The Mesolithic samples show a distinct aquatic component, but the diet seems to have been mixed and rather complex, perhaps to be associated with a variable habitation regime throughout the year, the river area in winter and (possibly) the higher areas at other times of the year. Mesolithic diets in Denmark also display a complex nature with a terrestrial and aquatic component (Richards et al. 2003b). In the Meuse valley the Mesolithic diet was mixed with a major terrestrial signature (Bocherens et al. 2007).
The population of Swifterbant had a diet with a larger proportion of protein from terrestrial sources, but also with an aquatic element. The 13C values are comparable with the Mesolithic samples but the 15N values are more modest. The utilization of local food sources, both aquatic and terrestrial in nature, is not fully in agreement with the environment and may point to a similar seasonal exploitation of upland territory as the Late Mesolithic Hardinxveld series.
The coastal situation of Schipluiden, near the estuary of the Meuse, favoured the consumption of marine food. This is evident from the isotope values as well. Both 13C and especially 15N are indicative of a largely marine/aquatic diet. The presence of sturgeon may have been important in this case.
The high proportion of marine and aquatic protein in the diet of the Schipluiden people is in line with the archaeozoological evidence, showing that these people practised an ‘extended broad spectrum economy’, combining the traditional exploitation of a wide range of natural resources with the ‘new’ crop farming and animal husbandry, but estuarine fishing must have been of far greater importance than reflected in the recovered remains. The residues from food vessels at Schipluiden confirm this conclusion as having contained aquatic food. The results of Schipluiden are comparable to those of the two millennia older Iron Gates gorge sites of Lepenski Vir and Vlasac, where the consumption of sturgeon and fish roe probably played an important role in the diet as well (Fig. 14; Bonsall et al. 1997, 2000; Borić et al. 2004). The data derived from the Danish and Portugese Mesolithic and Neolithic sites show a clear change in time in favour of terrestrial food sources (Richards et al. 2003b; Lubell et al.1994). The N values are lower compared to our populations of the Lower Rhine Basin indicating the consumption of food from sources that held a lower position in the food chain.
This demonstrates that Neolithisation was still in an initial stage as far as diet is concerned even as late as 3500 BC, almost two millennia after agriculture was introduced by the Bandkeramik farmers in the loess zone of the Rhineland, Limburg and Belgium, less than 200 km to the south.
Fig. 14 Stable isotope ratios δ13C and δ 15N for human bones from Hardinxveld, Schipluiden and Swifterbant (cf. figure 11) compared to those from the Iron Gate sites Lepenski Vir, Vlasac and Schela Cladovei, from Portugal (after Lubell et al. 1994), and from Denmark (after Richards et al. 2003b).
The richness in aquatic food sources present in the Lower Rhine Basin shows up in the isotopic signature of the populations studied. The composition of the diet with respect to proteins seems to be highly related to the exploitation of the natural surroundings, more than on the available knowledge of food production. Some outsiders display a more terrestrial diet, which is understandable when they originated from other regions with other resources, but some locally born and grown people had a more terrestrial diet. One can think in those cases of a special social position, food taboos or personal tastes which led to a diet lower in fish.