Collecting the sediment core, dividing the core into 1 cm subsamples and recording vital data
The main conclusion of the work
is that there is evidence for some recent increases in erosion and nutrient enrichment in roughly the last 5cm of the sediment core.
The erosion is shown by the decline in organic content near the top of the core which suggests increase input of inorganic material
to the lake, presumably as a result of land clearing and greater erosion. The nutrient enrichment is indicated by the increase in
the relative abundance of the diatom species Fragilaria pinnata and the decline in the chrysophyte to diatom ratio. Fragilaria pinnata
are in some respect the “weeds” of the diatom world and can grow well under low light and higher nutrient conditions. Chrysophytes
are another kind of algae that thrive in lower nutrient conditions and therefore a decline in the chrysophyte to diatom ratio suggest
nutrient enrichment. Overall, there is evidence of some recent nutrient enrichment."
The author of the report, Katherine Sweet, states
in the abstract of her paper:
“White Lake is a large, shallow lake with unique characteristics and a sensitive ecosystem. A shift encountered
in the chrysophyte to diatom ratio and an increase in Fragilaria pinnata within the last five centimetres of the core sample is indicative
of recent water quality changes within the lake. The variation in species abundance and loss of biodiversity encountered in the sediment
sample over time is likely due to increasing anthropogenic nutrient additions to the system. These impacts are visible in the diatom-inferred
decline of water quality revealed in this study.”
Fragilaria pinnata (left) and Chrysophyte (right) diatoms
Paleolimnology is a scientific sub-discipline closely related to limnology and paleoecology. Limnology is the study of any inland water body including rivers, lakes, even ground waters, fresh or salt. Paleoecology is the study of past climate conditions in an area using techniques including chemical analysis and the study of diatom species and populations in lake sediments.
Paleolimnological studies are concerned with reconstructing the paleoenvironments of inland waters and especially changes associated with such events as climate change and human impacts. Depending on the study and the methods used, the time scale for climate reconstructions can vary from thousands to millions of years or can be applied to changes which have occurred in the recent past from less than 10 to 150 years.
In late summer 2014, Professor Jesse Vermaire, Assistant Professor of Environmental Science at Carleton University (Ottawa), recovered a sediment core for study from White Lake. He was assisted by Conrad Gregoire. The core sample was taken midway between the eastern tip of Hardwood Island and the western tip of McLaughlin's Island. The core represented approximately 150 years of sedimentation at that location. This project was a student project undertaken by Kathryn Sweet under the supervision of Prof. Vermaire.
A second paleolimnological study was completed in 2019 as part of a Masters thesis. The work was done by Michael Murphy under the
supervision of Professor Vermaire of Carleton University. Conrad Gregoire and David Overholt contributed to the study as well. The
full text of the thesis can be viewed here.
Ecological response of a shallow mesotrophic lake to multiple environmental stressors:
a paleolimnological assessment of White Lake, Ontario
Michael Murphy, B.Sc.
White Lake, located in Eastern
Ontario, Canada is a large (surface area 56.08 km2), shallow (mean depth = 3.1 m), recreational lake that has a recent history of
poor water quality due to water level changes, nutrient loading and invasive species. With monitoring data only extending to 2015,
lake managers lack the long-term data needed to make informed decisions regarding lake management strategies. A paleolimnological
study was conducted to assess historical water quality change in White Lake using diatoms as indicators of water quality. The recent
introduction of zebra mussels (Dreissena polymorpha) has lowered nutrient levels and greatly reduced turbidity with Secchi depth reading
jumping from 1.8 m to 7.5 m depth. However, the largest single change in the diatom assemblage of White Lake likely relates to water
level changes through the damming of the lake in 1845 and subsequent changes to the water level management plan for the lake.