NWT RESEARCH DATABASE

Tags: mercury, water quality, bioaccumulation, arsenic, climate change, fish, metals, sediment quality, cumulative effects

Objective(s): To investigate the ecosystem health of Yellowknife Bay.

Project Description: The main objective of this study is to investigate the ecosystem health of Yellowknife Bay. We will address the following questions through a field study: 1) What is the quality of water and sediment in Yellowknife Bay (focusing on metals, nutrients and cyanobacteria)? 2) What are the main sources and transport pathways of metals accumulating in the food web of Yellowknife Bay? 3) How much of the sediment and water-borne metals are entering the food web? This study will involve field programs to measure metal concentrations (including lead, mercury, arsenic) in different environmental compartments of Yellowknife Bay and the main body of Great Slave Lake. The research team will collect lake sediment cores with a gravity corer to provide a historical perspective on metal accumulation in sediment over the last century. Tree lichens will be examined as an indicator of current atmospheric metal deposition. Benthic algae, aquatic invertebrates and fish will be collected to examine accumulation in the aquatic food web. Sediment cores will also be collected to investigate the release of arsenic and methylmercury from sediment to the water column. These measurements will be conducted by inserting specialized passive samplers into the cores and then incubating them on the lake bottom for 3-4 days. The specialized passive samplers are called DGTs (Diffusive Gradient in Thin film samplers) and they consist of a small, hand-held plastic casing with gel inside that binds dissolved metals in order to measure levels in water and sediment pore water. Lead isotopes will be measured in the various environmental compartments to investigate the transport of legacy metal pollution from local mining activities. Lead released from local mining has a distinct fingerprint (isotopic ratio), allowing it to be distinguished from other lead sources. Using models, the team will estimate the contribution of lead from local mining to levels accumulated in sediment and fish in Yellowknife Bay. Aquatic invertebrates will be collected with a d-framed kicknet, Ekman grab, benthic sled or plankton net. Fish will be collected by gill net, beach seine, backpack electrofisher or baited lead line. The objective is to collect up to 25 fish of various species from Yellowknife Bay and a reference area in the main body of Great Slave Lake to examine the accumulation and biomagnification of metals in the aquatic food web. Fish tissues will be analyzed for a suite of metals (including arsenic, lead, mercury) as well as lead isotopes. Fish muscle will also be analyzed for carbon and nitrogen stable isotopes to provide biological information that is relevant for metal bioaccumulation, namely dietary carbon sources and trophic position of the fish. Another water quality component of the project is to examine cyanobacteria blooms in the study area. Water will be collected to characterize the phytoplankton composition and measure microcystin concentrations in water. The research team are partnering with the Yellowknives Dene First Nation (YKDFN) on this study of the ecosystem health of Yellowknife Bay. There is local concern about legacy metal pollution in Yellowknife Bay, and the team are collecting information on levels in water and sediment, and bioaccumulation in the food web. The YKDFN is providing input and feedback on the study design, and assisting with the coordination of the field program. The results will be communicated through face to face meetings with local stakeholder organizations. A plain language report will be prepared at the end of the study that will be distributed and uploaded to the NWT Discovery Portal. The fieldwork for this study will be conducted from June 1, 2015 to December 31, 2015.