Sarah A. Finkelstein

A Database and Synthesis of Northern Peatland Soil Properties and Holocene Carbon and Nitrogen Accumulation

Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45°N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 ± 3% (standard deviation) for Sphagnum peat, 51 ± 2% for non-Sphagnum peat, and at 49 ± 2% overall. Dry bulk density averaged 0.12 ± 0.07 g/cm3, organic matter bulk density averaged 0.11 ± 0.05 g/cm3, and total carbon content in peat averaged 47 ± 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 ± 2 (standard error of mean) g C/m2/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25–28 g C/m2/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.

RANGE DYNAMICS AND INVASIVE TENDENCIES IN TYPHA LATIFOLIA AND TYPHA ANGUSTIFOLIA IN EASTERN NORTH AMERICA DERIVED FROM HERBARIUM AND POLLEN RECORDS

Typha species are increasingly considered invasive weeds in wetlands of eastern North America. Typha angustifolia and T. × glauca are often seen as more invasive than T. latifolia, but there are few comparative biogeographic data on these three species. We examined 1,127 Typha specimens archived in major herbaria to map changes in the distributions of these species since the late-19th century. We also analyzed pollen records from the North American Pollen Database (NAPD) to examine longer-term trends in abundance of each Typha species. Proportion curves comparing the relative spread of T. angustifolia and T. latifolia reveal a period of enhanced range increase in T. angustifolia in the early to mid-20th century. From the mid-20th century onwards, the two species increased at the same rate. The relatively higher rate of spread in T. angustifolia levels off after 1930 in the more coastal region of New England, but does not stop increasing inland and in more northern regions such as Ontario until after 1970. Pollen data suggest that 80% of relevant sites in the North American Pollen Database showed an increase in the abundance of one or both Typha species over the past 1,000 years. However, there was no significantly greater increase in one type of pollen compared to the other. Typha-type pollen grains in the form of tetrads and monads are recorded in the database throughout the Holocene and late Pleistocene; however, few studies analyzed the morphology of the pollen grains sufficiently to allow for positive identification of T. angustifolia. In the few recent records that made those measurements, small numbers of pre-settlement incidences of T. angustifolia and T. × glauca are recorded. Pollen and herbarium data suggest that T. angustifolia may have been present in North America prior to European settlement, but was not widespread. Herbarium data confirm that the range increase has been considerably larger in T. angustifolia than in T. latifolia since 1880, but both Typha species have been increasing at the same rate for the past several decades, and both will continue to display invasive tendencies in disturbed wetlands.

Carbon storage and potential methane production in the Hudson Bay Lowlands since mid-Holocene peat initiation

Peatlands have influenced Holocene carbon (C) cycling by storing atmospheric C and releasing methane (CH4). Yet, our understanding of contributions from the worlds second largest peatland, the Hudson Bay Lowlands (HBL), Canada, to peat-climate-C-dynamics is constrained by the paucity of dated peat records and regional C-data. Here we examine HBL peatland development in relation to Holocene C-dynamics. We show that peat initiation in the HBL is tightly coupled with glacial isostatic adjustment (GIA) through most of the record, and occurred within suitable climatic conditions for peatland development. HBL peatlands initiated most intensively in the mid-Holocene, when GIA was most rapid and climate was cooler and drier. As the peat mass developed, we estimate that the HBL potentially released 1-7 Tg CH4 per year during the late Holocene. Our results indicate that the HBL currently stores a C-pool of ~30 Pg C and provide support for a peatland-derived CH4 contribution to the late Holocene atmosphere.

Pollen-Derived Paleovegetation Reconstruction and Long-Term Carbon Accumulation at a Fen Site in the Attawapiskat River Watershed, Hudson Bay Lowlands, Canada

Abstract The Hudson Bay Lowlands (HBL) constitute a globally significant carbon pool; the paleoecological record provides an opportunity to investigate long-term drivers of change in carbon accumulation and related changes in vegetation. We present a Holocene record from the Victor Fen site (VM-3-3) in Ontarios HBL to reconstruct vegetation history, quantify rates of carbon accumulation, and determine the role of paleoclimatic drivers. Pollen analysis indicates initiation of peat accumulation over a mineral substrate, accompanied by relatively rapid rates of carbon accumulation, following emergence from the Tyrrell Sea ∼6900 yrs BP. The earliest vegetation assemblage consisted of a tidal marsh, quickly succeeding to a Typha marsh, then a poor fen dominated by Sphagnum and Cyperaceae by 6400 yrs BP. Rapid rates of isostatic uplift at the time likely contributed to these changes. Once established, this fen community persisted without major vegetation change until the most recent century, when the abundance of shrub and Cyperaceae pollen increased, suggesting increasingly minerotrophic conditions. Average rate of long-term carbon accumulation (LORCA) for the whole record (mean = 22.8 g C m-2 yr-1) is similar to other northern peatlands, and higher than the Holocene average for an adjacent bog. Increased precipitation after ∼2400 yrs BP may have contributed to the higher LORCA reconstructed for the late Holocene, but the increased precipitation did not coincide with any apparent changes in vegetation as inferred from pollen assemblages.

