URBAN LANDSCAPE DESIGN AND MANAGEMENT IMPLICATIONS FOR
REDUCING WEST NILE VIRUS
A Thesis
Presented to
The Faculty of Graduate Studies
of
The University of Guelph
by
MATTHEW WALTNER-TOEWS
In partial fulfillment of requirements
for the degree of
Master of Landscape Architecture
April, 2008
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URBAN LANDSCAPE DESIGN AND MANAGEMENT IMPLICATIONS FOR REDUCING WEST NILE VIRUS
Matthew Waltner-Toews Advisor: University of Guelph, 2008 Robert Corry
This thesis is an investigation of the influences of urban and landscape design on urban
West Nile virus (WNV) risk. Through meta-analysis of urban ecology and epidemiology literature and existing WNV models, this paper shows how risk of WNV infection varies with urban landscape elements, form, and local mosquito control management in two neighbourhoods in Winnipeg, Manitoba. A multi-scale design and management approach is described and evaluated using a GIS comparing the effects of the principles on WNV infection risk. Results suggest that surface-warmed stagnant subsurface water in conjunction with mature tree canopy and open lawn create a high-risk environment. ACKNOWLEDGEMENTS
I would like to thank a number of people, without whom this thesis would not have been possible. I would like to thank Dr. Robert Corry for his patience, support, persistence,
and guidance during the process of writing and editing this thesis. Dr. Ian Barker from
the Ontario Veterinary College and Canadian Cooperative Wildlife Health Centre
provided extremely useful input and advice without which this thesis would not have
been possible. Dr. Bob Brown provided useful input, inspiration, and mentorship through
the many stages of the researching and writing process.
I would also like to thank Dr. Robbin Lindsay from the Canadian National Microbiology
Laboratory Public Health Agency of Canada (PHAC), and Taz Stuart from the City of
Winnipeg Mosquito Control Division for providing invaluable data and information
about West Nile Virus transmission and mosquitoes in urban areas. Ken Dalton from the
City of Winnipeg Waste and Water Department provided useful insight into drainage,
and provided valuable data. Paul Beach from the Sault Ste. Marie Community
Geomatics Centre, for providing useful insight into the mapping of urban mosquitoes.
1 TABLE OF CONTENTS
1.0: INTRODUCTION TO THE STUDY 1
1.1 PURPOSE 4 1.2 PROBLEM STATEMENT 5 1.3 DEFINITIONS 6 2.0 LITERATURE REVIEW 7
2.1 WEST NILE VIRUS ECOLOGY 7 2.1.1 Explanation of the Disease 7 2.1.2 History of Spread 9 2.1.3 Urban Mosquitoes 10 2.1.3.1 The Life of a Mosquito 11 2.1.3.2 Culex Mosquitoes 13 2.1.4 Avian Ecology in Cities 16 2.1.4.1 Avian Biodiversity 16 2.1.4.2 West Nile Virus in Urban Birds 17 2.2 WEST NILE VIRUS AND BEST MANAGEMENT PRACTICES 18 2.2.1 Surveillance 19 2.2.1.1 Avian Surveillance 19 2.2.1.2 Mosquito Surveillance 20 2.2.2 Source Reduction 21 2.2.2.1 Maintenance and Sanitation 21 2.2.2.2 Water Management 21 2.2.2.3 Avian Habitat 25 2.2.3 Insecticidal Control 26 2.3 MODEL AND RISK ASSESSMENT 27 2.3.1 Environmental and social determinants of human risk in Chicago, 2002 28 2.3.2 Habitat Mapping in Wyoming 30 2.3.3 Risk Assessment in British Columbia 31 2.3.4 Land Cover and Environmental Temperature Influence in Southern Ontario. 33 2.4 KEY INFERENCES FROM THE LITERATURE 36 2.4.1 Mosquito Risk 36 2.4.2 Avian Risk 37 2.4.3 Human Risk 38 2.4.4 Best Management Practices 38 2.4.5 Variables in WNV Risk 38 3.0 METHODOLOGY 40
3.1 SITE SELECTION 40 3.2 STUDY NEIGHBOURHOODS IN WINNIPEG 42 3.3 SITE OBSERVATION 42 3.4 VARIABLE SELECTION 43 3.5 NEIGHBOURHOOD MAPPING 44 3.6 NEIGHBOURHOOD ANALYSIS 46
li 4.0 FINDINGS AND INSIGHTS 48
4.1 WINNIPEG OVERVIEW AND CONTEXT 48 4.2 NORTH RIVER HEIGHTS 49 4.2.1 Population Statistics 50 4.2.2 Income 50 4.2.3 Dwelling Types and Age 51 4.2.4 North-West Quadrat 51 4.2.5 North East Quadrat 52 4.2.6 South East Quadrat 54 4.2.7 South West Quadrat 55 4.2.8 North River Heights Discussion 56 4.3 FORT RICHMOND NORTH 59 4.3.1 Population Statistics 60 4.3.2 Income 60 4.3.3 Dwelling Types and Age 61 4.3.4 North Quadrat 61 4.3.5 North-Central Quadrat 63 4.3.6 South-Central Quadrat 64 4.3.7 Southern Quadrat 65 4.3.8 Fort Richmond North Discussion 67 4.4 COMPARISON BETWEEN NEIGHBOURHOODS 69 4.5 SUMMARY 73 5.0: CONCLUSIONS AND RECOMMENDATIONS 75 5.1 WNV IN THE URBAN LANDSCAPE 75 5.2 HIGHEST RISK 75 5.3 EXISTING GUIDELINES 77 5.4 REDUCING RISK 79 5.4.1 Correcting a Neighbourhood 79 5.4.2 Designing a Neighbourhood 80 5.4.3 Risk Reduction through Subsurface Drainage 81 5.5 LIMITATIONS AND OPPORTUNITIES FOR FUTURE RESEARCH 82 5.5.1 Subsurface Infrastructure 83 5.5.2 Urban Land Cover Classification 83 5.5.3 Urban Birds 84 5.5.4 Validation of Study and Future Studies 84 LITERATURE CITED 85 APPENDIX A 90 APPENDIX B 100
in LIST OF FIGURES
Title Page
CHAPTER 2
White Stork Migration and Wintering Grounds Compared with WNV 9 Positive Countries in Europe and Africa The spread of West Nile Virus across North America 11 Mosquito Life Cycle 12 Water Pooling in a Culvert Under a Path 23 Area Ground-Truthed in Residential Toronto to Validate the Actual 35 Urban Habitat Classified as Wetland, Forest, and Farmland by Meyers (2006) CHAPTER 3
Relative Locations of North River Heights and Fort Richmond North 43 in Winnipeg Pythagorean Theorem to Find the Chord of a Circle and Surface Area 47 of Water in a Pipe
CHAPTER 4
North River Heights Stagnant Water by Quarter 57 North River Heights Tree Canopy by Quarter 58 Fort Richmond North Stagnant Water by Quarter 67 Fort Richmond Tree Canopy by Quarter 68 Total Stagnant Water (Both Neighbourhoods) 69 Major Risk Variable Comparison Between Neighbourhoods 71
iv LIST OF TABLES
Table # Title Page
CHAPTER 2
2.1 North American Mosquito Genera 14 2.2 Suburban West Nile Virus Risk Variables Compiled from Models and 39 Research
CHAPTER 4
4.1 North River Heights North West Quadrat Risk Variables 52 4.2 North River Heights North West Quadrat Tree Cover 52 4.3 North River Heights North West Quadrat Water Area 52 4.4 North River Heights North East Quadrat Risk Variables 53 4.5 North River Heights North East Quadrat Tree Cover 53 4.6 North River Heights North East Quadrat Water Area 53 4.7 North River Heights South East Quadrat Risk Variables 54 4.8 North River Heights South East Quadrat Tree Cover 55 4.9 North River Heights South East Quadrat Water Area 55 4.10 North River Heights South West Quadrat Risk Variables 56 4.11 North River Heights South West Quadrat Risk Variables 56 4.12 North River Heights South West Quadrat Water Area 56 4.13 Fort Richmond North Northern Quadrat Risk Variables 62 4.14 Fort Richmond North Northern Quadrat Tree Cover 62 4.15 Fort Richmond North Northern Quadrat Water Area 62 4.16 Fort Richmond North North-Central Quadrat Risk Variables 63 4.17 Fort Richmond North North-Central Quadrat Tree Cover 64 4.18 Fort Richmond North North-Central Quadrat Water Area 64 4.19 Fort Richmond North South-Central Quadrat Risk Variables 65 4.20 Fort Richmond North South-Central Quadrat Tree Cover 65 4.21 Fort Richmond North South-Central Quadrat Water Area 65 4.22 Fort Richmond North Southern Quadrat Risk Variables 66 4.23 Fort Richmond North Southern Quadrat Tree Cover 66 4.24 Fort Richmond North Southern Quadrat Water Area 66
v 1.0: Introduction to the Study
Landscape architects and landscape designers are concerned with shaping and improving the spaces that we move through daily, and enhancing, shaping, creating, and improving the sense of place (or identifiability of location) The range of work that these designers do is quite broad, ranging from Disney Land to healing gardens near hospitals. While the driving forces behind the projects are varied, one constant is that landscape architects are ultimately trying to make our surroundings better to make our lives better (Thompson
2000).
There is a connection between where we live and how healthy we are. People in wealthier societies or groups tend to be healthier and have longer life spans than those in poorer ones (Lynch et al. 1998). People in poor, densely populated urban areas are more likely to contract illnesses from random contact with other ill people than individuals in less densely populated areas (EPA 2001). People in walkable neighbourhoods tend to be healthier than people in neighbourhoods without sidewalks (EPA 2001). By improving the quality of the landscape, urban planners and landscape architects are, in effect, attempting to improve the health (physical or mental) of the society they are serving
(Thompson 2000).
In Our Built and Natural Environments the EPA (2001) concludes, "the urban form directly affects habitat, ecosystems, endangered species, and water quality through land consumption, habitat fragmentation, and replacement of natural cover with impervious surfaces" (EPA 2001). It follows from this that by reducing habitat cities also have lower
1 biodiversity than surrounding natural areas. Many species of plants, mammals, birds, and insects, living as populations in ecosystems with low biodiversity tend to be more adversely affected by host-specific disease and better at spreading it than populations in ecosystems with high biodiversity because potential hosts are more densely distributed
(Ostfeld and Keesing 2000; Jackman et al. 2007). This "dilution effect" of high biodiversity ecosystems holds true for Lyme disease transmission in the United States, for instance (Ostfeld and Keesing 2000).
Ecosystems with low biodiversity are also more likely to have disease-carrying animals in them than others: Malaria, for instance, is carried by Anopheles mosquitoes, which typically live in drainage ditches and other still, clear-water environments with low biodiversity (Chin 2000). The very name "malaria" means 'bad air' in Italian, and was so named because people of the 19th century believed that the disease was caused by swamp gas, since people who spent more time around swamps were more likely to catch the disease (Barrett 2001). Anopheles mosquitoes in poor draining surface water in tropical and subtropical countries commonly carry the parasite that causes the disease (Chin
2000). The association between location and malaria was understood long before the true mechanism of infection was known.
The connection between ecosystem biodiversity and human health is a complex one. The link between the two is not always clear, and difficult to show. If we live in an environment with lower biodiversity of plant and animal life, do we always put ourselves at risk of disease? This question should be a concern to landscape architects, because
2 design is not intended to compromise health. Landscape architects carefully consider pedestrian and vehicular circulation in urban environments to minimize risk, and should apply the same thoughtfulness in design towards other aspects of human health.
Urban environments are well suited to some species of insects, and mosquitoes in particular (Reisen 2002; Crans 2007). Cities tend to be warmer than the surrounding landscape because of surface albedo, and because we heat them: this is often called a heat-island effect (EPA 2001; Register 2006). Cities are built over long periods of time using a variety of materials, and using construction techniques and standards that change from generation to generation, creating an infrastructure with many sheltered habitat niches that are below street level and out of sight. Urbanized areas tend to be inhospitable to many insect eating birds, because of the constant light and relatively poor quality habitat (Sandstrom et al. 2006). The main sources of food for mosquitoes (nectar and blood) (Rutgers 2007) are abundant.
West Nile Virus (WNV) has become a threat to both birds and humans in North America since its introduction in 1999 (Glaser 2004; LaDeau et al. 2007). Mosquitoes carrying the disease have found a suitable ecology in North American cities. The environmental conditions that make WNV a threat are probably not unique to WNV, however.
Mosquitoes carrying different diseases (eg. St. Louis Encephalitis, Western Equine
Encephalitis, Dengue Fever) may be able to exploit the same ecological niche (Chin
2000).
3 1.1 Purpose This thesis will be an exploration of the relationship between the built landscape and
WNV, with a look towards bettering the way cities are built and maintained to reduce the risk of mosquito-borne disease.
Many city mosquito control strategies use adulticide and larvacide programs to reduce populations (Brenner et al. 2003). However, the monetary cost of annual urban pesticide application is high, and there is increasing concern over the health risks of these programs (Sibbald 2002). There is also historical evidence globally from other similar programs that mosquitoes develop a tolerance to pesticides, leaving no way to control outbreaks in an emergency (Magdalena et al. 2000).
WNV-infected mosquitoes are routinely found in North American city infrastructure, such as road catch basins, city sewers, drainage ditches, and underground transformer vaults, and WNV-positive birds are found every summer on golf courses and along river banks (Ruiz et al. 2004; Lindsay, personal communication, 2007). Given the apparent connection between civil engineering, urban design and WNV "hotspots", testing the specific connections between mosquito-borne disease and landscape characteristics, such as drainage and tree planting choices, should be of concern to designers and health professionals. These issues are especially pressing for cities with a high annual burden of
WNV infection, such as Winnipeg Manitoba; Bakersfield California; or Fargo North
Dakota: cities that have a river running through them, are on flat or flood plain land, and are surrounded by agriculture (USGS 2007).
4 There is a need to further understand the relationship between urban environments and mosquito-borne disease and to come up with appropriate solutions. Chemical control may alleviate disease where properly applied, and is an important part of many integrated pest management strategies. Given the risk of new mosquito borne disease and chemical resistance in the mosquitoes, however, source reduction through design is necessary for any long-term solutions.
1.2 Problem Statement Through Geographic Information Systems (GIS) layering risk assessment and a landscape analysis of two neighbourhoods, this paper will explore the relationship between urban infrastructure and landscape design and risk of WNV infection in the city of Winnipeg, MB. This paper will suggest urban design principles and compare them with current integrated pest management strategies, in order to reduce the risk of WNV infection in new urban developments, thus lessening dependence on pesticide application and promoting healthier landscapes.
In particular, this paper will endeavour to answer the following questions:
1) How does WNV vary across an urban landscape?
