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NUTRIENTMANAGEMENTRESEARCH INSIGHTS FOR DECISION MAKERSNovember 2017

CONTENTS

2 Acknowledgements

3 Preface

4 Executive Summary

6 Eutrophication: A Persistent Challenge

8 The History of Nutrient Management in North America

10 State-of-the-Science: Nutrient Mechanisms

Nutrient Sources and Legacies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Nutrient Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

14 Implications of the Science for Adaptive Management

Establishing and Attaining Watershed-based Goals . . . . . . . . . . . . . . . . . .15

Linking Management Practices across Spatial and Temporal Scales . . .16

The Need for New Data Collection and Monitoring Approaches . . . . . . . 17

18 Evolving Nutrient Management Paradigms: What do we Need to Know Next?

20 Conclusion

21 References

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NUTRIENT MANAGEMENT2017 Research Insights for Decision Makers

ACKNOWLEDGEMENTS

Dr. Nandita Basu

University of Waterloo

Waterloo, Ontario, Canada

Dr. Indrajeet ChaubeyPurdue University

West Lafayette, Illinois, USA

Darryl FinniganOntario Ministry of Agriculture, Food and Rural Aff airs

Guelph, Ontario, Canada

Dr. Merrin Macrae University of Waterloo


Dr. Mohamed MohamedOntario Ministry of Environment and Climate Change

Toronto, Ontario, Canada

Dr. Deanna Osmond North Carolina State University

Raleigh, North Carolina, USA

Keith ReidAgriculture and Agri-Food Canada

Guelph, Ontario, Canada

Dr. Dave Rudolph University of Waterloo


Dr. Douglas R. Smith United States Department of Agriculture

Temple, Texas, USA

Dr. Mike Stone University of Waterloo


This white paper is built upon information provided during an expert workshop held on March 29-30, 2016, as well as in subsequent discussions convened via teleconference and email correspondence.

Canadian Water Network would like to acknowledge the important contribution made by each of these experts and their leadership in these discussions and thank them for sharing their time and expertise.

The information in this report is based on views expressed by the respective contributors and does not necessarily represent the views of their employers.

Lead Writer

Alex H.S. ChikCanadian Water Network


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CANADIAN WATER NETWORK

Canadian Water Network convened an expert workshop in March, 2016 to update Canada’s conceptual model of nutrient source and transport. The experts’ discussion, as well as the research cited, informed the insights that are presented in this white paper, which has been written to support those who make decisions about nutrient management actions.

During the workshop, discussion focused on phosphorus as a primary limiting macronutrient in freshwater watersheds. However, the implications of nutrient legacies and event-based loading to nutrient management practices are similarly applicable to nitrogen and other nutrients that may also be infl uential and/or limiting to overall ecosystem conditions. Some studies (e.g., Harpole et al., 2011) have suggested the potential for nitrogen and phosphorus to act as co-limiting nutrients for primary production, meaning that the inputs of one nutrient may have implications for the cycling of the other.

Whereas the workshop discussions focused on land-based impacts to freshwater systems and phosphorus as a key factor, the infl uence of nitrogen on estuarine and marine environments, which are often found at the confl uence of multiple freshwater watersheds, should be noted (Conley et al. 2009; Paerl, 2009; Xu, Paerl, Qin, Zhu, & Gao, 2010).

PREFACE

Harmful algal blooms are a pressing environmental, economic and public health concern in the Great Lakes, Lake Winnipeg, Lac St. Charles, Lake Simcoe and other water bodies. These blooms are fed by excess nutrients in the water, and can impact drinking water treatment, commercial fi sheries and tourism. In 2011 and 2014, toxic algal blooms in Lake Erie caused nearly $71 million and $65 million USD in service interruptions (Bingham, Sinha, & Lupi, 2015).

Government organizations like Environment and Climate Change Canada, the Ontario Ministry of Agriculture, Food and Rural Aff airs, the U.S. Environmental Protection Agency and the U.S. Department of Agriculture are responsible for setting goals, overseeing implementation and monitoring, and evaluating outcomes of nutrient management. Decisions need to be made, and a clear articulation of the current state-of-the-science — including potential limitations and uncertainties that informs those decisions, is vital for their work.

Canadian Water Network is Canada’s trusted broker of research insights for the water sector. When decision makers ask, ‘What does the science say about this?’ we frame what is known and unknown in a way that usefully informs the choices being made.

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EXECUTIVE SUMMARY

“… the challenges facing nutrient management and eutrophication control bear the hallmarks of ‘post normal’ science, where uncertainties are large, management intervention is urgently required, and decision stakes are high.

(Jarvie, Sharpley, Withers, et al., 2013, p. 295)

In March 2016, Canadian Water Network invited a team of leading international scientists to deliberate over two days on the current understanding of nutrient source, fate and transport in freshwater systems. Their discussion informed the insights that Canadian Water Network developed for those who make decisions about nutrient management actions.

Nutrients from activities like farming, wastewater treatment and urban runoff eventually end up in our water bodies, where they impact public health, the environment and the economy. In Canada, point sources of phosphorus have largely been reduced over the past fifty years, and more recent efforts have focused on non-point (i.e. diffuse) sources. However, researchers and practitioners have been finding that the anticipated ecosystem responses to these reductions either have not been fully realized, or have only been temporary, as illustrated by the return of algal blooms to Lake Erie.

Recent research has focused on nutrient legacies in terrestrial and aquatic systems and how they contribute to ecosystem behaviour and responses such as algal blooms. Agriculture comprises the predominant, non-point nutrient source in many watersheds, but rural non-farm sources, urban sources, atmospheric deposition and mobilized nutrients from both diffuse and legacy sources are also contributors. The need to account for and effectively manage diffuse and legacy nutrient sources is critical in the development of effective nutrient management policies and practices.

What are the relevant insights that can be drawn from the evolving science?

