How was the health of Western Lake Erie calculated?

This report card provides a transparent, timely, and geographically detailed assessment of health in Western Lake Erie and it's watershed using data from 2018 defined as the progress of five indicators toward scientifically-derived thresholds or goals. The indicators are combined into two overall health scores, one score for the Lake, and one for the Watershed.

Each sample is compared to a threshold to calculate a score from 0 to 100. All sample scores are averaged for each sampling location to reach a station score. All stations in each region are averaged to a region score. Region scores are area-weighted to get the overall score.

Overall Health Index

The Western Lake Erie report card compares 11 lake indicators (total phosphorus, dissolved phosphorus, nitrate-nitrate, chlorophyll a, walleye, yellow perch, emerald shiner, bloom index, source water toxin, and recreational toxin) and 10 watershed indicators (total phosphorus, dissolved phosphorus, total nitrogen, nitrate-nitrite, source water toxin, total suspended solids, fish, macroinvertebrates, habitat quality, and fish consumption) to scientifically derived thresholds or goals. The lake indicators were combined into an overall lake health index, which is presented as a subregion percent score. The watershed indicators were combined into an overall watershed healh index, which is presented as a subregion percent score. Both scores were calculated as an average of the subregions weighted by geographic area.

Total Phosphorus

Total phosphorus is indicative of too much phosphorus in the water. Phosphorus is an essential nutrient for all plants and animals. However, too much phosphorus in the water causes algae to grow in large, dense blooms, which deplete oxygen for fish and other aquatic organisms. Phosphorus enters rivers and lakes when it is washed off the land, particularly from agricultural lands that have been fertilized.


How is it scored?

Total phosphorus (TP) was used as an indicator in both the watershed and lake analysis. Year-round data for 2018 were analyzed. For each TP sample, the measurement was compared to the threshold on a pass/fail basis. Site scores were averaged into an overall region total phosphorus score.

The total phosphorus threshold used for the western Lake Erie basin analysis was the U.S. EPA threshold 0.015 mg/L.

The total phosphorus threshold used for the western Lake Erie watershed analysis was the U.S. EPA ecoregion threshold 0.07635 mg/L.

Dissolved Phosphorus

Dissolved phosphorus is indicative of too much phosphorous in the water. Phosphorus is an essential nutrient for all plants and animals. However, too much phosphorus in the water causes algae to grow in large, dense blooms, which deplete oxygen for fish and other aquatic organisms. Phosphorus enters rivers and lakes when it is washed off the land, particularly from agricultural lands that have been fertilized.

How is it scored?

Dissolved phosphorus (DP) was used as an indicator in both the watershed and lake analysis. Year-round data for 2018 were analyzed. For each DP sample, the measurement was compared to the threshold on a pass/fall basis. Site scores were averaged into an overall region dissolved phosphorus score.

The dissolved phosphorus threshold used for the Western Lake Erie basin analysis was 0.001 mg/L, from Tomlinson et al. 2010.

The dissolved phosphorus threshold used for the Western Lake Erie watershed analysis was based on the working group recommendation. The threshold was 0.02 mg/L.

Total Nitrogen

Nitrogen is important to all living things. Nutrients such as nitrogen occur naturally in both freshwater and saltwater. Plants and animals need nutrients to grow and survive. But too much nitrogen in the water fuels the growth of excessive algae, creating dense blooms that block sunlight and reduce oxygen for fish and other organisms. In the lake, total nitrogen was used to assess nitrogen intensity. Total nitrogen is a sum of organic nitrogen as well as ammonia and nitrate-nitrite compounds.

How was it scored?

Total nitrogen (TN) was used as an indicator in both the watershed and lake analysis. Year-round data for 2018 were analyzed. For each TN sample, the measurement was compared to the threshold on a pass/fail basis. Site scores were averaged into an overall region total nitrogen score.

The total nitrogen threshold used for the western Lake Erie basin analysis was 0.8 mg/L, from Chaffin et al. 2014.

The total nitrogen threshold used for the western Lake Erie watershed analysis was the U.S. EPA ecoregion threshold 2.18 mg/L.

Nitrate + Nitrite

Nitrogen is important to all living things. Nutrients such as nitrogen occur naturally in both freshwater and saltwater. Plants and animals need nutrients to grow and survive. Too much nitrogen in the water fuels the growth of excess algae, creating dense blooms that block sunlight and reduce oxygen for fish and other organisms. Nitrate and nitrite together are of interest because they are the form of nitrogen most available to algae.