2) Which landscape variables seem to be related to WNV risk the most?
3) Given the above, do existing guidelines and practices mitigate WNV risk, and
what landscape design or best management practices could further reduce risk?
Ultimately, the hope is that this research will bridge some of the gap between the public health and urban design professions. The findings should be useful for landscape
5 architects, planners, urban designers and public works managers who strive to better the public health of our cities.
1.3 Definitions
This research is based partly in epidemiology (the study of patterns of disease in a population), and partly in spatial geography and landscape architecture. Epidemiological terms necessary for understanding issues in this thesis are defined here.
The term vector refers to a living organism that transmits a disease. The infectious agent replicates in a biological vector, but is carried by a mechanical vector (Park 2007).
A reservoir or amplification host refers to a living organism that is infected by the disease agent and increases its prevalence and distribution, thereby increasing the risk of human infection (Park 2007). This is in contrast to a dead-end host - a host that can be infected by the disease agent without increasing its prevalence or distribution (Park
2007).
A zoonotic disease, or a zoonosis, is a disease of animals that can be transmitted to humans (Park 2007). A classic example of a zoonosis is the black plague (caused by
Yersinia pestis), a disease of rats, transmitted by flea vectors, that humans can get.
Arboviruses are viruses that replicate in and are carried by arthropods, typically blood- feeding insects such as mosquitoes or ticks (Park 2007). Dengue virus, Colorado tick fever virus, and West Nile virus are all arboviruses. Many arboviruses are also zoonotic.
6 2.0 Literature Review
This literature review will be broken up into three main parts, those being West Nile
Virus Ecology, Best Management Practices, and Models and Risk Assessment. The purpose of this review is to explain how cities facilitate WNV spread, to list some of the things that people have tried to do to control the disease, and to see how other researchers have assessed the problem of WNV risk. This review will conclude with a discussion of some of the major variables associated with WNV risk, and discuss some of the ways that cities can mitigate further spread.
2.1 West Nile Virus Ecology
West Nile Virus is a significant urban disease risk for both humans and urban birds in
North America (Ruiz et al. 2004; Beach, personal communication, 2006; Meyers 2006).
In order to understand why this is so, its spread (both globally and in North America) and aspects of mosquito and avian ecology in cities needs to be understood.
2.1.1 Explanation of the Disease
West Nile Virus is a zoonotic arbovirus in the family of Japanese encephalitis (Nash et al.
2001; Ruiz et al. 2004). It is carried by mosquitoes and spread among birds, which amplify the virus and then re-infect mosquitoes, in which the virus also replicates (Hayes et al. 2005). Humans and a few other animals (most notably horses) can get the disease, but are considered dead-end hosts, and cannot spread it directly or indirectly (Hayes et al.
2005).
7 In humans, WNV causes disease in a small proportion of the individuals it infects, though most are asymptomatic. The disease is characterized by flu-like symptoms (fever, aches, nausea), which in some individuals escalates into encephalitis, potentially causing death
(Hayes et al. 2005). It is very similar to St. Louis Encephalitis Virus (SLEV), in that both diseases involved mosquito carriers and avian hosts, and are transmitted by Culex sp. mosquitoes (Chin 2000). What sets WNV apart from SLEV is that WNV is relatively new to North America, has a higher transmission rate, causes disease in some reservoir species, and has a much wider geographic range, thus making it potentially dangerous to many more people (Shaman et al. 2005).
In birds, WNV infects many organs, regardless of the level of infection, and has been shown to cause high mortality in corvids (Kramer and Bernard 2001). Some birds are more susceptible to WNV than others because of differences in bird foraging and nesting behaviour, such as a preference for nesting or feeding in the same areas where WNV- carrying mosquitoes are likely to be breeding, and bird immune responses, which vary greatly from one species to another (Kilpatrick et al. 2007). This will be explained in more detail in Section 2.1.3.
The rate at which WNV can replicate inside a mosquito is largely determined by environmental temperature (Dohm et al. 2002). Higher temperatures mean faster replication, up to a point, although the relationship is not linear. At 18 degrees Celsius, it takes 25 days for a mosquito to become infectious. However, at 30 degrees Celsius, it can take as little as four days to become infectious (Dohm et al. 2002).
8 2.1.2 History of Spread
WNV was discovered to be endemic in Uganda in the early 20th century, and has since been recognized as endemic in much of Africa and Europe, where people have developed tolerance to it (Nash et al. 2001; Zeller and Schuffenecker 2004). The disease spreads north from Africa as migratory birds, acting as reservoirs, return home to Europe (Nash et al. 2001; Zeller and Schuffenecker 2004). Local, non-migratory birds occasionally pick up WNV from mosquitoes that have bitten infected birds. The spread of West Nile in the
Old World is implied in the migration routes and wintering grounds of the White Stork
(Ciconia ciconia) compared with countries that are WNV positive.
Figure 2.1: White Stork Migration and Wintering Grounds compared with WNV positive countries in Europe and Africa. (Bamse 2007; CDC 2000)
9 The disease was first recognized in North America in the summer of 1999 in Queens,
New York, and was originally diagnosed as an encephalitis (Hayes et al. 2005). It is not known how WNV arrived and there are many possibilities, although it is likely that an infected mosquito was accidentally transported from the Old World by plane or ship.
WNV spread outward from New York radially and covered almost all of North America, with the exception of British Columbia, over the course of four years (Rappole et al.
2006).
The fact that WNV spread in this way was contrary to the expected pattern, given the observed patterns in Africa and Europe. Some of the literature still suggests migratory birds as being the dominant amplifying hosts in North America (as they are in Europe and Africa), but this has not been positively confirmed, and not all observation supports this hypothesis (Kilpatrick et al. 2007). If migratory birds had been the primary carriers, then WNV would have spread rapidly south into the winter grounds of Central America, and then spread up north again the following spring. Instead, the disease spread out from a central point. This pattern suggests that either local birds or mosquitoes over-wintered with the disease, and spread it the following season. Models comparing migratory birds with non-migratory birds and rate of spread support this hypothesis (Rappole et al. 2006), but further research is needed to explore the spread of WNV in North America.
2.1.3 Urban Mosquitoes With thousands of species in the world, some of which feed on cold-blooded animals or breed in salt water, mosquito ecology can be complex. However, understanding the
10 basics of mosquito ecology, and that of a few specific mosquitoes in particular, is key to understanding how WNV has managed to do so well in an urban setting.
Figure 2.2: The spread of West Nile Virus across North America (Tachiiri et al. 2006)
2.1.3.1 The Life of a Mosquito
All mosquitoes go through a very similar life cycle that consists of four larval stages (or instars), a pupa stage, and then an adult stage (Rutgers 2007). The length of time that a mosquito spends in each stage is specific to the species and environmental conditions.
Some mosquito species will go through several cycles, from egg to adult, through a year, while others may go through the cycle only once. The egg to pupa phases of a mosquito's life are spent in water, though not all mosquitoes lay their eggs directly into water (some will lay eggs in a place that gets seasonally flooded, for instance) (Rutgers
2007).
11 Figure 2.3: Mosquito Life Cycle (Purdue 2007)
The time a mosquito spends as an egg depends on species, day length in the season, contact with water, and temperature (Rutgers 2007). The time a mosquito spends in the larval and pupa stage depends on temperature and food availability, usually in the form of organics in the water upon which the mosquito filter feeds. Mosquito larvae breathe though a straw-like structure that breaks the surface tension of the water, which is why it is important for them to be in still water (Rutgers 2007).
Mosquitoes may overwinter as eggs, larvae, or adults (Rutgers 2007). Culex spp., in particular, overwinter in a hibernation state as unfed, but fertilized female adults, and lay their eggs in the spring after they've found a blood meal (Rutgers 2007). Male
12 mosquitoes live for months, feeding on nectar and plant juices, and live to mate. Females can survive on plant juices and nectar, but need protein to produce their eggs, and blood has much more protein in it than plant juices (Rutgers 2007). Mosquitoes have anticoagulant in their saliva to make their feeding faster and less noticeable (Ribeiro
1984). Females are attracted to carbon dioxide and heat, which helps them track their prey, and explains why hikers are swarmed when they get out of a hot car (Rutgers 2007).
There are 166 species of mosquito in 13 genera in North America (VanDyk and Bartlett
2006) (Table 2.1). Many mosquito species are not a nuisance to humans, preferring to feed on birds, small mammals, and even reptiles or amphibians (Rutgers 2007). They are a valuable food source for larger insects, like dragonflies, and amphibian young, such as frog tadpoles, which means that their existence is necessary for a host of larger creatures.
It also means that, for management, it important to know exactly what species of mosquito are in a particular location (Rutgers 2007).
2.1.3.2 Culex Mosquitoes
Over 20 mosquito species have been implicated in the spread of WNV in North America.
The mosquitoes that are of most concern in North America are Culex pipiens in the east and C. tarsalis in the west (Rutgers 2007). Both of these mosquitoes are primarily avian feeders, which is why WNV primarily infects birds. They are active at dusk and dawn, spending most of their time in the tree canopy (Jackson 2004; Rutgers 2007). However, for reasons unknown, C. pipiens and C. tarsalis shift host preference from birds towards the end of the season, spend more time at ground level, and start to feed on mammals as well (Jackson 2004; Kilpatrick et al. 2007).
13 Table 2.1: North American Mosquito Genera (VanDyk and Bartlett 2006; Wilkerson et al. 2008). Genera General Larval Habitat Female Primary Food Source Aedes Any transient water (floodplains, Mammals. ditches, tin cans, tires, etc) Anopheles Wetlands and water bodies with Mammals. emergent vegetation. Coquillettidia1 Shallow water with emergent Mammals. vegetation. Culex Transient water, often urban, Birds, sometimes mammals. (polluted, high nutrient water tends to produce larger broods) Culiseta Lowland acidic wetlands Birds. Deinocerites Small natural containers, such as Amphibians, Reptiles, Birds. tree holes and rock holes. Mansonia1 Shallow water with emergent Mammals. vegetation. Ochlerotatus Freshwater bogs and marshes. Mammals. Orthopodomyia Tree holes, sometimes artificial Birds. containers. Psorophora2 Freshwater pools with vegetation. Mammals, especially livestock. Toxorhynchites3 Transient water where other Nectar. mosquitoes are present. Uranotaenia Sunlit permanent water with Amphibians, Reptiles, Birds. emergent vegetation. Wyeomyia Predacious pitcher plants. None - protein derived entirely from carcasses in pitcher plants. 1 Coquillettidia and Mansonia require emergent vegetation because they insert a modified air tube into the roots and stem of the aquatic plant. They use the plants to breath. 2 In large numbers, Psorophora have been reported to kill livestock. 3 Toxorhynchites have predatory larvae that feed on other mosquito larvae. This gives them enough protein to lay eggs as adults.
It is possible to determine the food choices of mosquitoes by analyzing the blood they have consumed, but there is more than preference to consider. Some birds are more infectious than others because they build up larger amounts of WNV in their blood (the rate at which birds build up virus is referred to as viral competence). Some birds can tolerate this increased virus load and others cannot, but regardless, mosquitoes biting high competence birds are much more likely to become WNV-infected (Kilpatrick et al.
2007). Apperson et al. (2004) found that Culex species in New York, New Jersey and
14 Tennessee had a clear preference for American robins (Turdus migratorius), but would take blood from a wide range of bird and animal species (Apperson et al. 2004). The ten most competent avian hosts for WNV, in order from most infectious to least, are blue jays {Cyanocitta cristata), western scrub jays (Aphelocoma californica), American crows
(Corvus brachyrhynchos), common grackles (Quiscalus quiscula), house finches
(Carpodacus mexicanus), house sparrows (Passer domesticus), ring-billed gulls (Larus delawarensis), black-billed magpies (Pica hudsonia), American robins (Turdus migratorius), and song sparrows (Melospiza melodia) (Kilpatrick et al. 2007).
Culex pipiens and C. tarsalis mosquitoes are well suited to urban environments. Culex pipiens prefers water that is high in organics, and is possibly the most pollution-tolerant of all mosquitoes, being frequently found in sewage treatment plant effluent (Crans
2007). Larval habitat can be anything that collects stagnant water, including tin cans or garbage (Crans 2007). Culex tarsalis seek out water with decomposing vegetation
(roadside ditches, for instance), and have been known to be capable of developing the first batch of eggs without a blood meal in as little as 4 days after emergence (Reisen
2002). Both mosquito species are opportunistic container breeders, and will lay eggs in nearly any standing water. Both species overwinter as adults, and seek out humid, sheltered areas to overwinter (e.g., sewers and storm sewers) (Reisen 2002). In addition, the females' blood meals of choice, for both species, come from birds, including common urban species. Culex pipiens and C. tarsalis will typically travel less than 500m to get a blood meal, and often less than 100m (though they are capable of going further) (Rutgers
2007).
15 2.1.4 Avian Ecology in Cities
Urban bird biodiversity is another key to the WNV cycle in North America. Urban avian ecology describes bird habitat and interactions. The urban birds in North America include those most commonly infected by WNV (Kilpatrick et al. 2007).
2.1.4.1 Avian Biodiversity In agriculture, biodiversity is thought to provide ecosystem resilience (Jackman et al.
2007). This means that the more complementary or similar species there are, the less chance they all have of being wiped out by disease or disaster. In many cases this can be difficult to prove, but makes intuitive sense - if a landscape is disturbed, a richer seed- bank should be able to reestablish faster than a poorer one. This idea of ecosystem stability has been thoroughly tested in grassland studies, which showed that high biodiversity fields were 70% more stable than monocultures (Tilman et al. 2006).
The idea of ecosystem resilience transcends agriculture, and is applicable to animal populations as well. In Sweden, Sandstrom et. al. (2006) found a direct relationship between the amount of bio-diverse green space (forest and preserved natural ecosystems) and bird populations in urban areas (Sandstrom et al. 2006). Their study split up the city of Orebro, Sweden into four distinct strata: the city centre, residential, greenway (a forested riparian park that wedges into the city), and the periphery (the outer greenbelt).
Bird species were defined as woodpeckers, forest birds, urban birds, and hole nesters, with some of the birds falling into more than one category (Sandstrom et al. 2006).
Species diversity for woodpeckers, hole nesters, and forest birds increased from the city centre to the periphery, along with vegetation diversity (Sandstrom et al. 2006).
However, urban birds were concentrated in the residential area. While the residential
16 habitat supported large numbers of birds, the species diversity was actually quite low, suggesting that while the habitat was good for specific urban birds, it was hostile or unsuitable for many other species (Sandstrom et al. 2006). The researchers suggested that the green wedge of the greenway increased species richness for nearby areas, and they concluded from the data that increasing the number of green wedges into the city should increase the species diversity for the entire area, including the residential and city centre (Sandstrom et al. 2006). Vegetative groundcover was also positively correlated with species richness (Sandstrom et al. 2006).
