CE 394K.3 GIS in Water Resources
Fall Semester 2004
University of Texas at Austin
Instructor: David R. Maidment
GIS RESULTS AND DATA ANALYSIS
The Great Lakes -Superior, Michigan, Huron, Erie and Ontario- contain roughly ninety percent
of the United States’ freshwater supply and eighteen percent of the world’s. In fact, the Great
Lakes system is the largest surface freshwater system on Earth. The volume of water
contained in these lakes could cover an area the size of the forty-eight contiguous US states
with nearly ten feet of water.
The Great Lakes were formed by the repeated advancing and retreating of glaciers over a
period of millions of years. They now cover an area over 94,000 square miles. Canada and
the United States share the responsibility for the environmental status of this system, a critical
resource. The Great Lakes system provides drinking water and power and supports
recreation, agriculture, transportation, and industrial development. The health of these lakes,
therefore, controls the quality of life of millions of people. General information on the lakes is
summarized in Table 1.
Table 1: Great Lakes General Information
Source: US EPA
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Before 1972, the year that the United States passed the Clean Water Act and the US and
Canada developed the Great Lakes Water Quality Agreement, the pollution of the Great
Lakes with excess nutrients and toxic chemicals was essentially going unchecked. This
pollution was accelerating eutrophication, the natural process of lake aging, and creating a
health risk for humans or other organisms consuming or coming in contact with the water.
Sources of this pollution include agricultural and urban runoff, industrial discharges, landfill or
disposal site leachate, and atmospheric pollutants. In the first half of the twentieth century,
development and industrial growth resulted in the discharge of untreated sewage, untreated
industrial waste, phosphate detergents, non-organic fertilizers, and chemicals such as
polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDT) to the Great
Lakes. The PCBs, DDT, and other toxic chemicals introduced a health risk – people and
other organisms could be not only directly exposed to the polluted water, but also indirectly
exposed to chemical levels higher than that of the polluted water due to bioaccumulation in
the food chain. The Great Lakes ecosystem was and is also adversely affected by nutrient
pollution – the nutrients accelerate the aging process of the lakes. When biologically useful
chemicals are present in a lake in excess, large algal blooms can occur. These algal blooms
exert a high oxygen demand as the algae decay and this high BOD results in low dissolved
oxygen levels in the water. If the DO becomes too low, if it falls below around 7 mg/L, most
fish cannot survive. A lake experiencing eutrophication can go from having a large number of
species to having a large mass of a few pollution-tolerant organisms such as worms and carp.
Since the increase in water quality consciousness materialized in the form of the Clean Water
Act and the Great Lakes Water Quality Agreement, the condition of the lakes has improved
and become more stable. Areas significantly impaired by pollution were labeled Areas of
Concern and Remedial Action Plans (RAPs) were developed to guide their rehabilitation.
Pollutant discharges to the lakes were reduced. Phosphorus concentrations, for example,
were reduced to levels below maximum set concentrations for Lakes Superior, Michigan, and
Huron and at or near maximum concentrations for Lake Ontario and Lake Erie. Figure 1
shows the general improvement in PCB levels over time, Figure 2 shows reductions in total
phosphorus, and Figure 3 shows reductions in a pesticide, dieldrin.
Figure 1: PCB Levels over Time
Source: Donna Myers, USGS, State of the Lakes Ecosystem Conference
Figure 2: Total Phosphorus Concentration over Time
Source: Donna Myers, USGS, State of the Lakes Ecosystem Conference
Figure 3: Dieldrin (pesticide) Concentrations over Time
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GIS RESULTS AND DATA ANALYSIS
ArcGIS may be helpful in the assessment of Great Lakes water quality, particularly its
Tracking Analyst, which presents time series data with helpful animations. The majority of
data used in the following analysis was obtained from the Great Lakes Environmental
Database (GLENDA) in tabular form, the Great Lakes Information Network (GLIN) and the
United Nations’ Global Environment Monitoring System (GEMS) in the form of shapefiles, and
Environment Canada in the form of .e00 interchange files. All feature classes were assigned
the spatial reference data of glwsheds, the feature class that includes watershed boundaries.
The NAD 1927 was used.
Interchange files were imported using the “Import from Interchange File to Coverage” tool
under Coverage Tools. Data obtained in tabular format were edited to contain the desired
data and saved as database files. The XY data from these dbf tables was displayed, made
permanent by exporting, and added to the Tracking Analyst Temporal Data Wizard.
