We investigated the recovery of sediment characteristics in four moraine, headwater streams in
north-central Minnesota after forest harvest. We examined changes in fine sediment levels from 1997 (preharvest)
to 2007 (10 years postharvest) at study plots with upland clear felling and riparian thinning, using canopy
cover, proportion of unstable banks, surficial fine substrates, residual pool depth, and streambed depth of refusal
as response variables. Basin-scale year effects were significant (p < 0.001) for all responses when evaluated by
repeated-measures ANOVAs. Throughout the study area, unstable banks increased for several years postharvest,
coinciding with an increase in windthrow and fine sediment. Increased unstable banks may have been
caused by forest harvest equipment, increased windthrow and exposure of rootwads, or increased discharge and
bank scour. Fine sediment in the channels did not recover by summer 2007, even though canopy cover and
unstable banks had returned to 1997 levels. After several storm events in fall 2007, 10 years after the initial
sediment input, fine sediment was flushed from the channels and returned to 1997 levels. Although our study
design did not discern the source of the initial sediment inputs (e.g., forest harvest, road crossings, other natural
causes), we have shown that moraine, headwater streams can require an extended period (up to 10 years) and
enabling event (e.g., high storm flows) to recover from large inputs of fine sediment.
Merten, Eric, C.; Hemstad, Nathaniel, A.; Kolka, Randall, K.; Newman, Raymond, M.; Verry, Elon, S.; Vondracek, Bruce.
RECOVERY OF SEDIMENT CHARACTERISTICS IN MORAINE, HEADWATER STREAMS OF NORTHERN MINNESOTA AFTER FOREST HARVEST.
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