carbon fluxes

Warming-El Nino-Nitrogen Deposition Experiment (WENNDEx): Soil Temperature, Moisture, and Carbon Dioxide Data from the Sevilleta National Wildlife Refuge, New Mexico (2011 - present)

Abstract: 

Humans are creating significant global environmental change, including shifts in climate, increased nitrogen (N) deposition, and the facilitation of species invasions. A multi-factorial field experiment is being performed in an arid grassland within the Sevilleta National Wildlife Refuge (NWR) to simulate increased nighttime temperature, higher N deposition, and heightened El Niño frequency (which increases winter precipitation by an average of 50%). The purpose of the experiment is to better understand the potential effects of environmental drivers on grassland community composition, aboveground net primary production and soil respiration. The focus is on the response of two dominant grasses (Bouteloua gracilis and B eriopoda), in an ecotone near their range margins and thus these species may be particularly susceptible to global environmental change.

It is hypothesized that warmer summer temperatures and increased evaporation will favor growth of black grama (Bouteloua eriopoda), a desert grass, but that increased winter precipitation and/or available nitrogen will favor the growth of blue grama (Bouteloua gracilis), a shortgrass prairie species. Treatment effects on limiting resources (soil moisture, nitrogen availability, species abundance, and net primary production (NPP) are all being measured to determine the interactive effects of key global change drivers on arid grassland plant community dynamics and ecosystem processes. This dataset shows values of soil moisture, soil temperature, and the CO2 flux of the amount of CO2 that has moved from soil to air.

On 4 August 2009 lightning ignited a ~3300 ha wildfire that burned through the experiment and its surroundings. Because desert grassland fires are patchy, not all of the replicate plots burned in the wildfire. Therefore, seven days after the wildfire was extinguished, the Sevilleta NWR Fire Crew thoroughly burned the remaining plots allowing us to assess experimentally the effects of interactions among multiple global change presses and a pulse disturbance on post-fire grassland dynamics.

Core Areas: 

Data set ID: 

305

Keywords: 

Methods: 

Experimental Design

Our experimental design consists of three fully crossed factors (warming, increased winter precipitation, and N addition) in a completely randomized design, for a total of eight treatment combinations, with five replicates of each treatment combination, for a total of 40 plots. Each plot is 3 x 3.5 m. All plots contain B. eriopoda, B. gracilis and G. sarothrae. Our nighttime warming treatment is imposed using lightweight aluminum fabric shelters (mounted on rollers similar to a window shade) that are drawn across the warming plots each night to trap outgoing longwave radiation. The dataloggers controlling shelter movements are programmed to retract the shelters on nights when wind speeds exceed a threshold value (to prevent damage to shelters) and when rain is detected by a rain gauge or snow is detected by a leaf wetness sensor (to prevent an unintended rainout effect).

Each winter we impose an El Nino-like rainfall regime (50% increase over long-term average for non-El Nino years) using an irrigation system and RO water. El Nino rains are added in 6 experimental storm events that mimic actual El Nino winter-storm event size and frequency. During El Nino years we use ambient rainfall and do not impose experimental rainfall events. For N deposition, we add 2.0 g m-2 y-1 of N in the form of NH4NO3 because NH4 and NO3 contribute approximately equally to N deposition at SNWR (57% NH4 and 43% NO3; Bez et al., 2007). The NH4NO3 is dissolved in 12 liters of deionized water, equivalent to a 1 mm rainfall event, and applied with a backpack sprayer prior to the summer monsoon. Control plots receive the same amount of deionized water.

Soil Measurements

Soil temperature is measured with Campbell Scientific CS107 temperature probes buried at 2 and 8 cm In the soil. Soil volume water content, measured with Campbell Scientific CS616 TDR probes is an integrated measure of soil water availability from 0-15 cm deep in the soil. Soil CO2 is measured with Vaisala GM222 solid state CO2 sensors. For each plot, soil sensors are placed under the canopy of B. eriopoda at three depths: 2, 8, and 16 cm. Measurements are recorded every 15 minutes.

CO2 fluxes are calculated using the CO2, temperature, and moisture data, along with ancillary variables following the methods of Vargas et al (2012) Global Change Biology

Values of CO2 concentration are corrected for temperature and pressure using the ideal gas law according to the manufacturer (Vaisala). We calculate soil respiration using the flux-gradient method (Vargas et al. 2010) based on Fick’s law of diffusion where the diffusivity of CO2 is corrected for temperature and pressure (Jones 1992) and calculated as a function of soil moisture, porosity and texture (Moldrup et al. 1999).

