Letter to the Editor pubs.acs.org/est
Nitrogen is Not a ‘House of Cards’
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there is evidence that high N:P ratios may lead to increased toxin production among strains.4 This problem may also be exacerbated by increasing use of N fertilizers in the form of urea.5 Is N a house of cards? Only if the implication was that if we do not do anything about it, we are in a lot of trouble.
ear Professor Schindler and others, In your recent publication “Reducing Phosphorus to Curb Lake Eutrophication is a Success” (http://pubs.acs.org/doi/abs/10. 1021/acs.est.6b02204)1 you provided an historical perspective and excellent context for why we should manage P in lakes. However, your title, recommendations, and abstract were misleading and contradictory. While you recognize the need to control N, (i.e., Box 2), in your abstract you referred to P as a brick wall while N was a “house of cards”. This comment might be perceived as inflammatory to portions of our scientific community who have advocated for control of both P and N, but you later contradicted yourselves when you suggested ‘that increasing anthropogenic emissions of nitrogen must be controlled’ as well. Furthermore, to claim that reducing P has been a “success” was a vast overstatement. The frequency and duration of harmful algal blooms due to excess nutrients is increasing,2 not decreasing, so we should not be congratulating ourselves on a job well done just yet. One of the main reasons for a lack of success has to do with the fact that much of the N and P gets into freshwater via nonpoint sources. In your article, you equate managing WWTPs to managing lakes, but it is much more complicated. P discharge limits for WWTPs worked better in the 70s and 80s when a much higher proportion of nutrients came from point sources, but new approaches are needed to address the substantial and growing threat from agricultural nonpoint source pollution, which is a significant N source. We need to manage all of our freshwater resources, including groundwaters, and the nutrient sources that are enriching them. Thousands of communities in the U.S. Upper Midwest and elsewhere are near or above nitrate standards for drinking water and managing nearby lakes to remove P will absolutely not fix this problem. Controlling both of these nutrients is common sense from multiple perspectives and that is why the U.S. EPA, the EU, and WWTPs are already doing it. BMPs such as buffer strips near waterways are effective for removing both nutrients. New technologies in WWTPs, such as facilitation of anammox performing microbes, rather than denitrifying bacteria, are making N removal much less expensive due to a net energy recovery.3 In any ecosystem, including ELA, organisms living in the same systems can be limited by multiple nutrients leading to complex responses when presented with several resources in excess. If the work in Lake 226 had included a treatment where only P was added (and not N), would you have observed as strong a response as you did? I doubt it. Even if you are correct that N is not limiting to production in lakes, you are essentially arguing for a repeat of the ELA experiment across multiple continents. In the meantime, continuing to add N will serve the purpose of priming the pump for more intense blooms when P is available. Lastly, there is growing evidence that harmful algal blooms are actually more “harmful” when there is an excess of N relative to P, which seems to trivialize the idea of a most limiting nutrient. Microcystin is an N-rich polypeptide and © XXXX American Chemical Society
James B. Cotner*
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Department of Ecology, Evolution and Behavior University of Minnesota St. Paul, Minnesota 55108, United States
AUTHOR INFORMATION
Corresponding Author
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[email protected]. Notes
The author declares no competing financial interest.
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REFERENCES
(1) Schindler, D. W.; Carpenter, S. R.; Chapra, S. C.; Hecky, R. E.; Orihel, D. M. Reducing phosphorus to curb lake eutrophication is a success. Environ. Sci. Technol. 2016, 50, 8923. (2) Hudnell, H. K. The state of US freshwater harmful algal blooms assessments, policy and legislation. Toxicon 2010, 55, 1024−1034. (3) Kartal, B.; Kuenen, J. G.; Van Loosdrecht, M. C. M. Sewage treatment with anammox. Science 2010, 328, 702−703. (4) Van de Waal, D. B.; Verspagen, J. M.; Lürling, M.; Van Donk, E.; Visser, P. M.; Huisman, J. The ecological stoichiometry of toxins produced by harmful cyanobacteria: An experimental test of the carbon-nutrient balance hypothesis. Ecology Letters 2009, 12, 1326−35. (5) Donald, D. B.; Bogard, M. J.; Finlay, K.; Leavitt, P. R. Comparative effects of urea, ammonium, and nitrate on phytoplankton abundance, community composition, and toxicity in hypereutrophic freshwaters. Limnol. Oceanogr. 2011, 56, 2161−2175.
Received: September 26, 2016 Revised: October 28, 2016 Accepted: December 9, 2016
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DOI: 10.1021/acs.est.6b04890 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
