Good Water Gone Bad
Eutrophication results when the fertilizers that nourish soil-based plants also feed water-based ones.
Ironically, since the word itself means "well-nourished," many stormwater managers and government agencies are worried about eutrophic bodies of water. What could be so bad about a well-nourished lake? Nothing—if the lake's purpose is to provide habitat for plants and animals of all sorts. Everything—if the lake is to be used by humans as a drinking-water source or as a recreational area.
Lakes and other bodies of water are usually classified by their trophic ("nutrition," "growth") state. Oligotrophic bodies of water contain low nutrient concentrations and plant growth; eutrophic lakes have high nutrients and plant growth; mesotrophic lakes contain percentages of nutrient concentrations and plant growth that fall somewhere in between the other two categories. To provide examples of the three trophic types:
- Oregon's Crater Lake is a clear, sky-blue ultra-oligotrophic lake.
- The blue water section of Lake Superior is ultra-oligotrophic—it's the most oligotrophic of the Great Lakes.
- Lake Michigan and Lake Huron are classified as meso-oligotrophic.
- Lake Ontario is mesotrophic.
- Lake Erie is still considered eutrophic, although, ironically enough, the problematic, invasive zebra mussels have been improving its clarity.
A number of attributes contribute to a lake's trophic status; however, three main factors regulate a lake's trophic state:
- The rate of nutrient supply. This is affected by the bedrock geology of the watershed, the surrounding soils and vegetation, and local human land uses and land management.
- Climate. This includes the amount of sunlight that hits the lake, the ambient and water temperature, and the particular hydrology (precipitation plus lake basin turnover time) the lake experiences.
- The shape of the lake's basin. This includes not only depth, volume, and surface area, but also the watershed-to-lake surface area ratio.
It's interesting to note that, of all these factors, only one is directly related to human activity. However, in many cases, it's human activity—or inactivity—that will tip the scales in a body of water's delicate ecological balance.
Every Spring, Stir Well
A certain amount of nutrients naturally exists in bodies of water; algae, phytoplankton, and zooplankton use and create nutrients during different parts of their life cycles. For example, when dead plankton sink to lower depths and decompose, nutrients are redistributed from the upper water where the plankton had been living. Essential nutrients (bioavailable forms of phosphorus and nitrogen) typically increase in the spring from snowmelt runoff and from the mixing of accumulated nutrients from the bottom during spring turnover.
Spring turnover can be explained as follows: In higher-elevation lakes, before the ice cover melts, the water near the bottom will be around 4°C; just under the ice, water temperatures approach 0°C. As the weather gets warmer, the ice melts, and the surface water heats up and decreases in density. When the surface water and the bottom water reach the same density, just a little wind will mix the lake completely.
As summer approaches, surface water continues to absorb heat and becomes lighter than the water below. Eventually, the upper water is too warm and buoyant to mix completely with the denser, deeper water. When this happens, any additional input of nutrients into the upper water may trigger an algae bloom. These nutrients can come from upstream tributaries after rainstorms, die-offs of aquatic plants, urban stormwater runoff, lawn fertilizer runoff, and nearby faulty septic systems. Nutrients can also be deposited by high winds. Nitrogen and phosphorus may come from fine soil particles and agricultural fertilizer.
Water quality suffers greatly during eutrophication. Although the added nutrients feed the "good" algae (those consumed by wildlife), it also feeds the noxious algae, such as scums and blue-greens—those algae that look and smell bad. The blue-green algae aren't eaten by some zooplankton (some blue-green species can be toxic), which reduces food chain efficiency—eventually, all the way up. If enough algae cover the water surface, the lake loses clarity and the growth smothers eggs and beneficial insects. Overgrowth also affects dissolved oxygen levels, causing loss of habitat for fish and the organisms on which they feed. Toxic gases such as ammonia may develop in bottom water, causing more fish habitat loss.
Higher plants that exist near or on the shores can also be affected. Overfertilization of these plants can cause them to grow excessively, leading to a loss of open water. Near-shore plants might be smothered out as the hyper-fed algae block young plants from the light.
