Using δ<sup>15</sup>N to Assess Coupling between Watersheds and Estuaries in Temperate and Tropical Regions

Bowen, Jennifer L.; Valiela, Iván

doi:10.2112/05-0545.1

Cited by 24 publications

(14 citation statements)

References 50 publications

(15 reference statements)

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“…1). The surrounding area is subject to different land uses including agriculture and urban development; however, the bay is largely decoupled from the watershed so that nutrient inputs from land are low (Bowen and Valiela 2008). The bay is fringed by mangroves and, to a large extent, the bay floor is covered by seagrasses.…”

Section: Site Descriptionmentioning

confidence: 99%

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass Thalassia testudinum in Jobos Bay, Puerto Rico

Olsen

Valiela

2010

Estuaries and Coasts

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We examined the effect of nutrients and grazers on Thalassia testudinum in Jobos Bay, Puerto Rico by fertilizing sediment and manipulating grazer abundances. Bottom-up effects were variable: Added nutrients did not increase seagrass aboveground biomass, but decreased belowground biomass-perhaps as a result of less biomass being allocated to belowground structures in response to greater nutrient supply in porewater. Experimental fencing of 1.5×1.5 m plots provided shelter that attracted large aggregations of fish, including seagrass herbivores. Seagrass biomass and shoot density decreased with increasing abundance of herbivorous fish, indicating a significant topdown effect. There were interactions between nutrient supply, provision of shelter, and grazing pressure. Fertilization enhanced seagrass %N; however, %N also increased in unfertilized plots that were fenced, most likely due to uptake of N excreted from the large numbers of fish associated with the fences. Only plots where shelter was provided and fertilizer was applied to sediments exhibited evidence of heavy grazing, reducing both seagrass cover and aboveground biomass. In the unfertilized fenced plots, signs of grazing were fewer despite large abundances of fish and enhanced nutritional quality of seagrass leaves. This suggests the possibility that high nutrient availability in sediments lowered concentrations of chemical defense compounds in the seagrass and that cues other than %N may have been involved in stimulating grazing. This study highlights the complexity of bottom-up and top-down interactions in seagrass systems and the important role of refuge availability in shaping the relative strengths of these controls.

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Section: Site Descriptionmentioning

confidence: 99%

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass Thalassia testudinum in Jobos Bay, Puerto Rico

Olsen

Valiela

2010

Estuaries and Coasts

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“…iron, zinc; Manley 1981) for growth and reproductive success, as well as on a source of dissolved inorganic carbon (DIC), such as aqueous CO 2 (CO 2(aq) ) or bicarbonate (HCO 3 -) for photosynthesis (Raven 1970, Raven et al 2008. In nearshore marine systems, the source of essential nutrients and DIC may have multiple origins, including atmospheric, terrestrial, and/or oceanic (Fogel et al 1992, Matsunaga et al 1999, Bowen & Valiela 2008. We focused our attention in this study on the delivery of allochthonous DIC and nitrate (hereafter referred to collectively as subsidies) delivered to nearshore M. pyrifera communities from terrestrial and oceanic sources.…”

Section: Introductionmentioning

confidence: 99%

Correlation between allochthonous subsidy input and isotopic variability in the giant kelp Macrocystis pyrifera in central California, USA

Foley¹,

Koch²

2010

Mar. Ecol. Prog. Ser.

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Isotope values of primary producers can vary greatly across space and time due to changes in physiological status and the source of subsidies used in photosynthesis. Forests of the giant kelp Macrocystis occur in temperate oceans around the world and are positioned at the land -sea interface where they may receive subsidies from terrestrial and open ocean sources. In this study, we investigated the spatial and temporal variability in δ 13 C and δ 15 N values of M. pyrifera over 3 yr in Big Sur, California, USA. During each of those 3 yr, δ 13 C and δ 15 N values of M. pyrifera varied significantly by season, with low values occurring in the spring, and high values in the fall. To examine the possible mechanisms driving this seasonal variability, we used step-wise multiple regression analyses to test whether the variability in kelp isotope values was correlated with the variability in nitrate concentration or the delivery of subsidies via upwelling circulation and river discharge. We found that temporal variation in kelp isotope values was most strongly related to the strength of upwelling and the concentration of nitrate in surface waters. The results of this study increase our understanding of the mechanisms that drive the temporal and seasonal isotopic variability in marine primary producers. This study also highlights the importance of measuring isotope variability at the base of the food chain in order to create more robust trophic predictions.

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“…Tidal marshes provide valuable ecosystem services including carbon cycling, storm surge protection, and nutrient retention ( Bowen and Valiela, 2008 ;Barbier et al, 2011 ) largely due to the presence of macrophytes that tolerate regular fl ooding associated with tides. Cordgrasses in the family Poaceae belonging to the genus Spartina Schreb.…”

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confidence: 99%

Polysaccharide addition effects on rhizosphere nitrogen fixation rates of the California cordgrass,Spartina foliosa

2009

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Using δ¹⁵N to Assess Coupling between Watersheds and Estuaries in Temperate and Tropical Regions

Cited by 24 publications

References 50 publications

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass Thalassia testudinum in Jobos Bay, Puerto Rico

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass Thalassia testudinum in Jobos Bay, Puerto Rico

Correlation between allochthonous subsidy input and isotopic variability in the giant kelp Macrocystis pyrifera in central California, USA

Polysaccharide addition effects on rhizosphere nitrogen fixation rates of the California cordgrass,Spartina foliosa

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Using δ15N to Assess Coupling between Watersheds and Estuaries in Temperate and Tropical Regions

Cited by 24 publications

References 50 publications

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass Thalassia testudinum in Jobos Bay, Puerto Rico

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass Thalassia testudinum in Jobos Bay, Puerto Rico

Correlation between allochthonous subsidy input and isotopic variability in the giant kelp Macrocystis pyrifera in central California, USA

Polysaccharide addition effects on rhizosphere nitrogen fixation rates of the California cordgrass,Spartina foliosa

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Using δ¹⁵N to Assess Coupling between Watersheds and Estuaries in Temperate and Tropical Regions