Osoyoos Lake Aquatic Plant Mapping

Transcription

1 Osoyoos Lake Aquatic Plant Mapping AquaTechnex, LLC Presented to Okanogan County NWCB by PO Box Bellingham WA,

2 Introductions Myriophyllum spicatum or Eurasian Milfoil has for a number of years been considered the most problematic invasive aquatic species in the northern areas of North America. There are a number of other noxious aquatic weeds on the march in the Pacific Northwest as well. Flowering Rush has been discovered a number of drainages linked to the Columbia River System. Hydrilla has been found in a tributary to the Snake River in Idaho that could eventually reach the Columbia River system. Curly Leaf Pondweed is an emerging problem in many Washington Lakes and the Columbia River system. In the Western United States, one of the first major invasion of Eurasian milfoil was noted in the Okanogan Chain of Lakes in British Columbia in the early 1970's. The residents of this area noted the dramatic expansion of this noxious weed and both the British Columbia Ministry of the Environment and the Okanogan Basin Water Board teamed to develop control strategies for provincial waters. Over the late 1970's and early 1980's, all known control technologies were deployed in both research and operational mode to combat the building milfoil problem. Over time, the agencies charged with management in Canada settled on a system of mechanical control technologies to maintain high use areas. A good history of the control program in the region can be viewed at Lake Osoyoos is the southern most lake in the Canadian Okanogan chain of lakes and has been subject to this invasive species. The Okanogan Chain of Lakes drains south into the United States and the Columbia River. Lake Osoyoos is a 5,800 acre water body with a maximum depth of 208 feet and an average depth of 46 feet. The northern 2/3 of the lake is located north of the US Border, the southern 1/3 of the lake is located in Okanogan County, Washington. The Okanogan River drains from the south end of the lake to the Columbia River. The primary mode of spread for Eurasian Milfoil is by plant fragments. These vegetative propagates result from boat traffic cutting through weed beds, mechanical control operations that don't capture all of the plant material and from auto fragmentation processes that the plant goes through in the fall. Fragments as small as 1 2 inches will float and develop white root hairs. As some point they sink to the lake bottom and take root there. Once established, the plant can grow up to one foot per week. Over the course of a few years, this process can completely fill the littoral area of a lake or river system with a monoculture of milfoil. As Lake Osoyoos is downstream from the original infestations in the Okanogan, it was just a matter of time until this noxious weed spread to the lake and beyond downstream. AquaTechnex, Inc. 1

3 Lake Osoyoos is located at the Canada/United States Border at the southern end of the Okanogan Lakes Chain. As such, the residents of Lake Osoyoos have been plagued by Eurasian Milfoil for decades. In the early to mid 1980's, the US Army Corps of Engineers teamed with the Washington Department of Ecology and Okanogan County to develop a control program for the milfoil threat. In 1982 and 1983, experimental treatments with aquatic herbicides were performed and evaluated by Corps scientists. In 1984, the program went operational and Aquatechnex biologists treated approximately 100 acres of the noxious weed. In 1985, the County experienced legal threats from environmental groups in the region and soon after that the Corps operational funding for control efforts came to an end. In recent years lake residents working with the Okanogan County Noxious Weed Board have taken on the mission of development management strategies to deal with the problems posed by this weed. The County was successful in obtaining funding to develop an Integrated Aquatic Vegetation Management Plan (IAVMP) from the Washington Department of Ecology. There are a number of mapping components that are required in the process of developing these plans. Aquatechnex was selected to develop and implement a mapping program to define the conditions within the lake with respect to invasive aquatic weed growth during the summer and fall of This report summarizes our efforts in this regard. Methods The mapping effort we proposed for this project takes into account the significant size of Lake Osoyoos. Ecology documents indicate that the lake is 5,800 acres in size and has over 27 miles of shoreline. While some of this shoreline is in Canada and outside the scope of this mapping effort, that is still a large area to effectively cover. As such, our team used a combination of AquaTechnex, Inc. 2