When algae become a problem, humans living nearby often resort to chemical measures to fight it. However, some of those treatments can pollute, causing drinking-water degradation, and carcinogens such as chloroform can develop from the increased organic matter reacting with disinfectants such as chlorine. Eutrophication soon appears to become a "no-win situation": Do nothing, and the lake becomes a swamp; try to treat the problem with chemicals and run the risk of creating a vast toxic soup.
How Much Is Too Much?
The best solution, of course, is to avoid the problem in the first place. However, the increased use of fertilizers, whether agricultural or residential, makes this a daunting task. In addition, how much nitrogen and phosphorus is too much?
"People are doing nothing. We do not have regulatory approaches for managing nutrients," says G. Fred Lee of El Macero, CA's G. Fred Lee & Associates, a consulting firm concerned with surface-water and groundwater quality. "Ten years ago, EPA started to develop criteria for chemically based nitrogen and phosphorus in water, with levels measured in parts per million. In its original proposals on it, EPA wanted all states to have this numeric criteria finalized by 2004. EPA has backed off 2004 as a deadline but has told the states, 'We want you to get on it.' After establishing Regional Technical Assistance Groups [RTAGs] about a year ago, EPA drastically cut the funds for this work. It told a supplier to finish a project and then no more work was done."
What impact would standards have on stormwater management? "Stormwater people are not worried about it quite yet, because there are no standards," Lee continues. "The costs would be horrendous, though—just to put in grassy swales and retention ponds to keep runoff from natural bodies of water—at least a dollar per person in one's jurisdiction per day, and upwards to $10 per day, because you'd have to buy land. However, until we have an approach for managing stormwater runoff that's economically feasible, what was proposed by the EPA on nutrient criteria just won't do it.
"Agriculture is understandably upset, as water quality will force them to do something about their fertilizers," he notes. "But you get about 10 times as much fertilizer runoff from urban areas as you do from agricultural areas. It's all paved, and water doesn't percolate into the ground. When you pave only 10% of available land, you change the water source. Residential fertilizing is a primary cause of nutrient overload when you're dealing with an urban lake or stream. When the nutrients get to other water bodies, you have urban and agricultural sources."
Lee believes phosphorus needs the most scrutiny. "In almost all the US, there's enough nitrogen for the algae's needs. Seventy to eighty percent of them are phosphorus limited. Typically, you want to focus in on available phosphorus, in a form that can be converted or used by algae. The phosphorus that's important is dissolved, but most is not dissolved. Phosphorus comes into the water with soil particles, and it remains particulate, with only about 20% of it available for algae."
Thirty years ago, environmentalists urged manufacturers to remove phosphates from laundry detergents; has that helped the problem? "During that time, phosphorus pollution went down to about 6% from about 12%. The detergents really didn't have an impact," says Lee. "It was—and is—the fertilizer."
In late May, the EPA's Region 9 RTAG, California's State Water Resources Control Board Technical Advisory Group and Nutrient TMDL (total maximum daily load) Work Group, and Tetra Tech Inc. held a telephone conference to provide an update of activities and findings related to the development of nutrient criteria and numeric endpoints for nutrient TMDLs. (Reports and other data for this conference are posted for download at http://rd.tetratech.com/epa.)
Lee participated in the phone conference. "We reviewed work done by Tetra Tech, an EPA contractor, which over the past year has reviewed a lot of data and has been developing nutrient content for California. Tetra Tech came to conclusions for nutrient data: Site-specific nutrient criteria must be developed. You can't do it generically over the whole state. We're moving in that direction in California, but standards are still a long way away because we don't have a database on what impact nutrients have on our water—and we don't know the amount of nutrients in our water." He notes that no funding currently exists for monitoring to obtain these data. "How does that leave us? The EPA's current position: If a state is making satisfactory progress toward water standards by 2007—initially the date was 2004—EPA will not force criteria on the state. California's Region 9 RTAG is indicative of satisfactory progress. We're ahead of the rest of the country, making sure the Clean Water Act is finally being enforced."
