Palæoecological investigation of
an early-Mediæval site at
Leiderdorp
J
IPPEK
REUNINGBSc project Bèta-gamma, major Biology
St. No. 10011390 & 6221769
July 2014
Supervisor: dr. B
AS VANG
EELInstitute for Biodiversity and Ecosystem Dynamics (
IBED)
Research group Palaeoecology and Landscape Ecology
Abstract
A large archaeological excavation was carried out in 2013, near the village of Leiderdorp, the Netherlands. The site revealed habitation traces dating from the early Middle Ages (500-850 CE).
Historical sources from that time are scarce, and historians mostly turn to archaeology to provide answers to their questions about life during this period. In this context, the field of archaeobotany can be of much use to an archaeological investigation by adding interdisciplinary knowledge to the excavation. The present study aims to provide the archaeologists with an environmental reconstruction of the site, using both microfossils and macrofossils from samples taken at the excavation. Based on the pollen records, three distinct phases in the vegetational history have been identified. In the first phase, dated c. 200–750 CE, the results of this study show an open parkland landscape along a river bank. Throughout this phase, there is evidence of some human activity at or near the site, most likely being of agricultural nature. In the second phase, dating from 750-850 CE, the parkland landscape opens up, most likely due to logging activities. The recorded plant species indicate a very strong human impact on the vegetation. Several types of encountered spores of coprophilous fungi indicate the presence of grazing animals. The third phase, of which the precise dating is unknown, represents the return of the parkland landscape after 850 CE. Although there are still taxa present that can be interpreted as being indicative of human impact, there is strong evidence that suggests the abandonment of the sampled site. Several types of ecological indicators recorded in both parkland landscape phases suggest there was a marine influence present at the site. This could be explained by storm surges flooding the area with salt water. This reconstruction of marine flooding could potentially be useful for the archaeological interpretation of the site, as flooding may have been the cause of the abandonment of the site. However, the full extent of the influence of marine flooding is inconclusive and directions for further research into this phenomenon are presented.
Archaeological introduction
It was around the year 782, that an English scholar named Alcuin of York made a perilous boat-journey from his native England to Rome. He was ordered by his king, Ælfwald I of Northumbria, to visit the pope to strengthen the position of York as archbishopric. Alcuin’s travels took him by boat along the river Rhine through what is now the Netherlands, then part of the vast Carolingian empire. Along the way Alcuin encountered some of the -in his eyes- rather unpleasant locals. In a famous poem he complains, in Latin, about how in the barbaric Frisian lands along the Rhine there is no olive oil or red wine available. He describes ‘that greedy prior’ Haddo of Utrecht who refuses to give him more than one bowl of porridge with honey. Furthermore, he strongly advises the reader not to stay in the trading town of Dorestad. There, Hrobrecht (‘the sulky merchant’) allegedly refuses to give one shelter for the night and the people do definitely not appreciate poetry there. It is a good thing for Alcuin that later on in his voyage down the Rhine he meets Charlemagne, who invites him to become an important advisor at the Carolingian court in Aachen (for more of Alcuin of York’s travels, see Smit, 1998).
Although Alcuin’s characterisation of the inhabitants of the Rhine delta some 1200 years ago may seem like a caricature, relatively little is known about the daily lives of these people in the Carolingian era. The early Middle Ages, sometimes controversially named ‘the Dark Ages’, are regarded as an important period in the development of long-distance trade in Europe and are considered to be crucial in the onset of urbanisation. Trade is seen as especially important in this part of the Netherlands, specifically in the lower Rhine delta. The Carolingian trade networks spanned extremely long distances, encompassing the British Isles, Scandinavia, southern Europe and -through the Baltic regions, present day western Russia and Constantinople- even reached the Abbasid Caliphate in the Middle East. Urbanised trading centres began to emerge along important trading routes, mainly rivers. The most famous Dutch example is Dorestad (Wijk bij Duurstede) but also Hamwic in England and Birka in Sweden are notable (see Wickham, 1998).
After the collapse of the Roman Empire in Northern Europe, these ‘trading emporia’ began to grow significantly in size and importance from the sixth century on. Initially, these trading centres were located on coastlines and sheltered places where boats could easily be beached, but they also began to appear along rivers (Hodges, 1982). The Rhine delta, one of the major river deltas in Europe, had been in use as an important transport route since its function as the northern frontier of the Roman Empire. Its central location and navigability proved to be vital in the early mediaeval trading network (Hodges, 1982). The part of the Rhine in the Low Countries was dominated by the trading town of Dorestad also mentioned in Alcuin’s account, but more of these so-called trading emporia
were developing all over the river delta, but archaeological information about these centres is scarce. Only Dorestad has been thoroughly excavated (van Es, 1978), and further detailed excavations have, hitherto, not been conducted.
