doi: 10.1016/j.marenvres.2018.01.003. Epub 2018 Jan 8.
Indicators of nutrient pollution in Long Island, New York, estuarine environments
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- PMID:29373137
- PMCID: PMC5937021
- DOI: 10.1016/j.marenvres.2018.01.003
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Indicators of nutrient pollution in Long Island, New York, estuarine environments
Elizabeth Burke Watson et al. Mar Environ Res.2018 Mar.
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Abstract
Roughly eight million people live on Long Island, including Brooklyn and Queens, and despite improvements in wastewater treatment, nearly all its coastal waterbodies are impaired by excessive nitrogen. We used nutrient stoichiometry and stable isotope ratios in estuarine biota and soils to identify water pollution hot spots and compare among potential indicators. We found strong gradients in δ15N values, which were correlated with watershed land cover, population density, and wastewater discharges. Weaker correlations were found for δ13C values and nutrient stoichiometric ratios. Structural equation modeling identified contrasts between western Long Island, where δ15N values depended on watershed population density, and eastern Long Island where δ15N values reflected agriculture and sewage discharges. These results illustrate the use of stable isotopes as water quality indicators, and establish a baseline against which the efficacy of strategies to reduce nutrients can be measured.
Keywords: Denitrification; Eutrophication; Pollution monitoring; Stable isotope; Urbanization; Water treatment.
Copyright © 2018 Elsevier Ltd. All rights reserved.
Figures
Map of Long Island showing sampling locations, permitted wastewater treatment outfalls (in millions of gallons per day) (NYDEC 2004), population density in people per square km (US Census 2016), and dominant 2011 land cover type (Homer et al. 2015). Numbers for research sites are listed in Table 1. Counties are shown in bold, water bodies in italics.
Dendrogram of hierarchical cluster analysis based on average linkages of squared Euclidean distances.
Correlation matrix showing inter-relationships between δ15N and δ13C values and molar nutrient stoichiometric ratios in estuarine biota. Where Pearson product-moment correlation coefficients were found to be significant at thep<0.01 level, they are shown in bold. Where coefficients were not found to be significant at thep<0.05 level, they were listed as ‘NS’ or non-significant.
(a) Spatial patterns in stable nitrogen isotope ratios across Long Island, including the NYC boroughs of Brooklyn and Queens in soils, macrophytes, snails, and fish. (b) spatial patterns in stable carbon isotope values.
(a) Spatial patterns in stable nitrogen isotope ratios across Long Island, including the NYC boroughs of Brooklyn and Queens in soils, macrophytes, snails, and fish. (b) spatial patterns in stable carbon isotope values.
Differences in stoichiometric and stable isotope ratios in estuarine biota along different waterbodies. Analysis of variance indicated statistically significant differences between sites for δ15N for soil (F7,37= 9.841;p<0.001), macrophytes (F6,35= 5.941;p<0.001), snails (F6,34= 5.945;p=0.002), and fish (F6,36= 6.015;p<0.001), and for δ13C for macrophytes (F6,35= 4.547;p=0.02), snails (F6,34= 3.280;p=0.01), and fish (F6,36= 6.377;p<0.001), although not for molar C:P, C:N, or N:P ratios for soil or macrophytes, nor δ13C values for soils. Box and whisker plots denotes range (whiskers), interquartile range (boxes), and median (vertical line). Results of LSD post-hoc tests are denoted by letters on the figures, with different letters signifying statistically significant differences between sites.
Within-site and season variability in macrophyte δ15N and molar C:N ratios. Within-site variability samples were collected in August 2014, and plots show boxes that encompass minimum and maximum observations and all observed values as lines. Seasonal samples were collected across years: May and July samples were collected in 2013, August samples were collected in 2014, and October samples were collected in 2012. Seasonal variability plots are labeled BB (Black Bank, Jamaica Bay), EC (East Creek, Long Island Sound), FC (Frost Creek, Long Island Sound), HC (Hubbard Creek, The Peconic Bays), and BC (Bass Creek, Shelter Island Sound). For seasonal variability in macrophyte C:N ratios, different letters reflect differences between sampling dates. Station locations are given in Table 1.
Initial hypothesized model to predict change in stable nitrogen isotope signature in estuarine biota as a function of watershed characteristics. Arrows show directionality between independent and predictor variables. Ovals represent latent variables, and variables in rectangles were measured. Small arrows denote measurement error.
This model reflects observed dependencies between watershed characteristics and estuarine soils and biota. Values of path coefficients in bold represent relationship variables in the western Long Island model, while coefficients in italics represent relationship variables for the eastern Long Island model. Dashed lines and dashed box represents variable present in the western Long Island model only. Zero values represent path restrictions present in western Long Island model.
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