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Late Holocene Records of Changing Moisture Regime from Wetlands in Southwestern Nova Scotia, Canada: Implications for Wetland Conservation and Restoration
Ian Spooner, Sarah Principato, Nicholas Hill, Hilary White, Dewey Dunnington, Tom Neily, and Susann Stolze

Northeastern Naturalist, Volume 24, Issue 3 (2017): 331–348

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Northeastern Naturalist Vol. 24, No. 3 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 331 2017 NORTHEASTERN NATURALIST 24(3):331–348 Late Holocene Records of Changing Moisture Regime from Wetlands in Southwestern Nova Scotia, Canada: Implications for Wetland Conservation and Restoration Ian Spooner1,*, Sarah Principato2, Nicholas Hill3, Hilary White4, Dewey Dunnington1, Tom Neily3, and Susann Stolze5,6 Abstract - An understanding of the morphological stability and succession of open water and wetland ecosystems in Nova Scotia is a priority for informing the conservation management of critical habitats for a complex of nationally listed, rare, disjunct wetland species. Baltzer Bog and Big Meadow Bog in southwestern Nova Scotia contain stratigraphic records of late Holocene moisture variability. Baltzer Bog is a shrub bog that formed in an elevated, enclosed kettle basin. Excavated sections exposed by peat mining revealed 2 distinct wood-rich horizons that are located above a well-developed soil and wood horizon that yielded a radiocarbon-dated age of 3260 cal. BP from an upright stump. The overlying wood-rich horizons were dated at 1640 and 1045 cal. BP and were overlain by Sphagnum species transitions indicative of increasing wetness. At Big Meadow Bog, a thin wood mat in Sphagnum at 90 cm depth was dated at 1760 cal. BP. These records are broadly correlative with pollen and stratigraphic data from Pleasant River Fen in central Nova Scotia that indicate periods of high and low productivity and a fluctuating water table from 1950 cal. BP until present. Though other high-resolution paleoclimate records from the region indicate that the late Holocene was a time of increasing precipitation and cooler air temperatures, these wetland records demonstrate that in Nova Scotia this time period was characterized by rapid variations in effective moisture and that significant and sustained dry periods likely occurred. This record of late Holocene moisture variability and its influence on habitat structure serves to better establish the potential for long-term residency of threatened and endangered species at wetland sites. Introduction Nova Scotia, Canada has one of the densest archives of regional paleoenvironmental data in Eastern North America because of the excellent preservation of lake sediments of Late Wisconsinan and Holocene age (Stea and Mott 1998). Although climate-change records interpreted from lake sediments provide a detailed chronology for the Last Glacial Maximum, the Younger Dryas, and the Early Holocene, there are gaps in the record during the last 5000 years. Wetlands have received far 1Department of Earth and Environmental Science, Acadia University, Wolfville, NS, B4P 2R6, Canada. 2Environmental Studies, Gettysburg College, 300 North Washington Street, Gettysburg, PA 17325. 3Fern Hill Institute for Plant Conservation, 424 Bentley Road, Berwick, NS, B0P 1E0, Canada. 4Department of Geography and Environmental Studies, Wilfrid Laurier University, 75 University Avenue West, Waterloo, ON N2L 3C5, Canada. 5Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401. 6Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80303. *Corresponding author - ian.spooner@acadiau.ca. Manuscript Editor: Gail Chmura Northeastern Naturalist 332 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 Vol. 24, No. 3 less attention than lake sites, though they have the potential to preserve long (>9000 years) and continuous records of hydrological variability, a proxy for moisture regime (Robichaud and Bégin 2009, Spooner et al. 2014, Suarez-Gonzalez et al. 2016). Abiotic proxy records indicate that the middle Holocene thermal maximum was followed by a transition to cooler and moister climate, though the timing of this transition is poorly constrained (Lennox et al. 2010, Spooner et al. 2014). Similarly, most pollen records from lake and wetland archives in Nova Scotia indicate a muted response to this transition (Davis 1983, Green 1987, Ogden 1987). At Pleasant River Fen, southcentral Nova Scotia, sediment stratigraphy, pollen data, and various proxies suggest a changing late Holocene moisture regime, in particular an increase in precipitation and water-table fluctuation from 5250 cal. BP onwards (Spooner et al. 2014). An understanding of moisture regime in Nova Scotia and its impact on both open water and wetland environments is a priority because these environments provide habitat