These studies support the importance of considering watershed-specific differences in historical wetland cover, information that is readily available to jurisdictions in southern Ontario, in older as well as in updated reports i. In applying this guideline, current wetland cover, topography, soils and extent of impervious surfaces in a specific watershed must also be considered.
While the maintenance of wetland functions is as or more important than the maintenance of wetland area, given the limited nature of our current understanding of wetland functions, particularly at the watershed scale, wetland area serves as a useful surrogate measure. In many watersheds in southern Ontario, particularly urbanized watersheds, it is not possible to return to historical or pre-urbanization levels of wetland cover or function because of the degree and nature of alteration that has already occurred. The guideline can be achieved, in order of priority, through: 1 protection of extant wetlands; 2 enhancement of extant wetlands; 3 restoration of wetlands in historical locations; and 4 creation of wetlands in suitable areas.
Wetlands can provide benefits anywhere in a watershed, but particular wetland functions can be achieved by rehabilitating wetlands in key locations, such as headwater areas for groundwater discharge and recharge , floodplains and coastal wetlands. Consideration should also be given to protecting networks of isolated wetlands in both urban and rural settings. Wetlands anywhere within a watershed will provide both ecological and hydrological benefits, but are increasingly being understood to provide different functions depending on their location in the watershed, as well as the characteristics of the watershed itself.
The extent to which wetlands can provide water quality benefits has been linked to the biophysical characteristics of the watershed Norton and Fisher as well as the land use context Mitsch and Gosselink ; Zedler Model-based analyses indicate that water quantity and quality benefits are derived from protection of a range of wetland sizes throughout the watershed, with small i.
Earlier literature has also shown that wetlands can perform different functions depending on flow levels. These results support the need for wetlands of various sizes and in various locations in the watershed, at least for provision of a more full range of water quality benefits. In headwater areas, wetlands can provide beneficial functions. In turn, good water-quality conditions in higher portions of watersheds are likely to benefit downstream coastal wetland ecosystems e. Further downstream, palustrine and riverine wetlands are important in reducing and asynchronizing peak flows, improving water quality, and providing habitat for aquatic invertebrates, fish and other wildlife.
They documented reduced downstream water pulses, nutrients, coliform bacteria and stream erosion; a substantial attenuation of nitrogen and phosphorus; and an increase in wetland plant abundance and diversity within the floodplain. In coastal areas such as the Great Lakes, marshes are crucial habitat for fish.
This is supported by observations that changes in the amount and type of wetlands at Long Point have affected the fish assemblages populating all of Lake Erie T. Whillans, Trent University, Peterborough, pers. McKinney and Charpentier found that geographically isolated wetlands contribute to stormwater retention, flood prevention and maintenance of water quality. Wetlands can also provide benefits that address specific objectives or problems at a watershed or more site-specific scale. Wetlands located within urban or agricultural settings act to improve water quality by retaining nutrients and sediments, and providing stormwater management Flanagan and Richardson ; McKinney and Charpentier Flanagan and Richardson found that former wetland areas converted to agricultural uses were linked to higher levels of phosphorus in nearby water bodies and recommended restoration of at least some of these areas to wetland to address this issue.
Some of these more localized benefits are discussed in the following section. Critical Function Zones should be established around wetlands based on knowledge of species present and their use of habitat types. Protection Zones should protect the wetland attributes from stressors. Recommended widths should consider sensitivities of the wetland and the species that depend upon it, as well as local environmental conditions e.
Stressors need to be identified and mitigated through Protection Zone design. The amount of natural habitat that is located adjacent to wetlands can be important to the maintenance of wetland functions and attributes, particularly for wetland-dependent species that rely on these adjacent natural areas for portions of their life cycle.
In cases where these adjacent natural areas form an intrinsic part of the wetland ecosystem, providing a variety of habitat functions for wetland-associated fauna that extend beyond the wetland limit, these lands can be described as Critical Function Zones CFZs. These stressors are typically associated with human-induced changes in land use and include sedimentation, contaminants, noise, light, physical disturbances e. These adjacent areas that serve primarily a protective function are best described as Protection Zones PZs.
Determining the appropriate amount of natural area adjacent to a wetland requires independent consideration of the CFZ and the PZ , and the functions of the two should not be confused. Critical Function Zones and Protection Zones defined The term Critical Function Zone CFZ describes non-wetland areas within which biophysical functions or attributes directly related to the wetland occur. This could, for example, be adjacent upland grassland nesting habitat for waterfowl that use the wetland to raise their broods.
The CFZ could also encompass upland nesting habitat for turtles that otherwise occupy the wetland, foraging areas for frogs and dragonflies, or nesting habitat for birds that straddle the wetland-upland ecozone e. A groundwater recharge area that is important for the function of a wetland but located in the adjacent lands could also be considered part of the CFZ. Effectively, the CFZ is a functional extension of the wetland into the upland. It is not a buffer for the wetland. Once identified, the CFZ along with the wetland itself needs to be protected from adverse effects that originate from external sources by a Protection Zone PZ.
PZs are analogous to filter strips and are typically vegetated areas for intercepting stormwater runoff and attenuating and transforming associated nutrients or other contaminants. They also provide physical separation from one or more stressors such as noises or visual disturbances. And they protect against direct human-associated intrusions into the wetland. Such functions are well-established in the literature e. Depending on the nature of the stressors and the sensitivities of the wetland, alternative PZ design features such as a fence can be effective.
Fundamentally, the PZ is aimed at reducing impacts on wetland functions that originate from the upland side. Figure 8. The Critical Function and Protection Zones. In How Much Habitat is Enough? This is because adjacent lands may have buffer functions, important non-buffer habitat functions, or both. These distinctions are important. These are typically prescribed as a set distance e. Management objectives, individual characteristics of the wetland, ecological interactions with upland areas, and the source, magnitude and frequency of potential stressors and engineering options all contribute to the design of effective CFZ and PZ areas.
For CFZ determination, a good understanding of the local biophysical context, hydrologic regime and the species using the given wetland, as well as the nature and extent of their non-wetland habitat requirements, is required e. For wildlife, the variability in ranges of CFZs is great because of both inter- and intra-species variability in documented distances travelled for feeding and overwintering, as well as variability among breeding sites e.
In time, more data will become available as further research e. Like CFZs , optimal PZ widths also vary depending on a number of site-specific factors as well as the land use context. Of primary importance is understanding the desired function s that the PZ is expected to perform.
