Cattail eradication effects on decomposition in a seasonally dry tropical wetland

Background/Question/Methods

In Palo Verde National Park, Costa Rica, increasing dominance of the native cattail Typha domingensis has prompted management efforts to reduce cattail coverage to facilitate migratory and resident waterfowl populations (i.e., Black-Bellied Whistling Duck).  Consequently, large areas of open water are created within the wetland complex and are colonized by a variety of macrophyte species, including the invasive water hyacinth Eichhornia crassipes. 

Given that decomposition of plant material is an important source of energy and nutrients in freshwater wetlands, this study aimed to investigate cattail management effects on wetland decomposition dynamics by examining decomposition of Typha domingensis (TD) and Eichhornia crassipes (EC).  10-g of air-dried TD and EC litter in one of two states (freshly senesced and dry, dead litter from the previous wet season [past season]) was placed into 3-mm mesh plastic bags.  Bags were attached to posts within one of two habitat types (open water habitat and Typha-dominated habitat [N = 5]), and decomposition bags from each litter type and habitat were collected 7, 14, 34, 76 and 134 d after initial placement on 1 June 2009.  Upon collection, mass loss, changes in tissue chemistry (i.e., C:N, total phenolics, tannins, and lignins), and associated macroinvertebrate communities were determined.

Results/Conclusions

Decomposition rates were estimated by fitting the exponential decay model to mass loss data and examining litter species, litter state and habitat effects on the decay constant k. Although no differences were detected in decomposition rates between habitat types, rates were reduced in TD litter compared to EC litter and were reduced for EC litter from the past season compared to freshly senesced litter; however, litter state had no effect on TD litter decomposition rates (litter species: P = 1.4 X 10^-9; litter state: P =  0.03; habitat = 0.86).  Patterns of lignin content correlated with decomposition rates.  Removal of TD has clear consequences for decomposition dynamics within the Palo Verde wetland, and these alterations in decomposition could affect wetland food webs.