Turkey Lakes watershed: storage and release of toxic contaminants

Rationale

Atmospheric transport and deposition of toxic contaminants (e.g. organo-chlorine pesticides, PCBs, Hg, etc.) occurs throughout the Great Lakes basin and beyond. Deposition of these substances directly to water surfaces has been extensively studied in recent years and is now considered a significant input pathway to the Great Lakes. The low concentration of contaminants usually observed in rivers flowing from undisturbed watersheds is generally taken as evidence supporting the supposition of contaminant retention within drainage basins and the relatively minor significance of riverine inputs to lakes from such basins. Yet this supposition is based on very meagre observational information and even less knowledge of the biogeochemical processes and pathways that control contaminant storage within and release from drainage basins. Some open questions include:

• what is the nature of contaminant movement and cycling within the terrestrial basin?
• do primary (headwater) watersheds exhibit the same contaminant storage/release characteristics as secondary and tertiary watersheds?
• what is the role of the network of lakes and streams (above the Great Lakes inflow) in storing and/or transporting contaminants?
• do hydrological conditions influence contaminant transport?
• what are the predominating sinks in the drainage basins (e.g. forest soils, vegetation, wetlands, within-basin lake sediments, etc.)?
• can conditions arise (e.g. climatic extremes, anthropogenic disturbance, etc.) that result in mobilization of stored contaminants?

Objectives

This study will initiate a comprehensive, long-term project to address uncertainties in watershed storage and release of toxic contaminants by making use of the research infrastructure already present in the TLW. During 1999/2000, research will be intentionally simple, focussing on whether watershed retention of atmospherically deposited contaminants is influenced by watershed scale, hydrology, and forest vegetation. This "black-box" approach will provide information to justify and guide future work on specific biogeochemical processes and to maximize its effectiveness.

Research activities:

Atmospheric input

The concentration of persistent organic pollutants (POPs), metals and haloacetic acids (HAAs) in precipitation will be measured year-round at the main precipitation monitoring (CAPMoN) site in the TLW. The POPs (e.g. chlorobenzenes, organochlorine pesticides, PCBs, PAHs, toxaphene, etc.) will be isolated using XAD2 adsorption columns. Toxic metals samples are collected in polyethylene containers except Hg, which is collected using a separate teflon and glass collection vessel. Sampling frequency will be determined by precipitation quantity. Air concentrations of organic contaminants will be monitored with a PUF sampler, of metals in particulates using a Hi-Vol sampler, and of Hg using a Tektran sampler (summer only). Additional snow samples will be collected to address specific questions (e.g. importance of events).

Watershed export and hydrology

The influence of watershed scale on contaminant export will be determined by measuring POP, HAA and metal concentrations at a nested sequence of hydrological gauging stations, i.e. 2 forested, headwater catchments (Streams 47 and 50) draining into the southern basin of Batchawana Lake (drainage areas = 4 to 12 ha respectively); the Turkey Lake outflow station (drainage area = 803 ha) which will reflect the effect of the 4 upstream lakes and associated terrestrial drainage basins; and the WSC station near the mouth of the Batchawana River (drainage area = 11900 ha) which will reflect the effect of the entire tertiary watershed draining into Lake Superior. Sampling will be related to water flow (i.e. fewer samples during low flow and more during high flow) and use the XAD2 adsorption column technique. The increased sampling activity to occur during high flow will permit evaluation of hydrology-related variation in contaminant concentrations (the concentration of many other chemical species exhibit strong relationships to flow). Approximately 50 samples/yr is anticipated at each of the four stations. Mass export will be calculated as the product of water export and concentration.

Batchawana Lake South mass balance

A preliminary mass balance for POPs, HAAs and metals will be determined. Export from the 2 headwater catchments will be used to estimate terrestrial input. Input from Batchawana Lake North will be measured as will output at the lake's outflow. Some information on in-lake processes will be obtained by seasonally sampling lake surface and bottom waters, suspended sediments, and the material collected in sediment traps.

Vegetation

The waxy coating on leaves offers a surface which may have a good affinity for collecting organic contaminants. Hence litterfall may be a significant input pathway of contaminants to forest soils and lakes. Samples will be obtained to determine the contaminant input associated with this material.

Contact

For more information, contact D.S Jeffries.