Search

The eddy covariance technique (EC) is used worldwide to measure surface fluxes of greenhousegases and energy balance components. Nevertheless, in the scientific community it is well-knownthat EC presents an imbalance of the energy components. In this regard, the atmospheric boundarylayer (ABL) directly influences the mass and energy transfer between surface and atmosphere.Thus, knowledge and characterization of the ABL might be essential to disentangling the driverscausing the imbalance of the energy components measured by EC. This work aims to relate ABLcharacteristics to the accuracy of the surface energy balance closure (SEBC) obtained by EC.The study was carried out in an irrigated olive orchard (Olea europaea var. europaea L.) in theSoutheastern Iberian Peninsula (37.9427º N, 3.3002º W and 370 m asl) during the intensiveBLOOM (turBulence and oLea pOllen prOperties experiMent) campaign, from May 19th to June20th 2022. In order to characterise ABL dynamics, remote sensing techniques are commonly used.One of them is via Doppler lidar, which provides measurements of wind components andturbulence-related products at high spatial and temporal resolutions. In particular, a Doppler lidarStream Line (HALO photonics) with a temporal resolution of 2 seconds and 10 minutes (for verticaland scanning measurements, respectively) and 30 m of vertical spatial resolution was used toretrieve the turbulent kinetic energy dissipation rate (ε) and wind shear (sh) with a commonresolution of 3 minutes as indicators of convective and mechanical sources of turbulence,respectively. To assess the SEBC, we used (1) a three-axis sonic anemometer (CSAT-3, CampbellScientific, Logan, UT, USA) and an enclosed path infrared gas analyser (IRGA, Li-Cor 7200;Lincoln, NE, USA) on a tower 9 m tall to measure latent heat (λE) and sensible heat (H) fluxes; (2)an incoming and outgoing short- and long-wave 4-component radiometer (CNR-4, Kipp & Zonen,Delft, Netherlands) to measure net radiation (Rn); and (3) two each: soil moisture probes (CS616,CSI), thermocouples (TCAV, CSI) and heat flux plates (HFP01, Hukseflux, Delft, the Netherlands)at 0.10 m, 0.04 m and 0.08 m depth, respectively to calculate the soil heat flux (G).Preliminary results show that SEBC enhances under turbulent conditions (slope and R2 from 0.49and 0.92 to 0.81 and 0.94, respectively). However, when the source of turbulence is mechanical theSEBC is less accurate (slope and R2 from 0.82 and 0.94 to 0.77 and 0.9, respectively). A moredetailed study based on principal component analysis of the ABL height, skewness of the verticalwind velocity and vertical profile of horizontal wind, together with ε and sh, among other Dopplerlidar-derived products is expected to offer reliable information that is highly relevant regarding theinfluence of the ABL on the SEBC.ACKNOWLEDGMENTS: This work was supported by theSpanish Ministry of Science and Innovation through project PID2020-117825GB-C21(INTEGRATYON3), the Andalusian regional Development through the projects B-RNM-60-UGR20 (OLEAGEIs) and P18-RT-3629 (ICAERSA), including European Union ERDF funds.