Data sources: 

sev305_wenndex_soiltemp_moisture_co2_2011
sev305_wenndex_soiltemp_moisture_co2_2012
sev305_wenndex_soiltemp_moisture_co2_2013
sev305_wenndex_soiltemp_moisture_co2_2014
sev305_wenndex_soiltemp_moisture_co2_2015

Instrumentation: 

Instrument Name: Solid State Soil CO2 sensor
Manufacturer: Vaisala
Model Number: GM222

Instrument Name: Temperature Probe
Manufacturer: Campbell Scientific
Model Number: CS107

Instrument Name: Water Content Reflectometer Probe
Manufacturer: Campbell Scientific
Model Number: CS616

Monsoon Rainfall Manipulation Experiment (MRME) Soil Temperature, Moisture and Carbon Dioxide Data from the Sevilleta National Wildlife Refuge, New Mexico (2012- present)

Abstract: 

The Monsoon Rainfall Manipulation Experiment (MRME) is designed to understand changes in ecosystem structure and function of a semiarid grassland caused by increased precipitation variability, by altering rainfall pulses, and thus soil moisture, that drive primary productivity, community composition, and ecosystem functioning. The overarching hypothesis being tested is that changes in event size and frequency will alter grassland productivity, ecosystem processes, and plant community dynamics. Treatments include (1) a monthly addition of 20 mm of rain in addition to ambient, and a weekly addition of 5 mm of rain in addition to ambient during the months of July, August and September. It is predicted that changes in event size and variability will alter grassland productivity, ecosystem processes, and plant community dynamics. In particular, we predict that many small events will increase soil CO2 effluxes by stimulating microbial processes but not plant growth, whereas a small number of large events will increase aboveground NPP and soil respiration by providing sufficient deep soil moisture to sustain plant growth for longer periods of time during the summer monsoon.

Core Areas: 

Data set ID: 

304

Keywords: 

Methods: 

Experimental Design

MRME contains three ambient precipitation plots and five replicates of the following treatments: 1) ambient plus a weekly addition of 5 mm rainfall, 2) ambient plus a monthly addition of 20 mm rainfall. Rainfall is added during the monsoon season (July-Sept) by an overhead (7 m) system fitted with sprinkler heads that deliver rainfall quality droplets. At the end of the summer, each treatment has received the same total amount of added precipitation, delivered in different sized events. Each plot (9x14 m) includes subplots (2x2 m) that receive 50 kg N ha-1 y-1. Each year we measure: (1) seasonal (July, August, September, and October) soil N, (2) plant species composition and ANPP, (3) annual belowground production in permanently located root ingrowth cores, and (4) soil temperature, moisture and CO2 fluxes (using in situ solid state CO2 sensors).

Soil Measurements

Soil temperature is measured with Campbell Scientific CS107 temperature probes buried at 2 and 8 cm In the soil. Soil volume water content, measured with Campbell Scientific CS616 TDR probes is an integrated measure of soil water availability from 0-15 cm deep in the soil. Soil CO2 is measured with Vaisala GM222 solid state CO2 sensors. For each plot, soil sensors are placed under the canopy of B. eriopoda at three depths: 2, 8, and 16 cm. Measurements are recorded every 15 minutes.

CO2 fluxes are calculated using the CO2, temperature, and moisture data, along with ancillary variables following the methods of Vargas et al (2012) Global Change Biology

Values of CO2 concentration are corrected for temperature and pressure using the ideal gas law according to the manufacturer (Vaisala). We calculate soil respiration using the flux-gradient method (Vargas et al. 2010) based on Fick’s law of diffusion where the diffusivity of CO2 is corrected for temperature and pressure (Jones 1992) and calculated as a function of soil moisture, porosity and texture (Moldrup et al. 1999).

Data sources: 

sev304_mrme_soiltemp_moisture_co2_2012
sev304_mrme_soiltemp_moisture_co2_2013
sev304_mrme_soiltemp_moisture_co2_2014
sev304_mrme_soiltemp_moisture_co2_2015

Instrumentation: 

Instrument Name: Solid State Soil CO2 sensor
Manufacturer: Vaisala
Model Number: GM222

Instrument Name: Temperature Probe
Manufacturer: Campbell Scientific
Model Number: CS107

Instrument Name: Water Content Reflectometer Probe
Manufacturer: Campbell Scientific
Model Number: CS616

Additional information: 

Additional Study Area Information

Study Area Name: Monsoon site

Study Area Location: Monsoon site is located just North of the grassland Drought plots

Vegetation: dominated by black grama (Bouteloua eriopoda), and other highly prevalent grasses include Sporabolus contractus, S.cryptandrus, S. lexuosus, Muhlenbergia aernicola and Bouteloua gracilis.

