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Title: Carbon-water Cycling in the Critical Zone: Understanding Ecosystem Process Variability Across Complex Terrain

Abstract

One of the largest knowledge gaps in environmental science is the ability to understand and predict how ecosystems will respond to future climate variability. The links between vegetation, hydrology, and climate that control carbon sequestration in plant biomass and soils remain poorly understood. Soil respiration is the second largest carbon flux of terrestrial ecosystems, yet there is no consensus on how respiration will change as water availability and temperature co-vary. To address this knowledge gap, we use the variation in soil development and topography across an elevation and climate gradient on the Front Range of Colorado to conduct a natural experiment that enables us to examine the co-evolution of soil carbon, vegetation, hydrology, and climate in an accessible field laboratory. The goal of this project is to further our ability to combine plant water availability, carbon flux and storage, and topographically driven hydrometrics into a watershed scale predictive model of carbon balance. We hypothesize: (i) landscape structure and hydrology are important controls on soil respiration as a result of spatial variability in both physical and biological drivers: (ii) variation in rates of soil respiration during the growing season is due to corresponding shifts in belowground carbon inputs from vegetation; andmore » (iii) aboveground carbon storage (biomass) and species composition are directly correlated with soil moisture and therefore, can be directly related to subsurface drainage patterns.« less

Authors:
 [1];  [2]
  1. Univ. of Colorado, Boulder, CO (United States)
  2. Univ. of Utah, Salt Lake City, UT (United States); Univ. of Arizona, Tucson, AZ (United States)
Publication Date:
Research Org.:
Univ. of Colorado, Boulder, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Contributing Org.:
Univ. of Utah, Salt Lake City, UT (United States); Univ. of Arizona, Tucson, AZ (United States)
OSTI Identifier:
1257514
Report Number(s):
DOE-Colorado-06968
DOE Contract Number:
SC0006968
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; 59 BASIC BIOLOGICAL SCIENCES

Citation Formats

Barnard, Holly, and Brooks, Paul. Carbon-water Cycling in the Critical Zone: Understanding Ecosystem Process Variability Across Complex Terrain. United States: N. p., 2016. Web. doi:10.2172/1257514.
Barnard, Holly, & Brooks, Paul. Carbon-water Cycling in the Critical Zone: Understanding Ecosystem Process Variability Across Complex Terrain. United States. doi:10.2172/1257514.
Barnard, Holly, and Brooks, Paul. Thu . "Carbon-water Cycling in the Critical Zone: Understanding Ecosystem Process Variability Across Complex Terrain". United States. doi:10.2172/1257514. https://www.osti.gov/servlets/purl/1257514.
@article{osti_1257514,
title = {Carbon-water Cycling in the Critical Zone: Understanding Ecosystem Process Variability Across Complex Terrain},
author = {Barnard, Holly and Brooks, Paul},
abstractNote = {One of the largest knowledge gaps in environmental science is the ability to understand and predict how ecosystems will respond to future climate variability. The links between vegetation, hydrology, and climate that control carbon sequestration in plant biomass and soils remain poorly understood. Soil respiration is the second largest carbon flux of terrestrial ecosystems, yet there is no consensus on how respiration will change as water availability and temperature co-vary. To address this knowledge gap, we use the variation in soil development and topography across an elevation and climate gradient on the Front Range of Colorado to conduct a natural experiment that enables us to examine the co-evolution of soil carbon, vegetation, hydrology, and climate in an accessible field laboratory. The goal of this project is to further our ability to combine plant water availability, carbon flux and storage, and topographically driven hydrometrics into a watershed scale predictive model of carbon balance. We hypothesize: (i) landscape structure and hydrology are important controls on soil respiration as a result of spatial variability in both physical and biological drivers: (ii) variation in rates of soil respiration during the growing season is due to corresponding shifts in belowground carbon inputs from vegetation; and (iii) aboveground carbon storage (biomass) and species composition are directly correlated with soil moisture and therefore, can be directly related to subsurface drainage patterns.},
doi = {10.2172/1257514},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jun 16 00:00:00 EDT 2016},
month = {Thu Jun 16 00:00:00 EDT 2016}
}

Technical Report:

