Phosphorus Mitigation to Control River Eutrophication: Murky Waters, Inconvenient Truths, and “Postnormal” Science
TL;DR: A case is argued for a more holistic approach to eutrophication management that includes more sophisticated regime-based nutrient criteria and considers other nutrient and pollutant controls and river restoration to promote more resilient water quality and ecosystem functioning along the land-freshwater continuum.
Abstract: This commentary examines an "inconvenient truth" that phosphorus (P)-based nutrient mitigation, long regarded as the key tool in eutrophication management, in many cases has not yet yielded the desired reductions in water quality and nuisance algal growth in rivers and their associated downstream ecosystems. We examine why the water quality and aquatic ecology have not recovered, in some case after two decades or more of reduced P inputs, including (i) legacies of past land-use management, (ii) decoupling of algal growth responses to river P loading in eutrophically impaired rivers; and (iii) recovery trajectories, which may be nonlinear and characterized by thresholds and alternative stable states. It is possible that baselines have shifted and that some disturbed river environments may never return to predisturbance conditions or may require P reductions below those that originally triggered ecological degradation. We discuss the practical implications of setting P-based nutrient criteria to protect and improve river water quality and ecology, drawing on a case study from the Red River Basin in the United States. We conclude that the challenges facing nutrient management and eutrophication control bear the hallmarks of "postnormal" science, where uncertainties are large, management intervention is urgently required, and decision stakes are high. We argue a case for a more holistic approach to eutrophication management that includes more sophisticated regime-based nutrient criteria and considers other nutrient and pollutant controls and river restoration (e.g., physical habitat and functional food web interactions) to promote more resilient water quality and ecosystem functioning along the land-freshwater continuum.
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TL;DR: This study examined the drivers of legacy P at the watershed scale, specifically in relation to the physical cascades and biogeochemical spirals of P along the continuum from soils to rivers and lakes and via surface and subsurface flow pathways.
Abstract: The water quality response to implementation of conservation measures across watersheds has been slower and smaller than expected. This has led many to question the efficacy of these measures and to call for stricter land and nutrient management strategies. In many cases, this limited response has been due to the legacies of past management activities, where sinks and stores of P along the land-freshwater continuum mask the effects of reductions in edge-of-field losses of P. Accounting for legacy P along this continuum is important to correctly apportion sources and to develop successful watershed remediation. In this study, we examined the drivers of legacy P at the watershed scale, specifically in relation to the physical cascades and biogeochemical spirals of P along the continuum from soils to rivers and lakes and via surface and subsurface flow pathways. Terrestrial P legacies encompass prior nutrient and land management activities that have built up soil P to levels that exceed crop requirements and modified the connectivity between terrestrial P sources and fluvial transport. River and lake P legacies encompass a range of processes that control retention and remobilization of P, and these are linked to water and sediment residence times. We provide case studies that highlight the major processes and varying timescales across which legacy P continues to contribute P to receiving waters and undermine restoration efforts, and we discuss how these P legacies could be managed in future conservation programs.
726 citations
Cites background from "Phosphorus Mitigation to Control Ri..."
...During the last decade, it has become apparent that many watershed-based conservation programs have failed to deliver improvements in water quality within timescales predicted by watershed managers and scientists ( Jarvie et al., 2013; Meals et al., 2010; Mulla et al., 2008)....
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...…and Peter Kleinman During the last decade, it has become appar-ent that many watershed-based conservation programs have failed to deliver improvements in water quality within timescales predicted by watershed managers and scientists ( Jarvie et al., 2013; Meals et al., 2010; Mulla et al., 2008)....
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TL;DR: Four French research institutes were mandated to produce a critical scientific analysis on the latest knowledge of the causes, mechanisms, consequences and predictability of eutrophication phenomena and the methodology and the main findings are provided.
521 citations
TL;DR: The suite of current mitigation strategies and the potential options for adapting and optimizing them in a world facing increasing human population pressure and climate change are examined.
426 citations
TL;DR: A review of river restoration can be found in this article, where the authors critically examine how contemporary practitioners approach river restoration and challenges for implementing restoration, which include clearly identified objectives, holistic understanding of rivers as ecosystems, and the role of restoration as a social process.