Leiderdorp site description
A large-scale excavation was carried out in the summer of 2013 by archaeologists of the University of Amsterdam (Diachron UvA BV) near the town of Leiderdorp, Zuid-Holland, the Netherlands (see figure 2). This area is situated in the Rhine delta, with the current position of the ‘Oude Rijn’ branch situated approximately 300 m to the southwest of the excavated site. Over the last one-thousand years, the Oude Rijn discharge decreased dramatically due to changes in the delta (Berendsen & Stouthamer 2000, 2001). Hence, in the early Middle Ages, the Oude Rijn was a much larger river than it is today. The site in Leiderdorp is thought to have a very high archaeological potential, especially regarding the relative obscurity of the early mediaeval period in the Netherlands. The excavation results are at the time of writing still being analysed, and the present study aims to provide the archaeologists with an environmental reconstruction of the excavated site.
As the excavation results are still under investigation, reference can only be made to Koot et al. (2008), who presented the excavation plan as submitted to the Dutch Heritage Service (Rijksdienst voor het Cultureel Erfgoed, RCE)
Crevasse splays were formed in the lower part of the delta, on a dynamic floodplain. This resulted in a system with tributaries leading away from the main river. In geological terms, the excavated site revealed both banks of an east-west orientated tributary channel. The earliest phase of the channel, which was uncovered on the north bank, is believed to date from the late Roman period (c. 200 - 550 CE). The river moved north during the following centuries, the Merovingian era (550-750 CE), depositing sediment on the south bank. This process of sedimentation resulted in the river slowly filling in, a process that continued into the Carolingian era (750-900 CE) and into the post-Carolingian period.
The archaeology of the site revealed layers of deposited archaeological material dating from the Merovingian and Carolingian eras, along with very well preserved remains of wooden structures that probably functioned as timbering. This type of wooden structure was probably used to slow down the process of channel migration. The Merovingian layers are considerably smaller than the Carolingian remnants. Where the Merovingian remains are present in a thin layer of c. 20 cm, the Carolingian remains form a rich, 30 to 50 cm thick layer . Both layers consist almost entirely of waste: offal, human bones but also objects that were used on a daily basis such as bone or antler combs and different types of pottery. Some finds suggest that the site might have been used as a ritual deposition site. Metal objects such as axes, scissors, remains of two swords and even a set of needles, beads and other objects relating to sewing were among the many finds. Extensive remains of a settlement were, unfortunately, not found during the excavation. Only some postholes were found, probably belonging to a type of small building for storing cereals (‘spieker’), and a few wells and waste pits. The extensive range of finds indicates high human activity along the riverbank, but it remains a mystery as to what the use of this site was through time. M.F.P. Dijkstra (Amsterdam, pers.comm., 2014) suggested that the excavated area could be just outside the early mediaeval settlement, or that it was an area that was used seasonally. The preliminary results suggest that after the end of the Carolingian period (c. 900 CE) the site fell out of use, as no post-Carolingian artefacts were discovered.
Materials and Methods
Sediments were sampled during the excavation in eight 50x10x20cm metal boxes. These boxes were pushed in a profile of trench no. 7, which cuts through both river banks (see figure 1). Twenty samples for both micro- and macrofossil analysis were selected from these eight sampling boxes. The selection of sub-samples was based on stratigraphical evidence and the related chronological sequence, linked to the local archaeological record and dating of artefacts. Another criterium for the selection was the presumed state of preservation of the material. Fifteen of these twenty samples (nos. 1-15, see table 1) form a succession through time while the remaining five were taken from an archaeologically significant feature on the south bank of the river. This highly organic layer cuts into the main Carolingian waste-layer and these two features are thought to have a chronological connection.
Table 1: sample numbers and corresponding archaeological find numbers.
Micro- and macrofossils
The microfossil slides were prepared according to the standard procedures as described by Faegri and Iversen (1989). The samples were analysed at 400x magnification and - when necessary - at a 1000x magnification. The pollen were identified using the keys by Moore et al. (1991) and Beug (2006). Non-pollen palynomorphs (NPPs) that were encountered, such as fungal spores, were identified using van Geel et al. (2003) and van Geel and Aptroot (2006).