— Extreme weather events and preferential transport pathways can dominate phosphorus transport. Transport of particle-associated nutrients is still considered the dominant mechanism of phosphorus loading to water bodies overall. As the frequency and severity of hydrologic events increases, the recognition of the likely significance and dominance of these events with respect to the total loadings to water bodies — either through surface runoff or subsurface preferential pathways — is receiving increased attention. This work is pointing to the fact that the overall efficacy of various management practices may be strongly influenced not by how they address average conditions, but by their ability to manage nutrient fluxes during short-lived, more extreme events.

— Nutrient legacies may be critical to how systems respond to management actions. Nutrients that are already present in the landscape and aquatic ecosystems (for example, in the subsurface and in river and lake beds) as a result of past activities may act as a controlling factor on how systems behave. This may complicate, obscure, or prevent the intended results of nutrient management actions focused only on ongoing inputs or field-based management systems. Nutrient legacies are also increasingly considered one of the main reasons for the failure of management actions to attain intended or sustained results.

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— Timeframes between management actions and ecosystem responses can be very long. The goal of most agricultural nutrient management practices is to retain nutrients in the growing layer, where they can be taken up by plants, thus minimizing their loss to nearby water bodies. Nutrient retention on the landscape can be highly variable and is infl uenced by the type, magnitude, timing and location of application. The timing between land-application of phosphorus and when it arrives at a receiving water body may be short in response to storms or where travel is enhanced by preferential fl ow paths. In other cases, depending on where it accumulates in the system, research suggests that phosphorus may require months to decades to work through a system from land-application to ultimate impact on a water body. This knowledge is infl uencing thinking on how or where success should best be defi ned or measured for nutrient management actions.

— Soluble reactive phosphorus may be a key contributor to algal blooms. Although it comprises a smaller proportion of the total phosphorus load, the occurrence or transport of soluble reactive phosphorus is increasingly being considered an important contributor to impacts like algal blooms. This has brought into more recent focus the need to consider its importance for landscapes with high infi ltration of precipitation or surface runoff , particularly where features like tile drains create preferential pathways for more rapid transport to adjacent rivers and streams. Understanding where there is a high likelihood of soluble reactive phosphorus occurrence or transport could enable improved focus on priority fl uxes in management schemes.

Even as knowledge increases about nutrient transport and impacts to aquatic systems, ongoing research also confi rms the complexities and high degrees of variability inevitable in natural systems. The result is signifi cant uncertainties in predicting how systems will behave in response to management actions. Eff ective nutrient management, while improved by increased knowledge, requires an approach that acknowledges and responds to that reality of complex, watershed-level considerations and an acceptance of inevitable uncertainties and unknowns. This has brought nutrient management squarely into the realm of integrated watershed management, with the need for an eff ective adaptive management approach.

Prioritizing and evaluating the eff ectiveness of nutrient management actions will increasingly focus on how these actions infl uence regional or watershed conditions. Taking a regional or watershed approach will require new monitoring, modeling and management strategies, as well as techniques for integrating observations and predictions across spatial and temporal scales in a way that can meaningfully inform management decisions.

Canadian Water Network sees an increasing need to better integrate and coordinate that science going forward, and to continue to frame what is known and unknown in a way that usefully informs these complex decisions.

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Nutrients from fertilizers, manure from agricultural fields, wastewater treatment plant discharges, and stormwater runoff from urban landscapes are being delivered to surface water bodies through various pathways, which can fuel the growth of nuisance or toxic algal blooms. The decomposition of these algal blooms exhausts dissolved oxygen supplies in the water, which then impacts other aquatic organisms. This process is known as eutrophication.

Eutrophication can negatively impact drinking water quality and safety. A dramatic example is the toxic algal bloom that covered more than 5,000 km2 of the surface of Lake Erie in 2015, leading to a ‘do not drink’ advisory for half a million households in Toledo, Ohio and Pelee Island, Ontario. Reports of nuisance and harmful algal blooms are on the rise across Canada, and communities surrounding water bodies like Lake Winnipeg in Manitoba, Lac St. Charles in Quebec and Lake Simcoe in Ontario are similarly experiencing changes in water quality, beach closures and declining commercial fisheries.

EUTROPHICATION: A PERSISTENT CHALLENGE

Various government-directed nutrient management programs have been implemented in Canada over the past 50 years, but ecosystem responses to nutrient management are seldom immediate or direct, and are often subject to varying degrees of uncertainty. Factors that contribute to the complexity of the problem include:

— Growing global food demands

— Land use changes like urbanization and evolving agricultural practices

— Ever-changing hydrological conditions

— Increased frequency and intensity of hydrological events attributable to climate change

— Coupled nutrient biogeochemical processes with varying, scale-related effects

— Diverse and changing ecosystem responses

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1 Ontario’s Nutrient Management Act (O. Reg 267/03) supersedes municipal by-laws if they address the same subject matter.

In Canada, nutrient management directives are generally designed by regulatory agencies and implemented by practitioners like farmers and land use managers. Regulatory agencies use policy frameworks, regulations and guidelines to establish objectives and the criteria that defi ne approaches as they oversee compliance, all informed by the evolving state-of-the-science.

Federal jurisdiction in Canada is established by the Fisheries Act, implemented by Environment and Climate Change Canada. The Fisheries Act prohibits the deposit of a deleterious substance into waters frequented by fi sh. However, nutrients are not directly called out as a prescribed deleterious substance as defi ned by the Wastewater Systems Effl uent Regulations specifi ed in the Fisheries Act.

Primary responsibility for agricultural nutrient management regulation and enforcement generally falls within the jurisdiction of provincial or territorial agricultural or environmental departments, or a combination of both. Management actions for other non-agricultural water quality impacts attributable to wastewater or urban stormwater discharges vary across provinces and territories. They are typically administered by environmental government departments, including conservation authorities. In the case of the Great Lakes and other boundary waters, both provincial and U.S. state jurisdictions are involved.

