Veget Hist Archaeobot DOI 10.1007/s00334-017-0651-x

ORIGINAL ARTICLE

An 800 year record of mangrove dynamics and human activities in the upper Gulf of Thailand Paramita Punwong1,3 · Sanpisa Sritrairat1 · Katherine Selby2 · Rob Marchant3 · Nathsuda Pumijumnong1 · Paweena Traiperm4 

Received: 24 April 2017 / Accepted: 29 October 2017 © Springer-Verlag GmbH Germany 2017

Abstract  A multiproxy record comprising pollen, charcoal, loss on ignition and particle size analyses from two radiocarbon dated sediment cores from Klong Kone subdistrict on the western coast of the Gulf of Thailand provides insights on mangrove dynamics, environmental changes and human activities during the last 800 years. The mangroves were dominated by Rhizophora which indicates that the area has been influenced by the sea level from at least 820 cal bp until 720 cal bp. An intertidal area may have formed that supported mangrove development as part of an old shoreline during 820–720 cal bp. After 720 cal bp, mangroves decreased and were replaced by grasses, suggesting that a lower sea level caused the mangroves to grow closer to the sea until around 140 cal bp. Cereal pollen increased from 720  cal bp suggesting probable use of the shoreline for intensive cultivation. The mangroves were characterised by Avicennia, which increased toward the top of the 2 cores, suggesting that the mangroves then grew further inland, Communicated by F. Bittmann. Electronic supplementary material  The online version of this article (https://doi.org/10.1007/s00334-017-0651-x) contains supplementary material, which is available to authorized users. * Paramita Punwong [email protected] 1



Faculty of Environment and Resource Studies, Mahidol University, Salaya, Nakhon Pathom 73170, Thailand

2



Environment Department, University of York, York YO10 5NG, UK

3

York Institute of Tropical Ecosystems, Environment Department, University of York, York YO10 5NG, UK

4

Department of Plant Science, Faculty of Science, Mahidol University, Ratchathewi, Bangkok 10400, Thailand



probably due to recent sea-level rise. Intensive human activity is recorded during the 20th century, as indicated by increased particle size, charcoal and carbonate content. At present, human activity in the area includes dams and construction as well as aquaculture. Keywords  Sea-level change · Pollen · Charcoal · Klong Kone · Dvaravati

Introduction Mangroves form a coastal ecosystem that provides important ecological and socio-economic services for people who live close to tropical coastal habitats. Mangroves are physiologically adapted evergreen trees and shrubs that grow in the intertidal zone (Duke 1992; Hogart 1999). They can tolerate a wide range of salinities that vary between fully marine sea water in the lowest intertidal area to fresh water in upstream rivers, depending on the gradient of the flood tide and fresh water runoff (Ball 1988; Hogart 1999; Krauss et al. 2008). In response to sea level fluctuations, mangrove communities will shift landward or seaward as sea levels rise or fall, respectively (Punwong et al. 2013a, b, c). Mangrove ecosystems are sensitive to climate change; changing regional rainfall patterns can influence fresh water runoff, sediment and nutrient discharges, leading to changes in salinity and resulting mangrove composition (Alongi 2008; Gilman et al. 2008; Mikhailov and Isupova 2008; Eslami-Andargoli et al. 2009). Mangrove ecosystems are also very sensitive to human influence (Gilman et al. 2008; Punwong et al. 2013a, c) and record human activities (Hogart 1999; Gilman et al. 2008). In Thailand, mangroves currently cover approximately 1,900  km 2 and have relatively high species diversity

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(Kathiresan and Rajendran 2005). The recent degradation and loss of mangroves is a global issue (Spalding et al. 2010); Thailand is no exception, with the area covered by mangroves decreasing by approximately 50% from 1975 to 1996 (Pumijumnong 2014). As a result of the rapid decrease in mangrove habitat and extensive degradation of the coastal ecosystem which has affected matters such as storm protection, there have been a number of recent restoration and conservation efforts (Aksornkoae 2004). Most mangrove degradation is caused by increased demand for land and to a lesser extent wood, leading to the conversion of land to agriculture for rice fields and aquaculture, particularly shrimp ponds (Tomlinson 1986; Aksornkoae 1993; Spalding et al. 2010; Pumijumnong 2014). Although mangrove management is taken into account in policies towards public awareness and conservation of mangrove resources (Aksornkoae 2004; Spalding et al. 2010; Pumijumnong 2014), there is still considerable concern for the sustainable use and management of mangrove ecosystems and a lack of understanding of the links between sea level, climate change, mangrove response and the sustainable use and management of these ecosystems. In order to understand how mangrove ecosystems may respond to future environmental change, and how they may consequently affect human communities, it is important to study long-term past ecosystem change (Jackson and Hobbs 2009). Mangrove pollen preserved in sediments provides important information about past vegetation changes and changes in sea level (Ellison 2008; Tossou et al. 2008; Hait and Behling 2009; Punwong et al. 2013a, b, c). Holocene sea level changes in southeast Asia, including Singapore (Hesp et al. 1998; Bird et al. 2007), Indonesia (Azmy et al. 2010), Malaysia (Tjia 1996; Mallinson et al. 2014), Vietnam (Stattegger et al. 2013), Cambodia (Penny 2008; Li et al. 2012) and the upper Gulf of Thailand (Sinsakul 2000) and MalayThai peninsula (Tjia 1996; Scoffin and Tissier 1998; Horton et al. 2005; Scheffers et al. 2012) have been reconstructed using various proxies. The sea level fluctuations recorded over the Holocene vary significantly in their magnitude, timing and duration. However, a mid Holocene high sea level is always recorded before its fall to its present state. These long-term data also provide insight on how ecosystems actually responded to change in the past and whether these responses were driven by the climate or human activity. This study focuses on the mangrove ecosystems in the Gulf of Thailand, an area that, particularly in the upper part, is densely populated and comprises a major area for producing food such as rice, shrimp and salt (Aksornkoae and Bird 2010). This research adopts a palaeoecological approach, using pollen to identify vegetation and sea level changes, charcoal to identify the frequency and intensity of fire events caused by the climate and human activity (Clark 1988; Daniau et al. 2010), and geochemical analyses to