The macrofossil samples (volume ca. 20 ml) were soaked before analysis in a 5% KOH solution and shortly warmed, as described by Mauquoy & van Geel (2007). The resulting suspension was then
sieved over a 150 μm mesh sieve. Using a stereo binocular microscope, all samples were screened for
botanical and zoological remains such as seeds, fruits, insect remains etc. These were stored in glycerine, awaiting further identification. Fruits and seeds were identified using the atlas of Cappers et al. (2006) and the reference collection of the Amsterdams Archeologisch Centrum (AAC) with help of drs. Anja Fischer of Diachron UvA BV. Juncus seeds were identified using the key by Körber-Grohne (1964). Taxa recorded during the macrofossil and macrofossil analysis were grouped based on their ecology and habitat preference, following Tamis et al. (2004). The microfossils were classified into seven groups: Trees and Shrubs; Human Impact Indicators and Economic plants; Other herbaceous taxa; Swamp and Aquatic taxa; Spore plants; Algae, Fungi and Types; and Zoological material. Microfossils were counted to a pollen sum of 300, and the pollen sum included the groups Trees and Shrubs; Human Impact Indicators and Economic plants; and Other
11 V1170 23-24 cm 12 V1170 45-46 cm 13 V1023 7-8 cm 14 V1023 17-18 cm 15 V1023 37-38 cm 16 V1127 1-2 cm 17 V1127 10-11 cm 18 V1127 29-30 cm 19 V1127 34-35 cm 20 V1127 39-40 cm
Sample No. Find no. & depth
1 V1159 12-13 cm 2 V1166 7-8 cm 3 V1159 43-44 cm 4 V1167 19-20 cm 5 V1168 22-23 cm 6 V1168 46-47 cm 7 V1169 5-6 cm 8 V1169 13-14 cm 9 V1169 39-40 cm 10 V1170 11-12 cm
herbaceous taxa. Six groups of macrofossils were identified: Crop weeds, Human impact indicators, Fen and Bog taxa, Halophytes (salt tolerant taxa) Other plant remains and Zoological material. The category of taxa that are indicative of human impact on the environment were based on Hellman et al. (2009), van der Linden et al. (2008) and Poska et al. (2004).
Dating of the material
All samples originate from an archaeological context and as no direct dating methods were applied, only approximate archaeological dating was possible. The chronological sequence of samples ranges from the late Roman or early Merovingian eras (c. 200 - 550 CE) and ends in the post-Carolingian era. Samples 16-20 originate from the south bank and based on stratigraphic interpretation at the excavation, these are thought to date from the period between 750 and 850 CE.
Figure 1 (left): Map of the excavated area bordered by the blue lines, in purple the tributary channels. Figure 2 (right): Map of the west of the Netherlands, with in dark blue the Oude Rijn (Old Rhine)
463 10 0 96450 96450 0 0 4 6 9 0 5 3 6 9 46300 0 46300 0 4630 50 001 36 4 05 03 64 46 315 0 46 31 50 46320 0 46320 0 0 0 4 6 9 0 5 3 6 9 0 0 3 6 9 96300 legenda plangebied
sloten op de kadastrale kaart van 1832 reconstructie geul in de Karolingische tijd (ca. 800) grens opgravingsgebied
afkleiingsbaan
ovenkuil
WC-kuil
waterput Vroege Middeleeuwen
overige grote kuilen paardengraf
bijgebouw (schuurtjes) Vroege Middeleeuwen schuur Romeinse tijd
erfschutting (?)
greppel
waterput Romeinse tijd zuidgrens Romeinse geulinsnijding
‘onderhangende geul’ voor ca. 600 jongste, Karolingische beschoeiide geul aangroei oever in Merovingische periode richting noorden zijgeul Romeinse tijd? noordgrens Romeinse geulinsnijding? geul opgraving RMO 1950
Samsom veld DE MUNNIK HOOGM ADESE WEG ESSEN LAAN 1 2 10 7 8 11 12 13 14 15 16 21 22 1 2 3 4 5 6 31 32 33 23 24 25 26 27 28 29 30 9 Leiderdorp Location of profile in trench 7. Note how the profile in the trench wall cuts through the entire reconstructed tributary channel. See figure 3 for a drawing of the profile and the location of the samples in the stratigraphy.
Results and Interpretation
Three distinct local assemblage zones (A, B and C) have been identified from the archaeological context and the position of the botanical samples therein. These results are visualised in Diagrams 1 and 2. Samples 20-16 are discussed separately, as they are part of a separate, distinct archaeological feature. These five samples will be referred to as Feature-A and the results are visualised in Diagrams 3 and 4.
Zone A (samples 15-8)
Dating and description
Based on archaeological data this interval represents the Late Roman/Early Merovingian (2nd/3rd centuries or 6th century) period through the late Merovingian period (early 8th century). Sample 10 corresponds to the thin Merovingian waste deposition layer (see figure 3).
Microfossils
Zone A is mainly characterised by a mixed assemblage of pollen of trees and herbaceous taxa. Arboreal pollen fluctuate around 50%, indicating an open parkland landscape. Alnus trees dominate this landscape. Other taxa present include mainly Quercus, Corylus, and -to a lesser extent- Fraxinus,
Fagus and Betula, pointing to at least a regional presence of these taxa. The relatively high abundance
of Myrica indicates moist soils, which is conceivable on a river bank.
