THE ROLE OF TRIBUTARY STREAMS IN SEDIMENTATION OF
LIONS LAKE, WARRENSBURG, MISSOURI
by
Neena Williams-Strange
An Abstract
presented in partial fulfillment of the
requirements for the degree of Master of Arts in the
Department of Biology and Earth Science
University of Central Missouri
April, 2012
ABSTRACT
by
Neena Williams-Strange
Sedimentation of aquatic ecosystems is a natural process which can be detrimental in manmade
lakes and restored wetlands. It caused a problematic decrease in water depth in Lions Lake
resulting in increased hydrophyte growth and a negative impact on fish populations. Five water
overflow and stormwater drainage channels carry sediment into the lake. Planned restoration
includes dredging the lake and constructing wetlands to trap sediment, but concerns about the
sources of the majority of the sediment prompted further investigation.
I examined the amount of sediment contributed by water channels from January 2010 October 2010 by collecting water samples during rain events and dry periods and filtering out the
suspended sediment. Three drainage channels on the east side of the lake carried significantly
more sediment than the other two channels. Results can be used to identify the most effective
placement of mitigation structures in order to minimize continued sedimentation.
THE ROLE OF TRIBUTARY STREAMS IN SEDIMENTATION OF
LIONS LAKE, WARRENSBURG, MISSOURI
by
Neena Williams-Strange
A Thesis
presented in partial fulfillment of the
requirements for the degree of Master of Arts in the
Department of Biology and Earth Science
University of Central Missouri
May, 2012
© 2012
Neena Williams-Strange
ALL RIGHTS RESERVED
THE ROLE OF TRIBUTARY STREAMS IN SEDIMENTATION OF
LIONS LAKE, WARRENSBURG, MISSOURI
by
Neena Williams-Strange
May,2012
APPROVED:
ACCEPTED:
~
Chair, Department of Biology and Earth Science
UNIVERSITY OF CENTRAL MISSOURI
WARRENSBURG, MISSOURI
ACKNOWLEDGMENTS
This research was supported by the Alumni Fund. I would like to thank my fellow
graduate students, my family, and Dr. Stefan Cairns for their support and advice. In addition, I
would like to recognize Tom Workoff with the Midwest Regional Climate Center as he provided
me with weather data that was not yet available on their website. I would also like to offer
special thanks to my thesis committee Dr. Victoria Jackson, Dr. Joseph Ely, and Jennifer
Mittelhauser for their valuable guidance and support.
TABLE OF CONTENTS
List of Tables ............................................................................................................................... viii
List of Figures ................................................................................................................................ ix
Introduction ..................................................................................................................................... 1
Materials and Methods .................................................................................................................... 3
Study Site .................................................................................................................................... 3
Field Collection of Samples ........................................................................................................ 7
Laboratory Methods .................................................................................................................... 8
Quality Assurance/Quality Control ............................................................................................. 8
Precipitation Data ........................................................................................................................ 9
Statistical Analysis ..................................................................................................................... 10
Results ........................................................................................................................................... 10
Field Collection of Samples ...................................................................................................... 10
Statistical Analysis .................................................................................................................... 12
Discussion ..................................................................................................................................... 14
Field Collection of Samples ...................................................................................................... 14
Laboratory ................................................................................................................................. 14
Recommendations ..................................................................................................................... 18
Literature Cited ............................................................................................................................. 21
vii
LIST OF TABLES
Table
Page
1. Number of Samples Collected Per Site…………………………………………….……...11
2. Data for Rainfall and Weather by Sampling…….………………………………….….......11
3. Mean Sediment Load in mg/L By Site and Rainfall Event………………….………….....12
4. Relationships Among the Sites…………………………………….………...…………….13
viii
LIST OF FIGURES
Figure
Page
1. Maps Showing the Location of Johnson County Within the State of Missouri,
the Town of Warrensburg, and My Study Site……………………………………………..4
2. Map of Lions Lake Study Area Showing Sites Where Samples Were Collected………….6
3. Mean Amount of Sediment in mg/L Contributed by Each Site Throughout the Study
Period. Standard Error Bars Are Shown……………………………………………..…...12
ix
INTRODUCTION
In 1893, J.H. Christopher was awarded the first water works franchise in Warrensburg,
Missouri located at a natural springs named Pertle Springs (Johnson County Historical Society
2011). He built dams in the area to create a system of small lakes. Lions Lake was known as
Pumphouse Lake when it was a part of Pertle Springs. At that time, it was used by the City of
Warrensburg as its water source since it was the largest lake in the springs. In 1962, the City of
Warrensburg purchased approximately 26 acres of the property including what is now called
Lions Lake. In the mid 1960’s, the Lions Club of Warrensburg raised funds to help develop the
lake into a recreational area for the community, and in 1966 the city leased the land to the Lions
Club (Johnson County Historical Society 2011). The rest of the park area, still known as Pertle
Springs, is now owned by the University of Central Missouri and is used as an educational
outdoor laboratory.
