ORIGINAL PAPER

An Early Pliocene lake and its surrounding vegetationin Zhejiang, East China

Jin-Feng Li Æ Ya-Qin Hu Æ David Kay Ferguson ÆYu-Fei Wang Æ Cheng-Sen Li

Received: 9 December 2008 / Accepted: 29 July 2009 / Published online: 12 August 2009

� Springer Science+Business Media B.V. 2009

Abstract The palynomorph composition of an Early

Pliocene assemblage from Du’ao Lake, Zhejiang

Province, East China, including sporomorphs and

algae, was analyzed to reconstruct the vegetation and

climate around the lake, as well as the environmental

conditions in the lake. A subtropical evergreen and

deciduous broad-leaved mixed forest surrounding the

lake is inferred from the pollen data. The composition

of the green algae community indicates a clear,

shallow (about 5–6 m deep), mesotrophic freshwater

lake. The inferred pH was about 7.0–8.0 during the

algae growing season. Applying the Coexistence

Approach, the climatic conditions in Early Pliocene

Du’ao were: (1) mean annual temperature ranged

from 18.1 to 22.0�C, (2) difference in temperature

between the coldest and warmest months ranged from

14.2 to 15.1�C, (3) mean temperature of the coldest

month varied from 10.7 to 12.1�C, (4) mean temper-

ature of the warmest month ranged from 23.5 to

25.4�C, (5) mean annual precipitation varied from

about 994 to 1,255 mm, (6) minimum monthly

precipitation ranged from about 9 to 11 mm, and (7)

maximum monthly precipitation varied from approx-

imately 219 to 245 mm. These values indicate that the

Early Pliocene climate was subtropical.

Keywords Algae � Palynology � Paleovegetation �Paleoclimate � Paleolimnology � East China

Introduction

Pollen in lake sediments is useful for inferring

paleovegetation and paleoclimate (Davis 1999; Jan-

kovska et al. 2002; Vincens et al. 2005). Pollen from

aquatic plants can help reconstruct past aquatic

communities. Pollen production by aquatic plants is

largely dependent on temperature, pH, or the nutrient

J.-F. Li � Y.-Q. Hu � Y.-F. Wang � C.-S. Li (&)

State Key Laboratory of Systematic and Evolutionary

Botany, Institute of Botany, Chinese Academy

of Sciences, 100093 Xiangshan, Beijing,

People’s Republic of China

e-mail: lics@ibcas.ac.cn

J.-F. Li

e-mail: lijinfeng@live.com

Y.-Q. Hu

e-mail: huyaqin21@hotmail.com

Y.-F. Wang

e-mail: wangyf@ibcas.ac.cn

J.-F. Li

Graduate University of the Chinese Academy of Sciences,

100039 Beijing, People’s Republic of China

Y.-Q. Hu

Institute of Archaeology, Chinese Academy

of Social Sciences, 100710 Wangfujing, Beijing,

People’s Republic of China

D. K. Ferguson

Institute of Palaeontology, University of Vienna,

Althanstrasse 14, 1090 Vienna, Austria

e-mail: david.kay.ferguson@univie.ac.at

123

J Paleolimnol (2010) 43:751–769

DOI 10.1007/s10933-009-9366-z

status of the lake water (Edwards et al. 2000).

Remains of green algae in lake sediments, for

example the coenobia of Pediastrum, Botryococcus,

and zygospores of Spirogyra, Zygnema and Pseud-

oschizaea, can play an important role in inferring past

lake conditions (Jankovska and Komarek 2000;

Medeanic 2006; Medeanic et al. 2003; Tell and

Zamaloa 2004; Zamaloa and Tell 2005; van Geel and

Grenfell 1996). Diatoms are useful indicators of

water quality. In addition to the microfossils men-

tioned above, seeds of plants and other organic

remains may also provide paleolimnological infor-

mation (Argant et al. 2006; Fontana 2005; Robinson

2004; Torres et al. 2005; van Geel et al. 1989;

Whitehead et al. 2001).

Lake sediments serve as natural archives of paleo-

environmental information by accumulating spores,

pollen, and macro-remains from the plants growing in

the catchment. In addition, the remains of hydrophytes

are preserved in the lake sediments, and these plant

remains can provide valuable information about the

vegetation surrounding the ancient lake, past climate,

and even the water body itself. Early Pliocene sediments

from Du’ao Lake, Zhejiang Province, East China,

contain abundant pollen, and coenobia and zygospores

of green coccal and filamentous algae. These remains

were used to investigate the Early Pliocene Lake and its

surrounding vegetation and climate.