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understand sedimentary sources and deposition from sediment cores covering the last 1,000 years, a time when little is known about how mangrove ecosystems in the Gulf of Thailand responded to sea level, climate and human activities. Study site Location Klong Kone subdistrict is situated in Mueang District, Samut Songkhram Province on the west coast of the upper Gulf of Thailand (Fig. 1). It is characterised by mudflats and a belt of dense mangroves occurring in a northwest-southeast alignment that extends from 100 to 1,200 m in width. Samut Songkhram Province has experienced extensive land conversion from natural vegetation, for intensive shrimp farming (Tookwinas 2004; Shimoda et al. 2009). There has also been mangrove management for conservation and rehabilitation with extensive planting in this area (Tookwinas 2004). Geology and geomorphology Samut Songkhram is situated in the Mae Klong river basin and it is dissected by the Mae Klong river flowing from north to south out to the Gulf of Thailand (Fig. 1). The area is influenced by a semi-diurnal tide with a range of 0.5–1.3 m at Mae Klong river mouth (Admiralty Tide Table 2014). The Mae Klong river basin is situated in the Lower Central Plain, where recent floodplain sediments overlie a thick accumulation of unconsolidated sediments which were deposited during a marine transgression in the Holocene and known as Marine Clay or Bangkok Clay (Sinsakul 2000). The coastal area of Samut Songkhram is characterised by shallow tidal creeks, from which fresh water from terrestrial sources causes a temporary decrease in salinity during the heavy rainy season (Choo-In et al. 2013). Climate and vegetation The climate of the upper Gulf of Thailand is tropical with a north–south migration of the Inter Tropical Convergence Zone (ITCZ) that controls the two monsoon periods. The northeast monsoon dominates from November to January, bringing cool and dry air, and the southwest monsoon occurs from May to October, bringing abundant precipitation that can cause flooding within the Central Plain. The total annual rainfall is 800–1,400 mm (1982–2011) (Komori et al. 2012) and the average annual temperature varies from 24 to 29 °C (Mikhailov and Nikitina 2009). Mangrove vegetation composition in Thailand has been classified according to the varying degrees of inundation (Watson 1928; Santisuk 1983), as mangroves found along seaward areas and covered by the sea during high tide, and

Veget Hist Archaeobot Fig. 1  Location map of the upper Gulf of Thailand. a The mangrove areas in Sumut Songkram Province with the study area boxed. b The coring site at Klong Kone

back mangroves, which are only reached by the sea at very high tides and consist of other species that tend to occur in more inland areas such as fresh water swamps, peat swamps and in dry land forest. The eastern edge of the Mae Klong river mouth in Samut Songkram can be characterised into three zones, the Nypa fruticans zone, the Rhizophora apicu‑ lata zone and the Rhizophora mucronata zone (Piyakarnchana 2007). The Nypa fruticans zone is dominated by N. fruticans along with Xylocarpus granatum, R. apiculata, Thespesia pop‑ ulanea and Ceriops tagal. The Rhizophora apiculata zone is

characterised by R. apiculata, Xylocarpus granatum and N. fruticans. The Rhizophora mucronata zone is characterised by R. mucronata, Avicennia officinalis, A. alba, R. apiculata, N. fruticans, Bruguiera cylindrica, Sesuvium portulacastrum and Sueada maritima. The west side of the river mouth is characterised by the Nypa fruticans zone, the Nypa and Rhizophora zone and a planted Rhizophora zone. Sonneratia caseolaris, Avicennia marina and Acrostichum aureum are also found in Samut Songkram (Havanond 2008; Shimoda et al. 2009).

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Materials and methods Fieldwork and sampling Three sediment cores (A-KK, B-KK and C-KK) were collected along a transect perpendicular to the coastline from seaward, mid mangrove and landward locations adjacent to the village of Klong Kone (Fig. 1). A peat auger was used to test the stratigraphy and a 50 cm long, 5 cm diameter Russian corer was used to extract sample cores from adjacent boreholes at overlapping depths. The A-KK core site was located on a mudflat area. The B-KK core site was about 600 m landward from A-KK and the C-KK core site was located in the landward area of the mangrove ecosystem approximately 400 m away from B-KK and bordered by shrimp farms. All three coring sites were influenced by tidal inundation from the sea. The characteristics of the sediments were described using a modified version of the Troels-Smith (1955) classification (Kershaw 1997). The sample cores were extruded into PVC pipes, wrapped in aluminium foil and plastic sheeting and then labelled and packaged. The lengths of the cores were 400 cm (A-KK), 410 cm (B-KK) and 465 cm (C-KK). A vegetation survey of 10 m2 plots around the coring sites was also undertaken. Laboratory work Subsamples at intervals of 10 cm along the length of the A-KK, B-KK and C-KK cores were extracted for both pollen and charcoal analyses using the acetolysis method (Erdtman 1969; Fægri and Iversen 1989). Sample residues were stored in silicon oil. Pollen and spores were identified by comparison with pollen from modern mangrove references (Thanikaimoni 1987; Chumchim 2010). Bruguiera gymnorhiza and Ceriops tegal were grouped together as Bruguiera/Ceriops type because they could not be distinguished by light microscopy (Grindrod 1985). Poaceae pollen greater than 40 μm can be separated by its size from wild grass pollen and is defined as cultivated rice (Chaturvedi et al. 1998). To determine the pollen count needed, five samples from each site were counted and the number of taxa recorded for each 20 grains up to number of 200 grains. After 80 grains, no more new taxa were found; accordingly, at least 150 pollen grains were counted each level. This pollen count also follows other palaeoecological mangrove studies (Ellison 1989). The pollen concentration in a few samples was extremely low and therefore inadequate for a count of 150 grains. Pollen slide charcoal analysis was performed by means of the size classes of microscopic charcoal modified from Tinner and Hu (2003), Rucina et al. (2009) and Punwong et al. (2013b). The charcoal of each size class is given as the total number of fragments counted within a complete pollen slide. The total charcoal accumulation is