Lions Lake is a 30 acre park located in Johnson County, Missouri within the city of
Warrensburg and is home to migrating waterfowl and other wildlife. The lake is important as a
water source for terrestrial wildlife and as habitat for fish and other freshwater organisms. The
park benefits the city as members of the community can fish, picnic, or explore and appreciate
nature with their families. Unfortunately, the lake has been filling up with sediment in recent
years which is endangering the park’s ability to be a suitable recreational area and habitat for
aquatic and terrestrial organisms.
Recent construction near the park is the suspected cause of the sedimentation in the lake
via tributary streams and stormwater drainage channels. A rapid rate of construction can
increase the amount of flash flooding uphill from rivers, which leads to an increase in the amount
of sediment load, and results in an alteration of wetland ecosystems (Nilsson et al. 2003).
1
Tiemann (2004) states disturbances such as logging and construction tend to result in a decline of
the suitability of stream habitats. In addition, he found that restoration or recovery of the
freshwater habitat can take as little as one year to as long as fifty years and is dependent on water
flow, sedimentation, and the topography of the watershed.
Another issue associated with sediment deposition into the lake is the negative effect on
the wildlife community. The sediment load and influx of particulate material during rainfall
inhibits the reproduction process of area organisms, particularly invertebrates (Gleason et al.
2003). As sediment is deposited, it buries invertebrate egg masses and plant seedlings that are
found in the moist soil of the banks. As little as 0.5 centimeters can prevent invertebrate and
plant seedling emergence, which may be due to the sediment interfering with environmental
hatching cues such as temperature and sunlight (Gleason et al. 2003). The negative effect of
sedimentation on primary productivity has been an important factor in the reduction of aquatic
flora and fauna across North America (Henley et al. 2000). As a result a decline of food
available at each trophic level can also lead to poor growth rates, decreased reproductive output,
and recruitment of juveniles into adults (Henley et al. 2000). If sedimentation continues to
occur, the terrestrial wildlife population in the area could decline as they move elsewhere to find
a suitable water source. Aquatic organisms potentially could perish due to the degradation and
destruction of their habitat and the sediment load may prohibit the growth of new aquatic
vegetation and larval organisms.
According to a City of Warrensburg official in charge of the project, the city planned to
restore Lions Lake by dredging the bottom, thus making the lake deeper so it can continue to be
used by the community and area wildlife. Before the lake can be restored, the sediment
contributed by each stream must be measured to locate the primary sources so that mitigation
2
measures can be taken. Mitigation includes improving, conserving, and/or adding water to
drained wetlands to ensure future run-off is prevented (Morgan and Roberts 2003). The goal of
my research was to determine the rate at which sedimentation is occurring in the lake due to
tributary streams and stormwater drainage channels and to identify which tributary stream(s) are
contributing the most sediment.
