A comparative study of the mollusc communities of two oligohaline intertidal marshes: Spatial and temporal distribution of abundance and biomass     

T. Dale Bishop  Courtney T. Hackney 《Estuaries and Coasts》1987,10(2):141-152

Molluscs were collected monthly for a year from two low salinity (0–9‰) intertidal marshes dominated by the macrophytesJuncus roemerianus orSpartina cynosuroides in St. Louis Bay, Mississippi. TheJuncus marsh had lower soil organic matter, higher pH and was more frequently inundated than theSpartina marsh. Eight species of gastropods were abundant and dominated in the higherSpartina marsh, while three bivalve species were dominant in theJuncus marsh. Of the common species,Succinea ovalis, Vertigo ovata andDeroceras laeve are gastropods of terrestrial origins;Geukensia demissa granosissima (bivalve) andMelampus bidentatus (gastropod) are euryhaline estuarine species and the remaining gastropods (Detracia floridana, Littoridinops palustris, Onobops jacksoni) and bivalves (Polymesoda caroliniana, Cyrenoida floridana) are brackish species. Most species were capable of continuous recruitment (based on size class analysis), but exhibited peak activity in particular seasons. Bivalve abundance correlated to temperature, and gastropod abundance was negatively correlated to soil pH. These correlations reflect the influence of flooding regime at the two sites. Biomass was greater in theJuncus marsh because of the increased presence of the large-bodiedPolymesoda. Polymesoda represented >90% and >50% of the total biomass in theJuncus andSpartina (except summer) marshes respectively but always <-5% of the individuals collected. Gastropod biomass was the same in both marshes. Species diversity (H′) was greater inSpartina except for summer months. TheJuncus marsh always exhibited greater species richness. Evenness (J′) determined seasonal changes in diversity (H′). Similarity values (C_z) were always quite low, with highest values in spring In contrast to faunal studies from Gulf and East Coast salt marshes, we found 1) fewer species, 2) communities comprised of unique species combinations, 3) greatest mean densities in summer, and 4) potentially less productivity by the molluscs of our sites. These mollusc communities exhibit structural characteristics that emphasize the unique ecotonal nature of the oligohaline marshes within which they are found.  相似文献   

Erosion and reorientation of the Sapodilla Cays,Mesoamerican Reef Belize from 1960 to 2012   总被引：1，自引：0，他引：1  

Chris Houser  Tiffany D’Ambrosio  Courtney Bouchard  William Heyman  Kellie Darbonne  Samantha Kuykendall 《自然地理学》2014,35(4):335-354

The Sapodilla Cays Marine Reserve in southern Belize includes nine low-relief sand cays that were first surveyed in 1960. The purpose of this study is to reconstruct a 52-year history of the Sapodilla Cays (1960–2012) using a combination of historical topographic surveys, satellite imagery, and additional field data collection. Results suggest that the majority of islands are eroding with some islands having lost over 70% of their area, and many have become swash aligned, which suggests limited sediment availability. The proportion of area lost on each island is related to the width of the reef platform (to the 5?m isobaths) in the direction of the reef edge, while island area is dependent on the width of the reef platform in the direction of the resultant wind. This suggests that the width of the reef platform is a primary determinant of sediment supply between storms that tend to erode the eastern shoreline of the island through refraction along the reef edge. While storm erosion tends to be concentrated along the eastern shoreline through the loss of sediment offshore, alongshore transport to the lagoon shoreline, and the transfer of sediment to the interior of the island, net shoreline retreat is greatest along the lagoon, suggesting that the relatively small winter “northers” and a lack of sediment supply from the reef lagoon are responsible for the observed erosion. Extrapolations based on contemporary loss-rates suggest that the smallest cays will disappear by 2020, while the largest cays will begin to disappear by the end of century.  相似文献   

Changes in bark properties and hydrology following prescribed fire in Pinus taeda and Quercus montana     

Courtney Siegert  Anna Ilek  Adam Wade  Callie Schweitzer 《水文研究》2023,37(1):e14799

In the eastern United States, the use of prescribed fire as a silvicultural technique to manage for desirable upland tree species is increasing in popularity. Bark physical properties such as thickness, density, and porosity have known associations with fire tolerance among species. These physical properties simultaneously influence rainfall interception and canopy storage and thus are of interest across a range of disciplines. Furthermore, while these characteristics are innate to a species, it is unknown whether repeated exposure to fire facilitates physical change in bark structure and whether these changes are consistent among species. To answer these questions, bark samples were collected from mature pine (Pinus taeda L.) and oak (Quercus montana Willd.) trees from sites across the Bankhead National Forest in Alabama, USA under three different burn regimes: 3-year cycle, 9-year cycle, and no fire. Samples were analysed in the laboratory for bulk density, porosity, water storage capacity, and hygroscopicity (the amount of atmospheric water vapour absorbed by bark during non-rainfall conditions). Drying rates of saturated samples under simulated wetting conditions were also assessed. Oak bark had higher bulk density, lower porosity, and dried slower than pine bark. Interestingly, bark from both species had lower bulk density, higher porosity, greater water storage capacity, and dried faster in stands that were burned every 3 years compared to other fire regimes (p < 0.001). In summary, this study demonstrates that prescribed fire regimes in an eastern US forest alter bark structure and thus influence individual tree control on hydrological processes. The increase in bark water storage capacity, coupled with faster bark evaporation times may lead to less water inputs to the forest floor and drier overall conditions. Further investigation of this fire-bark-water feedback loop is necessary to understand the extent of these mechanisms controlling landscape-scale conditions.  相似文献