Draft Annual/Final Report for FFWC-U.S. Army Corp. of Engineers Calooshatchee
Research Project (USF award #DO137724) Summer 2005
University of South Florida – Dr. Kendall Carder
1.0 Introduction
Colored dissolved organic matter (CDOM) or gelbstoff is the only relatively
conservative riverine constituent quantifiable from space. It provides a near-shore tracer
of other riverine constituents (e.g. nutrients, pollutants) as they are diluted on entering
and moving about the Gulf of Mexico. CDOM is produced when plant material in water
or soil degrades. It causes the yellow/brown color often seen in Florida Rivers. When
considering the Caloosahatchee River, CDOM can be treated as a quasi-conservative
property of the water since the degradation of CDOM occurs slowly in comparison to the
time a parcel of water remains in the river.
We investigated the remote sensing properties of the Caloosahatchee River,
making our measurements in coordination with personnel from the Florida Fish and
Wildlife Conservation Commission’s Fish and Wildlife Research Institute (FWRI). Of
particular interest on the Caloosahatchee River was the concentration of Colored
Dissolved Organic Matter (CDOM, traditionally referred to as gelbstoff) and how it’s
variation was coupled with salinity, chlorophyll concentrations, and the nutrient
measurements made by FWRI. One of our primary goals is to link the physical and biooptical properties of the water to above water observations.
The conservative nature produces a measure observable from space of the dilution
effects of mixing Caloosahatchee River water with seawater. The concentration of
CDOM tends to vary inversely with salinity and can be used as a measure of dilution as
high CDOM waters, such as a fresh surface-water source, mixes with lower CDOM
water, such as the saline waters of the Gulf of Mexico. Since the CDOM is coloring the
water because of it’s strong absorption of blue light, it will affect the color of the water as
reflected to an above water observer. This allows CDOM concentrations to be estimated
from remote sensing reflectance or satellite observations (such as performed by C. Hu
(USF) for the Caloosahatchee).
Using CDOM as a proxy for the dilution of terrestrial nutrients provides a visible
indication of a nutrient pathway in satellite imagery. When these nutrients are
transported to coastal waters they will influence the coastal ecosystem, and may have a
role in the formation and/or maintenance of algal blooms such as red tides. Hence, the
pathway and dilution of nutrients, pollutants, and other materials carried by the river into
the Gulf of Mexico can be estimated remotely if the source waters constituents are
adequately quantified by autonomous sampling platforms such as MARVIN.
2.0 Data
2.1 Data Collection
Coastal field data were collected during one 5-day, FWRI directed, West Florida
shelf (WFS) cruise in April 2005. River Field data was collected during four 1-day
Caloosahatchee River cruises in April, May, July, and August 2005 (Table 1). Data
collected prior to the beginning of the contract were collected in anticipation of the
Carder report for Summer’05 Caloosahatchee Project
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proposal being funded. The contract period encompassed only the processing and
analysis of these data.
One of the stations visited during the Caloosahatchee River sampling was the
FWRI’s MARVIN (MERHAB autonomous research vessel in situ sampler) sampling
platform. A description of the MARVIN program can be found at
http://www.merhabflorida.org/marvin.htm. In August 2005 we added a CDOM
fluorometer (WETLabs CDOM_WETStar) to the MARVIN sampling system. The
information from this fluorometer is integrated into the MARVIN data stream and an
initial time series is being generated. Since the instrument only became available for
integration in August, a preliminary calibration using lab and comparisons with other
field instruments is being used until more calibration and validation measurements of
CDOM can be made at the MARVIN station on the Caloosahatchee.
2.1.1 WFS cruise
Between April 25th and 29th surface water measurements were collected from the
R/V Suncoaster during a FWRI expedition which ranged from Tampa Bay (~27.7oN) to
the Florida Keys (~25oN) and from ~5 to 50km offshore (Fig. 1). Data collected include
remote-sensing reflectance spectra, Rrs(), (n=15) and spectral light absorption (n=42)
due to total particles, ap(), detritus, ad(), and gelbstoff, ag() (Fig. 2). Chlorophyll a
concentrations were determined at each station and ranged from 0.26-3.6 mg m-3 (n=42).
Surface underway measurements of temperature, salinity, beam-attenuation, chlorophyll
and gelbstoff fluorescence, and backscattering were also collected using a deck-mounted,
flow-through system (Fig. 3).
