Abstract
Characterizing the specific inherent optical properties (SIOPs) of water constituents is fundamental to remote sensing applications. Therefore, this paper presents the absorption properties of phytoplankton, gelbstoff and tripton for three small, optically-diverse South African inland waters. The three reservoirs, Hartbeespoort, Loskop and Theewaterskloof, are challenging for remote sensing, due to differences in phytoplankton assemblage and the considerable range of constituent concentrations. Relationships between the absorption properties and biogeophysical parameters, chlorophyll-a (chl-a), TChl (chl-a plus phaeopigments), seston, minerals and tripton, are established. The value determined for the mass-specific tripton absorption coefficient at 442 nm, a∗ (442), ranges from 0.024 to 0.263 m2·g−1. The value of the TChl-specific phytoplankton absorption coefficient (a∗ ) was strongly influenced by phytoplankton species, size, accessory pigmentation and biomass. a∗ (440) ranged from 0.056 to 0.018 m2·mg−1 in oligotrophic to hypertrophic waters. The positive relationship between cell size and trophic state observed in open ocean waters was violated by significant small cyanobacterial populations. The phycocyanin-specific phytoplankton absorption at 620 nm, a∗ (620), was determined as 0.007 m2·g−1 in a M. aeruginosa bloom. Chl-a was a better indicator of phytoplankton biomass than phycocyanin (PC) in surface scums, due to reduced accessory pigment production. Absorption budgets demonstrate that monospecific blooms of M. aeruginosa and C. hirundinella may be treated as “cultures”, removing some complexities for remote sensing applications. These results contribute toward a better understanding of IOPs and remote sensing applications in hypertrophic inland waters. However, the majority of the water is optically complex, requiring the usage of all the SIOPs derived here for remote sensing applications. The SIOPs may be used for developing remote sensing algorithms for the detection of biogeophysical parameters, including chl-a, suspended matter, tripton and gelbstoff, and in advanced remote sensing studies for phytoplankton type detection.
Highlights
IntroductionKnowledge of the inherent optical properties (IOPs), including the absorption of phytoplankton, gelbstoff (or chromophoric dissolved organic matter) and tripton (non-living minerals and detritus), is critical to water remote sensing
Knowledge of the inherent optical properties (IOPs), including the absorption of phytoplankton, gelbstoff and tripton, is critical to water remote sensing
IOPs are required for remote sensing algorithm development and for physically-based bio-optical models simulating the behavior of light in water (e.g., [1])
Summary
Knowledge of the inherent optical properties (IOPs), including the absorption of phytoplankton, gelbstoff (or chromophoric dissolved organic matter) and tripton (non-living minerals and detritus), is critical to water remote sensing. IOPs are required for remote sensing algorithm development and for physically-based bio-optical models simulating the behavior of light in water (e.g., [1]). Physically-based water constituent retrieval remote sensing algorithms, especially those targeting specific water types or classes, rely heavily on IOPs, as do biogeochemical models. There is an ongoing need to investigate the variability that might be encountered across these diverse systems, especially those that are hypertrophic. This poses an ongoing challenge for satellite-based remote sensing applications aimed at characterizing the phenology and ecological state of Earth’s precious and vulnerable fresh waters
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