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1. A Sensor Probe with Active and Passive Humidity Management for In Situ Soil CO2 Monitoring

   https://doi.org/10.3390/s24186034  

   Anderson, Jacob F; Huber, David P; Walsh, Owen A (September 2024, Sensors)

   Soil CO2 concentration and flux measurements are important in diverse fields, including geoscience, climate science, soil ecology, and agriculture. However, practitioners in these fields face difficulties with existing soil CO2 gas probes, which have had problems with high costs and frequent failures when deployed. Confronted with a recent research project’s need for long-term in-soil CO2 monitoring at a large number of sites in harsh environmental conditions, we developed our own CO2 logging system to reduce expense and avoid the expected failures of commercial instruments. Our newly developed soil probes overcome the central challenge of soil gas probes—surviving continuous exposure to soil moisture while remaining open to soil gases—via three approaches: a 3D printed housing (economical for small-scale production) following design principles that correct the usual water permeability flaw of 3D printed materials; passive moisture protection via a hydrophobic, CO2-permeable PTFE membrane; and active moisture protection via a low-power micro-dehumidifier. Our CO2 instrumentation performed well and yielded a high-quality dataset that includes signals related to a prescribed fire as well as seasonal and diel cycles. We expect our technology to support underground CO2 monitoring in fields where it is already practiced and stimulate its expansion into diverse new fields. 

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2. Representing methane emissions from wet tropical forest soils using microbial functional groups constrained by soil diffusivity

   https://doi.org/10.5194/bg-18-1769-2021  

   Sihi, Debjani; Xu, Xiaofeng; Salazar Ortiz, Mónica; O'Connell, Christine S.; Silver, Whendee L.; López-Lloreda, Carla; Brenner, Julia M.; Quinn, Ryan K.; Phillips, Jana R.; Newman, Brent D.; et al (January 2021, Biogeosciences)

   Abstract. Tropical ecosystems contribute significantly to global emissionsof methane (CH4), and landscape topography influences the rate ofCH4 emissions from wet tropical forest soils. However, extreme eventssuch as drought can alter normal topographic patterns of emissions. Here weexplain the dynamics of CH4 emissions during normal and droughtconditions across a catena in the Luquillo Experimental Forest, Puerto Rico.Valley soils served as the major source of CH4 emissions in a normalprecipitation year (2016), but drought recovery in 2015 resulted in dramaticpulses in CH4 emissions from all topographic positions. Geochemicalparameters including (i) dissolved organic carbon (C), acetate, and soil pH and (ii) hydrological parameters like soil moisture and oxygen (O2)concentrations varied across the catena. During the drought, soil moisturedecreased in the slope and ridge, and O2 concentrations increased in thevalley. We simulated the dynamics of CH4 emissions with theMicrobial Model for Methane Dynamics-Dual Arrhenius and Michaelis–Menten (M3D-DAMM), which couples a microbialfunctional group CH4 model with a diffusivity module for solute and gastransport within soil microsites. Contrasting patterns of soil moisture,O2, acetate, and associated changes in soil pH with topographyregulated simulated CH4 emissions, but emissions were also altered byrate-limited diffusion in soil microsites. Changes in simulated availablesubstrate for CH4 production (acetate, CO2, and H2) andoxidation (O2 and CH4) increased the predicted biomass ofmethanotrophs during the drought event and methanogens during droughtrecovery, which in turn affected net emissions of CH4. A variance-basedsensitivity analysis suggested that parameters related to aceticlasticmethanogenesis and methanotrophy were most critical to simulate net CH4emissions. This study enhanced the predictive capability for CH4emissions associated with complex topography and drought in wet tropicalforest soils. 

