Sunshine Lake/Sunrise Waterway Study · 2016-09-06 · Sunshine Lake Study Atkins Final Report April 2012 6 1. Introduction 1.1. Background The Sunshine Lake/Sunrise Waterway system,

Sunshine Lake/Sunrise Waterway Study Charlotte County

April 2012

Sunshine Lake Study

Atkins Final Report April 2012

Table of contents Chapter Pages

Executive Summary 4

1. Introduction 6 1.1. Background 6

2. Data Gathering – Methods and Results 11 2.1. Initial Data Gathering - Methods 11 2.2. Initial Data Gathering – Methods and Results 12

3. Management of Sunshine Lake 24 3.1. Potential Techniques 24

4. Literature Cited 30

Tables Table 1. Summary of water quality data from Sunshine Lake. 20 Table 2. Chemical analyses of agal mat (taken at mid water column).

Values as percent dry weight. 20 Table 3. Various weight measures of the algal mat (taken at mid water column). 20 Table 4. Sediment grain size analyses. 21

Figures Figure 1. Sunshine Lake and its approximate watershed. 6 Figure 2. Aerial photo of present position of Sunshine Lake (outline in yellow)

overlaid on the same area in the 1940s. 7 Figure 3. Aerial photo of Sunshine Lake (outline in yellow) from the 1970s. 7 Figure 4. Color aerial photo of Sunshine Lake/Sunrise Waterway system from 2006. The green color

of the lake indicates that water quality issues might have existed in 2006. 8 Figure 5. Color aerial photo of Sunshine Lake/Sunrise Waterway system from 2011. The green color

of the lake indicates that water quality issues existed in 2011. 8 Figure 6. Photo of Sunshine Lake looking north from Gertrude Avenue along

McGuire Park from October 2010. 9 Figure 7. Similar photo from January 2012 of the same portion of the southern

end of Sunshine Lake as shown above. 9 Figure 8. Photo of Sunshine Lake from January 2012. 10 Figure 9. Photo of Sunrise Water taken in mid 2010. 10 Figure 10. Sunshine Lake study area showing initial sampling locations. 12 Figure 11. Approximate boundary of the watershed of Sunshine Lake. 13 Figure 12. History of recent County works within the Sunshine Lake/Sunrise

Waterway Watershed. 14 Figure 13. Photograph of lake levels, weep holes in seawall, and two potential water lines. 15 Figure 14. Illustration of condition suggestive of lowered lake levels. 16 Figure 15. Photograph of grassy swale stormwater conveyance system

along Aaron Street on the east side of Sunshine Lake. 16

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Atkins Final Report April 2012

Figure 16. Location of septic tank systems (purple dots) in Port Charlotte with circle centered on Sunshine Lake (data from FDEP). 17

Figure 17. Location of sewage collection and conveyance infrastructure in the vicinity of Sunshine Lake (data from Charlotte County). 18

Figure 18. Photograph from northeast corner of intersection of Indiana Avenue and Elkcam Boulevard, looking to west. Lift station is in foreground. Entrance to stormwater pipe that discharges to Sunshine Lake is visible as concrete outlined metal grate located in the grassy swale between the sidewalk and Elkcam Boulevard. 19

Figure 19. Thickness (feet) of algal mat within Sunshine Lake. 22 Appendix A This appendix contains photographs of the Sunshine Lake / Sunrise Waterway system depicting

the extent of the algae bloom. Appendix B The second appendix presents, in a full page format, selected graphics from the report as well

as additional supporting figures.

Executive Summary The primary focus of the Sunshine Lake/Sunrise Waterway Study was to ascertain the potential cause(s) of the existing and persistent algal blooms, to assess the potential factors that may have initiated and exacerbated the ongoing degradation of water quality in the system, and then to recommend appropriate restoration activities, directed toward restoring and enhancing water quality. The following summarizes the existing condition. Relatively older, highly urbanized watershed: Sunshine Lake‟s immediate watershed is characterized by

a relatively older highly urbanized mixture of single family and multi-family homes. While the immediate watershed of the Sunshine Lake/Sunrise Waterway system has central sewer, most of the surrounding urban area is serviced by on-site sewage disposal system (i.e., septic tanks). Stormwater conveyances draining to the lake are primarily characterized by grassy swales, which correspond well with current suggested Best Management Practices (BMPs) for stormwater treatment.

Part of larger surface water system: The Sunshine Lake/Sunrise Waterway system appears to have been part of a larger natural feature that was incorporated into the planned overall surface water/master drainage management system for Port Charlotte. The system is one of the oldest in the area, and unlike many of the other major canal systems in Port Charlotte, it does not include a drop structure on the north side of US 41. A number of stakeholders believe that long-term seasonal dry-season water levels in the system have declined. Without accurate records of stage elevations it is difficult to determine the relative influences of what has been a series of unusually warm/dry periods that have characterized normal dry-season rainfall patterns since 2006, and various stormwater conveyance projects recently (2010) undertaken by the County.

Past water quality of the lake was better: Based on anecdotal evidence and observations by long-term resident stakeholders, the evidence suggests that water quality within the system was good for decades and did not begin to seriously degrade until relatively recently.

Recent highly noticeable algal problem: Local residents seem to have noticed the algae problem as early as 2007 to 2009, with conditions progressively worsening over time. Currently, the main algal problem is focused in Sunshine Lake where the algal mat is growing from the bottom, up toward the surface. Measurements made in January 2012 found the algal mat in Sunshine Lake varied from 2 to 6 feet in depth, occupying more than 50% of the lake‟s volume. Observations indicate the same growth of a similar extensive algal mat along the bottom of Sunrise Waterway, with the greatest concentration just downstream of the Gertrude Avenue culvert. Microscopic examination indicated the algal mat to be dominated by a number of blue-green algal (cyanobacteria) species. Under certain conditions some cyanobacteria produce toxins (cyanotoxins) which can produce a wide variety of symptoms depending on exposure. Eye and breathing irrigation can be associated with volatilization of these compounds, while direct skin contact can cause itching and rashes. Both these conditions have been reported by local residents.

This study recommends undertaking the development of a Water Quality Management Plan (WQMP) incorporating a number of elements that have previously been found to be effective in other hypereutrophic (severely nutrient-enriched) Florida lakes. Generally, the types of projects that have had the greatest success, in terms of restoration of water quality, have been those that focused on removing point sources of nutrient pollution, combined with actions to reduce the impacts of past nutrient loading events. Simply treating the symptoms (killing the algae) has generally proven to be both difficult and ineffective without continued high levels of ongoing treatment. The study recommendations include the following series of actions, which should be implemented in sequence.

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Atkins Final Report April 2012 5

Specific focused studies to identify nutrient sources: Calculations of the existing load of nutrients contained and currently recycling within the Sunshine Lake system suggest that it is highly unlikely that the current nutrient load within the lake has been primarily derived from surface stormwater inputs. The surrounding grassy swale conveyances should provide enhanced sediment and nutrient removal. The most likely other source is groundwater and/or sewage collection systems. A time-limited and focused study on nutrient levels in up-gradient surficial groundwater could help identify and potentially reduce or eliminate potential sources. Depending on the number and depth of surficial groundwater wells selected as well as the study design, such a study might be expected to cost between $40,000 and $80,000.

