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Biogeochemistry

Current research reports and chronological list of recent articles..




The international scientific journal Biogeochemistry publishes original papers and occasional reviews dealing with biotic controls on the chemistry of the environment, or with the geochemical control of the structure and function of ecosystems.

The publisher is Springer. The copyright and publishing rights of specialized products listed below are in this publishing house. This is also responsible for the content shown.

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Additional research articles see Current Chemistry Research Articles. General information about this topic see biogeochemistry.



Biogeochemistry - Abstracts



Decoupling of silica, nitrogen and phosphorus cycling in a meromictic subalpine lake (Lake Iseo, Italy)

Abstract

Silica (Si), nitrogen (N) and phosphorus (P) loads and stoichiometry are key factors controlling the trophic status of lakes and coastal seas. In the hydrographic network, lakes also act as biogeochemical reactors, controlling both nutrient retention and fluxes. This work aimed to examine the coupling of Si, N and P cycling, together with their stoichiometry in a deep meromictic subalpine lake (Lake Iseo, Northern Italy). Si, N and P mass budgets were calculated by quantifying loads in the inlets and in the outlet over a period of 30 months (May 2016−October 2018), in-lake sedimentation rates and net nutrients accumulation in the water body. Lake Iseo acts as a biogeochemical filter, which differentially retains the external Si, N and P loads. Retention of Si and P was similar (75–79%), but considerably higher than N (45%), evidencing a decoupling of their fate due to in-lake processes. This differential retention is likely to be exacerbated by meromixis which enhances Si and P accumulation in the monimolimnion, while impairing denitrification, thus limiting N removal. Such decoupling resulted in an increase of the N:Si and N:P ratios in both the epilimnion and in the outlet compared to the inlets, whereas the ratios decreased in the monimolimnion. As a result, there may be a stronger Si and P limitation of the photic zone, leading to a shift towards more oligotrophic conditions. This transient equilibrium could be impaired in the case of water overturn produced by extreme climate events—a highly relevant issue, considering that a growing number of deep lakes are turning from holo-oligomictic to meromictic as a result of combined eutrophication and climate change.


Datum: 01.07.2022


Clarifying the fate of dissolved organic carbon in turbid glacier meltwater rivers in Svalbard via a series of incubations

Abstract

The dissolved organic carbon (DOC) of Svalbard’s glacier meltwater has received limited attention. Due to the northward ocean current, terrestrial DOC output from Svalbard eventually enters the Arctic Ocean, rather than travelling southward into the Atlantic. This makes the role of Svalbard glaciers in the Arctic marine carbon budget significantly different from that of Greenland glaciers. Field work was conducted in Ny-Ålesund, Svalbard in late summer, 2017 to reveal the fate of DOC in turbid glacier meltwaters in Svalbard. Based on mixing incubation over 25 h, bio- and photo-degradation over 10 days, and long-term biodegradation over 13 months, it is believed that glacier meltwater DOC fraction is linearly mixed and diluted with seawater in the turbid plume area due to light limitation. When the light limitation is removed (e.g., in the clear offshore waters), 78% of the DOC undergoes photo-degradation or photo-triggered synergistic degradation within 10 days, rather than solely microbial degradation. Over the long-term, 73% of initial DOC was lost after being kept in the dark for 13 months. This work underlines that 4/5 of the Svalbard glaciers DOC would be degraded in Arctic coast within 10 days after entering the sea, generating a positive feedback to global warming. Photo-degradation, and/or photo-triggered synergistic degradation, is the key mechanism. Approximately one-fifth of the original concentration exhibited resistance and this fraction of DOC would be transported out of the fjord and likely into the Arctic Ocean.


