Georgian Bay Research Articles

Changes in aquatic vegetation and fish communities following 5 years of sustained low water levels in coastal marshes of eastern Georgian Bay, Lake Huron

AbstractAquatic vegetation in the relatively pristine coastal wetlands of eastern Georgian Bay provides critical habitat for a diverse fish community. Declining water levels in Lake Huron over the past decade, however, have altered the wetland plant assemblages in favour of terrestrial (emergent and meadow) taxa and have thus reduced or eliminated this important ecosystem service. In this study, we compared IKONOS satellite images for two regions of eastern Georgian Bay (acquired in 2002 and 2008) to determine significant changes in cover of four distinct wetland vegetation groups [meadow (M), emergent (E), high‐density floating (HD) and low‐density floating (LD)] over the 6 years. While LD decreased significantly (mean −2995.4 m2), M and HD increased significantly (mean +2020.9 m2 and +2312.6 m2, respectively) between 2002 and 2008. Small patches of LD had been replaced by larger patches of HD. These results show that sustained low water levels have led to an increasingly homogeneous habitat and an overall net loss of fish habitat. A comparison of the fish communities sampled between 2003 and 2005 with those sampled in 2009 revealed that there was a significant decline in species richness. The remaining fish communities were also more homogeneous. We suggest that the observed changes in the wetland plant community due to prolonged low water levels may have resulted in significant changes in the fish communities of coastal wetlands in eastern Georgian Bay.

Distribution of nuisance Cladophora in the lower Great Lakes: Patterns with land use, near shore water quality and dreissenid abundance

Selected shorelines and offshore shoals in Lakes Erie, Huron and Ontario were surveyed with a high frequency hydroacoustic system to investigate current spatial patterns of nuisance benthic filamentous algal (e.g., Cladophora) cover and stand height. Cladophora reached nuisance levels at all sites in Lakes Erie and Ontario, but not in Lake Huron or Georgian Bay. Despite clear gradients in coastal land cover, near shore water quality gradients were generally weak, and for Lakes Erie and Ontario, measures of near shore water quality were similar to that at offshore shoals. Hierarchical partitioning analysis suggested that while dreissenid mussel abundance appeared to be important in determining the magnitude of Cladophora standing crop, the joint contribution of catchment land cover, near shore water quality (nutrient levels and suspended matter) and dreissenid mussel abundance explained nearly 95% of the total variance in nuisance Cladophora standing crop observed in this study. Although the results from this study are necessarily correlative in nature and definition of causal relationships is not possible, these results provide corroborating evidence from sites across a gradient within and across the lower Great Lakes that is consistent with the operation of the near shore shunt model.

Sea lamprey wounding in Canadian waters of Lake Huron from 2000 to 2009: Temporal changes differ among regions

Lake Huron has undergone a number of substantial changes in recent years, including changes to management of the parasitic sea lamprey, Petromyzon marinus. While control strategies of lamprey involving lampricides have had some success, lamprey spawning in St. Marys River has been a major and persistent problem and has led to intensified treatment beginning in 1998. The objective of our study was to broadly examine lamprey spatial wounding dynamics of lake whitefish ( Coregonus clupeaformis) and lake trout ( Salvelinus namaycush) within the Canadian waters of Lake Huron from 2000 to 2009. Temporal trends were evident and these differed among regions (North Channel, northern Main Basin, southern Main Basin, northern Georgian Bay, and southern Georgian Bay). There was a monotonic annual increase in probability of wounding for both lake trout and lake whitefish in three of the five regions, with high increases seen in both northern and southern Georgian Bay. The increases in three of the five regions are unexpected given the ongoing treatment of St. Marys River.

Application of a glyphosate-based herbicide to Phragmites australis: Impact on groundwater and near-shore lake water at a beach on Georgian Bay

