Response of chironomids to Neolithic land-use change in north-west Ireland

Abstract

This study provides the first decadally resolved chironomid and organic geochemistry record of the Irish Neolithic from a small lake adjacent to the Carrowkeel-Keshcorran complex in County Sligo, Ireland. Chironomid (non-biting midge fly) sub-fossils and lake sediment geochemistry (δ¹³C, δ¹⁵N and C:N) from the Templevanny Lough core were used to assess the timing and magnitude of within-lake responses to Neolithic farming activity. When compared with decadally resolved pollen and macroscopic charcoal records from the same core, the limnological data show a direct influence of prehistoric farming on a freshwater lake system through nutrient loading and lake eutrophication. Elevated nutrient levels, suggesting a more productive lake system, and a subsequent turnover in the chironomid community indicate a period of intensive farming activity from c. 3790–3620 BC in the early Neolithic. This was followed by a decline in farming with short periods of small-scale human activity, exemplified through nutrient loading and short-lived increases in eutrophic chironomid taxa during the middle to late Neolithic. A return of farming activity can be seen in all proxy data in the late Neolithic (c. 2720–2480 BC). The chironomid community composition typically lagged land-use change by c. 10–20 years and exhibited predictable and proportional responses to agricultural activity. The timing and magnitude of limnological changes show that land-use, rather than climate, is the main control on chironomids at Templevanny Lough, thus showing the potential prominence of the anthropogenic signal during the Neolithic.

Keywords

Chironomids geochemistry Ireland lake response Neolithic Palaeolimnology

Introduction

The Neolithic period in Ireland (c. 4000–2500 BC; cf. Cooney, 2000) coincides with the first widespread evidence of substantial human impacts on the landscape (Waddell, 2010). The transition from hunter–fisher–gatherer Mesolithic societies to Neolithic farming-based economies saw the arrival of domesticated animals, grain cultivation, woodland clearance and more permanent settlement (Cooney, 2000). North-western Ireland, and particularly County Sligo, had an especially prominent Neolithic, including one of the highest concentrations of megalithic tombs in Ireland (Bergh, 1995) and the large passage tomb complexes of Carrowmore and Carrowkeel-Keshcorran.

Neolithic cultivation is typified by small, permanent plots of mostly wheat and barley, best described as intensive garden agriculture (Whitehouse et al., 2014). Neolithic farming also saw the introduction of cattle, pig and sheep/goat, with cattle dairying becoming especially prominent across the region (Smyth and Evershed, 2015). These activities have been shown to enhance soil erosion rates and increase nutrient loading through both farming activities such as tillage and trampling and increased deposition of animal waste (Taylor et al., 2013). Palaeolimnological data can provide insights on human–environment relationships through time (Heiri and Lotter, 2003), including degree of environmental degradation, scale and intensity of farming activity or proximity of farming to a lakeside.

Chironomid analysis is a powerful tool in limnological reconstruction, as chironomid larvae are extremely sensitive to lake conditions (Walker, 2001). Due to their susceptibility to changing environmental conditions and frequent abundance in freshwater lake systems, chironomids have been increasingly used in palaeoenvironmental reconstructions to qualitatively assess past land-use change and its impact on the environment (O’Brien et al., 2005; Ruiz et al., 2006; Taylor et al., 2013). Geochemical indicators (δ¹³C, δ¹⁵N and C:N) have been applied to complement chironomid analysis, as they provide information on lake productivity, sources of lake sediment organic matter and changing land-use practices (Cohen, 2003; Woodward et al., 2012). The combination of these proxies with pollen and macroscopic charcoal data allows for a systematic investigation into the limnological impacts of prehistoric human activities. This methodology proved successful at Lough Dargan, County Sligo, where close linkages were established between human land-use and lake eutrophication, with farming and associated nutrient loading being the main influences on the chironomid community during the Neolithic and Bronze Age (Taylor et al., 2013). However, a low sampling resolution and staggered sub-sampling did not permit a detailed investigation of magnitude and timing of lake response to land-use change.

The aim of this study is to provide a high-resolution assessment of the timing and intensity of Neolithic land-use and its impact on Templevanny Lough, a small lake adjacent to the Carrowkeel-Keshcorran complex, County Sligo (Figure 1). Present knowledge of the Carrowkeel-Keshcorran complex and prehistoric landscape change derives mainly from archaeological and pollen investigations (Bergh, 1995; Göransson, 1984, 2002; Hensey et al., 2013; McAulay and Watts, 1961; Mitchell, 1951; Mount, 1996; Stolze, 2012; Stolze et al., 2012, 2013a, 2013b). This paper provides the first reconstruction of lake response to anthropogenic activity at a decadal resolution of the Neolithic in Ireland, using chironomid sub-fossils, lake sediment geochemistry (δ¹³C, δ¹⁵N and C:N ratios), macroscopic charcoal and a new extended pollen stratigraphy.

Figure 1.

(a) Maps showing the study region in north-west Ireland and (b) County Sligo with locations of Neolithic archaeological sites, previously investigated lakes and Templevanny Lough, studied in this contribution. (c) Map illustrates the study site showing minor inflow and outflows and the location of a crannóg within the Templevanny Lough catchment. The coring location is indicated.

Study site

The study site is situated in the south-eastern Ballymote Lowlands, County Sligo. Carboniferous limestone forms the bedrock which is overlain by glacial deposits (MacDermot et al., 1996). Templevanny Lough (54°2.100′N, 08°24.350′W) is a small oval-shaped lake of approximately 2 ha in size located at an elevation of 84 m a.s.l. (Figure 1). The lake has a number of minor inflows and a stream that drains to the south-west. Templevanny Lough is bordered by farmland. The Bricklieve Mountains are located approximately 1 km to the north-east of the study site.

The Carrowkeel-Keshcorran complex is one of the four major passage tomb complexes of Ireland and is located on the summit plateaus of the Bricklieve Mountains and hill of Keshcorran. It is one of the less thoroughly studied complexes in Ireland (Hensey et al., 2013), with a series of some 20 passage tombs spread across the upland landscape (Bergh, 1995; Moore, 2004). A cluster of 153 hut sites is located on the limestone plateau of Mullaghfarna at the eastern side of the Bricklieve Mountains (Bergh, 2006). Use of the monuments and activity at the Carrowkeel-Keshcorran complex is dated from the middle Neolithic to the middle Bronze Age (Hensey et al., 2013). The most recent dating evidence has raised the possibility that Carrowkeel cairns were in use as early as c. 3500 BC, several hundred years before Newgrange (Hensey, 2015). The passage tomb of Newgrange is part of the internationally renowned archaeological complex of Brú na Bóinne in County Meath (Hensey, 2015; Lynch, 2014) and was most likely constructed between 3200 and 3000 BC (Lynch, 2014).

