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Table Levels (table + level)
Selected AbstractsSeed dispersal in a polder after partial tidal restoration: Implications for salt-marsh restorationAPPLIED VEGETATION SCIENCE, Issue 1 2008Armel Dausse Abstract Question: The vegetation in a polder after partial tidal restoration does not resemble the targeted salt-marsh vegetation. Is this difference in vegetation due to lack of dispersal or unsuitable abiotic conditions? What could be done for a better restoration of the site? Location: Northwestern France. Methods: Seeds were trapped at the single inlet of the polder with a 200- , m mesh net to estimate inputs of seeds from the bay. In parallel, seed dispersal was studied in the polder by placing Astroturf® seed traps on the surface of the sediment at three different elevations in three distinct areas. Abiotic conditions such as flooding frequency, water table level and soil salinity were monitored. Results: All but one species from the adjacent salt marshes were trapped at the inlet. Not all of these species were on the seed traps inside the polder. Seed dispersal was not homogeneous in the polder and seed trap content mostly discriminated in function of their elevation. Salinity and water logging at the bottom of the slope were very high compared to tolerance of most halophytes but decreased rapidly higher up the slope. Conclusions: The development of salt marsh target species is highly restricted by limited hydrochory inside the polder but also by unfavourable soil conditions induced by the actual hydrological regime. Halophytes are excluded at the bottom of the slope by abiotic conditions and out-competed by sub-halophytes higher up. In order to restore salt marsh vegetation inside the polder, a larger opening should be induced in order to increase the flooded surface, and diminish water logging and flooding frequencies. [source] Investigation of an onsite wastewater treatment system in sandy soil: Site characterization and fate of anionic and nonionic surfactantsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2002Allen M. Nielsen Abstract This study reports on the fate of linear alkylbenzene sulfonate (LAS), alcohol ethoxylate (AE), and alcohol ether sulfate (AES) surfactants in a home septic system near Jacksonville (FL, USA) that has been used since 1976. The drainfield at this site resides in fine sand (<6% silt and clay) with an unsaturated zone that ranges from 0 to 1.3 m. During the wettest times of the year, it is likely that effluent from the septic system passes directly into the groundwater without exposure to an unsaturated zone of soil. Groundwater was collected during two sampling events, representing seasonal high and low groundwater table levels, and analyzed for the surfactants LAS, AES, and AE. During the wet season, the unsaturated zone was approximately 0.01 m beneath the drainfield. During the dry season, the unsaturated zone was about 0.4 m below the drainfield. Alcohol ethoxylate was not detected in any groundwater samples during either sampling. Alcohol ether sulfate was not found in the dry season sampling, but traces of AES had migrated downgradient about 4.7 m horizontally and 1.8 m vertically in the wet season. Linear alkylbenzene sulfonate was detected in some dry season samples and had moved downgradient some 11.7 m horizontally and 3.7 m vertically in the wet season. These observations demonstrate that these surfactants were removed to a great extent; otherwise, they would have traveled more than 260 m downgradient, which is the calculated distance that a conservative tracer like bromide would have moved downgradient over the life of the system. The most likely removal mechanisms for these surfactants were biodegradation and sorption. Therefore, this study indicates that LAS, AE, and AES are readily removed from groundwater in soils below septic system drainfields even in situations with minimal unsaturated soil zones. [source] Freshwater availability as the constraining factor in the Middle Paleoindian occupation of North-Central FloridaGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 3 2009David K. Thulman The locations of reliable surface water exposures during the Middle Paleoindian period (10,800,10,200 14C yr B.P.) in north-central Florida are reconstructed and compared to the concentrations of Middle Paleoindian projectile points. Estimates of water table levels and surface water flow in Florida's karst geology confirm prior climate reconstructions for that time indicating the area was arid and supported a xeric ecology in most upland locales. Surface water flow data from recent extreme droughts and water table estimations are used to identify the areas of highest probability for surface water availability. The distribution of the highest concentrations of Middle Paleoindian points correlates with the areas of highest probability, indicating that scarce surface water sources were the strongest constraint on occupation location during that time. © 2009 Wiley Periodicals, Inc. [source] Regional-scale measurements of CH4 exchange from a tall tower over a mixed temperate/boreal lowland and wetland forestGLOBAL CHANGE BIOLOGY, Issue 9 2003Cindy Werner The biosphere,atmosphere exchange of methane (CH4) was estimated for a temperate/boreal lowland and wetland forest ecosystem in northern Wisconsin for 1997,1999 using the modified Bowen ratio (MBR) method. Gradients of CH4 and CO2 and CO2 flux were measured on the 447-m WLEF-TV tower as part of the Chequamegon Ecosystem,Atmosphere Study (ChEAS). No systematic diurnal variability was observed in regional CH4 fluxes measured using the MBR method. In all 3 years, regional CH4 emissions reached maximum values during June,August (24±14.4 mg m,2 day,1), coinciding with periods of maximum soil temperatures. In 1997 and 1998, the onset in CH4 emission was coincident with increases in ground temperatures following the melting of the snow cover. The onset of emission in 1999 lagged 100 days behind the 1997 and 1998 onsets, and was likely related to postdrought recovery of the regional water table to typical levels. The net regional emissions were 3.0, 3.1, and 2.1 g CH4 m,2 for 1997, 1998, and 1999, respectively. Annual emissions for wetland regions within the source area (28% of the land area) were 13.2, 13.8, and 10.3 g CH4 m,2 assuming moderate rates of oxidation of CH4 in upland regions in 1997, 1998, and 1999, respectively. Scaling these measurements to the Chequamegon Ecosystem (CNNF) and comparing with average wetland emissions between 40°N and 50°N suggests that wetlands in the CNNF emit approximately 40% less than average wetlands at this latitude. Differences in mean monthly air temperatures did not affect the magnitude of CH4 emissions; however, reduced precipitation and water table levels suppressed CH4 emission during 1999, suggesting that long-term climatic changes that reduce the water table will likely transform this landscape to a reduced source or possibly a sink for atmospheric CH4. [source] | |||||||||||||