Huo, S., He, Z., Ma, C., Zhang, H., Xi, B., Xia, X., Xu Y., Wu, F. (2019). Stricter nutrient criteria are required to mitigate the impact of climate change on harmful cyanobacterial blooms. Journal of Hydrology, 569(8), 698–704. https://doi.org/10.1016/j.jhydrol.2018.12.030
There are usually hundreds of boats gathering in Lake Hopatcong for Independence Day, but this year swimmers, boaters, and kayakers were warned to stay onshore due to a harmful algal bloom. At this lake and others in neighboring states, the algae reached levels greater than it had in the past 17 years. Researchers from Beijing predict these blooms to be more common as climate change progresses, but are also developing models to help managers prevent them.
News reports frame the cause of the algal bloom as the perfect storm of short, intense rainfall followed by high temperatures, leaving some to think that the bloom is a random act of nature. In reality, these algal blooms are tied with our actions. But this is good news– it means we have a chance of future prevention.
Behind the Bloom
Harmful algal blooms can occur when surface runoff filled with nutrients empties into a body of water, such as a lake. These nutrients, from leaking septic systems, stormwater, or agricultural fields can make the lake eutrophic or “well-nourished”. High temperatures help the process along, making the water warmer at a deeper depth, which helps the algal bloom to proliferate.
People who went swimming in the lake emerged with rashes, but harmful algal blooms can also cause respiratory problems or gastrointestinal problems if ingested. That’s because of the abundant blue-green algae, or cyanobacteria, that produce cytotoxins. The NJ Department of Environmental Protection cites Microcystis and Anabaena as the common culprits, which are not true algae but carry a resemblance.
Not only does the harmful algal bloom affect would-be swimmers, it can also deplete the oxygen within the lake. At its highest severity, the depleted oxygen can kill fish and other aquatic life.
The Phosphorus Problem
Predictions of climate change forecast more extreme temperatures and extreme weather events, both of which could work together to bring about more frequent harmful algal blooms. This means that lakes which have never experienced a harmful algal bloom before may be in danger of one from climate change alone.
But there’s a part of the equation that people can control: the nutrient inputs into the lakes. The researchers focused on this aspect, among others, in their models. They wanted to define the nutrient criteria: the amount of nutrients that the lake could take on before it becomes a problem.
By measuring the content of Chlorophyll a in response to nitrogen and phosphorus over the years of a warming climate, the researchers made model predictions for the future. In their study of lakes and reservoirs in China, they found that phosphorus was in shorter supply than nitrogen– and this also generally applies to the freshwater bodies of the northeast US. This means that any added phosphorus can have a big impact.
By limiting phosphorus input, they reasoned, more algal blooms can be suppressed as the climate changes.
The role of phosphorus in algal blooms and eutrophication is not a new discovery. In the 1970’s, there was a movement to ban phosphates from laundry detergents for this very reason, and now laws are in place to keep phosphates out of detergents. But there still remains phosphorus inputs from fertilizers and erosion, which can leach into the lakes from improper stormwater design.
Authorities say if the weather stays on course, the algal blooms can continue through the summer. If all we can do it wait, this is a good time to plan for it not to happen again. But more than that, it takes a shift in attitude and buy-in from all stakeholders to see these lakes both as places of recreation, but also pieces of nature to be conserved.
Feature Image: Algae near Three Sister Islands, Lake Hopatcong, NJ. Photo by Abigail Bezrutczyk