Middle and Back Rivers are two adjacent Chesapeake Bay estuaries located near Baltimore, Maryland. Preliminary observations suggested that Middle River was typical of most local estuaries, while Back River exhibited several atypical characteristics. This study was undertaken to compare various ecological parameters in an attempt to document and explain any differences found in the two estuaries.
Sampling stations were established at three locations in each estuary while a single station was established in Chesapeake Bay. Sampling trips were conducted at approximately weekly intervals between March and September, 1964. Observations were made on water temperature, salinity, hydrogen ion concentration, methyl orange and phenolphthalein alkalinity, free carbon dioxide, and dissolved oxygen. Net plankton samples were collected and returned to the laboratory for identification and counting in a Sedgewick-Rafter chamber. Concentrations of chlorophyll a, b and c as well as astacin and nonastacin type pigments in each estuary were measured.
Mean water temperature, dissolved oxygen concentration, pH, and methyl orange and phenolphthalein alkalinity were significantly higher, and mean salinity and free carbon dioxide were significantly lower in Back River. Back River exhibited net plankton counts significantly higher than those for Middle River. Zooplankton was less abundant than phytoplankton in Back River, while an opposite condition existed in Middle River. No differences were observed in the genera of plankton found in the two estuaries. Total pigment as well as chloroyhyll a, b and nonastacin type pigment concentration measurements for Back River were significantly higher than similar measurements for Middle River. Phytoplankton appeared to be the dominant ecological factor in Back River and accounted for the high dissolved oxygen concentrations, high pH, high phenolphthalein alkalinity, and low free carbon dioxide values recorded in that estuary.