This data set reports daily estimates of bulk atmospheric deposition from event-based chemistry of precipitation water that was sampled at the Marcell Experimental Forest (MEF) in Itasca County, Minnesota. The data come from sites in two research catchments instrumented for hydrologic monitoring - the meteorological station located in an upland clearing in the S2 research catchment (S2 MET, or South MET) and the S1 bog as part of the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. Sample collection and analyses started during June of 2008 at the S2 site and is ongoing. Sample collection and analyses started during December of 2013 at the SPRUCE S1 sites and will continue for the duration of the experiment (expected to end during 2025). The MEF is operated and maintained by the USDA Forest Service, Northern Research Station. The SPRUCE experiment is a multi-year cooperative project among scientists of the Oak Ridge National Laboratory operated by UT-Battelle, LLC and the USDA Forest Service, Northern Research Station. The SPRUCE experiment is funded by the US Department of Energy, Biological and Environmental Research Program.
Daily estimates were calculated for anion concentrations (chloride, sulfate), cation concentrations (calcium, magnesium), nutrient concentrations (ammonium, nitrate, soluble reactive phosphorus, total nitrogen), and total organic carbon (TOC) concentrations. Atmospheric deposition is reported in units of milligrams per square meter per day.
SITE DESCRIPTION:
The catchments are separated by about 1.5 km. Each catchment has a central peatland surrounded by upland mineral soils. The overstory trees on uplands in the MEF are predominately trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera). The peatlands, which are both ombrotrophic bogs, are vegetated with plants ranging from Sphagnum to low shrubs to mature black spruce (Picea mariana) and tamarack (Larix laricina) trees.
There are 10 experimental plots in the SPRUCE experiment located in the S1 bog: 5 temperature treatments (+0, +2.25, +4.5, +6.75, +9 degrees C) at ambient carbon dioxide, and the same 5 temperature treatments at elevated carbon dioxide (+500 ppm). While bulk deposition sampling occurs under ambient conditions outside of the SPRUCE experimental enclosures, these data span the pre- and post-treatment periods when enclosed plots were exposed to warming and elevated carbon dioxide within the SPRUCE experiment.
BULK DEPOSITION SAMPLERS:
Precipitation samples were collected year round on an event-basis from one collector located in an upland clearing at the meteorological station in the S2 research catchment (S2 MET) and three individual collectors (B1, B2, B3) located at the end of three boardwalks that are used to access the S1 bog and SPRUCE plots. Samples from the three collectors in S1 were either composited or individually analyzed, depending on the total volume of water available relative to the amount needed to complete all laboratory analyses. Both individual (B1, B2, B3) and composite (S1) samples from the three SPRUCE collectors in S1 were analyzed when enough precipitation water was available. Funnel/bottle collectors were used to collect rainfall and buckets were used to collect snowfall.
When rainfall was expected, typically from March or April through October or November, a 20.3 cm (8 inch) diameter high density polyethylene (HDPE) funnel was used to capture rainfall. At S2 MET, rainfall drained through about 1 m of reinforced clear vinyl tubing into a 2-L HDPE wide-mouth, graduated collection bottle. The collection bottle sits on the ground and is exposed to sunlight. At the B1, B2, and B3 collectors in S1 bog, rainfall drained through about 2 m of reinforced clear vinyl tubing into a 2-L HDPE wide-mouth, graduated collection bottle. A narrow (0.95 cm / 3/8 inch) adaptor was used to connect tubing to a bottle cap. The narrow adaptor relative to the wide (approx. 5 cm), flat bottle cap reduces evaporative loss from a sample bottle. In addition, collection bottles at B1, B2, and B3 were placed underneath the boardwalks (used to access the SPRUCE infrastructure in the bog) to shield the samples somewhat from sunlight and create a cooler environment near the saturated bog surface to further reduce evaporative potential and photo-exposure that may alter sample chemistry.
After March 5, 2011, the funnel at S2 MET was surrounded by a shield with a spiked upper surface to discourage birds from perching on and defecating into funnels (a common occurrence when shields are not used). The rim of the funnel is at about the tops of the spikes. The B1, B2, and B3 collectors were always surrounded by those types of shields.
