Beavers affect carbon biogeochemistry: both short‐term and long‐term processes are involved

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Variability and transport of suspended sediment,particulate and dissolved organic carbon in the tidal freshwater Hudson River

Measurements of suspended matter, particulate organic carbon and dissolved organic carbon were made over a three year period at stations spanning 150 km of the tidal freshwater Hudson River. Suspended matter concentrations varied from year-to-year and were not related to freshwater discharge. The increase in suspended matter with depth in vertical profiles suggests that, during medium to low flow conditions, resuspension of bottom sediments was as important a source of sediment as loadings from tributaries. Particulate organic carbon showed significant variability among stations, and both autochthonous primary production and detrital organic matter are contributing to POC standing stocks. Dissolved organic carbon represented over half of the total organic carbon in the water column and showed little variation among stations.Examining downstream changes in transport showed that there was significant production of both suspended matter and POC within the study reach during the ice-free season. Tributary loadings within the study reach do not appear to be the cause of these increases in downstream transport. Dissolved organic carbon behaved conservatively in that there was no evidence for net production or net consumption within the river.The spatial/temporal patterns and analyses of transport suggest that suspended matter and POC, but not DOC, were controlled to a significant extent by processes occurring within the river and were not simply related to loadings from outside.     

Conceptualizing soil organic matter into particulate and mineral‐associated forms to address global change in the 21st century

Managing soil organic matter (SOM) stocks to address global change challenges requires well‐substantiated knowledge of SOM behavior that can be clearly communicated between scientists, management practitioners, and policy makers. However, SOM is incredibly complex and requires separation into multiple components with contrasting behavior in order to study and predict its dynamics. Numerous diverse SOM separation schemes are currently used, making cross‐study comparisons difficult and hindering broad‐scale generalizations. Here, we recommend separating SOM into particulate (POM) and mineral‐associated (MAOM) forms, two SOM components that are fundamentally different in terms of their formation, persistence, and functioning. We provide evidence of their highly contrasting physical and chemical properties, mean residence times in soil, and responses to land use change, plant litter inputs, warming, CO₂ enrichment, and N fertilization. Conceptualizing SOM into POM versus MAOM is a feasible, well‐supported, and useful framework that will allow scientists to move beyond studies of bulk SOM, but also use a consistent separation scheme across studies. Ultimately, we propose the POM versus MAOM framework as the best way forward to understand and predict broad‐scale SOM dynamics in the context of global change challenges and provide necessary recommendations to managers and policy makers.     

Carbon bio‐sequestration within the phytoliths of economic bamboo species

The rates of carbon bio‐sequestration within silica phytoliths of the leaf litter of 10 economically important bamboo species indicates that (a) there is considerable variation in the content of carbon occluded within the phytoliths (PhytOC) of the leaves between different bamboo species, (b) this variation does not appear to be directly related to the quantity of silica in the plant but rather the efficiency of carbon encapsulation by the silica. The PhytOC content of the species under the experimental conditions ranged from 1.6% to 4% of the leaf silica weight. The potential phytolith carbon bio‐sequestration rates in the leaf‐litter component for the bamboos ranged up to 0.7 tonnes of carbon dioxide (CO₂) equivalents (t‐e‐CO₂) ha^?1 yr^?1 for these species. Assuming a median phytolith carbon bio‐sequestration yield of 0.36 t‐e‐CO₂ ha^?1 yr^?1, the global potential for bio‐sequestration via phytolith carbon (from bamboo and/or other similar grass crops) is estimated to be ～1.5 billion t‐e‐CO₂ yr^?1, equivalent to 11% of the current increase in atmospheric CO₂. The data indicate that the management of vegetation such as bamboo forests to maximize the production of PhytOC has the potential to result in considerable quantities of securely bio‐sequestered carbon.     

Carbon source utilization and accumulation of respiration-related substances by freshwater Thioploca species

Carbon source utilization of Thioploca species from freshwater and brackish lakes in Japan was investigated. Microautoradiography demonstrated that freshwater and brackish Thioploca samples assimilate acetate. In addition, vertical nitrate transportation by freshwater Thioploca was examined by measuring substances accumulated in Thioploca filaments. The filaments of Thioploca sp. from Lake Biwa, a Japanese mesotrophic lake, contained nitrate at concentrations higher than ambient by two to three orders of magnitude. They also accumulated high concentrations of sulfate and abundant elemental sulfur. The results suggest that the Thioploca-specific strategy for sulfur oxidation, migration with accumulated nitrate, is effective even in freshwater habitats of lower sulfide supply.     

