TY - JOUR

T1 - Headwater gas exchange quantified from O2 mass balances at the reach scale

AU - Rovelli, Lorenzo

AU - Attard, K.M.

AU - Heppell, C.M.

AU - Binley, Andrew Mark

AU - Trimmer, M.

AU - Glud, R.N.

PY - 2018/10

Y1 - 2018/10

N2 - Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon-relevant gases. Thus, we characterized variability in the re-aeration coefficient (k2) and dissolved oxygen (O2) gas transfer velocity (k) in two lowland headwaters of the River Avon (UK). The traditional one-station open-water method was complemented by in situ quantification of riverine sources and sinks of O2 (i.e., groundwater inflow, photosynthesis and respiration in both the water column and benthic compartments - sediments) enabling direct hourly estimates of k2 at the reach–scale (~150 m) without relying on the nighttime regression method. Obtained k2 values ranged from 0.001 – 0.600 h-1. Average daytime k2 were a factor two higher than values at night, likely due to diel changes in water temperature and wind. Temperature contributed up to 46% of the variability in k on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that k variability is aligned with dominant temperature trends rather than with short-term changes. Similarly, wind correlation with k increased when clustering wind speeds in increments correspondent with dominant variations (1 m s-1). Time scale is thus an important consideration when resolving physical drivers of re-aeration. Mean estimates of k from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O2 budget assessment (within <15%), adding further support to the validity of upscaling efforts aiming at quantifying large-scale riverine gas emissions.

AB - Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon-relevant gases. Thus, we characterized variability in the re-aeration coefficient (k2) and dissolved oxygen (O2) gas transfer velocity (k) in two lowland headwaters of the River Avon (UK). The traditional one-station open-water method was complemented by in situ quantification of riverine sources and sinks of O2 (i.e., groundwater inflow, photosynthesis and respiration in both the water column and benthic compartments - sediments) enabling direct hourly estimates of k2 at the reach–scale (~150 m) without relying on the nighttime regression method. Obtained k2 values ranged from 0.001 – 0.600 h-1. Average daytime k2 were a factor two higher than values at night, likely due to diel changes in water temperature and wind. Temperature contributed up to 46% of the variability in k on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that k variability is aligned with dominant temperature trends rather than with short-term changes. Similarly, wind correlation with k increased when clustering wind speeds in increments correspondent with dominant variations (1 m s-1). Time scale is thus an important consideration when resolving physical drivers of re-aeration. Mean estimates of k from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O2 budget assessment (within <15%), adding further support to the validity of upscaling efforts aiming at quantifying large-scale riverine gas emissions.

U2 - 10.1002/lom3.10281

DO - 10.1002/lom3.10281

M3 - Journal article

VL - 16

SP - 696

EP - 709

JO - Limnology and Oceanography: Methods

JF - Limnology and Oceanography: Methods

SN - 1541-5856

IS - 10

ER -