Clean Water, Clean Lakes -The Science of Urban Watersheds
By: Daniel Weber, Ph.D. University of Wisconsin-Milwaukee
What is a watershed?
A watershed is a drainage area that collects and then drains all surface water from one water source to another. We all know the famous saying, "All roads lead to Rome." In many respects, that is an effective way to think of watersheds, in that everything in the watershed area (streams, pollution, litter, and household water) drains into a larger body of water: a pond, lake, larger river, or the ocean. Some small stream watersheds drain less than 100 square kilometers, while the Mississippi River watershed drains 2/3 of the continental United States. [While watersheds only include surface water, the water below the surface, called groundwater, also affects water quality. More on groundwater below.]
Human survival depends on the creation of efficient and sustainable systems of water use. Yet, human populations seem to take our dependence on water for granted and we usually do not realize that everyone, even desert populations, lives in a watershed. To exist, every civilization needs to design mechanisms such as wells, aqueducts, or irrigation systems to maintain self-sufficiency in water quantity. Yet, repeated failures to maintain water quality have lead to the downfall of many of these societies.
Today's societies, particularly in urban areas, are facing an increasing level of human pressure. This pressure is based upon expanding populations using greater amounts of water that has resulted in continued degradation of water quality. In order to educate the lay public on the effects water usage has on the watershed, Wisconsin's Milwaukee River Watershed planned the "Clean Rivers, Clean Lakes: Watershed Planning Conference," which was recently held in Milwaukee. This year, nearly 300 people including scientists, government regulators, members of the business community, and other interested parties met to examine the history, science, and policy development for the Milwaukee River Watershed. Since these watershed pressures are similar to other areas in the United States and worldwide, we can all gain valuable watershed management insights in order to preserve the watersheds upon which each of us depends.
Case Study: Watershed Mismanagement
Water has shaped the history and culture of many coastal towns-including Milwaukee. Early Native American tribes utilized the rice marshes and abundant fisheries at the confluence of Lake Michigan and the area's three major rivers. The completion of the Erie Canal led to increased migration of European settlers into the region, which increased commerce and population. Shipbuilding, wheat exports, and fishing dominated the local economy in the late 1800s. Rivers were dammed to create mills for processing lumber and flour. These dams prevented migratory fish from reaching their breeding streams.
During the 1890s, the thriving and fertile river valleys were filled for industrial development. The combined effects of destroying marshes, losing green space, and using horses for transportation (resulting in large amounts of manure that washed into the streams) created rivers that were biologically dead by the turn of the century.
Finally, in 1925, Milwaukee began to treat its sewage. Additionally, the last major dam along the Milwaukee River was finally removed throughout the last decade. Today the lower stretches of the Milwaukee River Watershed are becoming ideal fishing and living sites.
Despite the improvement, watershed health issues still remain. Increased population pressure caused by diffuse subdivision construction creates excessive demands on water resources. This is the major underlying cause for changes in watershed species composition, which includes the loss of native species key to ecosystem stability, invasive species, and water quality (surface and groundwater).
Species Composition Changes
To demonstrate the effect of human abuse of our water sources, the story of a small, shrimp-like invertebrate called Diporeia is instructive. Although Diporeia is small, in an aquatic food chain, small size does not imply small importance. In Lake Michigan, the Diporeia is at the bottom of the food chain. Yet, it directly or indirectly supports 70% of the lake's life. In 1980, this invertebrate was found throughout the lake, especially where the fish spawn in the inshore regions. Today, it is found only in isolated pockets on the western shores of Lake Michigan.
Scientists fear that Diporeia may become extinct possibly due to competition from those non-native species that use a similar niche space. Today, the lake contains more than 170 invasive species that have entered the basin through purposeful or accidental introductions. While some native fish are finding alternative food sources, they are not nutritionally equivalent. For example, zebra mussels, the species being eaten by whitefish, have little nutritional value. As a result, the whitefish in the Lake are displaying signs of malnutrition.
