«By John A. Hribljan A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY In Forest Science ...»
THE EFFECT OF LONG-TERM WATER TABLE MANIPULATIONS ON
VEGETATION, PORE WATER, SUBSTRATE QUALITY, AND CARBON CYCLING
IN A NORTHERN POOR FEN PEATLAND
John A. Hribljan
Submitted in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHYIn Forest Science
MICHIGAN TECHNOLOGICAL UNIVERSITY© 2012 John A. Hribljan This dissertation has been approved in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in Forest Science.
School of Forest Resources and Environmental Science Dissertation Advisor: Dr. Rodney A. Chimner Committee Member: Dr. Molly A. Cavaleri Committee Member: Dr. Thomas G. Pypker Committee Member: Dr. Merritt R. Turetsky School Dean: Dr. Terry L. Sharik Table of Contents Preface
Chapter 1. Introduction
1.1 Climate Change effects on Northern Peatland Carbon Stocks
1.2 Northern Peatland Carbon Cycling
1.3 Project overview
1.4 Literature cited
Chapter 2. Vegetation Structure, Biomass, and Productivity across a Long-term Water Table Gradient in a Poor Fen Peatland
2.3.1. Study sites
2.3.3. Understory vegetation survey
2.3.4. Overstory biomass and primary productivity
2.3.5. Understory aboveground biomass and primary productivity
2.3.6. Understory belowground biomass and primary productivity
2.3.7. Statistical analysis
2.4.1 Hydrology and microtopography
2.4.2. Vegetation composition
2.4.3. Vegetation primary production
2.4.3. Vegetation biomass
2.4.4. Overstory productivity
2.5.1. Understory vegetation community structure
2.5.2. Understory vegetation biomass and NPP
iii 2.5.3. Shifts in overstory primary production
2.8. Literature cited
Chapter 3. The Effect of Long-term Water Table Manipulations on Dissolved Organic Carbon Production and Quality in a Poor Fen Peatland
3.3.1. Study sites
3.3.2 Hydrological monitoring
3.3.3 Field sampling methods
3.3.4 Chemical constituent analyses
3.3.5 Statistical analysis
3.4.1. Site Topography and Hydrology
3.4.2. Site electrochemistry and pore water chemical constituents
3.4.3. Spectrophotometer indices
3.4.4. DOC incubation experiment
3.5.1. Water table effects on DOC dynamics
3.5.2. Pore water residence time
3.5.3. Pore water DOC chemical characteristics and lability
3.5.4. Potential algae influence on DOC dynamics
3.8. Literature cited
Chapter 4. The Effect of Long-term Hydrology Changes on Peat Substrate Quality in a Northern Peatland
4.3.1. Study sites
4.3.2. Hydrological monitoring
4.3.3. Peat physical and chemical analysis
4.3.4. Mineralization experiment
4.3.5. IR spectroscopy
4.3.6. Statistical analysis
4.4.1. Hydrology and surface topography
4.4.2. Soil core physical and chemical parameters
4.4.3. Nitrogen extractions
4.4.4. IR spectroscopy
4.4.5. Mineralization experiment
4.5.1. Long-term water table manipulation effects on peat quality
4.5.2. Water table effects on potential aerobic CO2 production
4.5.3. Water table effects on anaerobic carbon mineralization
4.5.4. Microtopography peat quality and lability
4.5.5. Nitrogen stabilization
4.8. Literature cited
4. 9. Tables
Chapter 2. Hribljan, J.
A., Pypker, T.G. & Chimner, R.A. Vegetation Structure, Biomass, and Productivity across a Long-term Water Table Gradient in a Poor Fen Peatland. Manuscript.
Chapter 3. Hribljan, J.
A., Kane E.S., Turetsky, M.R., & Chimner, R.A. The Effect of Long-term Water Table Manipulations on Dissolved Organic Carbon Production and Quality in a Poor Fen Peatland. Manuscript.
Chapter 4. Hribljan, J.
A., Kane E.S., Pypker, T.G., & Chimner, R.A. The Effect of Long-term Hydrology Changes on Peat Substrate Quality in a Northern Peatland. Manuscript.
The completion of this dissertation was successful because of the support, financial backing, and encouragement of multiple individuals. I am deeply indebted to my advisor Dr. Rodney Chimner for his patient guidance throughout this endeavor. I am also extremely appreciative of the freedom he gave me to explore and contemplate the fascinating realm of peatland ecology. I would also like to thank my committee members Dr. Molly Cavaleri, Dr. Thomas Pypker, and Dr. Merritt Turetsky who gave me valuable insights and direction when I was faced with uncertainty. Dr. Evan Kane provided incredibly valuable mentorship, especially concerning the chapters on peatland dissolved organic carbon and peat substrate quality. Dr. Andy Burton provided generous use of his laboratory facilities. I received assistance from many students with field and laboratory work including: Drew Ballantyne, Jim Bess, Elizabeth Boisvert, Shawna Bork, Jamie Bourgo, Ellen Brenna, Robin Conklin, Aleta Daniels, Arielle Garrett, Laura Kangas, Chris Johnson, Laura Matkala, and Cassandra Ott.
This research was supported by the U.S. Department of Energy's Office of Science (BER) through the Midwestern Regional Center of the National Institute for Climatic Change Research at Michigan Technological University. Additional support was provided by the Ecosystem Science Center at Michigan Technological University and the USDA Forest Service Northern Research Station. This project would not have been possible without the generous cooperation and support of the Seney National Wildlife Refuge, in particular Dr. Greg Corace and Dave Olson, providing research support and access to the study site.
I would like to give special recognition to my wife Christa Luokkala for her endless support and encouragement. Without her help this dissertation would not have been possible. Thank you.