For the last decade there has been a continuous increase in atmospheric methane. Methane (CH4) is the second most important greenhouse gas (after carbon dioxide, CO2). However, despite the recent international effort to quantify global CH4 fluxes, such information is still limited, with a significant source of uncertainty (from 51% to 82%) mainly attributed to emissions from wetlands and other inland waters. On the other hand, some research in arid ecosystems (drylands) has shown that they play an important role in the CH4 cycle as CH4 sinks. These uncertainties in quantifying potential methane sinks highlight the need to increase our understanding of this effect of dryland ecosystems.In this study we have quantified the capacity of two Mediterranean ecosystems as methane sinks. A lowland site located at 200 m.a.s.l and 6 km from the coast, in Cabo de Gata Natural Park (Almería, Spain; N36°56′26.0″, W2°01′58.8). This lowland is dominated by Stipa tenacissima at 60 % cover. And a subalpine site located at 1,600 m.a.s.l. and 25 km from the coast, in Sierra de Gádor (Almería; 36º55′41.7″N; 2º45′ 1.7″W). This site is a shrubland plateau derived from an open forest and its climate is Mediterranean with hot summers. Both study sites are included in the international network FLUXNET (https://fluxnet.org/about/).For this purpose, two techniques have been used, the Eddy covariance technique to measure CH4 fluxes at the ecosystem scale and a standardized camera system composed by an infrared gas analyser (LI-7810, Li-Cor, Lincoln, NE, USA) connected to a Smart Chamber (8200-01S, Li-Cor, Lincoln, NE, USA), to measure soil CH4 fluxes in intensive campaigns. The Eddy covariance technique was applied for several weeks during the dry season, while the camera system was used to measure fluxes during the rainy season and in the middle of the growing season. Thanks to this study we will be able to establish an approximate range of CH4 assimilation by these ecosystems, comparing this value with those obtained in other studies; additionally, we will analyse the effect of the different soil conditions (humidity, temperature, porosity, texture...) on CH4 fluxes in these "drylands".This work was supported by the projects P20_00016 (BAGAMET) and LifeWatch-2019-10-UGR-01, co-funded by the MICINN through the FEDER funds.

Olive groves occupy a large area in the Mediterranean and their management has repercussions on the carbon cycle in this region. Weed suppression is the most common management in this crop, but its implications for soil respiration (Rsoil) are not well estimated due to the lack in continuous Rsoil measurements. In this research we present a full year of Rsoil in an irrigated olive grove in which a glyphosate-based herbicide was applied to prevent spontaneous weeds (conventional management). For that, an automatic multi-chamber Rsoil system was used (LI-8100 + LI-8150 with 6 chambers, Li-Cor). In addition, soil temperature (Tsoil) and soil water content (SWC) were measured next to each chamber. To study the influence of olive trees on Rsoil, 3 chambers were placed near the olive trunk and another 3 in the middle of the alleys. Results show seasonal and spatial variability, with higher Rsoil in warm months and lower Rsoil in cold months. Also, Rsoil near the trunk was always larger than in the alleys. The spatial difference increased in the cold months. Diurnal variability was observed with higher Rsoil as the soil temperature increased in the alleys, but this was not observed near the trunks. Under the canopy, a decrease in the Rsoil is observed as the VPD increases, suggesting a major contribution of autotrophic respiration under the canopy. In addition, there is no positive and negative relationship with temperature and SWC under the canopy, while in the alleys, a strong hysteresis occurs in some periods. Finally, rain events were followed by Rsoil peaks. However, low intensity and short duration rain pulses did not manifest on the ground under the olive canopy, so interception is inhibiting this process in part of the agrosystem. This work was supported by the projects PID2020-117825GB-C21 & PID2020-117825GB-C22 (INTEGRATYON3), B-RNM-60-UGR20 (OLEAGEIs), P18-RT-3629 (ICAERSA) and PPJIB2022-08 funded by University of Granada.

