Saturated Wetland Research Articles

Techno-economic and life cycle analysis of circular phosphorus systems in agriculture

Fertilizer runoff is a global nuisance that disrupts biogeochemical cycles of nitrogen and phosphorus. We perform techno-economic and life cycle analyses of selected approaches for enabling a circular economy of phosphorus. We consider four schemes: capturing P with ion-exchange resins followed by precipitation, interception by wetland and recovery in char after biomass pyrolysis, removal by bioreactor and recovery in char after bioreactor substrate pyrolysis, and using legacy phosphorus accumulated in a saturated wetland to grow crops by wetlaculture. For each system, we analyze the mass flow, calculate the degree of circularity, and examine the feasibility by techno-economic and life cycle analyses. We find that although ion exchange outperforms the others, the associated economic and emissions burden are too high. Approaches that rely on wetlands are most economically attractive and can have lower impact. However, without policy interventions, the linear economy of phosphorus is likely to remain economically most attractive.

Methylmercury Transport and Fate Shows Strong Seasonal and Spatial Variability along a High Arctic Freshwater Hydrologic Continuum.

The presence of toxic methylmercury (MeHg) in Arctic freshwater ecosystems and foodwebs is a potential health concern for northern Indigenous people. Addressing this issue requires a better understanding of MeHg production, fate during transport, and uptake into foodwebs. We used methylation assays and spatiotemporal surveys of MeHg concentrations, during the ice-covered and open water seasons, across a hydrologic continuum (composed of thaw seeps, lake/ponds, and a wetland) to identify Hg methylation hotspots and seasonal differences in MeHg cycling unique to Arctic ecosystems. Ponds and saturated wetland soils support methylation hotspots during the open water season, but subsequent export of MeHg to downstream ecosystems is limited by particle settling, binding of MeHg on soil organic matter, and/or demethylation in drier wetland soils. During the ice-covered season, MeHg concentrations in lake waters were approximately ten-fold greater than in summer; however, zooplankton MeHg concentrations were paradoxically five times lower at this time. Despite limited evidence of snow-phase methylation, the snowpack is an important MeHg reservoir. Changes in ice-cover duration will alter MeHg production and bioaccumulation in lakes, while increased thaw and surface water flow will likely result in higher methylation rates at the aquatic-terrestrial interface and more efficient downstream transport of MeHg.

Nitrogen removal efficiencies and pathways from unsaturated and saturated zones in a laboratory-scale vertical flow constructed wetland

A laboratory-scale vertical flow constructed wetland system was designed and monitored to compare nitrogen removal rates and pathways from both saturated and unsaturated zones under a hydraulic loading rate and influent total nitrogen concentration of 1.5 m3/m2.d and 508 mg/L respectively. Weekly measurements of the concentrations of nitrogen compounds, chemical oxygen demand, temperature, dissolved oxygen, oxidation-reduction potential, and hydrogen ion concentration were taken throughout the study. At the end of the experiments, PCR analysis of 16S rRNA gene sequencing was performed to identify microbial communities in the unsaturated and saturated parts of the system. The nitrogen compounds were removed from the system after 182 days, with similar total nitrogen removal efficiencies (94% and 93%) for the unsaturated and saturated zones respectively. Heterotrophic nitrification/aerobic denitrification was the major pathway responsible for the removal of nitrogen compounds. Adsorption into the gravel bed also contributed to ammonium removal. Proteobacteria were the dominant bacterial strains involved in nitrogen transformation and accounted for 80% of the total bacteria in the unsaturated zone and 60% in the saturated zone. With little difference in the concentration removal efficiencies of the unsaturated and saturated zones, a more effective design would be an entirely saturated wetland as the total mass removal of nitrogen depends on the water volume stored, which at full saturation in this design was seven times greater per unit wetland volume than the unsaturated zone.

Modeling Nitrogen and Carbon dynamics in wetland soils and water using a mechanistic wetland model.