Actions targeting improved water quality through nutrient management eff orts are rarely limited to one level of government. Across Canada, programs are implemented at and across multiple levels. In Ontario for example, these include:

— Farm-level nutrient management plans and strategies

— Municipal nutrient management by-laws, such as those implemented in some southwestern Ontario counties1

— Watershed strategies, such as the Lake Simcoe Phosphorus Reduction Strategy and Domestic Action Plans under development for the Lake Erie basin

— Provincial legislation, such as the Ontario Nutrient Management Act (O. Reg 267/03) and the Great Lakes Protection Act (2015)

— International agreements, such as the Great Lakes Agreement between Canada and the U.S.

These directives all share a common intent to improve water quality through nutrient management. However, the objectives and metrics at each level are tailored for diff erent watershed uses, considering diff erent aspects of the science in determining priorities and options.

As nutrient management practices and scientifi c understanding evolve, our policies, practices, tools and metrics will need to be adapted. A clear articulation of the updated state-of-the-science, including potential limitations and uncertainties, will help regulators and practitioners elucidate the questions that are being asked of the science and ascertain the relevance of the science within a decision making context.

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THE HISTORY OF NUTRIENT MANAGEMENT IN NORTH AMERICA

Nutrient Management in Lake Erie

During the 1960s, Lake Erie was declared “dead” due to explosive algal growth and hypoxia that led to a signifi cant decline in native aquatic species. Over the subsequent two decades, total phosphorus loading to chlorophyll a empirical relationships (Vollenweider, 1976) were used to set targets for reversing eutrophication impacts. Clean-up eff orts were focused on priority point sources, including the elimination of phosphate-based detergents, which was estimated to comprise 50% of all phosphorus input to the lake, excluding infl ow from Lake Huron (IJC, 1970).

However, despite meeting the 1978 Great Lakes water quality objectives for annual total phosphorus target load, algal blooms have returned over the last seven years, resulting in signifi cant ecological and economic impacts. Service interruptions during severe events in 2011 and 2014 have been valued at nearly $71 million and $65 million USD (Bingham et al., 2015).

Some studies suggest that nitrogen may be the limiting nutrient for primary production in some environments (e.g. Chaffi n, Bridgeman, & Bade, 2013), while others suggest that more biologically available forms of phosphorus have increased from agricultural non-point sources (Jarvie et al., 2017; Joosse and Baker, 2011; Kane, Conroy, Richards, Baker, & Culver, 2014; Richards, Baker, Cumrine, & Stearns, 2010) and/or from the internal cycling of nutrients (Michalak et al., 2013; Nürnberg, LaZerte, Loh, & Molot, 2013).

Recent models suggest that the scale of nutrient reduction eff orts to achieve lake ecosystem objectives as set out in the Great Lakes Water Quality Agreement 2012, Annex 4 (IJC, 2012) may be substantial. A binational target to reduce phosphorus loading by 40% in Lake Erie has been adopted on the basis of these modeling eff orts (Annex 4 Objectives and Targets Task Team, 2015).

The role of excess nutrients in eutrophication of aquatic ecosystems has been well-demonstrated. Phosphorus has long been and continues to be regarded as the limiting nutrient for primary production in most freshwater systems (Hecky & Kilham, 1988; Howarth & Marino, 2006; Schindler, Carpenter, Chapra, Hecky, & Orihel, 2016). Reducing phosphorus has been the main focus of nutrient management to mitigate water quality impairment over the past half century (see Figure 1) and eff orts to reduce point sources of phosphorus have been applied across the globe (e.g. Carpenter et al. 1998; Scavia et al., 2014; Thornton, Rast, Holland, Jolanki, & Ryding, 1999). Canada was one of the fi rst countries to limit phosphorus in laundry detergents, and has since expanded its regulations to include other detergents (International Joint Commission [IJC], 1972).

Because eff orts have largely focused on reducing inputs from point sources of phosphorus and the relative ease of controlling these sources, non-point (i.e. diff use) sources are accounting for an increasingly larger share of the loading in receiving water bodies (Crowder & Young, 1988; Scavia et al., 2014; Schultz, Gregory, & Engelstag, 1993). As a result, recent nutrient management eff orts have shifted to more comprehensive strategies that address both point and non-point source loadings. However, despite successful phosphorus reduction eff orts from point and non-point sources, anticipated ecological improvements have often not occurred, or have only been temporary (Jarvie, Sharpley, Spears, et al., 2013; Lemke et al., 2011; Sharpley, Kleinman, Flaten, & Buda, 2011).

While it is certain that nutrient enrichment is a major driver of eutrophication and that nutrient reduction in aquatic ecosystems is required for re-establishing former ecosystem states (e.g. Carpenter et al., 1998), controlling these nutrient fl uxes may not be enough. Additional factors (such as complex biogeochemical processes) that are not simply related to nutrient levels and are not fully understood may be impeding successful outcomes. An evolving understanding of the role of other processes in achieving desired outcomes will help decision makers better prioritize management options and identify opportunities to further advance nutrient management.

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• 1960s — Signifi cant declines in water quality are observed in rivers and lakes

• 1970s — Nutrient enrichment is linked to eutrophication

— Research connects phosphorus to water quality and also suggests that controlling nitrogen is important, particularly in estuarine systems

— Government agencies initiate measures to reduce phosphorus from point sources

• 1980s — The World Health Organization issues guidelines for wastewater reuse

— Canada regulates phosphates in laundry detergents

— Remedial Action Plans (RAPs) and lake management plans are developed for areas of concern

• 1990s — We learn more about the seasonal and site-specifi c nature of phosphorus and nitrogen impacts

— Soil phosphorus indices are used to identify agricultural fi elds that are vulnerable to phosphorous loss

— The U.S. Environmental Protection Agency introduces CAFO, a unifi ed strategy for concentrated animal feeding operations

• 2000s — Integrated water resource management and holistic ecosystem approaches are increasingly adopted

— CAFOs are required to conduct phosphorus loss assessment for regulated nutrient applications

— In 2015 a 5,000 km2 harmful algal bloom develops in Lake Erie

— The U.S. Environmental Protection Agency and Environment and Climate Change Canada establish specifi c water quality targets under the the Great Lakes Water Quality Agreement. This includes a 40% reduction target for total phosphorus entering the western and central basins of Lake Erie, and similar targets for selected Lake Erie tributaries.