2.1.4.2 West Nile Virus in Urban Birds Sandstrom et a/.'s (2006) analysis of avian biodiversity in cities is especially pertinent to
WNV. All of the ten most virally competent birds in Apperson et a/.'s (2004) study could be qualified as 'urban birds' in Sandstrom et a/.'s (2006) study, based on their prevalence in annual backyard bird counts (Audubon 2007). Jays, robins, and grackles are common backyard birds across North America, while crows and magpies are common urban scavengers. Both finches and sparrows are also ubiquitous in urban areas.
While many of these birds migrate in the wild, many urban birds stay all winter, because their food sources (backyard bird feeders, roadkill, and dumpsters, to name a few) don't go away when the snow starts to fall (Audubon 2007).
Urban birds, such as those mentioned above, are successful in cities and neighbourhoods because they can use urban environments better than others birds, based on their dietary and nesting requirements (Sandstrom et al. 2006). What ties many of these birds together
17 is their need for clear ground to forage on and large trees for nesting or roosting (Cornell
2007). The finches and sparrows are well adapted to living without trees altogether, often preferring to nest in the habitat provided by buildings and foraging for insects around lights or getting seeds from parks and bird feeders (Cornell 2007). Many forest birds and hole nesters cannot successfully compete in an urban setting outside of preserved park space because their dietary and nesting conditions are not met (Sandstrom et al. 2006).
Viral competence does not mean viral tolerance. For instance, crows have a high viral competence, meaning that they build up large quantities of the virus rapidly, easily allowing mosquitoes that feed on them to become infected (Kilpatrick et al. 2007).
However, WNV-infected crows also have a high mortality rate - studies show that crows in some areas may experience as high as 70% mortality due to WNV infection alone
(Yaremych et al. 2004), which is why crow deaths can be a good early indicator of a
WNV outbreak. Chickadees, on the other hand, have a viral competence value of 0, which is lower than American alligators; however, chickadees appear to experience mortality rates similar to crows (LaDeau et al. 2007). Other birds, such as the common grackle, have high competency, but have not declined in numbers (Kilpatrick et al. 2007;
LaDeau et al. 2007).
2.2 West Nile Virus and Best Management Practices
Over the past several years, governments and municipalities have come up with best management practices for dealing with WNV that seem to follow similar patterns. In
2003 the US CDC organized its strategy into Surveillance, Source Reduction, Control
18 (chemical and biological), and Public Education, and the city of Winnipeg has a strategy organized around similar lines (CDC 2003; Winnipeg 2005; Manitoba 2007). None of the CDC's policies are law, and municipalities are encouraged to come up with their own solutions (CDC 2003). However, the actual steps to reduce WNV (source reduction and the various stages of control) are ordered by their effectiveness (CDC 2003). The overall emphasis is on mosquito habitat control (CDC 2003).
2.2.1 Surveillance The first step in any program to manage WNV is to see if the virus is actually present in the local birds or mosquitoes, and assuming it is present, identifying and mapping the habitats of the vectors and hosts (CDC 2003).
2.2.1.1 Avian Surveillance Because corvids experience high mortality, they are good indicator species for the presence of WNV, although testing is expensive (Ruiz et al. 2004). Testing varies from province to province. In 2006, Manitoba and the city of Winnipeg noted that WNV was showing up in the same hotspots annually and decided that dead corvid analysis was not as accurate a measure of human health risk nor as cost effective when compared with municipal mosquito larva surveillance (Winnipeg 2005; Manitoba 2007). In Ontario the
Canadian Cooperative Wildlife Health Centre tests crows, blue jays, and ravens submitted by the public (CCWHC 2007). However, in general only the first bird found to be positive in a locality is mapped, after which the region is declared WNV positive, and no more submissions are accepted (CCWHC 2007).
19 2.2.1.2 Mosquito Surveillance The primary mosquito vector in central and western North America is Culex tarsalis, while C. pipiens is the main vector in Ontario and eastern North America (Rutgers 2007).
Central North American cities have to deal with both species, and devise strategies that may be generalizeable to both western and eastern cities. In the remaining literature I will draw examples from Winnipeg, Manitoba.
2.2.1.2.1 Mosquito Larva Surveillance
Larval surveillance involves trained inspectors sampling from a wide range of potential aquatic breeding pools. An established program will take larval samples from known habitats, and continue to look for new sources. Manitoba has divided the province into sampling districts, and the cities are further subdivided (Manitoba 2007). Winnipeg is divided into quarters, with known breeding pools as well as potential breeding sites (for instance, shallow culverts) being sampled regularly (Winnipeg 2005). Mosquito identification specialists distinguish the larvae of WNV vectors from those of nuisance species of mosquitoes (CDC 2003; Manitoba 2007).
2.2.1.2.2 Adult Mosquito Surveillance
Adult mosquitoes can be collected using various traps, using light and/or carbon dioxide as bait. Monitoring adult mosquito populations is important for determining species presence and abundance, which can be used to set action thresholds (Winnipeg 2005) and evaluate control efforts (CDC 2003). As in larval surveillance, it is important to set traps in both known and potential habitats. Winnipeg uses adult mosquito surveillance to evaluate effectiveness of control (Winnipeg 2005).
20 2.2.2 Source Reduction The CDC considers source reduction to be the best and most cost-effective way to control mosquito populations. This involves the elimination or alteration of mosquito habitat
(CDC 2003). Examples of this would vary from cleaning birdbaths and rain gutters to altering stormwater management ponds and modifying a city's drainage infrastructure.
Because source reduction reduces mosquito breeding habitat, it substantially reduces pesticide dependence (CDC 2003). Both the CDC and the province of Manitoba divide source reduction into sanitation and water management, focusing on mosquito habitat
(CDC 2003; Manitoba 2007). Source reduction could include also the possibility of altering avian host habitat, though this is not explicitly addressed in the literature.
2.2.2.1 Maintenance and Sanitation Litter, from humans or vegetation, is often good mosquito breeding habitat. Anything that holds water, from a discarded plastic wrapper to a hollow created by leaf-litter on the pavement, is a potential breeding area (CDC 2003; Curry 2004). Much of the public education having to do with WNV prevention goes towards ensuring that private property owners keep their bird baths, pool covers, and roof gutters clean (Murnaghan 2004).
Winnipeg also has policy related to maintenance of roadside culverts and ditches, because during the dryer months of the summer, shallow stagnant water can pool in these areas (Winnipeg 2005; Manitoba 2007).
2.2.2.2 Water Management Water management is one of the best ways to reduce vector mosquito breeding habitat.
According to the CDC, however, due to restrictions on modifying aquatic habitats, many
areas are using water management methods less frequently (CDC 2003). Given that
some of the primary sources of vector mosquito breeding habitat in Canadian cities are
21 swales and storm sewers (Dalton, personal communication, Sept. 2007; Murnaghan 2004;
Winnipeg 2005), and not natural water bodies, there may be ways to manage our water more responsibly.
Connecting mosquito-producing areas to deep water via a series of shallow ditches allows larvivorous creatures (such as fish, tadpoles, or insects) access to a food source while effectively reducing or eliminating mosquito larvae (CDC 2003; Magdalena et al. 2000;
Murnaghan 2004). Shallow ditching (using ditches less than a metre deep) produces fewer unnatural hydrological impacts on natural marshes than deep ditching, and can actually benefit a hydrological system by improving connections between a marsh and estuary (CDC 2003). However, if the connection to deep water is lost and the ditches become intermittently pooled, mosquitoes can potentially use the ditches as habitat
(Murnaghan 2004; Winnipeg 2005).
Storm sewers and stormwater retention structures, most notably those built underground, can be high-quality mosquito habitat in all seasons, including winter (Beach, personal communication, Nov. 2006; Dalton, personal communication, Sept. 2007; Murnaghan
2004). Surface stormwater retention structures, such as stormwater management ponds, when maintained properly, tend to be poor mosquito habitat, even though they are perceived by the public as a potential threat (Murnaghan 2004).
Proper care still needs to go into the design of surface retention structures, or they can become a hazard. In 2003, the vast majority of stormwater ponds around Toronto
22 contained no mosquito larva of any kind, and one of the pools that actually contained vector mosquitoes was a poorly drained and designed algae-dominated farm pond
(Mumaghan 2004). In a city like Winnipeg, where many neighbourhoods use ditches to both move and retain stormwater, both the ditches and culverts can provide high-quality
C. tarsalis habitat when water pools at the low points (Figure 2.4) (Manitoba 2007).
This is not to say that stormwater management ponds are not a potential risk: they still need to be designed and maintained properly. One way to decrease the likelihood of creating mosquito habitat is to ensure the pond is suitable habitat for mosquito predators, like dragonflies, fat-head minnows {Pimephales promelas), or mosquito fish (Gambusia affinis) (Schueler 1992) by increasing the depth of the ponds and ensuring they are properly vegetated. Unfortunately, this can increase the perceived risk of wet ponds, because deeper ponds are seen as a drowning risk (the reality of the actual risk of deeper ponds is debated) (Schueler 1992; Murnaghan 2004). Vegetation around pond edges has also been suggested as prime habitat for mosquitoes, including Culex tarsalis
(Murnaghan 2004), although the specific vegetation type may be important, since plants
23 can also provide habitat for mosquito predators. Proper maintenance by thinning out excessively dense vegetation and removing debris to allow mosquito predators access would reduce the risk of creating more mosquito habitat (Murnaghan 2004). A benefit
(beyond the actual mosquito reduction or elimination) of having fish and dragonflies around ponds is that their visibility increases public perception that something positive is being done (Murnaghan 2004).
Subsurface drainage can be a problem because the earth insulates the drainage pipes from temperature extremes and shelters them from the elements. Sewage systems also produce their own heat through decomposition, keeping water from freezing. While Winnipeg has winter temperatures well below freezing, the city has a policy of plowing suburban roads to a compact snow surface, which would further act as an insulator for the subsurface drainage (Winnipeg 2007). This is a problem, since Culex mosquitoes are known to overwinter in sheltered areas in the wild (Curry 2004), and have been found overwintering in underground transformer vaults in Sault Ste. Marie, Ontario, in sewers in Winnipeg, and in storm sewers in Windsor, Ontario (Beach, personal communication,
2006; Lindsay, personal communication, 2007).
The CDC has general guidelines recommending that a mosquito biologist or specialist advise on the design of all stormwater retention structures, to reduce mosquito habitat
(CDC 2003). While this occurs in both Manitoba and Ontario for water retention structures on the surface (Manitoba 2007), there are no policies or recommendations
(federal, municipal or otherwise) on exactly how to design storm sewers to be mosquito
24 resistant. Since the problem with sub surface drainage is that the water is stagnant, climatically stable, and poor habitat for anything other than bacteria and mosquito larva, one solution would be to maintain water movement and create a viable habitat for mosquito predators, for instance, by improving water quality and day-lighting the storm sewer to allow plants to grow. An alternative solution would be to somehow make the water inaccessible or inhospitable to mosquitoes. In either case, sub-surface drainage in its current form will probably always be reasonably good mosquito habitat, and should therefore be either re-designed or minimized as much as possible.
2.2.2.3 Avian Habitat There are no guidelines in Canada or in the US for reducing avian host habitat for WNV control. However, as discussed in the section on avian ecology, the birds that are primarily responsible for WNV transmission in Canadian cities are known, as are their feeding, nesting, and roosting habitats. Furthermore, several studies show clear patterns in WNV distribution across habitats in cities, and all share at least one similarity: in relative terms, downtown urban areas are not at risk, while suburbs built in the 1950s-
1970s are at risk (Meyers 2006; Ruiz et al. 2004; Stuart 2006; Tachiiri et al. 2006).
Clearly, downtown areas have storm sewers, so mosquito habitat is present. However, most downtown areas have much lower avian biodiversity, and lack the suburban bird species that carry WNV (Sandstrom et al. 2006). Downtown areas usually do not have the extensive bird feeding habitat found in the suburbs (lawns) or the preferred nesting and roosting habitat for birds like corvids, robins and cardinals (large trees) (Sandstrom et al. 2006). A design recommendation for downtowns to mitigate WNV risk might be to
25 restrict extensive greening at street level, so that the host birds do not move in. This is contrary to the desire of many cities that wish to increase downtown green space simply by planting more trees.
A study in Sweden showed that the suburban area was the largest contiguous habitat within the city limits, and had roughly the same avian biodiversity and density throughout
(Sandstrom et al. 2006). Since corvids and robins prefer mature trees to nest and roost in, one design recommendation to mitigate WNV risk might be to limit planting of tall- growing trees in the suburbs. Again, this is contrary to the typical North American design aesthetic, which tends to favour tall, canopy-forming street trees (Jackson et al.
2006).
Corvids and robins are hopping birds that are well adapted to feeding on ground that is open and free of understory. Since a lawn is an ideal feeding ground for all of these birds, reducing lawn and using varied lawn alternatives should also reduce the number of
WNV host birds. This would need to be done over large areas to have a significant effect, and would require a shift in North American aesthetic ideology.
2.2.3 Insecticidal Control Where source reduction is not possible, too late, or ineffective, municipalities and cities need to control WNV vector mosquitoes though biological or chemical means. This can be done at the larva or adult phase, though control at the larva stage is more effective
(CDC 2003). Source reduction can facilitate macro biological control by providing habitat for natural predators such as fish and insects (CDC 2003; Murnaghan 2004),
26 however, for the purposes of this discussion, larvacide and adulticide refers to application of chemical and microbial treatments.
Larvaciding is the application of biological or chemical control to mosquito larvae or pupae by ground or aerial treatment (CDC 2003). This tends to be more effective than adulticide because larvae group together, so control measures can be focused, whereas adults are more dispersed (CDC 2003). In Canada, Bacillus thuringiensis israelensis {Bti) is the most commonly used larvacide, because it has minimal impact on other insect species (Manitoba 2007).
Adulticiding is generally considered to be the least effective way to control mosquitoes.
However, a well timed adulticide program can reduce adult mosquitoes at peak times and significantly reduce risk (CDC 2003). Adulticiding is probably the most controversial mosquito control method. On the one hand, when done properly, fogging or spraying with ultra-low-volume pesticides has an immediate effect on mosquito populations (CDC
2003; Manitoba 2007). On the other hand, spraying pesticides in residential areas is unpopular, despite assurances of chemical safety in humans, and protestors in Winnipeg have actually stopped fogging trucks from leaving the truck yard. (Police Service 2004).
It is also the least cost effective method of control (Murnaghan 2004).
