Organic Matter In Wetlands Research Articles

Molecular-chemical characterization of soil organic matter in wetlands by pyrolysis-gas chromatography/mass spectrometry

The carbon cycle in ecosystems is fundamentally controlled by the composition and transformation of organic molecules. Alpine wetland soils have enormous carbon storage, but they are sensitive to climate change, and can easily shift from carbon sink to carbon source. However, we currently lack understanding in molecular-chemical composition of soil organic matter (SOM) in alpine wetlands. In this study, we tried to decipher molecular-chemical features of SOM in typical alpine wetlands using the pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results indicated that nitrogen-containing compounds were the most abundant moieties among pyrolytic products of SOM. More than 83 % of pyrolytic moieties had a molecular weight of no more than 200 Daltons and a H/C ratio of no more than 2.0. O/C ratio of most pyrolytic products were less than 0.5. A van Krevelen diagram potentially indicated that SOM in wetlands might consist of massive heterogeneous molecules where aromatic compounds and their derivatives served as the core, with aliphatic hydrocarbon molecules of varying carbon chain lengths attached externally. About 72.25 % of variances in SOM were explained by 50 pyrolytic products, of which toluene was the most important. A significantly negative relation was observed between molecular weight (MW) and abundance of pyrolytic products, while positive relations were found between H/C, O/C, and abundance of pyrolytic products. Our work implied that SOM in wetlands was mainly composed of molecules with low MW and aromatic function groups.

Heterotrophic aquatic metabolism and sustained carbon dioxide emissions in a mineral-soil wetland restored with treated effluent

Wetlands are economically valuable ecosystems, in part because they purify wastewater by retaining and processing nutrients, organic matter (OM), and other pollutants. While natural wetlands are highly productive and sequester large pools of carbon (C), it is unclear whether the C cycle of restored treatment wetlands is functionally consistent with natural systems. This knowledge gap limits our appreciation for the role that wetland restoration can play as a natural solution to climate change. Here, we quantified metabolic and C cycling patterns of a restored, multi-basin wetland (Frank Lake, Alberta, Canada) receiving municipal and beef processing plant effluents rich in nutrients and OM. We conducted metabolic measurements in all three basins using dissolved oxygen sensors deployed under ice and in open water. Extreme production and respiration indicated that effluent was largely mineralized and replaced with wetland OM in transit. The heterotrophic status of all basins aligned with a published mass budget demonstrating the aquatic habitat of the wetland was an OM sink under current drought conditions that lengthen effluent processing time. Floating chamber measurements in open water zones confirmed that the wetland was a source of CO2 to the atmosphere. From input to outflow, sustained emissions led to declining pCO2 and a decline in the ratio of dissolved inorganic to organic C. Over 30 years post-restoration, the open water habitats in Frank Lake remain heterotrophic and a net source of CO2, suggesting that the trajectory of aquatic C cycling may be distinct from wetlands restored with non-effluent water sources.

Quantifying mineral-associated organic matter in wetlands as an indicator of the degree of soil carbon protection

As atmospheric carbon (C) concentrations increase, so too has interest in understanding the mechanisms that preserve C within the soil organic matter (SOM). Mineral-associated organic matter (MAOM) is one pool of SOM recently shown to protect soil organic C from mineralization. However, most MAOM research has been in agriculture and forest mineral soils. Given the magnitude of soil C stored in wetlands, this study sought to determine the abundance of MAOM in wetlands. A standard method for quantifying MAOM in terrestrial soils was tested, modified, and optimized with three unique wetland soils. Using a physical fractionation method followed by a density fractionation, it was concluded that field moist soils and a dispersant were necessary for fractionating wetland soils (0–50 cm). The Bayhead Swamp soil had the greatest total C (484.07 ± 1.25 mg C g soil -1), but the smallest MAOM pool (0.63 %); most of the C was in the light fraction as particulate organic matter (POM, >98 %). The sandy-peat Cypress Dome soil also lacked MAOM (1.09 %) and was dominated by POM (66.26 %). The silt-rich Brackish Marsh had the least total C (94.37 ± 1.67 mg C g soil -1), but the largest fraction of protected C (24.60 % MAOM). Nitrogen (N) followed similar trends to C, except in the Brackish Marsh where nearly half the total N was MAOM. This research represents the first step in evaluating the role of MAOM in C persistence in organic-rich wetland soils; future work should consider C physical fraction, in addition to C quantity.