Examples of recommended PZ buffer widths for wetlands are provided in Table 4. PZ width can also vary depending on its anticipated uses. This approach encourages the identification and prioritization of various criteria that are selected on a site-specific basis. This could result, for example, in the encouragement of some land uses or activities within the PZs e.
For example, an appropriately sized and designed PZ can accommodate trails that support opportunities for hiking and cycling, as well as nature interpretation and appreciation, or urban infrastructure such as stormwater management facilities. Based on current knowledge, the literature increasingly indicates that the habitat requirements for wildlife tend to result in the widest and most varied CFZs e. There are no known studies that actually test the ability of different buffer types or widths to protect wetland habitats whether for plants or wildlife or both.
Therefore, PZ recommendations related to wildlife, where provided, are typically extrapolated from measurements of impacts to various wetland species. Such recommendations may overestimate or underestimate the actual buffer widths required, and more research is required to address this knowledge gap. Useful guidance is also available from review papers that summarize data from a wide range of sources.
Notably, even protection of wetlands and their functions through the identification and implementation of CFZs and PZs will not fully conserve the habitat functions of wetlands on a landscape scale. Implementation of these site-specific measures must be considered in the broader context of natural heritage protection on a watershed or regional scale. Capture the full range of wetland types, areas and hydroperiods that occurred historically within the watershed.
Swamps and marshes of sufficient size to support habitat heterogeneity are particularly important, as are extensive swamps with minimum edge and maximum interior habitat to support area-sensitive species. Extensive, heterogeneous wetlands as well as less extensive, isolated wetlands both make significant contributions to supporting biodiversity at the local and watershed scales.
The presence of larger, contiguous swamps and marshes e.
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However, the presence of complexes of smaller, more isolated wetlands in the landscape are also important in that they provide habitat for many wetland-dependent amphibians and reptiles. Swamps have the potential to support area-sensitive wildlife species i. In some watersheds with many land use pressures, treed swamps may be the only remaining significant contributors to interior-forest habitat, and the discussion on forest size and species that may be expected see Section 2.
However, treed swamps provide interior habitat for a different suite of specialist area-sensitive forest species compared to large patches of upland forest. Larger marshes also have the ability to support area-sensitive wildlife species Smith and Chow-Fraser Black Tern will nest in smaller marshes if larger feeding areas are located nearby.
Some other species, such as Least Bittern and King Rail, occasionally occur in smaller marshes, but long-term viable populations are associated with extensive marshes. Extensive swamps and marshes also tend to have greater habitat heterogeneity i. High levels of habitat interspersion e.
For example, some species require extensive stands of emergent plants with few or no openings e. However, area remains a key factor, and more extensive marshes are more likely to be used as productive habitat by more species of wildlife e. Relatively isolated i. For example, amphibians such as Wood Frog and Spotted Salamander have been documented in wetlands ranging in size from 0. These wetlands can have variable hydroperiods, may be permanently wet i.
Complexes of relatively isolated wetlands also tend to be more supportive of biodiversity than single, isolated ponds. Some birds have specifically adapted to use wetland complexes in the landscape and will readily move between them to forage e. The presence of coarse woody debris in many wetland types--particularly swamps, but also riparian areas and terrestrial areas associated with wetland pockets--is important to many species.
The functions of this debris include providing cover and nutrients for fish and other aquatic organisms, and providing important cover and overwintering habitat for pond-breeding amphibians that spend the bulk of their life cycle in associated uplands Keddy Maintenance of the full range of wetland vegetation community types that occur in a watershed is also key to sustaining biodiversity. The role of wetland shape in supporting habitat and species diversity is difficult to discuss independently because it is so closely related to, and in the literature is often confounded with, habitat area and fragmentation in the landscape Ewers and Didham The limited available data indicate that the optimum shape of a wetland varies by wetland type.
Swamps, which are a type of forest, are better able to support area-sensitive and edge-intolerant species when they are relatively compact and regularly shaped e. However, some other wetland-dependent species require ecotonal or edge habitat e. Long, narrow marshes may also provide more water quality benefits since they maximize water contact with vegetation that is responsible for the uptake and transformation of many nutrients and other contaminants.
The link between wildlife species diversity and abundance, and the presence of wetlands, has been made repeatedly for amphibians. Wetlands that are in close proximity to each other, based on their functions, or that are in close proximity to other natural features, should be given a high priority in terms of landscape planning.
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Fragmentation of wetland habitats degrades their functions by reducing habitat for species that are less tolerant of disturbances, that require more contiguous habitat, or both, compromising the ability of individuals of a species to effectively disperse and mate with individuals from other populations, and increasing habitat for opportunistic species such as exotic invasive species and pests.
Some of these negative impacts of fragmentation can be offset, at least for some species, by maintaining concentrations of natural habitat fragments within relatively close proximity in a given landscape. The benefits of this type of land use planning may be further enhanced by minimizing the scale and extent of built-up land uses e.
Fragmentation of marshes within lakes can result in depletion of zooplankton and the fish species that depend on them. Even in systems where zooplankton is not a concern, small marsh patches may be ecological traps. They attract fry of many fish species as nursery habitat, but predation rates by common piscivorous fish eating fish such as Rock Bass may be very high. Small marshes--especially high concentrations of small marshes in a landscape--have traditionally been conserved and restored for waterfowl production. Increasingly, the importance of adjacent natural areas, as well as proximity between patches of wetland, has become recognized for a number of other wildlife species.
Figure 9. Wetlands in close proximity with adjacent natural areas. While most of the available research on the effects of wetland fragmentation is focused on birds and amphibians, it is intuitive that maintaining hydrologic connections between nearby wetlands where they exist , as well as wetlands and other nearby natural areas, could also be critical to maintaining their functions.
Focus on restoring marshes and swamps. Restore fens under certain conditions. For effective restoration, consider local site conditions, have local sources to propagate new vegetation, and wherever possible refer to historic wetland locations or conditions. Prioritize headwater areas, floodplains and coastal wetlands as restoration locations. In the current land use context of southern Ontario, it is simply not possible for many watersheds and jurisdictions to return to estimated historical levels of wetland cover.
Also, the ability to restore the diversity and complexity of wetlands, and their wildlife functions, remains questionable, and where possible even partial restoration of a wetland can take many years. Regardless, where necessary, targeted and well-planned wetland restoration can help priority restoration areas meet water quality and wildlife habitat targets at watershed-wide and ecozone scales. Despite the limitations, restored wetlands can provide habitat for a range of species.
