Abstract
The community of Kotzebue, located on the coast of Kotzebue Sound, which
is northeast of the Bering Straits adjacent to the Chukchi Sea, is
reliant on the waters around Kotzebue Sound for food and economy. There
have been reports of cyanobacterial blooms in these waters around
Kotzebue but they have not been systematically studied yet, because the
region is sparsely populated with few in-situ observations.
Cyanobacteria often form surface blooms in freshwater and coastal
ecosystems which can be detected using remote sensing techniques.
Cyanobacteria are found to have low nutritional value and many species
of cyanobacteria produce cyanotoxins, and thus can be harmful to aquatic
life and cause public health hazards. In addition, consumption of
decaying cyanobacterial blooms by microbes depletes oxygen level which
can lead to hypoxia, adversely impacting the benthic community. As the
Arctic is warming twice as fast as the rest of the planet due to climate
change, thawing permafrost is releasing nutrients that might be
enhancing cyanobacterial blooms in the coastal, marine and lacustrine
waters of Alaska. In this study, we used remote sensing to study
phytoplankton biomass, turbidity and cyanobacterial blooms between
mid-June to end of September each year from 2013 to 2019 when the waters
around Kotzebue are ice-free. Using images from Landsat-8 and
Sentinel-2, processed using ACOLITE software, we investigated spatial
and temporal changes in water quality parameters such as turbidity and
chlorophyll concentration between June and September. We used a
combination of true-color images and fai (floating algal index) to
detect cyanobacterial blooms. There were about two scenes from
Sentinel-2 and about one scene from Landsat-8, for a total of about
three scenes every week between June and September. Of these, only 49%
of the images were cloud-free. Of the cloud-free images, 29% were found
to have a cyanobacterial bloom between August and September for an
average of two to four scenes every year. Most of the cyanobacterial
blooms were detected in Kobuk Lake near Kotzebue, and nearby sites in
Hotham Inlet and Selawik Lake. In 2013, 68% of the images were cloudy
which was the highest in the observed years and no cyanobacterial blooms
were detected.