Throughfall samples were constructed of 7.6 cm diameter PVC pipe (79 cm length) with a ~3
cm opening along the length of the top of the collector. Collectors were elevated approximately
35 cm above the ground and angled slightly downwards to promote drainage through a vinyl
tube connected to the lower end of the collector and connected to a 1 L polyethylene bottle.
Collectors were placed directly below the canopy approximately 30 cm from the trunk.
Beginning in 2023, open precipitation samples were collected in a polycarbonate all-weather
rain gauge (10.15 cm funnel diameter). Following collection, samples were filtered through a
0.45-micron syringe filter and refrigerated at 4°C until analysis.
Soluble reactive phosphorus concentrations were determined colorimetrically using a modified
Murphy-Riley method (1). Ammonium concentrations were determined colorimetrically by the
salicylate/nitroprusside method (2). Nitrate and nitrite analysis were determined colorimetrically
using the cadmium reduction method (3). Total organic carbon was determined via high-
temperature combustion (4).
1. U.S. EPA. 1978. Method 365.3: Phosphorous, all forms (colorimetric, ascorbic acid, two
reagent). USEPA.
2. Determination of Ammonia in 10 mM H 3 PO 4 by Flow Injection Analysis. 2017. Quikchem
Method 10-107-06-2-R, Lachat Instruments, Loveland, CO.
3. Determination of Nitrate/Nitrite in Surface and Wastewaters by Flow Injection Analysis”.
Quikchem Method 10-107-04-1-A, Lachat Instruments, Loveland, CO, 2007
4. American Public Health Association, American Water Works Association, Water Environment
Federation. 2017. Standard methods for the examination of water and wastewater. 34rd ed.
Am. Public Health Assoc., 800 I Street, Washington, DC 20001.