The role of vegetated buffers in agriculture and their regulation across Canada and the United States

Journal of Environmental Management 243 (2019) 12–21

Contents lists available at ScienceDirect

Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman

Review

The role of vegetated buffers in agriculture and their regulation across Canada and the United States

T

S.M. Genea, P.F. Hoekstrab, C. Hannamc, M. Whitee, C. Trumane, M.L. Hansond, R.S. Prossera,∗ a

University of Guelph, School of Environmental Sciences, Guelph, ON, Canada Syngenta Canada Inc., Guelph, ON, Canada c Synthesis Agri-Food Network, Guelph, ON, Canada d University of Manitoba, Department of Environment and Geography, Winnipeg, MB, Canada e Syngenta Crop Protection LLC, Greensboro, NC, USA b

A R T I C LE I N FO

A B S T R A C T

Keywords: Agroecosystems Buffers Nutrients Pesticides

A vegetated buffer, barrier, or filter strip is a parcel of land that is designated to separate land used for agriculture from valued aquatic or terrestrial habitats. It exists partly with the intent to diffuse runoff and to impeded sediment, nutrients, pesticides, and other constituents from reaching off-site surface waters. Mandatory buffer implementation is regulated at various levels of government in North America - from the federal to the state and provincial levels, and by some municipalities and counties. To better understand the degree and breadth of oversight, we undertook a comprehensive search and review of vegetative buffer regulations across North America. We determined the width of buffer required, under what habitat or field conditions, for which pesticides, and application type, amongst other attributes. For ground application, margins ranged from 1 m to upwards of greater than 4000 m depending on protection goals, with some being compound specific and others being generally applied to all registered pesticides/compounds. These buffers tended to be used most often to protect surface water, groundwater (e.g. drinking water wells), and nearby sensitive crops, but the required distances are generally not consistent between jurisdictions, regardless of the stated protection goals. We recommend that a thorough science-based review take place, with input from relevant stakeholders, to harmonize vegetated buffer size for effective surface water protection where ecological, climatic, and agricultural conditions are sufficiently similar in North America.

1. Introduction For the purpose of this paper, a vegetated buffer (or ‘buffer’) is defined as a parcel of land supporting grasses or broadleaf vegetation that separates sloping land used for agriculture from valued aquatic (e.g., streams, lakes, wetlands) or terrestrial habitat (e.g., forest, other agriculture land, human development) (Fig. 1). Vegetated buffers are traditionally used to minimize soil erosion, to attenuate the off-field release of compounds (e.g. pesticides, nutrients) into waterways, along with providing habitat for beneficial wildlife in the agroecosystem. However, the regulations and promotion of vegetative buffers as a mitigation tool or risk management option in enhancing and protecting aquatic habitats varies across North America, meaning they may not be meeting their assumed goals in all cases, or are possibly overly restrictive. These buffer systems are generally composed of three important units; 1) surface vegetation, 2) their root zone, and 3) sub-soil ∗

(subsurface) horizon (Grismer et al., 2006) (Fig. 2). When runoff from an agricultural field enters a buffer strip, it will infiltrate the root zone. The presence of the root zone facilitates a greater magnitude of infiltration, but also a greater depth of infiltration into the sub-soil. Infiltration in the vegetated buffer is considered the most important process of reducing the movement of nutrients, pesticides, and pathogenic microorganism from agricultural fields (Grismer et al., 2006). Infiltration facilitates the sequestration of nutrients by plants within the buffer, sorption to soil particles, and denitrification by the microbial community. Studies have consistently shown that buffers can effectively sequester a significant portion of the total phosphorus and nitrate load in field runoff from reaching surface water (Dillaha et al., 1989; Magette et al., 1989; Patty et al., 1997; Barfield et al., 1998; Schmitt et al., 1999; Lee et al., 2000; Uusi-Kamppa et al., 2000; Janssen et al., 2018). The soil microbial community also plays a critical role in degradation of pesticides, select nutrients, and pathogenic microorganisms, which is made possible by infiltration within the buffer (Aislabie

Corresponding author. Ryan Prosser University of Guelph School of Environmental Sciences 50 Stone Rd. East Guelph, Ontario, N1G 2W1, Canada. E-mail address: [email protected] (R.S. Prosser).

https://doi.org/10.1016/j.jenvman.2019.05.003 Received 12 April 2019; Received in revised form 1 May 2019; Accepted 1 May 2019 Available online 09 May 2019 0301-4797/ © 2019 Elsevier Ltd. All rights reserved.

