Changes in dissolved organic matter quality in a peatland and forest headwater stream as a function of seasonality and hydrologic conditions

Peatlands and peaty riparian zones are major sources of dissolved organic matter (DOM), but are poorly understood in terms of export dynamics and controls thereof. Thereby quality of DOM affects function and behavior of DOM in aquatic ecosystems, but DOM quality can also help to track DOM sources and their export dynamics under specific hydrologic preconditions. The objective of this study was to elucidate controls on temporal variability in DOM concentration and quality in stream water draining a bog and a forested peaty riparian zone, particularly considering drought and storm flow events. DOM quality was monitored using spectrofluorometric indices for aromaticity (SUVA254), apparent molecular size (SR) and precursor organic material (FI), as well as PARAFAC modeling of excitation emission matrices (EEMs). Indices for DOM quality exhibited major changes due to different hydrologic conditions, but patterns were also dependent on season. Stream water at the forested site with mineral, peaty soils generally exhibited higher variability in DOM concentrations and quality compared to the outflow of an ombrotrophic bog, where DOM was less susceptible to changes in hydrologic conditions. During snowmelt and spring events, near-surface protein-like DOM pools were exported. A microbial DOM fraction originating from groundwater and deep peat layers was increasing during drought, while a strongly microbially altered DOM fraction was also exported by discharge events with dry preconditions at the forested site. This might be due to accelerated microbial activity in the peaty riparian zone of the forested site under these preconditions. Our study demonstrated that DOM export dynamics are not only a passive mixing of different hydrological sources, but monitoring studies have to consider that DOM quality depends on hydrologic preconditions and season. Moreover, the forested peaty riparian zone generated the most variability in headwater DOM quantity and quality, as could be tracked by the used spectrofluorometric indices

Sulfate-Reducing Microorganisms in Wetlands – Fameless Actors in Carbon Cycling and Climate Change

Freshwater wetlands are a major source of the greenhouse gas methane but at the same time can function as carbon sink. Their response to global warming and environmental pollution is one of the largest unknowns in the upcoming decades to centuries. In this review, we highlight the role of sulfate-reducing microorganisms (SRM) in the intertwined element cycles of wetlands. Although regarded primarily as methanogenic environments, biogeochemical studies have revealed a previously hidden sulfur cycle in wetlands that can sustain rapid renewal of the small standing pools of sulfate. Thus, dissimilatory sulfate reduction, which frequently occurs at rates comparable to marine surface sediments, can contribute up to 36–50% to anaerobic carbon mineralization in these ecosystems. Since sulfate reduction is thermodynamically favored relative to fermentative processes and methanogenesis, it effectively decreases gross methane production thereby mitigating the flux of methane to the atmosphere. However, very little is known about wetland SRM. Molecular analyses using dsrAB [encoding subunit A and B of the dissimilatory (bi)sulfite reductase] as marker genes demonstrated that members of novel phylogenetic lineages, which are unrelated to recognized SRM, dominate dsrAB richness and, if tested, are also abundant among the dsrAB-containing wetland microbiota. These discoveries point toward the existence of so far unknown SRM that are an important part of the autochthonous wetland microbiota. In addition to these numerically dominant microorganisms, a recent stable isotope probing study of SRM in a German peatland indicated that rare biosphere members might be highly active in situ and have a considerable stake in wetland sulfate reduction. The hidden sulfur cycle in wetlands and the fact that wetland SRM are not well represented by described SRM species explains their so far neglected role as important actors in carbon cycling and climate change

Plant community controls small-scale variation in nutrient stoichiometry in a Patagonian peatland

