Dewey W. Dunnington

Late Holocene Records of Changing Moisture Regime from Wetlands in Southwestern Nova Scotia, Canada: Implications for Wetland Conservation and Restoration

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.

Anthropogenic activity in the Halifax region, Nova Scotia, Canada, as recorded by bulk geochemistry of lake sediments

ABSTRACT Dunnington DW, Spooner IS, Krkošek WH, Gagnon GA, Cornett RJ, Kurek J, White CE, Misiuk B, Tymstra D. 2018. Anthropogenic activity in the Halifax region, Nova Scotia, Canada, as recorded by bulk geochemistry of lake sediments. Lake Reserv Manage. 34:334–348. Separating the timing and effects of multiple watershed disturbances is critical to a comprehensive understanding of lakes, which is required to effectively manage lacustrine systems that may be experiencing adverse water quality changes. Advances in X-ray fluorescence (XRF) technology has led to the availability of high-resolution, high-quality bulk geochemical data for aquatic sediments, which in combination with carbon, nitrogen, δ13C, and δ15N have the potential to identify watershed-scale disturbance in lake sediment cores. We integrated documented anthropogenic disturbances and changes in bulk geochemical parameters at 8 lakes within the Halifax Regional Municipality (HRM), Nova Scotia, Canada, 6 of which serve as drinking water sources. These data reflect more than 2 centuries of anthropogenic disturbance in the HRM that included deforestation, urbanization and related development, and water-level change. Deforestation activity was documented at Lake Major and Pockwock Lake by large increases in Ti, Zr, K, and Rb (50–300%), and moderate increases in C/N (>10%). Urbanization was resolved at Lake Fletcher, Lake Lemont, and First Lake by increases in Ti, Zr, K, and Rb (10–300%), decreases in C/N (>10%), and increases in δ15N (>2.0‰). These data broadly agree with previous paleolimnological bioproxy data, in some cases identifying disturbances that were not previously identified. Collectively these data suggest that bulk geochemical parameters and lake sediment archives are a useful method for lake managers to identify causal mechanisms for possible water quality changes resulting from watershed-scale disturbance.