Figure 1. Nutrient management in North America through the decadesAdapted from Gumbo, 2005; Lory & Nelson, 2015

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STATE-OF-THE-SCIENCE: NUTRIENT MECHANISMS

Determining the relative contributions from various point and non-point sources of different forms of nutrients and their timing of delivery is an active area of research within many watersheds. Significant gains have been made in point source management over the past five decades due to the relative ease of identification, quantification and reduction, as compared to the case of more diffuse, non-point sources. Significant opportunities remain to better understand impacts and control options for non-point sources, and more recent research has been focused on this issue.

Agriculture is assumed to be the predominant nutrient source after urban point sources in many watersheds (Puckett, 1995). However, rural non-farm sources and atmospheric deposition are also contributors of nutrients to aquatic systems (Anderson & Downing, 2006; Yang, Qin, Hu, Luo, & Song, 2007). In some settings, naturally phosphorus rich soils/sediment can be a substantial contributor (Porder, Vitousek, Chadwick, Chamberlain, & Hilley, 2007). There is increasing evidence that these various non-point sources comprise much of the nutrient loads to receiving water bodies and will continue to be the focus of management efforts in the foreseeable future.

Chemical fertilizers and manure containing phosphorus and other nutrients are used in agriculture to support crop growth, but phosphorus retention on the landscape and its uptake by crops is influenced by the type, magnitude, timing and location of application as well as crop growth and harvest factors. When phosphorus is applied in excess of plant demand, the phosphorus not utilized by crops may be mobilized during hydrological events and other landscape disturbances, and transported to receiving water bodies. This non-point source of excess nutrients contributes to eutrophication. The soil solution phosphorus concentrations that are critical for crop growth are approximately one to two orders of magnitude higher than the concentrations asserted to create unacceptable algal growth in surface waters (Daniel, Sharpley, & Lemunyun, 1998). Accordingly, impacts associated with the reduction of non-point source phosphorus, if any, are anticipated to be incremental rather than radical in nature.

Recent efforts have focused on an improved understanding of how, when and in what form phosphorus sources are mobilized, especially when introduced through human activities like fertilizer application. Estimates of nutrient uptake by crops, coupled with attempts to quantify nutrients lost through overland flow, suggest that current estimates are not fully accounting for the fate of all nutrients applied to the landscape. Updated assumptions underlying the elements of nutrient balance may be required, such as nutrient uptake estimates that reflect the adoption of new crop varieties. Increasing attention is being given to estimating phosphorus content stored within sediments, soils and the deeper subsurface that comprise legacy nutrient build-ups or “pools” that have accumulated from past nutrient additions.

The 2015 study by the International Plant Nutrition Institute provides an up-to-date snapshot of the phosphorus present within Ontario cropland soils. Based on soil test phosphorus, 28% of the soils are considered to be at the optimum levels for crop growth while 36% are considered to be below these levels and may respond to added phosphorus. The remaining 36% of tested soils are considered to be at very high or excessive soil test phosphorus, where additional phosphorus application will likely have little if any impact on crop yields. In these soils, the excess phosphorus pool may take as long as a quarter century or more to return to optimum levels for crop yield. While some pools will more readily respond to changes in management practices (e.g., phosphorus losses attributable to surface broadcast averted by subsurface placement of phosphorus), the response of other pools might be much slower (e.g., build-up of phosphorus in soils). Though the effect of phosphorus legacies has long been recognized in aquatic systems themselves (e.g. Carignan & Kalff, 1980; Marsden, 1989), the effect of legacy nutrients on and beneath the adjacent landscapes and their eventual transport to receiving water bodies have only more recently been considered in a significant way.

Nutrient Sources and Legacies

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Nutrient Legacies

Excess phosphorus stored in soils, sediments and biomass may involve a signifi cant lag time in their delivery and impacts to receiving water bodies (Dodd & Sharpley, 2015; Jarvie, Sharpley, Spears, et al., 2013; May, Defew, Bennion, & Kirika, 2012; McDowell and Sharpley, 2001; Meals, Dressing, & Davenport, 2010; Seo & Canale, 1999). Various mechanisms have been postulated based on controlled laboratory and fi eld studies (Hamilton et al., 2012; Haggard & Soerens, 2006; Kleinman et al., 2007; Withers et al., 2009), as well as numerical models to support the nutrient legacy hypotheses (e.g., Basu et al., 2010; Jarvie et al., 2013; Powers et al., 2016).

Accumulations of phosphorus in or directly below fi elds are fairly well-documented, but the amounts and forms of phosphorus stored in toe slope positions, stream beds, stream banks and lake beds remain highly uncertain (Fox, Purvis, & Penn, 2016; Miller et al., 2014; White & Stone, 1996). Time lags for mobilization and transport to receiving water bodies are estimated to last years or decades (Jarvie, Sharpley, Spears, et al., 2013; Sharpley et al., 2013). In agricultural settings, the surface source (i.e., annual fertilizer applications) may be well-controlled, but the proportion of phosphorus not incorporated into crop biomass that is transported through subsurface, near-surface and overland pathways contributing to legacy nutrient sources is an area of increasing relevance for the design of management activities.

Nutrient legacies in soils, sediments and the biota living in these environments, coupled with legacies in groundwater systems and water bodies, means that management strategies focused on controlling current landscape actions may have limited near-term observed impacts on aquatic conditions related to nutrients. For example, legacy issues could be a key factor contributing to the successes of nutrient management strategies implemented within the highly agricultural Maumee Basin since the late 1990s, which have had only a minor infl uence on the >200 kilotons of phosphorus accumulated from the preceding decades (Powers et al., 2016). Until signifi cant depletion of this pool can be achieved, major algal blooms may persist in Lake Erie.