Sedimentation of ballasted cells‐free EPS in meromictic Fayetteville Green Lake

Fayetteville Green Lake (FGL) is a recognized, extensively studied present‐day model of the stratified Proterozoic ocean. Nonetheless, biomass sedimentation in FGL remains hard to explain: while virtually all sediment pigments belong to photosynthetic sulfur bacteria from a chemocline, the isotopic carbon signature of the bulk organic matter suggests its epilimnetic phytoplankton origin. To explain the epilimnetic origin of sedimented carbon, we studied the dominant Synechococci, isolated from FGL. Here, we present experimental evidence that FGL Synechococci produce copious extracellular polysaccharides (EPS) especially when availability of inorganic carbon (C_i) is high relative to availability of other macronutrients, for example phosphorus. The accumulating EPS become impregnated with calcium, magnesium, and sodium cations and are released to the environment as ballasted cell coverings. Sedimentation of these cell‐free EPS can constitute the bulk of pigment‐free organic material in FGL sediment. Because increased availability of C_i specifically stimulates production of EPS and the accumulated EPS adsorb cations and become ballasted, we propose the universal role of cyanobacterial EPS in biomass sedimentation in the high‐C_i Paleoproterozoic ocean as well as in modern aquatic systems like FGL.     

Key Issues Concerning Biolog Use for Aerobic and Anaerobic Freshwater Bacterial Community‐Level Physiological Profiling

Bacterial heterotrophy in aquatic ecosystems is important in the overall carbon cycle. Biolog MicroPlates provide information into the metabolic potential of bacteria involved in carbon cycling. Specifically, Biolog EcoPlates™ were developed with ecologically relevant carbon substrates to allow investigators to measure carbon substrate utilization patterns and develop community‐level physiological profiles from natural bacterial assemblages. However, understanding of the functionality of these plates in freshwater research is limited. We explored several issues of EcoPlate use for freshwater bacterial assemblages including inoculum density, incubation temperature, non‐bacterial color development, and substrate selectivity. Each of these has various effects on plate interpretation. We offer suggestions and techniques to resolve these interpretation issues. Lastly we propose a technique to allow EcoPlate use in anaerobic freshwater bacterial studies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On fertilizer‐induced soil carbon sequestration in China's croplands

Applications of fertilizer, often thought to enhance carbon sequestration in agricultural soils, are of no value to the mitigation of climate change if the carbon dioxide released during the production and distribution of nitrogen fertilizer exceeds the incremental carbon storage in soils from its use. Nitrogen fertilizer is also a source of the greenhouse gas nitrous oxide. The recent analysis of carbon sequestration in cropland soils of China does not apply these ‘discounts’ to the global warming mitigation expected from greater use of fertilizer; doing so would likely eliminate all the climate benefits of the postulated enhanced carbon sequestration.     

Long‐term organic carbon sequestration in tidal marsh sediments is dominated by old‐aged allochthonous inputs in a macrotidal estuary

Tidal marshes are vegetated coastal ecosystems that are often considered as hotspots of atmospheric CO₂ sequestration. Although large amounts of organic carbon (OC) are indeed being deposited on tidal marshes, there is no direct link between high OC deposition rates and high OC sequestration rates due to two main reasons. First, the deposited OC may become rapidly decomposed once it is buried and, second, a significant part of preserved OC may be allochthonous OC that has been sequestered elsewhere. In this study we aimed to identify the mechanisms controlling long‐term OC sequestration in tidal marsh sediments along an estuarine salinity gradient (Scheldt estuary, Belgium and the Netherlands). Analyses of deposited sediments have shown that OC deposited during tidal inundations is up to millennia old. This allochthonous OC is the main component of OC that is effectively preserved in these sediments, as indicated by the low radiocarbon content of buried OC. Furthermore, OC fractionation showed that autochthonous OC is decomposed on a decadal timescale in saltmarsh sediments, while in freshwater marsh sediments locally produced biomass is more efficiently preserved after burial. Our results show that long‐term OC sequestration is decoupled from local biomass production in the studied tidal marsh sediments. This implies that OC sequestration rates are greatly overestimated when they are calculated based on short‐term OC deposition rates, which are controlled by labile autochthonous OC inputs. Moreover, as allochthonous OC is not sequestered in‐situ, it does not contribute to active atmospheric CO₂ sequestration in these ecosystems. A correct assessment of the contribution of allochthonous OC to the total sedimentary OC stock in tidal marsh sediments as well as a correct understanding of the long‐term fate of locally produced OC are both necessary to avoid overestimations of the rate of in‐situ atmospheric CO₂ sequestration in tidal marsh sediments.     