for disjunct and genetically distinct populations of a number of threatened and endangered species such as Emydoidea blandingii (Holbrook) Blanding’s Turtle; COSEWIC 2017, Mockford et al. 2005) and a suite of rare Atlantic Coastal Plain, arctic–alpine, and boreal plants including Geum peckii Pursh (Eastern Mountain Avens; Hill and Keddy 1992, Munro et al. 2014). The survival of these species may depend, in part, on the stability of wetland habitat when subjected to environmental change. Recent studies on the suitability of wetlands in Nova Scotia for restoration and species re-introduction have focused on reversing the impact of anthropogenic alteration of local hydrology (e.g., Eastern Mountain Avens at Big Meadow Bog) and determining optimum forest and wetland structure (e.g., Blandings’s Turtle at Pleasant River Fen) (Newton and Herman 2009, Spooner et al. 2014). An understanding of how these wetlands responded to past environmental change is required to provide context for habitat management and restoration efforts given predicted future changes. In this study, we investigated biostratigraphic records from 2 wetlands in southwestern Nova Scotia. At Baltzer Bog, in the Annapolis Valley, a peat section 2.3 m thick and containing wood-rich layers and upright stumps is exposed in a kettlelake bog (elevated, closed basin wetland) that overlies Wisconsinan glacial outwash sand. At Big Meadow Bog on Brier Island, NS, trenching and vibracoring the central zone of a raised bog formed on the base of marine sand revealed a wood-rich layer at the base of the peat and a succession of Sphagnum types. As Smith (1957) speculated, the former population ranges of many species are based almost exclusively on modern ranges. The Baltzer Bog and Big Meadow Bog paleoenvironmental records provide a 3500-year perspective on moisture variability that may offer insight into species resilience to environmental change and habitat suitability for wetland restoration and/or species re-introduction (Spooner et al. 2014). Study Sites Baltzer Bog is a 28-ha shrub bog located in Coldbrook, NS, Canada (45°04'N, 64°35'W; Fig. 1). Abies balsamea (L.) Mill (Balsam Fir), Rubus allegheniensis PorNortheastern Naturalist Vol. 24, No. 3 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 333 ter (Common Blackberry), Juniperus communis L. (Common Juniper), Pinus strobus L. (White Pine), Pinus resinosa Aiton (Red Pine), Betula papyrifera Marshall (Paper Birch), and Acer rubrum L. (Red Maple) are all common along the edges of Figure 1. Location of the Baltzer Bog study site and sections (indicated by stars). The site is located within a closed basin on top of an extensive kame deposit and is presently being mined for both peat and aggregate. Site stratigraphy was obtained from drainage ditch exposures at sections S1 and S2 and logs from hydrogeological wells (after Hennigar 2006). Northeastern Naturalist 334 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 Vol. 24, No. 3 the bog. Plants found in the bog include: Picea mariana (L.) Mill. (Black Spruce), Gaylussacia dumosa (Andrews) Torr. & A. Gray (Dwarf Huckleberry), Larix laricina (Du Roi) K. Koch (Eastern Larch), Rhododendron groenlandicum (Oeder) Kron & Judd (Labrador Tea), Sphagnum spp. (peat moss), Rhododendron canadense (L.) Torr. (Rhodora), and Carex scoparia Schkuhr ex Willd. (Broom Sedge) (Munro et al. 2014). Standing water is often present where the bog has been cut at Wood Lake (Fig. 1), which is the lowermost point in the bog. Baltzer Bog has been mined for peat and aggregate and has been farmed sporadically over the past 50 years. The site is located within an elevated, closed basin on top of an extensive kame deposit. The sand and gravel that underlies the peat deposits is relatively coarse and contains a low percentage of silt- and clay-sized material. As a consequence, this sand is very well drained and has high conductivity and low soil-moisture retention capacity (Langille et al. 1993). The well-drained sand is underlain by a silty sand that is moderately to poorly drained and results in the development of a local perched water table (Fig. 1). Baltzer Bog likely initiated as a kettle-lake bog when reeds, sedges, and mosses slowly expanded across a very shallow pond (now Wood Lake; Fig. 1) in response to a rising water table. A paludification bog likely formed around the periphery of the study site as previously dry land was covered by bog vegetation. These conditions can occur due to an elevation in the water table brought about by climatic change, local hydrological change caused by beaver dams or logging, or the natural advancement of a peatland. In both kettle-lake and paludification bogs, the accumulation and compression of lower layers of peat can detach the underlying mineral-rich soil from the water table creating acidic conditions that may kill existing