EXECUTIVE SUMMARY
With a surface area of approximately four square miles (2,534 acres),
Lake Tarpon is the largest freshwater lake in the three county (Pinellas,
Hillsborough, Pasco) Tampa Bay Area. In
addition to being classified as an Outstanding Florida Water by the Florida
Department of Environmental Protection, the lake was formally designated as a
state Fish Management Area by a Special Resolution of the Pinellas Board of
County Commissioners in 1963. This
sport fishery, along with historically good water quality and the existence of
two regional County parks on its shore has made Lake Tarpon a significant
environmental, economic and recreational resource to the Tampa Bay area.
However, in recent years, Lake Tarpon and its associated natural
resources have begun to exhibit signs of ecological stress. In the summer of 1987, this stress was
represented by a major blue-green algae bloom that covered about 80 percent of
the lake. The bloom persisted for much
of the summer and impeded recreational and aesthetic uses of the lake during
the prime recreational season. This
algae bloom was seen as an indication that the trophic state (or productivity) of
the lake is increasing.
The algae bloom of 1987 and citizen concerns regarding the health of the
lake prompted the Pinellas County Board of County Commissioners to pass
Pinellas County Resolution 87-275, creating the Lake Tarpon Management
Committee (LTMC). The LTMC was
originally made up of representatives from the agencies charged with protecting
the lake and its resources, including the Southwest Florida Water Management
District (District), and of various representatives from local government,
citizens groups and the development community.
Coincident with these events, during the late 1980's, concern for the
quality of lakes, streams and estuaries throughout the State was increasing and
this prompted the Legislature to pass the Surface Water Improvement and
Management (SWIM) Act of 1987. The
threat to the health of the lake represented by the algae bloom and the
ecological, environmental and recreational importance of Lake Tarpon prompted
the District to include the lake as the seventh ranked waterbody on the
District’s SWIM Priority Waterbody List.
Subsequently, with assistance from the LTMC, the first Lake Tarpon SWIM
Plan was developed and approved in 1989.
This first SWIM Plan focused on diagnostic studies since little was
known about water quality, hydrology and ecology of the lake. The diagnostic studies, completed in 1992,
characterized existing water quality and hydrological and ecological conditions
of the lake and established a scientific basis for setting a number of
management goals for the lake and its watershed.
Based on the findings of the diagnostic studies and that water quality
had appeared to improve since the 1987 algae bloom, the 1994 revision of the
Lake Tarpon SWIM Plan identified Lake Tarpon as a "preservation"
waterbody from the SWIM perspective.
The plan did note that there were still some problems including
recreational user conflicts, increases in biomass of certain noxious aquatic
plants, possible groundwater loading of nitrates from as yet undetermined
sources and pollutant loading from areas developed prior to implementation of
stormwater treatment regulations.
Although Lake Tarpon was identified as a preservation waterbody, this
did not imply that management strategies would no longer be necessary. On the contrary, some management strategies
would be necessary to "hold the line" to prevent further degradation
and these should be implemented when opportunities exist.
Pinellas County has monitored Lake Tarpon water quality monthly since
1987, and in 1993, they noted a decline in water quality. This, along with requirements in their
Growth Management Plan, prompted the County to initiate the development of a
comprehensive watershed management plan for the Lake Tarpon drainage
basin. Therefore, this third revision of
the Lake Tarpon SWIM Plan was deferred until the Lake Tarpon Drainage Basin
Management Plan (PBS&J 1998) was completed. The Lake Tarpon Drainage Basin Management Plan (DBMP) was
prepared with input from and consistent with the goals of the LTMC.
The primary concern with Lake Tarpon continues to be declining water
quality as demonstrated by long-term water quality data collected by Pinellas
County. Declining water quality can
lead to the increase of undesirable blooms of algae, loss of more desirable rooted
aquatic plants, changes to the fish community structure and other adverse
ecological changes. Consistent with the
DBMP (PBS&J, 1998), this revision of the Lake Tarpon SWIM Plan identifies
management issues, strategies and goals for maintaining and where feasible,
restoring the hydrological and ecological integrity of the lake and its
watershed.
Strategies to improve and protect water quality are aimed at reducing
external nutrient loading through stormwater retrofit projects. Additionally, the Plan provides for
hydrologic and habitat restoration projects in the Brooker Creek watershed
which will improve the ecological condition of the natural systems and may
assist in lowering external nutrient loads.
Reduction in internal nutrient loads relies on macrophyte harvesting and
the implementation of an enhanced lake fluctuation schedule. Public education, although difficult to
measure direct benefits to the lake, is
necessary to inform the public about lake and watershed management issues and
to solicit public support and volunteers to assist in the management of Lake
Tarpon.
