overview

Water sampling from the south side of Tempe Town Lake at a depth of ~ 1 meter. We make in situ measurements of water quality parameters (pH, Temp, O2, Conductivity) and collect samples for analysis of dissolved organic carbon/total nitrogen in the laboratory.

pH

Measured in the field with hand-held YSI or Thermo-Orion sensors. Sensors are calibrated each day with a 3-point calibration curve (pH = 4, 7, 10).

conductivity

Measured in the field with a handheld Orion conductivity sensor. Sensor is calibrated each day with a one-point, 1000 microSieman conductivity solution. Values in microSiemans (temperature compensated).

dissolved oxygen

Measured in the field with a hand-held YSI sensor. Sensor is altitude compensated and calibrated relative to an air saturated water solution each day. Values in mg O2/L.

temperature

Measured by each of the above sensors. Values in degrees Celsius.

water collection and filtration

Water samples are collected into 1L Nalgene bottles that are rinsed 3x with lake water before collection. Samples are collected below the surface and an effort is made to exclude floating debris. Samples are immediatedly transported to the lab for filtration. Samples are filtered through GF/F filters on a vacuum manifold. Samples are collected in an ashed (450°C) flask and distributed in to centrifuge tubes for storage until analysis.

sample storage

Polypropylene centrifuge tubes (VWR) are rinsed with deionized water and leached for 48 hours prior to use. Filtered samples for dissolved organic carbon analysis are acidified to pH<2 with HCl and stored in the dark at 4 deg C until analysis. Every effort is made to analyze samples within 1 month of collection.

dissolved organic carbon/total nitrogen analysis

Dissolved organic carbon concentration was measured using a Shimadzu TOC-V carbon analyzer where samples are combusted at 680°C in an oxygen-rich environment with a platinized-alumina catalyst to convert all carbon in the sample to carbon dioxide gas (Hedges et al. 1993; Sharp et al. 1993; Sharp 1993; Sharp 1997). Dissolved organic carbon is detected as CO2(g) by a non-dispersive infra-red gas analyzer. Total nitrogen is detected from the same analysis as NO using a chemiluminescence nitrogen detector. The instrument is calibrated daily with a 5-point calibration curve for carbon and nitrogen, and quality check standards are evaluated with each run.

alkalinity and bicarbonate

Determined by Gran titration with hydrochloric acid.

turbidity

Measured with a Hach turbidity meter in normalized turbidity units

suspended sediment

Determined by mass. One liter of water was filtered onto GF/F filter (25 mm); filter was dried at 60 deg C and weighed to determine mass of sediment.