trees and allow bog vegetation to dominate (Cwikiel 2003). Excavation and trenching corresponding with past commercial peat extraction has exposed 2–3-m sections of peat and wood mats (Fig. 2). A recent hydrological study of Wood Lake in Baltzer Bog (Jacques Whitford 2005) indicated that water is lost by evaporation and seepage through the bottom of the lake at approximately equal rates. Natural groundwater fluctuations average about 3 m in range. Big Meadow Bog is an oval-shaped peatland 2 km in length with a central raised bog that formed between the East Ferry and Brier Island member basalt ridges of the North Mountain at Brier Island, the westernmost land of the Digby Peninsula (44°15'N, 66°21'W; Fig. 2). The climate is boreal with average summer temperatures below the July isotherm delimiting the southern edge of the Boreal forest. Groundwater flow along the east and west edges of the peatland from minerotrophic swamps on the basalt ridges creates a marginal fen bounded and influenced by both the central raised bog and the surrounding swamps. This is a classic “lagg” ecotone (Howie and Tromp-van Meerveld 2011), and the Big Meadow Bog lagg originally consisted of a system of pools and streams that set up a dynamic habitat for a complex of rare boreal organisms (e.g., Carex livida (Wahlenb.) Willd. (Livid Sedge), Betula michauxii Sarg. (Michaux’s Birch), the fishing spider Dolomedes striatus Giebel, and the endangered (COSEWIC 2010) Eastern Mountain Avens. Ditching of the lagg zones and the central raised bog in 1958 accelerated outflow and lowered Northeastern Naturalist Vol. 24, No. 3 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 335 the water table (Environment Canada 2010). The lowered water table made the bog attractive for nesting gulls, and the accumulated guano from nearly 40 years of gull nesting (1978 to present) has transformed an ombrotrophic, Sphagnum-based bog containing Sphagnum Section Acutifolia, S. magellanicum Brid. (Magellan’s Sphagnum), and S. affine Ren. & Card. with ericad shrubs and Rubus chamaemorus L. (Cloudberry), into a weedy mosaic of introduced grasses, canes (Rubus spp.) and non-ericad shrubs (Environment Canada 2010). Brier Island at the mouth of the Bay of Fundy is believed to have been the earliest land on Nova Scotia to deglaciate during the Chignecto Phase (15.9–14.7 cal. BP; Stea et al. 2011). The relatively early deglaciation of the Digby Peninsula may have afforded boreal and arctic–alpine plants a refuge as competitive processes at the margin of the retreating continental glacier led to arctic–alpine communities being replaced by boreal species and these in turn by the temperate flora as climate Figure 2. Location of the Big Meadow Bog study site on Briar Island, southwestern Nova Scotia. Big Meadow Bog is an oval-shaped peatland 2 km in length that has drainage ditches excavated in the late 1950s. A minerotrophic swamp on basalt drains into the lagg on each side of the bog. The star indicates the section location. Northeastern Naturalist 336 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 Vol. 24, No. 3 rapidly warmed. Upon deglaciation, the Eastern Mountain Avens would have had to follow its arctic–alpine community type north and eastward to keep from being outcompeted by the more competitive vegetation that would have replaced the low biomass communities of stress-tolerant plants at the glacier edge. Brier Island may have deglaciated 2000–2500 years before alpine New Hampshire (cf. values in Stea et al. 2011 and Thompson et al. 1999). Stea et al. (2011) suggested that a corridor for animals and plants likely was available along the edges of the Bay of Fundy in the Chignecto phase of the Appalachian Glacier Complex (R.R. Stea, Nova Scotia Depratment of Natural Resources, Halifax, NS, Canada, 2015 pers. comm.). The thin maritime band of boreal climate along Nova Scotia’s shoreline suggests a potential pathway for the continued migration of the boreal organisms on Brier Island; however, a geological interval of almost 500 km of incompatible rock type (Meguma Formation slate and metaquatzite) exists between Big Meadow Bog and calcium-rich rock of Richmond County, Cape Breton, limiting eastern migration. Climate Due to the high precipitation rates associated with maritime air masses and the wide annual temperature range associated with its continental location, the climate of Nova Scotia is classified as a moist continental climate (Shaw et al. 1996). The ocean modifies the continental climate of Nova Scotia. The North Atlantic Drift, an extension of the Gulf Stream, brings warm water (~16 °C) several hundreds of kilometers south of Nova Scotia, warms summer air temperatures, and extends the fall season by several weeks (Jetté and Mott 1995). The cool Nova Scotia Current, an extension of the Labrador Current, has the opposite effect: this cold