The lateral transport of carbon has been increasingly recognized as an important component of carbon budget in wetlands. We studied a typical coastal salt marsh located at the estuary of the Yangtze ...River by measuring lateral transfer of macro-detritus carbon within a creek during each month’s largest spring tide period, and simultaneously, we measured the gross primary production (GPP) by the eddy covariance (EC) method. The results showed a bimodal seasonal pattern of net detritus carbon export, with one peak associated with mainly green/fresh carbon materials and the other peak associated with mainly yellow-dark/senescent carbon materials. We also found that the export of green detritus carbon was highly correlated with plant phenology and the height of tides, suggesting influences from both the standing stock of living biomass and the force of tides. GPP measured by the EC technique (GPP
EC
) and by remote sensing (GPP
RS
) differed substantially. We found this difference was correlated well with the net export of green macro-detritus. In general, we concluded that the lateral flux is an important component of the carbon budget in the marsh and that to cross validate between GPP
EC
and GPP
RS
, it must be included as a calibration term for computing GPP
EC
.
Compost amendment to rangelands is a proposed nature‐based climate solution to increase plant productivity and soil carbon sequestration. However, it has not been evaluated using quasicontinuous ...ecosystem‐scale measurements. Here, we present the first study to utilize eddy covariance and footprint partitioning to monitor carbon exchange in a grassland with and without compost amendment, monitoring for 1 year before and 1 year after treatment. Compost amendment to an annual California grassland was found to enhance net ecosystem removal of carbon. Our study confirmed that compost‐amended grasslands, similar to nonamended grasslands, are net carbon sources to the atmosphere; however, the amendment appears to be slowing down the rate at which these ecosystems lose carbon by 0.71 Mg C ha−1 per growing season. Digital repeated imagery of the canopy revealed that compost‐amended grasslands experienced an earlier green‐up, resulting in an overall longer growing season by >60 days. Notably, we did not detect significantly higher amounts of soil carbon in compost‐amended soils. High variability in soil carbon demands greater sampling replication in future studies. A longer growing season and higher productivity are hypothesized to be a result of greater availability of macronutrients and micronutrients in the top layer of soil (specifically nitrogen, phosphorus, and zinc).
Plain Language Summary
Previous research in California rangelands has shown that spreading a single thin layer of compost on grasslands can improve plant growth and therefore help to store more carbon in the soil. However, this previous research was constrained to small research plots. This is the first study that continuously monitored how compost affects the flow of carbon into and out of the grassland across multiple acres using a technique called eddy covariance. Our study confirmed that grasslands that receive compost have overall higher productivity or photosynthesis compared to control grasslands. Soil measurements found significantly elevated nutrients in the top layer of soil, specifically nitrogen, phosphorus, and zinc. Further, this was the first study to continuously take digital pictures to understand how compost affects the life cycles of grassland ecosystems. Examining these images revealed that the compost extended the growing season of the grasslands by >60 days. We hypothesize that the compost added essential nutrients to the soil that allowed the grasses to have a longer growing season and have higher productivity, confirming earlier studies that compost amendment to grasslands may be a viable approach for mitigating climate change.