Using historical data and reference sites as a starting point for setting realistic targets and identifying appropriate locations for wetland restoration is an ecologically sound approach. Restoration by wetland type Only two wetland types--marshes and, to a more limited extent, swamps--may be restored with some confidence. Currently, limited information is available on the science of rehabilitating fens and bogs, and the best management strategy as for all wetlands is to protect them by protecting their water sources and not altering their watersheds.
In some cases, abandoned pits and quarries that are connected to the water table may offer unique opportunities for fen creation Hough Woodland Naylor Dance Limited and Gore and Storrie Limited Although there is also little published research on successful reproduction of mature forested wetlands, these wetlands are considered less complex from a restoration perspective than bogs or fens, and are generally considered reasonable candidates for restoration given the right conditions and sufficient time for trees and tall shrubs to grow. Marshes are considered the most readily restored type of wetland and can be at least partially functional within a few years.
As a result, marsh restoration has been widely implemented. Despite this, restoration has often been unsuccessful. Available data for regulated wetland restoration from the United States, from hundreds of projects evaluated over five different states, indicate that less than a third to a quarter were considered successful in terms of area of wetland replaced for area lost. Furthermore, when specific wetland functions were compared between reference and restored wetlands, most restored or created sites had less organic matter, lower plant species diversity and structural complexity, and lower diversity of other groups of wildlife e.
Common problems included failure of wetland vegetation to establish throughout the site, and lower levels of vegetation and wildlife diversity compared to reference sites. The relatively low level of documented success provides a good rationale for working towards replacement ratios of more than one to one.
Another argument for wetland replacement ratio of more than one to one is presented by Gutrich and Hitzhusen , who found time lags for restored wetlands to attain the floristic and soil equivalency of reference wetlands to range from 8 to 50 years. Restoration considerations Successful wetland restoration requires technical expertise. Key variables that need to be considered include soil conditions and fertility including the presence of organic matter , water level fluctuations, and plant competition and structure as determined by gradients along wetland edges.
The presence of rare species is also important, not just for intrinsic value, but because they indicate the presence of rare habitat conditions that may also be valuable to other species Keddy ; Keddy and Fraser It should also be remembered that humans are not the only mammals playing a role in wetland creation: Muskrats and Beavers influence many wetland functions, and are often active participants in restoration e. A practical process of implementing headwater wetland restoration in agricultural southern Ontario has been developed in Aylmer District of the Ontario Ministry of Natural Resources in southwestern Ontario.
The process involves local biologists, drainage superintendents, landowners and others. The methodology incorporates current science, land use considerations, landowner interests and hydrological and biodiversity benefits. A guide book has been produced. This is a valuable strategy for wetland restoration that can be copied across southern Ontario A. Restoration by location Wetlands restored anywhere within a watershed will provide an array of benefits including regulation of peak water flows and increases in biodiversity, provided that they are in suitable sites.
However, the scientific literature is increasingly demonstrating that restoration of wetlands in some areas can be more beneficial than in others. Some guidance for determining the best locations for wetland restoration projects is available Almendinger ; Bedford ; DeLaney ; Griener and Hershner Restoration of some major wetland areas such as Great Lakes coastal wetlands can result in extremely valuable ecological benefits; however, these projects can be technically challenging due to their size and complexity.
In considering wetland location see Section 2.
Lands adjacent to streams and rivers are referred to as riparian. The riparian zone is an area where terrestrial and aquatic systems influence each other Knutson and Naef , and it functions as an ecotone and ecosystem Naiman and Decamps The extent of the riparian zone is defined here as the area where vegetation may be influenced by flooding or elevated water tables Naiman and Decamps , by its related ecological functions, or both.
Riparian zones provide two broad types of ecological function. They provide essential services to aquatic habitats as both a buffer between aquatic ecosystems and terrestrial systems, and as contributors of resources including woody structure, nutrients and shade. Riparian zones also provide habitat in their own right, which may be moderated or enhanced or possibly diminished by both the aquatic system on one side and the broader terrestrial systems on the other side. Watershed attributes beyond the riparian zone, such as land cover and land use, will also have an influence on stream habitat quality.
The habitat guidelines presented here relate to the tributaries of the Great Lakes and St. Lawrence River. The focus of this section is principally on terrestrial habitat and its relation to watercourses and wetlands. As such, it does not include in-stream habitat guidance. There is a large and growing body of knowledge on in-stream habitat and hydraulic parameters that should be considered when specifically assessing stream health and considering stream rehabilitation. The width of the riparian zone and the percent vegetated stream length guidelines directly address the amount of riparian area present to provide both direct terrestrial habitat and ecological services to aquatic habitat.
It is important to recognize that this entire complex environment requires overarching general protection. Fluvial processes in the form of floods and regular variations in water levels also contribute to functional and species diversity within the floodplain Ward and Tockner In order to best address stream quality as well as terrestrial and aquatic habitat functions, the area of natural riparian vegetation should encompass the floodplain and upland transition zone or ecotone.
Where there is a strong physical disjunct between the stream and upland, such as a bluff, riparian vegetation may have less direct habitat value, although it may have strong value in terms of erosion control and some habitat attributes. Widths necessary to provide effective buffering capability may also be influenced by the sensitivity of the receiving watercourse and its ability to assimilate any stressors. The width and percent vegetation guidelines represent a generic riparian zone that is applicable under the greatest range of geographic, biotic and abiotic conditions.
Impervious land cover within the broader watershed will have significant impacts on the quality of aquatic habitat within streams. These impacts may be mitigated to some degree by riparian zones. Relatively narrow riparian zones may be adequate when the broader area is in good condition i. Finally, measures of water quality and of fish communities provide feedback on the effectiveness of the riparian zone--in conjunction with the surrounding watershed land cover--in protecting and maintaining the aquatic environment. Fish communities may be affected by direct influences on aquatic habitat such as point source and upstream tributary inputs, or by other in-stream disturbances human-induced or otherwise , or both.
However, the quantity and quality of riparian habitat can help to directly mitigate watershed landscape effects on both water quality and aquatic life. Modifying factors beyond land use such as in-stream barriers including dams , channel modifications and point-source discharges will have a significant effect on stream and aquatic community qualities Stantec Table 7 shows stream response to human alteration based on underlying conditions.
