Radiative transfer within seagrass canopies: impact on carbon budgets and light requirements

Richard C. Zimmerman; Curtis D. Mobley

doi:10.1117/12.266465

6 February 1997 Radiative transfer within seagrass canopies: impact on carbon budgets and light requirements

Richard C. Zimmerman, Curtis D. Mobley

Proceedings Volume 2963, Ocean Optics XIII; (1997) https://doi.org/10.1117/12.266465
Event: Ocean Optics XIII, 1996, Halifax, Nova Scotia, Canada

Abstract

Seagrasses are ecologically important but extremely vulnerable to anthropogenic modifications of the coastal zone that affect light availability within these unique ecosystems. Strongly pigmented seagrass leaves can extend for more than 1 m above the substrate and biomass is distributed unevenly throughout the canopy. in this study, light attenuation in a 7 m water column that contained a seagrass canopy extending 1.5 m above the bottom was calculated by the radiative transfer model Hydrolight using the spectral absorbance of eelgrass leaves and a non-uniform vertical distribution of biomass. Runs were performed in clear and turbid water columns, over san d and mud substrates, and with shoot densities ranging from 25 to 200 m^-2 using solar angles for both winter and summer solstices. The flux of photosynthetically active irradiance (E_PAR) reaching the top of the seagrass canopy was twice as high in summer compared to winter, and in clear water compared to turbid water. Sediment type had a measurable effect on E_PAR only within the bottom third of the canopy. Light penetration within the canopy was inversely proportional to shoot density. Introduction of daylength and a sinusoidal distribution of E_PAR throughout the day greatly increased the importance of solar elevation on daily integrated production relative to water column turbidity and sediment type. Shoot-specific productivity decreased and the position of maximum shoot productivity within the canopy shallowed as shoot density increased. Positive net photosynthesis for entire shoots was possible only when plant density was lower than 100 shoots m^-2 in winter; values consistent with field observations. Although very simplistic with regard to inherent optical properties of real seagrass leaves, this model was able to generate estimates of maximum sustainable shoot density that were fully testable by, and wholly consistent with, field observations.

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Richard C. Zimmerman and Curtis D. Mobley "Radiative transfer within seagrass canopies: impact on carbon budgets and light requirements", Proc. SPIE 2963, Ocean Optics XIII, (6 February 1997); https://doi.org/10.1117/12.266465

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