The sweet relief of rain after bushfires threatens disaster for our rivers



After heavy rainfall, debris could wash into our waterways and threaten fish, water bugs, and other aquatic species.
Jarod Lyon, Author provided

Paul McInerney, CSIRO; Gavin Rees, CSIRO, and Klaus Joehnk, CSIRO

When heavy rainfall eventually extinguishes the flames ravaging south-east Australia, another ecological threat will arise. Sediment, ash and debris washing into our waterways, particularly in the Murray-Darling Basin, may decimate aquatic life.

We’ve seen this before. Following 2003 bushfires in Victoria’s alpine region, water filled with sediment and debris (known as sediment slugs) flowed into rivers and lakes, heavily reducing fish populations. We’ll likely see it again after this season’s bushfire emergency.




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Large areas of northeast Victoria have been burnt. While this region accounts only for 2% of Murray-Darling Basin’s entire land area, water flowing in from northeast Victorian streams (also known as in-flow) contributes 38% of overall in-flows into the Murray-Darling Basin.

Fire debris flowing into Murray-Darling Basin will exacerbate the risk of fish and other aquatic life dying en masse as witnessed in previous years..

What will flow into waterways?

Generally, bushfire ash comprises organic carbon and inorganic elements such as nitrogen, phosphorous and metals such as copper, mercury and zinc.

Sediment rushing into waterways can also contain large amounts of soil, since fire has consumed the vegetation that once bound the soil together and prevented erosion.

And carcinogenic chemicals – found in soil and ash in higher amounts following bushfires – can contaminate streams and reservoirs over the first year after the fire.

A 2014 post-fire flood in a Californian stream.

How they harm aquatic life

Immediately following the bushfires, we expect to see an increase in streamflow when it rains, because burnt soil repels, not absorbs, water.

When vast amounts of carbon are present in a waterway, such as when carbon-loaded sediments and debris wash in, bacteria rapidly consumes the water’s oxygen. The remaining oxygen levels can fall below what most invertebrates and fish can tolerate.

These high sediment loads can also suffocate aquatic animals with a fine layer of silt which coats their gills and other breathing structures.

Habitats are also at risk. When sediment is suspended in the river and light can’t penetrate, suitable fish habitat is diminished. The murkier water also means there’s less opportunity for aquatic plants and algae to photosynthesise (turn sunshine to energy).




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What’s more, many of Australia’s waterbugs, the keystone of river food webs, need pools with litter and debris for cover. They rely on slime on the surface of rocks and snags that contain algae, fungi and bacteria for food.

But heavy rain following fire can lead to pools and the spaces between cobbles to fill with silt, causing the waterbugs to starve and lose their homes.

This is bad news for fish too. Any bug-eating fish that manage to avoid dying from a lack of oxygen can be faced with an immediate food shortage.

Many fish were killed in Ovens River after the 2003 bushfires from sediment slugs.
Arthur Rylah Institute, Author provided

We saw this in 2003 after the sediment slug penetrated the Ovens River in the north east Murray catchment. Researchers observed dead fish, stressed fish gulping at the water surface and freshwater crayfish walking out of the stream.

Long-term damage

Bushfires can increase the amount of nutrients in streams 100 fold. The effects can persist for several years before nutrient levels return to pre-fire conditions.

More nutrients in the water might sound like a good thing, but when there’s too much (especially nitrogen and phosphorous), coupled with warm temperatures, they can lead to excessive growth of blue-green algae. This algae can be toxic to both people and animals and often closes down recreational waters.




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Large parts of the upper Murray River catchment above Lake Hume has burnt, risking increases to nutrient loads within the lake and causing blue-green algae blooms which may flow downstream. This can impact communities from Albury all the way to the mouth of the Murray River in South Australia.

Some aquatic species are already teetering on the edge of their preferred temperature as stream temperatures rise from climate change. In places where bushfires have burnt all the way to the stream edge, decimating vegetation that provided shade, there’ll be less resistance to temperature changes, and fewer cold places for aquatic life to hide.

Cooler hide-outs are particularly important for popular angling species such as trout, which are highly sensitive to increased water temperature.

Ash blanketing the forest floor can end up in waterways when it rains.
Tarmo Raadik

But while we can expect an increase in stream flow from water-repellent burnt soil, we know from previous bushfires that, in the long-term, stream flow will drop.

This is because in the upper catchments, regenerating younger forests use more water than the older forests they replace from evapotranspiration (when plants release water vapour into the surrounding atmosphere, and evaporation from the surrounding land surface).

