Distribution of phosphatase activity in marsh sediments along an estuarine salinity gradient

Abstract

Acid phosphatase activity (APA) was measured in intertidal marsh sediments located along the Cooper River estuary, South Carolina, at North Inlet, SC, and in a marsh on the Rowley River, MA. We found that APA increased from 4.3 ± 2.3 to 29.3 ± 18.8 μmol p-nitrophenol released g-1 h-1 with decreasing sediment salinity from 22 g l-1 to 0.1 g l-1. A study of APA kinetics revealed that the maximum specific activity (Vmax) followed the same trend as in situ phosphatase activity. Sediment salinity (p < 0.05; R2 = 0.43) and pH (p < 0.01; R2 = 0.56) were negatively correlated with APA, while soil organic matter (SOM) content (p < 0.01; R2 = 0.57), clay content (p < 0.05; R2 = 0.37) and sediment organic P (SOP) (p < 0.0; R2 = 0.50) were positively correlated. Collectively, these variables accounted for 78 % of the variation in APA (p < 0.05). APA was not significantly correlated with sulfide, NH4+, soluble reactive phosphorus (SRP), sediment total P, the N:P ratio, aboveground biomass, or macro-organic matter content. In salt marsh plots at North Inlet that were experimentally fertilized with N and P, we found that fertilization with only P had no effect on APA, while N-only or N + P fertilization significantly increased APA to 6.4 μmol p-nitrophenol released g-1 h -1 from 1.5 μmol p-nitrophenol released g-1 h -1 in control plots. However, even in the fertilized salt marsh plots, APA was still significantly lower than in freshwater, oligohaline and mesohaline marshes. © Inter-Research 2005.