In addition, Lake Trout and Yellow Perch have shown dramatic population declines; the former declined due to the invasion of the non-native sea lamprey and the latter for reasons still unclear. A possible explanation for the decline of native fisheries is the loss of inshore and nearshore breeding sites. These key breeding areas have been destroyed to build homes, industrial sites, and marinas. To date, Lake Michigan alone has lost nearly 2/3 of its original coastal wetlands (21.9 million acres).
Watershed Changes Effect Water Quality
Changes in water quality are due to inputs from the atmosphere, land, and connected waterways. Water quality is dependent upon the interaction of human activities with each of part of the hydrologic, or water, cycle. The hydrologic cycle uses the sun and gravity to move water between aquatic, atmospheric, and terrestrial components. Solar energy is responsible for evaporation and the atmospheric currents that drive our weather and climate patterns. Precipitation results in water movement over land by runoff, underground by infiltration, or into plants and animals where it is used for biological processes or is evaporated from the organism's surface. (See Kohellet 1:7 for a Biblical description of this process.) Human inputs that can affect the water cycle include: contaminated precipitation (acid rain), human activity on flood plains, erosion from construction sites, covering the soil with impermeable materials, stream alterations, and municipal sewer systems.
Acid rain becomes acidic as a result of the nitrous oxides and sulfur produced by automobiles and coal-powered electricity generating plants. As lakes become more acidic, the solubility of toxic metals that may exist in the aquatic sediments, such as aluminum, lead, and mercury, increases. Once these metal contaminants enter the aquatic cycle, they induce toxic responses in aquatic plants and animals. These responses include changes in: reproductive success, lower growth rates, suppression of the immune response, and damage fish gills and the exoskeletons of aquatic invertebrates-the base of the food chain.
As mentioned above, construction site erosion increases the sedimentation of lakes and streams, which destroys habitats and causes death in aquatic species. Increasing impervious surfaces in a watershed, i.e., parking lots, rooftops, or roads, decrease the soil's ability to filter water. Since less water infiltrates the soil, more water runs off into lakes and streams, which creates a hydrologic and chemical nightmare. For example: the increased incidence of flash flooding in urbanized streams scours the streambed and deprives fish and invertebrates of useful niche space. The channelized streams of many urban regions, including Milwaukee, only intensify these problems and create open sewers where a functional stream once flowed.
Surface water quality is also affected by the region's sewer system. Sanitary sewers collect the residential and industrial wastewater and direct it to sewage treatment facilities. In many municipalities, sanitary sewers are combined with pipes that also collect stormwater runoff from streets, parking lots, etc.; these are called combined sewers. Heavy rainfalls can overwhelm the capacity of these systems and they discharge their contents directly to the region's waterways as raw, untreated, sewage. Although the causes of sewer overflows vary between municipalities, common sources of sewer problems are: pipe blockages from tree roots, groundwater infiltration through deteriorated pipes, pipes that have become misarranged, power failures that interrupt service to homes and businesses, and small sewer systems for regions with a high volume of stormwater runoff. Once raw sewage is dumped into the waterways, the streams and lakes become contaminated with bacteria associated with viruses, protozoa, roundworms, and a variety of allergens.
The Story Under The Surface
The damage caused by urban and urbanizing regions to the groundwater could be a more fundamental problem. Sometimes called the underground river system, groundwater is water that has percolated through the earth's surface layers into the spaces within permeable rocks. Infiltration moves water through the pores and cracks in the underlying rock creating aquifers. Hydrogeologists use the term "groundwatershed" to denote the region in which this subsurface water flows toward a body of surface water. Watersheds and groundwatersheds do not always exist with similar spatial boundaries. Whereas the watershed relies on surface topology, the groundwatershed relies upon underlying rock formations. Today, this disconnect results in significant water usage conflicts between competing municipalities and regional authorities.
In the case of the Milwaukee River Watershed, the subcontinental divide is the dividing line between surface water flowing east to the Great Lakes or west to the Mississippi River. Federal law and international treaties prevent water diversions from the Great Lakes Basin, although exceptions do exist. Regions west of this divide and the arid southwestern United States, eye the seemingly limitless water capacity of the Great Lakes to fuel their own population and economic growth. Already, the expanding suburban communities of Milwaukee are overusing the groundwater supply and drawing down the water table. This causes stream levels to drop and groundwater to be redirected away from Lake Michigan to fill in the new areas. If water levels in Lake Michigan drop further (lake levels are already low due to 6 years of little snow pack), ecological and economic harm will depress a region whose vitality is dependent upon water. Furthermore, Chicago's suburbs have increased pumping from the Great Lakes Basin. Due to the increasing demand outside of the Great Lakes Basin, groundwater flow of communities in southern Milwaukee now moves toward Chicago and the Mississippi River watershed, which continues to deplete our limited water supplies.