It’s particularly troubling for the Murray-Darling Basin, where large areas are already enduring ongoing drought. Bushfires may exacerbate existing dry conditions.

So what can we do?

We need to act as soon as possible. Understandably, priorities lie in removing the immediate and ongoing bushfire threat. But following that, we must improve sediment and erosion control to prevent debris being washed into water bodies in fire-affected areas.




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One of the first things we can do is to restore areas used for bushfire control lines and minimise the movement of soil along access tracks used for bushfire suppression. This can be achieved using sediment barriers and other erosion control measures in high risk areas.

Longer-term, we can re-establish vegetation along waterways to help buffer temperature extremes and sediment loads entering streams.

It’s also important to introduce strategic water quality monitoring programs that incorporate real-time sensing technology, providing an early warning system for poor water quality. This can help guide the management of our rivers and reservoirs in the years to come.

While our current focus is on putting the fires out, as it should be, it’s important to start thinking about the future and how to protect our waterways. Because inevitably, it will rain again.The Conversation

Paul McInerney, Research scientist, CSIRO; Gavin Rees, , CSIRO, and Klaus Joehnk, Senior research scientist, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We built a network of greenhouses and rain shelters to simulate what climate change will do to soils



Mimicking the future.
Joe Fontaine, Author provided

Anna Hopkins, Edith Cowan University; Christina Birnbaum, Deakin University; Joe Fontaine, Murdoch University, and Neal Enright, Murdoch University

As most of the science community knows, the climate emergency is here now. Weather extremes such as droughts and heatwaves are increasing in frequency and intensity and are measurably exacerbated by climate change. The significant impacts of these extremes are well documented on both our native terrestrial and marine ecosystems.

Less documented is what’s happening beneath our feet. Changes below the ground are hard to measure, so most previous research has focused on what can be readily observed above the ground, such as tree deaths.

But soil is a crucial element of the climate system, being the second-largest store of carbon after the ocean. Climate change can result either in an increase in soil carbon storage (through plant growth), or in more carbon being released into the atmosphere (through plant death). Soil is also full of microbes such as fungi, bacteria and algae, and these organisms play a vital role in determining how well an ecosystem functions and how it responds to changes in climate.




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We have completed one of the first studies to examine the impact of drought and warmer temperatures on living organisms below the ground (known as the soil biota), in biodiverse shrublands in Western Australia, near Eneabba, about 280km north of Perth. These areas are already suffering immense climate-related stress above ground as a result of rising temperatures and longer droughts. This is making these ecosystems extremely vulnerable with many plant species facing likely extinctions in the future.

We documented significant impacts for soil biota too, with implications for the health of ecosystems in regions that are expected to experience increased drought and climate warming in the future.

We found that lower rainfall and higher temperatures are likely to affect the overall composition of soil fungal communities, and that some groups may be lost altogether.

We saw an increase in the number of fungal species that cause plant disease, whereas many common and beneficial fungi declined in response to warming and drying. These beneficial fungi contribute to many important ecosystem processes, such as boosting plant growth, and ensuring that plants get enough water and nutrients such as phosphorus.

Western Australia’s shrublands are already suffering climate stress.
Joe Fontaine, Author provided

How we did it

We built specially constructed shelters and mini-greenhouses over plots of shrubland 4x4m in size, to recreate the drier, hotter weather conditions predicted to arise between now and the end of the 21st century. This allowed us to assess how the projected future climate will affect the composition, richness and diversity of soil fungi.

Our rain shelters consisted of a roof made of gutters, widely spaced so as to intercept about 30% of the rain that fell on the plot and funnel it away.




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To study the impact of increased temperature, we enclosed separate plots on the same sites in walls made of transparent fibreglass sheeting. These worked in a similar way to a greenhouse, by reducing air flow and increasing daytime temperatures inside the shelter by 5.5℃.

We left the rain shelters and mini-greenhouses in place for four years. Then we collected soil from each plot and examined the fungi in the soil using DNA sequencing techniques.

