Landscape controls of surface-water/groundwater interactions on shallow outwash lakes: how the long-term groundwater signal overrides interannual variability due to evaporative effects

The spatial and temporal controls on variability of the relative contributions of groundwater within and between flow systems to shallow lakes in the low-relief glaciated Boreal Plains of Canada were evaluated. Eleven lakes located in a coarse glacial outwash, of varying topographic positions and potential groundwater contributing areas, were sampled annually for stable O and H isotope ratios over the course of 8 years. It was demonstrated that landscape position is the dominant control over relative groundwater contributions to these lakes and the spatial pattern of the long-term isotopic compositions attributed to groundwater overrides interannual variability due to evaporative effects. Lakes at low landscape positions with large potential groundwater capture areas have relatively higher and more consistent groundwater contributions and low interannual variability of isotopic composition. Isolated lakes high in the landscape experience high interannual variability as they have little to no groundwater input to buffer the volumetric or isotopic changes caused by evaporation and precipitation. An alternative explanation that lake morphometry (area and volume) control long-term isotopic compositions is tested and subsequently refuted. Landscape position within coarse outwash is a strong predictor for relative groundwater input; however, surface-water connections can short circuit groundwater pathways and confound the signal. A hydrogeological case study for three of the study lakes is used to contextualize and further demonstrate these results.

Potential Impacts of Changing Precipitation Patterns on Biological Nitrogen Fixation in Soybean (Glycine Max L.) as Mediated by Landscape Position and Tillage

PurposeExpected changes in rainfall patterns will affect the timing of N-mineralization and other N transformations, potentially promoting or suppressing biological nitrogen fixation (BNF). We test the hypotheses that BNF is more sensitive to changing rainfall patterns in summit vs. toeslope positions and in till vs. no-till consistent with patterns of soil texture and organic matter.MethodsAt a site in the upper Midwest USA, we measured soybean BNF 15N natural abundance at different landscape positions with and without supplemental rainfall and in till vs. no-till rainfall exclusion shelters to lengthen the dry periods between rainfall events. ResultsSoybean BNF was 41% higher at summit than toeslope positions, consistent with lower soil OM and coarser texture at summits. When precipitation was increased by 20%, BNF decreased at summit positions and was unaffected at toeslope positions. In a separate tillage experiment, with 3-week (but not 2-week) rainfall intervals, %BNF decreased 15% under conventional tillage and increased 14% under no-till. ConclusionsChanging rainfall patterns affected BNF differentially depending on landscape position and tillage in well-drained Alfisols. BNF was greater in summit than in toeslope positions and decreased with added rainfall. BNF under conventional tillage was more sensitive to longer rainfall intervals than was BNF under no-till. Models that incorporate these interactions will be better able to characterize legume crop performance and N use across landscapes and improve global estimates for BNF.

Agricultural N2O emission is influenced by N-fertilization form rather than landscape position

