1. Solving Graph Data Puzzles
Castle Point data buoy, HRECOS
Steve Stanne, Estuary Education Coordinator, Hudson River Estuary Program
Of Time and Rivers Flowing: Teaching About the Dynamic Hudson
December 1, 2016

2. Hudson River Environmental Conditions Observing System
Using HRECOS
Hudson River Environmental Conditions Observing System
This is a screenshot of the HRECOS home page. The map shows the location of HRECOS stations; the status table on the lower right indicates whether the station is currently collecting data. In slide show mode, click on the YouTube link to see a video about the HRECOS remote sensing system.

3. HRECOS Current Conditions page
Use dropdown menus to choose station, parameter, etc. Choose Units and whether to plot Continuous readings or Daily averages. Use Start Date/End Date or Set Start/Set End to choose dates (within limits - click ? in the red button for more details). Plot one parameter or compare
two in one graph.
This screen shot shows the HRECOS current conditions page. If desired, click on the hyperlink in the title when showing the PowerPoint to go to the HRECOS home page; once there, click on Current Conditions to go to this interface. Then manipulate it to see the capabilities of the system. Click on this plot of wind gusts overlaid on the depth graph., showing how two parameter plots can be directly compared.

4. In the Products column, click on Preliminary Water Level to see graph.
1. NOAA (National Oceanic & Atmospheric Administration) tide gauge at the Battery, New York City:
In the Products column, click on Preliminary Water Level to see graph.
2. NOAA data buoy in the Atlantic Ocean at the entrance to New York Harbor:
Scroll down the page to view or graph conditions.
3. US Geological Survey Hudson River gages (Albany, Poughkeepsie, links to others):
4. HRECOS (Hudson River Environmental Conditions Observing System) network:
Click on Current Conditions; select sites & parameters; create graphs.
5. NYHOPS (New York Harbor Observing & Prediction System):
Click on Forecast Region; select parameters.
Click on a link to go a website and explore. The sites all present data differently; it would be helpful to explore them on your own before doing so with a class.

5. HRECOS Current Conditions page
Interpreting graphs: What is the story that each of these graphs tells?
Working in small groups, answer these questions:
What time period is shown in this graph?
Where is the measurement being made?
What parameter is being measured in this graph?
What happens to it over the time period shown?
What is your hypothesis about what caused this to happen?
Measurements of what other parameters would help you test and verify your hypothesis?
HRECOS Current Conditions page
These questions are helpful in interpreting the stories told in the following graph puzzles.

6. 2011
Ask students how oxygen (molecular oxygen - O2, not the atom of O in H2O) gets into the water: diffusion from the atmosphere, maybe aided by winds; photosynthesis by aquatic plants and phytoplankton; inputs from tributaries. At Norrie Point in summer, DO levels rise and fall in a pattern – rising from morning into mid-afternoon, falling through late afternoon and overnight. Why?
DO-01

7. Click through a number of hypotheses: wind, temperature, and sunlight
Click through a number of hypotheses: wind, temperature, and sunlight. In each case, a graph appears with plots of both DO and the parameter in question. Winds might be a factor on 7/22 and 7/23, but fall off the next two days with little reduction in DO. Temperatures rise with DO into the afternoon, but since warmer water holds less DO than cold water, it doesn’t make sense that rising temperatures would be directly impact DO levels. What about sunlight (reported as radiation in HRECOS)? A clear correlation. Why? Sunlight promotes photosynthesis Click by submerged aquatic plants, which produces oxygen.

8. 2011
The 24 hour cycle of DO, caused by photosynthesis during the day and respiration at night, is evident through 8/27. On 8/29, DO % saturation drops sharply. From 8/30 on, DO % saturation continues to go down, and the 24 cycle of DO concentration is no longer seen. Why?
DO-02

9. 2011
One possibility might be a sudden change in water temperature. However, temperature drops in concert with DO; with cooler water, one might expect an increase in DO. What might limit photosynthesis? Lack of sunlight would; checking turbidity Click, a sharp, significant increase in turbidity is apparent. What caused it? Click Rainfall and flooding from Irene.

