Citation:

Collins, S., S. Matter, I. Buffam, AND J. Flotemersch. A patchy continuum? Stream processes show varied responses to patch‐ and continuum‐based analyses. Ecosphere. ESA Journals, 9(11):e02481, (2018). https://doi.org/10.1002/ecs2.2481

Impact/Purpose:

In this study, we compared patch- and continuum-based models for watersheds. Neither appear to be sufficient for explaining overall variation in stream nutrients and metabolism. Perhaps a more productive conceptual approach would be to think of watersheds as ecologically integrating units composed of interacting biologic, geologic, and hydrologic processes, and further, a recognition that these interactions can, and do, vary within and across watersheds. If this paradigm indeed better reflects reality, it then follows that we should not be seeking a single model that works within, let alone across, watersheds, but rather endeavoring to understand the extent that a given model, or suite of models, has some degree of applicability to the suite of prevailing processes.

Description:

Many conceptual syntheses in ecology and evolution are undergirded by either a patch‐ or continuum‐based model. Examples include gradualism and punctuated equilibrium in evolution, and edge effects and the theory of island biogeography in ecology. In this study, we sought to determine how patch‐ or continuum‐based analyses could explain variation in concentrations of stream macronutrients and system metabolism, represented by measures of productivity and respiration rates, at the watershed scale across the Kanawha River Basin, USA. Using Strahler stream order (SSO; continuum) and functional process zone (FPZ; patch) as factors, we produced statistical models for each variable and compared model performance using likelihood ratio tests. Only one nutrient (i.e., PO3−4) responded better to patch‐based analysis. Both models were significantly better than a null model for ecosystem respiration; however, neither outperformed the other. Importantly, in most cases, a combination model, including both SSO and FPZ, best described observed variation in the system. Our findings suggest that several patch‐ and continuum‐based processes may simultaneously influence the concentration of macronutrients and system metabolism. Nutrient spiraling along a continuum and the patch mosaic of land cover may both alter macronutrients, for example. Similarly, increases in temperature and discharge associated with increasing SSO, as well as the differences in light availability and channel morphology associated with different FPZs, may influence system metabolism. For these reasons, we recommend a combination of patch‐ and continuum‐based analyses when modeling, analyzing, and interpreting patterns in stream ecosystem parameters.

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