In this article, extension and application to variably-saturated wetland conditions of a process-based wetland model, namely WetQual is demonstrated. The new model described in this article is an improved version of an earlier model, which was only capable of capturing nutrient dynamics in continuously ponded wetlands. The upgraded model is capable of simulating nutrient cycling and biogeochemical reactions in both ponded and unsaturated zones of the wetland. To accomplish this goal, a comprehensive module for tracking water content in wetland soil was implemented in the model, and biogeochemical relationships were added to explain cycling of nitrogen (N) and carbon (C) in variably saturated zones of wetlands. The developed model was applied to a small, restored wetland receiving agricultural runoff, located on Kent Island, Maryland. On average, during the two year study period, the ponded compartment of the study wetland covered 65% of the total 1.2 ha area. Through mass balance analysis, it was revealed that the mass of nitrogen lost to denitrification at the variably saturated compartment of the study wetland was about 3 times higher than that of the ponded compartment (32.7 ± 29.3 kg vs. 9.5 ± 5.5 kg) whereas ammonia volatilization at the variably saturated compartment was a fraction of that of ponded compartment (1.2 ± 1.9 kg vs. 11.3 ± 11.8 kg). Sensitivity analysis showed that cycling of carbon related constituents in variably saturated compartment had high sensitivity to temperature and available soil moisture.

Unrestricted dairy cattle grazing of a pastoral headwater wetland and its effect on water quality

Unrestricted cattle access to pastoral wetlands can result in increased pollutant loads from agricultural areas. We quantified the time a herd of dairy cattle spent grazing a pastoral headwater wetland and its associated impact on water quality. Over a two year period a herd of ∼220 dairy cattle rotationally grazed a paddock containing a permanently saturated pastoral wetland. Flow and turbidity were continuously monitored at a v-notch weir and baseflow and event samples were collected and analysed for TSS, Escherichia coli and various forms of N and P. Cattle were detected grazing the wetland paddock on 18 days by time-lapse cameras. Cattle only entered and grazed the saturated wetland area for 30–40% of the time and there were usually only a few animals in the wetland at one time. Cattle that did graze the wetland tended to remain near the edge. We attribute the low level of wetland grazing to the cattle recognizing the risk of entrapment in the deep (up to 2m), boggy wetland soil. A measurable increase in pollutants (attributable solely to cattle generated disturbance) occurred only once. This occurred when a cow became entrapped in close proximity to the water quality monitoring location on a day when wetland flow was elevated. Exclusion of cattle from our study wetland by fencing is therefore unlikely to substantially improve downstream water quality. Further research is required to determine whether this is the case for similar wetlands in different environments.

Clogging of vertical-flow constructed wetlands treating urban wastewater contaminated with a diesel spill

Clogging often leads to a decrease of the treatment performance of wetlands. The aims of this study were to compare the impact of different design and operational variables on the treatment efficiency and clogging processes and to model suspended solid (SS) accumulation within the saturated wetland zone using the Wang-Scholz model. Different vertical-flow constructed wetlands were operated from June 2011 until April 2014. Four treatment periods were assessed: set-up, first year after set-up period, second year after set-up period and diesel spill (for selected filters only). The filter with the highest chemical oxygen demand (COD) loading but no diesel contamination performed the best in terms of COD and biochemical oxygen demand (BOD) removal for the fourth and final treatment period. Filters contaminated by diesel performed worse in terms of COD and BOD but considerably better regarding nitrate-nitrogen removal. Serious clogging phenomena impacting negatively on the treatment performance and the hydraulic conductivity were not observed. Modelling results were generally poor for the set-up period, adequate for the first 2years after the set-up period and variable after the diesel spill. The Wang-Scholz model performed well for less complex operations.

