LCZO -- Overland Water Chemistry, Nutrient Fluxes, Throughfall Chemistry, Rainfall Chemistry -- Including weekly bulk rain chemistry -- Bisley -- (1988-2007)

Long-term rainfall and discharge data from the Luquillo Experimental Forest (LEF) were analysed to develop relationships between rainfall, stream-runoff, and elevation. These relationships were then used with a Geographic Information System (GIS) to determine spatially-averaged, mean annual hydrologic budgets for watersheds and forest types within the study area. Model estimates indicate that a total of 3864 mm/yy (444 hm3) of rainfall falls on the forest in an average year. The Tabonuco, Colorado, Palm and Dwarf Forest types receive an estimated annual rainfall of 3537, 4191, 4167, and 4849 mm/yy, respectively. Of the average annual rainfall input, 65% (2526 mm/yr) is converted to runoff and the remainding 35% (1338 mm.yr) is lost from the system by evapotranspiration and other abstractions. In comparison to other tropical forests, the LEF as a whole has more evapotranspiration than many tropical montane forests but less evapotranspiration than many lowland tropical forests.

Dataset Methods:

Field Collection:

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.
Lab Analysis:

Chemistry
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:

(http://luq.lternet.edu/data/lterdb20/metadata/lterdb20.htm).

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).

本研究对来自洛奎罗实验森林（LEF）的长期降雨和径流数据进行了分析，以建立降雨、河流径流和海拔之间的关系。随后，利用地理信息系统（GIS）技术，对这些关系进行了应用，以确定研究区域内流域和森林类型的空间平均年水文预算。模型估算结果显示，在平均年份，森林上方的降雨总量达到3864毫米/年（444立方米）。塔博努科、科罗拉多、棕榈和矮林等森林类型分别接收到的年均降雨量约为3537、4191、4167和4849毫米。在平均年降雨输入中，65%（2526毫米/年）转化为径流，其余35%（1338毫米/年）通过蒸发蒸腾作用和其他吸收作用从系统中流失。与其它热带森林相比，洛奎罗实验森林整体蒸发蒸腾作用高于许多热带山地森林，但低于许多低地热带森林。

数据集方法：

实地采集：

降雨和穿透雨收集
在本研究中，降雨和穿透雨的收集和测量方式与先前发表的出版物（Scatena, 1990; Schellekens et al., 1999; Holwerda, 2006）一致，并在研究期间持续进行。总降雨量在距树冠25米的塔楼上收集，该塔楼位于两个集水区之间，海拔361米。穿透雨通过20至35个随机放置但固定的仪器进行测量，这些仪器分布在集水区的脊梁、山坡、空隙和溪流通道上（Scatena, 1990）。降雨收集器和每个穿透雨收集器都配备有相同的143平方厘米漏斗。在任何给定时间，最多有35个收集器被用于此处呈现的时间序列。在1989年飓风雨果期间，承载气候站和降雨收集器的树冠塔被摧毁，但大多数穿透雨收集器保持完好。被摧毁的收集器被随机重新放置在原始位置10米范围内，穿透雨收集未间断。气象塔也在几个月后得到了更换。

实验室分析：

化学分析
在每次收集过程中，均收集了大量降雨和穿透雨进行化学分析。降雨分析用水来自树冠上方的降雨收集器。穿透雨样本是由八个收集器中收集的水组成的复合样本。这八个穿透雨收集器在研究开始时被选中，因为它们的平均穿透雨体积和电导率与所有瓶子的平均值相似，因此被认为能代表该地点。这些收集瓶每周清洁或更换一次，并包含过滤器以防止青蛙和碎片进入瓶子。

水样在收集当天送达实验室。化学分析的方法与洛奎罗实验森林（LEF）的先前研究（McDowell et al., 1990; McDowell and Asbury, 1994; McDowell, 1998）相同。协议和原始数据可在洛奎罗LTER网页上找到：（http://luq.lternet.edu/data/lterdb20/metadata/lterdb20.htm）。

在实验室中，pH值和电导率按照NADP（1984）和McDowell et al.（1990）指定的程序进行测量。样品使用预先烧毁的玻璃纤维过滤器（Whatman GF/F）进行过滤。直到1997年，样品被冷藏保存以进行分析，其中一部分样品通过硫酸酸化保存以进行铵分析（McDowell et al., 1990）。1997年后，样品被冷冻保存直到分析，除了硅，硅是在冷藏子样中分析的。在研究的头九年，大多数样品在波多黎各大学进行分析。1997年后，所有样品在纽黑文大学进行分析。在整个研究期间，使用分光光度法使用Technicon AA II或Lachat Quickchem分析了硅（磷钼酸盐）、磷（铵钼酸盐）和铵（苯酚次氯酸盐）。1988-1994年使用原子吸收分光光度法分析了阳离子，1994年后使用离子色谱法。阴离子使用离子色谱法进行测量。在1997年之前，使用过硫酸盐消化（McDowell et al., 1987; Solorzano and Sharp, 1980）测量溶解有机碳和氮，1997年后使用高温铂催化燃烧（Merriam et al., 1996）。跨实验室比较和不同方法对样品的分析表明，不同实验室和方法可以获得可比的结果（例如，McDowell et al., 1990; Merriam et al., 1996）。