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Fig. 1. Diagram illustrating areas (red crosshatching) within in an agriculture landscape that would likely be identified for planting of a vegetated buffer. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2. Cross-section of water flow through vegetated buffers. Adapted from Grismer et al. (2006).

native pollinators, which can contribute to increases in colony size, fitness of larvae, overwintering success, and overall species abundance. Increases in these factors in the pollinator community can lead to increases in the rate of crop pollination and crop yield. Consequently, not only can vegetated buffers help to protect ecologically important aquatic and terrestrial systems, they can also play a role in increasing the productivity and sustainability of agricultural yields (Jobin et al., 2001; Wratten et al., 2012). Studies have investigated the cost-benefit relationship associated with the installation of buffers (Santhi et al., 2001; Yuan et al., 2002; Qui, 2003). Establishment of buffers often involves removing an area of the field out of production, which translates into lost revenue for the farmer. However, vegetated buffers may also benefit the farmer through incentive programs and/or a cost reduction associated with reduced erosion and nutrient losses. Majority of studies have concluded that vegetated buffers represent a net benefit, although the size of the benefit varies (benefit:cost ratios ranged from 1.2 to 4.1) (Santhi et al., 2001; Qui, 2003). Due to the importance of vegetated buffers in promoting enhanced water quality and habitat within the agricultural landscape, this article reviews the variation in regulations governing the implementation of vegetated buffers in Canada and the United States of America (U.S.), while briefly highlighting the types of vegetated buffers that are employed. This article will also discuss the range of recommended buffer structure and the incentive programs that have been implemented in different jurisdictions to encourage the construction of different types of vegetated buffers in Canada and the U.S. The information on the

and Lloyd-Jones, 1995; Bradford et al., 2013). Infiltration also facilitates the sorption of pesticide residues on soil particles, which significantly reduces transport to off-site areas, and increases residence time, and possible physical or biodegradation. Studies have shown that pesticide residues in runoff can be reduced from 47 to 100% when vegetated buffers are incorporated in an agriculture field (Barfield et al., 1992; Cole et al., 1997; Patty et al., 1997; Moore et al., 2001; Otto et al., 2012). Buffers can also trap sediment, with estimates ranging for 41–100% of inputs (Hayes and Hariston, 1983; Coyne et al., 1995; Daniels and Gilliam, 1996) as well as serving as an effective measure to capture nutrients, promote degradation, and transformation of agrochemicals, and remove pathogens found in agricultural runoff (Grismer et al., 2006; Helmers et al., 2008; Delta F.A.R.M., 2013). Water mobilized due to precipitation, irrigation or thaw events is the major vehicle by which sediment, nutrients, agrochemicals, and/or pathogenic microorganisms can move off the field into surface water and/or non-agricultural land (Wood et al., 1998; Rice et al., 2001; Berry et al., 2007). Movement of water through vegetated buffers allows for the sequestering and/or decrease of the previously mentioned potential outputs from an agricultural field. Finally, buffers serve as a “multifunctional landscape”, and provide habitat for wildlife and a refuge for native pollinators in the agroecosystem (Smith et al., 2008; Wratten et al., 2012). For example, Jobin et al. (2001) observed that vegetated field margins were important habitat for birds that contribute to controlling crop pests. Wratten et al. (2012) outlined that vegetated buffers can increase floral resources for 13

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usually more effective in reducing concentrated runoff when combined with vegetative barriers. Riparian forest buffers (‘streamside management zones', ‘forest buffers', ‘riparian forests', and ‘riparian management zones') are found adjacent to ponds, rivers, lakes, streams and wetlands, and consist of areas dominated with trees and shrubs (Fig. 3A) (e.g., Richard A. Cooksey et al. (1997)). Riparian buffers created on the farm may consist of two or three zones running parallel to the water body that mimic natural reforestation while being cognisant of cost and logistical challenges such as planting and regeneration time (Stewart et al., 2010). For intensively used cropland or pasture, two-zone buffers may be preferred. This two-zone system consists of three to four rows of trees and shrubs closest to the water body, followed by typically grassy species chosen specifically for the site. For other conditions, such as highly erodible soils or gently sloping riverbanks, a three-zone buffer is recommended. With this design, trees form zone one (adjacent to the waterbody and edge/bank), followed by a mixture of trees and shrubs to form zone two, with grasses planted in an area to form zone three. Riparian forest buffers not only reduce sediment, nutrients and pesticide transport into adjacent water bodies but they also lower and maintain water temperatures, which improves habitat for many aquatic species. Riparian forest buffers also facilitate the restoration of native, riparian plant communities along with increasing carbon storage in plant biomass and soil. Riparian herbaceous cover is often implemented as a transitional zone between upland and aquatic habitats along perennial or intermittent water bodies (e.g. (USDA, 2015, 2018),). Under typical (i.e. “normal”) conditions, the fringe of these water bodies would naturally be dominated by grasses, sedges, rushes, ferns, legumes and/or forbs that can grow in areas of periodic flooding or saturated soils. This transitional zone of intermittent flooding and saturated soils would not be suitable for a riparian forest buffer. Riparian herbaceous covers provide habitat for fish and wildlife and maintain habitat corridors and native plant communities, along with improving water quality. This type of vegetated buffer also benefits pollinators by providing sources of pollen, nectar, and nesting habitat. The herbaceous cover will also trap sediment and decrease a watercourse's energy, which will limit streambank erosion. Like riparian forest buffers, herbaceous cover will increase carbon storage in the soil. Ecological buffers (eco-buffers) or conservation cover is an example of a multi-function, multi-species dense planting design for field edge and riparian zones (e.g., Schroeder et al. (2012)). These buffers are designed to mimic large natural buffers in a narrower space. Multiple rows of native trees and shrub species are interspersed in each row, including long- and short-lived species with a variety of growth rates and habits. High density (5000 plants/100 m compared to 350 plants/ 100 m in a traditional buffer) reduces the need for long-term weed control (Schroeder et al., 2012). Conservation cover helps to reduce sheet, rill, and wind erosion, while being an important source of habitat for wildlife, pollinators, and organisms that will aid in agricultural pest control.

