Bronx River Plankton Sampling
As part of an effort to evaluate the potential factors that explain the absence of anadromous fish in the Bronx River, Lehman College researchers gathered data on food supply in the river system.
Plankton samples were taken from the shallow waters of the Bronx River at Lafayette Avenue (40°49.040'N:73°52.801'W) on the 3rd, 17th, and 24th of May and on the 3rd of June 2002. Approximately 0.866 m^3 of water was sampled during each collecting period using a handheld plankton net (mesh size 125 microns).
20 March 2003
40°48.84'N:73°52.33'W to 40°48.8'N:73°53.021'W
27 March 2003
40°48.057'N:73°51.421'W to 40°48.212'N:73°50.514"W
3 April 2003
40°48.9'N:73°52.6'W: to 40°48.0'N:73°51.8'W
Plankton Sampling Sites
Mid-channel Plankton Sampling Results
|March 20th||March 27th||April 3rd|
|Cypris Barnacle Larvae||59||13||70|
|Total Number of Individuals in a 3 ml concentrated sample||3524||4878||4526|
|Number of Individuals in a 1 ml concentrated sample||1175||1626||1509|
|Concentrated Sample Volume||280||360||180|
|Total Volume sampled by net in m^3||208.6||177.4||178.87|
|Plankton Number m-3||1.6X103||3.3X103||1.5X103|
Shore-side Plankton Sampling Results
|1st week May||2nd week May||3rd week May||1st week June|
|Copepod Nauplii Larvae||94||24||62||53|
|Harparticoid Nauplii Larvae||1||3||2|
|Filamentous Type (unidentifiable)||94||58||74||45|
|Seasquirt Tadpole Larval Stage||1|
|Total Number of Individuals in a 3 ml concentrated sample||425||342||2660||595|
|Number of Individuals in a 1 ml concentrated sample||142||114||887||198|
|Concentrated Sample Volume||175ml||175ml||125ml||125ml|
|Total Volume sampled by net in ml||885,960||1,181,280||885,960||885,960|
|Plankton Number ml-3||2.8X10-2||1.7X10-2||1.3X10-1||2.8X10-2|
|Plankton Number m-3||2.8X104||1.7X104||1.3X105||2.8X104|
Plankton Occurrence of Special Note: Dinoflagellate Bloom
During our 9 August 2002 cruise we observed that the waters just south of Lafayette Avenue began to take on a color, which could best be described as that of red wine. This color pattern was noted to continue up the river for a considerable distance. We obtained a sample for examination and determined that the waters color was due to a dinoflagellate bloom. The dinoflagellate was identified as a member of the Genus Gymnodium. Using a Sedgewick Rafter counting cell we determined that the dinoflagellate concentration at this site to be 17,000cells/mL.
On 12 August 2002 we went to Lafayette Ave to see if the bloom was still occurring. It was as observed on 9 August 2002.
On 23 August 2002 we again visited our sampling site at Lafayette Ave and found that the water had returned to is usual color. We obtained water samples and upon examination found that the dinoflagellates were still present but at a much reduced concentration of 5,000 cells/mL.
— Joseph Rachlin