From the Rivers to the Sea: Ngā Kōrero Webinar Recap

Fri, 01 October 2021

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The first webinar in the six-part ‘Ngā Kōrero’ series was live on the evening of 30 September during which three guest speakers discussed the interconnectedness of our lives on land with life in the sea - Ki uta ki tai – from the mountains to the sea. The webinar was moderated by the talented Alison Ballance, former RNZ broadcaster. 

Our fabulous guests speakers were, Dr. Conrad Pilditch, Dr. Carolyn Lundquist, and Dr. Mike Joy. You can watch the recording here or you can scroll down for a paraphrased version of each speaker's presentation and their answers to our final question of the webinar to get an idea of what was covered in this webinar. Found towards the bottom of this page are links to resources and articles to learn more about the research discussed and how to take action.


Dr. Conrad Pilditch started things off with introducing us to ‘mudification’.

We are so intertwined with the health of our ocean, especially in Aotearoa. We have a lot of coastlines, hills, short rivers and steep catchments which deliver the sediments to our coastline quicker. Where New Zealand is located, in the westerly wind belt, we naturally lose a lot of sediments to the ocean. Today though, our sedimentation rates per day are ten times higher than pre-European times. The influx of sediments into estuaries is mostly due to land use changes: from changing native forest to forestry land, forests to farmland and undeveloped land transformed into urban areas. NZ represents .05% of the global land surface area, yet our highly erosive volcanic soils contribute around 2% of the global sediment input! (20 billion tons) per year. Per square basis we deliver 40 times more sediment than the global average.

Usually, filter feeders like mussels, pipis and cockles would filter out the sediments and nutrients, cleaning up the estuaries, where the river meets the sea. However, due to the increased sediment and nutrient load, the marine life can’t filter out all the excess sediments. Then a layer of mud begins to choke the life in the estuaries. This can result in a multitude of issues disrupting the food web and includes; macroalgae blooms, shellfish mortality, and generally less productivity in estuaries.

Elevated turbidity, noticeable by the degree to which the water loses its transparency due to the presence of fine suspended sediment, alters the nutrient cycling of the estuaries and cuts down the light available to primary producers. This all contributes to ‘mudification’, the changing of our estuaries; gradually sandflats are transitioned into muddier substrates, altering the sediment’s properties and communities of animals that can occupy that habitat. Primary production is reduced, density and diversity of organisms decreases and we lose the benefit of primary producers which help get rid of excess nutrients - the compounding stressors erode the resilience of our estuaries.

Dr. Pilditch’s take home messages: 
  1. Estuaries are valuable, productive, diverse habitats that deliver intrinsic benefits (to the marine ecosystem and society).

  2. Sediment input from the land is a large-scale issue which can impact estuaries in many different ways.

  3. Sediments are not the only stressors to the coastal zone. The interaction of sedimentation with other stressors can lead to rapid and unexpected changes to estuarine health.


Dr. Carolyn Lundquist shared her knowledge and expertise on all things mangroves.

Mangroves, predominantly found on the North Island of NZ, play a big role in our estuaries and our ecosystem, they live in the intertidal zone, and love sediments! Mangroves are typically found in tropical climates, but the mangrove species we have here are different, temperate mangroves! In contrast with the rest of the world, mangroves are actually increasing quite rapidly (3-4% per year) in NZ, whereas mangroves in other parts of the world are decreasing. As more sediments enter the coastal ecosystem and as sea level rises, so will our mangroves, replacing other important habitats, which is what we are seeing now. In estuaries, mangroves play many roles, they act as a coastal buffer, produce lots of seed and leaf litter for other creatures, sequester carbon, and trap sediments, before they go out to the sea.

Mangroves love mud, so as our estuaries and coastline become muddier, the mangroves will fill in, which is why we see this a lot in New Zealand, with our high sedimentation rate. Unfortunately, you need to remove mangroves a specific way to avoid long-term habitat degradation. If adult mangroves are removed in a way that doesn’t promote ecological health, they can cause bacterial mats, anoxic sediments, hydrogen sulfide odour, and macroalgal blooms. Methods have been developed to minimize impacts of mangrove removal, but it doesn’t necessarily mean we should. Our best control for mangrove expansion is to manage catchments, reduce sediment load into estuaries and harbours.

Dr. Lundquist’s take home messages:
  1. Mangroves play many positive roles in our coastal ecosystems.

  2. Because of 'mudification', sediment infills estuaries causing our mangroves to expand, which can displace other habitats.

  3. We need to manage catchments and consider environmental impacts from upstream activities to avoid sedimentation.


Dr. Mike Joy gives us sobering news of our freshwater ecosystem.

The health of our freshwater ecosystems are far from good. New Zealand has the highest proportion of threatened freshwater species in the world (74%), almost half our lakes are polluted (44%), and over half of our rivers are unsafe for swimming  due to pathogens (62%). According to Hydrology and Earth System Science study: “The greatest negative impact on river quality in NZ in recent decades has been high-producing pastures that require large amounts of fertiliser to support high densities of livestock.”  This highlights the need to shift our farming practices to be more regenerative, and less nitrate intensive, so what is put in the soil doesn’t wash down to our coastline. We can’t afford to ignore the impacts of intensive industrial farming any longer.