Bog Turtle (Glyptemys muhlenbergii) Wetland Habitat: an Emphasis on Soil Properties

Bog turtles (Glyptemys muhlenbergii) access saturated wetland soils and move through them to thermoregulate, find cover, and hibernate. Variability in the physical properties of the soil that affects suitability for turtle use is little understood. We identified dominant soil series and measured soil organic carbon (SOC) content and particle size in the top 18 cm of surface soils from Southwestern Virginia wetlands frequently used by bog turtles and similar wetlands not known to be used. A static cone penetrometer was used to evaluate soil strength in specific locations where bog turtles were found and adjacent random areas. Soils were poorly developed alluvium with aquic soil regimes. Levels of SOC were greater in locations with more continuous surface saturation and averaged 10% in the wettest locations. Proportions of sand, silt, and clay in wetlands were consistent with loam and silt loam textures. Levels of SOC and dominant particle sizes were not different in similarly saturated areas of wetlands that were frequently used or not known to be used by bog turtles. However, some wetlands not known to be used completely lacked areas that were always saturated. Based on penetrometer data, bog turtle use was centered on low strength soils. The physical qualities of surface soils in bog turtle wetlands result from the depositional environment and hydrology. The soil information derived from this study may assist biologists to determine whether wetlands are used by bog turtles, and also establishes reference soil conditions for use during wetland restoration projects that occur within the geographic range of the bog turtle.

Estimating density of a forest‐dwelling bat: a predictive model for Rafinesque's big‐eared bat

Data on species distribution and abundance are the foundation of population ecology. However, due to difficulties in surveying bats, abundance estimates for tree-roosting microchiropterans are non-existent. Therefore, our objective was to develop methods for estimating colony abundance and density, taking as our model Rafinesque's big-eared bat Corynorhinus rafinesquii, a species of conservation concern found in cypress-gum swamps of the southeastern United States. We searched 123 transects at eight study sites in the Coastal Plain of Georgia, USA to locate and characterize diurnal summer roosts of C. rafinesquii. We modeled the relationship between the number of bat colonies and landscape-scale habitat variables with zero-inflated negative binomial regression and used Akaike's information criterion to select the most parsimonious models. We generated a predictive density map to identify areas of high colony density and to estimate overall abundance. Colony density was predicted by the duration of wetland flooding, wetland width, and study site. Application of the regression model to a GIS indicated there were 3,734 colonies containing 6,910 adult bats on the eight study sites. Predicted density ranged from 0.07 colonies/ha and 0.07 adult bats/ha in saturated wetlands to 0.47 colonies/ha and 1.18 adult bats/ha in semi-permanently flooded wetlands. This study is the first to estimate density and abundance of forest-dwelling microchiropterans over a large area. Such data can serve as a baseline for future work on population trends in C. rafinesquii. In addition, our approach could be replicated for other bat species with moderately cryptic roosts.

Quantifying of Soil Denitrification Potential in a Wetland Ecosystem, Ochi Experiment Site, Japan

Nitrate contamination has become one of the most important issues for surface water and groundwater. N2O, with an increasing contribution to global warming, has been more and more attention by the IPCC recently. As well known, denitrification plays a major role in nitrogen cycle of aquatic ecosystems and operates at rates far below its potential under proper conditions. Sediments are the single largest pool of nitrogen in wetland ecosystems. During this process, facultative anaerobic bacteria transform nitrite into nitrogen gas which dissolves in the groundwater and diffuses into the atmosphere finally when it shows up with seepage or spring in the wetland. To seek a mechanistic understanding of N removal in natural wetland ecosystem, a case study was carried in terms of denitrification rate at the Ochi catchment, Chiba, Japan. In this study, samples of intact soil cores in 0–20cm were taken along the groundwater flow path, which including 2 samples in the unsaturated zone and 2 in saturated wetland ecosystem. Denitrification capacity of soil was quantified using acetylene (C2H2) inhibition/gas chromatography ECD method with time intervals of 0, 2, 6, 12, 24 h. Total—N and Total—C contents and amount of denitrifying bacteria were also analyzed. It is found that denitrification ability is low for all 2 samples in the unsaturated zone and high in saturated zone. Results show that N2O emission flux after C2H2—inhibition ranges from 0 to 1.17 gN m-2h-1, with an increase value prior 6 hours and slow down after that.

