Seasonality in Contaminant Concentrations in the Niagara River and Lakes Erie and Ontario

Abstract

Knowing the seasonal variation of contaminant concentrations in lakes is important for designing effective monitoring studies and when comparing or combining results from different studies. However, there is a paucity of such information for the lakes covering both the entire year and the long term. Since 1986, we have collected large volume water samples for both dissolved and particulate phase contaminant analyses from stations at the head (Fort Erie—FE) and mouth (Niagara-on-the-Lake—NOTL) of the Niagara River throughout the whole year, including winter. Many of the organic contaminants measured over the period 1986 to 2001 exhibited seasonal variation. The different seasonal patterns were due to three general causes: (1) the exchange of contaminants across the air/water interface; (2) the seasonal nature of specific activities such as the application of agricultural insecticides and herbicides, and residential heating; and (3) the effect of suspended particulate material (SPM) quantity and composition on the particulate phase concentrations of contaminants. These are illustrated by the four contaminant examples (α-HCH, α-endosulfan, acenaphthylene, PCB) discussed in this paper. Where data were available for comparison, the seasonal patterns of these four contaminants in the river were generally consistent with those observed in Lakes Erie and Ontario over the period 1992 to 1995. Results suggest that the evaluation of contaminant concentrations, cycling and trends based on single temporal samples from the Great Lakes water column should be questioned. This is a significant issue given its widespread practice. Sampling Connecting Channels water may be, in general, a useful alternative to temporal lake sampling.