Materials and methods

Du’ao Village lies in the northeastern part of Ninghai

County, Zhejiang Province (Fig. 1). The geological

section referred to as the Du’ao section (29�200N,

121�310E, Alt. 134 m) is about 1 km from the village.

This section is Early Pliocene in age (RGZP 1982). We

collected a sample of basaltic rock from the Xidawan

section in Shengzhou County for isotope dating. The

Xidawan section is about 80 km from the Du’ao

section, and possesses the same sediments as Du’ao,

with the basaltic bed overlying the lake deposit.

Analysis by 40Ar-39Ar was performed in the State

Key Laboratory of Lithospheric Evolution, Institute of

Geology and Geophysics, Chinese Academy of Sci-

ences in March of 2007 and yielded a date of

4.03 ± 0.09 Ma, confirming that the section is of

Early Pliocene age (Fig. 2). This result was only

slightly older than results of a previous study at the

same locality, using the same method, which gave an

age of 3.0 ± 0.1–3.5 ± 0.1 Ma (Ho et al. 2003). We

use the Early Pliocene age of the section in this work.

The section is 6.8 m thick and divided into seven layers

(Fig. 3). In total, 27 palynological samples were

collected from the section. Samples were numbered

from bottom (sample 1) to top (sample 27). Water

chestnut fruits and other organic remains were found in

the top of Layer 1,*2.5 m above the bottom. Wood of

Quercus and Liquidambar was also collected from the

sediments. The present landscape can be described as

low hills with small plains in the northern and eastern

coastal areas. There is no natural large lake in this area

today, only ponds and artificial reservoirs.

The palynological samples were treated by heavy

liquid separation (density = 2.0 g/ml) (Li and Du

1999; Moore et al. 1991). The microfossils were

mounted in glycerin and observed under a Leica DM

2500 microscope. The identification of the pollen and

spores was achieved using three principal references

(Wang 1995; IBCAS and SCIBCAS 1982; Zhang et al.

1976) and other literature. Individual sporomorphs

were examined under a FEI Sirion 400 scanning

electron microscope using the single-grain technique

(Ferguson et al. 2007). Treatment with hydrogen

peroxide and hydrochloric acid was done to obtain

diatoms, but few were recovered from the samples.

To understand the climate around Du’ao Lake in the

Early Pliocene, the coexistence approach (CA) (Liang

et al. 2001; Mosbrugger and Utescher 1997) was

applied. Based on the pollen taxa, the NLRs (nearest

living relatives) and their geographic distributions (Wu

and Ding 1999) were collated. The modern climatic

variables used in the CA were taken from Surface

Meteorological Data of China (1951–1980) (IDBMC

1983a, b, c, 1984a, b, c) and the Paleoflora Database

(http://www.geologie.uni-bonn.de/Palaeoflora/Palaeo

flora_home.htm). Seven paleoclimatic variables were

obtained (MAT = mean annual temperature, WMMT =

mean temperature of the warmest month, CMMT =

mean temperature of the coldest month, DT = differ-

ence between temperature of the coldest and warmest

months, MAP = mean annual precipitation, MaMP =

maximum monthly precipitation, and MiMP = mini-

mum monthly precipitation). Additional information

on the hydrological conditions of Early Pliocene Du’ao

Lake was obtained by analyzing the pollen of aquatic

taxa and algae in the residue.

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Fig. 1 Map showing the location of the sampling point

Fig. 2 Dating data of the Du’ao section

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Results

Sporomorph analysis

No sporomorphs or algae were observed in Samples

11–27. The palynomorphs obtained from Samples

1–10 consist of 81 taxa, including 63 angiosperms

(77.8%), 5 gymnosperms (6.2%), 7 pteridophytes

(8.6%), 5 algae (6.2%) and Pseudoschizaea (1.2%)

(Table 1). More than 11,700 palynomorph grains

were identified in this work. Angiosperm pollen

constituted 53.7% of the grains, gymnosperm pollen

3.0%, pteridophyte spores 0.9%, algae 42.3%, and

unknown pollen and spores 0.1%. Of the angiosperms

Fig. 3 Lithological

sequence of Early Pliocene

from Du’ao (No

sporomorphs were present

in Samples 11–27)

