Prepared in cooperation with the City of North Port and Sarasota County 

Discharge, Water Temperature, and Water Quality of 

Warm Mineral Springs, Sarasota County, Florida: 

A Retrospective Analysis

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2016–1166
Cover. Photograph of Warm Mineral Springs taken by diver at 154 feet below the spring surface, July 29, 2015. 

Photograph by Curt Bowen, ADM Exploration Foundation, 2015. 

Title page. Photograph of warm water vapors rising from the surface of Warm Mineral Springs on a cool 

winter morning, January 29, 2015. Photograph by P.A. Metz. 
Discharge, Water Temperature, and

Water Quality of Warm Mineral Springs,

Sarasota County, Florida: A Retrospective Analysis

By Patricia A. Metz

Prepared in cooperation with the City of North Port and Sarasota County

Open-File Report 2016–1166

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Metz, P.A., 2016, Discharge, water temperature, and water quality of Warm Mineral Springs, 

Sarasota County, Florida—A retrospective analysis: U.S. Geological Survey Open-File Report 2016–1166, 31 p., 

http://dx.doi.org/10.3133/ofr20161166.

ISSN 2331-1258 (online)
iii

Contents

Acknowledgments........................................................................................................................................vi

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................3

Methods of Investigation..............................................................................................................................3

Retrospective Analysis .................................................................................................................................5

Climate of the Myakka River Basin....................................................................................................5

Geologic Setting....................................................................................................................................5

Hydrologic Setting ................................................................................................................................8

Regional Groundwater Levels and Water Use of the Upper Floridan aquifer...................8

Discharge...............................................................................................................................................8

Water Level in the Sarasota 9 Well and Relation to Spring Discharge ............................13

Water Temperature ............................................................................................................................15

Groundwater Geochemistry..............................................................................................................16

Water Quality.......................................................................................................................................21

Discussion ....................................................................................................................................................24

Summary........................................................................................................................................................24

References Cited..........................................................................................................................................28

Figures

 1. Maps showing location of Warm Mineral Springs, other springs in Florida, and 

 the extent of the Florida Platform.......................................................................................................2

 2. Photograph showing aerial view of Warm Mineral Springs and 

 Warm Mineral Springs Creek .............................................................................................................3

 3. Graph showing annual precipitation in the Myakka River Basin, 1940–2015..............................5

 4. Diagram showing relation of stratigraphic and hydrogeologic units of the 

 Florida Platform in central Florida......................................................................................................6

 5. Map showing the geology of Warm Mineral Springs and photograph showing 

 flowstones located on the walls of Warm Mineral Springs ..........................................................7

 6. Map showing area of recharge and discharge, potentiometric surface of the 

 Upper Floridan aquifer for September 2010, generalized groundwater 

 flow path in the Southern West-Central Florida Groundwater Basin, 

 and location of wells used in this study............................................................................................9

 7. Graphs showing estimated groundwater use in the Southern West-Central Florida 

 Groundwater Basin and estimated groundwater use in Sarasota County ...............................11

 8. Maps showing change in the potentiometric surface of the Upper Floridan aquifer 

 between predevelopment levels and May 1975 levels, and change between 

 predevelopment levels and May 2007 levels .................................................................................11

 9. Graph showing instantaneous discharge and water temperature measurements 

 at Warm Mineral Springs .................................................................................................................13
iv

10. Diagram of the bottom of Warm Mineral Springs showing the location of 

 spring vents A–E and photographs showing some of the spring vents ....................................14

11. Graph showing time series of instantaneous discharge at Warm Mineral Springs 

 and annual mean and monthly water-level elevation of the Upper Floridan 

 aquifer in the Sarasota 9 well...........................................................................................................15

12. Graph showing annual mean or instantaneous discharge at Warm Mineral Springs 

 and water-level elevation of the Upper Floridan aquifer in the Sarasota 9 well......................15

13. Graph showing time series of water temperature readings from sensors 

 attached to divers during a sampling event on April 29, 2015.....................................................17

14. Cross section of hydrologic units along ROMP wells and well 224B-1, 

 showing a pattern of increasing groundwater temperatures from 

 Highlands to Sarasota Counties.......................................................................................................18

15. Geophysical temperature logs showing the possible mixing of cooler 

 Gulf of Mexico water with groundwater from several high permeable zones 

 within the Floridan aquifer system...................................................................................................19

16. Stiff diagrams of water from Little Salt Spring and Warm Mineral Springs, 

 Gulf of Mexico, and Upper Floridan aquifer and middle confining unit 

 within the Avon Park Formation in a recharge and discharge area ..........................................20

17. Diagram showing comparison of water quality, temperature with depth, 

 and flow directions within the Avon Park Formation of the Upper Floridan 

 aquifer and the underlying middle confining unit..........................................................................22

18. Photographs showing sulfur-reducing bacteria and green algae that coat 

 the walls of Warm Mineral Springs .................................................................................................25

19. Photographs showing Warm Mineral Springs water clarity at 40 feet 

 below the spring surface during a dry period and at 154 feet after an 

 extended period of rain......................................................................................................................26

Tables

1. Water levels above or below land surface for selected Regional Observation 

 Monitor-Well Program wells, 2007–15.............................................................................................10

2. Instantaneous discharge and water temperature measurements made at 

 Warm Mineral Springs outlet and average, annual water levels for the 

 Upper Floridan aquifer.......................................................................................................................12

3. Water-quality characteristics of samples collected at four vents at the 

 bottom of Warm Mineral Springs, April 29, 2015 ...........................................................................17

4. Median values of water-quality data collected at Warm Mineral Springs, 

 Baird Creek Head Spring, and numerous west-central Florida springs 

 and the Gulf of Mexico.......................................................................................................................23
v

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

million gallons (Mgal) 3,785 cubic meter (m3

)

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second (ft3

/s) 0.646 million gallons per day (Mgal/d)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

cubic meter per second (m3

/s) 22.83 million gallons per day (Mgal/d) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as °C = (°F – 32) / 1.8.

Datum

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C).

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) or 

micrograms per liter (μg/L).

Abbreviations

bls below land surface

FGS Florida Geological Survey

IRF Impulse Response Function

ka thousand years ago

Ma million years ago

ROMP Regional Observation and Monitor-Well Program

SWFWMD Southwest Florida Water Management District

USGS U.S. Geological Survey
vi

Acknowledgments

The author is grateful to the public and private sector for providing information pertaining 

to Warm Mineral Springs and to the City of North Port and Sarasota County for allowing access 

to the spring property for data-collection purposes. Acknowledgments are extended to the City 

of North Port employees Daniel Schult, Michele Norton, and Jim McAllister; and Sarasota 

County employees Cliff Harrison, Chris Cole, John Ryan, and Rachel Herman for technical 

discussions pertaining to Warm Mineral Springs. The author acknowledges the assistance of 

Sarasota County employees Cliff Harrison, Rene Janneman, Ashley Melton, Cesar Rodriguez, 

and Heather Bryen for their technical field support. Also, gratitude is extended to Curt Bowen 

of ADM Exploration Foundation and Jim Culter of Mote Marine Laboratory for assistance with 

collecting water samples from the vents at the bottom of the spring during 2015. Curt Bowen 

also provided underwater videography and detailed mapping of the spring for this study. Special recognition is given to both William Royal and William Cockrell for their archaeological 

research over the years at Warm Mineral Springs. 

The author acknowledges Joseph D. Hughes, U.S. Geological Survey, Office of Groundwater, John F. Stamm, U.S. Geological Survey, Caribbean-Florida Water Science Center, and 

Dave DeWitt, Southwest Florida Water Management District, for their constructive technical 

reviews of the report.
Discharge, Water Temperature, and Water Quality 

of Warm Mineral Springs, Sarasota County, Florida: 

A Retrospective Analysis

By P.A. Metz

Abstract

Warm Mineral Springs, located in southern Sarasota 

County, Florida, is a warm, highly mineralized, inland spring. 

Since 1946, a bathing spa has been in operation at the spring, 

attracting vacationers and health enthusiasts. During the winter 

months, the warm water attracts manatees to the adjoining 

spring run and provides vital habitat for these mammals. Wellpreserved late Pleistocene to early Holocene-age human and 

animal bones, artifacts, and plant remains have been found in 

and around the spring, and indicate the surrounding sinkhole 

formed more than 12,000 years ago. The spring is a multiuse 

resource of hydrologic importance, ecological and archeological significance, and economic value to the community.

The pool of Warm Mineral Springs has a circular shape 

that reflects its origin as a sinkhole. The pool measures about 

240 feet in diameter at the surface and has a maximum depth 

of about 205 feet. The sinkhole developed in the sand, clay, 

and dolostone of the Arcadia Formation of the Miocene-age 

to Oligocene-age Hawthorn Group. Underlying the Hawthorn 

Group are Oligocene-age to Eocene-age limestones and dolostones, including the Suwannee Limestone, Ocala Limestone, 

and Avon Park Formation. Mineralized groundwater, under 

artesian pressure in the underlying aquifers, fills the remnant 

sink, and the overflow discharges into Warm Mineral Springs 

Creek, to Salt Creek, and subsequently into the Myakka River. 

Aquifers described in the vicinity of Warm Mineral Springs 

include the surficial aquifer system, the intermediate aquifer 

system within the Hawthorn Group, and the Upper Floridan 

aquifer in the Suwannee Limestone, Ocala Limestone, and 

Avon Park Formation. The Hawthorn Group acts as an upper 

confining unit of the Upper Floridan aquifer.

Groundwater flow paths are inferred from the 

configuration of the potentiometric surface of the Upper 

Floridan aquifer for September 2010. Groundwater flow 

models indicate the downward flow of water into the Upper 

Floridan aquifer in inland areas, and upward flow toward the 

surface in coastal areas, such as at Warm Mineral Springs. 

Warm Mineral Springs is located in a discharge area. Changes 

in water use in the region have affected the potentiometric 

surface of the Upper Floridan aquifer. Historical increase in 

groundwater withdrawals resulted in a 10- to 20-foot regional 

decline in the potentiometric surface of the Upper Floridan 

aquifer by May 1975 relative to predevelopment levels and 

remained at approximately that level in May 2007 in the 

area of Warm Mineral Springs. Discharge measurements at 

Warm Mineral Springs (1942–2014) decreased from about 

11–12 cubic feet per second in the 1940s to about 6–9 cubic 

feet per second in the 1970s and remained at about that 

level for the remainder of the period of record. Similarity of 

changes in regional water use and discharge at Warm Mineral 

Springs indicates that basin-scale changes to the groundwater 

system have affected discharge at Warm Mineral Springs. 

Water temperature had no significant trend in temperature over 

the period of record, 1943–2015, and outliers were identified 

in the data that might indicate inconsistencies in measurement 

methods or locations. 

Within the regional groundwater basin, Warm Mineral 

Springs is influenced by deep Upper Floridan aquifer flow 

paths that discharge toward the coast. Associated with these 

flow paths, the groundwater temperatures increase with depth 

and toward the coast. Multiple lines of evidence indicate 

that a source of warm groundwater to Warm Mineral Springs 

is likely the permeable zone of the Avon Park Formation 

within the Upper Floridan aquifer at a depth of about 1,400 

to 1,600 feet, or deeper sources. The permeable zone contains saline groundwater with water temperatures of at least 

95 degrees Fahrenheit.
2 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

The water quality of Warm Mineral Springs, when 

compared with other springs in Florida had the highest temperature and the greatest mineralized content. Warm Mineral 

Springs water is characterized by a slight-green color, with 

varying water clarity, low dissolved oxygen (indicative of 

deep groundwater), and a hydrogen sulfide odor. Water-quality 

samples detected ammonium-nitrogen and nitrates, but at 

low concentrations. The drinking water standard for nitrate 

adopted by the U.S. Environmental Protection Agency is 

10 milligrams per liter, measured as nitrogen. Water samples 

collected at spring vents by divers on April 29, 2015, had concentrations of 0.9 milligram per liter nitrate-nitrogen at vent A 

and 0.04–0.05 milligram per liter at vents B, C, and D. Typically, the water clarity is highest in the morning (about 30 feet 

Secchi depth) and often decreases throughout the day. 

