The vehicle provided researchers at Clear Lake, California, with unsurpassed, never-before-possible sensed data of the entire lake.
Harmful algal blooms (HABs) are so prevalent in Clear Lake, California, that it is one of the most heavily monitored lakes in North America. To better understand what causes algal blooms at the lake, researchers from the University of Southern California in Los Angeles (USC) and the Southern California Coastal Water Research Project (SCCWRP) deployed the i3XO EcoMapper from Xylem’s YSI brand. This autonomous vehicle traveled underwater to all parts of the lake, capturing data about depth, water quality and temperature, giving researchers unprecedented, high-resolution data about the blooms.
Although algae are fundamental to life on earth, producing 50% of the oxygen in the Earth’s atmosphere, certain algae can produce toxins. When these algae grow unchecked, the result is harmful algal blooms (HABs), which are one of the greatest global threats to surface water quality. The effects of HABs can range from taste and odor problems in drinking water, to the production of powerful toxins that can sicken animals and humans.
There is a wide range of algal species that produce toxins, and each species thrives in different environmental conditions. The main causes of HABs are well documented, such as excessive nutrient loading in water bodies, particularly from nitrogen and phosphorous. In addition, warmer temperatures caused by climate change can give toxin-producing algae an advantage.
Clear Lake is the largest freshwater lake wholly within California, with a surface area of 68 square miles (27.4 km²). At around 2.5 million years old, it is also the oldest lake in North America. HABs are of particular concern for the Clear Lake community, since 18 drinking water utilities use the lake as a water source to serve more than 40,000 residents.
Scientists know that HABs at the lake can be a result of temperature and eutrophication – a condition where excessive plant and algal growth is caused by, among other things, nutrient fertilizers. To understand the blooms in detail, however, researchers have been limited by the data they get from discrete samples, and by the shape of the lake, which is made up of three arms with different characteristics.
While discrete samples provide vital information about the lake at a particular place and time, researchers also need to understand how the physical structure of the lake and the dynamics of the water at different depths – its water column – contribute to blooms.
The recent study at Clear Lake aimed to overcome some of these challenges with Xylem’s YSI technology. One of the main objectives of the study was to link new data about the water column and environmental parameters with other data collected from discrete water samples.
“If we can tie these disparate pieces of information together through space and time, it will provide unprecedented information on species succession and trophic interactions within the plankton of Clear Lake,” writes Dr. David Caron of the University of Southern California and principal investigator on the study.
Correlating this data across a lake the size of Clear Lake is not easy, yet it is essential for understanding the biological processes leading to blooms and toxins. The study also aimed to help researchers prioritize where they should collect discrete samples, which can be a costly process.
The researchers partnered with Xylem to map the lake’s HABs in incredible detail with YSI’s i3XO EcoMapper, a next-generation autonomous underwater vehicle (AUV). The i3XO generates high-resolution maps of water quality, water currents and depth. The i3XO is the combination of the latest AUV technology with YSI’s EXO platform, a smart and field-ready water monitoring system.
The researchers’ study was designed to monitor the lake at two very different spatial scales. The first scale was conducted along the major axes of the three arms of Clear Lake to examine lake-wide characteristics. The second scale was a high-resolution mapping mission of a portion of a bay in the lower arm of the lake, in order to examine in detail the distribution of blue-green algae (cyanobacteria) and their toxins.
The full sensor capacity of the i3XO was leveraged for the missions. Every i3XO is fitted with a YSI EXO1 sonde with sensors for conductivity/temperature, total algae, dissolved oxygen, and pH. The instrument data was used to construct 2D depictions of the water column as the vehicle automatically moved up and down across the lake at varying depths. The vehicle’s long battery life and accurate navigation system meant it could stay underwater longer to maximize data collection. On one mission, it took the vehicle roughly 6.5 hours to cover over 21 miles (34 km) of Clear Lake.
The i3XO missions provided unsurpassed, never-before-possible sensed data about the lake and its harmful algal blooms. Researchers now have a better understanding of the lake’s water column structure, and they were able to generate testable hypotheses about what factors are most important for driving HAB events in the lake.
The data obtained at the whole-lake scale also provided vital information on where and how to expend limited resources for choosing sampling sites. Follow-up missions are planned to add to the data set, and to continue to better understand the relationship between water quality and algal blooms at Clear Lake.
Download the white paper on the study: High-Resolution Mapping of a Harmful Algal Bloom
Watch a webinar about the study: Expand your HAB Horizons with High-Resolution Mapping
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