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Nutrient Transport

However, smaller fluxes of soluble reactive phosphorus may present a more imminent ecological impact to the receiving water body by more effectively feeding algae and other organisms. The concept of a continuum of phosphorus species with varying degrees of lability, rather than clearly discernible particulate and dissolved phosphorus fractions, is increasingly gaining acceptance (McDowell et al., 2002; Liu et al., 2014). This may lead to a more intricate understanding of biogeochemical mechanisms that ultimately underpin eutrophication. It has been speculated that soluble phosphorus and the more labile phosphorus forms that are loosely bound to particles are generally more bioavailable — that is, they are more readily available for direct uptake by plants and algae (Nürnberg & Peters, 1984) — and may accelerate impacts on ecosystem functions. Coupled with the highly seasonal and opportunistic dynamics of the biological processes, this could result in potentially more immediate ecosystem responses within the receiving water body.

The existence of nutrient legacies within soil profiles and in the subsurface implies that other transport pathways besides conventional particle-associated transport via overland flow do exist. Landscapes that promote infiltration of precipitation and runoff also increase the likelihood of soluble reactive phosphorus transport through the subsurface. This effect may be further enhanced in areas with high phosphorus concentrations and low phosphorus soil sorption capacity (Fuchs, Fox, Storm, Penn, & Brown, 2009; Vadas, Srinivasan, Kleinman, Schmidt, & Allen, 2007). Substantial contributions of soluble reactive phosphorus through various pathways have been observed, particularly during the non-growing season and snowmelt in shallow subsurface lateral flows and artificial subsurface drainage systems (Buda, Kleinman, Srinivasan, Bryant, & Feyereisen, 2009; Glavan, White, & Holman, 2012; Heeren, Mittlelstet, et al., 2012; Jarvie et al., 2017; King, Williams, Macrae, et al., 2015; King, Williams, & Fausey, 2015; Macrae, English, Schiff & Stone, 2007; Mittelstet et al., 2011; Robinson, 2015; Ruark, Kelling, & Good, 2014; Smith et al., 2015; Van Esbroeck, Macrae, Brunke, & McKague, 2016). In a few cases, phosphorus concentrations in springs and groundwater baseflows alone can exceed environmental targets set for surface waters (Glavan et al., 2012).

Nutrient management practices on the landscape have focused on phosphorus control through soil and sediment retention because phosphorus is primarily transported by its association with particles to receiving water bodies during major hydrological events (Haygarth et al., 2006; McDowell & Wilcock, 2004; Sharpley, Kleinman, McDowell, Gitau, & Bryant, 2002). This means that storms and extreme events that result in significant particle transport are key to management efforts. The increasing severity and frequency of storms and other extreme hydrological events due to climate change heighten the consideration of how short-term, more extreme events that represent only a very small overall management time frame can become a dominant factor in overall phosphorus transport and loading. This may change our understanding of the efficacy of specific management practices if their primary role becomes minimizing phosphorus losses during extreme events. The large role of event-based control on fluxes will continue to challenge the thinking on the ability of nutrient management practices to mitigate phosphorus losses. Local hydroclimatic conditions remain an important consideration when evaluating nutrient management programs (Owens & Walling, 2002; Søndergaard, Jensen, & Jeppesen, 2003; Stone & English 1993; Walling, 1983).

Particle-associated phosphorus comprises much of all phosphorus loads delivered to surface water bodies. This particle-associated phosphorus has the potential to comprise an ongoing source of phosphorus to the aquatic system, sustaining longer-term internal phosphorus loading processes in lake and reservoir beds (e.g. Correll, 1998; Stone & English, 1993).

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Tile Drains

Tile drain networks are used extensively in agricultural landscapes to lower and control water table levels. Phosphorus applied as manure or fertilizer is usually integrated into and retained in the upper soil horizons situated above tile drains. Phosphorus transport in these environments will be controlled by the nature of the hydrological event and the soil permeability – when the rainfall intensity is greater than the capacity of the soil to absorb it, overland fl ow will dominate. However, the existence of vertical preferential fl ow paths may exacerbate the delivery of phosphorus from the upper soil horizons to artifi cial subsurface drainage pathways such as tile drains.

Tile drains can therefore act as rapid, lateral conduits of subsurface nutrient pools to surface water bodies during high fl ow events (Heeren, Fox, et al., 2012; King, Williams, & Fausey, 2015; Macrae et al., 2007). It is important to recognize vertical preferential subsurface fl ow paths, such as those that promote the delivery of phosphorus to tile-drained environments, in monitoring programs designed to assess the performance of implemented nutrient management practices.

When evaluating the effi cacy of nutrient management practices, the relative contribution of tile drains for subsurface transport should be examined alongside other potential sources and pathways. The dismissal of other potential sources and pathways without supporting observations/data can lead to errant conclusions (e.g., Holman et al., 2010; 2008; Jarvie et al., 2014) that can be misrepresented in models. This may ultimately compromise modeling eff orts that evaluate the effi cacy of management practices.

Freeze-thaw cycles that are common in colder climates like those present in Canada are also suspected to play an infl uential role in nutrient release and transport through the disruption of plant growth or soils (Bechmann, Kleinman, Sharpley, & Saporito, 2005; Kreyling, Beierkuhnlein, Pritsch, Schloter, & Jentsch, 2008; Wang, Liu, Zhao, Wang, & Yu, 2007). The frequency, duration and/or magnitude of these cycles is changing due to climate change in many regions of Canada (Henry, 2008). It has been speculated that climate change may exacerbate nutrient delivery to freshwater bodies as well as shifting overall nutrient balances in terrestrial and aquatic ecosystems.

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The evolving science related to phosphorus behavior in the environment, has increased the overall understanding of the processes that are important to consider for nutrient management systems. This is improving the ability to prioritize the design of both management actions and their assessments of effectiveness related to established goals. But it has also confirmed the significant complexities and considerable variabilities that are characteristic of natural systems, as well as the inevitable and continuing unknowns related to the science.

