Submitted to: Ellen M. Porter

Air Quality Branch

U.S. Fish and Wildlife Service

Denver, Colorado

CHASSAHOWITZKA

NATIONAL WILDLIFE REFUGE

STATUS AND TRENDS

A Report

Submitted by : L. Kellie Dixon

Ernest D. Estevez

Mote Marine Laboratory

1600 Ken Thompson Parkway

Sarasota, Florida 34236

July 10, 1998

Mote Marine Laboratory Technical Report Number 579

This document is printed on recycled paper.

Suggested reference: Dixon LK, Estevez ED. 1998.

Chassahowitzka National Wildlife Refuge status and trends.

U.S. Fish and Wildlife Service, Air Quality Branch. Mote Technical

Report no. 579. v 37p and appendices. (Available from Mote

Marine Laboratory Library) 
ACKNOWLEDGMENTS

Research sponsored by the U.S. Fish & Wildlife Service - Air Quality Branch, and Mote Marine

Laboratory. Ellen Porter, Cam Shaw, Joyce Kleen, Rolf Olson, Bob Quarles, Jay Sprinkel, Jon

Perry, Patricia Minotti, Ari Nissanka, Amy Rhues, and Dimitrious Papadimitriou provided

valuable assistance. Kevin Summers and the GIS staff of EPA Gulf Breeze Laboratory aided in

study design and station mapping.
TABLE OF CONTENTS

Page No.

TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..v

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..l

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..l

MATERIALS AND METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

RESULTS AND DISCUSSION ....................................... 11

StudyArea................................................ ll

Weather.. ................................................ 12

SAVSampling ............................................. 13

Water Chemistry - Physical Parameters ............................. 17

Water Chemistry - Nutrients .................................... 22

Phytoplankton .............................................. 28

Biomass.. ................................................. 29

Sediments ................................................. 31

Summary ................................................. 33

Recommendations ........................................... 35

LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

APPENDICES

Appendix A: SAV Quadrat Data

Station and Species Summary

Appendix B: In Situ Water Quality Data

Appendix C: Water Quality Data

Phytoplankton Data

Trophic State Indices

Appendix D: Biomass Data

Appendix E: Sediment Nutrient Data

Sediment Grain Size Data

ii
LIST OF FIGURES

Page No.

Figure 1.

Figure2.

Figure 3.

Figure 4.

Figure 5.

Figure6.

Figure7.

Figure 8.

Figure 9.

Figure10.

Figure 11.

Chassahowitzka National Wildlife Refuge, Chassahowitzka Florida. Thirty coastal

stations, secondary spring vents sampled (CH#l, CRAB, POTTR),

meteorological station (MET), and water level station (WL). . . . . . . . . . . . . . . . . 6

Chassahowitzka and Homosassa River gradient stations and the tidal creek stations

at Seven Cabbage Cutoff (7CABG), Rose Creek (ROSE), Mason Creek

(MASON), upper Mason Creek (UMAS), and Petty Creek (PETTY) . . . . . . . . 10

Relative tidal heights, air temperature, and insolation during the May 1997

sampling. Tidal heights unregistered. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Relative tidal heights, air temperature, and insolation during the September 1997

sampling. Tidal heights unregistered. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Distribution of salinity within the Chassahowitzka National Wildlife Refuge,

September 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Total Kjeldahl nitrogen as a function of salinity; all samplings and station

categories. (COAST - coastal stations, TCRKS - tidal creeks, HOMOS -

Homosassa River, SPGS - secondary spring vents, RIVER - Chassahowitzka

River.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Inorganic Nitrogen:Phosphorus ratios as a function of salinity; all samplings and

station categories. (COAST - coastal stations, TCRKS - tidal creeks, HOMOS -

Homosassa River, SPGS - secondary spring vents, RIVER - Chassahowitzka

River.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Spatial distribution (by latitude) of trophic state indices; all samplings, for

Chassahowitzka riverine (RIVER) and coastal stations (COAST) only. . . . . . . . . 24

Lack of dependence of trophic state on salinity; coastal stations, all

samplings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Gradient of nitrate-nitrite-nitrogen with respect to salinity; all Chassahowitzka

River samplings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Gradients of Chlorophyll a, corrected for pheophytin, with respect to

salinity; all Chassahowitzka River samplings. . . . . . . . . . . . . . . . . . . . . . 26

iii
(List of Figures, Continued)

Page No.

Figure 12.

Figure 13.

Figure 14.

Figure 15.

Figure 16.

Figure 17.

Figure 18.

Figure 19.

Figure 20.

Figure 21.

Figure 22.

Gradients of Trophic State Index with respect to salinity; all Chassahowitzka River

samplings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Reverse gradients of organic nitrogen with respect to salinity; all Chassahowitzka

samplings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Comparison of total nitrogen as a function of salinity, in the Chassahowitzka and

Homosassa Rivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Comparison of chlorophyll a, corrected for pheophytin, as a function of salinity,

in the Chassahowitzka and Homosassa Rivers. . . . . . . . . . . . . . . . . . . . . . . . . 28

Dinoflagellate abundance as function of total phytoplankton concentration; riverine

and coastal stations. Scales truncated. A - May 1996, B - May 1997, C -

September 1997. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Riverine gradients of biomass, as the average of “light,” “typical,” and “heavy”

growth, during May 1997. Allocated into vascular submerged aquatic vegetation

(SAV) and macroalgal components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Riverine gradients of biomass, as the average of five evenly spaced (across

channel) or randomly placed (open water) quadrats during September 1997.

Allocated into vascular submerged aquatic vegetation (SAV) and macroalgal

components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Riverine gradients of sedimentary total Kjeldahl nitrogen and total phosphorus

during May 1997. Rocky substrate and no sample at Stations R4 and 44. . . . . . . 31

Riverine gradients of sedimentary N:P ratios (N from TKN only) and percent

organics during May 1997. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Riverine gradient of total Kjeldahl nitrogen and total phosphorus, normalized for

sediment organic content, during May 1997. . . . . . . . . . . . . . . . . . . . . . . . . . 32

Sediment total Kjeldahl nitrogen content as a function of percent organic content

during May 1997. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

iv
LIST OF TABLES

Page No.

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Specific conductance, nitrate-nitrogen concentrations and occurrence of tidal

variation in individual springs. Water quality data are averages of a number of

samplings between 1993 and 1997. (From Jones et al, 1997.) . . . . . . . . . . . . . . . 3

Scalars used for Braun-Blanquet cover-abundance ratings of submerged aquatic

vegetation in Chassahowitzka Bay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Detection limits, analytical methods, and data quality objectives for water quality

samples; Chassahowitzka River and the coastal region. . . . . . . . . . . . . . . . .

Geographic locations of all stations, decimal degrees. . . . . . . . . . . . . . . . . .

Species list for attached macroalgae and vascular SAV in the coastal area of the

Chassahowitzka National Wildlife Refuge. . . . . . . . . . . . . . . . . . . . . . . . . .

Braun-Blanquet estimates of frequency, abundance, and density of the following

species within the coastal vegetated regions in the Chassahowitzka National

Wildlife Refuge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Average surface or mid-depth observations of physical parameters at 30 coastal

stations, including both morning and afternoon samplings. . . . . . . . . . . . . . .

Summary regional nutrient and chlorophyll values for May and September 1997.

Values less than the limit of detection averaged as a zero value. Units are mg/l

for nutrients, ug/l for chlorophyll, mg:mg for nutrient ratios, and unitless for TSI

values. “Riverine” comprised of Chassahowitzka River stations only. . . . . . . .

7

8

9

16

18

19

23

V
ABSTRACT

Shallow water environments offshore of the Chassahowitzka River, west-central Florida, were

sampled for submerged aquatic vegetation and water quality to establish baseline estuarine

conditions in a relatively unstudied national wildlife refuge, and identify indicators of trophic

status. Samplings were a continuation of a program begun in May 1996 and were conducted

during Spring (May 1997) and early Fall (September 1997) to characterize conditions

accompanying historical minimum and maximum periods of freshwater inflow. Stations were also

selected to characterize conditions within the Chassahowitzka and Homosassa Rivers, within tidal

creeks between the two rivers, and at several of the major spring vents of the Chassahowitzka

Spring complex.

Chassahowitzka Bay is a large, shallow (< 2 m), exposed mosaic of saltmarsh, seagrass beds, and

algal assemblages growing on an extensive karstified limestone shelf. Algal and/or seagrass cover

was nearly continuous with moderate densities. Drift algae, followed by Caulerpa paspaloides

were the most common species during the spring samplings with reduced drift algal densities

during the fall sampling of 1997. Other changes in species abundances and density were also

noted.

