Natural fluorescence of freshwaters of the Hudson Bay Lowland: A sentinel of water quality and envir
Parameters: CDOM
The Hudson Bay Lowland is the third largest contiguous wetland in the world, stretching over 300,000 square kilometers in central Canada surrounding southern shores of the Hudson Bay and James Bay. The majority of the Lowlands, which have formed since the last continental glaciation, are within the Province of Ontario but also reach into Quebec and Manitoba. This wetland is extensively blanketed by a layer of peat which exerts a strong influence on the water quality of rivers and streams that drain the landscape. Water quality is very important to the First Nation’s inhabitants of that region as the waters are a source of drinking water and fish, an important traditional food. Up until now, very little has been known about water quality in the region, in part because of the difficulty in accessing the remote region to sample water. An emerging strategy with great promise is to use autonomous sensors to make unattended measurements.
Dr. Brian Branfireun and his graduate student Tara Despault of the University of Western Ontario in London Ontario, with support from Canada’s Natural Sciences and Engineering Research Council, Western University, and DeBeers Canada Inc., are conducting new research in the Hudson Bay Lowland using in situ sensors to make fluorescence measurements along with turbidity, pH, conductivity, temperature, water depth and dissolved oxygen. Fluorescence measurements of dissolved organic matter (DOM) in natural waters provide valuable information on the source of the DOM (such as microbial processes or terrestrial decomposition) and the degree of degradation of that DOM. Fluorescence measurements of chromophoric DOM (CDOM) and indices calculated from specific fluorescence wavelengths have also been used as continuous measures of DOM and, by proxy, dissolved mercury because of the strong association between mercury and DOM in natural waters. Two custom RBRmaestro multi-channel loggers were engineered by RBR Limited (Ottawa, Ontario) for this research. In addition to the standard water quality sensors, two custom Turner Designs Cyclops sensors were built to characterize the properties of the DOM. The custom fluorometers use an excitation of 370nm coupled with emission filters of 470 and 520nm.
Decreasing water levels in the Nayshkootayaow River result in increases and decreases in Fluorescence Index (FI) and Coloured Dissolved Organic Matter (CDOM), respectively, measured in situ over a 10-day period in June. The direction and magnitude of change observed for FI and CDOM reveal a decoupling of the Nayshkootayaow River from wetland contributing sources and a shift towards a groundwater-dominated base flow condition.
The instruments have been deployed in a larger river, the Nayshkootayaow, and a smaller tributary, the North Granny Creek. Periodic water samples are also being taken from both of these sites for lab analysis of DOM and mercury as well as Excitation Emission Matrix Spectroscopy (EEMS) to develop relationships with in situ continuous data from the RBRmaestros and Turner Designs’ sensors. If the results are promising, then the use of this in situ system will reduce physical sampling requirements by providing continuous proxies for DOM and mercury concentrations and helping to eliminate gaps in field data that can result from infrequent sampling in remote regions.
The peatlands of the Hudson Bay Lowlands have accumulated over thousands of years and are sensitive to many potential future changes, including climate, which are predicted to be large in this region. Effective autonomous monitoring of these waters will provide valuable information on the direction and magnitude of changes in water quality including mercury, allowing for the development of effective management policies and guidance on fish consumption for local residents.
The two circles above represent the two excitation and emission pairs of the custom fluorometers against the background of a lake water sample EEMs. These excitation and emission pairs are used to calculate fluorescence indexes (FI).
Photo Courtesy: Carpenter, K.D., Kraus, T.E.C., Goldman, J.H., Saraceno, J.F., Downing, B.D., McGhee, Gordon, and Triplett, Tracy, 2013, Sources and characteristics of organic matter in the Clackamas River, Oregon, related to the formation of disinfection by-products in treated drinking water: U.S. Geological Survey Scientific Investigations Report 2013–5001, 78 p.
The photo above shows one of the RBR systems at the Nayshkootayaow River prior to deployment.
Turner Designs would like to thank Dr. Brian Branfireun and Tara Despault of the University of Western Ontario for their contributions to this article. Turner Designs would also like to acknowledge contributions and information from RBR Limited. For more information about RBR, please visit their website.
Authors: Dr. Brian Branfireun and Tara Despault Institution: University of Western Ontario, Location: Hudson Bay Lowland