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Stable nitrogen and carbon isotopes (δ15N and δ13C) and elemental content (% nitrogen, % carbon) in oysters (Crassostrea virginica) grown by a network of 132 citizen–scientists (11,600 km2, 87.9 km2 site−1) were examined to test effects of land use, salinity, flushing time, and oyster size on bioindication of human and/or animal nitrogen sources. Oyster δ15N sampled from shallow waters sites throughout Chesapeake Bay and its tributaries exhibited nested spatial patterns: (1) decreasing toward the mouth of Chesapeake Bay (1000s km2) and (2) decreasing, increasing, and not changing toward tributary mouths (100s km2). Distinct isotopic ‘signatures’ in tributaries were associated with the composition of land use, water quality in tributaries and freshwater streams, human and/or animal nitrogen sources, and marine vs. terrestrial nitrogen and carbon sources. Yet at 1000s km2, oyster δ15N varied with flushing time, salinity, and bioindicator size, thus constraining the upper extent for inferring nitrogen sources from bioindicator δ15N to the scale of gradients in these confounding physical and biological factors. Nevertheless, at 100s km2 isotopic ‘signatures’ can be used to infer nutrient sources and transport mechanisms and might have implications for fishery management/enforcement. Ultimately, δ15N and δ13C in bioindicators distributed to citizen–scientists may add substantial value to existing and ongoing programs, networks, monitoring and databases, and might have some use for imputing data gaps where intensive water quality monitoring is lacking.

Long-term non-linear ecosystem-scale changes in water quality and biotic communities in coastal lagoons have been associated with intensification of anthropogenic pressures. In light of incipient changes in Johnson Bay (an embayment of Chincoteague Bay, Maryland-Virginia, USA), examination of nitrogen sources was conducted through synoptic water quality monitoring, stable nitrogen isotope signatures (δ15N) of in situ bioindicators, and denitrification estimates. These data were placed in the context of long-term and broader spatial analyses. Despite various watershed protection efforts, multiyear summer time studies (2004–2007) suggested that high levels of terrestrially derived nutrients still enter Johnson Bay. Total nitrogen concentrations in Johnson Bay were 132% the concentrations in the broader Chincoteague Bay during the late 1970s (mean 2004–2007 was 40.0 – 73.2 μM). Comparing total nitrogen concentrations in Johnson Bay to St. Martin River (consistently the most eutrophic region of these coastal bays), Johnson Bay has increased from 62.5% to 82.5% of the concentrations in St. Martin River during the late 1970s. Though specific sources of nitrogen inputs have not yet been definitively identified, the long-term increase in total nitrogen concentrations occurred despite increased and continued conservation and protection measures. We suggest that investigating nutrient sources can reveal potentially ineffective nutrient policies and that this knowledge can be applied towards other coastal lagoons.

Previous investigations of eelgrass (Zostera marina L.) beds in the Barnegat Bay-Little Egg Harbor Estuary, New Jersey (USA) revealed a significant decline in plant biomass associated with ongoing nitrogen enrichment of the system and declines in light availability. Here, we update trends in eelgrass characteristics (aboveground and belowground biomass, shoot density, percent cover, blade length) for 2008–2010 and compare these to previous datasets (2004–2006). Analysis of quadrat, core, and hand samples collected at 120 transect stations in 4 disjunct eelgrass beds of the estuary showed a distinct, continued reduction in Zostera biomass. In 2010, Z. marina biomass decreased to its lowest level ever recorded in the estuary (mean aboveground biomass = 7.7 g DW m−2; mean belowground biomass = 27.0 g DW m−2). Reduced biomass and other characteristics indicated that eelgrass beds had not recovered from previous reductions observed 2004–2006. The rate of decline was related to nutrient loading and associated symptoms of eutrophication. Additionally, the rate of degradation changed over time. The decline in plant parameters was evident in all of the eelgrass beds investigated, indicating that an estuary-wide stressor was responsible.

a b s t r a c t 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