Hydrography of the Penobscot River (Maine) Estuary

Abstract

A hydrographic survey of the Penobscot River (Maine) estuary, made during 1963–65, showed that the lower estuary is subject to a high degree of stratification, extensive mixing occurs within intermediate strata in the middle reaches of the estuary, and near-uniform conditions prevail at the head of the estuary. This pattern generally prevails throughout the year, but it is subject to seasonal and tidal variations.Cold weather and high spring river discharge establish uniformly cold water temperatures, high dissolved oxygen, and low salinity conditions in the upper half of the study area. A pycnocline is readily identifiable and high dissolved oxygen prevails throughout the lower half of the estuary.Summer temperatures and low freshwater inflow accompanied by high turbidity and extensive pollution lead to partial stagnation and anoxic conditions in the upper estuary. Conditions improve slightly in the middle reaches and are favorable in the lower estuary, where marked vertical stratification exists for temperature, salinity, and density.Qualitative bottom samples indicated an absence of benthos in the upper estuary, limited numbers of species in the middle reaches, and an enriched fauna in the lower estuary. These findings are discussed with reference to bottom types and prevailing hydrographic data.