NIWA uses satellite imagery to monitor the health of New Zealand’s coastal waters


NIWA has analyzed images from NASA’s Aqua MODIS satellite to measure changes in suspended sediment in New Zealand’s coastal waters.
Photo: CC 4.0 BY-NC-SA / NIWA

For the first time, NIWA has used satellite imagery to monitor the health of the coastal waters around Aotearoa by tracking the levels of suspended sediment in those waters.

Satellite data has already been used to monitor algal blooms, oil spills and water temperature, NIWA said.

Now, NIWA has analyzed images from NASA’s Aqua MODIS satellite that images the entire Earth’s surface every two or three days to measure changes in suspended sediment — or total suspended solids (TSS) — in New Zealand’s coastal waters.

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TSS contains a range of materials such as mud, silt and microalgae that in high concentrations can cause problems for estuaries, coasts and oceans, and aquatic life.

Scientists looked at more than 20 years of monthly satellite images of New Zealand’s coasts and found that the concentration of TSS generally increased in the South Island and decreased in the waters of the North Island.

High TSS can affect the ability of marine life, such as little blue penguins, to catch food. NIWA said it can also block light from reaching underwater plants and is associated with increased levels of pathogens, nutrients and pollutants.

NIWA released a report prepared for the Department of Conservation entitled Monitoring Coastal Suspended Sediment in Aotearoa, New Zealand: Utility of Satellite Remote Sensing.

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DOC technical advisor Helen Kettles said too much sediment reaching coastal waters poses a serious threat to marine life.

“This research helps us understand which coastal areas are likely to benefit from improved conservation efforts and track how conditions change over time. It’s good to know more about how useful satellite monitoring will be for water clarity in the future,” said them in a statement.

NIWA chief scientist for remote sensing Dr. Matt Pinkerton said the trends were driven by a combination of factors such as changes in phytoplankton, the effects of waves and coastal storms on coastal erosion and land use changes.

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“On a smaller level, what happens in catchments and in rivers affects the clarity of downstream water in estuaries and on the coast,” Dr Pinkerton said in a statement.

“Because of the damage that TSS can cause at high concentrations, there is concern about its ecological and environmental impacts on our coastal marine area.”

The NIWA report includes 15 recommendations to improve the value of satellite remote sensing over the next five years. These include the continued use of satellite data alongside in-situ sampling and modeling to develop the best insights and management of suspended coastal sediment in the future.