Macroalgae blooms and δ~(15)N in subtropical coastal lagoons from the Southeastern Gulf of California: Discrimination among agricultural, shrimp farm and sewage effluents

摘要

Macroalgae blooms of Gracilaria vermiculophylla, Hypnea spinella and Spyridiafilamentosa have been found in coastal lagoons in the SE Gulf of California. Agriculture, livestock, shrimp and poultry farms and sewage contribute anthropogenic nitrogen to the systems. The δ~(15)N of these sources, water column and macroalgae were studied in order to identify the N supply for macroalgae blooms. δ~(15)N of three species of macroalgae (4.3-13.6‰ were enriched compared to the water column δ~(15)N-NO_3 3.7-6.8‰), probably because of fractioning from the macroalgae. δ~(15)N of POM (1.4-10.3‰) was similar to the water column but the relationship was unclear. Depending on the site, macroalgae showed different δ~(15)N values since some sites receive more or less influence from one given source of the associated watershed, which is reflected in the different δ~(15)N values of the macroalgae of the same system and in the relative contributions of the sources.