Additionally, these systems receive and transport large volumes of beneficial organic matter e. Headwater streams are significantly more efficient at retaining and transforming organic matter than larger streams. The retention and transformation of organic matter upstream affects downstream water quality and the survival and condition of organisms reliant on in-stream food sources Cappelia and Fraley-McNeal Drawing from studies on a small shaded stream, Nakano and Murakami found biomass fluxes between stream and forest accounted for In addition, England and Rosemond suggest that relatively low levels of riparian deforestation along headwater streams can weaken terrestrial-aquatic linkages.
From a watershed perspective, effective management practices must consider how riparian zones contribute to conditions within local streams--especially for stream orders one through three--both directly and indirectly, and how they provide terrestrial habitat in their own right. The discussions presented below provide scientifically supported guidance for the minimum habitat parameters under which riparian zones can function as aquatic buffers, wildlife corridors and in situ habitats. The definition of the riparian zone within a management context should be flexible enough to encompass these functions as well as address the need for enhanced functions to mitigate potential future impacts.
Within watersheds where targets higher than these guidelines can be met and supported, they should be. Watershed land cover and habitat health Watershed land cover beyond the riparian zone does influence stream ecosystems; however, the relationship is difficult to quantify. This finding supports the use of detailed subwatershed studies in advising stream management decisions. However, there has been only partial success at quantifying associations between land use and effects on stream systems given covariation of human and natural influences, mechanisms operating at different scales, nonlinear stream responses, and underlying historical influences Allan Beyond impervious cover, other potentially important aspects of watershed land cover can include measures such as urban land with tree cover, forest fragmentation e.
Allan , in a summary of several studies, noted that there are declines in stream ecosystem health as agricultural land use increases in a watershed. Also, row crops and other more intense uses may have a greater impact on stream health than pasture. Lastly, agricultural landscapes support fewer sensitive fish and insect taxa than forested watersheds.
Stream responses in terms of overall ecosystem health vary widely depending upon the study and the nature of the watershed being studied. In the same summary study, urban land use is seen as having a substantial impact on stream ecosystems, more so than agricultural land use. A number of papers examined links between aquatic ecosystems and percentage of forest cover in the surrounding landscape, and found strong connections between levels of forest cover and aquatic ecosystem health. Johnston and Schmagin found annual streamflow yields were greatest in Great Lakes basin watersheds with the highest forest cover and topographic relief.
Stephenson and Morin found that forest cover at the catchment scale explained more variation in algal, invertebrate and fish biomass than any other metric. Chang cited studies that found forested watersheds normally yield streamflow of higher quality than that from other land uses. Other North American studies support the importance of forests for stream health.
Moreover, higher percentages of porous land cover across the watershed, such as forest, wetland and meadow, will have a positive effect on stream ecology on the basis that they are not impervious surfaces. Both sides of streams should have a minimum metre-wide naturally vegetated riparian area to provide and protect aquatic habitat.
Vegetation communities within the riparian zone can directly influence aquatic habitat and affect water quality for aquatic life. These functions include moderation of temperature through the provision of shade, filtration of sediments and nutrients, provision of food inputs through organic debris and leaf litter, and contribution to physical habitat in terms of fallen woody material. Vegetated riparian zones also serve as terrestrial habitat and corridors for wildlife as well as places where terrestrial and aquatic food webs interconnect.
These diverse functions can be interactive or independent and will vary with watershed context. For example, the ability of riparian vegetation to moderate water temperature may decline with increasing stream width and volume, but it may still provide terrestrial habitat. The riparian zone width requiring maintenance or protection may vary depending on the size order of the stream, the steepness of the banks, and the specific management concerns of the local system USDA The metre width guideline provided here is a minimum general approximation intended to capture processes and functions typical of the active riparian zone of a floodplain and the floodplain-to-upland transition with respect to ecological services provided to aquatic habitat.
The riparian width guidelines do not directly include transition buffers beyond the riparian zone, but transition buffers should be considered in managing the riparian zone and from an ecosystem management approach. The type of vegetation and other site-specific conditions beyond the immediate riparian zone may be of particular importance in the management of urban watersheds, as urban development entirely changes the characteristic of surface flow that laterally enters the riparian. The effects of vegetation and land cover beyond the riparian zone on stream aquatic habitat are discussed below and in the following section.
Also, while adjacent vegetation should be maintained next to lakes for similar reasons as for streams, this guideline was not developed specifically for lakes. In terms of buffering and habitat functions, there are parallels with PZs as discussed in Section 2. Principally, the metre riparian adjacent vegetation guideline is not based on a species- or function-specific need but reflects a general threshold distance for aquatic health and riparian functions. Also, the metre width is meant to capture a variety of protection and habitat functions. And some of the riparian habitat functions, such as wildlife corridors, do not reflect upland habitat needs of aquatic species but the needs of upland species that utilize the riparian system or stream.
Knutson and Naef reviewed numerous published sources on varying riparian widths and the effect on stream health. A partial removal or loss of some riparian trees, however, may not necessarily impair some riparian buffer functions. However, watershed land cover, and more specifically the ratio of natural cover especially, but not necessarily forest cover to human-dominated impervious land covers, will change the effectiveness of riparian buffers.
The effects of catchment land cover are important and are further discussed in subsequent sections. The relationship between width and sediment removal was non-linear, with disproportionately wider riparian strips required for relatively small improvements in sediment removal. For example, in one test case, widths of The frequency and intensity of sediment inputs are important criteria for the effectiveness of the riparian zone in mitigating the effects of sediment inputs.
Adjacent lands with established vegetation are fairly efficient at removing excess nutrients from surface runoff. In some studies, areas with widths as narrow as 4. A metre-wide adjacent land area along a stream next to logging operations greatly reduced nutrient levels to better than drinking water standards. Riparian zones as wildlife habitat Riparian systems can provide important wildlife habitat. Habitat may be valuable for its intrinsic values, for example as forested habitat for breeding birds or as habitat for flora or as linear features providing connectivity for terrestrial wildlife movement Knutson and Naef , rather than any particular relationship to the riparian zone itself.
Corridor and habitat widths for mammals, reptiles and amphibians are often dependent on the requirements of individual species, and these are discussed elsewhere in this document. However, it is worth noting that widths to address ecological concerns are much wider than those recommended for water quality concerns Fischer ; Fischer and Fischenich As the width increases, factors such as overall habitat heterogeneity become important and the habitat requirements of species exceed the area of the riparian zone. Riparian areas, specifically due to their association with water, provide core habitat areas for many herpetile reptile and amphibian species.
