Land-use type influence environmental characteristics of
freshwater rivers
Previous studies exploring the impacts of land-use type on N and P
dynamics have focused on soil environments, with a few studies conducted
in freshwater river ecosystems (Enanga et al., 2011 and Leblanc, 2008).
In the present study, environmental data were obtained from freshwater
rivers under disturbance by different land-use types. We observed that
land-use type could induce shifts in the ecological environments of
rivers. For example, Cond, TN, NH4+-N,
and NO3--N in water samples increased
with an increase in the proportion of agricultural land (Fig. 4). The
sensitivity of the environmental factors to land-use type may indicate
increases
in
soil erosion and agricultural or municipal sewage discharge. As a
tributary of the Yellow River and Loess Plateau, Weihe River is
associated with severe soil erosion (Wei et al., 2010).
Agricultural land use increases water demand, whereas rapid urbanization
and population growth exacerbate water pollution (Song et al., 2015).
Through Pearson’s correlation analysis, we observed that Turb, Cond, TN,
TP, NH4+-N, and
NO3--N in water samples all
significantly increased with an increase in disturbance by agricultural
and urbanized land use (Fig. 4). Urban and agricultural land border
river basins and runoff from such land areas loads nutrients into the
adjacent canals, and ultimately flow into Weihe River.
Anthropogenic land uses reduce microbial diversity and alter
microbiotacomposition
in rivers
Based on 16S rRNA gene sequencing, we observed that agricultural land
use could induce microbial diversity loss and community compositional
changes in river water and sediment. The alpha diversity of microbiota
in water samples was lower in the river area mainly under agricultural
land use. We speculated that due to
soil
erosion in agricultural land, abundant N was released into water (Li et
al., 2017), negatively affecting microbial diversity, which is
consistent with the finding of a former study that reported changes in
microbial diversity with
an
increase in N concentration in a freshwater river (Tai et al., 2013).
Microbial community composition in sediment samples showed trends
similar to those observed in water samples, which could be attributed to
the long-term fusion of microbiota between river water and sediment
(Kristensen, 1984).
We also explored the impacts of land-use type on microbial community
composition in the river ecosystems. The NMDS and UPGMA clustering
results showed that microbiota in water samples were congregated in
the
river area dominated by agricultural land. Notably,
high levels ofAcinetobacter spp. occurred
at a few agricultural and urbanized land sites in spring.Acinetobacter spp.
reportedly utilize a wide range of organic compounds as sole sources of
carbon and energy (Hommel et al., 2014), so that they can degrade a
variety of organic pollutants (Zhang et al., 2021; Hommel et al., 2014),
which is consistent with the environmental characteristics of our study
area; in spring, TN and NO3--N
concentrations in water samples were as high as 6.94±0.97 (mg/L) and
5.22±1.32 (mg/L), respectively, which were 14.3% and 40.3% higher than
those in autumn. The increased N nutrients could stimulateAcinetobacter spp. proliferation. In many previous studies, N has
been considered to have a prominent impact on microbial community
composition in freshwater environments (Xing et al., 2020 and Maritz et
al., 2019).
We subsequently studied the relationship between environmental factors
and microbial community composition using the Mantel’s test. According
to the results, both TN and NO3--N
concentrations in water samples increased with increases in proportions
of agricultural and urbanized land areas; furthermore, microbial
community composition was shaped by specific environmental factors. In
contrast, the proportions of forest and shrub land areas were negatively
correlated with N concentrations, and shaped microbial community
composition. He et al. (2016) also observed that land-use type
considerably influenced microbial community composition in a karst
underground river.