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(Fig. 4; Table 1), pollen of Castanopsis dominated,

with a percentage range of 15.0–47.1%, and an

average percentage of 35.5%, followed by Liquid-

ambar (1.9–9.6%, average of 5.4%) and Betula (1.3–

4.6%, average of 2.6%). Twenty-five herbaceous

angiosperm taxa were identified, representing 2.6%

of the angiosperms. Gesneriaceae (0–4.8%, average

of 1.0%) and Polygonum (0–1.3%, average of 0.2%)

were common among the herbs. Myriophyllum

(0–0.1%, average of 0.1%) was found in every

sample and was the most common aquatic macro-

phyte taxon. Cyperaceae (0–0.1%, average of 0.03%)

and Potamogetonaceae (0–0.1%, average of 0.1%)

pollen were rare in the samples. Although Trapa

pollen was only found in sample No. 7, its fruits were

found in the sediments of Layer 1. Gymnosperms

include five genera (Pinus, Abies, Tsuga, Picea and

Larix), all of which belong to the Pinaceae. They had

an average percentage of 3.0%. Seven genera of

pteridophytes, with an average percentage of 0.9%,

were found in the samples. Athyriaceae (0–1.0%,

average of 0.3%), Polypodiaceae (0–1.0%, average of

0.2%), and Pteris (0–0.7%, average of 0.2%) were

the most common taxa.

Table 1 List of Du’ao taxa grouped by ecological requirements and their percentages (Table style based on Jimenez-Moreno et al.

2007)

Taxa % Taxa % Taxa %

Megathermic elements Carya 1.75 Chenopodiaceae 0.09

Rutaceae 0.09 Castanea 1.08 Compositae 0.03

Flacourtiaceae 0.02 Ulmus 1.11 Plantaginaceae 0.01

Loranthaceae 0.01 Oleaceae 0.07 Caryophyllaceae 0.08

Dipterocarpaceae 0.01 Caprifoliaceae 0.09 Umbelliferae 0.02

Ebenaceae 0.16 Anacardiaceae 0.24 Leguminosae 0.12

Proteaceae 0.08 Campanulaceae 0.05 Polygonum 0.20

Aquifoliaceae 0.13 Araliaceae 0.20 Gramineae 0.09

Symplocaceae 0.03 Magnoliaceae 0.04 Ericaceae 0.18

Piperaceae 0.05 Meso-microthermic elements Aquatic Macrophytes

Pittosporaceae 0.02 Pinus 1.99 Cyperaceae 0.03

Sapindaceae 0.03 Tsuga 0.27 Potamogetonaceae 0.06

Myrsinaceae 0.01 Microthermic Myriophyllum 0.14

Melastomataceae 0.01 Abies 0.72 Trapa 0.01

Mega-mesothermic elements Picea 0.01 Pteridophytes

Hamamelidaceae 0.13 Larix 0.02 Pteris 0.24

Euphorbiaceae 0.45 Non-significant elements Hemionitidaceae 0.11

Liquidambar 5.43 Rosaceae 0.02 Athyriaceae 0.28

Castanopsis 35.49 Herbs and shrubs Polypodiaceae 0.22

Myrtaceae 0.09 Cucurbitaceae 0.16 Dennstaedtiaceae 0.07

Guttiferae 0.04 Labiatae 0.07 Hymenophyllaceae 0.01

Cornaceae 0.01 Gentianaceae 0.02 Botrychiaceae 0.01

Mesothermic elements Thymelaeaceae 0.05 Algae

Quercus 0.68 Rubiaceae 0.08 Spirogyra 1.00

Betula 2.57 Gesneriaceae 0.96 Zygnema 0.01

Corylus 0.32 Amaranthaceae 0.21 Botryococcus 39.99

Alnus 0.13 Lobeliaceae 0.03 Pediastrum 1.17

Ostryopsis 0.02 Saururaceae 0.08 Pseudoschizaea 0.09

Tilia 0.20 Ranunculaceae 0.01 Coelastrum 0.01

Pterocarya 0.02 Convolvulaceae 0.01 Other elements

Juglans 0.03 Cruciferae 0.03 Unknown 0.14

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Algae in the paleolake

Three morphological types of Botryococcus colonies

were identified using features of cell shape and

intracellular structure (Komarek and Marvan 1992)

(Plate 1). They displayed an average percentage of

40.0%, and thus dominated the green algae. Three

morphological types of Spirogyra zygospores (Plate 2)

were found in every sample, with a total percentage of

1.0%. These types differ from one another mainly in

wall ornamentation. Pseudoschizaea also regularly

occurs in samples, with a percentage of 0.1%. Six types

of Pediastrum coenobia were identified as Pediastrum

simplex var. clathratum, P. simplex var. pseudogla-

brum, P. simplex var. sturmii, P. musteri, P. sculptatum

and P. boryanum var. boryanum (Plates 3, 4), with a

percentage of 1.2%. A zygospore of Zygnema (Plate 2,

Fig. 4) and a Coelastrum (Plate 1, Fig. 14) were found

in sample No. 1 and sample No. 7, respectively.

