Great Meadows National Wildlife Refuge Management at the Concord Impoundments,2000-2007
The Great Meadows National Wildlife Refuge (NWR) was established in 1944, “...for use as an inviolate sanctuary, or for any other management purpose, for migratory birds”, 16 U.S.C.§ 715d (Migratory Bird Conservation Act); and for purposes, “...suitable for (1) incidental fish and wildlife-oriented recreational development, (2) the protection of naturalresources, (3) the conservation of endangered species or threatened species...”, 16 U.S.C. § 460k-1 (Refuge Recreation Act). In order to achieve quality habitat for migratory and resident bird species, the Concord Impoundments on Great Meadows NWR must be actively managed.
____________________________________________________________________________________Photo by Ken Andrews
Background:
The impoundments at Great Meadows NWR are each approximately 100 acres in size. Each impoundment has one water control structure on the “back dike” that connects to the Concord River. There is also a water control structure on the cross dike that connects the two impoundments to each other. Each of the three water control structures consists of a cement culvert under the dike, with stop log structures located on either end of the culvert. There are two rows of stop logs on each side of the culvert. The stop logs may be removed to draw-down water levels, and replaced to maintain or increase water levels. The upper impoundment (upstream pool) is drained by removing stop logs from the water control structure connected to the Concord River and the water control structure at the cross dike between the two impoundments. The lower impoundment (downstream pool) is drained by removing the stop logs at the water control structure connected to the Concord River. At high water stages within the Concord River, water can be allowed to flow into each impoundment through its “back dike” water control structure. At extremely high river stages, water flows uncontrolled over the top of the back dike into the impoundments. This occurs almost every year in the spring. Two different methods of draw-downs can usually be accomplished at the Concord Impoundments (if weather cooperates): a fast draw-down wherein all stop logs are removed at one time to rapidly drain an impoundment as quickly as possible; or, a slow draw-down wherein a fewer number of stop logs are removed, and the results are monitored through water level measurements. Every year, the impoundments are reflooded before winter freeze, and remain flooded until the following spring.
Great Meadows NWR and 15 other Refuges from Virginia to Maine were involved in a U.S. Fish and Wildlife Service Regional Shorebird Study and Waterfowl Study from 2000 - 2002. Collectively, the study’s objectives were to: (1) identify the Region-wide contribution toward shorebird resources during their migration, (2) determine the most effective actions at managed impoundments for various species or guilds of shorebirds which have a Regional priority, (3) evaluate the effects of management for shorebirds on food resources and non-breeding waterfowl use, and (4) coordinate shorebird management among Refuges in Region 5 of the Service (the 13 northeast States). Impacts of fast draw-down vs. slow draw-down were the primary variable being measured and compared in this study. We found the slow draw-downs to be more beneficial overall in terms of waterbird use and vegetative response, but results are highly dependent on natural rainfall. These studies were of great importance to the Refuge. The results helped us focus management goals and resources, and guided our management efforts in 2003 and 2004. In 2005, another Regional study was initiated, with over 15 Refuges participating. This study incorporates many of the same data collection techniques as the previous study, but is primarily measuring the differences in waterbird use and vegetative response to slow drawdowns at different times of the season. This will also be a three year study, with treatments varying in the two impoundments each year.
Table 1 summarizes impoundment water level management since 2000. Although study protocols were in place from 2000-2002 and 2005, sometimes actual water level fluctuations and management varied due to weather and other maintenance needs. “Drawdown” refers to active management through water control structure board removal, but in many cases, the water levels were already naturally declining through evapotranspiration, before boards were actively removed. Water levels have been checked regularly since 2000, and detailed logs have been kept regarding water level management. Table 1 is just a general synopsis of this data.
Year |
Upper Impoundment |
Lower Impoundment |
2000 |
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2001 |
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2002 |
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2003 |
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2004 |
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2005 |
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2006 |
Plan to:
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Plan to:
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2007 |
Plan to:
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Plan to:
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Wildlife and Habitat Monitoring Activities:
Changes in Vegetation and Invertebrates :
Fluctuating water levels through the spring, summer and fall impact vegetation by promoting seed germination and growth of various plants. In addition, lower water levels typically lead to warmer water temperatures which can result in increased stimulation of invertebrate production. The effects of the draw-downs on vegetation composition, seed production, and invertebrate production are important because they all impact use by waterfowl, shorebirds, marsh and wading birds. Data collection relative to vegetation changes is usually conducted in September or October. Specific protocols and data collection has varied slightly each year, depending on the study. The annual minimum sampling scheme, however, has consisted of 30 random points annually visited in each impoundment. At each point, all of the species and abundance of each within a 1-m square are recorded. This data will be collected again in 2006 and 2007. In some years, seed heads of the five dominant wetland plant species were collected to determine the effects of the drawdowns on seed production and total biomass. Beneficial wetland plants that have dominated both impoundments during the last five years include: beggars ticks (Bidens spp.), Walter’s millet (Echinochloa walteri) and umbrella sedges (Cyperus spp.). Data collection on invertebrate changes is usually conducted multiple times during the year. Specific protocols and data collection has varied slightly each year, depending on the study, but sediment and water column samples were collected in 2000, 2001, and 2005. For each sample, all invertebrates have been sorted from the samples and counted, dried, and weighed to determine overall mass. Invertebrate sampling will occur twice each year in 2006 and 2007.
