5.4 Results
5.4.3 Macro and Microelements
The present study showed clear gradients in the soil pore water concentrations of the micro- and macroelements across the catchment. The highest PO43- content in the pore water was detected in the bog zone, whereas the highest SO42-, NO2- andDN concentrations were observed in the pore water of the lagg site (Table 5.2). No NH4+ and NO3- were detected in the pore waters of all sites. The measurement of the NO2-
content during the SEN period demonstrated that in contrast to the VAG phase, the nitrite concentration in the lagg site at a depth of 10 cm (0.09 0.01 mg L-1) was higher than the concentration at a depth of 60 cm (0.07 0.01 mg L-1) during the SEN season. The NO2- concentrations at the bog and fen sites did not differ significantly between seasons (VAG: fen 0.03 0.003 mg L-1, bog 0.02 0.006 mg L-1, outflow 0.06 0.04 mg L-1; SEN: fen 0.04 0.02 mg L-1, bog 0.03 0.01 mg L-1). During the VAG season, the PO4
3-, SO4
2-, and DN concentrations exhibited minor fluctuations with depth (Table 5.2).
Table 5.2 PO43-, SO42-, and DN concentrations with depth at the mire site.
Site Depth PO43- conc.
(mg L-1)
SO42- conc.
(mg L-1)
NO2- conc.
(mg L-1)
DN conc.
(mg L-1)
Outflow - 0.101 1.18 0.067 n/a
10 cm 0.081 1.49 0.053 0.8
Lagg 30 cm 0.073 1.55 0.059 0.9
60 cm 0.084 1.39 0.067 1.0
10 cm n/d 1.11 0.032* 0.9
Fen 30 cm 0.044* 1.0 0.04* 0.8
60 cm 0.037* 1.05 0.04* 0.8
10 cm 0.204 n/a n/a n/a
Bog 30 cm 0.127 0.28 0.027* 0.4
60 cm 0.079 0.24 0.032 0.5
*indicates that the presented value is under the analytical measurement range. Measurement dates:
PO43-: 8 August 2010; NO2-, DN and SO42: 26 July. n/a-not available.
The depth and seasonal variations in the concentrations of Ca, Mg, Fe, Na, Mn, and K during the VAG and SEN periods are presented in Table 5.3. The results obtained in August are presented in Table 5.4 (Appendix). Except for CK, all elemental concentrations were highest in the lagg zone and lowest in the bog zone. According to the ANOVA statistical analyses of all site measurements, sampling periods, and various depths, the concentrations of Ca, Mg, Fe, Na, and Mn were significantly different among the sites. At the lagg site, the Ca and Fe concentrations differed significantly among the sites and increased with depth. The CK did not differ among the sites but decreased and varied significantly with depth at the bog and fen sites.
During the SEN period, the CK exhibited a significant upward trend at the fen and bog sites. Seasonal changes in the CCa and CMn were also detected. During the SEN period, the CCa decreased at the lagg site at a depth of 60 cm. The value of CMn decreased at the lagg (10 cm) and fen (10 and 60 cm) sites. The CNa and CZn concentrations were not significantly different among sites, depths, or seasons. The mean CZn across the field sites was 0.03 0.02 mg L-1.
Table 5.3 Seasonal variability of the mean concentrations (C) of chemical species measured in the pore waters at different sites in the mire complex. From all sites and depths except the outflow* and bog* sites at a 10-cm depth, water samples were collected during the following periods of vegetation active growth (VAG: 7, 12, 19, and 26 Jul 2010) and vegetation senescence (SEN: 19, 22, and 26 Sep 2010 and 3 Oct 2010).