The lake is in a low lying area and is subject to receiving run-off from all around its
perimeter. In addition, sediment is carried into the lake by five water sources channeled into the
lake by under-the-road culverts. Strategic placement of collection ponds or small wetlands will
be instrumental in reducing the rate of sedimentation so that the lake can be preserved. The
objective of my research was to determine the sediment in mg/L contributed to the lake by each
stream over a ten month study period and determine the main source(s) of the sediment. Results
of my study can be used by city managers to determine the best placement of mitigation
structures such as artificial wetlands.
MATERIALS AND METHODS
Study Site
My study site, shown in Figure 1, is within Warrensburg, Missouri in Johnson County
and focused on Lions Lake which is owned by the City of Warrensburg. Lions Lake is part of
the Post Oak sub basin within the Blackwater Watershed. The area receives an average of 38.89
inches of rain per year with highest average precipitation falling in May and June and lowest
levels in January and December (NOAA 2011).
3
Figure 1. Maps showing the location of Johnson County within the State of
Missouri, the town of Warrensburg, and my study site.
4
A large portion of the bank on the west side of the lake is met by a steep slope covered
mostly with a deciduous tree wooded area and grasses along the edge of the lake. The northwest
corner, as well as the other sides of the lake, is bordered by two lane paved roads. Much of the
area between the lake’s banks and the roads is mowed, except the slope on the west side.
The overflow and stormwater diverted into Lions Lake are all channeled into the lake by
culverts and are either overflow from nearby ponds or are storm drainage, with one exception. I
chose seven sample sites which are shown on Figure 2. Site 1 (a fork upstream of site 3) is
stormwater drainage near a residential and college campus housing area. Site 2 (a fork upstream
of site 3) is a shallow, narrow stream going through a wooded area. During seasonal dry periods,
this stream has no water flowing through it. Therefore, the stream at Site 3 is a combination of
storm drainage and normal stream erosion. It is also channeled into the lake via an under-theroad culvert.
Site 4 is overflow diverted from Culp Swamp within Culp Park which is owned by the
City of Warrensburg. The University of Central Missouri owns Pertle Springs, and overflow
from Lake Cena in that pond system is diverted into Lions Lake at Site 5. Sites 6 and 7 are both
storm drainage entering the lake via culverts. Unlike the other sites, the culvert for Site 7 is
several meters from the lake, and I took samples nearer the lake along the narrow stream leading
from the culvert to the lake.
5
Figure 2. Map of Lions Lake study area showing sites where samples were
collected.
Water samples were taken from each of the five channels during heavy rain events,
moderate rain events, and during periods of dry weather beginning in January 2010 through
October 2010. Rain events were classified into low, moderate, and high rainfall amounts. Zero
centimeters was classified as low, 0.025 – 1.0 cm was classified as moderate, and 1.1 cm and
more was classified as high. Precipitation levels among sampling events ranged from 0 cm to
2.44 cm. Sample collection and subsequent filtering were conducted using standard methods for
the examination of water (American Public Health Association et al. 1985).
6
Field Collection of Samples
I chose seven sampling sites and collected three replicates at each site in one-liter plastic
containers during each sampling event. Five of the sample points were at the mouth of the storm
drainage channels, and the other two points were along the forks upstream from Site 3. The
containers were dated and marked indicating site (1, 2, 3, etc) and if it was replicate A, B, or C of
that site. I collected a total of 189 samples across twelve separate dates January 2010 – October
2010. My goal was to collect samples during as many rain events as possible, but I did not
collect samples every time it rained during the study period.
Samples were stored in a refrigerator between collection and analysis to prevent break
down of sediment. I reused the one-liter bottles throughout the ten month sampling period. I
rinsed and scrubbed the bottles with a bottle brush in between uses to prevent contamination of
succeeding samples. I conducted two Quality Assurance/Quality Control (QA/QC) measures to
ensure that storing the samples in a refrigerator until they could be processed and reusing sample
bottles did not have a significant effect on results.
The amount of sediment was determined by taking samples from the tributary streams
during dry periods and periods of heavy and moderate rainfall. I filtered the samples to separate
the sediment and to determine which streams were contributing the most sediment load to the
lake. Determining the origin of the run-off indicates where the city should install deterring
devices, such as collection ponds, to reduce erosion that causes sedimentation. The effect of
rainfall on sedimentation was compared to predict the rate at which the lake will fill in if the city
does not to take preventive measures.