Sediment/algal biomass removal or inactivation: This study evaluated the effectiveness and costs of a number of sediment/muck removal projects for lakes in Florida, and developed comparative cost estimates. Potential algal biomass removal efforts should also include removal (not chemical treatment) of the Cattails (Typha sp.) that have begun to establish along the banks of both the lake and waterway. Depending on the method chosen and economic conditions, estimates are that such an effort might cost between $500,000 and $1,000,000.

Enhanced circulation/aeration: Improved water quality via artificial circulation/aeration may be applicable to maintain improved water quality in Sunshine Lake once the sources of nutrient inputs are addressed, and the existing algae biomass is removed. Typically this is accomplished using aeration pumps to provide enhanced vertical and horizontal circulation. These types of projects typically produce higher levels of dissolved oxygen, reduced quantities of dissolved phosphorus, and reduced concentrations of ammonia and hydrogen sulphide, while simultaneously reducing phytoplankton productivity through net transportation of phytoplankton to deeper, and thus darker, parts of the lake‟s water column. Depending on the selected number of units and design, the setup costs for such a system for the Sunshine Lake/Sunrise Waterway system is expect to cost between $50,000 and $100,000.

Modification of lake levels: Experience indicates that seasonally lowered lake levels generally appear to increase the susceptibility of lakes to algal blooms as a result of nutrient enrichment. There is a general impression among the Sunshine Lake/Sunrise Waterway stakeholders that for at least the dry-season (and possibly other times of the year as well) water levels have declined over time. The following two suggestions could be implemented at relatively moderate costs. 1. A relatively inexpensive structure could be constructed to raise the invert level (elevation of the

bottom of the pipe) at the large culvert at the Tamiami Trail frontage road. This could retain additional water (especially in Sunrise Waterway) in the system during the normal dry-season, and could potentially lessen algal growth enhanced due to seasonal lowering of water levels.

2. In the absence of being able to increase lake water levels in the Sunshine Lake/Sunrise Waterway

system, or perhaps in combination with such a project, the addition of a non-potable well to maintain lake levels in the dry-season should be investigated. A well less than 6” in diameter, with a flow rate of less than 100,000 gallons per day could be relatively inexpensive to permit and install. Such a well could produce a volume of water that would offset lake losses due to evaporation during the dry-season months, thus reducing the lake‟s susceptibility to algal blooms during this time of the year.

The presented cost are provided as planning tools estimating what might be expected to be the relative

costs based on other similar efforts. They do not include costs or time estimates for the permitting that will be required for each of the described mitigation efforts. These could be highly variable depending for example on what alternative dredging method might be selected and/or if the County might chose to handle elements of the necessary permitting in-house.

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1. Introduction 1.1. Background The Sunshine Lake/Sunrise Waterway system, in Charlotte County, has over the past number of years experienced extensive and persistent algal blooms (public comments at stakeholders meeting, 2/16/2012). The lake itself is approximately 8.5 acres in size, while the Sunrise Waterway‟s open water is approximately 3.7 acres in size. The watershed (land that drains into the open waters) of the combined Sunshine Lake and Sunrise Waterway is approximately 297 acres (Figure 1).

Figure 1. Sunshine Lake and its approximate watershed.

Sunshine Lake is a man-made water body, which was constructed out of a landscape of mostly pine flatwoods uplands and some wetlands (Figure 2). There is an indication of the prior existence of a potential small open-water feature in the far northwest portion of the present day lake, but nothing as extensive as the current lake‟s boundaries. The lake‟s watershed had been substantially developed by the 1970s (Figure 3).

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Figure 2. Aerial photo of present position of Sunshine Lake (outline in yellow) overlaid on the same area in the 1940s.

Figure 3. Aerial photo of Sunshine Lake (outline in yellow) from the 1970s.

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Figure 4. Color aerial photo of Sunshine Lake/Sunrise Waterway system from 2006. The green color of the lake indicates that water quality issues might have existed in 2006.

Figure 5. Color aerial photo of Sunshine Lake/Sunrise Waterway system from 2011. The green color of the lake indicates that water quality issues existed in 2011.

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Earlier photos received from the public, when compared to current conditions, indicate that the ongoing extensive algal blooms present throughout the lake/waterway system have been present since at least mid 2009 (Figures 4 and 5). Figures 6 to 8 illustrate the widespread and obvious manifestations of the algal bloom throughout both Sunshine Lake and the Sunrise Waterway.

Figure 6. Photo of Sunshine Lake looking north from Gertrude Avenue along McGuire Park from October 2010.

Figure 7. Similar photo from January 2012 of the same portion of the southern end of Sunshine Lake as shown above.

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Figure 8. Photo of Sunshine Lake from January 2012.

Prior to the current extensive blue-green algal bloom both within Sunshine Lake and the downstream Sunrise Waterway, there is evidence of growth (bloom) within Sunrise Waterway of a type of green algae (Chlorophyta) that looks like a vascular plant (identified as Chara sp. by a local resident; Figure 9).

Figure 9. Photo of Sunrise Water taken in mid 2010.

Based on earlier photos and public comments received at the February 2012 public meeting, as well as personal comments received from local residents, it appears that sometime in the past few years, perhaps in

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2009 or earlier, Sunshine Lake changed from being a relatively healthy lake with good water clarity and a mostly sandy bottom to a green lake, with noxious odors and deep mucky sediments. This rapid degradation suggests that a number of serious insults might have occurred relatively recently, rather than the gradual and slow degradation that is often seen in other highly eutrophic lakes. Evidence strongly suggests that algal blooms began and intensified in Sunshine Lake, and have more recently extended south of Gertrude Avenue.

This report focuses on the collection of water and sediment quality data from Sunshine Lake, an assessment of the likely cause(s) of the observed ecological problems, a proposed course of action and a preliminary cost estimate of activities that could be perused to restore the health of both Sunshine Lake and the Sunrise Waterway.

2. Data Gathering – Methods and Results

2.1. Initial Data Gathering - Methods A series of initial data gathering efforts were undertaken to assess the potential causes of water quality changes and algal/macrophyte development in Sunshine Lake. These efforts included:

Developing an approximate GIS based delineation of the Lake‟s watershed Gathering existing information showing stormwater conveyance routes, characteristics of the stormwater

conveyance system, sewer lines, etc. in the Sunshine Lake watershed Developing a timeline and summary of County‟s infrastructure activities and efforts in the watershed Determining local and regional patterns of both sewer and in-ground septic systems Collection and analyses of water quality samples

pH specific conductance water temperature dissolved oxygen total suspended solids total nitrogen total phosphorus chlorophyll-a

Collection and analyses of lake sediment samples sediment grain size percent organic total nitrogen total phosphorus

Based on preliminary field work, it was determined that Sunshine Lake appears to be “filling in” from the bottom with a thick mixture of various types of blue-green algae (scientifically known as cyanobacteria). Field work and GIS-based methods were used to map the contours of the lake bottom, and to develop an estimate of the spatial distribution and overall volume of the amount of algae within the lake. Nearly 400 locations were chosen at random throughout the lake and the upper portion of the waterway system. The depth between the surface of the lake and the top of the algal mass was recorded, and then the overall depth of the water was measured by pushing a pole through the algal mass until it reached the bottom sediments of the lake. These sediments were found to be mostly hard sand with little if any indication of organic material.