10. 2016
At Castle Point off Hoboken, data is collected from a floating buoy. In August 2016, DO concentration is elevated (up to 14 mg/L!) over nearly a week in the middle of the month. The 24 hour cycle of DO concentration is evident. Remember that photosynthesis by day and respiration at night is generally responsible for this pattern. What might be the cause of these elevated DO levels?
DO-03

11. Going through the usual suspects, DO concentration goes up with water temperature; it should be going down. Strong winds could push more oxygen into the water. The Castle Point buoy did not record wind speed during this period. We can go to another station nearby, Pier 84 in Hudson River Park, to check winds, Click but there’s nothing unusual about wind speeds over this period. Are there plants in the Hudson off Lower Manhattan? There is no SAV, but there are phytoplankton. Unfortunately, most HRECOS stations don’t measure chlorophyll, which would tell us if there was a bloom of phytoplankton, so we have to get at this indirectly. Phytoplankton blooms are not that common in the Hudson because of the estuary’s rapid flushing rate. Currents are especially swift during spring tides, carrying plankton out of the system. However, currents are slower during neap tides, sometimes allowing phytoplankton to bloom. Checking the spring/neap tide cycle – again at Pier 84 since the Castle Point buoy does not record depth – Click we see that the increase in DO did occur during a neap tide. The likely cause was a phytoplankton bloom.

12. 2011
In late August, 2011, salinity at Castle Point dropped suddenly from ~20 psu (essentially the same as ppt) to 0. In early September it started rise, but then fell back to 0 around 9/10. Why?
Sal-01

13. 2011
A likely reason would be an major influx of fresh water due to heavy rains. But where would rain have fallen? A heavy summer thundershower in NYC would not have caused this much runoff. Look for rainfall in the watershed, we go to Albany meteorological data and select Rainfall Daily Accumulation Click to see that there was a lot of rain in the watershed – nearly 5 inches in less than a day in Albany around 8/29. (You would see similar results from any HRECOS weather station further up the river.) This was due to Irene, which dumped up to 14 inches of rain in some parts of the Catskills. That runoff was slacking off when the remnants of Tropical Storm Lee moved through the area over several days in early September. Runoff from Lee’s heavy rains again drove the salt front south. The Hudson was fresh all the way to NY Harbor as a result of these storms.

14. 2014
Don’t be scared off by the units - specific conductance in microsiemens per centimeter. It’s just one more way of measuring salinity. At West Point, salinity rose sharply starting around 2/10/14, stayed high for a couple of weeks, and then dropped back down at the end of the month. Why?
Sal-02

15. 2014
When dealing with movements of salt in the estuary, it’s always a good idea to see what’s going on in the watershed, as runoff has a major role to play in salinity changes. Looking at Rainfall Daily Accumulation at the Port of Albany, we can see that lots of rain towards the end of the month would have caused runoff to push the salt south. But why did salinity increase sharply at West Point earlier in the month? There’s not a lot of evaporation in winter. What else might have reduced runoff? Click Cold temperatures. A couple of weeks of mostly below freezing temperatures caused any precipitation to fall as snow, and icy conditions would have prevented melting and runoff. It’s not unusual to see the salt front creep north during cold snaps in midwinter.

16. Effects of flooding due to runoff are generally limited to the upper estuary.
For the next few case studies, which focus on water level, it’s important to know that flooding due to runoff is generally limited to the upper estuary. Water levels are usually equilibrated to sea level from Catskill south. This graph shows flooding in Albany, but little evidence of it at Norrie Point in the same time span. There are exceptions during extreme events.

17. 2011
Water level (depth) at the Port of Abany started rising 4/26 and remained elevated for several days, though high and low tides still occurred.
WL-01

18. Lots of rain fell over 3 days, causing flooding
Lots of rain fell over 3 days, causing flooding. Why did the flooding peak on 4/30 instead of 4/28, the last day of heavy rain? It takes time for runoff to move down the tributaries and into the mainstem Hudson.

19. 2012
This graph shows a peak in water level at Pier 84 in Manhattan. What caused it?
WL-02

20. Rainfall is a possible cause
Rainfall is a possible cause. A check of rainfall daily accumulation in Albany shows little rain there – less than 0.2 inches. What about wind? Click Wind was not being recorded at Albany during this period, but just a few miles downriver at Schodack Island the same water level peak was recorded, and gusts there reached 35 knots. What direction were they from? Click During the time that the water level jumped up, winds came from degrees (think compass bearing) – southeast to south. Wind effects generally impact Hudson River water levels by influencing water levels in the coastal Atlantic Ocean. This water level peak was due to storm surge from Hurricane Sandy.

21. This graph of water levels at NOAA’s Battery tide gauge for the same time period shows Sandy’s destructive storm surge in NY Harbor.

22. 2016
Water level dropped in Albany on 3/29 – 3/30
WL-03

23. This is a blowout tide caused by strong winds over coastal waters - Piermont was the closest station to the ocean with available wind gust data. What direction were the winds from? Click. Northwest, blowing water away from the coast and lowering levels in the Hudson.

24. This graph from NOAA’s tide gauge at the Battery shows water levels up to 1.75 feet lower than predicted.

25. For more information, contact
Steve Stanne, Education Coordinator
NYSDEC – Hudson River Estuary Program & NYS Water Resources Institute – Cornell University
21 South Putt Corners Road
New Paltz, NY 12561