Methodology

Coring and sub-sampling

The two parallel 13-m-long cores were extracted using a Usinger piston corer, at a water depth of 6 m close to the centre of Templevanny Lough in 2008 (Stolze et al., 2013b). The sediment interval between 999.5 and 839.5 cm was contiguously sampled at 1-cm resolution for chironomid, geochemical, macroscopic charcoal and pollen analyses.

Radiocarbon dating

Age control for Templevanny Lough is based on 16 ¹⁴C accelerator mass spectrometry (AMS) determinations from Stolze et al. (2013b). An additional six dates were obtained for this study using terrestrial plant material retrieved from the sediments (Stolze et al., in preparation). The sediment samples were treated with 10% HCl and rinsed with deionized water through a 125-µm sieve. The plant material was picked under a stereo microscope. Radiocarbon dating was performed at the ¹⁴CHRONO Centre, Queen’s University Belfast. A new depositional model was calculated for the 160-cm-long sediment sequence with the program OxCal 4.2 (Bronk Ramsey, 1995, 2001, 2009), applying the IntCal13 curve (Reimer et al., 2013). Calculation of the Poisson depositional model was performed at 0.5-cm increments and a number of events per unit length of 10 cm⁻¹. Boundaries were set at 975.5 and 897.5 cm. Outlier analysis was performed and identified 6 of the 22 samples as not reliable. Ages obtained by Bayesian age–depth modelling are expressed as the mean of the posterior probability distributions and rounded to the nearest 10 years. The 95.4% highest probability density intervals are used as a measure of uncertainty of this age estimate, which range from 25 to 85 years, with a median value of 40 years.

Chironomid analysis

Chironomid analysis followed standard procedures outlined by Walker (2001). Between 0.75 and 4.5 cm³ of sediment was deflocculated in a 10% KOH solution and heated at 30°C for 30 min. The sediment slurry was sieved through a 90-µm mesh, and the sieve residue was poured into a Bogorov plankton counting tray to be sorted at 10–40× magnification using a Motic^® SMZ series dissection microscope. A minimum of 50 head capsules per sample were removed with forceps and permanently mounted on slides with Entellan^® for identification. Chironomid identifications were made using a Motic B3 professional series compound microscope at 100–400× magnification. Taxa were identified to genus, sub-genus or species level following Brooks et al. (2007), Larocque-Tobler (2014), Rieradevall and Brooks (2001) and Wiederholm (1983). Chironomid ecology and distribution information are based on Brooks et al. (2007), Moller Pillot (2009, 2013) and Vallenduuk and Moller Pillot (2007).

For presentation purposes, chironomid types associated with rivers and streams were grouped together in the chironomid stratigraphy. Total stream taxa include Corynoneura lobata-type, Epoicocladius, Euryhapsis, Heleniella, Krenosmittia, Paracricotopus, Parametriocnemus/Paraphaenocladius, Paratrissocladius, Stilocladius, Rheocricotopus undifferentiated, Rheocricotopus chalybeatus-type, Rheocricotopus effusus-type, Rheocricotopus fuscipes-type and Thienemanniella clavicornis-type.

Geochemical analyses (δ¹³C, δ¹⁵N and C:N)

All contiguous samples were analysed for stable isotope ratios of nitrogen and organic carbon (δ¹⁵N and δ¹³C) and the elemental concentrations of C and N. Sediment samples of 1 cm³ were dried, pulverized with a mortar and pestle and passed through a 200-µm sieve. Between 2 and 5 mg of homogenized material was weighed into silver capsules and HCl-fumigated following Harris et al. (2001) and measured for δ¹³C values. A separate analysis was conducted to measure δ¹⁵N values of a non-acidified portion of the samples. Stable isotope ratios of C and N were determined using a Thermo Fisher Delta V Advantage elemental analysis–isotope ratio mass spectrometry (EA-IRMS) at the Isotope Biogeochemistry Laboratory, University of Hawai’i at Mānoa. C:N was calculated from organic carbon and total nitrogen (TN) elemental concentrations. Isotope ratios are reported as ‰ relative to the Vienna PeeDee Belemnite (VPDB) standard and atmospheric nitrogen for δ¹³C and δ¹⁵N, respectively. Accuracy, that is, the offset between measurements and standards, for both δ¹³C and δ¹⁵N, was ±0.3‰.

Macroscopic charcoal analysis

For all 160 samples, macroscopic charcoal particles (⩾90 µm) were counted in concert with the chironomid extraction, and charcoal accumulation rates (particles cm⁻² yr⁻¹) were determined.

Loss-on-ignition and pollen analyses

To provide a complete pollen and geochemical record for the Neolithic period from Templevanny Lough, the previously published loss-on-ignition (LOI) and pollen stratigraphies (Stolze et al., 2013b) were each complemented by the analysis of 32 additional sediment samples taken between 870.5 and 839.5 cm. Detailed preparation protocols for both analyses are given in Stolze et al. (2013b). The organic (LOI₅₅₀) and inorganic carbon (LOI₉₅₀) contents determined at 550°C and 950°C (Heiri et al., 2001) as well as the non-combustible fraction (NCF) are presented here. In the present contribution, a percentage curve summarizing pollen types largely indicative of grassland communities (cf. Behre, 1981; Brun, 2011) and the arboreal pollen curve are displayed. These pastoral pollen indicators (PPIs) include Cirsium, Tubuliflorae, Lactucae, Plantago lanceolata-type, Poaceae: wild grass group, Rumex acetosa-type, Plantago major–media-type, Ranunculus-type and Trifolium-type. In addition, the Plantago lanceolata-type curve is shown. Due to the nearly consistent occurrence of Hordeum-type pollen in the pollen stratigraphy, possibly reflecting the presence of Glyceria on the lake fringe rather than the cultivation of Hordeum (cf. Stolze et al., 2012), this pollen type is not considered as an anthropogenic indicator here. Calculation of the pollen percentages is based on the terrestrial pollen and spore sum.