How is it scored?

Nitrate + Nitrite (NN) was used as an indicator in both the watershed and lake analysis. Year-round data for 2018 were analyzed. For each NN sample, the measurement was compared to the threshold on a pass/fail basis. Site scores were averaged into an overall region nitrate+nitrite score.

The nitrate-nitrite threshold used for the western Lake Erie basin analysis was 0.1 mg/L from Chaffin et al. 2014.

The nitrate-nitrite threshold used for the western Lake Erie watershed analysis was the Ohio EPA warm water habitat threshold 1.5 mg/L.

Chlorophyll a

Chlorophyll a is the green pigment in photosynthesizing algae that helps them produce food. Measuring chlorophyll is an indicator of the amount of algae in the water, which uses both nitrogen and phosphorus to grow. Too much algae in the water reduces the oxygen available for other organisms, and some algal blooms produce toxins that are harmful to all living things.

How is it scored?

Chlorophyll a (Chla) was used as an indicator in lake analysis. Data from April 1–September 30, 2018 were analyzed, representing the algae growing season. For each Chla sample, the measurement was compared to the threshold on a pass/fail basis. Site scores were averaged into an overall region chlorophyll a score.

The chlorophyll a threshold used for the western Lake Erie basin analysis was the Great Lakes Water Quality Agreement Annex 4 – nutrients threshold 0.1 mg/L.

Walleye

The walleye is a popular fish for commercial and recreational fishing. The largest walleye population in the world occurs in the Ohio portion of Lake Erie. Increased water pollution in Lake Erie led to a walleye population decline. Lake water quality improved following the Clean Water Act, leading to a walleye resurgence. Population size can be maintained by setting bag limits on commercial and recreational fishing.

How is it scored?

Walleye abundance was used as an indicator in the lake analysis. Walleye abundance is estimated by catch-age analysis for the entire Lake Erie area, not just the Western basin. The walleye abundance indicator was the 2018 data scored based on the long-term mean (1984–2017).

The walleye abundance threshold used for the western Lake Erie basin analysis was the long term mean (1984–2017) abundance. For more information on the walleye analysis, visit XX.

Yellow Perch

The yellow perch is a popular fish for commercial and recreational fishing. The yellow perch is common prey for larger species of fish such as the walleye. Yellow perch populations tend to be lower when walleye are abundant, and vice versa. The yellow perch competes for food with the white perch and the invasive zebra mussel, which feeds on the zooplankton that young yellow perch prefer.

How is it scored?

Yellow perch abundance was used as an indicator in the lake analysis. Yellow perch abundance is estimated by catch-age analysis for the Western basin. The yellow perch abundance indicator was the 2018 data scored based on the long-term mean (1984–2017).

The yellow perch abundance threshold used for the western Lake Erie basin analysis was the long term mean (1984–2017) abundance. For more information on the walleye analysis, visit XX.

Emerald Shiner

The emerald shiner is a small fish that serves as a bait species for fishing. They are important forage for larger sport fish such as the yellow perch and walleye. The emerald shiner diet consists primarily of plankton and small insects. Emerald shiner populations in Lake Erie have been low in recent years, likely due in part to the expanding walleye population.

How is it scored?

Emerald shiner abundance was used as an indicator in the lake analysis. Emerald shiner abundance is estimated by SCANMAR trials, trawling effort distance, and catches from the August interagency trawling program for the Western basin. The emerald shiner abundance indicator was the 2018 data scored based on the long-term mean (1988–2017).

The emerald shiner abundance threshold used for the western Lake Erie basin analysis was the long term mean (1988–2017) abundance. For more information on the emerald shiner analysis, visit XX.

Bloom Index

The bloom index developed by NOAA measures the severity of an algal bloom based on the biomass of harmful algae and the duration of the bloom. The size of the bloom is largely unrelated to its severity. Some amount of algae in Lake Erie is considered normal and even healthy, because algae provides food for valuable fish species. Blooms that produce toxins, however, are cause for concern and are reflected in the bloom index. Blooms with an index above 5 are considered potentially harmful.

How was it scored?

Bloom index was used as an indicator in the Western Lake Erie lake analysis. This index is published every year and was developed by NOAA, Heidelberg University, University of Michigan-NCSU-GLERL, and LimnoTech. The index is based on the amount of biomass over the peak 30 days of the bloom. The bloom index value was converted to the 100-point report card score scale and the single value was used for the overall region score for all regions in Lake Erie.

