Environmental response to climate and human impact during the

Science of the Total Environment 385 (2007) 196 – 207
www.elsevier.com/locate/scitotenv
Environmental response to climate and human impact during the last
400 years in Taibai Lake catchment, middle reach of
Yangtze River, China
Enfeng Liu, Xiangdong Yang ⁎, Ji Shen, Xuhui Dong, Enlou Zhang, Sumin Wang
Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences,
73, East Beijing Road, Nanjing 210008, PR China
Received 30 January 2007; received in revised form 21 June 2007; accepted 22 June 2007
Available online 20 July 2007
Abstract
Element content, grain size, pollen and 210Pb dating analysis were performed on 80 cm sediment core from Taibai Lake, a
shallow lake in the middle reach of Yangtze River in China, to reveal the response of catchment environment to climate changes
and human activities during the past four centuries. The 210Pb dating suggests that 0–39.5 cm of the core represents the past
163 years and bottom of the core is at ca. 1590 AD. Major changes showed in the core are compared with the records from
historical documents, including population, cultivation and climate etc. 1700–1810 AD was the period with intensive human
activities in Taibai Lake catchment, behaving as deforestation and cereal cultivation expansion, signaled in the sediments by low
percentage of pinus pollen and high percentage of Gramineae pollen, high content of b 16 μm fraction. Another period with
intensive human activities was since 1928 AD, behaving as deforestation, reservoir construction, land reclamation, soil loss. The
high sedimentation flux epochs, such as 1900–1920 AD, 1931 AD, 1938–1939 AD and 1954 AD, were correlated with high
precipitation; nevertheless, the high sedimentation flux epochs in 1958–1970 AD and 1983–1993 AD were correlated with the
land reclamation around Taibai Lake and soil loss due to intensive cultivation development respectively. The two coldest stages
during the “Little Ice Age” were in 1650–1700 AD and 1810–1900 AD, consistent with the historical records generally,
characterized by weak weathering, high forest coverage and weak human activities in Taibai Lake catchment.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Human activities; Climate changes; Sedimentary environment; Taibai Lake
1. Introduction
The reconstruction of climate and environment
changes is essential to understand the impact of natural
processes and human activities on the ecosystems. It is
especially contributive in the middle and lower reaches of
⁎ Corresponding author. 73, East Beijing Road, Nanjing 210008, P.R.
China. Tel.: +86 25 86882149; fax: +86 25 57713063.
E-mail address: [email protected] (X. Yang).
0048-9697/$ - see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.scitotenv.2007.06.041
Yangtze River in China. Yangtze River catchment, a
sensitive area to climate changes and human activities
(Chen et al., 2001; Du et al., 2001; Gao et al., 2004; Liu,
2000; Liu et al., 2000; Xiang et al., 2002; Yasuda et al.,
2004; Yin and Li, 2001), was the economic developed,
population denseness area in China for thousands of years
(Zhang, 1990; Zhang et al., 2005). The development in
economy and increase in population in recent decades had
exerted great pressure on the ecological environment,
especially water pollution, soil loss, siltation on lake and
E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
river bed, and lake ecological degeneration in the middle
and lower reaches of Yangtze River (Du et al., 2001;
Xiang et al., 2002; Yin and Li, 2001; Yang et al., 2002a).
In comparison to the environment evolution at
millennium scale, there had rapid population increase
and frequent climate fluctuation during the last hundreds
years (Zhang, 1980, 1990; Yang et al., 2002b), linking
closely with current ecological environment. But
seldom study was performed on this time scale,
especially linking sedimentary and historical records
to interpret the ecological environment evolution. It is
challenging due to the difficulties obtaining sedimentary
records of sufficient temporal resolution and chronological accuracy, and corresponding documentary data.
Lake sediments, as the excellent archives of regional
environment changes, have the characteristics of continuity, high resolution and abundant information, are
playing a more important role in the research on regional
human activities and environment change reconstruction
(Liu et al., 2000; Huang and Connell, 2000; Tibby, 2003).