There is a wide range of suggested appropriate riparian widths based on function, with the published range in the literature varying from a few metres to over metres, depending on the study and level of representation and confidence e. The recommended metre width is supported in the literature as a general guideline minimum for many riparian systems. The metre guideline may provide for basic terrestrial habitat; however, a greater width may be required to provide for a highly functional wildlife habitat. As described, riparian zones contribute to stream habitats in many ways.
At the local scale, natural but otherwise open landscapes i. Gartner Lee Limited b also noted that the presence of cold water streams is heavily dependent on the geological characteristics of the area. Riparian vegetation provides proportionately greater benefits to stream aquatic habitat along the headwaters of streams.
From a watershed perspective, planting vegetation along smaller systems i. Given that the form and function of headwater streams are strongly influenced by the character of adjacent lands, a lack of adjacent natural vegetation can result in dramatic alterations in flow and sediment regimes. Figure Stream order, showing extent of first- to third-order streams. Riparian vegetation, however, will still be of great value along larger rivers for species such as waterfowl, reptiles and amphibians, as well as mammals such as North American River Otter, American Mink and Beaver.
In this context, there is a similarity to wetland CFZs see Section 2. Lower-order streams comprise the majority of stream systems in the lower Great Lakes basin. Effective management approaches should consider local watershed conditions land cover when applying this guideline, as discussed in the following section. As part of the hydrologic cycle, water falling as precipitation will soak into the ground replenishing ground water and deeper aquifers infiltration , or will flow above ground as surface water.
Both ground and surface water may enter streams, rivers and lakes, eventually flowing into oceans. The base flow of a stream relies on ground water. During a precipitation event, if precipitation exceeds the infiltration capacity, water runs along the surface, either infiltrating elsewhere or entering streams directly. Total surface runoff flowing directly into streams increases with impervious land surfaces, such as pavement and concrete, or even with reduced infiltration, such as on compacted soils Stanfield and Jackson The loss of fish and wildlife habitat, along with channel erosion and downstream flooding, are primary components of a stream system decline that result from high impervious levels within a watershed Booth ; Booth ; Knutson and Naef The debate on identifying reasonable thresholds for impervious surfaces within a watershed began in In addition, Booth stated that urban development both magnifies peak discharges and creates new peak runoff events.
Schueler reported on a number of studies that relate imperviousness to runoff characteristics, stream morphology, water quality, pollutant loading, stream warming, as well as aquatic biodiversity. Snodgrass reported that water quality became degraded when hard surfaces from development e. Contemporary stormwater management could not prevent stream-quality impairment in the study provided by Snodgrass In the past two decades, stormwater best management practices have evolved considerably. However, the primary focus of control of peak flow rate and the reduction of suspended solids has not mitigated the widespread and cumulative hydrologic modification to both streams and the broader watershed CVC and TRCA Various indicators of aquatic macroinvertebrate community health are widely used as relationship indicators between watershed imperviousness and aquatic systems.
At a study conducted in Washington, D. This value is proposed as a defensible minimum standard for a guideline. Not every watershed, though, will respond uniformly or as anticipated to proposed impervious surface thresholds. In southern Ontario, impervious surfaces are often associated with particular land uses, and the relationships between land cover and stream water quality depends, in large measure, on how land cover is classified Stantec While urban lands are generally more impervious than agricultural lands, there can be significant differences in permeability within these categories Stantec Imperviousness also varies with the agricultural type and intensity level.
In relatively undeveloped rural watersheds, stream base flow is dictated by underlying soils and geologic conditions that influence the amount of ground water discharge. Within urbanizing watersheds, however, careful planning may mitigate some of the effects of impervious surfaces. Extreme peak flows typical of urban environments can be reduced through minimizing hard surfaces. Imperviousness provides a surrogate measure of a variety of stream impacts associated with watershed development and land use conversion. In determining conservation policies, however, it is important to understand that impervious cover should not only be considered as the percent of a watershed or subwatershed that is paved or developed.
In this study, an urban intensity value was derived using 24 landscape variables and measured at 30 sites representing different levels of watershed development. From this, a gradient of urban intensity was developed that allowed estimates of expected stream condition based on level of urbanization. Stanfield and Kilgour in review examine a land disturbance index in southern Ontario as a more inclusive measure of disturbance that measures the cumulative development within a watershed.
Beyond the simple percent impervious guideline value, effective conservation planning and policy should consider where the imperviousness is located in a watershed. If headwater areas have minimal impervious cover, and urban areas with high imperviousness are located only in the higher-order sections of the watershed, streams may have a better chance of maintaining integrity. Future changes can be anticipated both in the way in which imperviousness is calculated and the manner in which intensity of land uses is factored into this assessment.
In the interim, the guidelines provided make the best use of the science surrounding this subject. Physical and chemical water quality parameters Physical and chemical measures of water quality should be within federal and provincial guidelines. Measures of water quality such as total suspended solids, pH, oxygen, and concentrations of nutrients, metals and other contaminants are important in monitoring the health of streams. Water quality parameters are affected by influences on aquatic habitat such as point source and non-point source upstream tributary inputs, in-stream disturbances anthropogenic or otherwise , or both, and by the conditions in the broader watershed such as levels of impervious cover as discussed above.
The quantity and quality of riparian habitat can mitigate watershed landscape effects on water quality Brabec Canadian Environmental Quality Guidelines provide chemical-specific guideline fact sheets indicating environmental limits for over different chemicals and water quality parameters CCME Each fact sheet summarizes key scientific information and the rationale for the limit. They also provide detailed implementation advice.
Beyond individual parameter guidelines, the CCME has also developed a spreadsheet tool that summarizes multiple water, sediment and soil quality variables into a single measure of overall water, sediment or soil quality. The Water Quality Index was developed to provide a standard metric for jurisdictions to track and report water quality information. It is available, along with associated support material. In southern Ontario, provincial water quality objectives PWQOs also provide standard guidelines for physical and chemical water quality parameters for the protection of the health of aquatic life.
PWQOs provide guidance in making water quality management decisions and should be considered in the management of riparian zones and broader watersheds, given their influence on streams and other aquatic habitat. Fish communities are a product of stream and watershed characteristics, and there are various guides available to measure the health of aquatic habitats and to establish fish community targets. The fundamental characteristics of the stream and watershed dictate the limits and potential of the stream system.
