Date

5-1-2019

Document Type

Thesis

Degree

Master of Science

Department

Earth and Environmental Sciences

First Adviser

Zicheng Yu

Abstract

The long-term carbon (C) dynamics in tropical mountain peatlands are poorly understood. Here I present radiocarbon-dated paleoecological results from four high-elevation peatlands in the northern Andean páramo (alpine tundra) of the Sierra Nevada del Cocuy in the Cordillera Oriental of Colombia, along with modern microclimate data, to assess the late Holocene history and environmental controls on peatland initiation and C accumulation rates of currently Distichia muscoides-dominated peatlands. Furthermore, I carried out a regional synthesis of existing studies to place my new results in broad geographic and longer-term context. I used loss-on-ignition and macrofossil analysis of a well-dated 4,300-year-old peat core to reconstruct the response of peatland vegetation to hydroclimate changes and to understand the effects of botanical composition on C accumulation. Results show that the current Distichia-dominated peatlands are a recent feature in this region, occurring in present form only during the last 150 years. Before this, paleo records indicate that small Distichia cushions have only grown, typically after the peatland was flooded with mineral sediments. Flooding and mineral sediment deposition occurred at 3290, 2590, 1620, 930, and 860 cal yr BP. The modern Distichia peatlands are accumulating C at an extremely high rate, between 270 and 900 g C m-2 yr-1 depending on elevation. To place these results in a regional context, I use a modified “Super-Peatland” approach to determine an average late Holocene C accumulation rate of 48.6 g C m-2 yr-1 and by comparing the expected, modeled C accumulation trend to the observed ones, I show that modern Distichia C accumulation represent an acceleration of C accumulation rates at much higher rates than expected by autogenic ecological effects. However, even before recent acceleration, páramo peatlands have higher late Holocene C accumulation rates than boreal or austral peatlands. This is likely due to the strong diurnal climate variability that enhances plant productivity during days and reduces organic matter decay at nights as well as periods of enhanced inputs of water and nutrients associated with flooding and elevated plant production. Taken together, I show that modern Distichia cushion peatlands on El Cocuy are a recent occurrence and have experienced a greater shift in vegetation and C accumulation rates in the last 150 years than any other time during the last 4,000 years.

Available for download on Friday, February 26, 2021

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