River phytoplankton: a spatially dataset
River phytoplankton data were collected as a part of the Water Pollution
Control Program in the Huaihe River Basin
(30。55′-36。36′N,
111。55′-121。25′E) (HRB). The
basin, with a drainage area of 270,000 km2, is located
between the Yangtze River and the Yellow River in China (Wang and Xia
2010). It forms a geographical separation between northern and southern
China. Phytoplankton samples were collected from 217 randomly selected
sites during the low-water period in May 2013 (Fig. 1). Detailed field
and lab methods can be found in Zhu et al (2015). In each site, three
cross-section transects were established. We measured in situenvironmental variables including water temperature (WT), pH,
conductivity (Cond), turbidity and total suspend solids (TSS) using a
portable HACHCDC40105. We also measured Secchi depth (SD), water depth,
stream width, water velocity and elevation. Spectrophotometer (DR5000)
was used to measure total phosphorus (TP), total nitrogen (TN) and
chemical oxygen demand (CODMn) according to standard
methods(NEPAC 2002).
For phytoplankton, a 1L sample from the 0.5 m depth below surface was
collected from three cross-section transects, respectively. After
complete mixing, a 1L sample was preserved with 1% Lugol’s iodine
solution immediately in the field and concentrated to 50 mL after
sedimentation for 48 h. After complete mixing, 0.1 mL of the
concentrated sample was counted directly in a 0.1 mL counting chamber
under a microscope at 400× magnification. Phytoplankton was identified
according to the reference book by Hu & Wei (2006). At least 400 algal
units were counted in each sample. Phytoplankton biomass was expressed
as wet biomass and was estimated for individual species by assigning a
geometric shape similar to the shape of each phytoplankton species
(Hillebrand 1999).