Key Points
A compost amendment to a grazed CA grassland enhanced gross primary productivity, due to an earlier green‐up and longer growing season
Soil nitrogen, phosphorus, and zinc were significantly elevated in surface soils following compost amendment
Changes in phenology highlight the importance of scale‐emergent processes associated with nature‐based climate solutions
Hydroclimate in the montane cloud forest (MCF) regions is unique for its frequent fog occurrence and abundant water interception by tree canopies. Latent heat (LH) flux, the energy flux associated ...with evapotranspiration (ET), plays an essential role in modulating energy and hydrological cycles. However, how LH flux is partitioned between transpiration (stomatal evaporation) and evaporation (nonstomatal evaporation) and how it impacts local hydroclimate remain unclear. In this study, we investigated how fog modulates the energy and hydrological cycles of MCF by using a combination of in situ observations and model simulations. We compared LH flux and associated micrometeorological conditions at two eddy-covariance sites—Chi-Lan (CL), an MCF, and Lien-Hua-Chih (LHC), a noncloud forest in Taiwan. The comparison between the two sites reveals an asymmetric LH flux with an early peak at 0900 local time in CL as opposed to LHC, where LH flux peaks at noon. The early peak of LH flux and its evaporative cooling dampen the increase in near-surface temperature during the morning hours in CL. The relatively small diurnal temperature range, abundant moisture brought by the valley wind, and local ET result in frequent afternoon fog formation. Fog water is then intercepted by the canopy, sustaining moist conditions throughout the night. To further illustrate this hydrological feedback, we used a land surface model to simulate how varying canopy water interception can affect surface energy and moisture budgets. Our study highlights the unique hydroclimatological cycle in the MCF and, specifically, the inseparable relationship between the canopy and near-surface meteorology during the diurnal cycle.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Grazing profoundly influences vegetation and the subsequent carbon fluxes in various ecosystems. However, little effort has been made to explore the underlying mechanisms for phenological changes and ...their consequences on carbon fluxes at ecosystem level, especially under the coupled influences of human disturbances and climate change. Here, a manipulative experiment (2012–2013) was conducted to examine both the independent and interactive effects of grazing and watering on carbon fluxes across phenological phases in a desert steppe. Grazing advanced or delayed phenological timing, leading to a shortened green-up phase (GrP: 23.60 days) in 2013 and browning phase (BrP: 12.48 days) in 2012 from high grazing, and insignificant effects on the reproductive phase (ReP) in either year. High grazing significantly enhance carbon uptake, while light grazing reduce carbon uptake in ReP. Watering only delayed the browning time by 5.01 days in 2013, producing no significant effects on any phenophase. Watering promoted the net ecosystem exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP) only in the GrP. When calculating the yearly differences in phenophases and the corresponding carbon fluxes, we found that an extended GrP greatly enhanced NEE, but a prolonged ReP distinctly reduced it. The extended GrP also significantly promote GEP. Increases in growing season length appeared promoting ER, regardless of any phenophase. Additionally, the shifts in NEE appeared dependent of the variations in leaf area index (LAI).
•We developed a new method “co-flowering ratio” to connect phenology observations and ecosystem carbon fluxes by scaling the phenology from species to community level.•Grazing had complicate effects on green-up, reproductive and browning timing, leading to a contracted green-up phase (GrP: 23.60 days) in 2013 and browning phase (BrP: 12.48 days) in 2012. Intensive grazing significantly enhance carbon uptake, while light grazing reduce it in reproductive phase (ReP). Watering prolonged the browning time, and have no significant effects on any phenophases. Watering also promoted the NEE, ER, and GEP only in the GrP.•We examined whether the extended growing season enhancing carbon uptake at the region- or biome-scales are still stand at community level. We found that extra green-up phase enhanced the carbon uptake, while prolonged reproductive duration reduced the carbon uptake.•Photosynthetic area (i.e., LAI) is a critical proxy determining the divergent carbon contributions between green-up and reproductive phases.
•We applied the newly developed partial wavelet coherence to ecological time series data.•Between PAR and Ta, PAR was the major driver for NEE at short scales from hours to a day, and Ta was the ...major driver for NEE at long scales (seasonal to annual).•At the daily scale, Ta lagged NEE 2–3h and PAR did not lag NEE, while at the annual scale, Ta did not lag NEE but PAR led NEE by about 34 days.•Most of the variation of NEE happened at seasonal and annual scales, and significant variation at daily scales only in the growing seasons.
