What is Impairing Our Streams?
Stream Condition - How is it Assessed? The primary objective of the Clean Water Act (CWA) is to "restore and maintain the chemical physical and biological integrity of the Nation's waters". In the State of Ohio, streams are assigned "Aquatic Life Use" classifications based on a streams potential to support a health biological community. Attainment of a stream's Aquatic Life Use is based, in part, on biological criteria - scores on indices of biological condition for fishes and macroinvertebrate (bug) communities. In-stream biological communities are dependent primarily upon three factors: Water Chemistry, Physical Habitat, and Hydrologic Regime (Flow Pattern). Degradation of any one of these factors can result in impairment of the biological community. In addition to biotic community indices (fishes and macroinvertebrates), the State of Ohio has also developed indices of physical habitat quality. When this biological and physical habitat information is assessed in light of water chemistry and proxies for hydrologic alteration (percent impervious surface in the watershed), we can tease-out the sources of impairment to the biological community. Sources of Stream Degradation in Hamilton County Our local stream systems have been degraded by a range of human induced alterations of the landscape. Since the creation of the Clean Water Act in 1972, much has been done to improve stream condition through the elimination/reduction of industrial pollution. Water quality has improved drastically and biological integrity has also responded; however, for the last few decades, as we have pivoted to reducing "non-point sources" of pollution (stormwater pollution), improvements in biological integrity has slowed. We have learned that, in order to continue to progress toward our goal of attaining "Aquatic Life Use", we must address foundational limits to biological integrity: alteration of flow patterns and habitat. The primary impacts to local stream ecosystems in Hamilton County can be categorized as 1. Hydrologic Alteration 2. Habitat Impairment, and 3. Water Pollution. 1. Hydrologic Alterations - "Flashy Flows" are eroding your property value and in-stream habitat. Many Hamilton County residents have complained that small streams flowing through their backyards have begun to exhibit "dangerous" and "destructive" flows in response to moderate rain events. These "flashy" flows threaten both public and private infrastructure, destabilize stream channels, destroy in-stream habitat, and flush-out fishes and other aquatic organisms at a frequency higher than that from which they can recover. As the landscape is developed, forests are cleared and the ground surface is covered by impervious surfaces (e.g. roads, parking lots, buildings, driveways, sidewalks, etc.). Two consequences of this include 1) the inability of rain water to infiltrate into the soil resulting an increase amount of over-land flow (stormwater runoff) , and 2) stormwater runs-off of impervious surfaces much faster than it would flow over a vegetated landscape. As a result local stream flows become "flashy" - the figure below shows two different "hydrographs" (plots of stream flow over time in response to a rain event) for an urban watershed vs. a forested watershed. |
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Infiltration is also reduced in areas were forest has been replaced by lawns. Prior to development, Hamilton County's soils were covered by deep rooted native vegetation that constantly supplied organic material that was worked into the subsoil by a diverse assemblage of soil dwelling wildlife. Since that time, native vegetation has been replace by shallow rooted turf plants, organic material has been exported to the landfill (via bagging of grass clippings and raked leaves), soil turning wildlife have become less diverse - the result is compacted soils deplete of organic material. This has resulted in reduced infiltration, increased stormwater runoff, increase erosion rates, reduced capacity for pollution attenuation, and infertility.
2. Habitat Impairment - the physical condition of the habitat within which fishes, amphibians, and other aquatic organisms live, is critical to their survival. Habitat impairment is the largest cause of non-attainment of "Aquatic Life Use" in Ohio. In the absence of pollution or hydrologic alteration, a stream that has had its physical habitat directly altered will be unable to support a healthy community of fishes and other aquatic organisms. Three important components of healthy stream habitat are:
a) Healthy Headwater Stream Habitat |
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b) Impaired Headwater Stream Habitat.
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3. Water Pollution - Water pollution is a threat to human health and wildlife in Hamilton County. While industrial discharges of pollution ("point source" pollution) into streams is relatively easy to regulate, pollution delivered to streams in stormwater runoff ("non-point source" pollution) is a much harder problem to address. Urban/Suburban Runoff contributes a range of pollutants (e.g. fertilizers, pesticides, heavy metals, petroleum products, road salt, litter etc.) to local streams. Anything that is spilled or dropped on a parking lot, road, or driveway is likely to end up in a nearby stream the next time it rains - Learn more from Hamilton County Public Health and Hamilton County Stormwater District. Agricultural Runoff contributes four primary categories of pollutants: fertilizers, pesticides, livestock waste, and sediment. Much of agricultural pollution occurs in seasonal patterns corresponding to agricultural practices such as tillage, chemical application and harvest - Learn More from the Natural Resources Conservation Service. Fecal Bacteria is a major contaminant in our local streams in Hamilton County. Many species of fecal bacteria are sources of waterborne human pathogenic diseases. Sources of fecal bacteria in streams include Combined Sewer Overflows (CSOs) & Sanitary Sewer Overflows (SSOs) (Learn more from the Metropolitan Sewer District of Greater Cincinnati [MSDGC]); Failing Septic Systems (Learn more from the Center for Watershed Protection and Hamilton County Public Health); and Pet and Livestock Waste (Learn more from the Center for Watershed Protection and the Natural Resources Conservation Service). Sedimentation/siltation (in combination with its contribution to habitat impairment) is the largest cause of non-attainment of "Aquatic Life Use" in Ohio. In urban and suburban contexts, most of the sediment pollution in streams originates form stream bank erosion (caused by Hydrologic Alteration); however, in agricultural areas (western Hamilton County) much of the sediment pollution can come from erosion of unvegetated soils in row-crop fields (e.g. corn and soy beans). Erosion is particularly sever between the time that fields are tilled and when the crops become rooted and form coverage over the soil. Agricultural Best Management Practices (BMPs) have been developed to help farmers keep their valuable soil resource on their fields - Learn More from the Natural Resources Conservation Service. Nutrient Pollutions has become a major problem in streams around the world. Nutrient pollution is discharged into streams constantly from waste water treatment plants (WWTPs). Nutrient pollution is also delivered to streams in the form of fertilizers applied to lawns and agricultural fields in stormwater runoff. Nutrient pollution from runoff events is delivered intermittently, but can come at much higher concentrations that that from WWTPs; however, elevated nutrient levels during low flow (from WWTPs) is a significant cause of biological impairment in Ohio. Nutrient pollution can also lead to the formation of Harmful Algal Blooms (more below) in our lakes and rivers and they contribute the hypoxic "Dead Zone" in the Gulf of Mexico. Harmful Algal Blooms (HABs) have become a major topic of concern in Hamilton County following the 2015 HAB in the Ohio River stretching from Pennsylvania to the Mississippi River causing multiple drinking water treatment plants along the river to shut down. The 2015 Ohio River HAB was dominated by a cyanobacterium called Microcystis aerugenosa which produces neurotoxins and hepatotoxins (liver toxins). Boiling tap water will not destroy these toxins. The 2014 HAB in western Lake Erie led to the City of Toledo issuing a drinking water advisory to 500,000 people and the Ohio Governor declaring a "state of emergency". The causes of HABs in the Ohio River are complex, but two primary ingredients are 1) elevated nutrient levels (particularly phosphorous) from wastewater treatment plant discharges, and agricultural/residential fertilizer over-use, and 2) low flows of warm water. The requirement of low flows of warm water does provide a seasonal predictability of HAB event - occurring from late summer to early fall. Learn more from Ohio EPA. Pesticides have varying effects on aquatic organisms depending on specific the product, dosage, and tolerance of the specific organisms exposed. Generally, it is clear that pesticides (manufactured poisons) are harmful to wildlife. |