Late in the evening, on the third day of spring, I stooped in the rain to help a spotted salamander cross the road. The amphibians had begun their spring migration! This is one of my favorite signs of spring.
Like the amphibians marching through its watershed, the Hudson River is also responding to the spring. Water temperatures have been steadily rising since the middle of February. Chlorophyll concentrations, those molecules used by plants to harvest the sun's energy for sugar production, have been rising since late February. Dissolved oxygen, the gas released by sugar producing plants, has been rising in percent saturation since the beginning of March (note that the total concentration of dissolved oxygen has declined because the gas is less soluble in warmer waters).
The most dramatic response to spring in the Hudson River, however, is the freshet. The freshet is the sudden increase in river discharge caused by melting snow and ice. This year, the freshet occurred on March 23.
The USGS gauge at Green Island records discharge in the Hudson River just before it passes over the Troy dam. On March 23, recorded values rapidly rose from 40,000 cubic feet per second to over 100,000 cubic feet per second in less than 24 hours.
The contribution from each section of the watershed was not uniform. The Mohawk contributed more than the upper Hudson and, among the Mohawk tributaries, the eastern tributaries contributed more than the western tributaries. It's possible that we will see a second freshet event as these other regions release their snow-melt.
The response to this spring freshet in the Hudson River Estuary was observed immediately. Water levels jumped noticeably at the Schodack Island and the Norrie Point HRECOS Stations. According to the Storm Surge Warning System, developed by the Center for Maritime Systems at the Stevens Institute, the water levels at Albany rose over five feet.
In addition to a rise in water level, we also observed a noticeable change in turbidity. At Schodack Island, turbidity rose 245 NTU in less than 40 hours. The response at Norrie Point was less dramatic and spread over a longer period of time with values climbing 145 NTU over the course of four days. Despite the weaker response at Norrie, employees at the Norrie Point Environmental Education Center described the river as chocolaty brown.
Temperatures are due to hit the eighties by the end of the week. I'm curious to see if we'll have another freshet event as snows from the northwestern section of the watershed are melted away. In addition, the heavy rains we've been having across the watershed should help to unlock the remaining run-off. Keep your eye on the river this week for change is quickly coming!