Maria E. Hernandez

Creating Wetlands: Primary Succession, Water Quality Changes, and Self-Design over 15 Years

The succession of vegetation, soil development, water quality changes, and carbon and nitrogen dynamics are summarized in this article for a pair of 1-hectare flow-through-created riverine wetlands for their first 15 years. Wetland plant richness increased from 13 originally planted species to 116 species overall after 15 years, with most of the increase occurring in the first 5 years. The planted wetland had a higher plant community diversity index for 15 years, whereas the unplanted wetland was more productive. Wetland soils turned hydric within a few years; soil organic carbon doubled in 10 years and almost tripled in 15 years. Nutrient removal was similar in the two wetlands in most years, with a trend of decreased removal over 15 years for phosphorus. Denitrification accounted for a small percentage of the nitrogen reduction in the wetlands. The wetlands were effective carbon sinks with retention rates of 1800–2700 kilograms of carbon per hectare per year, higher than in comparable reference wetlands and more commonly studied boreal peatlands. Methane emission rates are low enough to create little concern that the wetlands are net sources of climate change radiative forcing. Planting appears to have influenced carbon accumulation, methane emissions, and macrophyte community diversity.

Influence of Hydrologic Pulses, Flooding Frequency, and Vegetation on Nitrous Oxide Emissions from Created Riparian Marshes

The effects of hydrologic conditions, water quality gradients, and vegetation on nitrous oxide gaseous emissions were investigated in two identical 1-ha surface-flow created riverine wetlands in Columbus, Ohio, USA. For two years, both wetlands experienced seasonal (winter-spring) controlled hydrologic flood pulses followed by one year in which they received a steady flow rate of water. Nitrous oxide fluxes were quantified in a transverse gradient at different elevations (edge plots and high marsh plots with alternate wet and dry conditions, and low marsh plots and open water plots that were permanently flooded). The highest average of N2O fluxes was observed in high marsh plots (21.8 ± 2.5 μg-N m−2 h−1), followed by edge plots (12.6 ± 2.5 μg-N m−2 h−1), open water plots (9.9 ± 2.1 μg-N m−2 h−1), and low marsh plots (7.0 ± 4.8 μg-N m−2 h−1). Highest nitrous oxide fluxes were consistently observed in high marsh plots during summer when soil temperatures were ≥ 20°C. In permanently flooded plots without vegetation, nitrous oxide fluxes were low, regardless of flood-pulse conditions. In high marsh plots, water table remained near the soil surface one week after flooding, causing an increase in N2O fluxes (25.9 ± 13.9 μg-N m−2 h−1) compared with fluxes before (2.4 ± 6.4 2.2 μg-N m−2 h−1) and during (6.9 ± 2.2 μg-N m−2 h−1) flooding. In edge plots, nitrous oxide emissions increased during and after the flooding (11.3 ± 3.2 and 7.3 ± 3.3 μg-N m−2 h−1) compared with fluxes before the flood pulse (4.1 ±1.8 μg-N m−2 h−1). In low marsh and edge zones, no significant (P> 0.05) differences were observed in the seasonal N2O fluxes in the pulsing year versus steady-flow year. Spring N2O fluxes from high marsh plots were significantly (P=0.04) higher under steady-flow conditions (26.2 ± 5.5 μg-N m−2 h−1) than under pulsing conditions (9.6 ± 3.6 μg-N m−2 h−1), probably due to the water table near the surface that prevailed in those plots under steady flow condition. N2O fluxes were higher in plots with vegetation (39.6 ± 13.7 μg-N m−2 h−1) than in plots without vegetation (−3.6 ± 13.7 μg-N m−2 h−1) when plots were inundated; however, when no surface water was present, N2O fluxes were similar in plots with and without vegetation. Implications for large-scale wetland creation and restoration in the Mississippi River Basin and elsewhere for controlling nitrogen are discussed.

Ecosystem services of wetlands

Wetlands are among the most valuable ecosystems on the planet. As described in Mitsch and Gosselink (2015, pp. 3–4) and earlier editions: Although the value of wetlands for fish and wildlife protec...

