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.     

Leaching of solutes by the action of acidic rain: a comparison of efflux from twigs and single needles of Picea abies (L. Karst.)

Abstract. Leaching of inorganic cations (K⁺, Mg²⁺) and in some cases of inorganic anions and sugars from detached twigs and single needles of spruce Picea abies L. Karst.) in the presence of acid rain (H₂SO₄, 1 mol m^?3) or salt solutions (Na₂ SO₄, 1 mol m^?3) was examined under laboratory conditions. Cation leaching (as percentage of the total water soluble ion content of the tissue per hour) was: K⁺: 0.01-0.02%; Mg²⁺: 0.005-0.01%; Ca²⁺: 0.1-0.2%. Leaching rates of anions were even lower than that and concentrations in the leachate were often below the detection limit of anion chromatography. Spraying with H₂SO₄ (pH 2.95, 1 mol m^?3) increased leaching only transiently. Similar effects were found when Na₂SO₄ was used instead of H₂SO₄. The transiently enhanced leaching was apparently due to H⁺/cation or cation/cation exchange at the twig or leaf surfaces. Feeding of K⁺ or Al³⁺ through the stems increased leaching of all cations within a few hours, again demonstrating rapid ion exchange in the apoplast. Leaching of potassium and magnesium from single needles occurred at similar relative rates as from twigs. Loss of Ca²⁺ ions, however, was even smaller from needles than from twigs. Apparently, a large part of the Ca²⁺ lost from twigs originated from the bark and not from the needles. Efflux of ions from longitudinal needle sections was about 1000 times taster than the rates obtained with intact needles, indicating that the cuticle was the main barrier Preventing solute loss. In relation to the total amount of mineral nutrients in trees, leaching is considered to be too small to be the primary cause of damage to trees stressed by acid rain, as has been suggested in the literature.     

Origins and introductions of the Caribbean frog, Eleutherodactylus johnstonei (Leptodactylidae): management and conservation concerns

Johnstone's Whistling Frog, Eleutherodactylus johnstonei, is a highly successful colonizer that has become widely distributed throughout the Caribbean region. It has been introduced both purposefully and unintentionally by humans, and it continues to expand its range locally and regionally. Its current distribution and recent expansion do not support the hypothesis that E. johnstonei is expanding into new habitats exclusively by outcompeting native species. Instead, its range expansion progresses mainly parallel to human expansion (habitat disturbance through land development) and extreme climatic events (habitat disturbance through hurricanes and volcanism). Once a habitat has been disturbed and E. johnstonei has arrived, any previously existing endemic Eleutherodactylus species tend not to be found again at their previous ranges or population densities. The most probable explanation for this is that the broader physiological tolerance of the ecological generalist E. johnstonei allows it to become permanently established in a disturbed biota, whereas ecologically specialized endemics are prevented from recolonizing such habitats. Invasion of E. johnstonei can result in a parapatric distribution with endemics (e.g. E. euphronides, E. shrevei) or in sympatry (e.g. E. martinicensis), and habitats include areas with widely divergent climatic conditions (e.g. xeric: Anguilla, Barbuda; mesic: Grenada, St Vincent). Management for this species includes prevention of further or repeat introductions, close monitoring of ranges, and preservation of native habitats to ensure survival of local endemics.     

A Note on Idle Oil and Gas Platforms (Idle Iron) in the Gulf of Mexico

U.S. federal regulations require that an offshore oil and gas lease be cleared of all structures within one year after production on the lease ceases. Recently, the Minerals Management Service has begun to encourage operators to remove idle oil and gas platforms (known as "idle iron") on producing leases in a more timely manner. The purpose of this note is to quantify the amount of idle iron that exists in the Gulf of Mexico and to describe its geographic distribution and ownership patterns.­     

Intensified organic carbon dynamics in the ground water of a restored riparian zone

1. River restoration projects usually aim at improving the physical habitat for aquatic organisms. The extent to which biogeochemical processes and microbial activities are intensified in restored river reaches remains uncertain. 2. Here, we investigated the relationships between the distribution and composition of organic carbon (OC), bacterial secondary carbon production and extracellular enzymatic activity (EEA) in the ground water below a restored riparian section of the River Thur, Switzerland, relative to a channelised section. The spatiotemporal variability in the stable C isotopic ratio, dissolved OC polydispersity (the distribution of molecular mass in a mixture of molecules) as well as bacterial abundance, EEA and secondary production were investigated in different process zones. 3. At high river discharge, humic as well as low molecular weight amphiphilic substances infiltrated into the subsurface in a zone dominated by the pioneer plants Salix viminalis (willow bush). Concurrently, bacterial abundance, EEA and secondary carbon production increased at this location. 4. The willow plants leached bioavailable substrates into the ground water when the water table was high. The flood‐driven soil–groundwater coupling stimulated EEA and bacterial secondary production of the suspended groundwater bacterial community. 5. Establishing riparian habitat diversity adds hot spots of OC inputs during flood events, potentially providing valuable ecosystem services (e.g. degradation of organic pollutants) that accompany.