In this study, the environment response to climate changes
and human activities was reconstructed for Taibai Lake
catchment, by the systemic analyses of the physical,
element geochemistry and pollen proxies in sediment
core of Taibai Lake, and the sequential information of
population and plantation records in Susong County since
197
17th century, and indirect climate records in the middle
and lower reaches of Yangtze River.
2. Modern setting of Taibai Lake catchment and
historical records
2.1. Modern setting of Taibai Lake catchment
Taibai Lake lies to the north of Yangtze River and the
south foot of Dabie Mountain (Fig. 1), where was the
ancient Penglize Lake in early Holocene (Qu et al.,
1998). The catchment area of Taibai Lake was 607 km2,
and the surface area was 28.98 km2 in 2002. The
average water depth of Taibai Lake is 3.2 m in recent
years, with Vallisneria denseserrulata as the main
submerged macrophyte (Jian et al., 2001). The main
inflow rivers of Taibai Lake are in the north of its
catchment, and the water drains into Longgan Lake from
the outlet southeast of Taibai Lake.
The pH of Taibai Lake water is 7.4–8.0 and the
degree of mineralization is 65–112 mg/L. Its hydrochemical type is of carbonate calcium, with main cations
Ca2+, Mg2+, Na+ + K+and main anions HCO3−, SO42− and
Cl−, the average concentrations of which are 20.0 mg/L,
3.65 mg/L, 2.97 mg/L and 45.0 mg/L, 3.65 mg/L and
2.67 mg/L respectively (Wang and Dou, 1998).
Fig. 1. Location map of Taibai Lake and core site.
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E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
It is characterized by a subtropical monsoon climate
in Taibai Lake catchment as well as in the middle and
lower reaches of Yangtze River, with mean annual
precipitation 1273 mm concentrating in summer (June–
September), mean annual evaporation 1041 mm. The
zonal vegetation in the catchment should be evergreen
broad-leaved forest; nevertheless, it had been destroyed
and substituted by secondary vegetations (mainly pines).
2.2. Cultivation scale and population variations in
history
Susong County, lies to the northeast of Taibai Lake,
was one of the established district since 598 AD, with
relatively changeless administrative boundaries since
1645 AD (Annals of Susong County, 1935). The
population, plantation scale, and historical events,
though not continuous annually, were systematically
collected from the Annals of Susong County (1935) by
the authors for the first time, and the statistics in recent
50 years were also used in this paper (Fig. 2).
The population of Susong County was about eighty
thousand in 1590–1670 AD, it was one hundred and
forty thousand in 1712 AD and up to three hundred and
ninety thousand in 1772 AD (Fig. 2). Thus, the rapid
population increase in Susong County was from late
17th century to mid 18th century. Nevertheless, the
population decreased rapidly since 1810s and reduced to
one hundred and eighty thousand in 1868 AD mainly
due to the war dead of peasant uprising, such as the
Taiping Heavenly Kingdom (Annals of Susong County,
1935). The population increased slightly in late 19th
century, but was still less than that in late 18th century.
The cultivation scale in Susong County, mainly rice,
wheat and sweet potato (Annals of Susong County, 1935),
increased by three folds from late 17th century to late 18th
century and then decreased to the level in late 17th
century, coincidently with population changes (Fig. 2).
Fig. 2. Climate fluctuation in the middle reaches of Yangtze River (Figure A from Zhang, 1980; Figure B from Ye et al., 1994) and the variation of
population and cultivation scale in Susong County.
E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
In order to understand the variations of population and
cultivation in Susong County, the dynasty subrogation for
China should be introduced. Ming Dynasty was in 1368–
1644 AD, and Qing Dynasty was in 1644–1911. The
population increased slowly from North Song Dynasty
(960–1127) to mid Ming Dynasty, which was between
20 million and 100 million in China (Ding, 1993). The
rapid population increase was in Qing Dynasty, it was up to
400 million in 1820s from 100 million in mid 17th century
in China (Ding, 1993). It can be seen that, population
variation in Susong County in Qing Dynasty was not a
especial case, it was consistent with that of China.
