“Lake snot” spreading among iconic South Island lakes

“Lake snot” spreading among iconic South Island lakes

By Marc Schallenberg1

Summary

A floating mucous (lake snot) caused by algae has now appeared in three iconic South Island lakes (Wanaka, Coleridge and Wakatipu) and is causing problems with recreation and water supply, particularly in Wanaka.

A team of scientists from the University of Otago, Landcare Research and Université Laval (Canada) have established that the recent appearance of lake snot is linked to the recent occurrence and dominance of an algae, which is a relative of didymo, in the lakes.

Lake snot has already affected swimmers, people who use the Wanaka Township water supply and fishers (including commercial fishing guides) and investigations by the Queenstown Lakes District Council into a water treatment system that can remove the slime are ongoing.

Although funding has been sought to study the lake snot algae and its production of slime, funding hasn’t materialised yet and questions such as how the algae arrived in the lakes, why it has become a dominant algae only in recent times and why it secretes slime to nuisance levels remain to be answered.

The local communities affected by lake snot remain supportive of the research and are concerned that a number of environmental changes occurring in the South Island’s lakes regions and high country may have encouraged the establishment and dominance of this nuisance organism in the lakes.

Understanding the potential relationships between these environmental changes and this new nuisance algae will require careful study.

What is lake snot?

Starting in around 2004, people fishing in Lake Wanaka began noticing an unusual slime sticking to their fishing lines and lures. In 2008, Dr. Marc Schallenberg from the University of Otago identified this slimy substance as a rare phenomenon called “lake snow” and, together with his PhD student at the time, Tina Bayer, linked it to unusually high numbers of a new algae in the lake waters. “I had studied over 100 lakes in Canada and New Zealand and had never seen lake snow before, but when we collected a routine sample of zooplankton from Lake Wanaka in 2008, I recognised the sticky flocs floating in the sample as lake snow, which had been reported in the scientific literature from only a few overseas lakes,” said Dr. Schallenberg. He connected the growing reports of a slimy substance affecting fishing in the lake and causing the clogging of domestic water filters in the Wanaka Township to this rare and new occurrence of lake snow and the new algae in the lake called Cyclotella bodanica (recently renamed by algologists as Lindavia intermedia). “While scientists call the slimy flocs floating in the water ‘lake snow’, we think it looks more like lake ‘snot’, said Dr. Schallenberg.”

What is its significance?

Schallenberg began talking to science colleagues, the regional and district councils and to Wanaka locals about this intriguing lake snot. Then, scientists working in the Seattle public utility (Washington State, USA) contacted him to say they had the exact same problem with a similar alga in a relatively unpolluted lake which was part of the Seattle City water supply. “We were scratching our heads as to why this problem should suddenly appear in these relatively unpolluted lakes”, said Dr. Schallenberg: “There was an obvious similarity to the invasion of relatively unpolluted South Island rivers by the nuisance algae, Didymosphenia geminata (didymo, also known as “rock snot”), in around 2004.”

Both Cyclotella and didymo are members of group of algae known as diatoms, and the nuisance factor related to both of these algae in the South Island is the fact that under certain environmental conditions, they can secrete large amounts of mucous, known as polysaccharide. In the case of didymo, the cell is attached to the river bed by a long polysaccharide stalk and dense growths of stalks make didymo colonies look like a thick mat on the river bed. In the case of Cyclotella, the mucous is secreted in long sticky threads which cause the cells to stick to each other and to other particles suspended in the lake water, eventually forming flocs visible to the naked eye, containing a wide range of bacteria, protozoa, algae and detritus. “These flocs become sticky ‘hotspots’ of biological activity, floating in the very clear and clean lake waters. While they are a nuisance to people using the lake, their presence in the lake also undoubtedly changes the way the lake ecosystem functions”, said Dr. Schallenberg. Commercial fishing guides who take tourists fishing in Lake Wanaka have virtually given up their guiding operations because the lake snot accumulates quickly on fishing lines and lures. The Queenstown Lakes District Council (QLDC) is concerned that lake snot is taken into the municipal water supply, clogging domestic and industrial water filters, annoying residents of Wanaka and costing time and money to deal with the resulting water supply problems. In 2010, QLDC trialled a filtration system to remove lake snot from the town water supply, but the cost was deemed prohibitive at the time. Last summer, the Council installed a pilot filtration system at one of its water intakes and the decision to upscale to include the whole water supply system or not will depend on the results of the trial. Effects of lake snot on the recreational use of the lake haven’t been studied yet, but earlier this year there were reports that swimmers involved in a multisport event emerged from the lake with lake snot visibly attached to them.

Why did it show up in Lake Wanaka?

