Bisley rainfall and throughfall, and chemistry of rainfall and throughfall

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This data set contain summaries and analyses mean of collected weekly measurements expressed as mm per day,  and calculation of fluxes, rates and means calculated after water chemistry analyses are conducted. Rainfall and throughfall are collected weekly at the Bisley LEF site. These data sets begin March 1988 and ends December 2003.

Rain and throughfall samples are the total catch for the week, and are exposed to field conditions for that time. No event sampling is conducted on a routine basis. Rainfall Collected in Bisley (RCB) are bulk or always-open collectors that receive dry deposition by sedimentation.

All samples are measured for pH and conductivity, and then filtered (pre-combusted Whatman GF/F glass fiber filter) prior to further analysis. From 1983-1994 samples were cooled and returned to the San Juan chemistry laboratory for analysis. During those years, samples for NH4 and NO3 analyses were refrigerated continuously until analysis. Sub samples for NH4 analysis were also preserved with 1 molar HCl. From 1994 on, samples for NH4 and NO3 were frozen until analysis, were not acidified, and all analyses were conducted at the University of New Hampshire.

Nutrient fluxes in rainfall and throughfall were measured weekly in a mature subtropical wet forest in NE Puerto Rico over a 15-year period that included the effects of five hurricanes and several prolonged droughts. Annual inputs of K, Ca, Mg, Cl, Na, and SO4-S are similar to those reported from other marine-influenced tropical forests. Rainfall input of nitrogen is comparatively low and reflects the relative isolation of the air shed. Mean annual rainfall and throughfall were 3482 and 2131 mm yr-1 respectively. On average, rainfall, throughfall, rainfall pH, and rainfall flux NH4-N and NO3-N had small but significant decreases throughout the study period. More nutrients fluxes had seasonal differences in rainfall (6 out of 12) than throughfall (4 out of 12). All volume weighted enrichment ratios calculated for the 15-year period were greater than one. However, median weekly enrichment ratios were less than 1 for sea salts and dissolved organic carbon and between 1 and 2 for Mg, Ca, SiO2 and SO4-S. In contrast, median weekly enrichment ratios were greater than 10 for NH4-N, PO4-P, and K and reflect biological enrichment within the canopy. Droughts reduced enrichment ratios of cations and sea-salts, but increased enrichment ratios for NH4-N, PO4-P and K. In the weeks following hurricanes relative throughfall tends to be higher and enrichment ratios tend to be lower. These long-term observations indicate that physical and biological processes associated with water passing through the canopy act to buffer internal nutrient cycles from inter-annual, and seasonal variations in rainfall inputs.

Date Range: 
1988-03-08 00:00:00 to 2015-10-27 00:00:00

Publication Date: 

2011-06-07 00:00:00

Additional Project roles: 

Name: Eda Melendez-Colom Role: Data Manager
Name: Ariel Lugo Role: Associated Researcher
Name: Carlos Estrada-Ruiz Role: Associated Researcher
Name: William H. McDowell Role: Associated Researcher


Rainfall and throughfall collection
The rainfall and throughfall measured in this study were collected and measured in the same manner for the duration of the study, and in accordance with our previous publications (Scatena, 1990; Schellekens et al., 1999; Holwerda, 2006).  Bulk rainfall and throughfall were collected weekly (i.e. every Tuesday morning) and occasionally before and after major storms.  Total rainfall was collected in a 25 m above canopy walk-up tower that is located on the divide between the two catchments and at an elevation of 361 m above sea level.  Throughfall was measured throughout the watershed using 20 to 35 randomly placed but fixed gauges that were placed across the ridges, hill-slopes, gaps, and stream channels of the watershed (Scatena, 1990).  The rainfall collector and each throughfall collector had identical 143 cm2 funnels.  As many as 35 collectors were operated at any given time for the time series presented here. During Hurricane Hugo in 1989, the canopy tower that held the climate station and rainfall collector was toppled, but most of the throughfall collectors remained intact.  Those that were destroyed were randomly re-located within 10 m of their original site and throughfall was collected without interruptions.  The meteorological tower was also replaced after a few months. 

During every collection, bulk rainfall and throughfall were collected for chemical analysis.  Water for the rainfall analysis was collected from the above-canopy rainfall collector.  The throughfall sample was a composite of water collected in eight collectors.  These eight throughfall collectors were selected at the beginning of the study because their mean throughfall volume and conductivity was similar to the mean of all the bottles and therefore considered representative of the site.  These collection bottles were cleaned or replaced on a weekly basis and contained filters to prevent frogs and litter from entering the bottles. 
Water samples were delivered to the laboratory on the same day they were collected.  Chemical analysis was conducted in the same manner as previous studies of the LEF (McDowell et al., 1990; McDowell and Asbury, 1994; McDowell, 1998).  Protocols and the original data are available on the Luquillo LTER web-page:

In the laboratory, pH and conductivity were measured following the procedures specified by NADP (1984) and McDowell et al., (1990).  Samples were filtered using pre-combusted glass fiber filters (Whatman GF/F).  Until 1997, samples were held refrigerated for analysis, with a sub-sample for ammonium analysis preserved by acidification with sulfuric acid (McDowell et al., 1990).  After 1997, samples were stored frozen until analysis for all constituents except silica, which was analyzed on a refrigerated subsample.   During the first nine years of the study, most samples were analyzed at the University of Puerto Rico.  After 1997, all samples were analyzed at the University of New Hampshire.  Silica (phospho-molybdate), phosphorus (ammonium molybdate), and ammonium (phenol-hypochlorite) were analyzed throughout the study period using spectrophotometric methods using a Technicon AA II or Lachat Quickchem.  Cations were analyzed with atomic absorption spectrophotometry from 1988-1994, and with ion chromatography from 1994 on.  Anions were measured with ion chromatography.  Dissolved organic carbon and nitrogen were measured using persulfate digestion (McDowell et al., 1987; Solorzano and Sharp, 1980) prior to 1997, and with high temperature Pt-catalyzed combustion after 1997 (Merriam et al., 1996).  Cross-lab comparisons and analysis of samples using the different techniques indicated that comparable results were obtained with different laboratories and methods (e.g. McDowell et al., 1990; Merriam et al., 1996).

Rainfall and throughfall fluxes (kg ha-1 day-1) were calculated from weekly concentration values multiplied by the corresponding amount of weekly rainfall or throughfall.



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