Influence of pelagic sargassum influxes on the δ15N in Thalassia testudinum of the Mexican Caribbean coastal ecosystem.

The conservation of Mexican Caribbean Ecosystems (MCE) involves ensuring their capacity to provide resources and ecosystem services to society. Monitoring programs are necessary to establish their management and ensure their sustainability. Thalassia testudinum is the community used to determine anthropogenic influence, in which wastewater is the primary anthropogenic nitrogen source. The extensive amount of pelagic sargassum that enters the area and its decomposition may be additional nitrogen sources in MCE. In the present study, the δ15N in T. testudinum was examined from 2009 to 2019 to infer the nitrogen contribution from pelagic sargassum to MCE. T. testudinum δ15N values showed significant depletion from June/October 2014 to 2019 concerning previous periods. Pelagic sargassum was an alternative nitrogen source, and its leaching reduced T. testudinum δ15N values in MCE.

Water quality in the eastern karst region of the Yucatan Peninsula: nutrients and stable nitrogen isotopes in turtle grass, Thalassia testudinum.

Water quality in the Mexican Caribbean is affected by increases in tourism infrastructure and poor wastewater treatment. Additionally, karst geomorphology facilitates the infiltration of organic matter to subterranean water and coastal fresh water that originates from submarine groundwater discharges (SGDs), altering the environment. The tourism infrastructure grows at different rates along the Caribbean coast, characterizing zones with diverse levels of tourism impact. The aim of this work was to measure nutrient concentrations in superficial coastal water and fresh water to evaluate the water quality through different zones along a gradient from intermediate- (Riviera Maya) to low-tourism (Costa Maya) development regions. Furthermore, this study aimed to compare the measured nutrient concentrations with the Mexican ecological criteria of water quality 001/89 (CE-CCA-001/89), detect possible contributions by SGDs, and determine whether the nitrogen (N) sources are anthropogenic using stable nitrogen isotopes in the seagrass Thalassia testudinum. According to the results, nutrient concentrations (ammonium, nitrate, nitrite, and orthophosphate) differed significantly between the Riviera Maya and Costa Maya (P = 0.0001). Sites such as Shambala, Chávez, Tankah, Mahahual 2, Tulum, Akumal, and Xahuayxol exceeded the upper levels set by the CE-CCA-001/89. Tankah, Shambala, and Chávez were influenced by SGDs. The nitrogen isotope ratio in Akumal and Tulum coast water shows that they are under N loading derived to the sewage percentage of δ15N in Akumal, Tulum, and Mahahual, showing that these sites suffer N loading due to sewage. Our study recommends continuous monitoring and coastal characterization to detect SGD and to regulate, treat, and dispose of sewage.