Abstract
Harmful algae blooms (HAB) in coastal marine environments are increasing in number and duration, pressuring local resource managers to implement mitigation solutions to protect human and ecosystem health. However, insufficient spatial and temporal observations create uninformed management decisions. In order to better detect and map blooms, as well as the environmental conditions responsible for their formation, long-term, unattended observation platforms are desired. In this article, we describe a new cost-efficient, autonomous, mobile platform capable of accepting several sensors that can be used to monitor harmful algae blooms in near real-time. The Navocean autonomous sail-powered surface vehicle is deployable by a single person from shore, capable of waypoint navigation in shallow and deep waters, and powered completely by renewable energy. We present results from three surveys of the Florida Red Tide harmful algae bloom (Karenia brevis) of 2017-2018. The vessel made significant progress towards waypoints regardless of wind conditions while underway measurements revealed patches of elevated chl. a likely attributable to the K. brevis blooms as based on ancillary measurements. Measurements of colored dissolved organic matter (CDOM) and turbidity provided an environmental context for the blooms. While the autonomous sailboat directly adds to our phytoplankton/HAB monitoring capabilities, the package may also help to ground-truth satellite measurements of HABs if careful validation measurements are performed. Finally, several other pending and future use cases for coastal and inland monitoring are discussed. To our knowledge, this is the first demonstration of a sail-driven vessel used for coastal HAB monitoring.
Highlights
In the last few decades, harmful algae blooms (HABs) have increased in number, intensity, and duration due to cultural eutrophication, increasing rainfall, and warming temperatures (Brand and Compton, 2007; O’Neil et al, 2012)
Recent years have experienced extreme HAB events with unparalleled public recognition, for example, the summer of 2014 and 2016 Microcystis aeruginosa blue-green cyanoblooms in Lake Erie and the Indian River Lagoon (Florida) (Smith et al, 2015; Stockley et al, 2018) that poisoned drinking water and decreased property values, respectively, the Pseudo-nitzschia bloom of 2015 in California waters that led to the closing of the Dungeness crab fishing season (McCabe et al, 2016), and the 2017–2018 Karenia brevis bloom in west Florida that has led to a declaration of a state of emergency
Two-dimensional Autonomous Surface Vehicles (ASV) such as those powered by sail or waves, e.g., “Wave Gliders” or Saildrone (Daniel et al, 2011; Mordy et al, 2017), while not providing depth data, may alleviate these constraints and are more conducive in accepting complex instrumentation payloads
Summary
In the last few decades, harmful algae blooms (HABs) have increased in number, intensity, and duration due to cultural eutrophication, increasing rainfall, and warming temperatures (Brand and Compton, 2007; O’Neil et al, 2012). For the 77-h deployment beginning 1422 UTC December 20, 2017 (Figure 3B), the Nav was again deployed directly from Sanibel Beach The intent of this mission was to sail through an area with a known HABs bloom. Shorter deployments, a large and intense K. brevis (Florida Red Tide) bloom was present nearshore (∼2 km) toward which the vessel was directed (Figures 6A,B) These deployments simulate a potential mission to map spatial HAB bloom patterns in localized areas in response to a bloom, perhaps to guide adaptive sampling, generate semi-quantitative spatial maps and locate hotspots, and determine bloom heterogeneity (i.e., patchiness). Correlation coefficients between OCLI CDOM and Nav CDOM were between 0.65 and 0.39 (Table 3), with the strength of the correlation decreasing with increasing mission duration, probably an analytical artifact because a single satellite image corresponding to a single day was compared to multiple-day Nav missions
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