Wetland hydrologic class change from prior to European settlement to present on the Des Moines Lobe, Iowa

It has been hypothesized that wetland restoration policies have favored the restoration of the wettest classes of wetlands on the Des Moines Lobe of the prairie pothole region. To test this hypothesis we compared pre-drainage wetland distributions based on soils data and National Wetland Inventory (NWI) estimates of contemporary wetland distributions on the Des Moines Lobe. Based on the NWI data, the Des Moines Lobe today has only 3–4% of the wetland area that it had prior to the onset of drainage. On the basis of their soils, pre-drainage wetlands were predominantly temporarily flooded to saturated wetlands (84%), with only about 6% of the wetlands with water regimes classified as semi-permanently to permanently flooded. Depending on the interpretation of wetland modifiers on NWI maps, wetlands classified by the NWI as semi-permanent to permanently flooded make up more than 41% of the wetland area while wetlands with temporarily flooded to saturated water regimes account for 45–58% of the Lobe’s wetland area. The water regimes of contemporary wetlands when compared to their historic regimes suggest that many of today’s wetlands have different water regimes than they did prior to the onset of drainage. Because of the regional lowering of the groundwater table, many of today’s wetlands have drier water regimes, but some have wetter water regimes because they receive drainage tile inputs. Our results indicate that restoration has favored the wettest classes of wetlands and that temporarily to saturated wetland classes have not been restored in proportion to their relative abundance in the pre-drainage landscape.

Partially Acetylated Sugarcane Bagasse for Wicking Oil from Contaminated Wetlands

AbstractSugarcane bagasse was partially acetylated to enhance its oil‐wicking ability in saturated environments while holding moisture for hydrocarbon biodegradation. The water sorption capacity of raw bagasse was reduced fourfold after treatment, which indicated considerably increased hydrophobicity but not a limited capability to hold moisture for hydrocarbon biodegradation. Characterization results by Fourier transform infrared (FT‐IR), scanning electron microscopy (SEM), X‐ray diffraction (XRD), and surface area analyzer suggested that treated bagasse exhibited enhanced hydrophobicity and surface area. Oil wicking test results indicate that treated bagasse is more effective in wicking oil from highly saturated environments than raw bagasse and suggest that application of this material in remediation of oil spills in highly saturated wetlands is promising.

Spatial distribution of historical wetland classes on the Des Moines Lobe, Iowa

We estimated the pre-settlement density and area of different classes of palustrine wetlands on the Des Moines Lobe based on soil characteristics. Six wetland classes, ranging from temporarily flooded to permanently flooded, were identified based on soil properties that persisted after artificial drainage. Prior to drainage, wetlands covered nearly half of the Des Moines Lobe and there were differences in both the types and relative abundance of wetlands among the four geologic subdivisions of the Lobe (Bemis, Altamont, and Algona till plains and Altamont Lake). In the flat Altamont Lake zone, the most common wetlands were equally split between temporarily flooded and saturated water regimes. Among the three till plain zones, saturated wetlands were the dominant wetland type. Differences in wetland distributions among the zones probably derive from differences in initial topography and post-glacial processes such as erosion-deposition processes and stream-network formation.

Phylogenetic Comparison of the Methanogenic Communities from an Acidic, Oligotrophic Fen and an Anaerobic Digester Treating Municipal Wastewater Sludge