2.3 Model and Risk Assessment While many municipalities have published best management practices, and map out the locations of "hot spots" (vector mosquito breeding areas), few municipalities publish
27 their risk assessments or the models used to determine risk in their areas. The body of published, publicly available knowledge relating to WNV risk assessment is small. The following models and approaches are applicable to the scales used in this thesis, focusing primarily on Culex tarsalis and C. pipiens as primary vectors, and using commonly available data.
2.3.1 Environmental and social determinants of human risk in Chicago, 2002 West Nile Virus became established in the Chicago area in the summer of 2002, with 884 human cases and 66 deaths (Ruiz et al. 2004). Researchers found WNV in some crows in the area the previous summer, but no human cases were reported at that time. The mosquitoes that carry WNV in the Chicago area are Culex pipiens (Ruiz et al. 2004).
Chicago is located in the Chicago Lake Plain, which is the floodplain of the Des Plaines
River flowing into Lake Michigan. Within the study area of greater Chicago, an attempt was made to determine the social and environmental conditions that distinguished places that had human cases of WNV disease from those that did not, and to determine the conditions that distinguished areas with many cases from those with only a few (Ruiz et al. 2004). Links between place and human health were sought.
Vector-based risk maps of the area were created using census tract data and cluster based spatial autocorrelation statistical methods (Local Indicator of Spatial Association, or
LISA, and the ClusterSeer software program) (Ruiz et al. 2004). Population density per square kilometre, median household income, race (by percent), median age, mean elevation and elevation range, percentage vegetated cover, positive bird specimens (by
28 proximity in metres), housing age (average, by decade), physiographic region, and
Mosquito Abatement District (MADs) were mapped. The MADs are four zones created early in the 20th century in Cook County for mosquito control. Unlike studies that followed in other parts of North America, the Chicago study did not consider proximity to water, although physiographic regions included data on drainage conditions (Ruiz et al.
2004).
The study found that the most important risk factors varied. Proximity to a dead bird, housing age between 1950 - 1959, race as percent white, and low housing density were the most important factors when considering if a tract had any cases or not. However, when looking at the likelihood of a tract being in a cluster of cases, the most important positive factors were drainage, race as percent white, median age, housing from 1950
-1959, and vegetation. In all cases, older neighbourhoods with a higher percentage of older, white residents in low housing density, highly vegetated areas with poor drainage and close to a dead bird were at the highest risk (Ruiz et al. 2004). The local policies of the MAD may have also played an important role. The centrally-located DesPlaines
MAD, which would in all other ways be considered 'high risk', had very few cases and no clusters, suggesting that effective control strategies can overcome obstacles (Ruiz et al. 2004).
The link to race is an interesting one not explored in other WNV studies. With St. Louis
Encephalitis, a flaviviral infection, it has been found that exposure to another flavivirus, such as Dengue, may reduce risk (Ruiz et al. 2004). The researchers suggest that older
29 black residents who migrated from the southern US may have immunity by way of exposure to the Dengue outbreak in 1934, and that possible genetic predisposition bears further investigation (Ruiz et al. 2004).
Vegetation also might play a larger role if downtown Chicago was eliminated from the study area, because the relative lack of vegetation in downtown Chicago, coupled with the lack of cases there, may have skewed the data for that region (Ruiz et al. 2004).
2.3.2 Habitat Mapping in Wyoming In Wyoming new areas of potential WNV habitat were mapped in 2004, based on readily available Landsat data (Zou et al. 2006). The Powder River Basin in Wyoming is good
Culex tarsalis larval habitat, because it has many small ponds as a result of coal-bed methane extraction techniques. The methane extraction process requires that water be pumped out of the coal, and it is usually pumped onto the surface or into small catchment ponds (Zou et al. 2006).
Historical Landsat imagery from 1999 was used to develop habitat classification techniques, and then two images (from 2001) were classified according to those techniques in a GIS, and the spatial and temporal changes noted. Finally, high-resolution aerial photography from 2004 was used in conjunction with field observations to validate the results - researchers went out into the field with global positioning systems (GPS) and mapped out ponds that were Culex spp. positive, and correlated that with the air photo. All of the images were taken in mid-August of their respective years. GIS data included elevation, major hydrological features, and land cover (vegetation). Areas
30 where small water bodies and dense vegetation overlapped on flat terrain, but where they did not intersect with either a river or a large water body, were specifically sought (Zou et al. 2006).
Zou et al (2006) found that between 1999 and 2004 there was a 75.2% increase in Culex habitat, which correlated strongly with a 74.8% increase in area covered by water during the same span, and a corresponding increase in methane extraction. In 2002, the Powder
River Basin accounted for 30% of all WNV human infections in Wyoming, and by 2003 it accounted for 70% of all cases in Wyoming (Zou et al. 2006). The data shows that an increase in water edge around vegetated, stagnant water has a strong relationship not only with increased C. tarsalis habitat, but with human infection rate (Zou et al. 2006).
2.3.3 Risk Assessment in British Columbia
British Columbia is the only WNV-free territory in continental North America, so introduction of the disease to the province seems inevitable, especially considering that
British Columbia is on the west-coast migration flyway and the mosquitoes necessary for transmission, Culex tarsalis and C. pipiens among others, are already present (Tachiiri et al. 2006). In 2004, a GIS-based risk assessment model for the province was created, based on a unique mosquito population dynamics model, combined with data from high- risk bird abundance and the human population; it was validated with mosquito trap data
(Tachiiri et al. 2006). The mosquito population dynamics model used published data on mosquito biology and temperature (Tachiiri et al. 2006). The goal of the study was to predict where vector mosquitoes would likely be, and which communities would be at greatest risk (Tachiiri et al. 2006).
31 Because the mosquito population dynamics model used temperature data from weather stations, it was only accurate for mosquitoes breeding at the surface air temperature
(Tachiiri et al. 2006). When compared with trap data, they found that the model did not match the real C. pipiens populations, possibly because C. pipiens spends most of its time underground, in storm sewers, catch basins, and other underground public utilities that are thermally insulated (Tachiiri et al. 2006). The risk assessment model also used digital elevation model (DEM) data and breeding bird survey data from the USGS, wetland and lake data from the provincial Terrain Resource Information Management Program, and census data from Census Canada 2001 (specifically, number of people over the age of 60)
(Tachiiri et al. 2006). All of the data was set to a 2x2 km grid, to match the DEM data
(Tachiiri et al. 2006).
The risk maps showed that highly-populated lowlands and coastal areas were at risk.
Specifically, Greater Vancouver, southeastern Vancouver Island, the Fraser and
Okanagan Valleys, and Kamloops were at high risk of WNV infection (Tachiiri et al.
2006). High-risk birds share the same habitat as C. tarsalis, which makes sense, given that those birds are high risk specifically because C. tarsalis preferentially feeds on them.
Risk of the birds and mosquitoes forming a viremic feedback cycle was related strongly to temperature (Tachiiri et al. 2006). Human risk was understandably highest where more people over the age of 60 lived in warmer areas (heat island effect from urbanization) close to high-risk bird and C. tarsalis habitat (Tachiiri et al. 2006).
32 2.3.4 Land Cover and Environmental Temperature Influence in Southern Ontario Robert Meyers investigated the relationships between environmental land cover and human WNV infection in the Greater Toronto Area (GTA), and the relationship between temperature and WNV in seven locations in Southern Ontario (Meyers 2006). He postulated that the relationship between land cover and WNV could be used to predict where human infection was likely to occur, and that environmental temperature could be used to predict when (Meyers 2006).
The Greater Toronto Area was classified by land use type using 20m resolution land cover data and airphoto imagery. Since the mosquitoes around the GTA had a typical range of 1 km, Meyers set the study area into a lxl km vector based grid, and reclassified the land use types to urban, grass, farm land, forest, wetland, cloud, bare area, water, and no value, based on airphoto reflectance (Meyers 2006). The classified land use data combined with the airphoto imagery showed a significant amount of 'wetland' and forest in suburban areas. Population density was calculated for each quadrat using information from Statistics Canada. Finally, Meyers calculated the rate of human WNV cases per
100,000 population for each quadrat (Meyers 2006).
Using a univariate analysis of land cover and human WNV case rate, Meyers concluded that forest, urban, farmland, and wetland land classifications were most associated with
WNV risk (Meyers 2006). Multivariate Poisson regression analysis reduced the list down to only one significant variable: wetland. The rate of WNV infection increased with wetland area in a quadrat, up to 25% of the quadrat area (Meyers 2006). After that
33 threshold, risk decreased, possibly because population density decreases with increased wetland area, reducing the number of people exposed.
Meyers points out that most of the area that is classified as wetland is not actually such
(Meyers 2006). The classification methodology was designed for natural areas, not urban areas like Toronto, and to remain replicable, the methodology precluded ground-truthing
(Meyers 2006). However, if one compares a section of Meyers' residential map with freely available satellite imagery from the internet - for instance, the residential block bordered by Yonge Street, Laurence Avenue, Eglington Avenue, and Avenue Road - the classification is immediately put into context (Figure 2.2). Eglinton Park, in the south, which consists of several baseball diamonds, is classified as farmland. In the North,
Chats worth Ravine and Duplex Park are correctly classified as mostly forest, though a walk though Chatsworth Ravine in fall or spring will tell you that there is also at least ephemeral wetland present. The majority of the block, however, is made up of residential lots with large backyards, nearly all of which are classified as wetland. Wide streets
(including suburban streets) and large buildings (including large residential buildings) are classified as 'urban areas', so the association of wetland seems really to be with private yards. To be certain, one would need to look at Meyers' digital data more closely.
However, this suggests that 'residential yard' ' is at least sometimes confused with
'wetland' in Meyers' data. The implications for urban planning of the two possible associations are quite different.
34 iiVf
Memorial - Pjrk
Jf x—- jrVl_*t™* 1 0 500 lOtiOm
Figure 2.5: Area Ground-Truthed in Residential Toronto to Validate the Actual Urban Habitat Classified as Wetland, Forest, and Farmland by Meyers (2006) (Google 2008; Meyers 2006)
The second part of the research focused on using temperature as a temporal determinant of WNV risk at seven sites in Southern Ontario. Meyers first defined a degree-day as
(Max Temp°C. - 16)/2 +(Min Temp°C. -16)/2. Using a 30-day moving window, Meyers found that at least 150 degree-days were necessary for human infection to occur within the given study area. This is useful for temporal risk prediction. It also suggests that areas that are regularly warmer are at higher risk than cooler areas (Meyers 2006).
35 2.4 Key Inferences from the Literature We can conclude several things from the literature about mosquito, avian, and human derived risk factors.
2.4.1 Mosquito Risk Both the speed at which WNV replicates and the speed at which mosquitoes can breed is temperature-dependent (Dohm et al. 2002; Meyers 2006). While cities provide regular atmospheric temperature data at a city-wide scale, it is not possible to get data on mosquito micro-habitat temperature, and therefore temperature risk must be inferred from other variables. In particular, sub-surface mosquito habitat temperature, which is thermally insulated from surface air temperature, is not commonly available.
Culex pipiens need still water that is high in organics, and C. tarsalis need still water with vegetation (Reisen 2002; Crans 2007). The highest risk in an urban environment for mosquito breeding habitat is therefore drainage, especially where sewage and stormwater drainage interact. Swale culverts that retain water and contain decomposing vegetation are also a risk, as are bird baths (which get high in organics) and pool covers (which can get high in organics and leaf litter) if not cleaned regularly.
Underground drainage is probably higher risk than at-grade drainage, because underground drainage is thermally insulated, allowing mosquitoes to overwinter.
Underground drainage on streets that are not completely plowed in winter are further thermally insulated, and are even higher risk. The danger is not necessarily that the mosquitoes will breed faster underground, but that they can breed uninterrupted and out of sight. Open drainage ditches should be considered moderate linear risk elements, and
36 drainage inlets that lead to underground drainage should be considered high risk point sources. Since slope is the main element in built drainage, well sloped drainage should not be considered a risk. In the absence of slope data, the age of built infrastructure could be used in proxy in some locations, since according to the City of Winnipeg, older infrastructure has a tendency to level out (Dalton, personal communication, 2007).
2.4.2 Avian Risk Habitat for urban birds is a combination of good nesting or roosting habitat and good feeding habitat. Meyers' study suggests that these two variables are probably related to large residential yards (Meyers 2006). Areas of open lawn provide good foraging habitat for most urban birds. Mature tree canopy provides ideal roosting and nesting habitat for urban birds. However, neither of these variables is a high risk alone, since it is the combination that provides the ideal urban bird habitat. Large trees in a forest can provide forest species and hole nesters with good habitat, while large open fields may be good for field birds, but not birds that require large trees to nest in.
Sandstrom et a/.'s (2006) study defined the greenway as forested area within 50 m of the Svartan River (Sandstrom et al. 2006), and for this study it makes sense to use a similar definition. Forested areas that are at least 50 m away from residential areas could be considered low risk, but trees within 50 m of a residential area provide nesting and roosting habitat for urban birds, and should therefore be considered moderate risk. Areas that are clearly a combination of trees and lawn are residential habitat, and should be considered high risk. This risk associated with forest/urban edge has also been noted in Lyme disease (another arthropod-borne zoonoses), and for somewhat similar reasons (Jackson et al. 2006).
37 2.4.3 Human Risk Built structures can provide habitat for both birds and mosquitoes. Based on the study in
Chicago, older built-up areas are higher risk (Ruiz et al. 2004). Highly urbanized areas are not risky in any of the studies, possibly because they are biological deserts for the majority of birds and mosquitoes. Literature also suggests that the elderly (defined in this case as over the age of 60) are generally at higher risk than younger people (Ruiz et al.
2004; Tachiiri et al. 2006).
2.4.4 Best Management Practices
Few best management practices address landscape risk specifically, and many of the landscape solutions for reducing mosquito habitat, such as deepening ponds, introducing mosquito predator habitat, or increasing vegetation are still controversial, despite strong evidence that complex habitats supporting multiple insect species have fewer nuisance or disease vector mosquitoes. Other than the general advice that underground drainage infrastructure be designed with the help of a mosquito habitat consultant, there are no best management practices for subsurface drains or drainage inlets. There are no official best management practices for addressing risk from birds or bird habitat, even though the
WNV vector bird species and their habitat are known. Pesticide application does not address the root causes of WNV risk, and reduction of adult mosquito populations through pesticide use is possibly more controversial than source reduction methods through habitat modification.
2.4.5 Variables in WNV Risk
Table 2.2 summarizes the main variables for consideration. There are essentially three main groups of variables in WNV risk for humans: Culex sp. mosquito habitat, urban bird habitat, and human risk factors. It is clear from the literature that these risk variables are
38 interrelated. For instance, Culex sp. mosquito habitat is related directly to urban drainage infrastructure, and urban bird habitat is related directly to aesthetic choices in urban plantings, both of which are related to how a city is built and the age of that particular city (and maybe its population).
