Spatial and temporal variation of the δ15N in Thalassia testudinum in the Mexican Caribbean (2009–2017)

Abstract

Wastewater pollution in seagrass has been documented for decades. In areas where baseline data are lacking, such as the Mexican Caribbean, the δ15N of seagrass can provide information on status and trends. The aims of this study were to determine the spatial and temporal variation in δ15N values of T. testudinum from 2009 to 2017, to explore the nature and causes of isotopic variability, which must be fully understood, and to examine how isotopic variability is linked to wastewater on the coast. Samples of T. testudinum were collected during 2011–2017 in Cancún and from 2009 to 2017 in Mahahual, and analysed on a mass spectrometer. The δ15N values in Cancún (9.0±1.3 ‰) were significantly (P<0.005) higher than those in Mahahual (1.9±0.9 ‰). Our results reflect the continuous supply of wastewater as a source of 15N in Cancún and the atmospheric deposition of dissolved inorganic nitrogen from uncontaminated groundwater in Mahahual. Mahahual is an ideal site to continue environmental monitoring of the healthy seagrass in the southern Mexican Caribbean. Meanwhile, measures on the treatment and final disposal of wastewater in Cancun must be addressed with a great priority.

Variabilidad espacio-temporal del nitrógeno en hojas de Thalassia testudinum en el Caribe mexicano

“…Sin embargo, la condición oligotrófica del Caribe mexicano se ha ido perdiendo en las últimas décadas, debido a la presión antropogénica asociada principalmente con el desarrollo turístico y el crecimiento poblacional de la región que demandan cada vez más bienes y servicios (Guimarais et al, 2021). En algunas regiones costeras del Caribe mexicano, la concentración del NID es >1 μM, sobrepasando con mucho la naturaleza oligotrófica de las praderas de T. testudinum (Camacho-Cruz et al, 2020;Velázquez-Ochoa and Enríquez, 2023). Las únicas fuentes de NID son la fijación de nitrógeno y las descargas de aguas residuales domésticas y turísticas, siendo esta última fuente la responsable del incremento de NID (Sánchez et al, 2020).…”

“…En algunas regiones costeras del Caribe mexicano, la concentración del NID es >1 μM, sobrepasando con mucho la naturaleza oligotrófica de las praderas de T. testudinum (Camacho-Cruz et al, 2020;Velázquez-Ochoa and Enríquez, 2023). Las únicas fuentes de NID son la fijación de nitrógeno y las descargas de aguas residuales domésticas y turísticas, siendo esta última fuente la responsable del incremento de NID (Sánchez et al, 2020).…”

Isotopic niches of juvenile and adult green turtles (Chelonia mydas) in feeding and nesting areas in Brazil, southwestern Atlantic Ocean

“…If very different values of d 15 N are found in different regions for primary producers, consumers will also reflect these different values between these regions, since they are enriched in 15 N in relation to their diet (Minagawa and Wada, 1984). Furthermore, sources of nitrogen reaching the sea can alter the d 15 N baseline values of marine biota, due to land runoff, atmospheric deposition, NO 3 and N 2 (Minagawa and Wada, 1984;Sańchez et al, 2020). Variations in d 13 C values are caused by temperature, carbon dioxide concentration in surface water and the differences in plankton synthesis or metabolism (Rubenstein and Hobson, 2004).…”

Translating seagrass science into action

“…Their data and models suggest that carbon sequestration may be lower than previously thought, and they highlight the need for greater certainty regarding model assumptions that are key to understanding how seagrasses can be part of a solution to climate change. Sánchez et al (2020) and Seng et al (2020) investigate issues of environmental quality: a well-established pollution issue (nitrogen rich wastewater), and an emerging one (microplastic pollution). Sánchez et al (2020) used d 15 N to determine the presence of nitrogenous nutrients of anthropogenic origin in Thalassia testudinum collected from two sites in the Mexican Caribbean (Cancún and Mahahual).…”

“…Sánchez et al (2020) and Seng et al (2020) investigate issues of environmental quality: a well-established pollution issue (nitrogen rich wastewater), and an emerging one (microplastic pollution). Sánchez et al (2020) used d 15 N to determine the presence of nitrogenous nutrients of anthropogenic origin in Thalassia testudinum collected from two sites in the Mexican Caribbean (Cancún and Mahahual). They found strong evidence for tourism driven wastewater as a source of d 15 N at Cancún and encourage action to be taken to improve water treatment and disposal.…”