The Mediterranean region has a great surface of olive crops where about 98% of the world’s olive agricultural area is represented. Of these lands, 2.7 Mha are in Spain with more than half concentrated in the Southeastern Iberian Peninsula. In this type of crop, the maintenance of natural herbaceous-cover in the alleys from autumn to spring is a common practice to protect the soil against erosion, but little is known yet about its contribution to CO2 and H2O fluxes and their seasonal variability. The eddy covariance technique is used worldwide to measure GHG fluxes at the ecosystem level. Additionally, this technique has been used successfully to measure fluxes below the canopy in closed forests and pastures. In this regard, continuous monitoring of eddy covariance CO2/H2O fluxes above and below the trees canopy was carried out in an irrigated olive grove (Olea europaea L.) in the Southeastern Iberian Peninsula in the hydrological year 2020-2021. The olive trees are distributed in a plantation frame of 12×12 m and the area is divided into two plots: 1) with natural herbaceous-cover from autumn to spring, then cut and left on the surface (hereafter HC); and 2) kept herbaceous-free by glyphosate-based herbicide application (hereafter HF). Each plot has two eddy covariance towers, one above the canopy (ecosystem tower) and the other below the canopy (subcanopy tower).A comparison between fluxes measured with the subcanopy towers and those measured with ecosystem towers showed the need for wind-direction filtering of the fluxes measured at the subcanopy level. Results show the relevance of selecting those fluxes coming from wind directions where the alleys are located in order to get accurate subcanopy CO2/H2O fluxes, avoiding those eddies coming from the olives. Regarding seasonal variability of the CO2/H2O fluxes measured at the subcanopy level, preliminary results showed that the HC plot behaved as a C light sink in winter (Dec., Jan., Feb.), being February the month with the most absorption averaging around 1.5 g C m-2 day-1 while HF behaved as C neutral. In the month before mowing (March), HC behaved as a sink, absorbing, on average, around 2.5 g C m-2 day-1, while HF acted as a light source emitting around 0.2 g C m-2 day-1. After mowing (from April to June) both HC and HF acted as sources, with HC yielding the largest values in April (around 2.1 g C m-2 day-1). Finally, in summer and autumn (from July to Nov.) both HC and HF appear to behave as weak C sources at the subcanopy level.

Olive grove management entails environmental and socio-economic repercussions for the Mediterranean region. Maintaining bare soil in alleys is the most common management in this crop, but its implications for soil respiration (Rsoil) are not well understood. Although previous studies have quantified Rsoil at specific moments, soil respiration has not yet been continuously measured in olive groves. In this study a complete year of Rsoil measurements was taken in an irrigated olive grove in southeast of Spain. To avoid spontaneous weed growth a glyphosate-based herbicide was periodically applied. Six automated soil CO2 efflux chambers with additional sensors of soil temperature (T) and soil water content (SWC) were controled by a multichamber monitoring system (Li-8100A, Li-cor). With the aim of know the spatial variability in Rsoil and facilitate scaling up to estimate ecosystem soil respiration, 3 chambers were installed under the olive tree canopy and 3 chambers in the alleys.Preliminary results show that Rsoil increased in the warmer months and decreased in the colder months as expected. Also, daily Rsoil values under the trees are normally several times higher than in the alleys but this ratio changed with the seasons. In warm months, daily Rsoil under the tree was 2-3 times higher than daily Rsoil in the alley, while in cold months (like January) it was 6 times higher. In the alleys, diurnal variability was detected in Rsoil except in winter. While Rsoil under the trees was practically constant throughout the day during the year except in summer when there appears to be a relationship with the decrease in the flux of photosynthates in environments with high VPD. In spring Rsoil-alleys was double at midday versus night-time. Additionally, a positive and a negative relationship was established with temperature and SWC respectively. On the other hand, we found no clear relationship for Rsoil under the tree with respect to T or SWC. These preliminary results suggest a considerable Rsoil component of total ecosystem respiration influenced by the tree which does not depend on changes in T and SWC and that should be included in the partition models.