Analysis of existing data provided some insight into 

the hydrologic processes affecting Warm Mineral Springs; 

however, data have been sparsely and discontinuously collected since the 1940s. Continuous monitoring of hydrologic 

characteristics such as discharge, water temperature, specific 

conductance, and water-quality indicators, such as nitrate and 

turbidity (water clarity), would be valuable for monitoring and 

development of models of spring discharge and water quality. 

In addition, water samples could be analyzed for isotopic 

tracers, such as strontium, and the results used to identify and 

quantify the sources of groundwater that discharge at Warm 

Mineral Springs. Groundwater flow/transport models could 

be used to evaluate the sensitivity of the quality and quantity 

of water flowing from Warm Mineral Springs to changes in 

climate, aquifer levels, and water use.

Introduction

Warm Mineral Springs, in southern Sarasota County, 

Florida, (fig. 1A), is a warm (about 85 degrees Fahrenheit 

[°F]), mineralized spring (Rosenau and others, 1977). Since 

1946, a bathing spa has been in operation at the spring, 

attracting vacationers and health enthusiasts (Scott and others, 

2004). Archaeological evidence indicates that the spring has 

been visited by humans for thousands of years; well-preserved 

Pleistocene- to early Holocene-age human and animal bones, 

artifacts, and plant remains have been found in and around the 

spring (Clausen and others, 1975; Cockrell, 1975). In addition, the warm water from the spring attracts manatees to the 

adjoining spring run during the winter months and provides 

vital habitat. Warm Mineral Springs is a multiuse resource, 

with several stakeholders expressing interest in its development, management, and sustainable use.

Warm Mineral Springs is a third-magnitude spring, which 

is defined as having discharge less than 10 cubic feet per second (ft3

/s; Copeland, 2003). The spring pool measures about 

240 feet (ft) in diameter at the surface (Clausen and others, 

1975) and has a maximum depth of about 205 ft (Bowen, 

1996). The circular shape (fig. 2) and depth of the pool reflects 

its origin as a sinkhole that developed in the underlying 

carbonate rocks. Caverns, or “vents,” along the sinkhole 

bottom discharge warm water to the spring (Rupert, 1994; 

Bowen, 2015).

Little Salt Spring

Myakka 

River

SARASOTA COUNTY

Myakka River Basin

Sarasota 9 well

Warm Mineral Springs

Central axis of the 

Florida Platform

Edge

of the

Platform

Florida

SARASOTA COUNTY

Tampa Bay

Warm Mineral 

Springs 

Outlet Salt Creek

Myakka River

EXPLANATION

A

B

Extended land mass 

of Florida, approximate 

late Pleistocene shoreline, 

20,000 years ago

Holocene

 to current

 shoreline

ROMP 8 well

Homosassa 

Springs

Wakulla 

Springs

Silver Springs

Baird Creek

 Spring

Base modified from Esri, DeLorme, HERE, TomTom, Intermap, increment P Corp., 

GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, 

Esri Japan, METI, Esri China (Hong Kong), swisstopo, and the GIS User Community 

Gulf of Mexico

Gulf of Mexico

Atlantic 

Ocean

Charlotte Harbor

N

N 0 50 MILES

0 50 KILOMETERS

0 5 MILES

0 5 KILOMETERS

Well location 

and identifier 

Location of other 

Florida springs

ROMP 14

ROMP 8 ROMP 13

ROMP 8

ROMP 9

ROMP 16.5

ROMP 12

Warm Mineral Springs

224B-1 well Stevens #1 well

Figure 1. Location of A, Warm Mineral Springs and B, other 

springs in Florida and the extent of the Florida Platform.
Methods of Investigation 3

Purpose and Scope

The purpose and scope of this report is to provide a 

summary of retrospective studies (available from published 

reports and databases) pertaining to the geologic and hydrologic setting of the region, and the water temperature, 

discharge, and water chemistry of Warm Mineral Springs. 

The study area includes Warm Mineral Springs and the 

Myakka River Basin (fig. 1A). Data were compiled from 

published sources from various agencies including the Florida 

Geological Survey, Sarasota County, Southwest Florida Water 

Management District (SWFWMD), and the U.S. Geological 

Survey (USGS). Data from the SWFWMD Regional Observation Monitor-Well Program (ROMP), and other wells, were 

used to assess regional groundwater levels. 

The USGS in cooperation with the City of North Port and 

Sarasota County, Florida, conducted a study to review, summarize, and analyze existing data pertaining to Warm Mineral 

Springs. The retrospective summary addresses (1) the regional 

hydrologic and geologic setting, (2) anthropogenic effects 

such as water use, (3) sources of warm water, (4) discharge 

and water temperature, and (5) geochemistry and water quality. The associated analyses are intended to provide information to local, regional, and State water-resource professionals 

to better understand and sustainably manage Warm Mineral 

Springs. 

Methods of Investigation

The results presented in this report are based on published 

reports and data pertaining to Warm Mineral Springs and the 

surrounding region. Warm Mineral Springs has a long history 

of scientific research pertaining to archaeology and paleoecology, geology, hydrology, and water temperature/quality within 

and surrounding the spring. Hereinafter, “water temperature” 

will be referred to as “temperature” unless otherwise noted. 

Some notable studies of Warm Mineral Springs and other 

related investigations include the following: archaeological 

Base modified from Esri, DigitalGlobe, GeoEye, i-cubed, 

USDA, USGS, AEX, Getmapping, Aerogrid, IGN, 

IGP, swisstopo, and the GIS User Community

Warm Mineral Springs

Warm Mineral Springs Creek

Figure 2. Aerial view of Warm Mineral Springs and Warm Mineral Springs Creek.
4 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

and paleoecology investigations (Royal and Clark, 1960; 

Clausen and others, 1975; Cockrell, 1988; McDonald,1990), 

regional geologic framework (Miller, 1986; Reese and Richardson, 2008; Williams and Kuniansky, 2015), local geologic 

framework (Hutchinson, 1992; Thompson, 1997; Baldini, 

1998; Clayton, 1998, 1999, 2010; Gates, 2001), geologic 

setting of Warm Mineral Springs (Rupert, 1994), mapping of 

the spring configuration and videography of caves (Bowen, 

1996, 2015), regional hydrology (Kohout, 1965; Stringfield, 

1966; Vernon, 1970; Henry and Kohout, 1972; Kohout and 

others, 1977; Johnston and others, 1980; Ryder, 1985; Metz 

and Lewelling, 2009), groundwater temperature (Darton, 

1920; Kohout, 1967; Griffin and others, 1969; Clausen and 

others, 1975; Griffin and others, 1977; Kohout and others, 

1977; Sproul, 1977; Sacks and Tihansky, 1996), water quality 

(Rosenau and others, 1977; Hutchinson, 1992; Sacks and 

Tihansky, 1996; Scott and others, 2004; and Ryan and others, 

2011), modeling of groundwater levels, temperature, and 

chloride (Hughes and others, 2007, 2009), and analysis of 

collapsed geologic features or structural anomalies and their 

relation to the movement of groundwater (Popenoe and others, 

1984; Hutchinson, 1992; Spechler, 1994, 1996; Spechler and 

Wilson, 1997; Odum and others, 1999; Cunningham, 2013).

Regional analyses were based in part on analyses of 

groundwater levels in wells. Hereinafter, the term “water 

level” will be used for the elevation of the groundwater in 

a well open to an unconfined aquifer and for the elevation 

to which groundwater would potentially rise in a well that 

penetrated a confined aquifer. If the water level rises above 

the confining layer that overlies the aquifer or if groundwater 

flows to the surface, the well is considered an artesian well 

(Fetter, 2001; Perlman, 2016). In confined aquifers, groundwater levels could potentially rise to elevations above the land 

surface. Water levels and temperatures were analyzed from 

six ROMP wells (ROMP 8, 9, 12, 13, 14, 16.5), the Stevens 

#1 well (Kohout and others, 1977), Sarasota 9 well, and a 

deep exploratory Gulf of Mexico well (State of Florida Lease 

224-B, well #1; USGS well 264107082190301; Kohout and 

others, 1977; fig. 1). When necessary, water levels in wells 

were corrected for salinity based on methods by Guo and 

Langevin (2002). Salinity corrections were applied to aquifer 

water levels from the ROMP 8, 9, 12, and 16.5 wells. Data for 

ROMP wells and the Sarasota 9 well were obtained from the 

Southwest Florida Water Management Information System 

(Southwest Florida Water Management District, 2016a). 

Potential areas of groundwater recharge and discharge 

were identified by comparing the elevation of the potentiometric surface of the Upper Floridan aquifer for September 

2010 (Ortiz, 2011) and land-surface elevation data (U.S. 

Geological Survey EROS Data Center, 1999). The potentiometric surface represents the level to which groundwater 

would rise in a cased well (Fetter, 2001). A potentiometric 

surface is constructed by interpolating the water levels in wells 

over an area of interest at a given time. Four wells in Sarasota 

County used to compute the September 2010 potentiometric 

surface were corrected for salinity (Ortiz, 2011). Areas where 

the potentiometric surface was below the land surface were 

considered potential areas of groundwater recharge, and areas 

where the potentiometric surface was above the land surface 

were considered potential areas of groundwater discharge. 

Potentiometric surfaces for predevelopment levels (Johnston 

and others, 1980) were compared with May 1975 levels (Mills 

and Laughlin, 1976) and May 2007 levels (Ortiz, 2008), 

as reported by Metz and Lewelling (2009). Three wells in 

Sarasota County were corrected for salinity on the May 2007 

potentiometric surface (Ortiz, 2008). 

Climate data for the Myakka River watershed were 

obtained from the Southwest Florida Water Management 

Information System (Southwest Florida Water Management 

District, 2016b). Discharge data at the spring outlet were 

obtained from various sources, including Rosenau and others 

(1977), Scott and others (2004), USGS site numbers 02299260 

and 270333082154000 (National Water Information System 

[NWIS]; http://nwis.waterdata.usgs.gov/fl/nwis/nwis), Southwest Florida Water Management Information System (Southwest Florida Water Management District, 2016a), and from 

Hydrologic Data Collection, Inc. (http://www.hydrologicdata.

com). Water-use data for counties in Florida for the period 

1965–2010 were obtained from the U.S. Geological Survey 

(2016), and from Metz and Lewelling (2009). 

Groundwater geochemistry of Warm Mineral Springs, 

and wells and springs in the region were obtained from 

archives by the USGS NWIS, and the Southwest Florida 

Water Management Information System (Southwest Florida 

Water Management District, 2016a). Geochemical and waterquality data are also compiled in reports by Rosenau and 

others (1977), Scott and others (2004), Harrington and others, 

(2010), Ryan and others (2011), and databases of Sarasota 

County (2016a), Southwest Florida Water Management 

District (2016a), and the USGS NWIS (USGS site numbers 

02299260 and 270333082154000). Water samples collected 

on January 31, 1985, at Warm Mineral Springs (USGS site 

number 02299260) were analyzed for anthropogenic compounds; however, no compounds were detected above the minimum reporting level, and this analysis will not be discussed in 

this report.

The City of North Port contracted divers to collect water 

samples and temperature data from Warm Mineral Springs on 

April 29, 2015. Samples were collected at four vents at the 

spring bottom and were analyzed to assess nutrients and major 

chemical constituents. During this sampling event continuous 

water temperature sensors that collected data at 1-second intervals were attached to two divers on a descent to the bottom 

spring vents. Data were stored in the Sarasota County Water 

Atlas (Sarasota County, 2016b, 2016c). 

Statistical analyses were computed using the R statistical 

package (R Core Team, 2012). Statistical significance of 

trends were based on the Kendall’s tau non-parametric test 

(Helsel, and Hirsch, 2002). Significance was based on a 

0.05 probability of a type I error (probability of rejecting the 

null hypothesis when true).
Retrospective Analysis 5

Retrospective Analysis

The retrospective analysis of Warm Mineral Springs 

includes a summary of the climate, geologic setting, and 

hydrologic setting at a statewide to local scale. This description is followed by a discussion of the local geologic and 

hydrologic characteristics of Warm Mineral Springs, including 

the discharge, water temperature, geochemistry, and water 

quality of the spring. 