Most of our native freshwater fish are diadromous, they spend a lot of their lives in rivers but require to be in the ocean at some stage in their lifecycle, usually to spawn. If the rivers, or estuaries are too polluted, or if travel up and downstream is inaccessible in some way, it threatens our endemic freshwater species greatly. Restoration of our freshwater habitats and catchments is key, as well as moving our dependency away from industrial monocultures to regenerative farming and permaculture.

Dr. Joy’s take home messages: 
  1. Support the protection of waterways to avoid them becoming damaged; its cheaper and easier to not pollute or damage them in the first place.

  2. We need a radical change in farming and food production away from industrial to regenerative.

  3. It is vital to be involved in advocacy and protection; be political and vocal.


When we asked our guest speakers, “what would be the one thing that YOU would do first to make a start towards making positive change in this (from the rivers to the sea) context?” (answers are paraphrased) 

Mike: "We need to have grown-up conversations about the intensity of industrial farming in NZ and the harm that’s it doing and what we actually gain out of it. I think it would be money well spent to pay farmers to drastically reduce their impacts. Often they are caught up in this model where they’ve gone into it having to pay huge amounts of money for the land. So I don’t want blame them, they’re kind of the meat in the sandwich. It’s not the farmers it’s the farming industry, the fertiliser companies, and Fonterra and the big dairy companies that have driven this. The only way we’re going to get out of this, it’ll cost, but it’s a one off cost, and that’s to cut back on that intensity of farming greatly..... When we stop and think about what we’re allowing to happen, it’ll be quite a simple thing to cut back on the intensity of farming and will have so many positive outcomes, like I had in my last slide of my talk. It’ll be so good for everybody, that as soon as we’ve done it we’ll wonder  why we went for so long down this stupid road of industrialization."

Conrad: "We need a change in policy towards a more interconnected way in which we think about how we can manage the land and the sea as one. At the moment we have a government structure, policy structure that disconnects the activities on land with what the downstream effects on our estuaries are. One thing I'd like to see change would be that we actually join up and we treat the ecosystem as a whole, as a continuum - and not separate the Resource Consents we’re issuing out on the land without thinking about those downstream effects. A much more holistic way of managing and restoring our ecosystems, certainly in our coastal environments.

I’d like to see action that leads to an upward trajectory, rather than the continual downward trajectory that’s facing many of our coastal environments due to this disconnect between managing on land and the effects on the coastal ocean. Community groups, keep doing what you’re doing. Because these local scale actions do make a huge difference - so you may think It's small but that little bit of riparian planting, that little bit of cleaning up the creeks and estuaries in these urban areas, you are helping these estuaries that I love to study, so don’t give up on that, that’s a really important component."

Carolyn: "I think the one of the things that we’re not very good about talking about is housing, and how are all these new housing developments are affecting sediment transport. I know there’s one a bit north of Auckland that was reasonably controversial when it got approved but I’ve heard stories of the amount of sediment that’s coming down. We did a lot of studies looking at sedimentation when we had that northern motorway extension put in about 20 years ago and we often go for infrastructure but without really looking at what are the actual impacts of that on sediment - and if could we do better.

It might cost a little bit now, but then the things that we have to do to fix it would be a lot cheaper in the long run. We often don’t consider those environmental impacts, we go for the ‘we need new houses, we need them now’. We should be making sure we reconsider how we’re doing developments. We need to look at development practises carefully and see what we can do to make sure we are building houses for all the New Zealanders who need houses; but making sure we do do it in the right way so that we’re not having long-term impacts on the environment."

Please have a look at some of these links for further information.

  • NZ National Commission for UNESCO NZ’s Decade of Ocean Science programme. There are 53 different projects highlighted on this site which span across Aotearoa. Some include a collaboration with Ngai Tahu and Plant and Food Research to enable conservation and recovery of our freshwater taonga species, or building the capacity of existing marine spatial management tools to include assessment of cumulative effects.

  • The Sustainable Seas Challenge has developed an Ecosystem-Based Management (EBM) tool, with input from stakeholders and Māori partners, it will create a holistic and inclusive way to manage marine environments and the competing uses for, demands on, and ways that New Zealanders value them. Research through the Sustainable Seas challenge will focus on improving marine resource decision making and the health of our seas through EBM, and will also focus on transforming New Zealand’s ability to enhance our marine economy into a blue economy. Here's an awesome video to explain EBM: a remedy for Aotearoa New Zealand's oceans.  
  • Manaaki Tuna: lifeline for longfins - learn about protecting and restoring our endangered and iconic Longfin EEL (Tuna). Their numbers have been reduced by years of excessive commercial exploitation, habitat loss and declining water quality. Nowadays very few Tuna are reaching breeding age and the population is facing collapse.


More Sustainable Seas Challenge Resources related to monitoring and completed research:  


Department of Conservation Teacher Resources


NIWA Resources

  • Iwi estuarine monitoring toolkit Ngā Waihotanga Iho, the estuarine monitoring toolkit for Iwi, has been developed to provide tangata whenua with tools to measure environmental changes in their estuaries.

  • Manual on managing mangrove expansion, while maintaining the ecological integrity of estuaries and harbours. You’ll find a lot of information about mangroves in this excellent document. From the history of mangroves, biodiversity, how to remove mangroves, monitoring them, etc.

Interesting Articles
  • Early signs of improvement for Maketū Estuary according to Bay of Plenty Regional Council.