THE SIGNIFICANCE OF WETLANDS IN URBANIZED LOCATIONS
Dusty L. Reed, Department of Earth Sciences, University of South Alabama, Mobile, AL, 36688-0002. Email: Dustbowl_1980@yahoo.com.
The purpose of this research project is to determine the differences between urban stream water quality when wetlands are present or when they have been modified or destroyed. The creeks used in this study are Second and Milkhouse Creeks. They are part of the Dog River watershed, located in Mobile County, Alabama. They have differing amounts of wetland acreage, they are roughly the same lengths, and they have roughly the same sized watersheds. The methods used in this study were finding two creeks that had differing amounts of wetland acreage, taking water samples from the two creeks, analyzing the extracted data, and organizing the data into a presentable form. The water samples taken test turbidity and dissolved oxygen. The temperatures of both creeks are measured on-site. The results of the data indicate a correlation between the amount of wetlands and improved water quality. Although the results found can be debated with a quality vs. quantity (of wetlands) standpoint, they nevertheless show the sensitivity of an urbanized watershed to wetland modification with regards to water quality, and that wetland preservation is a viable approach to overall environmental health of the watershed.
Keywords: wetlands, water quality, urbanization
project focuses on the significance of wetland habitats as a valuable
environmental player regarding water quality in watersheds. Oftentimes, construction of urbanized
locations tends to modify the land in such a way that it no longer resembles
its native state, and it also functions differently. Wetland environments are one of the
areas affected by modifications such as urban construction.
To define wetlands in one single simple definition is very difficult. Wetlands have been described as being an in between area with both terrestrial and aquatic characteristics; part water, part land (Salveson, 1994). Often, they are found alongside lakes, rivers, streams, creeks, and oceans in low-lying areas (Salveson, 1994). No two wetlands are alike; each has its own hydrology (water properties), soil condition, and dominant vegetation (Salveson, 1994). In broader terms, there are two types of wetlands, those affected by the daily tidal ebb and flow, and those unaffected by them (Salveson, 1994). However, in order to be classified as a wetland, two conditions must be met: 1) There must be soil that is at least periodically saturated or covered with water, and 2) There must be hydrophilic (water-loving) vegetation present (Salveson, 1994).
The value of wetlands is often misunderstood in relation to watershed health. They make up one of the Earth’s most valuable ecosystems (Salveson, 1994). Wetlands are described as being “the kidneys of the landscape” (Mitsch & Gosselink, 1986) for their ability to cleanse chemical and biological materials. Wetlands are recognized for providing these and other functions, including nutrient and contaminant retention and transformation, groundwater recharge, and production export (Kent, 1994), or what you would consider the cleaner water after the chemicals and other biological materials have been “filtered out”.. They capture and store sunlight through photosynthesis, which complements their ability to retain nutrients and recycle materials efficiently (Salveson, 1994). Because of their characteristics, wetlands “help maintain water quality” (Salveson, 1994).
For most of the time in recorded history, wetlands have not
been revered as valuable ecosystems. Before the mid 1970s, wetland drainage
and destruction were accepted and sometimes encouraged practices in the United
States (Mitsch & Gosselink,
1986). If that
trend had been allowed to continue, wetlands would be on the verge of
extinction today (Mitsch & Gosselink,
early sign of the United States showing interest in the preservation of
wetlands was through the sale of “duck stamps,” which
began in 1934, whose revenues were used to acquire up to 3.5 million acres of
wetlands with the intent of preservation (Mitsch
& Gosselink, 1986).
Any time one modifies a stream through physical alterations (including the removal or modification of wetlands) or stream channelization, it affects the stream’s structures (Riley, 1998). This, in turn, degrades the functions of the local ecosystem (Riley,1998). If one modifies the wetlands adjacent to a creek or stream, the functions that promote good water quality are compromised, resulting in degraded water quality.
