Human activities have impacted zooplankton community structure and diversity since industrialization

Background/Question/Methods

While it is now well accepted that human activities are having pronounced effects on natural ecosystems, the regional picture of the rate and magnitude of these impacts is unclear. Moreover, the effects of land use change on natural aquatic communities have only relatively recently begun to be explored. Canada is a global steward of a substantial number of lakes, which in turn provide many ecosystem services that are integral to cultural and economic sustainability. Crustacean zooplankton occupy a key position as primary consumers within lake food webs, acting as early indicators of wider ecosystem shifts that can cascade to higher trophic levels. As part of the NSERC Canadian LakePulse Network project, 101 lakes across Canada were selected along a gradient of human impact, according to contemporary watershed land use, to analyse crustacean zooplankton changes through time. We used a combination of α-and β-diversity, along with taxonomic and functional approaches to understand how and where Canadian lakes have changed over the course of industrialization in relation to land use. We also considered how contemporary land use variables could explain differences in cladoceran assemblages among lakes (spatial β-diversity) and through time (temporal β-diversity), both taxonomically and functionally.

Results/Conclusions

Cladoceran assemblages have changed significantly over the course of industrialization, and especially in more highly impacted watersheds, underscoring the important role of human land use in watershed in shaping diversity. Although country-wide (gamma) diversity remained stable, we observed significant changes in species composition over time; local α-diversity losses were greatest in highly impacted lakes where agriculture and pasture are prevalent. Land use also affected temporal species turnover (temporal β-diversity) with greater turnover in urbanized watersheds. In contrast to the results from taxonomic metrics, we found that cladoceran function remained relatively resilient over time at the landscape scale, and both taxonomic and functional spatial homogenization did not increase over time despite important environmental shifts. Our results demonstrate the importance of combining taxonomic and functional dimensions, and both α- and β-diversity to help answer important questions about how and where lakes have changed over the Anthropocene. Overall, this research furthers understanding of the health status of Canadian lakes and the consequences of human activities, especially in relation to agriculture and urbanization, on lake zooplankton.