The resulting uncertainties in the understanding of exactly how various systems function and in the predictions of future behavior in response to nutrient management actions requires use of an adaptive management approach; one that acknowledges the uncertainties and moves forward, while being flexible enough to adjust to ongoing learning by doing and observing.

IMPLICATIONS OF THE SCIENCE FOR ADAPTIVE MANAGEMENT

Figure 2. Adaptive nutrient management across spatial and temporal scales. The red arrows represent the propagation of impacts of management practices that are implemented at small scales to larger spatial and temporal scales. These impacts are evaluated to make sure they are in alignment with goals and strategies disseminated at larger scales (blue arrows). As impacts of nutrient management are propagated to larger scales, the uncertainty associated with their contribution towards the intended outcomes becomes greater.

Adaptive management relies on an approach that:

1 — Makes the most reasonable management choices for a given scale or setting based on current knowledge and understanding,

2 — Predicts conditions that will result from those management actions,

3 — Monitors how the system actually behaves over time relative to the expectations, and

4 — Modifies actions as needed in response to what is actually observed.

Both the management actions themselves and the resulting impacts of those actions occur at different scales and over variable timeframes, adding to the complexity of the analysis. Therefore, to achieve established goals for ecosystem results, adaptive management frameworks must acknowledge the interplay of different spatial and temporal scales. They also require the support of policy that aligns across scales and levels of nutrient management. This is needed in order to identify and implement scale-appropriate tools and establish appropriate targets and evaluative metrics dedicated to those scales (see Figure 2).

This is a challenging area that is being faced by resource managers and regulators for more than just nutrient management. It is increasingly the focus of programs that seek to develop effective cumulative effects management frameworks and regulations, or integrated watershed resource management (IWRM) frameworks. It is not an area for which there is currently an easy scientific answer, nor a consensus on best approaches, but it is currently an area of active discussion about how science can be best used to inform development of effective and integrated frameworks (Canadian Water Network, 2016).

• Re-align phosphorus inputs• Reduce phosphorus losses• Recycle phosphorus• Recover phosphorus in

wastes• Redefine phosphorus in

food systems

SPA

TIA

L SC

ALE

TEMPORAL SCALE

Hours Days Months Seasons Years Decades

Field

Strea

ms

Rivers

Lak

esW

atersh

eds

Ecosystem Health• Establish watershed-based goals• Evaluate strategies' alignment

with goals

Point-source mitigation strategies

Non-point source conservation practices

Prioritization of nutrient management strategies across sectors (i.e. urban, agriculture, rural land uses)

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A watershed provides a logical, practical planning base and scale for the purpose of achieving integrated land and water management. It makes sense then to defi ne overall goals for adaptive, nutrient management frameworks at the watershed scale. Analytical frameworks built around a watershed can provide for spatially-explicit, process-oriented scientifi c assessment to guide sound management decisions (Montgomery, Grant, & Sullivan, 1995).

Usually, the hydrological, ecological and biogeochemical features — as well as socioeconomic, hydroclimatic and agro-ecologic values — are used to defi ne a range of management goals (for example, % reduction in phosphorus loadings to a lake, reductions in algal blooms, or achieving aquatic species abundance or biodiversity) that are appropriate to a particular watershed and are considered attainable within a defi ned area. Ecological and economic data can be used to inform the choice of goals by supporting the estimates of the total economic value aff orded by improving water quality (e.g., Nelson et al., 2015). Social factors are also important to establishing values and the goal setting process.

As understanding of watershed behavior changes in light of the evolving science — and as part of an adaptive management approach — the selection and prioritization of nutrient management strategies may need to be adjusted to achieve overall watershed goals. Reducing phosphorus inputs to water bodies by decreasing maximum daily or annual loads from point sources has been an important and pragmatic tool when nutrient enrichment is comprised of well-characterized, easily-quantifi able and well-controlled point sources. However, as gains have been made in reducing point-source impacts, research and results have shown that it is often insuffi cient by itself to achieve the desired goals. Impacts from more diff use non-point sources are now being seen, and the magnitude of their impacts better understood. This increases understanding of the signifi cance of managing non-point sources to achieve watershed goals, as well as raising the question of where the point of diminishing returns is for actions on point sources.

Using a 5-R framework to prioritize nutrient management strategies within a watershed

The 5-R framework uses a systems approach to nutrient management strategies that can also be used to help prioritize and coordinate nutrient management strategies among multiple uses. Emphasis on specifi c strategies will be dependent on the watershed use involved (for example, agriculture, municipal waste treatment, food processing, etc.).

— Re-align phosphorus inputs (e.g., match phosphorus application to crop requirements)

— Reduce phosphorus losses (e.g., reduce losses from rural septic systems)

— Recycle phosphorus(e.g., apply manure or biosolids instead of fertilizers)

— Recover phosphorus in wastes (e.g., consider phosphorus recovery technologies)

— Redefi ne phosphorus in food systems (e.g., reduce food waste and phosphorus in food additives/preservatives)

More information about how these various strategies can be coordinated within a watershed is presented in Schoumans, Bouraoui, Kabbe, Oenema, & van Dijk, 2015; Withers et al. (2015).

The “5-Rs” are a stewardship framework which allows for more integrated and holistic prioritization of nutrient management strategies between diff erent sectors in a watershed. This framework is useful for coordinating multiple activities in a complex system and establishing clearer paths to common watershed goals.

Establishing and Attaining Watershed-based Goals

15


Linking Management Practices across Spatial and Temporal Scales

of dedicated, high-quality field datasets to support the development, calibration and validation of these complex models (Arhonditsis & Brett, 2004; Loucks, van Beek, Stedinger, Dijkman, & Villars, 2005). As the predictive capacity of these models continues to improve through increased understanding of mechanisms and greater precision of analytical laboratory and field methods, there remains a tremendous opportunity to continue to use current models for hypothesis generation, scenario development and sensitivity analysis. Another innovative use of these models is for identifying “hot spots” that present a higher vulnerability to diffuse nutrient loads based on topographic and hydroclimatic controls.