Throughout this interval, the acritarch microfossils Micrhystridium and Cymatiosphaera (Type HdV-115 and -116 respectively) are present. They are both associated with marine environments (Pals et al., 1980) and thus could indicate the nearby presence of salt water. The presence of these two Types coincides with the occurrence of two other microfossils indicative of a salt-water influence: Dinoflagellates and Foraminiferae (both marine zooplankton). Sample 10, as mentioned earlier, originates from an archaeologically distinct layer consisting of waste material dated to the late Merovingian period (550 - 750 CE). Human indicator species are not present in higher abundances in sample 10. Cerealia are common throughout zone A, indicating a regional human presence. Fungal spores of Chaetomium (Type HdV-7A) show a low peak. Chaetomium is usually considered to be a human indicator (see Buurman, 1995 & van Geel et al., 2003) and its presence in the context of a waste deposition layer is not unusual. High amounts of fungal spores of Epicoccum
purpurascens (Type HdV-1011, as described in van Geel, 2011) were also recorded in this layer. This
saprophytic fungus is known as a secondary invader of dead plant material (Domsch et al., 1980) and is also mentioned by Ellis (1971) to occur on animals, textiles and other materials associated with human activity.
Macrofossils
Remains of fruits and seeds and other small plant remains of various taxa were recorded in zone A. Several helophytic taxa are present throughout this interval. Alisma plantago-aquatica, Bolboschoenus
maritimus, Eleocharis palustris/uniglumis, Lythrum salicaria, Phragmites australis and Typha latifolia
were present in or near the local environment. These taxa are indicative of eutrophic conditions and their preferred habitat of shallow water or a river bank is in line with the reconstructed depositional environment. The appearance of Juncus subnodulosus, recorded in relatively high amounts, is also noticeable. J. subnodulosus has ecological preferences similar to Phragmites australis and is often associated with a terrestrialising habitat (Schaminée et al., 1995). Pieces of wood are encountered in the sample taken from the Merovingian waste deposition layer (sample 10) and it is plausible that these pieces have an anthropogenic context. There is no further direct evidence of specific human activity in the archaeologically defined Merovingian layer. Taxa indicating eutrophic conditions are present throughout all samples, indicating a human influence present throughout the zone. Two halophytic (salt-tolerant) taxa were recorded in zone A. Glaux maritima and Triglochin maritima occurred in the upper half of the interval. Compared with the occurrence of the marine indicators
encountered in the microfossil analysis, their presence coincides with the appearance of marine indicators Types 115 and 116, and the Dinoflagellates. Remains of freshwater organisms such as Ostracoda, freshwater sponges and Bryozoans (Plumatella type) indicate that there was sufficient (fresh) water present for these organisms to thrive.
Zone B (samples 5-7)
Dating and description
Based on the archaeological information this zone represents a thick waste-deposition layer, dating from the Carolingian habitation phase (750-850 CE).
Microfossils
The microfossil spectrum in this interval is dominated by a sudden drop of arboreal pollen and a dramatic increase of Poaceae, the latter fluctuating around 60% with a maximum abundance of 80% in sample 7. The dramatic decrease of tree pollen in the landscape can most likely be attributed to intensive logging of the (mainly Alnus) trees. This is reflected in the archaeological findings, as the wooden timbering found in this layer was mainly constructed of Alnus wood (M.F.P. Dijkstra, Diachron UvA bv, in prep.). It is not surprising in this zone, characterised by an obvious archaeological context, to see the microfossil spectrum dominated by taxa indicating human impact. Cerealia, although common throughout the entire sequence, show a strong increase during this specific interval. Many of the other recorded taxa can be interpreted as being indicative of human presence. Fabaceae, Ranunculaceae and Plantago major are present in high amounts. These taxa are mainly represented by apophytes growing on ruderal areas, meadows or other disturbed habitats where humans are most likely the cause of the disturbance (van der Linden et al., 2008; & Poska et al., 2004). Their presence, combined with the strong decrease in tree pollen, suggests a strong human impact on the regional and extra-local vegetation, and suggests nearby cultivated land (Dimbleby, 1967). Two fungal spore types were recorded in high amounts in this interval. Chaetomium, the cellulose decomposing fungus mentioned earlier in zone A, shows a high maximum in this zone. Although Chaetomium is known to occur on a variety of substrates (van Geel et al., 2003) its presence here adds to the evidence of human activity. Moreover, ascospores of the Sordaria type (Type HdV-55A), which are also a strong indicator for human influence, were recorded throughout the entire diagram but show a marked increase during zone B. Sordaria type spores represent fungi belonging to the Sordariales. These are mainly coprophilous fungi occurring on herbivore dung (Lundqvist, 1972; van Geel et al., 2003; Buurman et al., 1995).
