Waikaraka Estuary, NZ

Waikaraka Estuary, NZ

By Hannah Glover

Field work here in New Zealand is in full swing! We have spent 6 busy days so far at Waikaraka Estuary in Tauranga Harbor. This beautiful estuary is the perfect place to study how an ecosystem changes following mangrove removal. Unlike other parts of the world, mangroves have been expanding in New Zealand. These mangroves provide many benefits, including stabilizing coastlines. However, they also change the habitat by trapping mud, which prevents bivalves (clams and oysters) from growing. People living along the coast cut down mangroves to prevent them from “muddifying” their estuaries.

Left: Location of Tauranga Harbor on Google Maps. Center: Google Earth Image of Waikaraka Estaury in 2003. Note the extensive mangroves. Right: Same view in 2018; the mangroves are almost completely gone.

In Waikaraka Estuary, local citizen groups began clearing mangroves starting in 2003. My host, Deb, examined the changes in the 5 years immediately after mangrove removal. Now we’re studying the estuary more than 10 years later. This sort of long-term study is rare and provides valuable information on the evolution of a coastal system. Its exciting to finally be working on site after so many months of planning and preparation!

Left: A deforested part of the estuary. You can still see the trucks sticking out of the mud. Right: Can you spot Deb working in the mangroves? Photo credit: Hannah Glover

We are looking at both physical and biological changes. Last week we deployed instruments that measure the water temperature, salinity, flow, and turbidity (muddiness). These instruments will provide a continuous record that we can analyze and use to develop computer models of the estuary.

Most of our time in the field is spent collecting collect cores of sediment to look at changes below the surface. We measure the grain sizes of the sediment, the age of the sediment, and the amount of root material. We can use the age of the sediment to calculate how fast mud has been accumulating or eroding in the estuary. And, the amount of root material tells us how fast the mangrove roots decay after the trees are cut down. Finally, we count and measure all the bivalves we find, so that we can tell if they’re returning to the estuary. Next week I will talk more about how we process these samples in the lab.

Me with our sled full of coring equipment. Photo credit: Debra Stokes

This sort of field work is exactly why I became a geologist. It involves crawling through knee deep mud, playing with shovels, and enjoying the sunshine… all in the name of science!

Scroll to Top