Arsenic and phosphorus in seagrass leaves from the Gulf of Mexico

Arsenic is a common contaminant in the marine environment, but little is kn own about arsenic in seagrasses. Arsenate is taken up by the phosphate upta ke systems of plants, and there is often a relationship between P availabil ity and As uptake. We sampled green leaves of the seagrass Thalassia testud inum from six estuaries in the Gulf of Mexico to document the As content of seagrasses and to determine the relationships between P availability and A s. Arsenic content of seagrasses was generally lower than literature values of other marine primary producers. Arsenic content varied from 0.90 to 3.3 6 ppm and phosphorus content varied from 544 to 6294 ppm, and there were si gnificant differences among the estuaries studied. Nutrient stoichiometry ( N:P) indicated that there were differences in P availability among estuarie s: Charlotte Harbor had high P availability, while St. Joseph Bay and Flori da Bay were P-limited. The Homosassa River, the Anclotte Estuary and Tampa Bay had intermediate P availability. When data from all estuaries were pool ed, there was a significant, negative relationship between P and As content , as predicted by the model of competitive uptake of As and P. However, mor e extensive sampling within one estuary (Florida Bay) showed a significant positive relationship between P and As, suggesting that factors other than strict competitive uptake kinetics influence the relative content of As and P. We suggest that the P and As availability ratio in estuaries, and there fore in the seagrasses that inhabit them, is largely controlled by the rela tive importance of freshwater and marine inputs of the two elements. (C) 20 01 Elsevier Science B.V. All rights reserved.