Iron sulfide mineral may help lock phosphorus in lake sediments
A Concordia University study found that mackinawite, an iron sulfide mineral formed in oxygen-depleted sediments, can bind phosphorus even when other phosphorus-trapping minerals become unstable. This previously overlooked process could help explain why some lakes still suffer algal blooms after phosphorus reductions. The findings may improve predictions of how freshwater ecosystems recover from nutrient pollution.
Mackinawite forms naturally in lake beds where oxygen is scarce, a product of iron and sulfur chemistry in those deep layers. Unlike other minerals that release phosphorus under changing conditions, mackinawite appears to hold onto it more reliably, offering a stable sink for the nutrient.
This mechanism was not previously accounted for in models of lake nutrient cycling. Because phosphorus fuels algal growth, understanding where it remains trapped—and where it does not—matters for predicting how waterways respond to cleanup efforts. The finding gives researchers a new variable to consider when forecasting recovery timelines for lakes affected by nutrient pollution.
This discovery could sharpen how scientists and water managers assess lake recovery after phosphorus reduction programs. If mackinawite's role is confirmed, predictions of algal bloom persistence may become more accurate, potentially guiding where cleanup resources are directed. Communities reliant on lakes for drinking water, recreation, or fishing could benefit from better-informed restoration timelines, though the practical effects will depend on further research into how widespread this mineral's influence actually is.