water current (~8–12 °C) decreases sea surface temperatures along the Scotian Shelf, moderates winter temperatures, and delays the onset of spring by a couple of weeks (Jetté and Mott 1995). The Digby peninsula (Big Meadow Bog) has a total annual precipitation of 140 cm, an average low temperature of 4 °C , and an average high temperature is 11 °C., whereas the eastern Annapolis Valley (Baltzer Bog) is somewhat drier (average precipitation = 100 cm) and warmer in the summer months and cooler in the winter (average high = 12 °C, average low = 2 °C) (Environment Canada 2016). Methods We conducted stratigraphic description and macro- and microfossil collections at Baltzer Bog and Big Meadow Bog at peat sections centrally located within the bogs (Figs. 1, 2) and exposed by past commercial activities. At the Baltzer Bog site, we used a small percussion corer to obtain samples from below the waterline. Peat samples were refrigerated until analysis at Acadia University. At Big Meadow Bog, we dug a pit 90 cm deep to intersect a wood mat revealed in a nearby drainage ditch. At both sites, we sampled the sections at 10-cm intervals to determine section stratigraphy and to interpret vegetation assemblages. At the Big Meadow Bog site, the peat stratigraphy exposed in the dug pit was extended by vibracorNortheastern Naturalist Vol. 24, No. 3 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 337 ing. We collected macro- and microfossils as potential indicators of changing local environmental conditions and for radiocarbon dating. We measured water content for peat samples at Baltzer Bog and Big Meadow Bog using a drying oven at 50 °C for 24 hours, and recorded the Munsell color of dry samples. We determined the degree of decomposition (humification index-bog surface wetness index) of peat in the sections at both Big Meadow Bog and Baltzer Bog using the methods of Blackford and Chambers (1993). A 0.2-g ground sample was simmered in 100 mL of 8% NaOH for one hour. Humic acids were extracted from this solution following a series of filtrations. The percent light transmission and absorbance of the extracted humic acid were measured using a spectrophotometer set at 540 nm. We present humification data for the excavated section as raw data and normalized values using the calculation of Blundell and Barber (2005:fig. 2). Normalized data are referred to as the bog surface wetness (BSW) index. We developed a stratigraphic profile of the Sphagnum moss community for the Big Meadow Bog section to explore whether shifts in the relative abundances of Sphagnum species might reflect changes in peatland conditions. The Sphagnum study was initiated in conjunction with and supported by Environment and Climate Change Action Plan for the Eastern Mountain Avens in Canada. Sphagnum species are known indicators of both the hydrological and nutrient status of peatlands (Galka and Lamentowicz 2014, McQueen 1990) and we developed a successional history for each peatland from the relative abundance of Sphagnum leafs in each 10-cm depth interval. Five forceps samples (less than 1 cm3) were taken from refrigerated peat collections from each 10-cm interval of the section and vibracore from Big Meadow Bog. For each sample, we made a peat slurry in 25 mL of water and counted the number of different Sphagnum leaf morphotypes using a dissecting microscope. Section Sphagnum was recognized at low magnification by its large, ovate, cucullate branch leaves and confirmed at high power, by the resorption furrow evident in cross section on the leaf margin. Sphagnum magellanicum of Section Sphagnum was readily recognizable with large, spoon-leaves (~2.5 mm long) and chlorophyllose cells of branch leaves that were completely enclosed (McQueen and Andrus 2007). The other Section Sphagnum species was identifiable as either S. affine or S. austinii Sull. in Aust. (Austin's Sphagnum); green cells were not enclosed and were shaped like equilateral triangles, and hyaline cells had ridge-like comb fimbrils (Andrus and McQueen 2007). There were no attached stem leaves observed in this study, a common impediment to specific determinations in Sphagnum (Barber et al. 1998). At another fen on Brier Island, stem leaves for S. affine/S.austinii were found but only in peat just below surface (ca. 300 BP applying the depth-to-age relation from Big Meadow) in 3 of 5 subsamples. The lack of comb-fimbrils in the stem leaves in these subsamples identified the material as S. affine (Allen 2006). The 2 taxa (S. affine and S. austinii) occur in distinct regions and microhabitat of peatlands; whereas S. affine occurs in minerotrophic fens, S. austinii is usually found in bog hummocks (Gunnarsson et al. 2002). Sphagnum affine is more common in the contemporary fen landscape on Brier Island (T. Neily, unpubl. data). Smaller acute and narrow leaves in the slurries belonged to