199
in Fig. 2, which was deduced mainly from chorography
by Ye and Zhao (1994) and Zhang (1980). There were two
cold stages during the “Little Ice Age” in the studied
period, one was 1650s–1700s and the other was 1790s–
1900s (Fig. 2). The annual average temperatures for the
two cold periods were 0.55 °C and 0.58 °C lower than that
in 1900–1979 AD. Since the end of the “Little Ice Age”,
the temperature increased rapidly and plentiful precipitation occurred in 1900–1920s (Fig. 9) (Gong et al., 2001).
3. Materials and methods
3.1. Coring and sampling
2.3. Human activities in recent half-century
Human activities influencing Taibai Lake and
catchment environment were the construction of water
conservancy facilities and land reclamation around the
lake. In order to facilitate the agricultural irrigation and
flood control, three reservoirs were built in the upper
reach of Taibai Lake in 1958–1962 AD, such as
Jingzhu, Kaotian and Xianrenba reservoirs (Fig. 1).
Correspondingly, land reclamation around Taibai Lake
flourished since late 1950s. The area of Taibai Lake was
69.2 km2 in 1930s (Wang and Dou, 1998). It was
63.70 km2, with the water area of 60.10 km2 in mid1950s. Nevertheless, the water area shrunk to 40.01 km2
by mid-1960s due to land reclamation, decreased 33.4%
compared with that in mid-1950s, reducing at a rate of
2.0 km2 annually. The water area was only 27.02 km2 in
1978 AD, decreased 32.5% compared with that in mid1960s, reducing at a rate of 1.08 km2 annually. The area
of Taibai Lake changed little since 1978 AD (Fig. 3).
2.4. Climate changes inferred from the historical
documents
Climate change is one of the main factors influencing
catchment environment and human activities (Stebich
et al., 2005). Here, the temperature change in the middle
reach of Yangtze River during the last 450 years is shown
The sediment cores (TB-03) about 80 cm long were
taken at the deeper area of Taibai Lake with a piston
corer in 2003 (Fig. 1). The core sediments were subsampled at a 0.5 cm resolution for 0–50 cm and 1 cm
resolution for 50–80 cm. The sub-samples were sealed
in plastic bags to be transported to laboratory.
3.2. Methods
The frozen dried samples were used for 210 Pb dating,
TOC, TN, and metal element analysis. The wet samples
were used for grain size and pollen analysis. The main
methods used were as following.
Pb dating: The concentration of 210Pb for each
samples was measured with low level germanium
detector gamma-ray spectrometer (EG & G
ORTEC, HPGe GWL-120-15). The standard
counting errors of which are less than 10%.
Supported 210Pb was estimated following the
method of Appleby et al. (Appleby and Oldfield,
1978; Appleby et al., 1986; Binford et al., 1993),
and was subtracted from the total 210Pb to obtain
unsupported 210Pb (210Pbex).
(2) Grain size: Particle size spectra of the samples
were determined using a Malvern automated laseroptical particle-size analyzer (Mastersizer-2000)
(1)
210
Fig. 3. Surface area and shape of Taibai Lake (calculated from relief map for the two former, from remote sensing image for the two latter).
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E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
after removal of organic matter by 10% H2O2
treatment. The particle size compositions are given
in percentage.
(3) TOC and TN: The CE-440 elemental analyzer
(EAI Company) was used for the determination of
TOC and TN content of the samples.
(4) Metal elements analysis: The standard EPA
method 3052 was used in this paper for metal
elements (K, Mg, Ca, Al, Fe, Na) analysis
(USEPA, 1996). An accurately weighed sediment
sample (∼ 125 mg) was placed in a Teflon
nitrification tank, 6.0 ml HNO3, 0.5 ml HCl, and
3.0 ml HF were added. The sealed tank was then
placed in a microwave oven (Berghof MWS-3
Digester) and nitrified at 180 ± 5 °C for 15 min.