Climate of the Myakka River Basin

Warm, wet summers and relatively mild, dry springs 

characterize the subtropical climate of Myakka River Basin, 

where Warm Mineral Springs is located (fig. 1A). Rainfall 

varies seasonally, and more than half of the annual rainfall 

typically occurs during the summer months (June through September; Basso and Schultz, 2003). Rainfall can be unevenly 

distributed throughout Sarasota County during the summer 

rainy season because the rain is derived from localized, convective thunderstorms. Winter rainfall is more evenly distributed because storms generally come from frontal air masses 

that move from north to south across the State (Metz and 

Lewelling, 2009). The median annual rainfall for 1940–2015 

for the Myakka River Basin was 53 inches per year (in/yr; 

fig. 3). There was no significant trend in annual precipitation 

for water years 1940–2015, based on the Kendall’s tau nonparametric test.

Geologic Setting

Warm Mineral Springs is located near the central axis of 

the Florida Platform (fig. 1B). The Florida Platform throughout its history has been flooded by the sea or exposed as dry 

land (Randazzo, 1997; Hine, 2013). Warm Mineral Springs 

is located on the Pleistocene-age (2.6–0.01 million years ago 

[Ma]) Palmico terrace (Healy, 1975), which formed when 

sea level rose to an elevation of about 25 to 30 ft (MacNeil, 

1949); the land surface at Warm Mineral Springs is at an 

elevation of about 10 ft NGVD 29 (at USGS site number 

270333082154000). The dominant bedrock of the Florida 

Platform consists of carbonate rocks, such as limestone and 

dolostone, that span the Cenozoic Era (66–0 Ma; Hine, 2013; 

fig. 4). The geologic formations exposed at Warm Mineral 

Springs consist of the late Oligocene-age (the Oligocene 

Epoch spans 34–23 Ma) to Miocene-age (23–5 Ma) Arcadia 

Formation of the Hawthorn Group (fig. 5A). The Hawthorn 

Group is composed of carbonate rocks with sand and clay 

layers (Clayton, 2010). The Arcadia Formation includes 

dolostone, phosphatic sand, and dolomitic clay (Rupert, 

1994). Underlying the Hawthorn Group are Oligocene-age to 

Eocene-age (56–34 Ma) limestones and dolostones, including 

the Suwannee Limestone, Ocala Limestone, and Avon Park 

Formation (fig. 4).

The carbonate rocks surrounding and underlying Warm 

Mineral Springs were deposited in both open and restricted 

marine environments. Later erosion and weathering of these 

carbonate rocks resulted in the vugs, cavities, and solution 

35

40

50

60

70

80

45

55

65

75

85

1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

Annual precipitation, in inches

Year

Median 1940–2015

53.2 inches

Figure 3. Annual precipitation in the Myakka River Basin, 1940–2015. Data source is the Southwest Florida Water 

Management District (2016b).
6 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

fractures. Eventually, with continued enlargement of these 

features, sinkholes can form. Such features constitute a major 

part of the porosity and permeability of carbonate aquifers in 

Florida (Williams and Kuniansky, 2015).

The Warm Mineral Springs pool has a circular shape 

(fig. 2) and was created when the sinkhole formed in the sand, 

clay, and dolostone of the Arcadia Formation (Rupert, 1994; 

fig. 5A). A debris cone, which measures about 225 ft wide 

and 125 ft thick, covers much of the bottom of Warm Mineral 

Springs and formed from material that collapsed into the 

sinkhole (Cockrell, 1990; Rupert, 1994). Several of the largest 

springs in Florida (Silver Springs, Homosassa Springs, and 

Wakulla Springs; fig. 1) probably originated as sinkholes that 

became springs as a result of rising groundwater and sea levels 

during the Holocene Epoch (since 11.7 thousand years ago 

[ka]; Upchurch and Randazzo, 1997). 

Numerous flowstones or stalactites and water channels 

are present on the carbonate walls that are currently (2016) 

below the pool surface of Warm Mineral Springs, indicating 

exposure to air and flow of water down the exposed wall at 

some time in the past (fig. 5A, B). The water level during the 

Late Pleistocene was initially estimated as at least 75 ft below 

the spring pool surface (Clausen and others, 1975). A later 

report by Cockrell (1990) indicated the Late Pleistocene water 

level to be at 100 ft (30 meters) below the modern spring pool 

surface at about 12 ka on the basis of plant material and radiometric dating of human remains found in the sink (fig. 5A). 

As sea level rose during the Holocene Epoch, groundwater 

levels also rose, and Warm Mineral Springs gradually filled 

with mineralized groundwater. Collapsed geologic features 

and structural anomalies have been known to act as preferential avenues for groundwater flow (Spechler, 1994; Metz and 

Lewelling, 2009; Cunningham, 2013).

SERIES STRATIGRAPHIC UNIT GEOLOGY AND LITHOLOGY HYDROGEOLOGIC UNIT

Miocene

Oligocene

Eocene

Paleocene

Undifferentiated

 surficial deposits

Sand and fossil fragments Surficial aquifer system

(surficial aquifer)

Sand, silt, and clay

Sand, clay, marl, 

limestone and dolostone. 

Fossils common. 

Hawthorn

Group

Peace River Formation

Arcadia Formation

Intermediate aquifer

 system1

Tampa 

Member

Suwannee Limestone

Ocala Limestone

Avon Park Formation

Oldsmar Formation

Cedar Keys Formation

Limestone, sandy limstone 

and sand. 

 Dolostone beds and fossils common. Fractured dolostones common

 in the Avon Park Formation 

Upper Floridan aquifer

Middle confining unit, 

II and VI

Lower Floridan aquifer

Sub-Floridan confining unit

Floridan aquifer system

Limestone and dolostone with

some intervals containing

inclusions of gypsum

and anhydrite

Limestone and dolostone with

beds of gypsum and anhydrite

Confining unit

Confining unit

Semiconfining unit

Upper Arcadia aquifer

Lower Arcadia aquifer

Suwannee permeable zone

Ocala low permeability zone

Avon Park 

permeable zone

Arcadia Formation

Holocene and

Pleistocene

Pliocene

Venice Clay

Caloosahatchee

Formation

1

A proposed revision by DeWitt and Mallams (2007) and Mallams and DeWitt (2007) replaces zone 2 and zone 3 from Knochenmus (2006) with the upper and lower Arcadia aquifers, 

respectively. This revision also proposes to rename the intermediate aquifer system in southwestern Florida to the Hawthorn aquifer system (excluding the upper and lower confining 

units). There is not a current consensus, however, on the use of “Hawthorn aquifer system,” so in this report only the proposed upper and lower Arcadia aquifer names are used.

Figure 4. Relation of stratigraphic and hydrogeologic units of the Florida Platform in central Florida

(modified from Metz and Lewelling, 2009; Clayton, 2010).
Retrospective Analysis 7

Surface

Pleistocene

Undifferentiatedsurficial deposits

N S

Debris cone

Miocene

Hawthorn Group - Arcadia Formation

Depth, in feet below pool surface

30

60

90

120

150

180

210

0

Cave system (vent B)

EXPLANATION

Approximate water level, 

12,000 years before present

Location of 

water channels

Location of 

water channels

Homo sapien burial site

100

110

Location of 

flowstones

Location of 

flowstones

A

B

Photograph by Curt Bowen, ADM Exploration Foundation, 2015

Greenish-gray dolomitic clay 

Yellowish-gray recrystallized dolostone containing phosphatic sand, 

mollusk molds, and recrystallized echinoid fossils

Yellow-gray to light olive, microcrystalline dolostone containing 

variable amounts of sand and phosphatic sand, mollusk molds, 

sporadic vertebrate bones, and benthic foraminifera 

Surficial sand 

Gray, sandy dolostone, 

containing fossils 

Greenish-gray to olive green 

dolostone containing 3 to 

5 percent phosphate sand 

Figure 5. A, The geology of Warm Mineral Springs (modified from Rupert, 1994). B, Flowstones located 

on the walls of Warm Mineral Springs.
8 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

Hydrologic Setting

The hydrologic units in the Warm Mineral Springs area 

are described at the ROMP 8 well (fig. 1A, B), located approximately 1.3 miles north-northeast of Warm Mineral Springs 

(Clayton, 2010). Exploratory coring in the first phase of the 

ROMP 8 well construction extended to a depth of 1,283 ft 

below the land surface (bls). The ROMP 8 well penetrated 

three aquifers: the surficial aquifer system, the intermediate 

aquifer system, and the Upper Floridan aquifer. The stratigraphy and corresponding aquifer units for the study area are 

shown in figure 4. In locations where the geologic units that 

compose the intermediate aquifer system do not have aquifer 

properties, this unit is referred to as the upper confining unit. 

At the ROMP 8 well, the lower most unit of the intermediate 

aquifer system was considered to be a “semi-confining unit” 

and not very effective as a confining unit (Clayton, 2010). 

Underlying the Upper Floridan aquifer is the middle confining 

unit and the Lower Floridan aquifer (fig. 4).

Regional Groundwater Levels and Water Use of 

the Upper Floridan aquifer

Warm Mineral Springs is located in the Southern WestCentral Florida Groundwater Basin (SWCFG Basin), which 

covers an area of approximately 5,000 square miles (fig. 6). 

Lateral flow paths of groundwater can be estimated from the 

configuration of the potentiometric surface of the Upper Floridan aquifer. The potentiometric surface for the Upper Floridan 

aquifer for September 2010 (Ortiz, 2011) for the approximate 

area of the SWCFG Basin indicates a relative high to the north 

and east (areas of recharge in Polk and Highlands Counties) 

and a relative low to the west and south (areas of discharge in 

Manatee, Sarasota, DeSoto, and Charlotte Counties; fig. 6). 

Groundwater flow paths inferred from the configuration 

of the potentiometric surface for September 2010 are generally 

from areas of recharge (in Polk and Highlands Counties) to 

areas of discharge (in Manatee, Sarasota, DeSoto, and Charlotte Counties). Warm Mineral Springs is located in an area 

with the potential for discharge to the surface. 

Analysis of a series of ROMP wells along a cross-section 

line (fig. 6) were used to assess the groundwater flow patterns 

in the region of Warm Mineral Springs. Water levels indicate 

that the ROMP 13 and 14 wells were in an area of recharge, 

and the ROMP 8, 9, 12, and 16.5 wells were located in an area 

of discharge (fig. 6). Mean annual water levels for 2007–15 in 

ROMP wells were analyzed for the surficial aquifer system, 

Peace River Formation, upper Arcadia aquifer, and Upper 

Floridan aquifer (Suwannee Limestone and Avon Park Formation). Artesian conditions from the Upper Floridan aquifer 

were indicated for wells located in discharge areas: ROMP 8, 

9, 12 and 16.5 (table 1). The ROMP 8 and 9 wells, located 

closer to the coast, had water levels for the Upper Floridan 

aquifer that were 15 to 19 ft above land surface, respectively. 

On the basis of these ROMP groundwater levels, there is an 

increase in the potential for groundwater discharge in areas 

closer to the coast. Ryder (1985) developed a steady-state 

model of groundwater flow for west-central Florida. Along a 

cross section approximately 30 miles north of Warm Mineral 

Springs (figure 19 of Ryder, 1985), groundwater flow was 

simulated as downward from the surface and intermediate 

aquifer systems into the Upper Floridan aquifer in inland 

areas (Hardee and Polk Counties), and upward groundwater 

flow from the Upper Floridan aquifer was simulated in coastal 

regions, such as Sarasota County.

Groundwater from the Upper Floridan aquifer is the 

largest component of the water supply in the counties within 

the SWCFG Basin, (Marella, 2014). The 10-year moving average for estimated groundwater withdrawal during 1991–2010 

in the SWCFG Basin was about 650 million gallons per day 

(Mgal/d), which represents a twofold increase from the 1950s; 

much of the increase occurred from the 1950s to the 1970s 

(fig. 7A). In contrast, total groundwater use in Sarasota County 

has had no significant temporal trend from 1965 to 2010 (estimated every 5 years), with significance based on the Kendall’s 

tau non-parametric test (fig. 7B). Water use from groundwater 

sources (as a fraction of total water use) in Sarasota County 

ranged from 98 percent in 1965 to 78 percent in 1995. 