variation in regulation and incentive programs among jurisdictions in North America was collected by systematically reviewing information from relevant municipal, provincial, state, and federal ministries and departments. Based on these summaries, we will make a series of recommendations around the future use and oversight of buffers in North America. 2. Types of vegetated buffers There are two general types of vegetative buffers in agriculture: temporary (i.e. seasonal areas) and permanent (i.e. long-term commitment of land and designation of habitat), which can be further subdivided into specific types. In agriculture these can serve many purposes. Their primary purposes can be to address soil erosion through the use of contour buffer strips and grassed waterways. While other types of vegetated buffers can have the primary purpose of improving water quality, such as through the use of filter strips. 2.1. Temporary buffers Temporary buffers are often considered as a portion of the crop or landscape earmarked to be untreated (i.e. not planted with a crop, or area of the crop that does not receive a pesticide application) and large enough to minimize the off-field risk or impact from spray drift, runoff, and soil erosion. These areas are known as flexible buffers or setbacks and their size and location are determined on an individual case-bycase basis. For example, pesticide product labels outline a “buffer zone” that should remain unsprayed during field application. A buffer zone is described by the distance from the end of the spray boom to sensitive habitat, such as aquatic areas. The buffer zone will vary between commercial products and vary according to the method of application, the type and structure of the protected habitat (e.g. depth of water body) and, in certain cases, the application rate. The vegetative structure of these recommended spray buffers, spray set-backs, or buffer zones is often not described and may include areas of the field in which the crop is not treated with the pesticide in question. In addition, certain pesticide labels may require a vegetative buffer be included on fields that receive a pesticide application to a certain cropping system. These temporary features may be put back into production when a different crop is planted, and/or a different pesticide is selected for application. 2.2. Permanent buffers Certain areas of land around an agricultural field that have permanent vegetation that has been established through planting, natural regeneration, or remnant of the initial ecosystem are referred to as permanent buffers. While the longevity of these areas is dependent upon many factors, such as land ownership and intended land use, they are intended to help maintain and enhance water quality for the long term. Permanent buffers are most common at the edge of agricultural fields, but they can also be located within the field. Types of permanent buffers are illustrated in Fig. 3 and discussed in more detail below.

2.2.2. Within-field buffers Grassed waterways are strategically constructed or naturally vegetated channels within an agricultural field (Fig. 3B). These waterways slow the flow of water, thereby preventing gully and rill (i.e. shallow channel) erosion, increase infiltration, and help sequester pesticides, nutrients, and retain sediments. Contour buffer strips are narrow strips of permanent vegetation that alternate between cultivated strips that are usually wider than buffer strips (Fig. 3B). These strips help reduce the risk of sheet and rill erosion, concentrated flow and pesticide runoff by partitioning large cultivated areas into small strips (Sahu and Gu, 2009). This type of buffer is constructed to follow the contour of slops in cropland, which can include not only traditional field crops (e.g. corn, soybeans) but also vineyards and orchards. A type of buffer similar in nature to contour

2.2.1. Edge-of-field buffers Field borders are permanent vegetation established on the edges of crop fields. Field borders are established to inhibit wind and water erosion, while providing habitat for wildlife (e.g., USDA (2010)). These borders may reduce the off-target movement of pesticides and nutrients present in runoff and can trap sediment containing adsorbed pesticides when runoff water flows over them. Filter strips are an area of herbaceous vegetation located between crop fields and water bodies, with the intent of removing contaminants from overland flow (Fig. 3A). (e.g., Schmitt et al. (1999). They often consist of areas of grass and permanent vegetation. Filter strips are 14

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Fig. 3. Types of permanent edge-of-field and in-field vegetated buffers used in agriculture: A) Grass filter strip and riparian buffer B) Grassed waterway, contour buffer strips, wind breaks (Photos courtesy of United States Department of Agriculture and Ontario Ministry of Agriculture, Food, and Rural Affairs).

profile is reduced.

buffer strips is the vegetative barrier. Vegetative barriers contain stiff stemmed, dense, and tall perennial vegetation that do not alternate in as small as area as contour buffer strips. By being placed parallel to each other and perpendicular to the slope, they help disperse concentrated flow, trap sediment via improved infiltration. Alley cropping is another form of alternating buffer that can occur in-field. Alley cropping involves planting crops between strips composed of a single or multiple row of trees or shrubs. Alley cropping not only reduces erosion (water and wind) and off-site movement of nutrients and chemicals, it also enhances habitat for wildlife and beneficial insect and increases crop and forage quality and quantity by improving microclimatic conditions (Quinkenstein et al., 2009). Wind buffers (‘windbreaks' or ‘shelter-belts' or ‘herbaceous wind barriers’) that protect crops from intense and damaging winds and subsequent wind erosion of the topsoil (Fig. 3A) (Cleugh, 1998). These buffers consist of single or multiple rows of trees and are sometimes planted along the edges of fields. By lowering the wind speed, these areas can help reduce pesticide drift. If placed perpendicular to the slope, they also help to reduce runoff. One variation of wind buffers are herbaceous wind barriers that usually consist of tall grasses that have been planted in thin rows, perpendicular to the general wind direction. These grasses reduce wind speed and intercept wind-borne nutrients and pesticides. Another variation, cross wind trap strips, reduce wind erosion but not wind speed to intercept wind-borne sediments, nutrients, and pesticides.

