WATER QUALITY AND ITS DEPENDENCY ON RIPARIAN VEGETATION
Andrea L. Peterson, Department of Earth
Channelization of the Dog River Watershed has resulted in the separation of riparian vegetation from its tributaries compromising water quality and overall health of the watershed. Riparian vegetation helps to maintain and improve water quality by functioning as a buffer, filtering out sediments and debris. It provides habitats for organisms that contribute to the water’s health, and it creates an obstacle that slows down stream flow, especially after a rain event. This study shows that where vegetation occurs, water quality is enhanced. Water quality tests were conducted at two sites in the watershed to test temperature of air and water, pH, and dissolved oxygen levels. Site 1 is Halls Mill Creek, which lies in an undisturbed forest area, and site 2 is Woodcock Branch, which is channelized and removed from its riparian vegetation. These tests indicated that water quality is superior in streams and creeks where vegetation occurs along its banks. Information available to the public and government officials on efficient and cost effective ways to protect the watershed could lead to the removal of less riparian vegetation and positive long-term health of the entire watershed.
Keywords: water quality, channelization, riparian vegetation.
Due to extensive areas of development in the Dog River Watershed, riparian vegetation is no longer a distinguished part of the watershed’s ecology. “A riparian area of any stream or tributary functions as sponges, absorbing and filtering out sediment and other debris as well as providing unique habitats for some organisms” (Simmons, 2004). This inopportune fact of less vegetation affects the health of not only tributaries but the entire watershed. “If riparian areas are not protected, we fear the loss of: water quality and quantity, habitats for plants and animals, native plant and animal species, recreation, natural filtering of sediment and connectivity with other landscapes” (Verry, 2000).
In the event of a rainfall, intense runoff from the impermeable
as paved roads and driveways, carries large sediment loads that drain
A recent study in coastal
Is there a measurable difference in temperature, pH, and dissolved oxygen levels between areas where vegetation occurs such as Halls Mill Creek at Schillinger Road (Figure 1), and areas where vegetation does not occur such as Woodcock Branch at Government Street (Figure 2)?
To generate a water quality profile that would represent vegetative and non-vegetative areas in the Dog River Watershed, I chose Halls Mill Creek and Woodcock Branch due to their vegetative state. Halls Mill Creek lies in an undisturbed, forest area and Woodcock Branch sits in the center of an urbanized area and has been channelized and removed from its riparian sources.
Water quality testing, including temperature of air and water, pH levels to test acidity, and dissolved oxygen levels were obtained and measured using a LaMotte Testing Kit which is the testing kit used by the Alabama Water Watch Association. These tests took place over a period of two weeks, and during the recommended timeframe for testing, between and . If any rain occurred, water quality tests will show the impact of intense runoff.
Both sites in the watershed were chosen based on the presence or absence of vegetation in and along the streambed. Two water quality tests were taken at both sites for a total of 4 tests. The results of the tests were then compiled to show the difference in water quality between the vegetated and non-vegetated areas. These results were inserted into a Microsoft Excel spreadsheet and later graphed.
Table 1 is the Alabama Water Use Classification and Standards for pH, Water Temperature, and Dissolved Oxygen ppm (Temperature, 1992-2002). Using my results (Figure 3) we will see how vegetated and non-vegetated sites compare to regulations.
