Spatial biogeochemistry

February 25, 2012 – 12:30 pm

I’ve seen a couple interesting papers recently on spatial biogeochemistry, a topic I enjoyed working on during my dissertation. Here’s how I described the importance of spatial biogeochemistry in one of my dissertation papers. In this case, I was discussing nitrogen (N) import and export from ecosystems, but the same case can be made for other biogeochemical processes.

Our current understanding of N import and export is based primarily on point estimates or on integrated estimates from hydrologic data. While these estimates provide a valuable foundation for understanding these processes, more detailed measurements that take spatial heterogeneity into account are likely to reveal important biogeochemical phenomena at larger scales, especially in the complex terrain of mountain ecosystems.

In a study of interannual variation in landscape carbon flux, Diego Riveros-Iregui and his colleagues found that:

Based on soil respiration measurements taken at a subalpine forest in central Montana, we found that locations with high drainage areas (i.e., lowlands and wet areas of the forest) had higher cumulative soil respiration in dry years, whereas locations with low drainage areas (i.e., uplands and dry areas of the forest) had higher cumulative soil respiration in wet years.

A nice finding. From this, they conclude:

These results highlight that evaluating and predicting ecosystem-scale soil C response to climate fluctuation requires detailed characterization of biophysical-topographic interactions in addition to biophysical-climate interactions.

I think they are correct that taking spatial variation into account is one of final frontiers in understanding ecosystem carbon cycling. Diego was a postdoc at CU when I was  a grad student there; now he’s faculty at the University of Nebraska. They are lucky to have him as I think he is becoming a leader in this research area.

In another recent study of N export from watersheds, Ross et al. were able to make a quantitative link between the magnitude of soil processes and N export in streams.

Stream NO3 export was positively related to nitrification rates … These spatial relationships found here suggest a strong influence of near-stream and near-watershed-outlet soils on measured stream NO3 export.

There were a few caveats to this relationship, but it is impressive that they were able to document this link at all since it is difficult to meaningfully measure the magnitude of these soil microbial processes.

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