Crawford Lake (Halton Region)

Crawford Lake () is a lake near the community of Campbellville, in the town of Milton, Regional Municipality of Halton, Ontario, Canada. It is located within Crawford Lake Conservation Area, a Regionally Environmentally Sensitive Area, an Ontario Area of Natural and Scientific Interest, and part of the Niagara Escarpment World Biosphere Reserve.

The primary inflow to the lake is an unnamed creek.

Crawford Lake is meromictic, which means it has sequentially deposited seasonal sediment laminations called varves at the bottom; these allow for accurate dating of sediment cores and make Crawford Lake a prime site for archeological and geochemical studies.

History

Using pollen analysis of the lake, reconstruction of the history of the area over several hundred years was possible. The analysis revealed the agricultural history of the native Iroquoians and a pre-European contact village, through the presence of corn and squash pollen motes. The Wendat-Huron village has been reconstructed in the conservation area based on many years of work by archaeologists, historical references, and First Nations oral traditions.

Further analysis revealed evidence of European colonists through sawdust and ragweed pollen from the construction of nearby settlements.

Lake environment

Crawford Lake developed over thousands of years ago in Southern Ontario as water filled in a limestone cliff sinkhole. Due to its meromictic attributes, the lake is separated into two layers: its upper layer is mixed with external factors such as wind, and its bottom layer is undisturbed, leading to sediment accumulating at its bottom. When temperatures and acidity are high during summers, the water produces calcite that forms a white layer over the lake bed's sediment layer.

Crawford Lake is highly unusual among meromictic lakes in that, in contrast to the anoxic basin waters typical of meromictic lakes, the monimolimnion is also oxygenated.

Ecology

Flora

Stratigraphic evidence using charcoal analysis of Crawford Lake's sediments showed a record of increased charcoal accumulation, when pollen analysis showed a change between northern hardwoods to a white pine and oak forest.

Anthropocene epoch

In 2009, the Anthropocene Working Group of the Sub-commission on Quaternary Stratigraphy began debating on a candidate for the Anthropocene Global Boundary Stratotype Section and Point (GSSP), where the area had to preserve, in good condition, changes of human impacts on the environment.

Geochemical analysis of sediment cores has allowed for the reconstruction of the environmental history (e.g. human impact, pollution) of the area. This analysis has revealed the trends and sources of air pollution over approximately 150 years. The well-distinguished stratigraphy led to the lake becoming a candidate for determining the start date of the proposed Anthropocene epoch, with a base date at 1950 CE.

Crawford Lake was chosen in July 2023 to represent the "key site that shows we're in a new climate epoch". The lake has been described as the "golden spike" showing the global human impact on earth. The first age of the Anthropocene could be named the "Crawfordian," after the lake.

References

* Crawford Lake Trail and Village Guide, Conservation Halton, August 9, 2010

External links

Crawford Lake Conservation Area

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Lakes of Ontario
Landforms of the Regional Municipality of Halton
Meromictic_lakes