Benthonic foraminifera and geochemical tracers as indicators of the enviromental health of La Paz lagoon, B.C.S.

BENTHONIC FORAMINIFERA AND GEOCHEMICAL TRACERS AS INDICATORS OF THE ENVIROMENTAL HEALTH OF LA PAZ LAGOON, B.C.S.

 

Geological Oceanography.

Magallanes Cordova Karla Grisel¹, Sánchez González Alberto².

¹ Faculty of Marine Biology, Universidad Autónoma de Baja California Sur, La Paz, B.C.S., ²Centro Interdisciplinario De Ciencias Marinas del Instituto Politécnico Nacional, La Paz, B.C.S.

Kama_22@alu.uabcs.mx, alsanchezg@ipn.mx

 

Abstract. The health of transitional marine environments can often be compromised by inputs of particulate and dissolved material from runoff originating in urban settlements adjacent to coastal zones. In the present study, the abundance of benthic foraminifera was analyzed, the mean grain size was determined, and the contents of organic carbon and calcium carbonate were quantified in two sediment cores collected from the La Paz Lagoon, with the aim of inferring the environmental health conditions of the area. The absence of benthic foraminifera in both sediment cores may be associated with unfavorable environmental conditions. Organic carbon content ranged from 0.2 to 1.1%, showing a decrease with increasing sediment depth. Calcium carbonate content ranged from 0.3% to 0.9%, with variations of approximately 0.20% throughout the core depth. Mean grain size showed a predominance of fine sands (60%–80%). Mean grain size exhibited a decrease from the base to the upper part of both cores. The absence of benthic foraminifera suggests unfavorable environmental conditions and is associated with the decrease in organic carbon and calcium carbonate values, indicating that their availability may not be sufficient to support benthic fauna. A significant reduction is evident compared to the results obtained in 2024 by Sánchez and Gómez. The predominant sediments are fine sand with little silt, which have a reduced capacity to retain organic matter, thereby affecting the feeding of these organisms and confirming the low sedimentary quality. The current absence of foraminifera indicates that conditions have worsened beyond the tolerance of stress-related species such as the genera Ammonia and Elphidium, which previously accounted for more than 80% of dominance.

 

Keywords: Organic carbon, Calcium carbonate, Sediment, Cores, Isotopes.