Identifying nutrient sources to three lagoons at Ofu and Olosega, American Samoa using δ15N of benthic macroalgae

Garrison, Virginia H.; Kroeger, Kevin D.; Fenner, Douglas; Craig, Peter

doi:10.1016/j.marpolbul.2007.08.016

Cited by 9 publications

(3 citation statements)

References 29 publications

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“…Because longer subsurface travel distance may provide increased time for attenuation reactions for nutrients (e.g., denitrification and sorption) the overall distance CGW travels between N-sources and the coast likely plays a role in final SGD nutrient compositions. [35]. Calculated nutrient loads to Oa Bay were significantly lower than in other watersheds, which is a factor of both low concentrations of N in CGW and the watershed's small size (Table 4).…”

Section: Moderately Impactedmentioning

confidence: 89%

Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa

et al. 2019

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Anthropogenic nutrient loading is well recognized as a stressor to coastal ecosystem health. However, resource managers are often focused on addressing point source or surface water discharge, whereas the impact of submarine groundwater discharge (SGD) as a nutrient vector is often unappreciated. This study examines connections between land use and nutrient loading through comparison of four watersheds and embayments spanning a gradient of human use impact on Tutuila, a high tropical oceanic island in American Samoa. In each study location, coastal radon-222 measurements, dissolved nutrient concentrations, and nitrogen isotope values (δ15N) in water and in situ macroalgal tissue were used to explore SGD and baseflow derived nutrient impacts, and to determine probable nutrient sources. In addition to sampling in situ macroalgae, pre-treated macroalgal specimens were deployed throughout each embayment to uptake ambient nutrients and provide a standardized assessment of differences between locations. Results show SGD-derived nutrient flux was more significant than baseflow nutrient flux in all watersheds, and δ15N values in water and algae suggested wastewater or manure are likely sources of elevated nutrient levels. While nutrient loading correlated well with expected anthropogenic impact, other factors such as differences in hydrogeology, distribution of development, and wastewater infrastructure also likely play a role in the visibility of impacts in each watershed.

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Section: Moderately Impactedmentioning

confidence: 89%

Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa

et al. 2019

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“…Whereas the molar C/N ratio of phytoplankton is commonly close to the Redfield ratio (i.e. around 7; Redfield et al 1963, Anderson & Sarmiento 1994, the C/N ratio in benthic macroalgae is higher and more variable due to a higher structural C content or due to N limitation (Garrison et al 2007). Experiments have shown that Enteromorpha intestinalis is capable of storing nitrate and (to a lesser extent) ammonium in its tissues (Cohen & Fong 2005).…”

mentioning

confidence: 97%

Stable isotope variability in a Chilean fjord food web: implications for N- and C-cycles

Mayr

Försterra²,

Häussermann³

et al. 2011

Mar. Ecol. Prog. Ser.

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We analysed carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios of organisms and biogenic tissues from Comau Fjord (southern Chile) to characterise benthic food webs and spatial isotope variability in this ecosystem. These values were intended to serve as a baseline for detecting anthropogenic impacts on Patagonian marine fjord ecosystems in later studies. Benthic macroalgae and invertebrate suspension feeders were primarily considered, with some supplementary data from cyanobacteria, plankton, fish, and coastal vertebrates. Six depth transects typified the lateral salinity gradients from the innermost part of the fjord to its mouth, as well as the vertical density gradients caused by freshwater inflow. Carbon isotope signatures indicated predominant consumption of either CO 2 or HCO 3 -for benthic macroalgal. All CO 2 users belonged to rhodophytes. The δ 15N values of benthic macrophytes decreased with decreasing salinity, both vertically and along the fjord axis. This implies the influence of 15 N-poor terrestrial dissolved inorganic nitrogen (DIN) at these sites. Enhanced influence of freshwater influx also lowered N contents and increased C/N ratios in algal tissues. Exceptionally high macroalgae δ Mar Ecol Prog Ser 428: [89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104] 2011 2007, van Ofwegen et al. 2006, Esteves et al. 2007, Sinniger & Häussermann 2009). The driving forces behind these patterns are not yet fully understood (Fernandez et al. 2000, Escribano et al. 2003. Possible environmental factors affecting biodiversity are specific physical and chemical gradients or highly dynamic nutrient and organic matter fluxes. However, few oceanographic data are available (e.g. Pickard 1971, Silva et al. 1995, Strub et al. 1998). An understanding of the functioning of the Chilean fjord ecosystem is a prerequisite in order to assess the consequences of the intensified exploitation of marine resources and of rapidly expanding aquaculture, the latter adding additional nutrient sources to benthic ecosystems. In addition to species inventories, a deeper understanding of the biogeochemical cycles in Patagonian fjords is the basis for environmental monitoring.Stable isotope methods are frequently applied to characterise marine food webs (Minagawa & Wada 1984, Schoeninger & DeNiro 1984, Bergmann et al. 2009, Steinarsdóttir et al. 2009). The nitrogen and carbon isotopic compositions of natural samples are given as delta values (δ), representing the isotope ratio of the heavy to the light isotope (‰) relative to an international standard and is defined as: δ y X = (R sample / R standard -1) × 1000, with R being the ratio of the heavier to the lighter isotope ( The carbon isotope composition (δ 13 C) of an organism can be used to distinguish isotopically different sources in food webs (DeNiro & Epstein 1978). Minor δ 13 C differences of 0 to 1 ‰ are observed between animals and their food (Peterson & Fry 1987). Thus, the much larger carbon isotope discrepancies between certain groups of prim...