Methanogens play a critical role in the decomposition of organics under anaerobic conditions. The methanogenic consortia in saturated wetland soils are often subjected to large temperature fluctuations and acidic conditions, imposing a selective pressure for psychro- and acidotolerant community members; however, methanogenic communities in engineered digesters are frequently maintained within a narrow range of mesophilic and circumneutral conditions to retain system stability. To investigate the hypothesis that these two disparate environments have distinct methanogenic communities, the methanogens in an oligotrophic acidic fen and a mesophilic anaerobic digester treating municipal wastewater sludge were characterized by creating clone libraries for the 16S rRNA and methyl coenzyme M reductase alpha subunit (mcrA) genes. A quantitative framework was developed to assess the differences between these two communities by calculating the average sequence similarity for 16S rRNA genes and mcrA within a genus and family using sequences of isolated and characterized methanogens within the approved methanogen taxonomy. The average sequence similarities for 16S rRNA genes within a genus and family were 96.0 and 93.5%, respectively, and the average sequence similarities for mcrA within a genus and family were 88.9 and 79%, respectively. The clone libraries of the bog and digester environments showed no overlap at the species level and almost no overlap at the family level. Both libraries were dominated by clones related to uncultured methanogen groups within the Methanomicrobiales, although members of the Methanosarcinales and Methanobacteriales were also found in both libraries. Diversity indices for the 16S rRNA gene library of the bog and both mcrA libraries were similar, but these indices indicated much lower diversity in the 16S digester library than in the other three libraries.

EFFECT OF SAND PARTICLE SIZE, OIL CONTAMINATION, AND WATER TABLE LEVEL ON THE EFFECTIVENESS OF SORBENTS IN WICKING OIL FROM CONTAMINATED WETLAND

ABSTRACT Oil spill cleanup in wetlands is problematic because of the limited remediation techniques that can be applied in such environments. The use of sorbents to clean up oil spills presents many advantages due to simplicity of approach and the inexpensive nature of these materials. Furthermore, sorbents can be used not only as wicking agents but also as microbial media that mediate hydrocarbon biodegradation. Once a sorbent is applied to an impacted wetland, it absorbs the contaminating oil. It retains the oil for a sufficient length of time to allow biodegradation of hydrocarbons by indigenous bacteria under aerobic conditions. In addition, plant-derived organic sorbents are biodegradable, thus leaving no permanent residue. Ammoniated bagasse is one of the biodegradable organic sorbents that contain nitrogen as a nutrient needed to support the activity of oil degrading bacteria. In this study, we evaluated the effectiveness of sorbents in wicking oil from the subsurface of oil-contaminated sediments under various conditions. Several microcosms were prepared to simulate saturated wetland environments. Glass cylinders, 10 cm in diameter and 10 cm in height, enclosed these microcosms. Each microcosm was layered in the following sequence (from the bottom to the top): a clean sand layer, an oiled-sand layer, and an overlying sorbent layer. Sand, sorbent, and water were sterilized prior to use to ensure that no biodegradation occurs during the experiment. The different conditions included: 2 particle sizes of sand (20 × 30 and 60 × 80 U.S. Mesh), 2 levels of oil contamination (25% and 75% of saturation), 3 water levels (at the oiled-layer/clean sand interface, at the oiled-layer/sorbent-layer interface, and at the sorbent-layer/air interface), and 2 levels of sorbent (presence or absence). Oil wicking experiments were performed in airtight microcosms for a period of 3 months. At the termination of an experiment, each layer of the microcosms was separated and samples were taken. Samples were extracted with dichloromethane and quantified by gas chromatography/mass spectrometry (GC-MS). Mass balances in each microcosm were established in terms of total petroleum hydrocarbons (TPH). TPH includes alkanes (C10-C35); pristane; phytane; hopane; 2-, 3-, and 4-ring PAHs; and pyrogenic PAHs (5- & 6-rings). The TPH change in each layer from time zero to 3 months was used to determine the effectiveness of the sorbent under each condition tested.

Methane flux in subalpine wetland and unsaturated soils in the southern Rocky Mountains

