Sediment and soil quality at Ashfield Flats Reserve, Western Australia
Description
Elemental (including Al, As, B, Ba, Be, Ca, Cd, Ce, Co, Cr, Cu, Fe, Ga, Gd, Ge, K, La, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, S, Sc, Si, Sr, Th, Ti, V, Y, Zn, Zr) concentrations, pH, electrical conductivity, microplastics, Longitude-Latitude and UTM Zone 50 coordinates, sample material type, sampling strata, and sample identification codes for 231 samples of sediment or soil collected in 2019, 2020, and 2021 from Ashfield Flats Reserve, an urban nature reserve in Western Australia. Ashfield Flats Reserve (approx. 40 ha) is listed as a Western Australian Bush Forever Site (No. 214) and fringes the Swan-Canning Estuary. It is also listed in the Directory of Important Wetlands in Australia and contained a threatened ecological community of temperate saltmarsh plant species. It is the largest remaining salt marsh in the Swan-Canning Estuary, but is impacted by altered hydrology, several stormwater drains, and poor water quality from historical groundwater contamination. Sampling and analysis was conducted to assess the severity and extent of contamination of sediments and soils with trace elements, nutrients, and microplastics. In particular it was of interest whether stormwater drains which cross the reserve were contributing contaminants to adjacent wetlands.
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Sampling was on 15 March 2019, 13 March 2020, and 5 March 2021. Sampling design used transects across anticipated contamination gradients, or regular or irregular grids within strata, depending on sampling year. Soils and wetland sediments were sampled as composites of triplicate cores at each location at 0-10 cm depth, and air dried at 40 °C prior to chemical analyses. EC of 1/5 solid/deionised water suspensions of soil and sediment samples was determined using a calibrated conductivity cell electrode. pH was measured on the same suspensions using a glass-reference pH electrode after 2-buffer calibration. Filtered, acidified water samples were used for analyses. Al, As, Ba, Ca, Cd, Ce, Co, Cr, Cu, Fe, Ga, Gd, K, La, Li, Mg, Mn, Mo, Na, Nd, Ni, P, Pb, Rb, S, Sc, Sr, Th, Ti, V, Y, and Zn were measured on sediment and soil samples by ICP-OES following digestion of samples in concentrated nitric and hydrochloric acids at 130 °C. Samples were ground to ≲ 50 µm using a ceramic mortar and pestle prior to digestion. Reagent blanks, and grinding blanks composed of acid-washed silica sand, were included to check contamination and for calculating lower limits of detection (3x blank S.D.). The standard reference material STSD-2 was included to assess analytical accuracy. Measurement precision was assessed using analytical duplicates. Microplastics were enumerated in sediment and soil samples following removal of non-plastic organic matter using Fenton’s Reagent, followed by separation from mineral grains by density separation in 40% w/v potassium iodide solution. Floating material in supernatants was collected by vacuum filtration onto paper filters, and microplastics counted using a dissecting microscope. Blank samples were taken through identical laboratory steps, keeping blanks uncovered for the same time as samples.