2012 Chlorophyll Sampling Results

chlorophyll2 chloropyll

October 4, 2012

The Day - October 4, 2012 was a wet and overcast day, although most of the participating groups sampled before strong rains hit the area. Weather is important to record as the chlorophyll molecule absorbs sunlight, using this energy to build carbohydrates. This means that bright sun levels are linked to increased algal and phytoplankton production, and it is this productivity that we are measuring with our chlorophyll a sampling.

Methods - The sampling methods are described in the main chlorophyll page. Note in our 2012 data:

If a single river site had more than one sample the results were averaged for reporting on this webpage.
All results were rounded to two decimal places.
An excel file of the data is included in the overall 2012 excel downloadable dataset.

Units: 2012 results are listed in ug/L and 2005 results are listed in mg/m³. How does the unit 'ug/L' compare to 'mg/m^3' Micrograms/liter (ug/L) are the same as milligrams/cubic meter (mg/m³) and are completely interchange.

2012 data

Results for the 2012 sample show that the southern end of the estuary, from Brighton Beach at RM -9 up through Piermont Pier at RM 25, had consistently low chlorophyll levels compared to the rest of the estuary. However, looking at the overall chlorophyll data plotted by River Mile (RM) there seems to be a high degree of variability in the chlorophyll results. Putting a trend line through the data to examine chlorophyll as a function of RM will help with our analysis.

Examining trends in the data. A trend line is a straight line used to connect multiple points in the data or the best fit connecting the data. The steepness of the trend in the data indicates the strength of the trend, the flatter the line the lower the strength of the trend. Once a trend line has been established an R² value is used to see how well the line fits the data, in other words is there a consistent relationship between the two variables being plotted on the graph (in our case this is chlorophyll and RMs)? A perfect match would be a value of 1.0, a strong relationship would be 1.0-0.7, and a moderate linear relationship would have values between 0.7 and 0.4. Our value of 0.36 falls below even a moderate relationship, suggesting that there is not a strong relationship between river mile and chlorophyll. This means we would not want to make predictions on chlorophyll levels in the river just using river miles.

Below is a chart of those sections of the river with the highest and the lowest Chlorophyll readings. Note that Cohotate in Athens, NY has recorded one of the higher readings for chlorophyll each year of our posted results. Also note that in 2011 Ulster Landing Park recorded one of the highest readings, but this year it has one of the lowest readings.

*Chlorophyll Readings > 3.0 ug/L*				*Chlorophyll Readings < 0.5 ug/L*
Location	RM	ug/L	5 highest	Location	RM	ug/L	8 lowest
Hook Mt., Nyack	31	3.27	The highest levels of chlorophyll (levels over 3.0 ug/L) from our sample locations included the sites listed on the left.	Brighton Beach	-9	0.22	The lowest levels of chlorophyll (levels below 0.5 ug/L) from our sample locations include the sites listed on the left.
Riverfront, Peekskill	43	3.49		Brooklyn Bridge Pk.	1	0.35
Kingston Pt. Park	92	3.08		Pier 40	2	0.20
Cohotate, Athens	115	3.32		Pier 95	5	0.21
Green Island, GI	153	5.11		Beczak, Yonkers	18	0.38
				Piermont Pier	25	0.37
				Quiet Cove, POK	78	0.11
				Ulster Landing Park	97	0.47

What are some of the parameters that can impact chlorophyll levels in the river?

Sunlight is one of the biggest factors:
- Long sunny summer days promote photosynthesis producing higher chlorophyll values than shorter cloudy days in fall and winter.
- Turbidity levels in the river directly affects the amount of sunlight that can penetrate the water column. In very turbid sections of the river the chlorophyll clusters closer to the surface where the light penetration is highest.
Nutrients also contribute to chlorophyll values. Nutrient levels in the estuary would be expected to be higher than nutrient levels in the open ocean.
Water depth and water speed (currents) are also important. Shallow, slow moving water will be more easily penetrated by sunlight and often has higher nutrient levels.
Local water input from smaller tributaries that enter the Hudson can contribute additional nutrients, as well as chlorophyll directly.

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