Hilltops to oceans

This series of projects studies the flow of organic matter and nutrients from the land to the sea, aiming to understand the role of natural ecosystems and identify methods for protecting them.

Experimenting in Mahurangi Harbour
Experimenting in Mahurangi Harbour

Land-use intensification, particularly in agriculture, is significantly increasing the amount of sediment, nutrient, and organic matter in freshwater and coastal ecosystems.

Recent research suggests there may be a tipping point where muddiness (or turbidity) exceeds a critical level, significantly affecting denitrification (in estuaries), carbon cycling and storage (on coasts). This reduces the health and functioning of coastal ecosystems and negatively impacts kaimoana, particularly shellfish beds.

“We are looking at the cascading effects of land use on carbon and nutrient cycling in freshwater and coastal ecosystems around the Hauraki Gulf, the role of natural ecosystems in mitigating these negative effects and the potential for enhancement through the restoration of our estuarine and coastal ecosystems,” says Associate Professor Luitgard Schwendenmann, a member of the research team.

Cascading effects of land use

The flow of water that moves organic matter from hillslopes to sea intimately connects terrestrial, freshwater and marine systems. Often organic matter is highly biologically reactive, influencing the productivity in streams and estuarine systems, and driving greenhouse gas emissions.

With supervision from Associate Professor Luitgard Schwendenmann, PhD student Julia Jakobsson is investigating the effects of land use (e.g. fertilisation, grazing) and other stressors (e.g. storm events) on organic matter fluxes and bioavailability across seasons along the soil-stream-estuary continuum. 

Luitgard and Julia hope the project will help to improve projections of ecosystems’ responses to disturbances and identify strategies for sustainable land-use management and ecological restoration.

About the researchers

Associate Professor Luitgard Schwendenmann
School of Environment, University of Auckland

Julia Jakobsson
PhD student

The role of estuaries in nitrogen processing

Sampling water during an experiment in Mahurangi Harbour
Sampling water during an experiment in Mahurangi Harbour

Dr Emily Douglas, a research fellow from the University of Waikato*, is collaborating with the Institute of Marine Science on a new Hilltops to oceans project.

The study, conducted with the guidance of Professor Conrad Pilditch (University of Waikato) and Associate Professor Luitgard Schwendenmann (University of Auckland), looks at how estuaries store and process nitrogen.

“The rationale for this project comes from an urgent need to advance the knowledge and awareness of estuary ecosystems and the important part they play in storing, processing and especially removing (by denitrification) excess land-derived nitrogen,” Emily explains.

“We will use an interdisciplinary approach to determine the linkages between stressors (excess nutrients, organic matter and muddy sediments) and impacts on biogeochemical processes (especially denitrification) in receiving estuary habitats."

Using four experimental sites across a variety of habitat types, the research team are studying how the attributes of different ecosystems influence their response to nitrogen enrichment. The research measures ecosystem function and nitrogen cycling processes including, productivity, oxygen consumption, denitrification, and greenhouse gas fluxes (or emission).

By improving understanding of nitrogen movement in estuaries, the experiment will aid estuary management and highlight the value of healthy ecosystems in the reduction of nitrogen pollution.

*Emily now works for NIWA Hamilton full time, but is still writing up the experiment that she did as part of this project.

About the researchers

Associate Professor Luitgard Schwendenmann
School of Environment, University of Auckland

Professor Conrad Pilditch
University of Waikato

Dr Emily Douglas
Marine Ecologist, NIWA

Mapping primary production in the Hauraki Gulf

Kelp forest
Kelp forest

Marine and coastal vegetation provide an important role as a primary production source in the marine ecosystem. However, as human activities increase the stress on coastal ecosystems, there is a need to assess the current status and distribution of these vegetated habitats, such as kelp forests.

As part of the Hilltops to oceans project, research fellow Dr Caitlin Blain is working to quantify primary production in the Hauraki Gulf. Caitlin and Dr Nick Shears are leading a team to provide images for validating and improving the habitat maps provided by Auckland Council.

Using drop-camera photo surveys from the Mokohinau Islands in the outer Hauraki Gulf to Motutapu and Rangitoto Islands in the inner Gulf, Catlin and Nick hope to produce an accurate habitat map of the Hauraki Gulf. This important first step in measuring productivity will also allow researchers to set a carbon value on conserving and restoring habitats and areas within the Gulf.

About the researchers

Associate Professor Nick Shears
Institute of Marine Science

Dr Caitlin Blain
Institute of Marine Science

Restoring shellfish beds

Research fellow, Jenny Hillman.
Research fellow, Jenny Hillman.

Research fellow Dr Jenny Hillman aims to develop new technologies and techniques that give communities the tools to successfully restore shellfish beds in the Hauraki Gulf.

Coastal marine ecosystems have high cultural, social, economic and environmental value in New Zealand. Shellfish beds make a significant contribution to the health and resilience of coastal ecosystems.

With a focus on the endemic Green Lipped Mussel (Perna canaliculus), Jenny is working to improve the health, productivity, resilience and mauri (life force) of these areas.

The project aims to provide novel low-cost techniques to assist in future restoration efforts, by underpinning the science behind successful restorations of shellfish beds and through effectively communicating the benefits of restoration to the wider public.

Jenny says iwi and communities are frequently keen to engage in marine restoration, particularly of shellfish beds. But, community-led projects often lack the scientific knowledge and practical tools needed to support their good intentions, and the risk of failure is high.

“I'm hoping to develop some new ways to measure the services provided by these beds, and possibly innovative, accessible monitoring techniques,” she says.

About the researchers

Dr Jenny Hillman
Institute of Marine Science