Abstract: River restoration is one of the most prominent areas of applied water-resources science. From an initial focus on enhancing fish habitat or river appearance, primarily through structural modification of channel form, restoration has expanded to incorporate a wide variety of management activities designed to enhance river process and form. Restoration is conducted on headwater streams, large lowland rivers, and entire river networks in urban, agricultural, and less intensively human-altered environments. We critically examine how contemporary practitioners approach river restoration and challenges for implementing restoration, which include clearly identified objectives, holistic understanding of rivers as ecosystems, and the role of restoration as a social process. We also examine challenges for scientific understanding in river restoration. These include: how physical complexity supports biogeochemical function, stream metabolism, and stream ecosystem productivity; characterizing response curves of different river components; understanding sediment dynamics; and increasing appreciation of the importance of incorporating climate change considerations and resiliency into restoration planning. Finally, we examine changes in river restoration within the past decade, such as increasing use of stream mitigation banking; development of new tools and technologies; different types of process-based restoration; growing recognition of the importance of biological-physical feedbacks in rivers; increasing expectations of water quality improvements from restoration; and more effective communication between practitioners and river scientists.
419 citations
TL;DR: In this paper, the authors discuss the role of nitrogen and phosphorus in the degradation of rivers and streams in many parts of the world, including the USA and Canada, and their role in this process.
Abstract: Flowing waters receive substantial nutrient inputs, including both nitrogen (N) and phosphorus (P), in many parts of the world. Eutrophication science for rivers and streams has unfortunately lagge...
398 citations
Cites background from "Phosphorus Mitigation to Control Ri..."
...It will be crucial to examine the speed with which eutrophic flowing waters respond to N and P loading controls and the degree to which hysteresis effects can be expected to occur during the eutrophication recovery process (Jarvie et al. 2013)....
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References
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University of Michigan1, College of William & Mary2, McGill University3, Western Washington University4, Arizona State University5, Imperial College London6, University of Minnesota7, Swedish University of Agricultural Sciences8, Stanford University9, Centre national de la recherche scientifique10, United States Geological Survey11, University of British Columbia12, Columbia University13
TL;DR: It is argued that human actions are dismantling the Earth’s ecosystems, eliminating genes, species and biological traits at an alarming rate, and the question of how such loss of biological diversity will alter the functioning of ecosystems and their ability to provide society with the goods and services needed to prosper is asked.
Abstract: The most unique feature of Earth is the existence of life, and the most extraordinary feature of life is its diversity. Approximately 9 million types of plants, animals, protists and fungi inhabit the Earth. So, too, do 7 billion people. Two decades ago, at the first Earth Summit, the vast majority of the world's nations declared that human actions were dismantling the Earth's ecosystems, eliminating genes, species and biological traits at an alarming rate. This observation led to the question of how such loss of biological diversity will alter the functioning of ecosystems and their ability to provide society with the goods and services needed to prosper.
5,244 citations
"Phosphorus Mitigation to Control Ri..." refers background in this paper
..., 2007); complex and lagged ecological responses arising from multiple (physical, chemical, and biological) stressors and feedbacks that make it diffi cult to diff erentiate the impacts of nutrient reductions (Ormerod et al., 2010; Cardinale et al., 2012); a range of “complicating factors” with increasing scale from the fi eld to the watershed, including the confounding eff ects of multiple and complex P sources (Withers et al....
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...…and biological) stressors and feedbacks that make it diffi cult to diff erentiate the impacts of nutrient reductions (Ormerod et al., 2010; Cardinale et al., 2012); a range of “complicating factors” with increasing scale from the fi eld to the watershed, including the confounding eff ects…...
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TL;DR: In this article, a new type of science called post-normal science is proposed to cope with many uncertainties in policy issues of risk and the environment, which can provide a path to the democratization of science, and also a response to the current tendencies to post-modernity.
3,306 citations
TL;DR: In this paper, the authors review emerging ways to link theory to observation, and conclude that although, field observations can provide hints of alternative stable states, experiments and models are essential for a good diagnosis.
