A geostatistical analysis of small-scale spatial variability in bacterial abundance and community structure in salt marsh creek bank sediments

Abstract

Small-scale variations in bacterial abundance and community structure were examined in salt marsh sediments from Virginia's eastern shore. Samples were collected at 5 cm intervals (horizontally) along a 50 cm elevation gradient, over a 215 cm horizontal transect. For each sample, bacterial abundance was determined using acridine orange direct counts and community structure was analyzed using randomly amplified polymorphic DNA fingerprinting of whole-community DNA extracts. A geostatistical analysis was used to determine the degree of spatial autocorrelation among the samples, for each variable and each direction (horizontal and vertical). The proportion of variance in bacterial abundance that could be accounted for by the spatial model was quite high (vertical: 60%, horizontal: 73%); significant autocorrelation was found among samples separated by 25 cm in the vertical direction and up to 115 cm horizontally. In contrast, most of the variability in community structure was not accounted for by simply considering the spatial separation of samples (vertical: 11%, horizontal: 22%), and must reflect variability from other parameters (e.g., variation at other spatial scales, experimental error, or environmental heterogeneity). Microbial community patch size based upon overall similarity in community structure varied between 17 cm (vertical) and 35 cm (horizontal). Overall, variability due to horizontal position (distance from the creek bank) was much smaller than that due to vertical position (elevation) for both community properties assayed. This suggests that processes more correlated with elevation (e.g., drainage and redox potential) vary at a smaller scale (therefore producing smaller patch sizes) than processes controlled by distance from the creek bank.

Diversity, Composition, and Geographical Distribution of Microbial Communities in California Salt Marsh Sediments

“…These fatty acids, along with 18:23c, accounted for more than 60% of the fatty acids in axenic Spartina roots (33), a plant that is abundant in the unsaturated zones in all of the marshes sampled. Franklin et al (16) found significant small-scale differences due to tidal cycles in east coast salt marshes comparable to the marshes selected for this study. Microbial communities in this study were fingerprinted using a DNA-based method, and geostatistical analyses identified spatial patterns in microbial communities in salt marsh sediments.…”

“…Elevation directly controls many sediment characteristics that strongly influence microbial community structure (16). Tidal cycles create distinct habitats within marsh creeks in saturated, intermittently flooded, and unsaturated zones.…”

Factors Driving Potential Ammonia Oxidation in Canadian Arctic Ecosystems: Does Spatial Scale Matter?

“…Moreover, fine-scale patterns may not be captured with a grid design due to its even lag distance (minimum of 2 or 4 m). Variable (irregular) sampling design, adjacent steps separated by a repeated sequence, is a particularly useful design for substantiating multi-scale patterns in an ecosystem (20,21,42). Therefore, in the present study, we specifically used a variable-lag-distance transect approach to simultaneously capture the fine-scale (0 to 1 m), medium-scale (1 to 10 m), and large-scale (10 to 300 m) spatial patterns of microbial communities in three cryosolic ecosystems.…”

Spatial designs and properties of spatial correlation: Effects on covariance estimation

“…Numerous authors interpret the effective range in the exponential covariance function as a measure to describe the spatial heterogeneity or "patchiness" in a landscape (e.g., Saetre and Baath 2000;Franklin et al 2002;Schwarz et al 2003;Rufino et al 2004;Kennard and Outcalt 2006). Dalthorp et al (2000) demonstrated with discrete data that the range and nugget parameters influence the patch configuration on a simulated landscape, although Schabenberger and Gotway (2005, p. 140) questioned the use of the range parameter as an estimate of patch size.…”