Ms. Patricia Edelstein Friends of Lake Garfield c/o September 5, Dear Pat:

Transcription

1 Water Resource Services Inc. 144 Crane Hill Road Wilbraham, MA Ms. Patricia Edelstein Friends of Lake Garfield c/o September 5, 2013 Dear Pat: I am writing to follow up on the August 30 th 2013 survey of Lake Garfield and our subsequent meeting. While I would be willing to assist the Friends of Lake Garfield in any aspect of its management, I do not think you need to spend substantially more funds on consulting services with regard to the current rooted plant issues in the lake. The primary issue is seed producing species of Potamogeton (pondweed), particularly P. amplifolius (bigleaf pondweed) and P. richardsonii (Richardson s or clasping leaf pondweed). This has been a banner year for those species, and the problem may not be consistent among years. However, when plant density by these species is unacceptably high, harvesting is usually the best approach. This could include large mechanical harvesters with collection capacity that can be contracted through several firms, or could involve manual harvesting by trained divers, or could be as simple as manual removal of the seed heads (always at the surface for these species) from the water surface to limit production the following year. Because not all seeds germinate in the year following formation, it may take 3 to 5 years to see reduced densities, but this can be an economical approach to the problem if not too widespread in the lake. As background, I offer the following observations from my visit: Eurasian watermilfoil (Myriophyllum spicatum) remains a threat, but is not found in patches except for a few areas. While the presence of this species calls for vigilance and ongoing management action, its presence as scattered growths does not represent a serious impairment of recreation or habitat. The drawdown appears to be keeping milfoil from becoming dominant and should be continued as planned. There are three primary downsides to drawdown: the potential for late refill after a deeper drawdown if a dry winterspring period ensues, stimulation of populations of seed-producing annual plants (exposure of seeds during drawdown encourages germination), and decomposition of exposed sediment that releases nutrients that may support algal growths. Refill issues are best addressed by not drawing down by more than what can be replaced in a month or two, but there is still risk in any drawdown, as the weather is not easily or reliably predictable. The benefits of drawdown outweigh the drawbacks in most cases, and the practice at Lake Garfield has so far not caused refill issues of any major proportion. Page 1

2 Water Resource Services Inc. 144 Crane Hill Road Wilbraham, MA Some desirable seed producing species can become dominant, but several of the pondweeds can achieve nuisance densities. Bigleaf and clasping leaf pondweed are two such species. Both can survive the winter as rootstock, but denser growths are usually a function of seed germination. As seed distribution is not necessarily uniform or consistent among years, populations can shift in distribution and abundance among years; a problem one year does not signal a problem in the same are the next year for these species. Localized harvesting is probably the simplest way to deal with these species. Page 2

3 Algal mats can form at the sediment-water interface, trap their own photosynthetic gases, and float to the surface. Some stick to aquatic plants, and some will blow to shore with the wind, potentially creating unpleasant conditions in those areas. The release of nutrients diminishes over successive drawdowns, so this is not an ongoing problem in most cases. Simply raking up the mats is the simplest way to address them where necessary. If the problem persists over several years, an application of aluminum will bind up the phosphorus that is primarily responsible for these mats. Three other pondweeds were common and reached the water surface, but not really at nuisance densities: P. zosteriformis (flatstem pondweed), P. praelongus (boat tipped pondweed), and what I think is P. foliosus (leafy pondweed). If bigleaf and Richardson s pondweeds were not so abundant, these might be noticed, but do not require special attention. One additional pondweed forms a dense carpet in water >6 ft deep and down to about 10 ft, that being P. robbinsii (Robbins pondweed). This is a highly desirable species, possibly the most valuable to have in any Berkshire lake, as it forms a dense carpet that minimizes colonization by milfoil. It reproduces mainly by root runner, rarely producing seeds, so it grows fairly slowly and tends not to colonize distant areas too easily. It is somewhat tolerant of drawdown, but as it is not found in shallower waters of Lake Garfield, it may be restricted by the drawdown. It is outcompeted by milfoil once milfoil becomes established, but milfoil fragments find it difficult to reach the sediment and set roots, as Robbins pondweed maintains its vegetative carpet throughout the year. The expansive carpets of Robbins pondweed are valuable, and not actions that might harm existing plants should be taken. Spot treatments with contact herbicides and benthic barriers are examples of often useful techniques that should be avoided in areas with Robbins pondweed. As it is not common in shallower water, this should not impede residents who wish to use benthic barriers in swimming areas or around docks. Water celery (Valisneria americana) also forms dense carpets in water 6 to 10 ft deep, but not as dense as Robbins pondweed and with less ability to deter invasions. This plant sends up curly stems with small white flowers as reproductive parts, and can sometimes be a nuisance in swimming areas or for small motors. Water celery does form some small, dense patches in Lake Garfield, but does not require any special attention from my perspective. Water crowfoot, or water buttercup (Ranunculus tricophyllum) was found in some shallow areas and as part of floating rafts of uprooted aquatic plants. I do not know for sure what caused the formation of those rafts, but they contained a wide variety of species and may be the result of motorboat activity in shallow water. Motorboats should stay out of areas <10 ft deep whenever possible, and Page 3

