examined [2, 22]. The correlation of initial blooms was most significant when
compared to minimum temperature (P ¼ 0.048). These results were consistent with
another study [55] in which temperature was reported as a major factor in the growth
of phytoplankton. In addition, a tight correlation between algal recruitment and
cumulative temperatures during winter and spring was reported both in laboratory
and field studies in Lake Taihu [27]. The correlation between algal blooms and
temperature is related to enzymatic activities responsible for algal blooms [56],
as well as the stimulus effects of winter temperature on algal recruitment, one of
the important stages for algal blooms in the following year [57]. The winter of 2007
was one of the warmest winters, and the mean temperature from January to March
was higher than the mean monthly temperature in the preceding 25 years, with
increments of 0.36
C in January, 2.78
C in February, and 1.98
C in March; this
increase may explain the massive algal blooms occurring in the summer of 2007 [4].
4.2 Nutrient Loading
Algal blooms have been attributed to excessive nutrient loading, mainly nitrogen
and phosphorus. It is hypothesized that Lake Taihu HAB events are associated with
the nutrient loading resulting from human activities. For the time period, 1991–
1996, the annual average of total nitrogen concentration increased from 1.18 to
3.62 mg/L, and total phosphorus concentration increased from 0.10 to 0.18 mg/L
[58]. Moreover, the concentrations of total nitrogen and total phosphorus in 2006
were found to be 200 and 150 % higher than the prior decade. Inputs of total
nitrogen and total phosphorus from the Taihu watershed area increased from around
43,150 and 1,750 metric tons in 2002 to around 44,700 and 1,850 metric tons in
2003, respectively. The spatial dynamics of algal blooms indicated the influence of
nutrients on algal blooms. The increased coverage of algal blooms in the south part
of the Lake Taihu was likely a result of the declining gradient of nutrient concentration from nutrient loading in the northwest area of Lake Taihu. For example, the
total phosphorus loading from the northwest catchments area accounted for 55 % in
2002 and 53 % of the total lake loading in 2003, and the total nitrogen loading
accounted for 65 % in 2002 and 72 % in 2003. A southward flow of nutrients would
help explain the increasing occurrences of algal blooms in the center and south of
Lake Taihu. Previous studies confirm that Meiliang Bay and Zhushan Bay are the
most eutrophic bays of the Lake Taihu [16].
4.3 Human Activities
Elevated nutrient loading is most often the result of a combination of human
activities, e.g., sewerage, livestock waste drainage, and fertilizer runoff from
agricultural lands [59, 60]. For example, Duan et al. [2] used human population
and gross domestic production (GDP) per capita to establish a relationship between
102
P. Villa et al.
compared to minimum temperature (P ¼ 0.048). These results were consistent with
another study [55] in which temperature was reported as a major factor in the growth
of phytoplankton. In addition, a tight correlation between algal recruitment and
cumulative temperatures during winter and spring was reported both in laboratory
and field studies in Lake Taihu [27]. The correlation between algal blooms and
temperature is related to enzymatic activities responsible for algal blooms [56],
as well as the stimulus effects of winter temperature on algal recruitment, one of
the important stages for algal blooms in the following year [57]. The winter of 2007
was one of the warmest winters, and the mean temperature from January to March
was higher than the mean monthly temperature in the preceding 25 years, with
increments of 0.36
C in January, 2.78
C in February, and 1.98
C in March; this
increase may explain the massive algal blooms occurring in the summer of 2007 [4].
4.2 Nutrient Loading
Algal blooms have been attributed to excessive nutrient loading, mainly nitrogen
and phosphorus. It is hypothesized that Lake Taihu HAB events are associated with
the nutrient loading resulting from human activities. For the time period, 1991–
1996, the annual average of total nitrogen concentration increased from 1.18 to
3.62 mg/L, and total phosphorus concentration increased from 0.10 to 0.18 mg/L
[58]. Moreover, the concentrations of total nitrogen and total phosphorus in 2006
were found to be 200 and 150 % higher than the prior decade. Inputs of total
nitrogen and total phosphorus from the Taihu watershed area increased from around
43,150 and 1,750 metric tons in 2002 to around 44,700 and 1,850 metric tons in
2003, respectively. The spatial dynamics of algal blooms indicated the influence of
nutrients on algal blooms. The increased coverage of algal blooms in the south part
of the Lake Taihu was likely a result of the declining gradient of nutrient concentration from nutrient loading in the northwest area of Lake Taihu. For example, the
total phosphorus loading from the northwest catchments area accounted for 55 % in
2002 and 53 % of the total lake loading in 2003, and the total nitrogen loading
accounted for 65 % in 2002 and 72 % in 2003. A southward flow of nutrients would
help explain the increasing occurrences of algal blooms in the center and south of
Lake Taihu. Previous studies confirm that Meiliang Bay and Zhushan Bay are the
most eutrophic bays of the Lake Taihu [16].
4.3 Human Activities
Elevated nutrient loading is most often the result of a combination of human
activities, e.g., sewerage, livestock waste drainage, and fertilizer runoff from
agricultural lands [59, 60]. For example, Duan et al. [2] used human population
and gross domestic production (GDP) per capita to establish a relationship between
102
P. Villa et al.