Spatial variability of absorption coefficients over a biogeochemical gradient in a large and optically complex shallow lake

Abstract

In order to improve robustness of remote sensing algorithms for lakes, it is vital to understand the variability of inherent optical properties (IOPs) and their mass‐specific representations (SIOPs). In this study, absorption coefficients for particulate and dissolved constituents were measured at 38 stations distributed over a biogeochemical gradient in Lake Balaton, Hungary. There was a large range of phytoplankton absorption (aph(λ)) over blue and red wavelengths (aph(440) = 0.11–4.39 m−1, aph(675) = 0.048–2.52 m−1), while there was less variability in chlorophyll‐specific phytoplankton absorption (a*ph(λ)) in the lake (a*ph(440) = 0.022 ± 0.0046 m2 mg−1, a*ph(675) = 0.010 ± 0.0020 m2 mg−1) and adjoining wetland system, Kis‐Balaton (a*ph(440) = 0.017 ± 0.0015 m2 mg−1, a*ph(675) = 0.0088 ± 0.0017 m2 mg−1). However, in the UV, a*ph(350) significantly increased with increasing distance from the main inflow (Zala River). This was likely due to variable production of photoprotective pigments (e.g., MAAs) in response to the decreasing gradient of colored dissolved organic matter (CDOM). The slope of CDOM absorption (SCDOM) also increased from west to east due to larger terrestrial CDOM input in the western basins. Absorption by nonalgal particles (aNAP(λ)) was highly influenced by inorganic particulates, as a result of the largely mineral sediments in Balaton. The relative contributions to the absorption budget varied more widely than oceans with a greater contribution from NAP (up to 30%), and wind speed affected the proportion attributed to NAP, phytoplankton, or CDOM. Ultimately, these data provide knowledge of the heterogeneity of (S)IOPs in Lake Balaton, suggesting the full range of variability must be considered for future improvement of analytical algorithms for constituent retrieval in inland waters.

Spatial and temporal variations of the inherent optical properties in a tropical cascading reservoir system

“…A different scenario was observed at 675 nm in both reservoirs, with phytoplankton dominating the absorption in Nav (59 %) and BB (89 %) and noticed by Babin et al (2003) and Riddick et al (2015).…”

“…These coefficients influence the magnitude and the spectral distribution of the water-leaving reflectance. Inland waters typically present high concentration of coloured dissolved organic matter (CDOM), phytoplankton and inorganic particles (Riddick et al 2015). The mass-specific inherent optical properties (SIOPs) are considered the main source of uncertainty in the water-leaving reflectance interpretation.…”

Spatio-seasonal variability of chromophoric dissolved organic matter absorption and responses to photobleaching in a large shallow temperate lake

“…The hypertrophic Kis-Balaton wetland system is believed to be responsible for much of the DOM entering the lake, largely derived from luxuriant growth and decomposition of aquatic plants. Previous research (Palmer et al, 2013;Riddick et al, 2015) has shown that CDOM is usually significantly higher close to the Zala River inflow, and decreases towards the outflow but very little is known about the seasonal dynamics of CDOM in the system. Suspended particulate matter in Lake Balaton is highly variable (spatially and temporally) due to its very shallow depth, constant mixing and susceptibility to wind-driven resuspension events (Istvánovics et al, 2004).…”

“…Previous research has shown that CDOM can be responsible for up to 80 % of light absorption in Lake Balaton (Riddick et al, 2015) in spite of the fact that the lake also has high concentrations of phytoplankton and non-algal particles (NAP). The high input of DOC from the Zala River results in elevated concentrations in the western basin relative to the remainder of the lake (from 0.169 m −1 near the outflow to 7.89 m −1 at the mouth of the Zala river).…”

“…The intense absorption of UV light by CDOM protects phytoplankton from physiological damage and reduces the need for phytoplankton cells to manufacture UV-protective pigments. This can result in chromatic acclimation with phytoplankton in high CDOM waters investing less in UV-protective pigments (Riddick et al, 2015).…”