During the past decade, the invasive Phragmites australis (common reed) has established itself along beaches of the Great Lakes, causing detrimental impacts to both the natural ecological integrity of the shoreline and the recreational value of beaches. The herbicide Roundup®, containing the active ingredient glyphosate, was applied to Phragmites along a beach on the southern shore of Georgian Bay, Canada, to eradicate the Phragmites which was destroying the natural beach ecosystem. Groundwater and lake water were tested to determine if glyphosate enters the groundwater and lake at the beach and how long glyphosate will persist. Two days after application, the geometric mean concentration of glyphosate in the groundwater below the Phragmites was 0.060 μg/L with a maximum of 12.50 μg/L. Concentrations rapidly declined over the next two to three weeks to below minimum detection limits (< 0.020 μg/L). Glyphosate was also detected in the nearshore lake water with concentrations peaking at a geometric mean of 0.14 μg/L one week after application, and declining to 0.039 μg/L four weeks after application. Concentrations of glyphosate never exceeded the Canadian water quality guideline for the protection of aquatic life (65 μg/L) in either the groundwater or lake water. An approximate half-life for the dissipation of glyphosate by degradation and dilution/flushing as groundwater flows toward the lake, assuming a first order kinetic reaction, yielded a half-life of 3.5 during the 4 weeks after the herbicide was applied. The application of Roundup® resulted in an 90% reduction in the size of the stand of Phragmites.

Population Trends of Ring-billed Gulls Breeding on the North American Great Lakes, 1976 to 2009

After near extirpation in the early 20th century, Ring-billed Gulls (Larus delawarensis) are currently (2009) the most abundant colonial waterbird nesting on the Great Lakes. Nest count data are reported from four decadal censuses (1976–2009) conducted by the Canadian Wildlife Service and the U.S. Fish and Wildlife Service. Numbers increased from 305,790 nests (1976–80) to a peak of 718,887 nests (1989–90), then decreased to 652,664 (1997–2000) and to 585,984 nests (2007–09). Changes varied spatially after the second census with greatest losses (-38.6%) at North Channel, Georgian Bay and northern Lake Huron colonies, and greatest gains ( 324.2%) at Lake Michigan colonies. A total of 472 sites had nests in at least one census (Canada N = 319; U.S. N = 153). Eighteen (3.8%) colonies had >2,000 nests in all four censuses, and had 37.5–41.9% of all nests in each census. Site occupancy was fluid. A high proportion (56.8%, N = 268) of sites contained nests in only one of the four censuses, and few (N = 40, 8.5%) had nests in all censuses. Thirty-nine sites had >2,000 nests gains/losses between census periods; 14 (35.9%) were on urban/industrial lands with artificial substrates. Human management and predator activities at some colonies contributed to declines in nest numbers at these locations. Movement of breeding birds among colonies and changes in local food supply may have influenced changes in nest numbers elsewhere. Reasons for the overall nest losses across the Great Lakes after the second census are unknown.

Effects of landscape variables and season on reference water chemistry of coastal marshes in eastern Georgian Bay

We surveyed 34 marshes in relatively pristine Precambrian Shield catchments in Georgian Bay and related water chemistry to a suite of landscape-level variables, including characteristics of the marsh and its drainage basin. The first landscape principal component (explained 48% of variation) ordered marshes along a gradient with high values corresponding to marshes with large watersheds that contain extensive upstream wetland and that receive relatively high precipitation inputs. This axis was negatively related to specific conductivity, pH, nitrate nitrogen, and SO42– concentrations and positively related to total phosphorus, colour, suspended solids, ammonia nitrogen, and summer dissolved organic carbon. Stepwise regression models built using catchment- and marsh-level variables explained up to 64% of the variation in water chemistry variables. Average precipitation and snowmelt inputs to the catchments were first to enter the majority of models, alone explaining up to 43% of the variation (in the case of water colour), while drainage area alone explained 44% of the variation in pH. Concentrations of catchment-derived constituents in marshes were highest in spring, reflecting greater loadings from the watersheds, while ionic strength was highest during summer, reflecting increased contributions form other sources (i.e., lake water).

Use of ecological indicators to assess the quality of Great Lakes coastal wetlands

Over 2000 coastal wetland complexes have been identified in the Laurentian Great Lakes watershed, each providing critical habitat for numerous aquatic and terrestrial species. Research has shown there is a direct link between anthropogenic activities (urbanization and agricultural development) and deterioration in wetland health in terms of water quality and biotic integrity. In this study, we evaluate coastal marshes throughout the Great Lakes basin using a suite of published ecological indices developed specifically for coastal wetlands of the Great Lakes (Water Quality Index (WQI), Wetland Macrophyte Index (WMI), and the Wetland Fish Index (WFI Basin)). We surveyed 181 wetlands, including 19 in Lake Superior (11%), 11 in Lake Michigan (6%), 13 in Lake Huron (7%), 92 in Georgian Bay and the North Channel (51%), 18 in Lake Erie (10%), and 28 in Lake Ontario (15%), over a 13 year period (1995–2008). Water quality parameters were measured at every site, while paired fyke nets were used to assess the fish community (132 sites) and macrophytes were surveyed and identified to species (174 sites); all of this information was used to calculate the associated index scores. One-way ANOVA results showed that there were significant differences in wetland quality among lakes. According to the WQI, we found that over 50% of marshes in Lakes Michigan, Erie, and Ontario were in degraded condition, while over 70% of marshes in Lakes Superior, Huron, and Georgian Bay were minimally impacted. Georgian Bay had the highest proportion of wetlands in very good and excellent condition and least number of wetlands in a degraded state. The WMI and WFI showed similar results. This is the largest bi-national database of coastal wetlands and the first study to provide a snapshot of the quality of coastal habitats within the Great Lakes basin. We recommend this information be used to guide conservation and restoration efforts within the Laurentian Great Lakes.

