Fig 1.
Map of study watersheds in Trask River Watershed Study, western Oregon.
Locations of headwater sampling reaches are shown as triangles and downstream sites are noted as squares. Map was created using ArcGIS Pro with LiDAR terrain (https://www.oregongeology.org/lidar/) and derived hydrography. Reference watersheds are shown in dark green, clearcut with variable buffers are shown as orange and clearcut with uniform buffers are show as blue. Light green watershed was thinned with wide unharvested buffers. Created using ArcGIS Pro with LiDAR terrain (https://www.oregongeology.org/lidar/) and LiDAR-derived hydrography.
Table 1.
Study site characteristics.
Fig 2.
Percent of light reaching streams pre- and post-harvest.
The percent of overstory light reaching the streams, measured using hemispherical photos in 2008, pre-harvest, and in 2013, post-harvest. Sites are organized from left to right by percentage of overstory light reaching the stream post-harvest. Bars show site averages and standard deviation.
Table 2.
Statistical differences between pre- and post-harvest periods for headwater treatment groups.
Table 3.
Statistical summary from Partial Least Square models comparing pre- to post-harvest responses in headwater watersheds.
Fig 3.
Stream temperature and fine surface sediment.
Headwater sites are organized by harvest treatment and organized from left to right by the percentage of overstory light reaching the stream post-harvest. A) Average daily maximum stream temperatures in June during pre and post-harvest periods. B) Mass of fine surface sediment at annual sampling in June, for pre- and post-harvest periods. Bars show site averages and standard deviation.
Fig 4.
Average concentrations of dissolved nutrients and carbon at headwater sites.
Sites are organized from left to right by percentage of overstory light reaching the stream post-harvest. A) Dissolved organic carbon (DOC), B) Dissolved organic nitrogen (DON). C) Dissolved inorganic nitrogen (DIN), D) Soluble reactive phosphorus (SRP), E) Molar ratios of DIN:SRP. Bars show averages plus standard deviation during early summer annual sampling. Asterisks indicate that watershed values were significantly different using PLS analyses (Table 3).
Fig 5.
Average concentrations of nutrients at downstream sites during pre- and post-harvest periods.
A) Dissolved organic carbon (DOC), B) Dissolved organic nitrogen (DON), C) Dissolved inorganic nitrogen (DIN), D) Soluble reactive phosphorus (SRP), E) Molar ratio DIN:SRP. Bars show averages plus standard deviation during early summer annual sampling. RKDS is the reference for the downstream sites. UMDS is downstream of variable buffer sites, PHDS is downstream of uniform buffer sites and GSDS has mixture of harvest groups upstream.
Fig 6.
Average epilithon biomass and chlorophyll a concentration at headwater sites.
Sites are organized from left to right by percentage of overstory light reaching the stream post-harvest. A) Average epilithon biomass as ash free dry mass (AFDM) plus standard deviation; B) Average chlorophyll a concentration plus standard deviation. Samples were collected annually in early summer. Asterisks indicate which watersheds showed significant differences between pre- and post-harvest periods using PLS analyses (Table 3).
Table 4.
The most common and second most common algal taxa in selected headwater streams, based on cell counts of epilithon samples.
Fig 7.
Average epilithon biomass and concentration of chlorophyll a at downstream sites during pre- and post-harvest periods.
A) Epilithon biomass as ash free dry mass (AFDM); B) Chlorophyll a concentration. Bars show early summer average plus standard deviation. RKDS was the reference for the downstream sites. UMDS was downstream of variable buffer sites, PHDS was downstream of uniform buffer sites and GSDS had mixture of harvest groups upstream.
Fig 8.
Correlations between chlorophyll a, epilithon and instream factors at headwater sites.
These correlations compare site averages for each year and site during pre- and post-harvest periods. Headwater sites that were harvested are in the left column (A, C, E, G) and those were reference sites are in the right column (B, D, F, H). Chlorophyll a versus epilithon (A, B); Chlorophyll a versus canopy closure (C, D); Epilithon versus DIN (E, F); Epilithon versus molar ratios of DIN:SRP (Dissolved Inorganic Nitrogen: Soluble Reactive Phosphorus) (G, H). Data from pre-harvest period are indicated as dark green circles and from the post-harvest period are shown as triangles. R2 values are included for the correlations where p-values are equal to or less than 0.05.