Another area of increasing focus for nutrient management, as well as broader watershed management strategies, is the relevance of conducting multiple activities and actions concurrently. It has long been assumed that the implementation of multiple best management practices (BMPs) will lead to more effective nutrient management. Although additivity has been assumed by most practitioners and is supported by many models (Francesconi, Smith, Heathman, Wang, & Williams, 2015; Her, Chaubey, Frankenberger, & Smith, 2016; Smith et al., 2015), management practices applied must be appropriate for the dominant source and transport conditions in each field. Many past conservation efforts have either not accounted for existing conditions, or have introduced confounding source/transport interactions in the way they were implemented. For example, the adoption of conservation tillage has been generally effective at reducing total phosphorus and particle runoff simultaneously. However, some studies have shown increased soluble phosphorus loss from ground that is not tilled (e.g., Smith et al., 2015). Careful consideration of the dominant factors will enable the determination of appropriate management practices while precluding the treatment of symptoms that may have been introduced through the implementation of inappropriate management practices. Although considerable literature is available documenting the relative efficacy of individual BMPs, far fewer works have quantified interactions among BMPs to determine impacts which are additive, synergistic or antagonistic, and their unintended consequences on non-target nutrients.

Resolving the scale of actions required to deliver intended ecosystem outcomes remains a major challenge. It is difficult to link high-level, aggregated watershed goals and targets to actionable, measurable and practical nutrient management actions implemented at smaller scales (for example, individual farms) in order to ensure those actions contribute to the overall goal. Therefore, establishing effective and appropriate nutrient targets tailored to watershed assessments that serve as effective “guideposts” to attaining the overall goals represents an important task within this challenge. Relevant metrics at multiple scales (both spatially and temporally) need to be developed, implemented and monitored, including innovative opportunities to link them. The ideal metric could provide for nested checks and balances between various levels of the framework that are required to support iterative, adaptive nutrient management — for example, seasonal loading criteria at the plot scale that propagate to stream water quality impacts — which can ultimately be linked to the occurrence of algal blooms within the receiving water body of concern.

Regime-based water quality targets have been suggested as an innovative alternative to fixed loading targets. A distribution of water quality targets varying over space and time tailored to reflect the changing dominance of factors can facilitate the inclusion of variability and uncertainty (McClain et al., 2003; Poole et al., 2004). The thresholds determined should account for specific mechanisms controlling nutrient impacts, as opposed to purely empirical relationships that are often highly site- and environment specific (Collins et al., 2011). Seasonality of both management actions, hydroclimatic and biotic conditions have increasingly been seen as important bases for changed practices and targets. For example, biota (including harmful algal blooms) in many ecosystems may preferentially respond to seasonal hydroclimatic conditions (for example, temperature, sunlight), and/or seasonal nutrient loads that comprise of more bioavailable nutrient forms.

Numerical computer models are increasingly used to integrate consideration and interactions of various factors across spatial and temporal scales. While such models have been used extensively to evaluate relative contributions of source and transport pathways, resolving issues of scale relevance remains a challenge, as well as the sufficiency and availability

16


Whether in order to support laboratory studies, fi eld experiments or modelling exercises, the generation or collection of appropriate data sets to evaluate the impact of local-scale actions to watershed behavior is particularly challenging for nutrient management. Nutrient management actions are typically carried out as separate, individual activities based on the needs and decisions of individual facilities or practitioners (for example, farmers), rather than as a coordinated, watershed-wide management program. As a result, the magnitude and timing of these singular fi eld-scale management practices are not well coordinated in a way that would support larger scale assessments. Researchers have been increasingly working toward coupling fi eld-, sub watershed- and watershed-scale studies where possible, in order to model larger system behaviours to test and develop theories (for example, nutrient legacies) and to advance to a process-based understanding of the impacts of nutrient management practices within complex biogeochemical cycles (McDonnell et al., 2007).

Design of hierarchical/nested scale models and fi eld studies that generate data in terrestrial and aquatic environments from edge-of-fi eld to stream and include in-stream transformations and nutrient legacies represent the next step in research. Such models would enable investigation of critical relationships and improve the predictive capacity of models that would assist in the design and implementation of optimal nutrient management practices.

The question of appropriate temporal and spatial scales is important to the design of eff ective monitoring strategies for watershed studies. The possibility of legacy phosphorus and its signifi cant impact on the lag times between management practices and aquatic system impacts has led to an increased focus on the practicality of conducting longer-term monitoring and the need for longer-term data sets. The short seasonal to annual time-scales of many existing studies are not suffi cient to identify trends and causative mechanisms at the watershed scale. Given our current understanding of phosphorus legacies, it is suspected that the performance and effi cacy of land-based nutrient management practices may not be accurately evaluated (Dougherty, Fleming, Cox, & Chittleborough, 2004; Sharpley et al., 2002).

Challenges in measuring subsurface water fl ows and both phosphorus forms and fl uxes represent current major barriers to accurate estimation of nutrient reduction from management practices, particularly in deeper groundwater fl ow paths (Heathwaite & Dils, 2000). Preferential and changing fl ow paths in various hydrological conditions — which can be further exacerbated by climate change — may further confound and undermine the design and interpretation of monitoring programs (Buda et al., 2009; Fuchs et al., 2009; Simard, Beauchemin, & Haygarth, 2000).

Technological advancements in monitoring and numerical modelling will lead to the development of tools to gather more precise data related to quantifying nutrient management performance. Such advances will also improve the ability to generate more accurate data sets to characterize systems and model predictions. In many cases, “soft data,” or qualitative knowledge are essential for ground-truthing data accuracy and analyses (Seibert & McDonnell, 2002). Soft data can originate as qualitative knowledge based on laboratory and/or fi eld studies, as well as anecdotal evidence from practitioners, landowners and farmers. The engagement of multiple perspectives, although often time-consuming and resource-intensive, provides a realistic check of system constraints, as well as an opportunity to validate hypotheses and promote a culture of stewardship.