The locations of the sites where water quality and sediment quality samples were taken (not the 400 locations for algal mat thickness) are shown in Figure 10.

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Figure 10. Sunshine Lake study area showing initial sampling locations.

2.2. Initial Data Gathering – Methods and Results

2.2.1. Watershed Characteristics

2.2.1.1. Watershed size, influences on lake levels, and stormwater conveyance

Based on watershed maps, Graphical Information System (GIS) layers, and other data provided by the County, a map was created that shows both the lake/waterway system itself, as well as an estimate of the size of its watershed. These are illustrated in Figure 11.

Sunshine Lake appears to be approximately 8.5 acres in size, and the Sunrise Waterway is approximately 3.7 acres in size. The size of the watershed of both Sunshine Lake and the Sunrise Water is approximately 297 acres.

The seasonal low water level in Sunshine Lake proper is proximately controlled by the invert (bottom of the pipe) elevation at its southernmost boundary at Gertrude Avenue. Below Gertrude Avenue, Sunrise Waterway is up to 80 feet in width that takes outflows from Sunshine Lake (when they occur) approximately 2,000 feet to the south, where the canal flows under US 41. There are drainage pipes with inverts located at both the access roads for North Tamiami Trail and US 41. In April 2010 Charlotte County installed a rip-rap ditch block just south of the large culvert on the Tamiami Trail access road that, combined with the invert of the culvert, likely controls water levels within the Sunrise Waterway south of US 41. Streamside vegetation (i.e., mangroves) suggests that the waterway is brackish to marine. North of US 41, the streamside vegetation is more consistent with a freshwater environment.

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Figure 11. Approximate boundary of the watershed of Sunshine Lake.

The inverts of the large drainage pipes under and south of US 41 are sufficiently high that normal high tides do not bring saltwater into the pipes. Field observations this spring under the combination of very high tides and strong south winds indicated that even under these conditions saltwater does not normally extend upstream of US 41.

The invert (bottom elevation) for the drainage pipe at Gertrude Avenue is the likely factor controlling the elevation of Sunshine Lake under dry-season conditions. Thus, any activities that might alter the invert could be responsible for either raising or lowering the lake level. Alternatively, activities that may have altered the elevation of the bottom of the drainage ditch downstream of the Tamiami Trail frontage road could also have changed levels in Sunrise Waterway during the driest times of the year.

Figure 12 summarizes the location and timeline for major modifications of the locations that have the potential to have modified lake levels via changing the bottom elevation of drainage features below the outfall of Sunshine Lake.

Based on information provided by Charlotte County staff, there were a number of activities that took place in the year 2010 that could have potentially influenced water levels via either raising or lowering bottom elevations in various locations within the Sunshine Lake/Sunrise Waterway system. At Gertrude Avenue, the

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pipes underneath the road were lined in June of 2010, while a nearby boat ramp used for pest management (i.e., mosquito control/aquatic weed control) was modified in September of 2010. Farther downstream, that portion of the canal at the access road for North Tamiami Trail underwent channel maintenance via debris clearing in January of 2010, and the pipes under the road at that location were lined in June of 2010. Between that access road and US 41, a water elevation control structure was installed in April of 2010. In that same month, work was conducted on some of the pipes near the US 41 crossing.

Figure 12. History of recent County works within the Sunshine Lake/Sunrise Waterway Watershed.

Photographs (Figures 6 through 8) suggest that a substantial, persistent algal bloom was present within Sunshine Lake as early as 2009. There is some evidence that lake levels might have been lowered from previous elevations, based on photographs such as that in Figure 13. However, without long-term records of actual measurements of water levels within the system it is difficult to determine whether the waterlines shown in Figure 13 represent normal seasonal fluctuations between wetter and drier periods (as some residents believe) or rather reflect systematic changes due to changes in control elevations (as expressed by other stakeholders).

During meetings with stakeholders a number of homeowners stated that they were originally told by General Development Corporation sales representatives that Sunshine Lake was fed by one or more springs, which

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was responsible for the lake‟s historically clear conditions. Tampa USGS staff were contacted to determine if any records could be found to substantiate the historic presence of a spring in the area. No evidence of a spring was found, and Figure 2 does not indicate any such major feature. Another possibility is that there may have been an old artesian agricultural well in the area of the lake. There is at least one such well that was “cut off” during the construction of Cocoplum Waterway. Observations of changes in discharge observed between December and April suggest that if there were any such historic flows of spring or other flows into the system, water levels are now predominantly controlled by groundwater levels, which would be expected to decline substantially in the dry-season. This is particularly important, since the Port Charlotte canal systems were designed to lower groundwater levels, and southwest Florida has experienced a long-term series of extended unusually dry periods since 2006 (Atkins 2012).

Figure 13 is a photograph of Sunshine Lake showing apparent water lines. Based on a predicted size of the seawall weep holes of 2 inches in diameter, the presence of different waterlines (i.e., stain marks) suggest that lake levels had been perhaps 16 to 24 inches higher in the past than current levels. However, it is not known when the stain lines were formed (i.e., what year(s)) nor is it known if the stain lines are formed by water levels in the wet-season or whether they are indicative of higher water levels in the dry-season.

Figure 13. Photograph of lake levels, weep holes in seawall, and two potential water lines.

It has been noted by Atkins staff that the existing blue-green algae mat within Sunshine Lake is forming on the bottom and filling the lake from the bottom up. This leads to the possibility that the water levels in both the lake and waterway may appear to be lowering through the water level dropping down to a constant lake bottom, when perhaps the actual phenomenon is primarily that the lake bottom is rising up to a potentially seasonally fluctuating water level (Figure 14).

In the absence of a record of gaged lake levels, it is not clear whether or not Sunshine Lake is lower now than in the past, or if it is lower, whether lake levels are lower in the wet-season, the dry-season, or both.

The major land use within the Sunshine Lake watershed is residential, which has been found capable of producing significant nutrient loads to receiving water bodies in prior studies (i.e., Heyl 1992). However, most of the stormwater conveyance system throughout the watershed appears to be via grassy swales, which have been shown to reduce the quantity or stormwater runoff, and also to reduce the concentrations of nutrients and suspended materials (i.e., PBS&J 2010 a). Regional inflows of stormwater runoff into Sunshine Lake occur mostly via inflows from grassy swales (e.g., Figure 15) which act as a type of Best Management Practice (BMP) for stormwater treatment in developed landscapes.

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Figure 14. Illustration of condition suggestive of lowered lake levels.

Figure 15. Photograph of grassy swale stormwater conveyance system along Aaron Street on the east side of Sunshine Lake.

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Even in locations where stormwater is routed through pipes prior to discharge into the lake, such as the stormwater pipe that collects runoff at the northwest corner of Indiana Avenue and Elkcam Boulevard (south of the tennis courts), the runoff that enters into the pipe was first “treated” through the BMP of grassy swales. Stormwater runoff into Sunshine Lake is most likely lower in nutrients and suspended materials than would be the case if most runoff was routed to the lake via curbs and gutters and direct discharge via pipes.

