Reactive iron and organic carbon are intimately associated in soils and sediments. However, to date, the organic compounds involved are uncharacterized on the molecular level. At redox interfaces in ...peatlands, where the biogeochemical cycles of iron and dissolved organic matter (DOM) are coupled, this issue can readily be studied. We found that precipitation of iron hydroxides at the oxic surface layer of two rewetted fens removed a large fraction of DOM via coagulation. On aeration of anoxic fen pore waters, >90% of dissolved iron and 27 ± 7% (mean ± SD) of dissolved organic carbon were rapidly (within 24 h) removed. Using ultra-high-resolution MS, we show that vascular plant-derived aromatic and pyrogenic compounds were preferentially retained, whereas the majority of carboxyl-rich aliphatic acids remained in solution. We propose that redox interfaces, which are ubiquitous in marine and terrestrial settings, are selective yet intermediate barriers that limit the flux of land-derived DOM to oceanic waters.
Diffusive losses of nitrogen and phosphorus from agricultural areas have detrimental effects on freshwater and marine ecosystems. Mitigation measures treating drainage water before it enters streams ...hold a high potential for reducing nitrogen and phosphorus losses from agricultural areas. To achieve a better understanding of the opportunities and challenges characterising current and new drainage mitigation measures in oceanic and continental climates, we reviewed the nitrate and total phosphorus removal efficiency of: (i) free water surface constructed wetlands, (ii) denitrifying bioreactors, (iii) controlled drainage, (iv) saturated buffer zones and (v) integrated buffer zones. Our data analysis showed that the load of nitrate was substantially reduced by all five drainage mitigation measures, while they mainly acted as sinks of total phosphorus, but occasionally, also as sources. The various factors influencing performance, such as design, runoff characteristics and hydrology, differed in the studies, resulting in large variation in the reported removal efficiencies.
Many European lakes have suffered from reed die-back since the 1950s. Previous studies have concluded that this is due to a combination of several interacting factors, but possibly also a single ...threat with high impact might be responsible for the phenomenon. In this study, we investigated 14 lakes in the Berlin area differing in reed development and sulphate concentration from 2000 to 2020. To unravel the decline of reed beds in some of the lakes with coal mining activities in the upper watershed, we compiled a comprehensive data set. Thus, the littoral zone of the lakes was divided into 1302 segments considering the reed ratio relative to segment area, water quality parameters, littoral characteristics and bank usage of the lakes which all have been monitored for 20 years. We ran two-way panel regressions with a within estimator to consider the spatial variation between and within the segments over time. The regression results revealed a strong negative relationship between reed ratio and sulphate concentrations (p<0.001) as well as tree shading (p<0.001) and a strong positive relationship with brushwood fascines (p<0.001). Taking only sulphate into account, reeds would have covered an additional area of 5.5 ha or 22.6% in 2020 (total reed area: 24.3 ha) in the absence of increased sulphate concentrations. In conclusion, changes in water quality upstream the catchment cannot be ignored in the development of management plans for downstream lakes.
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•Reed decline and raising sulphate concentrations evolved in urban lakes in Berlin.•A comprehensive data set describes water quality and lake development over 20 years.•Panel regression model unravel spatial and temporal differences in 1302 lake segments.•Increased sulphate concentrations are tightly linked with reed decline.•Coalmining originated sulphate pollution may affect far-away downstream systems.
Acidification and salinisation of groundwater and surface water bodies are worldwide problems in post-mining landscapes due to acid mine drainage (AMD). In this study, we hypothesised that highly ...decomposed peat offers a suitable substrate for mitigating AMD pollution of water bodies and that hydraulic load affects the removal efficiency of iron and sulphate. A lysimeter experiment was conducted mimicking peatland rewetting to quantify iron and sulphate removal and pH changes at different loading rates. The low initial pH of 4 rose to 6 and electrical conductivity declined by up to 47%. The initially high concentrations of iron (>250 mg/L) and sulphate (>770 mg/L) declined by, on average, 87 and 78%, respectively. The removal efficiency of sulphate was negatively correlated with either the hydraulic or the sulphate load, respectively, i. e. the lower the hydraulic load, the higher the removal efficiency of sulphate. However, the removal of iron was not explained by the load. The results imply that desulphurication and thus subsequent precipitation of iron sulphides was the main removal process and that peatland rewetting is an effective measure to mitigate AMD pollution of freshwater systems. For the heavily AMD-polluted studied section of the River Spree, we estimated by combining experimental with field data that a sulphate load reduction of the river by about 20% (36,827 tons/yr) will occur if all peatlands in the sub-catchment (6067 ha; 6.7% of the total area) are rewetted. Future investigations must show if the pollutant removal is declining over time in decomposed peat layers due to acidification and/or lack of bioavailable carbon and how the rewetting of peatland with AMD will affect the restoration of their ecosystem functioning in the long term.