The water column during the study was well mixed and nutrients, chlorophyll, and trophic state

indices were low, indicating “Good” water quality overall. The northern region apparently

received a higher nutrient loading than the southern region, as indicated by higher trophic state

indices. Algal growth was nitrogen limited in the coastal region and nitrate contributed by the

Chassahowitzka Springs was rapidly removed from the water column within the Chassahowitzka

River. From the main spring to offshore, organic nitrogen in the water column increased with

increasing salinity. Biomass along the riverine gradient was bimodal with minimum values near

the mouth of the Chassahowitzka River in a zone of high salinity variation. Sediment nutrient

concentrations also displayed spatial patterns. The nitrogen content of sediment organics was

relatively consistent, while phosphorus appeared to be preferentially released.

As nitrogen loadings from both groundwater discharge and atmospheric deposition appear to be

increasing, continued monitoring should concentrate on obtaining the data necessary to evaluate

trends in water quality and submerged aquatic vegetation. For trend detection, more frequent

sampling is desirable.

INTRODUCTION

The Chassahowitzka National Wildlife Refuge, under the management of the U.S. Fish and

Wildlife Service, is a 115 square kilometer area that encompasses the mouth and a portion of the

Chassahowitzka River as well as numerous islands and near-shore marine waters out to a distance

of between 1 and 3 kilometers offshore. Located on the central west coast of Florida, this shallow

portion of the Gulf of Mexico is receiving more attention as trends of increasing nutrients in

1
groundwater discharges are documented (Jones et al, 1997; Dixon, 1997). Atmospheric loadings

of inorganic nitrogen in wet deposition have also increased in recent years (Dixon, 1997) at

national monitoring stations in Florida (National Atmospheric Deposition Program; Verna

Wellfield and Bradford Forest). In addition to documenting baseline conditions in the Refuge, the

USFWS has begun a data collection program designed to document trends in water quality and

vegetation which may be attributed to increasing nutrient loads to the region.

Chassahowitzka Bay and adjoining inshore waters are bounded by an extensive system of tidal

wetlands, intertidal shoals and oyster reefs, and include extensive, shallow, subtidal beds of

submerged aquatic vegetation. Geologically, the area represents a mixture of marsh archipelago

and a limestone shelf embayment situated along a low energy, low-gradient, micro-tidal, and nonbarrier coast (Hine and Belknap, 1986). Coastal hydrology is dominated by the discharge of

several spring groups (Homosassa, Hidden River, Halls River, Chassahowitzka). The

Chassahowitzka complex accounts for approximately 7.58 cubic meters per second, while the

various springs contributing to the Homosassa River total nearly 10.02 cubic meters per second

(Jones et al., 1997). Discharges are greatest in September and October, and least in June and July

(Yobbi, 1992). Spring flows from a groundwater basin of approximately 492 square kilometers

are supplemented by runoff from a poorly delimited coastal basin area of about 800 square

kilometers. Rainfall (142 cm per year average) is greatest from May through September and least

in November (Yobbi, 1992). Depending on their depths, individual spring vents’ discharge

variable mixtures of fresh and saltwater and both the quality and quantity of discharge can vary

tidally (Yobbi, 1992). Summarized from Jones et al. (1997), the specific conductance, nitratenitrogen concentrations and whether water quality varies tidally appear in Table 1 for individual

named springs of the Chassahowitzka and Homosassa systems. Water levels at the

Chassahowitzka main spring also vary tidally and are reported in real time by the Tampa District

Office of the U.S. Geological Survey (http://www-tampa.er.usgs.gov/Realtime/data/023 10650_

gh.html).

 2
Table 1. Specific conductance, nitrate-nitrogen concentrations and occurrence of tidal

variation in individual springs. Water quality data are averages of a number of

samplings between 1993 and 1997. (From Jones et al, 1997.)

Spring

Chassahowitzka

Chassahowitzka #1

Chassahowitzka Main

Crab Creek

Baird

Ruth

Potter Creek

Beteejay Head Spring

Blue Run

Homosassa

Abdoney

Belcher

Trotter #l

Trotter Main

McClain

Pumphouse

Homosassa River #l

Homosassa Main #l

Homosassa Main #2

Homosassa Main #3

Hall’s River Head

Hidden River Head

Hidden River #2

Specific

Conductance

(umhos/cm)

770 0.47 N

1730 0.42 Y

5294 0.46 Y

11426 0.21 Y

2977 0.44 Y

9770 0.33 Y

671 0.27 N

7747 0.26 Y

489 0.46 N

455 0.44 N

462 0.44 N

429 0.42 N

548 0.36 N

506 0.39 N

4160 0.39 Y(?)

3245 0.43 Y

5694 0.42 Y

1339 0.44 Y

7297 0.32 Y

1449 0.66 Y(?)

2162 0.53 Y(?)

N03-N

(mg/l)

Tidal Variation

In Quality

(Yes/No)

Major ion chemistry of Homosassa and Chassahowitzka springs is dominated by sodium chloride,

with more calcium and bicarbonate in the Chassahowitzka (Estevez et al., l991 ; Jones et al.,

1997). A groundwater and spring discharge monitoring program together with other trend

analyses conducted by the Southwest Florida Water Management District (SWFWMD, 1994;

Jones et al., 1997; Dixon, 1997) has documented increasing trends of nitrogen in spring

discharges with sources attributed to inland development and subsequent residential and golf

course fertilization (Jones et al., 1997). Nitrate levels in the discharge are presently near 0.4 -

0.5 mg/l or between 40 and 50 times background groundwater concentrations. Concentrations of

total phosphorus are typically near analytical detection limits (Yobbi, 1992).

3
Coastal plant communities are dominated by hammock forest, the wettest of which (with live oak

[Quercus virginiana], southern red cedar [Juniperus silicicola] , and cabbage palm [Sabal

palmetto]) intergrades with marshes of sawgrass (Cladium jamaicense) and saltmarsh dominated

by black needlerush (Juncus roemerianus). Cattail (Typha spp.) and giant reed (Phragmites

australis) also occur in the fresher regions. Spring runs punctuate the hammock forest and are

fringed by mixed hardwoods, bald cypress (Taxodium distichum) (Wolfe, 1990), and numerous

sedge, rush, and grass marshes intolerant of saltwater. Clear, mineralized flows in the spring runs

permit luxuriant growth of tape grass (Vallisneria neotropicalis). Other common submerged fresh

to brackish water species include sago pondweed (Potamogeton pectinatus), watermilfoil

(Myriophyllum spicatum), hydrilla (Hydrilla verticillata), and naiad (Naja guadalupensis) , with

Potamogeton illinoensis occurring near the spring head. Floating rafts of both Potamogeton and

Myriophyllum mixed with Enteromorpha spp. and filamentous algae occur at times in the upper

river, particularly in areas of low current velocity. Filamentous forms of green and blue-green

algae are also common with the blue green alga, Lyngbya spp., at nuisance levels in the main

spring.

The near shore bottom is shallow and low in relief. Bottoms are limestone covered by veneers

of organic and carbonate sediments lacking quartz sand (Hine and Belknap, 1986). In the coastal

area, submerged aquatic vegetation (SAV) is extensive. Contiguous beds of dense SAV cover

more than 90 % of inshore ( < 2 m depth) areas (McNulty et al., 1972; Wolfe, 1990). Dominant

vascular plants are turtle grass (Thalassia testudinum), manatee grass (Syringodium filiforme), and

shoalgrass (Halodule wrightii) (Iverson and Bittaker, 1986). Widgeon grass (Ruppia maritima)

grows in lower salinity inshore waters. Planktonic and benthic algal communities of the

immediate area are unstudied but reports from nearby, similar areas depict a rich, abundant flora

(Phillips, 1960; Earle, 1969; Dawes, 1974). The bulk of the waters within the study area are

designated as Class II (Shellfish propagation or harvesting, F.A.C. 17-302) by the Florida

Department of Environmental Protection (FDEP).

The present study was performed to describe SAV and water chemistry during a dry and a wet

season; to establish a 1996-97 baseline of ecological conditions; and to report on existing

indicators of eutrophication in the near coastal waters along an undeveloped area, the

Chassahowitzka National Wildlife Refuge (Figure 1).

MATERIALS AND METHODS

In 1997, sampling dates were chosen in May and September in order to sample historically dry

and wet conditions. The May sampling also provided continuity with the May 1996 sampling.

Sampling for SAV took place from May 19 through May 21, 1997, with methods described below.

Water quality sampling took place during the early morning of May 21 and was repeated during

the late afternoon of the same day. The wet season sampling took place September 15-17, 1997

with the water quality run conducted the early morning and late afternoon of September 17.

Sampling times were selected based on observed patterns of hypoxia and supersaturation in other

4
water bodies (Marshall and Leverone, 1994). Mote Marine Laboratory (MML) conducted all

sampling and analysis with sampling assistance from Refuge personnel and vessels.

For coastal SAV, the study area encompassed a 115 square kilometer coastal area. Most stations

were in open waters between Homosassa Point (28°46.5'N) to the north, to Raccoon Point

(28 °36.3'N), and seaward of saltmarshes and the extensive tidal creek system. Stations extended

out to the entrance marker for Chassahowitzka (82°44.3'W).

