Terrestrial litterfall is a well-documented subsidy of nutrients and organic matter to adjacent aquatic ecosystems. Nitrogen-fixing plants increase nutrient dynamics via nitrogen (N) - rich litterfall in both terrestrial and aquatic ecosystems, and the effects are often more pronounced when areas lacking native N2-fixers are invaded. This study examined differences in organic matter and nutrient inputs from the invasive, N2-fixing tree, Prosopis pallida, and the native, non N2-fixing tree, Thespesia populnea, to determine effects on anchialine ponds on Hawai`i Island's leeward coast. My objectives were to quantify: 1) tree basal area and density surrounding the ponds, 2) quality and quantity of P. pallida and T. populnea litter inputs, 3) inorganic N content of soil surrounding the ponds, 4) leached nutrients from P. pallida and T. populnea leaf litter. These response variables were then compared to water nutrient concentrations (i.e., phosphate, nitrate, ammonium, dissolved organic carbon (C), and total dissolved N and phosphorus (P)) in the ponds of interest. Basal area, density, litterfall mass, total N and C inputs, and leachate values were similar between pond types categorized as P. pallida – or T. populnea – dominated. Foliar N concentrations were 28 percent higher in P. pallida – dominated ponds compared to T. populnea – dominated ponds, but foliar P concentrations were three times greater in T. populnea ponds than P. pallida ponds. Total P inputs were greater beneath T. populnea ponds and there was a positive correlation between T. populnea size and abundance and pond water phosphate concentrations. These results suggest that the N if influencing water quality in Hawaiian anchialine ponds more than the invasive N2-fixing species, although high background water nutrient levels may be inhibiting our ability to detect any significant impacts. The transfer of T. populnea's P-rich litter to pond water appears to have a strong influence on ecosystem functioning.
|Commitee:||Hughes, R. Flint, Wiegner, Tracy|
|School:||University of Hawai'i at Hilo|
|Department:||Tropical Conservation Biology and Environmental Science|
|School Location:||United States -- Hawaii|
|Source:||MAI 52/04M(E), Masters Abstracts International|
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