Further Deciphering the Carbon Cycle . . .

The complexities of carbon cycling are far from understood. We need more basic information on where carbon is stored, how it is released from organic tissues, and what roles it plays in ecosystems. Such information will feed into attempts to control the negative features of this greenhouse gas. Several CGRER members are working to refine our knowledge of the flow of carbon in its various forms. Four examples follow.

Steve Heard (UI, Biology) has been studying the breakdown of dead leaves and other organic material within streams, a process that terminates in the release of CO₂. How much of this breakdown is due to the "shredders" and "collectors," invertebrates that break leaves into small, and then smaller still, particles? While these two types of invertebrates (along with microorganisms) are usually given credit for decomposing the majority of stream debris, Steve has shown that mechanical abrasion such as grinding by stones is also an important contributor to the breakdown process.

George Malanson (UI, Geography) has examined the cycling of carbon at alpine treeline and determined that the amount of carbon taken up by plants does not determine the location of treeline; instead, its specific location on any mountainside seems to be related to factors such as seedling establishment. In another project, he has determined that plants growing along a river’s edge take up more CO₂ through photosynthesis, and also supply more carbon to the adjacent river, than do plants in the interior of floodplain forests. These streamside forests thus serve as an important suppliers of carbon to river invertebrates. Lastly, George has assisted with ecological considerations and total environmental impacts of the use of biomass (such as poplar trees, or switchgrass as described earlier) as a fuel source in Iowa.

Jim Raich (ISU, Botany) has performed evaluations of carbon accumulation and cycling in fields of corn and soybeans, in comparison with adjacent streamside buffer strips composed of differing mixtures of trees, warm-season grasses, and cool-season grasses. He found that fine root density and biomass, rooting depth, soil respiration rates, and thus organic material cycling and carbon sequestration were greater in the plantings of trees and grasses than in croplands of corn or soybeans.

Taking carbon considerations into another realm, Dave Forkenbrock (UI, Public Policy Center) recently published a monograph comparing the societal costs of transporting freight by truck with costs of rail transport. Comparing the CO₂ emissions of trucks with those of three types of freight trains, he calculated that emissions of trucks were about 7 to 9 times greater than those of trains for each ton-mile of freight transported. Were the costs to society of CO₂ and various air pollutants from truck transport included in the user charges, the road use tax paid by truckers would triple.