7
Laboratory Methods
The water samples were tested for suspended sediment in the University of Central
Missouri’s geology lab using standard methods (American Public Health Association et al.
1985). I prepared glass fiber filters by placing each filter in an aluminum weighing pan and oven
drying them (103 – 105 oC) for 12 to 24 hours. Then they were cooled in a dessicator for at least
12 hours. A digital scale was used to determine pre-weights of each pan and filter out to four
decimal places.
Each one-liter sample was homogenized by overturning the bottle four times, and then 50
mL was poured into a graduated cylinder. Then the 50 mL sample was poured through a glass
fiber filter in a membrane holder clamped to a sidearm flask to separate out suspended sediment.
All apparati were rinsed with distilled water after each sample was filtered.
Next the filter was oven-dried (103 - 105 oC) in its pan to evaporate the moisture for a
minimum of one hour, and then the filter was cooled to room temperature in a dessicator for at
least 12 hours. Post-weight included the pan and filter. The formula for determining mg total
solids/L is (A – B) x 1,000 divided by 50 where A = the post-weight and B = the pre-weight of
the pan with filter. Total sediment for the testing period from each stream was measured to
determine which stream(s) contribute the most sediment.
Quality Assurance/Quality Control
Two quality assurance/quality control (QA/QC) protocols were used to ensure the
integrity of the sampling and analysis process. Processing a glass fiber filter with distilled water
was conducted to ensure that reuse of the bottles did not contaminate the results. A sampling
bottle was rinsed and filled with distilled water, and then 50 mL was filtered and processed in the
8
same way the actual samples were treated. I called this processing a “blank” sample, and a total
of three blank samples were processed on 05/20/10.
Three one-liter samples from different collection dates were retained for re-testing
throughout the study period as the second QA/QC measure. The re-test samples were stored in a
refrigerator to prevent microbial breakdown of the contents. Re-testing these samples
throughout this time period would indicate any change in the amount of sediment due to
decomposition based on the length of time between collection and testing. The samples I used
for re-testing were 3B from 09/09/10, 3B from 05/01/10, and 6B from 05/01/10. These samples
were each retested once.
Precipitation Data
Samples were collected during various weather events that were separated into low,
moderate, and high rainfall events. The majority of my precipitation data were obtained from the
Midwest Regional Climate Center. Their record for rainfall on April 16, 2010 was 0 cm, yet I
observed that it was raining that day. The National Oceanic and Atmospheric Administration
(NOAA) website showed a precipitation range of 0.025 – 0.25 cm for that day, and the Weather
Underground website listed precipitation at 0.04 cm (NOAA 2011, Weather Underground 2011).
I used Weather Underground’s rainfall data for April 16, 2010 since I observed it was raining,
and I wanted to use a set amount instead of a range.
Weather Underground is a comprehensive weather information website that operates
more than 42,000 weather stations across the United States (Weather Underground 2011). Two
thousand of those stations are at airports and are overseen by the Federal Aviation
Administration. More than 16,000 of their stations are personal weather stations governed by
stringent quality control measures. The remaining weather stations are included in the
9
Meteorological Assimilation Data Ingest System which is run by the NOAA (Weather
Underground 2012).
Statistical Analysis
I used 0.05 as my alpha for all statistical tests. I conducted the Anderson-Darling and
Kolmogorov-Smirnov tests for normality and both results indicated that my data were not
normally distributed. Means of total sediment (mg/L) contributed by site and standard error
were calculated in Excel. Since I collected replicates at each site on each sampling date (i.e.
Samples A, B, and C), I ranked the mg/L of sediment for each sample and ran a nested ANOVA
to examine any difference in the replicates within each site between Sites 3 through 7. Since
there was no significant difference among the replicates at each site on each sampling date, I
could test for differences between events and sites (Zar 2010). McDowell and Wilcock (2007)
used a two factor ANOVA on season and sample date in their sediment study, and I also chose to
run a two factor ANOVA. Event and site were my factors.