Resting cysts of freshwater dinoflagellates in southeastern Georgian Bay (Lake Huron) as proxies of cultural eutrophication

Resting cysts attributed to the freshwater dinoflagellate genus Peridinium were found in surface sediments from Severn Sound, southeastern Georgian Bay (Lake Huron, Laurentian Great Lakes of North America). Two distinct cyst morphotypes were present and they were assigned to Peridinium wisconsinense Eddy, 1930 and Peridinium willei Huitfeldt-Kaas, 1900 by establishing cyst–theca relationships through germinations and single-cell LSU rDNA analysis on an excysted cell of Peridinium willei. Sediments recovered from deep, sheltered portions of Severn Sound and restricted basins like Honey Harbour contained between ~ 750 and 8500 cysts/cm 3. However, winnowing by bottom currents and high concentrations of dissolved oxygen adversely impact the dinoflagellate cyst record on the lakebed, and cyst concentrations in easily remobilized muds on bathymetric highs were < 100 cysts/cm 3. Down-core changes in the relative abundances of these two cyst morphotypes were attributed primarily to cultural eutrophication related to land-use changes around Severn Sound over the last six centuries. Cysts of Peridinium willei, a cosmopolitan dinoflagellate species that occurs in a broad range of temperature, pH and nutrient conditions, comprise 60–74% of the cysts identified in Ambrosia (ragweed)-rich sediments in the upper 20 cm of a gravity core taken from Honey Harbour. Euro-Canadian settlement and land-clearing that began in the Midland-Penetanguishene region around A.D. 1840 are evident in the increase in Ambrosia (ragweed), Gramineae (grasses) and other herbs (non-arboreal pollen) that mark the base of the Ambrosia zone (pollen zone 4) as well as an overall increase in terrigenous flux. In addition to siltation, this terrigenous flux increased the availability of limiting nutrients to the previously oligotrophic waters of Severn Sound, leading to increased cyst flux in Honey Harbour peaking at nearly 3000 cysts/cm 2/y in A.D. 1966, an order of magnitude higher than cyst fluxes prior to the Euro-Canadian Ambrosia zone. Peridinium wisconsinense was the more common dinoflagellate cyst species in Honey Harbour prior to Euro-Canadian settlement, when cyst flux was an order of magnitude lower. This is consistent with the restriction of this species to relatively warm, oligotrophic to mesotrophic lakes in North America. An earlier increase in P. willei at the expense of P. wisconsinense in the core from Honey Harbour within pollen zone 3 d (~ 700 to ~ 150 yBP) is attributed to earlier land-clearing by the Wendat (“Huron”), who practiced agriculture in the Penetanguishene peninsula between ~ A.D. 1450–1650. The cysts of these freshwater dinoflagellates thus appear to be sensitive to cultural eutrophication.

Buried bedrock valleys and glacial and subglacial meltwater erosion in southern Ontario, Canada

