Spatial dynamics in physicochemistry and bacterio-and myco-plankton assemblages of Imo River in a Niger Delta community in Nigeria

Abstract

We investigated the spatial relationships between physicochemical variables and planktonic (bacterio-and myco -
plankton) assemblages of the middle reaches of the Imo River. In situ measurements and collection of water
samples for laboratory analyses of physicochemical characteristics and enumeration of microbial groups were
made at 7 sampling locations along the river between March 2007 and February 2008 according to standard
methods. The principal components analysis was used for data reduction in the physicochemical variables, while
one-way ANOVA was used to determine variance equality in means of physicochemical variables and planktonic
assemblages. Post structure detection was made with means plots and relationships between the physicochemical
variables and planktonic groups explored using correlation (r). Surface water temperature (SWT) varied between
24.00-28.10 (26.89 ± 0.12)°C, turbidity between 11.00-279.00 (96.70 ± 9.3) NTU, pH between 6.00-6.70 (6.40 0.02) and
total dissolved solids between 19.90-38.00 (28.40 ± 0.56) mg/l. Dissolved oxygen varied between 4.50-8.81 (6.96 ±
0.14) mg/l, biological oxygen demand between 2.10-3.90 (2.85 ± 0.05) mg/l, conductivity between 12.00-300.00 (107.80
± 9.91) µS/cm and total hydrocarbon (THC) between 0.000-0.038 (0.020 ± 0.001) mg/l. Nitrate varied between 0.10-1.35
(0.54 ± 0.04) mg/l, phosphate between 0.07-0.23 (0.13 ± 0.01) mg/l and sulphate between 0.90-8.10 (4.35 ± 0.25) mg/l.
A test of homogeneity of variance in inter-location means revealed significant inequality in both the
physicochemical variables [F(25.81)>Fcrit(3.90)] and planktonic groups [F(86.16)>Fcrit(3.93)] at P<0.05. The PC analysis
revealed two major components- sulphate and nitrate, forming the extraction solution and explaining nearly 62% of
the variability in the original 12 variables. PC 2 correlated negatively with HUF (r = -0.687) at P<0.01, even as
conductivity correlated negatively with HUF (r = -0.555), and THC with THB (r = -0.635), THF (r= -0.642) and HUB (r = -
0.596) at P<0.05. Seven HUB genera (Bacillus sp., Arthrobacter sp., Corynebacter sp., Pseudomonas sp.,
Escherichia coli, Micrococcus sp. and Serratia sp.) and 4 HUF genera (Rhizopus sp., Cladosporium sp., Aspergillus
sp. and Mucor sp.) were identified across the sampling locations. Though its comparatively low levels in this study
could infer biogenic origin in a hydrocarbon rich region, the contributory significant correlational effect, as well as
spatial variation in THC most probably determined planktonic assemblages abundance in the sampling locations