Northeastern Naturalist 338 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 Vol. 24, No. 3 Sphagnum Section Acutifolia, which we recognized at higher magnification by triangular to trapezoidal green cells with broader exposure over the inner leaf surface (Andrus and McQueen 2007). Leaves of Section Acutifolia could not be identified at the species level but were most common overall in the peat profile and in the contemporary peatland flora around Big Meadow Bog which contained 4 species of the Section in abundance (S. girgensohnii Russ. [Girgensohn’s Sphagnum] in swamps, S. flavicomans (Card.) Warnst. and S. capillifolium (Erh.) Hedw. in open fen and bog, and S. fuscum (Schimp.) Kinggr. on hummocks of raised bog). These species cover large ecological gradients, meaning that there is little habitat information in the Section Acutifolia data. We established the chronology of the Baltzer Bog and Big Meadow Bog sections using conventional radiocarbon dates of upright stumps located at the top of each wood mat exposed in excavated sections and from wood recovered from vibracoring (Table 1). The age assigned to each was calculated from the best-fit intercept of the radiocarbon age to the calibration curve using INCAL13 (Reimer et al. 2013). Results Baltzer Bog A gleyed soil horizon is located at the contact between the kame sand and the overlying organic sediment at Baltzer Bog (Fig. 3). The parent material is siliceous outwash sand and the gravel/cobble content is generally low in surface horizons. Drainage is moderate to poor due to its location in a depression and restricted vertical drainage due to the proximity of the water table (Fig. 1). The soil contains terrestrial vegetative matter including coarse woody material as well as seeds and other non-woody detritus. Mineral matter constitutes about 20% of the sediment by volume. A coarse wood mat ~50 cm thick overlies the soil horizon at 1.55 m depth (Figs. 3, 4). A date of 3260 cal. BP was obtained from a stump in life position. Stumps with boles are common in this lowermost wood mat and consisted primarily of Black Spruce and Chamaecyparis thyoides (L.) Britton, Sterns, & Poggenb (Atlantic White Cedar). Logs are also common in the lowermost layer and can have diameters in excess of 35 cm. The lowermost wood mat is overlain by wellpreserved, red-hued Sphagnum peat as well as Sphagnum leaves and stems. This sediment contains very little woody material or minerogenic sediment. Table 1. Radiocarbon data from wood collected from Baltzer Bog and Big Meadow Bog, NS, Canada. Radiocarbon analyses were performed at Beta Analytic, Miami, FL. Calibrated ages are given as mean calendar years (Stuiver and Reimer 1998). Depth Age Age Max–min age Site Lab # (cm) (14C yr BP) (2б-cal. BP) (2б-cal. BP) Material δ13C (‰) Baltzer Bog 204970 82 3070 ± 50 3260 3380–3150 Wood -21.7 Baltzer Bog 287386 61 1730 ± 40 1640 1720–1540 Wood -25.0 Baltzer Bog 299069 8 1110 ± 50 1045 1160–930 Wood -24.7 Big Meadow Bog 360367 92 1820 ± 30 1760 1820–1700 Wood -24.3 Big Meadow Bog 409374 193 8370 ± 30 9345 9385–9305 Wood -26.0 Northeastern Naturalist Vol. 24, No. 3 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 339 There were 3 discrete interruptions by wood layers above the lowermost wood mat at Baltzer Bog. Wood mats were encountered at 1.0 m and 0.6 m depths, and stumps were dated at 1640 cal. BP and 1045 cal. BP, respectively (Fig. 4, Table 1). Each of these mats contain upright stumps that have bole diameters of less than 10 cm. Small branch debris was very common in these wood mats, and Sphagnum was absent or occurred in trace amounts in the largely organic matrix surrounding the wood debris. Sphagnum samples above and below these 2 wood mats exhibited significant variability in percent light transmission values and Munsell color, which is indicative of changing degrees of humification. High percent light transmission values correspond with light Munsel colors (e.g., 51% and 7.5YR 4/6, strong brown) and are associated with a low degree of humification. Low percent light transmission corresponds to dark Munsel colors (e.g., 14% and 7.5YR 5/2, very dark brown) and a high degree of humification. The bog surface-wetness data (BSW; Fig. 4) record 3 increases indicative of relatively high decomposition that occur above wood mats at 1.25 m (ca. 3200 cal. BP), 0.77 m (ca.1550 cal. BP) ,and 0.53 m (ca. 1000 cal. BP). Strata in which little wood was found tended to exhibit Figure 3. Sediment section at Baltzer Bog (S1 in Fig. 1) showing (A) the contact between the kame sand and the overlying organic sediment, (B) coarse wood above the soil horizon, and a (C) wood layer overlain and underlain by Sphagnum peat. Northeastern Naturalist 340 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 Vol. 24, No. 3 higher BSW values, whereas BSW values for the wood-rich sections was