Geology topics

Nancy B. Rybicki

Publications and source records attributed to Nancy B. Rybicki.

23 records · Page 2Linked to original sources

USGS1999

Vegetative resistance to flow in south Florida: Summary of vegetation sampling at sites NESRS3 and P33, Shark River Slough, November, 1996

The U.S. Geological Survey is one of many agencies participating in the effort to restore the South Florida Everglades. We are sampling and characterizing the vegetation at selected sites in the Everglades as part of a study to quantify vegetative flow resistance. The objectives of the vegetation sampling are (1) to provide detailed information on species composition, vegetation characteristics, vegetation structure, and biomass for quantification of vegetative resistance to flow, and (2) to use this information to classify the vegetation and to improve existing vegetation maps for use with numerical models of surface-water flow. Vegetation was sampled at two sites in the Shark River Slough in November, 1996. The data collected and presented here include those for live and dead standing sawgrass, other dead material, periphyton biomass, vegetation characteristics and structure, and leaf area index.

Florida↗

USGS1999

Biomass and vegetative characteristics of sawgrass grown in a tilting flume as part of a study of vegetative resistance to flow

The U.S. Geological Survey is studying vegetative resistance to flow in the south Florida Everglades as part of a multidisciplinary effort to restore the South Florida Ecosystem. In order to test the flow resistance of sawgrass, one of the dominant species in the Everglades, uniform, dense stands of sawgrass were grown in a tilting flume at Stennis Space Center, Mississippi. Depth of water in the flume was controlled by adding or removing metal plates at the downstream end of the flume. A series of experiments were conducted at various flow depths, and the velocity, flow depth, and water-surface slope were measured. During each set of experiments, the sawgrass was sampled in layers from the sediment water interface for vegetative characteristics, biomass, and leaf area index. The results of the vegetation sampling are summarized in a series of tables.

Open-File Report↗

USGS1991

Tidal mass exchange between a submersed aquatic vegetation bed and the main channel of the Potomac River

Tidal mass exchange between a submersed aquatic vegetation (SAV) bed and the main channel of the Potomac River was investigated. Water levels were recorded at 5 minute intervals from August (when plants were present) through December (when plants were absent). Velocities were measured during individual tidal cycles both in the presence and absence of plants. Flow patterns were found to be altered significantly when plants were present. SAV impeded flow onto the shoal causing a water level phase lag between the bed and the channel, a reduction in flow speed and a change in flow direction. The phase lag was enhanced when the low frequency (subtidal) water level in the channel was below normal. The phase lag was further enhanced during spring tides. Ebb flow in the presence of plants was perpendicular to the edge of the SAV bed in the direction of the pressure gradient established by the lagging water level. Flood flow did not follow such a predictable pattern despite the strongest pressure gradients occurring during flood tides. In the absence of plants the flow speed increased by nearly an order of magnitude and the water-level phase lag disappeared.

Conference Paper↗

USGS1986

Effect of sediment depth and sediment type on the survival of Vallisneria americana Michx grown from tubers

Sedimentation resulting from storms may have been one of the reasons for the elimination of submersed aquatic vegetation from the tidal Potomac River in the late 1930's. Laboratory studies were conducted to investigate the effects of different depths of overlying sediment and composition of sediment on the survival of Vallisneria americana Michx (wildcelery) grown from tubers. Survival of plants grown from tubers decreased significantly with increasing sediment depth. Survival of tubers declined from 90% or more when buried in 10 cm to no survival in greater than 25 cm of sediment. Survival with depth in sand was significantly lower than in silty clay. Field investigation determined that the majority of tubers in Vallisneria beds are distributed between 10 and 20 cm in depth in silty clay and between 5 and 15 cm in depth in sand. Based on the field distribution of tubers and on the percent survival of plants growing from tubers at each depth in the laboratory experiment, we suggest that the deposition of 10 cm or more of sediment by severe storms such as occurred in the 1930s could contribute to the loss of vegetation in the tidal Potomac River.

Aquatic Botany↗

USGS1985

The effects of grazers and light penetration on the survival of transplants of Vallisneria americana Michs in the tidal Potomac River, Maryland

Poor light penetration and grazing are among the factors potentially responsible for the lack of submersed aquatic macrophytes in the tidal Potomac River. Between 1980 and 1983, plugs, springs and tubers of Vallisneria americana Michx were transplanted from the oligohaline Potomac Estuary to six sites in the freshwater tidal Potomac River. Transplants made in 1980 and 1981 were generally successful only when protected by full exclosures which prevented grazing. Grazing resulted in the removal of whole plants or clipping off of plant leaves in unprotected plots. Plants protected in the first year were permanently established, despite the occurrence of grazing in subsequent years, at Elodea Cove and Rosier Bluff, where light penetration was high (average 1% light level was 1.6–1.7 m). Plants were not permanent;y established at Goose Island, where light penetration was lower (average 1% light level was 1.4 m) and grazing occurred, or Neabsco Bay where light penetration was very low (average 1% light level was 1.0 m) and grazing may not have occurred. In 1983, Secchi depth transparencies in the upper tidal river were improved significantly compared to 1978–1981. Both protected and unprotected transplants thrived in 1983.

Maryland↗