Decreased water use in 1995 was associated with the maximum annual precipitation for the period 1940–2015 (fig. 3).

Declines in groundwater levels occurred within the 

SWCFG Basin from the 1930s to the 1970s as a result of 

water withdrawals for phosphate mining in the northern part 

of the basin (Polk County) and other uses (Metz and Lewelling, 2009). In the area of Warm Mineral Springs, the historical increase in groundwater withdrawals, and other factors 

(sometimes counteracting withdrawals) such as weather 

conditions and agricultural conservation, resulted in a 10- to 

20-ft decline in the potentiometric surface of the Upper Floridan aquifer by May 1975 relative to predevelopment levels 

(fig. 8); water levels remained at approximately the May 1975 

level in May 2007 (Metz and Lewelling, 2009, p. 32). Despite 

stabilization of groundwater levels since the 1970s, depressed 

aquifer levels have resulted in secondary effects, such as saltwater intrusion and lowered lake levels in the region (Southwest Florida Water Management District, 2016c). 

Discharge

Historical measurements of discharge were made on 

Warm Mineral Springs Creek (fig. 2), which flows southwestward to Salt Creek and eventually into the Myakka River 

(fig. 1A). While Warm Mineral Springs is classified as a thirdmagnitude spring (1–10 ft3

/s), recorded flows at Warm Mineral 

Springs Creek have exceeded 10 ft3/s. Ten instantaneous 

discharge measurements from 1942 to 1974 averaged 9.7 ft3/s 

and exceeded 10.0 ft3/s in 3 of 10 years. Discharge measurements since 1971 have been less than 10 ft3

/s (table 2; fig. 9). 

Measurements of discharge at Warm Mineral Springs Creek 

are sparse for the time period 1942–2014, but changes over 
Retrospective Analysis 9

Sarasota 

9 well

DESOTO

Gulf of Mexico

Little Salt 

Spring

Warm Mineral 

Springs

EXPLANATION

70

20

10

80

90

100

110

120

20

50

ROMP 14

ROMP 8 ROMP 13

A

A'

60

40

50

30

224B-1 well

SARASOTA 

GLADES

CHARLOTT E

LEE

ROMP 9 ROMP 16.5

ROMP 12

HIGHLANDS

HARDEE

HILLSBOROUGH

POLK

MANATEE

Base modified from Esri, DeLorme, HERE, TomTom, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, 

IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), swisstopo, and the GIS User Community 

Potentiometric-surface contour—Shows level that water would have stood in 

tightly cased wells tapping the Upper Floridan aquifer, in feet. Interval 10 feet. 

Datum is NGVD 29 (modified from Ortiz, 2011) 

Generalized groundwater flow paths 

Location of selected wells used in the study—Regional Observation Monitor-Well 

Program (ROMP)

50

A A'

Generalized area of potential discharge 

from the Upper Floridan aquifer 

Generalized area of potential recharge 

to the Upper Floridan aquifer 

Cross-section location—Cross section 

shown in figure 14 

N

0 20 MILES

0 20 KILOMETERS

10

10

Approximate extent of 

Southern West-Central

Florida Groundwater

Basin

Figure 6. Area of recharge and discharge, potentiometric surface of the Upper Floridan aquifer for September 2010, generalized 

groundwater flow path in the Southern West-Central Florida Groundwater Basin, and location of wells used in this study (modified 

from Ortiz, 2011).
10 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

Table 1. Water levels above or below land surface for selected Regional Observation Monitor-Well Program (ROMP) wells, 2007–15, 

stored by the Southwest Florida Water Management District (2016c).

[Location of wells shown in figure 6. SWFWMD, Southwest Florida Water Management District; ID, identification; ft, foot; SA, surficial aquifer; IAS, intermediate aquifer system; UFA, Upper Floridan aquifer; —, conditions did not occur]

ROMP 8 well 

(potential discharge area) 

SWFWMD 

site ID 

number

Aquifer

Land-surface 

elevation 

(ft)

Water levels below 

land surface (ft)

Water levels above 

land surface (ft)

Minimum Maximum Minimum Maximum

Surficial aquifer monitor 25987 SA 19 5.52 13.19 — —

Upper Arcadia monitor 25936 IAS 19 3.55 9.92 — —

Lower Arcadia monitor* 770430 IAS 19 — — 4.17 11.68

UFA Suwannee Monitor* 25937 UFA 19 — — 6.17 15.55

ROMP 9 well 

(potential discharge area) 

SWFWMD 

site ID 

number

Aquifer

Land-surface 

elevation 

(ft)

Water levels below 

land surface (ft)

Water levels above 

land surface (ft)

Minimum Maximum Minimum Maximum

Surficial aquifer monitor 25982 SA 25 6.05 10.53 — —

Peace River monitor 25979 IAS 25 2.94 9.49 — —

Upper Arcadia monitor* 25984 IAS 25 0.01 6.33 0.01 1.81

Lower Arcadia monitor* 25983 IAS 25 — — 9.11 17.4

UFA Suwannee Monitor* 25980 UFA 25 — — 11.06 19.33

UFA Avon Park monitor * 25981 UFA 25 — — 11.31 19.43

ROMP 16.5 well 

(potential discharge area) 

SWFWMD 

site ID 

number

Aquifer

Land-surface 

elevation 

(ft)

Water levels below 

land surface (ft)

Water levels above 

land surface (ft)

Minimum Maximum Minimum Maximum

Surficial aquifer monitor 24355 SA 40 0.01 2.24 0.01 3.12

Peace River monitor 24354 IAS 40 0.01 2.91 0.01 2.04

Lower Arcadia monitor* 24360 IAS 40 — — 1.42 10.36

UFA Suwannee Monitor* 24357 UFA 40 — — 0.55 9.86

UFA Avon Park monitor* 737414 UFA 40 1.21 10.05

ROMP 12 well 

(potential discharge area) 

SWFWMD 

site ID 

number

Aquifer

Land-surface 

elevation 

(ft)

Water levels below 

land surface (ft)

Water levels above 

land surface (ft)

Minimum Maximum Minimum Maximum

Surficial aquifer monitor 24222 SA 41 0.01 6.76 0.01 1.49

Peace River monitor 24219 IAS 41 0.01 4.91 0.01 2.17

Upper Arcadia monitor 24221 IAS 41 — — 0.13 8.84

Lower Arcadia monitor* 24215 IAS 41 — — 0.14 8.84

UFA Suwannee Monitor* 24218 UFA 41 — — 0.27 9.06

UFA Avon Park monitor* 25209 UFA 41 — — 0.13 9.16

ROMP 13 well 

(potential discharge area) 

SWFWMD 

site ID 

number

Aquifer

Land-surface 

elevation 

(ft)

Water levels below 

land surface (ft)

Water levels above 

land surface (ft)

Minimum Maximum Minimum Maximum

Surficial aquifer monitor 24194 SA 62 0.01 6.74 — —

Upper Arcadia monitor 24193 IAS 62 9.61 23.21 — —

Lower Arcadia monitor 24198 IAS 62 9.65 26.01 — —

UFA Suwannee Monitor 24195 UFA 62 9.17 25.03 — —

UFA Avon Park monitor 24196 UFA 62 9.92 23.78 — —

ROMP 14 well 

(potential discharge area) 

SWFWMD 

site ID 

number

Aquifer

Land-surface 

elevation 

(ft)

Water levels below 

land surface (ft)

Water levels above 

land surface (ft)

Minimum Maximum Minimum Maximum

Surficial aquifer monitor 23821 SA 145 3.22 9.85 — —

Upper Arcadia monitor 23820 IAS 145 32.11 40.29 — —

UFA Suwannee Monitor 23823 UFA 145 93.48 103.57 — —

UFA Avon Park monitor 23822 UFA 145 103.96 93.87 — —

*Water levels were adjusted to correct for saltwater density differences, using methods by Guo and Langevin (2002).
Retrospective Analysis 11

Figure 8. Change in the potentiometric surface of the Upper Floridan aquifer between predevelopment levels (Johnston and 

others, 1980) and May 1975 levels (Mills and Laughlin, 1976), and change between predevelopment levels and May 2007 levels

(Ortiz, 2008) levels (modified from Metz and Lewelling, 2009). 

Estimated groundwater use—Excluding Charlotte, Glades, and Lee Counties 

(Southwest Florida Water Management District, written commun., 2009)

10 year moving average

EXPLANATION

0

10

20

30

40

50

60

70

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

A B

900

800

700

600

500

400

300

200

100

Estimated groundwater use, Southern West-Central 

Florida Groundwater Basin, in million gallons per day

0

1950 1960 1970 1980 1990 2000 2010

Water withdrawal for Sarasota County, 

in million gallons per day

Year

Year

83° 82° 81°

28°

27°

POLK

SARASOTA

MANATEE

HILLSBOROUGH

HIGHLANDS

DE SOTO

HARDEE

CHARLOTTE

A. May 1975 B. May 2007

Peace River

Gulf of Mexico

Gulf of Mexico

PASCO

OSCEOLA

GLADES

HENDRY

LEE

COLLIER

LAKE

PINELLAS

83° 82° 81°

28°

27°

POLK

SARASOTA

MANATEE

HILLSBOROUGH

HIGHLANDS

DE SOTO

HARDEE

CHARLOTTE

Peace River

PASCO

OSCEOLA

GLADES

HENDRY

LEE

COLLIER

LAKE

PINELLAS

Approximate extent of 

Southern West-Central

Florida Groundwater

Basin

Approximate extent of 

Southern West-Central

Florida Groundwater

Basin

Warm Mineral Springs Warm Mineral Springs

0

0 40 KILOMETERS

40 MILES 0

0 40 KILOMETERS

40 MILES

EXPLANATION

Decrease in the potentiometric surface levels of the Upper Floridan aquifer, in feet—Based 

on predevelopment levels (Johnston and others, 1980) and May 2007 levels (Ortiz, 2008)

>50

>40 to 50

>30 to 40

>20 to 30

>10 to 20

0 to 10

Base modified form ESRI ArcGIS online data base: 1:100,000, 2014, 

World Geodetic System of 1984

Base modified form ESRI ArcGIS online data base: 1:100,000, 2014, 

World Geodetic System of 1984

Figure 7. A, Estimated groundwater use in the Southern West-Central Florida Groundwater Basin (adapted from Metz and 

Lewelling, 2009). B, Estimated groundwater use in Sarasota County.
12 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

this time period are indicated. Discharge decreased from about 

11–12 ft3/s in the 1940s to about 6–9 ft3/s in the 1970s, and 

remained mostly at that level for the remainder of the period 

of record. This pattern of decrease until about the 1970s is 

consistent with the trend of water withdrawals for the SWCFG 

Basin, previously discussed in the “Regional Groundwater 

Levels and Water Use” section, which indicates that basinscale changes to the groundwater system, such as groundwater 

use, have affected discharge at Warm Mineral Springs.

There are five known vents or solution conduits in the 

northern half of the spring bottom (Rupert, 1994; Bowen, 

2015; fig. 10A). The largest vent (vent B), and the primary 

inflow to the spring, emanates from a cave that extends about 

174 ft (53 meters) into the Arcadia Formation and descends 

slightly downward to a depth of about 220 ft (67 meters) 

below the pool surface (Rupert, 1994). The largest part of 

the vent is at the end of the cave, which opens into a room 

that measures about 33 ft long by 10 ft high by 10 ft wide. 

Table 2. Instantaneous discharge and water temperature measurements made at Warm Mineral Springs outlet (1942 to 

2015) and average, annual water levels for the Upper Floridan aquifer.

