Special to Winchendon Courier, May 10, 2006
By Ivan Ussach
How do the types of aquatic plants found in artificial ponds differ from those found at natural ponds? That was one of several research questions addressed by aquatic ecologist Matt Hickler and limnologist Stuart Ludlum as part of a recently completed study on the biodiversity of aquatic plants in lakes and ponds of the Worcester-Monadnock Plateau Ecoregion.
Dr. Hickler presented some of the findings of the study on Tuesday, April 25th at the monthly meeting of the Millers River Watershed Council, held at the Millers River Environmental Center in Athol. The study examined 25 of the 71 lakes and ponds in the ecoregion at least five hectares (about 12 acres) in size. The Worcester-Monadnock Plateau Ecoregion is a 440 square mile area in North-Central Massachusetts (the ecoregion also extends into Southern New Hampshire) characterized by having similar geology, soils, climate and vegetation. It includes all or part of 24 Massachusetts towns, and most of the Millers Watershed. About half of the towns of Athol and Orange are within its boundaries.
Tully Lake in Athol and Royalston had the richest diversity of aquatic plants among the 25 study sites, with 34 species found. Whitney Pond in Winchendon was second with 31 species. Packard Pond, also in Orange, had only six species and tied for the lowest species diversity. A total of 62 different species were found throughout the selected water bodies. However, most species are uncommon, with only one (watershield) found at all 25 ponds, and 14 of the species found at only a single pond.
The study sites were very thoroughly combed to find all the existing aquatic plants. A total of 14 occurrences of five different state-listed rare species were documented. Ten ponds had at least one rare species. The State-Threatened algae-like pondweed was found at five ponds. Floating bur-reed was also found at five sites.
In what some may find a surprising result, non-native “invasive” species were found at only three of the 25 ponds. In comparison, a recent study by Robert Bertin in Worcester County detected invasive aquatic plants in over half of the 45 lakes and ponds studied. The Worcester-Monadnock Plateau Ecoregion study identified variable milfoil in two lakes, and fanwort on one. Both plants are native to the southeastern United States and are introduced here. The fanwort is “spreading like wildfire in New England,” Hickler said.
Most of the ponds studied were man-made. The fact that about 80 percent of the lakes and ponds in the ecoregion are artificial is a legacy of the extensive damming of local streams in the 19th century to power mills. Others were built as water supply reservoirs and flood control projects. Many of the dams were built or restored in the 1930s by the Civilian Conservation Corps, which worked on over 300,0000 dams throughout the country. The answer to the question posed above is that the research study showed no statistically significant difference in the preference of rare species for either natural or artificial ponds. There was also no difference in the total number of species found in artificial and natural ponds. The size of the pond also was not a factor.
Given the abundance of artificially-created lakes and ponds, and their attractiveness to aquatic plants, Hickler suggested that artificial ponds need to be recognized for their biological richness. This comes at a time when most of these dams are no longer used for the purposes for which they were created, and concerns over liability from dam failure have led dam owners –mainly private citizens– and state officials to work on making dam removal easier and less costly. While dam removal would benefit some species, like anadramous fish that migrate between fresh and ocean water, it might cause unanticipated negative impacts on the biodiversity of aquatic plants. Hickler cautioned against drawing any conclusions prematurely, and suggested that studies of invertebrates and other aquatic animal communities found in lakes and ponds would be scientifically valuable, as well as help clarify the conservation impacts of dam removal. Such studies would be aided by not having to repeat all the landscape and physical chemistry analysis just completed.
The final report on the study will be released to environmental agencies and conservation groups within the week, Hickler said. It will also be posted on the website of the Millers River Environmental Center: millersriver.net.