|Alabama Water Use Classification and Standards (Adem 2001)|
|Classification||pH||Water Temperature º C||Dissolved Oxygen ppm|
|Outstanding National Resource Waters||No new discharge, Mandatory BMP||No new discharge, Mandatory BMP||No new discharge, Mandatory BMP|
|Outstanding Alabama Waters||6.0-8.5||32º (30º), 2.8 R||5.5|
|Swimming||6.0-8.5||32º (30º), 2.8 R||5.0|
|Shellfish Harvesting||6.0-8.5||32º (30º), 2.8 R||5.0|
|Public Water Supply||6.0-8.5||32º (30º), 2.8 R||5.0|
|Fish and Wildlife||6.0-8.5||32º (30º), 2.8 R||5.0|
|Limited Warm Water Fishery||6.0-8.5||32º (30º), 2.8 R||3.0 (May-Nov) 5.0 (Dec-Apr)|
|Agricultural and Industrial Water Supply||6.0-8.5||32º (30º), 2.8 R||3.0|
|►2.8 R indicates that no more than a 2.8º C rise above the normal (or ambient) stream temperature is permitted (not to exceed 32ºC or 30ºC).|
Temperature affects the physical and chemical properties of water and greatly influences aquatic organisms by affecting their feeding, reproduction, and metabolic rates. It also affects how much oxygen water can hold and how quickly nutrients will be cycled through aquatic systems. Runoff from heated impervious surfaces can increase water temperatures where as stream water temperatures are often lower than air temperature because of groundwater inflows or the shade of streamside vegetation. Most aquatic organisms can tolerate gradual changes in temperature, but drastic changes can cause thermal stress. Temperatures above 32 degrees Celsius may be lethal to many aquatic organisms. The temperature of the vegetated site during both tests averaged around 20 degrees Celsius and the non vegetated site averaged around 23.5 degrees Celsius. The temperature of the non vegetated site was and always will be higher because of more runoff and less shade due to the lack of riparian vegetation.
Like land organisms, aquatic animals and plants need oxygen to live. Oxygen enters water in several ways like when aquatic plants and algae release oxygen during photosynthesis and by diffusion from the atmosphere. A dissolved oxygen value of at least 5.0 ppm is desirable for most aquatic organisms and is required for streams classified as “Fish and Wildlife” or higher. The average DO ppm value for the non vegetated site was 8.9 ppm which is typically higher than the vegetated site’s average of 6.6 ppm which relates to the depth differences of the water. DO decreases with increasing depths and the non vegetated site is sufficiently shallower than the vegetated site.
Dissolved oxygen’s percent saturation is the amount of oxygen water can hold. When DO concentrations exceed 100% of the amount that can be dissolved by physical mixing alone they become supersaturated. An acceptable range for DO Percent Saturation is between 60% and 125%. Anything above or below this percentage range could be lethal to organisms. The average percent saturation of Halls Mill Creek is 72.5% and the DO percent saturation for Woodcock Branch is 106%. Both show percentages acceptable for stream animals but Woodcock Branch is supersaturated and could mean that the stream has unnaturally high levels of the nutrient phosphorus and/or nitrogen (which could come from runoff with excess fertilizers, animal waste, etc.) (Temperature, 1992-2002).
pH is a measure of how acidic or basic water is. A pH of 7.0 is neutral, values less than 7.0 are acidic, and those more than 7.0 are basic. According to the Alabama Water Use Classification and Standards table (see table 1), the optimal pH range for aquatic life is 6.5 to 8.5. A pH less than 4.0 or greater than 10.0 is usually lethal to fish and other organisms. The average pH for the vegetated sites was 7.0 (neutral) which is perfect for aquatic life where as the non vegetated site averaged at 6.0 which is slightly lower than the optimal pH range for aquatic life.
More streams and creeks becoming channelized and the removal of
vegetation has a detrimental impact on water quality. Without the
sources water cannot filter out pollution and sediment quickly enough
concrete channels, water moves more rapidly downstream and deposits
According to David Shankman’s 1996 article titled Stream Channelization and Changing Vegetation Patterns in the U.S. Coastal Plain, awareness of the physical and biological problems caused by channelization is growing. Environmental degradation of alluvial habitats has been given serious attention in channelization project planning in recent years. Less destructive channel modifications have been implemented and some attempts have been made to restore riparian habitats affected by channelization (Shankman, 1996).
more aware of this problem could minimize removal of riparian
result in a change for the better in water quality.
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