Contribution to the reduction‐induced fluorescence enhancement of natural organic matter: Aromatic ketones outweigh quinones

This work involves the comparison of the fluorescence excitation ? emission matrices of different low‐molecular‐weight carbonyl compounds and natural organic matter (NOM). The aim is to determine if quinone or aromatic ketone groups are more responsible for the reduction‐induced fluorescence enhancement of NOM. After reduction, the aromatic ketones showed a significantly greater fluorescence change than the quinones, proving that the former play a more important role. Further analysis of the fluorescence of the NOM samples after re‐oxidization by oxygen with a Cu²⁺ catalyst, provided additional reliable evidence in support of the dominant role of aromatic ketones in the fluorescence change. This work demonstrates that aromatic ketone moieties should be given more attention when considering the physicochemical properties of NOM and related environmental processes.     

中国北亚热带天然次生林与杉木人工林土壤活性有机碳库的比较

为了了解北亚热带东部地区天然次生林转变成杉木(Cunninghamia lanceolata)人工林对土壤活性有机碳库的影响, 以浙江省富阳市庙山坞森林生态系统定位研究站杉木人工林和天然次生林为研究对象, 对达到成熟林状态的两种林分类型0-60 cm内各土层土壤活性有机碳含量进行了比较研究。结果表明: 1)天然次生林土壤总有机碳、易氧化有机碳、水溶性有机碳和轻组有机质含量均高于杉木人工林, 与人工杉木林相比, 增幅分别为19.0%-32.6%、0.8%-30.3%、3.8%-54.1%和6.3%-38.6%, 且在0-10和10-20 cm土层差异显著(p < 0.05) (水溶性有机碳仅在0-10 cm土层差异显著); 2)杉木人工林土壤水溶性有机碳与易氧化碳占总有机碳的比率均高于天然次生林; 3)两个林分土壤水溶性有机碳、易氧化碳和轻组有机质与总有机碳含量均呈现极显著相关, 且天然次生林土壤易氧化碳、轻组有机质与总有机碳的相关系数均大于杉木人工林; 4)土壤有机碳、水溶性有机碳、易氧化碳和轻组有机质与土壤养分(全氮、水解氮、速效磷、速效钾、速效钙和速效镁)的相关性均达到显著(p < 0.05)或极显著(p < 0.01)水平。     

Nitrogen addition alters mineralization dynamics of 13C‐depleted leaf and twig litter and reduces leaching of older DOC from mineral soil

Recent reviews indicate that N deposition increases soil organic matter (SOM) storage in forests but the undelying processes are poorly understood. Our aim was to quantify the impacts of increased N inputs on soil C fluxes such as C mineralization and leaching of dissolved organic carbon (DOC) from different litter materials and native SOM. We added 5.5 g N m^?2 yr^?1 as NH₄NO₃ over 1 year to two beech forest stands on calcareous soils in the Swiss Jura. We replaced the native litter layer with ¹³C‐depleted twigs and leaves (δ¹³C: ?38.4 and ?40.8‰) in late fall and measured N effects on litter‐ and SOM‐derived C fluxes. Nitrogen addition did not significantly affect annual C losses through mineralization, but altered the temporal dynamics in litter mineralization: increased N inputs stimulated initial mineralization during winter (leaves: +25%; twigs: +22%), but suppressed rates in the subsequent summer. The switch from a positive to a negative response occurred earlier and more strongly for leaves than for twigs (?21% vs. 0%). Nitrogen addition did not influence microbial respiration from the nonlabeled calcareous mineral soil below the litter which contrasts with recent meta‐analysis primarily based on acidic soils. Leaching of DOC from the litter layer was not affected by NH₄NO₃ additions, but DOC fluxes from the mineral soils at 5 and 10 cm depth were significantly reduced by 17%. The ¹³C tracking indicated that litter‐derived C contributed less than 15% of the DOC flux from the mineral soil, with N additions not affecting this fraction. Hence, the suppressed DOC fluxes from the mineral soil at higher N inputs can be attributed to reduced mobilization of nonlitter derived ‘older’ DOC. We relate this decline to an altered solute chemistry by NH₄NO₃ additions, an increased ionic strength and acidification resulting from nitrification, rather than to a change in microbial decomposition.     

