@article{HoffmannJurischAlbaetal.2017, author = {Hoffmann, Mathias and Jurisch, Nicole and Alba, Juana Garcia and Borraz, Elisa Albiac and Schmidt, Marten and Huth, Vytas and Rogasik, Helmut and Rieckh, Helene and Verch, Gernot and Sommer, Michael and Augustin, J{\"u}rgen}, title = {Detecting small-scale spatial heterogeneity and temporal dynamics of soil organic carbon (SOC) stocks}, series = {Biogeosciences}, volume = {14}, journal = {Biogeosciences}, number = {4}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1726-4170}, doi = {10.5194/bg-14-1003-2017}, pages = {1003 -- 1019}, year = {2017}, abstract = {Carbon (C) sequestration in soils plays a key role in the global C cycle. It is therefore crucial to adequately monitor dynamics in soil organic carbon (Delta SOC) stocks when aiming to reveal underlying processes and potential drivers. However, small-scale spatial (10-30 m) and temporal changes in SOC stocks, particularly pronounced in arable lands, are hard to assess. The main reasons for this are limitations of the well-established methods. On the one hand, repeated soil inventories, often used in long-term field trials, reveal spatial patterns and trends in Delta SOC but require a longer observation period and a sufficient number of repetitions. On the other hand, eddy covariance measurements of C fluxes towards a complete C budget of the soil-plant-atmosphere system may help to obtain temporal Delta SOC patterns but lack small-scale spatial resolution. To overcome these limitations, this study presents a reliable method to detect both short-term temporal dynamics as well as small-scale spatial differences of Delta SOC using measurements of the net ecosystem carbon balance (NECB) as a proxy. To estimate the NECB, a combination of automatic chamber (AC) measurements of CO2 exchange and empirically modeled aboveground biomass development (NPPshoot / were used. To verify our method, results were compared with Delta SOC observed by soil resampling. Soil resampling and AC measurements were performed from 2010 to 2014 at a colluvial depression located in the hummocky ground moraine landscape of northeastern Germany. The measurement site is characterized by a variable groundwater level (GWL) and pronounced small-scale spatial heterogeneity regarding SOC and nitrogen (Nt) stocks. Tendencies and magnitude of Delta SOC values derived by AC measurements and repeated soil inventories corresponded well. The period of maximum plant growth was identified as being most important for the development of spatial differences in annual Delta SOC. Hence, we were able to confirm that AC-based C budgets are able to reveal small-scale spatial differences and short-term temporal dynamics of Delta SOC.}, language = {en} } @article{GerkeRieckhSommer2016, author = {Gerke, Horst H. and Rieckh, Helene and Sommer, Michael}, title = {Interactions between crop, water, and dissolved organic and inorganic carbon in a hummocky landscape with erosion-affected pedogenesis}, series = {Macromolecular rapid communications}, volume = {156}, journal = {Macromolecular rapid communications}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-1987}, doi = {10.1016/j.still.2015.09.003}, pages = {230 -- 244}, year = {2016}, abstract = {Hummocky soil landscapes are characterized by 3D spatial patterns of soil types that result from erosion-affected pedogenesis. Due to tillage and water erosion, truncated profiles have been formed at steep and mid slopes and colluvial soils at hollows, while intact profiles remained at plateau positions. Pedogenetic variations in soil horizons lead to spatial differences in the soil water balance at hillslope positions. Here, possible interactions between erosion affected soil properties, the water balances, and the crop growth and feedback effects of erosion on the leaching rates were assumed. The hypothesis was tested by water balance simulations comparing uniform with hillslope position-specific crop and root growths for soils at plateau, flat mid slope, steep slope, and hollow using the Hydrus-1D program. The boundary condition data were monitored at the CarboZALF-D experimental field site, which was cropped with perennial lucerne (Medicago sativa L.) in 2013 and 2014. Crop and root growth at the four hillslope positions was assumed proportional to observed leaf area index (LAI). Fluxes of dissolved organic and inorganic carbon (DOC, DIC) were obtained from simulated water fluxes and measured DOC and DIC concentrations. For the colluvic soil at hollow, the crop growth was initially highest and later limited by an increasing water table; here the predominately upward flow led to a net input in DIC and DOC. For the truncated soils at steep slopes, simulations support the hypothesis that reduced crop growth caused an increase in percolation and DIC leaching from the subsoil horizons, which in turn led to accelerated soil development and more soil variations along eroding hillslopes in arable soil landscapes. (C) 2015 Elsevier B.V. All rights reserved.