2.2.1.2. Wastewater disposal practices within the watershed

Based on data provided by FDEP and Charlotte County, it would appear that there are no septic tanks within the immediate watershed of Sunshine Lake (Figure 16).

Figure 16. Location of septic tank systems (purple dots) in Port Charlotte with circle centered on Sunshine Lake (data from FDEP).

Instead, the proximate watershed of Sunshine Lake appears to be completely sewered, with an infrastructure of distribution lines, sanitary sewer manholes and lift stations located west, north and south of the lake (Figure 17). Groundwater in southwest Florida generally tends to move toward the southwest. Thus, while the large portion of Charlotte County outside the immediate area surrounding Sunshine Lake is serviced by

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on-site disposal systems (ODS), the majority of any high nutrient groundwater coming from such systems would be expected to be intercepted by either the Elkcam Waterway (which runs to the east) or the Morningstar Waterway (which runs to the north and west).

Figure 17. Location of sewage collection and conveyance infrastructure in the vicinity of Sunshine Lake (data from Charlotte County).

There is a lift station for the regional sewerage collection system located at the corner of Indiana Avenue and Elkcam Boulevard, which members of the public have identified as having had problems with overflows at times (Figure 18). This lift station is located uphill and approximately 30 feet from an inflow to a stormwater drainage pipe that flows eastward for approximately 250 feet and then discharges into Sunshine Lake southeast of the south-eastern corner of the tennis courts.

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Figure 18. Photograph from northeast corner of intersection of Indiana Avenue and Elkcam Boulevard, looking to west. Lift station is in foreground. Entrance to stormwater pipe that discharges to Sunshine Lake is visible as concrete outlined metal grate located in the grassy swale between the sidewalk and Elkcam Boulevard.

If overflows at the lift station were to have occurred, there is a simple pathway for such overflows, and the nutrient loads they would represent, to be conveyed directly to Sunshine Lake.

2.2.1.3. Collection and analysis of water quality and algal composition samples

Water quality and algal composition results are shown in Tables 1 through 3. Overall, results indicate low levels of dissolved nutrients (both nitrogen and phosphorus) within the water column. However, this does not necessarily mean that nutrient loads to the lake are low, as it is more likely that nutrients brought into the lake would be taken up by the algal biomass, rather than being within the water of the lake.

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Table 1. Summary of water quality data from Sunshine Lake.

Station Conductivity

(us/cm) pH

(SU)

Dissolved Oxygen (mg/l)

Color (PCU)

Total Suspended

Solids (mg/l)

Nitrite+ Nitrate

Nitrogen (mg/l)

Total Kjeldahl Nitrogen

(mg/l)

Total Nitrogen

(mg/l)

Ortho- Phosphorus

(mg/l)

Total Phosphorus

(mg/l)

Chlorophyll a

(mg/m3)

1 333 8.47 11.81 10 1.0 0.004* 0.593 0.593 0.014 0.022 1.38

2 305 8.84 12.11 7.5 0.57* 0.006 0.559 0.565 0.010 0.019 0.870

3 307 9.00 12.34 7.5 1.0 0.004* 0.559 0.559 0.013 0.019 0.830

4 306 8.93 12.06 7.6 0.57* 0.004* 0.609 0.609 0.013 0.019 0.600

* Method Detection Limit (MDL)

The water quality results presented above would meet the State of Florida‟s recently adopted Numeric Water Quality Criteria for freshwater body, exhibiting nutrients (nitrogen and phosphorus) and chlorophyll a below the EPA established criteria (although EPA criteria are established on a geometric mean rather than a single sample). High dissolved oxygen values reflect the results of photosynthesis in the blue-green algal mat, while the relatively high observed pH values probably indicate that the algae have removed significant amounts of the available carbon dioxide.

Table 2. Chemical analyses of agal mat (taken at mid water column). Values as percent dry weight.

Sampling Site

Nitrite+Nitrate Nitrogen

Total Kjeldahl Nitrogen

Total Nitrogen Orthophosphorus

Total Phosphorus as

P 1 0.00061 0.459 0.459 0.00049 0.106

2 0.00087 0.548 0.548 0.00007 0.109

3 0.00068 0.298 0.298 0.00031 0.146

4 0,00058 0.426 0.426 0.00103 0.117

Table 3. Various weight measures of the algal mat (taken at mid water column).

Sampling Site

Percent of Weight Pounds per Cubic Foot Dry Weight Wet Weight Dry Weight Wet Weight

1 13.6 49.9 7.68 28.1 2 33.7 38.6 19.5 22.3 3 22.0 43.4 12.7 25.1 4 36.5 61.0 21.1 35.3

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2.2.1.4. Collection and analysis of sediment quality samples

Results of the sediment (not algal mass) characterization efforts are shown in Table 4.

Table 4. Sediment grain size analyses.

U.S. Standard Sieve Sizes

Sample Site #1 Sample Site #2 Sample Site #3 Sample Site #4

Percent of Sediment Passing Through Each Sieve Size

3/8 inch 100% 100% 100% 100%

#4 97.9% 98.8% 100% 100%

#10 86.9% 96.2% 100% 100%

#20 75.4% 92.8% 99.4% 99.1%

#40 57.3% 78.6% 93.2% 95.3%

#60 26.5% 21.7% 55.4% 76.1%

#100 14.5% 4.8% 26.6% 53.0%

#140 12.3% 2.0% 18.0% 40.0%

#200 8.8% 1.0% 10.3% 31.3%

Percent Organic Material in Sample 0.3% 0.3% 0.7% 0.8%

Sediment Description Based on Grain Size

Light Grey to Tan Slightly Silty Fine Sand with Shell Fragments

Light Grey to Tan Slightly Silty Fine Sand with Shell Fragments

Grey to Tan Silty Fine Sand

Grey to Tan Silty Fine Sand

Although not actually “sediments,” the algae within Sunshine Lake was the focus of a series of assessments meant to quantify the amount of algae within the lake, and to determine the amount of the nutrients nitrogen and phosphorus that are contained within that biomass.

Figure 19 illustrates the spatial extent and height of the algal biomass within Sunshine Lake. The algal mat is thickest in the north-eastern corner of the lake, but this is also the deepest part of Sunshine Lake (data not shown). In general, the algal mass within Sunshine Lake ranges between two and six feet in depth, depending upon the depth of the lake. In most areas, the algae either grows to the very surface of the lake (see photos attached in Appendix A) or a layer of very clear water exists on top of the algal layer. Typically, this layer of very clear water is not more than a foot in depth (see water quality data in Table 1).

Using the information shown in Figure 19, an estimate of the amount of algal biomass within Sunshine Lake was conducted using averaging methods in GIS. This estimate, 740,000 cubic feet of algae is for the lake itself. The scope of work and budget for this effort did not allow for an equally rigorous estimate of the amount of algae within Sunrise Waterway (down to US 41). However, an estimate can be derived using a few assumptions.