Sampling for SAV in 1997 revisited all 30 stations established in May 1996 (Figure 1). During

1996, station selection was performed with assistance from the U.S. Environmental Protection

Agency (Dr. Kevin Summers) following EMAP (Environmental Monitoring and Assessment

Program) protocols which allow the unbiased estimations of the area1 extent of a selected level of

a given parameter (i.e., the percentage of a region with dissolved oxygen values greater than

5.O mg L-l). The Refuge was gridded into fifty 1 km2 hexagons and a series of random stations

identified within each polygon. For SAV, the study area was limited to the near coastal waters

outside of the mouths of the Chassahowitzka and Homosassa Rivers. Polygons were eliminated

from consideration if they consisted of predominantly land rather than open water, as a study of

vegetation in tidal creeks was not intended. From the area bounded by the Refuge, 30 polygons

were selected for SAV sampling. Of the potential stations identified within the polygon, sites were

visited in order until SAV was observed.

Cover and abundance of submerged aquatic vegetation (SAV) were measured using a rapid-survey

technique (Braun-Blanquet, 1932). At each station, an observer on each side of the vessel

surveyed two quadrats, each 0.25 m2 in area. Each observer listed species and major plant groups

(seagrass; drift algae, etc.) and assigned a cover-abundance value for each taxon or group

(Table 2). Upper scale values (5-2, inclusive) pertained to cover only. Other scale values were

estimators of abundance (number of individuals per species). Four replicate quadrats were used

to assess within and between station variability. Attributes were calculated as follows:

Frequency = No

/Nt

Abundance = sum of B-B scale values/No

Density = sum of B-B scale values/Nt

where No is the number of occupied quadrats and Nt is the total number of quadrats. The drift

algae were lumped into a single category of miscellaneous algae with frequency, abundance, and

density estimated as for the attached species. Secchi depths were recorded during SAV surveys

and underwater photographs secured at most stations during both May and September. During

the September sampling, canopy height was also estimated by species to differentiate between

varying morphologies, growth habits, and resultant biomass of a given species.

5
Figure 1. Chassahowitzka National Wildlife Refuge, Chassahowitzka, Florida. Thirty

coastal stations, secondary spring vents sampled (CH#l, CRAB, POTTR),

meteorological station (MET), and water level station (WL).

6
On September 16, 1997, a researcher (Mr. Joe Conti) performing similar B-B surveys in the St.

Martin’s Marsh area to the north of the Refuge and the Homosassa River accompanied MML

crews and cross-calibrated techniques and species identifications. During May and September,

stations in the Chassahowitzka River and coastal Stations 24, 26, and 44 were sampled for wet

weight biomass and percentage of attached vascular SAV. During May, quadrats (0.25m2) for

biomass were placed in areas of light, typical, and heavy growth, while during September, five

Braun-Blanquet quadrats were sampled at either randomly (in the coastal region) or at equal

distances across the width of the river.

Table 2. Scalars used for Braun-Blanquet cover-abundance ratings of submerged

aquatic vegetation in Chassahowitzka Bay.

Value Relative Number Percent Cover Remarks

5 any number greater than 75%

4 any number 50%-75%

3 any number 25%-50%

2 any number 5%-25%

1 numerous less than 5% - or scattered with up to 5%

+ few small - assigned 0.5 value

r solitary small - assigned 0.1 value

During May and September, in situ parameters were collected in the early morning and late

afternoon at all 30 SAV stations. A subset of 20 polygons (generally those nearer shore) was

sampled during the morning for water quality (nutrients, chlorophyll, and phytoplankton). In situ

samplings consisted of measurements of depth, temperature, conductivity (salinity), dissolved

oxygen, and percent saturation of oxygen. Instrumental measurements were made at near surface

and near bottom unless depths were less than 1 m, in which case only a middepth reading was

made. Water quality analyses consisted of nutrients (nitrate-nitrite-nitrogen, ammonium-nitrogen,

total Kjeldahl nitrogen, orthophosphate, total phosphorus), chlorophylls (chlorophyll a, b, c,

pheophytin, and chlorophyll a corrected for pheophytin), and phytoplankton enumeration.

Analytical methods and detection limits were the same as used for the 1996 sampling and are

detailed in Table 3. Instrumental readings, collection, preservation and analysis of water quality

samples were performed according to MML’s Florida Department of Environmental Protectionapproved Comprehensive Quality Assurance Plan. Trophic state indices were calculated according

to the methods of Hand et al. (1988), as the average of individual percentiles for a limiting

nutrient, chlorophyll, and Secchi depth, with a “GOOD” rating equivalent to a value of 50 or lower

and analogous to a chlorophyll concentration of 10 ug/l. Indices were computed without Secchi

percentiles when Secchi depths were greater than bottom, and numeric values of one half of the

limit of detection used when sample concentrations, were less than the limit of detection. Samples

7
for phytoplankton enumeration were preserved with Utermohl’s solution (potassium iodide, iodine,

and acetic acid). Both total organisms and total dinoflagellates were counted using twelve 1.00 ml

aliquots in Sedgewick-Rafter counting chambers under 100X magnification. Dinoflagellates,

diatoms, and cysts were counted separately as increasing nitrogen nutrient concentrations favor

the growth of flagellates (Officer and Ryther, 1980).

Table 3. Detection limits, analytical methods, and data quality objectives for water quality

samples; Chassahowitzka River and the coastal region.

Parameter

Detection Method

Limit Number

Ortho-phosphorus

Total Phosphorus

Ammonium Nitrogen

Nitrate-Nitrite-Nitrogen

Total Kjeldahl Nitrogen

Chlorophylls

0.005 mg/l 4500-PF 1 5

0.05 mg/l 365.4 1 3

0.005 mg/l 350.1 20

0.005 mg/l 353.2 15

0.05 mg/l 351.2 18

0.5 ug/l 10200H (1,2) 28

Maximum

Precision

(%RSD)

Recovery

Limits

(%)

87-l 15

80-111

86-l 13

81-116

86-119

Not Appl.

Seven salinity-based stations in the nine kilometer run of the Chassahowitzka River (including the

main boil), were also sampled for in situ and water quality parameters, as were six stations in the

13 km run of the Homosassa River, and five in several of the tidal creeks between the two rivers.

Additional water quality samples were collected from three of the smaller individual spring vents

contributing to the Chassahowitzka system. Locations of all stations appear in Table 4.

Additional parameters measured at the springs during May, 1997, included calcium, sodium,

magnesium, and iron. The Homosassa, tidal creek, and spring stations were sampled for both

physical and chemical parameters, but were not sampled for SAV. Samples collected within the

riverine portions of the Chassahowitzka and the Homosassa Rivers were combined with selected

stations offshore to examine gradients in water quality with respect to salinity (Figure 2).

Incident photosynthetically active radiation (PAR) and air temperature were recorded continuously

for the duration of the sampling at the maintenance facility of the Chassahowitzka National

Wildlife Refuge (Figure 1, Station MET) using a LiCor 1000 (with 190SB) and a Ryan

Tempmentor, respectively. Temperature readings were made approximately 0.6 m above grade.

Relative tidal heights were recorded during the sampling periods, but do not permit inter-sampling

comparisons as instrument installations were not registered to a vertical datum. Tide levels were

recorded with an ISCO 4230 bubbler flow meter, located at 28°42.39'N, 82°37.12'W on the

eastern bank of Little Gator Creek, just off the main stem of the Chassahowitzka River (Figure

1, Station WL).

8
Table 4. Geographic locations of all stations, decimal degrees.

Station Latitude Longitude

Decimal Deg. Decimal Deg. Station Latitude LongitudeDecimal Deg. Decimal Deg.