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  • We have developed a geographically-distributed ecosystem model for the carbon, nitrogen, and water dynamics of the terrestrial biosphere TERRA. The local ecosystem model of TERRA consists of coupled, modified versions of TEM and DAYTRANS. The ecosystem model in each grid cell calculates water fluxes of evaporation, transpiration, and runoff; carbon fluxes of gross primary productivity, litterfall, and plant and soil respiration; and nitrogen fluxes of vegetation uptake, litterfall, mineralization, immobilization, and system loss. The state variables are soil water content; carbon in live vegetation; carbon in soil; nitrogen in live vegetation; organic nitrogen in soil and fitter; available inorganic nitrogenmore » aggregating nitrites, nitrates, and ammonia; and a variable for allocation. Carbon and nitrogen dynamics are calibrated to specific sites in 17 vegetation types. Eight parameters are determined during calibration for each of the 17 vegetation types. At calibration, the annual average values of carbon in vegetation C, show site differences that derive from the vegetation-type specific parameters and intersite variation in climate and soils. From calibration, we recover the average C{sub v} of forests, woodlands, savannas, grasslands, shrublands, and tundra that were used to develop the model initially. The timing of the phases of the annual variation is driven by temperature and light in the high latitude and moist temperate zones. The dry temperate zones are driven by temperature, precipitation, and light. In the tropics, precipitation is the key variable in annual variation. The seasonal responses are even more clearly demonstrated in net primary production and show the same controlling factors.« less
  • The southwestern United States experienced an extended drought from 1999-2002 which led to widespread coniferous tree mortality. Piñon-juniper (PJ) woodlands, which occupy 24 million ha throughout the Southwest, were extremely vulnerable to this drought. An abrupt die-off of 40 to 95% of piñon pine (Pinus edulis) and 2-25% of juniper (Juniperus monosperma) across 1.5 million ha triggered rapid and extensive changes in the structure of PJ woodlands with potentially large, yet unknown, consequences for ecosystem services and feedbacks between the carbon cycle and climate system. Given the spatial extent of PJ woodlands (3rd largest biome in the US) and climaticmore » predictions of increased frequency and intensity of drought in the region, it is crucial to understand the consequences of these disturbances on regional carbon and energy dynamics, biogeochemical processes and atmospheric CO2. The overall objective of our research was to quantify what impact widespread mortality of piñon trees has for carbon and water cycling in PJ woodlands. Our specific objectives for this proposal were: 1) Quantify the carbon, water and energy exchange trajectory after mortality in PJ woodlands; 2) Determine the mechanisms controlling the response and recovery of ecosystem production and respiration processes following large-scale piñon mortality; 3) Use the relationships we measure between ecosystem structure and function PJ woodlands recover from mortality to scale the results of our study up to the regional scale.« less
  • The major goal of this project was to improve understanding of processes that control the exchanges of CO 2 between the atmosphere and the land biosphere on decadal and longer time scales. The approach involves measuring the changes in atmospheric CO 2 concentration and the isotopes of CO 2 ( 13C/ 12C and 18O/ 16O) at background stations and uses these and other datasets to challenge and improve numerical models of the earth system. The project particularly emphasized the use of these data to improve understanding of changes occurring in boreal and arctic ecosystems over the past 50 years andmore » to seek from these data improved understanding of large-scale processes impacting carbon cycling, such as the responses to warming, CO 2 fertilization, and disturbance. The project also led to advances in the understanding of changes in water-use efficiency of land ecosystems globally based on trends in 13C/ 12C. The core element of this project was providing partial support for continuing measurements of CO 2 concentrations and isotopes from the Scripps CO 2 program, initiated by C. D. Keeling in the 1960s. The measurements included analysis of flasks collected at an array of ten stations distributed from the Arctic to the Antarctic. The project also supported modeling studies and interpretive work to help understand the origins of the large ~50% increase in the amplitude of the atmospheric CO 2 cycle detected at high northern latitudes between 1960 and present and to understand the long-term trend in carbon 13C/ 12C of CO 2. The seasonal cycle work was advanced through collaborations with colleagues at MPI Jena and Imperial College« less
  • Summary of research carried out under Interagency Agreement DE-AI02-07ER64355 with the USDA Forest Service at the Howland Forest AmeriFlux site in central Maine. Includes a list of publications resulting in part or whole from this support.
  • The monthly frequencies of nocturnal drainage flows in the Brush Creek valley were estimated over the period August 1982 to January 1985 for the purpose of evaluating the representativeness of the drainage flows observed during a few intensive study periods. These estimates were made on the basis of data from three short meteorological towers situated in the valley. The highest frequencies were observed during the June to October timeframes: 30 to 40% during 1983 and 10 to 30% during 1984. Of the ten experimental nights when intensive investigations were conducted within the Brush Creek valley, seven were during strong drainagemore » flow periods and three were during weaker drainage flow periods. The variability of sigma theta in complex terrain areas was investigated since this parameter is often used to estimate diffusion of pollutants. Measurements made during strong drainage flow periods within two valleys in The Geysers geothermal area in northern California and within the Brush Creek valley yielded hourly-averaged values that varied from a few degrees to a little over one hundred degrees at each measurement site. The median values typically ranged from 15{sup 0} to 40{sup 0}. Generally, the highest values were acquired at measurement sites situated on the valley floor; the lowest values on the ridges; and intermediate values along the slopes. This ordering may be due to the winds generally being stronger over the ridges than within the valley, since there is weak evidence for an inverse relationship between the median wind speeds and sigma theta values, even though this relationship was not in evidence between the individual measurements. 3 refs., 9 figs., 2 tabs.« less