The volume of data obtained for monitoring points from the GLENDA was overwhelming – the
data for each water quality parameter often exceeded 7,000 values. Data was available for a
variety of dates (1996-2003 for GLENDA, for example) at a variety of monitoring points and at
several depths. Therefore, in order to manage the data and perform the analysis, some of the
depths were not considered and often, duplicate data had to be eliminated. At times, some of
the lakes were not considered. For data analysis not involving all five lakes, only data for
Lake Ontario, the smallest of the lakes by surface area, and Lake Superior, the largest, were
Figures 1-7 are maps displaying water quality data from the United Nations. This data is
assumed to be data averaged for the lakes and the file indicates that the data was measured
from 1976-1990. The meaning of this date range is unclear, but because the water quality
survey was done for lakes all over the world, it is possible that this range represents the total
time frame over which values were determined. Even if this is true however, it is likely that the
Great Lakes data were gathered during the same year or few years. The values may also
represent an average over all of those years. Regardless of what is true, the data is still
valuable as means of comparison between the lakes. Water quality parameters represented
in these figures include Ca2+, Mg2+, K+, PO4-P, NO3-N, SO42-, Na+, and Total Dissolved Solids
With the GLENDA data, note that some of the monitoring points do not appear on the maps to
be contained within the lakes, even when the spatial reference data was the same for all
feature classes. A possible reason for the lack of alignment is that a grid was used to present
the points – only whole number latitude and longitude values were used. The monitoring
points are shown in Figure 9 and Figure Sets 10, 11, and 12 show data from screen captures
during Tracking Analyst analyses. Following those figure sets, links to Tracking Analyst
animations of temperature data and dissolved oxygen concentrations are available for two
Figure 1: Magnesium Concentrations Figure 2: Calcium Concentrations
Figure 3: Nitrate Concentrations (as N) Figure 4: Phosphate Concentrations (as P)
Figure 5: Potassium Concentrations Figure 6: Sodium Concentrations
Figure 7: Sulfate Concentrations Figure 7: Total Dissolved Solids Concentrations
Figure 9: Monitoring Point Locations
Figure Set 10: Tracking Analyst Alkalinity Analysis
Figure Set 11: Tracking Analyst Chloride Analysis
Figure Set 12: Tracking Analyst Total Phosphorus Analysis
Seasonal Temperature Change Dissolved Oxygen
Lakes Ontario and Superior Great Lakes
Tracking Analyst Animation Tracking Analyst Animation
CLICK ON SYMBOLS TO DOWNLOAD ANIMATION
To make data analysis more manageable and to give it a focus, the analysis of the Great
Lakes was narrowed to a comparison of Lake Superior, the largest of the lakes, and Lake
Ontario, the smallest by surface area. Lake Ontario has a watershed area to lake volume
ratio roughly 3.5 times greater than that of Lake Superior. This number does not take into
consideration the fact that the lakes are connected and water from Superior’s watershed may
enter Lake Ontario – Lake Superior’s watershed, in other words, is not counted as part of the
total watershed for Lake Ontario for this calculation. If this ratio were the only consideration in
evaluating the degree of pollution of the lakes, one would expect Lake Ontario to have higher
concentrations of contaminants. Although this is generally the case, that Lake Ontario shows
higher contaminant concentrations than Lake Superior, watershed area to volume ratio is not
the only causative factor. Lake Ontario has at least seven times more people living around it
than Lake Superior. The growth of the population around Lake Ontario is also much great
than that of the Lake Superior population – data up to 1990, shown in Figure 13, show that the
Lake Superior population barely shows any growth at all. Population growth means a greater
rate of development and more use and disposal of water quality degrading products. This
could be a contributing factor to the higher concentrations of nutrients, as seen in previous
figures, and other contaminants.
Source: US EPA,
and Resource Book
Figure 13: Population Figures for the Great Lakes
Another possible explanation for greater concentrations in Lake Ontario is the land use
surrounding the lakes. As shown in Table 2, Lake Superior’s basin is mostly forest, while
Lake Ontario’s basin has high agricultural land use, a use that often results in non-point
source nutrient pollution. This is consistent with the fact that Lake Ontario shows higher
nitrate and phosphate concentrations in the United Nations GIS data. Lake Ontario also has a
higher concentration of industry surrounding it than Lake Superior. This factor, illustrated in
Figure 14, no doubt contributes to greater pressure on the environment in that area.