North Coordinate:34.20143
South Coordinate:34.20143
East Coordinate:106.41489
West Coordinate:106.41489

Riparian Evapotranspiration (ET) Study (SEON) from the Middle Rio Grande River Bosque, New Mexico (1999-2011 ): CO2 Concentration and Flux data

Abstract: 

This study originated with the objective of parameterizing riparian evapotranspiration (ET) in the water budget of the Middle Rio Grande. We hypothesized that flooding and invasions of non-native species would strongly impact ecosystem water use. Our objectives were to measure and compare water use of native (Rio Grande cottonwood, Populus deltoides ssp. wizleni) and non-native (saltcedar, Tamarix chinensis, Russian olive, Eleagnus angustifolia) vegetation and to evaluate how water use is affected by climatic variability resulting in high river flows and flooding as well as drought conditions and deep water tables. Eddy covariance flux towers to measure ET and shallow wells to monitor water tables were instrumented in 1999. Active sites in their second decade of monitoring include a xeroriparian, non-flooding salt cedar woodland within Sevilleta National Wildlife Refuge and a dense, monotypic salt cedar stand at Bosque del Apache NWR, which is subject to flood pulses associated with high river flows. These data are CO2 concentration at canopy and CO2 flux from canopy collected as part of this study.

Core Areas: 

Data set ID: 

312

Keywords: 

Methods: 

Three-dimensional eddy covariance: Measures fluxes of latent heat, sensible heat, and momentum, integrated over an area such as a vegetation canopy. High frequency measurements are made of vertical wind speed and water vapor, and their covariance over thirty minutes is used to compute latent heat flux, the heat absorbed by evaporation, from the canopy surface. Latent heat flux (LE) is converted to a direct measurement of evapotranspiration (ET). Simultaneous, high frequency measurements of temperature are used with vertical wind speed to compute the sensible heat flux (H), the heat transfer due to vertical temperature gradients. Measuring net radiation (Rn) and ground heat flux (G), allows the energy balance to be calculated (Rn = LE + H + G), providing a self-check for accuracy and closure error.

Sites: Two Rio Grande riparian locations in P. deltoides forests, two in T. chinensis forests. In each forest type, one of the two sites is prone to flooding from elevated Rio Grande flows, and the other site does not flood. A fifth site was located in a mix of non-native Eleagnus angustifolia (Russian olive) and native Salix exigua (coyote willow) prone to flooding.

Design: Eddy covariance systems were mounted on towers in the turbulent surface layer 2-2.5 m above the canopy. Measurement period was 10 Hz and the covariance period was 30 minutes. Additional energy fluxes were made at 1 Hz and averaged over 30 minutes.

Data sources: 

sev312_bosqueETCO2_20160720.txt

Instrumentation: 

Current Instruments:

*Instrument Name: 3-D Sonic Anemometer
*Manufacturer: Campbell Scientific, Inc. (Logan, UT)
*Model Number: CSAT3

*Instrument Name: CO2/H2O Analyzer
*Manufacturer: Li-Cor, Inc. (Lincoln, NE)
*Model Number: LI-7500

*Instrument Name: Net Radiometer
*Manufacturer: Kipp & Zonen (Delft, The Netherlands)
*Model Number: CNR1

*Instrument Name: Barometric Pressure Sensor
*Manufacturer: Vaisala (Helsinki, Finland)
*Model Number: CS105

*Instrument Name: Temperature and Relative Humidity Probe
*Manufacturer: Vaisala (Helsinki, Finland)
*Model Number: HMP45C

*Instrument Name: Wind Sentry (Anemometer and Vane)
*Manufacturer: R.M. Young (Traverse City, MI)
*Model Number: 03001

*Instrument Name: Tipping Bucket Rain Gage
*Manufacturer: Texas Electronics, Inc. (Dallas, TX)
*Model Number: TE525

*Instrument Name: Quantum Sensor (PAR)
*Manufacturer: Li-Cor, Inc. (Lincoln, NE)
*Model Number: LI-190

*Instrument Name: Water Content Reflectometer
*Manufacturer: Campbell Scientific, Inc. (Logan, UT)
*Model Number: CS616