Elemental stoichiometry of plant litter is typically interpreted to reflect nutrient availability and limitation, e.g. the N:P ratio indicates whether plant growth is N- or P-limited and might point towards the presence of N-fixation. However, in the case of plant litter and peat organic matter, resorption of nutrients during senescence, and preferential loss of nutrients during decomposition have to be taken into account. Here we study how small scale variability in species composition within peatlands affects the stoichiometry and long term apparent uptake rates of nutrients (C, N, P, K, S, Ca, Mg) in an ombrotrophic peatland in southern Patagonia. Assuming that nutrient availability is similar within one site, observed variation should be driven by vegetation and decomposition processes linked to microtopography. We studied a transect spanning 800 m. where the vegetation changed from cushion plant (Astelia pumila) dominated, to graminoid dominated, ending in Sphagnum magellanicum dominated. From six peat cores along this transect we analysed nutrient concentrations by X-ray fluorescence. The peat decomposition state, expressed as FTIR-humification index, was the best predictor of stoichiometric variation (particularly ratios C:N, C:S, and N:P), followed by current plant species composition. Comparison of average peat core stoichiometry across the transect showed that C:N and C:S ratios were larger in Sphagnum cores than cushion plant and graminoid cores (C:N 56±14 vs. 38±6; C:S 312±61 vs. 268±57; respectively), controlled by lower decomposition state in Sphagnum cores and larger C:N ratios in living biomass of Sphagnum vs. A. pumila. Larger N:P ratios in cushion plant and graminoid vs. Sphagnum cores (N:P 50±12 vs. 38±11; respectively) could furthermore indicate the presence of N-fixation in the former. Comparison with two additional Patagonian bogs showed similar distinction in C:N and C:S ratios (both: Sphagnum > cushion plant), but variation between cores within sites was more pronounced than between different peatlands. Taking the variable peat accumulation rate (0.09 ? 0.52 mm yr-1) into account, there was notable variation in apparent long term nutrient uptake rates along the transect. N and S uptake rates were larger in cushion plant and graminoid versus Sphagnum cores, while Mg uptake rates were largest in Sphagnum cores. Overall, the stoichiometry of these Patagonian peatlands suggests lower availability of N, P, and Ca compared to peatlands in Ontario, Canada, resulting in lower apparent N, P, and Ca uptake rates. In contrast, apparent Mg uptake rates were larger in Patagonia than Ontario. These results indicate that small scale variability in long term accumulation of nutrients in these ecosystems might be more pronounced than variability in long term C accumulation, and highlights the variability in nutrient availability between peatlands of different regions.Fil: Mathijssen, Paul. University of Münster; AlemaniaFil: Münchberger, Wiebke. University of Münster; AlemaniaFil: Borken, Werner. University of Bayreuth; AlemaniaFil: Pancotto, Veronica Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Kleinebecker, Till. Justus Liebig Universitat Giessen; AlemaniaFil: Knorr, Klaus Holger. University of Bayreuth; Alemania21th European Geosciences Union General AssemblyVienaAustriaAsamblea General de European Geosciences Unio

Associative nitrogen fixation in nodules of the conifer Lepidothamnus fonkii (Podocarpaceae) inhabiting ombrotrophic bogs in southern Patagonia

Biological N2 fixation (BNF) in the rhizosphere of Podocarpaceae is currently attributed to unspecific diazotrophs with negligible impact on N acquisition. Here, we report specific and high associative BNF in dead cells of root nodules of Lepidothamnus fonkii distributed in ombrotrophic peatlands of Patagonia. BNF of nodulated roots, intact plants of L. fonkii and rhizospheric peat was assessed by 15N2 and acetylene reduction. Diazotrophs were identified by electron microscopy, analysis of nitrogenase encoding genes (nifH) and transcripts, and 16S rRNA. Nitrogenase encoding nifH transcripts from root nodules point to Beijerinckiaceae (Rhizobiales), known as free-living diazotrophs. Electron microscopy and 16S rRNA analysis likewise identified active Beijerinckiaceae in outer dead cells of root nodules. NifH transcripts from the rhizopshere peat revealed diverse active diazotrophs including Beijerinckiaceae. Both methods revealed high activity of nitrogenase rates in cut roots of L. fonkii (2.5 μmol N g−1 d.w. d−1 based on 15N2 assay; 2.4 μmol C2H4 g−1 d.w. d−1 based on acetylene reduction assay). The data suggest that (i) nodules recruit diazotrophic Beijerinckiaceae from peat, (ii) dead nodule cells provide an exclusive habitat for Beijerinckiaceae, and (iii) BNF in L. fonkii is one potent pathway to overcome N deficiency in ombrotrophic peatlands of Patagonia.Bavarian Research Alliance (BayFOR

Enhanced silicon availability leads to increased methane production, nutrient and toxicant mobility in peatlands

AbstractPeatlands perform important ecosystem functions, such as carbon storage and nutrient retention, which are affected, among other factors, by vegetation and peat decomposition. The availability of silicon (Si) in peatlands differs strongly, ranging from &lt;1 to &gt;25 mg L−1. Since decomposition of organic material was recently shown to be accelerated by Si, the aim of this study was to examine how Si influences decomposition of carbon and nutrient and toxicant mobilization in peatlands. We selected a fen site in Northern Bavaria with naturally bioavailable Si pore water concentrations of 5 mg/L and conducted a Si addition experiment. At a fourfold higher Si availability, dissolved organic carbon, carbon dioxide, and methane concentrations increased significantly. Furthermore, dissolved nitrogen, phosphorus, iron, manganese, cobalt, zinc, and arsenic concentrations were significantly higher under high Si availability. This enhanced mobilization may result from Si competing for binding sites but also from stronger reducing conditions, caused by accelerated respiration. The stronger reducing conditions also increased reduction of arsenate to arsenite and thus the mobility of this toxicant. Hence, higher Si availability is suggested to decrease carbon storage and increase nutrient and toxicant mobility in peatland ecosystems.</jats:p

