NOAA Tech Memo NMFS NE 167:
Assessment and Characterization of Salt Marshes
in the Arthur Kill (New York and New Jersey)
Replanted after a Severe Oil Spill

VIII. CONCLUSIONS

Before discussing the overall conclusions of the NMFS study, it is important to summarize the monitoring results and conclusions of the SMRT study for S. alterniflora biomass and stem densities, ribbed-mussel densities, mummichog abundances, and wading bird foraging success.

SMRT STUDY

The following summary of the SMRT study is based on Bergen et al. (2000) and Alderson et al. (Salt Marsh Restoration Team, Natural Resources Group, New York City Parks, 200 Nevada Ave., Staten Island, NY, pers. comm. and unpubl. data). No specific numbers will be given, and the results are confined to Old Place Creek and Con Ed Tower. In terms of S. alterniflora, above-ground biomass at Old Place Creek -- an oiled and replanted site -- has reached levels comparable to those reported in other studies at this latitude. In comparison, little or no S. alterniflora has been found at Con Ed Tower -- an oiled and unplanted site; natural recolonization via rhizomatous growth and seedling recruitment has failed to re-establish vegetation there. At Old Place Creek, annual increases in stem densities, and the height of S. alternilfora plants, indicate that the conditions for seed dispersal and possible germination, as well as the baffling and accretion of sediments, are being met at that site. The replanting of grass to areas at Old Place Creek denuded by oil, and the subsequent success of the seedlings and transplants, were not suggested by previous studies; indeed, at the time of the spill, managers considered replanting unnecessary (C. Alderson et al., Salt Marsh Restoration Team, Natural Resources Group, New York City Parks, 200 Nevada Ave., Staten Island, NY, pers. comm.). At Con Ed Tower, though, the grass does not appear to be able to return on its own, and a net loss of marsh greater than that caused by the oil spill may in fact be occurring due to erosion of the denuded shoreline (C. Alderson et al., Salt Marsh Restoration Team, Natural Resources Group, New York City Parks, 200 Nevada Ave., Staten Island, NY, pers. comm.).

Densities of mussels at Old Place Creek have increased annually, while the mussels at Con Ed Tower are still at very low densities.

Greater numbers of mummichogs were trapped at Old Place Creek, suggesting a preference by that species for the heterogeneous habitat provided by the replanted S. alterniflora as compared to the bare surface of the Con Ed Tower site. Other studies have also shown greater direct use of salt marshes by fishes in comparison with nonvegetated habitat (e.g., Rozas and Minello 1998).

For snowy (Egretta thula) and great egrets (Casmerodius albus), the number and duration of foraging visits, the number of strike attempts, and the number of successful strikes were significantly greater at Old Place Creek. This increased foraging success suggests that there were greater numbers of prey (i.e., mummichogs) available to the birds at the replanted site. Thus, the replanted site appears to provide better foraging habitat for the wading birds. Supplementary data show that the heterogeneity of the habitat in the replanted marsh is positively correlated with improved foraging success.

These monitoring studies by the SMRT suggest that the replanting of S. alterniflora after the 1990 oil spill was very important for the recovery and restoration of the saltmarsh ecosystem, especially at Old Place Creek, and even in such a heavily urbanized and degraded estuary as the Arthur Kill. The S. alterniflora provides much of the structural component of the marsh; restoring this component is important to the other members of the food web, such as the mussels, mummichogs [e.g., as a refuge from predation (Moy and Levin 1991; Halpin 2000)], and birds. It is particularly important in an urbanized landscape where habitats are isolated and their availability is limited (Simenstad and Thom 1996; Ehrenfeld 2000), and where restoration is critical for species of particular concern such as the great and snowy egrets.

