Controls on herbaceous litter decomposition in the estuarine ecotones of the Florida everglades

The effects of nutrient availability and litter quality on litter decomposition were measured in two oligotrophic phosphorus (P)-limited Florida Everglades estuaries, United States. The two estuaries differ in that one (Shark River estuary) is directly connected to the Gulf of Mexico and receives marine P, while the other (Taylor Slough estuary) does not receive marine P because Florida Bay separates it from the Gulf of Mexico. Decomposition of three macrophytes, Cladium jamincense, Eleocharis spp., and Juncus roemerianus, was studied using a litter bag technique over 18 mo. Litter was exposed to three treatments: soil surface + macroinvertebrates (= macro), soil surface without macroinvertebrates (= wet), and above the soil and water (= aerial). The third treatment replicated the decomposition of standing dead leaves. Decomposition rates showed that litter exposed to the wet and macro treatments decomposed significantly faster than the aerial treatment, where atmospheric deposition was the only source of nutrients. Macroinvertebrates had no influence on litter decomposition rates. C. jamaicense decomposed faster at sites with higher P, and Eleocharis spp. decomposed significantly faster at sites with higher nitrogen (N). Initial tissue C : N and C : P molar ratios revealed that the nutrient quality of litter of both Eleocharis spp. and J. roemerianus was higher than C. jamaicense, but only Eleocharis spp. decomposed faster than C jamaicense. C. jamaicense litter tended to immobilize P, while Eleocharis spp. titter showed net remineralization of N and P. A comparison with other estuarine and wetland systems revealed the dependence of litter decomposition on nutrient availability and litter quality. The results from this experiment suggest that Everglades restoration may have an important effect on key ecosystem processes in the estuarine ecotone of this landscape.