Comparison of paleobotanical and biomarker records of mountain peatland and forest ecosystem dynamics over the last 2600 years in central Germany

As peatlands are a major terrestrial sink in the global carbon cycle, gaining an understanding of their development and changes throughout time is essential in order to predict their future carbon budget and potentially mitigate the adverse outcomes of climate change. With this aim to understand peat development, many studies have investigated the paleoecological dynamics by analyzing various proxies, including pollen, macrofossil, elemental, and biomarker analyses. However, as each of these proxies is known to have its own benefits and limitations, examining them in parallel allows for a deeper understanding of these paleoecological dynamics at the peatland and a systematic comparison of the power of these individual proxies. In this study, we therefore analyzed peat cores from a peatland in Germany (Beerberg, Thuringia) to (a) characterize the vegetation dynamics over the course of the peatland development during the late Holocene and (b) evaluate to what extent the inclusion of multiple proxies, specifically pollen, plant macrofossils, and biomarkers, contributes to a deeper understanding of those dynamics and interaction among factors. We found that, despite a major shift in the regional forest composition from primarily beech to spruce as well as many indicators of human impact in the region, the local plant population in the Beerberg area remained stable over time following the initial phase of peatland development up until the last couple of centuries. Therefore, little variation could be derived from the paleobotanical data alone. The combination of pollen and macrofossil analyses with the elemental and biomarker analyses enabled further understanding of the site development as these proxies added valuable additional information, including the occurrence of climatic variations, such as the Little Ice Age, and more recent disturbances, such as drainage

Potential effects of sediment processes on water quality of an artificial reservoir in the Asian monsoon region

Sediment processes in lakes may affect water chemistry through the internal loading of phosphorus, ammonia, and sulfides released under anoxic conditions. Lake Soyang is a deep warm monomictic reservoir with a dendritic shape, located in the Asian summer monsoon region, South Korea. During summer, the lake is stratified and receives a large nutrient input via storm runoff, which forms a turbid intermediate layer with high concentrations of suspended particles. The lake water, the main inflowing stream (the Soyang River), bottom sediment, and porewater of the lake sediments were studied over a 2-year period (2012&ndash;2013). After intensive monsoon rain events, particulate organic carbon (POC), total phosphorus (TP), and turbidity were high in the inflowing water (C: 1.21 mg L&minus;1 in June 2013) and in the metalimnion (2.8 mg L&minus;1, 17.6 &mu;g L&minus;1, and 58.5 NTU, respectively in July 2013). Higher concentrations of iron (Fe) and manganese (Mn) were also associated with the turbid intermediate layer (37 and 8 &mu;g L&minus;1, respectively, in July 2013). During the summer stratification period, oxygen started to deplete in the hypoliminion (down to 0.5 mg L&minus;1 in September 2013), and sediment became anoxic, showing negative oxidation redox potential (ORP) in core samples. Diffusion of dissolved inorganic P and ammonia from sediment to the water column can be substantial, considering the concentration difference between the porewater and hypolimnetic water. Fe and Mn were abundant in the sediment porewater at the dam site, implying inorganic nutrients and minerals are well transported along the 60 km long lake axis by the density current of storm runoff. Sulfate and reduced sulfur were larger in the porewater of the top sediment than in the lower layer of the sediment core (below 10 cm). The results show that substantial amounts of inorganic nutrients and minerals are supplied to the lake by storm runoffs during monsoon and distributed through the lake by a density current, controlling the material cycle and flux at the sediment surface

Global CO2 fertilization of Sphagnum peat mosses via suppression of photorespiration during the twentieth century

Natural peatlands contribute significantly to global carbon sequestration and storage of biomass, most of which derives from Sphagnum peat mosses. Atmospheric CO2 levels have increased dramatically during the twentieth century, from 280 to > 400 ppm, which has affected plant carbon dynamics. Net carbon assimilation is strongly reduced by photorespiration, a process that depends on the CO2 to O-2 ratio. Here we investigate the response of the photorespiration to photosynthesis ratio in Sphagnum mosses to recent CO2 increases by comparing deuterium isotopomers of historical and contemporary Sphagnum tissues collected from 36 peat cores from five continents. Rising CO2 levels generally suppressed photorespiration relative to photosynthesis but the magnitude of suppression depended on the current water table depth. By estimating the changes in water table depth, temperature, and precipitation during the twentieth century, we excluded potential effects of these climate parameters on the observed isotopomer responses. Further, we showed that the photorespiration to photosynthesis ratio varied between Sphagnum subgenera, indicating differences in their photosynthetic capacity. The global suppression of photorespiration in Sphagnum suggests an increased net primary production potential in response to the ongoing rise in atmospheric CO2, in particular for mire structures with intermediate water table depths