Table 2: Land and Shoreline Uses
Source: US EPA
Source: US EPA, Great Lakes Environmental Atlas and Resource Book
Figure 14: Concentration of Industry
In addition to having some idea why Lake Ontario seems to have more water quality issues
than Lake Superior, having information with respect to how certain pollutants degrade the
water quality is useful. Chloride, for example, is present in Lake Ontario in concentrations
around 21-25 mg/L. While there is no health standard for chloride, a level of less than 10
mg/L is desirable because this is around the natural level in water.6 A high chloride
concentration may be a problem in water because of its corrosive effect on pipes. A higher
concentration of chloride in water may also be an indicator of contamination by septic
systems, landfill leachate, animal waste, fertilizer, or other wastes – measurement of chloride
concentration may act as a surrogate for the presence of more harmful substances or nutrient
pollution. Lake Ontario does in fact have high levels of nitrate and phosphate, nutrients which
can cause algal blooms and accelerate eutrophication.
Alkalinity is also higher (although not high in general) in Lake Ontario. Alkalinity is a measure
of the acid neutralizing capacity of water. It is usually directly related to hardness, a measure
of the magnesium and calcium in water (also higher for Lake Ontario). Water with high
alkalinity may cause scaling in plumbing and hard water results in scaling and soap scum
For both Lake Ontario and Lake Superior, dissolved oxygen levels over the past eight years
look satisfactory. Most fish require a minimum DO level of around 7 mg/L. The DO levels
meet or exceed this DO concentration for the available data. Anthropogenic eutrophication, or
acceleration of the natural aging of lakes, includes a decrease in the DO of the water.
Literature indicates that the Great Lakes are undergoing accelerated eutrophication; however,
the DO levels reported by GLENDA seem sufficient for biodiversity. Perhaps this process is
more apparent deeper in the lakes where organisms decay or perhaps in recent years, the
eutrophication process has been slowed to a closer-to-natural speed.
Finally, temperature data were available for the Great Lakes and while temperature can have
some effect on lake chemistry and the lake ecosystem, the most interesting information from a
comparison of station data for Lake Ontario and Lake Superior was the seasonal fluctuation
pattern. As one would expect, the temperature of the lakes varied along with seasonal
temperature changes. Lake Ontario, however, experienced greater fluctuations and this
makes sense because Lake Ontario has a smaller volume (and surface area) of water. It
therefore requires less energy to heat the water. Temperature was also compared between
depths of five meters and twenty meters for both lakes. In comparing these data, seasonal
fluctuations in temperature appeared greater at the five meter depth. This makes sense
because the water mixing at the surface of the lake has more contact with the hot or cold air –
this water therefore is more likely to change in temperature. The fluctuations are illustrated in
Figure 15 below.
Figure 15: Seasonal Temperature Fluctuations at Monitoring Stations
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Both hydrologic and human factors appear to have an impact on the water quality in the
Great Lakes. Lake Ontario, in comparison to the other lakes, seems particularly impacted by
the characteristics of its basin and the human activity surrounding it. Water quality seems to
be improving, however, for Lake Ontario and the other lakes because of the raised awareness
and concern codified in the Clean Water Act and Great Lakes Water Quality Agreement.
If work on this project were to continue, it would be useful to have more monitoring points so
perhaps interpolations of lake concentrations might be created – this would be more visually
exciting and it also would allow water quality to be compared, for example, to the bathymetry
of the lake or wind patterns and atmospheric pollution data. Other work beneficial to this
topic would be to find useable pre-1972 data to compare to data following passage of the
Clean Water Act. Tracking Analyst could be applied to this data to yield a nice illustration of
the process of cleaning up the Great Lakes.
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Donna Myers (USGS). “Pressures on the Great Lakes Ecosystem.” State of the Lakes Ecosystem
Conference, 2002. <http://www.epa.gov/glnpo/solec/2002/d1/sol02d102press1010.pdf>.
Environment Canada, Integrated Atmospheric Deposition Network.
Great Lakes Environmental Database (GLENDA), US EPA.
Great Lakes Information Network (GLIN). <http://www.great-lakes.net/gis/metadata/acp/index.html>.
National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory.
“About Our Great Lakes.” <http://www.glerl.noaa.gov/pr/ourlakes/>.
Shaw, Byron; Mechenich, Christine and Jim Peterson. University of Wisconsin – Extension. Wisconsin
Department of Natural Resources. “Interpreting Your Drinking Water Test Results.”
United Nations’ Global Environment Monitoring System (GEMS).
US EPA. Great Lakes Environmental Atlas and Resource Book.