4 aerial photography, GIS analysis and boat survey to develop the maps that document conditions in the lake. The first step in our effort was to organize the Geographic Information System (GIS) project files. GIS software allows for the display and analysis of geographic features as layers. ArcGIS 10.1 software from ESRI was utilized for this project as it is the most widely distributed GIS software available and the resulting data sets could be transferred to the County's GIS system. A project file was established that included a base layer of high resolution aerial imagery. This image data was downloaded from ArcGIS Online. We also created a geodatabase for the various aquatic plant communities expected to be found in the lake. The next step in our process was to locate and review bathymetry data for the lake. Ideally, GIS bathymetry files are located and moved into the ArcGIS project file as a layer. The littoral area of a lake is the portion of the water body that is shallow enough to support aquatic plant growth. Light necessary for plants for photosynthesis becomes extinct in water with depth. The depth of light penetration varies from lake to lake depending on water clarity and the level of suspended materials such sediment or algae that can absorb light. A bathymetry map displays the depth contours of a lake system and can be used to define areas of the lake that would be shallow enough to support aquatic plant life generally. This can be used to eliminate areas that are too deep from the areas necessary to survey. There is no GIS bathymetry layer available that we were able to locate, but an analysis of paper bathymetry maps show that generally the littoral zone of Lake Osoyoos is relatively uniform and follows the shape of the shoreline. AquaTechnex, Inc. 3 The next step was to fly an aerial shoreline analysis (ASA) mission to Lake Osoyoos. This process involves traveling in a fixed wing aircraft to the lake and collecting aerial imagery using ASA protocols of all littoral areas of the lake. This image data was collecting using a Nikon D90 digital camera with 16 megapixel resolution. The technique collects oblique photography through the open side window of a high wing aircraft and capturing the littoral area of the lake and shoreline. The flight protocols also required that shorelines be photographed with the sun angles are such that maximum lighting of the aquatic plant growth

5 occurs. A water penetrating filter and limiting flight operations to periods with little to no surface wind also helps to get a clear picture of the plant communities. The entire shoreline was filmed with a 30 percent or better overlap so that no areas of the lake were missed. In addition, a Trimble GPS receiver recorded the flight track of the aircraft and was used to help map the exact location of the image collection. On return from the flight, the imagery was downloaded into the mapping computer. It was then analyzed by aquatic biologists and the shapes and boundary of aquatic plant communities visible in the image data were created as layers in the GIS project file. This project file was then transferred onto a field computer for work on the lake. Our team then mobilized a mapping vessel to Lake Osoyoos. This unit was a 16 LUND with a Panasonic Toughbook computer running ArcGIS and Trimble's GPS Analyst Extension. The team traveled all of the littoral areas of the lake, viewed the mapped data and adjusted aquatic plant polygons as necessary. They also identified the major plant species in each plant community that was mapped. This data was then brought back to the mapping facility where the final GIS processing took place and maps were created for delivery. Results and Discussion While the lake has in excess of surface acres, the littoral areas of the basin on the US side of the border are generally limited to a relatively narrow band along the shoreline. Aquatic plants were found growing in depths of less than 20 feet so the vast majority of the lake surface AquaTechnex, Inc. 4

6 acres will never support aquatic weed growth because the water is too deep. From a management and cost perspective that is a good thing. We observed four general conditions within the littoral areas of the lake with respect to aquatic plant colonization. As would be expected in a lake and river system with a long history of Eurasian Milfoil present, there were dense beds of this noxious weed discovered and mapped during this process. These plant beds were well dispersed around the perimeter of the lake and generally were made up of monoculture stands. In most cases there was a understory of shorter native aquatic plants including Elodea canadensis or American Waterweed. GIS analysis found that there were approximately 93.5 acres of the littoral area of the lake with dense Eurasian Milfoil colonies present at the time of the survey. These areas are mapped as Red polygons. While we did not note the presence of Curly Leaf Pondweed, a submerged noxious aquatic weed that is listed by Ecology as present in the lake, this plant species generally crashes in mid summer after forming turrion reproductive structures. The timing of this survey is not ideal to note the presence or coverage of this noxious weed. There are also many areas of the littoral zone that have healthy native aquatic plant communities present. While there may be a scattered Eurasian Milfoil plant or two within these areas, they are dominated by Potamogeton species at the time of this survey. Species observed were: Potamogeton illinoensis (Illinois Pondweed ) Potamogeton nodosus (Floating leaf Pondweed) Potamogeton natans (Floating leaved Pondweed) Potamogeton amplifolus (Big Leaf Pondweed) Elodea canadensis (American Waterweed) Potamogeton Richardsonii (Richardson's Pondweed) These species were the dominate native aquatic plants observed in the littoral areas of the lake, More detailed survey focused on identifying all aquatic plants present in the lake have been performed by the Washington Department of Ecology and they note a number of additional species have been documented in the lake. This information is available on their web site. There are significant stands of native bulrush growing in colonies along both shorelines. Scipus acutus or Hardstem Bulrush is growing in small to large stands at a number of locations around the lake. Generally this is present in some of the more protected areas in the lake. Lastly there is a significant amount of the littoral area of the lake devoid of aquatic vegetation, or with extremely low densities of aquatic plant life present. These are generally exposed shorelines where wave action may impact growth and limit establishment. Many of these areas have features visible in the aerial imagery such as sand deposits that indicate wave activity. While at this point there are portions of the littoral area of the lake dominated by native aquatic plant growth or open areas devoid of growth, these areas are still threatened by invasive aquatic weed growth. Eurasian milfoil may still replace or outcompete native aquatic plant life in future in areas they currently dominate. Eurasian milfoil may also expand into areas that are currently devoid of aquatic plant growth. Any future management planning needs to AquaTechnex, Inc. 5

