Abstract: A time span of 15 years separated two surveys of the benthic macroinvertebrate community of the Hackensack Meadowlands. During each survey, three replicate grab samples were collected using a full-sized Ponar grab at 26 sampling locations during each season over a one year period. The original survey, conducted in 1987, recovered 65,565 organisms from 52 taxa in a total of 284 benthic collections. During the 2002 survey, 215,296 organisms representing 67 taxa were identified from 312 collections. A total of 89 benthic taxa were identified during both surveys.
During the 2002 survey, the benthic community within the Hackensack Meadowlands was composed primarily of polycheate worms (22 species and 45% of the total number of organisms collected) and amphipods (10 species, with a relative abundance of 35%). The total number of taxa ranged from 43 at river mile 3.0 (location S1), to 10 at river mile 12.2 (location GN3).
In 1987, the benthic community was dominated by gastropods (primarily one species with a relative abundance of 50%) and oligocheate worms (27%). The highest number of taxa collected (n=25) was also collected at river mile 3.0 (location S1), while the lowest number of taxa (n=4) were recorded at sites between river mile 10.9 to 12.5 (locations TN5, T5-S and TN6).
Although the highest diversity (i.e., number of taxa collected) occurred at the downstream sampling locations in both survey periods, the highest density of benthic organisms (40,000 to 65,000 organisms/m2) occurred in two tributary creeks (Mill and Cromakill) and the mainstem of the river at river mile 9.2. These high densities are primarily due to the amphipod Apocorophium lacustre and the polycheate worm Hobsonia florida that were collected during the 2002 survey.
Shannon diversity index (H’) values were calculated for each sampling location for each season, as well as for all seasons combined (i.e., a yearly total). The Shannon index values for each survey were then statistically compared using a specialized t-test. The results showed that, for all seasons combined, 19 of the 26 sampling locations had a significantly higher (p=0.05) diversity during the 2002 survey. On a seasonal basis, the H’ values were statistically higher in 2002 than in 1987 at nine locations during the winter, at 18 locations during the spring, and at 16 locations during autumn. During the summer, seven sampling locations were significantly higher in 2002, while the diversity from two locations was significantly higher in the summer of 1987.
It appears there have been significant improvements within the benthic community in the Hackensack Meadowlands in the 15 years since the original benthic survey was conducted. However, the overwhelming abundance of a few opportunistic species at several locations within the mid to upper portion of the Meadowlands provides evidence that this system is still stressed.