The editors of the scientific journal Limnology & Oceanography recognised Recovery of lakes and coastal marine ecosystems from eutrophication: A global meta‐analysis as one of 2017's most downloaded articles.

- In many cases, scientific publications report on the findings for one lake or one coastal area. What is unique about this paper is that we quantified the results of so many other studies using a statistical approach called meta-analysis, says McCrackin. 

The big picture of recovery

Michelle McCrackin
Michelle McCrackin

In the article, McCrackin and her colleagues combined the findings of 89 different studies to understand the extent to which and how quickly eutrophic lakes and coastal ecosystems respond to reductions in nitrogen and phosphorus inputs.

- We know that human activities contribute to eutrophication and there are many studies that show the consequences of nitrogen and phosphorus from sewage and agriculture. But it seems like there are fewer studies that document how water bodies respond when the nutrient inputs are reduced. We wanted to see if we could say something about the “big picture” of recovery from eutrophication by synthesizing the studies that have already been published, says McCrackin.

And the results of this work sends a cautious message.

- We see a general improvement when nutrient inputs are reduced or stopped altogether. But there were cases where the conditions did not change or even got worse. Overall, recovery takes time – from decades to centuries. This show how important it is to collect monitoring data for many years, she says. 

No quick fix, but measures can work

From an environmental management perspective, these results are not be fully satisfying. Society expects results for all the money that has been spent on measures to reduce nutrients to water bodies, such as improving sewage treatment infrastructure. But McCrackin points out that decision-makers should carefully consider the possibility of long recovery times when setting management goals.

- We know that nutrient inputs to the Baltic Sea, for example, have been reduced dramatically. This is a huge accomplishment. But it took decades for the sea to become eutrophic and it will take decades to recover. The target in the Baltic Sea Action Plan is year 2021, which is not achievable. I know that people like a quick fix, and nobody likes the answer "it takes a long time". But measures to reduce nutrient inputs do work and this is an important first step for recovery, she concludes.

Want to know more?:

Scientific publication: Recovery of lakes and coastal marine ecosystems from eutrophication: A global meta‐analysis

Baltic Eye magazine: "We must have patience"