Long‐term growth‐increment chronologies reveal diverse influences of climate forcing on freshwater and forest biota in the Pacific Northwest

Analyses of how organisms are likely to respond to a changing climate have focused largely on the direct effects of warming temperatures, though changes in other variables may also be important, particularly the amount and timing of precipitation. Here, we develop a network of eight growth‐increment width chronologies for freshwater mussel species in the Pacific Northwest, United States and integrate them with tree‐ring data to evaluate how terrestrial and aquatic indicators respond to hydroclimatic variability, including river discharge and precipitation. Annual discharge averaged across water years (October 1–September 30) was highly synchronous among river systems and imparted a coherent pattern among mussel chronologies. The leading principal component of the five longest mussel chronologies (1982–2003; PC1_mussel) accounted for 47% of the dataset variability and negatively correlated with the leading principal component of river discharge (PC1_discharge; r = ?0.88; P < 0.0001). PC1_mussel and PC1_discharge were closely linked to regional wintertime precipitation patterns across the Pacific Northwest, the season in which the vast majority of annual precipitation arrives. Mussel growth was also indirectly related to tree radial growth, though the nature of the relationships varied across the landscape. Negative correlations occurred in forests where tree growth tends to be limited by drought while positive correlations occurred in forests where tree growth tends to be limited by deep or lingering snowpack. Overall, this diverse assemblage of chronologies illustrates the importance of winter precipitation to terrestrial and freshwater ecosystems and suggests that a complexity of climate responses must be considered when estimating the biological impacts of climate variability and change.     

Biochar stability in soil: meta‐analysis of decomposition and priming effects

The stability and decomposition of biochar are fundamental to understand its persistence in soil, its contribution to carbon (C) sequestration, and thus its role in the global C cycle. Our current knowledge about the degradability of biochar, however, is limited. Using 128 observations of biochar‐derived CO₂ from 24 studies with stable (¹³C) and radioactive (¹⁴C) carbon isotopes, we meta‐analyzed the biochar decomposition in soil and estimated its mean residence time (MRT). The decomposed amount of biochar increased logarithmically with experimental duration, and the decomposition rate decreased with time. The biochar decomposition rate varied significantly with experimental duration, feedstock, pyrolysis temperature, and soil clay content. The MRTs of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years with pool sizes of 3% and 97%, respectively. These results show that only a small part of biochar is bioavailable and that the remaining 97% contribute directly to long‐term C sequestration in soil. The second database (116 observations from 21 studies) was used to evaluate the priming effects after biochar addition. Biochar slightly retarded the mineralization of soil organic matter (SOM; overall mean: ?3.8%, 95% CI = ?8.1–0.8%) compared to the soil without biochar addition. Significant negative priming was common for studies with a duration shorter than half a year (?8.6%), crop‐derived biochar (?20.3%), fast pyrolysis (?18.9%), the lowest pyrolysis temperature (?18.5%), and small application amounts (?11.9%). In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. This indicates that biochar stimulates microbial activities especially in soils with low fertility. Furthermore, abiotic and biotic processes, as well as the characteristics of biochar and soils, affecting biochar decomposition are discussed. We conclude that biochar can persist in soils on a centennial scale and that it has a positive effect on SOM dynamics and thus on C sequestration.     

Emission of CO2 from biochar‐amended soils and implications for soil organic carbon

Soil amendment with pyrogenic organic matter (PyOM), also named biochar, is claimed to sequester carbon (C). However, possible interactions between PyOM and native soil organic carbon (SOC) may accelerate the loss of SOC, thus reducing PyOM's C sequestration potential. We combined the results of 46 studies in a meta‐analysis to investigate changes in CO₂ emission of PyOM‐amended soils and to identify the causes of these changes and the possible factors involved. Our results showed a statistically significant increase of 28% in CO₂ emission from PyOM‐amended soils. When grouped by PyOM C (PyC):SOC ratios, the group of studies with a ratio >2 showed a significant increase in CO₂ emissions, but those with a ratio <2 showed no significant effect of PyOM application on CO₂ emission. Our data are consistent with the hypothesis that increased CO₂ emission after PyOM addition is additive and mainly derived from PyOM's labile C fractions. The PyC:SOC ratio provided the best predictor of increases in CO₂ production after PyOM addition to soil. This meta‐analysis highlights the importance of taking into account the amount of applied PyC in relation to SOC for designing future decomposition experiments.     

