Journal of Geophysical Research: Biogeosciences

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ISSN / EISSN : 2169-8953 / 2169-8961
Published by: American Geophysical Union (AGU) (10.1029)
Total articles ≅ 1,942
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Journal of Geophysical Research: Biogeosciences; https://doi.org/10.1029/2021jg006458

Abstract:
While a stimulating effect of plant primary productivity on soil carbon dioxide (CO2) emissions has been well documented, links between gross primary productivity (GPP) and wetland methane (CH4) emissions are less well investigated. Determination of the influence of primary productivity on wetland CH4 emissions (FCH4) is complicated by confounding influences of water table level and temperature on CH4 production, which also vary seasonally. Here, we evaluate the link between preceding GPP and subsequent FCH4 at two fens in Wisconsin using eddy covariance flux towers, Lost Creek (US-Los) and Allequash Creek (US-ALQ). Both wetlands are mosaics of forested and shrub wetlands, with US-Los being larger in scale and having a more open canopy. Co-located sites with multi-year observations of flux, hydrology, and meteorology provide an opportunity to measure and compare lag effects on FCH4 without interference due to differing climate. Daily average FCH4 from US-Los reached a maximum of 47.7 ηmol CH4 m-2·s-1 during the study period, while US-ALQ was more than double at 117.9 ηmol CH4 m-2·s-1. The lagged influence of GPP on temperature-normalized FCH4 (Tair-FCH4) was weaker and more delayed in a year with anomalously high precipitation than a following drier year at both sites. FCH4 at US-ALQ was lower coincident with higher stream discharge in the wet year (2019), potentially due to soil gas flushing during high precipitation events and lower water temperatures. Better understanding of the lagged influence of GPP on FCH4 due to this study has implications for climate modeling and more accurate carbon budgeting.
Tzu‐Shun Lin, Yang Song, Peter Lawrence, Haroon S. Kheshgi,
Journal of Geophysical Research: Biogeosciences; https://doi.org/10.1029/2021jg006304

Abstract:
A land process model, ISAM, is extended to simulate contemporary soybean and maize crop yields accurately and changes in yield over the period 1901-2100 driven by environmental factors (atmospheric CO2 level ([CO2]) and climate), and management factors (nitrogen input, and irrigation). Over the 20th century, each factor contributes to global yield increase; increasing nitrogen fertilization rates is the strongest driver for maize, and increasing [CO2] is the strongest for soybean. Over the 21st century, crop yields are projected under two future scenarios, RCP4.5-SSP2 and RCP8.5-SSP5; the warmer temperature drives yields lower while rising [CO2] drives yields higher. The adverse warmer temperature effect of maize and soybean is offset by other drivers, particularly the increase in [CO2], and resultant changes in the phenological events due to climate change, particularly planting dates and harvesting times, by 2090s under both scenarios. Global yield for maize increases under RCP4.5-SSP2, which experiences continued growth in [CO2] and higher nitrogen input rates. For soybean, yield increases at a similar rate. However, in RCP8.5-SSP5 maize yield declines because of greater climate warming, extreme heat stress conditions, and weaker nitrogen fertilization than RCP4.5-SSP2, particularly in tropical and subtropical regions, suggesting that application of advanced technologies, and stronger management practices, in addition to climate change mitigation, may be needed to intensify crop production over this century. The model also projects spatial variations in yields; notably, the higher temperatures in tropical and subtropical regions limit photosynthesis rates and reduce light interception, resulting in lower yields, particularly for soybean under RCP8.5-SSP5.
Yuanfeng Sun, Yuhao Feng, Yupin Wang, Xia Zhao, , , Shaopeng Wang, Haojie Su, Jiangling Zhu, , et al.
Journal of Geophysical Research: Biogeosciences; https://doi.org/10.1029/2021jg006472

Abstract:
Net primary productivity (NPP) in global grasslands is a critical component of terrestrial carbon cycling and the primary source of food for herbivores. However, the size and spatial distribution of NPP across global grasslands remain unclear, especially for belowground NPP (BNPP), which limits our understanding of above- and belowground carbon cycling and the assessments of herbivore food security. Here, we compiled a comprehensive grassland NPP database with 1467 field measurements to estimate the spatial distributions of aboveground NPP (ANPP), BNPP, total NPP (TNPP), and the fraction of BNPP (fBNPP) using the random forest (RF) model. The global mean grassland ANPP, BNPP, TNPP, and fBNPP were 433 ± 31, 593 ± 47, 979 ± 78 g m-2 yr-1, and 0.54 ± 0.02, respectively. The total ANPP, BNPP and TNPP over global grasslands were 6.84 ± 0.49, 9.36 ± 0.74, and 15.46 ± 1.23 Pg C yr-1, respectively. ANPP, BNPP and TNPP exhibited decreasing trends from low latitudes towards the poles. The spatial pattern of fBNPP was almost opposite to that of ANPP. Climate was a major determinant in shaping the spatial distribution of ANPP and TNPP, while soil and vegetation had significant impacts on that of BNPP and fBNPP. Our findings suggest that field data-driven estimation of NPP using the RF model could be a useful approach for obtaining spatially-explicit NPP of grasslands, particularly BNPP products, and that more attention should be paid on belowground and non-climatic factors to better assess the carbon cycle in global grasslands.
, G. Celis, J.D. Ledman, , , E.–F. Pegoraro, C. del Schä,
Journal of Geophysical Research: Biogeosciences; https://doi.org/10.1029/2021jg006376