Where does that leave Region 9—and the rest of the country? "Across the US, RTAG efforts are continuing. Most likely, 'site specific' is the process that will be followed, and each site will need detailed studies, as we need to understand nutrient load and its impact. Many bodies of water are rated for drinking use, even if they might not be used for that. How clean would we like the water? We want almost distilled water, but that kind of water won't support fish. A good example of this issue: Lake Erie was dying—actually there was too much life in it—now fishermen complain there's not enough fish in the lake because there's nothing in there for them to eat. Obviously, we need to strike a balance."
Nitrogen Causes Oxygen Loss
Nancy N. Rabalais, a professor at the Louisiana Universities Marine Consortium, has been studying the problem, which she refers to as hypoxia, in the Gulf of Mexico.
"In freshwater, usually phosphorus is the problem; in marine water, usually nitrogen is the problem, but it's not exclusively one or the other," she says. "Of course, we see both of them where the Mississippi River meets the Gulf. The more rain in the watershed, the more nitrogen gets to the Gulf, where we primarily have a nitrogen problem, which causes hypoxia—low oxygen—in the water. At its worst, hypoxia causes a 'dead zone.' Fish and shrimp that can swim get out of the area. As for things that can't swim, if the oxygen level is low enough, they die. There's been a long-term loss of biodiversity in the Gulf. One result we've noticed is that shrimp are moving from their preferred habitat.
"A whole suite of algal blooms result when there's too much nitrogen or phosphorus in runoff," Rabalais says. "This spring we had a massive algal bloom—we had slicks of algae grow. Algae is the basis of the food web, but there's too much for nature to use it up. Some, such as dinoflagellates, are toxic. What species you get depends on the ratio of nutrients. Silica in the water also makes diatoms grow; that carbon is mainly what contributes to decomposition and de-oxygenation."
Algal growth affects the water's beneficial uses. "Freshwater systems can become quite 'gummy looking,' and certain types of toxic algae can necessitate warnings—'Don't swim or fish in this area,' and so on," she explains. "Toxic algae can cause health problems in babies and kids, as well as problems for the catfish industry, because catfish feed on algae. Even if the algae isn't toxic, if there's too much of it, and it dies in the reservoir, that die-off can cause low oxygen in the water."
Suspended sediments can compound the problem as well. Most of the water flowing to the study area comes from the Ohio River, and most of the sediment comes from the Missouri River via the Mississippi River. "A lot of that sediment is in reservoirs right now, yet the Mississippi Delta is losing land," says Rabalais.
The influx of nutrients to the Gulf appears to be seasonal, as fertilizer applications take place in the fall and again in the spring. "When the snow melts, a lot of that fertilizer gets scooped off the land and washes into the river and eventually the Gulf. Nitrogen concentrations in the river are higher in spring. Agricultural fertilization does contribute nutrients to the Mississippi watershed, but some also comes out of the atmosphere. Residential runoff is not counted, as it's minimal, but in a local watershed residential runoff would be important. The fact remains: if every state along our riverways took care to reduce nutrient-rich runoff, we wouldn't have the problem."
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In the best-case scenario, with nutrients in runoff reduced, how long would it take the ecosystem to recover? "Who knows?" says Rabalais. "I can only give as an example a similar situation off the Danube River, in the Black Sea, where over time, a huge area was polluted by phosphorus and nitrogen. When the USSR dissolved, and there were no more agricultural subsidies, fertilizer use went down, which took the load off this waterway. Slowly, levels went from about 40,000 parts per square kilometer to about 1,000 per square kilometer—but that took about a decade to achieve."
What can be done in the meantime? "Strengthen the Clean Water and Clean Air Acts," Rabalais concludes. "It would be nice if we could re-oxygenate water, like one does for a tropical-fish tank, but that would be too costly. There's too much to do."
Author's Bio: Janis Keating is a frequent contributor to Forester Media Inc. publications.