Hydrophytes of Du’ao paleolake in the Early

Pliocene

Zygnemataceae

Spirogyra and Zygnema occur widely in freshwater

(Colbath and Grenfell 1995; Hoshaw and McCourt

1988). Unfortunately, there is little known about the

ecology of the individual species of Zygnemataceae.

The occurrence of the zygospores of Spirogyra and

Zygnema indicate a shallow, eutrophic water body,

with warm pluvial periods that supplied fluvial

sediments (Medeanic 2006; van Geel et al. 1989).

Zygospore formation occurs mostly in the spring

in clean, oxygen-rich, shallow, fresh water (van

Geel 1976). The optimal temperature for Zygnema is

15–20�C, and for most species of Spirogyra the

optimum is from 14 to 22�C (Hoshaw 1968). Such

high temperatures are easily reached in shallow water

exposed to direct solar radiation, at least during the

warm season (van Geel 1978). A pH value of 7.0–8.0

was inferred from the zygospores of Spirogyra (Grote

1977).

Pediastrum

Fossil Pediastrum in the pollen slides would indicate

a wide range of environmental conditions (Batten

1996). The genus has been largely used as a

biological indicator for freshwater environments and

temperate (or warm) climate (Zamaloa and Tell

2005). Crisman (1978) mentioned that species of

Pediastrum are common in hard-water, eutrophic

lakes. However, each Pediastrum species has specific

ecological requirements. Many phycologists are of

the opinion that the whole algal spectrum must be

considered when paleoecological reconstructions of

the aquatic environment are attempted. The larger the

Fig. 4 Diagram showing percentage values of main palynomorphs of Du’ao ( Indicates the presence of a taxon at a low

percentage)

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number of Pediastrum species, the more accurate the

interpretation of the ecological conditions (Komarek

and Jankovska 2001; Tell and Zamaloa 2004).

Pediastrum simplex

P. simplex has a sub-cosmopolitan distribution. At

present, P. simplex occurs in unpolluted, mesotrophic

water bodies (Komarek and Jankovska 2001). As it is

slightly thermophilic, P. simplex indicates a warm

water body. The occurrence of P. simplex is indic-

ative of mesotrophic conditions.

Pediastrum boryanum

P. boryanum is the most common cosmopolitan

species and there are more than nine varieties

recorded. Some of these may be indicative of tropical

conditions. P. boryanum is well known from the

Pleistocene, Late Glacial and Holocene in Europe and

from the Late Cretaceous of America (Komarek and

Jankovska 2001; Tell and Zamaloa 2004). At present,

P. boryanum var. boryanum occurs in mesotrophic to

eutrophic waters (Komarek and Jankovska 2001).

Pediastrum musteri

P. musteri is mainly described from lakes in arid

regions of Patagonia (southern Argentina) (Komarek

and Jankovska 2001). Other literature indicates that

this species probably occurs sporadically in clear

lakes in the temperate zones of both hemispheres

(Tell and Mataloni 1990).

Pediastrum sculptatum

P. sculptatum is known only from clear lakes and

peaty biotopes in the northern parts of the USA and

Canada, and as far north as the Arctic regions

(Komarek and Jankovska 2001). This is the first

report of this species in China.

Plate 1 1–8 Botryococcustype 1; 9–11 Botryococcustype 2; 12, 13 Botryococcustype 3; 14 Coelastrum sp.

(Scale bar = 30 l)

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Botryococcus

Botryococcus, which is mainly distributed in temper-

ate and tropical regions, is one of the most common

palynomorphs of coccal algae in lagoonal and

lacustrine sediments (Medeanic 2006). It has changed

little with time and no evolutionary pattern of

morphological change has been detected, so it was

obviously successful as an early colonizer and

evidently adapted easily to the aquatic habitats in

which it grew (Guy-Ohlson 1992).

The predominance of Botryococcus indicates

shallow water and clear, mesotrophic conditions

(Medeanic et al. 2003; Reynolds et al. 2002). Guy-

Ohlson (1992) showed that Botryococcus is more

widespread in brackish-water basins than other green

algae, and is usually abundant in shallow water with

relatively low rainfall and a seasonal climate.

