Finding the cold spot: SGD

Michael Drone (1).jpg

 

I use drones to study groundwater. Groundwater is hidden in the soil and rock beneath our feet, but it makes up nearly 2% of the water on Earth -- over 5,000 times more water than is in rivers. Groundwater moves very slowly through the soil and the rock, but eventually flows into rivers or the ocean. Groundwater that flows into the ocean is referred to as submarine groundwater discharge (SGD). Because it flows through the ground en route to the ocean, groundwater picks up nutrients from the soil and rock. The ocean water around Hawai‘i is naturally nutrient-depleted, so submarine groundwater discharge provides a vital source of nutrients to the coastal ecosystem.

 

 Michael collecting ground water samples upriver. 

Michael collecting ground water samples upriver. 

 

However, excess nutrients can cause invasive algae blooms and deplete coastal waters of oxygen, and human activities such as agriculture and waste disposal (e.g. cesspools) can add nutrients and other contaminants to groundwater. Because SGD flows from within the ground directly into the ocean, it is difficult to detect and measure. Most Hawaiian groundwater comes from rainfall at high elevations and remains buried beneath the surface, so it is colder than ocean water, which is continually heated by the sun. Measuring coastal water temperatures with UAS thermal infrared imaging allows easy detection of cold SGD entering the ocean.

 Live video from the infrared camera showing areas of hot and cold water from above. 

Live video from the infrared camera showing areas of hot and cold water from above. 

 

Because SGD is essential to Hawaiian coastal ecosystems, but a potential source of harmful contaminants, identifying locations of SGD is crucial for land-use planning and coastal resource management.

- Michael Mathioudakis