Multiple scales of temporal variability in ecosystem metabolism rates: results from two years of continuous monitoring in a forested headwater stream

Journal Article · Mon Jan 01 04:00:00 EST 2007 · Ecosystems

DOI:https://doi.org/10.1007/s10021-007-9059-2· OSTI ID:931962

Roberts, Brian J ^[1]; Mulholland, Patrick J ^[1]; Hill, Walter ^[1]

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1. ORNL

Headwater streams are key sites of nutrient and organic matter processing and retention, but little is known about temporal variability in gross primary production (GPP) and ecosystem respiration (ER) rates as a result of the short duration of most ecosystem metabolism measurements in lotic ecosystems. We examined temporal variability and controls on ecosystem metabolism by measuring daily rates continuously for two years in Walker Branch, a first-order deciduous forest stream. Four important scales of temporal variability in ecosystem metabolism rates were identified: (1) seasonal, (2) day-to-day, (3) episodic (storm-related), and (4) inter-annual. Seasonal patterns were largely controlled by the leaf phenology and productivity of the deciduous riparian forest. Walker Branch was strongly net heterotrophic throughout the year with the exception of the open-canopy spring when GPP and ER rates were similar. Day-to-day variability in weather conditions influenced light reaching the streambed, resulting in high day-to-day variability in GPP particularly during spring (daily light levels explained 84% of the variance in daily GPP in April). Episodic storms depressed GPP for several days in spring, but increased GPP in autumn by removing leaves shading the streambed. Storms depressed ER initially, but then stimulated ER to 2-3 times pre-storm levels for several days. Walker Branch was strongly net heterotrophic in both years of the study (NEP = -1156 and -773 g O2 m-2 y-1), with annual GPP being similar (488 and 519 g O2 m-2 y-1) but annual ER being higher in 2004 than 2005 (-1645 vs. -1292 g O2 m-2 y-1). Inter-annual variability in ecosystem metabolism (assessed by comparing 2004 and 2005 rates with previous measurements) was the result of the storm frequency and timing and the size of the spring macroalgal bloom. Changes in local climate can have substantial impacts on stream ecosystem metabolism rates and ultimately influence the carbon source and sink properties of these important ecosystems.

• Research Organization: Oak Ridge National Laboratory (ORNL); Oak Ridge National Environmental Research Park
• Sponsoring Organization: ORNL work for others
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 931962
• Journal Information: Ecosystems, Journal Name: Ecosystems Vol. 10
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CARBON SINKS
CARBON SOURCES
ECOSYSTEMS
FORESTS
METABOLISM
MONITORING
ORGANIC MATTER
Oedogonium
PRODUCTION
RESPIRATION
STREAMS
VARIATIONS
bryophytes
disturbance
ecosystem respiration
inter-annual variability
leaf litter
light
macroalgae
periphyton
primary production
reaeration
seasonal patterns
storms