The residue from the tank was then transferred into
a Teflon breaker and dissolved with 0.5 ml HClO4
by braising in a heating block at about 200 °C and
diluted to 25 ml with double-distilled de-ionized
water. The solution was then analyzed for metal
elements by inductively coupled plasma-atomic
emission spectrometry (Leeman Labs, Profile
DV). The accuracy of the analytical determination
was established using the reference material GSD9, supplied by the Chinese Academy of Geological
Sciences. The analytical results for all elements
were found to be in agreement with the certified
values, with an accuracy better than 93%.
(5) Pollen analysis: Pollen analysis was performed on
115 samples to provide information on terrestrial
vegetation in the catchment. Sub-samples with 3–
5 g wet weight were treated with 10% HCl and 15%
NaOH, and then separated with a liquid at density
of 1.88, which included zinc chloride, sodium
polyunsaturated, and mixtures of potassium iodide
and cadmium iodide (Nagakawa et al., 1998), and
then mounted in glycerol for counting. A calibrated
suspension of Lycopodium spores was added at the
beginning of processing to enable pollen concentration to be calculated. Pollen identification and
counting were performed under the Leitz optics
microscope with standard descriptions. For each
pollen sample, total count was above 400 grains.
Major results were expressed by percentage
diagrams.
12 cm of the profile and then a more regular exponential
decay in 12–39.5 cm. The large fluctuations for 210Pbex
may be caused by the unsteady sedimentation rate
(Fig. 5) (Appleby and Oldfield, 1978; Appleby et al.,
1986), which could be further proved by the detailed
discussion in Section 4.3. According to the characteristics of CRS (constant rate of supply) and CIC (constant
initial concentration) models, the CRS model was used
to determine the chronologies of Core TB-03, which
assumes that there is a constant fallout of 210 Pb from the
atmosphere to the lake water and a constant supply rate
to the sediments irrespective of any variations which
may have occurred in the sediment accumulation
processes (Appleby and Oldfield, 1978; Appleby
et al., 1986). The CRS model gave 60 dates between
1839 ± 16 (39.5 cm) and 2002 ± 1 AD (Fig. 5).
In order to extrapolated the age of the sediment core
bellow 39.5 cm, the compaction effect must be evaluated.
Water content of sediment was generally 40–60%, up to
70% at the top of the sediment core. The dry bulk density
increased with depth at 0–30 cm and then kept generally
constant values at 30–80 cm, having an opposite variation
with water content and TOC especially in 30–80 cm
(Fig. 6). It means that the variations of dry bulk density in
30–80 cm are influenced mainly by the organic matter
content, hardly by compaction effect comparing with that
in 0–30 cm of the sediment core. There had no
correlations for the sedimentation flux and grain size
composition at 0–39.5 cm, which reflects the limited
influence of the grain size on the 210Pbex concentration
and sedimentation flux (sedimentation rate) (Mil-Homens
et al., 2006). Thus, the dates bellow 39.5 cm of the
sediment core can be extrapolated by the average
sedimentation rate at 30–39.5 cm (1839–1895 AD)
(Smittenberg et al., 2004; Yamamuro and Kanai, 2005),
where the sedimentation flux had no large fluctuations.
4. Results and discussions
4.1. Radiometric dating
The distributions of 210Pbex in the sediment profile
are shown in Fig. 4. It shows large fluctuations in 0–
Fig. 4. Concentration of 210Pbex in the sediment Core TB-03.
E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
201
Fig. 5. Sedimentation flux and time-depth curve of Core TB-03.
The age at the bottom of the sediment core is ca. 1590 AD
and the ages at other depth are shown in Fig. 6–8.
Nevertheless, the accuracies of the chronology bellow
39.5 cm of the core are relatively lower comparing with
that in 0–39.5 cm.
4.2. Major sediment properties
The sediments were composed of grey silty-clay.
