McClain et al. - Biogeochemical hot spots and hot moments

McClain et al. "Biogeochemical Hot Spots and Hot Moments at the interface of Terrestrial and Aquatic Ecosystems"

Rates and reactions of biogeochemical processes vary in space and time, producing hot spots and hot moments of elemental cycling.
- Hot spots = patches that show disproportionately high reaction rates relative to the surrounding matrix (variation in space)
- Hot moments = short periods of time that exhibit disproportionately high reaction rates relative to longer periods (variation in time)

Often enhanced at terrestrial-aquatic interfaces; often coincide with ecotones (but are not ecotones - only rates change, not structure) and disturbances

Where hot spots and hot moments can occur:
- where hydrological flowpaths intersect, or where flowpaths meet a substrate containing certain reactants
- hyporheic zones (area of saturated sediment beneath and beside streams where groundwater and surface water mix)
- riparian zones
- confluence of two rivers with contrasting chemistries
- estuaries
- areas of upwelling/downwelling in oceans

Water essential to biogeochemistry: enhances biogeochemical fluxes by transporting elements across space and providing conditions that enhance cycling rates

Hot moments occur when hydrological flowpaths are variable in time
- ex. precipitation in a desert
They are also caused by other periodic phenomena
- ex. fire

A system is called "primed" to be a hot spot/hot moment when all but one ingredient is present
- ex. snowmelt

Hot spot reactions are often limited because a reactant is unstable or only proceeds under particular conditions

Hot spots and hot moments often overlap and are possible on different scales
- reading gives example of denitrification, which varies with:
- distribution of anoxic zones in soil and other soil characteristics (catena/small scale)
- interface of riparian and upland areas, hyporheic zones (upland-stream scale)
- distribution of wetlands (large scale)

Management implications of hot spots/hot moments
- concepts helpful for understanding how to manage for eutrophication, algal blooms, hypoxia, greenhouse gas flux, soil impoverishment, etc.
- role of hot spots and hot moments as sources and sinks of N and organic C
- role of hydrology in biogeochemical reactions

Research priorities with hot spots and hot moments
- investigate natural and man-made ocurrance of hot spots/hot moments of elemental cycles other than N and C at different scales
- improve ability to predict their spatial and temporal distribution
- use techniques from landscape ecology to understand their role in the biogeochemistry of the landscape
- evaluate utility of natural and man-made hot spots/hot moments as management tools
- which processes and where could have pollution-reduction potential
- their role in evaluating trade-offs landscape feature preservation
- human disturbances

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