Geology topics

D.G. McFarland

Publications and source records attributed to D.G. McFarland.

3 recordsLinked to original sources

USGS2001

Investigations of the availability and survival of submersed aquatic vegetation propagules in the tidal Potomac River

The establishment of submersed aquatic vegetation (SAV) at unvegetated sites in the freshwater tidal Potomac River was limited primarily by factors other than propagule availability. For two years, traps were used to quantify the amount of plant material reaching three unvegetated sites over the growing season. The calculated flux values provided a gross estimate of the flux of propagules that could potentially survive if other site factors were suitable. The mean flux of Hydrilla verticillata and all other species (≥0.01 gdw m −2 d −1 ) appeared sufficient to favor the establishment of vegetation, particularly considering the high viability (70–100%) of whole plants and fragments under controlled conditions. However, median water clarity values (i.e., for light attenuation, Secchi depth, total suspended solids, and chlorophyll a ) were below SAV restoration goals at all unvegetated sites. Additionally, sediments from unvegetated sites showed a potential for nitrogen limitation of the growth of H. verticillata . Our findings support the hypothesis that in the tidal Potomac River, water clarity and nutrient (especially nitrogen) levels in sediment are key to plant community establishment.

Virginia↗

USGS1998

The aquatic macrophyte seed bank in Lake Onalaska, Wisconsin

Submersed aquatic vegetation, dominated by Vallisneria americana Michx., declined dramatically in Lake Onalaska (Navigation Pool 7, on the Upper Mississippi River) following drought conditions in the late 1980s. Coinciding with the decline were marked increases in the abundance of phyllum spicatum L., particularly in areas vacated by A. americana. Recent evidence indicates that much of the lake has remained unvegetated, but that since 1994, beds of V. americana have made a partial recovery. While the production of vegetative propagules may largely account for increases in populations of both species, the extent to which seed production may contribute to their expansion in the lake is unknown. To assess the germination potential and distribution of the aquatic macrophyte seed bank in Lake Onalaska, sediment cores (5 cm deep) were collected from 74 sampling sites in July 1996. Seedling emergence from sediments was observed in an environmental growth chamber operated at 25 C and a 14-hr photoperiod over a period of eight weeks. Fifteen species of aquatic macrophytes germinated in sediments from 55 sites. V. americana seedlings emerged from sediments from 36 sites throughout the lake, but were most prevalent in sediments collected within or downstream (within 250 m) of established V. americana beds. Seedlings of M. spicatum emerged from only two collected sediments that had supported this species in protected areas. These findings suggest that seed production may play a greater role in the dispersal of V. americana than M. spicatum, and further emphasize basic differences in their survival strategies, particularly in flowing water systems.

Journal of Aquatic Plant Management↗

USGS1998

The aquatic macrophyte seed bank in Lake Onalaska, Wisconsin

Submersed aquatic vegetation, dominated by Vallisneria americana Michx., declined dramatically in Lake Onalaska (Navigation Pool 7, on the Upper Mississippi River) following drought conditions in the late 1980s. Coinciding with the decline were marked increases in the abundance of Myriophyllum spicatum L., particularly in areas vacated by V. americana. Recent evidence indicates that much of the lake has remained unvegetated, but that since 1994, beds of V. americana have made a partial recovery. While the production of vegetative propagules may largely account for increases in populations of both species, the extent to which seed production may contribute to their expansion in the lake is unknown. To assess the germination potential and distribution of the aquatic macrophyte seed bank in Lake Onalaska, sediment cores (5 cm deep) were collected from 74 sampling sites injury 1996. Seedling emergence from sediments was observed in an environmental growth chamber operated at 25 C and a 14-hr photoperiod over a period of eight weeks. Fifteen species of aquatic macrophytes germinated in sediments from 55 sites. V. americana seedlings emerged from sediments from 36 sites throughout the lake, but were most prevalent in sediments collected within or downstream (within 250 m) of established V. americana beds. Seedlings of M. spicatum emerged from only two collected sediments that had supported this species in protected areas. These findings suggest that seed production may play a greater role in the dispersal of V. americana than M. spicatum, and further emphasize basic differences in their survival strategies, particularly in flowing water systems.

Journal of Aquatic Plant Management↗