POND/PANNE TRENDS ON THE SALT MARSHES ALONG A NUTRIENT GRADIENT OF AN EUTROPHIC ESTUARY 1926 - 2007, HEMPSTEAD BAY, LONG ISLAND, NY

The continued loss of legally protected salt marshes on the east coast of North America is cause for concern, but it is unclear whether it is due to natural or remaining indirect anthropogenic impacts. It is not only the overall extent of marsh that we should measure, but also the internal structure as represented by the proportion of marsh area occupied by marsh vegetation. Hempstead Bay is a eutrophic estuary that still includes approximately 2,700 hectares of salt marsh islands that were grid ditched prior to the early 20th century, but were otherwise undisturbed. Over 15,000 patches of unvegetated marsh surface (ponds and pannes) on 12 focus islands were measured from 12 sets of aerial photographs (1926 - 2010) and trends through time were then compared with spatial patterns of nitrogen concentration. The persistence and growth of individual unvegetated patches was also analyzed, including the use of survival analysis. Loss of pond area was associated with intensive drainage efforts for mosquito control in the 1950s and 1960s, however the percentage of unvegetated marsh tended to return to 1926 - 1950 levels after side-ditching and maintenance were discontinued in the 1970s. Sections of the marsh associated with waterways having higher nutrient loading were more likely to remain vegetated, while marshes surrounded by water with falling nutrient levels had pond/panne coverages that more often grew and exceeded pre-1956 percentages. The persistence of pond/pannes did not seem to differ along the nutrient gradient.