Chemical
element Site/Depth Vegetation active growth season Senescence
10cm (SD) 30 cm (SD) 60 cm (SD) 10 cm (SD) 30 cm (SD) 60 cm (SD)
CCa1 Lagg 7.0 (0.3)2 7.7 (0.1) 7.9 (0.4)2, 3 7.0 (0.4) 7.6 (0.2) 6.9 (0.2)3
Fen 3.1 (0.1) 3.5 (0.5) 3.8 (0.2) 3.2 (0.5) 3.8 (0.3) 3.8 (0.2)
Bog 0.3 (0.01) 0.3 (0.04) 0.5 (0.01) 0.2 (0.1) 0.3 (0.1) 0.4 (0.1)
Outflow 4.8 (0.4)
CMg1 Lagg 1.5 (0.06) 1.6 (0.03) 1.7 (0.07) 1.6 (0.02) 1.7 (0.02) 1.7 (0.07)
Fen 0.9 (0.04)2 0.9 (0.1) 1.1 (0.07)2 0.9 (0.1)2 1.1 (0.08) 1.2 (0.03)2
Bog 0.1 (0.01) 0.1 (0.02) 0.1 (0.05) 0.1 (0.02) 0.1 (0.03) 0.1 (0.03)
Outflow 1.3 (0.1)
CFe1 Lagg 0.5 (0.08)2 0.5 (0.03)2 1.8 (0.6)2 0.4 (0.1)2 0.5 (0.03)2 1.9 (0.1)2
Fen 0.5 (0.08) 0.7 (0.06) 0.6 (0.10) 0.3 (0.08)2 0.7 (0.01)2 0.5 (0.05)2
Bog 0.06 (0.01) 0.08 (0.03) 0.1 (0.03) 0.06 (0.01) 0.08 (0.07) 0.2 (0.07)
Outflow 1.06 (0.4) CK
Lagg 0.1 (0.06) 0.2 (0.1) 0.2 (0.1) 0.2 (0.1) 0.2 (0.1) 0.6 (0.55)
Fen 0.6 (0.3)2, 3 0.3 (0.2)2 0.3 (0.3)2 1.7 (0.5)2, 3 0.6 (0.4)2 0.1 (0.09)2
Bog 0.4 (0.1)3 0.3 (0.1) 0.1 (0.1) 2.9 (0.8)2, 3 0.4 (0.2)2 0.3 (0.1)2
Outflow 0.3 (0.1) CMn1
Lagg 0.04 (0.005)3 0.05 (0.01)2 0.02 (0.01)2 0.01 (0.01)2, 3 0.04 (0.01)2 0.03 (0.01)
Fen 0.08 (0.01)3 0.07 (0.006) 0.07 (0.006)3 n/d 0.05 (0.01)2 0.03 (0.02) 2, 3
Bog n/d n/d n/d n/d n/d n/d
Outflow 0.03 (0.01)
CNa1
Lagg 1.2 (0.2) 1.2 (0.2) 1.3 (0.1) 0.9 (0.2) 0.7 (0.4) 0.8 (0.3)
Fen 1.3 (0.2) 1.0 (0.1) 1.1 (0.2) 1.5 (0.5) 1.1 (0.1) 0.9 (0.3)
Bog 0.7 (0.3) 0.6 (0.2) 0.6 (0.1) 0.6 (0.2) 0.4 (0.1) 0.4 (0.1)
Outflow 1.3 (0.4)
*The bog measurements for 10-cm depths were conducted during VAG (7 and 12 Jul 2010), and water samples were not collected during the second half of VAG (19 and 26 Jul 2010) due to a low water table. At the discharge point, measurements were conducted over a two-week VAG period (7 and 26 Jul 2010), but no water was collected during the SEN period because no water outflow from the mire toward the river was detected after the extreme drought in the summer. ANOVA analyses were conducted separately for the sites, depths, and seasons. Significant differences were detected if p < 0.05 (1 indicates that a significant difference was detected between sites, 2 denotes a significance difference between different depths, and 3 denotes a significant difference between seasons).
Figure 5.3 All concentrations of dissolved Ca, Mg and Fe plotted plotted against CDOC for the lagg (L), fen (F) and bog (B) sites during the summer and fall sampling periods. Pearson correlation coefficients were calculated separately for the overall study site values (n = 95) and separately for the values of each group (lagg n = 32, fen n = 33, bog n = 30).