Statistical analyses

Ordination analyses were performed using Canoco version 4.54 (Ter Braak and Šmilauer, 2006) on square root transformed chironomid percentage data for all common taxa, that is, taxa present in at least two samples with a relative abundance of ⩾2% in at least one sample (Quinlan and Smol, 2001). Both principal component analysis (PCA) and detrended correspondence analysis (DCA) were carried out. PCA results were used as this analysis gave a better overall explanation of the variance in the data. Redundancy analysis (RDA), a constrained linear ordination technique, was performed to identify which of the environmental variables could explain a statistically significant (p < 0.05) amount of the variance in the chironomid data set. The statistical significance of each variable was assessed using Monte Carlo permutation tests (499 unrestricted permutations). A series of partial RDAs was completed for six environmental variables (PPI, Plantago lanceolata-type, macroscopic charcoal, C:N, δ¹⁵N and δ¹³C) to determine which of the variables retained high explanatory importance for chironomid distribution.

The chironomid percentage diagram was constructed using C2 version 1.7.6 (Juggins, 2014), and zonation was performed on the percentage data of all taxa using Zone version 1.2 (Juggins, 1992). Zonation was based on optimal sum-of-squares partitioning, and statistical significance of zones was determined using BSTICK (cf. Bennett, 1996). All other graphs and linear regressions were completed using SigmaPlot version 12.0.

Results

The multi-proxy record from Templevanny Lough spans the time interval from c. 4120–2480 BC (999.5–839.5 cm), covering the Irish Neolithic. In the following, the down-core variations of the chironomid and other proxy data are presented (Figures 2 –5).

Figure 2.

Chironomid percentage diagram from Templevanny Lough, County Sligo, arranged by sub-family.

Figure 3.

Environmental variables – macroscopic charcoal, pastoral pollen indicators (PPIs), Plantago lanceolata-type, δ¹⁵N, δ¹³C and C:N plotted passively over principal component analysis (PCA) bi-plot for (a) chironomid samples, highlighting changes in species composition through time and (b) for common chironomid taxa.

Figure 4.

A comparison of geochemical data, LOI (550°C, 950°C and NCF), chironomid PCA Axis 1 values, pastoral pollen indicators (PPIs), Plantago lanceolata-type, total arboreal pollen and macroscopic charcoal for Templevanny Lough, County Sligo.

Figure 5.

Redundancy analysis (RDA) bi-plot for chironomid samples with environmental variables – macroscopic charcoal, pastoral pollen indicators (PPIs), Plantago lanceolata-type, δ¹⁵N, δ¹³C and C:N.

Chironomid stratigraphy and zonation

In total, four statistically significant zones were determined. The subdivision of Zone 4 is not statistically significant but was included here as the sub-zonation shows a noteworthy qualitative change within the chironomid community. Chironomid head capsules of 50–82.5 (mean = 56) were identified per sample. A total of 126 distinct taxa were identified in the Templevanny Lough core, with 19–40 different taxa (mean = 29) per sample.

Zone 1 = c. 4120–3790 BC (999.5–973.5 cm)

The chironomid taxa dominating Zone 1 are Chironomus anthracinus-type, Tanytarsus mendax-type and Corynoneura lobata-type (Figure 2). Chironomus anthracinus-type abundance is relatively high at ~12% in the beginning and end of Zone 1. Its dip in abundance in the middle of this zone coincides with a decrease in the total chironomid concentration. Tanytarsus mendax-type abundance increases from 5–17% between c. 3810 and 3800 BC (975–974 cm). Tanytarsus lugens-type emerges at 6% abundance at c. 3800 BC (974 cm). There is an increase in Corynoneura lobata-type from 0–12% between c. 3970 and 3930 BC (988–985 cm), with levels of ~7% for the remainder of this zone. Cladopelma and Microtendipes pedellus-type occur in the lower half of the zone. While Microtendipes pedellus-type remains present at a lower abundance in the upper portion of this zone, Cladopelma disappears at c. 3930 BC (985 cm).

Zone 2 = c. 3790–3610 BC (973.5–956.5 cm)

A noteworthy shift in the chironomid community composition is recorded from Zone 1 to Zone 2. Tanytarsus lugens-type dominates this zone, with an average of 26% between c. 3790 and 3720 BC (973–967 cm) and a peak of 33% at c. 3760 BC (970 cm). T. lugens-type decreases towards the end of this zone, with an average of 11% from c. 3660–3620 BC (961–957 cm). Chironomus anthracinus-type and Tanytarsus undifferentiated show higher values than in Zone 1 and exhibit an increasing trend throughout this zone. The largest sample-to-sample increases in Chironomus anthracinus-type (8%) are found at c. 3720 BC (967 cm) and c. 3680 BC (963 cm). Corynoneura lobata-type, Corynoneura type A, Paratanytarsus, Procladius and total stream taxa become less abundant in Zone 2. PCA Axis 1 (λ = 0.113) supports the noted shift in the chironomid community composition (Figure 3a). The species bi-plot shows a strong relationship between PPI, P. lanceolata-type and T. lugens-type, with T. lugens-type appearing to the extreme right of the taxa bi-plot (Figure 3b). The highest chironomid concentrations of 159 head capsules per cubic centimetre are observed in this zone (Figure 2).

Zone 3 = c. 3610–3140 BC (956.5–912.5 cm)

The main change in the chironomid community is reflected in the disappearance of Tanytarsus lugens-type from the stratigraphy by c. 3510 BC (947 cm). Chironomus anthracinus-type and Tanytarsus undifferentiated continue to dominate the chironomid stratigraphy. Chironomus anthracinus-type peaks on two occasions at c. 3550 BC (950 cm) and c. 3310 BC (928 cm) with a small peak also at c. 3280 BC (934 cm), while Tanytarsus undifferentiated has a small peak (15%) at c. 3580 BC (953 cm). Phaenopsectra flavipes-type, Micropsectra insignilobus-type, Paratanytarsus, Procladius, Corynoneura undifferentiated, Corynoneura lobata-type, Corynoneura type A, Limnophyes/Paralimnophyes, Parakiefferiella bathophila-type and Parametriocnemus/Paraphaenocladius occur in higher abundance and frequency than in Zone 2. The change in the community composition is evident in a shift back to the left in the PCA Axis (λ=0.113; Figure 3a).

Zone 4 = c. 3140–2480 BC (912.5–839.5 cm)

This zone is dominated by Microtendipes pedellus-type, Micropsectra insignilobus-type, Tanytarsus undifferentiated and Tanytarsus mendax-type, while Chironomus anthracinus-type is less abundant than in previous zones. Corynoneura undifferentiated and Corynoneura lobata-type are present at low abundance. Total stream taxa become more important in the stratigraphy. The change in the community composition is reflected in the PCA samples bi-plot, with samples from Zone 4 clustering to the left of the axis (Figure 3a). Division into two sub-zones acknowledges notable changes in the abundance of several chironomid types in this zone.