If one assumes that Sunrise Waterway is similar in its cross section to that portion of Sunshine Lake just north of Gertrude Avenue, then algal biomass might be five feet deep in the deepest portions, but only one or two feet along the channel banks. Assuming an average depth of three feet, the average depth can then be

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Figure 19. Thickness (feet) of algal mat within Sunshine Lake.

multiplied by the average channel width (ca. 80 feet) and length (ca. 2,000 feet) to produce an estimated 480,000 cubic feet of algae within Sunrise Waterway, between Gertrude Avenue and US 41. In total, there

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would appear to be approximately 1,220,000 cubic feet of algae within both Sunshine Lake and Sunrise Waterway down to US 41.

Assuming that algal problems first occurred in Sunshine Lake, and then spread to downstream waters, an assessment was made to determine the amount of nutrients that could be contained within the algal biomass. The algae bloom itself is mostly comprised of a mixture of various forms of blue-green algae (cyanobacteria) as identified by Dr. Ralph Montgomery. Typically, freshwater systems that have become overwhelmed with algae drift towards being dominated by blue-green algae, which out-compete other types of plants in nutrient-rich environments (i.e., Canfield et al. 1989, Downing et al. 2001). In freshwater systems dominated by blue-green algae, the presumption often made is that phosphorus, rather than nitrogen, is the nutrient most likely to be limiting to algal biomass (Smith 1983) which has shown to be true in Lake Hancock, the most polluted large lake in Florida (Tomasko et al. 2009). For these reasons, the amount of algae within Sunshine Lake “proper” (i.e., the area north of Gertrude Avenue) was used to determine the amount of phosphorus that would be required to account for the bloom.

2.2.1.5. Phosphorus and nitrogen quantity within algal biomass in Sunshine Lake

Using GIS-based analyses, the amount of algae within Sunshine Lake was estimated at 740,434 cubic feet. Laboratory determinations of density of the algae averaged 15.25 pounds of dry weight of algae per cubic foot. Combined, these two values give rise to an estimate of 11,287,921 pounds (dry weight) of algae within Sunshine Lake. Converting from pounds to kilograms, there is an estimated 5,120,115 kg (dry weight) of algae within Sunshine Lake.

Based on laboratory results of the average phosphorus content of the algae (0.119 percent of dry wt.) there is an estimated 6,119 kg of phosphorus within the algal biomass of Sunshine Lake. Based on the average nitrogen content of the algae (0.432 percent of dry wt.) there is an estimated 22,157 kg of nitrogen within the algal biomass of Sunshine Lake

To determine the potential impacts of various types of human activities, the ability of activities to produce 6,119 kg of phosphorus and 22,157 kg of nitrogen was examined.

2.2.1.6. Phosphorus and nitrogen loading estimates of various activities

Based on an assessment of the stormwater conveyance systems (i.e., Figure 17), it was determined that the majority of the Sunshine Lake watershed had BMP-type stormwater treatment already in place, and nutrient loads would likely be much lower than expected from a watershed with curb, gutter and drainage pipe conveyance systems (i.e., PBS&J 2010 a). It seems unlikely that the estimated 6,119 kg of phosphorus or 22,157 kg of nitrogen required to account for the algal bloom could have come from stormwater runoff alone.

Wastewater typically has much higher concentrations of phosphorus than stormwater runoff (e.g., Heyl; 1992) and thus the quantity of wastewater that would have been required to account for the algal bloom was estimated.

Assuming an average total phosphorus (TP) and total nitrogen (TN) content of untreated sewage of 15 mg TP / liter and 40 mg TN / liter (Heyl 1992), it would take approximately 400,000,000 to 500,000,000 liters of raw sewage to account for the phosphorus and nitrogen contents within the algal bloom. Converting to gallons, this would mean that between 100 and 150 million gallons of sewage would be required to account for the phosphorus and nitrogen contents within the algal bloom.

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While it is possible that instances of unintended discharges might have occurred at the lift station at the intersection of Indiana Avenue and Elkcam Boulevard, and for overflows at this location to be brought to the lake via the stormwater conveyance system located approximately 30 feet away, it is nearly impossible for the totality of all potential incidents to have brought in excess 100 million gallons of sewage into Sunshine Lake. The volume of wastewater required greatly exceeds any reasonable estimate of the potential loads from such loads.

However, 100 to 150 million gallons of sewage could have been loaded into the lake over time if, for example, the nutrient content of 50% of the effluent produced by 200 to 300 houses had accumulated in the lake over the course of 10 to 20 years. While this estimate is highly speculative, its merit is that it suggests that a single event, or a series of single events, are not likely to be the basis for loading Sunshine Lake with the amount of sewage-derived nutrients required to account for the algal bloom. The only possible explanation that the authors can realistically envision to account for the phosphorus amount in Sunshine Lake would be there was widespread leakage of phosphorus from the collection and delivery system of sewage treatment from hundreds of homes.

It is not known whether the sewage collection, delivery and treatment system in this portion of the City of Port Charlotte could have had as many “leaks” to account for such a volume of untreated sewage entering into Sunshine Lake. If that were the case ,Charlotte County Utilities has informed Atkins that the sewage distribution system throughout the Sunshine Lake watershed has been re-lined in recent years; if such widespread leakage could have been a cause of nutrient loads to the lake, it appears that this source has now been acted upon. A number of residents within the watershed have commented that they have either had to replace the piping connecting their homes to the central sewer system, or that surface areas of their yards indicate potential collapses in their piping. Again, no attempt was made in this study to determine if these observations reflect isolated events or reflect a wider issue with older elements of the central sewer system.

3. Management of Sunshine Lake 3.1. Potential Techniques

Prior studies in Florida have focused on the development of lake management plans for hypereutrophic (severely nutrient-enriched) lakes. For the City of Winter Haven, PBS&J (2010 b) determined that the types of projects that have had the greatest success, in terms of restoration of water quality, have been those that focused on removing point sources of nutrient pollution, as well as activities that sought to reduce the impacts of past nutrient loading events. Past nutrient loading impacts can often continue to harm the ecology of lakes, even if those loads have been successfully acted upon to minimize or cease. For the City of Winter Haven‟s Chain of Lakes complex, it was recommended that activities that removed or sequestered sediment nutrient pools were necessary to recover lost ecosystem functions, while large-scale stormwater retrofits had very little evidence of being a successful lake restoration technique (PBS&J 2010 b). A third technique, that of artificially increasing whole-lake circulation, was also encouraged for some of the smaller lakes in the Winter Haven Chain of Lakes (PBS&J 2010 b).

In Lake Hancock, widely considered to be the most polluted large-lake in Florida, the only two activities that had a reasonable chance of improving water quality were removing or sequestering the nutrient content of bottom sediments, and increasing the lake‟s water level via modification of the outfall structure (Tomasko et al. 2009).

These three project types, removal of the nutrient-rich algal biomass, increased water levels, and increased circulation, are discussed in greater detail below.