The historic condition provides a direction for rehabilitation. The existing conditions indicate how far the system is from being healthy or at least resembling historic conditions. Beyond these fundamental reference points and characteristics, there are a variety of approaches to restore stream environments and manage fisheries. In order to develop locally relevant fish community targets, it is advisable to contact agencies and organizations working in your local watershed, such as the Ontario Ministry of Natural Resources, Conservation Authorities or non-government groups.
This includes both upland forests and swamps as well as plantations. It generally does not include orchards or tree farms. Prior to European settlement, forest was the predominant habitat across the Mixedwood Plains. And today, if human influence and disturbance were to cease, it would be the land cover that would be most likely to naturally re-establish across most of the ecozone. Many of the types of wildlife that are currently found in the Mixedwood Plains, and the niches they occupy, are a legacy of this past forest matrix.
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The remnants of this vast forest now exist in a fragmented state with patches of various sizes distributed across the settled landscape, with higher levels of forest cover occurring along the northern edges of the ecozone and associated with features such as the Niagara Escarpment and Frontenac Axis. The forest legacy, in terms of species richness, ecological functions and ecosystem complexity is still evident in these patches and regional forest matrices. These ecological features are in addition to the previously discussed influence forests have on water quality and stream hydrology see Section 2.
Many flora and fauna species are obligate users of forested habitats--that is, they cannot survive without forested habitats. Structurally diverse compared to many other habitats , forests provide a great many habitat niches that are in turn occupied by a great diversity of species. They provide food, water and shelter for these species--whether they are breeding and more or less resident, or using forest cover to assist in their movements across the landscape. This diversity of species includes many that are considered to be species at risk.
From a wildlife perspective, there is increasing evidence that the total forest cover in a given area is a major predictor of the persistence and size of bird populations, and it is possible or perhaps likely that this pattern extends to other flora and fauna groups. The pattern of distribution of forest cover, the shape, area and juxtaposition of remaining forest patches, and the quality of forest cover also play major roles in determining how valuable forests will be to wildlife and people alike. This equates to a high-risk approach that may only support less than one half of the potential species richness, and marginally healthy aquatic systems;.
Forest habitat thresholds: proceed with caution… There is tremendous interest in minimum threshold levels for forest cover and other habitat types required to support healthy levels of native flora and fauna. Such thresholds can facilitate natural heritage planning and help support initiatives to protect and expand forest cover.
However, given the current data gaps in the site-specific and landscape-scale habitat requirements of different species and groups of species, the science that is currently available to support such thresholds is limited. Therefore, the values provided here should be viewed as generalized guidance based on the available science.
This makes intuitive sense, as there is seldom a clear-cut answer to a particular problem in ecology. There is potential to adopt this approach for further habitat guidance within the Mixedwood Plains. This is increasingly evident as levels of forest cover increase in a given landscape. A number of relatively short-term studies i.
Information related to the current atlas is available. These data support the general concept that regions with lower levels of forest cover also support lower diversities of forest-dwelling birds. The overall effect of a decrease in forest cover on birds in fragmented landscapes is that certain species disappear and many of the remaining ones become rare, or fail to reproduce, while species adapted to more open and successional habitats, as well as those that are more tolerant to human-induced disturbances in general are able to persist, and in some cases thrive.
Species with specialized-habitat requirements are most likely to be affected adversely. Current research has also begun to explore relationships between forest cover and amphibians. Studies on both mole salamanders and frogs have consistently found strong links between levels of local forest cover and both species diversity and abundance e. As with birds, variability among species has been observed. However, for some amphibians, such as Wood Frog, the presence of that forest cover in close proximity to the breeding ponds appears to be as important as the level of cover as shown in Table The overall amount of forest cover in a landscape also helps determine its ability to support large mammals.
Species such as Gray Wolf, Canada Lynx, and Elk that require extensive forests disappeared from southern Ontario shortly after forest clearing was initiated, and are now only found in central and northern Ontario where forest cover is more extensive. In general, the literature indicates that a complex relationship exists between the relative importance of overall forest cover versus forest patch size and the ultimate response of individual wildlife species e.
These studies and reviews have all shown or suggested that forest patch size and shape play a lesser role in maintaining regional or landscape-scale levels of biodiversity than the total amount of forest cover, although the three metrics are to some extent interrelated. Factors such as overall forest cover, forest patch area, shape and degree of fragmentation all affect the viability of habitat for wildlife species. However, for forest-dependent fauna, overall forest cover on the landscape is one of the most important habitat metrics.
This means that in landscapes with relatively low levels of forest cover e. Forest cover loss versus fragmentation Forest habitat loss and habitat fragmentation are widely recognized as two key factors in the decline of wildlife species in the Mixedwood Plains and elsewhere. However, there continues to be uncertainty around the relative importance of habitat fragmentation in influencing thresholds in wildlife populations Ewers and Didham ; McGarigal and Cushman ; Zuckerberg and Porter One of the concepts that helps in understanding the relationship between forest cover, fragmentation and species loss is that of metapopulations.
This is a term used to describe semi-isolated populations in a region that are linked by dispersion Merriam ; Opdam Local extirpations of wildlife populations tend to occur naturally within forests due to failed reproductive efforts linked to often stochastic phenomena such as predation, parasitism, adverse weather conditions, natural catastrophes e.
Downstream drift also occurs probably as an avoidance response to toxic conditions Beketov and Liess, b. All these effects were ignored for years, as the focus of neonicotinoid research was on bees, not on aquatic organisms. Obviously, some of these sublethal effects can be reversed if they do not rely directly upon the nervous system. Measurements of acute toxicity such as LC50s are useful to determine the potency of a chemical.
Equally useful are the estimations of lowest effect concentrations LOECs based on observations of chronic exposure, although they are less accurate and reliable. What matters is to protect the populations of as many species as possible so as to maintain the integrity of the aquatic ecosystem services. To achieve that goal, it is imperative to know the range of sensitivities amongst species in different taxonomic groups, so that an evaluation of risks can be made. For aquatic species, toxicity data are scarce for all neonicotinoids except for imidacloprid and, to a lesser extent, thiacloprid.
