Changes in soil pool capacity for lead in response to conversion of rainforest to rubber plantations in Hainan Island, China

Abstract

Land degradation caused by deforestation seriously affects the soil environmental capacity (SEC), with potential risks to soil health. However, conventional SEC theory is unable to quantitatively describe the saturation capacity of different soil fractions and environmental pollution levels of a heterogeneous system. Thus, a new concept, the soil pool capacity (SPC), was introduced to fill this gap. We undertook space-fortime substitution to investigate the responses of SPCand soil safety capacity (SSC) to changes in the soil physiochemical properties, chemical species, and molecular characteristics of soil lead (Pb) in the conversion of tropical secondary rainforest (TSR) to rubber (Hevea brasiliensis) monoculture plantations with 15-and 60-year histories (RP 15/60). Conversion of TSR to RP 15/60 caused adverse effects on soil properties (i.e., lower soil organic matter [SOM] and higher bulk density [BD]). The saturated SPC (SPC sat) for Pb in bulk soils under RP 15 (2,203.17 g m −2) and RP 60 (1,634.09 g m −2) decreased compared with that in TSR (2,227.10 g m −2). The contribution rates of SPC sat in the exchangeable (P1) and carbonate (P2) pools to the total capacity stabilized at approximately 94%. The contribution rate of potential SPC sat in P4 (OM-bound Pb) significantly decreased with increasing agricultural intensity. The SSC of labile fractions (P1 + P2) accounted for 81-85% (a critical level) of the total SSC when the soil loading capacity for Pb reached the SSC in bulk soil regardless of land-use type. Fourier transform infrared and X-ray diffraction spectra revealed the Pb-loaded species of SPC sat in TSR and RP 15/60 (i.e., TSR: Pb 2 SiO 4 in P2, (CH 3 COO) 2 Pb in P4, RP 15/60 : Pb 5 Si 8 O 21 and Pb 2 (P 4 O 12) in P2, and (CHOO) 2 Pb in P4). Correlation and factor analyzes showed that SOM and BD were key factors that had an opposite impact on SPC sat and SSC. These results are helpful to choose appropriate agronomic measurements to reduce land degradation and crop safety risks caused by deforestation.

The current situation and measures for the protection of marine intangible cultural heritage in Hainan in the context of big data

“…Its largest island Hainan Island has a large "coastal zone" around, namely the coastal zone, continental shelf, continental slope and the slope of the accumulation of the foothillscontinental ridge and so on [1][2][3]. The continental shelf is near the coast to the sea, gently sloping shallow sea area; its sufficient light conditions and warm sea environment have nurtured a diversity of marine biological resources [4][5]. People living here have developed and utilized these resources to create a variety of marine cultures.…”