Fine silt (4–16 μm) and clay (b4 μm) accounted for 60–
90% of the grain size composition, representing the
fine grain fraction and having an opposite variation
with the coarse silt fraction (16–64 μm); the percentage of sand (N 64 μm) in the sediments was less than
2% (Fig. 6).
TOC content in the sediments was generally low,
which was 0.8–2.0% (Fig. 6), similar to that in other
lakes in the middle and lower reaches of Yangtze River
(Wang et al., 2005). The low TOC content and relatively
higher primary productivity were probably due to the
higher mineralization rate of organic matters in lake
water, which was nearly 80% in Taihu Lake (Hu and Pu,
2000). Mineralization of organic matters can also
change the original C/N ratio. The research in Taihu
Fig. 6. Summary diagram grain sizes, water content, dry density, TOC and C/N ratio of Core TB-03.
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Fig. 7. Concentration of the metal elements and Na/K ratio of Core TB-03.
Lake also revealed that, the C/N ratio was not response
to nutrition level and origin changes of organic matters
from terrestrial vegetations and primary productivity of
algae or submerged macrophyte comparing with the
δ13C (Lin et al., 2006). Thus, the low C/N ratio in Taibai
Lake sediments and TOC content may not really
indicate the origins of organic matters and primary
productivity of the lake (Meyers and Ishiwatari, 1993), it
was not used in the discussion of environmental
evolution in Taibai Lake catchment.
The metal elements content variations in the core
sediments are presented in Fig. 7, and their correlation
coefficients are shown in Table 1. K, Mg, Ca and Fe had
similar variations and had significant positive correlations with the fine grain fraction (b 16 μm), but they
were all opposite with Na, which had a significant
Fig. 8. Percentage pollen diagrams of Core TB-03.
E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
203
Table 1
The correlation coefficients matrix for metal elements concentrations and different grain fractions
K
Mg
Ca
Al
Fe
Na
b16 μm
16–64 μm
Na/K
a
b
Mg
Ca
Al
Fe
Na
b16 μm
16–64 μm
0.739 a
0.275 a
0.317 a
0.282 a
0.399 a
− 0.396 a
− 0.451 a
0.054
0.123
0.218 b
0.357 a
− 0.351 a
− 0.373 a
0.648 a
0.066
0.146
−0.152
−0.203 b
− 0.125
0.239 a
− 0.244 a
− 0.433 a
-0.562 a
0.577 a
0.670 a
−0.998 a
−0.837 a
0.844 a
a
0.911
0.724 a
0.347 a
0.405 a
0.285 a
0.426 a
− 0.419 a
− 0.513 a
Correlation is significant at 0.01 level.
Correlation is significant at 0.05 level.
opposite correlation with the fine grain fraction. The Na/
K molar ratio had a similar variation to the coarse silt
fraction (16–64 μm).
Na in sediment is primarily enriched in feldspar,
especially in plagioclase, and K resides mostly in K
feldspar and partly in illite and mica, which imply
different weathering degree. So, the Na/K ratio has no
correlations with the sedimentation flux, and is one of
the proxies indicating the weathering degree of
sediments before they are transported into the lake.
High Na/K ratio shows low weathering degree of the
sediment (Nesbitt and Young, 1982; Sawyer, 1986;
Yang et al., 2004). Temperature and moisture are two
important factors influencing the weathering of debris in
the catchment. The evaporation was lower than
precipitation in Taibai Lake catchment, so the weathering was influenced mainly by the temperature (Li and
Zhang, 2003).
A total of 167 taxa pollen were identified (Fig. 8).
The arboreal pollen (AP) was mainly composed of
pines, which accounted for 93.8% of the average
concentration. Among the herbs (non-arboreal pollen,
NAP), Gramineae dominated 57.6% on average.
Maximum Gramineae pollen percentage and minimum
pines pollen percentage occurred at 62-36 cm and 170 cm of the sediment core.