The maintenance of spontaneous weed cover is a conservation practice used in olive groves. Herbaceous plants in alleys between the trees can increase the capacity of this agroecosystem to remove carbon. However, the influence of this practice on carbon assimilation at the leaf scale has not yet been studied in olive trees. Also, the presence of other species competing with olive trees for soil water has the potential to modify the water use efficiency, a key parameter in a climate change context. In this study, leaf-scale net carbon assimilation (Aleaf), transpiration (Eleaf) and water use efficiency as the ratio Aleaf/Eleaf(WUEleaf) were quantified in olive grove divided by two different treatments: (1) a weed-free (WF) ecosystem in which weed growth was inhibited by applying herbicide; and (2) a weed-covered (WC) ecosystem in which spontaneous herbaceous plants were kept and then mechanically mowed and left on the ground. A portable leaf photosynthesis system was used to measure olive leaf fluxes for both treatments, and likewise for the ecosystem scale via two eddy covariance towers assessing gross primary production (GPPeco), evapotranspiration (ETeco), and water use efficiency (WUEeco). We found that the average Aleaf was 24% higher in the WF treatment while GPPeco decreased 32% compared to WC treatment. However, Aleaf was significantly different between treatments only during weed growth: January-May (Aleaf-WF = 7.6±3.7 μmol CO2m−2s−1; Aleaf-WC = 5.1±3.1 μmol CO2m−2s−1) while Aleaf was similar between the two treatments after mowing. Mowed weeds decreased Tsoil and VPD, and these changes were accompanied by a decrease in Eleaf in olive trees. Therefore, this led to WUEleaf-WF>WUEleaf-WC when the weeds were growing and the opposite after mowing. Thus, although the presence of spontaneous weeds increased the annual ecosystem C uptake in the olive orchard, both Aleaf and seasonal fluctuations in WUEleaf were reduced with weed maintenance.

To the European Space Agency for the imagery of the Sentinel Missions and its open access. Special thanks to Radoslaw Guzinski for share and make accessible (https://github.com/radosuav/pyDMS) the implemented software for the used sharpening process (likewise to Hector Nieto for the implemented TSEB-PT, https://github.com/hectornieto/pyTSEB).To the Group of Castillo de Canena for the use of their farm as an experimental site and their people for continuous cooperation. We also give special thanks to Andrew S. Kowalski for his advice and suggestions. We would like also to express our gratitude to the anonymous reviewers for their comments and suggestions that enhanced this work. This work was supported by the Spanish Ministry of Science and Innovation through project CGL2017-83538-C3-1-R (ELEMENTAL) and PID2020-117825GB-C21 (INTEGRATYON3) Including European Union ERDF funds [grant number PRE2018-085638]. Funding for open access charge: Universidad de Granada/CBUA., Precipitation deficit and more extreme drought and precipitation events are expected to increase in the Mediterranean region due to global warming. A great part of this region is covered by olive orchards, representing 97.5% of the world’s olive agricultural area. Thus, the adaptation of olive cultivation demands climate-smart management, such as the optimization of water use efficiency, since evapotranspiration is one of the most important components of the water balance. The novelty of this work is the combination of the remote sensing data fusion and the Two Source Energy Balance (TSEB) model (through Sentinel-2 and Sentinel-3 imagery) to estimate the actual daily evapotranspiration (ETd), at high spatial (20 m) and temporal (daily) resolution, in an olive orchard under two management regimes: herbaceous free (HF) and herbaceous-cover (HC); along a three years period, based on the hypothesis that TSEB is still able to track and estimate the evapotranspiration over more complex canopies. The study was carried out from 2016 to 2019 in an olive orchard in the South of Spain, where the flux estimates were validated and assessed by in situ eddy covariance (EC) measurements. The results show better agreement in HC for net radiation (Rn) and the soil heat flux (G), but similar for both surfaces regarding the sensible (H) and latent (λE) heat fluxes, as well as ETd. On both surfaces greater differences obtained at higher H, and the magnitude of overestimation of λE and ETd were influenced by the EC energy imbalance. By contrast, G was overestimated with HC probably influenced by herbs, and equally underestimated for HF surfaces. The obtained results are in agreement with similar studies in tree crop orchards, and show the consistency of the used methodology and its usefulness for some farming activities, even on the more heterogeneous surface., Spanish Government CGL2017-83538-C3-1-R PID2020-117825GB-C21, European Commission PRE2018-085638, Universidad de Granada/CBUA