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3.1.1. Sediment/algal biomass removal or inactivation

Cost estimates were developed based on previous studies completed within Florida and the continental United States. Inflation conversions were completed to update previously generated cost estimates from 2001. For example, $1.00 in 2001 had the same buying power as $1.27 in 2011, resulting in a 27% increase in the cost of general goods and services (US Bureau of Labor and Statistics, http://www.bls.gov/data/inflation_calculator.htm). Costs associated with pre- and post-sampling and monitoring, including physical and chemical analyses, are not included in the estimates. Unless otherwise stated in previous examples, permitting costs are also not included.

Sediment accumulation within lakes is typically due to a combination of external, inorganic sediment loads from runoff and stream bank erosion and the in situ production of organic material associated with decomposing algal biomass or lakeside vegetation and/or leaf material. Sediments in eutrophic (nutrient-rich) lakes often have nutrient concentrations far in excess of those in the overlying water column. Removal of phosphorus-laden sediments from lakes may decrease or eliminate the release of phosphorus into the water column, thereby reducing the availability of nutrients utilized by algae and the subsequent increase in chlorophyll a (Atkins 2011). Lake management and restoration activities intended to improve water quality should focus on reducing external loads, as possible, as well as addressing internal loads through activities such as sediment removal, inactivation through whole-lake alum treatment, and artificial circulation (i.e., PBS&J 2010 b, Atkins 2011). While sediment removal has the benefit of long-term removal of nutrient sources, phosphorus inactivation may be more effective and cost-efficient (Cooke et al. 2005). However, frequent mixing of sediment layers that occurs in shallow, well-mixed lakes, similar to Sunshine Lake, may reduce the effectiveness of processes such as alum treatment (ERD 2007).

Sediment removal has been utilized as a lake management/restoration tool throughout Florida, as supported by the Florida Department of Environmental Protection (FDEP), through the issuance of a Wetland Resource Permit (WRP), and the U.S. Army Corps of Engineers (USACE) 404 Permit when accumulated organic sediments become a significant source of nutrients that impact water quality (PBS&J 2006). In many cases, the point and non-point sources of pollution responsible for causing eutrophic or hypereutrophic conditions and sediment accumulation were addressed but water quality problems continued. For example, in 1989 hydraulic dredging of Banana Lake, a 342-acre lake located in Polk County, was initiated as part of the Southwest Florida Water Management District (SWFWMD) Surface Water Improvement and Management (SWIM) program. The objective of this effort was to remove the nutrient-rich organic sediments hypothesized to be responsible for maintaining high phytoplankton concentrations despite the prior removal of agricultural stormwater runoff and wastewater treatment plant discharge sources. Similarly, in 1997 hydraulic dredging of nutrient-rich organic sediments was initiated in Lake Hollingsworth, a 356-acre lake in Polk County, as permitted by the FDEP and USACE, after several stormwater treatment projects did not significantly improve water quality. Hydraulic dredging of Lake Maggiore, a 380-acre lake in Pinellas County, was initiated in 2004 by the City of St. Petersburg, as supported by the FDEP and USACE, as part of a restoration plan designed to address hypereutrophic conditions as well as shallow water depths that were limiting historic recreational uses. More recently, removal of approximately six feet of muck from Lake Trafford (Collier County) was completed in November 2010 as part of the Water Resources Development Act of 1996 to improve and restore the health of the lake after years of receiving nutrient runoff from nearby agricultural lands and urban land use.

As noted by ERD (2007), increased lake water volume following sediment removal via hydraulic dredging has many benefits. For instance, improved water column depths help to decrease impacts associated with re-suspension of bottom sediments due to recreational activities and wind-induced waves. As pointed out in Bachman et al. (2000) deeper lakes are less likely to have re-suspension of bottom sediments during windy conditions. For Lake Hancock, Tomasko et al. (2009) found that a 1.3 meter increase in lake levels would increase the time period between whole-lake bottom re-suspension events from once a week to roughly once every two weeks.

http://www.bls.gov/data/inflation_calculator.htm

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3.1.1.1. Effectiveness of sediment removal activities and permitting issues

The effectiveness of sediment removal as a management tool for improving water quality in Florida lakes has been variable (Atkins 2011). Approximately one million cubic yards of sediments were removed from Banana Lake, resulting in a considerable reduction in both Total Nitrogen (TN) and Total Phosphorus (TP) concentrations (44 and 45 percent, respectively). The high level of TP concentration reduction may, however, be due to the extremely elevated initial concentration (1.48 mg/L) as similar results were not observed in Lakes Hollingsworth, Maggiore, and Trafford where a 38 percent increase, a 2 percent decrease, and a 20 percent increase in TP were observed, respectively. Unlike Banana Lake, initial TP concentrations at Lakes Hollingsworth (0.24 mg/L), Maggiore (0.08 mg/L), and Trafford (0.20 mg/L) were substantially lower. Although TP decreased in Banana Lake, there was no evidence of improved water clarity or chlorophyll a (PBS&J 2010 b). This is likely because the reduction in TP was still not sufficient to reduce phytoplankton biomass. In contrast, despite increases in TP levels at Lakes Hollingsworth and Trafford, chlorophyll a levels appeared to decrease following sediment removal, at least in the short term. Reductions in TN concentrations reached 13 percent in Lake Maggiore, 43 percent in Lake Hollingsworth, and 24 percent in Lake Trafford.

Typical sediment removal processes involve a hydraulic dredge that is used to remove either all or a portion of the organic sediments from the lake bottom. Use of a hydraulic dredge presents the potential for water quality impacts to the lake‟s surface waters. The dredge spoil collected by the dredge is transported via pipeline to a shoreline dewatering “facility,” if possible. Permitting agencies would evaluate potential associated impacts of the dredge pipeline to shoreline wetlands. The nature of the “dewatering facility” can be highly variable, ranging from the use of upland settling basins, geo-synthetic sediment containment tubes, or low-gravity belt filters designed to mechanically “squeeze” liquid out of sediments. Each of these techniques can be slow and land-intensive. In some instances, the addition of a polymer to the dredge slurry is required to facilitate flocculation of organics, separation from the water fraction, and more rapid settling (PBS&J 2006). If a polymer is utilized, the discharge of the polymer material in the return water is a potential concern. In this case, the permit would be conditional until a contractor is selected and the polymer is approved. In all instances, potential impacts of the dewatering “facility” (e.g., the containment tube footprint) on wetland and listed species would need to be assessed. The most critical issue to the permitting of the dewatering facility would likely be controlling the discharges to surface water and/or groundwater. If the dredged material is not sufficiently dried, there is a risk of spreading or spilling. In addition, problems associated with runoff from the dredged material following rain events could occur if it is not adequately contained during the drying and storing process. The decanted water resulting from the dewatering process is treated and eventually returned to the original lake in order to prevent significant lake level reductions. Permitting agencies will require that the returned lake water meet all applicable State Water Quality Standards.

Once dried, dredged material can either be used (e.g., agricultural soil amendment) or transported via truck to an appropriate disposal area. Regulatory agencies evaluate the impacts to wetlands, listed species, and water quality at the final dewatered sediment disposal site (PBS&J 2006). Professional experience has demonstrated that the best scenario for successfully permitting a sediment removal project is to dry the dredged material into a solid state and transport it to an upland disposal site or apply the dewatered material for beneficial use (personal communication, Doug Robison, PWS).

