Spatial variation of nitrous oxide fluxes during growing and non-growing seasons at a location subjected to seasonally frozen soils

Nitrous oxide (N2O) emissions from soils have been widely studied in the literature–mostly with the chamber method–due to the importance of this gas to climate change. Emissions of N2O derive from biological reactions and are controlled by soil parameters, which are by nature heterogeneous (i.e., “hot spots” for N2O emissions)–a source of uncertainty in chamber-based studies. Spatial variation in N2O fluxes has been assessed in the literature, but information is still needed for contrasting soil management practices (e.g., tillage) and for specific bioclimatic situations (e.g., non-growing seasons under cold weather–NGS). Here, we sub-sampled daily N2O data to assess within-plot and between-block spatial variation from an agronomic experiment under conventional (CT) and no-tillage (NT), identifying if patterns differ between growing season (GS) and NGS datasets. Within-plot spatial variation in N2O fluxes was a small source of uncertainties, but half of the comparisons in GS datasets presented a slope different from 1 for the regression of N2O averages from two vs. one chamber per plot–a source of uncertainty mitigated when within-plot duplication occurred during N2O “hot moments”. Between-block spatial variation in N2O emissions was much larger than within-plot errors–an effect more accentuated for NGS and CT than GS and NT datasets. Decreasing the number of sampled blocks resulted in averages that did not represent the N2O daily average of the whole field – but exceptions occurred. The methodology proposed here may be used in other locations, after appropriate verification, for improved planning and maximization of the resources associated with N2O measurements.

Strong changes in the relationship between storage and discharge during a period of thawing soils and climate warming in Northern Sweden

<p>The Arctic is warming at an unprecedented rate. This warming affects not just ecosystems, but also permafrost, landscape configuration, and water availability in watersheds. One relatively under researched process is how seasonally frozen soils and changes thereof affect the water cycle. As frozen soils thaw, flow pathways within a catchment open, allowing for enhanced hydrologic connectivity between groundwater and rivers. As the connectivity of flow paths increase, the storage-discharge relationship of a watershed changes, which can be perceived within a hydrograph. More specifically, previous studies hypothesized that storage-discharge relationships are relatively linear when soils are frozen and become increasingly non-linear as the landscape thaws.</p><p>The objective of our research is to expand on the assumption that soil thaw leads to increasingly non-linear storage-discharge relationships by quantifying trends and spatio-temporal differences of this relationship. We will present our analysis of sixteen watersheds within Northern Sweden throughout the years of 1951 and 2018. We focus on spring and summer storage-discharge relationships and show how they are affected by preceding winter conditions.</p><p>We found a clear increase in non-linearity of the storage-discharge relationship over time for all catchments with twelve out of sixteen watersheds (75%) having a statistically significant increase in non-linearity. For twelve watersheds, spring relationships were significantly more linear compared to summer, which supports the hypothesis that seasonally frozen soils have less hydrological connectivity leading to more linear storage-discharge relationships. Winter conditions that allow deep soil frost lead to more linear storage-discharge relationships for ten watersheds. Overall, we show that thawing soil leads to a more non-linear storage-discharge relationship which implies river runoff in the Arctic becomes more unpredictable.</p>

The current state and prospects of soil plate tests

The methods and results of determining the deformation characteristics of soils, the history and current state of soil plate tests are considered. Various types are described: flat rectangular — large-size, standard round, screw plates, dilatometer plates, devices for their anchoring and creating loads on them. A critical analysis of the results of testing dispersed soils with plates of various designs was performed, the influence of the used test methods on the obtained values of the soil deformability characteristics was considered. The issues of integration of field and laboratory methods of soil research are analyzed. In megalopolises such as Moscow, St. Petersburg, Yekaterinburg, often the height of buildings exceeds 150–200 m, and the depth of the designed objects is 25–30 meters or more. This leads to the study of soils at depths significantly greater than that performed in previous years. No less relevant is the study of specific soils with plates on urban areas previously used and reused for construction, especially in the conditions of renovation of dilapidated housing. A separate problem is the study of the physical-mechanical properties of soils (plate tests along with laboratory studies) in basement levels and other buried structures, the solution of which is under development. Equally important is the consideration of changes in the natural conditions during the plate tests in the process of engineering geological surveys in areas with permafrost and seasonally frozen soils. The developed methods and devices, taking into account the requirements of the current regulatory technical documents, allow the testing of soils with plates to the level of advanced technologies currently leading in this area.