Spatial and temporal heterogeneity of rainfall inorganic ion composition in northeastern Puerto Rico

TitleSpatial and temporal heterogeneity of rainfall inorganic ion composition in northeastern Puerto Rico
Publication TypeBook Chapter
Year of Publication2013
AuthorsMedina, E, González, G, Rivera, MM
Book TitleEcological Bulletins 54: Ecological gradient analyses in a tropical landscape
PublisherJohn Wiley & Sons
Accession NumberLUQ.1107
Keywordswater chemistry

We measured the ion composition of rainfall collected in stations located at different elevations in northeastern Puerto Rico to explore relationships between rainfall volume and distribution, and influence of marine aerosols on ion composition. Rainfall collected during the last two weeks of each month between February and December 2009 at different altitudes from sea level to 1000 m a.s.l., was analyzed by ion chromatography for Cl–, SO42–, Br–, NO3–, Na+, K+, Mg2+, Ca2+, and NH4+. Electrical conductivity was inversely related to rainfall volume following a power relationship. Conductivity varied little for rainfall above 100 mm. Upper montane stations showed smaller conductivity and variability than lowland stations. Na+ and Cl– accounted for the largest ion fraction in all rainfall stations, and were highly correlated indicating strong influence of marine aerosols. Cl–/Na+ and SO42–/Na+ ratios in rain water did not vary significantly with altitude, but other ion/Na+ ratios showed significantly higher values in rainfall stations located below 600 m a.s.l., indicating contributions of different aerosol sources. All stations had several times larger K+/Na+, Ca2+/Na+, and SO42–/Na+ ratios (μeq l–1), than the marine reference value, a result requiring confirmation with continued measurements. Comparison with previous studies in the Luquillo Experimental Forest showed that volume-weighted ion concentrations measured in the lower montane stations during 2009 (200–500 m a.s.l.) were similar to those of Bisley watershed and higher than those of El Verde station. Ion concentrations measured in rainfall from seven stations at and above the average cloud formation level (600 m a.s.l.) are much lower than those reported by a previous report from Pico del Este. Results emphasize the need to continue routine analysis of rainfall chemistry as a mean to monitor changes in element supply to terrestrial ecosystems.