Table 2.2 Suburban West Nile Virus Risk Variables Compiled from Models and Research Variable Variable Measured Description General Group Attribute Relationship to WNV1 Subsurface Catch basins, subsurface positive. Stagnant Water Mosquito Area drainage infrastructure. Surface Ditches, surface positive. Stagnant Water Mosquito Area drainage infrastructure. Drainage Age of the drainage. positive. Infrastructure Age Mosquito Age Urban Mature Area of urban tree positive. Tree Canopy canopy. Cover Bird Area Lawn Area planted with lawn. positive2 Groundcover Bird/Mosquito Area Area planted with other negative2 groundcovers (tall Other grasses, other Groundcover Bird/Mosquito Area herbaceous etc) Impervious Area taken up by roads, negative2 Surface Bird/Mosquito Area roofs, and rock. Forest (not just tree negative. Forest (>50m canopy) that supports from Urban) Bird Area forest birds. Average and maximum positive. daily air temperature, Degrees, especially days over 30 Temperature Mosquito Degree Days degrees. The year that buildings positive. Building Age Human Age were constructed. The average age of a positive. Population Age Human Age given population. 1 The column titled 'General Relationship to WNV' shows whether or not the variable is a positive or a negative risk factor. For instance, increased area of stagnant surface water is a positive risk factor, while increased area of forest cover (forest defined as a treed area with a complex understory capable of supporting forest bird diversity) is a negative risk factor. 2 These are not absolutes. Impervious surface can be a positive risk factor for heat island effect, for instance. Lawn is only a risk if close to good bird habitat. Monocultural non-lawn groundcover could be a positive risk. * Shaded cells not used in study (see Chapter 3).
39 3.0 Methodology
This chapter will detail site selection and appropriate choice of spatial scale, visits to the sites and observation, selection and measurement of WNV variables, and mapping and characterization of the selected neighbourhoods.
3.1 Site Selection Spatial scale is important in any epidemiological or landscape architecture project, and determines the scope of the project and what types of data can be used. The census statistics for the average age of a city might be useful for calculating national trends, but irrelevant for planning the specific location for an adult living community. City atmospheric temperature may be useful for analyzing county scale temporal patterns of
West Nile Virus outbreak, but not very useful for predicting when the mosquitoes in a particular neighbourhood block are likely to hatch.
There are already several published province-wide, statewide, countrywide, and worldwide analyses of West Nile Virus epidemiology. There are also published and unpublished models and papers about WNV on the scale of a city. At the other end of the scale, there are published works on the specific environmental conditions required for a mosquito to hatch, or to become infectious. Currently, there are no published works looking at WNV on the scale of a neighbourhood (a district with a unique community within a city). Many of the elements that are responsible for WNV risk, for instance, mosquito and bird habitat, are urban landscape features designed to accommodate humans in some way (they are designed at a human scale). Habitat for mosquitoes
40 especially can vary greatly over a distance of a few hundred metres. This relation to the human scale is what ultimately decided the spatial scale for this thesis.
The city chosen for the study had to meet several criteria. A Canadian city was preferable for accessibility of travel and data-sharing. West Nile Virus had to be established in the city, and there had to be a policy in place for dealing with it. There also had to be easily accessible data relating to WNV and fine-scale data in particular.
Two cities met these criteria, those being Toronto, Ontario, and Winnipeg, Manitoba.
Both cities have spatial and non-spatial data for assessing WNV risk. Winnipeg has had a difficult time with WNV and was willing to share data relating to mosquito hotspots and WNV-infected birds. Thus it was thus selected as the city for this case study based on accessibility of data.
Within Winnipeg I sought two neighbourhoods of approximately 2 km2. This size was important because it allowed for analysis of specific human-scale elements (such as tree- canopy, lawn cover, and sub-surface drainage) while still being generalizable to the neighbourhood. Though the Culex tarsalis and C. pipiens are capable of flying upwards of a kilometre, they typically travel less than 100m so I considered the rectangular shape of the neighbourhoods acceptable. The size of 2 km2 was applicable to the distance that both mosquitoes and urban birds are generally willing to travel to get food. It was also a useful scale because it was a manageable size to measure both larger, neighbourhood sized elements and smaller, human sized elements.. Both neighbourhoods were selected based on airphoto and on-site observation, and based on the risk elements in Table 2.2.
41 3.2 Study Neighbourhoods in Winnipeg North River Heights is located on the southern shore of the Assiniboine River, west of downtown Winnipeg. It was selected for its mature tree canopy, old buildings and infrastructure from around the 1950s, a combined sewer/storm sewer system, and proximity to a river, all of which appeared to be high-risk elements (Table 2.2). Because there is little variation in the street grid, I assumed that it would be relatively easy to make comparisons across the neighbourhood.
Fort Richmond North is located on the western shore of the Red River south of North
River Heights, and was selected as a comparison-contrast neighbourhood because it was designed in a different time period (late 1960s to the 1980s), with a less-mature tree canopy, a separated waste sewer and storm sewer system, and an organic street layout pattern, while still being relatively close to the river. Both neighbourhoods have a school and park, and both neighbourhoods had incidents of WNV positive dead crows in previous years. Figure 3.1 shows the relative locations of North River Heights and Fort
Richmond North within Winnipeg.
3.3 Site Observation
Both neighbourhoods were observed and photographed from a car and on foot between the hours of 9AM and 6PM on August 25th, 26th, 27th, and 28*, 2007. Easily recognizable tree species and bird species were recorded, and others were digitally photographed for later identification. An effort was made to go down each street in both neighbourhoods, although not all streets were photographed. The bird identification was not done as a systematic point count, but haphazardly while observing the neighbourhood more generally -1 have several years of previous experience as a bird bander and point count
42 Figure 3.1: Relative Locations of North River Heights and Fort Richmond North in Winnipeg (Google 2008) field worker, so this was not difficult for me. The approximate location of the sighted birds was mapped. This was done because the chosen neighbourhoods were not known prior to arrival in Winnipeg, and so no systematic methodology for a point count or tree identification had been planned.
3.4 Variable Selection There were numerous variables for a WNV risk analysis to choose from the literature, but not all were applicable to this study. In particular, much of the literature was concerned with discovering the causes of WNV risk. Table 2.2, minus the rows on subsurface
43 infrastructure age and air temperature, summarizes the variables that I used to assess
WNV risk at the neighbourhood level.
Air temperature is a very important risk variable that is, unfortunately, nearly impossible to measure accurately in the micro-climate of several hundred backyards and in the underground sewer and storm sewer infrastructure of a neighbourhood. It is assumed that the risk of all of the elements in Table 2.2 includes the risk associated with air and water temperature. Even though it is not possible to get into every backyard in a neighbourhood, urban tree canopy and ground-cover type (lawn, other, and impervious) can be estimated from airphoto interpretation and from photographs. Aged subsurface infrastructure is only a risk if the associated infrastructure does not drain properly
(thereby providing mosquito habitat). Rather than considering subsurface infrastructure age as a separate variable, it was used to estimate which pipes were likely to have become stagnant. Subsurface stagnant water and surface stagnant water can be estimated with reasonably high accuracy if needed, and the age of the neighbourhood (the people and the buildings) is available through Census Canada.
3.5 Neighbourhood Mapping
Variables summarized from the literature review were gathered from the City of
Winnipeg and spatially represented in ArcGIS using a UTM projection. Airphoto imagery was obtained from die City of Winnipeg Planning, Property and Development
Department at a resolution of 10m (for North River Heights) and 30m (for Fort
Richmond North) in GEO-TIFF format. This resolution was sufficient for distinguishing between buildings, planted areas, roads, and surface stagnant water, and was sufficient
44 for estimating area covered by lawn, other groundcover, and urban tree canopy when used in conjunction with on-site photography. Ken Dalton from the City of Winnipeg's
Water and Waste Department provided sub-surface drainage (sewer and storm sewer) data in ArcGIS and AutoCAD format. These layers contained information on the type, size, slope, and installation date for all sub-surface drainage infrastructure, as well as the locations of all the catch basins, drain inlets, and manholes. Mr. Dalton informed me that much of the city's infrastructure was installed at a 0.5% slope or shallower, and would most likely settle out after 50 years. Based on this conversation and simple geometry, it was possible to estimate the amount of stagnant water likely to be in these pipes and basins.
Additionally, Taz Stuart from the City of Winnipeg's Mosquito Control division provided data in Excel format on the latitude and longitude locations of WNV positive dead corvids found between 2002 and 2005. I projected this information onto the map as points. Taz Stuart also provided ArcGIS shape files showing properties that had Culex sp. in 2007, and the treatment that had been used to control the mosquitoes. The properties were delineated by legal boundary, and specific descriptions of where the
Culex sp. were located was included in the associated database. These data were primarily for surface mosquitoes found in areas such as drainage ditches, tire tracks, and surface ponding.
For detailed analysis, a 200m by 200m grid was overlaid on both neighbourhood maps using an ArcGIS analysis tool called HawkTools. The size of 200m quadrats was
45 selected because it fit evenly on both neighbourhoods, did not obviously bias the analysis, and was a convenient size for mapping out the surface elements. The outer grid cells were then omitted from further analysis to reduce boundary effects. Quadrats that entirely contained a park or school-ground were also removed from detailed analysis.
The neighbourhoods were then separated into quarters, and HawkTools was again employed to randomly select one grid square from each quarter for detailed study. Four
200m squares covered 21% of the North River Heights study area and 22% of Fort
Richmond North study areas.
3.6 Neighbourhood Analysis The variables in Table 2.2 were measured in detail for each quadrat. Road Area, including lanes and drives where possible, and Surface Stagnant Water (visible swimming pools, hot tubs, and ponds) were measured directly from the map. Urban Tree
Cover, Lawn Groundcover, and Other Groundcover were estimated from a combination of mapping (to calculate a total area of green space) and on-site photography (to estimate the area of that green space taken up by each cover type). The groundcover mapping was made easier because the airphotos were taken in spring, when the tree canopy was mostly transparent.
Subsurface drainage was estimated to settle at a rate of 0.01% per year, based on my conversation with Ken Dalton from the Water and Waste Department. From this and the age and size of the subsurface infrastructure, it was possible to estimate the total surface area for subsurface stagnant water in flat pipes. I decided to assume pipes that were almost completely empty (1% of the radius of the pipe), and calculated this chord at the
46 bottom of each flat pipe to calculate the total area of surface water in each pipe (Figure
3.2).
Where: r is the radius of the circle d is the perpendicular distance from the chord to the circle center (in this case, 0.99*r) chord length = 2*sqrt.(r2 - d2)
Figure 3.2 Pythagorean Theorem to Find the Chord of a Circle and Area of Water in a Pipe
Assuming mostly empty pipes is a plausible scenario in peak WNV season (the end of summer, when there is little rain). The size and shape of Winnipeg catch basins was freely available from the city's website (Figure 1 Appendix B), and the total surface area for water in all the catch basins in each quadrat was added to the stagnant pipe water to come up with a total area for Subsurface Stagnant Water.
Culex sp. positive properties were noted as additional general risk areas. Finally, WNV positive dead corvid point data was used in proxy of human cases, and their locations were noted in relation to all of the mapped risk elements.
Using the above mapping in conjunction with non-spatial Census Canada data for
Population Age and Building Age, it was possible to write detailed descriptions of each quadrat.
47 4.0 Findings and Insights
This chapter details the findings from the two chosen neighbourhoods of North River
Heights and Fort Richmond North.
4.1 Winnipeg Overview and Context Winnipeg is located on the floodplains at the confluence of the Assiniboine and Red
Rivers in southern Manitoba. The city was founded in 1873. The Canadian Pacific
Railroad arrived in 1885 and the city has grown into one of North America's primary hubs for wheat transportation. It has a current population of over 650,000.
Winnipeg soil is mostly poor-draining clay, with some alluvial soils around the inside bends of the rivers. Many streets are organized in grids off the rivers, though some neighbourhoods have more organic street layouts with cul-de-sacs. Winnipeg is well- known for its American elm-lined {Ulmus americana) streets, many of which will be taken down by the city in 2008 to 2010 because of Dutch elm disease. North River
Heights is an example of an older, grid neighbourhood with elm-lined streets, while Fort
Richmond North is a newer neighbourhood with a more organic street layout and varied tree canopy.
4.2 North River Heights
North River Heights is a neighbourhood located along the southern edge of the
Assiniboine River, just west of the confluence of the Assiniboine and the Red River .
The streets are laid out in a grid that is perpendicular to the Assiniboine. Blocks are
360m by 80m with a narrow alleyway going behind the houses. Laneways have
48 catchbasins that drain to the main combined sewer lines. Lot sizes vary. The largest lots are in the North-East (680m2) and the smallest are in the North-West (280m2) (Appendix
A Figure 1).
Summer airphotos and on-site observation show the neighbourhood has extensive tree cover. Lawns are the primary groundcover in most yards, with some non-lawn groundcover around the edges of buildings. Based on photographs, lawn is estimated at
80% of the groundcover green space. Tree canopy is total over the roads (100%), 70% over lawns and yards, and about 30% over buildings. The dominant tree species is
American elm.
I saw crows foraging on the ground at Grosvenor and Waterloo, Grosvenor and Niagara,
Grosvenor and Campbell; at Cordova Street and the Kingsway; and on Waverley between the Kingsway and Academy Road. I also saw and heard house) and house finches throughout the neighbourhood, and heard a robin in the park at Brock Street and
Grosvenor.
There are three schools in the neighbourhood: Queenston School in the northwest is a public K-6, Robert H. Smith School in the middle is a K-6 French immersion school, and
River Heights School, in the southeast, is a French immersion middle school. There is also a public park in the southwest. All of these areas are predominantly lawn with less than 10% tree cover.
49 North River Heights originally had a combined sewer system installed in the early 1920s, and this system is still in use on some streets. In general, there is very little slope to the land, the streets or to the waste water systems.
4.2.1 Population Statistics
In the 2001 census the neighbourhood had a population of 5,705, covered 1.73 km2, and had a density of 3297.7 people per km2 (Census 2001). Roughly 14.4% of the population is over the age of 60. On average, Winnipeg was 17.2% over the age of 60, so North
River Heights should actually be at lower risk for this variable according to the 2001 data. It should be pointed out, however, that 5.7% of the population was between 50-59
(compared with the average of 4.9%), and 8.5% was between 50-54 (compared with the average of 6.9%) which suggests that between 2001 and 2006, more people in NRH were reaching retirement age than Winnipeg average (Census 2001).
4.2.2 Income
The average employment income for North River Heights was $57,164, compared with the city average of $38,877. Approximately 26% of the population was considered low income (less than $30,000 per year) compared with the Winnipeg average of about 80%.
