Niwa used Nasa’s Aqua Modis satellite to measure changes in total suspended solids (TSS) which consist of mud, silt, microalgae and their breakdown products. Niwa remote sensing principal scientist Dr Matt Pinkerton said high concentrations of TSS could cause problems for estuaries, coasts, oceans and aquatic life.
It could affect the ability of marine life to catch food, it could block light from reaching underwater plants and it was associated with elevated levels of pathogens, nutrients and pollutants.
By looking at nearly 20 years of monthly satellite images of New Zealand’s coasts, he said scientists found varied trends in TSS over time across the country, but generally increasing concentrations around the South Island and decreasing concentrations around the North Island.
Doc technical adviser Helen Kettles said too much sediment reaching coastal waters was a serious threat to marine life.
Sediment could prevent some seabirds, such as penguins, shags and terns, from pursuing fish underwater.
It could also smother valuable coastal species like cockles and seagrass, she said.
"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."
Dr Pinkerton said the trends found in the satellite were driven by a combination of factors.
"We suspect that changes in phytoplankton across the New Zealand shelf because of climate variability and change, the effects of waves and coastal storms on coastal erosion and resuspension of seabed sediment, and changes to land use are all influencing these broad-scale trends.
"On a smaller level, what’s happening in catchments and in rivers is affecting downstream water clarity in estuaries and on the coast."
Because of the damage TSS could cause at high concentrations, he said there was concern about the ecological and environmental effects on our coastal marine area.
"This is particularly pertinent because of the severe winter weather we just experienced — steady rainfall doesn’t necessarily impact the concentration of sediment in our oceans, but huge storms like the one the South Island experienced in August can have a big knock-on effect."
In a report, Niwa has detailed 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.