Funnel/bottle collectors were not appropriate for solid precipitation collection. Solid precipitation would collect and remain in funnels increasing the likelihood of evaporation and evaporative enrichment of samples during exposure to the atmosphere. When snowfall or mixed precipitation (i.e., some combination of rain, sleet, hail, ice, or snow) was expected, a Nalgene (Rochester, New York) Large Cylindrical HDPE Container (snow bucket with outside diameter = 30.5 cm, height = 22.9 cm, capacity = 15 L) was placed in a mounted bracket. Buckets were not used until autumn/winter of 2010. No frozen precipitation samples were collected at S2 MET before then.
During transitions from above-freezing to below-freezing conditions when precipitation could be either liquid or solid, both types of samples could be placed side-by-side and the choice of which sample to retain for chemical analysis could be made upon collection. When both collector types were used, the funnel/bottle samples were always preferred due to the expected decreased likelihood of evaporation.
Collector openings are about 1.5 m above the ground surface (S2 MET) or about 2 m above the boardwalk surface and about 2.5 m above the bog or ground surface (S1 bog). The precipitation collectors are exposed to both wet and dry deposition.
PRECITATION AMOUNT:
Precipitation amount was measured at the S2 MET site. Belfort Instruments (Baltimore, Maryland) Universal Recording Precipitation Gauges (stripchart recorders) were used prior to replacement with digital NOAH IV total precipitation gauges (ETI Instrument Systems, Ft. Collins, Colorado) during 2010. Total daily precipitation was read from stripcharts or precipitation amount was accumulated on a daily basis from measurements recorded every 15 minutes with the digital rain gage (edi.563; see provenance metadata). The gauge is in an open area and has a USWB Alter-Type Windshield (NWS 2014). Daily precipitation amount data were used in the calculation of atmospheric deposition.
PRECIPITATION SAMPLING:
Bulk precipitation was collected on an event-basis, rather than a fixed interval, to minimize exposure of samples to evaporation, sunlight, excessive heat, or freezing if precipitation was collected as a liquid. Samples may have accumulated over successive, closely-spaced precipitation events or been collected mid-way through a long-duration precipitation event. In any case, the time between sample collection and retrieval was intended to be as minimal as possible, with sampling typically within 12 to 24 h of the end of a precipitation event. Precipitation events that ended after business hours, during weekends (Friday afternoon through Monday morning), or holidays were typically collected the next business day between 7 AM and 4 PM. The date/time reflects when the sample was retrieved, not when the precipitation event occurred or ended.
About 250 mL of water was required to complete bottle rinses and full chemistry and isotopic analyses. An individual sample was taken from each of the three funnel/bottle collectors in the S1 bog (B1, B2, B3) when there was sufficient volume of liquid water in each bottle. When less than 250 mL was available from each individual funnel/bottle in the S1 bog, all water or an equal proportion from each bottle was composited, usually into one of the three 2-L bottles, and labelled with location S1. When there was more than 500 mL from each individual funnel/bottle in the S1 bog, a sample was collected from each collector, plus approx. 200 mL from each collector was composited from all three collectors in a separate sample. Precipitation collected in the S2 catchment (S2 MET) was always analyzed individually. Samples were placed in the dark in iced-coolers for transport to the Forestry Sciences Laboratory in Grand Rapids where they were then processed, stored, and analyzed.
Frozen or mixed precipitation samples in snow buckets were retrieved, covered, and placed inside trucks. Liquid water was needed for further processing. Oftentimes, snow melted during the 35 min drive to the Forestry Sciences Lab. Sometimes, snow or ice samples were placed on laboratory counters to melt rapidly or left in a refrigerator to melt more slowly (for example, if retrieved late in the day and processing would not occur until the next day). Although volumes of snow and melted water were not measured (before 2018), if there appeared to not be enough sample in a single snow bucket to complete all analyses, melted water in the individual collectors from the S1 bog was composited like liquid water samples from funnel/bottle collectors. During and after 2018, melted precipitation water from large events was measured with a graduated cylinder. Whenever volumes were sufficient, an aliquot was saved from liquid or melted precipitation water in the B1, B2, and B3 collectors from large events and composited from each bucket. In addition, individual buckets were sampled.
