Canopy interactions of rainfall in an off-shore mangrove ecosystem dominated by Rhizophora mangle (Belize)

SummaryBulk precipitation, throughfall and stemflow were collected to study anthropogenic effects on above-ground nutrient cycling in an off-shore mangrove forest (Rhizophora mangle L.) on Twin Cays, Belize. Samples were collected in a nitrogen limited fringe and phosphorus limited dwarf zone, and from an adjacent nitrogen fertilized fringe and a phosphorus fertilized dwarf zone. Inorganic cations and anions, dissolved organic carbon (DOC) and nitrogen (DON) were analysed. Throughfall represented 84% of precipitation volume. Sea salt ions (Cl−, Na+, SO42- and Mg2+) and DOC accounted for the highest proportion of solutes in rainwater, throughfall and stemflow in R. mangle   stands. Non-marine sources dominated the flux of DON, DOC, NO3-, NH4+, and inorganic P (Pi) in bulk precipitation and throughfall and partially contributed to Ca2+ and K+. Deposition ratios (throughfall deposition:bulk deposition) showed that inorganic NH4+, and less so Pi were retained in the canopy of R. mangle from throughfall while all other solutes increased. Canopy leaching contributed in increasing order to net throughfall of Ca2+, Cl−, SO42-/K+, Mg2+ and Na+ but dry deposition dominated the net throughfall flux during the investigated period. Fertilizer treatment and zone did only slightly affect solute concentrations of hot-water extracts of leaves, of throughfall and stemflow in stands of similar stature. While litterfall and primary production have previously been shown to increase substantially upon nutrient enrichment of mangroves we therefore conclude that fertilization, as a surrogate of anthropogenic eutrophication, may not increase nutrient leaching from mangrove canopies, and thus may only have a minor effect on soluble organic matter cycling and inputs into mangrove food webs.