Datum: 01.07.2022


Surface soil organic carbon sequestration under post agricultural grasslands offset by net loss at depth

Abstract

Post agricultural grasslands are thought to accumulate soil organic carbon (SOC) after cultivation cessation. The Conservation Reserve Program (CRP) in the U.S. is a wide-scale, covering approximately 8.9 Mha as of 2020, example of row-crop to grassland conversion. To date, changes in SOC stock in CRP lands have mostly been evaluated at local scales and focused on the surface 20–30 cm of the soil profile. Thus, we lack knowledge of SOC dynamics in CRP lands on a continental scale, especially in the subsurface soil, after agricultural cessation. The Rapid Carbon Assessment (RaCA) project is the most recent effort by the United States Department of Agriculture (USDA) to systematically quantify C stock in the 0–100 cm soil profile across the conterminous US. Here we analyzed data from RaCA to evaluate the SOC stocks of both surface and subsurface soil of the CRP on a continental scale. We found there was no difference in SOC stock between croplands and CRP lands when comparing the 0–100 cm soil profiles, which indicates that the C sequestration in CRP lands is insignificant overall. We did find that CRP lands have higher SOC stocks in the surface soil (0–5 cm). However, such higher SOC levels in surface (0–5 cm) soil were offset by the lower SOC stock in the subsurface (30–100 cm) of the CRP. We also found that CRP lands in humid and warm regions may have net soil C sequestration because they have much more SOC in the surface as compared with croplands in the same regions. Whether the lower SOC in the subsurface of CRP lands is caused by legacy effects or is a result of C losses needs to be verified by long-term repeated sampling in both surface and subsurface soil. This analysis highlights the importance of examining C dynamics in subsurface soil after agricultural cessation to accurately measure and improve C sequestration rates in CRP lands.


Datum: 01.07.2022


Twenty years of litter manipulation reveals that above-ground litter quantity and quality controls soil organic matter molecular composition

Abstract

Global environmental change is altering the quality and quantity of plant inputs into soil. However, it is unclear how these long-term changes may fundamentally shift the biogeochemistry of soil carbon in forests. To better understand how varied detrital inputs alter soil organic matter (OM) biogeochemistry and composition at the molecular-level, soil samples were collected from a 20 year detrital manipulation experiment in an old-growth coniferous rainforest in Western Oregon. The experiment includes ambient (control) plots and six treatments: Double Litter, Double Wood, No Roots, No Litter, No Inputs and OA-less (replacement of O and A horizons with B horizon). Total soil carbon and nitrogen, molecular-level OM composition using solid-state 13C nuclear magnetic resonance, and targeted compound extractions were measured. Although soil carbon did not increase with Double Litter and Double Wood, microbial biomass and the decomposition of specific forms of soil OM (i.e., cellulose) increased, likely due to sustained soil priming over 20 years. Mineral (0–10 cm) soil carbon was similar across litter exclusion treatments (No Litter, No Roots, No Inputs), however, soil OM decomposition increased relative to the control. Microbial-derived lipids increased under Double Litter but decreased when above-ground litter was excluded. Notably, needle-derived lipids decreased with above-ground litter exclusion and root-derived compounds did not change under below-ground root exclusion. These results suggested that above-ground litter alters soil carbon biogeochemistry in surface soils to a greater extent than below-ground inputs. This study also demonstrated that long-term soil carbon biogeochemical trajectories were mostly governed by litter quality, quality and microbial processing of above-ground inputs.


Datum: 01.07.2022


Impacts of nutrient addition on soil carbon and nitrogen stoichiometry and stability in globally-distributed grasslands

Abstract

Global changes will modify future nutrient availability with implications for grassland biogeochemistry. Soil organic matter (SOM) is central to grasslands for both provision of nutrients and climate mitigation through carbon (C) storage. While we know that C and nitrogen (N) in SOM can be influenced by greater nutrient availability, we lack understanding of nutrient effects on C and N coupling and stability in soil. Different SOM fractions have different functional relevance and mean residence times, i.e., mineral-associated organic matter (MAOM) has a higher mean residence time than particulate organic matter (POM). By separating effects of nutrient supply on the different SOM fractions, we can better evaluate changes in soil C and N coupling and stability and associated mechanisms. To this end, we studied responses of C and N ratios and distributions across POM and MAOM to 6–10 years of N, phosphorus (P), potassium and micronutrients (K), and combined NPK additions at 11 grassland sites spanning 3 continents and globally relevant environmental gradients in climate, plant growth, soil texture, and nutrient availability. We found addition of N and NPK generally reduced C:N in MAOM and POM. However, at low fertility and at warm, sandy sites, nutrient addition promoted higher MAOM and POM C:N, respectively. Addition of NPK also promoted C storage in POM relative to MAOM, and this was consistent across sites. Our results suggest that addition of macro- and micronutrients consistently decrease SOM stabilization, whereas responses of soil C:N stoichiometry were contingent on SOM fraction and environmental conditions.