Sub-zone 4a = c. 3140–2720 BC (912.5–867.5 cm)

Corynoneura type A, Limnophyes/Paralimnophyes and Parametriocnemus/Paraphaenocladius are prominent in this sub-zone. Chironomus anthracinus-type is absent from c. 2950–2940 BC (894–893 cm) but re-enters the stratigraphy from c. 2930–2910 BC (892–890 cm) at 5%, in concert with small increases in abundance of Micropsectra insignilobus-type and Tanytarsus undifferentiated Chironomus anthracinus-type is absent once again at c. 2900 BC (889 cm). Orthocladius-type S, Endochironomus albipennis-type, Glyptotendipes pallens-type and Nanocladius branchicolus-type become more frequent in the chironomid stratigraphy in the upper half of this sub-zone. Symposiocladius, a wood miner in running water, is also present.

Sub-zone 4b = c. 2720–2480 BC (867.5–839.5 cm)

Chironomus anthracinus-type remains at an average of 5% in Sub-zone 4b, with an increase in abundance to 8% between c. 2530 and 2510 BC (845–843 cm). Chironomus plumosus-type enters the stratigraphy with an average of 5% between 2530 and 2510 BC (845–843 cm). Notably high abundances of Tanytarsus undifferentiated, Paratanytarsus, Micropsectra insignilobus-type and Microtendipes pedellus-type are recorded. Endochironomus albipennis-type, Glyptotendipes pallens-type and Nanocladius branchicolus-type remain low in abundance in continuation from Sub-zone 4a. Cladopelma, Cricotopus intersectus-type and the terrestrial taxon Smittia become more frequent than in Sub-zone 4b. Symposiocladius is also present. Total stream taxa average at 17% between 2680 and 2630 BC (862–857 cm).

Stable carbon and nitrogen isotopes and LOI

Values of lake sediment δ¹⁵N range from 2.3–5.4‰ with a mean of 3.9‰ and TN shows a range of 0.9–1.7% (mean = 1.3%; Figure 4). The values for δ¹³C vary from −30.5‰ to −32.6‰, with a mean of −31.6‰. C:N ratios of organic matter show a range of 11.3–14.6, with a mean value of 13.3. LOI₅₅₀ values range from 19.8–43.7% (mean = 32.7%), and NCF values vary from 44.9–61.7% (mean = 51.5%). The zones established for the chironomid data were also applied to the other proxies to allow for an easier comparison of the various data sets.

Zone 1 = c. 4120–3790 BC (999.5–973.5 cm)

Levels of δ¹⁵N show a gradual increase from 2.3‰ to 4.5‰ through Zone 1 (Figure 4). δ¹³C values increase from −32.5‰ to −31‰ by 3960 BC (987 cm) and decrease afterwards to −31.5‰. An increase in the C:N ratio from 13.0 to 14.3 is recorded between c. 4110 and 4010 BC (999–991 cm), after which it decreases to 12.4.

Zone 2 = c. 3790–3610 BC (973.5–956.5 cm)

Elevated δ¹⁵N levels of 4.1–4.6‰ are recorded, while δ¹³C decreases from −31.5‰ to −32.2‰ and C:N remains consistently low at 12 through this zone.

Zone 3 = c. 3610–3140 BC (956.5–912.5 cm)

δ¹⁵N ranges from 5.4–3.7‰. There are three peaks in δ¹⁵N at c. 3590 BC (954 cm; 4.8‰), c. 3390 BC (935 cm; 4.7‰) and c. 3260 BC (923 cm; 5.4‰), and a notable low of 3.8‰ is observed from c. 3480 to 3460 BC (944–942 cm). The C:N ratio shows an increasing trend.

Sub-zone 4a = c. 3140–2720 BC (912.5–867.5 cm)

δ¹⁵N is represented by generally lower values than in Zone 3. A peak of 4.2‰ is observed from c. 2980–2910 BC (897–890 cm), with an average of 3.7‰ through the remaining samples in this zone. δ¹³C shows higher levels than in Zone 3, with an average value of −31.4‰ and a peak of −30.8‰ at c. 2950 BC (894 cm). The C:N ratio shows a notable trough from c. 2980–2910 BC (897–890 cm), with values reaching 13.5 at c. 2940 (893 cm). Excluding this period, C:N values average at 14.2. LOI₅₅₀ shows a notable trough from c. 2980–2880 BC (897–886 cm) reaching a low of 32% at c. 2930 BC (892 cm).

Sub-zone 4b = c. 2720–2480 BC (867.5–839.5 cm)

δ¹⁵N values steadily increase throughout this sub-zone. δ¹³C values fluctuates substantially, with a large increase to −30.7‰ between c. 2660 and 2610 BC (860–854 cm). C:N values decline from c. 2600 BC (847 cm). LOI₅₅₀ shows a declining trend, with a decrease of 8% documented between c. 2680 and 2650 BC (862–859 cm). NCF values increase from 49% to 61% between c. 2680 and 2570 BC (863–850 cm).

Pollen and macroscopic charcoal

Macroscopic charcoal accumulation rates range from 0.1 to 8 particles cm⁻² yr⁻¹, with a mean value of 1.9 particles cm⁻² yr⁻¹ (Figure 4).

Zone 1 = c. 4120–3790 BC (999.5–973.5 cm)

High levels of macroscopic charcoal of 3–6 particles cm⁻² yr⁻¹ are found at the beginning of the stratigraphy from c. 4110 to 4000 BC (999–990 cm), with peaks at c. 4060 BC (995 cm; 7.3 particles cm⁻² yr⁻¹) and c. 4000 BC (990 cm; 7.3 particles cm⁻²yr⁻¹). Despite lower levels thereafter, another peak of 4.5 particles cm⁻²yr⁻¹ is recorded at c. 3860 BC (979 cm). Following low values of <1%, PPI values rise moderately from 1% to 8% between c. 3970 and 3850 BC (988–978 cm), followed by a steeper rise to 19% by c. 3820 BC (976 cm). Initially, Poaceae: wild grass group pollen contributes largely to this increase (cf. Stolze et al., 2013b). The P. lanceolata-type pollen curve begins to rise at 3850 BC (980 cm). The rise in PPI is accompanied by a decline in arboreal pollen from 95% to 88% between c. 3970 and 3850 BC (988–978 cm), falling to 76% by c. 3820 BC (976 cm).

