The significance of extracellular production and winter photosynthesis to estimates of primary production in a woodland stream community

Both winter photosynthesis and the release of extracellular DOC are commonly ignored in stream production studies. We examined these contributions in a second-order stream under a completely closed deciduous canopy. We estimate that in Sandy Run approximately 26% of the annual autochthonous particulate carbon is produced between December and March. Measured winter rates of photosynthesis were not significantly different than summertime rates. Contrary to implicit assumptions often made about stream primary productivity, winter production was as important as summer production. Highest rates of carbon assimilation, however, were measured in the spring and fall, and were significantly correlated with standing crops of stream algae as measured by chlorophyll concentration. The recovery of released DOC from stream algae indicated that this contribution was equivalent to 5% of the particulate contribution. Rates of DOC production were significantly correlated with rates of particulate production. We estimate that had winter photosynthesis and extracellular DOC production been ignored in Sandy Run, annual productivity would have been underestimated by about a third.