Datum: 01.07.2022


Post-depositional alteration of stable isotope signals by preferential degradation of algae-derived organic matter in reservoir sediments

Abstract

Post-depositional degradation of organic matter (OM) in freshwater sediments is crucial for driving the biogeochemical dynamics and influencing the carbon burial. This process also often causes diagenetic alteration on paleoenvironmental proxies. Yet, mechanisms behind degradation of sedimentary OM and depth-related variations in stable isotope ratios can so far only be explained in part. Degradation of sedimentary OM in two drinking water reservoirs with contrasting eutrophic and mesotrophic states and different catchment land use (agriculture versus forestry) was studied. A 4-step procedure was used to chemically separate sedimentary OM in terms of biochemical composition. Here we presented depth profiles of biochemical composition of sedimentary OM that helped to quantify preferential degradation of aquatic proteins and carbohydrates and the following removal of aquatic lipids. Sediment in the eutrophic reservoir, which reflected a larger contribution of algal-derived OM than the mesotrophic reservoir with a forest dominated catchment, was therefore subject to more intensive degradation of sedimentary OM along with δ13C and δ15N alterations. In addition, changes in the relative proportions of biochemical components in sedimentary OM had more pronounced impact on δ15N values relative to δ13C. Our findings suggest that the lability of algae-derived OM leads to uncertainties for the estimation of carbon burial in water bodies and obscures paleo-limnological information derived from isotopic proxies. Post-depositional modifications are more pronounced in eutrophic freshwaters that accumulated more readily degradable OM of algal origin in their sediments. Recognition of these modifications will help constrain carbon burial rates of productive lakes and reservoirs and assess the role of reservoirs in carbon cycling.


Datum: 01.07.2022


Artificial ponds as hotspots of nitrogen removal in agricultural watershed

Abstract

Small waters, like ponds, are the most abundant freshwater environments, and are increasingly recognized for their function in ecosystem service delivery. In agricultural watershed, artificial ponds play an essential role in reducing nitrogen pollution. However, until now artificial ponds remain the least investigated part of water environments. The importance of microbial activities has seldom been discussed, which makes the microbial pathways and processes rates in nitrogen removal poorly understood. To illustrate the role of artificial ponds in microbial nitrogen removal in agricultural watersheds, 21 pond sediments and 11 soils are collected in an agricultural watershed of China. Results show that surface sediments in ponds carry significantly higher dissolved inorganic nitrogen (9.1–21.9 mg/kg) and total organic matter (64.8–113.0 g/kg) compared to the surrounding agricultural soils. High rates of microbial nitrogen removal in ponds (12.4–25.5 nmol N g−1 h−1) are observed, which are 2–9 times higher than those in dryland soils. In pond sediments, denitrification dominates (> 90% N-loss) the microbial nitrogen removal process with only a minor contribution of anaerobic ammonium oxidation. A high potential of N2O production (up to 9.4 nmol N g−1 h−1) occurs in ponds along with the rapid nitrogen removal. For denitrifier genes, nir gene are always more abundant than nosZ gene. Additionally, the nirS gene is more abundant under flooded conditions, while nirK gene prefers higher dissolved oxygen and NO3 in drylands. These findings highlight the ecosystem function of ponds in agricultural watersheds, and provide new ideas on pollution control and global nitrogen cycling.


