529
The greatest threat to water quality is related to surface water contamination by
municipal discharge, industrial pollution, and nutrient runoff from agricultural
landscapes.
Although the Great Lakes are part of a single system, the challenges at the nexus
of food, energy, and water systems are different for each lake. Lake Superior is
characterized by low nutrient concentrations, high oxygen content, and a sparse
growth of algae and other organisms. It is the largest, deepest, and coldest of the
Great Lakes, and most of its basin is forested and sparsely populated, with little
agricultural activity, and thus it has had relatively lower anthropogenic impacts.
The other four lakes exist in basins with deeper, more fertile soils, and they have
undergone significant land use changes, from the clearing of forested land to intensive agriculture, industrialization, and urbanization. Lake Michigan is the second
largest of the Great Lakes, and it ranges from less developed areas in the north to the
most urbanized regions of the Great Lakes in the southern basin, including Chicago
and Milwaukee.
The more temperate southern region of the Great Lakes Basin is well suited for
agriculture because of a more favorable climate and more fertile soils. However,
nutrient runoff from farms in Indiana, Michigan, and Ohio has led to severe contamination in Lakes Michigan, Huron, and Erie, including areas that have experienced algal blooms from nitrogen and phosphorous loading, widespread algae
die-offs, and compromised public water utility systems (see Sect. 4.5.1 for a case
study on incorporating behavioral heterogeneity in FEW systems in the Lake Erie
watershed). Public health advisories about consumption of toxin-contaminated fish
are common throughout the region.
Water quality issues are further aggravated by altered hydrology. In a waterabundant region, the ecological systems reflect both water abundance and seasonal
fluctuations in-stream flows. Because the ecosystems have evolved in a water-rich
environment, their health is intricately connected to water availability and specific
hydrologic regimes. As a result, drops in lake water levels and stream flows are
more harmful than they might be in areas that have evolved under more waterstressed conditions. Drawdowns in groundwater for agricultural irrigation and
municipal consumption are one stressor, but climate uncertainty is adding further
complexity because the region could end up with a warmer and wetter climate that
leads to increased river flows, flooding, channel adjustments, bank erosion, and
increased sedimentation.
Contamination and hydrologic changes compromise the ability of ecosystems to
deal with other stressors. As a result, the lakes are particularly susceptible to invasive species introductions. Since 1840, more than 180 invasive species have been
identified in the North American Great Lakes, each of which has disrupted the balance of aquatic ecosystems (EC and EPA 2014). Because the Great Lakes are
historically nutrient poor, small increases in nutrient loadings lead to effects that are
of a greater magnitude. On the other hand, because the Great Lakes Basin is waterabundant, small changes in flows lead to small responses that are difficult to detect
or appreciate until a threshold has been crossed.
19 Watersheds at the Nexus
The greatest threat to water quality is related to surface water contamination by
municipal discharge, industrial pollution, and nutrient runoff from agricultural
landscapes.
Although the Great Lakes are part of a single system, the challenges at the nexus
of food, energy, and water systems are different for each lake. Lake Superior is
characterized by low nutrient concentrations, high oxygen content, and a sparse
growth of algae and other organisms. It is the largest, deepest, and coldest of the
Great Lakes, and most of its basin is forested and sparsely populated, with little
agricultural activity, and thus it has had relatively lower anthropogenic impacts.
The other four lakes exist in basins with deeper, more fertile soils, and they have
undergone significant land use changes, from the clearing of forested land to intensive agriculture, industrialization, and urbanization. Lake Michigan is the second
largest of the Great Lakes, and it ranges from less developed areas in the north to the
most urbanized regions of the Great Lakes in the southern basin, including Chicago
and Milwaukee.
The more temperate southern region of the Great Lakes Basin is well suited for
agriculture because of a more favorable climate and more fertile soils. However,
nutrient runoff from farms in Indiana, Michigan, and Ohio has led to severe contamination in Lakes Michigan, Huron, and Erie, including areas that have experienced algal blooms from nitrogen and phosphorous loading, widespread algae
die-offs, and compromised public water utility systems (see Sect. 4.5.1 for a case
study on incorporating behavioral heterogeneity in FEW systems in the Lake Erie
watershed). Public health advisories about consumption of toxin-contaminated fish
are common throughout the region.
Water quality issues are further aggravated by altered hydrology. In a waterabundant region, the ecological systems reflect both water abundance and seasonal
fluctuations in-stream flows. Because the ecosystems have evolved in a water-rich
environment, their health is intricately connected to water availability and specific
hydrologic regimes. As a result, drops in lake water levels and stream flows are
more harmful than they might be in areas that have evolved under more waterstressed conditions. Drawdowns in groundwater for agricultural irrigation and
municipal consumption are one stressor, but climate uncertainty is adding further
complexity because the region could end up with a warmer and wetter climate that
leads to increased river flows, flooding, channel adjustments, bank erosion, and
increased sedimentation.
Contamination and hydrologic changes compromise the ability of ecosystems to
deal with other stressors. As a result, the lakes are particularly susceptible to invasive species introductions. Since 1840, more than 180 invasive species have been
identified in the North American Great Lakes, each of which has disrupted the balance of aquatic ecosystems (EC and EPA 2014). Because the Great Lakes are
historically nutrient poor, small increases in nutrient loadings lead to effects that are
of a greater magnitude. On the other hand, because the Great Lakes Basin is waterabundant, small changes in flows lead to small responses that are difficult to detect
or appreciate until a threshold has been crossed.
19 Watersheds at the Nexus