The relationship between methane emissions and salinity is not well understood in tidal marshes, leading to uncertainty about the net effect of marsh conservation and restoration on greenhouse gas balance. We used published and unpublished field data to investigate the relationships between tidal marsh methane emissions, salinity, and porewater concentrations of methane and sulfate, then used these relationships to consider the balance between methane emissions and soil carbon sequestration. Polyhaline tidal marshes (salinity >18) had significantly lower methane emissions (mean ± sd=1±2 gm −2 yr −1) than other marshes, and can be expected to decrease radiative forcing when created or restored. There was no significant difference in methane emissions from fresh (salinity=0-0.5) and mesohaline (5-18) marshes (42±76 and 16±11 gm −2 yr −1, respectively), while oligohaline (0.5-5) marshes had the highest and most variable methane emissions (150±221 gm −2 yr −1). Annual methane emissions were modeled using a linear fit of salinity against log-transformed methane flux ( logðCH 4 Þ ¼ À0:056 Â salinity þ 1:38; r 2 = 0 . 5 2 ; p < 0.0001). Managers interested in using marshes as greenhouse gas sinks can assume negligible methane emissions in polyhaline systems, but need to estimate or monitor methane emissions in lower-salinity marshes.

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areas contract and expand within and between events. Variable source areas are a function of topography, The targeting of critical surface runoff-producing zones should soils, geology, climate, and management. Within VSA account for the influence of subsurface soil characteristics. In this study we assessed the runoff response of contrasting colluvial and hydrology, surface runoff generation is classified as eiresidual soils. The study was conducted along two hillslopes within a ther infiltration excess or saturation excess (Sklash, 39.5-ha mixed land use watershed in Pennsylvania. Six sites (four 1990). Infiltration excess, or Hortonian overland flow, colluvial, two residual) were monitored for runoff, hydraulic head, occurs when rainfall intensities exceed the infiltration water table depth, and soil water content. A total of 111 rainfall events capacity of a soil. Variable infiltration capacities in the were monitored during the periods of July to December 2000, April landscape cause partial areas of infiltration-excess surto December 2001, and April to December 2002. Two high-intensity face runoff (Betson, 1964). Saturation excess occurs (5-min peak Ͼ 8 cm h Ϫ1) events had return periods of 2.5 and 4 yr. when the water table rises to saturate the soil profile, The colluvial soils are somewhat poorly and moderately well drained filling storage zones and minimizing infiltration capacwith fragipans and high clay content (37-44%) argillic horizons (fine, ity. Ideally, P management strategies should differ demixed, semiactive, mesic Aquic Fragiudalfs); the residual soils are well drained with moderate clay content (24%) argillic horizons (fine-pending on the dominant surface runoff generation loamy, mixed, semiactive, mesic Typic Hapludults). Across all events, mechanism in a watershed. An infiltration-excess-based overall runoff yields averaged 2.4% from the four colluvial sites and approach should target soils with a low infiltration ca-0.01% from the two residual sites. The two colluvial sites with the pacity, while a saturation-excess-based strategy should greatest runoff production were located at the base of a primarily target near-stream and other zones that are subject to colluvial hillslope. The largest events at these sites occurred during surface saturation (Gburek et al., 1996) regardless of periods of surface saturation (soil surface to a depth of at least 30 cm). infiltration capacity at these sites. These results suggest that nonwinter P management for these residual The saturation-excess mechanism has been studied soils should focus on rare, large events. Nutrient management planning primarily under forest and grassland vegetation (Bonell, could be improved if runoff estimation methods were to better inte-1993). In most temperate forested landscapes, infiltragrate information on subsurface and upslope soil hydrologic properties.

Particulate organic matter (POM), an established soil quality indicator, is too costly for routine testing by analytical labs. Chemical oxidation of labile soil organic matter is less costly and may prove to be an equally effective indicator. The objectives of this study were to test the relationship between POM and chemically labile organic matter (CLOM) and to evaluate the effects of soil management on POM and CLOM. The study was conducted within a long‐term crop rotation × fertility treatment study in central Pennsylvania. Crop rotation sequences were continuous corn (Zea mays L.), corn–soybean [Glycine max (L.) Merr.], 4 yr of corn followed by 4 yr of alfalfa hay (Medicago sativa L.), and corn–oat (Avena sativa L.)–winter wheat (Triticum aestivum L.)–2 yr of red clover hay (Trifolium pratense L.). Fertilizer treatments were mineral fertilizer, N‐based liquid dairy manure, and P‐based liquid dairy manure. A significant linear relationship between POM‐C and CLOM‐C treatment means was observed (r2 = 0.74). Both POM‐C and CLOM‐C concentrations were greatest for manure‐based fertility treatments and for crop rotations receiving the most frequent applications of manure. Only CLOM‐C, however, distinguished between the N‐based and P‐based manure treatments. Further development of CLOM‐C as a soil quality indicator may yield a reliable, cost‐effective soil quality management tool.

This study investigated the effectiveness of bioretention as a stormwater management practice using repetitive bioretention columns for phosphorus removal. Bioretention media, with a higher short-term phosphorus sorption capacity, retained more phosphorus from infiltrating runoff after 3 mg/L phosphorus loading. A surface mulch layer prevented clogging after repetitive total suspended solids input. Evidence suggests that longterm phosphorus reactions will regenerate active short-term phosphorus adsorption sites. A high hydraulic conductivity media overlaying one with low hydraulic conductivity resulted in a higher runoff infiltration rate, from 0.51 to 0.16 cm/min at a fixed 15-cm head, and was more efficient in phosphorus removal (85% mass removal) than a profile with low conductivity media over high (63% mass removal). Media extractions suggest that most of the retained phosphorus in the media layers is available for vegetative uptake and that environmental risk thresholds were not exceeded. Water Environ. Res., 79, 177 (2007).

Bioretention is a low-impact technology used for the treatment of stormwater runoff in developed areas. The fates of mineral nitrogen compounds in two bioretention columns (RP1 and RP2) with different media-layering characteristics were investigated under multiple loadings of simulated urban runoff. The immediate capture of nitrogen was evaluated, with nitrogen transformation reactions that occurred during the drying periods between rainfall events. A greater proportion of ammonium was removed from runoff in RP2 (68 6 16%), which had a high permeability layer over a lower permeability layer, than in RP1 (12 6 6%), which had the inverse configuration. Both column systems demonstrated nitrate export (9 6 32% and 54 6 22% greater than input for RP1 and RP2, respectively), attributed to washout of nitrate resulting from nitrification processes between runoff loading events. Bioretention media with a less permeable bottom soil layer could form an anoxic/anaerobic zone for promoting nitrification/denitrification processes. Water Environ. Res., 79, 2404Res., 79, (2007.

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