December 13, 2018 – Oyster Bay NY: A review of water quality sampling data for 2018 through October finds a generally healthy bay complex. Data from some locations does however reflect water quality that is less ‘healthy’ than other areas. These are, not surprisingly, the locations where bay tributaries discharge – particularly Mill Neck Creek and Cold Spring Harbor’s Inner Harbor. In these areas one would expect higher bacterial and suspended solid loads from stormwater and waterfowl inputs and lower pH due to freshwater discharge. Observations from an examination of the data follow.
Map of Friends of the Bay sampling areas in the Estuary. (FB 1-19)
A review of pH averages indicates that FB-1 (Inner Harbor of Cold Spring Harbor) has the lowest pH. Lower pH is also found in FB-13-19 (Mill Neck Creek). Lower pH may be due to algal or bacterial respiration and/or from the discharge of lower pH freshwater (Cold Spring Harbor ponds and Beaver Lake respectively). At FB-17 (head of Mill Neck Creek) 50% of samples taken at 1 meter had a pH of less than 8.0 (the pH of marine waters is typically >8.1).
Similarly, at FB-16 (head of Mill Neck Creek) 30% of samples taken just off the bottom had a pH of less than 8.0. Average dissolved oxygen (DO) for samples taken at the top and near bottom of the water column is lowest near the head of Mill Neck Creek at stations FB-16 and FB 17. A DO of less than 3.0 mg/L is considered ‘hypoxic’ and inhospitable to virtually all marine organisms. Stations FB-1 and FB-2 in the Cold Spring Harbor Inner Harbor experienced a DO of less than 3.0 on several occasions. Similarly, stations FB-15, FB-16, and FB-17 near the head of Mill Neck Creek also experienced a DO of less than 3.0 on several occasions. In fact, 25% of the samples taken at the top of the water column at station FB-17 were below 3.0 and 30% of the samples taken near the bottom of the water column were below 3.0 at station FB-15.
Secchi Disk submerged in water sample.
Secchi depth is a measure of water clarity. Lower values reflect either higher suspended solid loads typically from tributary discharges or higher densities of phytoplankton (microscopic algae). The Cold Spring Harbor Inner Harbor (FB-1 and FB-2) had the lowest Secchi depths as a percent of all readings – 50% and 30% respectively were less than one meter.