Table 1.
Phosphorus forms, their potential biodegradability in sediment and their potential environmental effects.
Figure 1.
The research area and the sediment sampling stations.
(A) The sampling stations in Paimionlahti Bay (Paila10, Paila14, AS5, and AS3), in the Archipelago Sea (AS2), in the northern Baltic Proper (AS7), and in the western Gulf of Finland (JML, GF1, and C63). (B) A magnification of Paimionlahti Bay and the sampling sites located in the estuary. (C) Concentrations of reactive phosphorus (P) forms; redox-sensitive and labile organic P, and total P in the solid phase of the sediment samples. Arrows (in the upper part of the panel C) indicate sediment depth from 1 cm down to 25 cm below the seafloor (Refer to Dataset S2). Darkening colour of the arrows denotes the increasing subsurface depth.
Figure 2.
Relationships between bacterial community composition and chemical parameters of Baltic Sea sediments.
(A) Canonical analysis of principal coordinates (CAP) and (B) partial CAP (spatial autocorrelation was excluded). Samples (n = 42) and HaeIII digested terminal restriction fragments (T-RFs, n = 104) and chemical parameters (red arrows, n = 8) were plotted against canonical axis scores 1 and 2. Black axes correspond to scores of samples/T-RFs and red axes to scores of chemical parameters. T-RFs and their corresponding taxonomic assignments are indicated with violet numbers (in bp) and letters. Large font size (A) shows those T-RFs which correlated to important chemical parameters. T-RFs of 16S rRNA gene were identified by digestion of cloned 16S rRNA genes (refer numbers to Table 2 and Table S4). Taxonomic assignments of TFs: Ac = Actinobacteria, α = Alphaproteobacteria, An = Anaerolineae, Bac = Bacteroidetes, c = Cyanobacteria, δ = Deltaproteobacteria, F = Firmicutes, γ = Gammaproteobacteria, P = Planctomycetasia, Pr = proteobacteria, SRB = Sulphate reducers (Deltaproteobacteria), S = Sulphur/iron reducers (Deltaproteobacteria). Only T-RFs with canonical scores above ±1 for axis 1 and 2 were included. Scores were derived from canonical correlations. The arrow length indicates the strength of the correlation between the chemical parameter and sediment samples/T-RFs. The direction of an arrow indicates the increasing concentration of the chemical parameter. Chemical parameters: NaBDiP = iron-bound (redox-sensitive) phosphorus (P), NaBDFe = redox-sensitive iron (Fe), NaOHiP = aluminium-bound (alkali-extractable) P, NaOHSi = alkali-extractable silicon (Si), NRP = labile organic P, and HClMn = HCl-extractable manganese (Mn). TN = Total nitrogen (N), TC = Total carbon (C). *Positions of T-RFs 271 and 203 were changed for technical reasons. The real scores of T-RF 271 for axis 1 and 2 were 1.5 and −6.9 (A), and −8.8 and −1.5 (B). The axis scores T-RF 203 were −0.06 and 6.2 (B). ** Canonical scores of total carbon were nearly same than total nitrogen.
Table 2.
Identification of 16S rRNA gene terminal restriction fragments of class Deltaproteobacteria from Baltic Sea sediments.
Figure 3.
Effects of individual chemical variables on variation in bacterial community composition of Baltic Sea sediments.
Proportions were derived from the distance-based multivariate multiple regression analysis of chemical parameters and HaeIII terminal restriction fragments of 16S rRNA genes. P values (<0.05) of the forward selection procedure (conditional tests) are shown on the bars.
Figure 4.
Partitioning of the variation in bacterial community composition between chemical, spatial and environmental variables.
Proportions were derived from series of redundancy analysis of terminal restriction fragments (T-RFs) and chemical, spatial and environmental parameters (refer to table S3), which were used in variance partitioning according to Borcard et al. [50], Anderson and Gribble [48], and Legendre and Legendre [51]. Spatial parameters were geographic location and sediment depth and environmental parameters included sediment accumulation rate and water depth.
Figure 5.
Taxonomic distribution of 16S rRNA gene clones derived from the Baltic Sea sediment clone libraries.
Clones were assigned using taxonomic classifier (version 2.2, RDP training set 6) of Ribosomal Database Project (RDP) with confidence threshold of 80%.
Figure 6.
Distribution and relative abundance of potential sulphate- and sulphur/iron-reducing taxa in Baltic Sea sediments.
Size of the symbols (squares) corresponds to abundance of a 16S rRNA gene terminal restriction fragment (T-RF, indicated by the same number in bp as in Figure 2) in a sediment sample. The T-RFs were taxonomically assigned, based on in silico (virtually) and in vitro digested 16S rRNA gene clones (refer to Table 2). Letter c indicates the class, o the order, f the family, and g the genus. Potential iron reducers marked in bold.
Figure 7.
A sediment core from the western Gulf of Finland.
The core was sampled from the station JML. Black layers (white arrows) indicate presence of ferrosulphides which are formed via reaction of ferro-iron and sulphite, produced by sulphate reducing bacteria.