Introduction

Carbon can be derived and released by many sources. In a wetland environment, water and the underlying sediments with their associated microbial, plant and animal populations probably dominate carbon activity. However, external carbon sources may also play important roles. The following is a discussion of sources of carbon, measurement techniques of the various carbon inputs and outputs, and a general discussion of integrating this information into a modelling exercise of carbon activities.

Carbon Inputs

Inputs of carbon can be derived from many different sources. These sources can be both direct and indirect, and often involve transformations of the original material. One large source of carbon is found directly in the contents of water, including groundwater, surface-water runoff and precipitation. Carbon in groundwater reservoirs can be analyzed with piezometers and the appropriate chemical analysis of dissolved organic carbon or DOC and particulate organic carbon or POC. Surface water runoff carbon levels can be determined with the use of large container vessels and chemical analysis. Precipitation carbon levels can be analyzed with the use of collection vessels and chemical analysis.

Incorporation of atmospheric carbon also occurs, directly and indirectly (through water) by aquatic macrophytes (standing crop and growth rate measurements), phytoplankon (carbon-14 or C¹⁴ incorporation) and sessile algae (C¹⁴ incorporation). Lake water measurements of dissolved inorganic carbon or DIC, DOC and POC can also reveal carbon levels, although measurements on pond depth are needed to be able to assess total changes over time. Carbon is also found in other sources. Aeolian deposition (wind) can deposit soil containing carbon. These deposits can be analyzed with the use of aeolian deposition collectors for particulate carbon with chemical analysis of the collected material. As well, sediment analysis of DOC and POC and C¹⁴ dating can determine carbon storage rates. Carbon is also contributed by waterfowl through their life interactions, estimated by dead carcasses, and excretion rates.

Carbon Outputs

Just as carbon can be stored in many sources, it is also released through a variety of sources and processes. Carbon is found in fungi and bacterial biomass and can be measured in production and growth rates by radiolabelling techniques of the pelagic and sessile communities. Carbon is also released by invertebrate biomass and can be assessed by their growth rates and the rates at which they break down POC.

Biologically available DOC (BDOC) can be measured through the incubation of water samples followed by chemical analyses with an organic carbon analyzer. Photolysis (DOC breakdown by sunlight) of DOC (either to CO₂ or BDOC) and measurement of DOC breakdown can be obtained from changes in microbial production and/or the measurement of CO₂ and DIC production. However, the technology is not available to measure small changes in DOC in the large DOC and DIC pools characteristic of prairie wetlands. To estimate the potential importance of photolysis in these ponds, measurements of UV-radiation penetration through the water are required and can be obtained from a scanning underwater spectroradiometer.

Another output of carbon is greenhouse gases, the measurement of CO₂ and CH₄ from water and sediments using gas collectors and gas chromatography. Here, rates are needed for aerobic versus anaerobic conditions (i.e., windy versus calm, etc.). In addition, wind data measurements and profiles of diel cycles of dissolved oxygen concentration and vertical and horizontal changes in the water column are also needed.

Integration and Results

The inputs and outputs can be integrated through application of stable isotopes to determine carbon pathways and allochthonous versus autochthonous carbon inputs. The next steps involve choice of model construction and calibration of the modelling and results.

It is important to undertake rigorous experimentation to assess the relative roles of nutrients (especially nitrogen and phosphorous), temperature and UV radiation on the carbon processes and on the sources of carbon inputs and outputs listed above. These factors need to be incorporated in some manner into the modelling exercise. Models of whole wetland manipulations, such as the Marsh Ecology Research Program or MERP experiments, are likely the best way to test the models and theories about prairie wetlands and their responses to environmental disturbances.