I conducted a Fisher’s LSD post hoc test to find where difference occurred among the
sites. Fisher’s LSD test is preferred by some statisticians because of its consistency (Zar 2010)
and was used in a similar study by Gleason et al. (2003). According to the results of an
Anderson-Darling normality test, the data for both QA/QC measures were normally distributed;
therefore, I ran a paired-samples t test for those samples.
RESULTS
Field Collection of Samples
I collected 189 samples, and the number of samples collected per site is listed in Table 1.
The number of samples per site varies because seasonal low water flow conditions prevented
sample collection at some times.
10
Table 1. Total number of samples
collected from each site.
Number of Samples Per Site
Site
Samples
1
22
2
27
3
36
4
33
5
12
6
35
7
24
Samples were collected during varying rainfall events which were classified into low,
moderate, and high events. Dates I collected samples and their rainfall event classification are
listed in Table 2. I calculated how much sediment in mg/L was contributed by site and rainfall
event which is shown on Table 3. In addition, I calculated the mean amount of sediment
contributed by each site. Figure 3 is a bar graph showing mean sediment contributed by each
stream during the course of the study period.
Table 2. Sampling date, rainfall received on that date, and
weather event classification for that date.
Sample Date
01/27/10
02/21/10
03/08/10
03/11/10
03/25/10
04/16/10
05/01/10
05/10/10
06/08/10
07/08/10
09/09/10
10/21/10
Rainfall (cm)
0
1.70
0
1.91
2.44
0.04
1.60
0.30
0
0.53
0.03
0
11
Weather Event
low
high
low
high
high
moderate
high
moderate
low
moderate
moderate
low
Table 3. Mean sediment load in mg/L by site and
rainfall event.
Mean Sediment (mg/L) by Rainfall Event
Rainfall Event
Site
Low
Moderate
High
1
0.1020
0.1167
0.0276
2
0.0093
0.0253
0.0225
3
0.0388
0.1082
0.0402
4
0.0127
0.1469
0.0372
5
0
0.0207
0.0562
6
0.0098
0.0097
0.0096
7
0.0130
0.0200
0.0111
Mean Sediment (mg/L) by Site
0.09
0.08
Sediment in mg/L
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
Site 1
Site 2
Site 3
Site 4
Site 5
Sampling Site
Site 6
Site 7
Figure 3. Mean amount of sediment in mg/L contributed by each site throughout the study period.
Standard error bars are shown.
Statistical Analysis
Mg/L of sediment was not significantly different among the replicates within each site at
each sampling date (nested ANOVA). I did not consider Sites 1 and 2 in this part of my analysis
12
as they are forks that fed into the stream leading to Site 3, and their entire sediment load does not
necessarily make it to that outlet.
There were no significant differences between the replicates within each site by sampling
date and the data were considered not normally distributed, therefore, I decided it was
appropriate to run a two factor ANOVA on the ranked data on the events and sites. The mg/L of
sediment contributed between the rainfall events was significantly different (two factor ANOVA,
p << 0.001). There was a significant interaction between event and site (two factor ANOVA, p
= 0.001).
Finally, I conducted the Fisher’s Least Significant Difference (LSD) post hoc test to
determine where differences occurred among the sites. Fisher’s LSD test is used to compare
multiple treatment samples in pairs (Meier 2006). There was no significant difference in the
mg/L of sediment between Sites 3, 4, and 5; however, there was a significant difference in mg/L
of sediment contributed between Site 3 and 6, p << 0.001, and between Site 3 and 7, p = 0.002
(Fisher’s LSD). There was no significant difference in sediment loads of Sites 6 and 7, but there
was a significant difference between Sites 3, 4, and 5 collectively and Sites 6 and 7, p < 0.05
(Fisher’s LSD).
Table 4. Relationships among the sites.