Morphometric features from a recently compiled bedrock topography map by the Ontario Geological Survey suggest a glacial erosion origin for the buried large bedrock valleys and troughs in southern Ontario. The bedrock valleys at Milverton, Wingham and Mount Forest are tunnel valleys, resulting from subglacial meltwater erosion beneath the Huron ice lobe, probably during or shortly after the Late-Wisconsinan glacial maximum. Diagnostic features for this interpretation include abrupt valley beginning and termination, uneven longitudinal valley profiles and up-slope gradients. The Dundas bedrock valley is the western extension of the Lake Ontario Basin. No comparable bedrock valleys were found to connect it to the Milverton valley for a joint drainage system as previously suggested. The Laurentian bedrock trough is the southeastward extension of the Georgian Bay Basin, both developed along shale bedrock between the Precambrian shield highlands and the Niagara Escarpment, resulting from long-term mechanical weathering associated with Pleistocene glacial erosion. This bedrock low has a floor that exceeds 50 km in width and is 26 m and more below the current water level of Georgian Bay. It could drain Georgian Bay should the drift cover be removed. There is no evidence to suggest that a preglacial river channel, if it existed, is still preserved in the floor of the Laurentian trough as previously suggested. The framework for an intensely glacially sculpted bedrock surface differs from the previous view for simple modification of a preglacial landscape and is, therefore, important in regional subsurface geological mapping and groundwater studies.

Application of the index of marsh bird community integrity to coastal wetlands of Georgian Bay and Lake Ontario, Canada

Ecological indicators have gained increasing attention within the scientific community over the past 40 years. Several taxonomic groups have been used successfully as indicators including most prominently fish, invertebrates, plants, and birds because of their ability to indicate environmental changes. In the Laurentian Great Lakes region, there has been recent concern over the applicability of using indicators on a basin-wide scale due to species range restrictions and lake-based differences. The objective of this study was to determine the ability of the Index of Marsh Bird Community Integrity (IMBCI) to indicate land use disturbance surrounding coastal marshes of Georgian Bay and Lake Ontario. To meet this objective, we surveyed birds and vegetation at 14 marshes in Georgian Bay (low land use disturbance) and Lake Ontario (high land use disturbance). Even though Lake Ontario marshes were surrounded by significantly more altered land than Georgian Bay marshes, and had poorer water quality, we found significantly fewer birds in Georgian Bay marshes (mean = 8.2) compared to Lake Ontario (mean = 13.7) and no significant difference in IMBCI scores. This inconsistency could be due to vegetation differences affecting the strength of the index, because Georgian Bay wetlands had significantly more bulrush ( Schoenoplectus spp.) and floating vegetation, while Lake Ontario wetland vegetation was taller and cattail-dominated ( Typha spp.). These findings suggest that the IMBCI may not be useful on a basin-wide scale in the Great Lakes region in detecting human disturbance surrounding wetlands.

Using choice experiments to value catchment and estuary health in Tasmania with individual preference heterogeneity*

Choice experiments (CE) have become widespread as an approach to environmental valuation in both Australia and overseas. However, there are few valuation studies that have addressed natural resource management (NRM) changes in Tasmania. Furthermore, few studies have focussed on the estimation of estuary values. The CE study described in this paper aims to analyse community preferences for NRM options in the George catchment, Tasmania. Catchment health attributes were: the length of native riverside vegetation; the number of rare native animal and plant species in the George catchment; and area of healthy seagrass beds in the Georges Bay, which was used as a measure of estuary condition. Mixed logit models with interactions between socio‐economic variables and the choice attributes were estimated to account for systematic and random taste heterogeneity across respondents. Results reveal considerable variation in preferences towards the attributes and show that value estimates are significantly impacted by the way in which we account for preference heterogeneity. Preference heterogeneity thus needs to be considered when estimating community willingness‐to‐pay for environmental changes. This study further shows little responsiveness to the presented changes in estuary seagrass area.

Transferability of object-based rule sets for mapping coastal high marsh habitat among different regions in Georgian Bay, Canada

Coastal wetlands of eastern and northern Georgian Bay, Canada provide critical habitat for a variety of biota yet few have been delineated and mapped because of their widespread distribution and remoteness. This is an impediment to conservation efforts aimed at identifying significant habitat in the Laurentian Great Lakes. We propose to address this deficiency by developing an approach that relies on use of high-resolution remote sensing imagery to map wetland habitat. In this study, we use IKONOS satellite imagery to classify coastal high marsh vegetation (seasonally inundated) and assess the transferability of object-based rule sets among different regions in eastern Georgian Bay. We classified 24 wetlands in three separate satellite scenes and developed an object-based approach to map four habitat classes: emergent, meadow/shrub, senescent vegetation and rock. Independent rule sets were created for each scene and applied to the other images to empirically examine transferability at broad spatial scales. For a given habitat feature, the internally derived rule sets based on field data collected from the same scene provided significantly greater accuracy than those derived from a different scene (80.0 and 74.3%, respectively). Although we present a significant effect of ruleset origin on accuracy, the difference in accuracy is minimal at 5.7%. We argue that this should not detract from its transferability on a regional scale. We conclude that locally derived and object-based rule sets developed from IKONOS imagery can successfully classify complex vegetation classes and be applied to different regions without much loss of accuracy. This indicates that large–scale mapping automation may be feasible with images with similar spectral, spatial, contextual, and textural properties.

