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Learn about watersheds

Everyone lives in a watershed. A watershed is the area of land that drains into one particular stream or lake. We depend on reliable water sources for drinking, bathing, cooking, recreation and as a necessary resource for agriculture and manufacturing. Yet many of these same activities and uses can harm the watershed by changing how the river flows, how often and where it floods, and how clean it is. At this site and related sites, you can explore how people's activities can harm the watershed and how these activities can be managed to avoid such harm.

Find out how watershed quality is measured

Water quality can be measured in many ways. Here, you can explore what those measures are and what they can tell you about the water quality.

Look at what can be done to protect watersheds

It is very important to minimize the impact of development on watersheds. We can help maintain and protect the quality of watersheds by using best management practices (BMPs). You can learn about BMPs here and find out which are best suited for particular situations.

 

Characteristics of Watersheds

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A watershed is an area of land that forms the drainage system for a stream or river. This area collects surface water from land within specific topographic boundaries (such as hills, valleys, mountains, and other landscape characteristics).

Watersheds are characterized by the location of the pour-point, or mouth, of the main flow of water to which all the other points of flow join and eventually drain from the watershed. Some of the rainfall in the area of a watershed will flow on top of the ground or find its way via underground water paths to the stream in the watershed. Some of the water will evaporate into the atmosphere, be used by people or plants, or be held in the soil or underground. Watersheds are very dynamic places becoming alternately wet and dry, due to high water and low rainfall conditions, with many differences in quality and flow depending upon the season, the year, and even with what happens during an individual storm. This is best illustrated by examining the components of the hydrologic cycle. Click here to learn more about the hydrologic cycle.

Within a watershed, activities on the land interact with the natural hydrologic cycle. Important nutrients and chemicals are circulated throughout the watershed's system and supply a basic nutritional source for both aquatic (fish, aquatic insects, etc.) and terrestrial (birds, small mammals, etc.) species. People also use these environments to grow food, build their homes and businesses, and travel from one place to another. Where and how these human activities occur have major impacts on the movement of water, water quality, and the quality of the natural habitat which remains. Ideally, we wish to have watersheds that continue to function as healthy ecosystems and serve as productive systems for people.

 

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Many different attributes are needed to maintain a high quality, biotically rich, functioning watershed. Healthy watersheds provide stable habitats for both biological diversity and human recreational uses. These stable systems are capable of adapting to environmental changes over time and are good indicators of the quality of the surrounding habitat. The following characteristics are critical for a healthy watershed: (You can click on the pictures to see more details).

Riparian Habitat & Protected Banks		Riparian areas, areas along stream banks, are covered by transitional vegetation and act as buffers between a waterway and the surrounding area. These grasses, forbs, and trees reduce bank erosion by anchoring the soil. These buffer areas also function as a wildlife corridor and enable safer and more efficient wildlife migrations.
Good Water Quality		Good watersheds usually function best with low turbidity, minimal suspended sediment in the water, and infrequent shifts in water levels. Frequency and intensity of fluctuating water levels are also very important considerations.
Adequate Shade		A riparian canopy provides structure and shade, which decreases the amount of penetrable sunlight. This decrease results in less extreme temperature gradients of the surface and sub-surface water. Cooler water can hold more oxygen for aquatic species to use.
Meanders		Meanders in a river are turns in the banks that result in a winding course for the waterway. These meanders slow the water down and allow for deposition of sediment and other suspended material on their banks. As healthy rivers and streams age, they will naturally form more meanders.
Biological Diversity		Biodiversity is extremely valuable to both the natural order of the system and human recreation and non-consumptive uses. Different types of internal habitat and structure diversity, such as pool and riffle sequences and vegetation, also help to diversify the system and provide for increased stability.

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For more information on watersheds, visit these websites:

 

US EPA
Ohio EPA - Division of Surface Water

Sampling Watershed Quality

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Measuring Watershed Quality

 

• Traditional Water Quality Indicators


• Index of Biotic Integrity


• Invertebrate Community Index


• Qualitative Habitat Evaluation Index

Traditionally stream and river quality assessments have been conducted based solely on chemical analysis to analyze the impact of land use change on water quality. While variables such as pH, dissolved oxygen, hardness and concentrations of metals, soluble chemicals, nutrients, and organics were typically measured, other extremely valuable information regarding biological species diversity and overall habitat quality was lacking.

