Identification

Description

Valves are lanceolate with subrostrate apices. The valve face is convex in transapical plane, gradually merging with the mantle. The axial area is narrow, widening gradually from apices to central area. The central area is small and rhombic. The raphe is lateral and slightly bowed, concave to the primary side. Proximal raphe ends are inflated and bent towards the secondary side. Terminal raphe fissures are shaped like question marks. Striae are radiate, becoming parallel and then convergent near the apices. Striae are curved and alternately long and short around the central area. Internally, the striae are partially covered by an axial plate, the edges of which are visible in LM as longitudinal lines located about one-third of the distance from the axial area to the valve margin. Areolae are apically elongated and number 22–26 in 10 μm.

Autecology

Navicula subwalkeri is known from two adjacent headwater streams in the Cascade Mountains of Oregon and from a fossil deposit near Chiloquin, Oregon. Measured pH values in the two Cascade streams range from 6.7 to 7.7 and conductivity values range from 38 to 61 µS/cm.

Nu Upstream Of  Lemolo 1
Credit: Kurt Carpenter, USGS
North Umpqua River, Oregon: type locality of Navicula subwalkeri.

Original Description

Valves lanceolate with subrostrate apices. Length 101–165 μm, width 17–27 μm. Valve face convex in transapical plane, gradually merging with the mantle. Axial area narrow, widening gradually from apices to central area. Central area small, rhombic. Raphe lateral and slightly bowed, concave to the primary side. Proximal raphe ends inflated and bent towards the secondary side. Distal raphe ends shaped like question marks. Striae radiate, becoming parallel, then convergent near the apices, 8–11 in 10 μm. Striae curved, alternately long and short around central area. Internally, striae partially covered by axial plate. Edges of axial plate visible in LM as longitudinal lines at about one-third distance from axial area to valve margin. Areolae apically elongated, 22–26 in 10 μm. Cells solitary with two plate-like chloroplasts lying along the girdle on each side of the valve.

  • Author
    L.L.Bahls and Potapova 2015
  • Length Range
    101-165 µm
  • Width
    17-27 µm
  • Striae in 10µm
    8-11

Original Images

Figs34 46  Navicula Subwalkeri  Lm

Cite This Page

Bahls, L, and Potapova, M. (2015). Navicula subwalkeri. In Diatoms of North America. Retrieved August 19, 2018, from https://diatoms.org/species/navicula_subwalkeri

Responses

The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Navicula subwalkeri from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.