Other coccal green algae in the paleolake

The zygospores of Pseudoschizaea (syn. Concentri-

cystis) are considered to represent zygnemataceous

algae (Medeanic 2006). The genus is widely dis-

persed in shallow, freshwater localities (Ke 1995).

Although Pseudoschizaea has never been found alive,

it is considered to have lived mainly in marshy

habitats (Milanesi et al. 2006). Besides that, there is

little ecological information about this genus (Plate 4,

Fig. 4).

Coelastrum (Plate 1, Fig. 14) is a euplanktonic

taxon of freshwater lakes and ponds, and it develops

Plate 2 1 Spirogyra type

1; 2 Spirogyra type 2;

3 Spirogyra type 3;

4 Zygnema sp

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mainly from late spring to early autumn in shallow

water (Salmaso 2002). Little is known about the

ecological preferences of Coelastrum.

Reconstruction of the vegetation

Plant communities surrounding the paleolake

Pollen taxa (Plates 5, 6, 7, and 8) were grouped by

their ecological requirements (Jimenez-Moreno et al.

2007) (Table 1) based on the work of Wu and Raven

(1999). There are 13 megathermic elements, 7 mega-

mesothermic elements, 17 mesothermic elements, 2

meso-microthermic and 3 microthermic elements in

the vegetation surrounding the lake. Rosaceae is

distributed widely in different climatic zones. Though

the megathermic elements only have a percentage of

0.7% in total, this can be attributed to the low pollen

productivity of these largely entomophilous plants.

We suggest that many megathermic taxa were

growing in the forest and most of them are represen-

tatives of tropical-subtropical taxa, such as Rutaceae

(0.09%), Flacourtiaceae (0.02%), Loranthaceae

(0.01%), Dipterocarpaceae (0.01%), Pittosporaceae

(0.02%) and Myrsinaceae (0.01%). Castanopsis

(35.5%) and Liquidambar (5.4%) are very common

taxa in the palynological assemblages. Genera of

Betulaceae (3.7%) and Juglandaceae (2.9%) are the

most common mesothermic elements. Considering

the great pollen production of their catkins, these

mesothermic plants may not have been very common,

at least in the lowland forest. Ulmus pollen (1.1%) is

also relatively common. The meso-microthermic

and microthermic elements all belong to the Pinaceae

Plate 3 1, 2 Pediastrumsimplex var. clathratum;

3 Pediastrum simplex var.

pseudoglabrum;

4 Pediastrum simplexvar. sturmii

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(5 genera), representing only 3.0% of the assemblage.

Representatives of these genera were probably part of

the regional flora.

Vegetation at Du’ao in the Early Pliocene

We reconstructed the paleovegetation using the

pollen remains in the sediment. The pollen remains

suggest a subtropical-tropical evergreen and decid-

uous broad-leaved mixed forest in the landscape

around Du’ao Lake during the Early Pliocene.

Castanopsis and Liquidambar were the dominant

elements in the forests. The megathermic trees (e.g.

Loranthaceae, Flacourtiaceae, Dipterocarpaceae and

Pittosporaceae) must have been growing in the

valleys and/or the lowlands close to the lake. Some

representatives of Betulaceae and Juglandaceae grew

in the forests on the hillsides. Abundant herbs (25

herbaceous types) were living under the trees or on

the edge of the lake. Among the herbs, Gesneriaceae

and Polygonum were very common. Pteridophytes

such as Athyriaceae, Pteris and Polypodiaceae were

also common in the area. Considering the high

productivity of conifer pollen and their structure,

with two huge sacci (Ruffaldi 1994; Vermoere et al.

2001), we suggest that some of the conifer pollen

may have undergone long-distance dispersal.

Although it has sacci, Abies pollen is deposited

rapidly from the airshed. Larix does not have sacci.

Hence, the vegetation can be characterized as a

Plate 4 1 Pediastrummusteri; 2 Pediastrumsculptatum; 3 Pediastrumboryanum var. boryanum;

4 Pseudoschizaea

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subtropical-tropical type in the Early Pliocene. This

is supported by the work on mega-fossils from the

Early Pliocene of Shengzhou, Zhejiang Province

(Hu 2007).

The modern vegetation of the study area is mid-

subtropical (Jin 1994), with tropical and subtropical

families, such as Olacaceae, Flacourtiaceae, Myrsin-

aceae, and Myrtaceae composing 66.3% of all

spermatophytic families. Evergreen broad-leaved

forests are present below about 1,300 m (FZEB

1993). Castanopsis eyrei (Champ. ex Benth.) Tutch.

is the most common species in the evergreen broad-

leaved forests of Zhejiang (FZEB 1993; Jin 1994,

1998). Species of Liquidambar often occupy the

highest level of the forest community (Shi et al.