4.3. Environmental response to climate and human
impact in Taibai Lake catchment
The accuracy of the sediment records from Taibai
Lake is expected to be intrinsically limited by mixing
processes which may induced from resuspension of
material for the shallow depth. However, the 210Pb
activity and the large magnitude changes presented by
the sedimentary proxies indicate that mixing processes
did not smooth the signals. By the synthetical analysis
on sedimentary proxies referenced to statistical results
using CONISS software, six environment evolution
stages in Taibai Lake catchment during the last
400 years were deduced (Fig. 6–8), and the comparisons
between environmental changes and climate or human
activity events from the instrumental and historical
documents were also performed.
4.3.1. Stage VI (80–70 cm, 1590–1650 AD)
It was characterized by little fluctuation for the
sedimentary proxies. The high percentage of pinus
pollen and low percentage of Gramineae pollen
indicated a substantially wooded landscape in the
upriver area of Taibai Lake catchment and low human
disturbance, which is consistent with the small population in this period. The high content of fine fraction
(b 16 μm) and low Na/K ratio showed the well
weathering degree of the sediment, which was
corresponding with the mild climate during the “Little
Ice Age”, with relatively higher temperature (Zhang,
1980; Ye and Zhao, 1994).
4.3.2. Stage V (70–62 cm, 1650–1700 AD)
The high Na/K ratio and high percentage of coarse
fraction showed the weak weathering, which may be
due to the lower temperature during the second cold
period during the “Little Ice Age” (Ye and Zhao, 1994;
Zhang, 1980). The similar pollen percentage as in stage
VI indicated relatively weak human influence on the
vegetation composition in Taibai Lake catchment,
which is also consistent with the low population and
farmland scale.
4.3.3. Stage IV (62–36 cm, 1700–1855 AD)
Features of the pollen assemblage changed greatly in
this zone. The lower percentage of pinus pollen and
higher percentage of Gramineae pollen were unlikely
resulted from the climate factors, because this period
was corresponding with the warm climate during the
“Little Ice Age”, with low frequency of droughts and
floods especially in 1700–1810 AD (Ye and Zhao,
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E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
1994; Zhang, 1980). In this period, population increased
largely in Susong County (Fig. 2), which had resulted in
deforestation and cultivation expansion largely (Huang
and Connell, 2000; Yasuda et al., 2000; Stebich et al.,
2005). The pollen component implied that the main
deforestation stage was during 1700–1750 AD, and the
secondary tree (Pinus) restored rapidly during 1750–
1810 AD after the earlier deforestation. Relative balance
was kept between woodland and farmland since 1810
AD due to the decreasing population.
The other notable feature in this stage was high
content of fine fraction and metals, and low Na/K ratio,
which suggested that the large scale deforestation and
cultivation had aggravated erosion of the well weathered
soils (Huang and Connell, 2000). There was higher
content of Ca at 54–57 cm of the sediments, similar
features were also presented for Mg, but less distinct,
which indicated the high carbonate content in the
sediments. Coarse grain size composition, low water
content and high dry bulk density were also presented at
the same depth. The variation characteristics of the
proxies at 54–57 cm may be related to the lower lakelevel during that period, thus more coarse fractions
could be transported to the center of the lake (Dearing,
1997; Punning et al., 2006); meanwhile, the carbonate
precipitation by the concentration of the lake water, with
Ca2+, Mg2+and HCO3− as the main cations and anion
(Wang and Dou, 1998), would result in the high content
of Ca and Mg in the sediments.
The sub-fluctuations for the proxies in this zone
indicated climate or human activities fluctuations in
Taibai Lake catchment. Grain size composition was
coarser, the content of K, Mg and Ca decreased and Na/
K ratio increased since 1810 AD, which implied the
weak weathering of the sediment comparing with that in
1700–1810 AD. Historical documents showed that the
last cold period during the “Little Ice Age” begun at
1790–1810 AD in the middle and lower reaches of
Yangtze River (Ye and Zhao, 1994; Zhang, 1980). So
the weak weathering of the sediment since 1810 AD was
related to the lower temperature, similar as that in 1650–
1700 AD. The population decreased since 1810 AD, but
it was still a large scale comparing with that in 1590–
1700 AD. Due to the hysteresis effect of human
influencing on the lake sediment, the sediment from
soil erosion still had a big proportion.