H. Allen Brooks, 1925–2010

H. Allen Brooks, Georgian Bay, Ontario, in 2005 (Barbara Nettleton photograph) Harold Allen Brooks died quietly on 8 August 2010 in Hanover, New Hampshire. A renowned Frank Lloyd Wright and Le Corbusier scholar and past president of the Society of Architectural Historians (1965–67), Brooks spent most of his career teaching in the Department of Fine Arts at the University of Toronto. Born on 6 November 1925, in New Haven, Connecticut, he attributed his interest in architectural history to his parents' decision, when he was fourteen, to commission an architect to design their family home. As the family searched for an architect, young Brooks searched through design magazines for houses he liked. They eventually selected Andrew Euston, whose presentation drawing adorned Brooks's room at the end of his life. Brooks was drafted into the army in 1946 during his first year at Dartmouth College and spent two years stationed in the Philippines as an engineer. Back at Dartmouth, Brooks majored in art history, but it was the architectural history lectures of Hugh Morrison that influenced the course of his future career. He received his BA in 1950 and, interested in becoming an architect, spent the next two years …

A Curious Rusophycus (Arthropod Ichnofossil) Assemblage from the Upper Ordovician of Ontario, Canada

The ichnogenus Rusophycus includes a wide range of short bilobate excavations generally attributed to variable feeding behaviors of arthropods, especially trilobites. An unusual Rusophycus assemblage from Upper Ordovician Georgian Bay Formation in Ontario departs radically from previously described examples and presents new challenges for understanding the behavior represented by these traces. This specimen is unique in the arrangement of multiple Rusophycus burrows in a circular, lens-shaped array (as opposed to a linear or random arrangement typical of other Rusophycus assemblages). The size and shape of the individual Rusophycus components are consistent with traces attributed to the coeval trilobite Flexicalymene. Multiple Rusophycus assemblages likely reflect aggregations of trilobites in response to a local concentration of food. The topology of this particular Rusophycus assemblage suggests that the trilobites opportunistically exploited a rich and narrowly restricted food source, perhaps the decaying remains of a buried organism.

Carbon and oxygen dynamics in the Laurentian Great Lakes: Implications for the CO2 flux from terrestrial aquatic systems to the atmosphere

We collected samples in lakes Superior, Erie and Huron, including Georgian Bay, in mid-summer during the stratified period to determine the relative importance of production, respiration and atmospheric exchange to carbon dynamics in the lakes. In all lakes sampled, oxygen saturation averaged 107±2%, significantly greater than the atmospheric equilibrium, and the isotopic composition of dissolved oxygen, δ18ODO, averaged 22.8±0.1‰, significantly less than the isotopic composition of dissolved atmospheric oxygen, suggesting that biological production was greater than respiration in the epilimnion during the summer months.While lakes worldwide are commonly oversaturated in carbon dioxide, average pCO2 in the epilimnion of the lake studied was 342±42μatm and the isotopic composition of dissolved inorganic carbon, δ13CDIC, was 0.2±0.2‰, both values not significantly different from expected atmospheric CO2 equilibration (n=65, p=0.89, n=64, p=0.81). This trend is atypical; approximately ninety percent of lakes globally are oversaturated in carbon dioxide. The atmospheric equilibrium observed in the Laurentian Great Lakes and other studies suggest that pCO2 in large lakes is depleted relative to smaller lakes. This is also the case for rivers that are sourced from or flow though large lakes and they can be expected to have lower pCO2 downstream from the lakes and lower per unit area carbon fluxes than other rivers. An improved understanding of the global carbon cycle mandates that this be taken into account when considering CO2 fluxes from aquatic ecosystems.

