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Assessment of the climate and human impact on estuarine water environments in two estuaries of the Bay of Biscay

Arantza Iriarte
Arantza Iriarte
, 
Fernando Villate
Fernando Villate
, 
Ibon Uriarte
Ibon Uriarte
 e 
Santiago Arranz
Santiago Arranz
   | 12 dic 2016
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Article Category: Original research paper
Pubblicato online: 12 dic 2016
Pagine: 505 - 523
Ricevuto: 09 feb 2016
Accettato: 13 apr 2016
DOI: https://doi.org/10.1515/ohs-2016-0043
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© Faculty of Oceanography and Geography, University of Gdańsk, Poland. All rights reserved.
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1

Maps of the Bilbao and Urdaibai estuaries, showing the usual extent of water masses of 35, 34, 33, 30 and 26 salinity below the halocline during neap tides and high water. The map of the river catchment areas, showing the location of the meteorological and hydro-meteorological stations is also shown.
Maps of the Bilbao and Urdaibai estuaries, showing the usual extent of water masses of 35, 34, 33, 30 and 26 salinity below the halocline during neap tides and high water. The map of the river catchment areas, showing the location of the meteorological and hydro-meteorological stations is also shown.

Figure 2

Averaged inter-annual, seasonal and residual variability (SDy,m,ε) of air temperature, rainfall for the sites of Sondika (S), Abusu (A) and Muxika (M) and river flow for the Kadagua (K), Ibaizabal-Nerbioi (I-N) and Oka (O) rivers
Averaged inter-annual, seasonal and residual variability (SDy,m,ε) of air temperature, rainfall for the sites of Sondika (S), Abusu (A) and Muxika (M) and river flow for the Kadagua (K), Ibaizabal-Nerbioi (I-N) and Oka (O) rivers

Figure 3

Averaged inter-annual, seasonal and residual variability (SDy,m,ε), and time-series average values of the stratification index (ST) and Secchi disk depth (SDD, m) in the estuaries of Bilbao (A and C) and Urdaibai (B and D)
Averaged inter-annual, seasonal and residual variability (SDy,m,ε), and time-series average values of the stratification index (ST) and Secchi disk depth (SDD, m) in the estuaries of Bilbao (A and C) and Urdaibai (B and D)

Figure 4

Averaged inter-annual, seasonal and residual variability (SDy,m,ε), and time-series average values of temperature below the halocline (A and B) and in the halocline (C and D) in the estuaries of Bilbao and Urdaibai. 30* – above the halocline and 35* – the whole water column
Averaged inter-annual, seasonal and residual variability (SDy,m,ε), and time-series average values of temperature below the halocline (A and B) and in the halocline (C and D) in the estuaries of Bilbao and Urdaibai. 30* – above the halocline and 35* – the whole water column

Figure 5

Averaged inter-annual, seasonal and residual variability (SDy,m,ε), and time-series average values of DOS below the halocline (A and B) and in the halocline (C and D) in the estuaries of Bilbao and of Urdaibai. 30* – above the halocline and 35* – the whole water column
Averaged inter-annual, seasonal and residual variability (SDy,m,ε), and time-series average values of DOS below the halocline (A and B) and in the halocline (C and D) in the estuaries of Bilbao and of Urdaibai. 30* – above the halocline and 35* – the whole water column

Figure 6

Averaged inter-annual, seasonal and residual variability (SDy,m,ε), and time-series average values of chlorophyll a in the estuaries of Bilbao (A) and Urdaibai (B)
Averaged inter-annual, seasonal and residual variability (SDy,m,ε), and time-series average values of chlorophyll a in the estuaries of Bilbao (A) and Urdaibai (B)

