Nutrient Management for Harmful Algal Blooms: The Importance of Nitrogen and Micronutrients in the Great Lakes
Managing harmful algal blooms in the Great Lakes requires understanding the roles of nitrogen, phosphorus, and micronutrients, emphasizing a comprehensive approach beyond just phosphorus reduction.
To effectively reduce the occurrence, spread, and toxicity of harmful algal blooms (HABs), it's essential to understand what drives algae growth, how toxins are produced, and why certain types of phytoplankton become dominant. While nitrogen (N) and phosphorus (P) are key nutrients that support primary production, micronutrients are also important because they help activate the enzymes needed for quick growth and toxin production. The levels of both macro- and micronutrients can influence which types of cyanobacteria thrive in the environment, ultimately shaping the composition and functionality of the entire community.
Efforts to manage HABs in the Great Lakes have primarily centered on reducing phosphorus inputs, as excessive phosphorus is known to contribute to algal growth. However, recent research has revealed that when nitrogen is added and alters the ideal nitrogen-to-phosphorus (N:P) ratio, this can lead to an increase in the harmful algae Microcystis aeruginosa, along with a rise in the concentration of its associated toxin, microcystin.
Using a nutrient enrichment experimental design, USGS researchers are working to assess the role of ammonium, phosphate, and micronutrients (Fe, Mn, Mo, Ni, and Zn) on growth, toxicity and nearshore phytoplankton community composition to tease out role these constituents have in driving HABs in the Great Lakes. Recent study results showed that the composition of phytoplankton communities and their toxicity were greatly influenced by metals and nitrogen, even when phosphorus levels were low. While metals changed the community composition and potentially affected growth, the increase in toxicity was primarily due to changes in nitrogen availability. This study is part of a broader effort to assess how lake-scale management strategies aimed at preventing HABs could impact phytoplankton communities. Similar to other research, this study reinforces the idea that managing phosphorus alone may not produce the desired results in addressing HABs.
While reducing phosphorus is still a key part of managing HABs in the Great Lakes, there is increasing evidence that nitrogen and micronutrients also plays an important role in how these blooms develop, especially concerning toxin production. As a result, it is essential to take a more comprehensive approach that includes management strategies for both nitrogen and phosphorus, as well as attention to micronutrient availability, to effectively manage HABs.
This study was supported by the USGS Ecosystems Mission Area, through the Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and the U.S. EPA Great Lakes Restoration Initiative.
Managing harmful algal blooms in the Great Lakes requires understanding the roles of nitrogen, phosphorus, and micronutrients, emphasizing a comprehensive approach beyond just phosphorus reduction.
To effectively reduce the occurrence, spread, and toxicity of harmful algal blooms (HABs), it's essential to understand what drives algae growth, how toxins are produced, and why certain types of phytoplankton become dominant. While nitrogen (N) and phosphorus (P) are key nutrients that support primary production, micronutrients are also important because they help activate the enzymes needed for quick growth and toxin production. The levels of both macro- and micronutrients can influence which types of cyanobacteria thrive in the environment, ultimately shaping the composition and functionality of the entire community.
Efforts to manage HABs in the Great Lakes have primarily centered on reducing phosphorus inputs, as excessive phosphorus is known to contribute to algal growth. However, recent research has revealed that when nitrogen is added and alters the ideal nitrogen-to-phosphorus (N:P) ratio, this can lead to an increase in the harmful algae Microcystis aeruginosa, along with a rise in the concentration of its associated toxin, microcystin.
Using a nutrient enrichment experimental design, USGS researchers are working to assess the role of ammonium, phosphate, and micronutrients (Fe, Mn, Mo, Ni, and Zn) on growth, toxicity and nearshore phytoplankton community composition to tease out role these constituents have in driving HABs in the Great Lakes. Recent study results showed that the composition of phytoplankton communities and their toxicity were greatly influenced by metals and nitrogen, even when phosphorus levels were low. While metals changed the community composition and potentially affected growth, the increase in toxicity was primarily due to changes in nitrogen availability. This study is part of a broader effort to assess how lake-scale management strategies aimed at preventing HABs could impact phytoplankton communities. Similar to other research, this study reinforces the idea that managing phosphorus alone may not produce the desired results in addressing HABs.
While reducing phosphorus is still a key part of managing HABs in the Great Lakes, there is increasing evidence that nitrogen and micronutrients also plays an important role in how these blooms develop, especially concerning toxin production. As a result, it is essential to take a more comprehensive approach that includes management strategies for both nitrogen and phosphorus, as well as attention to micronutrient availability, to effectively manage HABs.
This study was supported by the USGS Ecosystems Mission Area, through the Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and the U.S. EPA Great Lakes Restoration Initiative.