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totalled by summing the multiples of the mean length of each size class with the number of fragments per calculated area of each sample slide. Pollen analysis of cores B-KK and C-KK was undertaken and pollen taxa were grouped into ecological categories of mangroves, back mangroves, terrestrial herbaceous, non-mangrove arboreal and unknowns. Mangroves and back mangroves are grouped according to Watson’s (1928) and Santisuk’s (1983) inundation classes. Pteridophyte spores were excluded from the pollen sum. The pollen data are presented as percentage pollen frequency diagrams and are zoned using stratigraphically constrained cluster analysis, CONISS. In A-KK, no pollen was preserved and therefore only the B-KK and C-KK cores could be analysed. Loss on ignition (LOI) at 550 and 950 °C following procedures outlined by Heiri et al. (2001) was used for organic matter and ­CaCO3 measurement, respectively. Grain size distribution of the sediment was measured using a Malvern Mastersizer 2000 analyser with a measurement range of 0.02–2,000 µm. Each sub-sample was pre-treated with 30% ­H2O2 to remove organic material and then with 10% HCl to remove carbonates. The pollen, charcoal, grain size and LOI data were plotted as diagrams using TILIA2 and TILIA*Graph (Grimm 1991). Chronology Seven bulk sediment samples were selected from notable biostratigraphical changes for AMS dating and submitted to DirectAMS Radiocarbon Dating Service Laboratory facility in Bothell, USA. The dates were calibrated with the northern hemisphere calibration of the Intcal13 curve (Reimer et al. 2013) using OxCal v4.10 (Bronk-Ramsey 2009).

Results Vegetation survey A zonation of the Samut Songkram mangroves has been developed, based on a combination of Watson’s (1928) and Santisuk’s (1983) inundation classes and fieldwork observations (Fig. 2). The swampy mangroves and back mangroves were used in Santisuk (1983) to refer to taxa growing in areas inundated by normal to all high tides (inundation classes 1–3) and in areas inundated by equinoctial to spring tides (inundation classes 4 and 5), respectively (Watson 1928). In this study, the ecology of mangroves with respect to sea level inundation is used to assist in the environmental reconstruction of the pollen record. Site A-KK, located on the seaward edge, consisted of mudflats exposed to wave action without vegetation present. B-KK was located in the middle of the mangrove belt 600 m away from A-KK and was dominated by Avicennia marina (80%) and Rhizophora

Veget Hist Archaeobot

Fig. 2  A cross section showing mangrove ecological distributions and response to tidal inundation regimes based on a combination of Watson’s (1928) and Santisuk’s (1983) inundation classes and fieldwork observations. HWSL high water spring level, MSL mean sea level

apiculata (20%) trees. C-KK was at the landward edge of the mangrove area 400 m away from B-KK, and was characterised by A. marina (70%) and R. apiculata (30%) trees. B-KK and C-KK were around 25 m from a tidal creek and were influenced by both tidal flooding and fresh water flow. Stratigraphy, particle size analysis and loss on ignition Detailed stratigraphy, particle size analysis and loss on ignition data are given in ESM. The stratigraphy of A-KK was homogeneous grey silt with fine sand throughout the entire core. No woody roots or barks were present. The basal unit of B-KK was comprised of grey silt and sand overlain by silt with undifferentiated organic material. Silt with small fragments of woody plant roots formed the top unit. The boundaries between stratigraphic units were transitional rather than distinct. Based on particle size analysis (Fig. 3), most of the cores consisted of poorly sorted medium to coarse silt. The particle size is coarsest from 407 to 330 cm and significantly larger than the rest of the core (p < 0.01). Further up the core, the particle size is smaller and increases in the top 60 cm. The stratigraphic description is therefore in agreement with the grain size distribution analysis. The organic content of B-KK core ranges from 4.1 to 12.1% (Fig. 3). Organic matter at 407–330 cm averages 7.4% and a decrease between 320 and 130 cm. Organic matter continues to decrease from 120 to 70 cm. Within the top 70 cm, organic matter content increases exponentially. The carbonate content of B-KK ranges from 4.2 to 7.8%. Samples between 200 and 110 cm have significantly lower carbonate percentages than the rest of the core (p < 0.01). Carbonate is highest in the top 100 cm.

