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Can we geo-engineer polluted freshwaters back to health?

July 20, 2016

Green algal bloom forming a thick surface layer in Lake Dora, Florida. Image: Nara Souza | Florida Fish and Wildlife Commision | Creative Commons

‘You broke it, you own it.’  That was political ecologist Paul Robbins’ take on the results of a new experimental trial (open-access) at the University of Alberta, Canada where adding iron to eutrophic lakes was found to help manage outbreaks of harmful algal blooms.  For Robbins (and others, such as the Ecomodernist movement), the damage humans have caused to the natural world means there is a pressing need for radical and often-interventionist management to reverse decades of ecological harm.

The University of Alberta experiments suggest that one way to positively ‘own‘ damaged freshwater ecosystems is through geo-engineering, the deliberate large-scale intervention in the Earth’s natural systems to counteract environmental damage (most often climate change).

In this case, the additions of iron in the Alberta study would be unlikely to occur in a ‘natural’ ecosystem, but given that we are living in a world where it is arguably impossible to find ‘pure’ nature (see for example, landscape historian Bill Cronon’s work (pdf), and recent debates over the Anthropocene), such an intervention may be justified in terms of the positive ecological impacts it may have.  In other words, geo-engineering finds novel strategies to help guide novel ecosystems towards (potentially new) states of health.

Freshwaters comprise some of the most highly altered and modified ecosystems in the world: new concrete geologies and diluted chemical flows.  In this context, a new special issue of the journal Water Research brings together 60 scientists from across the world to present findings on the effectiveness of geo-engineering approaches in managing the harmful effects of phosphorous pollution in freshwaters.

One of the special issue editors, Kasper Reitzel, from the Department of Biology, University of Southern Denmark outlines the pressing need for effective phosphorous management, stating that,  “In 40 % of Europe’s lakes the water quality does not meet the demands of EU’s Water Framework Directive, mainly due to phosphorus pollution. That is a huge problem for biodiversity and society and we need to put an effort into developing effective approaches to restore these lakes.”

Phosphorus is a major cause of water quality degradation across the world.  Reaching freshwaters through run-off from farmland fertilisers and feeds, industrial chemicals and domestic cosmetics and wastewater, phosphorous can create ecological “dead zones” and toxic algal blooms which can then cause biodiversity losses and increased health risks for the plants, animals and humans that come in contact with polluted waters.

Phosphorous pollution is particularly pervasive as it often accumulates in lake bed sediments.  This means that the ecological health of a lake may take many years to recover, even when phosphorous pollution is controlled, as particles stored in the sediments are gradually released back into the lake water.

This poses a number of challenges for freshwater management, both in the short-term (restricting phosphorous pollution); and in the long-term (managing the effects of phosphorous deposits on an ecosystem). Geo-engineering approaches have been used for a number of years in freshwaters, for example in adding aluminum salts or modified clays into a lake to lock excess phosphorus stored in the sediments.

However, the results have not always been effective, according to special issue editor Sara Egemose from the Department of Biology, University of Southern Denmark, who says, “Often lake managers have used geo-engineering uncritically in lakes where the external loading of phosphorous was not reduced enough, or they have applied too low a dosage because of economic restrictions.”

The new Water Research special issue presents findings of laboratory experiments, field studies and meta-analyses of existing research.  The geo-engineering techniques assessed include the use of modified clays and soils (e.g. with the chemical element lanthanum), coal fly ash, dissolved organic carbon, and flocculants which cause fine organic material (such as cyanobacteria) to clump together for removal. Aluminium and lanthanum modified compounds were among the most effective compounds for targeting phosphorous, whilst flocculants and ballast compounds may be used as short-term measures to clump and sink cyanobacteria blooms.

Whilst many of these techniques are shown to be successful in either mitigating phosphorous build-up or managing the resulting algal blooms, they are often expensive and difficult to apply across large areas.  As such, the issue editors emphasise that an ecosystem analysis that reveals the main water and phosphorous flows and the biological structure of the waterbody should be the first step of any management strategy so that geo-engineering approaches are effectively targeted.

The issue editors suggest that new technological developments in the use of modified zeolites – absorbent aluminosilicate minerals – may offer future possibilities for treating both phosphorous and nitrogen pollution simultaneously.  To maximise the potential of such emerging geo-engineering approaches in treating (or even reversing) human damage to freshwaters through nutrient pollution, the editors conclude with a call for the establishment of a new multi-national, interdisciplinary research centre for freshwater geo-engineering.

Special Issue on Geo-engineering to Manage Eutrophication in Lakes (2016), Edited by Miquel Lürling, Eleanor Mackay, Kasper Reitzel and Bryan M. Spears, Water Research, Volume 97, pp. 1-174

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