An Assessment of a Mesocosm Approach to the Study of Microbial Respiration in a Sandy Unsaturated Zone

Hendry, M. Jim; Mendoza, Carl; Kirkland, R.A.; Lawrence, John R.

doi:10.1111/j.1745-6584.2001.tb02323.x

Cited by 24 publications

(14 citation statements)

References 52 publications

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“…Researchers have demonstrated that microbial numbers and activities typically decline in the subsoils (up to several meters depth) beneath the root zone or plow layer at undisturbed sites, and there are often strong correlations of biological measures with organic matter content (Federle et al, 1986; Taylor et al, 2002). Our observations of uniform distributions of cells and activity with depth are similar to that of Hendry et al (Hendry et al, 2001), who examined microbial depth distributions in backfilled mesocosms. Hendry et al also reported soil gas CO 2 profiles in the mesocosms that were similar to ours—highest at depth and declining toward the surface.…”

Section: Discussionsupporting

confidence: 89%

Distribution of Microorganisms and their Activities in Capillary Barriers: Implications for Modeling of Hydrologic Transport through Capillary Barriers

Lehman

Baker

Mattson

2004

Vadose Zone Journal

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The capping of buried waste with surface barriers is a remediation approach designed to prevent the infiltration of water through the buried waste to minimize migration of waste constituents from the burial ground. The hydraulic performance of surface barriers and their long‐term effectiveness have been modeled based on soil physical and chemical characteristics, neglecting the potential contribution of soil microorganisms. We hypothesized that soil microorganisms may affect the long‐term performance of surface barriers by altering soil structure, soil wettability, or soil pore water surface tensions. Two field‐scale barrier prototypes were studied: the “thick soil” design and “capillary barrier” design. Two conceptual models for microbial distribution in the barriers were postulated: (i) due to excavation, mixing, and emplacement, soil microbial numbers and activity would be uniformly distributed throughout the barrier profile; and (ii) in capillary barriers, the presence of the coarse–fine interface would locally enhance microbial growth and create local effects on barrier properties. Our initial studies involved field sampling of thick and capillary barrier prototypes at two different locations, examination of the distributions of microorganisms and their activities in vertical transects through the barriers, and correlation of the biological measures with barrier hydraulic properties. We found relatively uniform distributions of microorganisms and activities across the barriers (both designs), consistent with the first conceptual model. The presence of a capillary barrier layer was not associated with a clear increase in microbial activities; however, finer resolution sampling may be required to evaluate the second conceptual model. Our observations of uniform (or increasing) microbial activities with depth in the barriers contrast with commonly observed decreases in soil microbial numbers and activities with depth at undisturbed sites. The indigenous soil microorganisms did not affect soil wettability or soil pore water interfacial tensions in these prototype barriers of <10 yr of age. However, on the time scales for which barriers are expected to be effective (100s to 1000s of years), microbially produced surface‐active substances may alter barrier hydraulic performance. We propose laboratory studies to evaluate long‐term consequences of microbially produced surface‐active substance on barrier integrity and indicate how these effects can be incorporated into models predicting long‐term barrier performance.

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Section: Discussionsupporting

confidence: 89%

Distribution of Microorganisms and their Activities in Capillary Barriers: Implications for Modeling of Hydrologic Transport through Capillary Barriers

Lehman

Baker

Mattson

2004

Vadose Zone Journal

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“…Moreover, substantial quantities of gas bubbles present in the immediate vicinity of the water table, resulting from geochemical and/or microbial activity, have also been reported (e.g., Ronen et al, 1989). Hendry et al (2001) measured microbial respiration rates through a 3.2‐m‐thick “mesocosm,” and found nonnegligible respiration rates in the CF, which increased upwards into the partially saturated zone.…”

Section: Chemical and Microbial Transport Through The Capillary Fringementioning

confidence: 99%

Impact of the Capillary Fringe on Local Flow, Chemical Migration, and Microbiology