Source Water Toxin

The presence of toxic microcystin, produced by algal blooms, in drinking source water is a threat to human health. Source water toxin indicates that harmful algal blooms have occurred in proximity to drinking water treatment plants. Algal blooms that produce toxins are caused by excessive nutrients, such as nitrogen and phosphorus. The threshold for human exposure to microcystin in drinking water is lower that the threshold of exposure by skin contact.

How was it scored?

Source water toxin was used as an indicator in both the watershed and lake analysis. Year-round data for 2018 were analyzed. For each sample, the measurement was compared to the threshold on a pass/fail basis. Site scores were averaged into an overall region source water toxin score.

The source water toxin threshold used for both the western Lake Erie basin analysis and watershed analysis was the Ohio EPA public drinking water supply beneficial use cyanotoxin indicators threshold 1 μg/L.

Recreational Toxin

The presence of toxic microcystin, produced by algal blooms, is a threat to human health when it contaminates water supplies. Recreational toxin indicates that there is enough microcystin in the water to harm humans who come in recreational contact with the water. Recreational contact is primarily skin contact, such as might occur while swimming or kayaking, as opposed to ingestion by drinking.

How was it scored?

Recreational toxin was used as an indicator in lake analysis. Data from the recreational season (Memorial Day to Labor Day) May 28–September 3, 2018 were analyzed. For each microcystin sample, the measurement was compared to the threshold on a pass/fail basis. Site scores were averaged into an overall region recreational toxin score.

The recreational toxin threshold used for the western Lake Erie basin analysis was the U.S. EPA recreational water quality criteria threshold 8 μg/L.

Total Suspended Solids

Suspended solids in water include a variety of things, from sediments and silt to decaying organic matter. This metric is used as an indicator of water clarity. Generally speaking, clearer water is cleaner water. In Lake Erie, some cloudiness in the water is considered normal because of persistent, non-toxic algae that provides food for fishes and invertebrates.

How is it scored?

Total suspended solids (TSS) was used as an indicator in the watershed analysis. Year-round data from 2018 were analyzed. For each TSS sample, the measurement was compared to the threshold on a pass/fail basis. Site scores were averaged into an overall region total suspended solids score.

The total suspended solids threshold used for the western Lake Erie basin analysis was the Maumee Watershed Action Plan (2014) threshold 25 mg/L.

Fish

Some fish species are more sensitive to environmental degradation than others. The collection of species living in an ecosystem is called an assemblage. Fish assemblages are used as indicators that are sensitive to habitat degradation, environmental contamination, and overall ecosystem productivity. Ecosystems with more fish species tend to be healthier, and the presence of certain, more sensitive species is a sign that the ecosystem is in good health.

Macroinvertebrates

Because they are small, invertebrates are particularly susceptible to environmental contamination. Some invertebrates are more sensitive to environmental change than others. The collection of species living in an ecosystem is called an assemblage. Ecosystems with more species tend to be healthier, and the presence of certain, more sensitive species is a sign that the ecosystem is in good health.

Habitat Quality

What goes on the land eventually ends up in the water. Certain types of land cover, such as forest, are better at reducing runoff into the rivers. Therefore, the quality of terrestrial habitat is an indicator both of current watershed health and of current and future waterways health.

Fish Consumption

The chemical byproducts of industry, such as mercury, are harmful to humans when ingested. These toxins can contaminate fish that reside in polluted rivers and thereby make their way into human diets. Each state within the western Lake Erie basin publishes their own advisories for maximum fish consumption. Cleaner rivers produce healthier fish with fewer consumption advisories, so this indicator is used to measure how clean rivers and lakes are from a human health perspective.

How was it scored?

The fish consumption indicator is based on fish consumption advisories which are issued by state or province. The thresholds are based on the number of servings of fish you can eat per month. Servings per month were assigned a report card score and these were averaged for an overall region score.

Pesticide

Large-scale agriculture is reliant on the use of chemical pesticides and herbicides to control the onset of pests that would eat the crops and weeds that would out-compete them. However, these chemicals can cause harm to people and animals if they end up in the water supply. Agricultural fields are particularly prone to runoff, and so are likely to leak chemicals into the water. There was not enough data available to score this indicator in any region, but it is an important factor to consider in water quality and overall ecosystem health.