The basal unit of C-KK was comprised of grey silt and sand overlain by silt and silt with undifferentiated organic material. Silt and sand with small fragments of woody plant roots were found from 60 cm to the top of the core. The boundaries between stratigraphic units were transitional. Based on particle size analysis, most of the C-KK core is categorised as sandy mud or sandy silt, ranging from very fine sand to coarse silt (Fig. 4). Sediment from 460 to 210 cm is significantly coarser (p < 0.01) than the upper layer. Samples between 200 and 80 cm have the smallest particle size. Particle size again increases in the top 70 cm of the core. The stratigraphic description fits with the grain size distribution analysis. The organic content of core C-KK ranges from 3.8 to 14.8%, while carbonate content ranges from 2.9 to 8.2%. Samples at depths from 460 to 80  cm have an average organic matter content of 5.0%. The carbonate content from 460 to 210 cm is significantly lower, but is higher (p < 0.01) between 280 and 240 cm than in the rest of the core. Organic matter content sees an exponential increase from 70 cm towards the top. Chronological results and sedimentation rates Seven radiocarbon dates have been obtained from cores B-KK and C-KK (Table 1; Figs. 3, 4). The sedimentation rate in the lower part of B-KK is 0.41 cm ­year− 1 (408–130 cm) and is higher in C-KK from 440 to 210 cm (2.74 cm y­ ear− 1). The dates from the upper parts of cores B-KK (70 cm) and C-KK (130 and 45 cm) represent recent times. Detailed agedepth relationships of cores B-KK and C-KK are shown in Fig. 5. In B-KK, sedimentation rates appear continuous from the bottom toward the surface layer, then with modern 14 C dates and a much higher sedimentation rate in the last

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◂ Fig. 3  Frequency plot showing pollen, charcoal, particle size and

loss on ignition (LOI) data from core B-KK. Charcoal represents pollen slide size class counts and the total charcoal contents. Zonations are based on a cluster analysis of the pollen data

century, suggesting that a hiatus is unlikely. Zone C-KK-2 has an extremely low sedimentation of 0.11 cm y­ ear− 1; 20 times less than other zones (2.74–3.92 cm y­ ear− 1), suggesting a possible hiatus. Since this is the depth with higher content of organic matter in both cores, it is possible that the soft sediment may have eroded away easily at times of low sea level or during high energy events such as storms. The sedimentation rates were far higher at the bottom and top of C-KK than in B-KK, indicating higher sedimentation rates further away from the shore. Pollen analysis of core B‑KK Pollen analysis of core B-KK was undertaken and pollen taxa were grouped into ecological categories as shown in Table 2. The pollen assemblages were divided into four zones in the pollen diagram based on cluster analysis (CONISS) (Fig. 6). Zone B‑KK‑1 (410–335 cm: 820–640 cal bp) Pollen zone B-KK-1 is mainly dominated by mangroves (30–62%) although the mangrove pollen decreases to 30% in the middle of this zone (Fig. 6). Rhizophora dominates (54%), followed by taxa growing higher up in the intertidal zone, Brugeira/Ceriops (4–19%) and Avicennia (0–10%). Pollen and spores from the back mangroves are present (14–36%), characterised by Suaeda (8–30%), Terminalia (1–2%), Acrostichum (1–3%) and Melaleuca (1–3%). Terrestrial herbaceous pollen is present (14–30%) with the highest values found in the middle of this zone and characterised by high values of Poaceae (9–24%) followed by Cyperaceae (1–3%), Asteraceae and Amaranthaceae (1%). Up to 3% cereal pollen (Poaceae with grains larger than 40 µm) is found at the top of this zone. Pollen from other shrubs and trees (non-mangrove arboreal taxa) is found in this zone (2–15%), such as Casuarina, Anacardiaceae and Myrtaceae. Pollen concentrations are low (1,200–7,200 grains ­cm− 3). Zone B‑KK‑2 (335–135 cm: 640–140 cal bp) B-KK-2 contains fluctuations between mangroves, back mangroves and terrestrial herbaceous taxa. However, the zone contains the greatest abundance of terrestrial herbaceous pollen. Terrestrial herbaceous taxa gradually increase (31–80%) and are characterised by Poaceae (18–68%), followed by cereal pollen (3–8%), Cyperaceae (3–6%) and Asteraceae (2–6%), while mangroves gradually decrease at

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◂ Fig. 4  Frequency plot showing pollen, charcoal, particle size and

loss on ignition (LOI) data from core C-KK. Charcoal represents pollen slide size class counts and the total charcoal contents. Zonations are based on a cluster analysis of the pollen data

the beginning of this zone to a depth of 260 cm. Mangroves (8–46%) are characterised by Rhizophora (4–37%), followed by Avicennia (5–12%) and Brugeira/Ceriops (3–9%). From 260 cm to the top of this zone, mangroves dominate again, except at the depths of 210–200 cm (8–24%) and 180 cm (12%), where terrestrial herbaceous taxa increase. In this layer, mangroves (8–62%) are characterised by Rhizophora (5–51%) followed by Brugeira/Ceriops (up to 15%) with the highest value of 15% at 200 cm and Avicennia (up to 7%). Terrestrial herbaceous pollen decreases (14–30%), except at the depths of 210–200 cm (53–83%) and 180 cm (63%), and is dominated by Poaceae (8–75%) followed by cereal pollen (0–8%), Cyperaceae, Asteraceae and Amaranthaceae (up to 4%). Pollen and spores of back mangroves vary throughout this zone (4–35%). Suaeda has the highest abundance among back mangrove taxa (2–25%) followed by Sonneratia caseolaris (2–7%), Acrostichum (1–3%), while Melaleuca and Terminalia are rarely found (< 1%). Pollen from non-mangrove arboreal taxa is present up to 18% in this zone, which fits with the increase of terrestrial herbaceous pollen. Non-mangrove arboreal pollen is characterised by Dipterocarpaceae (up to 5%) followed by Casuarina, Derris, Fagaceae and Pinus (up to 3%). Pollen concentrations are relatively low (500–5,800 grains ­cm− 3). Zone B‑KK‑3 (135–75 cm: 140 cal bp‑recent times) Mangroves increase in Zone B-KK-3 and are constant throughout it (52–59%). Rhizophora are the primary taxa and increase significantly at the top of the zone (25–36%), followed by Avicennia (7–26%) and Brugeira/Ceriops (3–11%). Terrestrial herbaceous pollen decreases (16–24%) and is characterised by Poaceae (9–14%) followed by Cyperaceae (3–5%), Asteraceae and cereal pollen. Typha is also present in this zone (up to 5%). Back mangrove pollen also increases in this zone (17–20%) and is characterised by Suaeda (5–12%) and an increase in Sonneratia caseolaris (1–10%) followed by Acrostichum (1–3%) and Melaleuca (1%). Pollen of non-mangrove arboreal taxa is rare and includes Casuarina, Derris, and Fagaceae. Pollen concentrations increase towards the top of this zone (900–25,000 grains ­cm− 3). Zone B‑KK‑4 (75–0 cm: recent times) Mangroves decrease at the beginning of this zone and gradually increase towards the top of the core (39–81%). Avicen‑ nia is the primary taxon and increases significantly at the