<p>Agricultural soils are an important source of nitrous oxide (N<sub>2</sub>O) emission and are mainly affected by the application of N fertilization. In addition to the effect of fertilizer form (mineral/organic), N<sub>2</sub>O production and consumption processes in agricultural systems are influenced by the soil characteristics. However, knowledge of this is still very limited for erosion-affected arable soils. Therefore, the aim of our investigations was to find the impact of soil erosion state associated with the landscape position and N fertilization form have on N<sub>2</sub>O emission. This information is needed to evaluate the effects/benefits of new agricultural practices in future mitigation strategies aiming towards lower N<sub>2</sub>O emissions.</p><p>We present 3 years of N<sub>2</sub>O flux measurements in a two-factorial experiment by using a non-flow-through non-steady-state (NFT-NSS) manual chambers. Three sites were established on the summit position having similar soil type (Albic Luvisols; non-eroded soil) and were treated with organic fertilizer (100% organic biogas fermented residues (BFR)), mineral fertilizer (100% mineral calcium ammonium nitrate (CAN)), and a mixture of both fertilizers (50% CAN + 50% BFR). Two additional sites were established on the extremely eroded soil (Calcaric Regosols; on a steep slope with very dense parent material) and at a colluvial site in a depression (Endogleyic Colluvic Regosols) and treated with 100% CAN. The crop rotation was identical for all sites during the study period which includes: Maize (Zea mays L.) – Maize (Zea mays L.) – ­Winter rye (Secale cereale L.) – Sorghum (Sorghum bicolor) – Triticale (Triticosecale).</p><p>Our results show that the N<sub>2</sub>O emission exhibited temporal and spatial variability and is mainly influenced by fertilization form and soil type. Among the three fertilization treatments within the same soil type (non-eroded soil), the site with the application of organic fertilization shows the highest cumulated N<sub>2</sub>O emission which is accumulated to 13.5 kg N<sub>2</sub>O-N ha<sup>-1</sup> compared to the site with mixed fertilization (11.4 kg N<sub>2</sub>O-N ha<sup>-1</sup>) and mineral fertilization (4.5 kg N<sub>2</sub>O-N ha<sup>-1</sup>). Among the three distinct soil types with an identical application of mineral fertilizer, the cumulated N<sub>2</sub>O emission is higher at the depression (7.3 kg N<sub>2</sub>O-N ha<sup>-1</sup>) compared to the non-eroded (4.5 kg N<sub>2</sub>O-N ha<sup>-1</sup>) and extremely eroded soil (1.6 kg N<sub>2</sub>O-N ha<sup>-1</sup>). In general, our results suggest a stronger influence of N fertilization form than erosion affected soil on N<sub>2</sub>O emission.</p><p><strong>Keywords: </strong>NFT-NSS manual chamber; soil erosion; N fertilization form, nitrous oxide, soil type</p>

Effects of landscape positions on soil physicochemical properties at Shenkolla Watershed, South Central Ethiopia

Background Understanding the effects of landscape positions on soil physicochemical properties is crucial for improving the soil productivity and to ensure the environmental sustainability. Three land use types forest land, grazing land and cultivated land all within upper, middle and lower landscape positions were selected to determine the effects of landscape positions, land use types and their interaction effects on soil physicochemical properties. Twenty seven soil samples were collected from lower landscape, middle landscape and upper landscape positions at the depth of 0–20 cm in nine replications. In addition, undisturbed soil samples were taken using core sampler from each land use type under upper, middle and lower landscape positions for the ascertainment of bulk density and water retentive capacity. The analysis of variance (ANOVA) was applied to determine variations in soil parameters among landscape positions and land use types. A Generalized Linear Models (GLMs) analysis was conducted to determine the influence of independent (fixed) factors, on the soil properties (response variables). Treatment means comparison was determined using the Least Significant Difference (LSD) at 0.05 level of significances. Results The result indicated that among the soil properties sand (p < 0.001), silt (p < 0.001), clay (p < 0.001), bulk density (p < 0.01), water holding capacity at FC (p < 0.001), water retention at PWP (p < 0.01), Available water content (AWC) (p < 0.01), soil reaction (pH) (p < 0.05), Soil organic carbon (SOC%) (p < 0.01), Total nitrogen (TN%) (p < 0.01), available phosphorus (p < 0.05) and CEC (p < 0.001) have shown a significant variation among the landscape categories. Similarly, variation of sand (p < 0.001), silt (p < 0.001), clay (p < 0.001), bulk density (p < 0.01), water holding capacity at FC (p < 0.001), water retention at PWP (p < 0.001), Available water content (AWC) (p < 0.01), soil reaction (pH) (p < 0.01), SOC (p < 0.01), TN (p < 0.001) available phosphorus (AP) (p < 0.001) and CEC (p < 0.001) were also statistically significant among the land use types. Moreover, lower landscape position and forest land had high mean value of SOC, TN, AP, CEC, EB (exchangeable bases), and available micronutrients, whereas upper landscape position and intensively cultivated land had low mean value of SOC, TN, AP, CEC, EB (exchangeable bases), and available micronutrients. Conclusion Landscape positions, land use types and interaction effects of landscape position and land use types (LSP * LU) significantly affected soil properties. Soil with best quality was found in lower landscape position and forest land, while less quality of soil was found in upper landscape position and cultivated land. Thus, efforts should be made to improve the quality of soil under upper landscape position and cultivated land using biological and physical soil conservation measures.