Seasonal occurrence and distribution of submerged aquatic macrophytes in the tidal Potomac River

Abstract

A systematic survey was conducted in the Tidal Potomac River in 1978 to determine the presence, abundance, and phenology of submersed aquatic macrophytes. The survey covered 81.5 km of main river and 59.3 km of tributary on the Maryland shore. Four regions were selected for the study: (1) Piscataway - Mattawoman Creek region (fresh-tidal river), (2) Nanjemoy Creek-Port Tobacco River region (transition zone), (3) Wicomico River region (estuary), and (4) St. Marys River region (estuary). The Wicomico River region was subdivided into fresh tidal river, transition zone and estuary for purposes of date analysis. Data were gathered by sampling each 15 m along transects running perpendicular to shore for a maximum distance of 300 m. Modified oyster tongs were used to sample both plants and benthic soils from an outboard boat. A total of 131 transects were established with a total of approximately 3500 grabs being taken per sampling period. Sampling was initiated in the spring and repeated in the summer and fall. Highest plant diversity and productivity were measured in the transition zone extending from Lower Cedar Point to beyond Maryland Point, a distance of approximately 30 km, and in the transition zone of the Wicomico River above Chaptico Bay. Fresh tidal areas were devoid of plants. The estuary had a sparse growth of horned pondweed (Zannichellia palustris) and widgeon grass (Ruppia maritima) in the spring: horned pondweed was not found in summer or fall. Redhead grass (Potomageton perfoliatus) was the most abundant pondweed; it matured in early summer and died back in mid-to-late summer. Wild celery (Vallisneria americana) and widgeon grass matured in early-to-late fall and were the most abundant plants during that period. Data analysis is being finalized and a publication is in preparation. This research will be continued over the next several seasons as part of the long term USGS effort on the Potomac