*Instrument Name: Soil Heat Flux Plate
*Manufacturer: Radiation and Energy Balance Systems, Inc. (Bellevue, WA)
*Model Number: HFT3

*Instrument Name: Averaging Soil Thermocouple Probe
*Manufacturer: Campbell Scientific, Inc. (Logan, UT)
*Model Number: TCAV

*Instrument Name: Measurement and Control System (Datalogger)
*Manufacturer: Campbell Scientific, Inc. (Logan, UT)
*Model Number: CR5000

*Instrument Name: Levelogger and Barologger (Water Table)
*Manufacturer: Solinst Canada Ltd. (Georgetown, ON, Canada)
*Model Number: 3001 LT M10 and 3001 LT M1.5

*Instrument Name: Mini-Diver, Cera-Diver, and Baro-Diver (Water Table)
*Manufacturer: Van Essen Instruments ((Delft, The Netherlands)
*Model Number: DI501, DI701, and DI500

Discontinued Instruments:

*Instrument Name: Krypton Hygrometer
*Manufacturer: Campbell Scientific, Inc. (Logan, UT)
*Model Number: KH2O

*Instrument Name: Net Radiometer
*Manufacturer: Radiation and Energy Balance Systems, Inc. (Bellevue, WA)
*Model Number: Q-7.1

*Instrument Name: Pyranometer
*Manufacturer: Kipp & Zonen (Delft, The Netherlands)
*Model Number: CM3

*Instrument Name: Micrologger
*Manufacturer: Campbell Scientific, Inc. (Logan, UT)
*Model Number: CR23X

*Instrument Name: Submersible Sensor Pressure Transducer (Water Table)
*Manufacturer: Electronic Engineering Innovations (Las Cruces, NM)
*Model Number: 2.0 (2 m) and 5.0 (4 m)

Quality Assurance: 

a] Before ET is computed from LE, various standard corrections are applied. These include: coordinate rotation to align the wind vector with the sonic anemometer, corrections developed from frequency response relationships that incorporate sensor line averaging and separation (Massman corrections), and corrections to account for flux effects on vapor density as opposed to mixing ratio measurements. Corrections are made in a data analysis (Perl) program. See Cleverly, et al., Hydrological Processes 20: 3207-3225, 2006 for more detail and references.

b] On days in which 1-4 of the 30 min LE values are missing, a general linear regression model between LE and Rn is used to estimate missing data whenever the regression coefficient was significantly different from 0 (i.e. p > 0.5). ET is not calculated from LE on days that do not match the above criteria.

c] Other missing data required for derived data values, as well as out of range data are filtered out in data analysis (Perl) programs.

d] Closure of the energy balance is achieved by adding the measured Bowen Ration (H/LE) components to H and LE. Closure represents the error introduced when applying the energy balance method to estimate ET: closure = Rn - LE - H - G. The measured Bowen Ratio, H / LE, is used to parse the closure value into component H and LE values.

e] Soil water content data are calibrated with soil water content (% vol) values measured from field samples by linear regression in a data analysis (Perl) program.

Additional information: 

SEV ET 3/18/2000--12/31/2011, water table 4/16/1999--12/31/2014
BDAS ET 3/16/2000--12/31/2011, water table 4/17/1999--6/30/2014
SHK ET 3/18/2000--12/31/2007, water table 3/16/2000--12/31/2013
BLN ET 3/22/2000--5/17/2004, water table 3/15/2000--11/18/2008
LARO ET 3/6/2003--12/17/2008, water table 4/16/2003--12/31/2009

Note: the data are not continuous--all sites have numerous breaks in the data. Additionally, instruments were introduced and retired at various times. For example, measurements of latent heat flux began with krypton hygrometers (LE_kh_c) and were replaced by infrared gas analyzers (LE_irga_c), which also commenced CO2 data (Fc_c, co2_a). Soil water content (soil_water) and a backup barometric sensor (P_mb_2) were added in 2003. Solar radiation (Rg_AVG) and photosynthetically active radiation (PAR_AVG) were added in 2006.

Monsoon Rainfall Manipulation Experiment (MRME): Soil Carbon Dioxide Concentration Data from the Sevilleta National Wildlife Refuge, NM (2010 - present)

Abstract: 

The Monsoon Rainfall Manipulation Experiment (MRME) is to understand changes in ecosystem structure and function of a semiarid grassland caused by increased precipitation variability, which alters the pulses of soil moisture that drive primary productivity, community composition, and ecosystem functioning. The overarching hypothesis being tested is that changes in event size and variability will alter grassland productivity, ecosystem processes, and plant community dynamics.  These data are CO2 concentrations collected at three depths.  