Datum: 01.07.2022


Spatial and temporal patterns of benthic nutrient cycling define the extensive role of internal loading in an agriculturally influenced oxbow lake

Abstract

Benthic habitats in shallow oxbow lakes may serve as permanent nitrogen (N) sinks by facilitating denitrification. Oxbow sediments may also accumulate nutrients through uptake, deposition and heterotrophic N2 fixation, and ultimately provide a significant internal source of N and phosphorus (P) through sediment release to the water column. To better understand nutrient source-sink dynamics in oxbow lakes, we explored seasonal and habitat specific patterns in sediment dissolved dinitrogen gas (N2-N) and nutrient flux within an oxbow in the Mississippi Alluvial Plain. Time series models indicate a higher probability of positive N2-N fluxes in fall through spring, significant negative summer fluxes, and clear differences among habitats with net annual N2-N fluxes, ranging from − 2.34 g m−2 Y−1 in open water habitat to 0.26 g m−2 Y−1 in shoreline areas. Integrated lake-wide N2-N sediment flux estimates were negative indicating the significant role of net N2 fixation. More complex models explained similar amounts of variation (Adj. R2 = 0.57 vs. 0.45) and indicated that benthic N2-N fluxes were associated with changes in temperature, dissolved inorganic N, sediment oxygen demand, and sediment carbon:N ratios. Ammonium and P flux from sediments were substantial across all habitats and internal N regeneration far outpaced removal from the system by sediment N2-N flux. Results indicate that nutrient release from sediments generate internal nutrient loads proportional to external loading from the watershed. Our results highlight the significant potential for internal nutrient loading and benthic N2 fixation within sediments to regulate biogeochemical processes within understudied oxbow lake ecosystems.


Datum: 01.07.2022


High initial soil organic matter level combined with aboveground plant residues increased microbial carbon use efficiency but accelerated soil priming effect

Abstract

Input of plant residue carbon (C) stimulates microbial growth and activity, and thus may alter native soil organic matter (SOM) mineralization. The partition of plant residue C between microbial growth and respiration, and priming effect on soil organic C (SOC) are affected by initial SOM levels and plant residue types. However, how the interaction between SOM level and plant residue on microbial C use efficiency (CUE) and soil priming effect remains not very clear. Here, we quantified the ratio of plant residue C converted to microbial biomass production (as MBC) over that uptake by microorganism (MBC + respiration) and the priming effect on native SOC in two soils (with low and high initial SOM levels, abbreviated as LSOM and HSOM, respectively) added with 13C-labeled maize residues (root, stem and leaf) through a 180-day incubation. Microbial CUE of maize residue was the highest in the HSOM soil with leaf residue addition, and was the lowest in LSOM soil with stem and leaf residues addition. About 37% ~ 47% of maize residue C was remained in the soil after 180 days. At the end of incubation, the positive cumulative priming effects on native SOC mineralization induced by stem and leaf residues were 23% and 30% stronger (P < 0.05) in the HSOM soil than those of the LSOM soil, respectively. In contrast the root residue addition induced the negative priming effect on native SOC in the two SOM levels of soils. Overall, microbial CUE of maize residue was higher in soil with high initial SOM level, which is likely to promote SOM formation via microbial biomass, although there are many other factors that influence SOM formation. The interactive effect between initial SOM level and plant residue quality should be considered when understanding long-term SOM storage.


Datum: 22.06.2022


Unexpected microbial metabolic responses to elevated temperatures and nitrogen addition in subarctic soils under different land uses

Abstract

Subarctic regions are particularly affected by global warming. As vegetation periods lengthen, boreal forests could gradually be converted into agricultural land. How land use alters the susceptibility of soil organic matter decomposition to rising temperatures or how changes in nutrient availability, such as nitrogen (N) fertilisation, affect carbon (C) cycling is unknown. Microbial carbon use efficiency (CUE) defines how much of the decomposed soil organic carbon is directed to growth or lost to the atmosphere. Here, we investigated the response of CUE (24 h) and soil organic matter decomposition (50 days) to + 10 °C warming and N addition in three subarctic soils derived from paired plots (forest, grassland, cropland) in the Yukon, Canada. Contrary to our literature-based expectations, boreal forest soils did not demonstrate the most sensitive response to warming and N addition. Temperature sensitivity was not affected by land-use type. In contrast to a generally assumed decline, short-term warming increased CUE by + 30%, which was positively correlated with microbial growth. N addition reduced overall CUE by − 7%, in contrast to the expectation that CUE would rise due to the alleviation of nutrient limitations. The response to N addition was negatively correlated with the ratio of fungi to bacteria, and presumably depended on the prevailing N-fertilisation regime. The temperature sensitivity of microbial metabolism was driven by site-specific parameters rather than by land-use type. Our results indicate that it may not be necessary to consider land use-specific temperature sensitivities when modelling soil organic carbon dynamics under future climate conditions.


