Wetland Water Column Research Articles

Bioaccumulation of nutrients and metals in sediment, water, and phoomdi from Loktak Lake (Ramsar site), northeast India: phytoremediation options and risk assessment.

In order to determine the potential of phoomdi to accumulate nutrients and metals, 11 dominant species belonging to 10 different families, sediment, and water were analyzed for a period of 2years from the largest freshwater wetland of north-east India, Loktak (Ramsar site). Results revealed nutrient (TN and TP) and metal (Fe, Mn, Zn, and Cu) compartmentalization in the order phoomdi > sediment > water. Iron concentrations in water (0.37 ± 0.697 to 0.57 ± 1.010mgL(-1)) and sediments (81.8 ± 0.45 to 253.1 ± 0.51mgkg(-1)) show high metal discharge into the wetland. Metal accumulation in phoomdi ranged up to 212.3 ± 0.46-9461.4 ± 1.09mgkg(-1) for Fe; 85.9 ± 0.31-3565.1 ± 0.87mgkg(-1) for Mn; 9.6 ± 0.41-85.39 ± 0.58mgkg(-1) for Zn; and 0.31 ± 0.04-9.2 ± 0.04mgkg(-1) for Cu, respectively. High bioaccumulation factors (BAF) for metals (S. cucullata, 5.8 × 10(4) Fe, 3.9 × 10(4) Mn, and 1.7 × 10(4) Cu, and O. javanica, 4.9 × 10(3) Zn) and nutrients (S. polyrhiza, 9.7 × 10(2) TN, and Z. latifolia, 7.9 × 10(4) TP) revealed good accumulation in phoomdi compared to the wetland water column and indicate their potential to maintain a safe environment of Loktak. Further, the paper analyzed the health hazard of metals via phoomdi wild edible consumption, with the results confirming potential risk. Thus, the paper showed the need of in-depth monitoring and ample management strategies to ensure nutritional safety conditions of locals from the metals.

Wind‐driven water motions in wetlands with emergent vegetation

AbstractWetland biogeochemical transformations are affected by flow and mixing in wetland surface water. We investigate the influence of wind on wetland water flow by simultaneously measuring wind and surface water velocities in an enclosed freshwater wetland during 1 day of strong‐wind conditions. Water velocities are measured using a Volumetric Particle Imager while wind velocities are measured via sonic‐anemometer. Our measurements indicate that the wind interacting with the vegetation canopy generates coherent billows and that these billows are the dominant source of momentum into the wetland water column. Spectral analysis of velocity time series shows that the spectral peak in water velocity is aligned with the spectral peak of in‐canopy wind velocity, and that this peak corresponds with the Kelvin‐Helmholtz billow frequency predicted by mixing layer theory. We also observe a strong correlation in the temporal pattern of velocity variance in the air and water, with high variance events having similar timing and duration both above and below the air‐water interface. Water‐side variance appears coupled with air‐side variance at least down to 5 cm, while the theoretical Stokes' solution predicts momentum transfer down to only 2 mm assuming transfer via molecular viscosity alone. This suggests that the wind‐driven flow contributed to significant mixing in the wetland water column.

Phosphorus retention of forested and emergent marsh depressional wetlands in differing land uses in Florida, USA

The translocation of phosphorus (P) from terrestrial landscapes to aquatic bodies is of concern due to the impact of elevated P on aquatic system functioning and integrity. Due to their common location in depressions within landscapes, wetlands, including so-called geographically isolated wetlands (GIWs), receive and process entrained P. The ability of depressional wetlands, or GIWs, to sequester P may vary by wetland type or by land use modality. In this study we quantified three measures of P sorption capacities for two common GIW types (i.e., emergent marsh and forested wetlands) in two different land use modalities (i.e., agricultural and least impacted land uses) across 55 sites in Florida, USA. The equilibrium P concentration (EPC0) averaged 6.42 ± 5.18 mg P L−1 (standard deviation reported throughout); and ranged from 0.01–27.18 mg P L−1; there were no differences between GIW type or land use modality, nor interaction effects. Significant differences in phosphorus buffering capacity (PBC) were found between GIW types and land use, but no interaction effects. Forested GIWs [average 306.64 ± 229.63 (mg P kg−1) (µg P L−1)−1], and GIWs in agricultural settings [average 269.95 ± 236.87 (mg P kg−1) (µg P L−1)−1] had the highest PBC values. The maximum sorption capacity (Smax) was found to only differ by type, with forested wetlands (1274.5 ± 1315.7 mg P kg−1) having over three times the capacity of emergent GIWs (417.5 ± 534.6 mg P kg−1). Classification trees suggested GIW soil parameters of bulk density, organic content, and concentrations of total P, H2O-extractable P, and HCl-extractable P were important to classifying GIW P-sorption metrics. We conclude that GIWs have high potential to retain P, but that the entrained P may be remobilized to the wetland water column depending on storm and groundwater input P concentrations. The relative hydrologic dis-connectivity of GIWs from other aquatic systems may provide sufficient retention time to retain elevated P within these systems, thereby providing an ecosystem service to downstream waters.