[NGVD 29, National Geodetic Vertical Datum of 1929; USGS, U.S. Geological; —, no data or not applicable; SWFWMD, Southwest Florida 

Water Management District; HDC, Hydrologic Data Collection, Inc. (http://www.hydrologicdata.com/)]

Agency or report Site number Date of 

measurement

Discharge, in 

cubic feet per 

second

Water 

temperature, 

in degrees 

Fahrenheit

Average annual 

Upper Floridan 

aquifer levels, 

in feet above 

NGVD 291

USGS 02299260 10/1/1942 11.7 — 32.54

Rosenau and others (1977) — 8/11/1943 — 86.0 32.40

USGS 02299260 4/29/1946 10.8 — 32.37

USGS 02299260 4/24/1956 9.5 87.8 30.10

USGS 02299260 12/14/1960 9.0 84.2 30.47

USGS 02299260 2/22/1962 9.4 86.0 28.03

USGS 02299260 4/9/1962 10.0 84.0 28.03

USGS 02299260 6/7/1962 9.3 87.8 28.03

USGS 02299260 6/15/1962 — 77.0 28.03

USGS 02299260 11/22/1971 11.2 — 23.76

USGS 02299260 4/24/1972 -- 85.1 22.97

USGS 270333082154000 5/31/1972 9.2 73.4 22.97

USGS 02299260 10/13/1972 — 84.2 22.97

Rosenau and others (1977) — 5/22/1974 7.6 — 19.36

USGS 02299260 6/3/1981 6.9 — 20.36

USGS-WRD 02299260 11/29/1984 — 84.2 21.97

USGS-WRD 02299260 1/31/1985 8.8 83.3 17.68

Scott and others (2004) DEP FGS-443 4/3/2003 8.5 86.4 22.88

SWFWMD 773331 8/11/2009 8.1 — 15.64

SWFWMD 773331 2/3/2011 7.0 — 15.99

SWFWMD 773331 7/20/2011 8.1 — 15.99

HDC — 5/2/2012 5.4 — 13.48

HDC — 6/6/2012 6.5 — 13.48

HDC — 7/11/2012 6.8 — 13.48

HDC — 8/22/2012 6.7 — 13.48

HDC — 9/28/2012 7.2 — 13.48

SWFWMD 773331 7/30/2013 8.8 — 17.22

USGS 02299260 4/11/2014 8.3 — 18.64

Sarasota County (2016b) — 4/29/2015 — 84.5 20.00

1

Sarasota 9 well (USGS site number 271938082251801 and SWFWMD site number 25682).
Retrospective Analysis 13

The discharge at the end of the cave was observed by Rupert 

(1994) as diffuse upward flow from the cavern floor. 

One discharge measurement (1971) of approximately 

30 ft3/s was made by divers at vent B at a depth of 205 ft 

(fig. 10B) on November 22, 1971. Discharge was computed 

by approximating cave cross-sectional area and measuring the 

velocity of fluorescein dye over a 15-ft length of the vent cave 

(Kohout and others, 1977). The instantaneous measurement 

of spring discharge at the outlet for that day was 11.2 ft3/s and 

was the second highest discharge recorded (table 2). Given the 

uncertainty of measuring velocity at the vent using fluorescein 

dye methods and uncertainty in vent geometry, conclusions 

regarding processes to explain the apparent differences in vent 

and surface discharge are not possible. A second measurement at vent B was attempted in May 1974, but velocity was 

very low (0.1 foot per second) and the discharge estimate 

was not considered valid for this analysis. The instantaneous 

measurement of spring discharge on May 22, 1974, was 

7.6 ft3/s. Kohout and others (1977) indicated that the 1974 

measurement was taken following a dry season, and suggested that flow from vents might be variable. In addition to 

warm vents, cool-water vents discharge from the walls of the 

spring. Bowen (1996) reported cool vents at depths of 198 ft 

(76 °F) and 8 ft. Cool vents could be used to infer that water is 

discharging from shallower aquifers, such as the intermediate 

aquifer system, into the spring.

Water Level in the Sarasota 9 Well and Relation 

to Spring Discharge

The relation was assessed between water levels of the 

Upper Floridan aquifer for the Sarasota 9 well (fig. 1) and the 

spring discharge at Warm Mineral Springs for 1942–2014. The 

Sarasota 9 well was the only Upper Floridan aquifer well in 

Sarasota County with long-term water level data (1931–2015), 

and water levels in this well are influenced by groundwater 

use. The annual mean of water levels was used to adjust for 

changes in water within a given year. The annual mean water 

level of the Upper Floridan aquifer at the Sarasota 9 well 

exhibits a pattern of decline since the 1950s, with the rate 

of decline decreasing following the 1980s to current (2015) 

levels (fig. 11). 

A significant linear relationship exists between the mean 

annual (if more than one measurement in a year) or instantaneous (if only one measurement in a year) discharge measurements at Warm Mineral Springs and the annual mean water 

level at the Sarasota 9 well (fig. 12). Uncertainty in estimates 

from the linear regression is reflected in the coefficient of 

determination (R2) for the regression of 0.58. Uncertainty is 

also indicated by analysis of residuals (predicted value minus 

observed), which had a standard deviation of 0.6 ft3/s, or 

about 7 percent of the mean annual discharge of 8.5 ft3/s for 

1942–2014. 

Discharge, in cubic feet per second

50

55

60

65

70

75

80

85

90

5

6

7

8

9

10

11

12

13

14

15

1940 1950 1960 1970 1980 1990 2000 2010 2020

Water temperature, in degrees Fahrenheit

Year

Discharge 

Water temperature in pool

EXPLANATION

Figure 9. Instantaneous discharge and water temperature measurements at Warm Mineral Springs, 1942–2015.
14 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

East

North

South

205 feet

Vent A

(Sample 1)

Vent B 

(Sample 2)

 205 feet

Vent D

(Sample 4)

 196 feet

182 feet

154 feet

120 feet

150 feet

180 feet 160 feet

173 feet

192 feet

202

feet

West

Outline of spring 

bottom within the 

Arcadia Formation 

Vent C

(Sample 3)

200 foot depth line

Vent E

(not sampled)

283 feet

265 feet

Vent D

Vent A Vent B entrance

Vent B (near the end of 174 ft long conduit system) Vent D

A

B

Figure 10. A, Diagram of the bottom of Warm Mineral Springs showing the location of spring vents A–E (modified from Bowen, 2015). 

B, Photographs showing some of the spring vents (photographs by Curt Bowen, ADM Exploration Foundation, 2015).
Retrospective Analysis 15

Given the uncertainty of simple linear models, 

understanding the relation between discharge and aquifer 

water levels could be improved with continuous discharge 

measurements at Warm Mineral Springs. The proximity of 

the ROMP 8 well makes it a valuable resource for developing 

relationships between discharge at Warm Mineral Springs and 

aquifer levels, providing local water levels for the surficial 

aquifer, upper Arcadia aquifer, and Upper Floridan aquifer 

(Suwannee Limestone; Southwest Florida Water Management 

District, 2016a). 

Water Temperature

Temperature was discontinuously measured at the Warm 

Mineral Springs pool, with 14 measurements made over the 

period 1943–2015. Historic temperature readings at Warm 

Mineral Springs (table 2; fig. 9) ranged from 73.4 °F (1972) 

to 87.8 °F (1956, 1962). Low temperature readings of 77.0 °F 

and 73.4 °F, during 1962 and 1972, respectively, are outliers. 

For example, a reading of 87.8 °F on June 7, 1962, was followed by a reading of 77 °F on June 15, 1962. The reading of 

73.4 °F in May 31, 1972, is bracketed by readings of 85.1 °F 

and 84.2 °F during 1972. The variability might reflect readings 

taken at different locations, but the reason for these outliers 

was not determined. Sparseness of temperature data makes 

identification of outliers difficult; continuously monitored 

temperature from a consistent location would allow for identification of outliers as valid or invalid readings, and increase 

confidence in future measurements. There was no significant 

trend in temperature over the period of record, based on the 

Kendall’s tau test, whether the outliers noted above were 

included or deleted in the analysis. 

Water temperature readings were recorded once a year 

from 2011 to 2016 for the outlet channel of Warm Mineral 

Springs by the Southwest Florida Water Management District 

(2016a; station number 773331) and ranged from 86 to 89 °F. 

An indirect comparison of the outlet with pool temperatures 

can be made for temperature readings in 2015. Pool temperatures on March 18 and August 29 were about 83 and 86 °F, 

respectively, whereas the outlet temperature measurement on 

July 28 was about 87 °F. Temperatures from 1995 to 2015 

0

5

10

15

20

25

30

35

40

5

6

7

8

9

10

11

12

13

14

15

1940 1950 1960 1970 1980 1990 2000 2010 2020

Water level elevation, in feet NGVD 29

Discharge, in cubic feet per second

Year

Discharge 

Monthly mean water level 

Annual mean water level

EXPLANATION

Figure 11. Time series of instantaneous discharge at Warm Mineral Springs and annual mean 

and monthly water-level elevation of the Upper Floridan aquifer in the Sarasota 9 well. 

Discharge = 0.1764·water level + 4.8945

R2 = 0.58

6

7

8

9

10

11

12

10 15 20 25 30 35

Discharge, in cubic feet per second

Water level, in feet NGVD 29

Figure 12. Annual mean or instantaneous discharge at Warm 

Mineral Springs and water-level elevation of the Upper Floridan 

aquifer in the Sarasota 9 well. 
16 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

were also recorded by the Southwest Florida Water Management District (2016a) from water samples collected from 

the spring (station number 25993); however, samples were 

pumped to the surface and exposed to the air temperature and 

would therefore not be representative of pool temperatures 

(D. Dewitt, Southwest Florida Water Management District, 

oral commun., 2016). These temperature measurements are 

not discussed further herein.

There are several vents in Warm Mineral Springs, both 

cool and warm. Clausen and others (1975) report that there 

were nine cool (73 °F) and two major hot water (99 °F) vents 

along the bottom of the northern spring wall at a depth of 

about 200 ft. Clausen and others (1975) also discuss the intermixing of the cool and warm waters that produce a year-round 

uniform temperature of about 88 °F in the upper two-thirds of 

the water column. Bowen (1996) reports there is a cool water 

inflow vent at 8 and 198 ft below the spring surface on the 

southwest side of the pool. Bowen (1996) reports temperatures 

of 97 °F for the two major bottom hot water vents.

Temperature sensors were attached to two divers on a 

descent to the bottom of Warm Mineral Springs on April 29, 

2015 (Sarasota County, 2016b). Temperature readings near the 

pool surface were about 85–86 °F and increased to about 88 °F 

at the major bottom vent at 205 ft (vent B; table 3; figs. 10A, 

10B, and 13). Other vents (A, C, and D) had similar temperatures of 87 to 88 °F. During the dive, diver 1 moved farther 

(10 to 20 ft) into the vents than diver 2, resulting in a slight 

increase in temperature as the diver moved farther into the 

conduit of the vents (fig. 13) These temperatures are similar 

to the temperatures measured during water-quality sampling 

events in 1973 by Kohout and others (1977) and in 1992 by 

Sacks and Tihansky (1996): 90 °F and 88 °F, respectively. 

The decrease in water temperature of about 3.4 °F from the 

bottom to the surface (87.9 to 84.5 °F) as measured by divers 

is consistent with warm water from vents mixing with cooler 

groundwater from shallower aquifer sources. Groundwater 

samples at the ROMP 8 well had water temperatures ranging 

from 78 to 80 °F between 10 and 205 ft bls (Clayton, 2010).

There are a number of hypotheses pertaining to the 

source of thermal water to springs in Florida. Kohout (1965) 

proposed that the source of the spring water is from deep, 

geothermally heated seawater that circulates under the Florida 

Platform (fig. 1B) from the Gulf of Mexico and the Atlantic 

Ocean to depths of 3,000 ft and then rises to the surface 

through fractures in the overlying carbonate rocks. Stringfield 

(1966) theorized that the source of thermal water is from 

pre-Miocene seawater trapped beneath Miocene sediments 

more than 30 million years ago. Vernon (1970) reported that 

the spring water originates as recharge water along inland 

ridge areas and becomes mineralized as it moves through rock 

formations and mixes with trapped seawater along preferential groundwater flow paths. Sproul (1977) described “hot 

spots” or temperature anomalies in Lee County that appear 

to be related to upwelling of warmer, highly mineralized 

water along fracture systems. Using high-resolution seismicreflection data along the east coast of Florida, Popenoe and 

others (1984), Spechler and Wilson (1997), and Cunningham 

(2013) documented some deep collapsed geologic features 

and structural anomalies that act as conduits for groundwater 

flow. Warm Mineral Springs may be similar to one of these 

collapsed geologic features where structural anomalies extend 

into deeper layers and provide an avenue for upwelling of 

deep groundwater with high temperatures. 

