Bio-Optical Assessment of Giant Kelp Dynamics
1
Bio-Optical Assessment of Giant Kelp Dynamics Richard.C. Zimmerman 1 , W. Paul Bissett 2 , Daniel C. Reed 3 1 Dept. Ocean Earth & Atmospheric Sciences, Old Dominion University, Norfolk, VA 2 Florida Environmental Research Institute, Tampa FL 3 University of California, Santa Barbara, CA INTRODUCTION CANOPY IMPACT ON THE SUBMARINE LIGHT ENVIRONMENT OPTICAL PROPERTIES OF GIANT KELP BLADES The productivity of giant kelp forests is highly variable across time and space. Winter storms and summer periods of nutrient limitation act as bottom-up regulators of kelp abundance and growth in a geography-dependent manner. The goal of this research is to develop to a predictive understanding of giant kelp forest dynamics s in the nearshore waters of California using a combination of (i) bio-optical modeling of kelp productivity, (ii) high-resolution remote sensing of kelp cover, biomass & its physiological state, and (iii) metapopulation modeling of kelp patch dynamics. Here we present progress on objectives (i) and (ii). ACKNOWLEDGEMENTS This research is supported by the National Oceanic and Atmospheric Administration (NOAA) National Aeronautics and Space Administration (NASA) and National Science Foundation (NSF) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 400 450 500 550 600 650 700 Wavelength (nm ) K elp BladeO pticalD ensity ( D ) M ature Senescent Imm ature Optical properties of kelp blades show age dependent differences that may provide useful signals for understanding how the age structure of kelp populations affects the submarine light environment and remote sensing reflectance. Reflectances are highest in senescent tissue, particularly in the NIR. Spectral slopes of NIR reflectance increase with tissue age. Mature tissues have the highest optical density and the lowest reflectance. A ge C lass = 2.78 + 1.04x10 4 -1x10 8 2 -1.E -04 -8.E -05 -6.E -05 -4.E -05 -2.E -05 0.E +00 2.E -05 4.E -05 Imm ature Mature S enescent Kelp A ge C lass Spectral Slope The giant kelp canopy significantly alters the light environment relative to adjacent open water. Example spectral coefficients of diffuse attenuation for downwelling plane irradiance (K d ) in open water adjacent to the kelp forests at Mohawk Reef and Arroyo Quemada range from 0.1 to 0.6 m -1 , with strongly defined minima in the green. Attenuation coefficients under the kelp canopies (including water) averaged 0.8 m -1 and were spectrally flat. Canopy absorbances retrieved from these measurements were quantitatively consistent with laboratory measurements of individual blades. 0 0.2 0.4 0.6 0.8 1 1.2 400 450 500 550 600 650 700 Wavelength (nm ) C anopy A bsorbance ( D ) BAI = 1.63 BAI = 0.55 BAI = 0.12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 400 450 500 550 600 650 700 W avelength (nm ) K d (m -1 ) Arroyo Q uem ado M ohaw k R eef 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 400 450 500 550 600 650 700 Wavelength (nm ) K d (m -1 ) A rroyo Q uem ado M ohaw k Reef RETRIEVAL OF GIANT KELP BIOMASS AND PRODUCTIVITY FROM OPTICAL MEASUREMENTS The consistent optical signature of the kelp canopy produces a Blade Area Index (BAI, identical to Leaf Area Index used in terrestrial vegetation studies) that is linearly related to diver counts of kelp abundance. The slope (0.1) indicates that the canopy structure exerts a strong package effect on the optical efficiency of light absorption. The ability to predict BAI allows retrieval of standing biomass and productivity from measurements of below- canopy irradiance. y = 0.1105x R 2 = 0.7823 0 0.5 1 1.5 2 2.5 0 5 10 15 20 D iverM easured BAI O ptically D eterm ined B A I y = 13.303x R 2 = 0.9829 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.05 0.1 0.15 0.2 0.25 0.3 Frond m ass(kg D W ) Frond BladeA rea(m 2 frond -1 ) Standing crop (kg m -2 ) 0.0 0.5 1.0 1.5 2.0 N PP (g dry m ass m -2 d -1 ) 0 10 20 30 40 R 2 = 0.623 P < 0.0001 a. Macrocystis pyrifera (giant kelp) NPP = 14.7 x Standing Crop 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 400 500 600 700 800 900 Wavelength (nm ) R rs (sr -1 ) M ature Imm ature Senescent PH ILLS C anopy Perhaps more importantly, the strong reflectance signal in the NIR allows absolute kelp abundance and productivity to be calculated and mapped across the habitat from remotely sensed hyperspectral imagery using the normalized difference vegetation index (NDVI). • Converting NDVI into absolute kelp abundance and productivity: – Optical BAI = NDVI/0.71 – True BAI = Optical BAI * 9.04 – Biomass = True BAI/13.3 – Productivity = Biomass * 14.7 Carmel Bay Pescadero Rocks Pt. Lobos Kelp Density (Kg DW m -2 ) 0.54 – 0.61 0.62 - 0.68 0.69 – 0.75 0.75 – 0.82 0.83 – 0.88 0.89 – 0.95 Kelp Productivity (g DW m -2 d -1 ) 8 – 9 9.1 – 10 10.1 – 11 11.1 – 12 12.1 – 13 13.1 - 14
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Bio-Optical Assessment of Giant Kelp Dynamics Richard.C. Zimmerman 1 , W. Paul Bissett 2 , Daniel C. Reed 3 1 Dept. Ocean Earth & Atmospheric Sciences, Old Dominion University, Norfolk, VA 2 Florida Environmental Research Institute, Tampa FL 3 University of California, Santa Barbara, CA. - PowerPoint PPT Presentation
Transcript of Bio-Optical Assessment of Giant Kelp Dynamics
Bio-Optical Assessment of Giant Kelp DynamicsRichard.C. Zimmerman1, W. Paul Bissett2, Daniel C. Reed3
1Dept. Ocean Earth & Atmospheric Sciences, Old Dominion University, Norfolk, VA 2Florida Environmental Research Institute, Tampa FL
3University of California, Santa Barbara, CA
INTRODUCTION
CANOPY IMPACT ON THE SUBMARINE LIGHT ENVIRONMENT
OPTICAL PROPERTIES OF GIANT KELP BLADES
The productivity of giant kelp forests is highly variable across time and space. Winter storms and summer periods of nutrient limitation act as bottom-up regulators of kelp abundance and growth in a geography-dependent manner. The goal of this research is to develop to a predictive understanding of giant kelp forest dynamics s in the nearshore waters of California using a combination of (i) bio-optical modeling of kelp productivity, (ii) high-resolution remote sensing of kelp cover, biomass & its physiological state, and (iii) metapopulation modeling of kelp patch dynamics. Here we present progress on objectives (i) and (ii).