Several states have opened wetland mitigation banks to help counter the effects of development. While many advances in creating and restoring wetlands have occurred, many early mitigation efforts were dogged with shortcomings and mistakes (Salveson, 1994). A mitigation by definition is: “to act in such a way as to cause an offense to seem less serious” (Lexico, 2005). Across the United States, wetlands are making a slow comeback (Salveson, 1994). Some that were drained years ago are now being filled (with water), and some are having to be “re-created.”
Since wetlands are notoriously difficult to “re-manifest,” it is essential that people try their best to keep what wetlands are left. A number of wetlands creation efforts will fail, some within a year or two, and others after several years (Salveson, 1994). The community can benefit from this information simply from understanding why wetlands are so important and why they should either be left alone or restored (instead of filled or drained) in an attempt to help maintain decent water quality.
Does the existence of wetlands significantly decrease
turbidity, increase the dissolved oxygen, and help moderate the temperatures of
creeks and streams in the watersheds of urbanized locations? In other words, do the wetlands
contribute to better water quality in urbanized locations?
I studied two creeks- Second Creek and Milkhouse
Creek- that are part of the Halls Mill Creek watershed, which is part of the
larger Dog River watershed.
These two creeks run north to south, roughly. They are located on the east and west
sides of Cody Road, and can be accessed at their respective intersections with
Cottage Hill Road (first bridge to the west and first bridge to the east). They are
essentially parallel (as far as meandering creeks go) and
also fairly close in size (Figure 1). These two creeks were selected for
their differences in the amount of available wetlands
in order to show a difference in their water quality trends.
The procedures for obtaining water quality data involved taking samples of water from each creek and analyzing them for turbidity (sediments, or foreign particles suspended in the water), dissolved oxygen, and temperature. I collected the samples five times on a once-a-week basis around 2 to 4 P.M. each time, using sampling kits available from the Alabama Water Watch organization. For the temperature readings, I placed an approved Celsius thermometer as close to the main creek flow as feasible at the beginning of each test to allow the thermometer to readjust to the water temperature and stabilize while I carried out the other procedures. I usually just tossed it over an overhanging tree branch and secured the end. I also took air temperatures by placing an identical thermometer off of the ground and in the shade nearby. To obtain water samples for turbidity and dissolved oxygen, I would hang out over the water of Second Creek via an angled tree and lower a water sampling tube into the water as close to the main flow of the creek as possible. Taking samples too close to the bank creates the risk of affecting turbidity readings by disturbing the bottom. After the sample was extracted, the oxygen bottles were filled first to avoid atmospheric oxygen contamination of the sample parcel of water. The two oxygen bottles (labeled for Second Creek) were completely filled (no bubbles inside) and then promptly capped. Next, the turbidity bottle (also labeled) was filled. After this, I emptied the sampling tube of any extra sample water, and began to “fix” (render chemically stable- no oxygen transaction between the water sample and the atmosphere) the oxygen samples. To do this, you need to add exactly 8 drops of manganese sulfate, followed immediately by exactly 8 drops of alkaline potassium iodide azide (AWW, 2002). At this point, I inverted and shook the bottles to encourage a cloudy brown precipitate to form (by mixing the chemicals). The final step in the fixing process involves the addition of another 8 drops of 1:1 sulfuric acid after the precipitate is allowed to settle some (AWW, 2002). Upon completion of filling the turbidity and oxygen sample bottles, I took the readings off of the air and water thermometers. The water thermometer is most accurate if you can leave it underwater (so evaporation cannot cool the bulb) or jerked out and read quickly to minimize evaporative cooling. The actual turbidity for 4 out of 5 samples was derived using a LaMotte Turbidimeter, whereas the first sample was derived from the methods and instruments provided through the Alabama Water Watch organization.
The gathering of samples from Milkhouse
Creek was identical to that of Second Creek’s
with the exception of not needing the water sampler. I located a spot that enabled me to
reach the main flow without assistance. The bottles were all
labeled accordingly as well.