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•Mining activity causes high iron and sulphate concentration in water bodies.•Lysimeter experiment run with rewetted peat and acid mine drainage.•Iron-II and sulphate concentrations decreased up to 91 and 87%.•Lower hydraulic load leads to higher sulphate removal but not affect iron-II removal.•Rewetting peatland is an effective management tool to treat acid mine drainage.
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•Microtopography controls carbon accumulation and nutrient release.•Soil organic matter content and carbon:nitrogen ratio were negatively correlated with surface elevation.•High ...ammonium concentrations are released from organic rich low-lying soils when flushed with brackish water.•Local geomorphological depressions are hotspots of carbon turnover and nutrient release in coastal peatland.
Coastal peatlands have been frequently blocked from the sea and artificially drained for agriculture. With an increasing awareness of ecosystem functions, several of these coastal peatlands have been rewetted through dike removal, allowing seawater flooding. In this study, we investigated a recently rewetted peatland on the Baltic Sea coast with the aim to characterize the prevailing soils/sediments with respect to organic matter accumulation and the potential release of nutrients upon seawater flooding. Eighty disturbed soil samples were collected from two depths at different elevations (–0.90 to 0.97 m compared to sea level) and analyzed for soil organic matter (SOM) content and carbon:nitrogen (C:N) ratio. Additionally, nine undisturbed soil cores were collected from three distinct elevation groups and used in leaching experiments with alternating freshwater and Baltic Sea water. The results demonstrated a moderate to strong spatial dependence of surface elevation, SOM content, and C:N ratio. SOM content and C:N ratio were strongly negatively correlated with elevation, indicating that organic matter mineralization was restricted in low-lying areas. The results also showed that the soils at low elevations release more dissolved organic carbon (DOC) and ammonium (NH4+) than soils at high elevations. For soils at low elevations, higher DOC concentrations were observed when flushing with freshwater, whereas higher NH4+ concentrations were found when flushing with brackish water. Recorded NH4+ concentrations in organic-rich peat reached 14.82 ± 9.25 mg L–1, exceeding Baltic seawater (e.g., 0.03 mg L–1) by two orders of magnitude. A potential sea level rise may increase the export of NH4+ from low-lying and rewetted peat soils to the sea, impacting adjacent marine ecosystems. Overall, in coastal peatlands, geochemical processes (e.g., C and N cycling and release) are closely linked to microtopography and related patterns of organic matter content of the soil and sediments.
Reservoirs in semi-arid areas are subject to water level fluctuations (WLF) that alter biogeochemical processes in the sediment. We hypothesized that wet–dry cycles may cause internal eutrophication ...in such systems when they affect densely vegetated shallow areas. To assess the impact of WLF on phosphorus (P) mobilization and benthic P cycling of iron-rich sediments, we tested the effects of (i) sediment drying and rewetting, (ii) the impact of organic matter availability in the form of dried Brazilian Waterweed (Egeria densa), and (iii) alternating redox conditions in the surface water. In principle, drying led to increased P release after rewetting both in plant-free and in plant-amended sediments. Highest P mobilization was recorded in plant amendments under oxygen-free conditions. After re-establishment of aerobic conditions, P concentrations in surface water decreased substantially owing to P retention by sediments. In desiccated and re-inundated sediments, P retention decreased by up to 30 % compared to constantly inundated sediments. We showed that WLF may trigger biochemical interactions conducive to anaerobic P release. Thereby, E. densa showed high P release and even P uptake that was redox-controlled and superimposed sedimentary P cycling. Macrophytes play an important role in the uptake of P from the water but may be also a significant source of P in wet–dry cycles. We estimated a potential for the abrupt release of soluble reactive phosphorus (SRP) by E. densa of 0.09–0.13 g SRP per m² after each wet–dry cycle. Released SRP may exceed critical P limits for eutrophication, provoking usage restrictions. Our results have implications for management of reservoirs in semi-arid regions affected by WLF.