Seasonal and tidal controls of the quantity and quality of dissolved organic matter at the marsh creek-estuarine interface

Tidal marshes are an important source of dissolved organic matter (DOM) to estuaries, and DOM plays an integral role in regulating water quality and health of coastal ecosystems. However, our understanding of temporal patterns of DOM quantity and composition at the marsh-estuarine interface is limited. This study investigated temporal changes in colored DOM (CDOM), an important component of dissolved organic carbon (DOC), exchanged across a brackish marsh-estuarine system. The sources of DOC were examined using stable carbon isotope values whereas the sources of CDOM were based on spectroscopic properties, including absorbance and fluorescence excitation-emission matrices (EEMs). Samplings at the Taskinas marsh creek-interface in Virginia (USA) captured a range of tidal stages, seasons, and environmental conditions over a three-year timeseries. Water from low and high tides was used to represent marsh and estuarine endmembers, respectively. Absorbance of CDOM at 440 nm ranged from 0.83 to 6.75 m-1, and the highest values were found during low tides (mean 2.78 ± 0.21 m −1). EEMs were composed of three humic-like components (C1, C2, C3) and one protein-like component (C4). Generally, the terrestrial humic-like (C1) and marine humic-like (C2) components were more abundant than other measured components. Seasonally, CDOM absorbance was highest in spring and summer. Contributions of CDOM from terrestrial sources increased in spring during periods of high runoff and peaked in summer during periods of high marsh productivity. Higher contributions of terrestrially derived CDOM were also measured in fall during periods of plant senescence. The aquatic component (C4) was higher during periods of increased phytoplankton production and during periods of high microbial respiration of terrestrial and planktonic organic matter. Although the amount of marsh exported CDOM varied with season, its composition varied considerably less, especially with respect to autochthonous CDOM. In a focused study in 2018, inferences about the terrestrial versus estuarine sources of CDOM were compared to source inferences made using measurements of stable carbon isotopes (δ13C) of DOC and DIC. δ13CDOC values ranged from −32.25 to −25.91‰, indicative of wetland organic matter and humic-like DOM; δ13CDIC ranged from −9.69 to −3.12‰, consistent with groundwater and estuarine sources. Overall, CDOM and stable isotope measurements indicate that humic materials were the primary source of DOM at this marsh-estuarine interface, including inputs from marsh plants and soils and products from microbial degradation of marsh and terrestrial materials, with lesser contributions from aquatic sources.

Nutrient Retention and Release in Eroding Chesapeake Bay Tidal Wetlands

AbstractThe worldwide loss of coastal wetlands has traditionally been addressed as the loss of ongoing nutrient retention ecosystem services. However, nutrient remineralization from eroded particles may further exacerbate water quality degradation. Using data on nutrient burial and denitrification from northern Chesapeake Bay, along with estimates of the bioavailability of eroded marsh particulates, the changing role of wetlands as an important sink for nutrients is examined. Although the erosion of wetlands results in the reintroduction of nitrogen and phosphorus into open‐water habitats, the potential for exacerbating eutrophication is highly diminished by the low lability of wetland organic matter. The impact of such erosion on the cycling of Fe‐bound phosphorus from marsh soils is highly dependent on both the amount of inorganic P, its solid phase association with Fe, and its potential remobilization from the estuarine sediments into which it is deposited. Although nutrient sequestration in newly constructed wetlands built from dredged materials suggested a rapid development of nutrient sequestration, a better understanding of nutrient ecosystem services provided by marshes created by transgression into uplands is necessary for understanding the long‐term nutrient retention value of coastal wetlands.

