4.5. The change of DO concentrations and pH values
In this study, pH increased when the temperature increased,
and the DO concentrations increased when the pH increased. However,
DO concentrations have no significant relationship with temperature.
It might be caused by a complex process: (1) The
seasonality of submerged plant or phytoplankton could decrease
the quantity of TN and TP in the water and release oxygen via photosynthesis
(Shimp et al., 1993). (2) Sediment might upfloat by the
increasing temperature, then metal ions were taken to the water,
oxygenation occurred once the DO was enough, and the alkalescency
of water increased (Zhou and Zhou, 1997; Zhou et al.,
2002; Xie et al., 2003). (3) Oxygen may be consumed by organic
matter degradation (Ellen and Joselito, 2001). (4) Algae photosynthesis
makes the pH increase, impel metal compound colloid
deposited, and P was released from colloid (Zhou and Zhou,
1997). (5) COD concentrations rose with the increasing quantity
of algae (Zhou and Zhou, 1997; Zhou et al., 2002; Xie et al., 2003).
The values of pH were in the highest in HT (Fig. 2B(k)), which
agreed to the pH values of Taihu Lake when blue-green algae were
blooming in HT (Fan and Wang, 2007). The algae bloom should
cause the pH raised in MT and HT. But COD concentrations might
be increased with algae blooming. COD concentrations always
low (<6 mg L_1) in any temperature in three lakes in this study,
so the quantities of algae might be little and oxygen might be
released via photosynthesis of algae or hydrophytes and pH
increased (Fig. 2B(l)). A lot of plants, such as Myriophyllum spicatum
L., Juncus effusus and Vallisneria natans (Lour.) Hara, effective plants
for water cleaning (Kagalou et al., 2008; Andrew and Patrick, Xie
et al., 2004), were found in studying area. Therefore, in small
natural shallow lake, DO concentrations were impacted by the
growth of hydrophytes and algae, pH were impacted by the upfloat
of sediment with the temperature increasing, the quantity of algae
should be low and pH value increased with sediment upfloat in MT,
algae bloom and sediment upfloat simultaneously in HT.
การแปล กรุณารอสักครู่..