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3. Baltimore Ecosystem Study: Soil moisture and temperature along an urban to rural gradient, 2011 - present

   https://doi.org/10.6073/pasta/76e44dc0b004859a661f74ebe1d8a610  

   Groffman, Peter M; Martel, Lisa D (January 2020, Environmental Data Initiative)

   Soil temperature and soil moisture have been measured at multiple locations in and around Baltimore Maryland to provide data on these variables in forests and lawns across an urban to rural gradient. In July 2011, we installed one Decagon Em50 Datalogger with five 5TM VWC/Temperature probes at four established forested, upslope, 20 x 20-m plots, two rural (ORU1, ORU2) and two urban (LEA1, LEA2), at 2 forested riparian sites at two transects along a stream (ORUR, ORLR), and two lawn plots on the campus of the University of Maryland Baltimore County campus (UMBC1, UMBC 2). Probes were buried horizontally at 10cm depth (except UMBC1 and UMBC2 where the five probes are mounted horizontally at a single location at depths of 50, 40, 30, 20 and 10 cm depth). At the upslope forested plots, the five probes are replicates. At the two riparian sites, probes are deployed in either "hummocks (drier, higher)" or in "hollows (lower, wetter)". Soil temperature and soil moisture were measured at hourly intervals on these plots beginning in July 2011. Earlier soil moisture data were collected monthly (1999-2011), and can be found in https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-bes&identifier=417 

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4. Soil moisture and temperature along an urban to rural gradient at the Baltimore Ecosystem Study 2011 - Present

   https://doi.org/10.6073/pasta/de49dcbb8c47169a02b92a0f6896f0d5  

   Groffman, Peter M; Martel, Lisa D (January 2020, Environmental Data Initiative)

   Soil temperature and soil moisture have been measured at multiple locations in and around Baltimore Maryland to provide data on these variables in forests and lawns across an urban to rural gradient. In July 2011, we installed one Decagon Em50 Datalogger with five 5TM VWC/Temperature probes at four established forested, upslope, 20 x 20-m plots, two rural (ORU1, ORU2) and two urban (LEA1, LEA2), at 2 forested riparian sites at two transects along a stream (ORUR, ORLR), and two lawn plots on the campus of the University of Maryland Baltimore County campus (UMBC1, UMBC 2). Probes were buried horizontally at 10cm depth (except UMBC1 and UMBC2 where the five probes are mounted horizontally at a single location at depths of 50, 40, 30, 20 and 10 cm depth). At the upslope forested plots, the five probes are replicates. At the two riparian sites, probes are deployed in either "hummocks (drier, higher)" or in "hollows (lower, wetter)". Soil temperature and soil moisture were measured at hourly intervals on these plots beginning in July 2011. Earlier soil moisture data were collected monthly (1999-2011), and can be found in https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-bes&identifier=417 

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5. Soil temperature and moisture as key controls of phosphorus export in mountain watersheds

   https://doi.org/10.1016/j.scitotenv.2024.170958  

   Gianniny, Gordon; Stark, John M; Abbott, Benjamin W; Lee, Raymond; Brahney, Janice (April 2024, Science of The Total Environment)

   Oligotrophic mountain lakes act as sensitive indicators of landscape-scale changes in mountain regions due to their low nutrient concentration and remote, relatively undisturbed watersheds. Recent research shows that phosphorus (P) concentrations are increasing in mountain lakes around the world, creating more mesotrophic states and altering lake ecosystem structure and function. The relative importance of atmospheric deposition and climate-driven changes to local biogeochemistry in driving these shifts is not well established. In this study, we test whether increasing temperatures in watershed soils may be contributing to the observed increases in mountain lake P loading. Specifically, we test whether higher soil temperatures increase P mobilization from mountain soils by accelerating the rate of geochemical weathering and soil organic matter decomposition. We used paired soil incubation (lab) and soil transplant (field) experiments with mountain soils from around the western United States to test the effects of warming on rain-leachable P concentration, soil P mobilization, and soil respiration. Our results show that while higher temperature can increase soil P mobilization, low soil moisture can limit the effects of warming in some situations. Soils with lower bulk densities, higher pH, lower aluminum oxide contents, and lower ratios of carbon to nitrogen had much higher rain-leachable P concentration across all sites and experimental treatments. Together, these results suggest that mountain watersheds with high-P soils and relatively high soil moisture could have the largest increases in P mobilization with warming. Consequently, lakes and streams in such watersheds could become especially susceptible to soil-driven eutrophication as temperatures rise. 

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