Droughts are recognized to impact global biogeochemical cycles. However, the implication of desiccation on in-stream carbon (C) cycling is not well understood yet. We subjected sediments from a ...lowland, organic rich intermittent stream to experimental desiccation over a 9-week-period to investigate temporal changes in microbial functional traits in relation to their redox requirements, carbon dioxide (CO
2
) and methane (CH
4
) fluxes and water-soluble organic carbon (WSOC). Concurrently, the implications of rewetting by simulated short rainfalls (4 and 21 mm) on gaseous C fluxes were tested. Early desiccation triggered dynamic fluxes of CO
2
and CH
4
with peak values of 383 and 30 mg C m
−2
h
−1
(mean ± SD), respectively, likely in response to enhanced aerobic mineralization and accelerated evasion. At longer desiccation, CH
4
dropped abruptly, likely because of reduced abundance of anaerobic microbial traits. The CO
2
fluxes ceased later, suggesting aerobic activity was constrained only by extended desiccation over time. We found that rainfall boosted fluxes of CO
2
, which were modulated by rainfall size and the preceding desiccation time. Desiccation also reduced the amount of WSOC and the proportion of labile compounds leaching from sediment. It remains questionable to which extent changes of the sediment C pool are influenced by respiration processes, microbial C uptake and cell lysis due to drying-rewetting cycles. We highlight that the severity of the dry period, which is controlled by its duration and the presence of precipitation events, needs detailed consideration to estimate the impact of intermittent flow on global riverine C fluxes.
The package RoughSets, written mainly in the R language, provides implementations of methods from the rough set theory (RST) and fuzzy rough set theory (FRST) for data modeling and analysis. It ...considers not only fundamental concepts (e.g., indiscernibility relations, lower/upper approximations, etc.), but also their applications in many tasks: discretization, feature selection, instance selection, rule induction, and nearest neighbor-based classifiers. The package architecture and examples are presented in order to introduce it to researchers and practitioners. Researchers can build new models by defining custom functions as parameters, and practitioners are able to perform analysis and prediction of their data using available algorithms. Additionally, we provide a review and comparison of well-known software packages. Overall, our package should be considered as an alternative software library for analyzing data based on RST and FRST.
The rewetting of drained peatlands alters peat geochemistry and often leads
to sustained elevated methane emission. Although this methane is produced
entirely by microbial activity, the distribution ...and abundance of
methane-cycling microbes in rewetted peatlands, especially in fens, is rarely
described. In this study, we compare the community composition and abundance
of methane-cycling microbes in relation to peat porewater geochemistry in two
rewetted fens in northeastern Germany, a coastal brackish fen and a
freshwater riparian fen, with known high methane fluxes. We utilized 16S rRNA
high-throughput sequencing and quantitative polymerase chain reaction (qPCR) on 16S
rRNA, mcrA, and pmoA genes to determine microbial community
composition and the abundance of total bacteria, methanogens, and
methanotrophs. Electrical conductivity (EC) was more than 3 times higher in
the coastal fen than in the riparian fen, averaging 5.3 and 1.5 mS cm−1,
respectively. Porewater concentrations of terminal electron acceptors (TEAs) varied
within and among the fens. This was also reflected in similarly high intra-
and inter-site variations of microbial community composition. Despite these
differences in environmental conditions and electron acceptor availability,
we found a low abundance of methanotrophs and a high abundance of
methanogens, represented in particular by Methanosaetaceae, in both
fens. This suggests that rapid (re)establishment of methanogens and slow
(re)establishment of methanotrophs contributes to prolonged increased methane
emissions following rewetting.
There have been widespread attempts to rewet peatlands in Europe and elsewhere in the world to restore their unique biodiversity as well as their important function as nutrient and carbon sinks. ...However, changes in hydrological regime and therefore oxygen availability likely alter the abundance of enzyme-inhibiting polyphenolic compounds, which have been suggested as a "latch" preventing large amounts of carbon from being released into the atmosphere by microbial mineralization. In recent years, a variety of factors have been identified that appear to weaken that latch including not only oxygen, but also pH. In minerotrophic fens, it is unknown if long-term peat mineralization during decades of drainage and intense agricultural use causes an enrichment or a decline of enzyme-inhibiting polyphenols. To address this, we collected peat samples and fresh roots of dominating plants (i.e., the peat parent material) from the upper 20 cm peat layer in 5 rewetted and 6 natural fens and quantified total phenolic content as well as hydrolysable and condensed tannins. Polyphenols from less decomposed peat and living roots served partly as an internal standard for polyphenol analysis and to run enzyme inhibition tests. As hypothesized, we found the polyphenol content in highly decomposed peat to be 8 times lower than in less decomposed peat, while condensed tannin content was 50 times lower in highly degraded peat. In addition, plant tissue polyphenol contents differed strongly between peat-forming plant species, with the highest amount found in roots of Carex appropinquata at 450 mg g-1 dry mass, and lowest in Sphagnum spp. at 39 mg g-1 dry mass: a 10-fold difference. Despite large and clear differences in peat and porewater chemistry between natural and rewetted sites, enzyme activities determined with Fluorescein diacetate (FDA) hydrolysis and peat degradation were not significantly correlated, indicating no simple linear relationship between polyphenol content and microbial activity. Still, samples with low contents of polyphenols and condensed tannins showed the highest microbial activities as measured with FDA.
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