Zooplankton

• This nutrient-rich material is then dried to make “biosolids”, which are used to fertilise agricultural soil.
• Unfortunately every kilogram of biosolids also contains thousands of tiny pieces of plastic.
• These pieces are so small they can only be seen under a microscope, so they’re called microplastics.

Biosolids as fertiliser

• The waste becomes a resource, a useful and economically viable fertiliser, rather than ending up in landfill.
• Read more:
  More than 1,200 tonnes of microplastics are dumped into Aussie farmland every year from wastewater sludge

Microplastics in Australian biosolids

• Wastewater treatment plants can capture anywhere from 60% to more than 90% of the microplastics in sewage before the wastewater is discharged.
• We assessed the abundance, characteristics and size ranges of microplastics in biosolids collected from 13 wastewater treatment plants across three states.

• We suspect this corresponds to people washing more synthetic fleece clothing and blankets.
• We estimate Australians release between 0.7g and 21g of microplastics per person into wastewater every year.
• This contributes to the amount of microplastics in biosolids.
• Our biosolid samples contained anywhere from 1kg to 17kg of microplastics per tonne.

What’s the problem?

• While natural weathering processes such as sunshine and rain will slowly break down microplastics into smaller and smaller particles, that only makes matters worse.
• Smaller particles cause more harmful effects to soil organisms.
• Microplastics in soil can be ingested by soil organisms such as earthworms and cause harmful effects on these vital organisms.

Here’s what we can do

• We need to put effective control measures in place to minimise the accumulation of microplastic in productive agricultural soils.
• The most effective way to do this is to reduce the level of microplastics in biosolids at the source.
• Australia’s National Plastics Plan recommends the Australian government work with industry to “phase-in” microfibre filters on all washing machines by 2030.
• Read more:
  'Humanity's signature': study finds plastic pollution in the world's lakes can be worse than in oceans

• This project was co-sponsored by Urban Utilities, Sydney Water, SA Water, Water Corporation (WA) and Eurofins Environment Testing Australia.
• Frederic Leusch receives funding related to this research topic from the Queensland Government through an Advance Queensland Industry Research Project, Water Research Australia, and various Australian water utilities.

• The journey isn’t far either, as we’re by the city of Kuopio, which is surrounded by Finland’s 10th largest lake.
• We’re crossing the icy bay not for sport or holiday activities, nor is it part of a plan to hike to north Pole.
• Mud – or sediments, as geologists call them – are deposited slowly at the bottom of lakes.
• Lake Kallavesi has a specific and rare type of sediments called annually laminated or varved sediments.

The history of plastic, buried in the mud

• It’s a continuation of our ongoing research, most recently published in the Journal of Soils and Sediments in February 2023.
• Widespread use of plastic started about 70 years ago, and since then, 9 billion metric tonnes has been produced.
• It would be nice to work on lake on a sunny summer day, but the thick ice serves as a stable platform.
• We use metal rods to push the core tubes down 11 metres to the lake floor and then into the sediment.
• This benefit is also plastic’s worst aspect: released into the environment, it doesn’t decompose but breaks into ever smaller pieces.

The ABCs of reading sediment layers

• It might be the noise or maybe it is just excitement – after all, you never know beforehand what the sediment will look like.
• The thicker the bright layer is, the more intensive the spring flood and higher the snow was during the winter.
• Building a bridge or a road involves digging and can increase erosion, and our sediment shows bright layers that can be several centimetres thick.
• Today, however, I’m planning my playing in more detail, having spent weeks in the laboratory preparing these sediments for analysis.

Two steps forward, one steps back

• Unfortunately, that’s not the case for microplastics – their presence in the sediments is increasing over time.
• The materials most frequently found are polyethylene, polypropylene and polystyrene, often employed for so-called single-use products such as packaging.
• To learn more, visit the site of the Axa Research Fund or follow on Twitter @AXAResearchFund.

• Coral reefs thrive in parts of the world’s oceans that are low in nutrients.
• This mystery has puzzled scientists for centuries and has become known as the “Darwin paradox of coral reefs”.
• We found that many species of coral cultivate and feed on the microscopic algae that live inside their cells.
• Coral reefs are important underwater ecosystems that provide a home and feeding ground for countless organisms, sustaining around 25% of the world’s ocean biodiversity.

Vegetarian diet

• This nutrient compound was marked by a technique called isotopic labelling, which uses nitrogen atoms that are heavier than normal.
• These “heavy” isotopes allowed us to track the movement of nitrogen between the partners of the symbiosis by ultrasensitive detection methods.
• Our data suggest that most species of symbiotic corals can supplement their nutrition through such a vegetarian diet.

From the laboratory to the ocean

• Together with our colleagues, we also analysed corals growing around remote islands in the Indian Ocean, some with seabirds on them and some without.
• Our results show that corals have the potential to farm and feed on their symbiont algae in the wild too.

Global warming could complicate matters

• In the future, some coral reefs could face a decrease in nutrient availability due to global warming.
• Research suggests that warming surface waters are less likely to receive nutrients from deeper water layers.
• The reduced water productivity could result in fewer nutrients for their symbionts and subsequently less food for the coral animals.

• This means the ocean is key to understanding the global carbon cycle and thus our future climate.
• The Intergovernmental Panel on Climate Change (IPCC) uses earth system models to project climate change.
• However, if we can’t accurately model the marine carbon cycle then we cannot truly understand how Earth’s climate will respond to different emission scenarios.

Marine carbon cycling is a $3 trillion thermostat

• If we price carbon at the rate the IPCC believes is needed to limit warming to 1.5℃, this adds up to over A$3 trillion worth of emission reductions accomplished naturally by the ocean every year.
• However, we know the size of the ocean carbon sink has changed in the past, and even small changes can lead to big changes in the atmosphere’s temperature.
• Any changes to the strength of this biological carbon pump will be felt in the atmosphere and will change our climate.
• Read more:
  Smoke from the Black Summer fires created an algal bloom bigger than Australia in the Southern Ocean

Right for the wrong reasons

Despite its importance for the global climate and food production, there are large gaps in our understanding of how the marine carbon cycle is expected to change. Most earth system models differ in how the cycle’s major components will respond to a changing climate. Models simply can’t agree on what will happen to:
• To diagnose what might be going wrong, we compared the marine carbon cycle in 11 IPCC earth system models.
• We found the largest source of uncertainty is how fast zooplankton consume their phytoplankton prey, known as grazing pressure.
• We can then tune models until we ensure they get the right answer.
• Yet, even though our best models can admirably recreate the present-day ocean, they do so for different reasons and with dramatically different assumptions about the role of zooplankton.

Tiny plankton with a big impact

• We ran a sensitivity experiment to show how small changes in zooplankton grazing can dramatically alter marine carbon cycling.
• This increase in how fast zooplankton can graze was only a fraction of the difference between assumed grazing rates seen across IPCC models.
• From a fisheries perspective, that leads to a 50% increase in the size of the global zooplankton population on which many fish feed.
• However, new technologies for measuring zooplankton are making it easier to make autonomous, high-resolution measurements of many important variables.