Composition Characteristics of Organic Matter and Bacterial Communities under the Alternanthera philoxeroide Invasion in Wetlands

The influence of Alternanthera philoxeroide (alligator weed) invasion on wetland organic matter (OM) accumulation and bacterial changes is rarely studied, but is possibly an important step for revealing the invasion mechanism. Thus, the distribution characteristics of light fraction organic carbon and nitrogen (LFOC and LFON), and heavy fractions organic carbon and nitrogen (HFOC and HFON) were analyzed. Sampling was done on two sediment depths (0–15 cm and 15–25 cm) of invaded and normal habitats of two natural wetlands and two constructed wetlands, and bacterial taxa and composition in surface sediments were also analyzed by high-throughput sequencing. In the surface sediments, the LFOC and LFON contents were significantly higher in the constructed wetlands (0.791 and 0.043 g·kg−1) than in the natural wetlands (0.500 and 0.022 g·kg−1), and the contents of the C and N fractions were also prominently higher in the invaded areas than in normal wetland habitats. The OM storage was relatively stable. Proteobacteria (55.94%), Bacteroidetes (5.74%), Acidobacteria (6.66%), and Chloroflexi (4.67%) were the dominant bacterial phyla in the wetlands. The abundance of Acidobacteria, Actinobacteria, and Gemmatimonadetes were significantly higher in the invaded areas than in the normal habitats. The relative high abundance-based coverage estimator (ACE) index in the constructed wetlands and invaded areas suggested the corresponding high bacterial diversity. The significant and positive relationship between Acidobacteria and organic nitrogen concentrations suggested their potential and positive interrelationships. This study demonstrated that the alligator weed invasion could significantly change the compositions of sediment organic matterand bacteria, thus further changing the nutrition cycle and wetland microhabitat.

Comparison of first-order kinetic models for sewage treatment in horizontal subsurface-flow constructed wetlands

ABSTRACT There are several techniques for sizing horizontal subsurface-flow constructed wetlands systems (CWs), and mathematical models have been frequently used for this purpose because they more accurately represent the liquid behaviour in these reactors. The P-k-C* model has already been used in the prediction of organic matter removal in CWs, but it has been little explored in the literature. On other hand, the model proposed by Chan and Chu [Modeling the reaction kinetics of Fenton’s process on the removal of atrazine. Chemosphere. 2003;51(4):305–311] was not known for prediction of organic matter removal in CW systems. In the present work, the kinetic data for chemical oxygen demand (COD) removal of 28 horizontal subsurface-flow constructed wetlands were used to compare the performance of two pseudo-first-order kinetic models (P-k-C* model and model from Chan and Chu. The comparisons of nonlinear regressions were performed considering Akaike information criterion (AIC), root-mean-square error (RMSE), and adjusted coefficient of determination (). In general, both models were able to provide good predictions of relative remaining concentration (C/C 0). However, the Chan and Chu model produced higher adjustment coefficients, showing the potential to be used in modelling and simulation of the degradation kinetics of organic matter in wetlands.

Multiple biomarkers highlight the importance of water column processes in treatment wetland organic matter cycling

A suite of biomarkers, including amino acids, pigments, and lignin phenols coupled with high resolution mass spectrometry were used to evaluate differences in the sources and fate of organic matter (OM) in Everglades treatment wetlands as a model for OM cycling in shallow water wetlands. Five components of the system (water column particulate matter, vertical traps, flocculent material, periphyton, and surface soil) were assessed for OM transformations down-profile (i.e. water column to soil) and between treatment cells dominated by emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV), with comparisons to reference sites within the remnant Everglades. We found that OM cycling is fundamentally different between EAV and SAV wetlands, and that SAV wetlands have some shared characteristics with similar habitats in the remnant Everglades. Other than locations densely populated by Typha spp., water column particulate organic C was predominantly derived from microbial/cryptomonad sources, rather than macroscopic sources (vascular plants and algal mats). Bacterial amino acid biomarkers were positively correlated with amino acid degradation indices and organic P (Po), respectively suggesting that microbial abundance is associated with less degraded OM, and that further investigation into relationships between microbial biomass and Po is warranted. Overall, this multi-biomarker approach can elucidate the relative degradation of OM pools, identify sources of OM, and highlight the importance of water column processes in shallow water wetlands.