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“…Isotope ratios of both elements usually show a constant change along different trophic levels with a mean trophic split of consumer tissue relative to their food source of around 2.9 to 3.8‰ for δ 15 N values and 0.5 to 1‰ for δ 13 C in marine systems 10, 11, 15, 16. Compared with temperate systems, few stable isotope studies have been conducted in coral reef systems, with most dealing with Scleractinian corals17, 18 and primary producers such as macroalgae,19, 20 seagrasses,21 and cyanobacteria 22. Isotope studies of sediment fauna from coral reefs6, 18, 23, 24 are scarce, and preparation techniques of tissue samples are often unclear and differ between studies.…”

mentioning

confidence: 99%

Effects of acidification on carbon and nitrogen stable isotopes of benthic macrofauna from a tropical coral reef

Kolasinski¹,

Rogers²,

Frouin³

2008

Rapid Comm Mass Spectrometry

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Stable isotope analyses are widely used to determine trophic levels in ecological studies. We have investigated the effects of carbonate removal via acidification on the stable carbon and nitrogen isotopic composition of 33 species of tropical benthic macrofauna, and we report guidelines for standardizing this procedure for higher taxa in tropical coral reef ecosystems. Many tropical benthic invertebrates are small in size, and therefore body tissue isolation (separating organic carbon from inorganic structures) is difficult and time-consuming. Literature reviews of invertebrate studies show a lack of consistent procedures and guidelines for preparation techniques, especially for carbonate removal via acidification of whole individuals. We find that acidification decreases the delta(13)C values of samples containing carbonate, with shifts ranging from 0.21 to 3.20 per thousand, which can be related to CaCO(3) content (assessed by a carbonate proxy), justifying acid pre-treatment. Carbonate-containing taxa benefiting from acidification included Amphinomida, Terebellida (Annelida), Anomura, Brachyura, Caridea, Amphipoda, Tanaidacea (Arthropoda) and Edwardsiida (Cnidaria). The delta(13)C shifts of samples containing no carbonate varied up to 0.02 +/- 0.20 per thousand. As this induced delta(13)C shift was lower than the range of an average trophic level shift (0.5 to 1 per thousand), we conclude that acid pre-treatment is unnecessary. Carbonate-free taxa consisted of Eunicida, Phyllodocida (Annelida) and Mollusca. We note minimal impact of acidification on delta(15)N values except for Brachyura, which showed a shift of 0.83 +/- 0.46 per thousand, which is still lower than a single trophic level shift (2.9-3.8 per thousand). We conclude that for trophic level studies, both the delta(13)C and the delta(15)N of carbonate-rich macrofauna can be determined from the same acidified sample.

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Identifying nutrient sources to three lagoons at Ofu and Olosega, American Samoa using δ15N of benthic macroalgae

Cited by 9 publications

References 29 publications

Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa

Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa

Stable isotope variability in a Chilean fjord food web: implications for N- and C-cycles

Effects of acidification on carbon and nitrogen stable isotopes of benthic macrofauna from a tropical coral reef

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