January-February 2005
Good Water Gone Bad
Eutrophication results when the fertilizers that nourish soil-based plants also feed water-based ones.
Ironically, since the word itself means "well-nourished," many stormwater managers and government agencies are worried about eutrophic bodies of water. What could be so bad about a well-nourished lake? Nothing—if the lake's purpose is to provide habitat for plants and animals of all sorts. Everything—if the lake is to be used by humans as a drinking-water source or as a recreational area.Lakes and other bodies of water are usually classified by their trophic ("nutrition," "growth") state. Oligotrophic bodies of water contain low nutrient concentrations and plant growth; eutrophic lakes have high nutrients and plant growth; mesotrophic lakes contain percentages of nutrient concentrations and plant growth that fall somewhere in between the other two categories. To provide examples of the three trophic types:
- Oregon's Crater Lake is a clear, sky-blue ultra-oligotrophic lake.
- The blue water section of Lake Superior is ultra-oligotrophic—it's the most oligotrophic of the Great Lakes.
- Lake Michigan and Lake Huron are classified as meso-oligotrophic.
- Lake Ontario is mesotrophic.
- Lake Erie is still considered eutrophic, although, ironically enough, the problematic, invasive zebra mussels have been improving its clarity.
A number of attributes contribute to a lake's trophic status; however, three main factors regulate a lake's trophic state:
- The rate of nutrient supply. This is affected by the bedrock geology of the watershed, the surrounding soils and vegetation, and local human land uses and land management.
- Climate. This includes the amount of sunlight that hits the lake, the ambient and water temperature, and the particular hydrology (precipitation plus lake basin turnover time) the lake experiences.
- The shape of the lake's basin. This includes not only depth, volume, and surface area, but also the watershed-to-lake surface area ratio.
It's interesting to note that, of all these factors, only one is directly related to human activity. However, in many cases, it's human activity—or inactivity—that will tip the scales in a body of water's delicate ecological balance.
Every Spring, Stir Well
A certain amount of nutrients naturally exists in bodies of water; algae, phytoplankton, and zooplankton use and create nutrients during different parts of their life cycles. For example, when dead plankton sink to lower depths and decompose, nutrients are redistributed from the upper water where the plankton had been living. Essential nutrients (bioavailable forms of phosphorus and nitrogen) typically increase in the spring from snowmelt runoff and from the mixing of accumulated nutrients from the bottom during spring turnover.
Spring turnover can be explained as follows: In higher-elevation lakes, before the ice cover melts, the water near the bottom will be around 4°C; just under the ice, water temperatures approach 0°C. As the weather gets warmer, the ice melts, and the surface water heats up and decreases in density. When the surface water and the bottom water reach the same density, just a little wind will mix the lake completely.
As summer approaches, surface water continues to absorb heat and becomes lighter than the water below. Eventually, the upper water is too warm and buoyant to mix completely with the denser, deeper water. When this happens, any additional input of nutrients into the upper water may trigger an algae bloom. These nutrients can come from upstream tributaries after rainstorms, die-offs of aquatic plants, urban stormwater runoff, lawn fertilizer runoff, and nearby faulty septic systems. Nutrients can also be deposited by high winds. Nitrogen and phosphorus may come from fine soil particles and agricultural fertilizer.
Water quality suffers greatly during eutrophication. Although the added nutrients feed the "good" algae (those consumed by wildlife), it also feeds the noxious algae, such as scums and blue-greens—those algae that look and smell bad. The blue-green algae aren't eaten by some zooplankton (some blue-green species can be toxic), which reduces food chain efficiency—eventually, all the way up. If enough algae cover the water surface, the lake loses clarity and the growth smothers eggs and beneficial insects. Overgrowth also affects dissolved oxygen levels, causing loss of habitat for fish and the organisms on which they feed. Toxic gases such as ammonia may develop in bottom water, causing more fish habitat loss.
