Ecosystem metabolism in coastal plain streams in southeastern Louisiana

Streams in the southern Mississippi Valley and southeastern plains of Louisiana are characterized by sandy substrates, clear water, and moderate flow velocities.  High discharge events move and re-sort sediment, scour algae, and in some streams, scour riparian vegetation from stream banks.  Two general types of streams can be distinguished based on the presence or absence of an intact canopy.  We studied ecosystem metabolism via diel dissolved oxygen curves in 17 coastal plain Louisiana streams in summer 2007 and 24 in summer 2008.  Streams ranged from 1st through 4th order and 3.5 to 25 meters in width.  Gross primary production (GPP) ranged from 0.01 to 1.84 g C/m²/day, while ecosystem respiration (ER) ranged from -0.01 to -2.10 g C/m²/day.  Streams with an intact canopy tended to be heterotrophic, with ER exceeding GPP and light-limited algal growth.  In contrast, streams with scoured banks tended to be autotrophic, even though unstable substrates may have limited development of dense algal communities.  Analyses revealed that watershed size and the timing of floods were more important than stream order in determining a stream’s trophic status.