Tidal Creeks

PETTY

7CABBG

ROSE

MASON

UMASON

Homosassa River

HO

HO.5

H1

H2

H3

H4

Other Spring Vents

POTTR

CRAB

Chassahowitzka Coastal Area

28.7660700 -82.6448334

28.7312645 -82.6567223

28.7361533 -82.6446666

28.7358200 -82.6449167

28.7603756 -82.6263056

28.7688478 -82.6448334

28.8005280 -82.5958890

28.7955978 -82.6049166

28.7854866 -82.6190000

28.7835422 -82.6278889

28.7751256 -82.6758056

28.7316670 -82.5972780

28.7174440 -82.5752780

2

3

4

6

7

8A

9

12

14

17

18

19

20

21

22

28.7697619

28.7674873

28.7603473

28.7552940

28.7474566

28.7494843

28.7417113

28.7281232

28.7202912

28.7116276

28.7121534

28.7078457

28.7024598

28.6985438

28.6969613

CH#l 28.7155560 -82.5749170 23 28.6930399

Chassahowitzka River

RO

R1

R1.3

R1.7

R2

R2.5

R3

R4

28.7157922 -82.5759167

28.7148478 -82.5765833

28.7161229 -82.5870556

28.7204843 -82.5992758

28.7142938 -82.6086689

28.7159866 -82.5871389

28.7026256 -82.6236666

28.6934589 -82.6405000

24 28.6841511 -82.6546688

25 28.6809056 -82.6788623

26 28.6748492 -82.6654727

27 28.6611806 -82.6733638

28 28.6239569 -82.6729453

30 28.6152076 -82.6583058

39 28.7460726 -82.6659716

4OC 28.6445134 -82.6735569

41 28.7613183 -82.6882500

42 28.7537383 -82.6868606

44 28.6605959 -82.6865281

45 28.6488478 -82.6878316

46 28.6305713 -82.6751662

47 28.6177342 -82.6778913

-82.7136666

-82.7004434

-82.6927508

-82.6702202

-82.7004702

-82.6612509

-82.7195300

-82.7094717

-82.7026642

-82.7088333

-82.6982493

-82.7127493

-82.6605267

-82.6778323

-82.6999176

-82.6676668
Figure 2. Chassahowitzka and Homosassa River gradient stations and the tidal creek stations

at Seven Cabbage Cutoff (7CABG), Rose Creek (ROSE), Mason Creek

(MASON), upper Mason Creek (UMAS), and Petty Creek (PETTY).

10
percent organics by combustion.

During both May and September samplings, sediment samples along the Chassahowitzka riverine

transect were collected as a single surface grab (generally the top 2-5 cm) and were processed for

grain size distribution (as % volume of various size classes) with a Coulter LS200 laser particle

sizer. Analysis of sediments included the fraction greater than 2 mm in diameter. During May,

riverine sediments were collected and processed for total phosphorus, total Kjeldahl nitrogen, and

On November 5, 1997, a survey of Thalassia was conducted on plants which appear to consist of

a single rhizome growing linearly in a fracture feature of a shallow limestone platform. Visited

at low tide, Thalassia samples were excavated for examination of shoot age and morphology. Dye

was used to determine that there was no obvious groundwater discharge from the fracture during

the collection effort. Fracture orientation and length were mapped for comparison with other

geological information of the area.

In other opportunistic surveys of the Chassahowitzka River and Refuge, a partial listing of

molluscs was identified from living specimens and shell material retained from qualitative

sediment samples by a 2mm sieve. The sampling was conducted on February 17, 1998 at nine

riverine and coastal stations and was accompanied by collection of in situ water quality

parameters.

RESULTS AND DISCUSSION

Study Area

The largest discharge for the Chassahowitzka River appears to be the main boil (Station RO)

immediately to the northwest of the Citrus County boat launching facility. Numerous smaller

vents were observed immediately upstream (including Chassahowitzka #l- Station CH#l) and

some very small discharges were noted during the 1996 sampling within some of the manmade

canals adjacent to the spring head. At that time, the upstream discharges were lower in

conductivity than the main springs, indicating source water from a more surficial aquifer.

Immediately downstream of the main spring area, the confluence with Crab Creek delivered the

discharge from another sizeable vent (Station CRAB), with a conductivity higher than that of the

main spring. Station R1 was immediately below this confluence, representing both discharges.

Floating mats of senescent filamentous vegetation and a few cattails (Typha sp.) lined the sides of

the river at this point, but the main stream was clear with a cloudy-blue appearance characteristic

of many groundwater discharges. Beds of tapegrass (Vallisneria) and pondweed (Potamogeton

pectinatus, Potamogeton illinoensis) were visible on the bottom with some Hydrilla, as well. Tidal

changes in water elevation, but no reversing flows, were observed at this site.

Baird Creek and Potter Creek also contribute spring flows to the River. Stations R1.3 and Station

R1.7 are located immediately downstream of each confluence. (Discharge from the spring at the

head of Potter Creek was sampled as Station POTTR.) The upper 4 kilometers of the river are

surrounded by a deciduous flood plain forest down to the eastern boundary of the Chassahowitzka

11
National Wildlife Refuge (Station R2). At the boundary, sawgrass (Cladium jamaicensis) and

cattail dominate the bank vegetation, cabbage palm(Sabal palmetto) hammocks and Juncus appear,

and the flood plain forest ends. Floating mats of enteromorpha-like algae, Eurasian water milfoil

(Myriophyllum spicatum), and Hydrilla verticillata are very dense here. Water clarity typically

decreases by this location and has acquired the brown color of dissolved humics. Reversing tidal

flows are observed at this station.

By just upstream of Crawford Creek (Station R2.5) and at Dog Island (Station R3), sawgrass lines

the river, while Juncus dominates the marsh at higher elevations. Some cattails remain and the

seagrass Ruppia maritima is present in the river. Water clarity at Station R3, as at R2, was

generally fairly low, presumably as humics precipitated with increasing salinity. At Station R4,

opposite Johns Island, the marsh was dominated by Juncus, some Spartina alterniflora was

present, and sawgrass ended. Water clarity was much improved by this station, and the remaining

coastal waters sampled were noticeably clear. The remaining coastal stations were within and

offshore of a dense archipelago of marsh (Juncus) islands. Oyster bars were observed in some

tidal creeks but were not a dominant land form. Mangroves (Rhizophora mangle) were not

numerous, being near the northern limits of cold tolerance for this species, and were evident

chiefly as either dead and weathered stumps, or as small seedlings in the 20-50 cm size range.

Offshore stations used to complete the riverine gradient analyses consisted of the coastal stations

 24, 26, and 44.

Tidal creek stations located between the Chassahowitzka and Homosassa Rivers, were located in

Seven Cabbage Cutoff (7CABG), Petty Creek (PETTY), Rose Creek (ROSE), and near the mouth

and upstream in Mason Creek (MASON, UMASON). Development on the land surrounding each

of these stations appears minimal with the exception of Mason Creek, where a medium density

residential land use appears on the north bank of upper Mason Creek. Juncus marshes, followed

by low elevation karst islands with cedars and palms are the dominant vegetation and land form

apparent adjacent to the tidal creek stations.

Stations sampled in the Homosassa River extended from the limit of boat traffic near Homosassa

Main (Station HO), to the mouth of the river. Forested wetlands lines both sides of the river down

to approximately Station H2. Residential development and recreational water-based industries are

mush more extensive than along the Chassahowitzka. Portions of the upper river are sea-walled.

Downstream of Station H2, Juncus marshes become more prevalent, with frequent limestone

platforms of low relief supporting cedars and cabbage palms. The limestone platforms are

analogous to Johns Island on the Chassahowitzka but are much more numerous. Residential

development becomes less frequent but is still a noticeable presence.

Weather

May 1997 was extremely dry, with the Northern Coastal Basin of the Southwest Florida Water

Management District reporting a rainfall of 1.8 cm; or a deficit of 7.6 cm below the historical May

mean of 9.4 cm. At this time, annual deficits from 12-month historical means totaled 30.9 cm

(SWFWMD, 1997a). Of the 16 Florida aquifer wells in the northern region monitored by

12
SWFWMD, all water level elevations were lower than in the prior May (SWFWMD, 1996) as

well as being below historical means for May by between 25 cm and 2.2 m. In September, rainfall

totaled 12.8 cm, a 3.3 cm deficit from the historical September value, and the annual deficit had

reached 42.2 cm (SWFWMD, 1997b). Groundwater elevations were between 17 cm and 1.9 m

lower than in September 1996, and were 37 cm to 2.8 m lower than historical averages for

September.

The solar irradiance and air temperature a short distance inland (Station MET, Figure 1), and tide

heights within the river (Station WL, Figure 1) as recorded during the sampling days appear in

Figures 3 and 4. During May, the weather was fair with scattered clouds, clearing for the

afternoon water quality run on the final day. Inland air temperatures were moderate (18-40°C).

During September, the initial sampling days were very clear with increasing cloudiness. Air

temperatures ranged from 20-45 ° C . During the last day, a severe thunder storm late in the

afternoon forced abandonment of the last water quality stations (Station 8A, 39). Water quality

samplings in May 1997 took place on a falling and low tide in the early morning, followed by the

afternoon sampling centered around a high tide. Tidal range was less than 0.75 m (2.5 ft) with

a predicted high of 0.94 m. Water quality data were collected on very comparable tidal phases

during September 1997, but with predicted highs of 0.83 m. Observed tidal range was also

somewhat smaller during September than in May, approximately 0.61 m (2 ft). Peak insolation

was also lower during September.