relatively low. The upper most wood mat occured at 10 cm depth, continued to the bog surface, and contained no stumps and few logs. Big Meadow Bog The single wood layer at 90 cm in the Big Meadow Bog occurred in a peat matrix dominated by Sphagnum magellanicum with Sphagnum Section Acutifolia where there were upright trunks of Black Spruce with root and trunk bases but little remnant preserved trunk material. A peat moss layer dominated by S. affine occurred directly above the S. magellanicum-dominated wood layer. The greatest percentages (≥ 50%) of S. affine among Sphagnum leaf types in the profile occurred from 60 to 90 cm; the last 700 years of peatland (i.e., 40 cm) was entirely Sphagnum Section Acutifolia. Figure 4. Section stratigraphy at Big Meadow Bog and Baltzer Bog showing age of wood mats, Sphagnum species composition (Big Meadow Bog), and BSW index. Northeastern Naturalist Vol. 24, No. 3 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 341 Similar to Baltzer Bog, Sphagnum samples exhibited variability in percent light transmission values and Munsell color. The bog surface wetness data (BSW) for Big Meadow Bog record an increase above the wood mat at 90 cm, indicating relatively high decomposition (Fig. 4). Conventional radiocarbon dates were from an upright stump (Fig. 5A), and a lower wood mat yielded an age 1760 cal. BP. A radiocarbon sample from the underlying marine mud yielded a date of 9345 cal. BP. Discussion High-resolution paleoclimate records from southwestern Nova Scotia generally indicate that the late Holocene was a time of increasing precipitation and cooler air temperatures (Lennox et al. 2010, Spooner et al. 2014). The Baltzer Bog and Big Meadow Bog records, however, demonstrate that during this time the water table Figure 5. Sediment section at Big Meadow Bog showing (A) an upright s p r u c e log with an intact root ball removed from a nearby drainage ditch at approximately the same depth from the bog surface as (B) the wood mats exposed in the test pit . Northeastern Naturalist 342 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 Vol. 24, No. 3 fluctuated and that significant and sustained dry periods likely occurred. The stratigraphic record at Baltzer Bog indicates that at least 3 woodland–wetland transitions have taken place. The wetland is located in a closed basin on an elevated kame and initially developed in response to rising water table at less than 3200 cal. BP. The presence of alternating wood mats and Sphagnum indicates that the water table fluctuated substantially after a rise in the water table inundated the site. The lack of appreciable Sphagnum and the development of a soil underneath the lower-most wood mat indicates that the Baltzer Bog site was not wet from the time of deglaciation (ca. 12000 cal. BP) until at least 3260 cal. BP. The preservation of the wood above the soil and the abrupt transition to Sphagnum likely indicates a rapid increase in water-table elevation. The preservation of wood depends upon its susceptibility to both aerobic and anaerobic decomposition by microbes, where it is located in the peat profile, how long it remains in the oxygenrich upper layer of the bog, and the density of the overlying Sphagnum which might reduce the accessibility to the microbial population (Moore 1989). While the earliest wood mat occurred on mineral substrate, its preservation was made possible by the Sphagnum matrix. The elevated water table resulting from the peat moss’s capillary action restricts oxygen diffusing into the surface peat layer. As a result, tree root metabolism and lignin oxidase of decomposers are inhibited causing trees to die and the lignocellulose of the dead trees to be preserved. No community-level insight into the Sphagnum Section Acutifolia community at Baltzer Bog was possible, but the 3 transitions to Sphagnum as well the pattern of tree decomposition (mostly stump and roots alone preserved) represent rapid increases in the water table. At Big Meadow Bog, a Black Spruce swamp with Sphagnum magellanicum had a 400-year occupancy, and the disappearance of the wood mat from the core coincided with the first appearance of Sphagnum affine, a fen species. The transition from swamp to fen runs counter to most cases of autogenic peatland succession models, although cases of forest paludification have been documented in Alaska (Noble et al. 1984). The ability to separate cases of Sphagnum successions driven by autogenic versus allogenic factors is informed by understandings of paleohistoric climatic changes particular to a regional setting (Payette 1988). Single landscapes may have wetlands that are out of phase due to autogenic (or cyclic autogenic) processes (Payette 1988). When different landscapes within a single region have wetland processes that are chronologically in-phase, paleo-reconstruction data serve to reinforce