Distribution and abundance of submersed aquatic vegetation in the tidal Potomac River and Estuary, Maryland and Virginia, May 1978 to November 1981

Abstract

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