SAV Sampling

Of the 30 polygons identified for sampling in 1996, vegetation was found at all but one of the

randomly chosen primary sites within each polygon. For Polygon 8, the primary site had no

vegetation and the first alternate site, Station 8A, was sampled instead. Data on frequency,

abundance, and density were computed on the 30 vegetated stations, and so represented an

assessment of the vegetated regions only, rather than an assessment of the entire submerged study

area. Assessments of the entire study area would employ data from the four unvegetated quadrats

of Station 8 rather than the data from Station 8A, but were not presented. The fact that only one

of the 30 primary stations was unvegetated indicates that coverage by SAV is extensive and almost

continuous. (Station 40C was the primary site for Polygon 40, as the other randomly selected sites

fell on land.) Sampling during 1997 revisited the 30 vegetated stations sampled during 1996, and

so again represents an assessment of the vegetated regions.

Sampling of SAV was carried out at the 30 vegetated stations during May and September 1997 and

individual quadrat data appear in Appendix A. Reported depths were observed and are not tidally

corrected. Secchi depths during May 1997 were all greater than the water depth. During

September, four stations in the northern portion of the study area (Station 3, 41, 6, and 39)

recorded Secchi depths at or less than total water depths. Species encountered during 1996 and

1997 appear in Table 5 and include representatives of the algal phyla Chlorophyta and Phaeophyta,

as well as marine angiosperms or seagrasses.

13

Figure 4. Relative tidal heights, air temperature, and insolation during the September 1997

sampling. Tidal heights unregistered.

15
Table 5. Species list for attached macroalgae and vascular SAV in the coastal area of the

Chassahowitzka National Wildlife Refuge.

May-96

Acetabularia crenulata

Batophora oerstedi

Caulerpa ashmeadii

Caulerpa paspaloides

Caulerpa prolifera

Halimeda incrassata

Halodule wrightii

Penicillus capitatus

Ruppia maritima

Sargassum spp.

Thalassia testudinum

Udotea flabellum

May-97

Acetabularia crenulata

Batophora oerstedi

Caulerpa paspaloides

Caulerpa prolifera l

Chara spp.

Halimeda incrassata

Halodule wrightii

Halophila englemannii

Penicillus capitatus

Ruppia maritima

Syringodium filiforme

Thalassia testudinum

Udotea flabellum

Sep-97

Acetabularia crenulata

Anadyomene stellata

Avrainvillea spp.

Batophora oerstedi

Caulerpa paspaloides

Caulerpa prolifera

Chara spp.

Digenia simplex

Halimeda incrassata

Halodule wrightii

Halophila englemannii

Penicillus capitatus

Sargassum spp.

Thalassia testudinum

Udotea flabellum

Anadyomene stellata, Avrainvillea spp., Chara spp., Digenia simplex, Halophila englemannii, and

Syringodium filiforme were recorded in the quadrats for the first time in 1997, while Caulerpa

ashmeadii was not found in 1997. Those attached species occurring most frequently were as

follows :

May 1996 Caulerpa paspaloides, Acetabularia, Batophora, Halodule, and Thalassia

May 1997 Caulerpa paspaloides, Halodule, Batophora, Acetabularia, and Thalassia

Sept 1997 Caulerpa paspaloides, Halodule, Thalassia, Penicillus, and Batophora

The most frequently observed attached species in all three samplings to date (Table 6) was

Caulerpa paspaloides, recorded in 38 %, 36 %, and 37 % of all quadrats in May 1996, May 1997,

and September 1997, respectively. Acetabularia was observed approximately half as often in 1997

compared to May 1996. The September sampling recorded more instances of Penicillus,

Halodule, and Thalassia than during either of the previous May events. Comparable numbers of

species were observed during each sampling. Although not quantified, no problems of excessive

colonization by epiphytes were noted during the surveys.

16
Where it occurred, Caulerpa paspaloides averaged a B-B abundance value of 3.2 to 3.3 in 1997,

or 25-50 % coverage. This abundance was a decrease from that observed in 1996, when coverage

was estimated at 50-75 % . In general, the five most frequent species declined in abundance, both

between May 1996 and 1997, and between May and September 1997. Within the vegetated study

area, Caulerpa paspaloides has consistently been the attached species with the densest coverage,

near 5% coverage overall. Data by station and major species of Braun-Blanquet estimates of

frequency, abundance, and density also appear in Appendix A.

In addition to attached algal and seagrass species, drift algal species were also quite common.

During May 1996 and 1997, drift material was observed in 49 % and 43 % of all quadrats,

respectively. By September, however, drift species were only observed in 13 % of quadrats.

During May 1997, drift species were similar to those observed during May 1996; Chondria

tenuissima, Laurencia poitei, and Spyridia filamentosa. In addition, Digenia simplex and

Anadyomene stellata were collected as unattached species during the May 1997 sampling. In

September 1997, drift species consisted primarily of Laurencia poitei and Digenia simplex. The

attached but chlorotic Caulerpa paspaloides observed during 1996 was not present during the 1997

samplings.

Water Chemistry - Physical Parameters

Summary values of in situ parameters for all three samplings to date appear in Table 7 with

individual data from 1997 contained in Appendix B. The shallow coastal waters near the mouth

of the Chassahowitzka River were well mixed during both May and September samplings.

Average surface to bottom differences in salinity were less than 0.1 PSU with maximum

differences less than 1.6 PSU for all three samplings. Overall, September is noted for higher

salinity values and lower concentrations and percent saturation of dissolved oxygen.

17
Table 6. Braun-Blanquet estimates of frequency, abundance, and density of the following species within the coastal vegetated regions

in the Chassahowitzka National Wildlife Refuge.

Species

Frequency (%) Abundance (BB Units) Density (BB Units)

May-96 May-97 Sep-97 May-96 May-97 Sep-97 May-96 May-97 Sep-97

Caulerpa paspaloides

Acetabularia crenulata

Batophora oerstedi

Halodule wrightii

Thalassia testudinum

Caulerpa prolifera

Penicillus capitatus

Ruppia maritima

Sargassum spp.

Udotea flabellum

Halimeda incrassata

Caulerpa ashmeadii

Anadyomene stellata

Avrainvillea spp.

Chara spp.

Digenia simplex

Halophila englemannii

Syringodium filiforme

Misc. Algae

Unvegetated

38

31

18

18

18

13

8

5

5

3

3

 1

0

0

0

0

0

0

49

3

36 37 4.0 3.3 3.2 1.5 1.2 1.2

17 12 2.1 2.2 0.6 0.7 0.4 0.1

18 13 0.8 1.3 0.6 0.2 0.2 0.1

20 26 3.8 2.9 2.6 0.7 0.6 0.7

15 23 3.2 2.9 2.9 0.6 0.4 0.7

11 11 2.6 2.2 1.6 0.3 0.2 0.2

8 21 1.9 0.6 1.5 0.2 0.0 0.3

5 0 3.1 1.7 0.0 0.2 0.1 0.0

0 7 3.5 0.0 1.5 0.2 0.0 0.1

3 3 0.2 0.3 0.2 0.0 0.0 0.0

12 6 0.7 1.4 0.5 0.0 0.2 0.0

0 0 2.0 0.0 0.0 0.0 0.0 0.0

0 3 0.0 0.0 0.1 0.0 0.0 0.0

0 3 0.0 0.0 0.9 0.0 0.0 0.0

7 1 0.0 3.5 3.0 0.0 0.2 0.0

0 8 0.0 0.0 2.4 0.0 0.0 0.2

12 3 0.0 3.4 1.3 0.0 0.4 0.0

3 0 0.0 3.3 0.0 0.0 0.1 0.0

43 13 3.6. 3.5 2.4 1.8 1.5 0.3

0 3 5.0 0.0 5.0 0.1 0.0 0.1

18
Non-parametric testing (Kruskal-Wallis) identified a number of significant differences between the

three sampling dates, with May 1996 to May 1997 varying significantly only with respect to

temperature, while May to September 1997 recorded significant differences (p < =0.05) in all four

physical parameters.

Table 7. Average surface or mid-depth observations of physical parameters at 30 coastal

stations, including both morning and afternoon samplings.

Salinity Temperature Dissolved Oxygen Percent Saturation

(PSU) (Deg C) (mg/l) %

May 1996 20.5 27.1 6.8 97

May 1996 20.7 28.4 6.6 96

Sept 1997 26.0 29.4 5.5 83

Despite the effort to sample a wet season in September 1997, rainfall and groundwater deficits

were reflected in the increased salinities observed during this month, as compared to the prior two

May samplings. Predicted tidal heights were lower in September with no major weather patterns

noted which would have elevated salinity values. During September, the stations with higher

salinity were located in the southern portion of the Refuge (Figure 5). Salinity in May 1996

ranged between 12 and 27 PSU in the coastal stations, 14 to 28 PSU during May 1997, and 21

to 32 PSU during September 1997.

Violations of Florida water quality criteria occurred at several locations. During the early

morning samplings of May 1996, May 1997, and September 1997, three, two, and 16 stations,

respectively, had surface dissolved oxygen values less than the 4.0 mg/l instantaneous criteria.

