Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

The influence of recent geography, palaeogeography and climate on the composition of the fauna of the central Aegean Islands

Partial Mantel tests and structural equation models were used to investigate the influence of recent geography, palaeogeography and climate on the composition of the fauna of the central Aegean Islands. The composition of land snail and isopod island faunas was significantly influenced by recent and by Pliocene geography. Only Pleistocene palaeogeography had a significant influence on the composition of tenebrionid beetle island faunas. The composition of butterfly island faunas was influenced by recent and by Miocene geographical distances. The composition of reptile island faunas was correlated with recent and Pliocene geography as well as with Pleistocene and/or Miocene geographical distances. Island area influenced only the composition of the island faunas of the volant butterflies, and not that of the less mobile land snails, land isopods, tenebrionid beetles and reptiles. This might indicate that butterflies are able to colonize large islands with suitable habitats even if such islands are comparatively far from source areas more frequently than can the nonvolant groups. Influence of a climatic parameter, namely annual precipitation, on faunal composition was found only for reptiles.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 785–795.