Leaf Production of Sabal minor (Jacq.) Pers. in a Louisiana Forested Wetland

Leaf production of Sabal minor (Jacq.) Pers. (dwarf palmetto) was estimated at two sites in a forested wetland near Thibodaux, Louisiana during a 1-year period. One site was flooded throughout the study period, while the other was a drier bottomland hardwood ridge, higher in elevation by 40 em. Palmetto leaves were tagged and measured for total length during May 1989 and May 1990 in two plots within each site. Information on plant trunk height, plants/m2, leaves (fronds)/ plant, and leaf biomass was also obtained. Significant differences were noted for all parameters tested between plants on the flooded site and those on the ridge site. Leaf production was highest in the ridge site (68 g/m2/yr) and lowest in the flooded site (48 g/m2/yr). Most leaves died during the 1-year study period, Upon turning brown, leaves became brittle and broke apart rapidly. This may represent an important source of organic matter to the system that past studies have not documented

Could Wild Pigs Impact Water Quality and Aquatic Biota in Floodplain Wetland and Stream Habitats at Congaree National Park, South Carolina?

2008 S.C. Water Resources Conference - Addressing Water Challenges Facing the State and Regio

Deformation and crystallization of Zr-based amorphous alloys in homogeneous flow regime

The purpose of this study is to experimentally investigate the interaction of inelastic deformation and microstructural changes of two Zr-based bulk metallic glasses (BMGs): Zr_(41.25)Ti_(13.75)Cu_(12.5)Ni_(10)Be_(22.5) (commercially designated as Vitreloy 1 or Vit1) and Zr_(46.75)Ti_(8.25)Cu_(7.5)Ni_(10)Be_(27.5) (Vitreloy 4, Vit4). High-temperature uniaxial compression tests were performed on the two Zr alloys at various strain rates, followed by structural characterization using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Two distinct modes of mechanically induced atomic disordering in the two alloys were observed, with Vit1 featuring clear phase separation and crystallization after deformation as observed with TEM, while Vit4 showing only structural relaxation with no crystallization. The influence of the structural changes on the mechanical behaviors of the two materials was further investigated by jump-in-strain-rate tests, and flow softening was observed in Vit4. A free volume theory was applied to explain the deformation behaviors, and the activation volumes were calculated for both alloys

Effects of Wing and Nacelle Modifications on Drag and Wake Characteristics of a Bomber-Type Airplane Model

An investigation of a model of a large four-engine bomber was conducted in the Langley 19-f'oot pressure tunnel to determine the effects of several wing and nacelle modifications on drag characteristics and air flow characteristics at the tail. Leading-edge gloves, trailing-edge extensions, and modified nacelle afterbodies were tested individual ly and in combination. The effects of the various modifications were determined by force tests, tuft observations, and turbulence s1ITveys in the region of the tail. Tests were made with fixed and natural transition on the wing and with propellers operating and propellers off. Most of the tests were con- ducted at a Reynolds number of approximately 2.6 x 106. The results indicated that application of certain of the modifications provided worth-while improvements in the characteristics or the model. The flow over the wing and flaps was improved, the drag was reduced, and the turbulence in the region of the tail was reduced. Trailing-edge extensions were the most effective individual modification in improving the flow over the wing with wing flaps neutral, cowl and intercooler flaps clos ed. Modified nacelle afterbodies were the most effectiv8 individual edification in reducing drag with either fixed or natural transition on the wing; however, trailin6-edge extensions were slightly more effective with fixed transition. Combinations of either leading or trailing-edge extensions and modified afterbodies were more effective than either modification alone. With cowl and intercooler flaps open, trailing-edge extensions with modified afterbodies provided substantial improvement in flow and drag characteristics. With wing flaps deflected, enclosing the flap behind the inboard nacelle within an extended afterbody or cutting the flaps at the nacelle appeared. to be the most promising methods of improving the f low over the flaps and the tail. Although the results of hot-wire-anenometer surveys were not conclusive in regard to buffeting characteristics, the modifications did educe the turbulence at the tail with wing flaps both neutral and deflected. The modifications, as a rule, were favorable to maximum lift. Appreciable reductions in longitudinal stability of the model were caused by addition of leading -edge gloves and tr ailing -edge extensions

Effects of salinity and wet–dry treatments on C and N dynamics in coastal-forested wetland soils: Implications of sea level rise

Forested wetlands dominated by baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) are commonly found in coastal regions of the southeastern United States. Global climate change and in particular sea level rise will alter the frequency and magnitude of wet/dry periods and salinity levels in these ecosystems. Soil microcosm experiments were set up to identify the effects of water level variations (0.4–3.0 g-water g-soil−1) and salinity changes (0, 1 and 5 ppt of NaCl) on greenhouse gas emissions (CH4, CO2, and N2O) and dissolved organic carbon (DOC) characteristics from forested wetland soils. Our results indicate that, the effect of water level was much greater than salt intrusion on C and N cycling. Wet–dry treatments significantly decreased DOC production and total CH4-C loss, aromatic and humic-like substance compounds in DOC were increased in both flooding and wet–dry treatments after 60-d incubation. The molecular weight (MW) of DOC, as indicated by E2/E3 ratio and spectral slope, after flooding treatments was higher than that in wet–dry treatments. A first order kinetic model showed there was a positive linear correlation (r2 = 0.73) between CO2 emission rate and DOC concentration which indicated that CO2was mainly generated from DOC. An exponential kinetic model was applied to describe the correlation between CH4 emission rate and DOC concentration (r2 = 0.41). This study demonstrates that an increase in salinity, and in particular variations in wet–dry cycles, will lead to changes in the formation of climate-relevant greenhouse gases, such as CH4, CO2, and N2O

Processes Contributing to Resilience of Coastal Wetlands to Sea-Level Rise

The objectives of this study were to identify processes that contribute to resilience of coastal wetlands subject to rising sea levels and to determine whether the relative contribution of these processes varies across different wetland community types. We assessed the resilience of wetlands to sea-level rise along a transitional gradient from tidal freshwater forested wetland (TFFW) to marsh by measuring processes controlling wetland elevation. We found that, over 5 years of measurement, TFFWs were resilient, although some marginally, and oligohaline marshes exhibited robust resilience to sea-level rise. We identified fundamental differences in how resilience is maintained across wetland community types, which have important implications for management activities that aim to restore or conserve resilient systems. We showed that the relative importance of surface and subsurface processes in controlling wetland surface elevation change differed between TFFWs and oligohaline marshes. The marshes had significantly higher rates of surface accretion than the TFFWs, and in the marshes, surface accretion was the primary contributor to elevation change. In contrast, elevation change in TFFWs was more heavily influenced by subsurface processes, such as root zone expansion or compaction, which played an important role in determining resilience of TFFWs to rising sea level. When root zone contributions were removed statistically from comparisons between relative sea-level rise and surface elevation change, sites that previously had elevation rate deficits showed a surplus. Therefore, assessments of wetland resilience that do not include subsurface processes will likely misjudge vulnerability to sea-level rise