Zone 2 = c. 3790–3610 BC (973.5–956.5 cm)

PPIs, dominated by Poaceae: wild grass group and P. lanceolata-type pollen, attain their highest abundance of 25% within the stratigraphy c. 3730–3690 BC (968–964 cm).

Zone 3 = c. 3610–3140 BC (956.5–912.5 cm)

Levels of macroscopic charcoal and PPI decrease from 3 to 0.5 particles cm⁻² yr⁻¹ and from 16% to 4%, respectively. Despite this trend, PPI, P. lanceolata-type and macroscopic charcoal show peaks at c. 3600–3560 BC (955–951 cm) and c. 3390–3300 BC (935–927 cm).

Sub-zone 4a = c. 3140–2720 BC (912.5–867.5 cm)

Macroscopic charcoal levels are very low at 0.1–1.4 particles cm⁻²yr⁻¹. PPI percentages are also low at c. 2%, with the exception of a slight peak of c. 3% between c. 2970 and 2940 BC (896–893 cm). P. lanceolata-type appears in trace amounts between c. 2960 and 2910 BC (895–890 cm). Arboreal pollen is present between 90–95%.

Sub-zone 4b = c. 2720–2480 BC (867.5–839.5 cm)

Values of macroscopic charcoal are higher than in the previous zone. Levels of PPI increase to c. 4%, and peak at 6% at c. 2550 BC (847 cm). Poaceae: wild grass group and P. lanceolata-type pollen are the main contributors to PPI.

RDA

RDA produced eigenvalues for Axis 1 of λ = 0.093 and for Axis 2 of λ = 0.040. Analysis identified that the six chosen environmental variables (PPI, P. lanceolata-type, macroscopic charcoal, δ¹⁵N, δ¹³C and C:N) have statistically significant (p < 0.01) relationships with the chironomid composition (Figure 5; Table 1).

Table 1.

Partial redundancy analyses (RDAs) for environmental variables by themselves and with the effects of other environmental variables partialled out.

Variable	Covariables	λ₁	λ₁/λ₂	p	% variance	PCA Axis 1 as predictor (r²)
PPI	None	0.084	1.292	0.002	8.4	0.689*
PPI	Charcoal, δ¹⁵N, δ¹³C, C:N	0.021	0.447	0.002	2.5	0.689*
Plantago lanceolata-type	None	0.061	0.801	0.002	6.1	0.444*
Plantago lanceolata-type	Charcoal, δ¹⁵N, δ¹³C, C:N	0.014	0.298	0.002	1.7	0.444*
δ¹⁵N	None	0.041	0.373	0.002	4.1	0.054*
δ¹⁵N	Charcoal, Plantago lanceolata-type, PPI, δ¹³C, C:N	0.022	0.468	0.002	2.6	0.054*
δ¹³C	None	0.043	0.518	0.002	4.3	0.312*
δ¹³C	Charcoal, Plantago lanceolata-type, PPI, δ¹⁵N, C:N	0.013	0.277	0.002	1.5	0.312*
C:N	None	0.060	0.870	0.002	6.0	0.470*
C:N	Charcoal, Plantago lanceolata-type, PPI, δ¹⁵N, δ¹³C	0.015	0.319	0.002	1.8	0.470*
Macroscopic charcoal	None	0.062	0.775	0.002	6.2	0.434*
Macroscopic charcoal	Plantago lanceolata-type, PPI, δ¹⁵N, δ¹³C, C:N	0.011	0.234	0.002	1.3	0.434*

PPI: pastoral pollen indicator; PCA: principal component analysis.

This table also includes for each variable a linear regression correlation co-efficient with chironomid PCA Axis 1.

p value of <0.01.

Partial RDAs show that PPI exhibited the strongest correlation with the chironomid community, explaining 8.4% of the variance on its own and 2.5% with other variables partialled out (Table 1). A linear regression further highlights a strong relationship between PCA Axis 1 and the PPI data (r² = 0.689, p < 0.01; Table 1). Macroscopic charcoal (6.2% variance), P. lanceolata-type (6.1% variance) and C:N (6.0% variance) also exhibited strong relationships with the chironomid assemblage data (Table 1).

The RDA bi-plot highlights that PPI and P. lanceolata-type are likely the main variables behind the chironomid community change in Zone 2 (Figure 5). C:N and δ¹³C show a relationship with the chironomid assemblage of Zone 4, with higher values in the environmental variables corresponding with Zone 4 samples in the bi-plot. RDA analysis also shows that the chironomid community in Zone 1 correspond with the low δ¹⁵N values.

Discussion

Based on the chironomid record, four phases of lake productivity and land-use change at Templevanny Lough during the Irish Neolithic were discerned. Comparison with pollen and macroscopic charcoal as proxies of terrestrial land-use change provides evidence that anthropogenic activity within the lake catchment had a measurable impact on the lake system through nutrient loading and subsequent lake eutrophication during the Neolithic.

Zone 1 – Early anthropogenic disturbance and onset of Neolithic farming

High levels of macroscopic charcoal recorded from c. 4110–4000 BC, indicate local natural or anthropogenic fire activity (Whitlock and Larsen, 2001), pre-dating widespread forest clearance in the region (cf. O’Connell et al., 2014; Stolze et al., 2013b). Microscopic and macroscopic charcoal were also present around this time at Cooney Lough (O’Connell et al., 2014) and Lough Dargan (Taylor et al., 2013), both located within a c. 20 km radius of the study site. The timing of this peak in macroscopic charcoal also coincides with the construction dates for the early causewayed enclosure at Magheraboy, County Sligo (Danaher, 2007). Together with the presence of Pteridium aquilinum spores (Stolze et al., 2013b) and occasional P. lanceolata-type pollen, the record points to human-related disturbances. Chironomids do not exhibit a noticeable response to this early activity, as it was likely not at a scale that would influence lake trophic status. However, high C:N ratios and increasing δ¹³C values infer greater terrestrial inputs during this time.

An initial decrease in the forest cover occurs between c. 3970 and 3850 BC and coincides with the mid-Holocene elm decline (Stolze et al., 2013b). The gradual increase in δ¹⁵N and NCF and decrease in C:N suggest nutrient influx and enhanced productivity of Templevanny Lough as a result of soil destabilization due to loss of canopy (cf. Cohen, 2003). The chironomid community shows a subdued response to this vegetational change. Cladopelma, which is not particularly tolerant of high nutrient conditions (Brooks et al., 2007; Moller Pillot, 2009), disappears by c. 3930 BC, only to return sporadically in low numbers for the remainder of the Neolithic period.