Berkowitz¹,

Silliman²,

Dunn³

2004

Vadose Zone Journal

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We critically examine historical and recent studies of flow and transport at the local scale within the capillary fringe (CF). The characterization of subsurface pathways traveled by water—and the impact of these pathways on the movement of chemicals and the viability of subsurface microbial populations—has been the subject of intensive investigation in the last 50 yr in the fields of soil science and hydrology. However, consideration of the complexity of local pathways within the CF has been largely ignored. Recent studies, as well as some historical ones, have reported observations of fluid flow and chemical transport within the CF, emphasizing the impact of physical heterogeneity and exchange of water and chemicals between the CF and the region below the water table. These observations lead to the conclusion that the CF may affect, at the local scale, the natural geochemical and microbial conditions present in the region of transition from unsaturated to saturated groundwater flow far more significantly than is usually assumed. Here, we examine underlying physical factors that control local flow and transport behaviors in and across the CF and illustrate these factors through examination of images collected in the laboratory. We also provide a brief survey of the literature on the CF. It is argued that existing definitions of the CF are inadequate to describe flow and transport behavior in the vicinity of the water table. We suggest replacing the concept of the CF with the concept of a partially saturated fringe, which involves multiphase transport in the immediate vicinity of (both above and below) the water table.

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“…This approach is commonly used in process-related research (Hendry et al, 2001;Thaysen et al, 2014;Artiola and Walworth, 2009;Aslam et al, 2015) as it minimizes experimental errors and bias caused by unknown factors including soil heterogeneity and microbial community variations. It is also more favorable in terms of quantifying soil carbon leaching loss as it circumvents pore-water contamination by vacuum suction in the field.…”

Section: Soil Column Experiments and Simulated Epesmentioning

confidence: 99%

Comparing soil carbon loss through respiration and leaching under extreme precipitation events in arid and semiarid grasslands

et al. 2018

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Abstract. Respiration and leaching are two main processes responsible for soil carbon loss. While the former has received considerable research attention, studies examining leaching processes are limited, especially in semiarid grasslands due to low precipitation. Climate change may increase the extreme precipitation event (EPE) frequency in arid and semiarid regions, potentially enhancing soil carbon loss through leaching and respiration. Here we incubated soil columns of three typical grassland soils from Inner Mongolia and the Qinghai-Tibetan Plateau and examined the effect of simulated EPEs on soil carbon loss through respiration and leaching. EPEs induced a transient increase in CO 2 release through soil respiration, equivalent to 32 and 72 % of the net ecosystem productivity (NEP) in the temperate grasslands (Xilinhot and Keqi) and 7 % of NEP in the alpine grasslands (Gangcha). By comparison, leaching loss of soil carbon accounted for 290, 120, and 15 % of NEP at the corresponding sites, respectively, with dissolved inorganic carbon (DIC, biogenic DIC + lithogenic DIC) as the main form of carbon loss in the alkaline soils. Moreover, DIC loss increased with recurring EPEs in the soil with the highest pH due to an elevated contribution of dissolved CO 2 from organic carbon degradation (indicated by DIC-δ 13 C). These results highlight the fact that leaching loss of soil carbon (particularly in the form of DIC) is important in the regional carbon budget of arid and semiarid grasslands and also imply that SOC mineralization in alkaline soils might be underestimated if only measured as CO 2 emission from soils into the atmosphere. With a projected increase in EPEs under climate change, soil carbon leaching processes and the influencing factors warrant a better understanding and should be incorporated into soil carbon models when estimating carbon balance in grassland ecosystems.

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An Assessment of a Mesocosm Approach to the Study of Microbial Respiration in a Sandy Unsaturated Zone

Cited by 24 publications

References 52 publications

Distribution of Microorganisms and their Activities in Capillary Barriers: Implications for Modeling of Hydrologic Transport through Capillary Barriers

Distribution of Microorganisms and their Activities in Capillary Barriers: Implications for Modeling of Hydrologic Transport through Capillary Barriers

Impact of the Capillary Fringe on Local Flow, Chemical Migration, and Microbiology

Comparing soil carbon loss through respiration and leaching under extreme precipitation events in arid and semiarid grasslands

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