The Pearson correlation coefficient for a sample size of n = 95 indicated a strong positive correlation between the CDOC values and the CCa (r = 0.96), CFe (r= 0.65), and CMg (r = 0.93) values (Figure 5.3), whereas within each group (lagg, fen, and bog zones), a strong correlation between the CDOC and the CMg, CCa, or CFe could not be observed. At a depth of 60 cm in the lagg zone, a distinctive difference in CFe was observed, and an additional separate Pearson correlation analysis was performed for this depth, which demonstrated a positive correlation with r = 0.37 (n = 8). A weak positive relationship was detected between the overall CDOC and CMn (r = 0.3).
The overall DOC concentration did not correlate with the CZn (r = 0.004) and was weakly negatively correlated with the CK (r = -0.15). Furthermore, within each group (lagg, fen, and bog zones), a strong correlation between the CDOC and the CMg, CCa, or CFe could not be observed.
Figure 5.4 shows that the Ca:Mg ratio was significantly different between the lagg and fen sites. However, because of the large variation of the values at the bog site, this site could not be differentiated from the fen and lagg sites with respect to the Ca:Mg ratio (Figure 5.4). The Ca:Mg ratio decreased and exhibited greater variability during the SEN period than during the VAG period.
Figure 5.4 Comparison of the Ca:Mg ratios in the pore waters for different depths in the lagg, fen, and bog zones during the vegetation active growth period (VAG; 7, 12, 19, and 26 Jul 2010) and during the vegetation senescence period (SEN; 19, 22, and 26 Sep 2010 and 3 Oct 2010). The error bars represent the standard deviation of the values obtained during the 4-week measurement period. On the x-axis, L, F, and B represent the lagg, fen, and bog sites, respectively, and 10, 30, and 60 correspond to the respective depths in cm.
At the mire, the silica content increased during VAG season at the 10-cm depth from 3.8 to 4.4 mg L-1 in the lagg zone, from 0.9 to 1.5 mg L-1 in the fen zone, and from 0.9 to1.5 mg L-1 in the bog site (Figure 5.5). In contrast to the 10-cm depth, higher concentrations were observed at the 60-cm depth, which showed relatively constant ranges in the lagg (9.4-10.4 mg L-1) and fen (1.5-2.6 mg L-1) zones but a wider variation in the bog zone (1.3-3.02 mg L-1). At the 30-cm depth, the observed silica concentrations were in the intermediate range between those of the 10-cm and 60-cm depths. The silica content at the outflow point was similar to the silica content in the lagg zone and increased during July from 3.8 to 6.8 mg L-1 (Figure 5.5). The bog and fen sites exhibited no visible trends over the sampling period and relatively similar ranges of SiO2 concentrations. The increase in the outflow water concentration was coincidental with the reduced flows. The concentration at the fen site was more similar to that at the bog site than to that at the lagg zone.
Figure 5.5 a. Silica contents in the surface and soil pore water at different depths in the lagg, fen, bog sampling sites. The error bars represent the standard deviation across the mean of four successive sampling weeks (sampling period: 7, 12, 19, and 26 Jul 2010). b. Silica content in the outflow water. The mean standard deviation of the analytical duplicate measurements is 0.08 mg L-1.
Agglomerative hierarchical clustering was conducted on the water chemistry data from the seasonal 10-cm pore and discharge samples collected during the VAG season (Appendix, Table 5.6). This study demonstrated that the main flow path was over the lagg zone, which was marginally influenced by the bog and fen chemistry.
Thus, the outflow water was most closely related to the lagg zone, and both sites were placed in the same group, whereas the bog and fen sites were placed in a separate group (Figure 5.6).
Figure 5.6 Dendrogram based on the agglomerative hierarchical clustering method. The agglomerative hierarchical clustering was performed based on a set of mean water chemical properties over the VAG period (n=11) as indicated in Table 5.5 (Appendix). The diagram shows that the water-chemical properties of discharge waters are similar to the ones of the waters at 10 cm depth in the lagg zone. Dissimilarity was calculated based on the Euclidean distance. The dotted line represents the automatic truncation, leading to the separation of groups (XLSTAT, Addinsoft, France).
Dendrogram
Bog
Fen
Lagg
Outflow
0 5 10 15 20
Dissimilarity