This revised Lake Tarpon SWIM Plan provides details for projects that
implement the above strategies and for projects that will be used to refine the
District and County’s understanding of the lake system. The Lake Tarpon SWIM Plan serves as the
guidance document for coordinating the efforts of the District, Pinellas County
and the State of Florida to restore and protect Lake Tarpon.
INTRODUCTION
The SWIM Act
In recognition of the need to place additional emphasis on the
restoration, protection and management of the surface water resources of the
State, the Florida Legislature, through the Surface Water Improvement and
Management (SWIM) Act of 1987, directed the state’s water management districts
to "design and implement plans and programs for the improvement and
management of surface water" (Section 373.451, Florida Statutes). The SWIM legislation requires the water
management districts to protect the ecological, aesthetic, recreational, and
economic value of the state’s surface water bodies, keeping in mind that water
quality degradation is frequently caused by point and non-point source
pollution, and that degraded water quality can cause both direct and indirect
losses of habitats.
Under the Act, water management districts prioritize water bodies based
on their need for protection and/or restoration. This prioritization process is carried out in cooperation with
the Florida Department of Environmental Protection (FDEP), the Florida Fish and
Wildlife Conservation Commission (FFWCC, formerly the Florida Game and
Freshwater Fish Commission or FGFWFC), the Department of Agriculture and
Consumer Services (DACS), the Department of Community Affairs (DCA) and local
governments.
Following the selection of the priority water bodies and in accordance
with the SWIM Act, a SWIM Plan must be drafted, reviewed and approved, before
SWIM funds can be spent on restoration, protection or management activities. The purpose of the Lake Tarpon SWIM Plan is
to set forth a realistic course of action, identifying the projects and the
efforts needed to accomplish them. The
Act also requires that the plans be updated at a minimum once every three
years. The history of Lake Tarpon SWIM
Plans is discussed in the following section.
Lake Tarpon SWIM Plan - The Third Generation
In the summer of 1987, Lake Tarpon experienced a widespread bloom of
blue-green algae (Anabaena circinalis).
The bloom persisted for most of the summer and impacted recreational and
aesthetic uses of the lake. Citizen
concerns regarding the health of the lake prompted the Pinellas County Board of
County Commissioners to initiate action by passage of Pinellas County Resolution
87-275, creating the Lake Tarpon Management Committee (LTMC). The LTMC was originally made up of
representatives from the Southwest Florida Water Management District
(District), the Florida Departments of Environmental Regulation and Natural
Resources (now FDEP), FFWCC and various representatives from citizens groups
and the development community. Later,
the City of Tarpon Springs was invited to participate. As a result of the SWIM Act, the regional
significance of Lake Tarpon and the blue-green algae bloom, Lake Tarpon was
designated as the District’s seventh ranked SWIM priority waterbody in late
1987.
The first Lake Tarpon SWIM Plan was approved in 1989 and focused on
diagnostic studies since little was known about water quality, hydrology and ecology
of the lake. A cooperatively funded
project between the District and Pinellas County, The Final Comprehensive
Report: Lake Tarpon
Diagnostic/Feasibility Studies (KEA, Inc. 1992), was completed in
1992. This report provided much of the
scientific data needed to characterize the existing water quality and
hydrological and ecological conditions of the lake. This report also established a scientific basis for setting a
number of management goals for the lake and its watershed.
As a result of the diagnostic and feasibility studies and the fact that
water quality had appeared to improve since the 1987 algae bloom, the 1994
revision of the Lake Tarpon SWIM Plan identified Lake Tarpon as a
"preservation" waterbody from the SWIM perspective. The plan did note that there were still some
problems including recreational user conflicts, increases in biomass of certain
noxious aquatic plants, possible groundwater loading of nitrates from as yet
undetermined sources and pollutant loading from areas developed prior to
implementation of stormwater treatment regulations. Although Lake Tarpon has been identified as a preservation
waterbody, this does not imply that management strategies are no longer
necessary. On the contrary, some
management strategies will be necessary to "hold the line" to prevent
further degradation and these should be implemented when opportunities exist.
Pinellas County has monitored water quality in Lake Tarpon monthly since
1987, and in 1993, they noted an increase in chlorophyll-a which represented
degraded water quality conditions.
This, along with requirements in their Growth Management Plan, caused
the County to initiate the development of a comprehensive watershed management
plan for the Lake Tarpon drainage basin and in 1994 the County entered into an
agreement with Coastal Environmental, Inc. (now PBS&J) to develop such a
plan. Therefore, this third revision of
the Lake Tarpon SWIM Plan was deferred until the Lake Tarpon Drainage Basin
Management Plan (PBS&J 1998) was completed. The Lake Tarpon Drainage Basin Management Plan (DBMP) was
prepared with input from and consistent with the goals of the LTMC.