Containers with insects or other obvious contamination were not always saved for analysis or compositing. When possible, water from samples with undecomposed plant parts or pollen was salvaged by decanting the water from the particulates. In S1 bog, if one field sampling container was not usable due to contaminants, only two of three individual funnel/bottle or snow bucket containers were composited. Some precipitation events were not saved for chemistry analysis due to long holding times in field collection containers or an insufficient total volume even if composited. For the funnel/bottle collector, the bottles were replaced with new acid cleaned bottles after each field visit whether a sample was collected or not. The tubing was periodically acid washed or replaced if necessary. The snow buckets were also replaced with acid cleaned buckets after each field visit.
At the time of collection, date/time of retrieval, sample location, sample volume (liquid samples only), and associated notes were recorded on field data sheets. Unfiltered water was decanted from the 2-L individual funnels/bottles or snow buckets into multiple storage containers: a 250 mL low density polyethylene (LDPE) bottle for pH, specific conductivity, ion, and nutrient analyses (refrigerated), After 2015, a separate 60-mL aliquot was saved in an HDPE bottle solely for nutrient analysis (frozen); and a 20 to 40-mL amber glass vial for TOC analysis (refrigerated). Sample bottles for ion and nutrient chemistry were triple rinsed with precipitation water before filling. Scintillation vials for water isotope samples were completely filled, with no headspace or bubbles. A unique serial ID number was assigned to all aliquots of the same sample for tracking purposes in the laboratory and data reporting. Samples from S2 MET have a 6 digit integer and started with 346,298. Samples from the S1 bog have 5 digit integer starting with 82,044.
ANALYTICAL METHODS:
Analytical methods used to measure solute concentrations are described in edi.609 (Marcell Experimental Forest event-based precipitation chemistry; see provenance metadata).
ESTIMATION OF ATMOSPHERIC DEPOSITION:
Daily atmospheric deposition was calculated for each solute (chloride, sulfate, calcium, magnesium, ammonium, nitrate+nitrite, SRP, total nitrogen, and TOC) by multiplying daily precipitation by the associated concentration value for the period during which the precipitation accumulated in a sampler. Bulk atmospheric deposition was calculated independently for each site (S2 Met or S1 Bog) using the chemistry values from the respective site. Because precipitation amount is not available for the S1 bog, we used precipitation amount from S2 MET for both the S2 MET and S1 bog bulk deposition estimates.
A concentration from the collection date to the previous sample collection date was assigned as the concentration for that period. Some precipitation events were not sampled for chemistry due to long holding times in the field collection container or events did not yield sufficient volumes for chemistry analyses, concentration values were applied to all days preceding the collection date until the previous sample. When samples were collected from each individual sampler, a mean of the multiple samples was calculated for a day. When both individual sampler and composited samples were collected, the composited sample solute concentration was used to estimate daily atmospheric deposition.
REPORTED VALUES:
Daily values are reported, except for periods (assigned -9999) when concentration data is not yet available for calculations, a particular solute was not measured, or for periods during which analytical problems (e.g., contamination or instrument errors) resulted in an extended period with no solute concentration values for calculations. The units are mg/square m/d.
Chloride is reported as -9999 for much of 2015 and 2016 when there was evidence of contamination of that analyte from inadequate rinsing of hydrochloric acid (HCl) after acid washing of funnels, tubing, and collection bottles used for field sampling.
Concentrations of nitrate and ammonium are only reported onward from 2015 for S1 samples and 2019 for S2 MET samples (when aliquots were frozen for analysis). Values are reported as -9999 prior to preservation with freezing.
MARCELL EXPERIMENTAL FOREST sites and data collection are described in further detail in:
Sebestyen, S.D., C. Dorrance, D.M. Olson, E.S. Verry, R.K. Kolka, A.E. Elling, and R. Kyllander (2011). Chapter 2: Long-Term Monitoring Sites and Trends at the Marcell Experimental Forest. In Randall K. Kolka, Stephen D. Sebestyen, Elon S. Verry, and Kenneth N. Brooks (Ed.). Peatland Biogeochemistry and Watershed Hydrology at the Marcell Experimental Forest (pp 15-71). CRC Press, Boca Raton, FL. https://www.fs.usda.gov/treesearch/pubs/37979.
SPRUCE Project Website with project plans and additional information:
http://mnspruce.ornl.gov/
REFERENCES:
NWS (2014), National Weather Service manual 10-1315: Cooperative station observations and maintenance, 130 pp, National Weather Service.