Quantifying spatial variability and biogeochemical controls of ecosystem metabolism in a eutrophic flow-through wetland

Wetlands are highly dynamic ecosystems that exhibit large temporal and spatial gradients in biogeochemical and metabolic processes. While previous studies have documented temporal variability of wetland metabolism, very little is known regarding how wetland metabolism varies spatially. This is particularly relevant for constructed flow-through wetlands used to treat agricultural runoff due to growing concern over the potential for these systems to act as incubators of biological oxygen demanding (BOD) substances (i.e., algal biomass) and contributors to downstream hypoxia. This study employed a spatially explicit characterization of wetland water column properties using multiparameter water quality sondes, thus allowing the calculation of wetland metabolism across a range of spatial scales (meters to 100s of meters). This study documented a high degree of spatial variability in metabolic rates within the wetland, with average gross primary productivity (GPP) ranging from 6.41 to 13.69gO2m−2d−1, community respiration (CR) ranging from 4.85 to 9.79gO2m−2d−1, and net ecosystem production (NEP) ranging from 0.35 to 2.42gO2m−2d−1. Linkages between metabolic rates and environmental controls were quantified using a spatial/temporal statistical approach. Five key environmental parameters (turbidity, dissolved reactive phosphorus, ammonium, electrical conductivity, and temperature) were found to correlate with ecosystem metabolism. Results from this study show that despite high rates of primary productivity, high respiration rates limited NEP in this wetland due to high heterotrophic activity.

Predicting wetland contamination from atmospheric deposition measurements of pesticides in the Canadian Prairie Pothole region

Although it has been suggested that atmospheric deposition alone can result in detectable levels of pesticides in wetlands of the Pairie Pothole Region of Canada, this is the first field study to compare the masses of pesticides entering wetlands by atmospheric deposition with those concentrations of pesticides detected in the water-column of prairie wetlands. Weekly air and bulk deposition samples were collected from May 26th to Sept. 15th, 2008 at the Manitoba Zero Tillage Research Association (MZTRA) Farm, Brandon, Manitoba, with four on-site wetlands (approximate sizes 0.15–0.45 ha) monitored every second week. Twelve pesticides were detected in the air, with MCPA (one of the three pesticides applied on the farm in 2008 in addition to clopyralid and glyphosate), triallate, and γ-HCH being detected every week. Calculations were performed to predict wetland pesticide concentrations based on bulk deposits alone for those pesticides that had detectable concentrations in the bulk deposition samples (in order of the highest total seasonal deposition mass to the lowest): MCPA, glyphosate, 2,4-D, clopyralid, bromoxynil, atrazine, dicamba, metolachlor, and mecoprop. The estimated concentrations were closest to actual concentrations for MCPA (Pearson correlation coefficient’s = 0.91 to 0.98; p-values < 0.001) and predictions were also reasonable for a range of other herbicides, but a source other than atmospheric deposition was clearly relevant to detections of clopyralid in the wetland water-column. Although the types and levels of pesticides detected in the wetlands of the current study suggest that regional pesticide applications can contribute to pesticide surface water contamination following atmospheric transport and deposition, the greater frequency and concentrations of clopyralid, MCPA, and glyphosate detections in wetlands confirm that on-farm pesticide applications have a greater impact on on-site water quality. Beneficial management practices that reduce application drift, as well as rainfall or snowmelt runoff, will be important measures in reducing pesticide loading into wetlands situated in agricultural fields of the Prairie Pothole Region of North America.

Sulfide Induced Mobilization of Wetland Phosphorus Depends Strongly on Redox and Iron Geochemistry