Data set ID: 

302

Additional Project roles: 

515

Core Areas: 

Keywords: 

Methods: 

MRME contains three ambient precipitation plots and five replicates of the following treatments: 1) ambient plus a weekly addition of 5 mm rainfall, 2) ambient plus a monthly addition of 20 mm rainfall. Rainfall is added during the monsoon season (July-Sept) by an overhead (7 m) system fitted with sprinkler heads that deliver rainfall quality droplets. At the end of the summer, each treatment has received the same total amount of added precipitation, delivered in different sized events. 

Data sources: 

sev302_mrmeCO2_20160323.txt

Biome Transition Along Elevational Gradients in New Mexico (SEON) Study: Flux Tower Seasonal Biomass and Seasonal and Annual NPP Data at the Sevilleta National Wildlife Refuge, New Mexico (2011 to present)

Abstract: 

The varied topography and large elevation gradients that characterize the arid and semi-arid Southwest create a wide range of climatic conditions - and associated biomes - within relatively short distances. This creates an ideal experimental system in which to study the effects of climate on ecosystems. Such studies are critical givien that the Southwestern U.S. has already experienced changes in climate that have altered precipitation patterns (Mote et al. 2005), and stands to experience dramatic climate change in the coming decades (Seager et al. 2007; Ting et al. 2007). Climate models currently predict an imminent transition to a warmer, more arid climate in the Southwest (Seager et al. 2007; Ting et al. 2007). Thus, high elevation ecosystems, which currently experience relatively cool and mesic climates, will likely resemble their lower elevation counterparts, which experience a hotter and drier climate. In order to predict regional changes in carbon storage, hydrologic partitioning and water resources in response to these potential shifts, it is critical to understand how both temperature and soil moisture affect processes such as evaportranspiration (ET), total carbon uptake through gross primary production (GPP), ecosystem respiration (Reco), and net ecosystem exchange of carbon, water and energy across elevational gradients.

We are using a sequence of six widespread biomes along an elevational gradient in New Mexico -- ranging from hot, arid ecosystems at low elevations to cool, mesic ecosystems at high elevation to test specific hypotheses related to how climatic controls over ecosystem processes change across this gradient. We have an eddy covariance tower and associated meteorological instruments in each biome which we are using to directly measure the exchange of carbon, water and energy between the ecosystem and the atmosphere. This gradient offers us a unique opportunity to test the interactive effects of temperature and soil moisture on ecosystem processes, as temperature decreases and soil moisture increases markedly along the gradient and varies through time within sites.

This dataset examines how different stages of burn affects above-ground biomass production (ANPP) in a mixed desert-grassland. Net primary production is a fundamental ecological variable that quantifies rates of carbon consumption and fixation. Estimates of NPP are important in understanding energy flow at a community level as well as spatial and temporal responses to a range of ecological processes.  Above-ground net primary production is the change in plant biomass, represented by stems, flowers, fruit and foliage, over time and incorporates growth as well as loss to death and decomposition. To measure this change the vegetation variables in this dataset, including species composition and the cover and height of individuals, are sampled twice yearly (spring and fall) at permanent 1m x 1m plots. Volumetric measurements are made using vegetation data from permanent plots (SEV253, "Flux Tower Net Primary Productivity (NPP) Quadrat Study") and regressions correlating species biomass and volume constructed using seasonal harvest weights from SEV157, "Net Primary Productivity (NPP) Weight Data."

Data set ID: 

292

Core Areas: 

Additional Project roles: 

470
471
472
473

Keywords: 

Methods: 

Data Processing Techniques to Derive Biomass and NPP:

Data from SEV253 and SEV157 are used used to calculate seasonal and annual production of each species in each quadrat for a given year. Allometric equations derived from harvested samples of each species for each season are applied to the measured cover, height, and count of each species in each quadrat. This provides seasonal biomass for winter, spring, and fall.

Seasonal NPP is derived by subtracting the previous season's biomass from the biomass for the current season. For example, spring NPP is calculated by subtracting the winter weight from the spring weight for each species in a given quadrat. Negative differences are considered to be 0. Likewise, fall production is computed by subtracting spring biomass from fall biomass. Annual biomass is taken as the sum of spring and fall NPP.

