IES scientists study not only Hudson River animal and plant life, but also the river's chemical and physical parameters. Working from an inflatable, Dr. Stuart Findlay uses fluorescein - a non-toxic dye - to study the flow of water over and through a bed of submersed vegetation in Haverstraw Bay in Rockland County, N.Y.

IES scientists have been studying and monitoring the Hudson River ecosystem since 1986. This long-term effort is broad in geographical and intellectual scope, and, as a result, has led to an unusually rich understanding of this large and important ecosystem. For example, some critical consequences of the zebra mussel invasion that began almost a decade ago are just now being brought to light by the IES research program. These changes have taken a decade to appear either because they are subtle, such as the 12% decline in dissolved oxygen, or because they are slow, such as the alarming extirpations of long-lived invertebrates. In addition to changes associated with the arrival of zebra mussels, there has been a long-term increase in dissolved organic carbon river-wide, possibly resulting from changes in vegetation or atmospheric nitrogen deposition in the surrounding drainage basin. Many of the trends over time are demonstrable with confidence only because of the IES researchers' extensive and consistent data set ... one that is constantly scrutinized for signs of change.

Rather than focusing on a single study site on the Hudson River, the IES program seeks to understand how the various parts of the river function as an integrated whole. This systems-view has produced important insights. As a result of the zebra mussel's depletion of phytoplankton (floating algae) in many parts of the river, for instance, IES scientists have observed shifts in the relative use of various habitats within the river by other organisms. Benthic invertebrates and some fish apparently have increased their reliance on submersed vegetation over the past eight years, drawing attention to the connections among the varied habitats in the river. Recent research also has shown that patches of different species of aquatic vegetation have opposite effects on water chemistry. Large stands of the invasive water chestnut dramatically deplete dissolved oxygen while stands of the native water celery actually add significant amounts of oxygen to the water column. Beds of the native plant can produce enough oxygen during daylight hours to lead to oxygen concentrations 50% higher than in the river's main channel. Understanding how water or organism movement among these adjacent habitats affects overall ecosystem function, organism survival or biogeochemical processes will be a focal point for collaborative research by IES staff in the future. The future health of the Hudson River ecosystem also will be affected by current and future management of pollutants and fisheries. Long-term, large-scale ecosystem research will help clarify these effects and evaluate the potential impacts of management practices and plans.