Northern peatlands are large reservoirs of soil organic carbon (C). Historically peatlands have served as a sink for C since decomposition is slowed primarily because of a raised water table (WT) that creates anoxic conditions. Climate models are predicting dramatic changes in temperature and precipitation patterns for the northern hemisphere that contain more than 90% of the world’s peatlands. It is uncertain whether climate change will shift northern peatlands from C sequestering systems to a major global C source within the next century because of alterations to peatland hydrology. This research investigated the effects of 80 years of hydrological manipulations on peatland C cycling in a poor fen peatland in northern Michigan. The construction of an earthen levee within the Seney National Wildlife Refuge in the 1930’s resulted in areas of raised and lowered WT position relative to an intermediate WT site that was unaltered by the levee.
We established sites across the gradient of long-term WT manipulations to examine how decadal changes in WT position alter peatland C cycling. We quantified vegetation dynamics, peat substrate quality, and pore water chemistry in relation to trace gas C cycling in these manipulated areas as well as the intermediate site. Vegetation in both the raised and lowered WT treatments has different community structure, biomass, and productivity dynamics compared to the intermediate site. Peat substrate quality exhibited differences in chemical composition and lability across the WT treatments. Pore water dissolved organic carbon (DOC) concentrations increased with impoundment and WT drawdown. The raised WT treatment DOC has a low aromaticity and is a highly labile C source, whereas WT drawdown has increased DOC aromaticity. This study has demonstrated a subtle change of the long-term WT position in a northern peatland will induce a significant influence on ecosystem C cycling with implications for the fate of peatland C stocks.
1.1 Climate Change effects on Northern Peatland Carbon Stocks Peatlands are classified as carbon (C) accumulating systems in which net primary production occurs in excess of organic matter decomposition resulting in the formation of peat (Rydin and Jeglum 2006). This delicate C balance is largely influenced and regulated by the rate of heterotrophic consumption of peat and to a lesser extent the loss of C through the leaching of dissolved and suspended particulate matter into the surrounding catchment (Moore and Basiliko 2006). Historically peatlands have served as a sink for C since decomposition is slowed primarily because of a raised water table (WT) creating anoxic conditions and at times a lowered peat temperature that inhibits microbial processing of peat (Vitt 2006). The lack of oxygen in water logged peat limits microbial access to oxidized electron acceptors that are favored for peat decomposition (Rydin and Jeglum 2006). In addition, cool peat temperatures created from the insulating properties of the thick organic horizon and the close proximity of the WT can slow enzymatic processing of peat (Davidson and Janssens 2006; Fenner et al. 2005).
Currently northern peatlands cover approximately 3% of the global land area and the organic matter stored in peatlands represents 12 - 30% of the global soil C pool (Gorham 1991) that is equivalent to approximately 60% of the current carbon dioxide (CO2) concentration in the atmosphere (Oechel 1993). Peatland C stocks are threatened by multiple disturbances that include forestry, agriculture, and peat extraction (Chapman et al. 2003). However, climate change has become an increasingly important concern because of the multiple and complicated responses of peatlands to climate induced changes in peat temperature and moisture. Furthermore, climate change will not only cause cumulative effects on current peatland disturbances but will also influence regions that are currently unaffected by direct anthropogenic disturbances (Seigal 1988; Turetsky and St Louis 2006). Therefore, climate change is a predominant and growing concern to global peatland C stocks.
It is estimated high-latitude regions in the northern hemisphere contain more than 90% of the world’s peatlands (Yu et al. 2010). Climate models are predicting warmer, drier conditions for the next century with the greatest temperatures increases of 4 – 8 ºC (IPCC 2001) occurring in locations resided by northern peatlands. In addition, dramatic changes in precipitation are predicted for the northern hemisphere (Stocks et al. 1998;
Tarnocai 2006; Thomas and Rowntree 2006). Future increases in global temperature with concurrent shifts in precipitation will influence both thermal and moisture regimes in northern ecosystems with implications for peatland primary production and decomposition dynamics (Ise et al. 2008). It is uncertain whether climate change will shift northern peatlands from C sequestering systems to a major global C source within the next century (Kim et al. 2007). Therefore, it is imperative to understand the potential effects of climate change on peatland C stocks and fluxes, since peatlands have the potential to become a significant source of atmospheric C (Freeman et al. 2001) from emissions of CO2 and methane (CH4), which are both potent greenhouse gases (Laine et al. 1996). Furthermore, increased emissions of CO2 and CH4 could create a positive feedback loop to climate change by increasing the greenhouse effect, leading to higher global temperatures and resulting in amplified climate induced disturbances to northern peatland C stocks (Friedlingstein et al. 2006) (Figure 1.1).
Alterations to peatland hydrology, especially a change in WT position, is a principal threat to peatland C cycling because of the tight coupling between WT and reduction/oxidation (redox) reactions that regulate oxygen availability for heterotrophic processing of peat (Reddy and DeLaune 2008; Grant et al. 2012). Therefore, a subtle shift in WT position has the potential to alter peatland C sequestering capacity (Bubier et al. 2003). However, uncertainty exists concerning the C cycling trajectory of peatlands (McGuire et al. 2009) affected by climate induced hydrological alterations since the changes can be multidimensional (Belyea and Malmer 2004; Whittington and Price 2006;
Ise et al. 2008). For example, an increased oxic zone created by WT drawdown can contribute to accelerated microbial decomposition of peat. However, increased oxygen availability can reduced CH4 production due to aerobic conditions inhibiting methanogens and enhanced methane oxidation by methanotrophs (Strack et al. 2004). In contrast, a raised WT will typically decrease CO2 production and increase CH4 emissions because of the elevated anoxic environment in the peat profile (Moore and Dalva 2006).