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Apr 07, 2016
OARS Report to the SUASCO CISMA
Project title: Mapping Water Chestnut in the Sudbury, Assabet, and Concord River System
Date: October 31, 2013
Address: OARS Inc., 23 Bradford Street, Concord, MA 01742 (www.oars3rivers.org) Executive Director: Alison Field-Juma ([email protected]) Staff Scientist: Suzanne Flint ([email protected]) Tel: 978-369-3956
Project objectives: To document the location and extent of water chestnut populations in the Sudbury, Assabet, and Concord River system to inform, support and, in the long-term, track the progress of remediation efforts. This work will be coordinated with the initial mapping of the distribution of purple loosestrife along the Sudbury River from Ashland to Concord proposed as part of the purple loosestrife control project. This project was proposed in response to the RFP titled: Mapping Water Chestnut According to the Nyanza Restoration Plan, issued by the SUASCO Cooperative Invasive Weed Management Area Steering Committee.
Project Summary: This project was designed to support the preferred restoration alternative identified in the Nyanza Restoration Plan (May 2012) under Aquatic Biological Resources: control of aquatic weeds in the Sudbury River watershed to benefit freshwater wetlands and riverine habitat. Specifically, this project mapped distribution of invasive water chestnut in the Sudbury, Assabet, and Concord River system (including Heard Pond and four ponds of the Hop Brook system) to inform, support and, in the long-term, start to track the progress of remediation efforts. Data collection for water chestnut was completed between June 3rd and August 16th, 2013, using GIS-enabled GPS units to ensure that the information could be readily shared between invasive plant control projects and could be presented as a snapshot of the whole watershed for that season. A total of 2,133 acres of river area was surveyed from the headwaters of the Assabet and Sudbury Rivers in Westborough to the Centennial Island dam on the Concord River in Lowell. In the upper sections of both the Assabet River and the Sudbury River where boating was not possible, spot surveys were conducted from road crossings where the rivers were visible; 164 acres of river area was not surveyed.
Water chestnut was found in sections of all three rivers throughout the system. The furthest upstream that water chestnut were found on the Assabet was in the impoundment upstream of the Rte 85 dam in Hudson and on the Sudbury was below the dam between Framingham Reservoirs #2 and #1. On the downstream end, water chestnut were found along the edges of the Concord River to the downstream-most end of the survey section at the Centennial Island dam in Lowell.
Methodology: Project area: The project area (overview map in Appendix) for water chestnut mapping included all boatable sections of the Sudbury, Assabet, and Concord Rivers from Westborough to Lowell, the four ponds of the Hop Brook system (Hager, Grist Mill, Carding Mill, and Stearns ponds), and Heard Pond in Wayland. Upper sections of both the Assabet River (upstream of Rte 20 in Northborough) and the Sudbury River (upstream of Cordaville Road, Ashland, including Cedar Swamp Pond) were, as anticipated, very difficult to access because of low flows in early August. Therefore, spot surveys were
conducted from road crossings where the rivers were visible for those sections. Hager Pond, where there is no public access, was not surveyed. Equipment: OARS borrowed two Magellan MobileMapper units from CISMA for data input in the field. OARS supplied one kayak, paddle, and the PFDs. Purchased for this project were: one kayak and paddle, roof rack and tie-downs for boat transport, two waterproof cameras to document conditions, additional memory cards for the MobileMapper units to accommodate loading background maps, and water-resistant binoculars. Grid system and data input: OARS staff worked with Mass Audubons Jeff Collins to adapt and extend the GPS/GIS data input system developed in 2012 comprising: (1) GIS survey grids of the project area hand -drawn based on ortho-photos and elevation maps obtained from Mass GIS (datum: GCS North American 1983) (Figure 1); (2) data input screens for the MobileMappers to accommodate both water chestnut and purple loosestrife survey data. Grids for the water chestnut data collection were drawn taking into account the likelihood of having vegetation: the near-shore grids are smaller, while grids in deeper water are larger for more efficient mapping. In the course of developing the grid system, it was determined that having separate water chestnut and purple loosestrife grids would be the most efficient way to collect information. The grid system is expandable for future projects (for