Olive groves are one of the most extensive crops in the Mediterranean region, hence, their management practices can result in significant environmental, social, and economic impacts. Given the generalized water stress conditions across the Mediterranean region, irrigation is usually applied to increase olive crop yield. In Spain, the country with the largest olive crop extension, 29% of the olive cultivated area is irrigated. Cover cropping (i.e. the maintenance of annuals and perennials in between tree rows) can be considered as one of the most widespread conservation practices. It is being increasingly adopted as a sustainable strategy to increase soil organic carbon content and mitigate soil degradation problems caused by soil erosion, apart from other benefits such as the increase of microfauna biodiversity. On the other hand, cover crops may also increase evapotranspiration and, consequently, water demand in olive production systems. While the influence of cover crops on carbon sequestration capacity of olive groves has been previously demonstrated to be positive, their effects on evapotranspiration and water use efficiency, defined as the ratio between carbon uptake and evapotranspiration, remain uncertain.In this study, we aim to assess the effect of cover crops on microclimate conditions, carbon sequestration, evapotranspiration and water use efficiency of an irrigated olive grove located in Jaén (SE Spain), where two adjacent areas were subjected to two different treatments: 1) weed-free treatment, in which a glyphosate-based herbicide is applied annually to avoid spontaneous weed growth (generally in early spring), and 2) weed-cover treatment (i.e. cover crop), where spontaneous weed cover was kept from autumn to spring. Both treatments are equipped with a wide range of environmental sensors to characterize short- and long-term variations in ambient conditions (e.g. air temperature, relative humidity, precipitation, incoming/reflected short- and long-wave radiation, soil moisture and temperature, soil heat flux). In addition, two eddy covariance towers allow the direct measurement of atmosphere-ecosystem exchanges of water, heat, carbon dioxide and momentum at a high temporal resolution (Preliminary results, based on data of the first hydrological year (2015-2016), show that cover crops increase ecosystem evapotranspiration. However, the net carbon uptake was higher in the weed-cover treatment compared to the weed-free treatment, leading to a net increase in ecosystem water use efficiency. Further, the Bowen ratio – conceived as the ratio between sensible and latent heat fluxes – was lower in the weed-cover than in the weed-free treatment. Therefore, despite the fact that cover crops increase water loss through evapotranspiration, they mitigate the carbon footprint of the agrosystem, likely having a positive effect on crop water use efficiency by maximizing the ratio of carbon assimilation to water loss.

Olive trees are one of the most important crops in the Mediterranean basin (10.5 Mha), accounting for 97.5% of the world’s olive cultivation area with relevant social and economic benefits and ecological consequences. Concretely, it takes up 2.7 Mha in Spain, of which more than 1.6 are in Andalusia. Olive cultivation demands climate-smart management to facilitate crop adaptation to climate scenario and predictable development. A more efficient water use and management optimization is an especially important issue and, therefore, quantifying and modeling evapotranspiration (ET) is essential.However, given the lack of a satellite thermal mission with both high spatial resolution and frequent revisit time, we have evaluated in this work a data fusion methodology (Gao et al., 2012) that combines Sentinel-2 and Sentinel-3 images with the two-source energy balance model (Norman et al.,1995) proposed by Guzinski & Nieto et al. (2019). Estimates of actual ET were produced at 20 m resolution from January 2016 to December 2019 in an irrigated olive grove in Southern Iberian Peninsula. Preliminary results have been validated (every 5-10 days depending on Sentinel images availability and cloud cover) by ground-based in situ data using Eddy Covariance (EC) technique, showing mean absolute errors between estimated values and those obtained by EC: 156 Wm-2 (net radiation), 76 Wm-2 (soil heat flux), 36 Wm-2 (sensible heat flux), 210 Wm-2 (latent heat flux).Gao, F., Kustas, W. P., & Anderson, M. C. (2012). A data mining approach for sharpening thermal satellite imagery over land. Remote Sensing, 4(11), 3287–3319. https://doi.org/10.3390/rs4113287Guzinski, R., & Nieto, H. (2019). Evaluating the feasibility of using Sentinel-2 and Sentinel-3 satellites for high resolution evapotranspiration estimations. Remote Sensing of Environment, 221, 157–172. https://doi.org/10.1016/j.rse.2018.11.019Norman, J. M., Kustas, W. P., & Humes, K. S. (1995). Source approach for estimating soil and vegetation energy fluxes in observations of directional radiometric surface temperature. Agricultural and Forest Meteorology, 77(3–4), 263–293. https://doi.org/10.1016/01681923(95)02265Y

