Andrew Swales talks about the big issues concerning estuaries, such as sedimentation, and what can be done to protect them. Proper management of estuaries requires an integrated management approach where the whole system is looked at. Besides restoring an estuary, you need to address what is causing the problem – to find the sources of pollution that are driving changes.
Fine sediments generally are one of the big issues because they have a number of effects. When they’re suspended in the water, they reduce the amount of light that’s available at the bed. So for aquatic plants like seagrasses, which support whole ecological communities within estuaries, once deposited, they change the nature of the sediments and the types of animals that can live in them. They actually accelerate the ageing of the infilling of estuaries, so they cause a major shift in the habitats in estuaries.
There’s a whole range of contaminants which are coming into our estuaries which primarily relate to human activities on the land. Around urban centres, we see heavy metals accumulating in estuarine sediments, which are getting to levels now that we start to see ecological effects, so those would be key contaminants. Also microbial contaminants, pathogens from animals or humans related to faecal material is also a human health hazard, particularly in the upper reaches of estuaries, which may be poorly flushed by the tide.
What can be done to protect our estuaries? This is something that many regional councils are aware of – the whole idea of integrated catchment estuary management plans, so considering the whole system.
You’ve got to be able to control inputs to an estuary to affect long-term changes. If you try and restore something in the estuary, like for example seagrass beds, but you don’t address the erosion that might be going on in the catchment – there’s a lot of fine sediment coming into the estuary. You are never get back those seagrass beds if you’re not controlling the cause of their decline, and the same goes for other parts of the system.
So it’s that integrated management that’s required – not just restoration but also getting to the crux of the matter in terms of what the sources of pollution are that are driving these changes
Apanui Skipper, Weno Iti, Andrew Swales and Raiha Tuahine, NIWA
Waipapa Marae, Kāwhia