Shorebirds, Waterfowl, Wading and Marsh Birds:
Waterbird use needs to be carefully monitored to further guide management of the impoundments, and to maximize the benefits for shorebirds, waterfowl and wading and marshbirds, on an annual basis. Careful monitoring and adaptive management has resulted in high quality habitat being provided for all of these species collectively among the two impoundments.
During spring and fall migrations, waterfowl require standing water for loafing, feeding and staging; submerged vegetation for feeding; and, taller cover vegetation for concealment. Nesting waterfowl require cover for concealment, brood protection and shelter from inclement weather, as well as healthy substrate that supports vegetation, invertebrates and other high protein foods for females and young. Migrating shorebirds require small puddles of invertebrate rich substrate and standing water. Marshbirds and wading birds require taller standing vegetation for cover and nesting, with near-by pools of water for foraging on amphibians, fish, small crustaceans, insects, and snakes. The Concord Impoundments provide excellent habitat for all of these groups of birds through active management.
Data collection for waterbird use usually begins in March and continues through November. Specific protocols and data collection has varied slightly each year, depending on the study, but we have conducted a minimum of weekly observational surveys from the dikes during most of the year. For various phases of the study, we have also often collected information on habitat use and behaviors of waterbirds (particulary shorebirds and waterfowl). Common waterbird species observed include: green-winged teal (Anas crecca), mallard (Anas platyrhynchos), American black duck (Anas rubripes), least sandpiper (Calidris minutilla), great egret (Ardea alba), and great blue heron (Ardea herodias). These surveys will continue in 2006 and 2007.
Secretive nesting marshbirds, such as the Virginia rail ( Rallus limicola ), require a completely different method for surveying. We have been using “callback surveys” to record nesting marshbird species since 2001, and since 2005 have actually conducted some of the survey points from canoe within the impoundments. These surveys consist of a tape of various marshbird calls, followed by periods of silence, in an attempt to elicit a vocal response from marshbirds that would otherwise go undetected. During these surveys, species observed include Virginia rail, sora (Porzana carolina), American bittern (Botarus lentiginosus), and least bittern (Ixobrychus exilis). These surveys will be conducted three times each year in 2006 and 2007 between May 1 and July 15.
Blanding’s Turtles :
The Blanding’s turtle (Emydoidea blandingii) is a State listed threatened species which uses the Concord Impoundments year round. In 2004 and 2005, Hyla Ecological Services conducted research on this species by trapping turtles in both pools and following some animals using radio telemetry. These researchers are collecting important information on habitat preferences and movement patterns in response to water level manipulations. This information helps us fine tune our management strategies to minimize impact to Blanding’s turtles during the spring, summer and fall. If funding is available, more research may be conducted in 2006 and 2007.
Invasive Species Control:
Water Chestnut:
Water chestnut (Trapa natans) is an invasive species that has plagued the Concord Impoundments since the mid to late 1950's. A draw down of the Lower Impoundment was done in 1994 and 1995, resulting in dramatic reductions of water chestnut. Unfortunately, it was not possible to continue the drawdown strategy through 1996-1998, primarily because of the condition of the drainage channels. In 1999, the lower impoundment drained completely due to an excessively hot summer, and active drawdowns since that time has helped maintain low populations of water chestnut. It’s not likely that we will ever completely eradicate water chestnut from the impoundments because of the extensive seed bed and continual flooding from the river, but annual or semiannual drawdowns have certainly reduced overall water chestnut populations.