Migration and Winter Movements of Double-Crested Cormorants Breeding in Georgian Bay, Ontario

Abstract. Double-crested Cormorants (Phalacrocorax auritus) breeding in the Great Lakes and wintering in the southeastern United States were implanted with satellite transmitters to assess their movements. During 2007 and 2008, 26 cormorants from Georgian Bay, Ontario, Canada, were tracked in order to, variously, identify staging areas, characterize migration routes, winter habitat use, and home range size, assess philopatry of returning breeders, and test for a relationship between winter habitat use and arrival at the breeding ground. Females left summer areas earlier and spent more time in staging areas than did males. However, both sexes left the staging areas and arrived in the wintering grounds at approximately the same time. There was no difference in latitude between wintering males and females, or in winter residency time (n = 136 days for both sexes). The predominant winter habitat types were lakes and coasts with only seven of 26 (26.9%) birds wintering on aquaculture sites. Contrary to expecta...

Mapping Floating and Emergent Aquatic Vegetation in Coastal Wetlands of Eastern Georgian Bay, Lake Huron, Canada

Expansion and contraction of floating and emergent vegetation due to fluctuating water levels has a direct impact on the amount of critical fish habitat in the coastal marshes of Georgian Bay, Lake Huron (Canada). Traditional mapping approaches developed for site-specific studies are too expensive to quantify such changes at the scale of Georgian Bay. Here, we use IKONOS images to develop a classification method (process-tree classification (PTC)), an automated, object-based, image-analysis approach that can produce regional maps of wetland habitat for south-eastern Georgian Bay (1466.7 Km). PTC discriminated among six wetland habitat classes (emergent, high-density floating, low-density floating, meadow, water, and rock) in four IKONOS satellite images with a mean accuracy of 87.4%. The PTC was then applied without modification to 17 other IKONOS images collected concurrently in 2002. Based on analysis of 50 randomly chosen wetlands in these images, we estimate that at 2002 water levels, at least 25% of an average wetland (6.5 ha) contains potential fish habitat. Although the PTC developed is specific to the 21 IKONOS images used in this study, the framework is transferable to satellite images acquired in other regions of Georgian Bay, and the approach itself could be applied to other large lakes.

Seasonal and annual patterns in density of double-crested cormorants in two coastal regions of Lake Huron

Aerial line transect distance sampling surveys of coastal areas in the North Channel and Georgian Bay, Lake Huron, were conducted to estimate density of double-crested cormorants ( Phalacrocorax auritus). Surveys were approximately every two weeks through summer from 2000 to 2005. In each year, density of cormorants declined towards late summer indicating a large scale outward migration of cormorants from Lake Huron. The seasonal pattern of decline differed between the two regions based on a mixed model analysis. Seasonal patterns in apparent fledging patterns may reflect differences between the North Channel and Georgian Bay in nesting phenology, nesting synchrony or some combination of these factors. Density was generally higher in the North Channel relative to Georgian Bay seasonally and during the period 2000–2002 likely reflecting higher per unit area productivity in the North Channel. In the years 2003–2005, density was lower in both regions and similar compared to earlier years of the survey likely reflecting a regime shift that occurred in Lake Huron at that time. The effect of this change was greater in the North Channel than in Georgian Bay as indicated by a greater decline in cormorant density in the North Channel after 2002.

Line transect distance sampling in aerial surveys for double-crested cormorants in coastal regions of Lake Huron

Line transect distance sampling was employed in aerial surveys of double-crested cormorants ( Phalacrocorax auritus) along the coasts of Georgian Bay and the North Channel, Lake Huron. A double-observer method was used to estimate detection probability near the transect line ( g(0) = 0.724). Detection of cormorants was not consistent but varied based on group size, location (water, land, flying), and season. Probability of detection in the area covered by the survey was often below 0.5. Incorporating both lack of detection on the flight line along with lack of detection over the covered area inherent in distance sampling provided defensible density estimates of free-ranging double-crested cormorants. Most cormorants were detected loafing on shore (land) among the many islands defining this area of the Lake Huron coast. Land detections exceeded the combined detections of birds on the water and flying. Density in 2004 ranged from a peak of 2.30 cormorants per km 2 (95% CI = 1.72–3.03) in late July to 1.21 cormorants per km 2 (95% CI = 0.78–1.70) in late August in the sampled areas extending from shore to approximately 20 km offshore. Aerial surveys employing distance sampling can be useful tools in monitoring the distribution and abundance of free-ranging double-crested cormorants and other waterbirds in the Laurentian Great Lakes.

Early Holocene brackish closed basin conditions in Georgian Bay, Ontario, Canada: microfossil (thecamoebian and pollen) evidence

Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods) record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones 2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800–7,200 (9,900–8,050 cal) BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians: predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate change and resource management in the Great Lakes, one of the world’s largest freshwater resources.