Quantifying Holocene variability in carbon uptake and release since peat initiation in the Hudson Bay Lowlands, Canada

Northern peatlands are a globally significant carbon (C) reservoir, yet also function as dynamic methane (CH4) sources to the atmosphere. The fate of peatland C stores and related climate system feedbacks remain uncertain under scenarios of a changing climate and enhanced anthropogenic pressure. Here, we present a synthesis of Holocene peatland C dynamics for the Hudson Bay Lowlands (HBL), Canada, in relation to the past atmospheric CH4 trends, glacial isostatic adjustment, and paleoclimate. We report that peatland age and trophic status, together with paleoclimate, contribute to explaining some of the temporal variation in C accumulation rates (CARs) in the HBL. Our results show that younger, minerotrophic peatlands accumulate C faster, and although detailed paleoclimate data are not available, the results suggest the possibility of higher CARs in association with warmer Holocene climates. Peat initiation rates and CARs were greatest during the mid-Holocene; however, our results reveal that two-thirds of the HBL C pool is stored in peat of late Holocene age, owing to long-term peatland expansion and development. Whereas the HBL has been a net C sink since mid-Holocene peat initiation, the HBL also appears to have been a modest C source, with 85% of the losses occurring during the late Holocene as a consequence of the gradual decay of previously accrued peat. Late Holocene peat decay, under wetter climatic conditions, and from a landscape occupied by an abundance of minerotrophic peatlands, indicates that the HBL may have been a natural terrestrial source of CH4 to the late Holocene atmosphere. While the peatlands of the HBL may continue to function as a globally significant C store, ongoing C losses from the HBL may have important implications for the global C budget and climate system.

Climate and peat type in relation to spatial variation of the peatland carbon mass in the Hudson Bay Lowlands, Canada

Northern peatlands store ~500 Pg of carbon (C); however, controls on the spatial distribution of the stored C may differ regionally, owing to the complex interaction among climate, ecosystem processes, and geophysical controls. As a globally significant C sink, elucidation of controls on the distribution of C in the Hudson Bay Lowlands, Canada (HBL), is of particular importance. Although peat age is related to timing of land emergence and peat depth in the HBL, considerable variation in the total C mass (kg m−2) among sites of similar peat age suggests that other factors may explain spatial patterns in C storage (Pg) and sequestration. Here we quantify the role of two key factors in explaining the spatial distribution of the C mass in the HBL (n = 364 sites), (i) climate variability and (ii) peat lithology, for two major peatland classes in the HBL (bogs and fens). We find that temperature, precipitation, and evapotranspiration each explained nearly half of the C mass variability. Regions characterized by warmer and wetter conditions stored the most C as peat. Our results show that bogs and fens store similar amounts of C within a given climate domain, although via distinct storage mechanisms. Namely, fen peats tend to be shallower and more C dense (kg m−3) compared to bogs. Following geophysical controls on the timing of peat initiation, our results reveal that both the widespread bog-fen patterning and variability in regional climate contribute to explaining the spatial distribution of the peat C mass in the HBL.

Long-term successional changes in peatlands of the Hudson Bay Lowlands, Canada inferred from the ecological dynamics of multiple proxies

Peatlands in northern Ontario, Canada, archive multiple biological indicators, including macrofossils, algae, testate amoebae, and pollen. These proxies can provide insights concerning the timing and nature of long-term climatic and environmental changes. The Hudson Bay Lowlands (HBL) of central Canada contain one of Earth’s largest continuous peatland complexes, and thus comprehensive spatial and temporal studies are needed to understand the implications of climate change on carbon cycling. Diatom assemblages were examined in three cores retrieved from ombrotrophic bogs across two Canadian terrestrial ecozones. Comparisons were made with testate amoebae and macrofossil data previously analyzed from these cores, as well as with regional pollen records from surrounding peatlands. From ~2000 to ~600 cal. BP, changes in diatom composition likely reflect hydrosere succession within the peatland, including fluctuations in connectivity to the water table and pH changes. From ~600 cal. BP to present, the synchronous timing of changes in diatoms and testate amoebae are tracking drying conditions and subsequent microhabitat variations that occur within bogs. It is possible that diatoms are tracking subtle changes in the stability of peat microforms including bog hollows and hummocks, highlighting their sensitivity to small chemical change, whereas testate amoebae are tracking the lowering of a peatland water table and subsequent drying of the peatland. The use of multiple proxies provides a more holistic approach to interpreting past ecological succession and responses to climate within peatlands. When present and well preserved, diatoms can be applied to track drying conditions in bogs, in terms of both hydrosere succession and present climatic change.