2.1.2 Caloosahatchee River cruises
We accompanied FWRI personnel during Caloosahatchee River sampling and
MARVIN maintenance field work from the mouth of the river upstream to Franklin
Locks (Fig. 1). During these journeys along the river Rrs() measurements were made
from the boat and ap(), ad(), ag(), and [Chl a] data were measured from discrete
surface seawater samples taken at the FWRI sampling stations (Fig. 4). Vertical profiles
of temperature, salinity, chlorophyll, and gelbstoff fluorescence were also collected at
these stations and the data were later processed into discrete depth ranges to aid
interpretation. The profiles were collected at <0.2 m intervals by slowly lowering and
raising an instrument frame containing an FSI 2”microCTD, a WETLabs Chl. WETStar
fluorometer, and a WETLabs Flashlamp CDOM fluorometer. Example profiles from
three stations are shown in Fig. 5. The Sanibel station is located near the mouth of the
Caloosahatchee, the West Redfish Pass station is downriver from Fort Meyer near Cape
Coral, and the MARVIN station is near Beautiful Island and the Orange River.
The variability of CDOM along the river, and between sampling trips can be seen
in Figure 6. This figure shows vertical profiles of ag(440) taken at different times at the
Caloosahatchee sampling locations.
2.1.3 Caloosahatchee River gelbstoff fluorescence time-series
On 18 August 2005, a WETLabs WETStar CDOM fluorometer (excitation at
370nm with emission measured between 400to 520nm) was integrated into the MARVIN
data-sampling regime. Water was collected every hour from two depths (near surface
Carder report for Summer’05 Caloosahatchee Project
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and ~ 4m) to allow the MARVIN instruments to measure salinity, temperature, chl_a.
fluoresence, pH, dissolved oxygen, turbidity, water level, and other meteorological
variables. This information is stored on the platform and also transmitted back to a data
archive and online display system at FWRI. Fluorometer voltages were converted to
preliminary ag(400) estimates based on several laboratory and field measurements. Figure
7 shows a one-week time-series of these preliminary ag(400) values from the autonomous
MARVIN measurements. Since CDOM fluorescence efficiency varies due to changes in
water source, light exposure, and other factors, continued validation measurements are
desired to separate CDOM variability from changing seasonal fluorescence or instrument
efficiencies.
2.2 Data Processing
Absorption spectra due to particles and detritus (ap() and ad()), were determined
using the quantitative filter technique (Yentsch, 1962; Kiefer & SooHoo, 1982).
Measurements were made with a custom-made, 512-channel spectroradiometer (~350850nm, ~2.5nm resolution). Pigments were extracted with hot methanol (Kishino et al.,
1985; Roesler et al., 1989) from which chlorophyll a concentrations were determined
fluorometrically (Holm-Hansen & Riemann, 1978). Phytoplankton absorption spectra,
aph(), were then calculated as the difference between ap() and ad().
Gelbstoff absorption spectra, ag(), were measured on 0.2m filtered surface
seawater samples using a dual-beam spectrophotometer (Perkin-Elmer® Lambda 18).
Data were processed using methods previously described by Mueller and Fargion (2002).
Remote-sensing reflectance spectra, Rrs(), were determined from the ratio of
water leaving radiance, Lw(), to downwelling irradiance, Ed(). Lw() and Ed() were
calculated from above-water measurements of upwelling radiance, sky radiance, and the
radiance reflected from a near-Lambertian greycard (Spectralon; ~10%) using methods
described previously by Lee et al. (1997). All measurements were made using a custommade, 512-channel spectroradiometer (~350-850nm; ~2.5nm resolution).
CDOM and chlorophyll fluorescence measurements were converted to absorption
and chlorophyll concentrations by comparing the instrument measurements to the discrete
measurements made that day on the appropriate portion of the river. The fluorescence
profiles were then binned into 0.5m increments using medians.
2.3 Data Analysis
Coastal observations, made offshore of the Caloosahatchee mouth during FWRI’s
April expedition, were processed to produce measurements of in-water optical properties,
chlorophyll and gelbstoff concentrations, and remote sensing spectra. Water samples
taken from four trips (occurring from April to August), each with several stations along
the Caloosahatchee river, were processed to yield absorption spectra and chlorophyll and
gelbstoff concentrations. In addition, remote sensing spectra and vertical profiles of
temperature, salinity, chlorophyll, and CDOM were derived from the small boat
measurements. The status of the data processing and analysis is presented in Table 2.