3. Regulation of buffers To review the regulation of buffers in Canada and the U.S., a search of the federal, state, and provincial websites was conducted. Environment, resource, agriculture, and legislative governmental websites were searched using key words such as; vegetated buffer, vegetative barrier, filter strip, grassed waterway, pesticide buffer, conservation incentives and agriculture buffers. The search was conducted in May and June of 2018. It was found that mandatory buffer implementation for the mitigation of certain compounds, such as pesticides and nutrients, are regulated at various levels of government within North America. The regulation of buffers for many jurisdictions is often tied to the use of pesticides and, in general, the protection of water quality. At the federal level in Canada and the U.S., pesticides and their corresponding management strategies are overseen by the Pest Management Regulatory Agency (PMRA) as part of Health Canada, and the United States’ Environmental Protection Agency (EPA) under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) (Government of Canada, 2009; United States Environmental Protection Agency, 2017a). These agencies regulate and determine the conditions under which the use of these products is acceptable. This includes the use of spray buffers, and in some cases vegetated buffers along agricultural land as a mitigation tool against the off-site impacts of pesticides to sensitive habitats. Government programs and regulations often refer to three types of buffers; setbacks, filter strips, and vegetative barriers. As has been described above, there is a greater number of vegetated buffer types than the three commonly described in regulations. Setbacks, sometimes called buffer zones, is a zone in which the application of pesticides or nutrients is prohibited. These vary in width but have no further specifications in terms of the type of vegetation to be planted (Ontario Ministry of Agriculture Food and Rural Affairs, 2011). Mandatory setbacks and other pesticide application information are detailed on pesticide labels, which are considered legal documents in North America (Government of Canada, 2009; United States Environmental Protection Agency, 2017a). The term “filter strip” and “vegetation barrier” are used by jurisdictions to simplify the classification of vegetated buffers into buffers composed of grasses and buffers composed of herbaceous vegetation, shrubs and/or trees. Filter strip and vegetative barrier used in this context are similar in structure, in that they require permanent vegetation. Filter strips are usually identified as containing dense

2.2.3. Constructed wetlands While not typically considered buffers, constructed wetlands can not only provide similar water quality benefits, but also bestow additional benefits when combined with vegetative buffer areas. For example, low concentrations of pesticides can drain directly into streams via tile drainage. Strategically located wetlands (e.g. at tile outlets) can be effective in degrading/sequestering pesticides and nutrients. For example, Kovacic et al. (2000) observed that constructed wetlands reduced the total nitrogen load in tile drainage effluent by 37% and an additional 9% reduction occurred when a buffer strip was constructed between the constructed wetlands and river. 2.2.4. Saturated buffers Similar to a constructed wetland, saturated buffers exist where tile drainage output is delivered underground to the root zone of a vegetative buffer (Transforming Drainage, 2018). The buffer stores the runoff and slowly releases it back to the natural draining as the moisture 15

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Fig. 4. Maps illustrating provinces and states in Canada and the United States that have a regulation in place for the inclusion of vegetated buffers (A & C)) and monetary programs to incentivize construction of buffers (B & D), as of March 2019. At the federal level, the United States Department of Agriculture's Natural Resources Conservation Service provides incentives for vegetated buffer construction in all states in the United States (not illustrated in D).

regulation at the municipal level. This includes; Alaska, Hawaii, Maine, Maryland, Utah, Nevada, and Vermont (Porter, 2010). These municipalities can mandate the implementation of setbacks and other buffer types for pesticide application to suit local conditions (Porter, 2010). Municipalities in the other states are pre-empted from regulating pesticides or must petition state governments for further regulation. In some cases, municipalities can mandate the use of buffers for watershed protection through ordinances; however, these ordinances often refer to general contamination or erosion, not pesticide application specifically (South Carolina Department of Health and Environmental Control; Porter, 2010). Not all buffer regulations and programs relate directly to pesticide control and regulation acts. Some regulations that are intended to protect watersheds, species at risk, sensitive populations, or prevent erosion, also require the use of a buffer zone (Alabama Department of Agriculture and Industries, 1993). At the federal level in the U.S., the EPA can mandate the use of a spray buffer under the Endangered Species Act to prevent harm to listed endangered species (United States Environmental Protection Agency, 2016). For example, in 2006 the EPA mandated an 18-m setback for ground applications, and a 61-m setback for aerial applications in California for 66 listed pesticides that were determined harmful to the endangered red footed frog (Rana draytonii)

grasses (Natural Resources Conservation Service, 2016a; Vermont Agency of Agriculture Food and Markets, 2018). The vegetation used in these areas are also present at a relatively high density, but usually require stiff stemmed vegetation (Natural Resources Conservation Service, 2016b). In some cases, these terms are used synonymously. Buffers can be further regulated at the state or provincial level. States and provinces can require more stringent regulations around the implementation of buffer zones and setbacks (Government of Canada, 2009; United States Environmental Protection Agency, 2017b). However, many states and provinces default to the federally registered pesticide label and the statement contained within these documents, which require users to follow best practices, such as adhering to buffer requirements when using pesticide products (Government of Canada, 2009; United States Environmental Protection Agency, 2017b). Therefore, additional buffer requirements may only be found in some jurisdictions (Fig. 4 A&C; Supplementary Information (SI) Table S1). For example, in the province of Prince Edward Island, a 15-m vegetated buffer strip is required between an agriculture field and a watercourse; 20-m is required if the slope is > 5% (Dunn et al., 2011; Government of Prince Edward Island, 2017). In some cases, states and provinces allow buffers with respect to pesticide application to be regulated by counties or municipalities. In the U.S. there are seven states that allow pesticide 16

