Fig 1.
Seawater quality monitoring and reference (Ref.) sites for the Barrow Island (MS800), Burrup Peninsula (MS757), and Cape Lambert (MS840) dredging projects in the Pilbara region (Western Australia).
Only sites that were near (<2 km) from the primary dredging activity and those that were considered un-impacted by dredging (references sites) were used in the analyses here and are labelled. Detail site information can be found in the (Table 1 and S1 File). The ministerial approval statements (MS) for these projects are available on the WA EPA website: http://www.epa.wa.gov.au. Dredge material placement sites (spoil grounds) and primary excavation areas are indicated as dark shaded boxes.
Table 1.
Data type collected and instruments used across three major dredging projects in the Pilbara (Western Australia) since 2007 including start and finish dates and volumes dredged.
Table 2.
Mean turbidity and photosynthetically active radiation (PAR) for the Barrow Island, Cape Lambert and Burrup Peninsula dredging programs.
Fig 2.
Instantaneous turbidity as maximum daily NTU (left column) and probability density function (far-right panels) at (A) MOF1 (B), SBS during the Barrow Island dredging project, (C) PWR and (D) DLI during the Cape Lambert dredging project, and (E) SUP2 and (F) WINI during the Burrup Peninsula project.
LNGI, PWR and SUP2 represent dredge impacted sites whereas SBS, DLI and WINI represent sites un-impacted by dredging (reference sites). The thick solid line on the left hand plots indicates the start of dredging for each project, whereas the dashed lines indicate the timing of cyclone events that may have had the potential to cause sustained periods of very rough seas in this region (Puotinen, pers comm) based on the cyclone size, intensity and proximity to sites (Beeden et al 2015). Annotations under each axis indicate each cyclone event, as follows: Nicholas (N), category 4; Billy (Bil), category 3; Dominic (Do), category 2; Bianca (Bia) category 4; Carlos (Ca), category 3; Lua (Lu) category 4. Cyclone categories indicate the intensity (Australian Ranking Scale) of each cyclone at closest approach to the sites. Time series and probability density function plots for all sites for the three projects can be found in the online supplementary information (Figures, A, B, C in S2 File).
Fig 3.
Running means percentile analysis for turbidity (NT U) at sites close to dredging (<2 km) or at reference sites during the Barrow Island, Cape Lambert and Burrup Peninsula dredging projects (see Fig 1).
The 100th (maximum), 99th and 95th and 80th percentiles for the running mean turbidity are shown. Percentiles were calculated separately for the baseline period (dashed grey lines) and during dredging (black solid lines).
Fig 4.
Turbidity (NTU) percentile values for running means calculated on time scales of one hour (h) and 1, 14 and 30 days (d) for all sites at (A) Barrow Island, (B) Cape Lambert and (C) Burrup Peninsula dredging projects.
White symbols represent percentiles for the baseline period (pre-dredging period), grey symbols represent reference sites during the dredging period and black symbols represent sites close to (<2 km) the dredging.
Table 3.
Turbidity (NTU) percentile values for various running mean time periods for the Barrow Island, Cape Lambert and Burrup Peninsula dredging projects.
Fig 5.
A comparison of mean versus median values as a statistical summary for daily turbidity (NTU) readings for selected near dredge and reference sites at Barrow Island.
Boxplots of the ratio of the mean daily value versus the median daily value are shown during (A) the baseline period and (B) the dredging phase. The central bar of the box represents the median value, with the hinges indicating the first and third quartiles, and whiskers extending to the most extreme data point within 1.5 times this interquartile range. Only days where the maximum turbidity reading at any time throughout the day was greater than 20 NTU were included. This ratio was greater than 5 fold for four days from two sites, and the turbidity readings (NTU) of these days are plotted in C (LNG0) and D (MOF1).
Table 4.
Intensity, duration and frequency (IDF) analysis of the seawater quality data at selected dredge-influenced site (Dredg.) and reference site (Ref.) for the Barrow Island, Cape Lambert and Burrup Peninsula dredging programs.
Fig 6.
Turbidity (NTU) and PAR (μmol photons m-2 s-1) during the Barrow Island dredging project measured every 10 mins over a 6 day period in April 2011 from (A) a terrestrial light sensor located on Barrow Island (B) at 4.5 m depth at a site ~150 m from dredging, and (C) at 4.5 m depth at reference site ~30 km from dredging (see Fig 1).
Numbers above the light profiles are the daily light integral (mol photons m-2 d-1) (see Material and Methods).
Table 5.
The photosynthetically active radiation (PAR) daily light integral (DLI, mol photons m-2) percentile values for various running mean time periods for the Barrow Island dredging project.
Fig 7.
Total daily light integral (mol photons m-2 d-1, left panels) and probability density function (right panels) at two dredge impacted sites (MOF1 and LNG1, see Fig 1) and at SBS (reference site) during the Barrow Island project.
Seawater depth at MOF1 and SBS were similar (~4.5 m) and at LNG1 was ~9 m. The red line on the left hand plots indicates the start of dredging for each project and dashed lines represent the timing of cyclone events that may have had the potential to cause substantial swell in this region (Puotinen, pers comm). Annotations at the base of the x-axis indicate each cyclone event, as follows: (a) Nicholas, max category 4, min distance 190 km; (b) Dominic, max category 2, min distance 20 km; (c) Bianca, max category 4, min distance 105 km; (d) Carlos, max category 3, minimum distance 0 km. Centre panels show the running means percentile analysis (50th, 20th, 5th, 1st and 0th (minimum)) PAR values, plotted as a function of the running mean time span from 1 to 30 days. Annotations under each axis indicate each cyclone event, as follows: Nicholas (N), category 4 minimum distance 190 km; Billy (Bil), category 3; Dominic (Do), category 2 minimum distance 20 km; Bianca (Bia) category 4, minimum distance 105 km; Carlos (Ca) minimum distance 0 km, category 3; Lua (Lu) category 4. Cyclone categories indicate the intensity (Australian Ranking Scale) of each cyclone at closest approach to the sites.
Fig 8.
(A) Total photosynthetically active radiation (PAR) daily light integral (DLI, mol photons m-2) percentile values for running means calculated on time scales of 1, 14 and 30 days for all sites for the Barrow Island project. (B) Mean, median, 80th percentile and maximum number of consecutive days in darkness and semi-darkness and (C) and mean fortnightly numbers of days for 4 different semi-darkness cut-off thresholds at all sites for the Barrow Island dredging project (1, 5, 10 and 20 μmol photons m-2 s-1; equivalent to DLI values of 0.04, 0.2, 0.4, and 0.8 mol photons m-2 d-1).
White symbols represent percentiles for the baseline period (pre-dredging period), grey symbols represent reference sites during the dredging period and black symbols represent sites close to (<2 km) the dredging.