We conclude from this study that OC mineralization (or re-mineralization)
can be effectively measured from oxidized OC flux in
sediments. Sediment heterotrophic production is a constantproportion of oxidized OC flux, with aerobic production measured
herein, and anaerobic microbial production unknown. Results
herein strongly suggest that sediment respiration is a metabolic
constant determined by production, regardless of the balance of
organism types included.Heterotrophic production (and thus respiration) was strongly
related to the ratio of organic/inorganic flux, rather than total organic
flux, explaining the previous finding that the region around
the river discharge is production ‘‘saturated’’, so that more food
is arriving at the sediments than can be processed by the biota
prior to burial from inorganic particulates. However, sediment biomass
inventory was strongly controlled by total sediment and organic
flux. As a result, P/B (biomass turnover) was lowest in the
high sediment accumulation location near the mouth of the Fraser
River, and highest in the high organic particulate deposition region
just north of the Iona outfall. Heterotrophic production is not
inhibited in areas of extraordinary organic input from a marine
outfall, however a shift in the types of producers towards microbial
forms results in a reduction in organic biomass. Thus the storage
capacity for biotic OC and bio-turbation potential of sediments is
considerably reduced near the outfall. Stable nitrogen isotopes differentiate
which macrofauna near the outfall utilize (a) outfall particulates,
(b) older buried organic material near the redox
boundary and (c) chemosynthetic symbiotic bacterial production.
These outfall-related effects appear to be spatially limited at the
present time. Conversely, biotic OC is very high and production is
dominated by macrofauna in high riverine sediment particulate
flux conditions, presumably until a threshold is reached limiting
the burrowing ability of larger infaunal detritivores such as
holothurians.Issues of concern related to climate change in this area include
declining bottom oxygen, increased bottom temperature and bottom
water acidification. All of these could exacerbate sediment
oxygen stress already evident in high outfall deposition areas. Finally,
changes to the temperature regime and particulate flux patterns
from the Fraser River could cause widespread changes in
sediment dynamics and carbon cycling throughout the southern
Strait of Georgia.