4.3.4. Stage III (36–29 cm, 1855–1900 AD)
This was a remarkable stage different with the
previous. The percentages of pinus and Gramineae
pollen resumed to the level before 1700 AD. It reflected
a general less human activity pressure and influence on
the catchment environment, which was also consistent
with the historical documents that the cultivation scale
decreased and the population decreased to the lowest
level during the last 200 years. Grain size composition
became coarser, with high content for the coarse silt and
sand, and high Na/K ratio, which indicated the weak
weathering degree for the sediments due to the lower
temperature in the last cold epoch during the “Little Ice
Age”. The sedimentation flux was higher between 1870
and 1880 AD, which may be related to the higher flood
frequency (Ye and Zhao, 1994), it was not further
analyzed due to the lower age resolution of the subsamples.
4.3.5. Stage II (29–17 cm, 1900–1928 AD)
The observation data and historical records showed
that the temperature rose rapidly since early 20th
century (Wang, 2001; Ye and Zhao, 1994). The grains
of the deposits became finer and the Na/K ratio
decreased gradually, which was related to the well
weathering degree of the sediment under the warmer
climate. The population was increasing gradually, but
there was no obvious increase in cultivation, and the
inconspicuous variation of pollen also indicated the
generally weak human activities during 1900–1928 AD
comparing with that in 1700–1810 AD. The average
sedimentation flux in this stage was 294.6 mg/cm2/a,
which was about two folds of that in stage III. The high
sedimentation flux was related to the strong erosion in
the catchment due to high precipitation (Fig. 9) (Gong
et al., 2001). But high sedimentation flux and strong
erosion didn’t induce coarse grain size composition of
Fig. 9. Sedimentation flux of Taibai Lake and annual anomalies of
summer precipitation in the middle and lower reaches of the Yangtze
River (lower figure from Gong et al., 2001).
E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
the sediment, which showed that grain size composition
had no correlations with precipitation or erosion, and it
mainly reflected the weathering degree of the sediment
as discussed above.
4.3.6. Stage I (17–0 cm, 1928–2002 AD)
There was a transition for the elements from zone II to
zone I, but no evidence of deposition break. The similar
features can also be found in other lakes in 1920s in the
middle and lower reaches of Yangtze River, such as Taihu
Lake, Yangcheng Lake, Longgan Lake etc. (Ji et al., 1997;
Yang et al., 2002b; Liu et al., 2006).
There was a rapid economy development in 1920s–
1930s in the middle and lower reaches of Yangtze River
(Zhang, 1990). For example, the production of cotton in
Xiaogan County, one precinct of Hubei Province,
increased 5.7 folds in 1928–1937 AD, and the forest
coverage rate decreased rapidly from the 16.65% in late
Qing Dynasty due to deforestation (Annals of Xiaogan
County, 1990). The rapid development in cultivation
and deforestation had induced the change of sediment
composition and sedimentary proxies.
The decreasing percentage of pinus pollen and the
increasing percentage of the Gramineae pollen in
1928–2002 AD were correlated with the continued
strengthening deforestation and cereal cultivation.
The sedimentation flux fluctuated obviously in this
zone. Three peak values (numbers b–d), in 1928 AD,
1937–1942 AD and 1954 AD were corresponding with
the high precipitation stages in summer of 1931 AD,
1938-1939 AD and 1954 AD in view of the errors of the
210
Pb dating, and the lower sedimentation flux stages at
1928–1954 AD were all corresponding with the low
precipitation periods (Fig. 9). So the sedimentation flux
variations in 1928–1954 AD were mainly controlled by
the precipitation of Taibai Lake catchment in summer.
