Output flow control and algae
Output flow control and algae
While Rebecca Trinh was sailing through Santa Monica Bay, just one mile off the coast of Los Angeles, the smell of chlorine and sewage flooded her nose. Seagulls were feeding on debris in the ocean, while a cloud of sewage spilled from the surface. Most people turned and walked away from the scene, but the stench was precisely what brought the microbial oceanographer here.
Trinh and a team from NASA's Jet Propulsion Laboratory were part of an effort to help LA Sanitation monitor water quality during the maintenance of the oldest and largest wastewater treatment plant in the city. The Hyperion water recovery plant serves about 4 million people, and treats wastewater from sinks, showers, toilets and surface runoff from storm drains. From September 21 to November 2, 2015, plant operators had to close the Hyperion main discharge pipeline to perform repairs on the internal structure.
The main outlet pipe normally transports wastewater five miles offshore, a distance where the seawater is deep enough so that the wastewater can be naturally diluted before reaching the surface. "The solution to contamination is dilution," said Trinh. During the repair, the plant operators were forced to use their one-mile backup discharge pipe, which releases the effluent much closer to the shore. Researchers like Trinh worked to observe and learn from the event.
the Operational Earth Imager (OLI) in Landsat 8 acquired a natural color image of Santa Monica Bay (above) on October 10, 2015, midway through the closure. The green areas near the coast are phytoplankton blooms caused by an excess of nutrients from the discharge of sewage from the one mile pipeline.
"The one-mile pipeline is closer to shore and in much shallower waters," Trinh said, "so there were many impacts on human health and ecological concern to people."
The one-mile pipeline was used for six weeks in 2015. With the use of satellites, the team was able to monitor the area almost in real time and provide information on possible biological hazards for sanitation in Los Angeles. The team published his findings in Borders.
These maps show the sea surface temperature of Santa Monica Bay before, during and after the transport of wastewater through the shorter pipeline. The data was acquired by the Thermal infrared sensor (TIRS) in the Landsat 8 satelite. During the diversion, a colder pool of water was formed near the mouth of the one-mile pipe, as the wastewater column also brought colder seawater from the ocean floor to the surface. The colder water pool served as a way to measure where the wastewater column was located.
"We knew that along with the temperature change, we were going to get all the excess nutrients and bacteria and potentially harmful chemicals associated with the pipeline effluent," Trinh said. The researchers had two main concerns about excess nutrients. First, they would stimulate the toxic blooms of phytoplankton. Second, that could lead to eutrophicationWhen extreme growth and subsequent death of algae, phytoplankton or other plant life severely depletes the oxygen supply to other marine animals.
The maps above show chlorophyll-a concentrations, an approximation of the amount of phytoplankton in the water, during the six-week pipe diversion period. Four phytoplankton blooms occurred during the detour, one of which is shown at the top of this page. Researchers identified phytoplankton field samples as non-toxic euglenoids, a type of green algae.
Measuring the concentration of chlorophyll-a in coastal environments, such as Santa Monica Bay, is a challenge. Temperatures fluctuate quite a lot, and there is a relatively high amount of phytoplankton production compared to marine waters. Trinh's team developed a new satellite algorithm, decreasing thesignal to noise"Relationship - to provide more accurate chlorophyll-to-shore measurements." The improved algorithm uses data collected by Trinh and his team with oceanic instruments from a ship and then compared with the Landsat 8 data.
"The satellite component provided a new perspective on the situation because, generally, Hyperion only monitors from the ship in a very small area around the pipes," said Trinh. "But we're actually showing that these wastewater deviations can have wide spatial impacts and you would not know without something like a satellite data set."
Trinh and his colleagues helped guide LA Sanitation on where to collect water samples to detect harmful bacteria. For example, satellite data showed higher concentrations of chlorophyll along the southern coast of Santa Monica Bay, so water quality monitors collected samples from Topanga Canyon to Malaga Cove. In this area, they he found that 10 percent of the samples contained faecal bacteria in amounts that exceeded state water quality standards. Multiple beaches were temporarily closed as a result.
Trinh said that this study was a good demonstration of how satellites can help monitor water quality, especially in coastal areas with high human activity and near wastewater outlets. "If a plant's pipes do not remain functional or have a catastrophic burst," he said, "we already know what kind of instruments and satellites we can use to make water quality monitoring as efficient as possible."
Images from the NASA Earth Observatory by Joshua Stevens, using data courtesy of Rebecca Trinh / Columbia University, and Landsat data from the United States Geological Survey. Tale of Kasha Patel.
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