Site 3
Site 4
Site 5
Site 6
Site 7
To determine if there was a difference between Site 1 and Site 2, I conducted a two factor
ANOVA on the ranks. There was a significant difference in the mg/L sediment load between
Site 1 and 2 (two-factor ANOVA, p = 0.018). There was no significant difference among the
events and no significant interaction between event and site.
13
The data for the blank samples and the resamples processed as QA/QC protocols were
normally distributed. There was no significant difference between pre-weight and post-weight of
filters for blank samples processed with distilled water (paired-samples t test). Furthermore,
there was no significant difference in the original mg/L of sediment and the resampled mg/L of
sediment in the samples chosen for re-testing (paired-samples t test).
DISCUSSION
Field Collection of Samples
Samples were not taken from each stream on every sampling date. Water flow in Sites 1,
2, 4, 5, and 7 was so low on a few sampling dates that sample collection was not possible. In
addition, Site 5 was sometimes obstructed by large amounts of leaf litter or vegetation.
I obtained my rain data from a few different sources. Most of the data were from the
Midwest Regional Climate Center, but I encountered a problem when they did not record rainfall
on April 16, 2010. I observed that it was raining that day and found precipitation data from
NOAA’s website and from the online weather database, Weather Underground, at
www.Wunderground.com. NOAA’s precipitation data were a range while Weather
Underground listed a specific amount. I expected some of my sampling dates to have received
more rainfall than my sources reported. My goal for the study was to have had higher rainfall
days than I had. Therefore, I would recommend using a weather station on the study site for
future studies so that rainfall is more accurate for the specific study site.
Laboratory
One sample from Site 2 collected on 2/21/10 was removed from the analyses due to an
undetermined error in processing. The sediment post-weight was a negative number, therefore
that filter was eliminated from the statistical analysis. Sample A from site 6 collected on 3/11/10
14
was lost and therefore, there are no data entered for that sample; however, samples B and C were
recorded.
My QA/QC tests in the lab showed that reusing the one-liter plastic bottles did not
contaminate subsequent samples. In addition, the second QA/QC test on the re-samples
indicated there was not a significant change in sediment load due to storage. Therefore, I feel
confident in the integrity of my sample collection and laboratory methods.
While it may be expected for low rain events to carry the least amount of sediment and
higher rainfall events to carry higher loads, my results did not always agree. For example, the
sediment load for Site 7 was higher for low and moderate events than it was for high rainfall
events. This can be explained by considering water velocity and volume during higher rainfall
events. The increased volume of water during a heavy rain can dilute samples and a one liter
sample bottle is filled quickly. While, during lower flow conditions, it takes longer to fill a
sample bottle giving more time for sediment to accumulate and there is less water to dilute the
sample.
As the results indicate there is a significant difference in the amount of sediment
contributed among the sample sites. Sites 3, 4, and 5 contributed the most sediment and are not
different from each other. Sites 6 and 7 contributed the least amount of sediment and are not
different from each other. The mean calculations show that Site 3 carries the highest sediment
load followed by Site 4, 5, 7, and 6. I expected differences as each stream enters the lake from a
different source and empties into various points of the lake and some streams have better erosion
control zones along their banks.
From visual observations alone, one can see that the stream emptying at Site 3 carries a
high amount of sediment. A small island supporting vegetation and a sand bar has developed
15
just a few meters from Site 3. The water in the arm of the lake near Site 3 is shallow enough for
waterfowl, such as ducks and geese, to wade into the lake.
Site 1 contributed significantly more sediment than Site 2 (both of which feed into the
stream emptying at Site 3). This is probably because the north fork stream of Site 1 flows
through a ditch along campus and residential housing along a paved road, whereas the south fork
stream of Site 2 flows through a wooded area lined with grasses and deciduous trees.