Therefore, assessments of risks and water quality thresholds for neonicotinoids are currently based on the acute toxicity of imidacloprid, mostly derived from short-term exposures of 2 or 4 days Morrissey et al. It is apparent that the most susceptible species are aquatic insects, followed by crustaceans such as amphipods, ostracods and shrimps, then tubicifid worms and mussels. All cladoceran crustaceans waterfleas are very tolerant except perhaps Ceriodaphnia dubia , which is as sensitive as ostracods. Waterfleas are, therefore, not representative of other invertebrate taxa for imidacloprid nor any other neonicotinoid compound Beketov and Liess, a ; Daam et al.
Figure 2. Species sensitivity distributions SSD, Figure 2 have been used by government agencies in some countries to derive water quality thresholds that protect their aquatic environment. In the Netherlands and other European countries the protective level for short-term peak concentrations of imidacloprid is 0. Thresholds for other neonicotinoids are about the same order of magnitude in the US, but most countries have not established yet any regulation concerning neonicotinoids, while many still base their ecological assessments on the misleading toxicity data for Daphnia and fish.
The above regulatory thresholds are only a guide. Unlike with previous pesticides, protective levels for neonicotinoids cannot be achieved by setting a concentration benchmark because, as already explained, the effects of neonicotinoids increase with exposure time. An alternative is to assess the impact on populations using the predicted affected fraction PAF of species, which is determined by comparing waterborne residue levels from monitoring surveys with the SSD.
Data on water residues for these compounds have been gathered in the past decade; prior to only a few surveys found some imidacloprid in a watershed and two streams of New York State USGS, ; Phillips and Bode, and in drains from potato fields in Canada Denning et al. A meta-analysis of all residue data from 11 countries available to date Table S1 revealed the following:.
Average concentrations were similar for all compounds, ranging from 0. Figure 3. Worldwide survey of neonicotinoid residues in water. The number of surveys reporting each chemical is in brackets. Boxes contain the residues between the first and third quartile; blue lines indicate the geometric mean; vertical lines show the outliers. Sources: see Table S1. Figure 4. Temporal trends of A concentrations of neonicotinoids in waters of the world, and B their frequency of detection. These findings are of concern. However, the increasing residue levels are of great concern, as they indicate that residues in soil, where most of these insecticides are applied, are accumulating over the years.
Indeed, there is evidence that such accumulation is happening in countries with a long history of using seeds treated with imidacloprid Jones et al. Degradation in sediments is faster for newly developed compounds like cycloxaprid Liu et al. The increasing use of products containing neonicotinoids and their repeated application as coated seeds in agricultural fields Douglas and Tooker, adds every year a new layer of residues to the soil, and hence to the waters, where residue levels are a reflection of those present in soil at any time Hladik et al.
By comparing the distribution of waterborne residues of imidacloprid to its SSD, estimations of the PAF are made to assess its current impact on aquatic organisms, i. Only streams and estuaries contaminated mostly with urban runoff, e. One can expect similar impacts for the other neonicotinoid residues, although it is not possible to assess them at this stage so long as the data available are insufficient. Figure 5. Distribution of waterborne residues of imidacloprid in several countries contrasted with the acute SSD for this compound.
This preliminary assessment is only based on the acute toxicity data Figure 2 as determined in laboratories. For more realistic assessments of the long-term impacts, field and mesocosm studies are required, as explained in the next section. Some 22 studies on the impacts of neonicotinoids on aquatic communities have been conducted to date. Most of them comprise mesocosms that used imidacloprid, with five studies using thiacloprid and one acetamiprid in addition to those two compounds Table S2.
These studies were carried out in Japan rice mesocoms , Portugal field trials , Canada, and Germany streams and microcosms. The most striking feature of these studies is their consistency in reporting population and community effects at levels well below the LC50s of the aquatic species tested. This is unusual, since field or mesocosms studies under realistic scenarios typically report fewer impacts of pesticides and other toxicants than in closed laboratory conditions Cleveland et al.
Reduced exposures, due mainly to chemical losses by microbial degradation, hydrolysis and other environmental factors, are usually responsible for the lesser impacts under field conditions Maund et al. Population reductions in the short-term are caused by direct toxicity, but in mesocosms such reductions affect the structure of the macroinvertebrate communities when residues are one or two orders of magnitude lower than the LC50s for most species, as more tolerant taxa tend to increase in numbers to fill the niche vacuum thus created in the ecosystem.
Some of these changes are predictable. In other cases, opportunistic predators e. Interestingly, the negative impacts on predatory copepod populations in rice fields are followed by upsurges of mosquitoes but not of chironomids. Consequently, the overall biodiversity of the aquatic communities is negatively affected Pestana et al. Similar impacts are observed in mesocosms treated with thiacloprid at 3. This is not surprising, as the HC5 for thiacloprid derived from outdoor stream mesocosms is 0. Figure 6. Relative abundance with respect to controls of aquatic invertebrates in imidacloprid-treated mesocosms.
A Communities in rice paddies for different initial concentrations of imidacloprid; dashed lines indicate average reductions. B Invertebrate taxa in rice paddies and streams; vertical dashed line indicates the control. Moreover, many of these populations are decimated and their recovery is either slow or, if there is competition with other species, it does not take place Liess et al. Nor does the structure of the communities revert to the original situation, because some species disappear while others take over and increase in numbers Beketov et al.
These impacts contrast with those caused by other pesticides, which tend to produce a large initial mortality upon target and non-target populations alike but allow the recovery of the species affected within a few weeks van den Brink et al. By contrast, many pyrethroids and organophosphates with the exception of persistent compounds like chlorpyrifos do not produce time-cumulative mortality Parsons and Surgeoner, since their exposure is limited in time Lahr et al.
Finally, when mayfly nymphs Baetis rhodani and Gammarus fossarum are exposed together to sublethal levels of thiacloprid, the amphipod increases its predation on the nymphs but reduces its shredding of litter at concentrations as low as 0. Imidacloprid also reduces the litter decomposition carried out by stoneflies Pteronarcys dorsata and crane flies Tipula sp.
The implications of these impacts for the larger ecosystem are discussed next. The consequences of all the above for the larger ecosystem have not been studied in detail yet. Difficulties in obtaining long-term experimental data that relates the effects on individual organisms to impacts on ecosystems prevent carrying out such studies. However, it is clear that some predictions can be made from the limited set of observations about the effects on aquatic communities reported so far. At least two main areas of concern can be identified: reduced capacity for decomposition of organic debris by aquatic organisms and starvation of insectivores and other vertebrate fauna that depend on invertebrates as a major or only food source Figure 7.
