but aromatic functionalities and lignin accumulated with depth. Significant correlations with humification indices, identified by FT IR spectroscopy, were found for C:N ratios. Incubation studies at 22 degrees C revealed the highest methane production rates, greatest CH4:CO2 production ratios, and significant O-alkyl-C utilization within this 30 and 75cm zone. Oxygen-containing functionalities, especially O-alkyl-C, appear to serve as excellent proxies for soil decomposition rate and should be a sensitive indicator of the response of the solid phase peat to increased temperatures caused by climate change and the field study manipulations that are planned to occur at this site. Radiocarbon signatures of microbial respiration products in deeper pore waters at the MEF resembled the signatures of more modern dissolved organic carbon rather than solid phase peat, indicating that recently photosynthesized organic matter fueled the bulk of subsurface microbial respiration. These results indicate that carbon cycling at depth at the MEF is not isolated from surface processes.},
	keywords = {FT-IR spectroscopy, humification, NMR spectroscopy, organic matter, peatlands, vertical stratification},
	issn = {2169-8953},
	doi = {10.1002/2013JG002492},
	author = {Tfaily, Malak M. and Cooper, William T. and Kostka, Joel E. and Chanton, Patrick R. and Schadt, Christopher W. and Hanson, Paul J. and Iversen, Colleen M. and Chanton, Jeffrey P.}
}
