Water Quality of Nearshore Lake Ontario
Lake Ontario Evenings
Protecting Our Source Edition
March 26, 2012
Todd Howell
Environmental Monitoring and Reporting Branch
Ontario Ministry of the Environment
Toronto, Ontario
Outline
Background
 What is the nearshore zone and why is important
Nearshore and lakewide trends in water quality over the years
 Cultural eutrophication, nutrient management and long-term reductions
in phosphorus levels
 Rising nitrate and chloride levels: signs of human stress
The heterogeneous nature of water quality at the shores of the lake
 Bi-national study of the Lake Ontario coastal zone in 2008
 Recurring features of variability in water quality over the coastline
Tributaries as a key linkage between the land and the nearshore
 Mixing zones of river discharge as a feature of nearshore variability
Invasive zebra and quagga mussels and interactions with water quality
 Declining phytoplankton levels and increasing water clarity
2
The nearshore variously defined as:
• arbitrary bottom depth or offshore distance
• depth to summer thermocline
• relative to coastal circulation boundary layer
• depth of the euphotic zone
It is where the lake interacts strongly with lakebed,
shoreline, tributaries and people
Natural Resource Values:
 beach and water recreation
 source for drinking water and
water for industry
 waste disposal
More Subtle Anthropogenic Values:
 natural areas valued on
aesthetic, cultural and historic
grounds
 prized commercial and
residential property
3
Ecological Values:
 the littoral zone (concentration of
habitat, energy and biodiversity)
 length of shoreline 1,146 km
Nearshore from a Whole Lake Perspective
 drainage basin: 64,030 km2
 Surface areas (to 30 m depth): 4253 km2 (23%)
 Volume (to 30 m depth):
64.5 km3 (4%)
Depth (m)
-1
-2
-30
-50
-100
-150
-180
-200
-220
-244
 mean depth: 86 m
 surface areas: 18,960 km2
 volume: 1,640 km3
4
 replacement time: 6 years
Data source: NOAA compilation
of Lake Ontario Bathymetry
Virden et al. 2000
Tracking Nearshore Water Quality by Monitoring Untreated Water From Intakes
 The MOE Great Lakes Water Intake Biomonitoring program is a longstanding
effort designed to track nutrient conditions and water quality in the nearshore
 Untreated water analyzed roughly weekly for nutrients at 16 Great Lakes drinking
water intakes since mid 1970s
 Data provide information on how water quality in the nearshore has changed over
time
Data from four WTP intakes
Presented in an article by
Winter et al. 2011
(J. Great Lakes Res.
doi:10.1016/j.jglr.2011.09.003)
used in this presentation
5
Lake-wide Efforts to Manage Phosphorus Where Largely Successful
 GLWQA of 1978 pivotal in meeting lake productivity and phosphorus
objectives and combating eutrophication
 Most of the nearshore similar to offshore, however, areas of nutrient
enrichment persist, located mostly along the shoreline
WTP intakes
Total Phosphorus
Chlorophyll a
Zebra Mussels
GLWQA nutrient objectives:
i) oligo-mesotrophic state,
ii) spring total phosphorus of 10 g/L
iii) chlorophyll a of 2.6 g/L
Arrival of the
phytoplankton feeding
zebra and quagga
mussels in 1990
complicates interpretation
of the time trend
6
Falling Tributary Phosphorus in the 1970 to 1980s Contributed to the Nearshore Decline
 Controls on key "point source" phosphorus sources set in motion by the 1978 GLWQA
are believed responsible for falling P levels in rivers, the nearshore and open lake
 Reductions in inputs of phosphorus from detergents and sewage were targeted
 Note that the phosphorus levels in the Don River, like many rivers in developed areas,
remains high; diffuse non-point phosphorus pollution remains a challenge
7
Total Phosphorus Distribution
(Spring 1981-1982)
Offshore Phosphorus
6
Neilson & Stevens 1984
Canadian Journal Fisheries
and Aquatic Sciences 44:2192-2203
7
8
6
8
7
0.04
 Environment Canada
lake-wide monitoring data
 Water column today
considered oligotrophic
7
GLWAQ objective:
10 g/L (0.01mg/L)
0.03
Total Phosphorus (mg P/L)
Values in red indicate
spring 2008
nearshore
background
concentration
Eutrophic
0.02
Mesotrophic
0.01
0
Dove (2009)
Aquatic Ecosystem Health and Management
12:281-285 Figure2
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Trends in Nitrates and Chloride Suggest Increasing Human Stress on the Lake
 Nitrates levels continue to rise
 Chloride levels are increasing after
an earlier decline
Chloride - Don River
Nitrates
Chloride
 Note higher chloride
and nitrate in urban
areas (dark symbols)
9
Trends in Nitrates and Chloride in the Open Lake Similar to Nearshore
Nitrate plus Nitrite Trend in Lake Ontario
Open Lake, Spring (April) Cruise, 1969 - 2011
Chloride Trend in Lake Ontario
Open Lake, Spring Cruise, Surface Data, 1971 - 2008
0.5
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0.45
Nitrates
Chloride
Chloride (mg Cl/L)
0.35
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0.3
20
start of the intake
data in previous slide
0.2
16
slides provided
by Alice Dove
Environment Canada
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1969
1970
1971
1972
1973
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1981
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1989
1990
1991
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1994
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2099
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2008
2009
2010
11
NO3 + NO2 (mg N/L)
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0.4
 Nitrates and chloride inputs to water (and indirectly via the air in the
case of nitrates) are associated with many aspects of human activity;
patterns of change in levels provide, in a relative sense, an indication
of the strength of interaction of humans with the aquatic environment
10
Temporal Changes at Intakes Provide Insight on Factors Affecting Water Quality
