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Amendments of biochar, a product of pyrolysis of biomass, have been shown to increase fertility of acidic soils by enhancing soil properties such as pH, cation-exchange-capacity and water-holding-capacity. These parameters are important in the context of natural organic matter contained in soils, of which dissolved organic matter (DOM) is the mobile and most bioavailable fraction. The effect of biochar on the content and composition of DOM in soils has received little research attention. This study focuses on the effects of amendments of two different biochars to an acidic acrisol and a pH-neutral brown soil. A batch experiment showed that mixing biochar with the acrisols at a 10 wt.% dose increased the pH from 4.9 to 8.7, and this resulted in a 15-fold increase in the dissolved organic carbon concentration (from 4.5 to 69 mg L −1 ). The pH-increase followed the same trend as the release of DOM in the experiment, causing higher DOM solubility and desorption of DOM from mineral sites. The binding to biochar of several well-characterised reference DOM materials was also investigated and results showed a higher sorption of aliphatic DOM to biochar than aromatic DOM, with DOM-water partitioning coefficients ( K d -values) ranging from 0.2 to 590 L kg −1 . A size exclusion occurring in biochar’s micropores, could result in a higher sorption of smaller aliphatic DOM molecules than larger aromatic ones. These findings indicate that biochar could increase the leaching of DOM from soil, as well as change the DOM composition towards molecules with a larger size and higher aromaticity. [ABSTRACT FROM AUTHOR]

This study investigated the effect of biochar amendments on the retention and availability of plant nutrients and Al in seven acidic tropical soils from Zambia and Indonesia. The experiments carried out investigated whether the adsorption capacity of NH $ _4^+ $ in the soils increased upon the addition of biochar and which effect biochar had on available concentrations of NO $ _3^- $, K+, Mn2+, Mg2+ , PO $ _4^{3‐} $, and Al3+. These nutrients were selected as they represent those important to plant growth and soil quality. No significant increases or decreases in aqueous NH $ _4^+ $-N concentration with additions of biochar were detected. The Gaines-Thomas model was used in order to calculate selectivity coefficients for NH $ _4^+ $ exchange (Kgt values). Following the addition of biochar to soil, Kgt values decreased showing a reduction in the selective binding of NH $ _4^+ $ in the biochar amended soil compared to the control. The concentration of NO $ _3^- $ increased following the addition of biochar to the soils. The addition of 5 and 10% biochar to the Indonesian soil did not significantly alter ( t-test confidence level 0.05) the sorption of PO $ _4^{3‐} $ to the soil-biochar mixtures as compared to the soil alone. However, the addition of biochar to the soil from Zambia increased the sorption of PO $ _4^{3‐} $ compared to the soil alone. The concentrations of K+ and Mg2+ were significantly increased for almost all soils ( t-test at the 0.05 confidence level) following the addition of biochar. Addition of biochar to all but two soils significantly decreased ( t-test confidence level 0.05) Mn2+ concentrations. The concentration of Al3+ in the soils decreased exponentially significantly ( t-test confidence level 0.05) following the amendment of biochar in accordance with the increase in pH observed when biochar was added to the soil. These results show that biochar has the ability to release essential plant growth nutrients as well as alleviate Al toxicity in these soils. [ABSTRACT FROM AUTHOR]

Fluvial and erosional release processes in permafrost-dominated Eurasian Arctic cause transport of large amounts of particulate organic carbon (POC) to coastal waters. The marine fate of this terrestrial POC (terr-POC), water column degradation, burial in shelf sediments, or export to depth, impacts the potential for climate-carbon feedback. As part of the International Siberian Shelf Study (ISSS-08; August-September 2008), the POC distribution, inventory, and fate in the water column of the extensive yet poorly studied Eurasian Arctic Shelf seas were investigated. The POC concentration spanned 1-152 μM, with highest values in the SE Laptev Sea. The POC inventory was constrained for the Laptev (1.32 ± 0.09 Tg) and East Siberian seas (2.85 ± 0.20 Tg). A hydraulic residence time of 3.5 ± 2 years for these Siberian shelf seas yielded a combined annual terr-POC removal flux of 3.9 ± 1.4 Tg yr-1. Accounting for sediment burial and shelf-break exchange, the terr-POC water column degradation was ~2.5 ± 1.6 Tg yr-1, corresponding to a first-order terr-POC degradation rate constant of 1.4 ± 0.9 yr-1, which is 5-10 times faster than reported for terr-DOC degradation in the Arctic Ocean. This terr-POC degradation flux thus contributes substantially to the dissolved inorganic carbon excess of 10 Tg C observed during ISSS-08 for these waters. This evaluation suggests that extensive decay of terr-POC occurs already in the water column and contributes to outgassing of CO2. This process should be considered as a geographically dislocated carbon-climate coupling where thawing of vulnerable permafrost carbon on land is eventually adding CO2 above the ocean. [ABSTRACT FROM AUTHOR]