In addition, nearly a quarter (23.6%) of the individuals in North River Heights made more than $60,000 per year and 29.9% of family households made combined incomes greater than $100,000, compared with the city averages of 8% and 10%, respectively
(Census 2001). This information, along with personal observation of the houses in North
River Heights, suggests the neighbourhood is wealthier than much of the rest of the city.
50 4.2.3 Dwelling Types and Age North River Heights is 2,215 single-detached homes, with almost no other housing types
(Census 2001). Most of the neighbourhood (72.6%) was built before 1946, with most of the rest of the neighbourhood (24.3%) built between 1946 and 1960, making North River
Heights one of Winnipeg's oldest areas. Winnipeg had housing booms in the 50s, 60s, and 70s, but growth slowed by nearly 15% in the following decades (Census 2001).
North River Heights was essentially finished in the post WWII era. The high number of older buildings and especially the large number of houses built in the post WWII era (a significant risk factor in the Chicago risk study) puts North River Heights at higher risk.
4.2.4 North-West Quadrat There are 64 properties, almost no surface water (only a couple of backyard hot tubs), and 201m2 lawn per property (Appendix A Figure 2). Elms completely shade the streets, and mixed trees shade the majority of yards. All of the combined sewer (CS) lines are sloped to drain properly. There are 13 catch basins total (3.25/ha), and there is an abandoned, capped clay sewer line running under Waterloo Street.
There are no surface Culex in the Northwest quarter of the neighbourhood, however, there was a dead corvid found in the school ground immediately to the west of the sampled grid square. Though not in the sample area, it is worth noting that the drainage infrastructure around the school is all original clay pipes from 1910 - 1923, and it was installed at a nearly flat grade. Table 4.1 shows the areas of the various risk factors.
Table 4.2 shows the amount of tree canopy cover, and Table 4.3 shows the amount of surface and subsurface water.
51 Table 4.1: North River Heights North West Quadrat Risk Variables
Variable Area (m2) Percent of Total Subsurface Stagnant Water (pipes) 0 0.00 Subsurface Stagnant Water (basins) 8 0.02 Surface Stagnant Water 45 0.11 Green Space (total) 16,113 40.28 Groundcover (lawn) 12890 32.23 Groundcover (other) 3223 8.06 Hardscape (total) 23,842 59.61 Hardscape (roads) 5373 13.43 Hardscape (other) 18,469 46.17
Table 4.2: North River Heights North West Quadrat Tree Cover
Variable Area (m2) Percent of Total Tree covered lawn 9023 22.56 Tree Covered other groundcover 2256 5.64 Open (no tree cover) greenspace 4834 12.08 Tree covered hardscape 10914 27.28 Open (no tree cover) hardscape 12928 32.32 Open Water 45 0.11
Table 4.3: North River Heights North West Quadrat Water Area
Variable Area (m2) Percent of Total Total Subsurface 8 15.09 Total Surface 45 84.91
4.2.5 North East Quadrat There are approximately 53 properties in this quadrat with 238m2 lawn per property
(Appendix A Figure 3). Many of the lots are larger on Montrose Street and to the
Northeast than on Oak Street and the properties to the south and west. There is a separate storm relief sewer (SRS) running along Kingsway as well as down Montrose Street, which also has a separate waste water sewer that was installed in 1990. The SRS in this grid square are all essentially flat (installed at a 0.16% slope) which makes them
52 (essentially) water retention structures. Elm Street has a capped, abandoned CS running down the middle of the street, with a properly draining combined sewer down the west side of the street. Table 4.4 shows the areas of the various risk variables.
Tree cover is similar to the NW quarter (Table 4.5), but there is quite a bit more subsurface water (17 catch basins, or 4.25/ha) (Table 4.6). There are no surface Culex or dead corvids in this quarter of the neighbourhood.
Table 4.4: North River Heights North East Quadrat Risk Variables
Variable Area (m2) Percent of Total Subsurface Stagnant Water (pipes) 69 0.17 Subsurface Stagnant Water (basins) 11 0.03 Surface Stagnant Water 26 0.07 Green Space (total) 15,764 39.41 Groundcover (lawn) 12611 31.53 Groundcover (other) 3153 7.88 Hardscape (total) 24,210 60.53 Hardscape (roads) 5200 13.00 Hardscape (other) 19,010 47.53
Table 4.5: North River Heights North East Quadrat Tree Cover
Variable Area (m2) Percent of Total Tree covered lawn 8828 22.07 Tree Covered other groundcover 2207 5.52 Open (no tree cover) greenspace 4729 11.82 Tree covered hardscape 10903 27.26 Open (no tree cover) hardscape 13307 33.27 Open Water 26 0.07
Table 4.6: North River Heights North East Quadrat Water Area
Variable Area (m2) Percent of Total Total Subsurface 80 75.47 Total Surface 26 24.53
53 4.2.6 South East Quadrat There are approximately 56 properties in this quadrat (Appendix A Figure 4). Houses are smaller with more yard space, at 277m2 lawn per property, which means there is less hardscape than in the NE or NW quarters (Table 4.7). The increased green space also means there is more tree cover than in the other quarters (Table 4.8). The CS south of
Grosvenor on Waverley, installed in 1921, is clay, non-draining, and still in use to the middle of the block. Most of Grosvenor Avenue's CS is also original clay from 1921, and both Montrose and Ash Street, which border the school (designated as a Culex hazard) to the west, have non-draining original clay CS from 1948. Waverley near
Grosvenor also has non-draining CS original clay pipes from 1921. Many of these flat pipes are relatively small (450mm diameter), but there are a lot of them. There are 13 catch basins total (3.25/ha), but no surface water visible (Table 4.9).
Table 4.7: North River Heights South East Quadrat Risk Variables
Variable Area (m2) Percent of Total Subsurface Stagnant Water (pipes) 19 0.05 Subsurface Stagnant Water (basins) 8 0.02 Surface Stagnant Water 0 0.00 Green Space (total) 19,422 48.56 Groundcover (lawn) 15538 38.84 Groundcover (other) 3,884 9.71 Hardscape (total) 20,578 51.45 Hardscape (roads) 5130 12.83 Hardscape (other) 15,448 38.62
54 Table 4.8: North River Heights South East Quadrat Tree Cover
Variable Area (m2) Percent of Total Tree covered lawn 10876 27.19 Tree Covered other groundcover 2719 6.80 Open (no tree cover) greenspace 5827 14.57 Tree covered hardscape 9764 24.41 Open (no tree cover) hardscape 10814 27.03 Open Water 0 0.00
Table 4.9: North River Heights South East Quadrat Water Area
Variable Area (m2) Percent of Total Total Subsurface 27 100.00 Total Surface 0 0.00
4.2.7 South West Quadrat
The sampled southwest grid square has approximately 58 properties, with 268m2 lawn per property (Appendix A Figure 5). Greenspace and hardscape areas are very similar to the southeastern quarter (Table 4.10), as are tree cover values (Table 4.11). There is an open, grassy park to the east of the grid square that is considered a Culex hotspot.
There are 14 catch basins (3.50/ha). The entire length of the CS south from Grosvenor
Avenue along Cordova Street is original clay from 1921, but it was laid down at sufficient slope that it is probably still draining properly. Campbell Street had the old clay pipe capped and the street is now serviced by a properly draining PVC pipe along the western side that was installed in 2001. Borebank Street, however, has a 1921 clay
CS that was installed at a 0.3% slope and is now (very likely) flat. There is a swimming pool in the southwestern corner of the grid square, but no other surface water (Table
4.12).
55 Table 4.10: North River Heights South West Quadrat Risk Variables
Variable Area (m2) Percent of Total Subsurface Stagnant Water (pipes) 13 0.03 Subsurface Stagnant Water (basins) 9 0.02 Surface Stagnant Water 24 0.06 Green Space (total) 19354 48.39 Groundcover (lawn) 15483 38.71 Groundcover (other) 3871 9.68 Hardscape (total) 20622 51.56 Hardscape (roads) 4050 10.13 Hardscape (other) 16572 41.43
Table 4.11: North River Heights South West Quadrat Tree Cover
Variable Area (m2) Percent of Total Tree covered lawn 10838 27.10 Tree Covered other groundcover 2710 6.77 Open (no tree cover) greenspace 5806 14.52 Tree covered hardscape 9022 22.55 Open (no tree cover) hardscape 11600 29.00 Open Water 24 0.06
Table 4.12: North River Heights South West Quadrat Water Area
Variable Area (m2) Percent of Total Total Subsurface 22 47.83 Total Surface 24 52.17
4.2.8 North River Heights Discussion The only WNV positive bird was found in the northwest quarter of the neighbourhood, not adjacent to a known surface Culex area; however, it is important to note that the bird was found in an atypical grid square (a school ground) and therefore not actually within the sampled area. The same can be said for both patches of Culex mosquitoes in the southeast and southwest of the neighbourhood. This means that any generalization or extrapolation of the sampled data to the neighbourhood quarter does not apply to either
56 the WNV positive bird or the Culex areas. They can be considered more generally, however (Appendix A Figure 1).
Figure 4.1 compares the areas of surface and subsurface water in m2/ha for each quarter.
D Subsurface Water • Surface Water
North West North East South West South East Quarter
Figure 4.1: North River Heights Stagnant Water by Quarter
As discussed earlier, however, surface water is much less of a potential risk than subsurface water. In terms of stagnant infrastructure, the northeast quarter seems to be at much higher risk than the other areas.
Much of North River Heights is canopy covered, with an average canopy cover of 54%.
The canopy is not uniform.
57 40
35
30
m t 20 D Canopy-Covered Greenscape B Canopy-Covered Hardscape o
15
10
North West North East South West South East Quarter
Figure 4.2: North River Heights Tree Canopy by Quarter
The Northern quarters are much closer to the 25% mark for canopy-covered yards than the southern quarters, but all areas are relatively close to 50% total canopy cover, meaning there is reasonably good bird habitat everywhere. In all cases, however, the only place where total canopy is likely to approach 25% (the risk point in Meyer's study) is next to a park or school. If we consider this with the subsurface stagnant water, the northern quarters could be considered slightly more risky than the southern quarters.
Finally, it should be noted that the WNV positive bird is within 500m of the Culex positive park in the south-west (well within the area that either a crow or mosquito would consider its foraging area).
58 4.3 Fort Richmond North Fort Richmond is located in the southern part of Winnipeg on the western side of the Red
River, just south of the University district. Fort Richmond North, a subset of Fort
Richmond, is located between the University of Manitoba and Highway 100, to the east of Highway 42. Roads are laid out loosely perpendicular to Highway 100, with a hierarchy of Cul-de-sacs and Bays coming off of wider Avenues and Drives (no blocks).
See Appendix A Figure 6 for the overview map.
Summer airphotos show very light tree canopy over most of the neighbourhood, with lots of larger houses and lawn. Compared with North River Heights, there are many more swimming pools and much more open pavement. Ninety percent of the greenspace is lawn, and perhaps 50% of the greenspace has tree canopy. Only 30% of the streets are shaded and very little of the houses or driveways (10%) are shaded. The trees are oak
(Quercus sp.), maple (Acer sp.), ash (Fraxinus sp.), and various ornamental. I did not see any elm trees. Crows were seen foraging at the corner of Dalhousie Drive and Killarney
Avenue; on Dalhousie Drive at Leeds Avenue, Rice Road, Rutgers Bay, and Purdue Bay; on Killarney Avenue at Acadia Bay and Briarcliff Bay; and at the corner of Rochester
Avenue and Rochester Place. House sparrows and house finches were seen in trees and yards across the neighbourhood. I saw a blue jay (Cyanocitta cristata) in the patch of forest at the corner of Dalhousie and Killarney, and heard at least two others as I was driving around the neighbourhood.
59 The neighbourhood has a separate Land Drainage System (LDS) and Waste Water
System (WWS), much of which was installed in the 1970s, and most of which is still in use today.
There are three schools in Fort Richmond North: Ryerson School is an English K-6 school in the south of the neighbourhood. Dalhousie School (K-6) and Acadia School (7-
9) share a large green space in the northern part of the neighbourhood. In addition to an expansive lawn, the shared space has a large patch of urban 'forest' that is 50m across at its widest point.
4.3.1 Population Statistics In the 2001 census Fort Richmond had a population of 11,760, covered 4.61 km2, and had a density of 2,551.0 people per km2, making it less densely populated, but larger than
North River Heights (Census 2001). Approximately 16.3% of the population was over the age of 60, which makes Fort Richmond slightly below the Winnipeg average. Fort
Richmond also had 13.4% of its population between 50-59, which means that as in North
River Heights more people in Fort Richmond were reaching retirement age than the
Winnipeg average (Census 2001).
4.3.2 Income The average employment income in Fort Richmond was $43,551, compared with the city average of $38,877. Unlike North River Heights, Fort Richmond had a little more than
80% of its population considered 'low income', which puts it roughly equal to the city average. While there were a few wealthier-looking residences in the neighbourhood, most of the buildings look like standard, small single-detached homes.
60 4.3.3 Dwelling Types and Age
Fort Richmond has 2,540 single-detached homes, 45 semi-detached, 380 row houses, 10 duplexes, 430 buildings with more than 5 floors, and 1,085 buildings (officially classified as apartment buildings) with less than 5 floors (keep in mind that this is for the entire neighbourhood, and not just the subsection of Fort Richmond North). Roughly 30% of the neighbourhood was built in the 60s, another 50% built in the 70s, and 15% built in the
80s, giving Fort Richmond a decidedly 70s feel compared with the rest of the city.
4.3.4 North Quadrat The northern selected grid square has approximately 43 properties and 337m2 lawn per property. There is a laneway running behind the houses on Silverstone Avenue, similar to the laneways in North River Heights. This quadrat had the highest amount of hardscape (Table 4.13) and corresponding lowest tree cover (Table 4.14) out of any sampled grid square in either neighbourhood (Appendix A Figure 7).
The entirety of the underground drainage infrastructure was installed between 1963 and
1965, making this an older part of the Fort Richmond. Almost all of the LDS are flat, and the WWS running along Silverstone is flat. There are five catch basins (1.25/ha).
There are five swimming pools and hot tubs that could act as surface stagnant water
(Table 4.15).
In 2005 a WNV positive dead crow was found at 207 Purdue Street. There is nothing exceptional about this property from the airphoto or the street.
