Report on a 2020 survey for State-listed plant species at Quonnipaug Lake, Guilford, Connecticut Christopher R. Mangels Botanical - Ecological Consultant New Fairfield, Connecticut Submitted to the Town of Guilford 27 December 2020 Survey background, objectives and methods This report details a brief botanical survey of Quonnipaug Lake (henceforth QL) conducted independently by the author in late August of 2020. The survey was commenced at the request of Kevin Magee, Environmental Planner for Town of Guilford (henceforth TOG), by whom I was contacted to provide outside expertise pertaining to rare species and plant surveys. Need for this survey arose in the context of review by Natural Diversity Database of CT-DEEP (hereafter NDDB) for continued authorization of aquatic herbicide application (NDDB Determination No.: 202000699, dated May 29, 2020). The survey’s primary objective was to investigate the status of two plant species, Capillary pondweed and Water-marigold, both previously known to occur at QL and currently listed as Threatened and Special Concern category species, respectively, by State of Connecticut (CT DEEP, 2015). Assuming one or both species were found, the survey further entailed fully documenting the population(s), including mapping and evaluation of size and viability. Three unaccompanied visits, each lasting 3-5 hours (total field time of 10.5 hours), were made on 26 August, 28 August and 30 August 2020. The aim on the first date was general site reconnaissance, e.g., checking access points and probing near-shore portions of the lake accessible by land. On the two later dates the survey followed a meandering route through the outer littoral zone, a purely visualized area extending roughly 10 meters inward from water’s edge, utilizing a 10-foot single-person kayak with very low draft that allowed access into minimal depths, as necessitated by shallow, mucky conditions at the southern end. A short rake (~1-meter long) was used for retrieving submersed plants. In a few places where it was feasible to disembark, closer scrutiny was achieved by wading. In practical terms, however, the kayak’s small size and instability made it unsuited for use with a longer rake and for onboard examination of more than a few specimens, thereby precluding more systematic collection of plant material, as is conventional practice in aquatic vegetation studies. Along with plants, photos and GPS points were also taken for identification purposes as well as for future reference. Due to initial uncertainty about how much time might be required to inspect the entire lake, the survey area was divided into northern and southern sectors, one of which was covered on each of the latter two dates. On both occasions the survey originated from the western side (town beach). In attempt to contain time and cost a small section near the middle of the eastern shoreline, within which neither species had been reported, was excluded per project proposal (see Fig. 1.). Along with site visits, the survey demanded considerable pre- and post-fieldwork review of maps and reports, aerial imagery and relevant scientific literature. Site description QL is situated in the northeastern corner of the town of Guilford (USGS Durham Quadrangle), which lies at the convergence of the state’s “South Central Lowlands” and “Southeast Hills” sub-ecoregions (Dowan and Craig, 1976). The surrounding area has an evident history of mixed agricultural and lakeshore recreational land uses, and at the present time QL is characterizable as a moderately dense residential lakeshore settlement. Major landowners and features include a state boat launch, town beach, and Choate Rosemary Hall club house on the western side, opposed by numerous terraced yards, small docks, and some bulk headed frontage along the eastern side. The southern end is largely undeveloped, with a near continuously vegetated shoreline and coves buffered by natural areas (formal or informal) owned by TOG and Guilford Land Conservation Trust. The lake main body covers an area of nearly 99 acres, with a maximum depth exceeding 42 feet and surface elevation of approximately 210 feet a.s.l. (CT DEEP, 2011). There is uncertainty surrounding ownership of open water portions, as is shown by the lack of attribution on town-level GIS, although jurisdiction of the lake bed is assumed by TOG to belong to the State of Connecticut (K. Magee, pers. com.). Fuller knowledge of title and the settlement history of the lake, while relevant and perhaps a matter of record, would have required research beyond the scope of this report. Judging from a combination of aerial imagery, maps and descriptions in earlier reports and first-hand observation, the lake and its margins encompass an array of vegetation or habitat