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The accurate and timely identification of soil morphological indicators of anaerobic conditions is critical for the proper documentation of hydric soils and prolonged soil saturation. Iron monosulfide (FeS) forms under anaerobic conditions following complexation of Fe and reduced S to form insoluble, black to very dark gray (value ≤ 4, chroma ≤ 1) concentrations and/or soil coatings. These features are observable as soft masses or pore linings or are dispersed throughout the soil matrix in the form of concentrated zones of FeS. Variation in soil and environmental conditions result in a wide range of FeS expression from <1 to 100% coverage of the soil matrix. We seek to explain the environmental conditions required for FeS formation and describe diagnostic methods to document FeS in a field setting. Field identification of FeS can be performed through an oxidized color change test (either ambient air or the application of 3% H 2 O 2 ) and via the evolution of H 2 S after the application of 1 M HCl. The use of Indicator of Reduction in Soil (IRIS) devices provides additional supporting evidence of S reducing conditions in soils and thus environmental conditions conducive to FeS formation when other necessary constituents are present. The concepts and techniques outlined in this review can serve as useful resources to inform our understanding of belowground redox chemistry and facilitate the accurate identification of FeS in wet soil environments.

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Globally, approximately 10–20% of peatlands have been drained for agricultural purposes. A strategy to protect peatlands and mitigate carbon dioxide (CO2) emissions, while continuing agricultural production, is the use of intermittent flooding and drainage. A potential drawback of this strategy could be increases in methane (CH4) and nitrous oxide (N2O) emissions. The objective of this study was to compare greenhouse gas (GHG) emissions from peatlands under various flooding–drainage cycles. A laboratory study was performed using intact soil cores subjected to different durations of flooding and drainage for 6 months. Average daily emissions of CO2 and N2O were significantly higher (P < 0.001) under drained (667 ± 37 mg CO2–C m−2 d−1 and 135 ± 19 μg N2O–N m−2 d−1) than flooded conditions (86 ± 6 mg CO2–C m−2 d−1 and 48 ± 2 μg N2O–N m−2 d−1). Methane emissions were not influenced by drained/flooded conditions, with an average rate of 116 ± 11 μg CH4–C m−2 d−1. Peaks of CH4 and N2O emissions were observed after flooding events and lasted less than 24 h. The peak emissions were approximately 8 and 19 times higher than the mean CH4 and N2O emissions, respectively. Carbon dioxide was the dominant component of GHGs, irrespective of hydrologic regime, accounting for more than 92% of overall global warming potential. Global warming potential was inversely proportional to the flooding period, indicating that prolonging the flooding period of peatlands would help mitigate soil oxidation and GHG emissions and enhance sustainability of these agricultural peatlands.

The Caernarvon Diversion meters Mississippi River water into coastal marshes of Breton Sound, Louisiana (29°51'40.15" N, 89°54'43.62" W). Elevated levels of N in river water have sparked concerns that nutrient-loading may affect marsh resilience and belowground biomass, as evidence from several marsh fertilization studies suggests. These concerns have resulted from casual observations that fresh and hrackish Breton Sound marshes, closest to the Mississippi River levee suffered extensive damage from Hurricane Katrina. The goal of this study was to determine the fate of nitrate (the dominant inorganic N form in the Mississippi River) in Breton Sound Estuary marshes. We hypothesized that the majority of the nitrate will be removed by denitrification and that nitrate-loading will not affect helowground biomass over several months of loading. To test this hypothesis, a mass balance study was designed using i^N-Iaheled nitrate. Twelve plant-sediment cores were collected from a brackish marsh and six cores received deionized water (control), while another six (treatment) received 2 mg L' of ^^N-labeled potassium nitrate twice a week for 3 mo. A set of three control and treatment cores were destructively sampled after 3 mo and analyzed for ^^N in the aboveground and belowground biomass and the soil. The N isotopie label allowed for a mass balance to distinguish N removal pathways, including denitrification, surface algae uptake, soil microhial uptake and incorporation into aboveground and helowground hiomass of the macrophytes. Twelve hours after the addition of the 2 mg N L"^ water, nitrate levels were typically below detection. Approximately 64% of all added labeled nitrate was unaccounted for which suggests gaseous loss. The remaining ^^N was incorporated in plant and soil compartments, the majority being the aboveground component. There were no significant differences in belowground biomass production between the nitrate loaded and the control cores after 3 mo.

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Core Ideas The α,α'‐dipyridyl dye displayed a ferrous iron detection limit of 0.31mg L−1. Liquid α,α' dipyridyl dye and indicator test strips exhibited similar reactivity. Light and heat exposure led to potential α,α'‐dipyridyl dye degradation. The α,α'‐dipyridyl dye provides a tool for hydric soil and wetland identification. Chemical dyes, including α,α'‐dipyridyl, can be used to identify ferrous iron in hydric soil studies and aid in conducting wetland delineations. Indicator test strips containing α,α'‐dipyridyl have been developed; however, limited data addresses the reliability of indicator test strips and questions remain regarding potential degradation of α,α'‐dipyridyl in liquid and paper formulations. Laboratory studies found ferrous iron detection limits of 0.31 mg L−1 using both liquid and indicator test strips. The liquid dye and indicator test strips displayed similar reactivity in five soils under simulated field conditions. Results suggest that indicator test strips provide a useful tool for ferrous iron detection across a range of soil conditions. Degradation studies indicate that both liquid dye and indicator strips were impacted by light and heat exposure, with a loss of reactivity observed within as few as 3 d under extreme conditions. Maintaining both liquid dye and indicator strips in cool, dark conditions and testing reactivity with laboratory solutions will ensure the reliability of α,α'‐dipyridyl results.

No abstract