The data generated from these experiments was organized and made into graphs via MS Excel program. Also, to determine the wetland acreage for 1982, I took a 1:24,000 scale Mobile, AL Springhill 7.5 minute 1982 Quadrangle map (see Figure 1), delineated the wetlands, and used an acreage calculating grid (Bryan, 1944) to determine the acres along the creeks. The same dot grid was also used on the Soil Survey for Mobile County in 1960 to determine the acreage for that time.
To enable my data to have a higher quantitative value, and thus help to reinforce the proportion of available wetlands as being relatively equal, I also calculated the watersheds’ acreage for both Second and Milkhouse Creek. I compared these numbers to the available wetlands for 1960 and then again for 1982 to get a rough percentage of the urban “loads” that the wetlands had.
A construction site was located about 50 yards upstream from the Second Creek sampling site. However, it was supervised by the Alabama Department of Environmental Management (ADEM) and was remarkably well managed. To verify this, I took two samples upstream of the construction site to determine whether or not the site was corrupting the sample data (especially the turbidity results). Surprisingly, the data returned did not vary enough to justify relocating upstream of the construction site.
The two creeks’ acreage of wetlands is as follows: Milkhouse Creek had
approximately 136.3 acres of wetland associated with it as of 1982, and Second
Creek had approximately 77.3 acres. The difference in wetland acreage
between the two creeks in 1982 was about 58 acres. The difference in wetlands back in
1960 was only 25 acres.
Figure 2 shows the above information.
The watersheds’ acreage was found to be 6,033 acres for Milkhouse Creek, and 5,113 acres for Second Creek, approximately. For 1960, this resulted in a comparatively identical wetlands availability for each watershed. Milkhouse’s watershed had a total of 2.77%, and Second Creeks watershed had a total of 2.78% available. Compared with the available wetlands in 1982, Milkhouse was down to 2.25%, and Second Creek was down to 1.5%- nearly half of its former 2.78% available 22 years previously .
The turbidity levels with Milkhouse Creek were consistently lower than those of Second Creek, with the exception of the first sample results, which were not recorded as accurately as the other four. There were two sampling sessions upon which the turbidity levels were very close, but Milkhouse Creek’s turbidity values were never more than Second Creek’s. Figure 3 shows turbidity results for both creeks. Sample 5 (not shown in Figure 3) followed a monumental “100-year” flood event in which Mobile received twelve inches of rain the night of March 31st, 2005. Turbidity levels for both creeks were very high, as were their water levels. The values for Second Creek and Milkhouse Creek’s turbidity levels for this rain event were 151 NTU’s and 121 NTU’s, respectively; as opposed to the single digit values shown on the graph.
The dissolved oxygen results had greater differences collectively than the turbidity. Again, Milkhouse Creek had the highest quality values for each sampling session (Fig. 4).
The results of the water temperatures indicated a higher fluctuation within Second Creek as compared to Milkhouse Creek (Fig. 5). The lower readings were lower, and the higher readings were higher, indicating Milkhouse Creek possesses a more “moderating” environment than Second Creek’s.
Discussion and Conclusion:
Based on the data analyzed with respect to the amount of wetland acreage available to each creek, it is understandable that Milkhouse Creek would have slightly better values across the board, since it had slightly more wetland acreage available for the improvement of the urban runoff. Although Second Creek did not necessarily have “poor” water quality, the results from it demonstrate the effect a difference of (at least) 58 acres of wetlands can have on water quality results within urban locations.
This research project provides adequate evidence to show the effectiveness of the remaining wetlands in urbanized watersheds on water quality and reinforces why they should remain as watershed components to promote healthy water quality and also a healthier local environment.
Dog River Clearwater Revival can benefit from this research project by learning from this research the benefits of having wetlands in their watershed as a way to promote water quality improvement that doesn’t require any human labor or money. The returns from allowing wetlands into our urban areas would demonstrate an intrinsic understanding of their functions and roles and also a simplistic and nearly passive approach to bring us one step closer to living with the environment instead of against it. Furthermore, recognizing that since Mother Nature can, and does, do a superior job of being “environmentally friendly”, we should make sure that no opportunity is overlooked.
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