Comparing the biogeochemical functioning of two arid subtropical coastal lagoons: the effect of wastewater discharges

Abstract

Nutrient flux, net metabolism, and N 2 fixation and denitrification processes were estimated and compared in two semi-arid subtropical coastal lagoons in the Gulf of California: El Soldado (ES), where no wastewater is discharged, and El Rancho (ER), where shrimp farm effluents are regularly discharged. Biogeochemical processes were evaluated with the LOICZ model. Flushing time was <2 days in both systems. Nutrient fluxes were higher in ER than in ES and both systems acted as nutrient sinks for most of the year. ER showed a larger nutrient flow rate in the summer and autumn due to the input of shrimp-farm effluents. Nitrogen fluxes increased in both ER and ES in the winter in response to the increased nutrient supply from coastal upwellings. ER and ES both showed autotrophic metabolism and N 2 fixation in the spring, autumn, and winter, but heterotrophic metabolism and denitrification in the summer. Denitrification dominated in ER (−2.21 mmol m 2 day −1 ) and values were higher than those estimated in ES (−0.45 mmol m 2 day −1 ). The comparative analysis between ES and ER evidenced the significant changes in its biogeochemical performance caused by the input of anthropogenic nutrients, and can orient the environmental management of coastal lagoons.

Hydrology, biogeochemistry and metabolism in a semi-arid mediterranean coastal wetland ecosystem

“…The high nutrients load, which cannot be consumed by primary production due to poor climatic conditions, is released to the atmosphere in the form of N 2 losses 31 . This highlights the role of coastal ecosystems in biological cycling at local, regional, and global scales, and their responses to excess nitrogen in addition to nutrient cycling 82 .…”

“…Likewise, this indicates the dominance of heterotrophic metabolism, during both seasons, which is similar to the Lagoon of Venice, Sacca di Goro, and Stagnone di Marsala 28 . The dominance of this process, which is more obvious in summer (− 693.50 mmol C m −2 yr −1 ) than in winter (− 182.50 mmol C m −2 yr −1 ), may be explained by the warm water conditions that favor the bacterial activity and the oxidation of the organic matter 82 . On the other hand, other watersheds located in European regions revealed seasonal patterns of net metabolism, with the predominance of autotrophic metabolism in winter as compared to a dominance of heterotrophic metabolism in summer 28 .…”

“…The predominance of the nitrogen fixation process in winter, in Ichkeul Lake (14.60 mmol N m −2 yr −1 ) was similar to that found in Marinello-Verde (14.60 mmol N m −2 yr −1 ), but lower compared to Sacca di Goro (916 mmol N m −2 yr −1 ), Orbetello Lagoon (1347 mmol N m −2 yr −1 ) and S'Ena Arrubia (767 mmol N m −2 yr −1 ) 28 . The high N 2 fixation in winter is a source of nitrogen that will be consumed in the system to boost the production 82 . Contrary to summer, the denitrification processes are mostly predominant 28 and were also observed in various lagoons in Italy with seasonal denitrification patterns and subjected to high material loading during the warm season 82 , 83 .…”

“…The high N 2 fixation in winter is a source of nitrogen that will be consumed in the system to boost the production 82 . Contrary to summer, the denitrification processes are mostly predominant 28 and were also observed in various lagoons in Italy with seasonal denitrification patterns and subjected to high material loading during the warm season 82 , 83 . Similar results were reported for these lagoons as well as a strong correlation between denitrification and oxygen demand, and between denitrification and relatively high temperature rates.…”

Estado trófico, dinámica de nutrientes y metabolismo neto de una laguna costera subtropical (Golfo de California) receptora de aguas residuales

“…En la costa este del Golfo de California existen lagunas costeras asociadas a sistemas deltaicos en los que se realizan actividades agrícolas y camaro-nícolas; también se han desarrollado e incrementado asentamientos humanos que en conjunto generan aguas residuales cuyo destino son las lagunas costeras (Ruiz-Ruiz et al 2017, Medina-Galván et al 2021. Esto implica efectos potenciales adversos a las funciones ecológicas y los servicios que dichos ecosistemas costeros brindan a la sociedad.…”