Alice Dove

Long-term trends in major ions and nutrients in Lake Ontario

The Great Lakes Surveillance Program has been monitoring water quality for almost 40 years in Lake Ontario. The program provides some of the most comprehensive, systematic and detailed information that is available in the world for such a large lake. The water quality in Lake Ontario has shown dramatic changes over the last 40 years, with the early measurements indicating high phosphorus concentrations that were subsequently reduced by management responses to the Great Lakes Water Quality Agreement. Other water quality parameters, such as some of the major ions, showed reductions during the 1970s and 1980s as well. Nitrate plus nitrite nitrogen has increased in the lake throughout the period of record, likely driven by increasing watershed and atmospheric sources. A major driver of more recent trends in water quality appears to be the invasion and subsequent expansion of invasive Dreissena mussel populations that first appeared in Lake Ontario in 1989. Total phosphorus concentrations have further declined, and the proportion of total phosphorus that is soluble is increasing, possibly due to the filtering action of these mussels. Concentrations of major ions that are incorporated in mussel shells such as calcium have declined, while those that do not, such as magnesium, have increased. Spring silica concentrations are increasing; an ominous signal of declining diatom populations, which may also be a symptom of the proliferation of invasive mussels in the lake.

Great lakes chloride trends: long-term mass balance and loading analysis.

ABSTRACT Surveillance data collected over the past 150 years are compiled and analyzed to identify chloride trends in the Laurentian Great Lakes. These data indicate that chloride levels started rising in the mid-19th century and began accelerating in the early twentieth century. Lake Superiors and Lake Michigans concentrations have continued to increase steadily and currently stand at their maximum recorded levels. In contrast, lakes Huron, Erie and Ontario reached peak levels between 1965 and 1975, but then began to decline. However, recent data indicate that the chloride concentrations in these lakes are now increasing again. Because loading data are not readily available, a mass-balance model is employed to estimate the chloride inputs required to account for the concentration trends. This inverse analysis yields computed load reductions that are consistent with reported industrial load reductions during the last three decades of the 20th century. Hence, it appears that the improvements were for the most part attributable to industrial controls. The model is also used to predict that if loads are held fixed at 2006 levels, concentrations in all lakes will continue to increase with the most dramatic rise occurring in Lake Michigan which will ultimately approach the level of Lake Erie.

Spatiotemporal patterns of water quality in Lake Ontario and their implications for nuisance growth of Cladophora.

ABSTRACT This study, motivated by a resurgence in Cladophora, investigates changes in the nutrient environment in the littoral zone of Lake Ontario. We measured nutrient concentrations from 2004 to 2008 at two littoral zone (2–12 m) sites on the north shore of Lake Ontario where Cladophora has experienced a resurgence and compared concentrations with data collected in the late 1970s. Spring total phosphorus (TP) and soluble reactive P (SRP) concentrations have significantly declined at these two sites. Furthermore, P loading from the major tributaries to our study sites declined between 1964 and 2008. Upwelling events were not detectably associated with increases in P concentrations at our sites. We conclude that a recent upsurge in nuisance Cladophora, at least at these sites, cannot be explained by deteriorating littoral zone water quality in terms of P concentrations or by changes in catchment loading. For additional context, we also examined trends in coastal (14–20m) and offshore (>50m) nutrients using Environment Canada epilimnetic surveillance data, 1975–2008. Significant declines in TP and SRP concentrations have occurred in north coast waters, concurrent with declines in the offshore. However, nutrient concentrations, notably spring SRP, have not decreased among south coast stations, potentially reflecting greater coastal entrapment of catchment-derived waters. We infer that EC-monitored north coast stations reflect integrated interannual water quality, while south coast stations are more strongly influenced by catchment loading. The effects of higher nutrient concentrations along the south coast, which co-occur with lower water transparency, on benthic algal growth have yet to be determined.

Metolachlor and atrazine in the great lakes.

Concentrations of atrazine and metolachlor and stereoisomer fractions (SF = herbicidally active/total stereoisomers) of metolachlor were determined in 101 surface water samples collected from the five Laurentian Great Lakes in 2005-2006. Geometric mean (GM) concentrations of atrazine ranged from 5.5 to 61 ng L(-1), decreasing from lakes Ontario approximately Michigan approximately Erie > Huron > Superior, while metolachlor concentrations ranged from 0.28 to 14 ng L(-1) and showed similar trends among the lakes. Median SFs ranged from 0.527 (Superior) to 0.844 (Erie) with an overall value of 0.708, and were significantly different among the Great Lakes (p < 0.05), except for Michigan vs Huron and Michigan vs Ontario. The SF in Erie was closest to that of the dominant product in use, S-metolachlor (SF = 0.880), while Superior showed an SF similar to that of racemic metolachlor (SF = 0.500). The median SFs in lakes Ontario, Huron and Erie were significantly lower than the median SF in Ontario stream samples collected in 2006-2007. The lower SFs in lakes suggest in-lake stereoselective processing of metolachlor or hold-up of older racemic metolachlor residues.

Spatial distribution and trends of total mercury in waters of the Great Lakes and connecting channels using an improved sampling technique.

Environment Canada recently developed a clean method suitable for sampling trace levels of metals in surface waters. The results of sampling for total mercury in the Laurentian Great Lakes between 2003 and 2009 give a unique basin-wide perspective of concentrations of this important contaminant and represent improved knowledge of mercury in the region. Results indicate that concentrations of total mercury in the offshore regions of the lakes were within a relatively narrow range from about 0.3 to 0.8 ng/L. The highest concentrations were observed in the western basin of Lake Erie and concentrations then declined towards the east. Compared to the offshore, higher levels were observed at some nearshore locations, particularly in lakes Erie and Ontario. The longer-term temporal record of mercury in Niagara River suspended sediments indicates an approximate 30% decrease in equivalent water concentrations since 1986.