Survival of a submerged aquatic weed (Egeria densa) during lake drawdown within mounds of stranded vegetation

Abstract

Dugdale TM, Clements D, Hunt TD, Butler KL. 2012. Survival of a submerged aquatic weed (Egeria densa) during lake drawdown within mounds of stranded vegetation. Lake Reserv Manage. 28:153-157. Lake drawdown, or water withdrawal, is often used to control invasive submerged macrophytes; however, regrowth of the target species often occurs rapidly. A mechanism proposed to explain such unsatisfactory results is that as water recedes and submerged aquatic weeds become exposed to the air, mounds of stranded vegetation form on the dewatered lakebed. These mounds may insulate underlying weeds, creating an environment protected from desiccation and frost. This study tests this mechanism by comparing the viability of the submerged aquatic weed Egeria densa Planch. from within mounds to the viability on the surface of these mounds during a winter drawdown of Lake Mulwala, Australia. After 22 days of exposure, no stems on the surface of weed mounds were viable, but 22% of stems on the bottom of mounds and 76% of crowns under the mounds were viable. Further, after 34 days, 12% of stems and 32% of crowns collected from the bottom of the weed mounds were still viable. We conclude that, in areas of lakes that are exposed during drawdowns, regeneration from in situ stem fragments and crowns following refilling are an important potential source of reestablishment for E. densa. © Copyright by the North American Lake Management Society 2012.