Macrofossils
Taxa dominating the macrofossil spectrum are mostly indicative of eutrophic conditions. Eleocharis
palustris and E. uniglumis both occur on eutrophic banks (Schaminée et al., 1995). Glyceria fluitans,
was recorded in high quantities. This grass species is known to have been used as a food source. Łuczaj et al. (2012) mention its use in Poland from the twelfth century onwards, while Germany was mentioned as the origin for the use of G. fluitans as a food plant. Its use as an economic plant in the Low Countries during the early Middle Ages could hence be possible. Species such as Persicaria
maculosa, P. lapathifolia, and Polygonum aviculare were recorded in high amounts. These species are
indicative (just as the genera mentioned earlier in the microfossil interpretation) of ruderal land or other disturbed habitats that indicate high human activity. Several taxa that indicate high concentrations of nitrogen in the soil also show an increase: Atriplex spec. and Chenopodium album. High concentrations of nitrogen can be linked to the presence of animal manure, latrines, waste pits, etcetera. Urtica urens also specifically occurs in this interval. This nettle species is especially indicative of high nitrogen concentrations, and it is described in Schaminée et al. (1996) as exceptionally nitrophilous and occurring mainly on disturbed habitats. This in stark contrast to the notably absent Urtica dioica, that specifically favours non-disturbed habitats and can grow to dominate its direct environment if left alone (Schaminée et al., 1996, 1998). Conditions created as a consequence of human activity and the production of waste and manure, are the most likely habitat
for this vegetational assemblage. The pieces of wood and bone are also not unexpected as there is waste deposition. Fish remains were exclusively found in this zone, probably indicating human fish consumption. The only recorded seed of Common Flax, Linum usitatissimum, was found in this zone. Flax has been cultivated since the 5th century BCE and is associated with human activity from western Europe to Asia (Dimbleby, 1967). Lastly, there are some taxa that again suggest a salt-water influence. Schoenoplectrus tabernaemontani occurs in brackish habitats and definitely does not occur in a freshwater-only habitat (Schaminée et al., 1995). Triglochin maritima is also present again, but as with zone A, there is no conclusive evidence for a strong marine influence. However, S.
tabernaemontani is known to remain long after the marine influence it needs has stopped, and is of
little use on its own as indicator for the presence of salt water at the specific time it is recorded. Zone C (samples 1-4)
Dating and description
This interval represents the post-Carolingian (from 850 CE onwards) filling-in of the tributary channel system.
Microfossils
During this phase, we see a marked decrease in grass and cereal pollen. All arboreal taxa return to the same values of zone A after the deforestation in zone B. The open parkland landscape as encountered in zone A is mostly restored. Most of the human indicator species recorded in zone B show a decrease or disappear entirely. Notable is the sudden rise in fern spores. It seems plausible that these ferns took advantage of the changing vegetation patterns during the transition between the two phases. Fungal spores of the coprophilous Sordaria-type decrease dramatically, and as these spores are indicative of faeces this could suggest the abandonment of the site as a place to keep livestock. The acritarch microfossil Micrhystridium (Type HdV-115), which is associated with marine conditions, exhibits a large peak with values reaching 10%. This could suggest the return of marine conditions similar to those of zone A. Type HdV-128A, as described by Pals et al. (1980) and van Geel et al. (1989), suddenly occurs in high amounts (at its peak c. 30%) in the upper part of this zone. The precise origin of these microfossils is still unknown but it is suggested to be an algal spore (van Geel et al. 1989), occurring in eutrophic and mesotrophic open water.
Macrofossils
Organic material in the samples of zone C were badly preserved, and the samples contained only few identifiable macrofossil remains. The peak of Juncus articulatus-type seeds and a much smaller peak of J. effusus-type seeds is a notable feature in this diagram. The appearance of these two taxa indicates a sudden abundance of rushes. After abandonment of man-made fields, especially in moist environments, it is highly unpredictable which species will dominate the vegetation immediately after abandonment (Osbornová et al., 1990). In this changing state, some unexpected species can suddenly exhibit a very strong increase during a short period and decline quickly afterwards when other species become dominant and an ecological balance is restored. The high amounts of Juncus seeds could possibly be explained by this process. In the upper part of zone A, a similar pattern concerning Juncus seeds can be identified, and the peak of fern spores recorded in the microfossils could be explained in the same way. The sudden peaks in Juncus remains during transitional phases could represent a temporary change in the competition between plant species during the opening up of the park landscape into the human influenced landscape, and back again to the park landscape. In this zone a peak of Bryozoa of the Plumatella-type was recorded. Francis (2001) reports that freshwater bryozoan activity is positively linked to eutrophication. At the Leiderdorp site, it could be argued that the increased eutrophication in the human influenced zone is causally linked to the bryozoan activity afterwards, although more evidence is needed to support this hypothesis.
Feature-A (samples 20-16)
Dating and description
The five samples representing feature-A were taken from a distinct archaeological feature, denoted by find number V1127 in figure 3. The material is characterised by its peaty, highly organic content. Based on the stratigraphic interpretation at the site, it is considered to be of similar age as zone B, viz. 750-850 CE.
Microfossils
The spectra of feature-A are almost entirely dominated by Poaceae pollen, with values at or near 90%. The peak of Galium-type pollen is exceptional. With values of around 20% this is an unusually high abundance in this almost fully grass-dominated spectrum. Cerealia occur in the upper part of the feature, together with some arboreal pollen in low amounts, mainly Alnus and Corylus. These tree pollen grains are most likely from a regional rather than a local origin. Several crop weeds and taxa associated with meadows or pastures are found in low percentages throughout the feature.