Site 4 contributed the most sediment following Site 3. Overflow is diverted underneath
the road from the Culp Park Swamp through a culvert at Site 4. Normally, a wetland such as a
swamp should trap sediment (Blahnik and Day 2000). Water flow through the wetland can
affect the efficiency at which the area acts as a sink for sediment. Higher water velocity or
discharge rates can lead to increased amounts of sediment being carried out of the wetland
(Blahnik and Day 2000). This problem may exist within Culp Park Swamp, where water
velocity may be strong enough to carry suspended solids away from the swamp before they can
settle out. Since my results did show a significant difference during low versus other rain events,
any rainfall may bring high enough water velocity to prevent the swamp from trapping sediment.
Harter and Mitsch (2003) agree that wetlands act as depositional environments for nutrients and
other materials and can facilitate recycling or transport them onto other systems. If the water
flow through the wetland is slow, then the wetland functions as sink (Harter and Mitsch 2003).
Blahnik and Day (2000) suggest studying a wetland of concern under non-flooded conditions to
determine actual mean residence time to determine management strategies for the wetland. In
addition, they recommend use of “physical control structures” to improve the effectiveness of the
wetland.
16
Site 5 carried the next highest sediment load, and again one can see from visual
observations that the littoral zone is wide spanning several meters covered by dense rooted
vegetation. This site is another point where overflow from Lake Cena within Pertle Springs is
diverted via an under-the-road-culvert.
Sites 6 and 7 carried the lowest sediment loads contributing a range of 0.002 – 0.01
mg/L. Both of these sites differ from the rest by flowing through areas covered with more
undisturbed vegetation and not carrying overflow from other aquatic systems. The stream
emptying into Lions Lake at Site 6 is diverted into the lake via an under-the-road-culvert, but the
stream goes through a wooded area. Site 7 is the only stream in which the culvert carrying runoff water is located at an edge of the park several meters from the lake. My sampling point was
closer to the lake to allow for sediment that may settle out in the stream before reaching the lake.
This stream is narrow and relatively deep in some places and is lined with tall grasses and some
trees.
Much of the area around Lions Lake is mowed, and there are few trees lining the banks.
The area around Lake Cena, which has run-off diverted into Lions Lake at Site 5, is also mowed.
Decreasing the width of the riparian zone makes the soils along the banks less stable and causes
erosion to occur (Tiemann 2004). Mowing much of the perimeter around Lake Cena may be
contributing to the higher sediment load being deposited at Site 5 and may also be contributing to
deposition all around Lions Lake.
While sedimentation has been blamed with decreasing the depth of Lions Lake, it can
also have a negative impact on the habitat diversity for aquatic organisms (Tiemann 2004).
Increased amounts of sedimentation may negatively affect the survival of native vegetation, and
higher levels of deposition are seen in agricultural areas and as a result of urban development
17
(Cavalcanti and Lockaby 2006). In addition, sediment deposition can compromise the
decomposition of organic material as it buries and compacts detritus, decreasing surface area and
promoting anoxic conditions (Cavalcanti and Lockaby 2006). Future studies of the area would
benefit by measuring water velocity. Since I did not consider velocity as a part of my study, I
can only speculate that velocity may have affected sediment deposition.
Recommendations
There is little that can be done about the fact that Lions Lake is going to receive run-off
and sediment all along its perimeter, as it is down slope from everything around it; however,
prevention methods can be focused on the three sites contributing the most sediment. One
challenge in planning a successful restoration project is the limited space available for
construction because the lake is surrounded by paved roads and some residential areas. Some
sediment collection methods that could be utilized include allowing the riparian zone to grow up,
installing artificial wetlands, and building Stormwater Detention Basins – Best Management
Practices (SDB – BMP) as discussed by Hogan and Walbridge (2007).
The presence of trees stabilizes the banks of water systems and protects terrestrial areas
against erosion (Sabo et al. 2005). Removal of riparian vegetation creates a source of sediment,
but allowing woody vegetation, including shrubs to grow up along the banks will reduce run-off
(McDowell and Wilcock 2007). Henley et al. (2000) recommended riparian buffer strips to
decrease sedimentation, and Schultz et al. (2004) suggests a graduated riparian design that
incorporates grasses, shrubs, and trees. Riparian buffer strips can be used to remove sediment as
well as other water pollutants, lower water temperatures by providing shade enhancing the
aquatic habitat, and to provide detritus and woody litter to the habitat structure (Schultz et al.
