Application and assessment of a nutrient pollution indicator using eelgrass ( Zostera marina L.) in Barnegat Bay–Little Egg Harbor estuary, New Jersey

Abstract

Eutrophication degrades numerous estuaries worldwide and a myriad of assessment metrics have been developed. Here, we apply an example of a previously developed metric ( Lee et al., 2004) designed to indicate incipient estuarine eutrophication to validate this technique in an already eutrophic estuary end-member, Barnegat Bay–Little Egg Harbor, New Jersey. The metric, termed ‘Nutrient Pollution Indicator’ (NPI) uses eelgrass ( Zostera marina L.) as a bioindicator and is calculated as the ratio of leaf nitrogen content (%N) to area normalized leaf mass (mg dry wt cm −2). Eelgrass samples were collected along the entire length of the Barnegat Bay–Little Egg Harbor from June to October 2008 to determine if leaf chemistry and morphology reflect eutrophication status and a north–south gradient of nitrogen loading from the Barnegat Bay watershed. Nitrogen content, area normalized leaf mass, and NPI values all significantly ( p < 0.05) varied temporally but not spatially. NPI values did not significantly correspond to the north–south gradient of nitrogen loading from the Barnegat Bay watershed. The NPI metric is therefore not deemed to reliably indicate estuarine eutrophic status. Differences between sampling effort (number of stations) and replication did not bias the overall conclusions.