Methane exchange between the atmosphere and subalpine wetland and unsaturated soils was evaluated over a 15‐month period during 1995–1996. Four vegetation community types along a moisture gradient (wetland, moist‐grassy, moist‐mossy, and dry) were included in a 100 m sampling transect situated at 3200 m elevation in Rocky Mountain National Park, Colorado. Methane fluxes and soil temperature were measured during snow‐free and snow‐covered periods, and soil moisture content was measured during snow‐free periods. The range of mean measured fluxes through all seasons (a positive value represents CH4 efflux to the atmosphere) were: 0.3 to 29.2 mmol CH4 m−2 d−1 wetland area; 0.1 to 1.8 mmol CH4 m−2 d−1, moist‐grassy area; −0.04 to 0.7 mmol CH4 m−2 d−1, moist‐mossy area; and −0.6 to 0 mmol CH4m−2 d−1, dry area. Methane efflux was significantly correlated with soil temperature (5 cm) at the continuously saturated wetland area during snow‐free periods. Consumption of atmospheric methane was significantly correlated with moisture content in the upper 5 cm of soil at the dry area. A model based on the wetland flux‐temperature relationship estimated an annual methane emission of 2.53 mol CH4 m−2 from the wetland. Estimates of annual methane flux based on field measurements at the other sites were 0.12 mol CH4 m−2, moist‐grassy area; 0.03 mol CH4 m−2, moist‐mossy area; and −0.04 mol CH4 m−2, dry area. Methane fluxes during snow‐covered periods were responsible for 25, 73, 23, and 43% of the annual fluxes at the wetland, moist‐grassy, moist‐mossy, and dry sites, respectively.

Nitrogen Transformations in Wetland Soil Cores Measured by (sup15)N Isotope Pairing and Dilution at Four Infiltration Rates

The effect of water infiltration rate (IR) on nitrogen cycling in a saturated wetland soil was investigated by applying a (sup15)N isotope dilution and pairing method. Water containing [(sup15)N]nitrate was infiltrated through 10-cm-long cores of sieved and homogenized soil at rates of 72, 168, 267, and 638 mm day(sup-1). Then the frequencies of (sup30)N(inf2), (sup29)N(inf2), (sup15)NO(inf3)(sup-), and (sup15)NH(inf4)(sup+) in the outflow water were measured. This method allowed simultaneous determination of nitrification, coupled and uncoupled denitrification, and nitrate assimilation rates. From 3% (at the highest IR) to 95% (at the lowest IR) of nitrate was removed from the water, mainly by denitrification. The nitrate removal was compensated for by the net release of ammonium and dissolved organic nitrogen. Lower oxygen concentrations in the soil at lower IRs led to a sharper decrease in the nitrification rate than in the ammonification rate, and, consequently, more ammonium leaked from the soil. The decreasing organic-carbon-to-nitrogen ratio (from 12.8 to 5.1) and the increasing light A(inf250)/A(inf365) ratio (from 4.5 to 5.2) indicated an increasing bioavailability of the outflowing dissolved organic matter with increasing IR. The efflux of nitrous oxide was also very sensitive to IR and increased severalfold when a zone of low oxygen concentration was close to the outlet of the soil cores. N(inf2)O then constituted 8% of the total gaseous N lost from the soil.

The incandescent electrical lamp decided to be Edison's invention

Unrestricted cattle access to pastoral wetlands can result in increased pollutant loads from agricultural areas. We quantified the time a herd of dairy cattle spent grazing a pastoral headwater wetland and its associated impact on water quality. Over a two year period a herd of ∼220 dairy cattle rotationally grazed a paddock containing a permanently saturated pastoral wetland. Flow and turbidity were continuously monitored at a v-notch weir and baseflow and event samples were collected and analysed for TSS, Escherichia coli and various forms of N and P. Cattle were detected grazing the wetland paddock on 18 days by time-lapse cameras. Cattle only entered and grazed the saturated wetland area for 30–40% of the time and there were usually only a few animals in the wetland at one time. Cattle that did graze the wetland tended to remain near the edge. We attribute the low level of wetland grazing to the cattle recognizing the risk of entrapment in the deep (up to 2 m), boggy wetland soil. A measurable increase in pollutants (attributable solely to cattle generated disturbance) occurred only once. This occurred when a cow became entrapped in close proximity to the water quality monitoring location on a day when wetland flow was elevated. Exclusion of cattle from our study wetland by fencing is therefore unlikely to substantially improve downstream water quality. Further research is required to determine whether this is the case for similar wetlands in different environments.