Data sources: 

sev292_fluxbiomass_20150305.txt

Additional information: 

Other researchers involved with collecting samples/data: Chandra Tucker (CAT; 04/2014-present), Megan McClung (MAM; 04/2013-present), Stephanie Baker (SRB; 2011-present), John Mulhouse (JMM; 2011-05/2013), Amaris Swann (2011-01/2013)

The Contribution of Biological Soil Crust Carbon and Nitrogen Exchange to the Net Ecosystem Exchange Along an Elevation Gradient at the Sevilleta National Wildlife Refuge, New Mexico

Abstract: 

The purpose of this project is to: 1.) determine how biological soil crust (BSC) cover changes along an elevation gradient and across seasons, 2.) determine how carbon and nitrogen exchanges of BSC communities vary with temperature along an elevation gradient in arid and semi-arid environments and, 3.) use photosynthetic and respiration rates of BSC communities to determine how the contribution of the BSC communities to whole ecosystem carbon exchange varies across the same gradient and over seasons.

Core Areas: 

Additional Project roles: 

247

Data set ID: 

280

Keywords: 

Methods: 

At each sampling site and sampling period a small amount of surface crust (approx. one teaspoonful per sample) was taken from each of 10 locations at approximately 1 meter intervals over a transect.  Samples were transported back to the laboratory in plastic bags.

On rare occasions we removed a larger sample, 0.5 liter volume or less, at one or two sampling stations.

Additional information: 

Study sites included: Flux tower sites, desert grassland, desert shrubland, juniper savanna, piñon-juniper woodland, ponderosa pine forest, and mixed conifer forest.

Biome Transition Along Elevational Gradients in New Mexico (SEON) AmeriFlux Data (ongoing since 2007)

Abstract: 

The varied topography and large elevation gradients that characterize the arid and semi-arid Southwest create a wide range of climatic conditions - and associated biomes - within relatively short distances. This creates an ideal experimental system in which to study the effects of climate on ecosystems. Such studies are critical givien that the Southwestern U.S. has already experienced changes in climate that have altered precipitation patterns (Mote et al. 2005), and stands to experience dramatic climate change in the coming decades (Seager et al. 2007; Ting et al. 2007). Climate models currently predict an imminent transition to a warmer, more arid climate in the Southwest (Seager et al. 2007; Ting et al. 2007). Thus, high elevation ecosystems, which currently experience relatively cool and mesic climates, will likely resemble their lower elevation counterparts, which experience a hotter and drier climate. In order to predict regional changes in carbon storage, hydrologic partitioning and water resources in response to these potential shifts, it is critical to understand how both temperature and soil moisture affect processes such as evaportranspiration (ET), total carbon uptake through gross primary production (GPP), ecosystem respiration (Reco), and net ecosystem exchange of carbon, water and energy across elevational gradients.

We are using a sequence of six widespread biomes along an elevational gradient in New Mexico -- ranging from hot, arid ecosystems at low elevations to cool, mesic ecosystems at high elevation to test specific hypotheses related to how climatic controls over ecosystem processes change across this gradient. We have an eddy covariance tower and associated meteorological instruments in each biome which we are using to directly measure the exchange of carbon, water and energy between the ecosystem and the atmosphere. This gradient offers us a unique opportunity to test the interactive effects of temperature and soil moisture on ecosystem processes, as temperature decreases and soil moisture increases markedly along the gradient and varies through time within sites.

Data for this project can be found on the website:  http://ameriflux.ornl.gov/

Additional Project roles: 

302

Core Areas: 

Data set ID: 

254

Keywords: 

Data sources: 

sev254_sevameriflux_20131211.csv

Methods: 

Data collection follows Ameriflux protocols.  

The varied topography and large elevation gradients that characterize the arid and semi-arid Southwest create a wide range of climatic conditions - and associated biomes - within relatively short distances. This creates an ideal experimental system in which to study the effects of climate on ecosystems. Such studies are critical givien that the Southwestern U.S. has already experienced changes in climate that have altered precipitation patterns (Mote et al. 2005), and stands to experience dramatic climate change in the coming decades (Seager et al. 2007; Ting et al. 2007).

Monsoon Rainfall Manipulation Experiment (MRME): Net Primary Production Quadrat Data at the Sevilleta National Wildlife Refuge, New Mexico (2006-present)

Abstract: 

The Monsoon Rainfall Manipulation Experiment (MRME) is to understand changes in ecosystem structure and function of a semiarid grassland caused by increased precipitation variability, which alters the pulses of soil moisture that drive primary productivity, community composition, and ecosystem functioning. The overarching hypothesis being tested is that changes in event size and variability will alter grassland productivity, ecosystem processes, and plant community dynamics. In particular, we predict that many small events will increase soil CO2 effluxes by stimulating microbial processes but not plant growth, whereas a small number of large events will increase aboveground net primary production (ANPP) and soil respiration by providing sufficient deep soil moisture to sustain plant growth for longer periods of time during the summer monsoon.