Filipendula and Symphytum are both key taxa in the Convolvulo-Filipenduletea syntaxonomic class
(Schaminée et al., 1995) that occurs mainly on wet soils and river banks. In addition Lysimachia,
Lotus and Thalictrum were recorded, taxa that are mainly associated with meadows or wet grasslands
(Tamis et al., 2004). Samples described as ‘peaty clay’ with a similar high organic content and also an unusually high percentage of non-arboreal pollen were interpreted by van den Bos et al. (2014) as containing faecal matter. The appearance of old faeces would be very similar to peaty material, and have a comparable organic composition. The unusually high grass pollen percentages and the other meadow-taxa that were identified suggest that feature-A is indeed of faecal origin. Food selection of grazing animals would be the cause of a strong bias of the pollen content, as one would mostly expect species that occur in grazed areas. If feature-A indeed represents faecal material than the extremely high values of Poaceae and Galium type would not be a reflection of the local vegetation (comparable with pollen records of sediments), but would be strongly biased because of the food preference of the animal. Seasonality, mainly the flowering season, can also play a role in the unusual pollen composition of this feature. If this feature would indeed consist of faeces, the pollen might represent only a very short period of time, in contrast to stratigraphic sediments that accumulate over longer timespans.
Macrofossils
The macrofossil samples of feature-A were of a peculiar nature. All samples consisted of very dark peaty material that after treatment with KOH and sieving appeared to contain mainly small fragments of unidentifiable plant material, all c. 0.5 mm in size. Van den Bos et al. (2014) report similar botanical fragments in their dung samples, which adds to the probability that our feature-A has a similar origin. Only a few taxa were found as macrofossils, Eleocharis palustris/uniglumis (not identifiable to species level) has a habitat on river banks and its occurrence in this context is not unusual. Highly unusual in this feature are the high quantities of Juncus seeds recorded.
Furthermore, several of the encountered taxa are known to be poisonous to animals, Ranunculus
flammula and Lychnis flos-cuculi being the most prominent ones (Frohne et al., 2005). Although
found in small quantities among large amounts of unidentifiable plant material, finding remains of poisonous plants in faecal remains would seem unlikely. On the other hand, these seeds may not necessarily have passed through the animal digestive tract, as they may have come into contact with the faecal remains after deposition of the faeces. This scenario would explain the occurrence of the poisonous taxa in this feature. It is however impossible to determine whether this feature does indeed consist of animal dung based on micro- and macrofossil analysis.Further investigation (chemistry, compare van Geel et al., 2014) into that matter is needed.
Discussion
Archaeology versus palaeoecology
As mentioned earlier, the archaeological report about the excavation is still in preparation, but preliminary results (M.F.P. Dijkstra, Amsterdam, pers. comm.) indicated that there were two distinct anthropogenic layers visible in the stratigraphy, the larger of the two being identified in the present study as zone B. The present palaeoecological study shows that people were present - at least at a regional level - throughout the entire period represented by the sampled deposits. High values of Cerealia are common throughout the diagram, indicating agricultural activity at or near the site. Van Geel et al. (2003) note that a high percentage of Cerealia pollen is not necessarily caused by wind-transport of the grains but that they may also originate from threshing at or near the sampling site. This would mean that the values of Cerealia are over-represented, as the pollen would be artificially released and the values would not be representative of the pollen rain under normal circumstances. In zone A, while archaeologically there is a distinct layer that can be identified as anthropogenic, palaeoecologically, the corresponding sample (sample 10) does not show much evidence of intensified human impact. Rather, the entire pollen record can be interpreted as being heavily influenced by human activity.
Marine influence and preservation
The marine influence, as suggested for zones A and C, should be a lead for further investigation. Several taxa indicate marine influence at the site, but only few salt-tolerant species were found.
Triglochin maritima and Glaux maritima were recorded in phase A, but the lack of any more
halophytes could mean that the marine influence was limited. Taking the geology of the area into account, it is possible that the river has cut through deeper, older marine layers (P. Vos, Delft, pers. comm.) which would mean that the marine indicators are reworked and redeposited and hence their ecological indicator value would be void. The area of Leiderdorp was already situated quite far from the sea in the Middle Ages. It would not be impossible for storm surges to reach the area , but it is quite unlikely that this occurred. Further research should include a study of diatoms, molluscs and other zoological material that could give a conclusive answer to whether or not there was a marine influence at the mediaeval site near Leiderdorp. The microfossils in most samples were very well preserved, but the uppermost sample (number 1) was heavily corroded and only resulted in a pollen sum of 58. This should be taken into account when interpreting the microfossil spectrum, as there are several taxa that show a high percentage in this sample. Mainly Type 128A and Type 115 (Micrhystridium) show a sharp increase but this may be heavily biased as a consequence of selective corrosion of pollen grains.