Climate change is expected to have a strong effect on the Eastem Siberian Arctic Shelf (ESAS) region, which includes 40% of the Arctic shelves and comprises the Laptev and East Siberian seas. The largest organic carbon pool, the dissolved organic carbon (DOC), may change significantly due to changes in both riverine inputs and transformation rates; however, the present DOC inventories and transformation patterns are poorly understood. Using samples from the International Siberian Shelf Study 2008, this study examines for the first time DOC removal in Arctic shelf waters with residence times that range from months to years. Removals of up to l0%-20% were found in the Lena River estuary, consistent with earlier studies in this area, where surface waters were shown to have a residence time of approximately 2 months. In contrast, the DOC concentrations showed a strong nonconservative pattern in areas with freshwater residence times of several years. The average losses of DOC were estimated to be 30%-50% during mixing along the shelf, corresponding to a first-order removal rate constant of 0.3 yr-1. These data provide the first observational evidence for losses of DOC in the Arctic shelf seas, and the calculated DOC deficit reflects DOC losses that are higher than recent model estimates for the region. Overall, a large proportion of riverine DOC is removed from the surface waters across the Arctic shelves. Such significant losses must be included in models of the carbon cycle for the Arctic Ocean, especially since the breakdown of terrestrial DOC to CO2 in Arctic shelf seas may constitute a positive feedback mechanism for Arctic climate warming. These data also provide a baseline for considering the effects of future changes in carbon fluxes, as the vast northern carbon-rich permafrost areas draining into the Arctic are affected by global warming. [ABSTRACT FROM AUTHOR]

A key issue to understanding the transformations of terrestrial organic carbon in the ocean is to disentangle the latter from marine-produced organic matter. We applied a multiple stable isotope approach using δ34 S and δ13C isotope signatures from estuarine dissolved organic matter (DOM), enabling us to constrain the contribution of terrestrial-derived DOM in an estuarine gradient of the northern Baltic Sea. The stable isotope signatures for dissolved organic sulfur (δ34SDOS) have twice the range between terrestrial and marine end members compared to the stable isotope signatures for dissolved organic carbon (δ13CDOC); hence, the share of terrestrial DOM in the total estuarine DOM can be calculated more precisely. DOM samples from the water column were collected using ultrafiltration on board the German RV Maria S Merian during a winter cruise, in the Bothnian Bay, Bothnian Sea, and Baltic proper. We calculated the terrestrial fraction of the estuarine DOC (DOCter) from both δ13CDOC and δ34SDOS signatures and applying fixed C: S ratios for riverine and marine end members to convert S isotope signatures into DOC concentrations. The δ34SDOS signature of the riverine end member was +7.02%, and the mean signatures from Bothnian Bay, Bothnian Sea, and Baltic proper were +10.27, +12.51, and +13.67%, respectively, showing an increasing marine signal southwards (δ34SDOS marine end member 5 18.1%). These signatures indicate that 87%, 75%, and 67%, respectively, of the water column DOC is of terrestrial origin (DOCter) in these basins. Comparing the fractions of DOCter in each basin-that are still based on few winter values only--with the annual river input of DOC, it appears that the turnover time for DOCter in the Gulf of Bothnia is much shorter than the hydraulic turnover time, suggesting that high-latitude estuaries might be efficient sinks for DOCter. [ABSTRACT FROM AUTHOR]