Rg. Young et Ad. Huryn, INTERANNUAL VARIATION IN DISCHARGE CONTROLS ECOSYSTEM METABOLISM ALONG A GRASSLAND RIVER CONTINUUM, Canadian journal of fisheries and aquatic sciences, 53(10), 1996, pp. 2199-2211
Longitudinal patterns of ecosystem metabolism were measured in a 310-k
m grassland river continuum (Taieri River, New Zealand) during two con
secutive summer-autumn periods with contrasting discharge (average 199
3-1994 = 76.8 m(3) . s(-1); 1994-1995 = 6.6 m(3) . s(-1)). Metabolism
was estimated from diel oxygen curves using the single-station open-ch
annel regression method. Ratios of gross primary production (<0.3-9.6
g O-2 . m(-2). day(-1)) to community respiration (0.7-9.8 g O-2 . m(-2
). day(-1)) ranged to 6.5, while net daily metabolism ranged from -8.2
to 6.2 g O-2 . m(-2). day(-1). Only the upper 70 lan of the river was
autotrophic during 1993-1994, while most of the river was autotrophic
during 1994-1995. Light saturation of gross primary production by nat
ural communities of autotrophs (bankside light intensities greater tha
n or equal to 250 mu mol . m(-2). s(-1)) was observed only in the head
waters during 1993-1994, but throughout the continuum during 1994-1995
. Patterns of gross primary production were controlled by fluctuations
in water depth and turbidity that determined light availability. In r
egions with oceanic climates, river discharge varies widely within and
between years. In such regions autotrophic river reaches should exten
d down continua during low-discharge periods, and retreat during high
discharge. This conceptual model explains how hydrological variability
may control longitudinal patterns of river metabolism.