Though funding and procurement constraints delayed the installation of a CDOM
fluorometer onto the MARVIN platform until August 18, an initial time series of CDOM
variability has been generated (Fig. 7). An immediate result of this series is showing that
not only is CDOM variable over several days, but that there is a circadian variability
Carder report for Summer’05 Caloosahatchee Project
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pattern. This diel variability may not only be affected by the sun, but also pH and river
flow. Since this station is located where much of the Caloosahatchee source water is
entering the estuary, and since it does show diel variability, it suggests that some of the
variability in CDOM fluorescence measurements taken downstream (Fig. 8) may be
explained by the time of day at which individual samples were taken.
The CDOM measurements were compared to salinity and a significant linear
relationship was derived for each river sampling day samples. This relationship was most
robust for April and May, but in July the variability of the CDOM at the upriver stations (
Franklin Locks, MARVIN, Fort Meyers) decreased the strength of a straight line fit to
these measurements. A different water source will also cause samples to diverge from a
linear relationship. Note in Figure 6 how the Franklin Lock CDOM absorption profiles in
May and July have smaller values than the MARVIN profiles. This is probably because
the locks are upstream of the Orange River, which enters into the Caloosahatchee just
upstream of the MARVIN site.
The profiles produced at each station along the river (e.g. Fig 5) not only provide a
means of interpolating our discrete samples, but also provide information about the
vertical structure of the river and the location of the mixing boundary of the gulf and river
water. Though the scales are varied in Figure 5 to clarify the vertical structure, it is
evident that on this day in May the tidal excursion of the more saline Gulf water below
the fresher, warmer, high gelbstoff river water does not extend as far upstream as the
MARVIN site. In fact, the MARVIN site shows weak vertical structure. It should also
be noted that the CDOM absorption does not necessarily co-vary with chlorophyll
concentrations at all stations.
Variability of the flow rate of surface water into the Caloosahatchee will have a
strong effect on physical and biological structure of the river. A plot of flow
measurements made near Lake Okeechobee and at the most downstream lock along the
river (Franklin Lock) is shown if Figure 9. Combining the flow rate observations with
the autonomous MARVIN observations and the river profiles is not yet complete.
3.0 Discussion and Future work
The relationship between CDOM and other conservative properties (such as
salinity) should be robust in a steady-state coastal estuary with only a constant single
source of fresh water. The Caloosahatchee is not a steady-state system, nor is there a
constant single source of water. We also see from the measurements described in this
report that CDOM concentrations are variable, even at upper estuary sites like MARVIN.
Despite this, the relationship between CDOM concentration and salinity has been shown
to be robust during sampling periods of a day. Thus, the remotely observable CDOM
absorption ( such as C. Hu’s work on satellite observations of the Caloosahatchee
outflow) should be a useful indicator of the distribution of Caloosahatchee water into the
Gulf of Mexico and may serve as visible proxy for other slowly changing nutrients or
material. Furthermore, the deflections of measured CDOM concentrations from a linear
prediction of their values can provide information about the input of water from other
sources into the Caloosahatchee.
We can see in Figure 9 that not all the water flowing downstream into the
Caloosahatchee estuary comes from Lake Okeechobee. In addition to variations in the
amount of water released from Lake Okeechobee, this Southern Florida region received
Carder report for Summer’05 Caloosahatchee Project
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considerable rain from multiple tropical storms or hurricanes in the last year. During the
anticipated continuation of the Caloosahatchee study we intend to further examine the
variability of CDOM concentration and fluorescence, recognizing that this estuary will
have multiple water sources whose contributions may vary considerably throughout any
particular year.
Since the CDOM fluorometer is now installed on MARVIN, a time series beyond
the one-week’s measurements presented here can be started. Combining a longer time
series with river flow measurements should not only help determine seasonal and flowrate dependant CDOM concentration variability, but also provide information about the
range and timing of daily CDOM fluorescence variability. Calibration and validation
measurements throughout the year will be needed to establish the accuracy of the
instrument, account for seasonal fluorescence efficiency variability, and provide alerts for
instrument degradation. We hope to continue to provide these measurements during
subsequent installments of this project. Since our measurements show CDOM
concentrations on the river can vary over 100%, and even can vary almost 20% during a
day, continued measurements of CDOM concentration will be needed to accurately
interpret remotely sensed color data.