Faecal content?
A more thorough investigation is needed to determine if samples 20-16 are of faecal origin as indicated by this study. Further research focusing on the identification of faecal matter should incorporate molecular biomarkers that can be used to recognise the origin of organic matter (van den Bos et al., 2014). The unusually high values of Juncus seeds in feature-A do suggest that seasonality played a large role in the microfossil composition of this layer. Taking into account the overall distribution of recorded taxa in feature-A, it is evident that the lower part is definitely poorer in taxa than the upper part. This supports the idea that this feature contains faeces originating from different seasons, as the flowering and seed germination of the Juncus plants is reflected in only two of the five samples. There arises the question how this feature came to contain faeces. It is not clear if it was, like the archaeological waste layers, a deposition layer building up over time, or a single deposition event. This could be an interesting lead for further (bio-archaeological) research.
Conclusions
Based on the pollen records, three distinct phases in the vegetational history have been identified: zones A, B and C.
The palaeoecology points to an open parkland landscape along a river bank in zone A, dated from the second through eighth century. The landscape is mainly dominated by Alnus trees, and many helophytes were also recorded, including Alisma plantago-aquatica, Bolboschoenus maritimus, Typha
latifolia and Phragmites australis. Throughout this zone, there is evidence of some human activity at
or near the site, most likely being of agricultural nature. This is indicated by the presence of Cerealia pollen as well as several fungal spores such as Chaetomium. During zone B, dating from 750-850 CE, the parkland landscape opens up, most likely due to Man’s logging activities. The recorded plant species reflect a very strong human impact on the vegetation. A grazed grassland emerges, indicated by several ruderal plants: Persicaria maculosa, P. lapathifolia, and Polygonum aviculare were recorded. Several types of coprophilous fungal spores indicate the presence of grazing animals.
Zone C, represents the return of the parkland landscape. Pollen from Poaceae decline sharply. Although there are still taxa present that can be interpreted as being indicative of human impact, there is strong evidence indicating the abandonment of the direct vicinity of the sampled site. Several types of ecological indicators recorded in both parkland landscape phases suggest there was a marine influence at the site. This could be explained by storm surges flooding the area with salt water. This conclusion could potentially be useful for the archaeological interpretation of the site, as flooding may have been the cause of the abandonment of the site. However, the full extent of this influence is still unclear, as the geology suggests that the river could also have redeposited older marine layers.
Finally, a distinct archaeological feature (termed Feature-A) yielded highly unusual pollen spectra. The over-representation of Poaceae pollen, and Juncus seeds indicate this feature being of faecal origin. Grazing animals’ food preference can heavily bias the fossil content of samples, with the timing of the flowering season also playing a role, reflected in the highly individual composition of each sample. It is likely that these samples have a high faecal content, but the true nature of this feature is still unclear, and more detailed bio-archaeological and chemical research into this feature should be able to provide more conclusive details about the origin of these samples.
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0
2
4
meters
V1170
V1127
V1169
V1168
V1167 V1166
V1159
V1023
Figure 3: Field drawing of the profile from trench 7. Superimposed is the computer generated sketch of the stratigaphy with in red the location of the pollen boxes, denoted by their find number. See table 1 for the corresponding sample numbers originating from these sampling boxes.
Feature A
Merovingian waste
deposition layer
Carolingian waste
deposition layer
Remains of campshedding
0
2
4
meters
Diagram 1 (above): Microfossils recorded in samples 15-1 Diagram 2 (below) Macrofossils recorded in samples 15-1
