Abstract

Aim: To assess whether climate directly influences aquatic ecosystem dynamics in
the temperate landscape of Tasmania or whether the effects of long-term climatic
change are mediated through the terrestrial environment (indirect climate influence).
Location: Paddy’s Lake is located at 1065 m a.s.l. in temperate north-west Tasmania,
a continental island south-east of mainland Australia (41°15–43°250 S; 145°00–
148°150 E).
Methods: We developed a new 13,400 year (13.4 kyr) palaeoecological dataset of
lake sediment subfossil cladocerans (aquatic grazers), bulk organic sediment carbon
(C%) and nitrogen (N%) and d13C and d15N stable isotopes. Comparison of this new
data was made with a recently published pollen, geochemistry and charcoal records
from Paddy’s Lake.
Results: Low cladoceran diversity at Paddy’s Lake is consistent with other temperate
Southern Hemisphere lakes. The bulk sediment d15N values demonstrate a significant
lagged negative response to pollen accumulation rate (pollen AR).
Compositional shifts of dominant cladoceran taxa (Bosmina meridionalis and Alona
guttata) occur following changes in both pollen AR and pollen (vegetation) composition
throughout the 13.4 kyr record at Paddy’s Lake. The d15N values demonstrate
a significant positive lagged relationship to the oligotrophic:eutrophic cladoceran
ratio.
Main conclusions: Long-term changes in cladoceran composition lag changes in
both pollen AR and terrestrial vegetation composition. We interpret pollen AR as
reflecting climate-driven changes in terrestrial vegetation productivity and conclude
that climate-driven shifts in vegetation are the principal driver of the cladoceran
community during the last ca. 13.4 kyr. The significant negative lagged relationship
between pollen AR and d15N reflects the primary control of vegetation productivity
over within-lake nutrient status. Thus, we conclude that the effects of long-term climate
change on aquatic ecosystem dynamics at our site are indirect and mediated
by the terrestrial environment. Vegetation productivity controls organic soil development
and has a direct influence over lake trophic status via changes in the delivery
of terrestrial organic matter into the lake.