our understanding of allogenic, cl imatic influence. Our reconstruction of the Big Meadow Bog wetland history based on wood and the 3 Sphagnum types is a simplified analog of a 6000-year peatland history for a Baltic bog which featured the same Sphagnum type transitions (Gałka and Lamentowicz 2014). In that study, S. magellanicum was a pioneer species correlated with treed phases of the bogs. At Big Meadow Bog, S. magellanicum (Section Sphagnum) with S. girgensohnii (Section Acutifolia) are the most common mosses in the swamp surrounding the open peatland. Sphagnum magellanicum is morphologically adapted to the low UV levels in the understory of trees or shrubs (Searles et al. 2002). Sphagnum affine is a known fen species (Crum 1992, Malmer et al. 2003) Northeastern Naturalist Vol. 24, No. 3 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 343 that occurs in the fen lagg of Big Meadow Bog in the contemporary landscape. Whereas S. magellanicum may be indicative of either shade or relative dryness, the appearance of S. affine at Big Meadow Bog may indicate periods of higher water table, and its placement in the succession after the demise of the trees (Black Spruce) strongly suggests that the disappearance of the trees is related to their inability to tolerate root-zone anaerobiosis. Despite the distribution of Black Spruce over a variety of treed wetland types, its root tips are highly sensitive to flooding (Levan and Riha 1985). A wetland stratigraphic record from Pleasant River Fen about 100 km southwest of Baltzer Bog demonstrated an increased influx of coarse minerogenic matter at 5250 cal. BP, which coincides broadly with other records of the development of cooler and wetter conditions during the late Holocene (Spooner et al. 2014). The apparent disparity in timing between these 2 records of increased precipitation might be attributed to the location of the 2 sections at Baltzer Bog at the side rather than the base of the kame depression leading to a lag between initial increase in precipitation and flooding at the location of the sections. Though the Baltzer Bog record does not constrain the timing of initiation of the late Holocene transition to moister climate, it provides a minimum date. It is likely that the elevation of the base of the Baltzer Bog section is sufficiently above the local (perhaps perched) water table that a significant time lag existed between the initial increases in moisture and the drowning of the forest that records the rise in the local water table. The basal date of 3260 cal. BP indicates increased moisture, a rising local water table, and drowning and subsequent preservation in a bog environment of a forest that existed at the site. The 2 later woodland–wetland transitions at the Baltzer Bog site, sometime after 1640 cal. BP and 1045 cal. BP, respectively, indicate 2 previously unrecognized transitions in the Nova Scotian late Holocene moisture record (Spooner et al. 2014). We dated tree samples at the top of the wood mat and as close to the woodland–wetland transition as possible to better constrain the timing of increased moisture. In the Pleasant River Fen record, rhythmicity is apparent from 1950 cal. BP onwards and is distinguished by slight changes in sediment color, likely indicating periods of high and low productivity, a fluctuating water table, and/or episodes of flooding, though this sequence is poorly constrained. The Baltzer Bog and Big Meadow Bog records represent 2 independent wetlands that, along with the Pleasant River Fen record, suggest the occurrence of a series of Holocene wetting periods as far back as 5250 cal. BP and as recent as 1045 cal. BP. In addition, the data indicate an apparent overlap between the timing of the loss of wood at Baltzer Bog (1640 cal. BP) and at Big Meadow Bog (1760 cal. BP). The 2 most recent of the apparent wetting events (i.e., 1045 cal. BP and 1640–1760 cal. BP) may be region specific given that these dates were interpreted by Payette (1988) as dry Holocene periods related to a period of expansion of Sphagnum nemoreum and drought stunting of Black Spruce. Paleoecological records from northeastern Canada indicate significant climate variability during the Little Ice age rather than sustained cooling, a condition also likely in Nova Scotia (Lemus-Lauzon et al. 2016, Roy et al. 2011). Northeastern Naturalist 344 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 Vol. 24, No. 3 Both Baltzer and Big Meadow bogs are now highly disturbed wetlands. The former was ditched and harvested for peat, the latter ditched for agriculture and then abandoned. In both cases, there are conservation reasons for wetland restoration: peat harvest has been halted at Baltzer Bog, and a detailed restoration effort is beginning at Big Meadow Bog that is driven by the Recovery Plan for the endangered Eastern Mountain Avens. This