No abstract

At the present rate of loss (since 1990), half of the remaining wetlands worldwide will be developed within ~140 years, underscoring the importance of improving the creation and restoration of wetlands. Organic amendments are sometimes used during wetland creation. To evaluate the effectiveness of adding organic amendments we used a combined numerical method to assign “scores” on five categories of evaluation metrics: plant growth, soil properties, carbon accrual, denitrification, and anaerobic processes (e.g. redox potential). We found that amendments identified as “topsoil” scored measurably higher and had consistently more positive values with fewer negative results compared to amendments identified as “allochthonous organic matter” (alOM). Organic amendments had about the same effect on soils with low soil organic carbon (<2.5%) compared to soils richer in organic carbon. Organic amendments are not uniformly effective, and in some cases may have negative side effects. For example, alOM often resulted in a loss of plant diversity. These outcomes along with site conditions should be evaluated before using organic amendments.

Indicator of Reduction In Soils (IRIS) technology is an important tool for identifying hydric soils, but it does not allow the user to monitor in real time. IRIS uses metal‐oxide coatings on a polyvinyl chloride surface that, under anaerobic conditions, are removed to varying degrees over a 4‐wk incubation period, during which time the user is not cognizant of the outcome. We document the viability of an alternative IRIS approach using clear‐IRIS tubes, made from cellulose acetate butyrate, that can be continuously monitored in situ with a Wi‐Fi–enabled video camera. This work shows that IRIS and clear‐IRIS tubes are statistically equivalent. Manganese‐oxide coated clear‐IRIS tubes correlated well with IRIS tubes (r = .79) and ferrous‐oxide had a high correlation (r = .97). A time‐series analysis showed that rain‐driven soil saturation induced IRIS metal‐oxide reduction and controlled the rate. Clear‐IRIS tubes enable remote sensing of metal‐oxide removal over time.

Abstract. Methane (CH4) emissions are a potent contributor to global warming, and wetlands can be a significant CH4 source. In a microcosm study, we evaluated how the practice of amending soils with organic matter as part of wetland restoration projects may affect CH4 production potential. Organic amendments including hay, manure, biosolids, composted yard waste, and wood mulch were evaluated at three different levels. Using 1 L glass microcosms, we measured the production of biogenic gases over 60 d in two soils designated by texture: a sandy loam (SL) and a sandy clay loam (SCL). Fresh organic amendments increased CH4 production, leading to potentially higher global warming potential and wetland C loss, and CH4 production was more pronounced in SL. We observed biogenic gas production in two sequential steady-state phases: Phase 1 produced some CH4 but was mostly carbon dioxide (CO2), followed by Phase 2, 2 to 6 weeks later, with higher total gas and nearly equal amounts of CH4 and CO2. If this is generally true in soils, it may be appropriate to report CH4 emissions in the context of inundation duration. The CH4 from the SCL soil ranged from 0.003–0.8 cm3kg-1d-1 in Phase 1 to 0.75–28 cm3kg-1d-1 in Phase 2 and from SL range from 0.03–16 cm3kg-1d-1 in Phase 1 to 1.8–64 cm3kg-1d-1 in Phase 2. Adding fresh organic matter (e.g., hay) increased concentrations of ferrous iron (Fe2+), whereas in some cases composted organic matter decreased both Fe2+ concentrations and CH4 production. Methanogenesis normally increases following the depletion of reducible Fe; however, we observed instances where this was not the case, suggesting other biogeochemical mechanisms contributed to the shift in gas production.

Abstract. Methane (CH4) emissions are a potent contributor to global warming and wetlands can be a significant CH4 source. In a microcosm study we evaluated how the practice of amending soils with organic matter as part of wetland restoration projects may affect CH4 production potential. Organic amendments including hay, manure, biosolids and compost were evaluated at three different levels. Using 1-liter glass microcosms, we measured the production of biogenic gases over 60 days in two soils, a sandy loam (SL) and a sandy clay loam (SCL). Fresh organic amendments increased CH4 production, leading to potentially higher global warming potential and wetland C loss, particularly in sandy soils. Organic amendments increased biogenic gas production in two sequential steady state phases: Phase 1 produced some CH4 but was mostly carbon dioxide (CO2) followed by Phase 2, two to six weeks later, with much higher total gas and nearly equal amounts of CH4 and CO2. The CH4 from the SCL soil ranged from 0.003–0.8 cc/Kg/day in Phase 1 to 0.75–28 in Phase 2 and the SL range from 0.03–16 cc/Kg/day in Phase 1 to 1.8–64 in Phase 2. We had set out to identify an organic amendment that would promote iron (Fe) reduction without excess CH4, but amendments were not needed to produce Fe and make soils hydric. Adding fresh organic matter (hay) resulted in both excess Fe2+ and CH4 whereas composted amendments had little effect. The potential for excess methanogenesis should be taken into account when considering organic matter amendments in mitigation wetlands.