Abstract:
Rapid Arctic warming is causing permafrost to thaw and exposing large quantities of soil organic carbon (C) to potential decomposition. In dry upland tundra systems, subsidence from thawing permafrost can increase surface soil moisture resulting in higher methane (CH4) emissions from newly waterlogged soils. The proportion of C released as carbon dioxide (CO2) and CH4 remains uncertain as previously dry landscapes transition to a thawed state, resulting in both wetter and drier microsites. To address how thaw and moisture interact to affect total C emissions, we measured CH4 and CO2 emissions from paired chambers across thaw and moisture gradients created by nine years of experimental soil warming in interior Alaska. Cumulative growing season (May – September) CH4 emissions were elevated at both wetter (216.1 – 1099.4 mg CH4-C m-2) and drier (129.7 – 392.3 mg CH4-C m-2) deeply thawed microsites relative to shallow thaw (55.6 – 215.7 mg CH4-C m-2) and increased with higher deep soil temperatures and permafrost thaw depth. Interannual variability in CH4 emissions was driven by wet conditions in graminoid dominated plots that generated >70% of emissions in a wet year. Shoulder season emissions were equivalent to growing season CH4 emissions rates in the deeply thawed, warmed soils, highlighting the importance of non–growing season CH4 emissions. Net C sink potential was reduced in deeply thawed wet plots by 4 – 42%, and by 3.5 – 8% in deeply thawed drier plots due to anaerobic respiration, suggesting that some dry upland tundra landscapes may transition into stronger CH4 sources in a warming Arctic.
, I.B. Fournier, , , , , J.B. Cotner, , S.E. Hampton, N.R. Lottig, et al.
Journal of Geophysical Research: Biogeosciences; https://doi.org/10.1029/2020jg006165

Abstract:
Millions of lakes worldwide are distributed at latitudes or elevations resulting in the formation of lake ice during winter. Lake ice affects the transfer of energy, heat, light, and material between lakes and their surroundings creating an environment dramatically different from open-water conditions. While this fundamental restructuring leads to distinct gradients in ions, dissolved gases, and nutrients throughout the water column, surprisingly little is known about the resulting effects on ecosystem processes and food webs, highlighting the lack of a general limnological framework that characterizes the structure and function of lakes under a gradient of ice cover. Drawing from the literature and three novel case studies, we present the Lake Ice Continuum Concept (LICC) as a model for understanding how key aspects of the physical, chemical, and ecological structure and function of lakes vary along a continuum of winter climate conditions mediated by ice and snow cover. We examine key differences in energy, redox, and ecological community structure and describe how they vary in response to shifts in physical mixing dynamics and light availability for lakes with ice and snow cover, lakes with clear ice alone, and lakes lacking winter ice altogether. Global change is driving ice covered lakes toward not only warmer annual average temperatures but also reduced, intermittent or no ice cover. The LICC highlights the wide range of responses of lakes to ongoing climate-driven changes in ice cover and serves as a reminder of the need to understand the role of winter in the annual aquatic cycle.
Lingjing Xu, , , Xingru Feng, Guandong Gao, Xuan Cui, Tao Bai,
Journal of Geophysical Research: Biogeosciences; https://doi.org/10.1029/2021jg006424

Abstract:
Dinoflagellates frequently cause harmful, large-scale spring algal blooms in the Changjiang Estuary and adjacent seas of China. However, the population source of some dinoflagellates in this area remains unknown. We deployed an adjoint model and a coupled physical-biological model to explore the possible nonlocal dinoflagellate population sources to the Changjiang Estuary and adjacent seas. Our simulation results revealed that the Taiwan Strait and the area east of Taiwan are two nonlocal source regions of May dinoflagellate blooms in the study area. Under different hydrodynamic and biochemical conditions, dinoflagellates from the Taiwan Strait directly triggered dinoflagellate blooms from south to north along the coast of China. Dinoflagellates from the area east of Taiwan first concentrated and bred in the offshore temperature frontal area and then spread southwestward, triggering dinoflagellate blooms along the Zhejiang coast. Due to the different influence mechanisms, it took longer for the initial dinoflagellate population in the Taiwan Strait to exert the same impact on dinoflagellate blooms in the study area as that from the area east of Taiwan. Moreover, the density and appearance time of the initial dinoflagellate population in the Taiwan Strait affected their biomass and bloom range in the study area. Even a small initial dinoflagellate population east of Taiwan could trigger a bloom in the study area. This study suggests the target domains for finding nonlocal dinoflagellate cysts and provides a strategy to predict dinoflagellate blooms in the Changjiang adjacent area by monitoring dinoflagellate biomass in the nonlocal source regions.
Krzysztof Rychert, Lisa Wink, Marcus Blohs, Christina Kumpitsch, Charlotte Neumann, , Magdalena Wielgat‐Rychert
Journal of Geophysical Research: Biogeosciences, Volume 126; https://doi.org/10.1029/2021jg006404