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species are the primary taxa (30–62%) followed by Brugeira/Ceriops (4–18%) and Avicennia (2–11%). Pollen and spores from back mangroves are present (12–29%), characterised by Suaeda (6–20%), Terminalia (1–5%), Sonnera‑ tia caseolaris, Acrostichum (1–4%) and Melaleuca (1–3%). However, Sonneratia caseolaris and Melaleuca disappear between the depths of 280 and 330 cm. Terrestrial herbaceous pollen is present (7–16%) and increases to its highest values at the top of this zone (up to 38%: 205–240 cm), with high values of Poaceae (5–37%) followed by Cyperaceae (1–3%), Asteraceae and Amaranthaceae (1%). Cereal pollen is rare (up to 1%). Non-mangrove arboreal pollen is rare in this zone (1–3%), with Casuarina and Myrtaceae present. Pollen concentrations are low at the base of the zone (1,700–2,200 grains c­ m− 3) and increase to 4,200–9,300 grains ­cm− 3 throughout it, with the exception of a decrease at the top of the zone (2,000 grains ­cm− 3).

Fig. 5  Age-depth diagram for cores B-KK and C-KK

top of the zone (10–61%) followed by Rhizophora (4–30%) and Brugeira/Ceriops (1–3%). Back mangrove pollen also increases in this zone (15–73%) and is characterised by Son‑ neratia caseolaris (6–23%) with the highest peak of 64% at 60 cm, followed by Suaeda (2–9%), Acrostichum (1–5%) and Melaleuca (1–3%). Terrestrial herbaceous pollen (3–23%) is characterised by Poaceae (2–16%). Cyperaceae, cereal pollen and Typha are also found (1–3%). Pollen of nonmangrove arboreal taxa is rare. Pollen concentrations are significantly high and increase towards the top of the core (8,600–89,800 grains ­cm− 3). Pollen analysis of core C‑KK Mangrove pollen was not preserved in the basal section of the core (445–460 cm). The pollen assemblages were divided into three zones based on cluster analysis (CONISS) as follows (Fig. 7). Zone C‑KK‑1 (445–205 cm: 820–720 cal bp) Pollen Zone C-KK-1 is mainly dominated by mangroves (61–76%) although the mangrove pollen decreases to 35–59% at the top of this zone (205–240 cm). Rhizophora Table 1  List of radiocarbon dates from the C-KK core including calibrated ages with the Intcal13 curve (Reimer et al. 2013) using OxCal v4.10 (Bronk-Ramsey 2009)

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Zone C‑KK‑2 (205–45 cm: 720 cal bp‑recent times) C-KK-2 contains the greatest abundance of terrestrial herbaceous pollen (59–74%) in the entire core, while the pollen of mangroves and back mangroves decrease. Terrestrial herbaceous pollen dominates this zone except at the depths of 170 (30%), 150 cm (40%), 130 cm (8%) and 100–90 cm (29–32%), where mangroves dominate. Poaceae are the dominant taxa (27–72%) and cereal pollen increases towards the top of the zone (1–5%). Mangroves occur at 6–75% and are characterised by Rhizophora (3–49%), with the peak at 130 cm followed by Avicennia (2–36%) with the highest value at 100 cm and Brugeira/Ceriops (1–14%) with a maximum at 130 cm. Pollen and spores of back mangroves are present with a value of 8–34%, and the maximum value found at 80 cm. Suaeda has the greatest abundance among back mangrove taxa (1–16%) with a peak of 24% at 80 cm followed by Sonneratia caseolaris (1–12%) and Acrostichum (1–3%), while Melaleuca and Terminalia are rare (< 1%). Pollen from non-mangrove arboreal taxa is present in this zone (1–10%) with Casuarina, Dipterocarpaceae and Fagaceae. Pollen concentrations are relatively low (900–6,100 grains ­cm− 3) with the highest value of 8,800

Site

Depth (cm)

Code

δ13C

14

Range cal bp

cal bp

ad

B-KK B-KK B-KK C-KK C-KK C-KK C-KK

70 130 408 40 130 210 440

D-AMS 018390 D-AMS 018391 D-AMS 018392 D-AMS 015359 D-AMS 018392 D-AMS 013924 D-AMS 013925

−43.7 −21.5 −23.5 −33.1 −32.6 −26.6 −27.2

Modern 184 ± 20 891 ± 37 Modern Modern 797 ± 27 868 ± 28

Modern 287 to (−3) 914 to 732 Modern Modern 760 to 676 904 to 700

Modern 142 ± 145 823 ± 91 Modern Modern 718 ± 42 802 ± 102

Modern 1663–1953 1036–1218 Modern Modern 1190–1274 1046–1250

C yr bp

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◂ Fig. 6  Diagram of B-KK showing percentage pollen frequency and total charcoal content profiles

