Abstract
Phytoplankton is a primary producer of organic compounds, and it forms the base of the food chain in ocean waters. The concentration of phytoplankton in the water column controls water clarity and the amount and quality of light that penetrates through it. The availability of adequate light intensity is a major factor in the health of algae and phytoplankton. There is a strong negative coupling between light intensity and phytoplankton concentration (e.g., through self-shading by the cells), which reduces available light and in return affects the growth rate of the cells. Proper modeling of this coupling is essential to understand primary productivity in the oceans. This paper provides the methodology to model light intensity in the water column, which can be included in relevant water quality models. The methodology implements relationships from bio-optical models, which use phytoplankton chlorophyll a (chl-a) concentration as a surrogate for light attenuation, including absorption and scattering by other attenuators. The presented mathematical methodology estimates the reduction in light intensity due to absorption by pure seawater, chl-a pigment, non-algae particles (NAPs) and colored dissolved organic matter (CDOM), as well as backscattering by pure seawater, phytoplankton particles and NAPs. The methods presented facilitate the prediction of the effects of various environmental and management scenarios (e.g., global warming, altered precipitation patterns, greenhouse gases) on the wellbeing of phytoplankton communities in the oceans as temperature-driven chl-a changes take place.
Highlights
The major factors affecting phytoplankton metabolism are nutrient availability, light and water temperature [1]
The maximum depth at which light intensity is adequate to maintain the plant is referred to as the depth of the photic zone, which is referred to here as the “photic depth” [2]. Light intensity at this depth reaches 1% of its surface daylight value, which is enough for photosynthesis to sustain phytoplankton growth and reproduction
The importance of light to phytoplankton has driven many researchers to develop quantitative methods to calculate light intensity in the water column. The complexity of this task arises from the variability in the spectral light intensity, and in the water column due to turbidity
Summary
The major factors affecting phytoplankton metabolism are nutrient availability, light and water temperature [1]. The following equations define the mathematical values for the absorption and backscattering coefficients according to the basic relationships presented in [3] for Case 1 waters These relationships uussee pphhyyttooppllaannkkttoonn cchhll--aa ccoonncceennttrraattiioonn ((μμgg·L·L−−11 == mmgg··mm−−3)3)aass aa rreeffeerreennccee ffoorr tthhee aabbssoorrppttiioonn rreellaattiioonnsshhiippss ooff pphhyyttooppllaannkkttoonn ppiiggmmeenntt,, NNAAPPss aanndd CCDDOOMM,, aass wweellll aass bbaacckkssccaatttteerriinngg ffrroomm pphhyyttooppllaannkkttoonn ppaarrttiicclleess aanndd NNAAPPss. LLiigghhtt aabbssoorrppttiioonn bbyy pphhyyttooppllaannkkttoonn,, NNAAPPss aanndd CCDDOOMM uusseess rreeffeerreennccee aabbssoorrppttiioonn vvaalluueess ooff pphhyyttooppllaannkkttoonn ppiiggmmeenntt aatt tthhee wwaavveelleennggtthh λλ == 444400 nnmm,, wwhhiillee lliigghhtt bbaacckkssccaatttteerriinngg uusseess rreeffeerreennccee pphhyyttooppllaannkkttoonn bbaacckkssccaatttteerriinngg vvaalluueess aatt λλ== 555500nnmm.
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