Though the precipitation chenged largely since 1960s,
there were no high values for the sedimentation flux
corresponding to the precipitation, which may be due to
the storage capacity of the reservoirs in the upper
reaches of Taibai Lake catchment built in 1958–1962
AD. In this case, the high sedimentation flux stages in
1958–1970 AD and 1983–1993 AD were attributed to
other factors, one of which was the land reclamation
around the lake, which could induce aggravated erosion
of the catchment and shrinking lake area (Yin and Li,
2001). There was land reclamation in large scale in the
middle and lower reaches of Yangtze River. The surface
area of Taibai Lake also shrunk 55% from mid-1950s to
1978 AD, so the high sedimentation flux for Taibai Lake
in 1958–1970 AD was mainly resulted from the
reclamation. But there almost had no land reclamation
205
around Taibai Lakes since 1978 AD, the high
sedimentation flux in 1983–1993 AD was not attributed
to land reclamation. It was related to the soil loss with
the rapidest agriculture development since 1980s, which
can also be proved by the relatively high percentage of
Gramineae pollen (Fig. 8).
Though the sedimentation flux fluctuated obviously
and the material source changed in a certain extent, the
elements content changed little. This was due to the
similar grain size composition and mineral composition
for the materials (Mil-Homens et al., 2006).
The different cultivation pattern in Qing Dynasty and
recent half-century induced the different sediment
features for Zone IV and I, though there had similar
higher population in the two periods. Cultivation scale
extension was the main measure to increase the output
of various foodstuffs for the demand of increasing
population in the 18th century because of the extensive
cultivation pattern in that period, large scale badlands
and woodland were reclaimed as farmland. Contrasting
with that was the intensive agriculture since 1950s, and
the food supply was mainly by the step of increasing
grain yield per unit area and the farmland scale increased
lesser. Thus, there was similar population increase in
Qing Dynasty and the last 50 years, but the sediment
features was not identical in the two periods due to the
different agricultural production patterns. The population increase in the early agriculture society had greater
influence on the catchment environment (Huang and
Connell, 2000).
5. Conclusions
The synthetical analysis on sedimentary proxies and
historical documents revealed the environmental response
to climate and human impact in Taibai Lake catchment
during the last 400 years. The main conclusions are as
follows:
(1) The last two cold stages during the “Little Ice Age”
were in 1650–1700 AD and 1810–1900 AD
reflected by the sedimentary proxies, with the
coldest epoch in 1855–1900 AD. The two cold
stages were represented by weak weathering, high
forest coverage and weak human activities intensity
in Taibai Lake catchment.
(2) Increasing population was with deforestation and
cultivation expansion in 1700–1750 AD, and the
stabilized population and cultivation in 1750–1855
AD was with the reforestation of the secondary
pines. Deforestation and cultivation destabilized well
weathered topsoil, thereby aggregated the erosion of
206
E. Liu et al. / Science of the Total Environment 385 (2007) 196–207
soil, inducing finer grain size composition and higher
metal elements contents in the sediment. Though
human activities influenced the catchment environment intensively, the chilling climate since 1810 AD
during the “Little Ice Age” can also be reflected by
the sedimentary proxies.
(3) Intensive human activities since early 20th century
mainly behaved as deforestation, land reclamation
and cereal cultivation expansion. 1958–1970 AD
was the period of large scale land reclamation
around Taibai Lake; rapid development of intensive
agriculture in 1983–1993 AD had induced soil loss
in Taibai Lake catchment. The two periods all
behaved as high sedimentation flux.
(4) The flood events or stages in history, such as
1900–1920s, 1931 AD, 1938–1939 AD and 1954
AD were all recorded in the sediments with high
sedimentation flux.
Acknowledgements
The work was financially supported by the national
natural science foundation of China (Grant No.
40572177) and Chinese Academy of Sciences (Grant
No. kzcx2-yw-319). The authors are thankful to Dr.
Yanhong Wu, Mr. Yuxin Zhu, Mr. Weilan Xia, Nanjing
Institute of Geography and Limnology, Chinese Academy
of Sciences, for their help in the field sampling and
experiment analysis.
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