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Department of Agriculture, 2018; Vermont Agency of Agriculture Food and Markets, 2018; Wisconsin State Legislature, 2018). Only Maryland's cost share program specifies that the land's slope should be between 1 and 5% (Maryland Department of Agriculture, 2013). Not all programs define these buffers in the same manner. There is some overlap between definitions of filter strip and vegetative barrier, however filter strips tend to be defined as grassed areas (Vermont Agency of Agriculture Food and Markets, 2018). Most filter strip incentive programs do not require that agricultural land border specific habitats or areas, however some do recommend use near sensitive areas and surface waters, as in the case of Maryland's 10.7 m filter strip program, and Vermont's high stem density 7.6 m filter strip program (Maryland Department of Agriculture, 2013; Vermont Agency of Agriculture Food and Markets, 2018). Implementation of vegetated barriers is incentivized through both government legislation or funding programs. While vegetative barrier regulations were found for a number of jurisdictions, some jurisdictions choose not to regulate but instead recommend vegetated barriers as part of BMPs or provide cost share programs (Table S5). Most of these regulations and incentive programs do not specify required plant species for the buffers, however many suggest or require the use of perennial vegetation, or vegetation native to the area (Harmel et al., 2017; Oklahoma Department of Agriculture, 2017; Indiana State Department of Agriculture, 2018). For instance, Indiana's monetary incentive program requires the use of perennial vegetation and native grasses along field borders to qualify for funding (Indiana State Department of Agriculture, 2018). Vegetated barriers are used largely to protect surface waters and riparian zones. In certain cases, a jurisdiction will require multiple vegetation types arranged in a series of zones to protect riparian areas. This is the case for Oklahoma's riparian buffer BMP, which requires three zones; a 4.6 m zone of undisturbed native trees and shrubs, an 18.3 m zone of manage trees, shrubs and grasses, and a 6.1-m zone of perennial grasses (Harmel et al., 2017). This type of BMP is not mandatory but may qualify for financial compensation in some jurisdictions through programs like the United States' Conservation Reserve Program (CRP) (West Virginia Conservation Agency, 2018). In West Virginia, voluntary BMPs are available; however, up to 50% of the implementation and management fees may be compensated by CRP (West Virginia Conservation Agency, 2018). In some instances, an investigation or management plan will dictate the type of vegetation required for the specific situation (West Virginia Conservation Agency, 2018). Other structural components, such as width and slope, can be site specific and may influence vegetation type. Within vegetated barrier programs identified, widths varied from 1 m to 60.7 m (Table S1 – S3). These may be altered given a farmer's unique situation and environmental conditions (Minnesota Board of Water and Soil Resources, 2016). This is the case in Minnesota where buffers around public water can range from 9.1 to 15.2 m depending on adoption of other water quality practices by agriculturalists (Minnesota Board of Water and Soil Resources, 2016, 2017). Characteristics like slope can influence the requirement and specification of a vegetative barrier. In Idaho, BMPs suggest that vegetative barriers are most effective when slope < 20% (Idaho Department of Environmental Quality, 2005b). In the province of Alberta, vegetated barriers are suggested for land with slopes between 1 and 10% as part of the province's beneficial management practices (Alberta Agriculture and Forestry, 2003). However, in some states like Vermont, slopes can mandate the use of a vegetative barrier. Specifically, a 30.5 m vegetated barrier consisting of perennial vegetation is required for manure application if the slope of the land is ≥ 10% (General Assembly of the State of Vermont, 2015). In the Canadian province of Prince Edward Island, a 10 m buffer zone is legislated between agricultural fields with a slope < 5% and streams, but the buffer zone must increase to 20 m when the field slope is > 5% (Dunn et al., 2011). The USDA's Natural Resources Conservation Service (NRCS)