Schallenberg and co-researchers have a number of hypotheses as to why lake snot suddenly appeared in Lake Wanaka in around 2004, but no single explanation seems satisfactory to the scientists. Many environmental factors have been changing over the past 20 years in the rapidly growing Central Lakes region. Population growth and urban development in the catchment are among the most rapid in the country. High country tenure review and changing commodity prices have been intensifying farming and fertiliser use in the catchment surrounding the lakes. Amy Weaver, A PhD student supervised by Dr. Schallenberg, has shown that even small amounts of rural land use intensification can have marked impacts on the movement of nitrogen and organic matter from the land to the lake. Tina Bayer, another of Dr. Schallenberg’s PhD students, has found evidence that climate change is probably subtly altering conditions important to algae in the lake. In addition, an exotic and invasive water flea (Daphnia ‘pulex’), which grazes on lake algae, colonised the lake in the early 2000s, displacing the native Daphnia carinata. Finally, intensive control of the invasive oxygen weed, Lagarosiphon major, by herbicide spraying is ongoing in Lake Wanaka. All of these factors, singly or in concert, have the potential to change the ecological balance in the open waters of the lake, potentially favouring the Cyclotella algae that produce lake snot.

A study by Dr. Schallenberg and Dr. Saulnier-Talbot (a diatom specialist from Canada) shows that Cyclotella is likely to be a new organism in Lake Wanaka. A microscopic analysis of algae remains preserved in the lake bed sediments showed the first appearance of Cyclotella cells in the lake occurred in around the year 2004, around the same time that slime problems were noticed. Prior studies in two other South Island lakes (Aviemore and Hayes) had found this organism to be present in those lakes, but in relatively low numbers. So the research to date indicates that the organism was present in South Island lakes in low numbers, without producing lake snot, before it found a more suitable habitat in Lake Wanaka, where it produces lake snot.

Lake snot spreads into other lakes

While the scientists have been trying to understand the appearance of lake snot in Lake Wanaka, the problem has been spreading to other lakes. In 2014, Dr. Phil Novis (an algal taxonomist from Landcare Research) was sent a sample of new slime found sticking to fishing lines at Lake Coleridge (Canterbury). He identified the algae embedded in the slime as Cyclotella and began to study the minute structural characteristics and the DNA of the organism. Identifying different species and strains of such tiny organisms requires careful microscopy and frequently involves DNA analysis.

These methods showed that the same organism was associated with lake snot in both Lakes Wanaka and Coleridge. He recently examined a sample of a similar, newly observed slime sent to him three weeks ago from Lake Wakatipu and confirmed that it is also the same Cyclotella. Dr. Novis’ comparison of the DNA extracted from the New Zealand samples with DNA sequences from the original European material for this species confirms that the New Zealand Cyclotella is extremely similar to the European material, although this does not necessarily mean it is a recent invader from Europe.

Why does Cyclotella produce so much slime?

This is a burning question for the QLDC and for Wanaka locals, who have had to put up with the lake snot problem for a number of years. The scientists have a number of hypotheses, based on published studies of lake snow, didymo and other slime-forming diatoms. The production of large amounts of slime by diatoms seems to occur in unpolluted lakes, rivers and marine environments, where the growth and reproduction of cells is slowed down due to very low concentrations in the environment of available plant nutrients such as nitrogen and phosphorus. However, studies by Amy Weaver have shown that lake snot production by the Lake Wanaka algae increases when more nitrogen and phosphorus are added to lake waters. So the role of nutrients is probably important but appears to be complex. Furthermore, slime production and the formation of large flocs may prevent animals that normally feed on algae, such as the water flea and freshwater mussels, from being able to feed on algae. In this way, slime production may be a defence mechanism for the algae. Finally, diatoms are quite heavy algae and they sink in the water column relatively rapidly.

Sinking to the dark depths of the lake is a death sentence for algae. So, it is possible that the formation of large flocs reduces the speed at which the algae sink, allowing them to live longer and reproduce to a greater extent than algae that don’t produce slime or form flocs.

Barriers to research

Answers to such questions can shed light on why lake snot has suddenly appeared in our lakes, which lakes are at risk from further invasions, what factors either help lake snot to form or prevent lake snot from forming and what could be done to prevent or slow the spread of lake snot from lake to lake, etc. Unfortunately, the research team has been frustrated by a lack of research funding to try to answer these questions. “I’m not sure if this reflects the general low levels of investment in science in New Zealand or that there is a reticence by governments to support research into emerging environmental problems for fear that our reputation as ‘clean-green’ country will be tarnished.” said Dr. Schallenberg.

Local support

Despite a lack of research funding to study the lake snot algae, the researchers have been overwhelmed by the interest and support of the local community at Wanaka for their work. “The local people understand the importance of Cyclotella and lake snot, not just to them and their lake, but to the bigger picture of New Zealand’s changing environment.”, said Dr. Schallenberg. “When this unpleasant material stops you fishing, sticks to you when you’re swimming and clogs the water filters on your washing machine, dishwasher and sprinkler, you get the picture pretty quickly. This has important implications not only for the environment and the economy but also for our well-being and sense of connection to the environment.”

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