Coastal wetlands form a crucial connection between the land and sea. They provide protection from erosion, habitat for important fisheries species, and store large amounts of carbon. While mangroves might be the most well-known type of wetlands, other elements of these ecosystems are just as important for broader ecosystem health. Salt marshes are one important element of the wetland system that have suffered significant losses in recent decades. Between 2000 and 2019, 1,452 square kilometres of salt marsh was lost globally. That’s about twice the size of Singapore.
Drones are helping researchers keep an eye on these habitats and track the success of efforts to restore them. Dr Vincent Raoult is part of a team from the University of Newcastle, led by Associate Professor Troy Gaston, that have been using drones to research and monitor the restoration of a salt marsh in NSW.
What happened to the salt marshes?
To the untrained eye, salt marshes just look like boggy, salty, grasslands. It’s not surprising then that people in the past thought they didn’t serve much of a purpose.
“Historically, people have just gone ‘it’s a waste of space,” Vincent said.
“That means that in the 1800s and 1900s, a lot of that salt marsh was drained and turned into agricultural land. And there’s also many places where there have been losses of salt marsh because it’s used for grazing,” he said.
But although they might not look like much, they’re doing a lot of important work in the background.
“They’re very important food sources for estuaries,” Vincent said.
“We’ve done a lot of work showing specifically that they are really important for the diets of a whole bunch of commercially and recreationally important fishes and crabs and prawns and stuff like that,” he said.
“There’s also evidence directly from the fishers themselves that saw that when they cut off salt marshes from the estuaries that almost all their catches disappeared. So cutting off that ecosystem really, really damaged the estuary more broadly.”
Many of Australia’s saltmarshes are also RAMSR listed, which means they are considered critical habitat for migratory birds.
Salt marshes are still at risk
Although salt marshes are officially a protected habitat, they still suffer from significant degradation.
“So officially, they are protected, but unofficially, in many places, people do not protect them,” Vincent said.
“In fact, if you go around most of the properties that are around estuaries or lagoons, a lot of the locals will literally just mow down the salt marsh that happens to grow on their yard, which is technically not legal,” he said.
“In many places they’re still affected by cattle and damaged by cattle, ” he added.
Salt marshes are also particularly vulnerable to sea level rise.
“So on one hand, you have climate change and sea level rise in particular, which means that mangroves want to grow higher…into the areas which would normally be salt marsh,” Vincent said.
“And then at the other end, the salt marsh doesn’t really always have areas to grow because there tends to be buildings or human land use higher up on the water table, so they kind of have gotten squeezed in.”
Burrill Lake salt marsh, NSW, which has suffered degradation from cattle grazing. Source: Vincent Raoult
Recent research efforts have focused on Burrill Lake salt marsh, near the township of Uladulla. The salt marsh suffered significant degradation in the past from cattle grazing, but is currently being restored as part of a joint project between the University of Newcastle and OzFish. The good news is that restoring salt marshes ecosystems is fairly easy.
“In general, salt marsh restoration, paradoxically, is probably one of the easiest habitats to restore, because it does happen naturally, if you just return the conditions to be appropriate,” Vincent said.
“Most salt marsh restoration is either building fences to exclude things like cattle or its undoing dams and weirs and stuff like that that prevent the salt water from going in, so reflooding that habitat,” he said.
For Burrill Lake, that meant fencing out the cattle to allow salt marsh species to return. Vincent and his team are monitoring how the salt marsh recovers with drones. Using multispectral sensors and the Normalised Difference Vegetation Index, he can monitor how species extent and condition changes with time. While the team could achieve this with traditional field work, salt marshes are muddy and difficult to work in. Drones allow them to collect data more quickly and easily, while reducing further disruption to the habitat.
Other ways drones are helping wetlands
Drones aren’t just helping monitor salt marshes. In Florida, researchers have used machine learning to identify and map species in a wetland undergoing restoration. They can also be used for more general habitat mapping of wetland habitats, like mangrove forests.
In Nova Scotia, Canada, researchers are using drones to track coastal erosion, in part caused by the loss of wetlands in the region.
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