Control Points in Ecosystems: Moving Beyond the Hot Spot Hot Moment Concept
- 2.6k Downloads
The phrase “hot spots and hot moments” first entered the lexicon in 2003, following the publication of the paper “Biogeochemical hot spots and hot moments at the interface of terrestrial and aquatic ecosystems” by McClain and others (Ecosystems 6:301–312, 2003). This paper described the potential for rare places and rare events to exert a disproportionate influence on the movement of elements at the scale of landscapes and ecosystems. Here, we examine how the cleverly named hot spot and hot moment concept (hereafter HSHM) has influenced biogeochemistry and ecosystem science over the last 13 years. We specifically examined the extent to which the HSHM concept has: (1) motivated research aimed at understanding how and why biogeochemical behavior varies across spatiotemporal scales; (2) improved our ability to detect HSHM phenomena; and (3) influenced our approaches to restoration and ecosystem management practices. We found that the HSHM concept has provided a highly fertile framework for a substantial volume of research on the spatial and temporal dynamics of nutrient cycling, and in doing so, has improved our understanding of when and where biogeochemical rates are maximized. Despite the high usage of the term, we found limited examples of rigorous statistical or modeling approaches that would allow ecosystem scientists to not only identify, but scale the aggregate impact of HSHM on ecosystem processes. We propose that the phrase “hot spots and hot moments” includes two implicit assumptions that may actually be limiting progress in applying the concept. First, by differentiating “hot spots” from “hot moments,” the phrase separates the spatial and temporal components of biogeochemical behavior. Instead, we argue that the temporal dynamics of a putative hot spot are a fundamental trait that should be used in their description. Second, the adjective “hot” implicitly suggests that a place or a time must be dichotomously classified as “hot or not.” We suggest instead that each landscape of interest contains a wide range of biogeochemical process rates that respond to critical drivers, and the gradations of this biogeochemical topography are of greater interest than the maximum peaks. For these reasons, we recommend replacing the HSHM terminology with the more nuanced term ecosystem control points. “Ecosystem control” suggests that the rate must be of sufficient magnitude or ubiquity to affect dynamics of the ecosystem, while “points” allows for descriptions that simultaneously incorporate both spatial and temporal dynamics. We further suggest that there are at least four distinct types of ecosystem control points whose influence arises through distinct hydrologic and biogeochemical mechanisms. Our goal is to provide the tools with which researchers can develop testable hypotheses regarding the spatiotemporal dynamics of biogeochemistry that will stimulate advances in more accurately identifying, modeling and scaling biogeochemical heterogeneity to better understand ecosystem processes.
Keywordsbiogeochemistry hot spots control points ecosystem
This paper arose from vigorous, weekly conversations among the authors over the course of 2015–2016. The authors would like to thank members of Duke’s River Center, Peter Groffman and two anonymous peer reviewers for constructive feedback and advice on this manuscript. Authors JB, KK, ES were supported by NSF GRFP fellowships and CF was supported by a DOE GO! graduate fellowship for some or all of this period.
- Christenson LM, Mitchell MJ, Groffman PM, Lovett GM. 2010. Winter climate change implications for decomposition in northeastern forests: comparisons of sugar maple litter with herbivore fecal inputs. Glob Change Biol 16:2589–601.Google Scholar
- Feinerer I, Hornik K. 2015. tm: Text Mining Package. R package version 0.6-2.Google Scholar
- Harms TK, Grimm NB. 2008. Hot spots and hot moments of carbon and nitrogen dynamics in a semiarid riparian zone. J Geophys Res Biogeosci. doi: 10.1029/2007JG000588.
- Hedin LO, von Fischer JC, Ostrom NE, Kennedy BP, Brown MG, Robertson GP. 1998. Thermodynamic constraints on the biogeochemical structure and transformation of nitrogen at terrestrial–lotic interfaces. Ecology 79:684–703.Google Scholar
- Lezama-Pacheco JS, Cerrato JM, Veeramani H, Alessi DS, Suvorova E, Bernier-Latmani R, Giammar DE, Long PE, Williams KH, Bargar JR. 2015. Long-term in situ oxidation of biogenic uraninite in an alluvial aquifer: impact of dissolved oxygen and calcium. Environ Sci Technol 49:7340–7.CrossRefPubMedGoogle Scholar
- Olefeldt D, Roulet NT. 2012. Effects of permafrost and hydrology on the composition and transport of dissolved organic carbon in a subarctic peatland complex. J Geophys Res Biogeosci. doi: 10.1029/2011JG001819.
- Peter S, Rechsteiner R, Lehmann MF, Tockner K, Vogt T, Wehrli B, Durisch-Kaiser E. 2011. Denitrification hot spot and hot moments in a restored riparian system. In: Schirmer M, Hoehn E, Vogt T, Eds. Gq10: groundwater quality management in a rapidly changing world. Wallingford: International Association of Hydrological Sciences. p 433–6.Google Scholar
- Risser PG, Karr JR, Forman RTT. 1984. Landscape Ecology: directions and approaches. Illinois Natural History Survey Special Publ. 2, University of Illinois, Urbana.Google Scholar
- Rode M, Wade AJ, Cohen MJ, Hensley RT, Bowes MJ, Kirchner JW, Arhonditsis GB, Jordan P, Kronvang B, Halliday SJ, Skeffington R, Rozemeijer J, Aubert AH, Rinke K, Jomaa S. 2016. Sensors in the stream: the high-frequency wave of the present. Environ Sci Technol 50:10297–307.CrossRefPubMedGoogle Scholar