To measure ANPP (i.e., the change in plant biomass, represented by stems, flowers, fruit and foliage, over time), the vegetation variables in this dataset, including species composition and the cover and height of individuals, are sampled twice yearly (spring and fall) at permanent 1m x 1m plots. The data from these plots is used to build regressions correlating biomass and volume via weights of select harvested species obtained in SEV157, "Net Primary Productivity (NPP) Weight Data." This biomass data is included in SEV206, "Seasonal Biomass and Seasonal and Annual NPP for the Monsoon (MRME) Study."

Core Areas: 

Data set ID: 

188

Additional Project roles: 

454
455
456
457

Keywords: 

Data sources: 

sev188_nppmonsoonquadrat_20170621

Methods: 

Experimental design:

The Monsoon Rainfall Manipulation Experiment (MRME) contains three ambient precipitation plots and five replicates of the following treatments: 1.) ambient plus a weekly addition of 5 mm rainfall; and 2.) ambient plus a monthly addition of 20 mm rainfall. Rainfall is added during the monsoon season (July-Sept) by an overhead (7 m) system fitted with sprinkler heads that deliver rainfall quality droplets. At the end of the summer, each treatment has received the same total amount of added precipitation delivered in different sized events.

Each plot (9m x 14 m) includes subplots (2m x 2m) that receive 50 kg N ha-1 y-1. Measurements are taken of: 1.) seasonal (July, August, September, and October through June) soil N; 2.) plant species composition and ANPP; 3.) seasonal root and fungal dynamics in mini-rhizotrons; and 4.) soil temperature, moisture, and CO2 fluxes (using in situ solid state CO2 sensors). Also, soil N2O fluxes, predawn and mid-day (10-12 AM) water potential, and mid-day leaf photosynthetic gas exchange and stomatal conductance of black grama are measured prior to and up to 5 days after scheduled precipitation events.

Above-Ground Net Primary Productivity (ANPP) measurements:

Above-ground net primary production data is collected in the spring and fall. Spring measurements are taken in April or May when shrubs and spring annuals have reached peak biomass. Fall measurements are taken in either September or October when summer annuals have reached peak biomass but prior to killing frosts.

Vegetation data is collected on a palm top computer. A 1-m2 PVC-frame is placed over the fiberglass stakes that mark the diagonal corners of each quadrat. When measuring cover it is important to stay centered over the vegetation in the quadrat to prevent errors caused by angle of view (parallax). Each PVC-frame is divided into 100 squares with nylon string. The dimensions of each square are 10cm x 10cm and represent 1 percent of the total area.

The cover (area) and height of each individual live (green) vegetative unit that falls within the one square meter quadrat is measured. A vegetative unit consists of an individual size class (as defined by a unique cover and height) of a particular species within a quadrat. Cover is quantified by counting the number of 10cm x 10cm squares filled by each vegetative unit. It is possible to obtain a total percent cover greater than 100% for a given quadrat because vegetative units for different species often overlap.

Niners and plexidecs are additional tools that can help accurately determine the cover a vegetative unit. A niner is a small, hand-held PVC frame that can be used to measure canopies. Like the larger PVC frame it is divided into 10cm x 10cm squares, each square representing 1% of the total cover. However, there are only nine squares within the frame, hence the name “niner.” A plexidec can help determine the cover of vegetative units with covers less than 1%. Plexidecs are clear plastic squares that are held above vegetation. Each plexidec represents a cover of 0.5% and has smaller dimensions etched onto the surface that correspond to 0.01%, 0.05%, 0.1%, and 0.25% cover.

It is extremely important that cover and height measurements remain consistent over time to ensure that regressions based on this data remain valid. Field crew members should calibrate with each other to ensure that observer bias does not influence data collection

Cover Measurements:

Grasses-To determine the cover of a grass clump, envision a perimeter around the central mass or densest portion of the plant, excluding individual long leaves, wispy ends, or more open upper regions of the plant. Live foliage is frequently mixed with dead foliage in grass clumps and this must be kept in mind during measurement as our goal is to measure only plant biomass for the current season. In general, recently dead foliage is yellow and dead foliage is gray. Within reason, try to include only yellow or green portions of the plant in cover measurement while excluding portions of the plant that are gray. This is particularly important for measurements made in the winter when there is little or no green foliage present. In winter, sometimes measurements will be based mainly on yellow foliage. Stoloniferous stems of grasses that are not rooted should be ignored. If a stem is rooted it should be recorded as a separate observation from the parent plant.

