Bottom Of Soil Profile Research Articles

Water yield, nitrogen and sediment retentions in Northern Japan (Teshio river watershed): land use change scenario analysis

We investigated the effects of changing land use on water yield, and nitrogen (N) and sediment retentions in the Teshio river watershed in northern Japan. The Land Use and it’s Effects (CLUE) model was used to predict land use change and multilevel Bayesian analysis was used to quantify relationships between water quality components and topographical slope. The Soil and Water Assessment Tool (SWAT) hydrology model was used to simulate water yield, N and sediment retentions under land use change scenarios. Most of the study area was covered by forest in 1976, 2006 and 2036, with rice fields totally converted to farmland by 2036. There were positive correlations between water yield, inorganic-N yield, sediment yield and organic-N yield and topographical slope, but there was negative correlation between nitrate nitrogen (NO3-N) in the bottom of soil profile and topographical slope. Sediment and organic-N yields of forest were less than those of other land uses. Water yield, organic-N and sediment retentions were largest in the southeast of the study watershed, while the inorganic-N retention was highest along the riverine area. In comparison with the 1976 land use pattern, water yield sediment retention and organic-N retention decreased under 2006 and 2036 land use patterns while inorganic-N retention increased. We conclude that planning a comprehensive adaptation and mitigation program (e.g. establishing riparian zones, planning nutrient management practices and integrating systematic conservation planning into agricultural expansion) is necessary to avoid negative impacts of land use change on water yield, N and sediment retentions in the watershed.

Lichen and soil as indicators of an atmospheric mercury contamination in the vicinity of a chlor-alkali plant (Grenoble, France)

Atmospheric mercury (Hg) deposition around a mercury cell chlor-alkali plant located near Grenoble, south-east France, was assessed using Hg concentrations in lichens and soils. Hg content in the epiphytic Xanthoria parietina lichen ranged from ∼0.07 to ∼2.51 μg g −1, and concentrations decreased with increasing distance to the plant, with a contamination radius of ∼2 km. Soil Hg concentration profiles were consistent with an atmospheric origin, with higher concentrations in the upper part of the profiles. Concentration of Hg in lichens and top soils (0–10 cm depth) as a function of the distance to the chlor-alkali plant exhibited highly similar variations. Using a simple first-order deposition model, mean Hg fallouts for the whole history of chlor-alkali plant are estimated to ∼36 g Hg day −1 in this area, compatible with values reported for reactive gaseous mercury (RGM) emissions of similar industrial plants. Using literature data on RGM to total Hg emission ratio, we estimate that the plant emitted ∼650 kg Hg year −1. Two kilometres away from the plant, Hg content in top soils falls to values of (0.13 ± 0.07) μg g −1 Hg, which is the local anthropogenic geochemical background level, but higher than unperturbed geochemical background found at the bottom of soil profiles (below 40 cm depth) estimated to (0.04 ± 0.01) μg g −1 Hg. The present study evidences that lichens are a pertinent proxy for soil Hg contamination around chlor-alkali plants. They are attractive biomonitoring tools since sampling and preparations protocols for lichens are less time consuming than those used for soils.

Paleovegetation reconstruction using δ<sup>13</sup>C of Soil Organic Matter

Abstract. The relative contributions of C3 and C4 plants to vegetation at a given locality may be estimated by means of δ13C of soil organic matter. This approach holds a great potential for paleoecological reconstruction using paleosols. However, two main uncertainties exist, which limits the accuracy of this application. One is δ13C-enrichment as the plant carbon becomes incorporated into soil organic matter. The other is due to environmental influences on δ13C of plants. Two types of data were collected and analyzed with an objective of narrowing the error of paleovegetation reconstruction. First, we investigated δ13C variations of 557 C3 and 136 C4 plants along a precipitation gradient in North China. A strong negative correlation is found between the δ13C value of C3 plants averaged for each site and the annual precipitation with a coefficient of −0.40‰/100mm, while no significant coefficients were found for C4 plants. Second, we measured δ13C of soil organic matters for 14 soil profiles at three sites. The isotopic difference between vegetation and soil organic matter are evaluated to be 1.8‰ for the surface soil and 2.8‰ for the soil at the bottom of soil profiles. We conducted a sample reconstruction of paleovegetation at the central Chinese Loess Plateau during the Holocene and the Last Glacial (LG), and conclude that, without corrections for δ13C-enrichment by decomposition, the C4 abundance would be overestimated. The importance and uncertainties of other corrections are also discussed.

Interpreting pH and nitrate concentration in solutions drained from acid soils. Possible artefacts of lysimeters

Abstract. Solutions collected from lysimeters of acid soils can show pH values close to or even above neutral. Laboratory experiments on an acid soil from Burundi were planned to test if denitrification or CO2 degassing might explain such a paradox. In the first experiment, soil profiles were reconstituted in columns and leached with 55 μm Ca(NO3)2 solutions at 30 °C and 4 °C. Two drainage regimes were applied: intermittent suction or no suction at the bottom of the columns. In the second experiment, pH values were measured in solutions drained from different horizons at 30 °C, before and after equilibration with ambient air. Sterilized soil was also tested in the same way. Results from experiment 1 showed that despite the accumulation of water in the bottom of soil profiles when no suction was applied, aeration still existed so that reduction reactions, namely denitrification, are not expected to affect greatly the percolate composition. Indeed nitrate concentration was similar in both drainage regimes and was close to the input value. The pH values in percolates were close to 7 at 30 °C and they dropped to about 5.5 when the columns were at 4 °C. In experiment 2, equilibration of percolates with ambient air resulted in pH increase which was greater for the top horizon (C‐rich) but negligible when the soil was first sterilized. These convergent results illustrate the very important effect of CO2 degassing on pH of drained solutions when microbial activity is stimulated at high temperatures, in C‐rich soil. This is of prime importance when interpreting results from lysimeter experiments. By chance, this study also showed that large quantities of nitrate can be produced in soil at low temperatures.