Within- and between-lake variability in the composition of bacterioplankton communities: investigations using multiple spatial scales

Abstract

This study examined the similarity of epilimnetic bacterial community composition (BCC) across several within- and among-lake spatial scales, and the environmental factors giving rise to similar bacterial communities in different lakes were also explored. Samples were collected from 13 northern and southern Wisconsin lakes representing gradients in lake size, productivity, dissolved organic carbon and humic acid contents, and pH. Hypotheses regarding patchy distribution of bacterial communities in lakes were tested by comparing samples collected from nearby (tens of meters) and distant (hundreds of meters) sampling sites in the same lake. BCC was characterized by using a molecular fingerprinting technique, automated ribosomal intergenic spacer analysis (ARISA). Overall, samples collected at the 10-m, 100-m, and between-lake scales differed by 13, 17, and 75%, respectively. Variation at these last two scales was significant. The development of within-lake variation in BCC appeared to depend on the isolation of water by lake shoreline features such as bays or narrow constrictions. ARISA profiles from northern lakes had fewer peaks and were less similar to each other than were those of the southern lakes, suggesting that regional features do not necessarily lead to the development of similar bacterial communities. Lakes at similar positions on productivity and dissolved organic carbon concentration gradients had similar bacterial communities, and bacterial diversity was positively correlated with lake productivity and water temperature. Factorial studies taking into account these gradients, as well as regional spatial scales, should provide much insight into the nature of aquatic bacterial biogeography.

FIG. 1.

Map and spatial details of the study design. (A) State map of Wisconsin showing the locations of the northern (Trout Lake) region and the southern (Madison Lakes) region. (B and C) Maps of the northern Trout Lake region (B) and the southern Madison Lakes region (C) showing lakes, stream connections, and study basins. The numbers within each study lake correspond to the basins described in Tables 1, 3, and 4. (D) Detail of the study design with Trout Lake as an example. The relationship of basin level and station level samples is shown. Numbers correspond to basins, and the points labeled A, B, and C correspond to the station level samples. Station names in bold and italics (e.g., 24B) indicate primary stations at which environmental samples were collected.

FIG. 2.

Mean Sorenson similarity and ARISA fragment richness of ARISA profiles obtained from northern and southern lakes. Bars represent SE, with 10 (south) and 28 (north) comparisons for similarity and 5 (south) and 8 (north) lakes comparisons for richness.

FIG. 3.

Three-dimensional nonmetric MDS plot for ARISA profiles collected from study lakes. Stress = 0.09. The symbols are coded to represent the lakes from which profiles were obtained. Lake abbreviations are listed in Table 1. The arrows indicate the directions in which scores on the various axes increase, and Pearson product-moment correlation coefficients of the axes with various environmental variables are provided in the insert. A, axes 1 and 2; B, axes 1 and 3; C, axes 2 and 3. temp, temperature; chl a, chlorophyll a; DN, dissolved nitrogen; DO, dissolved oxygen; epi, epilimnion.

FIG. 4.

Two-dimensional nonmetric MDS plots for ARISA fragments collected from northern and southern lakes. The symbols are coded to represent the lakes from which profiles were obtained. Lake name abbreviations are listed in Table 1. Because plots were generated from separate ordinations, absolute distances on different plots cannot be considered equal. The arrows indicate the directions in which scores on the various axes increase, and Pearson product-moment correlation coefficients of the axes with various environmental variables are provided. (A) Profiles for northern lakes. Stress = 0.12. (B) Profiles for southern lakes. Stress = 0.13. epi, epilimnion; temp, temperature; DP, dissolved phosphorus; DN, dissolved nitrogen; chl a, chlorophyll a.

FIG. 5.

Relationship between ARISA fragment richness and water temperature (A) or chlorophyll a (B). Data from each study basin are presented. ARISA fragment richness is the mean number of fragments seen at each primary station from which environmental samples were taken. ρ = Pearson product-moment correlation coefficient.

FIG. 6.

Nonmetric MDS plots for selected basin level analyses. For the spatial arrangement of the basins within these lakes, see Fig. 1. Depicted are the basin level plots for Little Rock Lake (A), Trout Lake (B), Lake Mendota (C), and Lake Monona (D). The numbers represent the basins from which the respective ARISA profiles were derived. Because plots were generated from separate ordinations, absolute distances on different plots cannot be considered equal. Stress values for plots are 0.01 (A), 0.17 (B), 0.13 (C), and 0.15 (D).