Improvements in Water Quality Offset Climate Debt in UK Rivers

We’re all getting old. While we are living our lives, the slow process of aging is creeping along in background. While we can’t fight it, the process of aging and how quickly we start sporting those wrinkles can be affected by our health choices. Getting better sleep, eating well, exercising regularly – all can impact our health and the aging process.

For the past several decades, the global temperature has also been steadily rising. Scientists across fields are trying to understand how  the changing climate affects natural ecosystems. In a recent study, researchers in the United Kingdom (UK) explored this question by looking at aquatic macroinvertebrates, i.e. organisms who live in or near water, are big enough to see without a microscope, and don’t have a backbone: think snails, worms, dragonflies, etc.

Aquatic macroinvertebrates are great study organisms to evaluate climate change because they are very sensitive to pollution and other environmental conditions, and respond rapidly to ecosystem changes. For example, you wouldn’t find species that have low tolerance to pollution in a highly polluted river. As a result, you can essentially look at what types of macroinvertebrates are living in a river and make a good guess about the water quality conditions of that river.

In theory, we should be able to see shifts in the communities of macroinvertebrates if they are being affected by rising temperatures. However, like our bodies, ecosystems are complicated. While the temperature has been rising, we’ve been doing other things to positively impact our rivers. Just like better sleep and eating well, eliminating pollution sources can affect the overall health of an ecosystem, and how organisms are responding to their environment.

In this study, researchers wanted to measure environmental lag, or in other words, how delayed the response is of macroinvertebrates to changes in their environment such as rising temperatures due to climate change. Have improvements in water quality over the last several decades offset the effects of climate change? Researchers analyzed over 20,000 macroinvertebrate samples to find out.

Figure 1. An example of macroinvertebrate sampling in a river. (“June 2012: Sampling for macroinvertebrates” by the US Environmental Protection Agency is marked with Public Domain Mark 1.0.)
A Large Sample Size

Researchers looked at over 20,000 macroinvertebrate samples collected as part of routine river monitoring in sites across the UK from 1991 to 2011. They split up the types of organisms into three classes by looking at each groups’ tolerance to pollution and low-oxygen environments, or in other words, which types of organisms would be present in poor vs. good water quality conditions. Class 1 contained macroinvertebrates that were found in good water quality conditions with Classes 2 and 3 containing organisms found in increasingly poorer water quality. Using mathematical modeling, researchers also explored how often each group was expected to be found throughout the study period. For example, the model predicted whether the study sites were likely to have macroinvertebrates from Class 1, 2, or 3 in each year. 

They also measured other metrics related to overall water quality in addition to the water temperature throughout the study period. By using another mathematical model with these metrics, the researchers were able to create a novel way to look at how much environmental lag, or climate debt, and water quality “credit” were created as part of the study period. They used a common metric – temperature in Celsius – to communicate these two metrics.

Water Quality Comes Out Ahead

From 1991 to 2011, the mean temperature in the rivers sampled increased; however, the types of macroinvertebrates sampled shifted to those normally found in streams with better water quality.

Researchers found that the improvements seen in water quality corresponded with a decrease in frequency of Class 3, and an increase in the Class 2 and 1 macroinvertebrate groups. Specifically, the amount of times Class 3  macroinvertebrates were found decreased by 50%. The mathematical model predicted similar shifts in the classes, meaning that overall environmental lag was low.

This overall environmental lag, or climate debt, was calculated to be 0.64°C. The water quality credit was calculated to be 0.89°C. You can think of the water quality credit as -0.89°C, in which it “pays” the increase in temperature seen from climate change, and even leaves a credit left over. Essentially, researchers were able to model that improvements in water quality over the study period offset the predicted effects of climate change on these macroinvertebrate communities.

This study demonstrated that local interventions can make a difference in how organisms are affected by climate change. But, how long can this trend continue? Just as it’s important to understand how our actions affect our health, it will be crucial that we continue to study how climate change is affecting our ecosystems.

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Brittany Maule

I earned my Master's in Biology from Ball State University in 2017, studying how everyday human products like the compounds in bug spray and Tylenol affect the organisms that live in our streams and rivers. I'm interested in how human pollutants play a role in our aquatic ecosystems, especially since we use them for so many important functions! Currently, I work at Green Seal - a nonprofit that strives to make all sorts of products safer for human health and the environment. When I'm not working on my science communication stuff, I can be found hiking or curled up with a book and warm mug of tea.

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