Introduction 1 Background 2 Historical distribution 2 Study site 6 Methods 6 Submersed aquatic vegetation survey 6 Factors affecting distribution and abundance 8 Salinity, specific conductance, temperature and pH 8 Water depth 8 Substrate 8 Light penetration and water transparency 8 Epiphytes 8 Heavy metals 10 Field studies 10 Laboratory studies 10 Storm damage 10 Nutrients 10 Submersed aquatic vegetation transplants 10 Results 12 Submersed aquatic vegetation survey 12 Distribution 12 Factors affecting distribution and abundance 20 Depth and distance from shore 20 Substrate 20 Salinity, specific conductivity, temperature and pH 20 Light penetration and water transparency 22 Storm damage 22 Heavy metals 24 Epiphytes 24 Transplants 24 Discussion 33 Factors affecting distribution and abundance 33 Storm damage 33 Light and nutrient enrichment 36 Grazing 41 Substrate 41 Environmental Implications 41 Summary and conclusions 42 References cited 44 FIGURES 1. Map showing upper part of tidal Potomac River at low water and distribution of aquatic vegetation in 1916. 4 2. Map showing the tidal Potomac River, transition zone, and Estuary. 4 3. Map showing distribution and number of species of submersed aquatic vegetation in the tidal Potomac River and Estuary during 1978-81. 5 4. Map showing intensive data collection sites and other naturally-vegetated sites in the tidal Potomac River. 9 Contents 12. Concentrations of lead, manganese and zinc in tidal Potomac River and transition zone, 1979-81. 26 13. Relative growth of Vallisneria americana exposed to indicated concentrations of lead, manganese and zinc, 1980. 26 14. Epiphyte mean dry weight, chlorophyll 0 and percent transmission of light through epiphyte-colonized artificial substrates in the tidal Potomac River and Estuary, 1981. 28 15. Mean lengths of CeratophyUum demersuin in suspended-cage experiments in the tidal
As part of a comprehensive interdisciplinary study of the tidal Potomac River and Estuary, the U.S. Geological Survey studied the distribution and abundance of submersed aquatic vegetation from 1978 to 1981. Sites were chosen throughout the tidal river and estuary. The plant species were identified; distribution and abundance of submersed aquatic vegetation were determined at the sites; and volumes, biomass-volume equivalents, and representative stem lengths were measured. Substrate types were identified, and particle size distribution, bottom nutrients, organic carbon, and heavy metals were measured at numerous sites. Water quality parameters that were measured included temperature, conductivity, salinity, secchi depth, photosynthetically active radiation, pH, chlorophyll a., nutrient concentrations, and epiphyte biomass. Experiments were performed in the field and in the laboratory to evaluate factors that would potentially affect distribution and abundance of aquatic macrophytes. For example, plants were suspended in cages and planted in exclosures, and transplant success was determined.
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