The recycling of organic matter that falls into water bodies is an essential ecosystem function that not only provides food for a wide range of aquatic and benthic organisms but also ensures the water quality is adequate for all other organisms that use it, including ourselves. It is well established that mayfly Ephemeroptera , caddisfly Trichoptera , and stonefly Plecoptera nymphs are the most sensitive aquatic organisms to most pollutants, so they are considered bioindicators of water quality Morse et al. They are shredders of leaves and other debris found at the bottom of creeks and streams that run through forested and agricultural areas, although not the only ones: larvae of crane flies Tipulidae , black flies Simulidae and other Diptera taxa perform the same function, together with amphipods, ostracods and aquatic isopods.
The fact that litter decomposition by stoneflies, crane flies, mayflies and amphipods is significantly reduced by concentrations of neonicotinoids that are currently found in many aquatic environments is of concern Kreutzweiser et al. Even if some individuals may survive in depleted populations, they still will be unable to carry out the decomposition function properly due to the feeding inhibition caused by these neurotoxicants, which will render those individuals unfit to do their job.
To many regulators of chemicals, whether mayflies or other macroinvertebrates are depleted is not important, or at least not as much as the increase in productivity that farmers may obtain from using products like neonicotinoids, although the latter benefits are questionable—see Seagraves and Lundgren, ; Macfadyen et al. Just because macroinvertebrates are not seen, since they are small and live at the bottom of ponds and streams, this does not mean they can be dispensed with. As Suter and Cormier have argued, these small creatures are present in ecosystems for an important reason Suter and Cormier, Given that more than half of the waters are contaminated Figure 4 with neonicotinoid levels that impair this important ecosystem function, higher organic and inorganic pollution can be expected wherever these insecticides are present.
Microbial degradation of the debris may still occur, but it would be slower and produce undesirable by-products such as methane and sulfides Sorrell and Boon, ; Kwok et al. The combined impacts by neonicotinoids and other pollutants could gradually poison the surface waters in many parts of the world. Thus, neonicotinoids do not cause fish mortality directly, but because aquatic invertebrates are a rich food source for many species of fish, depletion and disappearance of this source in waters contaminated with neonicotinoids could affect fish stocks in freshwater ecosystems.
In the Netherlands, where residues of imidacloprid in water are the highest in the world Table S1 , correlations between such residues and the decline of arthropod taxa such as Ephemeroptera, Odonata, Diptera and some crustaceans have been found van Dijk et al. Although not all the declines can be blamed on neonicotinoids, because other pesticide residues are also found and can have similar impacts Beketov et al.
As already mentioned, populations of aquatic species exposed to neonicotinoids often do not recover. This suggests that recovery of the extinct populations in the following year must require re-colonization from nearby areas. The elimination of predatory species results in the increase of prey species, with some of them, like mosquitoes Figure 6B , being a nuisance and a health hazard. In agricultural areas treated extensively with seeds containing neonicotinoids the chances of re-colonization are less frequent for species that are not very mobile. Aquatic insects and invertebrate species are being removed from many land and water areas and heading toward extinction.
This dire prediction is not far from the reality in some places. Many of these flying insects have aquatic life cycles, and their disappearance is probably due to their larvae not having survived in water. This astonishing reduction in entomofauna parallels the decline of wild bee species in North America and the British Isles Fitzpatrick et al. It must be remembered that neonicotinoids were introduced in the early s. Many of the vertebrates living around rivers, lakes and ponds are insectivorous species that depend almost exclusively on aquatic invertebrates as their food source: frogs, newts, skinks and lizards, a large array of birds including passerines and waders, bats and shrews.
All these animals, whether terrestrial or amphibian, draw their food from flying insects, their aquatic larvae, crustaceans and worms that live in the water environment. Consequently, the depletion of this food source must necessarily affect them Tennekes, b. To date, the only study available that makes a connection between bird declines and neonicotinoids in water was carried out in the Netherlands Hallmann et al. The authors of that study collected information on 15 species of passerine birds in that country over 20 years since , and correlated their abundance with residue concentrations of imidacloprid and other pesticide residues in water during the same period.
All bird species studied were either insectivorous or fed insects and larvae to their offspring during the breeding season. The only pesticide that explained the declining trends of 14 bird species was imidacloprid, whereas other factors that were taken into consideration, such as urban or agricultural area, availability of some cereal crops, fertilizer use and others, were discarded by the statistical analysis.
For the 6 species that showed a significant decline with imidacloprid residues, the average bird population decline was 3. These levels are below the HC5 for imidacloprid 0. However, as demonstrated in the microcosm and mesocosm studies, they are sufficient to cause sublethal effects and delayed mortality, all of which can eliminate entire populations of invertebrates, without recovery in many cases. Starvation by depletion of food sources due to pesticides was demonstrated for gray partridges Perdix perdix in England Potts, Also, applications of fipronil insecticide for locust control in Madagascar reduced the abundance of two species of tenrec, a skink and iguanian lizards that depended on termites as their main food source Peveling et al.
Evidence of similar impacts by neonicotinoids on vertebrate taxa other than birds does not exist because of difficulties in obtaining relevant long-term experimental data. However, if terrestrial birds, lizards and mammals can be taken as examples of what occurs in nature when pesticides reduce the food source, it is reasonable to think that other taxa that are experiencing worldwide declines, such as frogs and bats can be affected by indirect neonicotinoid impacts on the aquatic environment Mason et al.
Establishing the link between food depletion and population declines in some species is not difficult, but linking food depletion to individual chemical causes is a more challenging task. Negative impacts of neonicotinoids in aquatic environments are a reality. Initial assessments that considered these insecticides harmless to aquatic organisms may have led to a relaxation of monitoring efforts, resulting in the worldwide contamination of many aquatic ecosystems with neonicotinoids. The decline of many populations of invertebrates, due mostly to the widespread presence of waterborne residues and the extreme chronic toxicity of neonicotinoids, is affecting the structure and function of aquatic ecosystems.
Consequently, vertebrates that depend on insects and other aquatic invertebrates as their sole or main food resource are being affected. Declines of insectivore bird species are quite evident so far, but many other terrestrial and amphibian species may be at risk. Solutions must be found soon if we are to save the biodiversity not only of aquatic ecosystems, but all other ecosystems linked by the food web. Since the prophylactic use of seeds treated with neonicotinoids is responsible for most of the soil and aquatic contamination, while there is evidence of little productivity gain, one obvious solution is to stop the marketing of seeds coated with these insecticides van der Sluijs et al.
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