Disentangling Jenny's equation by machine learning.

The so-called soil-landscape model is the central paradigm which relates soil types to their forming factors through the visionary Jenny's equation. This is a formal mathematical expression that would permit to infer which soil should be found in a specific geographical location if the involved relationship was sufficiently known. Unfortunately, Jenny's is only a conceptual expression, where the intervening variables are of qualitative nature, not being then possible to work it out with standard mathematical tools. In this work, we take a first step to unlock this expression, showing how Machine Learning can be used to predictably relate soil types and environmental factors. Our method outperforms other conventional statistical analyses that can be carried out on the same forming factors defined by measurable environmental variables.

Abiotic factors influencing soil microbial activity in the northern Antarctic Peninsula region.

Microorganisms play a key role in the carbon (C) cycle through soil organic matter (SOM). The rate of SOM mineralization, the influence of abiotic factors on this rate and the potential behaviour of SOM are of particular interest in the northern Antarctic Peninsula and offshore islands. This is one of the most rapidly warming regions on Earth with numerous ice-free areas, some with abundant wildlife and with the greatest known soil organic carbon (SOC) storage in Antarctica. The latter implies extended Antarctic summer conditions promote increased terrestrial plant growth and soil microbial activity (SMA). SMA, determined by respirometry, is a measure of ecosystem function, and depends on microclimatic conditions and soil environmental properties. SMA and the effect of abiotic variables have been analysed in locations with different soil types, on Cierva Point (Antarctic Peninsula), Deception Island and Fildes Peninsula (King George Island). Soil microbial biomass carbon (SMBC) ranged from 5.66 to 196.6 mg SMBC kg-1and basal respiration (BR) from 2.86 to 160.67 mg CO2 kg-1 d-1. SMBC and BR values were higher in Cierva Point, followed by Fildes Peninsula and Deception Island, showing the same trend of SOM abundance. Except for Cierva Point, low nitrogen, phosphorus and C concentrations were observed. SMBC/total organic carbon (TOC) levels indicated that SOC was recalcitrant and SOM content was closely related to the extent of vegetation cover observed in situ. High metabolic quotient values obtained at Cierva Point and Deception Island (median values 7.27 and 6.53 mg C-CO2 g SMBC-1 h-1) and low SMBC/TOC in Cierva Point suggest a poor efficiency of the microbial populations in the consumption of the SOC. High SMBC/TOC values obtained in Deception Island indicates that SMBC may influence SOM stabilization. Mineralization rates were very low (negligible values to 1.44%) and sites with the lowest values had the highest SOM.

Processes and impacts of acid discharges on a natural substratum under a landfill.

Analyses of substratum samples under a landfill were performed to assess the pollution impact of waste over a clay-sand material after nine years of exposure. These samples presented different illite/kaolinite ratios and an acid pH, especially low near the waste/soil contact in a 1-1.5 m soil thickness with low density and despite the basic pH of the collected actual methanogenic leachate. This study has raised the effects of a presumably acid stage in the waste leachate on the substratum final quality of clay and its physical-chemical properties as an attenuation buffer. These effects were the dissolution of carbonate minerals, decrease of dry density, increase of hydraulic conductivity, release of metals and formation of clays with low cationic exchange capacity (CEC) as kaolinite. The large presence of H(+) and Al(OH)(3-x)(x+) depleted the neutralizing capacity of the substratum and occupied exchangeable sites, decreasing therefore the available sites for retaining leachate pollutants, which traveled further than the first-meter depth of the substratum. In order to combat and prevent pollution as well as to preserve the good barrier properties under new landfills it is proposed to select illitic materials better than kaolinitic substratum, to avoid acid landfilling and if not possible to add lime.