Permitting agencies will also need to see that the sediment removal project will be a net benefit to the lake (e.g., removal of nutrient load in sediments), despite any localized and/or temporary impacts. Impacts may include loss of wetland habitat and lake-ecosystem functions, including associated disruptions to fish and wildlife populations, during the dredging and refilling process. This is especially important if portions of the lake bottom are publicly-owned sovereign lands.

Other potential permitting hurdles may include limits to hours of dredge operation. For example, many dredging projects only allow for dredging to occur on weekdays during daylight hours. As a result, continuous operation of the dredging and sediment dewatering facilities is not possible, leading to extended

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project durations and higher costs. Additional issues that should be addressed in the permit include general impacts to the community associated with the dredging and disposal process such as truck traffic, noise, and odors.

3.1.1.2. Cost estimates of sediment removal

There is no standard process appropriate for every sediment removal project due to variations in physical and chemical characteristics of the sediments as well as project-specific environmental, economic, and logistical factors that require significant differences in design and permitting (PBS&J 2006). Costs for sediment removal vary mainly due to dredge capacity, pump requirements for transported dredged material, availability of and distance to disposal areas, and level of complexity of dewatering and treatment required

As a preliminary place-holder, cost estimates were developed for two different dredging approaches utilizing a hydraulic dredge for muck removal. In both instances, it is assumed that the dewatered sediment would be moved to a site where the material would be loaded and then trucked to its final disposal location. It should be noted that long hauls for trucking (> 20 miles) cause large increases in cost. Truckers can charge perhaps $3.50 per mile per load, although these prices fluctuate with the price of fuel.

The volume of organic-rich sediments in Sunshine Lake (not the canal below it) was estimated at 27,000 cubic yards (based on ca. 740,000 cubic feet estimate). In 2009, hydraulic dredging and disposal of approximately 200,000 cubic yards of sediments from Sawgrass Lake in Florida, including use of the Genesis Rapid Dewatering System for dewatering and treatment, was approximately $6.7 million. With this system, a polymer is added to the fine-grained sediment slurry to flocculate the sediments. Once the water is removed from the flocculated sediments, the resulting cake is ready for disposal or reuse, and the decanted water can be returned to the lake. Based on the Sawgrass Lake estimate, and scaling it down to a smaller Sunshine Lake, a similar dredge design and treatment process for Sunshine Lake might cost approximately $1 million.

PBS&J (2006) also evaluated the implementation of a sediment removal project for Lake Seminole. It was determined that the preferred combination of methods included the use of mechanical de-gritting, clarification, and high gravity sediment dewatering, resulting in an organic product that is approximately 50% solids and return water that meets all applicable state water quality standards. By increasing the percent solids of the cake to 50% using this process, the number of trucks required for disposal is decreased and costs are reduced. Implementation of this process was estimated to cost $13.9 million for an estimated sediment removal volume of one million cubic yards (764,554.86 m3). Based on the project cost for Lake Seminole in 2001, a reasonable cost estimate for similar work in Sunshine Lake in 2001 dollars would be approximately $400,000. Updating this cost estimate for 2011, the estimated total cost, based on Lake Seminole, would be approximately $480,000.

Using Sawgrass Lake and Lakes Maggiore and Seminole as examples, the average cost for removing the muck layer in Sunshine Lake in 2011 dollars would likely range between $500,000 and $1 million. It should be noted that this cost estimate is subject to unique characteristics related to disposal alternatives and requirements (e.g., space availability for material processing (dewatering), operating hours for dredging and dewatering facilities, level of treatment required, distance to disposal site, and method of sediment transport).

The use of sediment containment tubes for dewatering was also explored and a very preliminary cost estimate was provided by Sediment Removal Solutions of Michigan (SRSMI). This process utilizes a diver-focused hydraulic dredge to remove approximately 12” of suspended soft organic sediment in one acre in seven days. Based on an estimate of 1-3 feet of muck depth proposed for removal throughout the 8-acre lake, between 56 and 168 days would be required for sediment removal alone. The sediment is pumped into containment tubes that allow the lake water to leak out while retaining the solid material. Once the containment tubes are filled, they would need to dewater for a period of 3-5 months, depending on the time of year, sediment density, and weather. Typical use of the containment tubes allows the decanted water to

Sunshine Lake Study


leak directly back into the lake. Depending on the nature of this water, additional treatment (e.g., leaking the water over a grassy swale, use of a clarifier) may be necessary. Based on a preliminary survey of the area surrounding Lake Sunshine, there appears to be space for four 45‟ x 100‟ and one 30‟ x 50‟ containment tubes. Based on the limited area surrounding the lake, only 30 pumping days of sediment removal could be supported by the five tubes, allowing for 4 feet of muck to be removed from each acre of lake bottom. This effort would cost between $107,050 and $123,050. If additional space is identified for the placement of enough containment tubes (32 45‟ x 100‟ and 8 30‟ x 50‟ tubes) to remove the muck layer from the entire lake bottom, approximately 224 days would be required, costing approximately $900,100, a number that fits within the range of the two prior cost estimates developed. It should be noted that the cost estimate provided by SRSMI does not include site preparation, decanted water treatment, or sediment removal costs. The use of a polymer would increase the cost of this process as well.

3.1.2. Enhanced circulation/aeration

Whole lake aeration via circulation may be used as a water quality improvement project to treat eutrophication in Sunshine Lake (Atkins 2011). This process is designed to use electric powered pumps to pull deeper water to the lake surface where it becomes aerated (Pastorak et al. 1981, 1982) while reducing phytoplankton productivity by transporting phytoplankton biomass to the deeper, light-limited portion of the water column (Cooke et al. 1993). If iron is the factor controlling sediment phosphorus release, total phosphorus concentrations in the water column may be reduced through the aeration of the sediment-water interface and subsequent adsorption of phosphorus to the ferric complexes (Stumm and Leckie 1971). Improvements in water quality following aeration in Florida lakes have included reductions in ammonia and chlorophyll, total nitrogen, and total phosphorus (Kolasa and Kang 2005, Cowell et al. 1987).

The water intake system associated with the artificial circulation pump can be positioned in the water column based upon the lake‟s unique depth and sediment quality characteristics (Atkins 2011). Solar powered pumps (e.g., SolarBee®) can be used to reduce operation costs. The required number and size of the pumps is dependent on the lake‟s water quality, depth, size, and non-point source inputs. Artificial circulation is recommended only for small lakes (<75 acres) with poor water quality; Sunshine Lake might be a good candidate for including this technique. In August 2010, SolarBee® provided a design and cost estimate for Lake Blue, a 54-acre lake in Florida‟s Winter Haven Chain of Lakes. Given that each circulation pump is assumed to effectively circulate 16 to 20 acres, Lake Blue would require the purchase and installation of three SB10000 v 18 machines, totalling $160,000. In 2011, SolarBee® estimated that Huntsman Lake (approximately 29 acres in size) in Virginia would require the installation of one SB10000 v 18 unit, costing approximately $57,200 (without taxes). Based on these estimates, a single SB10000 v 18 unit would likely be sufficient for effective circulation in Sunshine Lake. A single unit would likely cost between $50,000 and $60,000 (not including taxes). Operation and maintenance costs are difficult to estimate, but would be an additional cost to the purchase itself.