The management of olive groves has a direct impact on the environment in the Mediterranean region since it is one of the most representative crops in this area. In order to prevent erosion and improve the physical-chemical conditions of the soil in these crops, the maintenance of weed cover in the alleys is an increasingly common practice. It increases the organic carbon content in the soil, improves biodiversity indices and enhances various ecosystem services such as pollination and infiltration. Now, the role of vegetation cover in olive groves on biogeochemical cycles is being studied. Although previous studies have quantified the combined effect of weed cover and olive trees on carbon and water at ecosystem level, the role of this conservation practice at the leaf level has not yet been explored.The aim of this study is to quantify the effect of weed cover on the net CO2 assimilation (An) and transpiration (T) rates in an irrigated olive grove. To do this, two plots of olive trees with irrigation (Olea europea L. "Arbequina") in southeast Spain were sampled. In the weed-cover one (WC), spontaneous vegetation is maintained until it is mechanically mowed and left in place. In the weed-free (WF) a glyphosate-based herbicide is applied. The data were taken with a portable gas analyzer (LI-6800, Li-Cor) controlling the following environmental variables on olive leaves: atmospheric CO2, relative humidity, photosynthetic active radiation and temperature. One campaign per month was carried out (from January-2018 to January-2019) where 10 random trees were analysed in each treatment. In addition, an eddy covariance tower provided CO2 and H2O fluxes at ecosystem level and they were compared with the fluxes obtained from leaf-level campaigns.The results shown significant differences for T only in the period after mowing with Twc= 2.0 ± 0.7 mmol H2O m-2s-1 vs Twf = 2.5 ± 1.0 mmol H2O m-2s-1. However, in this period ET is equal in both treatments, which suggests that the alleys with mowed weed has more ET than bare soil in the other treatment. On the other hand, there are significant differences for Anet only in the period before mowing with Anet-wc = 5.5 ± 3.1 μmol CO2 m-2s-1 vs Anet-wf = 8.0 ± 3.6 μmol CO2 m-2s-1. When the weeds are mowed, Anet is matched in both treatments. However, higher values of NEEwc than NEEwf are observed in the period before mowing. This suggest that the weed-cover olive groves at ecosystem level take up more carbon when the weed-cover is established although the leaves of olive trees are capturing less CO2.

Wetlands are crucial ecosystems modulating climate change due to their great potential to capture carbon dioxide (CO2), emit methane (CH4) and regulate local climate through evapotranspiration (ET). Common reed wetlands are particularly interesting given their high productivity, abundance and highly efficient internal gas-transport mechanism. However, little is known about the interannual behavior and dominant controlling factors of Mediterranean reed wetlands, characterized by seasonal flooding and remarkable weather variability. After 6 years of ecosystem carbon and ET flux measurements by eddy covariance (3 years for CH4 fluxes), this study shows the functional vulnerability of such wetlands to climate variability, switching between carbon (CO2+CH4) sink (660 g CO2-eeq m-2 y -1 , in 2014) and source (360 g CO2-eq m-2 y -1 , in 2016) in short periods of time. According to our analyses, the great interannual variability appeared to mainly depend on the behavior of reed growth dynamics during the transition to senescence period, what is confirmed through the Enhanced Vegetation Index as a proxy of photosynthetic activity. Additionally, a similar behavior of seasonal and daily patterns of carbon fluxes and ET was found compared with other wetlands under different climates.