Biodiversity in decline
How environmental stress endangers life in flowing waters
by Julia Weiler
May 5, 2014
In the past decades, humans have been interfering with the Earth’s ecosystems more strongly than ever before and have thus triggered a new wave of mass extinction. A report published as part of the "Millennium Ecosystem Assessment" in 2005 states that species have been going extinct up to one thousand times more quickly in the last 50 years, compared to the normal pace observed in the history of our planet. It's high time to do something for the preservation of biodiversity, says Dr Florian Leese, Group Leader of the "GeneStream" project (fig. 1). This is because biodiversity has more than just ethical value; it also fulfils specific functions for humans. Animals and plants are not just food; organisms in streams, rivers and lakes filter, for example, suspended sediments and pollutants from the water. "We have the technology to take care of many of those functions reasonably well – but not for free," says Florian Leese. "Why, then, should we destroy an ecosystem that provides us with drinking and non-potable water free of charge?"
Dr Florian Leese (2nd from the right), "GeneStream" project leader, studies the biodiversity of German water bodies and campaigns for the preservation of biodiversity. © RUBIN, photo: Nelle
Together with his junior research group at the Department of Animal Ecology, Evolution and Biodiversity, the biologist studies how environmental stress affects stream-dwelling organisms. Specifically, the team measured the impact of increased nutrient supply, sediment delivery and reduced flow velocity on the Breitenbach stream in Hesse (fig. 2). Nutrients in the form of phosphates and nitrates get flushed into the water due to fertilisers. Fine sediment such as sand is often washed off from open soil into the rivers, for example from cultivated land. Flow velocity is reduced when, for example, water is used for agricultural irrigation.
The Breitenbach stream in Hesse is the world's best-researched flowing water. The "GeneStream" team, too, did analyse it. © RUBIN, photo: Nelle
Unlike previous studies, the RUB biologists did not merely look into each of those stress factors individually. Rather, they analysed all possible combinations, for example the impact of a higher nutrient volume in combination with an increase in the volume of washed-in sediments. "It’s like in medical science," explains Florian Leese. "Certain active ingredients interact with other active ingredients. Different stress factors, too, may interact. However, it is difficult to predict in what way exactly."
The biologists set up 64 experimental channels into which they pumped water directly from the stream (fig. 3). Organisms smaller than five millimetres thus got flushed into the containers; larger stream dwellers were put there by the researchers by hand. The animals had the option to leave the experiment at any time. The idea behind it: if they cope well with the environmental conditions, they will remain in the containers. If not, they will leave them.
In 64 experimental channels, RUB biologists tested how well water organisms can cope with environmental stress, for example with excessive nutrient or sediment input. © RUBIN, photo: Nelle
Two months into the experiment, the researchers analysed which organisms had settled down under different environmental conditions in the containers – always comparing them against the control channels which were not subject to any particular environmental stress. All three stress factors had a negative impact on most of the species. That means that due to an increase in sediment or nutrient volume in combination with lower flow velocity the number of individuals in the test containers was significantly lower than in the control containers. The exposure to fine sediments in particular, i.e. an increase in sand volume, had most pervasive effects on the organisms. "There are a few mucky pups out there, such as roundworms or some fly larvae, who aren't bothered," says Florian Leese. Fine sediment exposure is actually a normal phenomenon – but only if it happens sporadically. "Our results show that a high sediment supply over the years is really bad for many species," says the biologist from Bochum.
An increased nutrient volume turned out to be not quite so harmful. Some organisms even thrived more when subjected to high phosphate and nitrate volumes than those in the control containers. However, that was only the case if no other stress factors occurred (fig. 4). "The more stressors we added to the experiment, the stronger the organisms' stress reaction," concludes Florian Leese. "Sometimes though, stressor one and stressor two put together will not merely be twice as bad, but rather three, four or eight times as bad." It is therefore crucial to analyse the interactions between different environmental impacts. Thus, the biologists can make a recommendation regarding proper water management, for example advise to avoid a particularly harmful combination of stress factors. "In the field of ecology, experimental multi-stressor research is still in its infancy," observes the "GeneStream" team leader.
As far as the mayfly (blue) is concerned, the more stress factors affect its habitat, the fewer individuals can be found in the Breitenbach stream. Unlike mayflies, freshwater shrimps can still thrive as long as only the flow velocity is reduced. If, however, a second stress factor is added to the mix, their numbers dwindle significantly. © RUBIN
In March 2014, the team from Bochum launched a new experiment: this time at the Felderbach stream in the Elfringhauser Schweiz region. In addition to the three stress factors that they had researched in the Breitenbach stream, they now also look into the effects of an increased salt concentration in water. It enters streams for example through thawing salt or mine drainage water. For the first time, the biologists will not only determine what kinds of organisms are present in the experimental containers, but also analyse their genetic makeup. "It's the same as with the polar bear," compares Florian Leese. "Just because there are currently still many individuals of a species left, it does not mean that the species will be able to survive in the long term." Only those species can survive in the long term that are particularly adaptable; and adaptable are those species that boast a high genetic diversity. "Genetic biodiversity is something of a species' life insurance," explains Leese. Accordingly, the extent to which single individuals of a species differ on a genetic level tells the researchers how vulnerable they are in the face of changing environmental conditions. Thus, "GeneStream" is going to provide wholly new insights into the state of waters in Germany.
Further information: http://GeneStream.de
EU Water Framework Directive
Under the Water Framework Directive, the EU member states have committed themselves to achieve good chemical and ecological status of all surface waters by 2027. "We are lagging far behind this ambitious schedule," says Florian Leese. "In NRW, less than five per cent of all flowing waters are still near natural; more than 60 per cent have been completely reshaped through human intervention." The RUB biologist considers the idea of the directive sound in principle and knows of instances where it could be implemented. However: "It has also triggered a number of pointless measures without proper planning that have not improved the biodiversity to any measurable extent. If there are no species in the vicinity of a renaturated water body that can repopulate it, the measures will remain pointless. Dovetailing basic research and water management is crucial."
Barcoding: genetic analyses for identifying species
In order to predict to what extent an ecosystem suffers from certain stress factors, it is necessary to determine which animals inhabit it. "Scientists who are able to identify organisms without fail are dying out," cautions Florian Leese. Before that happens, the "GeneStream" team plans to preserve their know-how by means of modern technology – independent of the human factor. Together with the GBOL project team (www.bolgermany.de), the RUB biologists have specialists from all over the world identify organisms of which they subsequently decode a characteristic gene sequence. Thus, a databank is being created containing genetic sequences, so-called barcodes, of all stream-dwelling organisms. In future, "DNA barcoding" will thus be used to determine which species live in a body of water. "We simply take a water sample and put everything in the blender," elaborates Florian Leese. The result will be a collection of DNA fragments of all organisms contained in the sample. They will subsequently be sequenced and compared with the databank. The comparison will be used to draw up a list of all organisms whose DNA fragments were present in the water sample.