Zooplankton assemblage structure and diversity since pre‐industrial times in relation to land use

Abstract

Aim: While it is now well accepted that human activities are having pronounced effects on natural ecosystems, regional variation in the rate and magnitude of various human impacts is unclear. Moreover, the effects of land use change on natural aquatic communities have only relatively recently begun to be explored. Our goal was to understand how and where assemblages of a central food web component of freshwater lakes have changed over the course of industrialization in relation to land use.Location: Canada.

Changes in midge assemblages reflect climate and trophic gradients across north temperate and boreal lakes since the pre‐industrial period

“…Two sediment cores were collected at each lake and sub-sectioned into 1-cm top (0-1 cm) and bottom (X-3 to X-2 cm, where X is the total length of the shortest of the two cores) intervals. The second sediment cores were kept at 4°C and shipped to Queen's University for chironomid and 210 Pb analyses (the first sediment cores were used in studies of diatom (Griffiths et al, 2022) and cladoceran (Paquette et al, 2022) compositional change). The lakes selected for chironomid analyses are an expansion of those examined in Griffiths et al (2021).…”

“…Land‐use modification was strongly associated with changes in diatom assemblages, with more pronounced compositional changes in lakes that were highly impacted by human modification of their catchments (e.g., the Prairies; Griffiths et al., 2022). Cladoceran remains also were examined using the top‐bottom approach, revealing greater taxonomic changes and declines in diversity in lakes surrounded by highly developed catchments, with notable increases in the relative abundance of eutrophic, salt‐tolerant and non‐indigenous taxa at highly impacted sites (Paquette et al., 2022).…”

Congruence of water column, contemporary and pre‐industrial sediment cladoceran assemblages in 85 Canadian lakes of contrasting human impact levels

“…Low impacted lakes had a human impact index <0.1 (n = 34); moderate impacted lakes ranged from ≥0.1 and <0.5 (n = 33); and high impacted lakes had an index ≥0.5 (n = 18). Further details on the human impact calculation and classification are available in Huot et al (2019) and Paquette, Griffiths, et al (2022). Mean environmental variable values among human impact classes are shown in Table 1 ( for the complete LakePulse dataset see Sánchez Schacht et al, 2023).…”

“…Activities of 210 Pb and 214 Bi measured in the bottom samples from a subset of 87 cores were used to validate that the bottom samples reached background conditions (at least pre-1880). Additional details on sediment core sampling and dating are provided in Griffiths et al (2021), Baud et al (2022) and Paquette, Griffiths, et al (2022).…”

“…Finally, we predicted (4) that sites with lower human impact (assessed using catchment land use data), would show greatest similarity among all three sample types, with the corollary that assemblages should be most distinct under high catchment human impact. Indeed, previous cross-lake evidence has demonstrated that cladocerans have changed more over time in highly impacted catchments (Paquette, Griffiths, et al, 2022).…”