Tong Li, Jihui Zhang, Dongling Li, Chengxu Zhou, Chenxi Liu, Hao Xu, Bing Song, Longbin Sha. Diatoms as indicators of environmental change in coastal areas: a case study in Lianjiang, East China Sea[J]. Acta Oceanologica Sinica.
Citation:
Tong Li, Jihui Zhang, Dongling Li, Chengxu Zhou, Chenxi Liu, Hao Xu, Bing Song, Longbin Sha. Diatoms as indicators of environmental change in coastal areas: a case study in Lianjiang, East China Sea[J]. Acta Oceanologica Sinica.
Tong Li, Jihui Zhang, Dongling Li, Chengxu Zhou, Chenxi Liu, Hao Xu, Bing Song, Longbin Sha. Diatoms as indicators of environmental change in coastal areas: a case study in Lianjiang, East China Sea[J]. Acta Oceanologica Sinica.
Citation:
Tong Li, Jihui Zhang, Dongling Li, Chengxu Zhou, Chenxi Liu, Hao Xu, Bing Song, Longbin Sha. Diatoms as indicators of environmental change in coastal areas: a case study in Lianjiang, East China Sea[J]. Acta Oceanologica Sinica.
Owing to the significant differences in environmental characteristics and explanatory factors among estuarine and coastal regions, research on diatom transfer functions and database establishment remains incomplete. This study analysed diatoms in surface sediment samples and a sediment core from the Lianjiang coast of the East China Sea, together with environmental variables. Principal component analysis of the environmental variables showed that sea surface salinity (SSS) and sea surface temperature were the most important factors controlling hydrological conditions in the Lianjiang coastal area, whereas canonical correspondence analysis indicated that SSS and pH were the main environmental factors affecting diatom distribution. Based on the modern diatom species–environmental variable database, we developed a diatom-based SSS transfer function to quantitatively reconstruct the variability in SSS between 1984 and 2021 for sediment core HK3 from the Lianjiang coastal area. The agreement between the reconstructed SSS and instrument SSS data from 1984–2021 suggests that diatom-based SSS reconstruction is reliable for studying past SSS variability in the Lianjiang coastal area. Three low SSS events in AD 2019, 2013, and 1999, together with an increased relative concentration of freshwater diatom species and coarser sediment grain sizes, corresponded to two super-typhoon events and a catastrophic flooding event in Lianjiang County. Thus, a diatom-based SSS transfer function for reconstructing past SSS variability in the estuarine and coastal areas of the East China Sea can be further used to reflect the paleoenvironmental events in this region.
Figure 1. Location of the study area in Lianjiang County. (A) Location of the study area within China, shown by the red circle. (B) Topography and distribution of rivers in the study area. The Aojiang River is in the northern part of the figure and the Minjiang River is in the southern part; the Lianjiang coast is influenced by both rivers. (C) Locations of surface sediment samples and a sediment core HK3.
Figure 2. Spatial distribution of diatom concentrations and the SW index of diatoms in surface sediment samples from the Lianjiang coastal area. (A) and (D) refer to October, (B) and (E) to January, (C) and (F) to April.
Figure 3. Summary of the results of the PCA of the environmental variables: variable loadings (arrows) and sample scores (coloured symbols) on PC1 and PC2. The solid arrows represent the primary environmental factors that have the maximum load on PCA1 and PCA2, respectively, and the dashed arrows represent secondary impact factors. The angle between arrows indicates the correlation between individual environmental variables. SST: sea surface temperature; ORP: redox potential; C: conductivity; Tur: turbidity; DO: dissolved oxygen; TDS: total dissolved solids; SSS: sea surface salinity; MD: sediment mean grain size.
Figure 4. CCA biplot of environmental variables and diatoms species. See Table S2 for abbreviations. Red symbols: diatoms associated with coarse-grained sediments (Zone I); green symbols: main freshwater diatom species (Zone II); blue symbols: predominantly marine diatoms (Zone III). SST: sea surface temperature; ORP: redox potential; Tur: turbidity; DO: dissolved oxygen; SSS: sea surface salinity; MD: sediment mean grain size.
Figure 5. Vertical profiles of 210Pbex activity, clay content, and calculated 210Pbex activity in core HK3. Error bars consider counting statistics uncertainties at 2σ.
Figure 6. Plots of observed versus predicted values and observed versus residual (predicted minus observed) values for four transfer function models derived for SSS. (A) and (B): PLS with 3 components model; (C) and (D): PLS with 5 components model; (E) and (F): WA-PLS with 4 components model; (G) and (H): WA-PLS with 5 components model.
Figure 7. Correlations between the diatom-based reconstructed SSS for core HK3 and the modern SSS data. (A) WA-PLS with 4 components model, (B) WA-PLS with 5 components model, (C) PLS with 3 components model, (D) PLS with 5 components model.
Figure 8. Time series of reconstructed sea surface salinity (grey intervals are error values), diatom concentration, Shannon-Weaver diversity index, sediment mean grain size, and relative abundance of freshwater and marine diatom species in core HK3. Note that abrupt decreases in the SSS occurred in 2019, 2013, and 1999.
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