More recently, scientists have recognized the need to incorporate this biological data in order to create a comprehensive investigation of watershed quality and response to change. This biological line of investigation is important because chemical assessments could not assess the effect of a particular pollutant after settling in the system, and could only accurately measure its short-term effects.

Biological methods take into account a variety of ecological indicators like topography, soil structure, water table levels, and surrounding vegetation and present a more conclusive picture of a watershed. These ecological variables are useful in measuring long-term effects and the ability of the water system to respond to major stress events. The Ohio EPA has highlighted the following as primary components of biological integrity:

 

Chemical Variables (pH, dissolved oxygen, phosphorous, etc.) Energy Source (sunlight, seasons, available nutrients) Biotic Interactions (reproduction, disease, parasitism, predation) Habitat Structure (vegetation, cover, sinuosity) River/Stream Flow Regime (precipitation, velocity, runoff)

Using ecological parameters is extremely valuable in assessing non-point pollution. With no known discharge sites and unknown times of origin, non-point pollution becomes very difficult to assess. Therefore, it is in the best interest of the planner, developer, and landowner to recognize the need for incorporating biological data into watershed assessments.

 

Biotic Integrity, according to Ohio EPA and watersystem scientists, is defined as the following:

An aquatic ecosystem's ability to support and maintain a community of organisms with diversity, species composition, and functionality comparable to natural habitats within a similar region. This community should also be well-balanced, integrated throughout, and adaptable to changes over time.

Best Management Practices

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Best management practices (BMPs) are effective practices that act to reduce the nonpoint pollution load in water systems and decrease the velocity of runoff after storm events. These practices are usually created and maintained for long-term use and coincide with the local water quality standards for a particular area. Selection and suitability of a BMP should be based on: site specific conditions, type of land use activity, the physical makeup of the watershed, and consideration of the pollutant(s) involved.

 

Agricultural

 

Conservation Tillage and No-Till

 

• Conservation tillage is an agricultural BMP that provides long-term crop residues and vegetation on croplands. This practice greatly reduces erosion and surface runoff of heavy metals and pesticides, which may reside in higher concentrations in the surrounding soil. No-plow is a similar practice that minimizes the spring influx of sediment into nearby waters by anchoring the soil to the plant root systems. Either way, by retaining crop residue and vegetative cover, this practice reduces time and energy on the farmer, it delays the warming and drying of the soil, and overall maintains a higher quality of soil.

 

 

Contour strip cropping

 

• Various rowcrops and hay in alternating strips planted side-by-side can reduce soil loss of about 50% compared to the same rotation contoured on its own. This practice is effective in that it provides rotated crops in different parts of the soil which act to strengthen the soil characteristics over time by not continually depleting the resource based on a monoculture. This process also decreases erosion and runoff and increases the stability of the local soil.

 

Livestock Husbandry

 

• Simple practices can be implemented to offset livestock impacts on nearby streams and rivers. By providing an alternative water source, for example, livestock would not be forced to wade in the streams and therefore would not be as likely to contribute to excess nutrient input from wastes. Large concentrations of wastes can speed up eutrophication of a stream, which will eventually decrease the effectiveness of the watershed's sustainability. Another effect of livestock in waterways is the increased potential for erosion by streambank deterioration from trampling and compaction. An alternative to better manage for the watershed could include creating a bridge to connect pastures where the animals can easily cross the stream without directly interacting with the water system.

Urban and Suburban

Vegetative Buffers

Filter Strips

• Filter strips are wide areas of vegetation that act to intercept runoff. They can consist of any type of dense vegetation from woodlands to grass and can remove various pollutants, such as heavy metals, sediment loads, and excess organic materials.

 

 

Grassed Swales

Swales are shallow channel depressions where runoff flows. These swales slow the flow of the runoff water and allow particulates to settle out and water to infiltrate into the soil. These swales can effectively remove small amounts of excess nutrients and heavy metals.

Constructed Wetlands

• Constructed wetlands are often used in mitigation of other areas that lost wetlands due to development. Both natural and constructed wetland areas are saturated for sufficient time periods and are able to support unique vegetation adapted for life in such conditions. Wetlands are extremely efficient in filtering sediment, nutrients, and some heavy metals from storm water runoff and overflow of nearby water systems.