 Nearshore water quality is highly changeable affected by a range of
factors operating both on the land and within the lake
 Seasonal patterns in biological activity, lake circulation and runoff to
the nearshore drive quasi-predictable patterns
Nitrates
Chloride
Two examples
 summer depression in
nitrates due to uptake of
phytoplankton
Nitrates
Chloride
 winter and spring peaks in
chloride due to heightened
land runoff at these times
11
Other Aspects of Nearshore Water Quality are Less Predictable Over Time
Total Phosphorus
 Unpredictable features of weather
(precipitation runoff, wave-induced
disturbance of the lakebed) result in
temporal patterns that appear more
erratic
 There is little seasonality in TP in the
water intake data (and the
nearshore in general) likely due to
the random weather effects
 Waves re-suspend shore and
lakebed sediments containing
phosphorus; land runoff containing
phosphorus is also variable over
time
12
Bi-national Cooperative Monitoring of Nearshore Water Quality in 2008
Motivating factors for study:
Cobourg
WTP
S. Peel
WTP
R.L.Clak
WTP
Grimsby
WTP
Focus is on spatial patterns in water quality that
provide Insight on factors affecting environmental
conditions in the lake
 recognition of the wide
variability in water quality of
the nearshore and the
challenge of representing
this variability in a useful
and integrated way,
 continuing uncertainty as
to the ecological changes
since the invasion of
dreissenid mussels in
~1990
 apparent resurgence in
shore-fouling by the benthic
green algae Cladophora
 growing appreciation of
the need to better relate
watershed features with
nearshore conditions
13
Runoff from Rivers and Shoreline Accounted for
Much of the Variability in Nearshore Water Quality
 Field mapping of conductivity used as tracer of
land discharges to the lake
 Elevated conductivity over mixing areas at the
mouths of the Credit River, Cooksville Creek and
Etobicoke Creek illustrated here indicate extent of
influence into the nearshore
Watersheds
Credit River
Etobicoke
Creek
Cooksville
Creek
14
14
Influence of Adjacent Land (as Inferred from Variability in Water
Quality) Drops Quickly Moving Away from the Shoreline
 Onshore-offshore variability (measured as the coefficient of
variation) in field-measured fluorescence of organic material
used to assess relative influence of land on the nearshore
Western Toronto/Eastern
Mississauga Shoreline
Cobourg Shoreline
 Patterns differed among
area: Most variability in
the Greater Toronto area
and the least in the
Cobourg areas
 Variability as measure of
“land effect” works
because the nature of
land-nearshore interaction
is to create blotches of
affected water along the
shoreline (as illustrated in
the previous slide)
15
Lands Adjacent to Shoreline Tends to be Urbanized
 Among the study areas, the influence of the adjacent land on
the nearshore was stronger in the more highly urbanized
Toronto area then elsewhere
 There are also larger rivers and a greater volume of tributary
discharge
16
Diagnostic Water Quality Features Among Areas
Percent of Nearshore with
Conductivity more than 10% of
Lake Background
 Nearshore areas above 10% of
background conductivity were
limited
2%
 Extent of elevation greatest in
GTA
Soluble Reactive
Phosphorus in the 25% of
samples with highest
conductivity
 Strongest influence on
nearshore (as inferred
from samples most
affected by land
discharges) is the GTA
17
Varying Quality and Quality of Tributary Discharges Over the Coastline
Affects Nearshore Water Quality Features Among Area
Differences in Water Quality Features among Toronto Area Rivers
Comparison of Water Quality by Watershed
Total Phosphorus
RAP Avg WET
RAP WET LL
0.400
RAP WET UL
RAP Avg DRY
RAP DRY LL
0.350
RAP DRY UL
Modelled WET
0.300
Modelled DRY
Concentration (mg/L)
PWQMN Avg WET
PWQMN Avg DRY
0.250
0.200
0.150
0.100
0.050
0.000
Etobicoke
Mimico
Humber
Don
Highland
Rouge
Watershed
18
Invasion of Zebra and Quagga Mussels has also Impacted the Nearshore
 Broad suite of effects/interactions with
nearshore ecology, some affecting water
quality
- (e.g.) filter feeding removes phytoplankton
and other particles from the water
Diatom Biovolume
1981
2003
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14
12
10
2
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Secchi Depth 1994 -2009
8
4
20
20
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1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
16
Secchi Depth (m)
18
Station 9713
Oakville
Secchi Depth (m)
20
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Secchi Depth (m)
Increasing Water Clarity After the Zebra and Quagga Mussels Invasion
Station 9712
Newcastle
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10
5
6
0
Station 3087
Prince Edward Point
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14
12
10
8
6
4
2
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Summary
 Water quality over most of the nearshore on the Canadian shores of
Lake Ontario is considered good
 Notwithstanding, strong human influences on water quality are evident
as indicted by areas of impacted water quality near the shores of the
lake, and long-term trends in chloride and nitrate
 Runoff from rivers strongly affects nearshore water quality and is a
critical connection between people, activities on the land and the lake
 Stresses on the lake ecosystems from invasive species, most notably
the zebra and quagga mussels, are also affecting water quality
21
Acknowledgements
 Joe
Makarewicz (State University of New York at Brockport)
 Jennifer Winter
 Greg Hobson, Wendy Page, John Thibeau and Lance Boyce (EMRB
Great Lakes field group)
 Alice Dove, Vi Richardson Environment Canada
 Jennifer Winter and Georgina Kaltenecker (EMRB)
 Krista Chomicki (University of Waterloo)
16