Independently, the surface water issues mentioned above are very problematic, but when combined with groundwater pollution, the damage to this critical source of water will spell disaster for the region's population. It is now documented that heavy metals, chlorides (from road salt), organic chemicals (e.g., pesticides), and petroleum-based chemicals are being found in the groundwater. Since it takes decades to millennia to recharge groundwater, contaminated sources have little chance for a speedy recovery.
Why is science-based action important in cooperative decision-making processes? Environmental problems respect neither political boundaries nor solutions from individual organizations. Thus, identifying appropriate solutions to improve watershed quality requires cooperation between scientists, policy makers, and the general public. Recently, a comprehensive watershed approach to problem solving has been developed to merge the various stakeholders of watershed quality. Central to this method is an understanding of the sources and effects of system stressors within a watershed, the role science plays in identifying appropriate action, and the efficacy of individual action.
How do we create a cooperative, science-based approach to environmental protection? The "watershed approach" to problem solving focuses on the resource itself, rather than the agenda of any interested organization. For example, historically the mission of the Army Corps of Engineers was to facilitate commerce on our nation's waterways. However, such a viewpoint did not consider how those changes alter the resource quality. Now, "single factor" missions are generally accepted to have limited long-term value. Thus, Congress expanded the Corps' mission to include the revitalization and restoration of America's wetlands.
The "watershed approach" involves seven steps to achieve ecological sustainability and economic stability:
- Set measurable goals. What parameters are critical in identifying positive changes in water quality? How are these changes quantitatively measured? How can we know that we are making progress toward achieving success?
- Define success as achieving goals via a rational set of specific objectives. For example: reducing the amount of PCBs in the river sediment by 80%. Stating the objective of "improving the environment" is not sufficient.
- Remember that cleanup is good, but prevention is better. Clean up costs are sometimes overwhelming, especially for municipalities or corporations. We need mechanisms that will avoid the mistakes that lead to environmental problems.
- Identify all relevant stressors, not just the convenient immediate political or economical factors. For example, current research is beginning to demonstrate that our medications end up in the water either due to disposal through our toilets or by excretion from our bodies. These drugs have now been shown to have potentially devastating effects on the normal nervous system development in embryos of aquatic species. This is a stressor that is just beginning to be considered. (To date, these are unregulated because no acceptable limits have been identified.)
- Address the source of these stressors, identify mechanisms to reduce these stresses, and quantify their reduction.
- Use any and all (legal and ethical) tools to achieve results. Utilize the standard mechanisms of regulatory or tax policy, land purchases, or more creative techniques like cost sharing, involving local business leaders, and community education, while remembering to keep focused on the goal.
- Involve everyone. Build partnerships between all the "stakeholders" in the watershed. Include these partners, whether they are government officials, business leaders, academia, service groups, civil activists, landowners, etc., in the decision-making process. The watershed approach implies that those who are upstream and downstream of the problem site should be involved. Broadening the base of support for action inevitably increases the chances of achieving the goals set down in step #1.
What can individuals do?
The simplest thing that individuals can do to protect valuable water resources is to reduce their own water use from the faucet and from appliances such as washing machines and dishwashers. In the United States and many other "water-rich" nations, we usually think of water as being a limitless resource. In fact, the vast majority of locations in the United States are using groundwater sources that are easily depleted and not quickly replaced. Such overuse of our groundwater resources can eventually deplete the rivers, streams, and lakes that depend on groundwater for recharging these surface waters. Even in places that rely on fresh surface water, such as the Great Lakes, pollution is taking its toll on water quality and availability.