grains ­cm− 3 at 130 cm and an increase of 3,400−12,000 grains ­cm− 3 from 110 cm to the top of the zone. Zone C‑KK‑3 (45–0 cm: recent times) Mangroves increase in pollen zone C-KK-3 (83%). Avicen‑ nia is the primary taxon and increases significantly at the top of the zone (45–65%) followed by Rhizophora (12–21%) and Brugeira/Ceriops (1–2%). Terrestrial herbaceous pollen characterised by Poaceae (6–26%) decreases towards the top of the core (7–30%). Back mangrove pollen also increases in this zone and then decreases towards the top. This increase is primarily due to a gradual increase in Suaeda (3–15%) and increases in Sonneratia caseolaris (3–14%), with a peak at 20–30 cm, followed by Acrostichum (1–3%). Pollen of nonmangrove arboreal taxa is rare in this zone. Pollen concentrations are relatively high and increase towards the top of the core (7,000–29,000 grains ­cm− 3). Charcoal analysis The total charcoal content throughout core B-KK fluctuates from 3,900 to 11,000 fragments ­mm− 2 (Fig. 3). The charcoal content in B-KK-1 is relatively low and increases towards Zone B-KK-2 with some peaks in all charcoal class sizes at 200 cm and at the beginning of Zone B-KK-4. After that, total charcoal content decreases towards the top. Large charcoal fragments were observed throughout the core. The total charcoal content of C-KK shows a similar pattern to B-KK, with charcoal content fluctuating from 2,200 to 11,000 fragments ­mm− 2 throughout the core (Fig. 4). There are some peaks in all charcoal class sizes at the top of Zone C-KK-2 (40 cm) and the beginning of C-KK-3 (50 cm). After these peaks, the total charcoal content decreases and then slightly increases again at the top of the core. Large charcoal fragments (75–150 μm and > 150 μm) were found at a higher concentration from 330 to 280 cm.

Interpretation and discussion The multi-proxy palaeoecological analyses enable reconstruction of past environmental changes and human activities in this area during the late Holocene. Environmental conditions during ~ 820–720 cal bp (ad 1130–1230) The bases of the B-KK and C-KK cores reveal that true mangrove taxa, dominated by Rhizophora along with other

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Table 2  List of all taxa identified found in the Klong Kone cores (B-KK and C-KK), Samut Songkram, the upper Gulf of Thailand Mangroves

Back mangroves

Terrestrial herbaceous

Non-mangrove arboreal

Avicennia [Verbenac.] Brugueira/Ceriops [Rhizophorac.] Lumnitzera [Combretac.] Rhizophora [Rhizophorac.] Sonneratia [Sonneratiac.] Xylocarpus [Meliac.]

Acanthus [Acanthac.] Acrostichum [Acrostichac.] Amaranthac. cf. Suaeda Barringtonia [Lecythidac.] Browlonia [Tiliac.] Combretac. cf. Terminalia Melaleuca [Myrtac.] Nypa [Arecac.] Sonneratia caseolaris [Sonneratiac.]

Amaranthac. (Gomsphrena-type) Asterac. Cyperac. Poac. Cereals (Poac. > 40 μ) Typha [Typhac.]

Altingia [Altingiac.] Anacardiac. Casuarina [Casuarinac.] Caesalpiniac. Derris [Fabac.] Dipterocarpac. Fagac. Myrtac. Pinus [Pinac.] Sapindac.

mangroves such as Brugeira/Ceriops and Avicennia, were well established in Klong Kone by 820−720 cal bp. Compared to the present day vegetation, the dominance of Rhiz‑ ophora along with other true mangrove taxa during this period in C-KK indicates that it was then an intertidal area influenced by the sea level until around 720 cal bp. Although the late Holocene marine regression has been recorded after the mid Holocene high level in the Lower Central Plain (Sinsakul 1992, 2000; Umitsu et al. 2002; Tanabe et al. 2003a), the presence of true mangroves is evidence that the sea still covered Klong Kone during that time. High carbonate content during this period may also represent marine influence or concentrations of marine organisms. The coarser sand at the base of C-KK may have been of marine origin. However, sea level fall may have resulted in finer sand deposition and denser mangrove growth. Trees with complex root systems such as Rhizhophora are known to result in higher sedimentation (Furukawa and Wolanski 1996). The occurrence of mangroves in C-KK-1 may have caused mud bank formation. During the marine regression recorded in the last 1,000 years, river sediment from the Mae Klong accumulated, leading to a building up of coastal deposits (Umitsu et al. 2002; Tanabe et al. 2003a) that may have resulted in a high sedimentation rate in the Klong Kone cores. It should be noted that the sedimentation rate during this period is much higher in C-KK and associated with coarser sediment than in B-KK; it is quite common for a site further from the sea shore to be characterised by a lower energy environment, with finer sediment settling at a slower rate as the river delta reaches deeper water. The appearance of the back mangrove taxa Sonneratia caseolaris and Melaleuca, which usually grow in fresh water conditions (Santisuk 1983), is evidence of fresh water influence from the rivers which have formed in the lower central plain since the late Holocene (Somboon and Thiramongkol 1992; Tanabe et al. 2003a). The occurrence of these two taxa, combined with low total charcoal concentrations at the base of both cores, suggest wet conditions; at a similar