 

Stormwater Retention

 

• Structures are often built in residential areas to alleviate stormwater runoff and retain or detain precipitation from storm events. Detention ponds are basins that temporarily store runoff from a site and release it at a controlled rate to minimize downstream flooding. These ponds are quite effective for pollutant removal, especially suspended sediments, if well designed.

 

Infiltration Trenches

 

• These trenches are shallow, usually three to eight feet deep, and backfilled with gravel to create underground reservoirs. Runoff, therefore, is diverted to the trenches and percolates into the subsoil. Such a practice effectively removes sediments and similar particles from stormwater runoff. This practice is commonly used in both commercial and residential areas.

 

Short-term Construction

 

• Construction sites, while under development, can implement many BMPs to reduce runoff, decrease pollutant loads to nearby water systems, and decrease the amount of soil washed from the site. Simple practices, such as setting up straw bales, silt fences, or even filter fabrics can act to slow runoff and retain sediment during storm events. Other practices, such as sediment basins to detain runoff or stabilizing entrances of construction, further decrease sediment and pollutant runoff.

 

Maintenance Practices

 

• Citizens, commercial businesses, and even local and state agencies can implement and maintain efficient BMPs by taking the conservative approach to many everyday landscaping events. For example, sufficiently seeding grass to promote long-term stabilization of soil surfaces and planting wildflower cover (a practice used by many highway departments to provide aesthetically pleasing vegetation along roadways) greatly reduces the potential for erosion by securing the surfaces with plant roots. Other practices such as sodding and mulching can also be applied and have similar effective results.

Under the guidance of Steven I. Gordon, graduate students and planners in The Ohio State University's City and Regional Planning Program (OSU CRP) have created a screening tool based on geographical information systems (GIS) and data provided by the Ohio Environmental Protection Agency (OEPA) and the United States Environmental Protection Agency (USEPA) that can provide planners, environmental organizations, government agencies, and concerned citizens an interactive opportunity to examine potential changes and their effects within particular watersheds throughout Ohio. It can also provide information on the potential impacts of certain changes on the biological diversity in the inter-related rivers and streams.

A full length report detailing the research and methods supporting this interactive mapping and web-based watershed information sharing approach can be viewed by clicking here - See full report. This report is available in PDF format.

Watershed Glossary

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Benthic - Referring to bottom-dwelling aquatic organisms.

Bioaccumulation - The increase in the concentration of a chemical in an organism that resides in an environment contaminated by low concentrations of various organic compounds.

Biological magnification - The increase in the concentration of a heavy metal (i.e., mercury) or organic contaminants (i.e., chlorinated hydrocarbons-CBCs) in organisms as a result of their consumption with in a food chain/web.

Biological Diversity - Describes attributes of species richness, genetic variation, and complexity within an ecosystem.

Buffer Zones - In general, an area used to separate conflicting uses. In relation to riparian and watershed management areas, its a zone that can be maintained to minimize impacts to the local water resource (i.e., vegetative buffer strips along a creek).

Channelization - Navigation or flood control projects that widen, deepen, or straighten streams, canals, or rivers. Environmental consequences associated with channelization include bank erosion, increased sedimentation and flooding, and decreased biomass.

Conservation Tillage - Any sequence of tillage that reduces loss of water or soil relative to conventional tillage.

Discharge - Volume of water flowing past a point in a water system for a specific time interval.

Ecosystem - A biological community and the local, surrounding non-biological factors associated with it

Erosion - Process of wearing away of a surface by physical means (water, wind, ice).

Eutrophication - Addition of excessive nutrients (usually nitrates or phosphates) to a body of water, leading to overgrowth of aquatic plants.

Frequency - Stable rivers can accommodate natural levels of water resulting from typical storms. However, with increased runoff water entering the system from surrounding areas with impervious roadways and surfaces lacking vegetation, water levels quickly rise to less manageable levels. High water levels, with greater than normal velocities can accelerate the rate of bank erosion, increase sediment load, and displace aquatic species of plants and animals.

 

Hydrologic cycle - The flows and stocks of water in the ecosphere including the processes of precipitation, evaporation, transpiration, condensation, and surface and subsurface runoff.

Impervious - Description of a material that prevents passage of a fluid (i.e., asphalt surfaces)

Infiltration - Downward entry of water into the soil profile

Interception - Capture of precipitation by surfaces and structures (i.e., vegetation)

Macrophytes - Large rooted or floating aquatic plants.

