Eutrophication: Time to Adjust Expectations

Abstract

D. J. Conley et al. (“Controlling eutrophication: Nitrogen and phosphorus,” Policy Forum, 20 February, p. [1014][1]) advocate a shift in strategies to control eutrophication of aquatic systems. We agree that the best hope for success rests with strategies couched in a systems perspective and founded on an understanding of interactions among biogeochemical cycles. Current efforts to control eutrophication focus on repairing past damage, with systems expected to return to a desired state after obvious stressors are reduced. One approach is to restrict nutrient inputs to waterbodies that are declared impaired by limiting total maximum daily loads. Although costly, managing anthropogenic loads of macronutrients represents an essential, sensible, and feasible strategy for controlling eutrophication and reversing its effects. Increased loads of nutrients drive, support, or enable eutrophication. Reducing loads of macronutrients, including simultaneous reductions for nitrogen and phosphorus, may not yield desired responses. Beyond lags due to “legacy loads,” systems may not return to undamaged states along desired trajectories if they have entered alternative stable states or baseline conditions have shifted ([ 1 ][2]–[ 3 ][3]). For example, ocean acidification may prevent corals from regaining ascendancy on reefs, and impacts from overfishing may cascade through trophic webs to create stable but undesirable assemblages of consumers and producers. In such cases, reversing eutrophication may require restoration of habitats, repair of trophic webs, or relatively drastic projects that remove accumulated effects and thus shift systems toward previous states. In some cases, our best efforts may not produce systems that are structurally identical to a previous, desired state, so we will have to settle for restoring dynamic functions that consistently yield desired services ([ 1 ][2], [ 2 ][4]). Sustainable control of eutrophication in aquatic systems requires all stakeholders to acknowledge our inability to predict the exact trajectory followed by any particular ecosystem in response to management interventions, including reduced loads of nitrogen and phosphorus. Stakeholders can foster success by embracing an adaptive approach supported by monitoring that evaluates alternative actions and endpoints, promotes continual learning, and fosters progressive improvement ([ 4 ][5]). 1. [↵][6]1. C. S. Holling , Ann. Rev. Ecol. Sys. 4, 1 (1973). [OpenUrl][7][CrossRef][8] 2. [↵][9]1. C. M. Duarte, 2. D. J. Conley, 3. J. Carstensen, 4. M. Sanchez-Camacho , Estuaries Coasts 32, 29 (2009). [OpenUrl][10][CrossRef][11][Web of Science][12] 3. [↵][13]1. A. V. Norstrom, 2. M. Nystrom, 3. J. Lokrantz, 4. C. Folke , Mar. Ecol. Prog. Ser. 376, 295 (2009). [OpenUrl][14][CrossRef][15][Web of Science][16] 4. [↵][17]1. C. S. Holling , Adaptive Environmental Assessment and Management (Wiley, New York, 1978). [1]: /lookup/doi/10.1126/science.1167755 [2]: #ref-1 [3]: #ref-3 [4]: #ref-2 [5]: #ref-4 [6]: #xref-ref-1-1 View reference 1 in text [7]: {openurl}?query=rft.jtitle%253DAnn.%2BRev.%2BEcol.%2BSys.%26rft.volume%253D4%26rft.spage%253D1%26rft_id%253Dinfo%253Adoi%252F10.1146%252Fannurev.es.04.110173.000245%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [8]: /lookup/external-ref?access_num=10.1146/annurev.es.04.110173.000245&link_type=DOI [9]: #xref-ref-2-1 View reference 2 in text [10]: {openurl}?query=rft.jtitle%253DEstuaries%2BCoasts%26rft.volume%253D32%26rft.spage%253D29%26rft_id%253Dinfo%253Adoi%252F10.1007%252Fs12237-008-9111-2%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [11]: /lookup/external-ref?access_num=10.1007/s12237-008-9111-2&link_type=DOI [12]: /lookup/external-ref?access_num=000262504600003&link_type=ISI [13]: #xref-ref-3-1 View reference 3 in text [14]: {openurl}?query=rft.jtitle%253DMar.%2BEcol.%2BProg.%2BSer.%26rft.volume%253D376%26rft.spage%253D295%26rft_id%253Dinfo%253Adoi%252F10.3354%252Fmeps07815%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [15]: /lookup/external-ref?access_num=10.3354/meps07815&link_type=DOI [16]: /lookup/external-ref?access_num=000263999900024&link_type=ISI [17]: #xref-ref-4-1 View reference 4 in text