7 focus both on targeting this noxious weed where it currently occurs, but must also be on the lookout for expansion because there are areas of the lake's littoral zone that this opportunity exists. Maps The following pages show an overview of the aquatic plant distribution in the lake system and close up maps that cover the littoral areas of the lake. After each map page, there is a page that shows the major infestations present. AquaTechnex, Inc. 6

8 Lake Osoyoos Aquatic Plant Coverage Summer, Legend Native Aquatic Plant E. Milfoil Emergent Aquatechnex, LLC

9 Sheet 1 This bay is on the west shoreline at the border. The bay has a defined band of Eurasian Milfoil in the inshore areas. There is also native Potamogeton communities in the offshore area that are dense enough to be considered problematic for boaters. Bulrush species are present on the bar that takes up the southern portion of this image This location is south of Boundary Point on the west shoreline. There is a narrow band of Eurasian milfoil at the drop off, and this picture shows one of the areas that is devoid of vegetation in the near shore area. Further south on Sheet 1, another example of near shore areas devoid of aquatic plant growth and narrow bands of Eurasian Milfoil at the outside margin of the shallows. AquaTechnex, Inc. 7

10 Lake Osoyoos Aquatic Plant Coverage Sheet 1 4 Legend Native Aquatic Plant E. Milfoil Emergent Aquatechnex, LLC

11 Sheet 2 Eurasian Milfoil beds defined near shore. This section of shoreline has extensive communities of hard-stem Bulrush present along the shallow zone. Eurasian Milfoil beds are further off shore. Another example of littoral areas of the lake with little or no vegetative cover present on the lake bottom in shallow near shore waters. There are plant beds at the drop off. AquaTechnex, Inc. 8

12 Lake Osoyoos Aquatic Plant Coverage Sheet 2 4 Legend Native Aquatic Plant E. Milfoil Emergent Aquatechnex, LLC

13 Sheet 3 Sheet 3 covers the southern end of the west shoreline of the lake to the outlet. This location again shows large areas of the littoral shelf devoid of vegetation with bands of Eurasian Milfoil in deeper water zones. The darker area of this image is a deep water zone that encroaches to the shoreline. There are bands of Eurasian milfoil on the drop off edges of this feature. The outlet of the lake is visible in this image. There are dense beds of Eurasian Milfoil concentrated in the channel while the shoreline at park beach is realatively free of aquatic plant growth. AquaTechnex, Inc. 9

14 Lake Osoyoos Aquatic Plant Coverage Sheet 3 4 Legend Aquatechnex, LLC Native Aquatic Plant E. Milfoil Emergent

15 Sheet 4 One of the larger Eurasian Milfoil dominated plant beds is located at the south end of the lake. This image is looking toward the east at the extreme south end of the lake at the Southeast shoreline Rouding the corner, this is the start of the eastern shoreline at the sothern end. A considerable amount of the littoral area here is free of aquatic plant life, there are bands generally dominated by native species. The next image to the north, Eurasian Milfoil beds are now evident at the deeper margins of the littoral zone of the lake. AquaTechnex, Inc. 10

16 Lake Osoyoos Aquatic Plant Coverage Sheet 4 4 Legend Aquatechnex, LLC Native Aquatic Plant E. Milfoil Emergent

17 Sheet 5 The waters adjacent to this resort are heavily impacted by dense Eruasian Milfoil beds from the beach area and toward the south. Further north of the resort noted above, the milfoil communities are smaller and more scattered with areas where the lake bottom is again devoid of aquatic vegetation. This bay is just south of Veranda Point. The lake littoral area is relatively clear of aquatic plants in the near shore area until the shoreline starts to bend toward the resort, then a dense band of Eurasian Milfoil is present. AquaTechnex, Inc. 11

18 Lake Osoyoos Aquatic Plant Coverage Sheet 5 4 Legend Aquatechnex, LLC Native Aquatic Plant E. Milfoil Emergent

19 Sheet 6 The narrow band of Eurasian milfoil on the beach front at Veranda Beach is visible, this band follows the deep water edge of the littoral zone around the corner toward the north. The shallow areas are dominated with emergent Hard Stem Bulrush species. Just north of Veranda Beach, the shallows again are dominated by Hard Stem Bulrush and there are dense bands of Eurasian Milfoil in deeper water at the transition. At this bay located on the Border, there is a dense community dominated by Eurasian Milfoil throughout the bay and additional bands present at the deep water drop off transition. AquaTechnex, Inc. 12

20 Lake Osoyoos Aquatic Plant Coverage Sheet 6 4 Legend Aquatechnex, LLC Native Aquatic Plant E. Milfoil Emergent