Increased fire activity at c. 3860 BC, as evident in the macroscopic charcoal record, precedes the accelerated deforestation at c. 3850 BC. The pronounced increase in PPI, in particular P. lanceolata-type pollen, from c. 3850–3820 BC indicates the onset of Neolithic pastoral farming activity in the catchment area of Templevanny Lough. The chironomid community composition shows a markedly stronger response to pastoral farming activity than to the previous loss in forest cover linked to the elm decline. However, the chironomids seem to experience a lagged response to the anthropogenic activity. The lagged effect occurs throughout the sampling range by 1–2 samples (~10–20 years). For example, the resulting impact of an increase in PPI from 3850–3820 BC is seen two samples later by an increase in Tanytarsus mendax-type from 5% to 17% and T. lugens-type from 0% to 6% from c. 3810–3800 BC. Tanytarsus mendax-type, a warm stenotherm has previously been associated with pastoral agriculture in western Ireland (Potito et al., 2014; Taylor et al., 2013). Tanytarsus lugens-type, however, is usually associated with oligotrophic lakes (Brooks et al., 2007; Saether, 1979) but appears to be responding to the increased nutrient input at Templevanny Lough. This taxon also shows an association with warm, productive lakes in western Ireland surface sediments (Potito et al., 2014). Wilson and Gajewski (2004) noted that T. lugens-type was common in shallow, productive lakes in Northern British Columbia and suggest the possibility that T. lugens-type has a more widespread ecological distribution than previously thought. Cool summer conditions in Ireland (~16°C July temperature average; Met Éireann, 2016) may result in T. lugens-type exhibiting a similar ecological response to nutrient enrichment, as T. lugens-type in colder regions. However, this taxon has been associated with cold late glacial conditions in a small lake in County Donegal, Ireland (Watson et al., 2010), suggesting that the full ecological distribution of T. lugens-type in Ireland may merit further investigation. Lag effects between land-use change and lake eutrophication could be due to within-lake nutrient cycling or delayed nutrient inwash (Genkai-Kato and Carpenter, 2005). Response times can be highly variable and are affected by catchment morphology and soil type, lake morphometry, temperature and dominance of macrophytes, among other factors (Genkai-Kato and Carpenter, 2005). In the short term, accumulation of nitrogen and phosphorus in the soils from manure is an important driver of nutrient input. Nutrient-rich soils are washed into lakes, where some of the phosphorus dissolves and stimulates growth of phytoplankton and aquatic plants (Carpenter, 2005). Within-lake recycling of nutrients from sediments and consumers can then act to enhance eutrophication through time (Carpenter, 2005; Carpenter et al., 1998). Templevanny Lough geochemistry does not show a lag with land-use change, so within-lake nutrient cycling, rather than delayed nutrient inwash, is likely responsible for the lagged chironomid response.

Chironomid larvae do not exploit nutrients directly but instead indirectly respond to changes in the availability of food (mainly diatoms, organic detritus and macro-invertebrates) and benthic oxygen conditions (Brooks et al., 2001). Chironomids can exhibit a gradual or threshold response to nutrient inputs, and response time to cultural eutrophication can often lag land-use change (Langdon et al., 2006). Lotter and Birks (2003) note a lag of several centuries in the chironomid community in response to changes within an aquatic ecosystem of a small lake, Sägistalsee in the Swiss Alps. A lagged chironomid response was not visible in the Lough Dargan record, presumably as a result of the low sampling resolution of 35 to 270 years (mean = 70 years; Taylor et al., 2013). Interestingly, lagging Templevanny Lough PPI and P. lanceolata-type pollen by two samples (~20 years) results in marginally more powerful partial RDAs (8.5% explained variance for PPI; 7.5% explained variance for P. lanceolata-type) and stronger relationships with chironomid PCA Axis 1 (r² = 0.713 for PPI; r² = 0.586 for P. lanceolata-type) than the non-lagged models used in this paper.

Zone 2 – Early Neolithic farming

The most intensive period of Neolithic farming activity at Templevanny Lough coincides with high levels of archaeological activity found in Ireland between c. 3750 and 3500 BC, including the construction of rectangular houses between 3715 and 3625 BC (Whitehouse et al., 2014). The causewayed enclosure at Magheraboy and the Carrowmore passage tomb complex provide evidence of human activity in the Sligo area during the early Neolithic (Bergh, 1995; Danaher, 2007; Hensey and Bergh, 2013). Neolithic farming at Templevanny Lough precedes dates from Carrowkeel-Keshcorran cairns by several centuries, although the Carrowkeel-Keshcorran dates may be compromised by insecure stratigraphic contexts (Hensey, 2015).

High levels of PPI and P. lanceolata-type indicate sustained open pasture between c. 3730 and 3690 BC (Figure 4). High δ¹⁵N values (4.1–4.6 ‰), together with the decrease in δ¹³C and low C:N suggest considerable nutrient enrichment in the lake system. High δ¹⁵N values in concert with decreasing levels of TN and δ¹³C are often indicative of pastoral farming around a lakeside and the inwash of animal waste into a lake (Botrel et al., 2014; Taylor et al., 2013; Woodward et al., 2012). A similar geochemical pattern of increased δ¹⁵N, low δ¹³C concomitant with high farming activity was recorded at Lough Dargan, supports the assumption of animal husbandry with substantial levels of animal waste reaching the lake during the Neolithic (Taylor et al., 2013). Furthermore, δ¹³C in modern lake sediment samples from agricultural catchments in western Ireland were more negative in value than δ¹³C in samples from non-impacted sites (Woodward et al., 2012). Averaged δ¹⁵N (4.4‰), δ¹³C (−31.8‰) and C:N (12.4) values place the early Neolithic at Templevanny Lough among lakes with >80% agricultural cover (mostly pastoral) within a 50-lake training set of modern lakes in western Ireland (Woodward et al., 2012).

The chironomid community in Zone 2 shows eutrophic taxa such as Chironomus anthracinus-type, Tanytarsus undifferentiated and Tanytarsus lugens-type dominating the stratigraphy (Figure 2). T. lugens-type is associated with modern agricultural activity in a western Ireland training set (Potito et al., 2014). T. lugens-type appears to have taken advantage of the new ecological opportunities following the onset of early Neolithic farming and rapidly dominates the chironomid stratigraphy. A decrease in T. lugens-type towards the end to this phase suggests that T. lugens-type may have been at a competitive disadvantage, eventually becoming replaced by other eutrophic taxa, mainly Chironomus anthracinus-type, an opportunistic eutrophic taxon linked to agriculture in western Ireland (Potito et al., 2014). The apparent decrease in Corynoneura lobata-type and Corynoneura type A appears to follow well with the decline in total stream taxa during Zone 2. Corynoneura as a genus can be found in a variety of different water bodies such as lakes, pools, streams, springs and marshes, with Corynoneura lobata-type in particular, being an inhabitant of running water (Moller Pillot, 2013).