4 should not go through plant stands that reach the surface to avoid cutting and spreading those plants. Submerged arrowhead (Sagittaria graminea) occurs as scattered growths in shallow (<6 ft) water and represents no threat to recreation or habitat. Common naiad (Najas flexilis) occurs as scattered growths in Lake Garfield. This species is an annual with copious seed production, but does not appear dominant anywhere in the lake. It can float free of the sediment later in the summer and produces nuisance mats, but no such conditions have been reported for this lake and no action appear necessary. White water lily (Nymphaea odorata) was found in small patches, most of which presented no threat to recreation and comprised valuable habitat, except in front of a few residences. These are best addressed by localized harvesting. Cattail (Typha latifolia) was present in relatively small but dense shoreline stands. Most presented no real threat to recreation or habitat, but where access is compromised, these can be cut or pulled up with a rake. Common reed (Phragmites communis) is an invasive species found along the shore in only a few locations, but is undesirable as habitat and can expand in a manner that restricts access and views. It can grow in water up to about 3 ft deep, so it could also interfere with swimming and non-motorized boating (e.g., canoes, kayaks). This is best controlled by cutting at this time of year followed by localized application of glyphosate or imazopyr based herbicides. These herbicides translocate into the roots and kill the entire plant. These herbicides can affect water lilies or other floating leaved plants, but are not effective on submergent species and do not represent a threat to overall lake ecology when used on a localized basis. Based on what I observed last week at Lake Garfield, I would continue the drawdown program as it has been conducted, support localized use of benthic barriers in shallow water as approved by the association, and look to establish a localized harvesting program for nuisance growths of any plant species. For the seed producing pondweeds, simply cutting off seed heads for disposal off the lake may be sufficient, but more aggressive harvesting of the whole plant is certainly possible. Seed head removal could be conducted by volunteers, or makes a great summer job for several high school or college students. A hand harvesting program for milfoil and the more abundant pondweeds would be advantageous and highly desirable, but would require a higher level of commitment by properly trained divers. Programs at several lakes that cover 60 to 100 ac range in cost from $10,000 to $15,000 per year. While Lake Garfield is larger, much of it is too deep for plant growth (any area Page 4

5 >15 ft deep), so a program would not have to address all 380 acres. An effective Lake Garfield program might have to cover something approaching 200 acres and would therefore be expected to cost on the order of $25,000 per year. However, the small bowl is on the order of 60 ac and could be addressed independently of the rest of the lake if so desired. I would recommend avoiding broad spectrum herbicide use in this case or installation of benthic barriers in any area with Robbins pondweed (mostly deeper than 6 ft, so not likely to interfere with most typical uses). Conditions are too favorable over much of the littoral zone of this lake for fish and recreational pursuits to risk creating colonization zones for invasive species. While the drawdown is not a perfect plant management tool, it appears to be doing an acceptable job with regard to milfoil management and the few negative aspects of that program can be managed by other means. If I can assist further with planning or implementation of plant control methods, do not hesitate to call on me. I will be at the LAPA West seminar this weekend, but have to leave immediately upon its conclusion, so will have limited time for discussions then. Thank you for your hospitality during my recent visit and pass on my thanks to Hy and Allen, who were also gracious hosts and great companions on the water. Sincerely yours, Kenneth J. Wagner, Ph.D., CLM Water Resources Manager, WRS INC. Page 5