Long-term directional trajectories among lake crustacean zooplankton communities and water chemistry

Understanding community responses to disturbance is a long-standing challenge in ecology and will remain a critical issue as human activity continues to alter environmental conditions. This is particularly concerning for freshwater communities, which are often subject to the effects of multiple disturbances on the landscape. With crustacean zooplankton community composition data and associated water chemistry from 19 Ontario lakes, we quantify the relative magnitude and directionality of change over three decades using distances in multivariate ordinations. The data span a gradient of impact from minimally disturbed reference lakes to lakes with known impacts from experimental acidification trials, atmospheric acidification, and regional land-use changes. Most communities exhibited changes from historical conditions, including previously described reference systems. Zooplankton communities in experimentally acidified lakes showed gradual, directional patterns with a return to historical conditions postmanipulation, but have since deviated again from historical conditions. Most zooplankton communities in atmospherically acidified lakes showed gradual, directional trajectories over time. Overall, our results demonstrate that zooplankton communities are changing among both minimally disturbed lake systems and lakes known to be impacted by human activities.

Emerging investigator series: geochemistry of trace elements associated with Fe and Mn nodules in the sediment of limed boreal lakes

We report on the geochemical legacy of the liming of acidified lakes in Norway. We document the occurrence of Fe–Mn nodules and the diagenetic redistribution of trace-elements at the sediment–water interface of limed boreal lakes.

Littoral benthic macroinvertebrates of mountain lakes in the Tatra Mountains (Slovakia, Poland)

Littoral benthic macroinvertebrates of 45 mountain lakes in the Tatra Mountains were sampled using a semi-quantitative method in September 2000. A total of 32,852 specimens were identified to 93 taxa belonging to 14 higher taxonomic groups. Multivariate statistics (CCA, RDA) and nine biotic metrics (AQEM/STAR) were used to explain relationships between macroinvertebrate assemblages and environmental variables. Up to 57% of the ecological position of littoral macroinvertebrate assemblages were explained by variance of environmental variables divided into chemical, trophic, physical, catchment and location. Five types of Tatra lakes were recognized using CCA: A — strongly acidified lakes (small catchment, low pH, high concentration of TP, DOC, highest amount of POM in littoral); B — alpine acidified lakes (low amount of POM, low values of biotic metrics); C — alpine non-acidified lakes (high value of diversity index, predominance of Diptera); D — subalpine acidified lakes (high values of biotic metrics: number of families, proportion of crenal and rhithral taxa/total taxa); E — subalpine non-acidified lakes (high values of biotic metrics: number of families, number of genera, BMWP score, number of taxa and abundance of EPT taxa). RDA was used to design five levels of macroinvertebrate taxa acidification tolerance. The Tatra Acidification Index (TAI) was established to assess the acidification status of the lakes in the Tatra Mts.