Comparing soil carbon pools and carbon gas fluxes in coastal forested wetlands and flooded grasslands in Veracruz, Mexico

Wetlands play an important role in carbon cycling. Perturbation of these ecosystems by human activities causes changes in the soil carbon storage and carbon gaseous emissions. These changes might have important repercussions for global warming. The aim of this study was to investigate whether the conversion of freshwater forested wetlands (FW) to flooded grasslands (FGL) has affected soil carbon cycling. Soil carbon pools and soil organic carbon (SOC) fractions (water-soluble carbon (WSC), hot-water-soluble carbon (HWSC), and HCl/HF soluble carbon (HCl/HF-SC)) were compared between FW and FGL. Additionally, the seasonal dynamic of methane (CH4) and carbon dioxide (CO2) fluxes were monitored in both ecosystems located in the coastal plain of Veracruz State Mexico. In FW, soil organic matter (SOM) concentrations were significantly (P ≤ 0.05) higher than FGL. Soil bulk density (BD) was slightly higher in FGL than FW but it was not significantly different (P ≥ 0.05). The average of WSC and HWSC in FW were not significantly (P ≤ 0.05) different. Total carbon pools (44 cm deep) were not significantly different (P = 0.735). During the dry season, CO2 fluxes (26.38 ± 4.45 g m−2 d−1) in FGL were significantly higher (P = 0.023) than in FW (14.36 ± 5.77 g m−2 d−1). During the rainy and windy seasons, both CH4 and CO2 fluxes were significantly higher (P = 0.000 and P = 0.001) in FGL compared with FW. It was concluded that converting FW to FGL causes loss of SOC and increases carbon gaseous fluxes.

Removal of selected organic pollutants and coliforms in pilot constructed wetlands in southeastern Mexico

The removal efficiency of selected emerging pollutants, total (TotCol) and faecal (FecCol) coliforms in surface (SF) and subsurface (SSF) flow constructed wetlands (CWs) was compared. The pilot plant (located in southeastern Mexico) consisted of eight CWs: four with SF and four with SSF. Two cells of each type were planted with Typha sp. and two were left without plant as controls. CWs were fed with water from Sordo river, which receives untreated urban sewage and industrial wastewaters. Water samples from river and outflow from each CW were collected in four sampling campaigns, they were filtered, extracted and analysed by GC/MS. Redox potential (Eh) was measured in all cells. The following pollutants were identified and quantified: Caffeine, CAF; Galaxolide, GAL; Methyl dihydrojasmonate, MDHJ; Linear alkylbenzenes, LAB; Butylated hydroxytoluene, BHT; Surfynol 104, SSURF; Alkylphenols, AP; 4-alkylphenol monoetoxylates, APE; Parsol, PAR. Typical removals of studied compounds were attained with slightly better results in SSFCW. A multiple linear regression analysis considering Eh, time, influent pollutant concentration (C0) and the presence of plants and filtering media (Fmedia) as independent variables showed that Eh has a significant influence in the removal for almost all the studied compounds with the exception of BHT and AP. C0 influences removal processes with the exception of coliforms. A significant influence of Fmedia in the BHT and PAR removal is observed, also positive for AP, APE, CAF, LAB and GAL in decreasing order. The effect of plants is positive for PAR (significant), GAL, CAF, BHT and MDHJ. SURF has a distinct behaviour with a negative coefficient for its C0. For TotCol and FecCol the most significant effects are Eh and time. This may be related to the fact that predation by aerobic microbial communities may be the predominant factor in their removal and the development of these microbial communities with time.

Mangrove and Freshwater Wetland Conservation Through Carbon Offsets: A Cost-Benefit Analysis for Establishing Environmental Policies

Mexico has extensive coastal wetlands (4,243,137 ha), and one of its most important sites is the Alvarado Lagoon System, located in the Papaloapan River Basin on the Gulf of Mexico. The land cover dedicated to livestock and sugarcane has increased: by 25 % in 2005 and 50 % in 2010, with a loss of wetland vegetation and the carbon that it stores. We found that the Net Present Value of mangrove carbon offsets profit is equal to

Hydrology, Soil Carbon Sequestration and Water Retention along a Coastal Wetland Gradient in the Alvarado Lagoon System, Veracruz, Mexico

5822.71, that of broad-leaved marshes is

Creating riverine wetlands: Ecological succession, nutrient retention, and pulsing effects

7958.86, cattail marshes

Denitrification in created riverine wetlands: Influence of hydrology and season

5250.33, and forested wetlands

Denitrification potential and organic matter as affected by vegetation community, wetland age, and plant introduction in created wetlands.

8369.41 per hectare, during a 30-year-carbonoffset contract. However, the opportunity cost from conserving wetland instead of growing sugarcane is positive according to REDD+ methodology, e.g., broad-leaved marsh conservation ranged from