A B C A B C 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 S am pl e AbiesAcer 20 40 Alnu s Betul a Carp inus 20 Cory lus Erica les Fagu s Frax inus Pice a Pinu s 20 Quer cus SalixTiliaUlmu s Vibu rnum Arte misia 20 Aste race ae lig . Aste race ae tu b. 20 Bras sicac eae Cent aure a cy anus 20 Cere alia Chen opod icaea e Faba ceae Plan tago lanc eolat a Plan tago maj or/m edia 20 40 60 80 Poac eae Polyg onum avic ular e typ e Ranu ncula ceae Rum ex a ceto sella type Solan um du lcam ara Apiac eae Cary ophy lloce ae cf Ri nant hus type Eu-R umex Gera nium Hede ra h elix Lotu s Lysim achi a Poten tilla type Rosa ceae und if. Trifo lium Cype race ae Equis etum Filip endu la Galiu m typ e Glom us Lem na Lyth rum Men tha ty pe Men yant hes Myri ca Myri ophy llum spica tum Nymp haea Persi caria mac ulosa Spar ganiu m Sym phytu m Thal ictru m Typh a ang ustifo lia Typh a lat ifolia cf Op hiog loss um vu lgatu m Kret zsch mar ia de usta Mon olete psil ate f ern spor es Mon olete verru cate fern spor es Osm unda rega lis Spha gnum 20 Chae tomi um (Type 7A) Lyco podiu m Mou geot ia lae tevir ens Pter idium Sord aria type (Type 55A) Botry ococ cus cf Ty pe 5 69 Pedia stru m Spiro gyra Tetra ploa (Type 89) Type 1011 20 Type 115 Type 116 20 40 Type 128A Type 128B Type 13 Type 140 Type 23 Type 27 Type 386 (Pod ospo ra ty pe) Type 503 Type 58 Type 729 Dino flage llate Fora mini fera e % 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 S am pl e Pers icaria mac ulosa Polyg onum avic ulare Sonc hus a sper Sonc hus o lerac eus Stell aria med ia Thlas pi ar vens e Urtic a ure ns Linum usita tissim um Alism a pla ntago -aqu atica Aster sp. Atrip lex p atula/ pros trata Atrip lex sp ec. Bolbo scho enus mar itimus Care x hirta /ripa ria Care x otru bae vulpi na Chen opod ium a lbum Chen opod ium fic ifoliu m Chen opod ium ru brum /glau cum Chen opod ium sp ec. Chen opod ium/A triplex 20 Eleo char is pa lustri s/unig lumis Glyc eria fluita ns Lythr um sa licar ia Pers icaria lapa thifo lia Phra gmite s aus tralis Plan tago majo r Poa palus tris Pote ntilla ans erina Ranu nculu s aqu atilis type Ranu nculu s sar dous Rume x cris pus t ype Rume x mar itimus Scho enop lectu s tab erna emon tani Solan um du lcama ra Typh a an gusti folia Typh a lat ifolia Urtic a dioi ca Zann ichell ia pa lustri s sub sp.pa lustris Dauc us ca rota Lych nis flo s-cuc uli Alnu s sp. Alnu s, bu d sca le Betu la sp . Care x cf r emota Callu na vu lgaris , sho ot Junc us su bnod ulosu s Ranu nculu s flam mula Glau x m aritim a Trigl ochin mar itima Bud scale unide ntifia ble Care x spe c. Char coal fragm ents Fern leaf frag ment s Glom us 20 40 60 80 100 Junc us ar ticula tus t ype 200 600 1000 Junc us ef fusus type Junc us un dif. Malv a/Al thaea Oena nthe sp. Poa sp. Ranu nculu s sp. Rhina nthus sp. Seta ria cf italic a Tree leaf frag ment s Trifo lium , peta ls Woo d Bith ynia Bone rema ins Ceno cocc um Coleo ptera Crist atella muc edo Fish rema ins 20 Fora minif erae Loph opus crys tallin us Moll uscs Oriba tidae Ostra coda 100 200 Plum atella type 20 Spon ge g emm ula
Crop weeds & economic plants Human Indicators Fen & Bog
Salt
Diagram 3 (above): Macrofossils recorded in samples 20-16 Diagram 4 (below): Microfossils recorded in samples 20-16
16 17 18 19 20 S a m p le Agos tem ma githa go Pers icaria mac ulosa Stell aria med ia Urtic a ur ens Bolbo scho enus mar itimus Chen opod ium/A triple x 20 Eleo char is pa lustr is/un iglum is Phra gmite s aus tralis Pote ntilla ans erina Rum ex m aritim us Care x cf d istich a Dauc us ca rota Lych nis flo s-cu culi Stell aria cf. g ram inea Care x lep idoca rpa type Erica tetra lix, le af Eriop horu m va ginat um Ranu nculu s flam mula Care x spe c. Char coal fragm ents Fern leaf frag men ts 500 1000 Junc us e ffusu s typ e Luzu la sp . Poa sp. Tree leaf frag men ts Crist atell a m uced o Loph opus crys tallin us Ostra coda 16 17 18 19 20 S a m p le Abie s Alnu s Betu la Cory lus Erica les Fagu s Pinu s Que rcus Salix Tilia Vibu rnum Arte misi a Aste race ae lig . Aste race ae tu b. Bras sicac eae Cent aure a cy anus 20 Cere alia Chen opod icaea e Plan tago majo r/med ia 20 40 60 80 100 Poac eae Poly gonu m avi cula re ty pe Ranu ncula ceae Rum ex a ceto sella type Sola num dulca mar a Apia ceae Cary ophy lloce ae Hede ra hel ix Lotu s Lysim achi a Pote ntilla type Rosa ceae und if. Trifo lium Cype race ae Filip endu la 20 Galium type Myr ica Pers icaria mac ulos a Sym phyt um Thal ictru m Typh a an gust ifolia Typh a lat ifolia Mon olete psila te fe rn spo res Mon olete verru cate fern spo res Spha gnum Sord aria type (Type 55A) Spiro gyra Tetra ploa (Type 89) 20 40 Type 101 1 Type 116 Type 128 B Type 23 Type 386 (Pod ospo ra ty pe) Type 58 Type 729