How to engineer an artificial drought.
Joe Fontaine, Author provided

Our study revealed that it is vital to understand patterns of below-ground ecosystems as well as those we can see, if we are to accurately predict how our shrublands and other valuable ecosystems will be altered by climate change.The Conversation

Anna Hopkins, Lecturer in conservation biology and microbial ecology, Edith Cowan University; Christina Birnbaum, Honorary Fellow, Deakin University; Joe Fontaine, Lecturer, Environmental Science, Murdoch University, and Neal Enright, Professor in Plant Ecology, Murdoch University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Droughts and flooding rains already more likely as climate change plays havoc with Pacific weather


Scott B. Power, Australian Bureau of Meteorology; Brad Murphy, Australian Bureau of Meteorology; Christine Chung, Australian Bureau of Meteorology; François Delage, Australian Bureau of Meteorology, and Hua Ye, Australian Bureau of Meteorology

Global warming has already increased the risk of major disruptions to Pacific rainfall, according to our research published today in Nature Communications. The risk will continue to rise over coming decades, even if global warming during the 21st century is restricted to 2℃ as agreed by the international community under the Paris Agreement.

In recent times, major disruptions have occurred in 1997-98, when severe drought struck Papua New Guinea, Samoa and the Solomon Islands, and in 2010-11, when rainfall caused widespread flooding in eastern Australia and severe flooding in Samoa, and drought triggered a national emergency in Tuvalu.

These rainfall disruptions are primarily driven by the El Niño/La Niña cycle, a naturally occurring phenomenon centred on the tropical Pacific. This climate variability can profoundly change rainfall patterns and intensity over the Pacific Ocean from year to year.

Rainfall belts can move hundreds and sometimes thousands of kilometres from their normal positions. This has major impacts on safety, health, livelihoods and ecosystems as a result of severe weather, drought and floods.

Recent research concluded that unabated growth in greenhouse gas emissions over the 21st century will increase the frequency of such disruptions to Pacific rainfall.

But our new research shows even the greenhouse cuts we have agreed to may not be enough to stop the risk of rainfall disruption from growing as the century unfolds.

Changing climate

In our study we used a large number of climate models from around the world to compare Pacific rainfall disruptions before the Industrial Revolution, during recent history, and in the future to 2100. We considered different scenarios for the 21st century.

One scenario is based on stringent mitigation in which strong and sustained cuts are made to global greenhouse gas emissions. This includes in some cases the extraction of carbon dioxide from the atmosphere.

In another scenario emissions continue to grow, and remain very high throughout the 21st century. This high-emissions scenario results in global warming of 3.2-5.4℃ by the end of the century (compared with the latter half of the 19th century).

The low-emissions scenario – despite the cuts in emissions – nevertheless results in 0.9-2.3℃ of warming by the end of the century.

Increasing risk

Under the high-emissions scenario, the models project a 90% increase in the number of major Pacific rainfall disruptions by the early 21st century, and a 130% increase during the late 21st century, both relative to pre-industrial times. The latter means that major disruptions will tend to occur every four years on average, instead of every nine.

The increase in the frequency of rainfall disruption in the models arises from an increase in the frequency of El Niño and La Niña events in some models, and an increase in rainfall variability during these events as a result of global warming. This boost occurs even if the character of the sea-surface temperature variability arising from El Niño and La Niña events is unchanged from pre-industrial times.

Although heavy emissions cuts lead to a smaller increase in rainfall disruption, unfortunately even this scenario does not prevent some increase. Under this scenario, the risk of rainfall disruption is projected to be 56% higher during the next three decades, and to remain at least that high for the rest of the 21st century.

The risk has already increased

While changes to the frequency of major changes in Pacific rainfall appear likely in the future, is it possible that humans have already increased the risk of major disruption?

It seems that we have: the frequency of major rainfall disruptions in the climate models had already increased by around 30% relative to pre-industrial times prior to the year 2000.

As the risk of major disruption to Pacific rainfall had already increased by the end of the 20th century, some of the disruption actually witnessed in the real world may have been partially due to the human release of greenhouse gases. The 1982-83 super El Niño event, for example, might have been less severe if global greenhouse emissions had not risen since the Industrial Revolution.

Most small developing island states in the Pacific have a limited capacity to cope with major floods and droughts. Unfortunately, these vulnerable nations could be exposed more often to these events in future, even if global warming is restricted to 2℃.

These impacts will add to the other impacts of climate change, such as rising sea levels, ocean acidification and increasing temperature extremes.

The Conversation

Scott B. Power, Head of Climate Research/International Development Manager, Australian Bureau of Meteorology; Brad Murphy, Manager, Climate Data Services, Australian Bureau of Meteorology; Christine Chung, Research Scientist, Australian Bureau of Meteorology; François Delage, Assistant scientist, Australian Bureau of Meteorology, and Hua Ye, Climate IT Officer, Australian Bureau of Meteorology

This article was originally published on The Conversation. Read the original article.