Abstract:
The main goal of astrobiological studies is the search for life beyond Earth. Developing life detection methods requires test locations that have similar environmental conditions to extraterrestrial sites or that simply have low organism abundances. In this study, we describe dune sand of a low organic matter content (0.11%) collected from a national park frequented by few people. It is located in temperate zone. We hypothesized that dune sand is characterized by the low abundance of microorganisms and metabolic rates that could be compared to analogs of extraterrestrial environments like the Antarctic McMurdo Dry Valleys or the Atacama Desert. Measurements of CO2 efflux and ATP concentration demonstrated that hydrating dune sand with sterile distilled water initiated a short period of substantial microbial metabolic activity that lasted from four to five days. The maximum CO2 efflux was 100 mgCO2 m-2 d-1, which was low compared to values reported for sandy dunes, deserts and poor soils, including McMurdo Dry Valleys. Microscopic observations demonstrated that the abundance of prokaryotic microorganisms in the dune sand was low at roughly one million per cm3 of sand and was comparable to the abundance reported from the Atacama Desert. The microbial communities in the dune sand were studied based on 16S rRNA gene analyses. The most prominent bacterial genera were Massilia and Bacillus. Study demonstrated that dune sand sampled from a national park area was as useful for testing life detection methods as are other well-established analogs of extraterrestrial environments.
Journal of Geophysical Research: Biogeosciences, Volume 126; https://doi.org/10.1029/2021jg006515

Abstract:
Ecosystem establishment under adverse geophysical conditions is often studied within the “windows of opportunity” framework, identifying disturbance-free periods (e.g., calm wave climate) where species can overcome establishment thresholds. However, the role of biogeophysical interactions in this framework is less well understood. The establishment of saltmarsh vegetation on tidal flats, for example, is limited by abiotic factors such as hydrodynamics, sediment stability and drainage. On tidal flats, raised sediment ridges colonized by algal mats (Vaucheria sp.) appear to accomodate high densities of plant seedlings. Such ridges were previously found to have higher sediment strength than substratum without algae. Here, we investigate whether these measurements can be explained by geophysical factors only, or that biological (Vaucheria-induced) processes influence tidal marsh establishment by forming stabilized bedforms. We performed two experiments under controlled mesocosm conditions, to test the hypotheses that i) Vaucheria grows better on elevated topographic relief, that ii) the binding force of their algal filaments increases sediment strength, and that iii) Vaucheria consequently creates elevated topographic relief that further facilitates algal growth. Our experimental results confirm the existence of this algal-induced biogeomorphic feedback cycle. These findings imply that benthic algae like Vaucheria may contribute significantly to tidal marsh formation by creating elevated and stabilized substratum. This suggests biogeophysical feedbacks can “widen” the windows of opportunity for further ecosystem establishment. Our results could be useful for the design of managed realignment projects aimed at restoring the unique ecosystem services of coastal wetlands, such as habitat biodiversity, carbon sequestration potential and nature-based flood defense.
, T. Andrew Black, Marion Nyberg, Markus Merkens, Zoran Nesic, Darian Ng,
Journal of Geophysical Research: Biogeosciences, Volume 126; https://doi.org/10.1029/2021jg006532

Abstract:
Rewetting of disturbed peatlands is an important restoration strategy for climate change mitigation. Previous work primarily focuses on the biogeochemical processes altered by rewetting and few studies have investigated the biophysical impacts, which can diminish or amplify biogeochemical effects beyond the ecosystem scale. We used a paired flux tower approach in a restored peatland to collect year-round eddy-covariance data to assess the biophysical impacts of disturbance and management practices. The first site was actively rewetted and is characterized by Sphagnum and white beak-rush with patches of open water. The second site represents a disturbed ecosystem which underwent natural regeneration, and is dominated by scrub pine, Sphagnum, and low shrubs. We found that the actively restored site had higher net radiation compared to the second site due to more surface water ponding; however, the higher aerodynamic conductance at the passively restored site contributed to enhanced daytime turbulent fluxes, and hence both sites had similar aerodynamic temperatures during the daytime. The actively restored site experienced warmer nighttime and seasonal aerodynamic temperature as much of the excess radiation during the day was stored in the water column and released at night. To achieve restoration goals, higher water tables are now maintained throughout large sections of the bog. The study implies that water table manipulation has the potential to minimize greenhouse gas emissions from the bog, thereby allowing the biophysical impacts of peatland restoration to enhance the biogeochemical benefits. Therefore, it is important to consider both biophysical and biogeochemical changes in peatland restoration management.
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