Individuals can protect their natural water sources in other ways. In the United States, 40% of contaminated rivers and lakes are damaged by "non-point source" pollution (pollution from ambiguous sources, e.g., urban or farmland runoff, or atmospheric deposition). Urban stormwater runoff from impervious surfaces such as rooftops and city streams is often contaminated with chemicals (such as petroleum, heavy metals, and pesticides). By reducing the quantity of water flowing on these surfaces we can create profound effects on water quality.
How can you reduce the amount of water flowing in your area? In some municipalities, downspouts drain into the sewer system, which, usually empties directly into the local streams. Individuals have three methods to intervene. Rain barrels are the easiest and least expensive method. By connecting to the downspout, these barrels capture the runoff from the rooftop before they enter the municipal sewer system. Water is stored until a spigot and hose opens, which allows the water to be released slowly back into the soil. This method is most effective when a rain garden, the second method, is also employed. A rain garden utilizes a combination of stone-lined holding pools and native species (especially those with deep roots, rather than the short-rooted lawns of most urban and suburban areas) that allows water to be reintroduced slowly back into the ground. Moving the water through the soil also minimizes the effects of stormwater runoff, since if it does not drain into the soil, the potentially contaminated water eventually drains into nearby sewers and streams. The Environmental Protection Agency web site has information about each of these two methods (http://www.epa.gov/greeningepa/water/stormwater_techniques.htm).
The third method is more expensive but has profound effects on the amount of stormwater entering urban streams. Green roofs prevent rooftop runoff. Additionally, it decreases the amount of heat radiated from rooftops. This heat creates the "urban heat island" effect. Urban regions tend to be significantly warmer than their surrounding rural areas. Green roofs on both residential and commercial buildings have the potential to play an important role in decreasing this source of global warming. A more detailed description of the benefits of green roofs can be found at the web site of the International Green Roof Association (http://www.greenroof.se). This method is most economically viable when designed into new constructions (e.g., apartment buildings and condominiums) rather than retrofitted.
How You Can Encourage Your Local Government to Take Action! Local governments can do much to promote sound, scientific-based watershed planning. Since any region with more than 12% impervious surfaces results in water quality degradation, low impact development should be encouraged through creative zoning regulations. Although an increasing number of housing contractors voluntarily utilize this concept to balance the natural resources and the number of homes built within a subdivision, we need to advocate for the requirement of such projects. Relevant websites include: http://www.lowimpactdevelopment.org andhttp://www.epa.gov/owow/nps/lid/lidnatl.pdf (this .pdf address may need to be cut and pasted into your web browser). Science-based planning of new subdivisions takes into account ecosystem function and a creative land ethic that is based upon 12 concepts:
- Smaller lot sizes with clustered development. To achieve this goal, more of the subdivision is reserved as open space and is integrated with individual lots.
- Attention to stormwater quality. Prepare maps of all potential sources of stormwater runoff.
- Decreases in the amount of water running off impervious surfaces. For example, subdivision developers may build narrow roads with little or no shoulder through existing forests to minimize the amount of rain falling on impervious surfaces.
- Restoration of degraded areas. Returning drained wetlands to their former status and replanting areas with native species can successfully reclaim natural resources even with human presence.
- Use of native species, especially mesic prairie species with deep root systems. Non-native species do not enhance native fauna and often become invasive species (next issue's science article).
- Integration of both passive and open spaces. By combining detention ponds and wetland preservation, the harmful effects of subdivision runoff are minimized.
- Minimize the amount of soil disturbance during construction. Reducing erosion during construction ensures a basis for successful natural landscaping.
- Use of trails to highlight natural areas in subdivision. Facilitating the use of the nature spaces in the subdivision not only enhances a sense of ownership of the entire integrated subdivision, but also encourages similar developments.
- Providing ecology education materials for residents.
- Creation of energy efficient homes.
- Rational transportation systems. This is critical since many new subdivisions are in rural areas far from sources of employment and/or shopping.
- Use of open space to enhance sewage/rainwater treatment.
As we learn more about watershed function and processes, we can develop sound management practices to the benefit of both humans and the natural world around us. Science-based approaches to managing our environment are not only possible and necessary, but also less expensive in the long run.
Originally posted in "On Eagles' Wings" March 9th and May 3rd 2004
This content originated at http://canfeinesharim.org.