A salt marsh that is largely natural and healthy can present a broad array of physical habitats, species diversity, abundances, and temporal variability. This range of conditions is due to the adaptations of salt-marsh flora and fauna to the variability in their physical environment. This variability has made it difficult to develop general health assessments for salt-marsh systems. Salt marsh health can be broadly assessed by considering:

· Physical habitat stability through sediment erosion and deposition
· Connectivity of the marsh with adjacent ecosystems
· Within-marsh ecological communities
· Overall water quality.

Because marshes sit at the high-energy interface of land and sea, a stable or benevolent physical setting is key for marsh development and stability. This stability, by definition, requires the efficient exchange of materials between the marsh and its adjacent upland and marine habitats, which can be defined as connectivity. In conjunction with physical processes, a persistent plant community is also required as a major positive feedback for habitat stability. Marsh plants also comprise the ecosystem’s base in terms of primary production and habitat structure. Thus, they play dual roles in physical and ecological health. Finally, water quality encompasses several key components of marsh health including nutrient regime, water and sediment exchange, and marsh surface hydrodynamics. Taken together, these multiple characteristics reflect key aspects of saltmarsh condition and might be used through monitoring or investigation to assess overall health.

No specific measure has been identified as a sufficiently reliable indicator of marsh health. In large part, this is because it cannot be assumed that pristine or healthy salt marshes are similar in key physical and biological characteristics. A way around this problem may be to think of indicators of health in the negative, in that monitoring would seek to measure differences from acceptable conditions. It may also be that the presence of clear and negative trends, such as rapid marsh loss and/or dominance of non-native species, would be another means of determining a marsh is not healthy.

Trend analysis is likely to be the more useful assessment means, because in most cases salt marshes are already altered or impacted, with limited possibility for restoration to pristine conditions. Thus, data trends can reveal whether an otherwise impacted marsh system is relatively healthy or is losing its health. In systems as complex and variable as salt marshes, just identifying such trends would be important and useful accomplishments.

There are several characteristics that might be expected of all salt marshes that are in reasonable health. These include a relatively stable vegetated area, limited extent of invasive plants, and presence of obligate marsh species. The table below suggests how these might be measured and evaluated to create first-order assessments of marsh health.

Proposed Indices for Marsh Health on Long Island