Net ecosystem exchange of CO2 (NEE) in temperate forests is modulated by multiple microclimatic factors. The effects of these factors vary across time scales, with some correlated to produce confounding effects. Photosynthetically active radiation (PAR) and air temperature (Ta) are among the two most important drivers of NEE in temperate forests and are highly correlated because of their similar diel and annual cycles. In this study, we attempted to disentangle the confounding effects of them on NEE at multiple time scales. We applied innovative spectral analysis techniques, including the continuous wavelet transformation (CWT), cross wavelet transformation (XWT), wavelet coherent (WTC), and partial wavelet coherence (PWC), on a seven-year time series (2004–2010) of PAR, Ta, and NEE from the Ohio Oak Openings Ameriflux site (N 41.5545°, W 83.8438°), USA. We found that PAR was the primary driver at short time scales (e.g., multi-hour and daily), while Ta dominated NEE at long time scales (e.g., seasonal to annual). At the daily scale, PAR co-varied with NEE without time lag, while Ta lagged PAR for 2–3h during growing seasons, which could be explained by the strong dependence of NEE on photosynthesis, which has a similar time lag of 2–3h of Ta to PAR. At the daily scale, during the non-growing seasons, NEE varied little and co-varied with Ta and PAR with no high common power. At the annual scale, Ta co-varied with NEE with no time delay, but PAR led NEE by about one month. This can be explained by the strong dependence of leaf area index (LAI) on Ta as well as the lag between the LAI/biomass development and the progress of sunlight. We also found that NEE distributes most of its variation at seasonal and annual scales, suggesting that Ta is more important than PAR in determining the annual and long-term carbon budget.
Aerodynamic canopy height (ha) is the effective height of vegetation canopy for its influence on atmospheric fluxes and is a key parameter of surface‐atmosphere coupling. However, methods to estimate ...ha from data are limited. This synthesis evaluates the applicability and robustness of the calculation of ha from eddy covariance momentum‐flux data. At 69 forest sites, annual ha robustly predicted site‐to‐site and year‐to‐year differences in canopy heights (R2 = 0.88, 111 site‐years). At 23 cropland/grassland sites, weekly ha successfully captured the dynamics of vegetation canopies over growing seasons (R2 > 0.70 in 74 site‐years). Our results demonstrate the potential of flux‐derived ha determination for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land use change, and disturbance. The large‐scale and time‐varying ha derived from flux networks worldwide provides a new benchmark for regional and global Earth system models and satellite remote sensing of canopy structure.
Plain Language Summary
Vegetation canopy height is a key descriptor of the Earth surface and is in use by many modeling and conservation applications. However, large‐scale and time‐varying data of canopy heights are often unavailable. This synthesis evaluates the applicability and robustness of the calculation of canopy heights from the momentum flux data measured at eddy covariance flux tower sites (i.e., meteorological observation towers with high frequency measurements of wind speed and surface fluxes). We show that the aerodynamic estimation of annual canopy heights robustly predicts the site‐to‐site and year‐to‐year differences in canopy heights across a wide variety of forests. The weekly aerodynamic canopy heights successfully capture the dynamics of vegetation canopies over growing seasons at cropland and grassland sites. Our results demonstrate the potential of aerodynamic canopy heights for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land use change, and disturbance. Given the amount of data collected and the diversity of vegetation covered by the global networks of eddy covariance flux tower sites, the flux‐derived canopy height has great potential for providing a new benchmark for regional and global Earth system models and satellite remote sensing of canopy structure.