1995). Most of the subtropical-tropical elements (e.g.

Dipterocarpaceae) that were present in this area

during the Early Pliocene are absent from present

forests. But the representative subtropical elements

(e.g. Liquidambar and Castanopsis) have lived in the

forests of this area until today.

Aquatic macrophytes in the paleolake

Myriophyllum and Potamogetonaceae are very com-

mon submerged aquatic plants that grow in water at

depths of 1–6 m. Trapa, a rooted or free-floating

aquatic plant, is represented in the sediments by its

pollen and fruits. As most of the leaves and seeds of

aquatic plants are found within 35 m of the parent

plants (Zhao et al. 2006), Trapa must have been a

local element (cf. Zetter and Ferguson 2001). The

Plate 5 1 Abies; 2 Pinus;

3 Pteris; 4 Polypodiaceae

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species of Polygonum and Gramineae could either

have lived on land or in the littoral zone.

Climatic conditions around Du’ao

in the Early Pliocene

Climatic conditions around Du’ao in the Early

Pliocene were inferred by applying the coexistence

approach (CA) to the palynological data. Figure 5

illustrates the ranges of the climate variables based on

68 spermatophytic taxa from Du’ao. They are:

MAT = 18.1–22.0�C (median value of 20.1�C),

DT = 14.2–15.1�C, CMMT = 10.7–12.1�C, WMMT =

23.8–25.4�C, MAP = 994–1,255 mm, MiMP = 9–11

mm, MaMP = 219–245 mm (Table 2).

Discussion

Reconstruction of the lake conditions

The organic-rich sediments belong to Facies 11 of

Torres (Torres et al. 2005), which represent shallow-

water conditions. Analysis of the hydrophytes in the

lake indicates a shallow, freshwater lake probably

existed at Du’ao in the Early Pliocene (Fig. 6). On

shore, Polygonum and Gramineae occupied the

largest area. The littoral zone of the lake was about

1–6 m deep, with much Myriophyllum, Potamogeton

and Trapa. Many green algae were living in the water

body, such as Spirogyra, Zygnema and Pediastrum.

The water must have been clear and mesotrophic.

Plate 6 1 Liquidambar; 2Symplocaceae; 3 Quercus;

4 Rutaceae

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During the rainy season, the lake filled with fresh

water. Seasonal variation of the water temperature

was not extreme and the water level of the lake was

probably relatively stable throughout the year. Based

on the hydrophytes in the samples, the water

temperature was about 14–22�C, at least during the

growing season. A water-column pH of 7.0–8.0, at

least during the reproductive phase of the algae, was

inferred from the diverse zygospores found.

Vegetation in the Early Pliocene and succession

of the vegetation in the Zhejiang area

Pliocene vegetation and climate in China

During the Pliocene, the vegetation and climate were

highly diversified in China. In Northwest China, the

vegetation of Qinghai Province was characterized by

grassland with mixed conifer/broad-leaved forests

dominated by Pinus, Picea, Quercus, Betula, Artemi-

sia, Chenopodiaceae, and Compositae (Shen et al.

1990). The vegetation in Xinjiang Autonomous

Region was regarded as a desert steppe, with mainly

Chenopodiaceae, Artemisia, Ephedra, Compositae,

and Tamarix (Xiao et al. 2003). Mixed conifer and

broad-leaved forests possessing Pinus, Picea, Betula,

Corylus, Juglans, and Quercus were found in Gansu

Province (Wu 2001). The presence of xerophytic

plants, such as Chenopodiaceae, Artemisia, and Ephe-

dra in this vegetation suggests that the climate was

becoming dry in Northwest China in the Pliocene.

In Southwest China, conifers, deciduous broad-

leaved trees (e.g. Tsuga, Picea, Quercus, Ulmus) and

xerophytic herbs (e.g. Artemisia and Chenopodiaceae)

Plate 7 1 Tilia; 2 Carya;

3 Ulmus; 4 Ericaceae

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were growing on the Tibetan Plateau. These plants

formed coniferous or conifer-broad leaved forests and

retama bushland (Li and Zhou 2001; Shen and Tang

1992; Wang 1992). The climate on the Plateau was

becoming dry and cold (Shen and Tang 1992). On the

other hand, the climate in Yunnan was mainly hot and

humid (Li 1994; Wang 1992; Yi et al. 2002) with

plants such as Euphorbiaceae, Liquidambar and

Anacardiaceae growing in subtropical broad-leaved

forests.

