NIWA has analysed 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 images to monitor the health of coastal waters around Aotearoa by tracking 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 analysed images from NASA's Aqua MODIS satellite which 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.
TSS contains a range of material such as mud, silt and microalgae which 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 generally, the concentration of TSS was increasing in the South Island and decreasing in North Island waters.
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 elevated levels of pathogens, nutrients and pollutants.
NIWA has issued a report prepared for the Department of Conservation titled Monitoring coastal suspended sediment in Aotearoa New Zealand: utility of satellite remote sensing.
DOC technical advisor Helen Kettles said too much sediment reaching coastal waters was a serious threat to marine life.
"This research helps us to understand which coastal areas are likely to benefit from improved conservation effort and track how conditions change with time. It is good to know more about how useful satellite monitoring for water clarity will be into the future," she said in a statement.
NIWA principal 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 changes to land use.
"On a smaller level, what's happening in catchments and in rivers is affecting downstream water clarity in estuaries and on the coast," Dr Pinkerton said in a statement.
"Because of the damage TSS can cause at high concentrations, there is concern about the ecological and environmental effects of it on our coastal marine area."
NIWA's report details 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 modelling to develop the best insights and management of coastal suspended sediment in the future.