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กำหนด C และความเข้มข้นของ NTo determine TN and TC concentrations, dried soil samples were ground to powder in a mortar to pass through a 100-mesh sieve. C and N analyses were performed on a FlashEA 1112 Series NC Analyzer(Italy). Organic C concentrations were also determined using the NC Analyzer after inorganic C as CO2 was removed by adding 1:1 HCl and ovendried to a constant weight.Soil NO3-N concentration was determined by KCl extraction colorimetry of fresh soil samples,whereas NH4-N concentrations were determined by indophenol blue colorimetry on KCl extraction(Liu 1996). Soil grain size was analyzed using a particle size analyzer (Mastersizer 2000, Malvern Instruments, England). Salinity was measured using a Metler SevenEasy conductivity meter.Statistical Analyses Three-way ANOVA was used to test the effects of burrow or burrow mimic size, duration of high tide(days since the first day of high tide) and habitat type (Phragmites, Spartina marshes and mudflats) on the amounts of soil excavated or deposited, deposition efficiency and soil net transport to the ground surface. In this study the soil net transported was calculated as the excavated soil minus deposited soil, collected per day. Burrow mimic trapping, that is soil deposition, is defined as the process in which surface soil and detritus are selectively deposited into burrow mimics through the interaction of burrow mimic openings and tidal water, and burrow mimic deposition is characterized by high organic content, fine grain size and low-density sediments that are easily moved by water flow and transported into crab burrow mimics. Two-way ANOVA was used to test the effects of habitat type and soil source (background surface soil, background subsurface soil, soil excavated or deposited into burrow mimics) on soilproperties. In addition, the effects of habitat type and burrow or burrow mimic diameter size on TN,TC, and TOC amounts daily transported were also evaluated using two-way ANOVA tests. One-way ANOVA was used to test the effects of burrow or burrow mimic size on several parameters of soil excavated by crabs and deposited into burrow mimics. Tukey’s test was used to determine a posteriori differences at P < 0.05. To meet the assumptions of statistical analyses, the data were appropriately examined and transformed prior to statistical analyses as necessary.The relationships between soil amounts excavated by crabs and deposited into burrow mimics, and between the amounts of soil excavated and burrow diameter were analyzed by linear regression. Analyses of covariance (ANCOVA) were used to test the differences of the above relationships among the three habitats. Linear regression was also used to examine relationships between soil amounts excavated or deposited and soil properties. The effects of soil sources (excavated or deposited) on relationships between soil amounts transported and soil Bioturbation of Burrowing Crabs in Salt Marshes 589 properties were tested with ANCOVA. Data were log (x + 1) transformed prior to regression analysis where necessary to linearize the relationships.The total amounts of soil nutrients excavated,deposited, and net transported to the surface for each day were calculated by multiplying soil nutrient concentrations by their corresponding soil amounts. The amounts of soil and nutrients transported per unit area were obtained by multiplying the mean amount of transported nutrients per burrow or burrow mimic by burrow density. Soil turnover rates through crab burrowing were also calculated, which are here defined as the total amount of soil transported, that is, excavation plus deposition, by crabs per unit area per day (compare Gutierrez and others 2006).Within the top 30 cm of soil, soil mass per m2 was determined by multiplying mean bulk density(for a depth of 0–30 cm) by volume (that is,0.3 m3). The soil C stock was calculated by multiplying soil concentration by soil mass of 0.3 m3.The calculation methods for TN and TOC stocks were similar to those for TC stocks. The turnover times of soil and nutrients, defined as the time required for crabs to complete a turnover of all the soil or nutrients for the top 30 cm soil, were calculated by dividing the total soil mass, TC, TN, or TOC stocks by corresponding turnover rates. All analyses were performed using a statistical package of Statistica (Version 6.0, StatSoft). All the results of statistic analyses are given in the supplemental Appendices (Tables A2–A7) for this manuscript.
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