NMFS STUDY

Bearing in mind that the NMFS assessment was limited in scope, our results are less clear in terms of the benefits of replanting, or even in evaluating the differences among the sites. Ehrenfeld (2000) stated that in urban wetlands, the range of variability, both within and among wetlands, is much higher than in nonurban wetlands, and this is certainly true in the Arthur Kill. For example, for the benthic infauna, while there may be similarities in invertebrate abundances between the replanted and reference sites, quantitative evaluation was confounded by the high variability in the data and the low number of replanted and reference sites sampled. What is clear is that many of the fauna found in these marshes appear to be tolerant of contaminants; however, this pollution and other anthropogenic impacts may affect their overall health and longevity (e.g., mummichogs). While it is true that the ribbed-mussels from the Mill Creek reference marsh grew faster and were larger and heavier than mussels from both replanted sites, this is more likely due to the relative undisturbed nature of this mature marsh, as well as differences in site-specific factors.

All the Arthur Kill marshes are polluted of course, as evidenced by, for example, the residual oil in the sediments (see also Bergen et al. 2000), and as suggested by the high percentages of detritus and algae as opposed to live prey in the mummichog stomachs, which may indicate a poor diet due to a polluted environment. However, the levels of contaminants are often site specific, depending, for example, as with sediment trace metals, on the types of sediment found at each site. Replanting may have reduced the amount of TPH in the sediments -- compare Old Place Creek to Con Ed Tower, and see also Bergen et al. (2000); however, replanting may not have had a great effect on the levels of other contaminants, such as trace metals in both sediments and mussels, and TPH in mussels.

Some measures of ecological function, such as biogeochemistry, also appear to be site specific, but are subject to many confounding factors, and it is questionable whether the biogeochemistry was affected by replanting. Others measures, such as mummichog food habits, may or may not be site specific, but a more thorough investigation would be necessary to discern any real patterns in the data, as has been demonstrated for several of our other investigations.

COMBINED STUDIES

In conclusion, replanting the oil-damaged marshes of the Arthur Kill may have successfully "restored" them, at least structurally, to the level of the existing marshes found within the Kill. Because this is an urban estuary, the extent to which the ecological functions of these marshes have been restored is more difficult to ascertain due to confounding factors such as pollution and other anthropogenic impacts.

Also, the time span of this preliminary assessment program may have been too short and the number of treatment sites chosen may have been too small to assess accurately the performance of the replanted marshes, especially given the many scales of natural spatial and temporal variability and anthropogenic perturbations inherent in this ecosystem. A number of habitat restoration investigators have also noted the value and importance of long-term studies of ecosystem processes in restoration research in order to obtain a better understanding of the time required to achieve functional equivalency and to also take into account this kind of variability (e.g., Simenstad and Thom 1996; Kentula 2000; West et al. 2000). Nevertheless, New York City's SMRT continues to replant and monitor these marshes where necessary, insuring that this vital habitat is protected from further loss and degradation.

REFERENCES CITED

Bergen, A.; Alderson, C.; Bergfors, R.; Aquila, C.; Matsil, M.A. 2000. Restoration of a Spartina alterniflora salt marsh following a fuel oil spill, New York City, NY. Wetlands Ecol. Manage. 8:185-195.

Ehrenfeld, J.G. 2000. Evaluating wetlands within an urban context. Ecol. Eng. 15:253-265.

Halpin, P.M. 2000. Habitat use by an intertidal salt-marsh fish: trade-offs between predation and growth. Mar. Ecol. Prog. Ser. 198:203-214.

Kentula, M.E. 2000. Perspectives on setting success criteria for wetland restoration. Ecol. Eng. 15:199-209.

Moy, L.D.; Levin, L.A. 1991. Are Spartina marshes a replaceable resource? A functional approach to evaluation of marsh creation efforts. Estuaries 14:1-16.

Rozas, L.P.; Minello, T.J. 1998. Nekton use of salt marsh, seagrass, and nonvegetated habitats in a south Texas (USA) estuary. Bull. Mar. Sci. 63:481-501.

Simenstad, C.A.; Thom, R.M. 1996. Functional equivalency trajectories of the restored Gog-Le-Hi-Te estuarine wetland. Ecol. Appl. 6:38-56.

West, T.L.; Cough, L.M.; Ambrose, W.G., Jr. 2000. Assessment of function in an oligohaline environment: lessons learned by comparing created and natural habitats. Ecol. Eng. 15:303-321.