The Need for New Data Collection and Monitoring Approaches

17


EVOLVING NUTRIENT MANAGEMENT PARADIGMS: WHAT DO WE NEED TO KNOW NEXT?

There are certain nutrient management paradigms and assumptions which require updating based on our evolving understanding.

EXISTING PARADIGM EVOLVING CONSENSUS WHAT DECISION MAKERS NEED TO KNOW

Implementing nutrient management practices directly and immediately improves water quality.

Nutrient legacies in land and aquatic ecosystems can cause substantial delays in water quality response, suggesting a need to account for contributions from past activities and an understanding of the lasting impacts.

A site-specific understanding of the dominant phosphorus source and transport mechanisms, as well as the responsiveness of different nutrient pools to management, allows an opportunity to quantify and manage direct losses from phosphorus application, despite the uncertainties associated with legacy phosphorus.

Which nutrient sources are accounted for? Which are still unaccounted for? What is the variability and uncertainty of such estimates? Do unaccounted sources comprise substantial contributions?

What actions are required/available for quantifying and reducing unaccounted, substantial contributions?

Are diffuse or subsurface nutrient sources substantial? How do we monitor/evaluate phosphorus legacy pools in both terrestrial and aquatic environments?

How long will it take to deplete the nutrient legacy?

How can improved understanding of nutrient sources and transport inform BMP selection, implementation and monitoring?

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EXISTING PARADIGM EVOLVING CONSENSUS WHAT DECISION MAKERS NEED TO KNOW

Phosphorus is transported on particles through surface pathways during signifi cant hydrological events.

Management activities should focus on surface runoff and particle retention, and the eff ectiveness of BMPs should be assessed against their ability to address this pathway.

Phosphorus can be mobilized by non-traditional hydrological events, including freeze-thaw. There is increasing evidence to suggest that seasonal loads comprise a considerable proportion of the phosphorus transported to receiving water bodies.

Although soluble reactive phosphorus comprises a smaller proportion of the total phosphorus load, its speciation and timing may increase the vulnerability of receiving water bodies to algal blooms.

Assessments of the eff ectiveness of BMP performance that target surface pathways, and don’t account for the impacts of preferential fl ow paths and other subsurface transport pathways may provide misleading results.

What is the fate and transport of phosphorus through the subsurface and beyond the edge of fi eld?

How can fi eld monitoring programs be used to quantify and characterize phosphorus loads (including speciation) at the edge-of-fi eld and link to their impact on receiving water bodies?

How do we best capture magnitude, form and timing of nutrient delivery using monitoring programs and incorporate this information in the prioritization of nutrient reduction eff orts?

What factors and mechanisms infl uence the magnitude, form and timing of nutrient delivery that ultimately results in short-term vs. longer-term ecosystem impacts?

How can we incorporate qualitative knowledge in models as a reality check?

How can fi eld studies coupled with modeling exercises be used to evaluate BMPs?

The impacts from BMPs are additive.

The implementation of multiple BMPs may have either synergistic and antagonistic eff ects. Unintended consequences may result in relation to one area while pursuing goals focused on another.

Coupled with hydroclimatic, biotic and geochemical diff erences unique to each site, the impact of any singular BMP when implemented in a diff erent environment may have signifi cantly diff erent performance.

How do multiple management actions interact?

How can fi eld studies be better designed to ascertain modeling predictions of additive impacts?

Where and when are BMPs most eff ective?

How do we evaluate the effi cacy of individual BMPs?

Which BMP interactions are additive, synergistic or antagonistic?

What are the unintended consequences of BMPs on non-target nutrients?

How do we couple laboratory-scale and fi eld-scale tests with models to better understand interactions between BMPs?

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Recognition that accumulation of excess nutrients in our rivers and lakes can cause conditions that lead to degradation and eutrophication of our water bodies is not new. Degradation began to be recognized in the 1960s, and the link to nutrients (particularly phosphorus as the key culprit) was made in the 1970s, leading to the initiation of nutrient management responses in the 1980s. In the past decade, practitioners and scientists have experienced a significant evolution in their understanding of how nutrients are cycled and transported and how that transport relates to important ecosystem responses such as algal blooms.

The dominance of diffuse, non-point sources of nutrients in watersheds from agricultural activities and rural and urban inputs, as well as accumulation over decades in terrestrial and aquatic ecosystems is now recognized, and will continue to drive a need to better account for and manage these sources. There have been numerous knowledge advancements in the area of nutrient management over the last 10 or 15 years. Key insights from the collective research that are particularly relevant for developing effective nutrient-management policies and practices are:

— Extreme weather events and preferential transport pathways can dominate phosphorus transport.

— Nutrient legacies may be critical to how systems respond to management actions.

— Timeframes between management actions and ecosystem responses can be very long.

— Soluble reactive phosphorus may be a key contributor to algal blooms.

CONCLUSION

The major implication of addressing phosphorus loading is a need to consider management and conditions across the whole watershed. This has brought nutrient management squarely into the realm of integrated watershed management. Although removing excess nutrients is an essential component of ecosystem restoration, these actions in and of themselves may not be enough. Thus, targeting individual “hot spot” areas of concern, while necessary as a first step, may not be sufficient to attain collective watershed goals.

Whereas focused studies to determine the efficacy of various BMPs conducted at the local scale will continue to be important, increasingly decision makers will be looking for the science to help support more challenging decisions, like:

— What are effective watershed goals and frameworks?

— How can we link local-scale management practices to watershed goals?

— What does success look like when evaluating a BMP in the context of overall watershed goals?

— What monitoring is needed to evaluate whether or not management programs are working? What should be measured, where, and over what timeframe?

It is these kinds of questions that will need to be supported in developing the adaptive management frameworks required to advance nutrient management. The questions raised are similar to those being asked in other aspects of watershed management, and cannot be answered through individual research projects or through research alone. Canadian Water Network recognizes that advances in scientific understanding must be accompanied by evolving conversations and framing of what is known and unknown to usefully inform decision making at all levels and across jurisdictional boundaries to achieve progress toward ecosystem health.

20


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