61 Table 4.13: Fort Richmond North Northern Quadrat Risk Variables
Variable Area (m2) Percent of Total Subsurface Stagnant Water (pipes) 29 0.07 Subsurface Stagnant Water (basins) 3 0.01 Surface Stagnant Water (pools) 129 0.32 Green Space (total) 16124 40.31 Groundcover (lawn) 14512 36.28 Groundcover (other) 1612 4.03 Hardscape (total) 23747 59.37 Hardscape (roads) 4671 11.68 Hardscape (other) 19076 47.69
Table 4.14: Fort Richmond North Northern Quadrat Tree Cover
Variable Area (m2) Percent of Total Tree covered lawn 7256 18.14 Tree Covered other groundcover 806 2.02 Open (no tree cover) greenspace 8062 20.16 Tree covered hardscape 3309 8.27 Open (no tree cover) hardscape 20438 51.10 Open Water 129 0.32
Table 4.15: Fort Richmond North Northern Quadrat Water Area
Variable Area (m2) Percent of Total Total Subsurface 32 19.88 Total Surface 129 80.12
4.3.5 North-Central Quadrat The north-central randomly selected grid square has approximately 48 properties
(Appendix A Figure 8). Killarney Avenue is the major street to the north, with school property along the northern edge. There is about 363m2 lawn per property, more overall
62 greenspace than the other selected quadrats in Fort Richmond North (Table 4.16), and more overall tree cover than the other selected quadrats (Table 4.17). In addition, the school grounds to the north have a large patch of urban forest which probably acts as nesting habitat for urban birds in surrounding areas. This grid square also has the highest area of road surface in selected Fort Richmond North quadrats.
There are two swimming pools in this grid square. There are only 3 catch basins
(0.75/ha) but 10 manhole covers. The drainage infrastructure was all installed in 1970, and it all drains properly with the exception of the WWS along Killarney Avenue
(1350mm diameter), which was installed at a 0.05% slope (see Table 4.18).
WNV positive birds were found in 2002 and in 2005 at two addresses on Acadia Bay.
The schoolyard directly north is also considered a Culex hotspot.
Table 4.16: Fort Richmond North North-Central Quadrat Risk Variables
Variable Area (m2) Percent of Total Subsurface Stagnant Water (pipes) 0 0.00 Subsurface Stagnant Water (basins) 1 0.00 Surface Stagnant Water 47 0.12 Green Space (total) 19365 48.41 Groundcover (lawn) 17429 43.57 Groundcover (other) 1937 4.84 Hardscape (total) 20588 51.47 Hardscape (roads) 4832 12.08 Hardscape (other) 15756 39.39
63 Table 4.17: Fort Richmond North North-Central Quadrat Tree Cover
Variable Area (m2) Percent of Total Tree covered lawn 9254 23.14 Tree Covered other groundcover 1028 2.57 Open (no tree cover) greenspace 10283 25.71 Tree covered hardscape 2935 7.34 Open (no tree cover) hardscape 16412 41.03 Open Water 88 0.22
Table 4.18: Fort Richmond North North-Central Quadrat Water Area
Variable Area (m2) Percent of Total Total Subsurface 14 13.73 Total Surface 88 86.27
4.3.6 South-Central Quadrat There are 44 properties in the quadrat, with 396m2 of lawn per property (Appendix A
Figure 9). Many of the houses are larger, and there are no major streets in this grid square, which means there is proportionally more greenspace per property than in other areas (Table 4.19). It has a similar amount of tree cover as the southern quadrat (Table
4.20).
All drainage is concrete or PVC installed in 1973 and properly sloped. There are 2 catch basins (0.50/ha), 11 manholes, and one swimming pool (Table 4.21) giving this grid
square the least amount of subsurface stagnant water out of all surveyed. There are no
WNV positive birds or nearby Culex hotspots.
64 Table 4.19: Fort Richmond North South-Central Quadrat Risk Variables
Variable Area (m2) Percent of Total Subsurface Stagnant Water (pipes) 0 0.00 Subsurface Stagnant Water (basins) 1 0.00 Surface Stagnant Water (pools) 47 0.12 Green Space (total) 19365 48.41 Groundcover (lawn) 17429 43.57 Groundcover (other) 1937 4.84 Hardscape (total) 20588 51.47 Hardscape (roads) 4832 12.08 Hardscape (other) 15756 39.39
Table 4.20: Fort Richmond North South-Central Quadrat Tree Cover
Variable Area (m2) Percent of Total Tree covered lawn 8714 21.79 Tree Covered other groundcover 968 2.42 Open (no tree cover) greenspace 9683 24.21 Tree covered hardscape 3025 7.56 Open (no tree cover) hardscape 17563 43.91 Open Water 47 0.12
Table 4.21: Fort Richmond North South-Central Quadrat Water Area
Variable Area (m2) Percent of Total Total Subsurface 1 2.08 Total Surface 47 97.92
4.3.7 Southern Quadrat
The southern randomly selected grid square has 45 properties with 384m2 lawn per property (Appendix A Figure 10). It has a comparable amount of greenspace and tree cover to the south-central quadrat (Tables 4.22 and 4.23). Rochester Place and Gonville
Place (two cul-de-sacs) back onto a treed berm.
65 There are seven swimming pools in this area, which gives it the highest amount of potential surface water risk out of all the grid squares in either neighbourhood. Rochester
Place's WWS and the WWS on Burgess Avenue do not drain properly. There are 8 catch basins (2.00/ha) and 13 manholes (Table 4.24).
The school grounds to the west are a Culex hazard. No WNV positive birds have been found in the vicinity.
Table 4.22: Fort Richmond North Southern Quadrat Risk Variables
Variable Area (m2) Percent of Total Subsurface Stagnant Water (pipes) 8 0.02 Subsurface Stagnant Water (basins) 5 0.01 Surface Stagnant Water (pools) 330 0.83 Green Space (total) 19203 48.01 Groundcover (lawn) 17283 43.21 Groundcover (other) 1920 4.80 Hardscape (total) 20467 51.17 Hardscape (roads) 3960 9.90 Hardscape (other) 16507 41.27
Table 4.23: Southern Quadrat Tree Cover
Variable Area (m2) Percent of Total Tree covered lawn 8641 21.60 Tree Covered other groundcover 960 2.40 Open (no tree cover) greenspace 9602 24.00 Tree covered hardscape 2839 7.10 Open (no tree cover) hardscape 17628 44.07 Open Water 330 0.83
Table 4.24: Fort Richmond North Southern Quadrat Water Area
Variable Area (m2) Percent of Total Total Subsurface 13 3.79 Total Surface 330 96.21
66 4.3.8 Fort Richmond North Discussion All of the WNV positive birds in both years were found in the northern part of the neighbourhood, conspicuously within less than 500m of the forest patch on the shared school grounds (the 3 within the sample area are all within 250m). There is nothing unique about the properties where dead birds were found. The properties in the north- central grid square both have catch basins in front of the property, but the dead bird found on Purdue Bay is not near a catch basin. The northern quarter has the highest amount of subsurface stagnant water in m2/ha out of all the sampled squares as well as the highest amount of hardscape and lowest tree cover (Appendix A Figure 6).
90
80
70
60
50 D Subsurface Water • Surface Water 40
30
20 10 =F North North Central South Central South Quarter
Figure 4.3: Fort Richmond North Stagnant Water by Quarter
There is a Culex positive property in the south as well as a large amount of potential
Culex breeding surface water on backyard pool covers. There is also nearly as much
67 subsurface stagnant water in the southern quarter as in the north-central quarter.
All quarters have similar amounts of canopy-covered hardscape, but the canopy-covered greenscape differs. The average total canopy for the neighbourhood is close to 31%.
30
25
20
DCanopy-Covered Greenscape • Canopy-Covered Hardscape 1.
North NortJh Central ISouth Centradl Southi m Quarter Figure 4.4: Fort Richmond Tree Canopy by Quarter
The entire neighbourhood has a total tree canopy dangerously close to the 25% mark.
The northern quarter has a total canopy cover of 27%. The north-central quarter has a canopy-covered greenspace total of 25.71%, but the south-central and southern quarters are not far behind (24.21% and 24.00% respectively).
4.4 Comparison Between Neighbourhoods Fort Richmond North is considered a higher risk neighbourhood because there are more dead corvids there. There are three types of risk that should be considered: Culex habitat,
68 bird habitat, and viral replication rate. Figure 4.5 compares the amount of water (in m2/ha) between the two neighbourhoods.
40
35 -
2 (mD 5 • Surface Water • Subsurface Water E20-
15 -
10 -
5
0 ^^^"^^^^ : ^^^HI^HflNMII^^H North River Heights Fort Richmond North Neighbourhood
Figure 4.5: Total Stagnant Water (Both Neighbourhoods)
Subsurface and surface stagnant water are not equal threats, because subsurface water is harder to maintain safely, and because it provides year-round habitat. If subsurface water is considered on its own, North River Heights appears to be the riskier neighbourhood.
However, in peak WNV season, Fort Richmond North certainly appears to have a lot of potentially risky surface water.
Surface water, as measured by the area of swimming pools and hot tubs, is only a risk if
69 homeowners let water stagnate in the pool covers long enough for mosquitoes to breed, but the area of that risk is easy to measure. A lot of surface water probably gets warmer faster than subsurface water, because it is exposed directly to the sun, which means that surface water that has Culex breeding in it will create infectious mosquitoes quickly. On the other hand, subsurface drainage is a definite risk, but the actual amount of risk water is only a best estimate, because what makes it particularly risky is that it is out of sight and therefore difficult or impossible to measure and maintain. In addition, the temperature of subsurface water (and therefore the speed at which Culex mosquitoes can breed and become infectious) may be partially determined by the amount of sun-exposed hardscape that is draining, though the thermal mass of the ground may mitigate this risk.
Keeping these things in mind, North River Heights may have more actual Culex breeding habitat than Fort Richmond North, but Fort Richmond North may have more dangerous breeding habitat.
Figure 4.6 compares the other major risk variables. As discussed above, more open hardscape is a risk because it increases a heat island effect, allowing mosquitoes and
WNV to replicate faster in subsurface infrastructure. Higher percentage cover of lawn is a risk because it provides more feeding habitat for urban birds. Canopy cover is both a risk and a mitigating factor, because high enough canopy reduces air temperature while potentially providing more diverse bird habitat, while low enough tree canopy doesn't provide most birds with habitat. If we go by Meyer's study, 25% total canopy is the highest 'risk' point.
70 60
50
40
n OTotal Canopy £ 30 • Total Lawn • Total Open Hardscape
20
10
North River Heights Fort Richmond North Neighbourhood
Figure 4.6: Major Risk Variable Comparison Between Neighbourhoods
Fort Richmond North is ahead on all of these risk factors. The only area of significant forest cover in Fort Richmond North is the patch of trees in the school grounds in the north. This could be described as the ideal urban forest bird nesting habitat, and is certainly the shadiest place in the neighbourhood. However, most of the neighbourhood is open lawn and open road. This means that, in the heat of summer, most of the water going into the land drainage system is reasonably warm, which means that mosquitoes that can find breeding habitat below the street are going to breed quickly, and WNV will replicate quickly. In addition, the high amount of lawn coupled with the low overall tree cover means that any surface water on the grass will also provide rapid mosquito and viral replication. The area around the forest patch in the north likely has the high WNV positive bird death count because there are more birds there than elsewhere, and the
71 mosquitoes in the neighbourhood have a high chance of being infectious because of the summer temperature.
Conversely, North River Heights has good bird habitat everywhere. It also has good mosquito habitat everywhere (underground). Mosquitoes are probably getting infectious more on the surface in grassy areas, however, because those are the only places, other than roofs, that are getting any significant amount of sun.
4.5 Summary North River Heights is a wealthier and more densely populated neighbourhood than Fort
Richmond North. While North River Heights maybe have riskier subsurface infrastructure, the combination of above-ground factors in Fort Richmond North make its birds, and probably people, more prone to WNV infection.
The risk factors in both neighbourhoods share a common element. All of the WNV positive birds are close to, or on, a habitat edge.
In North River Heights, the edges are the parks and school ground, where there is proportionally more lawn and less tree cover. Parks and school-grounds in North River
Heights are dangerous from a WNV perspective because they are sun-exposed, large, easy places for urban birds to forage, concentrating hungry urban birds in locations where viral replication is happening faster. A major part of this threat, the subsurface drainage, can probably be solved by replacing the flat pipes, which the city is already doing. If the
72 Elm trees in North River Heights are taken down before this process is complete, the neighbourhood may have a problem.
In Fort Richmond North the edge habitat is the school ground in the north, with the forest patch. This forest patch is a hazard because it concentrates resting urban birds in the one place with mature canopy cover, and the large amounts of sun-exposed lawn and road ensure that all Culex breeding habitat, above or below ground, become infectious quickly.
Getting rid of the forest patch would not solve the problem in the long term, because other trees in the neighbourhood will be reaching maturity, providing a more dispersed habitat. The solution for Fort Richmond North will likely be a complex one, and will be addressed in the following chapter (section 5.4.1).
73 5.0: Conclusions and Recommendations
Each year, thousands of people in North America are infected by WNV, and several hundred die. Culex mosquitoes and WNV exist in cities because the environmental conditions are suitable. Source reduction for vector species is necessary to reduce mosquito borne zoonoses. Landscape planning and management have implications for the environmental conditions that affect WNV spread.
5.1 WNV in the Urban Landscape It is clear from looking at the literature and the neighbourhood study that WNV varies with the urban landscape. Some areas are more suitable for WNV than other areas.
The studies at the end of the literature review show that WNV is unlikely to be found in urban 'downtown' areas. Furthermore, both Meyers (2006) study and the Chicago study
(Ruiz et al. 2004) show that certain suburban neighbourhoods are more likely to be
WNV-positive than other neighbourhoods. The Chicago study concluded that lower density neighbourhoods with high vegetation cover and poor drainage were at risk.
Meyers study concluded that neighbourhoods with wetland classified area close to 25% were at high risk (where wetland classified area was likely miss-classified canopy- covered urban greenspace). The analysis of the neighbourhoods of North River Heights and Fort Richmond North in Winnipeg, Manitoba support the conclusions from the literature.
5.2 Highest Risk The study in Chicago concluded that the risk factor of highest importance varied
74 depending on whether one was interested in clusters of cases or simply the presence of a case. Proximity to a dead bird was an important risk factor for the presence of a case, but not for clusters of cases; in clusters, drainage was more a more important variable. In all cases in Chicago, older residents in low density, poorly drained, highly vegetated neighbourhoods were at highest risk. Meyers study found that the most important risk variable overall was the amount of area classified as wetland (and specifically, risk increased the closer the area was to 25% coverage). The study in Wyoming (Zou et al.
2006) found that increasing exposed, vegetated stagnant surface water edge increased risk.