}, language = {en} } @article{RieckhGerkeSiemensetal.2014, author = {Rieckh, Helene and Gerke, Horst H. and Siemens, Jan and Sommer, Michael}, title = {Water and dissolved carbon fluxes in an eroding soil landscape depending on terrain position}, series = {Vadose zone journal}, volume = {13}, journal = {Vadose zone journal}, number = {7}, publisher = {Soil Science Society of America}, address = {Madison}, issn = {1539-1663}, doi = {10.2136/vzj2013.10.0173}, pages = {14}, year = {2014}, abstract = {Leaching of dissolved C in arable hummocky ground moraine soil landscapes is characterized by a spatial continuum of more or less erosion-affected Luvisols, Calcaric Regosols at exposed positions, and Colluvic Regosols in depressions. Our objective was to estimate the fluxes of dissolved C in four differently eroded soils as affected by erosion-induced pedological and soil structural alterations. In this model study, we considered landscape position effects by adapting the water table as the bottom boundary condition and erosion effects by using pedon-specific soil hydraulic properties. The one-dimensional vertical water movement was described with the Richards equation using HYDRUS-1D. Solute fluxes were obtained by combining calculated water fluxes with concentrations of dissolved organic and inorganic C (DOC and DIC, respectively) measured from soil solution extracted by suction cups at biweekly intervals. In the 3-yr period (2010-2012), DOC fluxes in the 2-m soil depth were similar at the three non-colluvic locations with -0.8 +/- 0.1 g m(-2) yr(-1) (i.e., outflow) but were 0.4 g m(-2) yr(-1) (i.e., input) in the depression. The DIC fluxes ranged from -10.2 g m(-2) yr(-1) for the eroded Luvisol, -9.2 g m(-2) yr(-1) for the Luvisol, and -6.1 g m(-2) yr(-1) for the Calcaric Regosol to 3.2 g m(-2) yr(-1) for the Colluvic Regosol. The temporal variations in DOC and DIC fluxes were controlled by water fluxes. The spatially distributed leaching results corroborate the hypothesis that the effects of soil erosion influence fluxes through modified hydraulic and transport properties and terrain-dependent boundary conditions.}, language = {en} } @article{RieckhGerkeSommer2012, author = {Rieckh, Helene and Gerke, Horst H. and Sommer, Michael}, title = {Hydraulic properties of characteristic horizons depending on relief position and structure in a hummocky glacial soil landscape}, series = {Soil \& tillage research : an international journal on research and development in soil tillage and field traffic, and their relationships with soil environment, land use and crop production}, volume = {125}, journal = {Soil \& tillage research : an international journal on research and development in soil tillage and field traffic, and their relationships with soil environment, land use and crop production}, number = {1}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-1987}, doi = {10.1016/j.still.2012.07.004}, pages = {123 -- 131}, year = {2012}, abstract = {The hummocky ground moraine soil landscape forms a spatial continuum of more or less eroded and depositional soils developed from glacial till under intensive agricultural cultivation. Measurements of soil hydraulic properties in the laboratory on soil cores are mostly limited to some characteristic horizons. However, these horizons can vary in thickness or structural and pedological development depending on relief position. This paper compares soil hydraulic properties of the same soil horizons sampled at different relief positions in a single field representing various degrees of soil erosion/deposition. Water retention curves were determined from undisturbed core samples using sand and kaolin beds with hanging water column and pressure chambers, and the unsaturated hydraulic conductivity using the double-membrane apparatus. Data were fitted to the van Genuchten-Mualem function (VGM) using the nonlinear curve fitting program RETC. The desorption water retention curves for the soil horizons were different and depended on the soil structural development that could be related with the intensity of erosion history at each landscape position. The greatest differences in hydraulic functions were found for the E, Bt, and C horizons. The fitted soil water retention curves reflected these differences mainly in the values of the VGM curve parameters n and theta(s). The landscape features that have the strongest differentiating effect are related to erosion and distance towards the water table. The results can help improving pedotransfer approaches for the estimation of spatially distributed hydraulic parameters for modelling the water movement in hummocky soil landscapes as basis for establishing landscape scale water and element balances.}, language = {en} }