Datum: 17.06.2022


Biogeochemical constraints on climate change mitigation through regenerative farming

Abstract

This review suggests that most of the management practices associated with regenerative agriculture are not likely to lead to a large net sequestration of organic carbon in soils. Some improved management practices, such as increased fertilizer use, manuring, and applications of biochar, are constrained by biogeochemical stoichiometry and the availability of organic inputs. Other management practices, such as fertilizer applications, irrigation, and applications of ground silicate minerals, entail ancillary and off-site emissions of carbon dioxide that reduce the net sequestration of carbon in soils. Carbon sequestration in agricultural soils, even with best management practices, is only likely to offer a small net storage of carbon that can be marketed as a credit to emissions from other sectors of the economy.


Datum: 14.06.2022


Landscape controls on total mercury and methylmercury export from small boreal forest catchments

Abstract

Mercury (Hg) is a widespread contaminant known to pose severe risks to wildlife and human health. While Hg emissions have declined in recent decades, legacy emissions and stored Hg will continue to impact watershed Hg cycling for the foreseeable future. Boreal forests are a major concern due to their capacity for storing Hg, vulnerability to disturbance, and record of high Hg concentrations in fish. Thus, there is a need to better quantify factors that influence Hg export from boreal forest catchments to inform watershed management decisions regarding Hg. Streamflow measurements, as well as approximately bi-weekly sampling for total mercury (THg), methylmercury (MeHg), and supporting stream chemistry were completed in 19 headwater streams near Dryden, Ontario during the ice-free season of 2019. The results were related to landscape and hydrological indices to elucidate the potential factors governing THg and MeHg export across these catchments. This study shows that while Hg concentrations are relatively low (0.50–20.46 ng l−1 THg; < 0.04–1.21 ng l−1 MeHg) across boreal streams in south central Canada, there are significant differences in Hg export. Catchments within boreal shield landscapes dominated by shallow soils and exposed bedrock export more methylmercury than catchments within glaciolacustrine plain landscapes dominated by thicker sand deposits. Coniferous forest cover is more significant than dissolved organic matter concentrations and more reliable than available % wetland cover data, two metrics commonly included in Hg transport models, for predicting THg and MeHg loads. In the absence of substantial mapped wetland cover, wet forest cover, as defined by the proportion of catchment cover by tree species favoring wet conditions, is shown to be an effective alternative metric. Considering the generally detailed and extensive data on tree species coverage available in Canada’s managed forests, wet forest cover, in addition to coniferous forest cover, could be useful for modelling Hg transport in boreal forest watersheds.


Datum: 09.06.2022


Molecular correlations of dissolved organic matter with inorganic mercury and methylmercury in Canadian boreal streams

Abstract

The molecular composition of dissolved organic matter (DOM) is increasingly recognized as fundamentally important to mercury transport and transformations, with numerous approaches undertaken to examine DOM characteristics beyond dissolved organic carbon concentrations. In this study, we use a high-resolution mass spectrometry approach, Fourier-transform ion cyclotron resonance mass spectrometry, to characterize DOM compound classes, DOM aromaticity (AImod), and the nominal oxygenation state of carbon (NOSC) across thirteen small boreal forest streams in central Canada. We then relate the relative abundance of hundreds of different DOM molecules with inorganic mercury and methylmercury (MeHg) concentrations across late spring and fall seasons. The number of significant correlations and the classes of DOM compounds significantly correlating with inorganic mercury and MeHg concentrations differs substantially across seasons and between mercury forms. For inorganic mercury, the abundance of nitrogen and sulfur containing DOM are most often positively correlated (mean ρ = 0.80) in the late spring, whereas during the fall, the abundance of low-oxidized lignins is more important, though with weaker correlations (mean ρ = 0.51). For MeHg, low-oxidized lignins and hydrolysable tannins, likely sourced from conifer throughfall and litter, account for up to 83% of all DOM-MeHg correlations regardless of season. Further network analyses reveal that the strongest and most significant inorganic mercury-DOM correlations are found across a wide range of NOSC values, indicating that DOM involved with the transport of inorganic mercury encompasses a wide range of polarities and thermodynamic stabilities. In contrast, DOM molecules exclusively correlated with MeHg concentrations have more positive NOSC and AImod values, implying the preferential transport of MeHg with more thermodynamically stable and aromatic DOM molecules. DOM molecules significantly correlated with both inorganic mercury and MeHg concentrations are found exclusively in the late spring. Overall, this non-targeted approach may help to inform further targeted investigations, especially as it relates to the underrepresented importance of plant biomolecules in facilitating mercury transport.