Organic matter sources and lateral sedimentation in a Bahamian karst basin (sinkhole) over the late Holocene: Influence of local vegetation and climate

Karst basins (e.g., blueholes, sinkholes) accumulate well-preserved sedimentary successions that provide transformative paleoclimatic and paleoenvironmental information. However, the sedimentary processes within these basins are not yet fully understood. Here we present stable carbon isotopic values (δ13Corg) and C:N ratios of bulk organic matter in well-dated sediment cores from Blackwood Sinkhole (Abaco, The Bahamas) to investigate the changing flux of organic matter into the sinkhole during the late Holocene. The provenance of preserved organic matter changed through the late Holocene between three primary sources, as determined by three-endmember mixing modeling: wetland organic matter from the adjacent epikarst surface, authigenic primary productivity in the oligohaline meteoric lens, and terrestrial organic matter from the surrounding landscape. Expansion of wetlands on the adjacent epikarst surface played a critical role by increasing the flux of wetland organic matter to the sinkhole, especially during the last 1000 years. Hurricanes and regional rainfall may have mediated organic matter delivery to the benthos, either through hampering wetland development (prior to 1000 cal yr BP) or by changing dissolved nutrient concentrations available in the basin for primary producers. These results demonstrate that organic matter provenance in karst basins is not constant through time, and is significantly dependent upon both landscape vegetation on the epikarst surface and changing hydrographic conditions that impacts nutrient availability to primary producers.

Humic acid composition and humification processes in wetland soils of a Mediterranean semiarid wetland

The present study focuses on a compositional characterization of the humic acid (HA) fraction of several wetland soils using solid-state 13C NMR spectroscopy. The data were analysed using the molecular mixing model (MMM), based on an empirical approach by Nelson and Baldock. The compositional data from HAs obtained with this model were used to obtain a wider assessment of the process of humification from comparison of total soil wetland organic matter composition and HA composition. Twenty samples of humic acids (HAs) isolated from a Mediterranean semiarid wetland (‘Tablas de Daimiel’, central Spain) were studied using elemental analysis and cross polarization magic angle spinning (CPMAS)13C nuclear magnetic resonance (NMR) spectroscopy. The NMR data were analysed with the molecular mixing model (MMM) considering up to six generic components (carbohydrate, protein, lignin, lipid, char and ‘carbonyl’). HAs are considered a conceptual mixture of these model components, and the MMM determines the proportions of the characteristic biomolecules contributing to HA composition. The composition of the HAs under study depends on local factors such as site vegetation and occurrence of fire. Correlations between the proportions of the six generic components and further comparison with those determined for the unfractionated OM (whole sample, WS), gave information on HA origin and humification mechanisms. In particular, the proportions of char and carbohydrate (R 2 0.637) and contents of lignin and protein (R 2 0.471) in the HAs were negatively correlated (P < 0.05). Significant correlations (R 2 0.439) also existed for char contents in whole sample (WS) compared to HA, and for carbohydrates in WS compared to HA (R 2 0.558). Char proportion grew in HA with respect to the WS, and carbohydrates dropped to a half on average in HA compared to WS. Two different humification mechanisms could be identified for no-fire and fire areas. In the former, HA-char was preserved selectively from char in the sample, whereas in the latter, char was newly formed by fire effect.

The impact of drying on structure of sedimentary organic matter in wetlands: Probing with native and amended polycyclic aromatic hydrocarbons

Wetland sediments undergo dry-wet cycles that may change their structural properties and affect geochemical behavior of associated organic compounds. In this study, we examined the effect of drying on particle size distributions and the rapid (24h) sorption reactions of polycyclic aromatic hydrocarbons (PAHs) with salt marsh sediments in Nueces Delta, South Texas. Drying reduced the fraction of fine particles in organically richer sediments, indicating structural rearrangement of organic matter and mineral aggregates. Among the 16 EPA priority PAHs examined, dried sediment preferentially released 1.0–7.5% of phenanthrene, fluoranthene and pyrene to added seawater (solid: water mass ratio of 1/100) - significantly greater than release from sediments maintained in the wet state. On the other hand, drying also increased the affinity of sedimentary organic matter (SOM) for experimentally amended (deuterated) phenanthrene relative to continually wet sediments. Further, deuterated phenanthrene was even more effectively retained when it was added to wet sediment that was subsequently dried and rewetted. These apparently contradictory results can be reconciled and explained by SOM having a heterogeneous distribution of hydrophobic and hydrophilic zones – e.g., a zonal model. We propose that drying changed the orientation of amphiphilic SOM, exposing hydrophobic zones and promoting the release of some of their native PAHs to water. Freshly amended PAHs were only able to penetrate into the surface hydrophobic zone and/or deeper but rapidly accessible (“kinetic”) zone in wet sediments due to the brief adsorption contact time. Subsequent drying presumably then induced structural changes in SOM that isolated these amended PAHs in sites inaccessible to water exchange in the next rewetting. These results provide insights into structural changes of SOM upon drying, and help predict the fate of compounds such as organic contaminants during drought/flood oscillations.

