the Lake Taihu watershed, including information about climatic condition and
nutrient loadings.
Monthly mean air temperature data from 2000 to 2012 were collected from the
weather station situated on Xishan Island, located on Lake Taihu. Previous studies
have determined that a critical water temperature for cyanobacterial blooms ranges
from 18 to 25
C [18, 26, 27]. In studies of vegetation growth, crop dynamics and
insect outbreaks, measures of accumulated temperature, expressed as the sum of
degrees by which temperature changes in relation to a fixed level over a prolonged
period, have been often used [28, 29]. In the present study, we used the effective
accumulated temperature [20] during the hot season, expressed as follows: (1) the
temperature >20
C, a sum of mean monthly temperature minus 20
C for the
hottest months (May to September) of each year, and (2) the duration of the period
for which monthly mean temperature was over 20
C (Fig. 4).
Total phosphorus (TP) and total nitrogen (TN) concentrations were determined
from monthly water samples collected from the center of two Lake Taihu sections
(Central and Meiliang Bay) at a depth of 0.5 m, from 2000 to 2010. TP and TN in
water samples were measured using combined persulfate digestion and spectrophotometric analysis for soluble reactive phosphorus and nitrate at the Taihu
Laboratory for Lake Ecosystem Research (TLLER) [25].
Results of previous studies have demonstrated that the Lake Taihu system goes
from a P-limited condition in winter months to an N-limited condition during the
spring and summer seasons, when N-fixing cyanobacteria blooms occur [30]. Nutrient loading during the year is generally characterized by a spring peak in TN
concentrations, which is probably linked to agricultural runoff (winter crops and
paddy rice starting season) [31]. For characterization of yearly nutrient loading
dynamics, we used in situ data of nutrient concentrations for deriving two distinct
features: (1) total nitrogen (TN) concentration accumulated during winter and early
Fig. 4 Mean temperature derived from monthly in situ time series for 2002
92
P. Villa et al.
nutrient loadings.
Monthly mean air temperature data from 2000 to 2012 were collected from the
weather station situated on Xishan Island, located on Lake Taihu. Previous studies
have determined that a critical water temperature for cyanobacterial blooms ranges
from 18 to 25
C [18, 26, 27]. In studies of vegetation growth, crop dynamics and
insect outbreaks, measures of accumulated temperature, expressed as the sum of
degrees by which temperature changes in relation to a fixed level over a prolonged
period, have been often used [28, 29]. In the present study, we used the effective
accumulated temperature [20] during the hot season, expressed as follows: (1) the
temperature >20
C, a sum of mean monthly temperature minus 20
C for the
hottest months (May to September) of each year, and (2) the duration of the period
for which monthly mean temperature was over 20
C (Fig. 4).
Total phosphorus (TP) and total nitrogen (TN) concentrations were determined
from monthly water samples collected from the center of two Lake Taihu sections
(Central and Meiliang Bay) at a depth of 0.5 m, from 2000 to 2010. TP and TN in
water samples were measured using combined persulfate digestion and spectrophotometric analysis for soluble reactive phosphorus and nitrate at the Taihu
Laboratory for Lake Ecosystem Research (TLLER) [25].
Results of previous studies have demonstrated that the Lake Taihu system goes
from a P-limited condition in winter months to an N-limited condition during the
spring and summer seasons, when N-fixing cyanobacteria blooms occur [30]. Nutrient loading during the year is generally characterized by a spring peak in TN
concentrations, which is probably linked to agricultural runoff (winter crops and
paddy rice starting season) [31]. For characterization of yearly nutrient loading
dynamics, we used in situ data of nutrient concentrations for deriving two distinct
features: (1) total nitrogen (TN) concentration accumulated during winter and early
Fig. 4 Mean temperature derived from monthly in situ time series for 2002
92
P. Villa et al.