Bloom cycles hold the key to cleaner lakes, study finds

Cyanobacterial blooms, those green mats that spread across summer lake surfaces—do more than just spoil the scenery. New research from Anhui University reveals how the rise and fall of these blooms can trigger a hidden recycling system that keeps polluted lakes trapped in poor condition long after the visible bloom has vanished.

In a controlled simulation of Lake Chaohu, one of China’s most eutrophic lakes, researchers led by Haojie Yin and Tao Huang tracked how algae growth and decay changed the composition of dissolved organic matter (DOM) together with the movement of nitrogen and phosphorus between sediments and overlying water. Their microcosm experiment followed a full 52‑day bloom cycle, capturing the delicate balance between microbial activity, oxygen levels, and nutrient exchanges that drive internal water quality.

The team discovered that during bloom growth, protein‑rich organic matter derived from algae accumulated at the water surface and promoted the release of phosphorus from sediments. As the bloom declined, decaying cyanobacteria released even more complex organic compounds, fueling microbial degradation and further stirring nutrient release. These processes together formed a feedback loop that sustained nutrient availability even when external pollution sources were absent.

Fluorescence measurements identified four key types of DOM, two humic‑like and two protein‑like components—that shifted in relative abundance through the bloom cycle. During the peak stage, protein‑like substances dominated, while humic‑like materials recovered as decomposition progressed. This changing fingerprint revealed how bloom residues directly influence the chemical and biological behavior of nutrients below.

According to the study, phosphorous release reached its highest rate during bloom outbreaks, mainly through mineralization of organic phosphorus and transformation of iron‑ and aluminum‑bound forms. Ammonium, another nutrient that supports algal regrowth, was also released from sediments through organic nitrogen breakdown. Together, these flows create self‑feeding eutrophication that can persist for months.

The researchers suggest that managing harmful algal blooms requires more than curbing fertilizer runoff. Controlling internal nutrient loading may be equally essential. Strategies such as dredging accumulated sediments, removing surface scums promptly, or encouraging oxygenation at the sediment‑water boundary could weaken the internal feedback that sustains blooms.

“This study provides new insight into how algal life cycles interact with sediment chemistry to lock lakes into a polluted state,” said Tao Huang. “Breaking that internal cycle is the next step toward cleaner, healthier freshwater ecosystems.” 

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Journal Reference: Yin, H., Bao, Y., Huang, T. et al. Effects of cyanobacterial growth and decline on dissolved organic matter and endogenous nutrients release at the sediment–water interface. Carbon Res. 4, 40 (2025). https://doi.org/10.1007/s44246-025-00203-x  

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About Carbon Research

The journal Carbon Research is an international multidisciplinary platform for communicating advances in fundamental and applied research on natural and engineered carbonaceous materials that are associated with ecological and environmental functions, energy generation, and global change. It is a fully Open Access (OA) journal and the Article Publishing Charges (APC) are waived until Dec 31, 2025. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon functions around the world to deliver findings from this rapidly expanding field of science. The journal is currently indexed by Scopus and Ei Compendex, and as of June 2025, the dynamic CiteScore value is 15.4.

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