Evaluation of stream chemistry trends in US Geological Survey reference watersheds, 1970–2010

The Hydrologic Benchmark Network (HBN) is a long-term monitoring program established by the US Geological Survey in the 1960s to track changes in the streamflow and stream chemistry in undeveloped watersheds across the USA. Trends in stream chemistry were tested at 15 HBN stations over two periods (1970-2010 and 1990-2010) using the parametric Load Estimator (LOADEST) model and the nonparametric seasonal Kendall test. Trends in annual streamflow and precipitation chemistry also were tested to help identify likely drivers of changes in stream chemistry. At stations in the northeastern USA, there were significant declines in stream sulfate, which were consistent with declines in sulfate deposition resulting from the reductions in SO₂ emissions mandated under the Clean Air Act Amendments. Sulfate declines in stream water were smaller than declines in deposition suggesting sulfate may be accumulating in watershed soils and thereby delaying the stream response to improvements in deposition. Trends in stream chemistry at stations in other part of the country generally were attributed to climate variability or land disturbance. Despite declines in sulfate deposition, increasing stream sulfate was observed at several stations and appeared to be linked to periods of drought or declining streamflow. Falling water tables might have enhanced oxidation of organic matter in wetlands or pyrite in mineralized bedrock thereby increasing sulfate export in surface water. Increasing sulfate and nitrate at a station in the western USA were attributed to release of soluble salts and nutrients from soils following a large wildfire in the watershed.

Regulation of soil enzyme activities in constructed wetlands under a short-term drying period

The activities of extracellular enzymes are important in understanding decomposition of soil organic matter in wetlands subjecting to drying. The activity of soil extracellular enzymes (β-glucosidase, N-acetylglucosaminidase, and phosphatase), and related physicochemical parameters were monitored in constructed freshwater wetlands during a one-month drying manipulation. Drying increased redox potential and decreased soil water content significantly (P<0.05). Higher content of soil organic matter (P<0.05) and higher concentrations of inorganic N (nitrate, P<0.01; and ammonia, P<0.001) were also observed significantly under drying condition. Soil hydrolase enzyme activities were stimulated significantly (β-glucosidase, P<0.05; N-acetylglucosaminidase, P<0.01; and phosphatase, P<0.001), and a two-phase pattern of enzyme activities was revealed under drying condition. The increase of soil enzyme activities under drying condition was significantly related to soil redox potential (P<0.001). Drying strongly affected soil enzyme activities only when soil water content remained above an optimal level for enzymatic catalysis (higher than 23% w/w), corresponding to redox potentials below 250–300 mV. Our results suggest that, under drying condition, potential enzyme activities may be regulated by redox potential, in respect to soil moisture, and consequently alter nutrient availability in wetlands.

Syntrophic Oxidation of Propionate in Rice Field Soil at 15 and 30°C under Methanogenic Conditions

Propionate is one of the major intermediary products in the anaerobic decomposition of organic matter in wetlands and paddy fields. Under methanogenic conditions, propionate is decomposed through syntrophic interaction between proton-reducing and propionate-oxidizing bacteria and H(2)-consuming methanogens. Temperature is an important environmental regulator; yet its effect on syntrophic propionate oxidation has been poorly understood. In the present study, we investigated the syntrophic oxidation of propionate in a rice field soil at 15°C and 30°C. [U-(13)C]propionate (99 atom%) was applied to anoxic soil slurries, and the bacteria and archaea assimilating (13)C were traced by DNA-based stable isotope probing. Syntrophobacter spp., Pelotomaculum spp., and Smithella spp. were found significantly incorporating (13)C into their nucleic acids after [(13)C]propionate incubation at 30°C. The activity of Smithella spp. increased in the later stage, and concurrently that of Syntrophomonas spp. increased. Aceticlastic Methanosaetaceae and hydrogenotrophic Methanomicrobiales and Methanocellales acted as methanogenic partners at 30°C. Syntrophic oxidation of propionate also occurred actively at 15°C. Syntrophobacter spp. were significantly labeled with (13)C, whereas Pelotomaculum spp. were less active at this temperature. In addition, Methanomicrobiales, Methanocellales, and Methanosarcinaceae dominated the methanogenic community, while Methanosaetaceae decreased. Collectively, temperature markedly influenced the activity and community structure of syntrophic guilds degrading propionate in the rice field soil. Interestingly, Geobacter spp. and some other anaerobic organisms like Rhodocyclaceae, Acidobacteria, Actinobacteria, and Thermomicrobia probably also assimilated propionate-derived (13)C. The mechanisms for the involvement of these organisms remain unclear.