Key Points
Aerodynamic canopy height can be calculated robustly and routinely from the eddy covariance momentum flux data
Our estimates match well with in situ measurements of canopy heights across a wide variety of vegetation and ecosystem types
Aerodynamic canopy height can be used to track the dynamics of vegetation canopies, including plant growth, harvest, and disturbance
Eddy covariance measurements were made in seven fields in the Midwest USA over 4 years (including the 2012 drought year) to estimate evapotranspiration (ET) of newly established rain‐fed cellulosic ...and grain biofuel crops. Four of the converted fields had been managed as grasslands under the USDA's Conservation Reserve Program (CRP) for 22 years, and three had been in conventional agriculture (AGR) soybean/corn rotation prior to conversion. In 2009, all sites were planted to no‐till soybean except one CRP grassland that was left unchanged as a reference site; in 2010, three of the former CRP sites and the three former AGR sites were planted to annual (corn) and perennial (switchgrass and mixed‐prairie) grasslands. The annual ET over the 4 years ranged from 45% to 77% (mean = 60%) of the annual precipitation (848–1063 mm; November–October), with the unconverted CRP grassland having the highest ET (622–706 mm). In the fields converted to annual and perennial crops, the annual ET ranged between 480 and 639 mm despite the large variations in growing‐season precipitation and in soil water contents, which had strong effects on regional crop yields. Results suggest that in this humid temperate climate, which represents the US Corn Belt, water use by annual and perennial crops is not greatly different across years with highly variable precipitation and soil water availability. Therefore, large‐scale conversion of row crops to perennial biofuel cropping systems may not strongly alter terrestrial water balances.
•Indirect effects drive the majority of interannual variability in CO2 fluxes.•Annual GEP and ER co-vary and dampen the variability in annual CO2 uptake.•CO2 fluxes respond differently to similar ...climate conditions in co-located ecosystems.
Recent climate variability and anomaly in the Great Lakes region provided a valuable opportunity in examining the response and regulation of ecosystem carbon cycling across different ecosystems. A simple Bayesian hierarchical model was developed and fitted against three-year (2011–2013) net ecosystem CO2 exchange (FCO2) data observed at three eddy-covariance sites (i.e., a deciduous woodland, a cropland, and a marsh) in northwestern Ohio. The model was designed to partition the variation of gross ecosystem production (GEP), ecosystem respiration (ER) and FCO2 that resulted directly from the short-term environmental forcing (i.e., direct effect) and indirectly from the changes of ecosystem functional traits (e.g., structural, physiological, and phenological traits) (i.e., indirect effect). Interannual variation of FCO2 was mainly driven by indirect effects, accounting for 54%, 89%, and 86% of the interannual variation at the woodland, cropland, and marsh sites, respectively. On the other hand, direct climatic effects accounted for 33% of interannual FCO2 variation at the woodland site and became irrelevant (<10%) at the cropland and marsh sites. In general, annual GEP and ER at each site tended to co-vary and dampen the interannual variability in FCO2. Yet, year-to-year changes of GEP and ER were not spatially synchronous, suggesting that the ecosystem's response to climate was strongly site-specific in terms of the annual net CO2 uptake. Future research should focus on the disparate response among ecosystems and develop a suitable framework to examine the mechanisms that drive differences in closely co-located ecosystems.
In this study, we propose a new technique for mapping the spatial heterogeneity in gas exchange around flux towers using flux footprint modeling and focusing on detecting hot spots of methane (CH4) ...flux. In the first part of the study, we used a CH4 release experiment to evaluate three common flux footprint models: the Hsieh model (Hsieh et al., 2000), the Kljun model (Kljun et al., 2015), and the K & M model (Kormann and Meixner, 2001), finding that the K & M model was the most accurate under these conditions. In the second part of the study, we introduce the Footprint‐Weighted Flux Map, a new technique to map spatial heterogeneity in fluxes. Using artificial CH4 release experiments, natural tracer approaches and flux chambers we mapped the spatial flux heterogeneity, and detected and validated a hot spot of CH4 flux in a oligohaline restored marsh. Through chamber measurements during the months of April and May, we found that fluxes at the hot spot were on average as high as 6589 ± 7889 nmol m−2 s−1 whereas background flux from the open water were on average 15.2 ± 7.5 nmol m−2 s−1. This study provides a novel tool to evaluate the spatial heterogeneity of fluxes around eddy‐covariance towers and creates important insights for the interpretation of hot spots of CH4 flux, paving the way for future studies aiming to understand subsurface biogeochemical processes and the microbiological conditions that lead to the occurrence of hot spots and hot moments of CH4 flux.