The initial measurements in the Caloosahatchee suggest that CDOM
concentration may be a useful indicator for the mixing and dilution of upstream
Caloosahatchee water and slowly changing material in the water. This CDOM dilution
should continue offshore where it should indicate the dilution and transport of riverine
nutrients through coastal waters. We hope to continue our efforts to refine the ability to
determine bio-optical properties of WFS waters from above-water measurements, and so
to provide a remote sensing indicator of the route and planktonic consequences of
riverine input to the coastal ecosystem.
References
Holm-Hansen, O. & Riemann, B. (1978), Chlorophyll a determination: improvements in
methodology. Oikos, 30, 438-447.
Kiefer, D.A. & SooHoo, J.B. (1982), Spectral absorption by marine particles of coastal waters of
Baja California. Limnol. Oceanogr., 27, 492-499.
Kishino, M., Takahashi, M., Okami, N., & Ichimura, S. (1985), Estimation of the spectral
absorption coefficients of phytoplankton in the sea. Bull. Mar. Sci., 37, 634-642.
Lee, Z., Carder, K.L., Steward, R.G., Peacock, T.G., Davis, C.O., et al. (1997), Remote-sensing
reflectance and inherent optical properties of oceanic waters derived from above-water
measurements. In: Ackleson, S.G., & Frouin, R. (Eds.), Ocean Optics XIII, SPIE 2963,
Halifax, Nova Scotia, Canada, pp. 1960-1966.
Mueller, J.L. & Fargion, G.S. (2002), Ocean optics protocols for satellite ocean color sensor
validation, revision 3, volume 2. NASA Tech. Memo. 2002-210004/Rev3-Vol2, NASA
Goddard Space Flight Center, Greenbelt, Maryland.
Roesler, C.S., Perry, M.J., & Carder, K.L. (1989), Modeling in situ phytoplankton absorption
from total absorption spectra in productive inland marine waters. Limnol. Oceanogr., 34,
1510-1523.
Yentsch, C.S. (1962), Measurement of visible light absorption by particulate matter in the ocean.
Limnol. Oceanogr., 7, 207-217.
Carder report for Summer’05 Caloosahatchee Project
page 5
Table 1. USF-Carder 2005 field activity summary with the number of samples collected
for each measurement and cruise.
Location
Month
Rrs()
ap()
ad()
ag()
[Chl a]
in situ
April
15
42
42
42
42
Surface
underwaya
April
Caloosahatchee May
River
July
August
7
6
6
7
6
7
6
7
6
7
6
7
6
7
6
7
6
7
6
7
Vertical
profilesb
Offshore
a
Surface underway measurements were taken of temperature, salinity, beam-attenuation, chlorophyll and
gelbstoff fluorescence, and particulate backscattering.
b
Vertical profile measurements were taken of temperature, salinity, and chlorophyll and gelbstoff
fluorescence.
Table 2. USF-Carder 2005 field data status.
Location
Month Collected Processed
WFS
April
X
X
April
X
X
X
X
Caloosahatchee May
River
July
X
X
August
X
-
Analysed
Preliminary
Preliminary
Preliminary
Preliminary
-
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page 6
Figure 1. Map of station locations for the WFS and Caloosahatchee River cruises.
Figure 2. West Florida shelf remote-sensing reflectance spectra, phytoplankton
absorption spectra, detrital absorption spectra, and gelbstoff absorption spectra collected
between 25-29 April 2005 aboard the R/V Suncoaster.
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page 7
28
Sea Surface
Temperature
(deg. C)
Salinity
(psu)
27.5
Latitude (deg. N)
27
26.5
26
25.5
25
20
24.5
83.5
24
83
28
82.5
82
32
81.5
36
81
80.5
21
80 83.5
23
83
82.5
Longitude (deg. W)
25
82
27
81.5
81
80.5
80
Longitude (deg. W)
28
Chlorophyll a
Concentration
(mg/m^3)
27.5
ag(400)
(1/m)
Latitude (deg. N)
27
26.5
26
25.5
25
0.1
24.5
83.5
1
83
82.5
82
0.01
10
81.5
81
80.5
80 83.5
83
0.1
82.5
Longitude (deg. W)
82
1
81.5
10
81
80.5
80
Longitude (deg. W)
Figure 3. Distribution of salinity, sea surface temperature, chlorophyll a concentration,
and ag(400) measured during the April 2005 west Florida shelf cruise.
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page 8
Figure 4. Caloosahatchee River remote-sensing reflectance spectra, particle absorption
spectra, detrital absorption spectra, and gelbstoff absorption spectra collected 14 April, 12
May, 21 July, and 18 August.