Decomposition Trends of Five Plant Litter Types in Mitigated and Reference Wetlands in West Virginia, USA

Decomposition of organic matter in wetlands is linked to numerous wetland processes, making it a useful metric to assess wetland function. We measured plant litter decomposition rates in three mitigated and three reference wetlands located in the Allegheny Mountains of West Virginia, from 2007 to 2009. Four common wetland species were used: broadleaf cattail (Typha latifolia L.), common rush (Juncus effusus L.), brookside alder (Alnus serrulata (Ait.)Willd.), and reed canary grass (Phalaris arundinacea L.). A fifth litter type was created from a mixture of common rush, brookside alder, and reed canary grass. Decomposition rates, based on percent of mass remaining, were similar between mitigated and reference wetlands. Percent mass remaining for reed canary grass was lower than all other litter types at the end of the study, and was significantly lower than cattail, which had the largest percent mass remaining on eight of the 14 collection dates. Linear decomposition rate constants for common rush, reed canary grass, and the mixed litter were similar, but were significantly larger than broadleaf cattail and brookside alder. Though some previous studies have found differing decomposition rates in mitigated and reference wetlands, this study observed similar environmentally mediated decomposition rates of a homogenized plant litter.

Spectroscopic Assessment of Soil Organic Matter in Wetlands from the High Andes

Wetlands are valuable for their function as C sinks, water conservation and filtering, flood control, and as a recreational landscape. In the Central and Southern Andes, peatlands (a.k.a., bofedales) are also a source of good quality pastures for wild and domestic South American camelids (Vicugna pacos, Lama glama, and Vicugna vicugna). In the present study, whole soil samples from seasonally and permanently flooded bofedales were analyzed using laser‐induced fluorescence spectroscopy (LIFS) and electron paramagnetic resonance (EPR) to assess soil organic matter (SOM) stability. The results obtained by both techniques were comparable (R2 = 0.88) and proven to be reliable indicators of increased or reduced SOM stability and thus suitable methods for assessing its humification index. The humification values determined in the permanently flooded bofedal were lower than for the seasonally flooded one. Deeper in the soil profiles of both bofedal types, the humification process of SOM attains more advanced stages, with a relative increase of more recalcitrant organic compounds. An important factor is the presence of water in permanently flooded bofedales, which slows down organic matter decomposition due to anaerobiosis. Results from a portable LIFS system also showed significant correlations when compared with both the bench LIFS system (R2 = 0.88) and the EPR (R2 = 0.62). The portable system constitutes an affordable option for the in situ characterization of SOM. This assessment is of outmost importance in agroecosystems acting as green house gases sink or sources under variable climatic conditions.

Molecular fingerprinting of wetland organic matter using pyrolysis-GC/MS: an example from the southern Cape coastline of South Africa