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period, several tree ring studies have indicated greater monsoons in the southeast Asia region around ad 1050–1100 (Buckley et al. 2010, 2014). Subsequently, the disappearance of these back mangrove taxa and a relatively high total charcoal content probably suggest less fresh water input to the area between the depths of 280–330 cm in C-KK and may correspond to a dry period occurring in southeast Asia from ad 1150 to 1180 (Buckley et al. 2010, 2014). Mangroves gradually retreated seawards and terrestrial herbaceous taxa increased before 720 cal bp. This evidence suggests that marine regression has occurred continuously along the upper west coast of the Gulf of Thailand during the last 1,000 years (Somboon and Thiramongkol 1992; Umitsu et al. 2002; Tanabe et al. 2003a) and corresponds to studies in other countries in the Gulf of Thailand such as the Mekong river delta of Vietnam (Nguyen et al. 2000; Tanabe et al. 2003b) and Cambodia (Tamura et al. 2009). Terrestrial herbaceous taxa together with a higher charcoal content suggest that less fresh water was present in the area and this may coincide with a decline in monsoons in southeast Asia from ad 1200 to 1250 (Buckley et al. 2010, 2014). The appearance of cereal pollen in both cores, along with an increase in the number of the larger-sized charcoal fragments (75–150 µm), suggests early human activities in the area, probably at higher inland places, after ~ 820 cal bp (ad 1130). Early settlements in the Lower Central Plain, and along the upper Gulf of Thailand, fall within the Dvaravati period from the 6th to 13th century ad (Mudar 1999; Letrit 2003; Songtham et al. 2015), although there are some settlements in the northern part of the Mae Klong river basin dating to pre-Dvaravati times (Khunsong et al. 2011). Rice farming was first recorded in the eastern part of the Gulf around 5,000  years ago. (Maloney et  al. 1989) and was mainly practised during the Dvaravati period (Mudar 1999). Dvaravati key cities located to the west of the plain were close to mangrove areas along the old shoreline (Hutangkura 2012; Songtham et al. 2015). It is likely that Klong Kone formed part of this shoreline during the Dvaravati period.

Veget Hist Archaeobot

◂ Fig. 7  Diagram of C-KK showing percentage pollen frequency and total charcoal content profiles

Environmental conditions during ~ 720 cal bp–140 cal bp (ad 1230–1810) Mangroves, particularly Rhizophora and Brugeira/Ceriops, gradually decline around 720  cal bp and are abruptly replaced by terrestrial herbaceous plants, mainly grasses, in both the B-KK and C-KK cores. Non-mangrove arboreal taxa are also present after this time, combined with low pollen concentrations, which may indicate that mangroves retreated seawards due to a lower sea level after 720 cal bp. It is possible that about ~ 720 cal bp the sea level did not flood the Klong Kone area, thus allowing for the establishment of terrestrial vegetation until around 140 cal bp. It should be noted that at the beginning of Zones B-KK-2 and C-KK-2, mangroves in C-KK-2 suddenly decrease while mangroves in B-KK-2 gradually decrease. This evidence along with the succession of terrestrial taxa during this period may be related to the retreat of the sea (Umitsu et al. 2002; Tanabe et al. 2003a; Songtham et al. 2015). Rapid building up of the fan delta in the Lower Central Plain due to increased river discharge may have resulted in the establishment and/or extension of swamps and wetlands with grasses and sedges recorded from 2,000 years ago (Tanabe et al. 2003a; Hutangkura 2012; Songtham et al. 2015). Such a situation may account for the highest values of terrestrial taxa and smallest particle sizes in both cores, suggesting that the Klong Kone area may have become a young deltaic plain during this time. During this period, the establishment of a deltaic system characterized by high sedimentation following a sea level fall is similar to that recorded in other locations along the Gulf of Thailand such as the Mekong delta in Vietnam (Tanabe et al. 2003b) and in Cambodia (Tamura et al. 2009). There are fluctuations in mangroves characterised by Rhiz‑ ophora followed by Brugeira/Ceriops, Avicennia and back mangroves with a reduction of grasses and non-mangrove arboreal taxa suggesting a fluctuating sea-level during this period. At the beginning of this time, there might have been more fresh water influence than previously, as suggested by an increase in Sonneratia caseolaris. This is possibly related to the Medieval Climate Anomaly in southeast Asia from ad 1250–1300 (Buckley et al. 2010, 2014; Lieberman and Buckley 2012). This is also supported by a lower charcoal content representing decreased regional fires. However, from ad 1200–1900; the climate fluctuated between wet and dry conditions across the southeast Asian mainland (Buckley et al. 2010, 2014; Cook et al. 2010; Lieberman and Buckley 2012) resulting in unstable charcoal levels as shown in this study during ad 1230–1810. An increase in cereal pollen is also present in Zones B-KK-2 and C-KK-2 suggesting possible agricultural activity, particularly paddy farming. It

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should be noted that the settlement of the old shore in this area probably started during the period of 720–140 cal bp with the Ayutthaya kingdom, which then spread throughout the Central Plain during the 14th–18th centuries ad. This was followed by the Thonburi and Rattanakosin (Bangkok) period after the 18th century ad (Baker and Phongpaichit 2014; Songtham et al. 2015), when rice was intensively cultivated as shown in the Klong Kone cores. Moreover, in its heyday when the Ayutthaya kingdom was recognised as a centre of sea trade, as it was connected to the sea by rivers and canals, trading in mangrove timber and firewood was common (Terwiel 2007; Baker 2011). Such use and clearance of mangrove areas for cultivation is likely to account for the decline in mangrove taxa during 720–140 cal bp. Environmental conditions during 140 cal bp to present (ad 1810–present) After 140 cal bp, mangroves re-colonised the site and were dominated by Rhizophora and Avicennia in core B-KK. Terrestrial herbaceous taxa with non-mangrove arboreal taxa declined, suggesting more frequent flooding that may have resulted in a landwards move of mangrove communities, possibly due to a rise in sea level in historical times. From 50 cm to the tops of B-KK and C-KK, which are dated as later than ad 1950; the vegetation is dominated by Avicen‑ nia, a seaside mangrove. Although the Klong Kone area has had new mangroves planted since ad 1993 (Erftemeijer and Lewis 1999; Tookwinas 2004), Rhizophora was planted only on new mudflats. An increase in Avicennia associated with very high pollen concentrations is likely to indicate a rise in sea level in recent times. This corresponds to a relative sea level rise of ~ 4.5 mm y­ ear− 1 recorded in the Gulf of Thailand during the last 50 years (Trisirisatayawong et al. 2011). However, a decline in Rhizophora and an increase in Avicennia are probably due to human use of mangroves for timber and charcoal (Aksornkoae 1993). An increase in Sonneratia caseolaris in both cores, peaking at 60 cm in B-KK, and the lowest mangrove values suggest more fresh water input than in any other period. This possibly correlates with an increase in precipitation recorded in the northwest of Thailand and southeast Asia as indicated by tree ring records after ad 1830 (Buckley et al. 2007; Cook et al. 2010; Pumijumnong and Eckstein 2011; Lieberman and Buckley 2012). This suggestion of increased fresh water flows is also supported by the increase in the particle size of sediment recorded at this time, which may have been caused by fresh water discharge from intensive monsoons. In addition, mangrove disturbances inland may also have resulted in more erosion. At 70 cm in B-KK and 60 cm in C-KK, grain size and sand percentage increase, suggesting more human disturbance. In the Mae Klong watershed, forest cover has been rapidly reduced in the last century. Maita et al. (1998)

