Hyperspectral Reflectance Characteristics of Cyanobacteria

Abstract

Potentially harmful cyanobacterial blooms are an emerging environmental concern in freshwater bodies worldwide. Cyanobacterial blooms are generally caused by high nutrient inputs and warm, still waters and have been appearing with increasing frequency in water bodies used for drinking water supply and recreation, a problem which will likely worsen with a warming climate. Cyanobacterial blooms are composed of genera with known biological pigments and can be distinguished and analyzed via hyperspectral image collection technology such as remote sensing by satellites, airplanes, and drones. Here, we utilize hyperspectral microscopy and imaging spectroscopy to characterize and differentiate several important bloom-forming cyanobacteria genera obtained in the field during active research programs conducted by US Geological Survey and from commercial sources. Many of the cyanobacteria genera showed differences in their spectra that may be used to identify and predict their occurrence, including peaks and valleys in spectral reflectance.Because certain cyanobacteria, such as Cylindrospermum or Dolichospermum, are more prone to produce cyanotoxins than others, the ability to differentiate these species may help target high priority waterbodies for sampling. These spectra may also be used to prioritize restoration and research efforts to control cyanobacterial harmful algal blooms (CyanoHABs) and improve water quality for aquatic life and humans alike.

Near real-time satellite detection and monitoring of aquatic algae and cyanobacteria: how a combination of chlorophyll-a indices and water-quality sampling was applied to north Texas reservoirs

“…In-situ hyperspectral reflectance data were qualitatively compared with in-situ chlorophyll-a, phycocyanin, turbidity, and Secchi depth data to evaluate the hyperspectral reflectance observed for the Grapevine Lake sampling sites. Hyperspectral reflectance data were used to explore the optical signatures of algae and cyanobacteria pigments, chlorophyll-a, and phycocyanin, entrained in or accumulating on the water surface to aid in the interpretation of what portion of the spectrum might be most valuable for highly performing spectral indices 57 . Hyperspectral reflectance data of the water surface were obtained using an ASD HandHeld 2 visible NIR, 400 to 900 nm, spectroradiometer 58 .…”

“…Hyperspectral reflectance data were used to explore the optical signatures of algae and cyanobacteria pigments, chlorophyll-a, and phycocyanin, entrained in or accumulating on the water surface to aid in the interpretation of what portion of the spectrum might be most valuable for highly performing spectral indices. 57 Hyperspectral reflectance data of the water surface were obtained using an ASD HandHeld 2 visible NIR, 400 to 900 nm, spectroradiometer. 58 Boat shadows and sun glint were avoided during the collection of spectral reflectance signatures.…”

“…Figure 9 depicts the relation between chlorophyll-a and phycocyanin spectral features acquired for the open-water and inlet sites compared with the Sentinel-2 spectral bands used in the chlorophyll-a detection indices (Table1). The reflectance and absorption brightness magnitude of the spectrum indicate photosynthetically active waters with the unique spectral signature of cyanobacteria:57 the green peak at about 560 nm (partially captured by Sentinel-2 band 3), the phycocyanin absorption trough at about 620 nm, the chlorophyll-a absorption trough at about 675 nm (partially captured by Sentinel-2 band 4), the NIR reflectance/scattering peak at about 700 nm (partially captured Sentinel-2 band 5), and NIR absorption by water at about 740 nm (partially captured Sentinel-2 band 6). Figure9shows there are more pronounced spectral features at the inlet site compared with the open-water site.…”

Mapping Benthic Algae and Cyanobacteria in River Channels from Aerial Photographs and Satellite Images: A Proof-of-Concept Investigation on the Buffalo National River, AR, USA

“…Not all algae are harmful, but a capacity to identify those that are potentially toxic could more effectively inform management actions. A plausible way forward was pioneered by Paine et al [56] and Slonecker et al [57], who showed that reflectance spectra measured in a lab while viewing algal samples under a microscope could be used to distinguish between taxa. Slonecker et al [58] have already published a spectral library consisting of 13 genera that is freely available to support this type of work; these authors plan to expand the library to include additional taxa [57].…”

“…A plausible way forward was pioneered by Paine et al [56] and Slonecker et al [57], who showed that reflectance spectra measured in a lab while viewing algal samples under a microscope could be used to distinguish between taxa. Slonecker et al [58] have already published a spectral library consisting of 13 genera that is freely available to support this type of work; these authors plan to expand the library to include additional taxa [57]. A logical next step toward a hyperspectral approach to algal mapping might involve acquiring hyperspectral images from a UAS in coordination with the collection of field samples processed for biomass and taxonomy.…”