Abstract: Occasionally, surprisingly large shifts occur in ecosystems. Theory suggests that such shifts can be attributed to alternative stable states. Verifying this diagnosis is important because it implies a radically different view on management options, and on the potential effects of global change on such ecosystems. For instance, it implies that gradual changes in temperature or other factors might have little effect until a threshold is reached at which a large shift occurs that might be difficult to reverse. Strategies to assess whether alternative stable states are present are now converging in fields as disparate as desertification, limnology, oceanography and climatology. Here, we review emerging ways to link theory to observation, and conclude that although, field observations can provide hints of alternative stable states, experiments and models are essential for a good diagnosis.
2,464 citations
"Phosphorus Mitigation to Control Ri..." refers background in this paper
...Transitions from one stable state to another in aquatic systems (a “regime shift ”) is oft en induced by interactions between internal ecosystem processes/feedbacks and external drivers (Scheff er and Carpenter, 2003)....
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TL;DR: It will be important to resolve ongoing debates about the optimal design of nutrient loading controls as a water quality management strategy for estuarine and coastal marine ecosystems.
Abstract: Cultural eutrophication has become the primary water quality issue for most of the freshwater and coastal marine ecosystems in the world. However, despite extensive research during the past four to five decades, many key questions in eutrophication science remain unanswered. Much is yet to be understood concerning the interactions that can occur between nutrients and ecosystem stability: whether they are stable or not, alternate states pose important complexities for the management of aquatic resources. Evidence is also mounting rapidly that nutrients strongly influence the fate and effects of other non-nutrient contaminants, including pathogens. In addition, it will be important to resolve ongoing debates about the optimal design of nutrient loading controls as a water quality management strategy for estuarine and coastal marine ecosystems.
1,638 citations
"Phosphorus Mitigation to Control Ri..." refers background in this paper
...For watershed management, P is regarded as the primary limiting nutrient for nuisance algal growth in freshwaters (Smith and Schindler, 2009), and over the last 40 years, mitigating P inputs from wastewater (point) and agricultural (nonpoint) sources has been adopted as the main watershed…...
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TL;DR: In this article, the authors brought together agricultural and limnological expertise to prioritize watershed management practices and remedial strategies to mitigate nonpoint-source impacts of agricultural P. The main issues facing the establishment of economically and environmentally sound P management systems are the identification of soil P levels that are of environmental concern; targeting specific controls for different water quality objectives within watersheds; and balancing economic with environmental values.
Abstract: The accelerated eutrophication of most freshwaters is limited by P inputs. Nonpoint sources of P in agricultural runoff now contribute a greater portion of freshwater inputs, due to easier identification and recent control of point sources. Although P management is an integral part of profitable agrisystems, continued inputs of fertilizer and manure P in excess of crop requirements have led to a build-up of soil P levels, which are of environmental rather than agronomic concern, particularly in areas of intensive crop and livestock production. Thus, the main issues facing the establishment of economically and environmentally sound P management systems are the identification of soil P levels that are of environmental concern; targeting specific controls for different water quality objectives within watersheds; and balancing economic with environmental values. In developing effective options, we have brought together agricultural and limnological expertise to prioritize watershed management practices and remedial strategies to mitigate nonpoint-source impacts of agricultural P. Options include runoff and erosion control and P-source management, based on eutrophic rather than agronomic considerations. Current soil test P methods may screen soils on which the aquatic bioavailability of P should be estimated. Landowner options to more efficiently utilize manure P include basing application rates on soil vulnerability to P loss in runoff, manure analysis, and programs encouraging manure movement to a greater hectareage. Targeting source areas may be achieved by use of indices to rank soil vulnerability to P loss in runoff and lake sensitivity to P inputs.
1,425 citations
"Phosphorus Mitigation to Control Ri..." refers background in this paper
...For watershed management, P is regarded as the primary limiting nutrient for nuisance algal growth in freshwaters (Smith and Schindler, 2009), and over the last 40 years, mitigating P inputs from wastewater (point) and agricultural (nonpoint) sources has been adopted as the main watershed management tool to control freshwater eutrophication (Daniel et al., 1994; Sharpley et al., 1994)....
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...…growth in freshwaters (Smith and Schindler, 2009), and over the last 40 years, mitigating P inputs from wastewater (point) and agricultural (nonpoint) sources has been adopted as the main watershed management tool to control freshwater eutrophication (Daniel et al., 1994; Sharpley et al., 1994)....
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