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Veget Hist Archaeobot

calculated the sediment yield in the Mae Klong basin and related its high load to the decreased amount of forest cover. Particle size and sediment loading depend on sediment supply, energy of the environment and vegetation setting. Particle size usually has a positive correlation with higher flow, water depth or water mixing among mangroves (Furukawa et al. 1997). Increased vegetation cover can also reduce flow and results in the deposition of smaller size particles (Sanders et al. 2012). Moreover, land in the upper Gulf of Thailand has been converted to intensive shrimp farms since the 1960s (Aksornkoae 1993; Tookwinas 2004). It is likely that an increase in particle size at 70 cm in B-KK and 60 cm in C-KK are a result of such land use change within the watershed, leading to an increase of sediment supply. This is also evident from the sedimentation rates that increase abruptly toward the top of both cores (B-KK < 2.12  cm ­year− 1; C-KK < 3.94 cm ­year− 1.) Towards the top of both cores, particle size declines. In the Mae Klong basin, the Sri Nakarind, Tha Thungna and Khao Laem dams were built in 1980, 1981 and 1985, respectively. They restrict water flow through the Mae Klong river into the Gulf of Thailand and cause sediment trapping behind the dams, resulting in lower sediment load (Hungspreugs et al. 2002). Walling and Fang (2003) analysed data from 145 rivers around the world and found a positive correlation between sediment load and flow, and that 50% of the world’s rivers have significantly altered sediment loading due to reservoir construction, land clearance, land use change and land disturbances. Organic matter content in both cores is the highest near the surface and gradually decreases with depth; this is typical in wetlands where the surface has the highest organic matter from new litter. Samples with higher organic matter are associated with sediment of smaller particle size; various studies found a negative correlation between nutrients and organic matter and particle size in mangrove areas (Duarte et al. 1998). The high sedimentation rate could be due to human activities and is similar to other Asian delta systems such as the Mekong river delta (Tamura et al. 2009). In both cores, especially in B-KK, the carbonate content is significantly higher in the last century. While sea level rise may contribute to increasing marine carbonate, the abrupt increase may indicate human influence in the form of mollusc aquaculture, which is common in the Gulf of Thailand (Chalermwat et al. 2003). However, shell fragments were not obvious in these samples. This might be consistent with various studies indicating the use of concrete which resulted in increases in carbonate in river sediment (Wright et al. 2011). Dumping, filling and erosion of such concrete material may cause an abrupt increase of calcium carbonate in the core. However, it is difficult to judge whether the environment or human influence on the surrounding landscape over the last centuries has driven these changes. It is most likely that

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there is a combination of natural sea level changes and climate processes combined with human activity that have all affected the mangrove dynamics of the Klong Kone area in the last 1,000 years.

Conclusions A combination of natural sea level changes, climate processes and human activities has driven the mangrove dynamics over the last 1,000 years of the Klong Kone area in the upper Gulf of Thailand. Palaeoecological analyses of two sediment cores from a mangrove forest in Klong Kone demonstrate evidence of environmental changes and human activity over the past 1,000 years. The appearance of cereal pollen indicates rice growing on the higher land and it is conceivable that Klong Kone was an old shoreline during the Dvaravati period. The loss of mangroves and rise in terrestrial vegetation may suggest a change of environmental conditions from coastal to terrestrial deltaic plain between ~ 700 and 140 cal bp relating to a fall in sea level. An increase in cereal pollen during this period suggests that farming, particularly rice paddies, could explain these ecosystem changes. The inter-tidal habitat reappeared again after 140 cal bp, as suggested by the re-colonisation of mangroves due to a recent sea-level rise. Over the last century, particle size and carbonate content records indicate that human factors have influenced mangrove ecosystems and sediment budgets due to a combination of dam construction and change in land use for aquaculture. Acknowledgements  Appreciation is expressed to Pratueng Cheuliang, Kamalaporn Kanongdate, Siraprapha Premcharoen and Klong Kone Mangrove Conservation Center as well as Mahidol students: Sureephorn Phomplin, Ausanee Sittiwong, Naruebet Permpoon, Jutamas Yimpray and Kanpong Duangpustra for their support and assistance throughout this fieldwork. We are grateful to Sureephorn Phomplin for laboratory assistance. We would like to thank Maria Gehrels, and the Environment Department, University of York for support in the laboratory and other areas. This study was fully funded by the Thailand Research Fund (TRG 5880181) and Mahidol University. The laboratory work in York was funded by a Researcher Links Travel Grant from the Newton Fund (2015).

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