Cattail:
In 1999, cattail (Typha latifolia) expanded in the upper impoundment due to decreased water levels, and created a nearly monotypic stand of vegetation in portions of that pool. Although native, dense stands of cattail can decrease avian diversity. In September 2000, cattail in the upper impoundment was controlled by mowing the stalks, and then flooding the pool to at least 6 inches above the cut stalks. These flooded water levels were maintained through the winter of 2000-2001 to prevent aerobic activity in the plant rhizomes. Mowing of cattail was limited to a portion of the new, green growth produced during 2000 growing season, but was discontinued before its completion as water levels naturally began to rise preventing further operations. Although mowing and flooding is considered a partial control measure (some cattail plants can survive anaerobic conditions), it has been successful at some sites. Attempts to mow additional areas of cattail in the upper impoundment in 2001 were thwarted by mechanical problems with the mower, and mowing has not been conducted since. However, slight changes in drawdown schedules each year seems to have halted the widespread germination and success of cattails in the impoundments. No mowing is planned for 2006 or 2007.
Purple Loosestrife:
Another invasive species that has benefited from water level manipulation is purple loosestrife (Lythrum salicaria). Purple loosestrife has been abundant along the dikes and in the floodplain between the impoundments and the river for many years now. However, the species spread extensively into the drained impoundments beginning in 2000. From 1996 to 2000, release of Galerucella pusilla and Galerucella calmariensis beetles was the primary method of control. A total of 28,000 beetles were released during this time at several different sites around the Concord Impoundments. From 2001-2004, beetle releases were small and only occasional, but in 2005, we released approximately 15,000 beetles. We hope to continue large releases in the next few years, especially in areas that are difficult to access for herbicide control. Beetles have been released mostly along the dike system and floodplain area. Careful records of release locations (using GPS) and a photo log has been established at release locations to monitor results. In addition, beginning in 2001, we have actively controlled purple loosestrife in the impoundments and along the dikes using Rodeo. Purple loosestrife was sprayed: in the lower impoundment in 2001, 2002, 2004, and 2005 and in the upper impoundment and along the dikes in 2004 and 2005. In 2006 and 2007, we plan to continue applying herbicide as necessary, in areas where we are not releasing beetles.
Common Carp:
Common carp (Cyprinus carpio) are an invasive species of fish in the Concord River that causes habitat destruction by uprooting all submerged aquatic vegetation. During 1999 and 2000, we installed fish screens in each water control structure to reduce the number of carp entering the impoundments. In 1999, a visitor at the Refuge removed both fish screens from the river-side water control structures allowing carp to enter both impoundments. In 2000, Refuge staff installed bolted, heavier gauge fish screens in the water control structures. However a visitor managed to pry open the fish screen at the lower impoundment, allowing carp to once again enter the impoundment. Water level manipulation has resulted in periodic fish kills from reduced water and oxygen levels in the pools. In most years since 2000, a few to a few hundred dead common carp have been removed from the impoundments and buried. However, in 2001 almost 1800 dead common carp were removed.
Dike Maintenance:
Dike maintenance is conducted on an annual basis. Woody vegetation at several locations along the dikes are manually cut and the brush is removed from the impoundment area. Removal of this vegetation along the impoundment dikes prevents potential structural failure of the dike due to roots weakening its integrity. The woody vegetation that is removed was primarily sapling-sized red maples growing on the top edge, and immediately adjacent side-slopes, of the dike. Mowing of herbaceous vegetation on the side slopes of the dike system is also conducted to maintain a wider walking path.
Recreational Impact Study:
In 2005, we initiated a 1-year research project in combination with the Biological Resources Division of the U. S. Geological Survey, to determine if jogging has an impact on wildlife at the Concord Impoundments. The primary purpose of the study is to assess the impacts of jogging around the impoundments on (1) use by waterbird species, and (2) behavior of waterbirds using these impoundments. Because we are interested in potential impacts of all public use at the impoundments, we collected data on all public use during the course of this study. The study period lasted from July 4 – December 4, and during each week, the impoundments were either closed or open to jogging. No other public use was affected. Data is still being analyzed, but 159 hours of bird response observations, and over 20 waterbird use surveys were conducted. During bird behavior observations, we recorded the behavioral response of birds within three hundred feet of the dike as joggers or other public approached. During waterbird surveys, we recorded the species of birds using the impoundments and whether they were within the three hundred foot zone adjacent to the trail system. We will analyze the data in the next several months to determine if jogging resulted in observable impacts on wildlife at the impoundments, and if further study is necessary. Cameras that were used to facilitate data collection for this study have been removed. As soon as the photo data has been analyzed, photos will be destroyed. Public use data will be used to determine the number of people visiting the impoundments as well as the number of people participating in activities such as jogging, birding, walking, or photography. The cameras were an extremely efficient way of collecting public use data, and without them, we would have had to hire several additional people to collect this data over the last 22 weeks.
For more information please contact:
Stephanie_Koch@fws.gov, 978-443-4661, x24
Eileen_McGourty@fws.gov, 978-443-4661, x37
Page updated on March 17, 2006