Ecosystem Changes Following Restoration of a Buckthorn‐Invaded Woodland

Shifts in plant‐community composition following habitat degradation and species invasions can alter ecosystem structure and performance of ecosystem services. In temperate North American woodlands, invasion by aggressive Eurasian shrubs has produced dense thickets with depauperate understory vegetation and increased rates of litter decomposition and nutrient cycling, attributes that could impair storage of carbon as soil organic matter (SOM). It is important to know if such impairment has occurred and, if so, the extent to which restoration can return this service. We used an oak‐woodland restoration chronosequence in northeastern Illinois to contrast structural and functional attributes of unrestored areas dominated by Rhamnus cathartica (common buckthorn) with areas that had undergone buckthorn removal and ongoing, active management for less than 1 to 14 years. With increasing age, restored areas had higher understory plant diversity and cover (p < 0.0001 and 0.005, respectively) and higher litter mass (p = 0.018). These structural differences were associated with some evidence of reduced soil erosion (p = 0.027–0.135) but greater soil CO₂ efflux (p = 0.020–0.033). Total particulate organic matter (POM) in the soil increased with restoration age, which was driven by increases in the slow‐turnover, mineral‐associated SOM fraction. However, variance was high and relationships were only weakly significant (p = 0.082 and 0.083 for total POM and mineral‐associated SOM, respectively). Our results suggest that, in addition to better documented biodiversity benefits, beneficial changes to ecosystem properties and processes may also occur with active, long‐term restoration of degraded woodlands.     

Potential for long‐term transfer of dissolved organic carbon from riparian zones to streams in boreal catchments

Boreal regions store most of the global terrestrial carbon, which can be transferred as dissolved organic carbon (DOC) to inland waters with implications for both aquatic ecology and carbon budgets. Headwater riparian zones (RZ) are important sources of DOC, and often just a narrow ‘dominant source layer’ (DSL) within the riparian profile is responsible for most of the DOC export. Two important questions arise: how long boreal RZ could sustain lateral DOC fluxes as the sole source of exported carbon and how its hydromorphological variability influences this role. We estimate theoretical turnover times by comparing carbon pools and lateral exports in the DSL of 13 riparian profiles distributed over a 69 km² catchment in northern Sweden. The thickness of the DSL was 36 ± 18 (average ± SD) cm. Thus, only about one‐third of the 1‐m‐deep riparian profile contributed 90% of the lateral DOC flux. The 13 RZ exported 8.7 ± 6.5 g C m^?2 year^?1, covering the whole range of boreal stream DOC exports. The variation could be explained by local hydromorphological characteristics including RZ width (R² = 0.90). The estimated theoretical turnover times were hundreds to a few thousands of years, that is there is a potential long‐lasting supply of DOC. Estimates of net ecosystem production in the RZ suggest that lateral fluxes, including both organic and inorganic C, could be maintained without drawing down the riparian pools. This was supported by measurements of stream DO¹⁴C that indicated modern carbon as the predominant fraction exported, including streams disturbed by ditching. The transfer of DOC into boreal inland waters from new and old carbon sources has a major influence on surface water quality and global carbon balances. This study highlights the importance of local variations in RZ hydromorphology and DSL extent for future DOC fluxes under a changing climate.     

Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition

We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (¹³C_POC) and suspended matter (¹³C_POC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest ¹³C_DIC values are observed due to enhanced input of CO₂ from decomposition of ¹³C-depleted terrestrial plant detritus (average ¹³C_DIC = –/14.3). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative ¹³C_DIC values (average ¹³C_DIC = –9.9). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 gl^–1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 gl^–1. Furthermore, in winter the very narrow range of ¹³C_POC (from –26.5 to –27.6) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer ¹³C_POC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in ¹³C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of ¹³C/¹²C fractionation by phytoplankton is attempted.     

Sensitive and rapid detection of Flavobacterium columnare in channel catfish Ictalurus punctatus by a loop-mediated isothermal amplification method

AIMS: To evaluate the loop-mediated isothermal amplification method (LAMP) for rapid detection of Flavobacterium columnare and determine the suitability of LAMP for rapid diagnosis of columnaris infection in channel catfish, Ictalurus punctatus. METHODS AND RESULTS: A set of four primers, two outer and two inner, were designed specifically to recognize 16S ribosomal RNA gene of this pathogen. Bacterial genomic DNA templates were prepared by hot lysis in a lysis buffer. Amplification of the specific gene segments was carried out at 65 degrees C for 1 h. The amplified gene products were analysed by agarose gel electrophoresis and detected by staining gels with ethidium bromide. A PCR assay was also included in this study. Our results demonstrate that the ladder-like pattern of bands from 204 bp specific to the Fl. columnare 16S ribosomal RNA gene was amplified. The detection limit of the LAMP assay was comparable to that of PCR in prepared genomic DNA reactions. In addition, this optimized LAMP assay was able to detect the Fl. columnare 16S ribosomal RNA gene in experimentally infected channel catfish. CONCLUSIONS: The LAMP assay for Fl. columnare detection in channel catfish was established. SIGNIFICANCE AND IMPACT OF THE STUDY: Because LAMP assay is a rapid, sensitive, specific, simple and cost-effective assay for Fl. columnare detection in channel catfish, it is useful for rapid diagnosis of Fl. columnare in fish hatcheries and the field.