Zone 3 – Decline in farming activity

Farming activity in the Templevanny Lough catchment wanes during the middle Neolithic, with periods of small-scale activity. Lower δ¹⁵N values in Zone 3 correspond with reduced farming activity as reflected in the PPI (Figure 4). Increasing C:N shows decreased lake productivity through time. This is in keeping with a lull in human activity, with settlement evidence appearing more ephemeral in Ireland between c. 3400 and 3000 BC (Whitehouse et al., 2014). Although farming was declining at Templevanny Lough, human impact on the lake system persisted, with Chironomus anthracinus-type and Tanytarsus undifferentiated remaining dominant during this time. This is expected, as lakes are known to take decades to centuries to recover from cultural eutrophication (Carpenter, 2005).

The PPI, P. lanceolata-type pollen, δ¹⁵N and macroscopic charcoal data indicate two main intervals of human activity in the area during the middle Neolithic at c. 3600–3560 BC and c. 3390–3300 BC. Small fluctuations in the abundances of Tanytarsus undifferentiated and Chironomus anthracinus-type suggest increased nutrient input as a result of this small-scale farming activity. This evidence shows that although farming activity is reduced, humans remain an active part of the landscape during this time.

Based on the proxy data, Templevanny Lough remains productive during the middle Neolithic likely due to sustained farming and/or prolonged lake recovery from earlier farming activity. The main chironomid taxa present during this time, including Chironomus anthracinus-type, Micropsectra insignilobus-type, Tanytarsus mendax-type, Tanytarsus undifferentiated, Paratanytarsus, Corynoneura undifferentiated, Corynoneura type A, Limnophyes/Paralimnophyes and Phaenopsectra flavipes-type, indicate a macrophyte-rich, eutrophic lake. Floating leaf macrophytes occurred in the lake throughout this period (Stolze et al., 2013b).

Micropsectra insignilobus-type appears anomalously in this stratigraphy as it is a cold stenotherm associated with oligotrophic lakes (Brooks et al., 2007). However, M. insignilobus-type sub-fossils are indistinguishable from M. atrofasciata-type (Brooks et al., 2007), which occurs in eutrophic rivers and increases below sewage discharges (Brooks et al., 2007; Wilson, 1989). Ruiz et al. (2006) also noted increases in M. insignilobus-type with nutrient enrichment in an investigation of a palaeochannel in the East Midlands, UK, and altered the identification of the M. insignilobus-type to M. atrofasciata-type based on its ecology.

Sub-zone 4a – Low farming activity during the late Neolithic

The palynological data and δ¹⁵N indicate low levels of farming activity and woodland recovery during most of the late Neolithic, with the exception of an increase in activity around c. 2980–2910 BC (Figure 4). A significant decrease in the abundance of the eutrophic taxon Chironomus anthracinus-type clearly reflects this downturn. Averaged δ¹⁵N (3.7‰), δ¹³C (−31.4‰) and C:N (14.2) values place this sub-zone, excluding the increase in values between c. 2980 and 2910 BC, among lakes with 20–80% agricultural cover within the 50-lake training set of modern lakes in western Ireland (Woodward et al., 2012). The chironomid community is largely dominated by taxa associated with macrophytes and/or terrestrial/semi-terrestrial habitat, including Microtendipes pedellus-type, Limnophyes/Paralimnophyes, Corynoneura undifferentiated, Corynoneura type A and Symposiocladius (cf. Stolze et al., 2013b).

The δ¹⁵N, P. lanceolata-type pollen and PPI data indicate a short-lived period of small-scale pastoral farming for 70 years between c. 2980 and 2910 BC, peaking at c. 2940 BC. Despite the ephemerality of this interval, the impact on the lake system is evident particularly in the geochemical data with fluctuations in δ¹⁵N, δ¹³C, C:N and LOI₅₅₀. C:N ratios infer increased lake productivity during this time, δ¹⁵N is elevated and LOI₅₅₀ decreases by 7%, possibly indicating inwash of allochthonous material (cf. Stolze et al., 2013b). The chironomid response to this period of small-scale farming activity is more subtle, with slight increases in Chironomus anthracinus-type, Tanytarsus undifferentiated and Micropsectra insignilobus-type during this time. This period of farming coincides with an interval of possible activity at the Carrowkeel-Keshcorran complex from approximately c. 3200–2900 BC, as evidenced by human bone remains and dated charcoal (Hensey et al., 2013). This period (3200–2900 BC) also represents a critical time in the passage tomb construction and use in the eastern part of Ireland (Hensey et al., 2013).

Sub-zone 4b – Return of farming at the end of the Neolithic period

Increases in δ¹⁵N, PPI and macroscopic charcoal signify a return of small-scale farming activity around Templevanny Lough. Sub-zone 4b marks the possible build up to the early Bronze Age farming in the Carrowkeel-Keshcorran area (cf. Hensey et al., 2013). The C:N ratio decreases at Templevanny Lough, suggesting an increase in autochthonous productivity from c. 2600 BC. A decrease in LOI₅₅₀ and increase in NCF values suggest influx of allochthonous material, possibly leading to nutrient enrichment of the lake system.

The δ¹³C values fluctuate substantially during the later Neolithic. The elevated values between c. 2660 and 2610 BC could be indicative of a possible inwash event, changes in lake level or an increase in macrophyte productivity. Increased C:N ratios during this time provide evidence of terrestrial material being deposited into the lake, which is supported by high NCF. δ¹⁵N, TN and the presence of P. lanceolata-type pollen and macroscopic charcoal suggest that this increase in δ¹³C is not directly land-use related. Chironomid taxa associated with terrestrial material, including Limnophyes/Paralimnophyes, Smittia and Symposiocladius, are present during this time. Furthermore, the increase in total stream taxa and δ¹³C values likely indicates increased inflow from the surrounding streams.

