European settlement of New England initiated a novel disturbance regime that was prolonged, intensifying through time, and spatially widespread. By the mid-20th century, human commercial and industrial activities had brought about the ecological collapse of several major rivers. Since the mid-1970s, river ecosystems have recovered substantially in response to primary treatment of industrial and municipal wastewaters mandated by the Clean Water Act of 1972. Here we reconstruct an environmental history of a river-estuary complex in mid-coast Maine to examine ecosystem degradation and collapse during three centuries of intensified human disturbance followed by ecosystem recovery over the three decades since the Clean Water Act and the ban on the general use of DDT pesticide in 1972.
Merrymeeting Bay is a large, freshwater tidal ecosystem formed by the confluence of six rivers, 30 km inland from Maine's Atlantic coast. It was once a major stopover for migrating waterfowl and provided vital spawning and nursery habitat for anadromous fish. However, human activities—beginning with overfishing, land clearance, and dam building in the 18th century and culminating in severe industrial and municipal pollution in the 20th century—fully degraded this important ecosystem. By the mid-20th century, summer dissolved oxygen concentrations were routinely depleted resulting in vast fish kills, and poisoning from DDT pesticide eliminated reproduction of Bald Eagles. Since primary treatment facilities began operation and the DDT ban went into effect, dissolved oxygen concentrations have generally been maintained above dangerously low levels, and reproduction has recovered in Bald Eagles and some species of anadromous fish. These improvements notwithstanding, the legacies of past human disturbance continue to impact this important ecosystem. Merrymeeting Bay is permanently shallower, its anadromous fish runs are vestiges of their former abundances, toxic substances remain in its biota and sediments, and it continues to receive excess nutrients from industrial and municipal sources. These legacies are varied and profound. Whereas some physical, chemical, and biological properties recovered rapidly with cessation of the disturbance, others will require considerable more time or may never fully recover.