Spray water volume and chemistry from the Ice Storm Experiment (ISE) at the Hubbard Brook Experimental Forest

The volume of water applied per plot was calculated as the product of application time and water flow (302.8 L/min). Two hoses sprayed water simultaneously and we estimated that 90% of the spray was applied inside the plot. To construct chemical budgets for the treatments, a 60 ml aliquot of Hubbard Brook stream water was collected prior to each icing, and analyzed for sulfate (SO4), nitrate (NO3) and chloride (Cl) on a Metrohm® Ion Chromatograph; calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) on an Agilent® 730 ICP optical emission spectrometer; dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) on a Shimadzu® TOCV with a TNM-1 nitrogen (N) detector; and ammonium (NH4) by colorimetry on a SEAL Analytical AQ2 discrete analyzer at the Louis C<emphasis role="strong">.</emphasis> Wyman Forest Sciences Laboratory, Durham, NH. Dissolved organic N (DON) was calculated as the difference between TDN and inorganic N (NO3-N + NH4-N). Total mass of elements applied to the canopy as iced ‘precipitation’ was calculated as the ‘precipitation’ chemistry from the stream aliquot multiplied by the ‘precipitation’ volume for each plot.每个样地的施水体积通过施水时长与水流速率（302.8 L/min）的乘积计算得到。本实验采用两根软管同时喷水，经估算，90%的喷洒水量均落在样地覆盖范围内。为构建各处理组的化学物质收支预算，每次结冰处理前均采集60 mL哈伯德布鲁克（Hubbard Brook）溪流水样作为等分试样，随后在路易斯·C·怀曼（Louis C. Wyman）森林科学实验室（新罕布什尔州达勒姆市）完成以下指标检测：采用Metrohm®离子色谱仪（Ion Chromatograph）检测硫酸盐（SO₄）、硝酸盐（NO₃）与氯化物（Cl）；采用Agilent® 730型电感耦合等离子体光发射光谱仪（ICP optical emission spectrometer）检测钙（Ca）、镁（Mg）、钾（K）与钠（Na）；采用搭载TNM-1氮检测器的Shimadzu®总有机碳总氮分析仪（TOCV with TNM-1 nitrogen detector）检测溶解性有机碳（Dissolved Organic Carbon, DOC）与总溶解氮（Total Dissolved Nitrogen, TDN）；采用SEAL Analytical AQ2型离散式分析仪通过比色法检测铵态氮（NH₄）。溶解性有机氮（Dissolved Organic Nitrogen, DON）通过总溶解氮与无机氮（NO₃-N + NH₄-N）的差值计算得到。施加至林冠的结冰模拟“降水”中各元素的总质量，通过对应样地的溪流等分试样的“降水”化学浓度，乘以该样地的“降水”体积计算得出。