In North China, the vegetation was dominated by

large numbers of herbs (e.g. Artemisia, Gramineae

and Chenopodiaceae) in Shandong Province (Wang

et al. 2002; Tan et al. 2000). At the same time, a few

subtropical plants, such as Carya, Euphorbiaceae and

Pterocarya, were living in the forests. The climate

changed from subtropical-warm temperate in the

Mid-Miocene (Liang et al. 2001; Liang et al. 2003;

Yang et al. 2007) to warm temperate in the Pliocene.

In Shanxi Province, many common plants, such as

Picea, Tsuga, Pinus and Amentiferae (catkin-bearing

trees), along with a few subtropical trees (e.g.

Rutaceae, Pterocarya), were found in the mixed

conifer/broad-leaved forests (Cao et al. 1998; Li et al.

2001; Li et al. 2004; Shi 1996). The climate was

warm-temperate in this area. Li et al. (2001, 2004)

also recognized warm-humid and warm-dry intervals,

as reflected by changes in the amounts of herbs (e.g.

Artemisia, Chenopodiaceae) and Ephedra in the

Early Pliocene.

In Southeast China, a pollen study in Anhui

Province showed that Picea, Tsuga, Carya, Liquid-

ambar and Podocarpus were well represented in the

forests. Meanwhile, the presence of Hemiptelea and

Plate 8 1 Polygonum; 2Araliaceae; 3 Vitaceae; 4Myriophyllum

764 J Paleolimnol (2010) 43:751–769

123

Ephedra indicates that the climate was getting colder

and drier, although the landscape was still covered

largely by subtropical conifer/broad-leaved forests at

that time (Yu et al. 1991). In Zhejiang Province, the

climate was subtropical-tropical in the Early Plio-

cene. At Du’ao, Castanopsis, Liquidambar, and

Fig. 5 Intervals of the seven climatic parameters of Du’ao in

Early Pliocene. (MAT the mean annual temperature, WMMTthe mean temperature of the warmest month, CMMT the mean

temperature of the coldest month, DT the difference of

temperature between the coldest and warmest months, MAPthe mean annual precipitation, MaMP the maximum monthly

precipitation, MiMP the minimum monthly precipitation.) 1

Pinus, 2 Abies, 3 Picea, 4 Tsuga, 5 Larix, 6 Liquidambar, 7

Castanopsis, 8 Castanea, 9 Quercus, 10 Betula, 11 Tilia, 12

Corylus, 13 Carya, 14 Alnus, 15 Pterocary, 16 Juglans, 17

Ostryopsis, 18 Ulmus, 19 Myrtaceae, 20 Oleaceae, 21

Ericaceae, 22 Euphorbiaceae, 23 Araliaceae, 24 Magnoliaceae,

25 Hamameliaceae, 26 Campanulaceae, 27 Anacardiaceae, 28

Rutaceae, 29 Cucurbitaceae, 30 Rosaceae, 31 Loranthaceae, 32

Caprifoliaceae, 33 Aquifoliaceae, 34 Labiatae, 35 Gentiana-

ceae, 36 Flacourtiaceae, 37 Thymelaeaceae, 38 Dipterocarpa-

ceae, 39 Ebenaceae, 40 Guttiferae, 41 Proteaceae, 42

Symplocos, 43 Cornaceae, 44 Piperaceae, 45 Pittosporaceae,

46 Sapindaceae, 47 Rubiaceae, 48 Myrsinaceae, 49 Gesneri-

aceae, 50 Amaranthaceae, 51 Melastomataceae, 52 Lobelia-

ceae, 53 Saururaceae, 54 Ranunculaceae, 55 Convolvulaceae,

56 Cruciferae, 57 Chenopodiaceae, 58 Compositae, 59

Plantaginaceae, 60 Caryophyllaceae, 61 Umbelliferae, 62

Leguminosae, 63 Polygonum, 64 Gramineae, 65 Cyperaceae,

66 Potamogeton, 67 Myriophyllum, 68. Trapa

J Paleolimnol (2010) 43:751–769 765

123

Betula made an important contribution to the mixed

evergreen/deciduous broad-leaved forest.

The climate in China during the Pliocene was

mainly affected by the East Asian monsoon system.

The control and interaction of the various monsoons,

including the northwestern monsoon from Siberia,

the southwestern monsoon from the Indian Ocean and

the southeastern monsoon originating in the Pacific

Ocean, resulted in a range of climate patterns in

different regions of China. During the Pliocene, there

was a gradient from a dry temperate climate in

Northwest China to a humid tropical-subtropical one

in Southeast China. Zhejiang Province is located in

southeastern China, and the Pliocene climate there

was subtropical, being influenced mainly by the

southeastern monsoon.