Carder report for Summer’05 Caloosahatchee Project
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FWRI station 1, near Sanibel Island
12 May 2005
0
0
0
0
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
5
0.38 0.40 0.42 0.44 0.46 0.48 0.50 0.52
5
5
5
32.6
25.8 25.9 26.0 26.1 26.2 26.3
32.8
33.0
Temperature (°C)
Depth
33.4
1.7
0.0
0.0
0.0
0.5
0.5
0.5
0.5
1.0
1.0
1.0
1.0
1.5
1.5
1.5
2.0
2.0
2.0
2.0
2.5
2.5
2.5
2.5
3.0
3.0
6
26.6 26.8 27.0 27.2 27.4 27.6 27.8
8
10
Temperature (°C)
12
14
16
18
20
0
1
1
2
2
3
3
4
4
Temperature (°C)
2.1
2.2
2.3
3.0
5C:
5
0.220
ag(440) (m-1)
FWRI station
6, MARVIN
0
0.224
Salinity
0.228
6
1
2
2
3
3
4
4
4.2
4.3
ag(440) (m-1)
10
12
14
16
18
20
22
0
1
4.1
8
Chl. Fluoresence (~g l-1)
5
26.5 27.0 27.5 28.0 28.5 29.0
2.0
1.5
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
Salinity
0
5
1.9
FWRI station 4, West of Redfish Pass
0.0
3.0
1.8
Chl. Fluoresence (~g l-1)
ag(440) (m-1)
Salinity
5B:
Depth
33.2
Depth
Depth
5A:
4.4
5
10.010.511.011.512.012.513.013.5
Chl. Fluoresence (~g l-1)
Figure 5. Example profiles of temperature, salinity, a g(400), and Chl_a fluoresence for 3 stations on the
Caloosahatchee River on 12 May 2005. 5A: near the southern tip of Sanibel Island and shows the river
flowing into (and above) Gulf of Mexico waters. 5B: West of Redfish Pass, downstream of both Cape
Coral and Fort Meyer and shows the tidal intrusion of the Gulf waters below the fresher Caloosahatchee
water. 5C: shows a profile from the MARVIN site.
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page 10
Gelbstoff (CDOM) absorption
14 April 2005
0
Depth (m)
1
2
3
4
5
6
7
Depth (m)
0
2
3
4
5
6
12 May 2005
0
1
2
3
4
5
6
7
near Sanibel
San Carlos
Matlacha
W. Redfish Pass
Fort Meyer
Marvin
Franklin Locks
0
Depth (m)
1
1
2
3
4
5
6
10
12
21 July 2005
0
1
2
3
4
5
6
7
0
2
4
6
-1
Ag(440) (m )
8
Figure 6. Blue absorption due to gelbstoff on three days. Note that the scale of the
absorption axis for the July samples is twice that of the April and May samples. The
amount of water flowing downstream in July was also significantly greater than the
volume for the previous months.
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Estimated CDOM absorption
at MARVIN from integrated CDM fluorometer
ag(400) (m-1) [preliminary calibration]
18
16
14
12
10
8
6
4
preliminary ag(400) at MARVIN surface
preliminary ag(400) at MARVIN bottom
2
0
8/19/05
8/20/05
8/21/05
8/22/05
8/23/05
8/24/05
8/25/05
time (m/d/y hour)
Figure 7. Preliminary CDOM absorption time series from the gelbstuf fluorometer
installed on MARVIN on August 18th. Note that there was no significant difference
between the values at the surface and at depth, which is to be expected since this site
shows little vertical structure (Fig. 5C). However, this initial series does show circadian
variablity which indicates that sampling times should be considered during further
analysis of CDOM concentrations along the river.
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Figure 8. Relationship between gelbstoff absorption at 400nm and salinity for the WFS
(April) and Caloosahatchee River (April, May, and July) cruises.
Carder report for Summer’05 Caloosahatchee Project
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600
20
15
10
5
Mean Daily Flow m3 s-1
Mean Daily Rain Fall (cm day-1)
25
500
Lock 79 at Franklin Lock
Lock 77 at Lake Okeechobee
Mean Daily Rain E. Calooshatchee Basin
400
300
200
100
0
0
-100
08/01/04
12/01/04
04/01/05
08/01/05
Date
Figure 9. Caloosahatchee River flow rate and rainfall as measured along the River by the
U.S. Army Corp of Engineers and retrieved from the South Florida Water Management
District (SFWMD) database. Lock 79 is Franklin Lock and is located just upstream of
this Caloosahatchee Estuary study area.
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