MEPS 292:75-83 (2005)  -  doi:10.3354/meps292075

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 (V_max) 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 < 0.01; 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.

KEY WORDS: Acid phosphatase activity · Marsh sediment · Salinity gradient · Estuary