This dataset provides the percentage-abundances of chironomid taxa identified in a set of surface sediment samples taken in the Plymouth area (Massachusetts, United States) in 2009. For each sample, a short sediment core was retrieved from a rubber dinghy using a gravity corer (both the Glew and the mini-Glew models were used) during field work in June and September 2009. Volumetric samples taken from the 0-1cm sediment depth sample were subsequently processed in the laboratory (University of New Brunswick, Canada) using standard protocols. The procedure involved placing the sample aliquot in a glass beaker and submerging it in warm 10% KOH for ca. 20 mins. Subsequently the material was rinsed over a 100µm mesh and individual head capsules were hand-sorted from the residue and mounted on microscope slides. Chironomid head capsules were identified using Brooks et al. 2007 and encountered taxa that were not present in that handbook are illustrated and described in Engels & Cwynar (2011). This dataset provides chironomid abundances (expressed as percentage of the total chironomid sum) as well as measurements of water depth for each of the samples; Engels & Cwynar (2011) provide additional environmental observations for each of the 8 lakes sampled. A total of 132 surface sediment samples were originally counted, but as 3 samples only reached total chironomid count sums of less-than-50 these were removed from the original dataset, resulting in a final dataset consisting of 129 samples. The chironomid data provides information on within-lake distribution patterns of chironomid taxa for each of the 8 lakes sampled. The dataset was used to determine depth-preferences of each of the taxa encountered, and to determine common threshold depths (i.e. those water depths where abrupt changes in the composition of the chironomid fauna take place). These data were subsequently used to produce site-specific (i.e. one lake) and regional (i.e. 7- or 8-lake) chironomid-water depth inference models.

Surface samples obtained from 8 lakes, with different number of samples taken from each lake: Bloody Pond – 19 samples; Crooked Pond – 26 samples; Deep Pond -5 samples; Dicks Pond – 6 samples; Little West Pond – 9 samples; Long Pond – 25 samples; Micajah Pond – 25 samples; UP: Union Pond – 14 samples. Ceratopogonidea head capsules and Chaeborus mandibles are included in line with other publications from the Nearctic region.Stenochironomus type "Mt" was counted as a separate taxon by Engels & Cwynar 2011; it is easily distinguished from the typical Stenochironomus morphotype as it only has 1 single median tooth. Later it was found that this taxon actually represents 1-instar Stenochironomus larval head capsules. In future studies, it should be amalgamated with Stenochironomus.