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

Abstract

Although rivers are of immense practical, aesthetic, and recreational value, these aquatic habitats are particularly sensitive to environmental changes. Increasingly, changes in streamflow and water quality are resulting in blooms of bottom-attached (benthic) algae, also known as periphyton, which have become widespread in many water bodies of US national parks. Because these blooms degrade visitor experiences and threaten human and ecosystem health, improved methods of characterizing benthic algae are needed. This study evaluated the potential utility of remote sensing techniques for mapping variations in algal density in shallow, clear-flowing rivers. As part of an initial proof-of-concept investigation, field measurements of water depth and percent cover of benthic algae were collected from two reaches of the Buffalo National River along with aerial photographs and multispectral satellite images. Applying a band ratio algorithm to these data yielded reliable depth estimates, although a shallow bias and moderate level of precision were observed. Spectral distinctions among algal percent cover values ranging from 0 to 100% were subtle and became only slightly more pronounced when the data were aggregated to four ordinal levels. A bagged trees machine learning model trained using the original spectral bands and image-derived depth estimates as predictor variables was used to produce classified maps of algal density. The spatial and temporal patterns depicted in these maps were reasonable but overall classification accuracies were modest, up to 64.6%, due to a lack of spectral detail. To further advance remote sensing of benthic algae and other periphyton, future studies could adopt hyperspectral approaches and more quantitative, continuous metrics such as biomass.

Cyanobacterial Harmful Algal Mats (CyanoHAMs) in tropical rivers of central Mexico and their potential risks through toxin production

“…Similar results have been seen in other studies, which even show that benthic cyanobacteria can grow by adapting to specific river conditions, influenced in principle by hydrological regimes (Robichon et al, 2023 ). Demonstrating that beyond responding to poor concentrations of nutrients, they can respond to larger scale and longer-term changes (Legleiter & Hodges, 2022 ). In this sense, our results contribute to the understanding of the ecology of proliferations in oligotrophic environments and the secondary metabolism related to toxin production (Aguilera et al, 2023 ; Reinl et al, 2021 ).…”

“…We propose the definition and use of the term Cyanobacteria Harmful Algal Mats (CyanoHAMs) defines growths of cyanobacteria that develop in the benthos and that can generate a large biomass with potentially toxic implications to mammals, including humans (Duana et al, 2022 ; Legleiter & Hodges, 2022 ; Rider et al, 2024 ). In general, growths are easily recognized in lentic environments because they are suspended in the water column, their color changes to a bluish-green tone, and they generally form a thick, viscous layer on the surface (Sanseverino et al .…”

“…As a result, studies on cyanotoxins have been biased toward populations of planktonic cyanobacteria that inhabit lentic ecosystems (Aguilera et al, 2023 ; Almuhtaram et al, 2021 ). The cyanoHABs concept is almost always associated with populations of phytoplanktonic cyanobacteria in lakes and reservoirs, but riverbeds HABs being much less studied even though they have recently been recognized as important producers of toxins with effects on the food weber (Legleiter & Hodges, 2022 ; Rider et al, 2024 ).…”

“…Furthermore, they are spatially and temporally variable and the timing and magnitude of the drivers of growth in benthic productivity have been described as varied and include streamflow velocity, light, nutrients, sediment deposition, substrate composition, and watershed characteristics (Rider et al, 2024 ; Schulte et al, 2022 ). Filamentous and mucilaginous colonies are usually the dominant growth forms with a higher report of anatoxins, microcystins, and saxitoxins production in rivers (Cantoral Uriza et al, 2017 ; Legleiter & Hodges, 2022 ; Loftin et al 2016 ). Reports of massive growths and their relationship with toxicity and bioaccumulation events at higher trophic levels such as benthic macroinvertebrates (Shahmohamadloo et al, 2020 ) and fish (Zamora-Barrios et al, 2019 ) are becoming more frequent, as well as the poisoning of domestic animals such as dogs and cattle (livestock) (Bouma-Gregson et al, 2019 ; Echenique-Subiabre et al, 2016 ; Gaget et al, 2020 ).…”

Interdisciplinary science approach for harmful algal blooms (HABs) and algal toxins—A strategic science vision for the U.S. Geological Survey

“…The USGS also has well-established statistical expertise (Helsel and Hirsch, 1993), including analyses of water-quality trends (Ryberg and Vecchia, 2013;Oelsner and others, 2017;Nustad and Vecchia, 2020), atmosphere and climate trends (Hirsch and Ryberg, 2012), and biological trends (Prevéy, 2020). Additionally, the USGS has experience in integrating satellite imagery with surface properties (Titus and others, 2022), water quality (Petrakis and others, 2022), and HABs (Clark and others, 2017;Legleiter and Hodges, 2022). Combined with the long-term data portals and real-time water quality networks, the capabilities of many USGS scientists could be helpful for quantifying HABs and estimating toxin concentrations.…”