Work

In search of light: Estimating diffuse attenuation coefficient of downwelling irradiance and its variation in optically complex shallow water habitats using Sentinel-2 imagery

Year: 2025

Type: article

Abstract: Frequent resuspension of sediments in the water column hampers photosynthesis in submerged aquatic vegetation due to decreased light, reduces gas exchange from sediment deposition and affects their anchoring ability. Remote sensing of light attenuation of the water column in form of diffuse attenuation coefficient of downwelling photosynthetically available radiation (K dPAR ) provides a spatial perspective to study light attenuation of water column. This study aims to use Sentinel-2 derived K dPAR to characterize light variation and test its significance in relation to occurrence of eelgrass ( Zostera marina ) at Horsens and Roskilde fjords located in coastal waters of Denmark. Areas with maximum of K dPAR (mean > 75 th percentile) coinciding with maximum and minimum variation (standard deviation >75 th and <25 th percentile respectively) were identified at the study sites. The standard deviation (SD) of K dPAR and fraction of surface irradiance reaching bottom (PAR Z ) was used to predict occurrences of eelgrass using Logistic regression (LR) and Support Vector Machine (SVM). The LR and SVM (linear kernel) could predict eelgrass presence-absence with 65 % overall accuracy and precision of 63 % and 62 % respectively on the test set ( n = 238). SD correlation with eelgrss occurrences (Point-biserial correlation = −0.11, p = 0.002) and with predicted probabilities of logistic regression (Pearson's r = −0.46) indicates increased K dPAR variation reduces chances of eelgrass. The K dPAR for this study was derived using Quasi Analytical Algorithm Version-5 (QAA-V5) and Case-2 Regional Coast Colour (C2RCC) and validated against in-situ matched observations ( n = 113) for duration of March to October of 2016–2018. • Light environment in submerged habitats changes due to resuspension. • Sentinel-2 derived K dPAR used for characterizing spatial variation of light. • Standard deviation of K dPAR used to predict eelgrass occurrence at study sites. • Logistic regression was able to predict eelgrass occurrence with 65 % accuracy.

Source: The Science of The Total Environment

DOI: 10.1016/j.scitotenv.2025.178598

Authors: Satish Pawar, Rafael Gonçalves-Araujo, Karen Timmermann

Institution: Technical University of Denmark

Language: English

Topic: Marine and coastal plant biology

Subfield: Oceanography

Field: Earth and Planetary Sciences

Domain: Physical Sciences

SDGs: Life below water, Clean water and sanitation, Climate action

Open Access status: hybrid

Estimated APC paid: $4,250