During September 1997, the majority of stations recording DO values below 4.0 mg/l were in the

northern portion of the Refuge. A D. O. value of 1.9 mg/l was recorded at Station 20, to the north

of the mouth of the Chassahowitzka River. In addition to low morning D. O. values, the average

of both morning and afternoon values of both D.O. and percent saturation were also lower during

September than during the May samplings. Percent saturation values account for differences in

salinity and temperature between samplings by evaluating oxygen present against what is

theoretically possible under thermodynamic laws. Although some portion of the low D.O. values

during the afternoon may be attributed to lower insolation values, storm conditions, and the

longer sampling during September, a comparison of data collected during the peak saturation

period (1500-1730 hours) still identified September as having lower percent saturation values

(108% versus 125% in May 1997).

19
Figure 5. Distribution of salinity within the Chassahowitzka National Wildlife Refuge,

September 1997.

20
Changes in the diurnal range of dissolved oxygen and percent saturation were also observed

between the three samplings. In addition to the depressed absolute values of dissolved oxygen in

September, the range in saturation was also less during this period. Early morning to late

afternoon percent saturation varied by 69 % , 60 % , and then 48 % for the coastal stations in May

1996, May 1997, and September 1997, respectively, although the difference between the 1997

samplings was not statistically significant for the coastal stations.. Riverine stations expressed

similar decreases in September, with the range in percent saturation approximately half of that

observed for the two prior samplings. While not conclusive, the sum of the B-B abundance values

at the coastal stations followed the same temporal, distribution, highest during the first May

sampling, and lowest during September. Other efforts to link station dissolved oxygen data (either

as concentration, percent saturation, or diurnal range) to abundances at individual stations were

not successful, due in part to the extremely heterogeneous nature of the coastal vegetation, and

comparatively strong tidal currents, which lessen the residence time of any particular water mass

over a particular site.

For riverine stations, stratification was also minimal, with average surface to bottom differences

in salinity of less than 0.5 PSU for all three samplings. A maximum value of 4 PSU was observed

at Station 1.7 during September, and other instances of stratification (of about 2 PSU) were

occasionally seen at Station 4, near the mouth of the River where the riverbed is deeper. Data

from riverine stations were consistent with the temporal trends seen in the coastal water mass.

Dissolved oxygen and percent saturation were lower in September 1997 than previously observed,

while salinity was increased from 5 to 10 PSU on average within the River. Oxygen data from

the Homosassa River are not strictly comparable with data from the Chassahowitzka, as it was

collected mid to late morning and only once during the day.

The tidal creeks exhibited a range of salinities with PETTY, UMAS, MASON, ROSE, and

7CABG ordered from freshest to most saline. Elevated September salinities were evident at these

locations also. Salinity values ranged from 8 to 17 PSU during May 1997, and from 16 to 25 PSU

during September. The tidal creek stations were sampled during early to mid-morning. Percent

saturation values ranged between 45-75 % with only one dissolved oxygen violation recorded, at

7CABG during May 1997 (3.2 mg/l).

Elevated September salinities were also apparent in the discharges from the other spring vents of

the Chassahowitzka system. The CRAB station ranged from 3.5 to 4.6 PSU, POTTR from 3.8

to 9.8 PSU, CH#l from 0.2 to 1.0 PSU, and the headspring, RO, from 0.6 to 3.2 PSU. The most

upstream Homosassa station (HO), although not located directly over a vent, ranged between 0.6

and 2.5 PSU. In each instance, the highest salinity was recorded during the September sampling.

Diurnal variations in salinity were also observed at each vent sampled directly. Dissolved oxygen

was typically low at most of the vents, consistent with undersaturated groundwater. POTTR, the

most saline of the vents, regularly recorded D.O. values below 4.0 mg/l. While some diurnal

variation in percent saturation was observed, extensive forest canopy at most of these locations

appeared to inhibit wide diurnal swings in oxygen, despite extensive rooted and algal vegetation.

21
Water Chemistry - Nutrients

Water quality is characterized by a strong salinity control and a stable riverine gradient. All

analytical results for the 1997 samplings appear in Appendix C, with summary values for coastal

and riverine stations below in Table 8. Coastal stations were distinguished by comparatively low

levels of inorganic nitrogen species, especially nitrate-nitrite-nitrogen. Inorganic or orthophosphorus levels were also low, but generally detectable ( > 0.005 mg/l), while total phosphorus

concentrations were less than the analytical limit of detection (0.05 mg/l) in 75 % of the 1997

samples. Total nitrogen values were moderate and increased with increasing salinity (Figure 6),

in both spatial and temporal scales and among all station categories: Inorganic N:P ratios indicate

the coastal waters were strongly nitrogen limited (values less than 10) during May 1997, while

increases in ammonia and nitrate-nitrite-nitrogen in September produced a more balanced system

(ratios between 10 and 30), albeit with higher inorganic nutrient concentrations overall. Figure

7 illustrates the inorganic N:P ratios for the various station categories of all three samplings to

date.

Figure 6. Total Kjeldahl nitrogen as a function of salinity; all samplings and station

categories. (COAST - coastal stations, TCRKS - tidal creeks, HOMOS -

Homosassa River, SPGS - secondary spring vents, RIVER -

Chassahowitzka River.)

22
Figure 7. Inorganic Nitrogen:Phosphorus ratios as a function of salinity; all

samplings and station categories. (COAST - coastal stations, TCRKS -

tidal creeks, HOMOS - Homosassa River, SPGS - secondary spring vents,

RIVER - Chassahowitzka River.)

Table 8. Summary regional nutrient and chlorophyll values for May and September 1997.

Values less than the limit of detection averaged as a zero value. Units are mg/l for

nutrients, ug/l for chlorophyll, mg:mg for nutrient ratios, and unitless for TSI values.

“Riverine” comprised of Chassahowitzka River stations only.

PO4-P 0.004 0.007 0.005 0.011

TOTP 0.00 0.03 0.00 0.02

NH4-N 0.017 0.064 0.016 0.032

NO23-N 0.001 0.010 0.115 0.143

TKN 0.54 0.71 0.20 0.39

TN 0.55 0.72 0.32 0.54

Chl a, corr. 1.9 1.7 1.8 2.5

IN:IP 4.7 10.5 20.2 15.0

TN:TP 21.9 21.3 14.7 18.3

TSI 30 36 31 35

Coastal 5/97 Coastal 9/97 Riverine 5/97 Riverine 9/97

23
Trophic state indices were almost all “GOOD” (less than 50), with the exception of Stations 6 and

41 during September. For these stations, Secchi depths were low and increased the trophic state

index from “GOOD” to a “FAIR” designation. Spatial patterns of TSI, indicate higher values (40-

49) in the northern Mason Creek-Homosassa Bay area (Figure 8). Conductivity values, however,

were comparable between the northern and southern regions and there is not an obvious

dependence of TSI on salinity (Figure 9).

Figure 8. Spatial distribution (by latitude) of trophic state indices; all samplings,

for Chassahowitzka riverine (RIVER) and coastal stations (COAST)

only.

Figure 9. Lack of dependence of trophic state on salinity; coastal stations, all

samplings.
The higher TSI in the northern region imply that nutrient loadings may be greater in this area,

perhaps attributable to higher residential density or to influences of some of the larger watershed

rivers to the north (Withlacoochee, Suwannee Rivers). A riverine influence to the north is

consistent with the patterns of total and organic nitrogen increasing with salinity from the mouths

of the Chassahowitzka and the Homosassa Rivers (Figure 6).

Using non-parametric tests (Kruskal-Wallis), all nitrogen and phosphorus species, trophic state

indices, and inorganic N:P ratios were significantly (p < 0.05) higher in May than in September of

1997 for the coastal waters. The only significant changes for the riverine stations as a group were

increases in ortho-phosphorus and total nitrogen between May and September. Comparisons of

May 1996 with May 1997 detected significant changes (increases) only for salinity, temperature,

ammonia, and inorganic N:P ratios in the coastal waters and no changes for the riverine stations.

Secchi depths, with few exceptions were greater than bottom in the shallow coastal waters and so

changes in water clarity are untested.

Notable among the water quality data are the nitrate-nitrite-nitrogen concentrations collected at the

various spring vents and, in the Chassahowitzka and Homosassa main stems, the rapidity with

which it is removed from the water column. The most upstream sample on the Homosassa River

averaged 0.38 mg/l, even though not collected directly over a spring vent. Station CH#l and

POTTR averaged between 0.43 and 0.44 mg/l, the Chassahowitzka Main spring (RO) averaged

0.40 mg/l, while CRAB recorded slightly above 0.42 mg/l. Waters in the upper river were

strongly phosphorus-limited due to the excess of nitrate-nitrite-nitrogen present. Background

groundwater concentrations of unimpacted systems are estimated to be near 0.01 mg/l (Jones et

al., 1997). Figure 10 illustrates the removal of nitrate within a short distance downstream for the

Chassahowitzka stations.

Figure 10. Gradient of nitrate-nitrite-nitrogen with respect to salinity; all

Chassahowitzka River samplings.

