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Eutrophication of freshwaters is already a problem in many regions globally and will probably worsen as human populations grow and consume more resources. The ability of researchers and gov...

Spatially detailed surveys were conducted in 2008 over 97 km of the Canadian coastline of Lake Ontario to describe patterns in water quality correlated with natural and anthropogenic features. Features of variability were used to infer lake-wide, regional, and location specific influences on nearshore water quality. Levels of solids, nutrients, major ions, Escherichia coli , and dissolved organic carbon were higher and more variable among tributary, embayment, and shoreside (0 to 1.2 m depth) areas compared with the open nearshore (~3 m depth to 5 km offshore). A recurring pattern was a sharp drop in these features away from the shoreline with little or subtle decline beyond 1 to 3 km into the nearshore. Conductivity and UV-induced fluorescence of organic material were used to detect discharges to the nearshore. Land-based influence on water quality was greatest in the urbanized Greater Toronto Area and the least over the less developed areas. Nearshore regions received inputs from the adjacent shoreline affecting water quality, the spatial extent of which was difficult to generalize, ranging from 10s of metres to several kilometres in breadth. Despite this, concentrations of total phosphorus, soluble reactive phosphorus, dissolved inorganic nitrogen, and silicate, when averaged over the entire nearshore, were typically similar to the open lake reflecting the broad distribution of the nearshore relative to the areas most influenced by adjacent lands. The development of environmental management to address water resource problems in the nearshore should proceed with awareness of the strong spatial dimensions that define nearshore water quality.

A combination of data from shipboard and deployed sensors, nutrient and major ion concentration data, and tributary discharge and current data was used to assess water quality patterns on the Canadian nearshore of Lake Ontario in 2008 and the factors that impact these patterns. Mixing areas at tributary mouths were characterized by high spatial and temporal variability in water quality. Conductivity at sensors offshore from tributaries was variably correlated with discharge, with the correspondence most evident during high spring flow. Tracers of land runoff were positively correlated with tributary discharge at three of five study locations. The spatial distribution of water quality was strongly influenced by the predominating alongshore circulations, with gradients frequently observed parallel to the shoreline away from tributary mouths. Upwelling, evident from temperature bands along the coastline, periodically created onshore–offshore gradients in chlorophyll a and dissolved inorganic nitrogen. Lake whiting, starting in July, further enhanced the effect of upwelling by accentuating differences in water clarity, suspended solids, and ionic composition between surface and bottom strata. In general, turbidity decreased and water clarity increased with lake depth. Gradients in water clarity and chlorophyll a suggestive of dreissenid mussel feeding were uncommon. Interacting land- and lake-based factors contributed to heterogeneous water quality over the coastline of Lake Ontario highlighting needs for water resource assessment methods sensitive to the temporal and spatial scales of problems as well as the connectivity between the land and the lake.

Passive samplers (SPMDs, semi-permeable membrane devices; POCIS, polar organic chemical integrative samplers) were deployed in Lake Ontario near Pickering, Ajax, and Port Hope, Ontario in 2008 and complemented with detailed water quality indicator and water current measurements. The intent was to examine the influences of source inputs and limnological features on the distribution and dilution patterns of several organic wastewater-associated chemicals (OWCs) in dynamic nearshore waters. Generally, concentrations ranged from 0.1 to 11 ng/L for most pharmaceuticals and up to 25 ng/L for gemfibrozil and 28 ng/L for caffeine based on previously determined POCIS sampling rates. Musk (HHCB and AHTN) and triclosan (TCS) concentrations were estimated using laboratory-derived sampling rates as part of this study (4.3–7.9 L/d) and ranged up to 10 ng/L for musks and 1.5 ng/L for TCS near Pickering–Ajax. Nitrate and conductivity maps indicated that alongshore currents were primary drivers of distribution and transport for tributary discharges and wastewater treatment plant (WWTP) effluents parallel to shore. Organic wastewater chemicals like HHCB, AHTN, TCS, gemfibrozil, and venlafaxine were greatest in the vicinity of the Pickering–Ajax WWTP and then dramatically declined. Ibuprofen, carbamazepine, and especially caffeine concentrations exhibited more uniform distributions both within and between the Pickering–Ajax and Port Hope study areas suggesting that transport via alongshore currents may contribute to a regional background of the relatively more persistent OWCs that may not be captured in onshore–offshore gradient studies.