The literature suggests that no single variable alone is responsible for risk and that the relationship is complex, involving not only the habitats of the mosquitoes and birds, but their behavioral patterns. In this study, the variables included subsurface and surface stagnant water, urban mature tree canopy, lawn groundcover, other groundcover, impervious surface, forest, building age, and population age, and they were assumed to co-vary. Considering subsurface stagnant water, for instance, North River Heights should have many more dead birds than Fort Richmond North. Many more dead birds would be expected in the south of Fort Richmond North if surface stagnant water was the most important risk factor. Urban tree canopy is clearly not risky inherently, since North
River Heights has very high canopy cover. However, tree canopy must play a major role in risk, since the majority of dead birds in Fort Richmond North are conspicuously located close to the largest patch of forest in that neighbourhood. What ties these observations together is that areas that are exposed to the sun (streets and lawn) that drain
75 poorly and have good bird habitat have dead birds near them. In North River Heights these conditions are best met around the parks and school grounds, where there are large open areas of lawn (there is good bird habitat everywhere). In Fort Richmond North these conditions are best met around the forest patch in the north of the neighbourhood
(there is sunny lawn and sunny roads everywhere).
5.3 Existing Guidelines It is difficult to say if the existing guidelines in Winnipeg are doing anything to mitigate the risk of WNV. The areas designated as surface Culex habitat (Appendix A, figures 1 and 6) are regularly treated with Malathion and/or Bti. In either neighbourhood it is impossible to tell if mosquitoes from any of the designated Culex areas were responsible for bird deaths, since crows could easily have contracted WNV in one field and then chosen to die in someone's yard. However, there does not appear to be a close relationship between these areas and WNV positive bird deaths, especially considering the other factors (edges of forests and fields in proximity to poor subsurface drainage).
Poor subsurface drainage is a risk, and the city is replacing and improving that drainage.
The infrastructure replacement is probably having a mitigating effect on WNV risk.
Many of the CDC's recommended guidelines are good in theory but difficult in practice.
Chemical application might control the surface risk of open lawn, but without knowing the extent and magnitude of subsurface drainage risk it becomes difficult (or expensive) to chemically control the entire subsurface drainage structure. This poses a problem for most North American cities that are built on the idea that subsurface drainage, some of which will probably always be stagnant, is the cornerstone of water management.
76 Suggesting that cities use municipally maintained surface land drainage, in order to be able to use biological control systems, like appropriate planting and mosquito predator habitat creation, is probably not a viable concept without a costly overhaul of the entire system (redesigning the street corridor, essentially), but providing incentive for private- scale yard initiatives could be relatively inexpensive.
A neighbourhood like North River Heights is only at low risk right now because it has a lot of mature tree canopy. That canopy is a monoculture of elms at risk of a species- specific disease (Dutch Elm disease). If the elms die before the infrastructure is fixed, the increase in neighbourhood air temperature - which could increase WNV replication rate - coupled with a decrease in available bird habitat (concentrating birds) could lead to an increase in WNV-infected birds, and an overall increase in WNV risk. If WNV had arrived in North America 30 years ago, North River Heights would have been hit much harder because there would not have been the same mitigating effect of the street canopy.
Regardless of what happens to the trees, there are no CDC policies related to canopy coverage or tree planting.
The existing CDC guidelines focus on early detection and source reduction through chemical application. Other guidelines consider biological control source reduction methods which are largely not applicable to the specific risk problems faced by a given neighbourhood. Since the risk factors are all design or engineering related (percent tree canopy cover, slope of subsurface drainage, edge boundaries between design elements like an urban forest patch and a school-yard, and the microclimatic conditions in a sewer
77 or in a backyard pool-cover), none of the existing guidelines are effective at permanently reducing WNV risk.
5.4 Reducing Risk It is easier to design a neighbourhood correctly than to correct a poorly designed neighbourhood. Design objectives should be considered early enough in the design process to mitigate risk (see section 5.4.2).
5.4.1 Correcting a Neighbourhood The major risk factors in Fort Richmond North are tied to how it was initially designed. It is low-density housing with lots of lawn, wide streets, big yards, and generally spotty urban bird habitat except in the north near the forest patch - that is, it has the attributes of bucolic suburban living. To reduce WNV risk, these risk factors must be addressed.
The simplest risk factor to address is the lawn. If the city and the vast majority of the neighbourhood residents decided to get rid of most of their lawn, and plant local prairie grasses and forbs instead, a large portion of the urban bird foraging ground would be gone, and overall avian biodiversity would increase. Removing the good urban bird foraging ground from around the forest patch in the north by removing the nearby lawn would especially reduce risk. Specifically, lawn favours crows and house sparrows
(which are high risk) and, at least in Manitoba, prairie and savannah landscapes are better
suited to brewer's blackbirds (Euphagus cyanocephalus), chipping sparrows (Spizella passerina), and catbirds (Dumetella caroliniensis) (to name only a few), all of which are low risk.
78 The most difficult risk factors to address are probably the streets and the housing density.
Changing the width of the streets would be major work, and narrowing streets is also not something often done. It might be possible to replace some of the streets with porous pavement to reduce runoff and surface albedo, thereby reducing the impact of the streets on the subsurface drainage. Doing both (narrowing the streets and making them porous) would be ideal. Increasing housing density would reduce lawn cover and (if we were to assume one tree in each lot) might increase tree canopy, but it would be difficult to orchestrate a partitioning of lots on this level, and would require a long time frame.
5.4.2 Designing a Neighbourhood The steps described above are much easier to implement if designing a new neighbourhood. Once the risks are known and the local ecology is known, the basic premises for designing a WNV-free neighbourhood are not difficult, even if they are not commonly applied in North America.
1) Reduce or remove mosquito habitat. This can mean different things in different
climates, but in general, it means increasing infiltration as much as possible, and
re-use of runoff water. In some climates this might mean rain gardens, and in
other climates it might mean rock gardens. If storm water is not going into
subsurface stagnant holding tanks or pipes, and is being reused and infiltrated into
the soil, then mosquitoes cannot use it as habitat. Many existing studies and
neighbourhoods around the world already apply these concepts. Where
79 infiltration is not possible, standing water needs to be capable of supporting
mosquito predators (as detailed in Chapter 2). Subsurface drainage (sewage
systems, or even independent black-water recycling schemes) should drain
properly.
2) Reduce heat island effect. Again, this can mean different things for different
climates. Narrower streets with porous paving or low-albedo paving material
would be effective in many places. 'Green roofs' on houses would also help in
this regard.
3) Effective greenspace. Not all greenspace is equal. Lawn, while good for a soccer
pitch, probably increases WNV risk through bird and mosquito habitat. Planting
native vegetation and attempting to create a complex, biodiverse urban ecosystem
would likely reduce mosquito borne risk. More bird species, more mosquito
predators, and less mosquito habitat would have a significant impact on WNV
risk. The impact of WNV on many bird species is still unknown, but the literature
is clear that open ground (lawn, primarily) favours the birds that are known to be
high-risk.
5.4.3 Risk Reduction through Subsurface Drainage
Subsurface drainage is an important part of many urban designs. Municipally owned and maintained sewage systems and land drainage systems are standard in North American city design. They do not have to be a risk.
80 1) Appropriate slope. Drainage that does not drain is underground mosquito habitat.
Knowing the rate at which pipes settle in a city's soil would be useful, but in the
absence of this data, cities should make a point of checking the infrastructure
regularly, especially if it was installed at a low slope.
2) Fewer catch basins, or innovative catch basin design. A standard catch basin is
designed to hold a certain volume (in order to reduce sedimentation), and is
therefore guaranteed standing water. Fewer catch basins mean less mosquito
breeding habitat, which means lower risk. If catch basins could be designed such
that they acted as French drains (sand and gravel beds open to the underlying
ground, for instance) this might also reduce standing water.
3) Innovative pipe design. In places where pipes cannot be sloped properly, it may
be possible to create pipes that intentionally 'leak' in the middle, to get rid of
standing water. Another possibility would be a system to flush out the pipes.
4) Reduction of land runoff. Policies and bylaws can be written to mandate that
properties must maximize the amount of water infiltration on their own property.
These sorts of policies have already been enacted in several European countries.
5.5 Limitations and Opportunities for Future Research Many of the limitations in this study are actually opportunities for future research. In particular, many of the important variables were set from expert estimations.
81 5.5.1 Subsurface Infrastructure The rate at which drainage pipes of various materials settle in different substrates is not published. The average microclimate in drainage infrastructure in various seasons is unmeasured (or at least unpublished). Given these two pieces of information, and having an accurate measure of the amount of water in a storm event, a city could much more accurately determine the amount and location of subsurface mosquito habitat, and then target those areas directly. The temperature-buffering capacity of subsurface drainage pipes should be quantified, to assess the influence of warmed runoff on mosquito habitat.
In addition, there is subsurface infrastructure that was not considered in this paper. Paul
Beach, the manager of the Community Geomatics Centre in Sault St. Marie, Ontario, informed me that they have found Culex spp. in underground transformer vaults (Beach, personal communication, Nov. 2006). Future studies should attempt to gather data on non-drainage related Culex spp. habitat.
5.5.2 Urban Land Cover Classification
Meyers study used a classification system designed for non-urban areas. A high- resolution image of a neighbourhood, correctly classified, could provide much more detailed and accurate information on the landscape elements that contribute to mosquito borne risk. In the case of this thesis, land cover risks like amount of lawn, tree canopy, and hardscape were estimated from photographs and airphotos. A detailed urban land classification system that could be applied to a GIS and high-resolution maps would remove a lot of the subjectivity in an analysis like this one. Such a classification scheme
82 would need to be able to differentiate between at least basic urban groundcover types.
This might be accomplished by ground-truthing Meyers study.
5.5.3 Urban Birds
There is a shortage of accessible data on urban bird foraging range, density, distribution, and general behaviour. The city of Winnipeg did not have a breeding bird survey, or a regular bird point count, for the city. Though I attempted to include personal observations about the birds that I saw in the neighbourhoods, a more systematic approach would have allowed more rigorous bird data to be gathered from specific or random parts of the neighborhoods, which could have been useful as another layer of risk data. Urban breeding bird surveys would be useful for many studies. This should be kept in mind for future studies of this type.
5.5.4 Validation of Study and Future Studies
This study used dead, WNV-positive corvids in proxy of human data. Though there is a relationship between where dead WNV-positive dead corvids are found and human cases, studies of this type are better served with human data. In addition, a cluster analysis, such as was done in the Chicago study, could be used in conjunction with a ground- truthed airphoto classification system to select neighbourhoods that are more appropriate, which would aid researchers in targeting truly high-risk areas. As was stated in Chapter
1, West Nile virus is not the only arbovirus that Culex mosquitoes can carry, and the habitat they are exploiting could be used by other mosquito vectors. Research is needed to explore the risk of other mosquito-borne diseases in urban environments.
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88 APPENDIX A
Neighbourhood Maps
89 ^--.IHttgffiiH
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94 Legend I I 200m Quadrat Grid Fort Richmond North Boundary ssg Randomly Selected Quadrat •n Grid Quadrats Not Allowed O Quarter Grid 1 1Privat e Lot 1 1Parkin g Lot ill Public Lane i Public Walkway Street Waterbody '///, Property with Culex sp present (2007) • WNV-Positive Dead Birds (2005) * WNV-Positive Dead Birds (2002)
0 125 250 500 750 1,000 i Meters N Fort Richmond North: Quadrat Seleetiorr A Figure 6
95 ON
Legend 0 15 30 60 90 120 | | Private Lot WNV-Positive Dead Birds (2005) i Meters N | | Parking Lot J • H Randomly Selected Quadrat Public Lane 200m Quadrat Grid Public Walkway rE m Sewer Catch Basins Fort Richmond North: Street ® Sewer Manholes A Waterbody Northern Quadrat Land Drainage Sewers Waste Water Sewers ~0
Legend j I Private Lot I | 200m Quadrat Grid 0 12.5 25 50 75 100 ll Parking Lot I Meters N 9|c WNV-Positive Dead Birds (2002) lllllf Public Lane Public Walkway ^ WNV-Positive Dead Birds (2005) Fort Richmond North: Street H Sewer Catch Basins A ^^^\/Vaterbody @ Sewer Manholes North-Central Quadrat ^^^^Bandomly Selected Quadrat -™«™ Land Drainage Sewers Waste Water Sewers f
M3 00
Legend 0 15 30 60 90 120 i Meters N [ I Private Lot 1 ^^wandomly Selected Quadrat j | Parking Lot ^^200m Quadrat Grid jjUJ Public Lane © Sewer Manholes Fort Richmond North: Public Walkway B Sewer Catch Basins South-Central Quadrat A Street Waste Water Sewers Waterbody •'•••••- Land Drainage Sewers Legend
| I Private Lot ^^^BRandomlRa y Selected Quadrat 0 15 30 60 90 120 I Meters N I | Parking Lot e| [ 202001 m Quadrat Grid Hi§| Public Lane Y//A Properties with Cuiex sp. present (2007) Fort Richmond North: Public Walkway Waste Water Sewers Southern Quadrat A Street __ Lanc| Drainage Sewers Waterbody @ Sewer Manholes 9 Sewer Catch Basins APPENDIX B
Standard Catch Basin Drawing
100 SEWER SERVICE FROM SEWER SERVICE FROM CATCH HOUSE OR BUILDING BASIN, CURB INLET OR CATCH PIT
EXCAVATION IN BOULEVARD
ANCHOR PLUG WHILE FILL SETS
ANCHOR PLUG IN ..CATCH BASIN OR EXCAVATION WHILF FILL SETS FILL SEWER SERVICE WITH CfcMfc'N I' STABILIZED EXISTING SEWER FLOWABLE FILL
SEWER SERVICE ABANDONMENT BENEATH PAVEMENT
10 B x75 LONG TYPE 316 STAINLESS STEEL BOLT AND WASHER 10 DIA, 0 JOINTED BAR SECTIONS ~j ROD COUPLER WITH WASHER/
• FERNCO FLEXIBLE COUPLING / Lur OR APPROVED EQUAL o L !> s
m;> *^
a - 2 LAYERS 19 THICK PLYWOOD LAMINATED TOGETHER 19 WIDE STAINLESS STEEL HOSE 19 WIDE STAINLESS \ CLAMP STEEL HOSE CLAMP —^ 2 THICK PLASTIC DISC ATTACHED TO PLYWOOD WITH 3 # 8x32 LONG STAINLESS STEEL SCREWS FRONT VIEW
SECTION AnA DIMENSIONS IN MILLIMETERS JL THE CITY OF WINNIPEG Reference Spec. No. CW2160 Winnipeg WATER & WASTE DEPARTMENT Designed By: Drawn By: Scale; TW BH N.T.S. SEWER SERVICE Checked By: Pate: 03-03-14 Drawing No. ABANDONMENT BENEATH TW Revision: PAVEMENT Approved: SD-021 UNDERGROUND WORKS COMMITTEE Figure I
101