New groundwater-level rise data from the Rhine-Meuse delta – implications for the reconstruction of Holocene relative mean sea-level rise and differential land-level movements

Abstract

Reconstructions of Holocene relative sea-level and groundwater-level rise are crucial for understanding the palaeogeographical and geological evolution of coastal plains, while also serving studies of differential land-level change, palaeoecology, and archaeology. At present, the quest for higher accuracy in sea-level reconstruction and for better understanding of differences between local groundwater-level curves is still ongoing.Studies of Holocene relative (ground)water change and sealevel change in the Netherlands are based primarily on radiocarbon-dated samples from the base of peats which accumulated on pre-Holocene substrates (e.g., Jelgersma, 1961Jelgersma, , 1979 AbstractWe present new local groundwater-level rise data from two Late Glacial aeolian dunes, located near Barendrecht and Oud-Alblas in the western Rhine-Meuse delta. These data are based on AMS radiocarbon dating of terrestrial macrofossils, collected from the base of peat formed on the slopes of these dunes. This method avoids contamination of bulk peat samples by old soil carbon or younger rootlets and rhizomes, as well as the hardwater effect. The new data are used to assess the reliability of previously published groundwater-level index data based on conventional radiocarbon dating of bulk basal peat samples from the slopes of the Late Glacial aeolian dunes at Barendrecht, Hillegersberg, Bolnes and Wijngaarden, all located in the western Rhine-Meuse delta.Comparison of the new and published groundwater-level data shows no significant systematic difference between conventionally dated bulk peat samples and AMS-dated samples of terrestrial macrofossils. The new data from the dune at Barendrecht confirm the reliability of the younger than 6600 cal yr BP age-depth data from the dunes at Hillegersberg and near Bolnes. This result supports the validity of this part of the mean sea-level (MSL) curve for the western Netherlands. Consequently, the position of the groundwater-level curve for Flevoland (central Netherlands) below this MSL curve can most likely be attributed to differential land-level movement.The available data show that the groundwater-gradient effect in the western Rhine-Meuse delta became less than 5 cm/km after 6600 cal yr BP. Finally, temporal correlation between temporary increases in local groundwater-level rise with known shifts of river courses in the delta plain suggests, that avulsions can explain sudden local deviations from the trend in groundwater-level rise. A general conclusion of this study is that a complex relationship exists between sea level and local delta-plain water levels.

Chronology of Wetland Hydrological Dynamics and the Mesolithic-Neolithic Transition along the Lower Scheldt: A Bayesian Approach

“…Assuming that both modern and earlier mean sea level (MSL) did not differ more than 10 cm between the Belgian and German North Sea coast (Kiden et al 2008), comparison between differing LGW curves has revealed a series of influencing variables (e.g. Roeleveld 1974;Van De Plassche 1982;Van Dijk et al 1991;Kiden 1995;Makaske et al 2003;Van De Plassche et al 2005Berendsen et al 2007;Kiden et al 2008).…”

“…Van Dijk et al (1991) also illustrates that as a consequence of the rising MSL and increasing sedimentation, the effect of the decreasing river gradient is visible in local basal peat curves along the Rhine-Meuse (see Cohen 2003: Figure 2.3). Finally, if the riverbed cuts through its natural levees to create a more favorable river gradient, this creates a short-term increase followed by a steady decrease in the speed of local MHW rise, superimposing the long-term RSL rise (Berendsen et al 2007). …”

“…Vertical errors in the age-depth plot can be introduced by several factors (Berendsen et al 2007): the assumed depth of the sample is imprecise because of (1) sample elevation measurement (0.05 m error); (2) the in-core measurement (0.03 m error); or (3) through the sample thickness (0.02 m error). Vertical errors due to compaction are minimal but can be approximated as an upward error of twice the vertical distance to the Pleistocene sand according to Van De Plassche et al (2005).…”

“…Wood peat, on the other hand, develops closer to the local groundwater level (0.2 m error). Using the method proposed by Berendsen et al (2007), a vertical standard deviation error of 0.21 m was estimated.…”

“…Throughout its history, the research has been refined from models of a country's coastal plain (Jelgersma 1961) to defining the variability between single dune flanks (Cohen 2003;Berendsen et al 2007). Such high-resolution date series were not available for the dunes surrounding the Sector B and M sites and the topographic setting of the dated samples could not always be accurately determined.…”