example, if mapping were extended to the tributaries). Background maps (ortho-photos for example) were added to the mappers to assist orientation in the field. Field data collection: Potential access points were identified and added to a Google Map for use by the surveyors; permissions for access were obtained as needed. OARS staff coordinated with US Fish and Wildlife and groups in Lincoln, Concord, and Wayland to ensure that the sections where water chestnut harvesting was anticipated were prioritized for mapping first, so that mapping occurred before harvesting. OARS hired, trained, and supervised two summer employees to conduct the survey work. Working mainly from kayaks, the surveyors paddled assigned sections visually assessing the presence, location and density of water chestnut. With the MobileMapper GPS on, surveyors could paddle the length of aquatic grids to estimate the size of the grid. For each grid cell where water chestnut were present, plants were visually identified, the diameter of a typical rosette measured, and the number of rosettes and percent cover in the grid square estimated. Ten percent of the grids in sections that have water chestnut were re-surveyed by OARS staff for quality control. Data handling, analysis, and reporting: At the end of each week of field work, data was downloaded from the MobileMappers to the central GIS database at the OARS office to ensure that data was backed up and data in the two MobileMapper units was synced. Field data were mapped in ArcGIS and exported for use by towns and groups conducting water chestnut remediation. Data input fields included (a complete list of the GIS data fields is included with the GIS files metadata):
OAR_ID (grid identification number)
Impoundment name (common name of the impounded area, if impounded)
Figure 1: MobileMapper map screen
Area (grid area in square meters)
Date (date of field survey)
Surveyor (initials of surveyor)
Number of water chestnut rosettes (0 = none, 1=1 to 5; 2 = 5 to 10; 3 = 10 to 25; 4= 25+)
Estimated percent cover (0 = 0%; 1 = 1 to 10%; 2 = 10 to 20%; 3 = 20 to 30%... etc. )
Measured rosette diameter (0 = not recorded; 1 = < 2; 2 = 2 to 4; 4 = 4 to 6; 6 = 6 to 8; 8 = 8 to 10; 10 = 10 to 12; 12 = 12 to 14; 14 = 14+)
Notes (field notes)
Water body (Sudbury River, Assabet River, Concord River, or pond name)
Complete (0 = not assessed; 1 = assessment complete) Findings: Survey: A total of 2,133 acres of river area was surveyed from the headwaters of the Assabet and Sudbury Rivers in Westborough to the Centennial Island dam on the Concord River in Lowell. Spot surveys were conducted from road crossings in the upper sections of the Assabet River upstream of Rte 20 in Northborough, and the Sudbury River upstream of Cordaville Road, Ashland, including Cedar Swamp Pond, where boating was not possible. Hager Pond, where there is no public access, was not surveyed. A total of 164 acres of river area was not surveyed. Raw GIS data will be provided in a separate file. Maps of all river sections are included in a zipped file. Plant density and growth: Of the 2,133 acres surveyed, 76% (1,629 acres) had no water chestnut while 3.7% (78 acres) had moderate to heavy density of plant coverage. The remaining 20.3% (426 acres) had emerging or light-moderate density populations (Table 2). Timing: Water chestnut is most readily observed and mapped once the plants have reached the water surface. Within the watershed, rosettes reached the water surface between mid-May and mid-June, measuring 2-4 inches. The average rosette diameter increased 5 inches between the end of June and the middle of August (Table 1). Unusually high streamflows at the end of June re-submerged plants and halted field work for more than a week. By September 30th, observations in the Saxonville impoundment showed that some plants still had seeds, ready to drop, on the rosettes.
Figure 2: Billerica Impoundment, May 28th.
Size: A minimum of ten rosette diameters were measured each field day, with the goals tracking plant growth over the season and of standardizing percent-cover estimates over the 10 weeks of the surveys. (Theoretically, it should take twice as many 6-inch rosettes as 12-inch rosettes to completely cover the same grid area.) Because there was only a weak correlation between plant diameters measured and percent coverage estimated, water chestnut density is reported only in field-observations of percent coverage (Table 2). Table 1: Rosette Diameters
Date Surveyed Average Maximum Diameter (inches) Max Maximum Diameter (inches)
June 1 15 6 10
June 15 - 30 6 10
July 1 - 15 7 12
July 15 - 31 9 14
August 1 - 16 11 14
Table 2: Assessed plant coverage
Assessed % Coverage Acres
80 - 100% heavy density 33
60 - 80 % 45
40 - 60% moderate density 22
20 - 40% 79
1 - 20 % light density 325