Measurements were conducted in a tank (50 cm wide, 57 cm high, 3.1 cm deep) containing approx. 47 cm sediment with 10 cm of overlying water (overlying water flow rate = 20 to 60 mL per minute). The pressure sensor was located 25 cm deep in the sediment on the right side of the tank. Images were taken at 30 second intervals.
Experiments were conducted at the Pacific Coastal Ecology Branch, Western Ecology Division, US Environmental Protection Agency, Newport, Oregon 97365, USA.
Planar Optode Imaging:
The lifetime imaging system is modified after Holst and Grunwald (2001). It comprises a cooled CCD camera (pco.1600MOD, PCO AG, Donaupark 11, 93309 Kelheim, Germany), a pulse delay generator (T560, Highland Technology, 18 Otis St, San Francisco CA), an array of blue-light emitting diodes (LEDs; lambda max = 455 nm, LXHL-LR5C, Philips Lumileds, 370 W Trimble Rd, San Jose, CA) attached to a heat sink (~5×5×2.5 cm), and a custom-made power supply. The camera accumulates multiple exposures with a programmable modulation time. By using the output of the exposure synchronization of the camera as a trigger for the pulse delay generator and subsequently the LED light pulse, any jitter between the camera exposure time and the preceding light flash can be avoided. The timing parameters is chosen as follows. After the LED pulse of 20 µs duration and a given delay, delta, the electronic shutter for camera exposure opens for D = 10 µs. The delays of delta_1 = 1 µs and delta_2 = 11 µs are applied for the accumulation of the first (I1) and second (I2) intensity window images (gates), respectively, which are acquired sequentially. Summing up all times to 41 µs for the longest delay reveals the minimum time interval for the accumulations of single exposures. Typically an interval of 44 µs is chosen, corresponding to a repetition rate of almost 23 kHz. Using the first and second intensity window images, the luminescence lifetime image is calculated as t = D/ln(I1/I2) (Holst and Grunwald 2001). The peak current through the LEDs (typically 200–300 mA) and the integration time during which both intensity windows are accumulated (typically 250–1000 ms) are adjusted to optimize image quality. The control of the camera and image acquisition through the IEEE 1394 (firewire) interface, and of the delay pulse generator through the RS232 (serial) interface, are done by a laptop computer using software developed by Lubos Polercky (Microsensors Group, Max Planck Institute for Marine Microbiology, Bremen, 28359, Germany) and Uli Henne (German Aerospace Center, Institute of Aerodynamics and Flow Technology, Göttingen, 37073, Germany) in Borland Delphi and C++. Optodes were calibrated using the lifetime values measured in the anoxic sediment and in the air-saturated overlying water. For details see Matsui, GY et al. 2011.
Porewater Pressure Sensing:
The differential pressure sensors (Honeywell 27PC) are piezoresistive bridges that provide a differential voltage proportional to the pressure difference between the 2 sides of the sensor. While one side of the sensor is indirect contact with the sediment porewater (gage pressure), the ambient (hydrostatic) pressure isdetected within a water-filled space within the PVC channels (plenum) that is in direct contact with the overlying water and isolated from the porewater. Data are typically collected at 200 Hz using autonomous 8-channel 16-bit data loggers (CF2, Persistor Instruments, 153-A Lovells Lane, Marston Mills MA). Amplifiers on the boards allow adjustment of the dynamic range of the sensors. Sensors are calibrated by varying the water heights on both sides of the sensors, i.e. the plenum and sediment side. Twelve positive and negative pressures are typically applied to each sensor, and the linear calibration between the gauge pressure and measured voltage has typically R2 > 0.95. The 200 Hz raw data are downscaled to 1Hz by taking the median of all values in each 1-second interval. The median of each 60 minute block was calculated, and linearly interpolated values of this median time series was subtracted from each 1Hz data value to remove long term drift from the signals.
Time-lapse photography:
Images of the shrimp tanks are taken with digital SLR cameras (Nikon D200 and D300) using flash, triggered by time-lapse controllers (Digi-Snap, Harbortronics) or by a digital delay generator (T560 Highland Technology). Images are typically taken at 15 to 30 s intervals.
Related files and references:
Optode system:
Matsui, GY, N Volkenborn, L Polerecky, U Henne, DS Wethey, CR Lovell, SA Woodin. 2011. Mechanical imitation of bidirectional bioadvection in aquatic sediments. Limnology and Oceanography: Methods 9: 84-96. DOI: 10.4319/lom.2011.9.84
These data are related to Figures 4, 5, and 6 in the following paper:
Volkenborn, N, L Polerecky, DS Wethey, TH DeWitt, SA Woodin. 2012. Hydraulic activities by the ghost shrimp Neotrypaea californiensis induce oxic-anoxic oscillations in sediments. Marine Ecology Progress Series 455: 141-156. DOI: 10.3354/meps09645
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