Quantcast Forestry (Cont.)

 
  
 
coastal plain studies in Texas. For these sites dissolved phosphorus increased from .01 to .03 mg/l after
the first year of windrowing. Nitrogen and phosphorus export in the lower coastal plain are relatively
insensitive to the disturbance of intense site preparation (Reikerk et al. 1989).
Glasser (1989) also reviewed literature on the effect of BMPs on water quality for major land
resource areas in the southern US and found most of the increases in stream nitrate concentration due
to forest practices were in the mountainous regions .
McClurkin et al. 1983 monitored the effect of clearcutting on sediment and nutrient for four
small 0.12-0.6 ha (0.3-1.5 acre) watersheds near Lexington, TN. BMPs included tree length skidding
on the contour, no stream crossings, and residue and the forest floor was left intact while planting was
done by hand. One third of the TKN and more than two thirds of the total phosphorus losses were via
the sediment-attached phase. Dissolved TKN and phosphorus losses were similar to the untreated
control.
Miller et al. (1988) studied sediment export from a clearcut, selection cut and an uncut control
watershed in the Ouachita Mountains of Arkansas for three years following harvest. For the first year
after harvest, clearcutting significantly increased sediment export, but not in the following two years.
Clearcut sediment losses averaged 237 kg/ha/year for the first year after harvest. Stormflow suspended
solids were less than 100, 50, and 20 mg/l for nearly all events.
Shearing and windrowing clearcut debris resulted in significantly higher mean annual sediment
losses compared to a clearcut watershed treated with chemicals for site preparation or control
watersheds on the southwestern plateau of Arkansas. (Beasley et al. 1986). On the flat Gulf Coastal
Plain of Arkansas. Beasley and Granillo (1988) found clearcutting and mechanical site preparation
significant increased runoff and sediment yield and average sediment losses were 264 and 64 kg/ha for
the first and second post harvest years. Runoff and sediment yield from selective harvest were not
significantly different from the undisturbed control .
In north central Washington a study of the effects of helicopter and longspan skyline harvesting
along with a riparian buffer the width of the stream valley evaluated the effects of these combined
practices in an area where erosion harvest was moderate to high (Fowler et al. 1988). For a period of
three years after the harvest, total nitrogen loading was not significantly different in the treated
watersheds compared to the controls.
Moore (1975) compiled the results 22 monitoring studies in Western Washington and Oregon,
two in eastern Washington, three in Northern Idaho and two in Alaska to summarize the
findings of fertilization studies its affect on stream chemistry. Typically, fertilizer nitrogen was applied by
helicopter at a rate of 168 to 224 kg/ha. Pretreatment total nitrogen concentrations for a representative
watershed were 0.01 mg/l. Peak nitrate in streams usually occurred 2 to 4 days after application.
Concentrations decrease, but remain above background for about 6 to 8 weeks. Maximum peak
4.2-8

 


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