(United States Environmental Protection Agency and Agency, 2007). The EPA similarly implemented a 18-m and a 91-m setback for ground and aerial application, respectively, in Oregon, California, and Washington around salmonid bearing streams to protect salmon and steelhead trout species for various pesticides (United States District Court Western District of Washington at Seattle, 2004). Much like the individual pesticide labels, these types of regulations are implemented on a case by case basis. In some instances, these types of regulations can be applied more broadly such as the case of Canada's Fisheries Act which prohibits the release of a contaminant into a body of water that poses harm to fish and fish habitats (Government of Canada, 1985). In such instances, vegetated buffers may be considered as a mitigation and management strategy. Provinces and states have implemented similar measures to protect specific watersheds and water resources, further specifying how pesticides and other anthropogenic activity can be carried out in proximity to areas of concern. For example, in North Carolina the Neuse Buffer Law preserves existing riparian buffers, limiting the proximity at which agricultural activity can occur. It mandates two zones that sum to create a buffer of 15 m (North Carolina Department of Environmental Quality, 1995). The first zone consists of a setback of 9 m and is followed by 6 m vegetated buffer zone. This state law is intended to protect the local Neuse water basin (North Carolina Department of Environmental Quality, 1995). Although many of these types of buffer laws and regulations apply to riparian zones, and not agriculture specifically, they may affect agriculturalists in close proximity. 4. Structure of buffers across jurisdictions Buffer structure varied greatly across jurisdictions. Most often the buffers referred to in pesticide application regulations are setbacks; however, crops may still be planted. True setbacks represent an area where pesticides cannot be applied and are often designated as an area which may not be cultivated (Ontario Ministry of Agriculture Food and Rural Affairs, 2004). The description of a setback usually does not include details on structure and/or the type of vegetation that may be represent. Setbacks are simply a distance from a landscape object that pesticides and/or nutrients cannot be applied. For instance, in the state of Georgia a 7.6-m setback is required from all state waters (Georgia Department of Natural Resources, 2013). Similarly, in Virginia a 30.5 m setback must be implemented between designated resource protection areas and areas of agricultural activity (Virginia Department of Conservation and Recreation, 2009). Similar laws exist in Canadian provinces such as Quebec where a 30 m setback is required for wide watercourses and protected water bodies larger than 4 m wide, and a 3m setback is required where a watercourse is < 4 m wide and has a flow area > 2 m2 (Government of Quebec, 2003). Setbacks and vegetated buffers are also sometimes used on sloped land. Florida recommends the use of a 35 m setback on land with a slope greater than 1% if it boarders a perennial stream (Florida Department of Agriculture and Consumer Services, 2015). Setbacks are found in many jurisdictions to protect a variety of resources and populations (Table S1 – S3). However, these regulations and programs usually do not specify structural elements other than width. Other types of buffers require the use of specific vegetation or other structural elements like zones. This is the case for Oklahoma's riparian buffer best management practice (BMP), which requires a total of 29 m split into three zones of native trees and shrubs, managed forest, and perennial grasses (Harmel et al., 2017). Filter strip programs across jurisdictions are incentive-type programs or a recommended practice by a ministry or department (e.g., BMP). These strips range from 7.6 m to 91.4 m in width, and require grasses or herbaceous, stiff stemmed, high density vegetation (Table S4). (Pennsylvania Department of Environmental Protection, 1996; Maryland Department of Agriculture, 2013; Pennsylvania State Conservation Commission, 2017; Indiana State Department of Agriculture, 2018; Kansas 17

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or territory must provide the other 40% and are responsible for the management of the program (Agriculture and Agri-Food Canada, 2018a). This is to ensure that the program meets specific needs of the region. However, not all provinces and territories have signed the bilateral agreement and the program is fairly new, having been implemented in 2018 (Agriculture and Agri-Food Canada, 2018a). As of June 2018, Alberta, British Columbia, Manitoba, New Brunswick, Ontario, Prince Edward Island, Quebec, and Saskatchewan have announced the signing of the bilateral agreement (Agriculture and AgriFood Canada, 2018a). Projects under CAP also include activities under the AgriAssurance program, which promote and support environmental sustainability and stewardship in agriculture (Agriculture and AgriFood Canada, 2018a). Implementation of vegetative buffers may fall under some of these programs in different provinces. For example, in Ontario, farmers with fields along streams, drains, rivers, ponds, wetlands and/or lakes can share 50% of the cost for vegetated buffer construction through CAP (up to $10,000 or 20,000 CDN depending on geographic region) (Ontario Ministry of Agriculture Food and Rural Affairs, 2017a, b). Illinois, Pennsylvania, and South Dakota use tax reduction incentive programs that use vegetated buffers. Illinois and South Dakota offer a reduction in property value to assist taxpayers that implement vegetated filter strips to the standard of the NRCS technical guides (South Dakota Department of Revenue (2012); Illinois General Assembly, 2016; Pennsylvania State Conservation Commission, 2017). In Illinois, permanently vegetated land between an agricultural field and a protected area or surface water is considered a vegetative filter strip. For tax purposes this land is valued at 16% of its fair cash value, or one sixth its equalized productivity index. To qualify for this tax reduction, the buffer must also meet requirements of NRCS's technical guides and standards (Illinois General Assembly, 2016). In South Dakota, vegetative barriers or filter strips bordering certain lakes and streams may qualify for a 40% reduction in property value as part of the state's tax relief program (South Dakota Department of Revenue, 2012. Pennsylvania has a different tax credit program for the implementation of BMPs. The state offers tax credits equal to 50–75% of the buffer's cost, given the credit's amount does not exceed $150 000 USD per farm (Pennsylvania State Conservation Commission, 2017). Some jurisdictions, like Idaho, provide BMP guidance documents for vegetated buffers but do not list any direct incentive or regulations (Idaho Department of Environmental Quality, 2005a, b). These BMPs are voluntary, though some farmers may find them useful for issues such as erosion (Idaho Department of Environmental Quality, 2005a, b). In some cases, BMPs may fall under other conservation initiatives within a jurisdiction like CRP, CREP, or CAP. Florida, Idaho, Oklahoma, Pennsylvania, Vermont, West Virginia, and Alberta all provide voluntary BMP documents and technical guides with no direct funding, but who's practices may fall under other conservation programs (Alberta Agriculture and Forestry, 2003; Idaho Department of Environmental Quality, 2005b, a; Florida Department of Agriculture and Consumer Services, 2015; Harmel et al., 2017; Pennsylvania State Conservation Commission, 2017; Vermont Agency of Agriculture Food and Markets, 2018; West Virginia Conservation Agency, 2018). Implementation year varies between regulations and incentive programs in all jurisdictions. Regulations specific to vegetated buffers have implementation dates that range from 1998 to 2018 (SI). Most incentive programs are more recent, having been implemented between 2013 and 2018 (SI). Similar to the wide range of implementation dates, the longevity of programs varies. Some programs are not intended to be long term activities. For instance, CAP was implemented in 2018, but it is only intended to provide funding for the next five years (Agriculture and Agri-Food Canada, 2017). The CAP was also created to replace the Growing Forward 2 program which supported similar conservation activities and buffer implementation until March of 2018 (Agriculture and Agri-Food Canada, 2018b). The jurisdiction of Hawaii is currently investigating possible buffer regulations by carrying out a vegetated