Higher plants that exist near or on the shores can also be affected. Overfertilization of these plants can cause them to grow excessively, leading to a loss of open water. Near-shore plants might be smothered out as the hyper-fed algae block young plants from the light.
When algae become a problem, humans living nearby often resort to chemical measures to fight it. However, some of those treatments can pollute, causing drinking-water degradation, and carcinogens such as chloroform can develop from the increased organic matter reacting with disinfectants such as chlorine. Eutrophication soon appears to become a "no-win situation": Do nothing, and the lake becomes a swamp; try to treat the problem with chemicals and run the risk of creating a vast toxic soup.
How Much Is Too Much?
The best solution, of course, is to avoid the problem in the first place. However, the increased use of fertilizers, whether agricultural or residential, makes this a daunting task. In addition, how much nitrogen and phosphorus is too much?
"People are doing nothing. We do not have regulatory approaches for managing nutrients," says G. Fred Lee of El Macero, CA's G. Fred Lee & Associates, a consulting firm concerned with surface-water and groundwater quality. "Ten years ago, EPA started to develop criteria for chemically based nitrogen and phosphorus in water, with levels measured in parts per million. In its original proposals on it, EPA wanted all states to have this numeric criteria finalized by 2004. EPA has backed off 2004 as a deadline but has told the states, 'We want you to get on it.' After establishing Regional Technical Assistance Groups [RTAGs] about a year ago, EPA drastically cut the funds for this work. It told a supplier to finish a project and then no more work was done."
What impact would standards have on stormwater management? "Stormwater people are not worried about it quite yet, because there are no standards," Lee continues. "The costs would be horrendous, though—just to put in grassy swales and retention ponds to keep runoff from natural bodies of water—at least a dollar per person in one's jurisdiction per day, and upwards to $10 per day, because you'd have to buy land. However, until we have an approach for managing stormwater runoff that's economically feasible, what was proposed by the EPA on nutrient criteria just won't do it.
"Agriculture is understandably upset, as water quality will force them to do something about their fertilizers," he notes. "But you get about 10 times as much fertilizer runoff from urban areas as you do from agricultural areas. It's all paved, and water doesn't percolate into the ground. When you pave only 10% of available land, you change the water source. Residential fertilizing is a primary cause of nutrient overload when you're dealing with an urban lake or stream. When the nutrients get to other water bodies, you have urban and agricultural sources."
Lee believes phosphorus needs the most scrutiny. "In almost all the US, there's enough nitrogen for the algae's needs. Seventy to eighty percent of them are phosphorus limited. Typically, you want to focus in on available phosphorus, in a form that can be converted or used by algae. The phosphorus that's important is dissolved, but most is not dissolved. Phosphorus comes into the water with soil particles, and it remains particulate, with only about 20% of it available for algae."
Thirty years ago, environmentalists urged manufacturers to remove phosphates from laundry detergents; has that helped the problem? "During that time, phosphorus pollution went down to about 6% from about 12%. The detergents really didn't have an impact," says Lee. "It was—and is—the fertilizer."
In late May, the EPA's Region 9 RTAG, California's State Water Resources Control Board Technical Advisory Group and Nutrient TMDL (total maximum daily load) Work Group, and Tetra Tech Inc. held a telephone conference to provide an update of activities and findings related to the development of nutrient criteria and numeric endpoints for nutrient TMDLs. (Reports and other data for this conference are posted for download at http://rd.tetratech.com/epa.)
Lee participated in the phone conference. "We reviewed work done by Tetra Tech, an EPA contractor, which over the past year has reviewed a lot of data and has been developing nutrient content for California. Tetra Tech came to conclusions for nutrient data: Site-specific nutrient criteria must be developed. You can't do it generically over the whole state. We're moving in that direction in California, but standards are still a long way away because we don't have a database on what impact nutrients have on our water—and we don't know the amount of nutrients in our water." He notes that no funding currently exists for monitoring to obtain these data. "How does that leave us? The EPA's current position: If a state is making satisfactory progress toward water standards by 2007—initially the date was 2004—EPA will not force criteria on the state. California's Region 9 RTAG is indicative of satisfactory progress. We're ahead of the rest of the country, making sure the Clean Water Act is finally being enforced."