Figure 7

Principal component analysis of the seasonal changes in the water environmental variables (ST: Stratification index; SDD: Secchi disk depth; WTT: Water temperature for the total water column; WTB: Water temperature below the halocline; WTH: Water temperature in the halocline; WTS: Water temperature in the surface layer above the halocline; DOT: Dissolved oxygen for the total water column; DOB: Dissolved oxygen below the halocline; DOH: Dissolved oxygen in the halocline; DOS: Dissolved oxygen in the surface layer above the halocline; CHL: Chlorophyll a at different salinity sites of the Bilbao and Urdaibai estuaries
Principal component analysis of the seasonal changes in the water environmental variables (ST: Stratification index; SDD: Secchi disk depth; WTT: Water temperature for the total water column; WTB: Water temperature below the halocline; WTH: Water temperature in the halocline; WTS: Water temperature in the surface layer above the halocline; DOT: Dissolved oxygen for the total water column; DOB: Dissolved oxygen below the halocline; DOH: Dissolved oxygen in the halocline; DOS: Dissolved oxygen in the surface layer above the halocline; CHL: Chlorophyll a at different salinity sites of the Bilbao and Urdaibai estuaries

Figure 8

Cumulative sums of month scores from January to December in PC1 and PC2 for different salinity sites of the Bilbao (A and C) and Urdaibai (B and D) estuaries. *Inverse values: positive values are reported as negative values and vice versa.
Cumulative sums of month scores from January to December in PC1 and PC2 for different salinity sites of the Bilbao (A and C) and Urdaibai (B and D) estuaries. *Inverse values: positive values are reported as negative values and vice versa.

Figure 9

Patterns of seasonal (SDm) and inter-annual (SDy) variability of water temperature at 35, 34, 33, 30 and 26 salinity sites in the estuaries of Bilbao (A, C, E and G) and Urdaibai (B, D, F and H). BH and H indicate below halocline and halocline waters, respectively. The dashed line for the above halocline layer at the 30 salinity site in the Bilbao estuary. At 35 salinity in the estuary of Urdaibai, the data are provided for the whole water column.
Patterns of seasonal (SDm) and inter-annual (SDy) variability of water temperature at 35, 34, 33, 30 and 26 salinity sites in the estuaries of Bilbao (A, C, E and G) and Urdaibai (B, D, F and H). BH and H indicate below halocline and halocline waters, respectively. The dashed line for the above halocline layer at the 30 salinity site in the Bilbao estuary. At 35 salinity in the estuary of Urdaibai, the data are provided for the whole water column.

Figure 10

Principal component analysis of inter-annual changes in water environmental variables (acronyms as in Figure 7) at different salinity sites in the estuaries of Bilbao and Urdaibai
Principal component analysis of inter-annual changes in water environmental variables (acronyms as in Figure 7) at different salinity sites in the estuaries of Bilbao and Urdaibai

Figure 11

Cumulative sums of year scores from 1998 to 2008 in PC1 and PC2 for different salinity sites in the estuaries of Bilbao (A and C) and Urdaibai (B and D)
Cumulative sums of year scores from 1998 to 2008 in PC1 and PC2 for different salinity sites in the estuaries of Bilbao (A and C) and Urdaibai (B and D)

Results of (Spearman rank) correlation analyses of the first (C1) and second (C2) components of PCA with the annual anomalies in rainfall, Kadagua and Oka river flows (RF) and summertime air temperature anomalies from different salinity sites (35, 34, 33, 30, 26) of the Bilbao (B) and of Urdaibai (U) estuaries. Only the p-values of significant correlations (in bold) are shown.

Site PCA component Air temperature Rainfall Kadagua (RF) Oka (RF)
B35 C1 -0.036 0.459 0.066
C2 0.882(p<0.001) -0.041 -0.005
B34 C1 0.736(p<0.01) 0.166 0.107
C2 -0.409 0.139 -0.158
B33 C1 0.609(p<0.05) -0.230 -0.358
C2 -0.018 0.283 0.066
B30 C1 -0.027 0.472 0.674(p<0.05)
C2 -0.327 0.251 0.110
U35 C1 0.891(p<0.001) 0.096 0.093
C2 0.227 -0.318 -0.353
U33 C1 0.700(p<0.05) -0.041 -0.201
C2 -0.364 0.271 0.263
U30 C1 0.773(p<0.01) 0.057 -0.048
C2 -0.109 0.042 0.040
U26 C1 0.491 0.295 0.184
C2 0.100 -0.718(p<0.05) -0.748(p<0.01)
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