spring, before bloom events generally start (around May), and (2) total phosphorus
(TP) annual mean concentration (Fig. 5).
3.2 Algal Bloom Monitoring
In past studies, the mean areal extent of algal bloom events from February 2000 to
November 2013 was determined using the Floating Algae Index (FAI) algorithm
[24, 25] with MODIS Level-0 data. Bloom initiation date was defined as the first
observation of surface bloom area larger than 150 km
2 . Considering Lake Taihu as
a whole, the spatial extent of the yearly maximum algal bloom extent was shown to
remain relatively constant from 2000 to 2003 (~400 km
2 ), increased to 900 km
2 in
2005, and reached a maximum of 1,500 km
2 in 2006. The maximum area remained
relatively stable at 1,000–1,200 km
2 for each year in the period 2007–2011, with the
exception of 2009 when it dropped to 550 km
2 .
Bloom extension of individual lake sections demonstrated a high heterogeneity.
In general, open lake areas showed lower bloom extent until 2006, while the bays
maintained a high spatial extent throughout the study period. The bloom extent
dynamics of Gonghu Bay were more similar to those of the open waters than the
eutrophic bays.
Algal blooms were first observed in Meiliang Bay and Gonghu Bay in June,
1987. In each year over the past two decades, the algal blooms were first observed
14 times in Meiliang Bay and 6 times in Zhushan Bay. The initial algal blooms were
seen simultaneously in Meiliang Bay and Zhushan Bay in 1991, 1994, 1997, and
2003. Since 2000, the initial algal blooms were found in the western and northern
bays and appear to begin to spread out in southward direction (see Fig. 1 for
Meiliang, Zhushan, and Gonghu Bays’ location).
Fig. 5 Total nitrogen (TN) and total phosphorus (TP) derived from monthly in situ time series
for 2002
Using Remote Sensing to Assess the Impact of Human Activities on Water. . .
93
(TP) annual mean concentration (Fig. 5).
3.2 Algal Bloom Monitoring
In past studies, the mean areal extent of algal bloom events from February 2000 to
November 2013 was determined using the Floating Algae Index (FAI) algorithm
[24, 25] with MODIS Level-0 data. Bloom initiation date was defined as the first
observation of surface bloom area larger than 150 km
2 . Considering Lake Taihu as
a whole, the spatial extent of the yearly maximum algal bloom extent was shown to
remain relatively constant from 2000 to 2003 (~400 km
2 ), increased to 900 km
2 in
2005, and reached a maximum of 1,500 km
2 in 2006. The maximum area remained
relatively stable at 1,000–1,200 km
2 for each year in the period 2007–2011, with the
exception of 2009 when it dropped to 550 km
2 .
Bloom extension of individual lake sections demonstrated a high heterogeneity.
In general, open lake areas showed lower bloom extent until 2006, while the bays
maintained a high spatial extent throughout the study period. The bloom extent
dynamics of Gonghu Bay were more similar to those of the open waters than the
eutrophic bays.
Algal blooms were first observed in Meiliang Bay and Gonghu Bay in June,
1987. In each year over the past two decades, the algal blooms were first observed
14 times in Meiliang Bay and 6 times in Zhushan Bay. The initial algal blooms were
seen simultaneously in Meiliang Bay and Zhushan Bay in 1991, 1994, 1997, and
2003. Since 2000, the initial algal blooms were found in the western and northern
bays and appear to begin to spread out in southward direction (see Fig. 1 for
Meiliang, Zhushan, and Gonghu Bays’ location).
Fig. 5 Total nitrogen (TN) and total phosphorus (TP) derived from monthly in situ time series
for 2002
Using Remote Sensing to Assess the Impact of Human Activities on Water. . .
93