Griffin and others (1977) describe a generalized increase 

in groundwater temperature in Florida from deep oil test wells 

(greater that 12,000 ft bls) of 1 °F per 100 ft, whereas Sproul 

(1977) and Sproul and others (1972) define a more variable 

range for shallower well depths (225 to 1,045 ft bls) at a rate 

of 1 °F per 50 to 150 ft of depth. Analysis of geophysical 

temperature logs of ROMP wells and well 224B-1 along a 

regional east to west cross-section line (fig. 14) indicates 

there is an increase in temperature with depth and also an 

increase in groundwater temperature toward the coast at lower 

depths within the Upper Floridan aquifer. At the ROMP 14 

well, located in an inland recharge area, the temperature at 

depth increases 1 °F per 138 ft, and at ROMP 8 well, located 

in a discharge area along the coast, the temperature at depth 

increases 1 °F per 92 ft.

Large-scale structural variations such as increased 

permeability, fracture zones, or faults can enhance the thermal 

gradients and transmit heated waters over substantial distances 

(Allen and others, 2014). A permeable zone within the Avon

Park Formation of the Upper Floridan aquifer, which has been 

identified in the ROMP well lithologic logs and in the deep oil 

exploration well, extends across most of the basin at a depth 

of about 1,100 to 1,600 ft (figs. 4, 15). Exploratory coring in 

the first phase of the ROMP 8 well construction extended to a 

depth of 1,283 ft bls. Water temperature at the bottom of the 

ROMP 8 well was 94 °F, which is within the range observed 

at vents (88–99 °F), indicating that the Avon Park Formation 

might be the source of warm water; however, given that water 

would be expected to cool during transit to the surface, water 

could be coming from deeper units. In addition to this permeable zone, Williams and Kuniansky, (2015, plate 23), identified another permeable zone within the Avon Park Formation 

at about 1,800 to 1,900 ft bls. Temperature logs at deep wells, 

such as Stevens #1 well and the 224B-1 well (fig. 1B; fig. 15), 

show a decrease in temperature along permeable zones or 

conduits within the Avon Park Formation, Oldsmar Formation, 

and the Boulder Zone, which may indicate mixing with cooler 

and saline waters from the Gulf of Mexico (Kohout, 1965; 

Kohout and others, 1977).

Groundwater Geochemistry

The groundwater geochemistry of Warm Mineral Springs 

was compared to Little Salt Spring, Gulf of Mexico seawater 

from Charlotte Harbor (USGS site number 26443508223300), 

and wells in the region. Little Salt Spring (USGS site number 

02299480) is located about 2 miles northeast of Warm Mineral 

Springs (fig. 1A) and is mineralized and periodically warm; 

temperature records range from 72 °F (1960) to 91 °F (1962). 
Retrospective Analysis 17

Table 3. Water-quality characteristics of samples collected at four vents at the bottom of Warm Mineral Springs, April 29, 2015

(Sarasota County, 2016b, c).

[mg/L, milligram per liter; ND, no detection; —, not applicable; μg/L, microgram per liter; N, nitrogen; P, phosphorus; μS/cm, microsiemen per centimeter]

Parameter Unit Vent A Vent B Vent C Vent D Surface

Temperature (field) Degrees Fahrenheit 87 88 87 87 84.5

pH — 7.14 7.16 7.20 — —

Specific conductance (field) μS/cm 30,960 33,280 29,280 28,320 28,580 

Alkalinitiy mg/L 128 124 113 — —

Calcium mg/L 558 459 565 491 —

Magnesium mg/L 694 594 709 609 —

Potassium mg/L 214 186 220 182 —

Sodium mg/L 6,010 5,220 6,180 5,280 —

Chloride mg/L 11,131 11,537 9,143 — —

Sulfate mg/L 1,624 1,662 1,322 — —

Strontium mg/L 33.0 25.1 35.4 32.8 —

Total dissolved solids mg/L 20,092 21,120 16,564 -- —

Arsenic μg/L ND ND ND 5 —

Inorganic carbon mg/L 31 30 28 — —

Ammonia nitrogen mg/L 0.12 0.17 0.27 0.24 —

Total Kjeldahl nitrogen mg/L 0.46 0.36 0.51 0.75 —

Total nitrogen mg/L 1.34 0.40 0.56 0.80 —

Nitrate nitrogen mg/L 0.88 0.05 0.04 0.05 —

Nitrite nitrogen mg/L ND ND 0.01 N/A —

Nitrate + nitrite as nitrogen mg/L 0.88 0.05 0.05 0.05 —

Total phosphorus mg/L 0.02 0.03 0.09 0.24 —

84

85

86

87

88

89

Water temperature, in degrees Fahrenheit

24-hour time (hour : minutes)

83

08:4508:5008:5509:0009:0509:1009:1509:2009:2509:3009:3509:4009:4509:5009:5509:58

Vent A

Vent B Vent C Vent D

Diver 1—Closer to vent 

Diver 2—Outside of vent

Near-surface temperature

Divers decompression rack (30 to 40 feet) Divers decompression rack (30 to 40 feet)

EXPLANATION

Figure 13. Time series of water temperature readings from sensors attached to divers during a sampling event on 

April 29, 2015. Locations of vents A–D are shown in figure 10 (Sarasota County, 2016b).
18 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

Surficial 

aquifer

 system

DESOTO CO.

SARASOTA CO.

DESOTO CO.

HIGHLANDS CO.

Gulf of Mexico

200

Sea Level

200

400

600

800

1,400

1,600

1,800

2,000

Freshwater

Saltwater

Saltwater Freshwater

Confining bed

Confining bed

Top of intergranular evaporites

Middle confining unit

WEST

Warm Mineral Springs

ROMP 8

ROMP 9

ROMP 16.5

ROMP 12

ROMP 13

ROMP 14

2,200

94 °F 90 °F

94 °F

EXPLANATION

Elevation, in feet below NGVD 29

A A'

*

 * ROMP geologic core data adjusted to land-surface elevations. 

** Temperature reading not available at 200 feet for 224B-1 well. 

82 °F Comparison of groundwater temperatures for ROMP wells 

in the intermediate aquifer system—At 200 feet, in 

degrees Fahrenheit (oF); temperature obtained from 

geophysical logs 

Comparison of groundwater temperatures for ROMP wells 

in the Avon Park Formation within the Upper Floridan 

aquifer—At 1,300 feet, in degrees Fahrenheit (oF); 

temperature obtained from geophysical logs

Increasing groundwater temperatures with depth

98 °F

224B-1 **

EAST

91 °F 88 °F 84 °F 84 °F

1,000

1,200

Intermediate aquifer system

Upper Flordian aquifer

Increasing groundwater temperature toward the coast 

82°F 78 °F 77 °F 77 °F 76 °F 76 °F

Modified from Ryder, 1985

High permeability fractured dolostone 

within the Avon Park Formation—Dashed 

lines represent inferred boundary 

Well in area of recharge for the 

Upper Floridan aquifer

Well in area of discharge for the 

Upper Floridan aquifer

Figure 14. Cross section of hydrologic units along ROMP wells and well 224B-1, showing a pattern of 

increasing groundwater temperatures from Highlands to Sarasota Counties (location of cross-section 

line shown in figure 6). 
Retrospective Analysis 19

Wells in the region that were examined include the ROMP 12 

and 13 wells at two levels within the Avon Park Formation: 

the Upper Floridan aquifer and the middle confining unit. 

Geochemical analyses can be represented by a Stiff 

diagram or pattern (Stiff, 1951). A Stiff diagram is a graphical 

representation (such as a polygon) of a geochemical analysis, 

and the width of the diagram is an approximate indication of 

total ionic content (Hem, 1985, p. 175). Herein, three horizontal axes are used to represent the concentrations of cations 

and anions. A “T” shaped diagram indicates large concentrations of sodium-chloride in groundwater (plotted along the 

top-most axis). Stiff diagrams indicate that all of the sampled 

waters were influenced by sodium-chloride by varying degrees 

(fig. 16). Warm Mineral Springs and nearby Little Salt Spring 

differ in both sodium-chloride concentration and total ionic 

content, despite the proximity of these two springs. The lowest 

sodium-plus-potassium and chloride concentration is from 

water samples of Little Salt Spring. The Stiff diagram for Little Salt Spring is similar to the Stiff diagram for the ROMP 13 

well, but with lower ionic content. The geochemistry of Little 

Salt Spring and the ROMP 13 well indicate a greater contribution from freshwater sources than at other sites examined. 

The ROMP 13 well is located in an area of recharge (fig. 6) to 

the Upper Floridan aquifer. The Stiff diagram for the bottom 

sample at Warm Mineral Springs is more similar to that of the 

ROMP 12 well Avon Park Formation sample (1,600 ft depth; 

Upper Floridan aquifer) than other sites examined.

Gypsum and anhydrite, which are sources of sulfate, are 

abundant at the base of the Upper Floridan aquifer, the middle 

confining unit, and the Lower Floridan aquifer (Miller, 1986). 

70° 80° 100° 110° 120°

1,000

3,000

4,000

224B-1 well

Stevens #1 well

Temperature, in degrees Fahrenheit

0

90°

198° at 12,442 feet

Depth, in feet below NGVD 29

Slight decrease in 

temperature may

indicate mixing

with cooler 

Gulf of Mexico 

waters within the 

Oldsmar Formation 

permeable zone

238° at 

13,971 feet

Slight decrease in temperature 

may indicate mixing with cooler 

Gulf of Mexico water within 

the Boulder Zone

Slight decrease in temperature 

may indicate possible mixing 

with cooler Gulf of Mexico 

water within the Avon Park 

Formation permeable zone 

 Floridan aquifer system

2,000

EXPLANATION

Zones of higher permeability

Figure 15. Geophysical temperature logs showing the possible mixing of 

cooler Gulf of Mexico water with groundwater from several high permeable 

zones within the Floridan aquifer system (location of wells shown in figure 1B; 

modified from Kohout and others, 1977; increased permeability zone adapted 

from Williams and Kuniansky, 2015, plate 23).
20 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

Cations Anions

500 400 300 200 100 0 100 200 300 400 500

Milliequivalents per liter

Little Salt Spring

Warm Mineral Springs (top)

Gulf of Mexico

ROMP 12 well Middle confining unit (2,142 feet; located in discharge area)

Warm Mineral Springs (bottom)

Chloride

Calcium

Sodium and Potassium

Sulfate

Bicarbonate

Magnesium

Calcium

Sodium and Potassium

Magnesium

Chloride

Sulfate

Bicarbonate

Calcium

Sodium and Potassium

Magnesium

Chloride

Calcium

Sodium and Potassium

Magnesium

Calcium

Sodium and Potassium

Magnesium

ROMP 13 well Avon Park (1,641 feet; located in recharge area)

ROMP 12 well Avon Park (1,600 feet; located in discharge area)

Calcium

Sodium and Potassium

Magnesium

Calcium

Sodium and Potassium

Magnesium

Calcium

Sodium and Potassium

Magnesium

ROMP 13 well Middle confining unit (2,084 feet; located in recharge area)

Sulfate

Bicarbonate

Chloride

Sulfate

Bicarbonate

Chloride

Sulfate

Bicarbonate

Chloride

Sulfate

Bicarbonate

Chloride

Sulfate

Bicarbonate

Chloride

Sulfate

Bicarbonate

Figure 16. Stiff diagrams of water from Little Salt Spring and Warm Mineral Springs, Gulf of Mexico, 

and Upper Floridan aquifer and middle confining unit within the Avon Park Formation in a recharge 

and discharge area.
Retrospective Analysis 21

Stiff diagrams (plotted in milliequivalents per liter) indicate 

that the sulfate concentration in water from Warm Mineral 

Springs (1,700 milligrams per liter [mg/L]) is more similar 

to groundwater from the Upper Floridan aquifer ROMP 12 

well in the Avon Park Formation (2,523 mg/L; 1,600 ft bls) 

rather than the more sulfate-enriched water from the middle 

confining unit in the Avon Park Formation (3,500 mg/L; 

2,142 ft bls). The similarity of sulfate concentrations for Warm 

Mineral Springs and the Upper Floridan aquifer in the Avon 

Park Formation indicates a deep source of water, possibly 

1,600 ft bls or deeper. Geologic logs near ROMP 9 wells indicate isolated anhydrite deposits at about 1,550 to 1,600 ft bls 

(Williams and Kuniansky, 2015, plate 23), which might act as 

a source of sulfate.