ACKNOWLEDGEMENTS This research is supported by the National Oceanic and Atmospheric Administration (NOAA) National Aeronautics and Space Administration (NASA) and National Science Foundation (NSF)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
400 450 500 550 600 650 700
Wavelength (nm)
Kel
p B
lade
Opt
ical
Den
sity
( D
)
Mature
Senescent
Immature
Optical properties of kelp blades show age dependent differences that may provide useful signals for understanding how the age structure of kelp populations affects the submarine light environment and remote sensing reflectance. Reflectances are highest in senescent tissue, particularly in the NIR. Spectral slopes of NIR reflectance increase with tissue age. Mature tissues have the highest optical density and the lowest reflectance.
Age Class = 2.78 + 1.04x104 -1x1082
-1.E-04
-8.E-05
-6.E-05
-4.E-05
-2.E-05
0.E+00
2.E-05
4.E-05
Immature Mature Senescent
Kelp Age Class
Sp
ect
ral S
lop
e,
The giant kelp canopy significantly alters the light environment relative to adjacent open water. Example spectral coefficients of diffuse attenuation for downwelling plane irradiance (Kd) in open water adjacent to the kelp forests at Mohawk Reef and Arroyo Quemada range from 0.1 to 0.6 m-1, with strongly defined minima in the green. Attenuation coefficients under the kelp canopies (including water) averaged 0.8 m-1 and were spectrally flat. Canopy absorbances retrieved from these measurements were quantitatively consistent with laboratory measurements of individual blades.
0
0.2
0.4
0.6
0.8
1
1.2
400 450 500 550 600 650 700
Wavelength (nm)
Can
opy
Abs
orba
nce
( D)
BAI = 1.63
BAI = 0.55
BAI = 0.12
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
400 450 500 550 600 650 700
Wavelength (nm)
Kd
(m-1
)
Arroyo Quemado
Mohawk Reef
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
400 450 500 550 600 650 700
Wavelength (nm)
Kd
(m-1
)
Arroyo Quemado
Mohawk Reef
RETRIEVAL OF GIANT KELP BIOMASS AND PRODUCTIVITY FROM OPTICAL MEASUREMENTS
The consistent optical signature of the kelp canopy produces a Blade Area Index (BAI, identical to Leaf Area Index used in terrestrial vegetation studies) that is linearly related to diver counts of kelp abundance. The slope (0.1) indicates that the canopy structure exerts a strong package effect on the optical efficiency of light absorption. The ability to predict BAI allows retrieval of standing biomass and productivity from measurements of below-canopy irradiance.
y = 0.1105x
R2 = 0.7823
0
0.5
1
1.5
2
2.5
0 5 10 15 20
Diver Measured BAI
Op
tica
lly D
ete
rmin
ed
BA
I
y = 13.303x
R2 = 0.9829
0
0.5
1
1.5
2
2.5
3
3.5
4
0 0.05 0.1 0.15 0.2 0.25 0.3
Frond mass (kg DW)
Fro
nd B
lade
Are
a (m
2 fro
nd-1
)
Standing crop (kg m-2)0.0 0.5 1.0 1.5 2.0
NP
P (
g dr
y m
ass
m-2
d-1)
0
10
20
30
40R2 = 0.623P < 0.0001
a.
Macrocystis pyrifera (giant kelp) NPP = 14.7 x Standing Crop
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
400 500 600 700 800 900
Wavelength (nm)
Rrs (
sr-1
)
Mature
Immature
Senescent
PHILLS Canopy
Perhaps more importantly, the strong reflectance signal in the NIR allows absolute kelp abundance and productivity to be calculated and mapped across the habitat from remotely sensed hyperspectral imagery using the normalized difference vegetation index (NDVI).
• Converting NDVI into absolute kelp abundance and productivity: – Optical BAI = NDVI/0.71– True BAI = Optical BAI * 9.04– Biomass = True BAI/13.3– Productivity = Biomass * 14.7
Carmel Bay
Pescadero Rocks
Pt. Lobos
Kelp Density(Kg DW m-2)0.54 – 0.610.62 - 0.680.69 – 0.750.75 – 0.820.83 – 0.880.89 – 0.95
Kelp Productivity(g DW m-2 d-1)
8 – 99.1 – 10
10.1 – 1111.1 – 1212.1 – 1313.1 - 14