Graphical abstract


Datum: 09.06.2022


Phosphorus availability and arbuscular mycorrhizal fungi limit soil C cycling and influence plant responses to elevated CO2 conditions

Abstract

Soil organic matter (SOM) decomposition and organic phosphorus (P) cycling may help sustain plant productivity under elevated CO2 (eCO2) and low-P conditions. Arbuscular mycorrhizal (AM) fungi and their role in P-acquisition and SOM decomposition may become more relevant in these conditions. Yet, experimental evidence of AM fungi and P availability interactive effects on soil carbon (C) cycling under eCO2 is scarce with the potential mechanisms of this control being poorly understood. We performed a pot experiment with soil and a grass from a low-P ecosystem where plant biomass and soil C cycling have been mostly unresponsive to eCO2. We manipulated AM fungi, P, and CO2 levels and assessed their impacts on soil C cycling and plant growth using continuous 13C plant labelling to isolate and measure short-term changes in total and SOM-derived fractions of respired CO2, dissolved organic C (DOC) and microbial biomass (MBC), as relevant components of the soil C cycle. Increases in SOM decomposition and microbial C use were hypothesised to support plant growth under eCO2 and low-P with AM fungi intensifying this effect. However, we did not detect simultaneous significant impacts of the three experimental factors. We observed instead increased root biomass and nutrient uptake with eCO2 and AM presence and lower SOM-derived DOC and MBC with low-P, decreasing further with AM inoculation. Taken together, our findings in this model plant-soil system suggest that, AM fungi can support root biomass growth and nutrient uptake under eCO2 and protect the SOM pool against decomposition even in low-P conditions. Contrary to reports from N-limited ecosystems, our results allow us to conclude that C and P biogeochemical cycles may not become coupled to sustain an eCO2 fertilisation effect and that the role of AM fungi protecting the SOM pool is likely driven by competitive interactions with saprotrophic communities over nutrients.


Datum: 07.06.2022


Small rain events during drought alter sediment dissolved organic carbon leaching and respiration in intermittent stream sediments

Abstract

With climate change, streams and rivers are at increased risk of droughts and flow intermittency. The full implications of these conditions for fluvial carbon (C) processing and stream-atmosphere CO2 emissions are not well understood. We performed a controlled drought experiment in outdoor hyporheic flumes. We simulated small rain events that increase sediment moisture content, but do not cause streamflow in order to investigate how these events affect streambed dissolved organic C dynamics, biofilm respiration and enzyme activity, and bacterial community composition. Flumes were subject to a non-flow phase of one month with small rain events with varying frequency (weekly, 3 × weekly, and no rain). Sediment was sampled at the surface and from the hyporheic zone at the end of the non-flow phase. We quantified microbial respiration of the dry sediments and sediment DOC leaching after simulated flow resumption. We found that, at the surface, more frequent rain events significantly increased microbial respiration from 12.6 ± 0.25 µg CO2 g−1 DW h−1 to 26.5 ± 11.3 µg CO2 g−1 DW h−1 between the control and 3 × weekly rain events. The average amount of DOC leached from surface sediments during flow resumption was reduced by 0.813 ± 0.62 mg L−1 with more frequent rain events. More frequent rain events also resulted in the leaching of fresher DOM with increased tryptophan fluorescence and a higher BIX. This, along with higher glucosidase activity in the biofilms, indicates higher OC processing during the drought period with more frequent rain events. Small rain events also enhanced Shannon diversity of microbial communities, with a stronger presence of ‘terrestrial-like’ bacterial clades. We propose that rain events during drought, even those of small size, are highly relevant for fluvial organic C processing during the dry phase. Future research should explicitly consider small rain events when investigating C fluxes in intermittent streams to fully understand the C processing in these systems with climate change. We conclude that small rain events impact DOM dynamics during reflow and likely impact the cascading C processing in the downstream river network.