3.1.3. Lake level modification

It is not known, at present, whether lake levels within Sunshine Lake are lower year-round, or only during the wet-season, or only during the dry-season, or if they are lower at any times of the year. While there is some evidence of lowered lake levels (i.e., Figure 13) there is no long-term gage data that provides proof. The pattern shown in Figure 13 could be caused by higher water levels in the wet-season, with a “normal” dry-season recession in lake levels. Also, it is possible that the lake appears to be lower than in past years, when in fact that is not the case (i.e., Figure 14).

However, it is known that lowered lake levels appear to make lakes more susceptible to the impacts of nutrient enrichment (Tomasko et al. 2009, PBS&J 2010 b) and that if there is evidence of an alteration to the lake level that could be explained by a particular activity (i.e., clearing drainage ditches, etc.) then the possibility of having inadvertently lowered the lake level should be addressed. It is suggested that a simple

Sunshine Lake Study


structure that would function to raise the invert level of the large culvert at the Tamiami Trail frontage road could retain added water during normal dry-season draw downs.

In the absence of the ability to increase water levels in the Sunshine Lake/Sunrise Waterway system, the addition of a non-potable well to maintain lake levels in the dry-season could be worth investigating. A well less than 6” in diameter, with a flow rate of less than 100,000 gallons per day (gpd) would not appear to need a Water Use Permit from the Southwest Florida Water Management District, although it would need a Well Construction Permit.

A well of this size could be permitted under the guidance of it being a “supplemental irrigation source,” which would be an accurate characterization of its purpose if Sunshine Lake was used by its residents as a supplemental water supply for their landscaping. As a number of homes along the lake have pipes that extend into the lake for such purposes, this is an accurate description of the lakes multiple uses (i.e., aesthetics, wildlife, recreation, and supplemental irrigation source).

Based on GIS-based assessments of the size and depth of the lake, it appears that Sunshine Lake is capable of holding approximately 10 million gallons of water. The addition of a 100,000 gpd water source could replace the lake‟s entire volume over the course of approximately 100 days. That amount of time (100 days) is far in excess of the amount of time it would take to get a massive algal bloom in the lake, therefore it is unlikely that a permitted supplemental water supply could change the residence time enough to reduce algal biomass through any type of flushing action. However, such a well could benefit the lake as a way to offset decreases in lake levels during the months of April and May, the time of year when hypereutrophic lakes often have their worst water quality (i.e., Tomasko et al. 2009, PBS&J 2010 b). During those two months, lake evaporation rates are likely to be around 6 inches per month, or one foot of combined water loss during these two months combined.

A one-foot loss of water from a lake that is approximately 8 acres in size is 8 acre-feet, or 2.6 million gallons of water. In comparison, a water source of 100,000 gpd over 60 days (i.e., April and May) is an amount of 6 million gallons, a volume in excess of the amount of water likely lost via evaporation alone. Therefore, it is possible that a supplemental water well could more than offset water losses via evaporation during the driest times of the year, which could benefit the lake by maintaining a higher lake level during times of the year when hypereutrophic lakes are particularly susceptible.

The costs of design, permitting, and construction of such a well have many details that would require further investigation; accurate cost estimates are premature at this point in time. However, total costs are likely to be minor when compared to the costs of sediment removal that would have to occur prior to this effort.

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4. Literature Cited Atkins. 2011. Huntsman Lake Water Quality and Sediment Characterization. Final Report to Fairfax County Department of Public Works and Environmental Services – Stormwater Planning Division.

Atkins. 2012. 2011 HBMP Annual Data Report. Peace River Manosota Regional Watersupply Authority, for the Southwest Florida Water Management District.

Bachmann, R.W., Hoyer, M.V., and D.E. Canfield. 2000. The potential for wave disturbance in shallow Florida lakes. Lake and Reservoir Management 16:281–291.

Canfield, D.E., Phlips, E., and C.M. Duarte. 1989. Factors influencing the abundance of bluegreen algae in Florida lakes. Canadian Journal of Fisheries and Aquatic Science 46:1232–1237. Downing, J.A., Watson, S.B., and E. McCauley. 2001. Predicting cyanobacteria dominance in lakes. Canadian Journal of Fisheries and Aquatic Science. 58:1905–1908.

Cooke, D., Welch, E.B., S. Peterson, and S.A. Nichols. 2005. Restoration and Management of Lakes and Reservoirs, Third Edition. Taylor and Francis Group, New York. 591 pages.

Cowell, B., Dawes, C., W. Gardiner, and S. Scheda. 1987. The influence of whole lake aeration on the limnology of a hypereutrophic lake in central Florida. Hydrobiologia 148:3-24.

ERD. 2007. Winter Haven Chain-of-Lakes Sediment Removal Feasibility Study Final Report. Report to the City of Winter Haven.

Heyl. 1992. Point and nonpoint source loading assessment of Sarasota Bay. Pp. 12.1-12.19. In: P.Roat, C. Ciccolella, H.Smith, and D. Tomasko (eds.). Sarasota Bay: Framework for Action. Sarasota Bay National Estuary Program, Sarasota, FL.

Kolasa, K. and W. Kang. 2005. Aeration of subtropical hypertrophic lake- a band-aid approach that is working. 69th Annual Meeting of the Florida Academy of Sciences. University of South Florida, Tampa, Fl. March 2005.

Pastorak, R.A., Lorenzen, M.W., and T.C.Ginn. 1982. Environmental aspects of artificial aeration and oxygenation of reservoirs: a review of theory, techniques, and experiences., Technical Report. No. E-82-3. U.S. Army Corps of Engineers. Pastorak, R.A., Gunn, T.C., and M.W. Lorenzen. 1981. Evaluation of Aeration/Circulation as a Lake Restoration Technique. 600/3-81-014 U.S.EPA.

PBS&J. 2006. Lake Seminole Sediment Removal Feasibility Study. Final Report to Pinellas County.

PBS&J. 2010 a. Event Mean Concentration (EMC) Monitoring in Support of Pollutant Load Modeling for Sarasota County. Final Report to Sarasota County. 31 pp.

PBS&J. 2010 b. Winter Haven Chain of Lakes WQMP Phase II: Final Report. Final Report to the City of Winter Haven, Florida.

Smith, V. H. 1983. Low nitrogen to phosphorus ratios favor dominance by blue-green algae in lake phytoplankton. Science. 221:669–671.

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Stumm, M., and J.O. Leckie. 1971. Phosphate exchange with sediments: its role in the productivity of surface waters. Proceedings of the 5th International Conference on Water Pollution. Research III-26/1-16. London.

Tomasko, D.A., Hyfield-Keenan, E.C., DeBrabandere, L.C., Montoya, J.P., and T.K. Frazer. 2009. Experimental studies on the effects of nutrient loading and sediment removal on water quality in Lake Hancock. Florida Scientist. 4: 346-366.

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Sunshine Lake/Sunrise Waterway Study · 2016-09-06 · Sunshine Lake Study Atkins Final Report April 2012 6 1. Introduction 1.1. Background The Sunshine Lake/Sunrise Waterway system,

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