Constructed and restored wetland soils play a key role in the cycling and retention of nutrients from polluted surface waters. Elevated SO42- loading from irrigated agriculture, however, has been shown to affect both the availability and mobility of P in wetland soils. This study investigated the biogeochemical cycling of Fe, S, and P in wetland pore waters and surface soils, to determine the role of sulfides in inducing mobilization of P in a constructed wetland in the Central Valley of California (CVC). Water column, pore-water, and solid-phase soil chemistry were measured at three sites, representing a range in wetland environmental conditions (i.e., sediment and nutrient loading, redox environment, and Fe–S–P geochemistry). High SO42- concentration and active SO42- reduction in wetland pore waters contributed to elevated pore water PO43- concentration (0.42 –1.29 mg L−1) via SO42- induced P mobilization. Although high concentrations of acid volatile sulfide (AVS) were present in the surface (0–5 cm) layer (: 6.5–10.3 μmol g−1), only ∼8% of the labile Fe pool was S2- bound, leaving sufficient Fe to buffer S2−. Additionally, surface soils experienced a three- to four-fold increase in P sorption index (PSI) under anaerobic versus aerobic conditions. Results from solid-phase chemical extractions and chemical equilibrium modeling showed that this higher PSI may be due to the conversion of crystalline Fe(III) oxides to poorly crystalline forms, the preservation of Fe(III) oxides due to kinetic constraints on microbial Fe reduction, and the formation of Fe(II) oxides. This study demonstrates that mineral dominated wetlands with sufficient Fe to buffer both dissolved sulfide and PO43- concentrations, can limit the effects of high SO42- loading and SO42- reduction on the mobilization and flux of soil PO43- to the wetland water column.

Carbon and nitrogen biogeochemistry of a Prairie Pothole wetland, Stutsman County, North Dakota, USA

The concentration and form of dissolved organic C (DOC) and N species (NH4+ and NO3-) were investigated as part of a larger hydrogeochemical study of the Cottonwood Lake Study Area within the Prairie Potholes region. Groundwater, pore water and surface wetland water data were used to help characterize the relationships between surface and groundwater with respect to nutrient dynamics. Photosynthesis and subsequent decomposition of vegetation in these hydrologically dynamic wetlands generates a large amount of dissolved C and N, although the subsurface till, derived in part from organic matter rich Pierre Shale, is a likely secondary source of nutrients in deeper groundwater. While surface water DOC concentrations ranged from 2.2 to 4.6 mM, groundwater values were 0.15 mM to 3.7 mM. Greater specific UV absorbance (SUVA254) in the wetland water column and in soil pore waters relative to groundwater indicate more reactive DOC in the surface to near-surface waters. Circumneutral wetlands had greater SUVA254, possibly because of variations in vegetation communities. The dominant inorganic nitrogen species was NH4+ in both wetland water and most ground water samples. The exceptions were 3 wells with NO3- ranging from 38 to 115 μM. Shallow groundwater wells (Well 28 and Well 13S) with greater connection to wetland surface water had greater NH4+ concentrations (1.1 mM and 120 μM) than other well samples (3–90 μM). Pore water nutrient chemistry was more similar to surface water than ground water. Nitrogen results suggest reducing conditions in both groundwater and surface water, possibly due to the microbial uptake of O2 by decaying vegetation in the wetland water column, labile organic C available in shallow groundwater, or the oxidation of pyrite associated with the subsurface.

Denitrification in Alluvial Wetlands in an Urban Landscape

Riparian wetlands have been shown to be effective "sinks" for nitrate N (NO3-), minimizing the downstream export of N to streams and coastal water bodies. However, the vast majority of riparian denitrification research has been in agricultural and forested watersheds, with relatively little work on riparian wetland function in urban watersheds. We investigated the variation and magnitude of denitrification in three constructed and two relict oxbow urban wetlands, and in two forested reference wetlands in the Baltimore metropolitan area. Denitrification rates in wetland sediments were measured with a 15N-enriched NO3- "push-pull" groundwater tracer method during the summer and winter of 2008. Mean denitrification rates did not differ among the wetland types and ranged from 147 +/- 29 microg N kg soil(-1) d(-1) in constructed stormwater wetlands to 100 +/- 11 microg N kg soil(-1) d(-1) in relict oxbows to 106 +/- 32 microg N kg soil(-1) d(-1) in forested reference wetlands. High denitrification rates were observed in both summer and winter, suggesting that these wetlands are sinks for NO3- year round. Comparison of denitrification rates with NO3- standing stocks in the wetland water column and stream NO3- loads indicated that mass removal of NO3- in urban wetland sediments by denitrification could be substantial. Our results suggest that urban wetlands have the potential to reduce NO3- in urban landscapes and should be considered as a means to manage N in urban watersheds.