globally rare, arctic–alpine plant thrives only in the mountains of New Hampshire and wetlands on Brier Island (Munro et al. 2014). The lagg fen of Big Meadow Bog provides a paleorecord of community change from sea lagoon to spruce swamp to fen then raised bog, direct evidence of the need for dynamic conservation land planning. Prior to the transition from Sphagnum affine to a community composed of Sphagnum Section Acutifolia, the entire “bog” expanse was likely a south- and north-flowing fen originating in the middle of the peatland. Though possible, it is unlikely that Eastern Mountain Avens would have successfully occupied a fen-only peatland because it is absent from such landscapes on Brier Island and over a 20-km stretch of intermittent fen north of Brier Island that supports the rare Lophiola aurea Ker Gawl. (Coastal Plain Goldcrest). However, in planning for critical habitat for the endangered Eastern Mountain Avens, the paleorecord suggests that in half a millennium, parts of this linear expanse of fen, between the same basalt ridges that formed Big Meadow Bog, will become raised bog with the attendant essential lagg habitats on either side. Rare plants are most often specialists (Griggs, 1940, Mobaied et al. 2015) and indicators of particular landscape features (Crain et al. 2015, Edwards and Weakley 2001, Miller 1986). This is clear for rare wetland Atlantic Coastal Plain herbs, the majority of whose Canadian habitat cases were associated with the low-biomass shorelines of lakes with large catchment-areas (Hill and Keddy 1992). A similarly strong landscape attachment may also hold for the arctic–alpine Eastern Mountain Avens and its associated complex of rare boreal organisms (Carex livida, Betula michauxii, Dolomedes striatus, and various Sphagna [S. teres, S. contortum, and a putative S. carolinianum]) that are most common in the portions of lagg fen where near-neutral swamp water forms pools at the edge of the bog rand that are least affected by ditching and gull guano enrichment. It should be emphasized that the lagg is a dynamic landscape both in terms of its contemporary natural disturbance regime that fosters diversity and also as a somewhat ephemeral feature at the millennial time scale. These 2 time scales inform the conservation planning for the Eastern Mountain Avens (Environment and Climate Change Canada 2016). Though the water table rise is a local phenomenon, the apparent persistent increase in moisture (and perhaps decrease in temperature leading to decreased evapotranspiration) recorded in all 3 sections at the 2 wetland sites likely indicates a significant climate regime shift. Other paleoenvironmental records indicate similar but much subtler late Holocene trends. Lennox et al. (2010), in a paleolimnological study at Canoran Lake, located about 80 km to the southeast of Big Meadow Bog, noted both fluctuating and higher than normal lake levels in the late Holocene. Historical records show that over the past 100 + years, Baltzer Bog and Big Meadow Bog have been in transition from wetland to woodland, which may be an Northeastern Naturalist Vol. 24, No. 3 I. Spooner, S. Principato, N. Hill, H. White, D. Dunnington, T. Neily, and S. Stolze 2017 345 indication of a declining water table but also may be influenced by drainage modification and peat harvesting on site, and the inability of Sphagnum to regenerate (Environment Canada 2010). The woodland transition at Pleasant River Fen from 200 cal. BP onwards was likely influenced by human activity in the region (fire, water-level management), which may have accelerated the trend in declining moisture availability (Lemus-Lauzon et al. 2016, Spooner et al. 2014). Conclusions Baltzer Bog and Big Meadow Bog contain stratigraphic records of a late Holocene transition to moister climate shortly after 3000 cal. BP. The 2 later woodland– wetland transitions at the Baltzer Bog site, sometime after 1640 cal. BP and 1045 cal. BP, indicate 2 previously unrecognized transitions in the Nova Scotian late Holocene moisture record. However, significant periods of late Holocene drying took place and are recorded stratigraphically by the presence of a conifer forest at both sites indicating a significantly lowered local water table. The Baltzer Bog record is in general agreement with other moisture-sensitive proxy records from the region, though the dry period that occurred ca. 1640 cal. BP was previously unrecognized. In light of recent studies that suggest long-term residency of disjunct species such as Eastern Mountain Avens and Blanding’s Turtle, the variability in water table and the coincident change in wetland habitat structure observed in wetlands in southwestern Nova Scotia can be used to better gauge species resilience in light of both anthropogenic and natural environmental change. 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