•We assessed relationships of SOC stocks to measured hydromorphic features.•Forest SOC stocks ranged between 99 and 149 t ha−1.•Former floodplains stored 33% less SOC than active ...floodplains.•Vegetation type did not affect SOC stocks.•SOC stocks were mainly controlled by factors representing relief and flooding regime.
We assessed key relationships of soil organic carbon (SOC) stocks to hydromorphic features, soil texture, C/N ratio, pH, and forest age in hardwood floodplain forests. Floodplain ecosystems play a significant role in the global carbon cycle, particularly due to their SOC storage potential. Interactions between heterogeneous micro-relief and anthropogenically affected vegetation and the hydrologic situation of floodplains make predicting SOC stocks difficult without field validation. Especially within hardwood floodplain forests, the controlling factors for SOC storage remain understudied, whereas these floodplain types can be the largest reservoir for carbon and have a substantial SOC sequestration potential. To determine the controlling factors for SOC storage, we selected 38 hardwood floodplain forest and 11 floodplain grasslands of the lower middle Elbe River and categorized them according to vegetation type (grassland, young forest, or old forest) and hydrologic situation (low-lying or high elevated and active or former floodplain). Profile SOC stocks were determined to a depth of 1 m, and topsoil SOC stocks were related to vegetation and soil characteristics, particularly pedological traits (e.g., hydromorphic features).
Forest SOC stocks ranged between 99 and 149 t ha−1. SOC stocks decreased with depth throughout all categories and were unaffected by vegetation type within the same hydrologic situation. Vegetation parameters such as age, basal area, or leaf litter carbon stock had no direct effect on SOC stocks. An active connection to the river had the strongest effect on SOC stocks, with former floodplain sites storing 33% less SOC than the active sites. Within the active floodplains, low sites stored 50% more SOC than high sites. This effect was mainly controlled by relief-affected features such as flooding duration and fine texture, which also were the strongest univariate predictors for SOC stocks (R2 = 0.39 and 0.63). A multiple linear regression showed that fine texture, pH, C/N ratio and forest age can be used to explain 86% of variance in SOC stocks.
We conclude that proxies for relief and sedimentation (i.e., hydromorphic features, flooding duration, soil texture, C/N ratio, and pH) are the strongest factors controlling SOC stocks in hardwood floodplain forests. Both can be related to allochthonous carbon inputs, increasing SOC stabilization through the accumulation of fine soil particles, and decreasing aerobic carbon mineralization potential through oxygen scarcity, while vegetation plays only a subordinate role.
Floodplain ecosystems play a significant role in the global carbon (C) cycle, particularly due to their C sink potential in hardwood floodplain forests. However, in these forests, interactions ...between a heterogeneous micro‐relief and anthropogenic landscape changes make estimating C loss through soil CO2 efflux difficult. To determine the drivers of soil CO2 efflux, we selected six hardwood floodplain forests at the lower middle Elbe River, which were distributed among different relief positions (low‐lying or high‐elevated) in the active and former flooding zone. We measured soil CO2 effluxes over a full year using the closed‐chamber method. Based on the response of soil CO2 efflux to soil moisture and temperature, annual efflux rates were determined, which were then related to soil properties, such as pH, texture, soil organic carbon (SOC) and nitrogen (N) content. Soil CO2 efflux ranged between 1006 (±99) and 2214 (±118) gC m−2 year−1. Maximum efflux occurred in a former floodplain forest that was disconnected from Elbe River water table fluctuations. SOC‐specific soil CO2 efflux (gC gSOC−1 year−1) was smallest in low‐lying forests of the active flooding zone and reflected by the appearance of redoximorphic mottling close to the soil surface. Fine texture (<6.3 μm), SOC and N were related positively and electric conductivity, C/N and pH negatively to total soil CO2 efflux. Soil pH and fine texture were the strongest univariate predictors for total soil CO2 efflux (both R2 = 0.59). Fine texture, pH and C/N ratio explained 66% of the variance in total soil CO2 efflux according to multiple linear regression. We conclude that, in hardwood floodplain forests, soil CO2 efflux is mainly controlled by fine texture and soil pH. Fine texture can be related to soil moisture and nutrient availability and may have a positive effect on the activity of microorganisms.
Highlights
Soil CO2 efflux ranged between 1006 (±99) and 2214 (±118) gC m2 year−1, whereby the maximum was measured in a disconnected floodplain forest
Maximum soil CO2 efflux was measured in a disconnected floodplain forest
SOC‐specific soil CO2 efflux was smallest in forests where redoximorphic mottling occurred close to the surface
Fine texture (<6.3 μm) and pH were the strongest predictors for annual soil CO2 efflux
Over the past 40 years, a clear trend towards an increasing humidity and a rising groundwater table has been observed in the south-eastern semidesert part of European Russia. According to the ...published data, two clear periods of climate are distinguished: 1950s-1970s and 1970s-2000s. The thin sections of a Solonetz sampled in different periods of time (1950s, 1960s, 1970s, 1982, 2002 and 2013) at the Dzhanybek research station were studied micromorphologically to observe how these natural changes influenced soil pedofeatures. A comparison of thin sections showed no significant changes in soil properties between 1950s and 1982, when the hydrological (ground water table) and climatic parameters remained relatively stable. However, between 1982 and 2013, due to a significant increase in climatic moisture and rising groundwater, the following changes in soil microfeatures took place: the activation of humus accumulation and biogenic structuring, the eluviation of the silty clay-humus matter, the development of solodic features, gleyization of the soil mass, and the accumulation of opaque black organic grains about 2-3 µm formed in the topsoil due to the long stagnation during the springtime after snow melting. The water table rise leads to the consequent rise of the upper boundary of the accumulation of gypsum and carbonates.
Soil morphology and frequency of diagnostic wet soil conditions Szogi, A.A; Hudnall, W.H
Quantifying soil hydromorphology : proceedings of a symposium sponsored by Divisions S-5 and S-10, and Committee S-884 of the Soil Science Society of America in Indianapolis, Indiana, 4 Nov. 1996 / editors, M.C. Rabenhorst, J.C. Bell, and P.A. McDaniel ; organizing committee, M.C. Rabenhorst, J.H. Huddleston, and J.L. Richardson,
1998
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