Table 2 A comparison of the climatic parameters of Du’ao in the Early Pliocene and Xiangshan at present

MAT/�C WMMT/�C CMMT/�C DT/�C

Du’ao (Early Pliocene) 18.1–22.0 23.8–25.4 10.7–12.1 14.2–15.1

Du’ao (Early Pliocene) 20.1a 29.6a 11.4a 14.7a

Xiangshan (Present) 15.8b 27.8b 3.7b 24.1b

MAP/mm MaMP/mm MiMP/mm

Du’ao (Early Pliocene) 993.8–1,254.7 218.9–245.2 9.3–11.3

Du’ao (Early Pliocene) 1124a 232a 10a

Xiangshan (Present) 1111b 155.6b 34.7b

a Median valueb Mean value

Fig. 6 Reconstruction of the vegetation in and around the Early Pliocene lake in Du’ao

766 J Paleolimnol (2010) 43:751–769

123

Climate change at Du’ao in the Pliocene

Climate of Du’ao in the Early Pliocene

The climatic inferences obtained from the CA analysis

indicate that the climate of Early Pliocene Du’ao was

subtropical and/or tropical. Xiangshan County, which

is the nearest site available in the IDBMC meteoro-

logical database, lies about 42 km southeast of Du’ao.

Compared with the present surface meteorological

data, the MAT of Early Pliocene Du’ao was a little

higher (ca. 4.3�C) than that of Xiangshan at present and

the MAP was similar, 1,124 mm during the Early

Pliocene compared to 1,111 mm at present. The

increase of the DT value, from a mean value of

14.7�C during the Early Pliocene to 21.7�C at present,

and the decrease of the CMMT value, from a mean of

11.4�C in the Early Pliocene to 3.7�C on average at

present, indicate that the climate has become more

variable. This could explain why the vegetation

changed considerably from the Early Pliocene to

present. The amount of precipitation during the Early

Pliocene was similar to that of the present.

Climate change in the Zhejiang area

after the Early Pliocene

We inferred a median value of 20.1�C for the MAT in

Du’ao (see the CA results) during the Early Pliocene.

A similar result (17.7–21.4�C, median value of

19.6�C) was obtained based on the mega-fossil flora

of a nearby diatomite deposit (Hu 2007). A study on

stalagmites (Wang et al. 1998) in Hangzhou, the

capital city of Zhejiang Province and about 120 km

from Du’ao, indicates that the MAT there was 9.4�C

at 50,000 years BP, 12.3�C at 42,000 years BP, 7.6�C

at 31,000 years BP, 14�C at 28,000 years BP, 6.6�C

at 16,000 years BP and 10.2�C at 9,700 years BP.

The MAT is 16.2�C at present in the Hangzhou area.

We assume that the temperature in Zhejiang dis-

played a downward trend from 20.1 to 16.2�C.

However, the Quaternary glaciations affected the

climate and caused temperature to fluctuate.

Conclusions

Analysis of fossil pollen assemblages in lake deposits

can reveal much about past vegetation composition

and climate, while study of the algae can provide

information on the chemistry of the water body. By

combining information from both microfossil sources,

a more complete picture of the paleoenvironment is

achieved. In this study, we attempted to infer both past

lacustrine conditions and the vegetation surrounding

the water body. Our results indicate that there was a

clear, shallow, mesotrophic freshwater lake at Du’ao,

Zhejiang Province, East China during the early

Pliocene. Vegetation surrounding the lake can be

described as subtropical-tropical evergreen, and

broad-leaved deciduous forest. The Early Pliocene

MAT was higher than at present. However, large

differences in CMMT and DT, between the Early

Pliocene and present, are inferred from the consider-

able changes in vegetation since the Early Pliocene.

Acknowledgments The authors thank Senior Engineer Nai-

Qiu Du for her help with pollen identifications. We are also

grateful to Su-Ping Li for her assistance with laboratory

analysis. Ya-Meng Li, Dr. Jian Yang, Dr. Yi-Feng Yao and

other colleagues also assisted. This investigation was supported

by the National Basic Research Program (No. 2004CB720205),

National Natural Science Foundation (No. 30530050), Beijing

Finance Special Fund (No. Jingcaiyuzhi[2008]0178) and State

Key Laboratory of Systematic and Evolutionary Botany

Special Found. The present publication is a contribution to

the NECLIME project.

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