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Because precipitation is coming now in short spurts, there is also the danger of intermittent stretches of drought. “We know that in a warmer world, the droughts will be more severe because warming enhances evaporation and transpiration,” Burns said. Because it’s an estuary, when the flow coming out of the Hudson gets low, as it does in the summer, the saltwater migrates up. This salt front, defined as 100 mg/L chloride concentration, is very sensitive to sea level and also to drought. While the position of the salt front also moves with the tides and, in fact, is furthest upstream when there is a full moon or high tide, one concern with climate change and the predictions about sea level rise is that this would tend to push the salt front even further upstream. The concern is for those cities and towns that draw drinking water from the Hudson.
Paul Lill, Plant Administrator at Poughkeepsie’s Water Treatment Facility, said that when the salt level rises, they adjust their schedule to pump only during high tides, when the river runs south and salt is less concentrated. The facility has the capacity to pump 19 million gallons per day but generally only uses 10 million. So they can pump at a high rate at high tide, and at a low rate, or not at all, at low tide, when the salt concentration is at its highest. That was their strategy during recent droughts. In 2001, because of the drought’s severity, the Army Corps of Engineers agreed to release water from the Sacandaga Reservoir in the Adirondacks into the river, freshening the saltwater they pumped. Newburgh is the southernmost community to pull water from the Hudson. Others include Highland, Hyde Park, Port Ewen, and several farther upstream. Lill said that in the short term, Poughkeepsie isn’t worried about drought. In the long term a desalination plant, though it’s not something they’re planning, is in the back of their minds. He estimated it would be a $50 million project, just to get the equipment, site planning, and engineering set up, exclusive of operating costs.
John Cronin, Director and CEO of The Beacon Institute, said that the location of the salt front is critical because, from an ecological point of view, the salinity of the water will have a more dramatic effect than other factors on the Hudson River’s marshes and wildlife. Right now, the Beacon Institute is in the development stages of a monitoring system that will document changes in the river due to sea level rise. As part of their Rivers and Estuaries Observatory Network, remote sensing technology will be deployed to create an interconnected network that will extend throughout the river. A fundamental part of their monitoring will be fresh water salinity, river level, river current, and other physical and chemical changes over time. Cronin said, “The Hudson’s tidal, so sea level rise is going to have a dramatic effect on the shoreline, the physical characteristics, and the ecosystem itself. There will be a displacement of habitat and altering of animal behavior.” A fish accustomed to particular water salinity and temperature may find itself dramatically affected by alterations. In order for the negative affects on river biology to be mitigated, human impacts will have to be managed more carefully. Cronin said that it’s premature to draw conclusions about the effects of climate change on the Hudson River. While he can’t reliably say it’s because of global warming, he noted that there has been infrequent icing of the river, once a reliable characteristic. “It’s important to remember,” Cronin said, “that ice serves a function in the river. It is not just the cold state of water.” River ice plays an important role in the chemistry and ecosystem sense; It cleans out detritus and brings nutrition to the fish. It serves to scour and clean marshland, and ice melt and retention on land is important to the hydrologic cycle.