The chironomid community indicates a eutrophic, macrophyte-rich lake with the presence of Chironomus anthracinus-type, Chironomus plumosus-type, Tanytarsus undifferentiated, Paratanytarsus, Endochironomus albipennis-type, Glyptotendipes pallens-type and Cricotopus intersectus-type in various lagged responses to the farming activity. The emergence of Chironomus plumosus-type and an increase in δ¹⁵N from c. 2530 BC coincide in an increase in PPI at c. 2550 BC, signifying substantial nutrient input to the lake system. Chironomus plumosus-type is a eutrophic taxon that has been used as an indicator of hypertrophic conditions in Danish lakes (Brodersen and Lindegaard, 1999).

Palaeolimnological impacts of Neolithic farming

The timing and magnitude of changes in the chironomid stratigraphy show that land-use, potentially influenced by climate change (Stolze et al., 2013b), is the main control on the chironomid community at Templevanny Lough during the Neolithic. Although chironomids have been mostly used as a palaeotemperature indicator in the past, as temperature tends to be the main driver behind chironomid community compositional change (Brooks and Birks, 2001), more recent studies have shown that even moderate human impacts are sufficient enough to over-ride the climate signal in the chironomid record (Brodersen and Quinlan, 2006; McKeown and Potito, 2016), which seems to be the case in Templevanny Lough.

RDA and partial RDAs show a strong statistical relationship between PPI and P. lanceolata-type pollen with the changes in the chironomid composition, with the relationship especially apparent for Zone 2 (Figure 5). The strong correlation between PCA Axis 1 and PPI further highlights that pastoral land-use was a dominant influence on chironomid community compositional change throughout the record. Additionally, the chironomid community as reflected in the PCA Axis and the main chironomid taxa (e.g. T. lugens-type) show the same structural coherence as the PPI data in a lagged response (Figure 4). The chironomid community composition thus exhibited a predictable and proportional lagged response of c. 10–20 years after the farming activity occurred. If the chironomid community was directly driven by climatic forcing, the composition would change before or at the same time as any increase or decrease in human activity occurred in the catchment area because farming around Templevanny Lough during the Irish Neolithic was shown to follow climatic variation closely (Stolze et al., 2013b).

Organic residue analysis from pottery shows cattle dairying to be especially prominent in this area during the Neolithic (cf. Smyth and Evershed, 2015), so it is likely that lake trophic status is tied to pastoral activity of cows during this time. As the palaeolimnological proxies show a scaled response, rather than a simple threshold response, to Neolithic land-use change (Langdon et al., 2006), they can be used as reliable proxies for prehistoric land-use intensity. However, the chironomid response was systematically lagged throughout the record, likely due to within-lake nutrient dynamics (cf. Carpenter, 2005). Therefore, palynological evidence should be used to represent and date the onset and timing of Neolithic farming, whereas palaeolimnological evidence can show the intensity and environmental impacts of these activities.

Early Neolithic farming resulted in environmental impacts and freshwater eutrophication that would put Templevanny Lough on a par with lakes from modern pastoral catchments in the region (Woodward et al., 2012). The considerable impacts could be due to scale of activity (i.e. sizeable cattle herds) or location of grazing activity (i.e. adjacent to the lakeside). Either way, evidence from Templevanny Lough and Lough Dargan (Taylor et al., 2013), both in fertile lowland areas, shows that prehistoric pastoral farming practices regularly result in lake eutrophication across the region.

Conclusion

This paper provides the first reconstruction of a lake’s trophic state in response to anthropogenic activity at a decadal resolution of the Irish Neolithic. The large volume of data enabled a detailed reconstruction of the chain of events associated with the onset of farming activity in the catchment area as well as providing information on the timing, intensity and environmental impact of anthropogenic activity. The chironomid community responded to farming activity in a lagged response of c. 10–20 years throughout the study period, and this is the first chironomid study to show such a systematic lagged response throughout a prehistoric record. This timeline of events can now be used to inform and enhance the archaeological database for the Carrowkeel-Keshcorran megalithic complex, including grazing location, timing and magnitude of land-use change within the Templevanny Lough catchment and environmental impacts of pastoral farming in the region.

Footnotes

Acknowledgements

We wish to thank W. Dörfler, I. Feeser, O. Nelle, M. O’Connell and P. O’Rafferty for their support during sediment coring at Templevanny Lough.

Funding

This work received the funding from the Irish Research Council (IRCSET) and the Hardiman Research Scholarship, and National University of Ireland Galway financed the stable isotope analysis. Part of this research was supported by a grant from the German Research Foundation (NE 970/2-1, 2-2).

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Response of chironomids to Neolithic land-use change in north-west Ireland

Abstract

Keywords

Introduction

Study site

Methodology

Coring and sub-sampling

Radiocarbon dating

Chironomid analysis

Geochemical analyses (δ13C, δ15N and C:N)

Macroscopic charcoal analysis

Loss-on-ignition and pollen analyses

Statistical analyses

Results

Chironomid stratigraphy and zonation

Zone 1 = c. 4120–3790 BC (999.5–973.5 cm)

Zone 2 = c. 3790–3610 BC (973.5–956.5 cm)

Zone 3 = c. 3610–3140 BC (956.5–912.5 cm)

Zone 4 = c. 3140–2480 BC (912.5–839.5 cm)

Sub-zone 4a = c. 3140–2720 BC (912.5–867.5 cm)

Sub-zone 4b = c. 2720–2480 BC (867.5–839.5 cm)

Stable carbon and nitrogen isotopes and LOI

Zone 1 = c. 4120–3790 BC (999.5–973.5 cm)

Zone 2 = c. 3790–3610 BC (973.5–956.5 cm)

Zone 3 = c. 3610–3140 BC (956.5–912.5 cm)

Sub-zone 4a = c. 3140–2720 BC (912.5–867.5 cm)

Sub-zone 4b = c. 2720–2480 BC (867.5–839.5 cm)

Pollen and macroscopic charcoal

Zone 1 = c. 4120–3790 BC (999.5–973.5 cm)

Zone 2 = c. 3790–3610 BC (973.5–956.5 cm)

Zone 3 = c. 3610–3140 BC (956.5–912.5 cm)

Sub-zone 4a = c. 3140–2720 BC (912.5–867.5 cm)

Sub-zone 4b = c. 2720–2480 BC (867.5–839.5 cm)

RDA

Discussion

Zone 1 – Early anthropogenic disturbance and onset of Neolithic farming

Zone 2 – Early Neolithic farming

Zone 3 – Decline in farming activity

Sub-zone 4a – Low farming activity during the late Neolithic

Sub-zone 4b – Return of farming at the end of the Neolithic period

Palaeolimnological impacts of Neolithic farming

Conclusion

Footnotes

Acknowledgements

Funding

References

Geochemical analyses (δ¹³C, δ¹⁵N and C:N)