LAKE TARPON MANAGEMENT ISSUES
The DBMP (PBS&J, 1998) identified management issues, goals and
strategies aimed at maintaining and where feasible, restoring the hydrological
and ecological integrity of the lake and its watershed. In preparing this revision of the Lake
Tarpon SWIM Plan, District staff reviewed the DBMP (PBS&J, 1998) and then
focused on management goals, issues and strategies that can be accomplished
within the legislative charge of SWIM, which is improving or protecting water
quality and natural systems. The
following management issues are the basis for this revision of the Lake Tarpon
SWIM Plan.
Water Quality
The algae bloom of 1987 has been seen as an indication that the trophic
state (or productivity) of the lake is increasing. An increase in trophic state should not be surprising given that Lake Tarpon is located
in the most densely populated county in Florida and that most of its watershed
has been converted from its natural state to urban land uses. Therefore, the primary concern with regard
to water quality in Lake Tarpon is related to cultural eutrophication which is
caused by unnatural and excessive increases in nutrients entering the
waterbody. This can lead to the
increase of undesirable blooms of algae, loss of more desirable rooted aquatic
plants and other adverse ecological changes.
The County has been monitoring water quality in Lake Tarpon since
1987. Annual average chlorophyll-a data
show a substantial increase in chlorophyll-a from 1992 to 1993 (Figure 1). After 1993, chlorophyll-a concentrations
continue to increase. This apparent
increasing trend and the observance of a trophic state index (TSI) value of
58.96 for the period from May 1996 to April 1997 are of concern to lake
managers for two reasons: 1) historical data indicate that Lake Tarpon had a
TSI of about 50 (SWFWMD 1994); and 2) a TSI value of 60 appears to be a
critical point in defining eutrophication, based on review of data from 573
Florida lakes (Huber et al. 1983 in DBMP PBS&J, 1998).
Aquatic Vegetation
Hydrilla (Hydrilla verticillata), a rooted exotic submerged
plant, and cattail (Typha latifolia), a native emergent species, are the
root of aquatic plant issues in Lake Tarpon.
The proliferation of cattail appears to have decreased diversity in the
emergent plant community over the last 25 years. Management of hydrilla has been correlated with degraded water
quality as a result of nutrients released into the water column from degrading
plant tissue. Lakes with healthy
submerged aquatic plant communities tend to have fewer problems with severe
nuisance algal blooms. Therefore, Lake
Tarpon should be managed to promote the
expansion of desirable endemic submerged aquatic vegetation, as well as,
to increase the diversity of the emergent community. However, due to the lack of a consistent quantitative monitoring
program, trends in the coverage of desirable native submerged aquatic
vegetation have been difficult to assess.
Additionally, quantitative data for submerged and emergent aquatic
species are necessary to evaluate the effects of implemented lake management
strategies such as an enhanced lake level fluctuation.
Fisheries
Lake Tarpon is an important sport fishing lake in Florida and was
formally designated as a state Fish Management Area by a Special Resolution of
the Pinellas Board of County Commissioners in 1963. The FFWCC has monitored
sport fish populations in the lake since the 1970's. Studies in the early 1990's indicated that the largemouth bass
and panfish fisheries were healthy, however, a study conducted during 1995/1996
indicated that fish biomass in Lake Tarpon had increased substantially
(Champeau 1996). This is of concern
since the rise in fish biomass could be a result of increasing productivity
(eutrophication). The FFWCC asserts that continued increases in trophic state
could lead to a decline in the sport fisheries of Lake Tarpon and they
recommend that strategies be implemented to minimize nutrient loadings to the
lake (Champeau 1996).
Flood Control
Flood control is not a primary management issue for the Lake Tarpon SWIM
Plan. Construction of the Lake Tarpon
Outfall Canal and Structure in the 1970's effectively addressed the severe
flooding problems that previously existed in the basin. This SWIM Plan does not recommend any
additional management strategies to address this issue. However, maintenance of the current level of
flood protection provided by the outfall structure will be a primary
consideration in implementing management strategies to address other lake management
goals.
Hydrologic and Habitat Restoration
The Lake Tarpon watershed is highly urbanized and many of the wetlands,
especially on the western shore, were filled prior to 1984 to accommodate
lakeshore development. (Since passage
of the Warren G. Henderson Wetlands Protection Act of 1984, wetlands have been
protected by both state and federal laws.)
The Brooker Creek watershed, which extends into the lakes region of
northwest Hillsborough County, was until relatively recently, characterized by
agricultural and low density rural residential uses. A large portion of the Brooker Creek watershed in Pinellas
County is now protected by the Brooker Creek Preserve (Preserve). Many of the wetlands in the Preserve and
those in Hillsborough County do not appear to have been filled to the extent
they were near the shores of Lake Tarpon, however, they have been impacted to
varying degrees by anthropogenic activities.