types, from open water with sparse to dense aquatic beds to fringing forest, and from highly modified to comparatively natural. The transition between these types is in places abrupt, such as along bedrock exposures on the eastern side, while at the southern end, where a small dam and road culvert create impoundment, far more gradual. Much of the vegetation corresponds to lacustrine and palustrine communities described by Metzler and Tiner (1992). Focal species descriptions Both focal species are strictly aquatic, naturally submersed, fine-leaved perennial or vegetative annual herbs (see below). While their relative contributions to the diverse macrophyte assemblage that exemplifies the native aquatic flora of QL might be minor, in terms of area—though this has never actually been quantified—generally speaking, such macrophyte assemblages carry high ecological value (Hotchkiss, 1964; Sculthorpe, 1967). Depending on individual size and phenological stage, plants of both species can be difficult to differentiate from many outwardly similar co-occurring species, particularly underwater. Altogether, these points underscore both the potential challenges and the importance of surveying for them. Capillary pondweed (Potamogeton gemmiparus), also known as Budding pondweed, is a rare species endemic to New England and neighboring Quebec. Within Connecticut there are six known extant populations currently, all from the coastal and eastern sub-regions (CT DEEP, 2015; CT NDDB, unpublished data). Across New England as a whole the species has been reported from just 30 sites in three states, of which as many as 20 may be historical only (Native Plant Trust, unpublished data; NHESP, 2015). Owing to this narrow geographic range and presumably other factors such as the number of historical-only sites, Capillary pondweed is recognized as a species of conservation concern at regional and national levels, with a rank of R3, defined as “Vulnerable”, meaning at moderate risk of extinction or decline (NatureServe, 2017). However, it has received less research attention than other regional rarities such as Ogden’s pondweed and Straight-leaved pondweed, both of which were subjects of conservation plans (Hellquist & Pike, 2004; Hellquist & Mertinooke-Jongkind, 2003). Consequently, many aspects of its ecology have not been fully elucidated. What is known its reproductive modus and life history has been summarized by Kaplan & Stepanek (2003) and Les (2020): Plants lack rhizomes but reproduce vegetatively by means of reduced, axillary, bud-like shoots (turions), which are formed near the end of one growing season and begin growth early (May) the following year. These are thought to be the main means of reproduction, with flowering occurring seldomly, especially in deep shaded or turbulent water, and seed recruitment being rare or non-existent. The importance of turions toward annual recruitment has possibly been underestimated due to the similarity of germinated turions to seedlings. Water marigold (Bidens beckii) is an odd aquatic member of the large, mostly terrestrial Aster family, as evidenced by heads with yellow ray flowers, which are born singly on aerial flowering stems. This species is heterophyllous, i.e., possessing two leaf types, those underwater being larger and finely dissected, with smaller, entire and merely toothed leaves on aerial flowering stems. Its growth habit varies from partly emergent in shallow depths to fully submergent in deeper water, the latter reportedly being more typical. The insect pollinated flowers and fruits are produced in late summer (July-Sept), sometimes in the first year (Strother & Weedon, 2006). Seed set is typically low, and in parts of the range only a small percentage of populations reportedly flower with regularity (Les, 2018; Scribailo & Alix, 2002). Although its geographic range is wide, extending across Canada and southward to MD and MO, it is considered rare in many of the states where it occurs (NatureServe, 2020; USDA, 2020). Taxonomic and identification issues The uniqueness of Water-marigold as a species is shown by its former segregation into the monotypic genus Megalodonta, still used in some references. When flowers are present the plants are virtually unmistakable, although in purely vegetative condition it can surely be overlooked, especially in mixed growths of other fine- leaved plants such as Cabomba and bladderworts (Utricularia species). Similarly, Capillary pondweed can be cryptic, but adding to this is considerable haziness surrounding its classification, due to its nesting within a species complex (Sect. Pusilli) regarded as the most taxonomically difficult in the genus and the Pondweed family (Haynes, 1974; Kaplan & Stepanek, 2003; Les et al., 2009). Over the past several