The chemistry of the wells located in the discharge 

area reflects a typical freshwater-saltwater coastal aquifer 

flow system, where less mineralized water overlies a deeper 

saltwater flow system (Cooper, 1959). Saline water occurs in 

deeper parts of the Upper Floridan aquifer (Avon Park Formation) near the Gulf Coast and below the base of the Upper 

Floridan aquifer in inland areas (Sacks and Tihansky, 1996). 

On a regional scale, the Stiff diagram for Avon Park Formation 

ROMP 14 and 13 wells, located in the recharge area, shows a 

more dilute ionic signature than ROMP 12, 16.5, and 9 wells, 

located in the discharge area (fig. 17). Stiff diagrams for wells 

in the discharge area below depths of about 1,500 ft bls have 

the “T” pattern similar to the Stiff diagram for Warm Mineral 

Springs, indicating a source of water from 1,500 ft bls or 

greater, and from the Avon Park Formation or deeper units. 

Water Quality

Geochemical data for Warm Mineral Springs are 

available from several sources, including Ferguson and others 

(1947), Rosenau and others (1977), Scott and others (2004), 

Ryan and others (2011), the USGS NWIS, the Southwest 

Florida Water Management Information System (Southwest 

Florida Water Management District, 2016a), and Sarasota 

County (2016a). Notable at Warm Mineral Springs are concentrations of chloride and sodium, levels of specific conductance, 

detection of nitrate and ammonium, and sulfate concentrations. Secondary effects on water quality include the presence 

of sulfur-reducing bacteria and changes in water clarity in the 

spring pool.

The five ions with the greatest concentrations in Warm 

Mineral Springs were, as listed in order of decreasing concentration: chloride, sodium, sulfate, magnesium, and calcium 

(table 4). The median concentrations of chloride and sodium 

in the spring water were about 9,500 and 5,100 mg/L, respectively; whereas, concentrations of these constituents in Gulf 

of Mexico seawater were about 18,000 and 9,900 mg/L, 

respectively. Water-quality characteristics of Warm Mineral 

Springs were also compared with another third-magnitude, 

brackish-water coastal spring (Baird Creek Head Spring) and 

103 other springs of varying size in Florida (Harrington and 

others, 2010; table 4). Warm Mineral Springs had the highest 

temperature and the greatest mineralized content (relative to 

the five constituent ions listed above) in comparison to these 

other springs, indicating a deeper source of water for Warm 

Mineral Springs than for Baird Creek Head Spring and the 

other 103 springs compiled by Harrington and others (2010).

Specific conductance can be used as a measure of salinity 

and water quality. On April 29, 2015, divers collected water 

samples from four out of the five major bottom vents (A–D, 

fig. 10A, B), and physical properties, major ions, and nutrients 

(Sarasota County, 2016c) were evaluated. The specific 

conductance varied slightly among the four vents sampled, 

and values ranged from 28,320 microsiemens per centimeter 

(μS/cm) at 25 degrees Celsius at vent D to 33,280 μS/cm at 

vent B (table 3). For comparison, the specific conductance of 

seawater is on the order of 50,000 μS/cm (Gulf of Mexico, 

USGS site number 264435082233000). Specific conductance measurements of the Upper Floridan aquifer (Avon 

Park permeable zone; 1,269–1,283 feet bls) for the ROMP 

8 well was 9,930 μS/cm (Clayton, 2010). This finding indicates that groundwater was derived from a source deeper 

than about 1,300 ft bls. Specific conductance at the ROMP 

9 well, sampled at a depth of about 1,500 ft bls in the Avon 

Park Formation of the Upper Floridan aquifer, had a specific 

conductance that was 38,240 μS/cm and the temperature was 

90 °F (Thompson, 1997). This finding indicates that aquifers 

at a depth of about 1,500 ft or greater might be a source of 

groundwater to the spring bottom vents. The specific conductance is lower at the surface of the Warm Mineral Springs 

pool (28,580 μS/cm) than at depth, which indicates the input 

of fresher groundwater from the shallower aquifers above the 

spring vents. The lateral input of groundwater from the upper 

part of the sink probably varies on the basis of wet or dry season. Continuous water-quality monitoring of specific conductance would provide information on the variations in dilution 

of Warm Mineral Springs by surface water.

Nitrate-nitrogen (nitrate, NO3) is the principal chemical 

indicator for nutrient enrichment of Florida springs (Harrington and others, 2010). Nitrate concentrations were less 

than 0.2 mg/L for most Florida springs prior to the 1970s, but 

recently concentrations exceeding 1 mg/L have been measured 

in many springs (Harrington and others, 2010). The drinking 

water standard for nitrate adopted by the U.S. Environmental 

Protection Agency is 10 mg/L, measured as nitrogen (U.S. 

Environmental Protection Agency, 2016). Water samples 

collected at the surface at Warm Mineral Springs had a low 

median nitrate concentration of 0.01 mg/L (Ryan and others, 

2011); nitrate samples collected at the spring vents on 

April 29, 2015, had concentrations of 0.04–0.05 mg/L for 

vents B, C, and D and 0.88 mg/L at vent A (table 3). Most of 

the groundwater discharge comes out of vent B with much 

smaller amounts of discharge out of vent A. The higher nitrate 

concentration from vent A indicates the variability of the 

source water between the adjoining vents. Additional monitoring is needed to determine trends or persistence of detection of 

nitrate at Warm Mineral Springs. 
22 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

ROMP 8 ROMP 9 ROMP 16.5 ROMP 12 ROMP 13 ROMP 14

ROMP 8 ROMP 9 ROMP 16.5 ROMP 12 ROMP 13 ROMP 14

Depth below land surface, in feet 1,200

1,400

1,000

200

0

1,600

600

400

800

1,800

2,000

2,200

89° F

WEST EAST

94 °F

90 °F

93 °F

84 °F

83 °F

91 °F

94 °F

90 °F

85 °F

79 °F

86 °F

86 °F

97 °F

95 °F

90 °F 88 °F 82 °F

91 °F

78 °F 78 °F 77 °F 77 °F 76 °F 76 °F

Lower permeable zones 

within the Avon 

Park Formation 

Highly fractured 

dolostone within the 

Avon Park Formation 

permeable zone 

Middle confining unit 

Top of Avon Park Formation 

below land-surface datum 

Bottom of well borehole depth 

Downward flow in recharge area 

Upward flow in discharge area 

EXPLANATION

Cations Anions

Milliequivalents per liter

500 0 500

Stiff diagrams of water from Warm Mineral 

Springs, the Avon Park Formation within 

the Upper Floridan aquifer, middle 

confining unit, and Gulf of Mexico 

Warm Mineral Springs

Gulf of Mexico

 Avon Park Formation 

Middle confining unit 

Chloride

Calcium

Sodium and 

Potassium

Sulfate

Bicarbonate

Magnesium

Figure 17. Comparison of water quality, temperature with depth, and flow directions within the Avon Park Formation of the 

Upper Floridan aquifer and the underlying middle confining unit.
Retrospective Analysis 23

Ammonia-nitrogen was reported in water samples 

collected at the pool surface of Warm Mineral Springs 

(table 3). Ammonia-nitrogen is seldom detected in spring 

water because of its tendency to degrade rapidly to other 

nitrogen forms; however, when detected, it can be an indicator 

of sources of potential contamination (Harrington and others, 

2010). Although ammonia-nitrogen concentrations are not 

considered high, they may indicate that the groundwater 

source for the spring was affected by human activities or a 

reduction of nitrate to ammonium ions (Cheng and others, 

1997). Additional monitoring is needed to determine trends or 

persistence of ammonia-nitrogen at Warm Mineral Springs.

Sulfate concentrations are relatively high (median value 

of 1,750 mg/L; Ryan and others, 2011) in Warm Mineral 

Springs compared to west-central Florida springs (median 

values as high as 400 mg/L; Harrington and others, 2010) 

and are more similar to sulfate concentration for the Gulf of 

Mexico (USGS site number 264435082233000), which ranged 

from 2,400 to 2,700 mg/L (table 4). With the relatively high 

sulfate concentrations in the spring, sulfur-reducing bacteria 

are prevalent in the spring. Sulfur-reducing bacteria, which 

can live in the low-oxygen environment of the spring, can 

reduce natural sulfates into hydrogen sulfide (Sacks and Tihansky, 1996). The combination of natural sources of dissolved 

Table 4. Median values of water-quality data collected at Warm Mineral Springs, Baird Creek Head Spring (also a coastal 

spring), and numerous west-central Florida springs and the Gulf of Mexico.

[mg/L, milligram per liter; PCU, platinum cobalt unit; ft3/s, cubic foot per second; N, nitrogen; P, phosphorus; μS/cm, microsiemen per centimeter; NTU, nephelometric turbidity unit; °F, degrees Fahrenheit; <, less than; >, greater than; —, missing or not applicable]

Parameter

Warm Mineral 

Springs 

water-quality 

characteristics 

(median)1

Baird Creek Head 

Spring near 

Chassahowitzka 

water-quality 

characteristics2

West-central 

Florida spring 

water-quality 

characteristics 

(median)3

Gulf of Mexico 

near Charlotte 

Harbor4

Alkalinity (mg/L) 132 143 115 121

Calcium (mg/L) 488 110 56 360

Chloride (mg/L) 9,470 2,750 21 18,000

Color, (PCU) 5 — 0 5

Discharge (ft3/s) 8.3 6.2 < 1 to > 100 —

Dissolved oxygen (mg/L) 1.2 3.3 3 7.8

Magnesium (mg/L) 580 185 7.6 1,200

Nitrate + nitrite (N) (mg/L) 0.01 0.21 0.48 0.02

Nitrogen, ammonia (N) (mg/L) 0.35 — 0.01 0.06

pH 7.2 7.6 7.6 7.8

Phosphorous, (P) (mg/L) 0.15 0.02 0.04 0.03

Potassium (mg/L) 179 22 1.2 440

Sodium (mg/L) 5,140 20 11 9,900

Silica (mg/L) 17 8 9 0.7

Specific conductance (μS/cm) 27,898 8,480 374 43,900

Sulfate (mg/L) 1,645 395 16 2,400

Total organic carbon (mg/L) 2.2 — 0.82 —

Total dissolved solids (mg/L) 17,845 — 228 32,400

Turbidity (NTU) 2 — 0.3 0.2

Surface-water temperature (°F) 84.5 74 72 84

1

Median values from data by Scott and others (2004), Sarasota County (2016a), Southwest Florida Water Management District (2016b), U.S. 

Geological Survey (USGS site numbers 02299260 and 270333082154000); discharge from August 11, 2014, at USGS site number 02299260; 

water temperature and specific conductance measured by divers on April 29, 2015.

2

USGS database site number 284230082344000 Baird Creek Head Spring near Chassahowitzka, November 15, 1988.

3

Median values based on 33 to 103 water-quality observations for various springs in west-central Florida (Harrington and others, 2010).

4

 USGS database site number 26443508223300 Charlotte Harbor sample site CH15 Gulf of Mexico, September 21, 1983.
24 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

sulfur and low dissolved oxygen concentrations facilitates the 

growth of the sulfur-reducing bacteria colonies (Tuttle and 

Molyneaux, 1975), which flourish on the upper walls of Warm 

Mineral Springs (fig. 18A). Sulfur-reducing bacteria colonies 

are thought to contribute to the low clarity of Warm Mineral 

Springs (F.A. Kohout, U.S. Geological Survey, oral commun., 

1976), but further research is needed to verify this assumption. 

The green algal mat that coats the upper walls is thought to 

contribute to the slight green color in the water (fig. 18B). 

The water clarity at Warm Mineral Springs varies 

considerably. Rosenau and others (1977) discuss “cloudiness” 

in the spring water that begins at sunrise and becomes progressively worse as the day continues, and improves at night. 

