Macrophyte communities are a key component of shallow water ecosystems and wetlands, due to their important role as metabolic regulator and their strong interconnections with water quality and trophic status, supporting many ecosystem services not least the recreational use of natural areas. However, macrophytes have exhibited a strong reduction worldwide that requires effective environmental management actions to counteract the disappearance. Remote sensing techniques are able to capture spectral features of aquatic vegetation and constitute powerful tools for monitoring vegetation characteristics and conditions (e.g. status, growth, phenology and bio-physical parameters).These information can effectively complement in situ-based environmental analyses enlarging the scale of observation from a local one to regional and even wider one. In particular, very good capabilities are ensured by the use of straightforward approaches based on Vegetation Indices (VIs) derived from optical multispectral data, especially for multitemporal studies. In this context, the new generation of satellite Earth Observation sensors, such as Landsat 8 OLI, are crucial step forward for achieving real spread capabilities for operational environmental monitoring of complex ecosystems, as inland shallow water bodies and wetlands areas, where macrophytes are one of the principal structural biological components. This work aims to assess macrophytes coverage and interannual dynamics in the Mantua Lake system (Northern Italy) using specific aquatic VIs derived from Landsat 8 OLI multitemporal data spanning from April to November 2013 (9 scenes). The Mantua Lakes (Superior, Middle and Inferior lakes), are three semiartificial shallow eutrophic lentic environment hosting dense macrophyte meadows. . For this purpose, Normalized Difference Aquatic Vegetation Index (NDAVI) time series are derived from atmospherically corrected reflectance data and used to (1) map macrophytes by discriminating the three different types locally present (submerged, floating-leaved and emergent macrophyte stands) and (2) assess their specific phenological cycle. On the other hand, a modified version of NDAVI, including the spectral response of OLI band 1 (0.43-0.45 micron) is tested, alongside with NDAVI itself, in order to evaluate the effects on aquatic VIs results and their capabilities to analyze vegetation features. The promising results reached with our work are the basis to implement a multitemporal monitoring approach based on Sentinel-2 data, as soon as they are operative. Compared to Landsat 8 OLI in fact, Sentinel-2 MSI will provide data with enhanced spatial (10 m) and temporal (5 days revisit time) resolution, as well as spectral bands configuration perfectly suited for monitoring vegetation features, especially over the red edge wavelength range. In this perspective, along with the possibility to integrate the use of both Sentinel-2 and Landsat 8 data, multitemporal remote sensing of macrophyte communities will be able to provide even more punctual and accurate information about short term evolution and functionality of shallow water ecosystems and wetlands.
Multitemporal assessment of macrophytes using aquatic vegetation indices
Paolo Villa;Mariano Bresciani;Monica Pinardi;Rossano Bolpagni
2014
Abstract
Macrophyte communities are a key component of shallow water ecosystems and wetlands, due to their important role as metabolic regulator and their strong interconnections with water quality and trophic status, supporting many ecosystem services not least the recreational use of natural areas. However, macrophytes have exhibited a strong reduction worldwide that requires effective environmental management actions to counteract the disappearance. Remote sensing techniques are able to capture spectral features of aquatic vegetation and constitute powerful tools for monitoring vegetation characteristics and conditions (e.g. status, growth, phenology and bio-physical parameters).These information can effectively complement in situ-based environmental analyses enlarging the scale of observation from a local one to regional and even wider one. In particular, very good capabilities are ensured by the use of straightforward approaches based on Vegetation Indices (VIs) derived from optical multispectral data, especially for multitemporal studies. In this context, the new generation of satellite Earth Observation sensors, such as Landsat 8 OLI, are crucial step forward for achieving real spread capabilities for operational environmental monitoring of complex ecosystems, as inland shallow water bodies and wetlands areas, where macrophytes are one of the principal structural biological components. This work aims to assess macrophytes coverage and interannual dynamics in the Mantua Lake system (Northern Italy) using specific aquatic VIs derived from Landsat 8 OLI multitemporal data spanning from April to November 2013 (9 scenes). The Mantua Lakes (Superior, Middle and Inferior lakes), are three semiartificial shallow eutrophic lentic environment hosting dense macrophyte meadows. . For this purpose, Normalized Difference Aquatic Vegetation Index (NDAVI) time series are derived from atmospherically corrected reflectance data and used to (1) map macrophytes by discriminating the three different types locally present (submerged, floating-leaved and emergent macrophyte stands) and (2) assess their specific phenological cycle. On the other hand, a modified version of NDAVI, including the spectral response of OLI band 1 (0.43-0.45 micron) is tested, alongside with NDAVI itself, in order to evaluate the effects on aquatic VIs results and their capabilities to analyze vegetation features. The promising results reached with our work are the basis to implement a multitemporal monitoring approach based on Sentinel-2 data, as soon as they are operative. Compared to Landsat 8 OLI in fact, Sentinel-2 MSI will provide data with enhanced spatial (10 m) and temporal (5 days revisit time) resolution, as well as spectral bands configuration perfectly suited for monitoring vegetation features, especially over the red edge wavelength range. In this perspective, along with the possibility to integrate the use of both Sentinel-2 and Landsat 8 data, multitemporal remote sensing of macrophyte communities will be able to provide even more punctual and accurate information about short term evolution and functionality of shallow water ecosystems and wetlands.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.