provides technical assistance on how to implement and manage a vegetated buffer. Recommendations include a width of 0.9- to 30.5-m, and planting gaps of no more than 7.6-cm (Natural Resources Conservation Service, 2016b). Species selected should be long-lived and well suited to local conditions. The NRCS documents also detail stem density per square foot as determined by stem diameter (Natural Resources Conservation Service, 2016b). Many programs in the United States, like the Conservation Reserve Program (CRP) cost share program, use these technical documents as guides or requirements for farmer qualification (Natural Resources Conservation Service, 2018b). 5. Incentives for vegetated buffers Many setbacks or vegetated buffers are mandated within jurisdictions through legislation. However, many conservation initiatives work with farmers to implement many types of buffers. Federal, provincial, and state funding is sometimes available, and incentives are often done through tax breaks or cost share programs which provides funding for a portion of the implementation and management costs (Agriculture and Agri-Food Canada, 2017; Natural Resources Conservation Service, 2018a). A number of non-governmental organizations (NGOs) have also developed programs to provide financial support for wildlife habitat conservation or rehabilitation, which can include support for vegetated buffer construction. For example, Fondation de la faune de Québec subsidizes approximately 400 wildlife conservation or habitat development projects each year through their various assistance programs (Fondation de la faune de Québec, 2018a). The Fondation de la faune de Québec has also developed a program called Biodiversity in Farming Communities with the aim to support farming organizations to develop an integrated management approach to farming and wildlife resources in the province of Quebec (Fondation de la faune de Québec, 2018b). Cost share programs exist throughout both Canada and the United States (Fig. 4 B and D). These programs usually have broader goals in conservation and sustainable agriculture but can provide financial and technical assistance to encourage implementation and management of vegetated buffers (Agriculture and Agri-Food Canada, 2018a; Farm Service Agency, 2018b; Natural Resources Conservation Service, 2018c). In the United States, FSA′ Conservation Reserve Program (CRP) and NRCS’ Environmental Quality Incentives Program (EQIP) provide technical and financial support to farmers who engage in conservation activities (Farm Service Agency, 2018b; Natural Resources Conservation Service, 2018c). The FSA also supports a joint state and federal program called the Conservation Reserve Enhancement Program (CREP) (Farm Service Agency, 2018a). This program is only applicable to states that have a joint agreement with the federal government. Currently, 33 states participate in the CREP program with differing conservation goals (Farm Service Agency, 2018a). Some states provide monetary awards depending on the CREP activity a farmer undertakes. For instance, Indiana provides incentives of $100 USD per acre for installing permanent native grasses, permanent wildlife habitat, or filter strips as buffers as small as 15.2 m in width and as large as 36.6 m, or a maximum of 91.4 m in alluvial soil (Indiana State Department of Agriculture, 2018). There are also $400 USD per acre payments available for hardwood tree planting buffers, and riparian buffers ranging from 10.7 m to 54.9 m in width, as well as cost shares available as determined by the federal Farm Service Agency (FSA) (Indiana State Department of Agriculture, 2018). Some cost share programs require the approval of a management plan and the use of NRCS technical guidance documents to qualify for funding (Nebraska Department of Agriculture, 2016; Wisconsin State Legislature, 2018). The Canadian Agricultural Partnership is a five year cost share program between Canada's federal government and the provincial and territorial governments that agree to the terms of a bilateral agreement (Agriculture and Agri-Food Canada, 2017; 2018a). The federal government invests 60% into the funds of the program, while the province 18

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Fig. 5. Proportions of areas and habitat types adjacent to land requiring a buffer as found in government programs and regulations concerning setbacks, vegetated barriers, and filter strips in North America, as of March 2019.