Relative importance of hydrological and climatic controls on Holocene paleoenvironments inferred using diatom and pollen records from a lake in the central Hudson Bay Lowlands, Canada:

Postglacial paleoenvironmental changes and landscape development in the Hudson Bay Lowlands in subarctic Canada were inferred using sediment properties and diatom and pollen assemblages in the sediments of a lake raised above the surrounding peatlands in an ice-marginal landform. Coarse-grained, inorganic sediments at the base of the Lake AT01 core suggest a high-energy periglacial environment, following isostatic emergence from Hudson Bay around 6840 cal. BP. Initial diatom assemblages dominated by Fragilaria spp., and pollen of Shepherdia canadensis, indicate early successional conditions in a recently deglaciated environment. Around 6200 cal. BP, tychoplanktonic Fragilarioid diatoms are replaced by large benthics. Coincident increases in Equisetum spores, Cyperaceae pollen and sediment organic matter suggest the establishment of a more productive macrophyte-rich shallow lake. While the Holocene Thermal Maximum and subsequent Neoglacial may have contributed to these shifts, pollen and diatom records suggest only subtle responses to Holocene climatic changes. A core chronology inferred from radioisotopes suggests a hiatus in sediment accumulation between 3650 and 200 cal. BP. Peaks in carbonate inferred from loss-on-ignition and increases in bulk density in that section of the core suggest some effect of erosional or thermokarst processes, or the breaching of a sandbar, now a remnant island in the lake, in the drainage of the lake and ensuing hiatus. Sediment accumulation resumed within the past two centuries; diatom assemblages in the uppermost section are characterized initially by benthic diatoms of smaller valve size compared with the pre-hiatus assemblages. More recently, increases in the planktonic diatom Cyclotella stelligera are recorded, signaling significant environmental changes.

MODERN POLLEN RAIN AND DIATOM ASSEMBLAGES IN A LAKE ERIE COASTAL MARSH

We present an analysis of modern pollen and diatom assemblages in surficial sediments in a coastal marsh at Rondeau Provincial Park, on the northern shore of Lake Erie in southwestern Ontario, Canada. The objectives of the study were (1) to determine how pollen and diatom assemblages in surface sediments vary as a function of the dominant vegetation community and moisture availability at the sampling site and (2) to analyze pollen-vegetation relationships of four dominant wetland plants: Cephalanthus occidentalis, Phragmites australis, Typha spp., and Zizania aquatica, in order to improve interpretations of fossil sequences. Canonical variate analysis (CVA) was used to compare pollen and diatom spectra from sampling sites in three marsh zones delineated on the basis of moisture availability. Using the pollen or the diatom datasets, the resulting discriminant functions correctly classified 86% of the wettest sites, 72% of those with intermediate moisture availability, and only 25% of the sites in the driest parts of the wetland. Since 35% of the sampling sites were misclassified by the CVA on the basis of pollen assemblages, a representation factor approach is needed to complement the comparative approach when analyzing pollen datasets from wetland contexts. Percent cover vegetation data at sediment sampling sites are used to illustrate pollen-vegetation relationships for the ecologically important wetland plants at the site. Phragmites australis and Typha spp. produce small amounts of pollen relative to their abundance, while Cephalanthus occidentalis and Zizania aquatica produce abundant pollen, which is deposited highly locally in the case of Cephalanthus. These data will enable improved interpretations of fossil pollen and diatom sequences from wetland contexts.

Relative importance of climatic and autogenic controls on Holocene carbon accumulation in a temperate bog in southern Ontario, Canada

Peat cores from Wylde Lake Bog in temperate southern Ontario, Canada, were examined to determine factors affecting Holocene ecological change and long-term rate of carbon accumulation (LORCA). By 10,250 cal. BP, a marsh was established, characterized by sediments with higher bulk density, highly decomposed material in the macrofossil record, and lower LORCA. By 8100 cal. BP, the marsh was replaced by a peat-accumulating fen dominated by herbaceous taxa and non-Sphagnum mosses. Around 4000 cal. BP, transition to a Sphagnum-dominated bog took place. These directional changes suggest a strong role for autogenesis, although periodic fluctuations in macrofossil assemblages and in LORCA suggest an important secondary role for climatic change and disturbance in explaining Holocene changes. LORCA remained fairly stable through the fen and bog zones, ~18 g C/m2/yr. In the high-resolution record spanning the most recent 1800 years, relatively higher values for LORCA and macrofossils associated with wetter conditions were recorded around 1400 cal. BP, partially coincident with the ‘Medieval Climate Anomaly’. LORCA decreases to minimum values for the record during part of the ‘Little Ice Age’ as woody macrofossils increase, suggesting a drier peat surface. The most recent portion of the record shows significant changes in LORCA and in bog vegetation associated with anthropogenic land clearance and damming. The charcoal record suggests that fire did not play an important role in peatland dynamics in the pre-industrial Holocene; however, a major anthropogenic fire in ad 1870 significantly altered the peatland, affecting surface vegetation heterogeneously.