25
Most nitrate-nitrite-nitrogen had been consumed by Station 2.5, although in September,

measurable quantities were recorded at the mouth of the river. Perhaps in response to the

increased nutrient levels in September, riverine chlorophyll concentrations (Figure 11) and TSI

values (Figure 12) were also elevated with respect to the May samplings.

Figure 11. Gradients of Chlorophyll a, corrected for pheophytin, with respect to

salinity; all Chassahowitzka River samplings.

Figure 12. Gradients of Trophic State Index with respect to salinity; all

Chassahowitzka River samplings.

26
Gradients of organic nitrogen (Figure 13) are the reverse of the gradients typical of the estuarine

portions of surface watershed rivers. Even during September, when efforts were made to sample

the most offshore stations for nutrients and salinities were higher than previous samplings, no

decrease in nutrients with distance offshore was generally observed. The reverse gradient was

present in riverine stations, as well as in coastal locations and tidal creeks (see also Figure 6).

Export of organic nitrogen compounds from the forested wetlands and extensive marshes, in

addition to the influence of watershed rivers to the north, would contribute to the observed reverse

gradient.

Figure 13. Reverse gradients of organic nitrogen with respect to salinity; all

Chassahowitzka samplings.

Interestingly, comparison of Chassahowitzka and Homosassa riverine gradients indicate that, for

a given fraction of saline waters, concentrations of nitrogen were higher in the Chassahowitzka

River (Figure 14). Patterns were similar for both May and September 1997. Sampling runs on

the two rivers were completed on successive days under similar tidal conditions and the results

indicate that for similar proportions of fresh and saline waters, the Chassahowitzka appears to have

a higher nitrogen load. Convergence of the offshore more saline stations indicate the influence

of a similar offshore water mass for each system. The smaller channel widths, fewer limestone

outcrops, and higher proportion of riverside marshes in the Chassahowitzka could all contribute

to this result. Despite the higher nitrogen concentrations in the Chassahowitzka, the Homosassa

River displayed higher chlorophyll (and therefore higher trophic state indices) for comparable

salinities (Figure 15). Residence times could differ sufficiently (higher in the Homosassa) to allow

phytoplankton to bloom in specific low salinity regions. Additionally, the organic nitrogen

exported from the wetlands and marshes as humic substances could be in a relatively nonbioavailable form.

27
Figure 14. Comparison of total nitrogen as a function of salinity, in the

Chassahowitzka and Homosassa Rivers.

Phytoplankton

During 1997, phytoplankton and the dinoflagellate portions of the total community were manifestly

different from the 1996 sampling. From a fairly coherent and uniform ratio of

dinoflagellate:phytoplankton counts in 1996, dinoflagellates in 1997 samples formed a much

smaller fraction of the total population with a greater variation in the relationship.

28
Whereas dinoflagellates had formed 40-60% of the total organisms counted in May 1996,

dinoflagellates averaged 6% and 8 % of the total during the May and September samplings,

respectively (Figure 16). Total phytoplankton counts for the coastal areas averaged 84000,

187000, and 106000 organisms/l during the three samplings. For either single samplings or for

the combined database, neither salinity variations, nor a variety of nutrient concentrations

displayed a direct relationship to either total concentrations or dinoflagellate ratios.

Figure 16. Dinoflagellate abundance as function of total phytoplankton concentration; riverine

and coastal stations. Scales truncated. A - May 1996, B - May 1997, C -

September 1997.

Biomass

A survey of wet weight biomass along a riverine transect in May and September 1997

demonstrated distinct spatial patterns in both algal and vascular abundance (Appendix D).

Although methods varied slightly between the two samplings, seasonal variations were also

captured. The May sampling recorded a maximum biomass of 12 kg/m2 at Station 1.3, distributed

evenly between rooted (Potamogeton pectinatus) and algal species. (May biomass values are the

arithmetic average of samples of “light”, “typical”, and “heavy” vegetation concentrations .) Total

biomass reached a minimum at Station 2.5 and 3, in an area of high salinity variation. Vascular

SAV (regardless of species) was primarily limited to the river (Figure 17), while algal species

(both attached and drift varieties) formed a bimodal pattern with a maximum in the low salinity

region of the river (generally filamentous green and blue-green varieties, minimal values at the

stations upstream of the mouth of the Chassahowitzka, and higher biomass values (Caulerpa

paspaloides, drift Rhodophyta) offshore.

29
Figure 17. Riverine gradients of biomass, as the average of “light, ” “typical, ” and

“heavy” growth, during May 1997. Allocated into vascular submerged

aquatic vegetation (SAV) and macroalgal components.

During September, biomass samples represented the arithmetic average of five samples across the

river channel, or randomly placed in open waters. The bimodal pattern of algal biomass is still

present but the filamentous algae at the headspring was quite heavy, at 16 kg/mg2. Other. than this

station ‘biomass values were lower overall with vascular species forming a minima1 portion of the

total (Figure 18).

Figure 18. Riverine gradients of biomass, as the average of five evenly spaced

(across channel) or randomly placed (open water) quadrats during

September 1997. Allocated into vascular submerged aquatic vegetation

(SAV) and macroalgal components.

30
Sediments

Results of sediment nutrient analyses are presented below and in Appendix E. For the purposes

of this exploratory sampling, total Kjeldahl nitrogen was assumed to be the majority of total

nitrogen in the sediments since nitrate porewater concentrations are typically low. (This

assumption will be tested in subsequent samplings.) During the May sample collection when

nutrients were analyzed, Stations R4 and 44 were on rocky substrate and no sample was possible.

Grain size results from both May and September samplings appear in Appendix E and reflect a

range of conditions within the river and coastal areas.

Within the upper river (Stations R0 through R1.3) water velocity is high in midchannel and

sediments consist of primarily the sand sized fraction. At Stations R1.7, R2, and at pockets

between limestone outcrops at Station 26 (and other offshore stations), sediments are very

unconsolidated and organic and nutrient content quite high, up to 10 mg TKN/kg dry sediment

(Figure 19).

Figure 19. Riverine gradients of sedimentary total Kjeldahl nitrogen and total

phosphorus during May 1997. Rocky substrate and no sample at Stations

R4 and 44.

The unconsolidated nature and total nutrient content of sediment is mirrored by the spatial

distribution of sediment organic content (Figure 20). Interestingly, stations with high percent

organic content also have a high N:P (TKN:TOTP) ratio and could indicate that zones of organic

accumulation preferentially release phosphorus (under hypoxic or anoxic conditions), and that

organic sediments could act as a temporary nitrogen sink.

31
The preferential mobilization of phosphorus from organic matter is supported by the spatial pattern

of phosphorus content per weight of organic matter in the sediment rather than per total dry weight

(Figure 21). In general, the phosphorus content of sedimentary organic material declines with

distance downstream, while nitrogen content although slightly variable, displays no monotonic

spatial trend and has a very direct relationship with sediment organic content (Figure 22). The

spatial pattern of phosphorus content of organic matter is also consistent with the strong

phosphorus limitation of upstream stations where nitrate-nitrite-nitrogen is present in quantity.

Figure 20. Riverine gradients of sedimentary N:P ratios (N from TKN only) and

percent organics during May 1997.

32
Figure 22. Sediment total Kjeldahl nitrogen content as a function of percent organic

content during May 1997.

Summary

The oligotrophic nature of the nitrogen-limited coastal waters within the Chassahowitzka National

Wildlife Refuge are threatened by the prospect of increased nitrogen loads both from groundwater

discharges and from atmospheric deposition. Spring discharges of the Chassahowitzka and other

major spring complexes in the region already have nitrate-nitrite-nitrogen concentrations nearly

50 times that of pristine background conditions. Tidal variation in both discharge quality and

quantity are evidence of a complex hydrologic structure. Within the river systems, there are

numerous smaller spring vents which are largely unmapped, and there is also a high potential for

substantial quantities of submarine freshwater discharge. The relative amount of direct

groundwater discharge to the coastal waters is unknown at this time. Groundwaters discharging

to the region are approximately 10 to 50 years old and so even the most aggressive management

actions enacted at this time will only demonstrate nutrient reductions within a comparable time

span.

The sampling conducted for this report was designed to collect statistically robust baseline

information against which future samplings can be evaluated. Submerged aquatic vegetation (both

vascular and attached macroalgal) was identified to species level and abundances estimated at 30

coastal stations. Water quality samples were collected from 20 coastal stations, as well as along

the Chassahowitzka and Homosassa riverine salinity gradients. Samplings were conducted in May

and September 1997, during periods of both groundwater and rainfall deficits. Ancillary

samplings included both biomass and sediment nutrients along a gradient from upriver to offshore.