Forbs-The cover of forbs is measured as the perimeter of the densest portion of the plant. If the forb is an annual it is acceptable to include the inflorescence in this measurement. If the forb is a perennial, do not include the inflorescence as part of the cover measurement. Measure all foliage that was produced during the current season, including any recently dead (yellow) foliage. Avoid measuring gray foliage that died in a previous season.

Cacti-For cacti that consist of a series of pads or jointed stems (Opuntia phaecantha, Opuntia imbricata) measure the length and width of each pad to the nearest cm instead of cover and height. Cacti that occur as a dense ball/clump of stems (Opuntia leptocaulis) are measured using the same protocol as shrubs. Pincushion or hedgehog cacti (Escobaria vivipara, Schlerocactus intertextus, Echinocereus fendleri) that occur as single (or clustered) cylindrical stems are measured as a single cover.

Yuccas-Make separate observations for the leaves and caudex (thick basal stem). Break the observations into sections of leaves that are approximately the same height and record the cover as the perimeter around this group of leaf blades. The caudex is measured as a single cover. The thick leaves of yuccas make it difficult to make a cover measurement by centering yourself over the caudex of the plant. The cover of the caudex may be estimated by holding a niner next to it or using a tape measure to measure to approximate the area.

Height Measurements:

Height is recorded as a whole number in centimeters. All heights are vertical heights but they are not necessarily perpendicular to the ground if the ground is sloping.

Annual grasses and all forbs-Measure the height from the base of the plant to the top of the inflorescence (if present). Otherwise, measure to the top of the green foliage.

Perennial grasses-Measure the height from the base of the plant to the top of the live green foliage. Do not include the inflorescence in the height measurement. The presence of live green foliage may be difficult to see in the winter. Check carefully at the base of the plant for the presence of green foliage. If none is found it may be necessary to pull the leaf sheaths off of several plants outside the quadrat. From this you may be able to make some observations about where green foliage is likely to occur.

Perennial shrub and sub-shrubs-Measure the height from the base of the green foliage to the top of the green foliage, ignoring all bare stems. Do not measure to the ground unless the foliage reaches the ground. Plants rooted outside but hanging into a quadrat-Do not measure the height from the ground. Measure only the height of the portion of the plant that is within the quadrat.

Recording the Data:

Excel spreadsheets are used for data entry and file names should begin with the overall study (npp), followed by the date (mm.dd.yy) and the initials of the recorder (.abc). Finally, the site abbreviation should be added (i.e., c, g, b, p). The final format should be as follows: npp_mons.mm.dd.yy.abc.xls. File names should be in lowercase.

August 2009 Burn:

On August 4, 2009, a lightning-initiated fire began on the Sevilleta National Wildlife Refuge. The Monsoon site was entirely burned on this date, with all plots subjected to fire of comparable intensity.

Maintenance: 

01/13/2011-Spring and Fall 2010 data was updated, QA/QC'd and uploaded. (JMM) 11/26/2009-Spring 2009 data was updated, QAQC'd and uploaded. Fall season data was not collected due to an unexpected fire at Sevilleta LTER in Aug 2009. (YX) 11/26/2009-Metadata complied for data from 2006 to 2009. (YX) 01/14/2009-Metadata compiled for data from 2006 to 2008. (YX) 12/20/2008-Data was QAQC'd in MySQL. I checked for duplicates, missing quads, and species codes. (YX)

Additional information: 

Other researchers involved with collecting samples/data: Chandra Tucker (CAT; 04/2014-present), Megan McClung (MAM; 04/2013-present), Stephanie Baker (SRB; 09/2010-present), John Mulhouse (JMM; 08/2010-06/2013), Amaris Swann (ALS; 08/2008-01/2013), Maya Kapoor (MLK; 08/2003 - 01/2005, 05/2010-03/2011),  Terri Koontz (TLK; 02/2000 - 08/2003, 08/2006 - 08/2010), Yang Xia (YX; 01/2005 - 03/2010), Karen Wetherill (KRW; 02/2000 - 08/2009); Michell Thomey (MLT; 09/2005 - 08/2008).Data updated 08/18/15: MOSQ changed to MUSQ3; ARPUP6 changed to ARPU9; SPWR changed to SPPO6.

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