TOPOGRAPHY & WEST NILE
The impact of changing elevation on vector species distribution along three major streamedge settings with exceptional elevation changes in shoreline and floodplain terrain.
Ecological Studies performed lengthwise along two Creek-edges.
The Fishkill Creek and the Wappingers Creek are the two main streams that cross Dutchess County between eastern county regions, in and close to Connecticut, and the Hudson River forming the county’s western edge. In spite of the relative proximity of each of these creeks to each another, each has its own distinct series of habitats and environmental settings situated along the creek. The more southern Fishkill Creek has a slightly more meandering-like behavior, with widely-defined floodplains formed along much of its central and southwestern portions before empying into the Hudson River. The more northern (actually central Dutchess County) Wappingers Creek traverses large farming and livestock areas in the eastnortheastern to northnortheastern portions of the county and in the central county passes through approximately 6 to 10 miles of heavily population suburban settings (depending on where you draw the urban/suburban boundary), half of which includes several sections of moderate to deep ravine settings (25′ to >50′ depth from water surface), before making its way through the last mile or so of creek which crosses deciduous forest areas, numerous gravelly creek-edge settings, one significant waterfall, a ravine and combined riparian-estuarine setting before emptying into the Hudson River. Most unusual for the Fishkill creek is that it passes through a channel formed at the base of a mountain ridge for approximately 3 miles, including one narrow channel in a well-forested area before reaching the river, with much of the region well shaded by trees. In terms of human ecological features, after passing through the agricultural setting, the Wappingers Creek passes through ten miles of numerous, consecutive, heavily populated settings, followed by an old manmade lake setting, and a narrow gorge with a channel leading into an old industrial setting (where the water and company boilers used this water to service entire factory setting during the 19th century). This creek then continued to the river along much slower flowing channel, much of it manmade, before emptying into the Hudson.
The ecological settings along the Fishkill creek demonstrate fairly natural settings crossing large flood plains (some portions 3+ miles wide), in spite of significant development of this region; wooded areas are less impacted by housing contruction and flood plain topography is transected but not changed throughout much of the river edge. In one area, a well-known dump site can be located (primary west nile vector setting). The Wappingers Creek agricultural settings also bear a floodplain, although perhaps only half the width and area of the largest Fishkill Creek floodplains. The lower area lacks floodplains (except immediately adjacent to the river), and bears significant housing along much of the river edge. Most of the large suburban settings in this former river floodplain were constructed on landfill sites, formerly serving as wetlands, therefore much of the wetlands for these natural sections of the river have been minimized. Mosquito populations along each of the two creeks demonstrate the difference in mosquito ecology between these two creeks. The manmade, seminatural settings make the Wappingers Creek an area where studies focused on human population and special landuse and topographic features can be reviewed in relation to mosquitoes and west nile ecology. The Fishkill Creek is an example of a series of fairly low-impact natural settings, defined by a combination of broad floodplain wetlands sections interspersed with several community suburban settings and a few very unique perimontane and ravine or channel ecology settings.
Most of the ecological aspects of these two creeks were evaluated for vector species spatial distribution and ecology, and reviewed extensively for other natural ecologic features focused on the impacts of topography, channel/ravine form and ecology, peririparian montane ecology, and plant-related geographic conditions on vector-host species spatial distributions. These in turn could be related to the human population features linked to west nile transmission behavior within this middle county in lower New York State. Due to human ecological features, the species along the Wappingers Creek are more likely to be West Nile carriers. Due to natural ecological and topographic features, the mosquito species along the Fishkill Creek, although capable of carrying west nile, is found to be in considerable competition with numerous other species, with a diversity of mosquito species more variable than that of the Wappingers Creek. Moreover, these species are less likely to carry the disease and transmit it to humans due to the distribution of human settlement areas in relation to the actual sources for Culex pipiens-restuans, the natural vector of west nile in this county. Cx. pipiens-restuans is more apt to reside and infect people with west nile in the more urban-suburban densely populated settings, where its primary hosts (crows and blue jays) tend to be in closer contact with human ecology related features such garbage-ridden former woodland sites, illegal dumpsites (former industrial settings), and stagnant water bodies that have little contact with a nearby creek feature.
Locating sources for positive testing host case clusters in a significantly rural housing setting: use of remote sensing, NLCD grid, vegetation, AVHRR and field surveillance techniques to identify an ecologically-defined infection nidus linked to several positive-testing hosts.
An Advanced Very-High Resolution Radiometric (AVHRR) Image was obtained for the Dutchess County region of New York and the data specific to Dutchess County extracted from this raster image. This was used to evaluate the impact of topographic features and ecological setting of host-species-vector behaviors along a portion of the Wappingers Creek situated in a fairly suburban region, but adjacent to several small towns, downstream from major agricultural communities, and slightly upstream from major urban settings. This section of the creek is unusual due to it passage through a fairly deep ravine setting, with houses situated uphill from the creek and on the downhill side of a roadway travelling parallel to parts of the creek edge. Traps were set up along a line 90 degrees from the river edge, with some additional traps set along lines parallel to the creek-edge immediately adjacent to the creek-edge and approximately halfway up the hill from the creek edge (adjacent to a homestead).
A digital elevation model (DEM) was applied to this study utilizing IDRISI32 to develop and analyze much of the AVHRR and NLCD data in relation to site ecology and trapping results. The purpose of DEMs in west nile research is to demonstrate the impact of small area topographic features on host and vector behavior. The value of researching plant ecology and species disrtibution at a three-dimensional level is well documented with regarding to researching mosquito species (see Medical Geography, by Meade for an example and illustration). For this study, terrain played an obvious role in both animal host (crow) and vector species ecology due to the role of forest ecology and terrain on landing sites for crow migratory and daily flying habits, and the relationships major terrain changes such as steep slope areas and the formation of landing peaks have not only on host migration but also species behaviors in relation to the effect these regions have on local climate, temperature, humidity, presence or absence of important water features (large or small), selection of potential biting hosts, and the availability of comfortable rest areas for non-biting periods.
In the DEM displayed, the low water surface sites, mid-rise homestead sites (paired lateral to the riveredge) and mid and upper terrace trap sites were selected due to obvious elevation differences, somewhat moderate differences in canopy and landuse features (the buildings are only between the creek edge and mid-level/mid-terrace), animal ecology differences, and the temperature and humidity differences related to elevation above a creek surface within a thick deciduous canopied ravine setting. Whereas the positive testing host was found along the narrow floodplain adjacent to the river edge, the species responsible for transmittting west nile was found only at higher locations throughout these series of evaluations. More importantly, an important ecological species of mosquito was found at the mid-terrace level adjacent to the homes. This frog-dependent species was not on the flood plain as expected, but rather situated further inland and upland from the creek. This may be due to the relative richness of Aedes species found along the creek edge, a characteristic trait of these particular Aedes species throughout the local county region. Most likely swarm density in relation to species dominance behaviors and ecological requirements kept the Uranotaenia from residing predominantly along the riveredge at the time of trapping. Although capable of swarming near the creek whilst residing at higher elevation this species apparently prefers the higher elevations for its swarm- and feeding-related activities as well. The species related to west nile transmission (Cx. pipiens-restuans), was trapped only at the highest location in this research area, approximately 300 feet from a creek edge.
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Brian Altonen, MPH, MS 