2004). Riparian zones have also been found to have a positive effect on water quality by
18
reducing nutrients, chemicals, and contaminants introduced into the system by agricultural
practices (Anbumozhi et al. 2005, Sabo et al. 2005).
Wetlands have a well documented reputation of functioning effectively at trapping or
slowing sediment and sequestering nutrients or pollutants. They act as sources, sinks, and
recyclers of nutrients and in low water velocity conditions will trap sediment (Harter and Mitsch
2003). Artificial wetlands are designed to utilize biological, chemical and physical systems to
improve water quality (Birch et al. 2006). Blahnik and Day (2000) confirm that wetlands recycle
nutrients and trap suspended particles in wastewater. In addition, wetlands are beneficial as they
prorate the decline of water quality by catching sediment and retaining nutrients (Craft and
Casey 2000).
Birch et al. (2006) conducted a study of a constructed wetland and discovered that trace
metals chromium, copper, lead, nickel, and zinc were efficiently removed from wastewater
within a range of 22% to 65%. In the same study, total phosphorus was removed at a rate of
12%, and between 9% and 46% of suspended solids was removed from water flowing out of the
wetland. While my study did not look at fecal coliform counts in the water, it is worthy to note
that wetlands can be effective in trapping this pollutant as well. In their study site, Birch et al.
(2006) found an average removal efficiency rate of 76% of fecal coliform counts during high
water flow events.
Stormwater detention basins are used to catch high stormwater flows, and SDB-BMP’s
are constructed considering topography and wetland plant species to retain nutrients and
sediment (Hogan and Walbridge 2007). These basins can provide the same services expected
from wetlands such as water quality improvement and biodiversity cultivation. By considering
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the area’s topography when designing the SDB-BMP, water velocity is decreased and run-off is
spread across the whole basin to better trap sediment (Hogan and Walbridge 2007).
The stream at Site 1 runs along a residential area and a paved road and there is little if
any space to build up a riparian buffer zone. Collection devices could be installed, but they
would have to be maintained on a regular basis. The riparian zone along Site 2 appears to be
effective at trapping or at least slowing sediment down enough that it is not a stream of concern.
It may be more effective to center preventive measures at the mouth of the tributary streams
where they enter the lake. Site 3 practically has a wetland forming on its arm of the lake as it is,
and that site is receiving the highest sediment load of all the sites. If a small wetland were
constructed on that arm, then sediment could be trapped closer to the banks and kept from
settling out further into the lake.
A prevention measure should be installed near Sites 4 and 5, and the area that is mowed
could be reduced. It may be effective to allow the riparian zone along the banks on either side of
Site 4 to grow up and to plant additional shrubs and native grasses. An SDB-BMP is another
option for the land area between the street and the bank on either side of Site 4. If high water
velocity is preventing Culp Swamp from trapping sediment, then a basin could be effective in
slowing the water and become a depositional environment for the sediment. The area near the
culvert at Site 5 is already developing wetland characteristics with the hydrophytic vegetation
present. If a wetland was constructed in that corner of the lake, then less sediment would be
washed out further into the lake. Sites 3, 4, and 5 are all along the east side of the lake and a
combination of artificial wetlands, an SDB-BMP, and/or an enhanced riparian buffer zone could
be very effective at trapping sediment and recycling nutrients.
20
Mitigating the sediment load carried into the lake will contribute to long term success of
the City’s planned restoration project for Lions Lake. It will benefit the park as a terrestrial and
aquatic habitat by increasing biodiversity. The lake will support a healthier fish population as
the water depth is not threatened by a rapid rate of sedimentation which will allow members of
the community to enjoy recreational fishing. Restoration is a tribute to this historic park, and
mitigation will help protect the city’s investment while maintaining a beautiful recreational area
for its citizens.
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