Methylation - The process by which an element (commonly a metal) is joined with a methyl group (CH4). For example, methyl mercury is produced from an atom of mercury bonded to a methyl group. This compound is produced in the natural environment chiefly by bacteria following contamination of ionic, inorganic forms of mercury. This new compound then becomes absorbed by various organisms, moves up levels of a food chain, and increases its concentration with each level.

Oxides - Gases containing (for our purposes) either nitrogen or sulfur combined with oxygen. The most common oxides contributing to pollution include nitrogen dioxide (NO2) and sulfur dioxide (SO2). Both types of gases are major air pollution contributors. Sources of pollution from oxides typically include smokestacks, exhaust, and sulfur-containing compounds.

Percolation - Downward movement of water within the soil profile.

 

Phytoplankton - Microscopic plants, such as algae, suspended in aquatic environments.

Riparian - Type of wetland transition zone between upland habitats and aquatic habitats. Lush vegetation along a stream is usually associated with a riparian area.

Runoff - The portion of storm water or snow melt that enters a water system instead of entering the ground through infiltration.

Sedimentation - Soil particles, clay, sand, or other materials settle out of a fluid suspension into the bottom of a body of water. Human caused earth-moving activities such as agriculture and construction greatly increase sediment load.

Slope - The degree of deviation of a surface from the horizontal plane, usually measured in a percent, degrees or numerical ratio.

Species Richness - A measure of the number of species in relation to the total number of individuals in a particular community.

Substrate - In terms of river/stream characteristics, substrate usually refers to both inorganic and organic particles on the stream bed. Examples of substrates include: bedrock, boulder, cobble, gravel, silt, sand, detritus, muck, and artificial.

Tillage - Mechanical manipulation of soil, usually associated with agriculture in terms of crop production.

Trophic Level - All the members of an ecological community that are the same number of food-chain steps from the primary source of energy.

Turbidity - A measure of the amount of suspended material (sediment) in water based on the relative ability of light to penetrate the water's surface. This cloudiness of water due to excess sediment, is an extremely important factor in maintaining aquatic diversity. Many sensitive organisms, especially fish, require relatively clear water conditions for reproducing and finding prey. Some organisms, like shell-fish are filter-feeders and continually filter the water in the environment. These organisms can become choked by sediment and eventually die in heavily turbid waters.

Watershed - The area of land that drains into a stream or lake, synonymous with drainage basin.

 

We are going to ask you to look at some data from a watershed and try to figure out how pollution and habitat changes have led to changes in the biology.  You can use any of the materials and the websites we showed you as sources of information.  You can also ask your teacher or any of the OSC instructors for help if you don't understand something.  All of you will do part of the exercise.  We will then ask each person in your group to take on a part of the detective work and to present what you find to your group when you are done.  Before you start, your teacher will assign you a number between one and four so that you know which part to do.

Here is the first part for everyone to do.  The graph below and all of the graphs are set up to show you the relationship between pairs of data.  In most cases, one of the data items will be one of the biological measures - IBI or ICI - the fish or macroinvertebrates that are impacted by pollution and habitat changes.  The other data item is a possible cause of that change.  The data items represent samples taken in the watershed over a sampling season - mostly the summer.  They were taken at different places so we divided the watershed into small parts and have reported the data so that each line represents a single year summary and one part of the watershed.  The data were taken at several times over the season so that we summarize the information by providing the average, maximum, and minimum values for each variable.

Here is the graph for average IBI versus average QHEI.  Study it and answer the questions on the next page.

What is Happening in Your Watershed?

As watershed detectives, you looked for patterns that indicated cause and effect relationships. In order to “prove” scientifically that there is a cause and effect relationship, we want to make sure that the relationship is almost always true. Because we are studying watersheds where many things happen at one time, where there are many causes and many effects, this is sometimes very difficult.

Look at the graph below. It appears that at most times and most places, when QHEI goes up, IBI also goes up and when QHEI goes down, IBI also goes down. We might hypothesize that this is true because good habitat should allow for a better fish population. For the 29 observations in the diagram below, count how many times/places where this is true, how many times it is not true, and how many times where there are no data.

 

Based on what you found, should we accept our hypothesis that better QHEI results in better IBI? Why or why not?

For the places where it is not true, what else could be happening? What would cause fish diversity to go down even if there is good habitat? How would we look for other evidence associated with the places and times where the other hypothesis did not hold?