33
Initial work in the Chassahowitzka National Wildlife Refuge and Chassahowitzka River has

established that the coastal area supports a heterogeneous and stable community of submerged

aquatic vegetation. During the May samplings to date, vegetation in the coastal region was

dominated by a variety of drift algal species, while during all samplings, Caulerpa paspaloides

was the most frequently observed attached species. Declines in drift species frequency were noted

during September 1997, and Acetabularia was observed approximately half as often in 1997 as in

May 1996. Riverine biomass was bimodal with minimum values observed in the area of high

salinity variation. September biomass values were generally lower than May observations, and

the percentages of vascular plants in September data were very small.

Coastal waters are shallow and were well mixed during all samplings. September 1997 was

notable for higher salinities than had been observed previously. Spring discharges were also more

saline during this sampling event. Dissolved oxygen values were generally above instantaneous

criteria, but some violations ( < 4.0 mg/l) were recorded during early morning samplings. The

D.O. violations were typically in the northern portion of the Refuge coastal waters. September

D.O. levels and percent saturation values were significantly lower than during the prior two

samplings. Secchi depths were almost all greater than water column depths.

In coastal waters, inorganic nitrogen species, ortho-, and total phosphorus were generally quite

low. During May 1997, coastal waters were strongly nitrogen limited, while higher levels of

ammonium and nitrate-nitrite during September produced a more balanced water column. Trophic

state indices recorded two instances of the “FAIR” category during September, with the remaining

stations categorized as “GOOD”. Despite waters being more saline, all nitrogen and phosphorus

species, trophic state indices, and inorganic N:P ratios were significantly (Kruskal-Wallis) higher

in September as compared to May 1997.

Riverine water quality is distinguished by discharge of slightly saline waters from a complex of

spring vents at the head of the Chassahowitzka River. The nitrate-nitrite nitrogen concentration

is generally above 0.4 mg/l, but is rapidly removed from the water column by the extensive

vegetation in the freshwater portion of the river. Similar patterns of nitrate removal appear in the

Homosassa River, as well. Another interesting feature of riverine water quality in both systems

is that organic nitrogen is low at the spring vents and steadily increases with salinity, implying that

the nearshore oligotrophic waters are diluted with higher nutrient content, more saline waters,

perhaps representing nutrient loads from larger surface drainage rivers to the north. Export of

organic nitrogen from forested wetlands and marshes may also contribute to the reverse gradient.

In comparing the Chassahowitzka and Homosassa Rivers, the Chassahowitzka had more nitrogen

content for comparable salinity values. Conversely however, the Homosassa recorded higher

chlorophyll content and trophic state indices. The differences may be attributable to comparative

size and possible longer residence time of waters in the Homosassa, as well as the apparently

greater proportion of marshes along the Chassahowitzka.

34
Specific regions of the Chassahowitzka River and offshore areas have unconsolidated, highly

organic sediments. Sediment nutrient data indicate a preferential demobilization of phosphorus

from organics materials, with relatively constant proportions of nitrogen in organic matter.

Recommendations

Water column nutrients in the Refuge have been consistently low with many values (particularly

of inorganic nutrients) below analytical detection limits. The oligotrophic and nitrogen-limited

waters of the Refuge, however, are subjected to a variety of nutrient loadings. Inorganic nitrogen,

primarily nitrate-nitrite-nitrogen, is present in substantial quantities in many of the known spring

discharges, but is rapidly removed from the water column. Downstream loadings would be in the

form of dissolved and detrital compounds originating from the extensive biomass in the upper river.

In-Refuge sources could also include contributions by water exchange with the extensive coastal

marsh system. External sources would include the import from nearby major riverine systems, direct

contributions of groundwater to the coastal area, and atmospheric deposition of nitrate and

ammonium nitrogen. Direct atmospheric loading of nitrogen to Refuge waters is roughly comparable

to that from the major Chassahowitzka discharges, while the remaining sources are not quantifiable

at this time.

As known loadings of nitrogen are predicted to increase over time, monitoring of the Refuge water

column and biota should be designed to quantify areas and systems where changes can be predicted

or are expected. The primary goals should be the ability to detect temporal trends in water quality

and vegetation (particularly trends due to increasing nutrient loads), and to collect quantitative

information at intervals, focusing on information suitable for ecological modeling. To aid in trend

detections, water quality samplings would benefit from increased sampling frequency, while SAV

monitoring of a more stable community do not require the same frequency. Due to the complexity

of nitrogen sources to the Refuge itself, work within the Chassahowitzka River would simplify the

identification of direct relationships between tidal freshwater and brackish water community

responses and nitrogen loadings. Work within the coastal waters of the Refuge will allow the

detection of trends, but due to the numerous sources or potential sources of nitrogen, may not be

attributable to any given source.

35
LITERATURE CITED

Braun-Blanquet, J. 1932. Plant sociology: the study of plant communities. Transl. rev. and ed.

by C.D. Fuller and H.S. Conard. Hafner, London, 439 p.

Dawes, C.J. 1974. Marine algae of the west coast of Florida. Univ. Miami Press, 201 p.

Dixon, L.K. 1997. Data inventory, trend analysis, and recommended monitoring: Florida

Springs Coast. Mote Marine Laboratory Technical Report No. 536 to the Southwest Florida

Water Management District.

Earle, S. A. 1969. Phaeophyta of the eastern Gulf of Mexico. Phycologia 7: 71-254.

Estevez, E.D., L.K. Dixon and M.S. Flannery. 1991. West-coastal rivers of peninsular Florida,

Chapter 10 in R.J. Livingston (ed.), The Rivers of Florida. Springer-Verlag Ecological Studies

83. New York. 289 p.

Hand, J., V. Tauxe and M. Friedemann. 1988. 1988 Florida water quality assessment - 305(b)

technical appendix. Florida Dept. of Environ. Regul.

Hine, A.C. and D.F. Belknap. 1986. Recent geological history and modem sedimentary

processes of the Pasco, Hernando, and Citrus counties coastline. West-central Florida. Florida

Sea Grant Report 79. Gainesville, FL.

Iverson, R.L. and H.F. Bittaker. 1986. Seagrass distribution and abundance in eastern Gulf of

Mexico coastal waters. Est. Coastal Shelf Sci. 22: 577-602.

Jones, G.W., S.B. Upchurch, K.M. Champion and D.J. Dewitt. 1997. The water quality and

hydrology of Homosassa, Chassahowitzka, Weeki Wachee, and Aripeka spring complexe, Citrus

and Hernando Counties, Florida: Origin of increasing nitrate concentrations. Report prepared by

the Ambient Ground-Water Quality Monitoring Program, Southwest Florida Water Management

District.

Marshall, M.J. and J.R. Leverone. 1994. The distribution and effects of hypoxia on marine

organisms in Sarasota Bay. Mote Marine Laboratory Technical Report to the Sarasota Bay

National Estuary Program.

McNulty, J.K., W.N. Lindall, Jr. and J.E. Sykes. 1972. Cooperative Gulf of Mexico estuarine

inventory and study, Florida: Phase 1, area description. NOAA Technical Report NMFS

Circ-368. 126 p.

Officer, C.B. and J.H. Ryther. 1980. The possible importance of silicon in marine eutrophication.

Mar. Ecol. Prog. Ser. 62: 83-91.

36
Phillips, R.C. 1960. The ecology of marine plants at Crystal Bay, Florida. Quart. J. Fla. Acad.

Sci. 23: 328-337.

Southwest Florida Water Management District. 1994. SWFWMD Ambient Monitoring Program:

First biennial report of the ambient monitoring program including a report on water quality trends

in five central Florida springs. SWFWMD Resource Projects Department Environmental Section.

July.

Southwest Florida Water Management District. 1996. Hydrologic Conditions in the Southwest

Florida Water Management District, April 1996: with provisional updates through May 20.

Prepared by Hydrologic Data Section, Resources Data Department of SWFWMD.

Southwest Florida Water Management District. 1997a. Hydrologic Conditions in the Southwest

Florida Water Management District, May 1997. Prepared by Hydrologic Data Section, Resources

Data Department of SWFWMD.

Southwest Florida Water Management District. 1997b Hydrologic Conditions in the Southwest

Florida Water Management District, September 1997. Prepared by Hydrologic Data Section,

Resources Data Department of SWFWMD.

Wolfe, S.H. (ed.) 1990. An ecological characterization of the Florida Springs Coast:

Pithlachascotee to Waccasassa Rivers. U.S. Fish Wildl. Serv. Biol. Rep. 90(21). 323 p.

Yobbi, D.K. 1992. Effects of tidal stage and ground-water levels on the discharge and water quality

of springs in coastal Citrus and Hernando counties, Florida. U.S. Geol. Survey Water-Resources

Investigations Report 92-4069. 44 p.

3 7
Appendix A

SAV Quadrat Data

Station and Species Summary


















Appendix B

In Situ Water Quality Data






Appendix C

Water Quality Data

Phytoplankton Data

Trophic State Indices










Appendix D

Biomass Data



Appendix E

Sediment Nutrient Data

Sediment Grain Size Data