Where does that leave Region 9—and the rest of the country? "Across the US, RTAG efforts are continuing. Most likely, 'site specific' is the process that will be followed, and each site will need detailed studies, as we need to understand nutrient load and its impact. Many bodies of water are rated for drinking use, even if they might not be used for that. How clean would we like the water? We want almost distilled water, but that kind of water won't support fish. A good example of this issue: Lake Erie was dying—actually there was too much life in it—now fishermen complain there's not enough fish in the lake because there's nothing in there for them to eat. Obviously, we need to strike a balance."
Nitrogen Causes Oxygen Loss
Nancy N. Rabalais, a professor at the Louisiana Universities Marine Consortium, has been studying the problem, which she refers to as hypoxia, in the Gulf of Mexico.
"In freshwater, usually phosphorus is the problem; in marine water, usually nitrogen is the problem, but it's not exclusively one or the other," she says. "Of course, we see both of them where the Mississippi River meets the Gulf. The more rain in the watershed, the more nitrogen gets to the Gulf, where we primarily have a nitrogen problem, which causes hypoxia—low oxygen—in the water. At its worst, hypoxia causes a 'dead zone.' Fish and shrimp that can swim get out of the area. As for things that can't swim, if the oxygen level is low enough, they die. There's been a long-term loss of biodiversity in the Gulf. One result we've noticed is that shrimp are moving from their preferred habitat.
"A whole suite of algal blooms result when there's too much nitrogen or phosphorus in runoff," Rabalais says. "This spring we had a massive algal bloom—we had slicks of algae grow. Algae is the basis of the food web, but there's too much for nature to use it up. Some, such as dinoflagellates, are toxic. What species you get depends on the ratio of nutrients. Silica in the water also makes diatoms grow; that carbon is mainly what contributes to decomposition and de-oxygenation."
Algal growth affects the water's beneficial uses. "Freshwater systems can become quite 'gummy looking,' and certain types of toxic algae can necessitate warnings—'Don't swim or fish in this area,' and so on," she explains. "Toxic algae can cause health problems in babies and kids, as well as problems for the catfish industry, because catfish feed on algae. Even if the algae isn't toxic, if there's too much of it, and it dies in the reservoir, that die-off can cause low oxygen in the water."
Suspended sediments can compound the problem as well. Most of the water flowing to the study area comes from the Ohio River, and most of the sediment comes from the Missouri River via the Mississippi River. "A lot of that sediment is in reservoirs right now, yet the Mississippi Delta is losing land," says Rabalais.
The influx of nutrients to the Gulf appears to be seasonal, as fertilizer applications take place in the fall and again in the spring. "When the snow melts, a lot of that fertilizer gets scooped off the land and washes into the river and eventually the Gulf. Nitrogen concentrations in the river are higher in spring. Agricultural fertilization does contribute nutrients to the Mississippi watershed, but some also comes out of the atmosphere. Residential runoff is not counted, as it's minimal, but in a local watershed residential runoff would be important. The fact remains: if every state along our riverways took care to reduce nutrient-rich runoff, we wouldn't have the problem."
In the best-case scenario, with nutrients in runoff reduced, how long would it take the ecosystem to recover? "Who knows?" says Rabalais. "I can only give as an example a similar situation off the Danube River, in the Black Sea, where over time, a huge area was polluted by phosphorus and nitrogen. When the USSR dissolved, and there were no more agricultural subsidies, fertilizer use went down, which took the load off this waterway. Slowly, levels went from about 40,000 parts per square kilometer to about 1,000 per square kilometer—but that took about a decade to achieve."
What can be done in the meantime? "Strengthen the Clean Water and Clean Air Acts," Rabalais concludes. "It would be nice if we could re-oxygenate water, like one does for a tropical-fish tank, but that would be too costly. There's too much to do."