Pyrolysis–gas chromatography mass spectrometry (py-GC/MS) allows the characterisation of complex macromolecular organic matter. In lakes and wetlands this can potentially be used to assess the preservation/diagenesis and provenance of sediment organic matter. It can complement palaeoenvironmental investigations utilising ‘bulk’ sediment variables such as total organic carbon (TOC) and TOC/total nitrogen ratios. We applied py-GC/MS analyses to a ~32,000-year sediment record from the southern Cape coastline of South Africa. We used the results to evaluate the sources and extent of degradation of organic matter in this semi-arid environment. Marked down-core changes in the relative abundance of multiple pyrolysis products were observed. Correspondence analysis revealed that the major driver of this down-core variability in OM composition was selective preservation/degradation. Samples comprising highly degraded OM are primarily confined to the lower half of the core, older than ~12,000 years, and are characterised by suites of low-molecular-weight aromatic pyrolysis products. Samples rich in organic matter, e.g. surface sediments, are characterised by products derived from fresh emergent or terrestrial vegetation, which include lignin monomers, plant-derived fatty acids and long-chain n-alkanes. Pyrolysates from the late glacial-early Holocene period, approximately mid-way down the core are characterised by distinct suites of long-chain n-alkene/n-alkane doublets, which may reflect the selective preservation of recalcitrant aliphatic macromolecules and/or enhanced inputs of the algal macromolecule algaenan/polymerised algal lipids. Increased TOC, lower δ13C and increased abundance of more labile lignin and fatty acid products at the same depths suggest this period was associated with increased lake primary productivity and enhanced inputs of terrestrial OM. TOC is the only ‘bulk’ parameter correlated with the correspondence analysis axes extracted from the py-GC/MS data. Distinct fluctuations in TOC/total nitrogen ratio are not explained by variation in organo-nitrogen pyrolysis products. Notwithstanding, the study suggests that py-GC/MS has potential to complement palaeolimnological investigations, particularly in regions such as southern Africa, where other paleoenvironmental proxy variables in sediments may be lacking or equivocal.

Dissolved Organic Matter in Wetlands

SL-294, a 3-page illustrated fact sheet by Alan L. Wright and K. R. Reddy, describes the importance of dissolved organic matter and its role in regulating nutrients in terrestrial and aquatic ecosystems. Published by the UF Department of Soil and Water Science, June 2009. SL 294/SS507: Dissolved Organic Matter in Wetlands (ufl.edu)

Soil fertility in wetland versus reclaimed land using plant parameters in relation to nitrogen content: The case of Yala Swamp, Western Kenya

A bioassay experiment was carried out to assess soil fertility of wetland and adjacent reclaimed wetland (agricultural-land) areas in comparison to their nitrogen contents. Though wetland soils had more total N than agricultural-land soils, the greenhouse findings suggest that organic matter in wetlands does not mineralize as readily as in soils drained for longer periods. Also, when total N increased, the roots to shoots (R:S) ratio decreased thus favoring shoot growth, but less so in wetland soil (r = -0.1) than in agricultural soil (r = -0.2). In fact, the C/N ratios indicated that poor nutrient quality in wetland soils as compared to agricultural-land soils. Wetland soils had more acidic pH values which impeded the growing of the maize and shifted the partitioning towards the roots. Key words: R:S ratio, total N, total biomass, maize, C/N ratio.

Hydrologic influence on stability of organic phosphorus in wetland detritus.

Accretion of organic matter in wetlands provides long-term storage for nutrients and other contaminants. Water-table fluctuations and resulting alternate flooded and drained conditions may substantially alter the stability of stored materials including phosphorus (P). To study the effects of hydrologic fluctuation on P mobilization in wetlands, recently accreted detrial material (derived primarily from Typha spp.) was collected from the Everglades Nutrient Removal Project (ENRP), a constructed wetland used to treat agricultural drainage water in the northern Everglades. The detrital material was subjected to different periods of drawdown and consecutive reflooding under laboratory conditions. The 31P nuclear magnetic resonance (31P NMR) spectroscopy analysis revealed that sugar phosphate, glycerophosphate, polynucleotides, and phospholipids (glycerophosphoethanolamine and glycerophosphocholine) were the major forms of P in the detrital material. After 30 d of drawdown, polynucleotides were reduced to trace levels, whereas sugar phosphate, glycerophosphate, and phospholipids remained the major fractions of organic P. Microorganisms seemed to preferentially utilize nucleic acid P, perhaps to obtain associated nutrients including carbon and nitrogen. At the end of the 30-d reflooding period, cumulative P flux from detritus to water column accounted for 3% of the total P (< or = 15 d of drawdown) and further decreased to 2% at 30 d of drawdown, but increased to 8% at 60 d of drawdown. The drawdown (< or = 30 d) not only reduced P flux to the water column, but also increased the humification and microbial immobilization of P. Excessive drawdown (60 d), however, triggered the release of P into the water column as the water content of detritus decreased from 95 to 11%.