Plain Language Summary
Wetlands are capable of sequestering large amounts of carbon in their soils but they also emit about a third of all the methane emissions to the atmosphere. These methane emissions vary significantly in space, with some places becoming hot spots of methane flux that so far remain understudied. In this paper, we present a new method to map the spatial heterogeneity in methane fluxes in wetlands as measured by flux towers called eddy covariance towers. We find that this new technique can be used to map the spatial heterogeneity in fluxes of multiple greenhouse gases, with a special ability to map hot spots of methane flux. The presence and the magnitude of these hot spots are validated using chamber measurements finding satisfactory results. This technique paves the way for future studies whose goal is to understand what are the chemical and microbiological processes in the soils leading to these high methane emissions, and thus create strategies to better model and mitigate the consequent warming of the atmosphere.
Key Points
We mapped hot spots of methane flux in wetlands using Footprint‐Weighted Flux Maps and validated them using tracer releases and chambers
The proposed method provides mapping of the spatial heterogeneity in sources/sinks of trace gases around eddy covariance towers
The flux footprint model of Kormann & Meixner (2001) had the best performance based on a methane release experiment
Tidal wetlands play an important role in global carbon cycling by storing carbon in sediment at millennial time scales, transporting dissolved carbon into coastal waters, and contributing ...significantly to global CH4 budgets. However, these ecosystems' greenhouse gas monitoring and predictions are challenging due to spatial heterogeneity and tidal flooding. We utilized eddy covariance and chamber measurements to quantify fluxes of CO2 and CH4 at a restored tidal saltmarsh across spatial and temporal scales. Eddy covariance data revealed that the site was a strong net sink for CO2 (−387 g C‐CO2 m−2 yr−1, SD = 46) and a small net source of CH4 (0.7 g C‐CH4 m−2 yr−1, SD = 0.4). After partitioning net ecosystem exchange of CO2 into gross primary production and ecosystem respiration, we found that high net uptake of CO2 was due to low respiration emissions rather than high photosynthetic rates. We also found that respiration rates varied between land covers with increased respiration in mudflats compared to vegetated areas. Daytime soil chamber measurements revealed that the greatest CO2 emission was from higher elevation mudflat soils (0.5 μmol m−2s−1, SE = 1.3) and CH4 emission was greatest from lower elevation Spartina foliosa soils (1.6 nmol m−2s−1, SD = 8.2). Overall, these results highlight the importance of the relationships between wetland plant community and elevation, and inundation for CO2 and CH4 fluxes. Future research should include the use of high‐resolution imagery, automated chambers, and a focus on quantifying carbon exported in tidal waters.
Plain Language Summary
At the ecosystem level, a restored tidal salt marsh in the South San Francisco Bay California took in more carbon dioxide (CO2) from the atmosphere through photosynthetic activity than it emitted through respiration, and it emitted very small amounts of methane (CH4). This site appears to be a stronger sink for CO2 compared to other tidal marsh sites due to the very low rate of CO2 being lost through respiration to the atmosphere, rather than strong photosynthetic rates. We also found that ecosystem level CO2 emissions and the responses to temperature and light varied based on land cover type. By measuring soil surface emissions from each of the main land cover types of pickleweed, cordgrass, and mudflats we found that on average soils with lower elevation where cordgrass grows were stronger sources of CH4 while mudflat soils with greater elevation were stronger sources of CO2.
Key Points
Soil chamber measurements were able to detect significant differences in CO2 and CH4 fluxes between land cover types
Vegetation and microtopography are drivers of the spatially heterogeneous CO2 and CH4 emissions within the wetland
At the ecosystem level, high net uptake of CO2 was the result of low respiration emissions, suggesting lateral transport of dissolved CO2
PDF
