Evaluating main factors controlling aluminum solubility in acid forest soils, southern and southwestern China

Abstract

The mechanism controlling Al solubility in Chinese acidic forest soils is not clearly understood. This is the main limitation to the ability to generate adequate dose-response prediction models of the ecological effect of acid rain. To evaluate the relative significance of possible processes, soils and soil solutions from five forest catchments, located in southern and southwestern China, were collected and analyzed for chemical parameters. Monitoring showed that inorganic Al (Al i ) was the dominant fraction in most soil solutions; organic Al (Al o ) was usually less than 10% of total monomeric Al (Al a ). Aluminum fractions varied significantly between and within the different sites, though appearing to follow a similar pattern. Over the entire pH range of 3.6-5.6, the pAl (i.e. Àlog of the Al 3+ activity) closely correlated with solution pH, following regression slopes of 1.28 and 2.00 for upper and lower soil horizons, respectively. The variations in Al 3+ activity could not be explained satisfactorily using mineral dissolution equilibria. Partial least square (PLS) regression showed that soil acidity (quality) and ionic strength (intensity) of the solution were the main explanatory variables for the variation in the concentration of Al fractions. Aluminum in upper horizons originated from both organic and inorganic solid Al pools, while aqueous Al in lower horizons was dominantly of inorganic origin. Aluminum solubility was strongly influenced by cation exchange, especially in the upper horizon. In the upper horizon, ionic strength (I) had a greater influence on Al solubility due to cation exchange reaction. In the lower horizon, dissolution of inorganic Al pools by the elevated H + concentrations was the main Al release mechanism. So Al activity was more dependent on H + (or pH) in the lower horizon.

Nitrogen saturation, soil acidification, and ecological effects in a subtropical pine forest on acid soil in southwest China

“…In line with earlier studies, we found a relatively small increase in Al 3+ concentration in soil water at Tieshanping with decreasing pH, in the pH range < 4. This minor increase in Al concentration with decreasing pH was not in accordance with Al(OH) 3 equilibrium reactions (Figure ) [ Mulder and Stein , ; Guo et al ., ]. The slope of the regression line was close to zero, much lower than the value of 1.65 for forests in North America [ Reuss et al ., ].…”

Long-Term Effects of Liming on Health and Growth of a Masson Pine Stand Damaged by Soil Acidification in Chongqing, China

“…The mean mineral soil depth is between 40 and 80 cm, and the soil was rather homogeneous [33] , [34] . This acidic soil is representative for Chongqing and characterized by low levels of exchangeable Ca and high levels of exchangeable Al [33] , [35] , [41] . In the last decades the Masson pine forest ecosystem has declined due to severe soil acidification [33] , [35] .…”

“…parts of China where pH value of rain water is lower than 4.5 and sulfur deposition exceeds the critical load, and the acid rain problem has been addressed by the national authorities [39] . The soil of Masson pine forests in Chongqing is generally acidic, with low amounts of exchangeable Ca and high amounts of exchangeable Al [33] , [35] , [40] , [41] . Masson pine is highly sensitive to Al [42] .…”

Metal accumulation in an artificially recharged gravel pit lake used for drinking water supply

“…Garcia-Rodeja1997; Guo et al, 2007;Van Hees et al, 2001) who found that the mobility of Al, as well as of other chemical elements including Ni, Zn, Mn, was enhanced by increasing the acidity of the soils where the type of soils determined which elements becomes mobile. The source for the acidity of the groundwater upstream of the DLV is probably a combination of acid rain, the production of H + during redox reactions caused by initial exposure of organic layers during lowering of the water table (Eq.…”