Datum: 01.06.2022


Soil greenhouse gas fluxes in floodplain forests of the Danube National Park: effects of flooding and soil microclimate

Abstract

The relevance of soil greenhouse gas (GHG) fluxes from temperate floodplain forests has yet remained elusive. We studied the soil methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) dynamics at three forest sites along a flooding gradient in the Danube National Park (Austria) to estimate annual GHG budgets and to assess if and how seasonal flooding affects individual GHG fluxes. Soil surface GHG fluxes were determined along with GHG concentrations in soil air and pore-water at a non-flooded (NF), an infrequently-flooded (IF), and a frequently-flooded (FF) site. Both study years were characterized by dry summers, and only the FF site was flooded during the study period. Soils at all sites were annual CH4 sinks (NF: − 4.50 ± 0.85, IF: − 2.54 ± 0.57, FF: − 0.67 ± 1.06 kg CH4-C ha−1 year−1) and the sink strength correlated positively with soil moisture. Pulse-like CH4 emissions were not observed during or after flooding. Soil N2O fluxes showed large temporal and spatial variations, without any significant differences between sites (average NF: 6.5 ± 7.1, IF: 10.4 ± 14.3, FF: 9.4 ± 10.5 µg N2O-N m−2 h−1). Pulse N2O emissions (up to ~ 80 µg N2O-N m−2 h−1) occurred during freeze/thaw events, but not during or after flooding. Mean annual soil CO2 effluxes at NF and IF were 9.4 ± 1.1 and 9.4 ± 2.1 t C ha−1 year−1, respectively. Soil CO2 efflux was significantly higher at the FF site (18.54 ± 6.21 t C ha−1 year−1). High soil air CO2 concentrations (> 10%) in aerated deeper soil layers indicated a substantial contribution of the usually waterlogged sub-soils to the summertime soil CO2 efflux at the FF site. Overall, our results suggest that the studied temperate floodplain forest soils do not absorb/emit substantially more CH4 and N2O than soils of comparable upland forests, whereas low groundwater level can lead to periodically enhanced CO2 emissions from normally waterlogged soil layers.


Datum: 01.06.2022


Estimating phytoplankton stoichiometry from routinely collected monitoring data

Abstract

Accurately estimating the elemental stoichiometry of phytoplankton is critical for understanding biogeochemical cycles. In laboratory experiments, stoichiometric ratios vary among species and with changes in environmental conditions. Field observations of total phosphorus (P) and total nitrogen (N) collected at regional and national scales can supplement and expand insights into factors influencing phytoplankton stoichiometry, but analyses applied to these data can introduce biases that affect interpretations of the observed patterns. We introduce an analytical approach for estimating the ratio between phytoplankton N and P from the particulate fraction of nutrient pools in lake samples. We use Bayesian models to represent observations of particulate P and N as the sum of contributions from nutrients bound within phytoplankton and nutrients associated with non-phytoplankton suspended sediment. Application of this approach to particulate nutrient data collected in Missouri impoundments yields estimates of the mass ratio of N:P in phytoplankton ranging from 8 to 10 across a variety of lakes and seasons. N:P in particulate matter ranged from 6 to 70, a variability driven by differences in nutrients bound to non-phytoplankton suspended sediment. We adapted the Bayesian models to estimate N:P using more commonly available measurements of total P and total N and applied this model to a continental-scale monitoring data set. We compared phytoplankton nutrient content estimated from the two analyses and found that when datasets lack direct measurements of particulate nutrient concentrations, the model estimate of phytoplankton nutrient content includes contributions from nutrients within phytoplankton and dissolved nutrients that are associated with changes in phytoplankton biomass.