parameter for determining its efficacy at inhibiting transport of sediment, nutrient, and pesticides in surface waters (e.g., Liu et al. (2007). Conversely, buffer width has important implications for the farmer as the buffer represents a loss in field area for cultivation. Consequently, in this example, there is a need to strike a balance between regulating a buffer width that effectively protects surface water while maximizing available land for farmers to cultivate. This leads to two recommendations. First, there is some consideration for the harmonization in vegetated buffer regulations across (similar) jurisdictions. Harmonization would make it easier for governments to communicate and promote regulations around implementation of vegetated buffers across jurisdictions. Not only do vegetated buffers vary between jurisdictions, but programs and regulations that concern them are difficult to find on government websites. A person may have to search websites of a number of departments and/ or levels of government to obtain information on vegetated buffer requirements and/or incentive programs. However, this call for harmonization is balanced with the recognition that a “one size fits all” approach may not be appropriate. Different geographies are subject to unique soil characteristics and hydrological conditions that may (and likely will) impact the effectiveness of vegetative buffers in attenuating the off-field movement of runoff, sediment, and chemicals. As a result, care should be taken when, for example, applying a single buffer width across a national or other vast area. The second recommendation is that the chosen structure of buffers should be based on an empirical understanding of factors that influence efficacy. Returning to our example of a 10-fold variation in width, what does the current literature tell us about the relationship between buffer width and efficacy? Does this relationship contain an asymptote? What buffer width maximizes protection and production? The same set of questions can be asked about other factors (e.g., soil type, vegetation in buffer) related to the structure of vegetated buffers. It is also important to understand variation in the magnitude of influence that each factor may have on the efficacy of vegetated buffers. This will aid in developing a harmonized approach for regulating vegetated buffers by allowing for regulation to focus on factors that maximize efficacy. It is also important to consider that a single type of vegetated buffer may not be appropriate across all landscapes, especially when we consider the variation in landscapes across Canada and the U.S. There are a number of landscape-specific factors that influence the efficacy of vegetated buffers in preventing off-field movement of sediment,

buffer pilot program that could result in further legislation (State of Hawaii, 2018). These examples demonstrate that while some programs are time limited, other funding and technical support could become available in the future. Materials that contain buffer regulation and implementation tend to vary by jurisdiction. They can be found in watershed regulations, environmental acts, BMPs for erosion or fertilization, riparian zone protection programs, or pesticide control acts, at multiple levels of government (Government of Canada, 2009; United States Environmental Protection Agency, 2017a). They are specific to topography, nearby resources, soil type, property goals, available funding, current programs, and selected pesticides and fertilizers (Government of Canada, 2009; Natural Resources Conservation Service, 2016b; 2018a). They can also be used to protect a variety of areas, populations, and resources (Fig. 5). In states like Delaware, setback and buffer requirements and programs can be found under multiple acts and government documents such as the Delaware pesticide rules and regulations, Regulations governing the pollution control strategy for the Indian River Bay, Rehboth Bay, and Little Assawoman Bay watersheds, and the CREP program for Delaware (Delaware General Assembly, 1995, 2008; Farm Service Agency, 2017). In other instances, like California, the presence of an endangered species may mandate further buffers and setbacks (United States District Court Western District of Washington at Seattle, 2004; United States Environmental Protection Agency and Agency, 2007). Since many factors are involved, regulations and programs can be found under multiple acts and departments making it difficult to find the necessary information on recommendations or mandatory requirements around vegetated buffers or cost share programs that could help facilitate the construction and management of a buffer. In many cases they are left to the applicator's discretion unless stated on pesticide label instructions (Government of Canada, 2009; Government of Newfoundland and Labrador, 2013; United States Environmental Protection Agency, 2017a). 6. Conclusions and recommendations Regulations and BMPs related to vegetated buffers vary considerably across jurisdictions. For example, recommended width of a buffer from surface waters without a specific conservation designation (e.g. not critical habitat for endangered species) ranges from 7.62 m (Georgia) to 76.2 m (New Hampshire). Width of a buffer is an important 19

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nutrients, and pesticides. For example, slope, soil type, mode of application, nutrient or pesticide being applied, crop, vegetation present in the buffer, and frequency and magnitude of precipitation will all factor into the appropriate vegetated buffer for a particular location. Consequently, variation in landscape needs to be considered in a harmonized approach to vegetative buffer regulation. These two recommendations highlight the need for a critical review of current literature surrounding landscape and structural factors that influence the efficacy of vegetated buffers to inhibit sediment, nutrient, and pesticide movement off agricultural fields, while providing habitat for wildlife and pollinators. A critical review will assist in the development of a science-based harmonized framework for vegetated buffers that will maximize protection and agricultural production. Finally, variation across jurisdictions in how they incentivize vegetated buffer construction. Some jurisdictions incentivize by creating regulation (i.e. the “stick” approach) which farmers are required to follow, other jurisdictions provide financial compensation (i.e. the “carrot” approach) of some form for buffer construction, and others implement a combination of the two approaches. Harmonization of these approaches to incentivize buffer construction across jurisdictions would, like buffer structure, make it easier for governments and farming organizations to communicate and promote the implementation of vegetated buffers. This is important as we consider the growing evidence that vegetated buffers not only reduce exposure of valued aquatic and terrestrial ecosystems but can also contribute to increased agricultural production by reducing nutrient loss, providing pollination services, and providing habitat for species that help control crop pests. Vegetated buffers play a critical role in sustainable agriculture, consequently, jurisdictions should consider approaches to encourage their construction that benefits the public and farmers.

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