Public Education
Residential surveys of people living in the Lake Tarpon basin indicate
that the public is generally not well informed regarding lake and watershed
management issues. However, these same
surveys indicate that many residents are interested in helping to monitor and
improve environmental conditions in the lake and watershed. Thus, there is a
need to better inform the public of issues facing Lake Tarpon and to solicit
public support and volunteers in the implementation of the Lake Tarpon SWIM
Plan.
Pollutant Load Reduction Goal
Pursuant to State Water Policy, Chapter 62-40, Florida Administrative
Code (FAC), a pollutant load reduction goal (PLRG) is to be developed for each
SWIM waterbody and adopted as part of the SWIM Plan. By definition a "PLRG means estimated numeric reductions in
pollutant loadings needed to preserve or restore designated uses of receiving
bodies of water and maintain water quality consistent with applicable state
water quality standards" (Chapter 62-40.210(18)). Chapter 62-40.432(5)(c) and (d) further
discuss the intent of PLRGs. From this
discussion, PLRGs refer to the reduction of pollutants from older stormwater
management systems that are necessary to restore or maintain the beneficial
uses of waters.
One method for setting a PLRG is referencing a desired TSI value and
establishing the PLRG as the reduction in nutrients needed to meet the desired
TSI. The 1994 Lake Tarpon SWIM Plan
proposed an interim PLRG for Lake Tarpon of zero for both nitrogen and
phosphorus. This PLRG was established
as an interim goal to allow the County time to determine the feasibility of
reducing nutrient loading sufficiently so that decreases in the TSI could be
achieved.
Pinellas County through development of the DBMP (PBS&J, 1998)
identified a multi-parametric TSI goal for Lake Tarpon of 55. In order to reach the TSI goal of 55, a
4-point reduction in TSI would be needed from the annual average TSI value of
58.96 calculated for the period from May 1996 to April 1997. The DBMP (PBS&J, 1998) proposed internal
and external pollutant load reduction strategies that if implemented would
achieve a 4-point reduction in the annual average TSI. (More recent data for the period from January 1999 to December 1999 show that
the annual average multi-parametric TSI was 60.64.)
The DBMP (PBS&J, 1998) concluded that internal pollutant loads could
be reduced by controlled harvesting of cattails and hydrilla and by increased
lake flushing and dilution. Load reductions achieved by lake flushing and
dilution are difficult to quantify due to a number of variables, including
quality of dilution water and the flushing or turnover rate. Further evaluation is needed to determine
whether these management strategies will be feasible and effective in improving
water quality. Management strategies to
address external anthropogenic pollutant loadings, including stormwater
treatment and installation of central sewer systems were also identified
(PBS&J 1998).
Based on the modeling work conducted for the DBMP (PBS&J, 1998)
attainment of a TSI equal to 55 will require total implementation of the
recommendations in the DBMP, including the enhanced lake level fluctuation and
dilution and stormwater retrofit projects, conversion of septic tanks to central
sewer and macrophyte harvesting.
LAKE TARPON SWIM PLAN GOALS
The goals of the Lake Tarpon SWIM Plan focus on the issues identified by
Pinellas County and the LTMC in the DBMP (PBS&J, 1998). These goals and the District’s PLRG are
listed below.
·
Maintain the
mean annual chlorophyll-a concentration at or below 14 µg/L.
·
Maintain the
mean annual multi-parametric TSI value at or below 55.
·
Limit the
areal coverage of hydrilla to 100 acres or less and, limit the areal coverage
of cattails to 60 acres or less.
·
Expand the
coverage of desirable endemic submerged aquatic vegetation to 600 acres and
maintain the areal coverage of emergent aquatic vegetation at 120 acres or
more. (Note: cattail should not account
for more than 60 acres of this coverage.)
·
Maintain a
fish community balance of F/C = 3.0-6.0 (e.g., the ratio of forage fish biomass
to carnivorous fish biomass)
·
Maintain
indices of Relative Stock Density for major sport fish species of: 20-40
percent >14 inches for largemouth bass; 40-60 percent > 6 inches for
bluegill; 40-60 percent > 7 inches for redear sunfish; and 40-60 percent
> 9 inches for black crappie
·
Manage water
levels to improve water quality and aquatic vegetation while maintaining the
existing degree of flood control provided by the Lake Tarpon Outfall Structure.
·
Restore
hydrologic and ecologic functions of wetlands and tributaries in the Lake
Tarpon and Brooker Creek watersheds where opportunities for such restoration
exist.
·
The PLRG for
Lake Tarpon is established as a 20.08 ton reduction in total nitrogen and a
3.02 ton reduction in phosphorus on an annual basis.
·
Provide
educational opportunities related to other goals of the Lake Tarpon SWIM Plan.