There are several theories that pertain to the “cloudiness,” 

which include the presence of sulfur-reducing bacteria that 

is activated in the oxygen-poor and hydrogen-sulfide rich 

environment, the amount of daily sunlight that activates the 

growth of algae and other microorganisms to form, and the 

stirring of sediments by bathers (Rosenau and others 1977). 

The cloudiness of the entire spring water column can decrease 

substantially after heavy and extended periods of rainfall, and 

the resulting clarity can persist for up to a week before the 

cloudiness returns (Rosenau and others 1977). 

 A Secchi depth reading of about 30 ft was taken during 

the morning of September 14, 2011 (Ryan and others, 2011), 

although the clarity appeared to have declined during the day. 

During July 15–31, 2015, rainfall accumulation at the ROMP 

8 Warm Mineral Springs rain gage was almost 12 inches, and 

during that time the clarity of the spring increased substantially to greater than 154 ft (extent of the exploratory dive was 

154 ft). Comparisons of the spring clarity are shown in the 

photographs taken on April 29, 2015 (fig. 19A) and July 29, 

2015 (fig. 19B). Frequent Secchi depth readings would better 

define the trends in water clarity and continuous water-quality 

monitoring, especially during high rainfall events with 

extended periods of cloud coverage, would verify the reasons 

for the increase in water clarity.

Discussion 

Analyses of existing data provide insights into the 

hydrologic processes affecting Warm Mineral Springs; however, existing data for Warm Mineral Springs were discontinuous and sparse, and outliers were detected. Confidence in 

data and trends would be improved if continuous hydrologic 

data were available at Warm Mineral Springs. Continuous 

monitoring would ideally monitor hydrologic variables, such 

as discharge and temperature, at a daily or finer time step. A 

more comprehensive study of Warm Mineral Springs could 

include continuous monitoring of hydrologic characteristics 

of the spring and the outlet over a period of several years. 

Continuous monitoring at the outlet could include discharge, 

while continuous monitoring in the spring could include water 

temperature and water-quality indicators such as specific 

conductance, nitrate, and turbidity (water clarity). Continuous 

water-quality monitoring could include measurements at each 

vent and at multiple depths in the spring. Periodic sampling, 

such as monthly sampling, of water from the different levels 

in the pool could be analyzed for additional constituents such 

as major ions and anthropogenic compounds. Sources of 

groundwater could be further examined using isotopic tracers. 

For example, concentration of isotopes of strontium in water 

samples could be compared to strontium concentrations 

measured in Cenozoic-age carbonate rocks in Florida. Isotopic 

tracers have by used to estimate sources of groundwater by 

Katz and Bullen (1996), Sacks and Tihansky (1996), Katz and 

others (1997, 2007), Phelps (2001), and Tihansky (2005). 

Continuous monitoring data could be used to calibrate 

models of the response and sensitivity of Warm Mineral 

Springs to regional factors, such as water levels of aquifers, 

precipitation, and evapotranspiration. For example, Impulse 

Response Functions (IRFs) have been used successfully 

to model karst aquifer systems (Long, 2015). Discharge 

(response) could be modeled using water levels of several 

aquifers, simultaneously (impulses). A strength of models, 

such as IRFs, is that historical data for the impulse (such as 

aquifer levels) could be used to back-cast the response, such 

as discharge, and fill in data gaps. Examples of applications 

of IRFs for springs in karst settings include Long and Mahler 

(2013) and Stamm and others (2015). Models that estimate 

the sensitivity of discharge and temperature to external affects 

(such as weather and aquifer levels), and mixing models 

might prove as a valuable tool for managing the response of 

Warm Mineral Springs to projected changes in climate, aquifer 

levels, and water use.

Summary

Warm Mineral Springs, located in southern Sarasota 

County, is a warm (85 degrees Fahrenheit [°F]), mineralized 

spring in Florida. Since 1946, a bathing spa has been in 

operation at Warm Mineral Springs, attracting vacationers 

and health enthusiasts. In addition, the warm water from the 

spring attracts manatees to the adjoining spring run during 

the winter months, which provides a vital thermal refuge for 

these mammals as well as an opportunity for environmental 

education. Archaeological evidence indicates that the spring 

has long been an attraction for humans. Well-preserved, late 

Pleistocene- to early Holocene-age human and animal bones, 

artifacts, and plant remains have been found in and around the 

spring, which adds to the unique characteristics of the spring. 

The spring is a multiuse resource of hydrologic importance, 

ecological and archaeological significance, and economic 

value to the community.

The circular shape and depth of Warm Mineral Springs 

indicate the spring formed as a large sinkhole that developed 

in the sand, clay, dolomite, and limestone of the Arcadia Formation of the intermediate aquifer system. The pool of Warm 

Mineral Springs measures about 240 feet (ft) in diameter at 

the surface and has a maximum depth of about 205 ft. A debris 
Summary 25

Photograph by Curt Bowen, ADM Exploration Foundation, 2015

Photograph by Rene Jannemann, Sarasota County, 2015

A

B

Figure 18. Photographs showing A, sulfur-reducing bacteria and B, green algae that 

coat the walls of Warm Mineral Springs.
26 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

Photograph by Curt Bowen, ADM Exploration Foundation, 2015

Photograph by Rene Jannemann, Sarasota County, 2015

A

B

Figure 19. Photographs showing Warm Mineral Springs water clarity at A, 40 feet below the spring surface 

during a dry period (April 29, 2015) and at B, 154 feet after an extended period of rain (July 29, 2015).
Summary 27

cone, which measures about 225 ft wide and 125 ft thick, 

covers much of the bottom of Warm Mineral Springs and 

was formed from the collapse of material at the surface. Late 

Pleistocene-age water levels were about 100 ft (30 meters) 

below the modern spring pool surface at about 12 ka, estimated on the basis of plant material and radiometric dating 

of human remains in the sink; this indicates that the sinkhole 

formed before 12 ka. 

The geologic formations exposed at Warm Mineral 

Springs consist of the late Oligocene-age to Miocene-age 

Arcadia Formation of the Hawthorn Group. The Hawthorn 

Group is composed of carbonate rocks with sand and clay 

layers. Underlying the Hawthorn Group are Oligocene-age to 

Eocene-age limestone and dolostone, including the Suwannee 

Limestone, Ocala Limestone, and Avon Park Formation. Three 

aquifers are described in the region of Warm Mineral Springs: 

the surficial aquifer system, the intermediate aquifer system 

within the Hawthorn Group, and the Upper Floridan aquifer 

in the Suwannee Limestone, Ocala Limestone, and Avon Park 

Formation. The Hawthorn Group also acts as an upper confining unit to the Upper Floridan aquifer.

Groundwater flow paths inferred from the configuration 

of the potentiometric surface of the Upper Floridan aquifer for 

September 2010 are generally from areas of recharge (in Polk 

and Highlands Counties) to areas of discharge (in Manatee, 

Sarasota, DeSoto, and Charlotte Counties). Warm Mineral 

Springs is located in an area with the potential for discharge to 

the surface. Groundwater flow models indicate that downward 

flow into the Upper Floridan aquifer occurs in inland areas, 

and upward flow toward the surface occurs in coastal areas, 

such as at Warm Mineral Springs.

Declines in groundwater levels occurred in the Southern 

West-Central Florida Groundwater Basin from the 1930s 

to the 1970s as a result of water withdrawals for phosphate 

mining and other uses. The historical increase in groundwater 

withdrawals, and other factors such as weather conditions and 

agricultural conservation, resulted in a 10- to 20-ft regional 

decline in the potentiometric surface of the Upper Floridan 

aquifer by May 1975 relative to predevelopment levels; the 

water level remained at approximately that same level in 

May 2007 in the area of Warm Mineral Springs.

Warm Mineral Springs is a third-magnitude spring, which 

is defined by a mean discharge of less than 10 cubic feet per 

second (ft3/s). Discharge at Warm Mineral Springs decreased 

from about 11–12 ft3/s in the 1940s to about 6–9 ft3/s in the 

1970s, and remained at about that level for the remainder of 

the period of record. This pattern of decrease until about the 

1970s is consistent with the trend of water withdrawals and 

changes in the potentiometric surface of the Upper Floridan 

aquifer in the region. This finding indicates that basin-scale 

changes to the groundwater system have affected discharge at 

Warm Mineral Springs. Similarity of changes in regional water 

use and discharge at Warm Mineral Springs indicates that 

basin-scale changes to the groundwater system have affected 

discharge at Warm Mineral Springs. No significant trend 

in water temperature was found over the period of record, 

1943–2015. 

Multiple lines of evidence, including Stiff diagrams of 

groundwater geochemistry and groundwater temperature, were 

used to estimate the sources of groundwater that discharges 

from Warm Mineral Springs. The Avon Park Formation 

within the Upper Floridan aquifer at a depth of about 1,400 to 

1,600 ft, or deeper, is a likely source of warm and mineralized 

groundwater. There are five known warm water vents or solution conduits at the bottom of the spring. Specific conductance 

at Warm Mineral Springs was high, and ranged from 28,320 

to 33,280 microsiemens per centimeter (μS/cm) at bottom 

vents. The specific conductance was approximately half of 

that typical for saltwater. Specific conductance at the nearby 

ROMP 8 well was 9,930 μS/cm at a depth of 1,269–1,283 ft 

below land surface (bls), indicating that groundwater at Warm 

Mineral Springs was sourced from more than 1,300 ft bls. 

Specific conductance of groundwater from the ROMP 9 well 

at a depth of 1,500 ft bls was similar to that of Warm Mineral 

Springs. The median concentration of chloride and sodium 

in the spring water was about 9,500 and 5,100 milligrams 

per liter (mg/L), respectively. For comparison, concentration 

of these constituents in Gulf of Mexico seawater was about 

18,000 and 9,900 mg/L, respectively. Water-quality characteristics of Warm Mineral Springs were compared with other 

springs of varying size in Florida; Warm Mineral Springs had 

the highest temperature and the greatest mineralized content. 

This finding might reflect a deeper source of water at Warm 

Mineral Springs than at other springs in the region.

Analysis of water-quality samples collected from Warm 

Mineral Springs detected ammonium-nitrogen and nitrates, but 

at low concentrations. The drinking water standard adopted by 

the U.S. Environmental Protection Agency is 10 mg/L nitrate, 

measured as nitrogen. Water samples collected at the surface 

at Warm Mineral Springs had a low median nitrate concentration of 0.01 mg/L. Water samples collected at the bottom 

spring vents by divers on April 29, 2015, had concentrations 

of 0.9 mg/L nitrate-nitrogen at vent A and 0.04–0.05 mg/L at 

vents B, C, and D. Spring water is characterized by a slightgreen color, with varying water clarity, low dissolved oxygen 

(indicative of deep groundwater), and a hydrogen sulfide odor.

Typically the water clarity is highest in the morning (about 

30 ft Secchi depth) and often decreases throughout the day. 

Analyses of existing data provide insight into the 

hydrologic processes affecting Warm Mineral Springs; however, data have been sparsely and discontinuously collected 

since the 1940s. Continuous monitoring of hydrologic characteristics such as discharge, temperature, specific conductance, 

and water-quality indicators such as nitrate and turbidity 

(water clarity) sensors, would be valuable for monitoring. 

Continuous data could be used for modeling and analyses of 

the sensitivity of the spring to external forcings. Models could 

include Impulse Response Functions, which have been used 

successfully in karst aquifer systems. Water samples could 

also be analyzed for isotopic ratios of tracers, such as strontium. Isotopic ratios and concentrations could be used to identify the subsurface source(s) of water discharging from Warm 

Mineral Springs through the development of mixing models.
28 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

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32 Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota County, Fla: A Retrospective Analysis

Manuscript was approved on September 19, 2016

Prepared by the USGS Science Publishing Network 

Reston and Lafayette Publishing Service Centers

For more information, contact:

Director

Caribbean-Florida Water Science Center

U.S. Geological Survey 

4446 Pet Lane, Suite 108

Lutz, FL 33559

http://fl.water.usgs.gov

Metz— Discharge, Water Temperature and Quality, Warm Mineral Springs, Sarasota Co., Fla.: A Retrospective Analysis—Open-File Report 2016–1166

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20161166