Evidence of hypoxia in the eastern coast of the Gulf of California as induced by stable nitrogen isotopes in surface sediments

Sánchez, Alberto; Aguíñiga‐García, Sergio; Rey-Villiers, Néstor

doi:10.1016/j.csr.2022.104716

Cited by 5 publications

(3 citation statements)

References 52 publications

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“…The d 15 N values cannot distinguish where denitrification is occurring, whether during N transport from the watershed or local processing within the estuary water column and sediment. Furthermore, denitrification is an anaerobic process, so hypoxia of the water column associated with eutrophication and hypoxic sediments increase d 15 N values (Ganeshram et al, 2000;Sańchez et al, 2022). Significant fractionation also occurs during nitrate uptake by biological assimilation in the estuary, therefore incomplete nitrate utilization would result in isotopically lighter d 15 N in organic matter that is then incorporated into sediments (Altabet, 2001).…”

Section: Limitations and Complexities Of Isotopesmentioning

confidence: 99%

“…Therefore, in areas of the modern estuary with high nitrate concentrations, incomplete nitrate utilization may drive a water column d 15 N signature that is even higher than represented in the sediments (White et al, 2013). Finally, degradation of N within the sediment layers over time increases d 15 N deeper in the core (Sańchez et al, 2022). We observed a trend of increasing d 15 N in modern sediments, opposite of the trend imparted by diagenesis, so the change may be even more pronounced than observed in sediment timeseries.…”

Section: Limitations and Complexities Of Isotopesmentioning

confidence: 99%

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Use of historical isoscapes to develop an estuarine nutrient baseline

Champlin,

Woolfolk,

Oczkowski

et al. 2023

Front. Mar. Sci.

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Coastal eutrophication is a prevalent threat to the healthy functioning of ecosystems globally. While degraded water quality can be detected by monitoring oxygen, nutrient concentrations, and algal abundance, establishing regulatory guidelines is complicated by a lack of baseline data (e.g., pre-Anthropocene). We use historical carbon and nitrogen isoscapes over ~300 years from sediment cores to reconstruct spatial and temporal changes in nutrient dynamics for a central California estuary, Elkhorn Slough, where development and agriculture dramatically enhanced nutrient inputs over the past century. We found strong contrasts between current sediment stable isotopes and those from the recent past, demonstrating shifts exceeding those in previously studied eutrophic estuaries and substantial increases in nutrient inputs. Comparisons of contemporary with historical isoscapes also revealed that nitrogen sources shifted from a historical marine-terrestrial gradient with higher δ15N near the inlet to amplified denitrification at the head and mouth of the modern estuary driven by increased N inputs. Geospatial analysis of historical data suggests that an increase in fertilizer application – rather than population growth or increases in the extent of cultivated land – is chiefly responsible for increasing nutrient loads during the 20th century. This study demonstrates the ability of isotopic and stoichiometric maps to provide important perspectives on long-term shifts and spatial patterns of nutrients that can be used to improve management of nutrient pollution.

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Section: Limitations and Complexities Of Isotopesmentioning

confidence: 99%

Section: Limitations and Complexities Of Isotopesmentioning

confidence: 99%

Use of historical isoscapes to develop an estuarine nutrient baseline

Champlin,

Woolfolk,

Oczkowski

et al. 2023

Front. Mar. Sci.

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“…While increased temperature positively affects digenean transmission, other local factors may be more critical, so latitudinal gradients in infection levels may not be observed [43]. The eastern coast of the Gulf of California has spatially distinct environmental conditions influenced by agriculture, mariculture, upwellings, seasonal currents, river discharges, and hypoxia [44,45]; these environmental factors along the shallow coastal waters might influence host-parasite interactions differently, thereby making noticeable spatial patterns that are challenging to observe.…”

Section: Infection-level Changesmentioning

confidence: 99%

Looking for Parasites as Potential Biological Tags for Pacific Thread Herring, Opisthonema libertate (Günther, 1867) (Clupeiformes, Dorosomatidae), in the Gulf of California

López-Moreno,

Vallarta-Zárate,

Marín-Enríquez

et al. 2023

Fishes

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The Pacific thread herring, Opisthonema libertate, is a fishery resource in the eastern tropical Pacific, yet its population dynamics are poorly understood. The aims of this work were to document the metazoan parasite species in O. libertate from the Gulf of California in Mexico, determine latitudinal changes in their infection levels, and assess their potential as biological tags. Six parasitic species were identified: Myosaccium ecaude and Parahemiurus merus digeneans, Cribromazocraes cf. travassosi and Mazocraeoides georgei monogeneans, Pseudoterranova sp. nematodes, and Lepeophtheirus sp. copepods. The monogenean and copepod species are reported for the first time in O. libertate. Many fish were infected with digeneans, and there was a rare occurrence of other parasites. While the prevalence and median intensity of M. ecaude and P. merus significantly varied among sampling localities, a multivariate analysis revealed a distinct separation between some localities; these results suggest that individual fish form several discrete populations. However, the utility of these parasites as biological tags will be further probed because they cannot satisfy all requirements for good biological tags. The present results might be helpful in complementing other techniques to determine the movement and stock structure of O. libertate, albeit with certain limitations.

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