The effects of river floodwaters on floodplain wetland water quality and diatom assemblages

We investigated the effects of river floodpulses on the water chemistry and diatom assemblages in a floodplain wetland. During the two year study period (November 2003-September 2005), the river and wetland exhibited three periods of surface hydrologic connectivity. The impacts of flooding depended on flood magnitude and duration. Both the long/high magnitude and short/high magnitude floods thoroughly mixed river and wetland waters, with conductivity, total nitrogen, and total phosphorus in the wetland decreasing to levels similar to the river. In contrast, the short/low magnitude flood did not mix water chemistry. Wetland conductivity, total nitrogen, and total phosphorus remained elevated. Changes in algal biomass followed changes in water chemistry with the high magnitude floods producing conditions unfavorable for algal growth. Algal biomass decreased in the wetland coinciding with the two high magnitude floods. Increases in algal biomass coincided with the short/low magnitude flood. Wetland and river water column diatom assemblages were dominated by periphytic taxa. The diatom assemblage in the river and wetland were distinct, except during the short/high magnitude flood. During this period, floodwaters brought diatoms into the wetland and both systems were dominated by planktonic centric taxa. Similar diatom taxa were observed in the wetland water column assemblage and the assemblage collected in settling chambers, although their relative abundances varied. Shifts in the settling diatom assemblage coincided with periods of flooding, indicating that river floodwaters leave a discernable signal within this assemblage. Our findings indicate that caution should be exercised when using diatom-based bioassessment in frequently flooded wetlands as the wetland diatom assemblage is influenced by river floodwaters and changes may depend on the duration and magnitude of flooding.

Factors that influence methylmercury flux rates from wetland sediments

Sediments are thought to be an important source of methylmercury (MeHg) to the water column of wetlands. We measured sediment MeHg pore water concentrations as a function of depth in four wetlands to determine the concentration gradient and used it determine sediment–water flux of MeHg. Fluxes of MeHg ranged from − 1.60 to 10.02 ng m − 2 day − 1 and were shown to be a function of 1) redox conditions at the sediment–water interface, 2) oxygen gradient above the sediment surface, 3) water temperature, and 4) pore water and water column-dissolved sulphide. MeHg water column concentration in each of the four wetlands was positively correlated with MeHg concentrations present in surface sediment and pore water, and with the calculated sediment–water MeHg flux rate. In addition to MeHg, ethylmercury (EtHg) was detected in the sediment in all four wetlands, but not in the pore water or the water column. EtHg levels in sediment exceeded MeHg concentrations in two of the wetlands. This demonstrates that Hg ethylation is a significant part of the Hg cycle in some aquatic environments.

The response of a freshwater wetland to long-term 'low level' nutrient loads: nutrients and water budget

Boney Marsh is a small constructed freshwater wetland located along thefloodplain of the Kissimmee River in south Florida, USA. River water, withaverage Tot-P concentrations of 0.052 mg l−1, Tot-N of 1.70 mgl−1, and Cl− of 15.95 mg l−1, wasdiverted through the marsh to quantify mass retention and fate.Comprehensive mass balance budgets for Tot-P, Tot-N, and Cl−were developed based on input (inflow, precipitation) and output (outflow,evapotranspiration, seepage). Cl−, as well asNa+, budgets indicated that groundwater accounted forapproximately 7% of the total water budget. Annual mass loadings toBoney Marsh were 0.5, 15.7, and 147.9 g m−2year−1 for Tot-P, Tot-N, and Cl−, respectively.Mean annual nutrient removal was estimated at 72% for Tot-P and34% for Tot-N, and P-assimilation capacity remained high andunchanged for the period of record. The subtropical marsh system accumulatedTot-P at a much higher rate than Tot-N, with averaged net sedimentationrates of 20.4 and 8.3 year−1, respectively. Boney Marsh netsedimentation coefficients were higher than lakes with similar depths. TheN:P mass ratio in the wetland water column increased during the period ofrecord, and was primarily due to a high P-sedimentation rate and a decliningN-sedimentation rate. The authors use the editor‘s suggestion forabbreviations.

Modelling nutrient retention of a freshwater coastal wetland: estimating the roles of primary productivity, sedimentation, resuspension and hydrology

A simulation model is developed for a coastal wetland of Lake Erie, one of the North American Laurentian Great Lakes, to determine the fate and retention of phosphorus in the wetland as water flows from an agricultural watershed through the wetland and into Lake Erie. Phosphorus retention in the wetland is a desirable to prevent eutrophication of Lake Erie. The model is developed with sub-models for hydrology, productivity, and phosphorus and a simulated barrier beach that can be opened or closed to Lake Erie. A simulation based on 1988 data is calibrated in step-wise fashion. Resuspension is a necessary inclusion in the model to predict phosphorus concentrations in the wetland's water column. Subsequent simulations are made for various combinations of increased flow from the watershed and changing Lake Erie water levels. Phosphorus retention varies from 17 to 52% with highest retention when high inflows are coupled with high lake levels. A nutrient budget constructed from the model for 1988 conditions showed marked differences with budgets developed from empirical models or field data. The model results suggest a near balance between inorganic sedimentation and resuspension but an active plankton sedimentation that results in a net phosphorus retention rate of 2.9 mg P m −2 day −1.