Macro-invertebrate survey Drentsche Aa 1996

The original monitoring in 1996 was performed by Lia Hemerik (ORCID 0000-0002-6892-2840), together with taxonomic specialists who assisted with field work and identified specific species groups. The specialists were Arnold Spee and Theo van Dijk at Biologisch Station Wijster, Matty Berg (ORCID 0000-0001-8442-8503), Aart Noordam, Michael Traugeot and Theodoor Heijerman (ORCID 0000-0002-9835-600X). Standardising the dataset into Darwin Core format, cross-checking and publication of the data were performed by Lia Hemerik, assisted by Gijs M. Gerrits (ORCID 000-0002-2315-9677).

The study area is located in the Drentsche Aa stream valley in the Province of Drenthe in the north-eastern part of the Netherlands (Fig. 1). The Drentse Aa is a 30 km² stream valley that has had a long history of agricultural exploitation with high levels of nutrient amendments and large alterations in the hydrological functioning of the Drentsche Aa stream and its tributaries, amongst which the Anlooer Diepje brooklet (Liu et al. 2021).

Figure 1.  

Location of the four grasslands in the valley of Anlooërdiepje in the north-eastern part of the Netherlands (see inset below left). The four black arrows point at the four experimental plots, indicated in black. The numbers in circles indicate the number of years the grassland was taken out of agricultural production at the time of sampling in 1996: plot O (7 years since last fertilisation), plot B (11 years since last fertilisation), plot C (24 years since last fertilisation) and plot K (29 years since last fertilisation). On each grassland, a randomly selected rectangle of 30 m by 15 m served as the sampling plot. See Suppl. material 1 for more information on palnt composition.

The four field study plots, all located along the banks of the Anlooer Diepje (Fig. 1), consisted of grass dominated vegetation, with Lolium perenne L., Holcus lanatus L., Festuca rubra L. and Anthoxanthum odoratum L., respectively, dominating in the chronosequence gradient. Management consisted of mowing once a year and the resulting hay was removed (Verschoor et al. 2001).

The reorganisation and publication of the data were made possible with a grant from NLBIF Netherlands Biodiversity Information Facility (grant number nlbif2021.003).

The sampling programme was designed as a block field study set up within randomly selected experimental plots that were situated in the four selected grasslands of the chronosequence.

Within each of the four grasslands taken out of agricultural production, a plot measuring 30 m × 15 m was selected for the sampling to take place. Each plot was divided into three subplots (10 m × 15 m). One pyramid trap was placed within each of the subplots (i.e. 3 pyramid traps per experimental plot) and moved randomly across the subplot every two weeks. Inside the pyramid trap, two pitfall traps were placed (i.e. 6 pitfall traps per experimental plot), flush with the soil surface. The soil samples that were dug out (i.e. 12 soil samples per experimental plot) to accommodate the pitfall traps were collected in plastic bags and taken to the laboratory in Wageningen, stored at a temperature of 4°C and hand-sorted for soil macrofauna. Both pyramid and pitfall catches were collected on a weekly basis and soil samples on a two-weekly basis. In total, 12 pyramid traps were placed in the four plots, together with 24 pitfalls and 48 soil samples. See Table 1 for details.

The pyramid traps consisted of an opaque grey plastic ring (diameter of 56 cm). Above this ring, a gauze net made of white net fabric formed an inverted funnel-shaped dome. On top of the funnel dome, a white plastic trapping container in the shape of a ring functioned as a lightfall, bringing the total height of the pyramid trap to 80 cm (Fig. 2). The lightfall at the top contained a 2% formaldehyde (CH₂O) solution, which served as a killing preservative. The pyramid traps were designed to catch flying insects that were either residing in the grass tussocks at the moment of placement or, more specifically, all insects that hatched from the soil during the time the trap was placed at each location. The pitfall traps consisted of white plastic cups (0.5-litre yoghurt cups) with a diameter of 9 cm. The pitfalls were also filled with a 2% formaldehyde solution.

Figure 2.  

Sampling was set up with pyramid traps and pitfall traps. The pyramid trap was 80 cm high and had a diameter of 56 cm. Light traps and pitfalls were emptied weekly. Soil samples were taken every two weeks and, at the same time, the light traps and pitfalls were moved to a new location within the experimental plot.

The specimens that were collected during sampling were stored in 70% ethanol, awaiting identification. The samples were destroyed after identification.

Table 1 provides an overview of the four plots and the trap numbers that were placed in each sampling plot.

Additional data were collected during the sampling programme on abiotic and botanical variables (see Table 2 for an overview). In addition, photographs of the research plots taken in 2021 are provided in Suppl. material 1, together with an overview of botanical composition in 1996 and in 2021.

Soil wet weight and dry weight were measured from the soil cores collected for placement of the pitfall traps. Furthermore, mean air temperature and total weekly precipitation in the week preceding a collection event were calculated from data available from the KNMI Meteorological Station Eelde (KNMI 2023), which is situated approximately 11 km from the research site. The measurements are connected to the eventIDs and published as a MeasurementOrFact table.

As part of a study on nematodes in the same plots, Verschoor et al. (2001) collected abiotic data, namely bulk density, clay-silt percentage, pH-H₂O, C-pool, N-pool and C/N ratio (see their table 1).

The study area was located in the Province of Drenthe, in the north-eastern part of the Netherlands, see Fig. 1. The plots O, B, C and K have their own pair of coordinates in GBIF. For the location of these plots on the map, we refer to Fig. 1.

53.0449 and 53.0502 Latitude; 6.6661 and 6.6799 Longitude.

After collection, the specimens were identified by taxonomy specialists. All specimens were first sorted and identified to order level; true flies (Diptera) and beetles (Coleoptera) were further identified to family level by Lia Hemerik. Arnold Spee and Theo van Dijk assisted with field sampling and identification of the carabid beetles. Matty Berg identified terrestrial isopods (Isopoda), millipedes (Diplopoda) and centipedes (Chilopoda). Aart Noordam identified spiders (Araneae) and harvestmen (Opiliones). Michael Traugeot identified beetle larvae. Theodoor Heijerman identified weevils (Curculionidae/Brentidae).

Before publication of the dataset, all original taxonomical assignments were cross-checked with the Checklist Dutch Species Register – Nederlands Soortenregister (Creuwels and Pieterse 2023) and provided with a currently valid assignment when necessary. For a complete list of taxa included in the dataset, see Table 3.