How to Calculate Community Respiration in Sediments

Community respiration describes energy transfers within an ecosystem. Respiration is the intake of oxygen and the release of carbon dioxide. To calculate energy transfers, sediment samples are measured for dissolved oxygen, converted to a dry weight to which the rate of dissolved oxygen is applied and then extrapolations are made to the entire community from which samples were taken.

Things You'll Need

• Sediment samples
• A dissolved oxygen meter, equipped with a biological oxygen demand (BOD) probe and stirrer
• Temperature gage
• Insulated cooler
• Test tubes

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Instructions

Sediment Sampling and Analysis

• 1

  Collect several soft sediment samples with a small plastic scoop. These samples should come from the top one inch layer of sediment from a random pattern with the sampling area. Combine several samples into one jar or plastic bag to obtain a composite sample about 250 mL total .

• 2

  Fill an insulated cooler with water obtained from the sampling area. Using the properly calibrated dissolved oxygen meter, measure the dissolved oxygen and temperature of the water. Record values. Mix the composite sample and transfer 10 mL of the sample to properly labeled tubes. Fill each tube to the top with water from the cooler, seal tubes and place in the cooler for a two hour incubation period. Re-calibrate the dissolved oxygen meter and measure the dissolved oxygen in each tube. Pour off remaining water from each tube, preserving the sediment, seal tube and place all tubes in the cooler on ice for transfer to a laboratory where samples will be converted to ash-free dry mass (AFDM).

• 3

  Convert sediment samples into a measurable dried volume in a lab. This volume is called ash-free dry mass. Sediment respiration is measured as the change in dissolved oxygen rate per hour of incubation per sediment sample. This rate is applied to the dry mass weight determining a measure of community respiration per gram of AFDM which can then be extrapolated to an estimated volume of sediment within an area of interest.

• 4

  Calculate rates of carbon dioxide production. Do so from community respiration rates because the carbon content of sediment is estimated as 0.5 X AFDM. Applying the dissolved oxygen rate to the AFDM and then multiplying by 0.5 will identify community sediment respiration factors of oxygen (intake) and carbon dioxide (release).

• 5

  Evaluate benthic, marine and sedimentary communities for respiration. These elements are used in carbon cycle models. The carbon cycle model identifies amounts of carbon continually cycling in our global ecosystem from decayed material to plant growth to the atmosphere and the ocean with the ultimate goal of identifying the global capacity to adjust to increased carbon emissions.