Actividades de aprendizaje con Retroalimentación:

Surface water samples were collected from ten easily accessible locations along the length of Wybong Creek, with sample sites located at regular intervals (Figure 2.1). Sampling occurred on three dates during the low flow conditions of 2001-2007: the 21st_-

22nd _{April; the 21-23}rd _{July 2006; and the 1}st _{June 2007. Average rainfall and higher}

flow conditions occurred in the catchment from mid-2007 onwards, with surface water samples collected on the 5th-7th July 2007; and the 17-18th June 2008. Samples were collected from the centre of the channel at one third of the total depth below the Creek’s surface, except at the 87 km site where water depth necessitated collection from the edge of the Creek. Rainwater samples were collected 13 km south of the catchment (Denman) on the 14th of June 2007, and 18th of July 2008, with all other rainwater samples collected 20 km west of Wybong Creek (Muswellbrook) during 2008.

2.2. Sample analyses

Water quality parameters were measured on unfiltered water samples at the time of sampling using Orion Gel-Filled pH and Eh electrodes and pH and Eh meters. An Orion DuraProbe™ 4-electrode conductivity cell and conductivity meter was used to measure electrical conductivity (EC). The EC cell and meter was calibrated in the field using Thermo Orion Application Solution (1413 µS cm-1), while the Eh meter and

55 km N 11 km 30 km 37 km 48 km 55 km 60 km 72 km 77 km 83 km 87 km 0

Chapter Two – Identification of solute sources to Wybong Creek 19

electrode were calibrated using Thermo Orion ORP standard solution. The pH meters were calibrated using LabChem pH buffer solutions at pH 4, 7, and 10. All meters were regularly calibrated and checked against standard solutions in the field.

Bicarbonate concentrations were determined on filtered samples by HCl titration using an Hach digital titrator, and methyl orange indicator (Franson 2005), with the exception of a number of rainwater samples which were at times collected independent of field work. Water samples collected for cation, anion, and isotope analyses were filtered in the field using 0.45 µm Millipore® nitrocellulose filters, and collected in new or HNO3 acid-washed 250 mL polyethylene bottles and/or 50 mL Falcon tubes.

Samples for cation and 87Sr/86Sr analyses were acidified using 2 mL 50 % Merck ultra- pure HNO3. Blanks made up of milli-Q water were prepared in the same way as samples

for cation and anion analyses at the time of sampling.

2.2.1. Cation, anion and isotope analyses

Reactive ions were analysed in the field using a Hach spectrophotometer and methods 8146, 1, 10-Phenanthroline for Fe2+; method 10209 phosphomolybdate for PO42-; cadmium reduction for NO32-; and BaCl for SO42-(Hach Company 2009).

Samples collected for ion analyses during 2006 and 2009 were sent to the Centre for Coastal Biogeochemistry, Southern Cross University, with Ben Macdonald

collecting samples in 2006. Samples for ion analyses collected in 2007 – 2008 were sent to the Department of Water and Energy Water Environmental Laboratory, New South Wales, for analyses. Ion Chromatography (IC) was used to analyse anions while cations were analysed using Inductively Coupled Plasma – Mass Spectrometers (ICP-MS) and Inductively Coupled Plasma – Atomic Emission Spectrometers (ICP-AES).

Modelling of saturation indices was conducted in PHREEQC Interactive version 2.13.2.1727 using the PHREEQC.dat database.

2.2.2. Oxygen and hydrogen isotopes

Select samples were analysed for O and H isotopes by Claudia Kietel and Hillary Stuart-Williams at the Research School of Biological Sciences, The Australian National University. The stable isotopes of O and H were measured using a Micromass Isoprime CF-IRMS (Continuous-Flow Isotope-Ratio Mass Spectrometer). Oxygen isotope ratios of the water were determined by equilibration with CO2. Water volumes measuring 250

µL were pipetted into screw top glass vials. A mixture of air and 5 % CO2 was then

gently flowed into the remaining spaces and screw tops with a PTFE lined, butyl rubber septum immediately fitted. The sealed samples were then stood in the mass

Chapter Two – Identification of solute sources to Wybong Creek

20

spectrometer room and held at a constant temperature of 0.5 °C for approximately 48 hours. Samples of standard waters with values spanning the anticipated analytical values were similarly treated. Two needles were inserted through septums (He carrier gas in and out) at the end of this period. Samples were then carried through a magnesium perchlorate moisture scrubber and a Porapak QS GC column which separated the CO2

from the other gases in the helium carrier stream using a loop valve. The δ18O of CO2

was then measured in the mass spectrometer with values normalised against a reference gas pulse. The analysed values of O in CO2 were equilibrated with standard waters at

the end of the run, in order that a slope and offset could be calculated to correct the analytical results to the Vienna Standard Mean Ocean Water (VSMOW) scale.

Hydrogen isotope values were calculated using the chromium method in which water is reduced on hot Cr metal to liberate 2_{H. Water samples measuring 0.9 µL}

aliquots were pipetted into Sn cups, sealed immediately using crimping pliers, and placed in an AS200 autosampler. The sampler sat atop a furnace which maintained a Cr- packed quartz column at 1000 °C, with a Ni crucible on top of the Cr to catch the excess Sn, and a He carrier flowing down through the column. The Cr in the column was used to bind the O in the water as chromium oxide and release the 2_{H to the column in the He}

carrier. The carrier gas was passed through a magnesium perchlorate scrubber to dry and then through a Porapak QS GC column to separate the H from traces of other gases and shape the peak. The gas then flowed into the mass spectrometer through a capillary system, with it’s ratios then determined. Each sample peak was placed between a large and a small reference pulse, permitting normalisation of the results and calculation of the H3+ _{correction. Each sample was typically run two or three times so that memory}

effects from one sample to the next were minimised. The slope and offset for the standard waters was determined finally and the results all corrected to the VSMOW scale. Precision for the δ18O runs was between 0.06 and 0.1 ‰, and for the δ2H was between 0.3 and 0.6 ‰ (C. Kietel, Pers. Comm., 2009).

2.2.4. Quality assurance

Sample contamination was monitored by creating blanks in the field using milli-Q water. Traces of Cd, Al, Ba, Zn, Ca, Mg, K, Si, Na, and Sr were found in many blanks (Appendix Two: Table A2.1). Zn contamination from suncream was likely to have contributed significantly to overall Zn concentration in blanks collected in July 2007, with the Zn concentration in blanks subtracted from sample concentrations to correct for

Chapter Two – Identification of solute sources to Wybong Creek 21

this. Anions were below detection limits (BDL) in all blanks (Appendix Two: Table A2.2).

The quality of cation and anion analyses were monitored using charge balances (Eq. 2.1): anions cations anions cations difference       100 % (2.1)

where cation and anion concentrations were in meq L-1. The majority of charge balance differences were below 10 % (Appendix Two: Table A2.3). Rainwater and blanks were not measured for HCO3 in the field, accounting for the large charge balance differences

seen for these samples. The 11 km samples collected on 21/07/2006 and 18/07/2008 had charge balances of -18.4 % and -20.0 % respectively. A major cation was unlikely the cause of the charge imbalances as all major and many minor and trace elements were included in analyses, with the poor charge balance therefore caused by inaccurate HCO3

measurement (which contributed most of the negativity). These samples were included in analyses though HCO3 may have been over-estimated.