The indirect response of an aquatic ecosystem to long-term climate-driven terrestrial vegetation in a subalpine temperate lake

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

Cladocera species composition in lakes in the area of the Hornsund Fjord (Southern Spitsbergen) – preliminary results

Species composition of benthic and planktonic Cladocera was analysed in four lakes and ponds located in the southern part of the Spitsbergen Island near the Fjord Hornsund. This is the first study to provide information on the species composition of the contemporary and subfossil Cladocera in this region. A total of eight Cladocera taxa were found in the sediments and waters of the lakes that have been chosen for the study. The sediments included remains of only five species, while seven Cladocera species were found in the zooplankton samples. The results imply that the lakes are subject to natural transformations driven by the fluctuating climate which was reflected by increasing the number of species, and in particular in the appearance of Bosmina longirostris. Absence of some littoral Cladocera species in the sediments (e.g., small Alona, Ophyroxus gracilis), with simultaneous occurrence of these species in the water, may be a result of physical and chemical processes influencing the destruction and lack of preservation of the remains in the sediments

Relationship between cladoceran (Crustacea) functional diversity and lake trophic gradients

Functional diversity (FD) as a biodiversity measure has an explicit role in ecosystem functioning because the effects of environmental changes in ecosystems are determined by biological functions, such as feeding type and trophic position, of particular species. We evaluated the usability of functional characterization and FD of an aquatic keystone group (Crustacea: Cladocera) for enhancing the understanding of long-term lake functional responses to environmental changes. The aims were to separate ecologically significant functional groups, investigate succession of such functional groups during nutrient enrichment process and determine the relationship between FD and lake productivity using a palaeolimnological approach. We selected two eutrophicated study lakes from southern Finland for down-core investigations, one with a centennial (past c. 350 years) and the other with a decadal (past c. 70 years) nutrient enrichment record. Cladoceran microfossils in the sediment cores were used to determine the taxonomic structure of the past communities. Ecologically relevant functional characteristics were determined to separate functional groups by utilizing a functional dendrogram and a weighted community-based FD index together with a set of multidimensional FD indices. The indices were applied to the down-core assemblages. The functional dendrogram separated cladocerans into functional groups where habitat type principally separated open-water filterers and predators from epibenthic scrapers and detritivores. Further separation in the pelagic branch was based on body size and feeding and among the benthic branch body shape. Functional assemblages changed markedly during the nutrient enrichment process. In the early stage of eutrophication, the largest functional changes were caused by small planktonic filterers and predators. Small filterers and epibenthos responded strongest during the eutrophic–hypereutrophic succession. FD had a positive long-term relationship with lake trophic status until eutrophic conditions that was likely caused by diversifying resources and versatile food webs. Under hypereutrophic conditions, and especially at a decadal temporal resolution, alternating predation regimes caused variance to FD. In the current records, cladoceran FD was positively related to lake productivity and bottom-up controls during the early stages of eutrophication in the long-term record but top-down controls apparently were more important at a decadal scale and under hypereutrophic conditions.peerReviewe

Subfossil faunal and floral remains (Cladocera,

The analysis of lake sediment cores have been long used as historical integrators of environmental changes. Nutrient poor isoetid lakes remain under studied in the north boreal region. Hence, the bottom sediments of two north boreal Lobelia lakes, located in NE Finland were analysed for the presence of Cladocera and Pediastrum remains. Sediment cores from the littoral zones were sampled, sectioned every centimetre and aged with 210Pb. The number of taxa of both Cladocera and Pediastrum identified in the cores was high, while the number of individuals in each taxon was low. In Lake Kevojärvi, twenty five Cladocera species and eight Pediastrum species were found. Along with widely distributed species, typical for north boreal regions, species preferring more temperate environments occurred. In Lake Petäjälampi, the species composition was similar. Twenty one Cladocera species and five Pediastrum species occurred there, however with a lower frequency of individuals in each taxon. In both Lobelia lakes, analyses of subfossil Cladocera and Pediastrum remains, from the sediments deposited within the last 30–40 years indicated a recent increase in trophic status

Cladocera species composition in lakes in the area of the Hornsund Fjord (Southern Spitsbergen) – preliminary results

Species composition of benthic and planktonic Cladocera was analysed in four lakes and ponds located in the southern part of the Spitsbergen Island near the Fjord Hornsund. This is the first study to provide information on the species composition of the contemporary and subfossil Cladocera in this region. A total of eight Cladocera taxa were found in the sediments and waters of the lakes that have been chosen for the study. The sediments included remains of only five species, while seven Cladocera species were found in the zooplankton samples. The results imply that the lakes are subject to natural transformations driven by the fluctuating climate which was reflected by increasing the number of species, and in particular in the appearance of Bosmina longirostris. Absence of some littoral Cladocera species in the sediments (e.g., small Alona, Ophyroxus gracilis), with simultaneous occurrence of these species in the water, may be a result of physical and chemical processes influencing the destruction and lack of preservation of the remains in the sediments

Algal and invertebrate microfossil assemblages from lake sediments in the reconstruction of past community dynamics - preliminary information

This pa per fo cuses on the use ful ness of a palaeolimnological method called the joint algological and zoo log i cal anal ysis. The joint algo-zoo log i cal anal y sis in volves count ing all iden ti fi able re mains of the main al gae groups (Bacillariophyta, Cyanophyta, Desmidiales, other Chlorophyta, Trachelomonas sp.) and in ver te brate groups (Cladocera, Ostracoda, Chironomidae, Chaoborus sp., and other in sects, Turbellaria, Bryozoa, Spongia and Testacida) in vol u met ric sam ples. We pres ent re sults from re cent sed i ments of Lake Glubokoe (Mos cow re gion, Rus sia) as an ex am ple of the ap pli ca tion of this method. We re con struct the struc ture of phytoplankton, zoo plank ton and zoobenthos com mu ni ties and their dy nam ics over the last 25 years. Our re sults sup port the va lid ity of this method in the re con struc tion of the struc ture of phyto- and zoo plank ton com mu ni ties and their dy nam ics, in for ma tion that may be lost when car ry ing out sep a rate anal y ses for in di vid ual groups. Sim plic ity is an other ad van tage of this meth od ol ogy