Collect dryfall and precipitation for analysis of atmospheric input of nutrients to tallgrass prairie.
LOCATION OF SAMPLING STATION
Headquarters weather station (grid C-16).
FREQUENCY OF SAMPLING
Weekly, continuous from August 17, 1982.
VARIABLES MEASURED
1) Amount of precipitation (inches/week), checked against headquarters weighing raingauge.
2) Conductivity of precipitation (fS/cm).
3) pH of precipitation. Analysis at Central Analytical Laboratory, Illinois State Water Survey, Champaign, IL include:
a) Conductivity of precipitation
b) pH of precipitation
c) Concentrations of the following (mg/1): SO4, NO3, NH4, C1, PO4, Na, K, Ca, and Mg.
METHODS
The Aerochem Metrics Wet/Dry collector is equipped with a movable lid and a precipitation sensor that electronically signals the lid to uncover a "wet" side bucket during precipitation events and recover the wet side when precipitation ceases. Every week (Tuesdays), the wet side bucket is replaced with a clean bucket. The previous week's wet bucket is fitted with a clean lid and transported back to campus in a plastic bag and shipping box. On campus, the bucket and lid are weighed (if any precipitation has been collected) and conductance and pH are determined on a 20 mL sub-sample (if more than 70 grams of precipitation was collected). Concurrently, a standard form is completed using the chart from the headquarters raingauge which records precipitation and time of event. The form, and raingauge chart, and bucket are then shipped to the Central Analytical Laboratory. This procedure is followed every week regardless of the amount of precipitation collected. An example of the form and the weighing raingauge and event recorder chart are shown in Fig. 2 and 3. More detailed instructions concerning bucket changing, and pH and conductivity determinations are available in the NADP Field Operators Manual located in Bushnell Rm 215.
Every eight weeks, the dry side bucket is also changed and replaced with a clean bucket. No analysis of dryfall is currently done. An example of the data output by the Central Analytical Laboratory is shown in Fig. 4. As of April 1992, we have requested regular updates of data for our site from the NADP/NTN Coordination Office.
Routine Maintenance:
Weekly, the precipitation sensor should be checked for proper operation (if touched, or if a drop of water is placed on the sensor, the lid should move to uncover the wet side bucket). Also, the sensor should be cleaned when necessary. The underside of the lid should be cleaned every time the dry side- bucket is changed. A clean kimwipe and distilled water should be used. The top of the lid should also be kept clean and free of snow or ice accumulation. During freezing weather, rain/ice storms may cause the lid to freeze to either bucket. The frozen lid must be broken free as soon as possible to avoid burning out the motor on the sampler. Finally, once a year, the foam underside of the lid should be changed. A new seal will be shipped from NADP automatically. Approximately every two to three years NADP will arrange for an inspector to survey the site, calibrate the raingauges, and observe the operator to determine necessary changes in operations. Last site visit was April 14, 1992.
SUMMARY OF ALL CHANGES UP TO 1993
Starting January 26, 1993, a one year study to compare two week collections of precipitation to the on-going weekly collections was initiated at our site. Data will be provided in the same manner as the existing set.