Datum: 01.06.2022


Plant community effects on soil moisture and nitrogen cycling in a semi-arid ecosystem

Abstract

Wildlands of the United States’ Intermountain West contain recurring interspersed plant-community types; namely native sagebrush (Artemisia tridentata spp. wyomingensis Nutt.), non-native invasive cheatgrass (Bromus tectorum L.), and crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.]. Soil nitrogen (N) cycling in these water and N co-limited ecosystems shows very strong spatial and temporal variability, but the mechanism(s) by which these semi-arid plant communities control soil N transformations are not well understood. Over two growing seasons, we conducted field and laboratory incubations of intact soil cores (0–10 cm) with and without water added, and created a mass balance model to predict N mineralization. We found that soils under cheatgrass had the highest net N mineralization, net nitrification and soil moisture compared to soils from under the other two plant communities. Moreover, water additions to field-incubated soil cores under cheatgrass more than doubled net N mineralization (0.18 ± 0.02 vs 0.07 ± 0.01 mg N kg−1 d−1). Temperature had a small effect on net N mineralization and net nitrification, with both rates increasing by < 0.005 mg N kg−1 d−1 per °C. The model’s ability to predict N mineralization was relatively low (R2 = 0.33). However, both our model and the data themselves strongly support plant community regulation of soil N cycling through modification of soil moisture.


Datum: 01.06.2022


Silicon concentrations and stoichiometry in two agricultural watersheds: implications for management and downstream water quality

Abstract

Agriculture alters the biogeochemical cycling of nutrients such as nitrogen (N), phosphorus (P), and silicon (Si) which contributes to the stoichiometric imbalance among these nutrients in aquatic systems. Limitation of Si relative to N and P can facilitate the growth of non-siliceous, potentially harmful, algal taxa which has severe environmental and economic impacts. Planting winter cover crops can retain N and P on the landscape, yet their effect on Si concentrations and stoichiometry is unknown. We analyzed three years of biweekly concentrations and loads of dissolved N, P, and Si from subsurface tile drains and stream water in two agricultural watersheds in northern Indiana. Intra-annual patterns in Si concentrations and stoichiometry showed that cover crop vegetation growth did not reduce in-stream Si concentrations as expected, although, compared to fallow conditions, winter cover crops increased Si:N ratios to conditions more favorable for diatom growth. To assess the risk of non-siliceous algal growth, we calculated a stoichiometric index to quantify biomass growth facilitated by excess N and P relative to Si. Index values showed a divergence between predicted algal growth and what we observed in the streams, indicating other factors influence algal community composition. The stoichiometric imbalance was more pronounced at high flows, suggesting increased risk of harmful blooms as climate change increases the frequency and intensity of precipitation in the midwestern U.S. Our data include some of the first published measurements of Si within small agricultural watersheds and provide the groundwork for understanding the role of agriculture on Si export and stoichiometry.


Datum: 01.06.2022


Too much of a good thing? Inorganic nitrogen (N) inhibits moss-associated N2 fixation but organic N can promote it

Abstract

Moss-associated nitrogen (N2) fixation is one of the main inputs of new N in pristine ecosystems that are characterized by low N availability. Previous studies have shown that N2 fixation is inhibited by inorganic N (IN) inputs, but if N2 fixation in mosses is similarly affected by organic N (ON) remains unknown. Here, we assessed N2 fixation in two dominant mosses in boreal forests (Pleurozium schreberi and Sphagnum capillifolium) in response to different levels of N, simulating realistic (up to 4 kg N ha−1 year−1) and extreme N addition rates in pristine ecosystems (up to 20 kg N ha−1 year−1) of IN (ammonium nitrate) and ON (alanine and urea). We also assessed if N2 fixation can recover from the N additions. In the realistic scenario, N2 fixation was inhibited by increasing NH4NO3 additions in P. schreberi but not in S. capillifolium, and alanine and urea stimulated N2 fixation in both moss species. In contrast, in the extreme N additions, increasing N inputs inhibited N2 fixation in both moss species and all N forms. Nitrogen fixation was more sensitive to N inputs in P. schreberi than in S. capillifolium and was higher in the recovery phase after the realistic compared to the extreme N additions. These results demonstrate that N2 fixation in mosses is less sensitive to organic than inorganic N inputs and highlight the importance of considering different N forms and species-specific responses when estimating the impact of N inputs on ecosystem functions such as moss-associated N2 fixation.


Datum: 01.06.2022


 


Category: Current Chemistry Research

Last update: 28.03.2018.






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