Water chemistry of lakes in Zackenbergdalen between 1997-2003, East Greenland

The ecology of arctic lakes is strongly influenced by climate-generated variations in snow coverage and by the duration of the ice-free period, which, in turn, affect the physical and chemical conditions of the lakes (Wrona et al., 2005, http://www.acia.uaf.edu/PDFs/ACIA_Science_Chapters_Final/ACIA_Ch08_Final.pdf). Most arctic lakes are characterised by a long period (8-10 months) of ice-cover, cold water and low algal biomass. The water temperature and nutrient concentrations, and most probably the nutrient input from the catchments, are closely related to the duration of snow- and ice-cover in the lakes. In years when the ice-out is late, - that is, in late July, - phytoplankton photosynthesis is limited by the lack of light and nutrients. Less food is then available to the next link in the food chain, such as copepods and daphnids, with implication on their growth rates

(Table 2) Radiocarbon ages of lake sediments from Boresø, East Greenland

This chapter provides a review of proxy data from a variety of natural archives sampled in the Wollaston Forland region, central Northeast Greenland. The data are used to describe long-term environmental and climatic changes. The focus is on reconstructing the Holocene conditions particularly in the Zackenberg area. In addition, this chapter provides an overview of the archaeological evidence for prehistoric occupation of the region. The Zackenberg area has been covered by the Greenland Ice Sheet several times during the Quaternary. At the Last Glacial Maximum (LGM, about 22,000 years BP), temperatures were much lower than at present, and only very hardy organisms may have survived in the region, even if ice-free areas existed. Marked warming at around 11,700 years BP led to ice recession, and the Zackenberg area was deglaciated in the early Holocene, prior to 10,100 years BP. Rapid early Holocene land emergence was replaced by a slight transgression in the late Holocene. During the Holocene, summer solar insolation decreased in the north. Following deglaciation of the region, summer temperatures probably peaked in the early to mid-Holocene, as indicated by the occurrence of a southern beetle species. However, the timing for the onset of the Holocene thermal maximum is rather poorly constrained because of delayed immigration of key plant species. During the thermal maximum, the mean July temperature was at least 2-3°C higher than at present. Evidence for declining summer temperatures is seen at around 5500, 4500 and 3500 years BP. The cooling culminated during the Little Ice Age that peaked about 100-200 years ago. The first plants that immigrated to the region were herbs and mosses. The first dwarf shrubs arrived in Northeast Greenland prior to 10,400 years BP, and dwarf birch arrived around 8800 years BP. The first people arrived about 4500 years BP, but the region was depopulated several times before the last people disappeared some time after 1823 AD, perhaps as a consequence of poor hunting conditions during the peak of the Little Ice Age

Reconstructing the salinity and environment of the Limfjord and Vejlerne Nature Reserve, Denmark, using a diatom model for brackish lakes and fjords

Diatoms in surface sediments from a data set of 27 brackish lakes and nine fjords in Jutland, Denmark (range 0.2 – 31 g·L–1 total dissolved solids (TDS)), were analysed using multivariate methods to determine response to measured parameters (depth, total phosphorus (TP), total nitrogen (TN), TN/TP, salinity, water body type). Water body type, salinity, depth and TP together explained 25.3% of the variation in the diatom data and were all independently significant predictors. A diatom–salinity model (r2 jack = 0.887, root mean square error of prediction = 0.246 log salinity, g·L–1) was developed from the 36 sample training set and applied to fossil diatom assemblages in three sediment cores from the east Vejlerne wetland, Denmark, a nature reserve created after the damming of an embayment of the polyhaline Limfjord (~26 g·L–1 TDS) in the late 19th century. The diatom-inferred salinity reconstructions reflect the known salinity history of the Limfjord and the freshwater–subsaline Vejlerne lakes, and appear sensitive to documented North Sea storms in the 16th and 17th centuries, which had major impacts on the brackish Limfjord herring fishery. Diatom–salinity models may be useful tools in long-term studies of coastal and estuarine areas to test hypotheses concerning aquatic resources and ecological, hydrographic, and cultural change

Interaction between non-native predatory fishes and native galaxiids (Pisces: Galaxiidae) shapes food web structure in Tasmanian lakes

Este artículo contiene 16 páginas, 6 figuras, 5 tablas.Non-native fish invasions threaten native fauna and ecosystem functioning, not least in isolated island lakes. In Tasmania, where the native fish are mostly galaxiids, 9 non-native freshwater fish species have been introduced over the past 150 years, with uncertain ecological outcomes. We evaluated the effects of non-native predatory fishes (NNPF) and various environmental and biological variables on the trophic niche of native fish (galaxiids) and potential cascading effects. We analysed Layman’s food web metrics based on both stable isotope (δ15N and δ13C) values and fish stomach contents in 14 shallow Tasmanian lakes along a NNPF abundance gradient. The food web metrics calculated were (1) range of δ13C (CR) and δ15N (NR) centroid distance (CD) and (2) standard ellipse area. Our results showed that NNPF relative abundance in the fish catch per unit effort was negatively related to the galaxiids’ trophic niche metrics (e.g., CRG, NR G, and CDG), trophic position, and the pelagic contribution to the diet. Moreover, the proportion of galaxiids in the diet of NNPF was higher in turbid lakes. The zooplankton standard ellipse area was negatively correlated with the pelagic contribution to the NNPF diet, and NNPF relative abundance was positively correlated with the maximum body size of calanoid copepods. While our results suggest a negative effect of NNPF on the trophic niche of galaxiids, the cascading effect on phytoplankton biomass was weak. Non-native predatory fish affect native fish prey, and the outcome of these interactions should be considered for conservation purposes, particularly for island lakes, such as those in Tasmania.The project was funded by Galathea 3, Carlsberg, Research Council of Nature and Universe (272-08-0406), the TK Foundation, Dronning Margrethes og Prins Henriks Fond, Torben og AliceFrimodts Fond, Christian og Ottila Brorsons Rejselegat, University of Copenhagen and Aarhus University. MM and NV were funded by SNI-ANII and the L’Oréal UNESCO Women for Science national award with support of DICYT, Uruguay. MV was supported by a Marie Curie post-doctoral grant (MEIF-CT-2005-010554) and TB by a Beatriu de Pinós post-doctoral grant (2005 BP-A 1004). EJ was supported by the MARS project (Managing Aquatic Ecosystems and Water Resources Under Multiple Stress) funded under the EU 7th Framework Programme, Theme 6 (Environment including Climate Change), Contract No.: 603378 (http://www.mars-project.eu), CIRCE and CRES. LAB was supported by the Australian Research Council (LP130100756). CT is a CONICET (Argentinean Council of Science) researcher; Fondation L’Oréal; Sistema Nacional de Investigadores (UY).Peer reviewe

Food Webs and Fish Size Patterns in Insular Lakes Partially Support Climate-Related Features in Continental Lakes

Disentangling the effects of climate change on nature is one of the main challenges facing ecologists nowadays. Warmer climates forces strong effects on lake biota for fish, leading to a reduction in size, changes in diet, more frequent reproduction, and stronger cascading effects. Space-for-time substitution studies (SFTS) are often used to unravel climate effects on lakes biota; however, results from continental lakes are potentially confounded by biogeographical and evolutionary differences, also leading to an overall higher fish species richness in warm lakes. Such differences may not be found in lakes on remote islands, where natural fish free lakes have been subjected to stocking only during the past few hundred years. We studied 20 species-poor lakes located in two remote island groups with contrasting climates, but similar seasonality: the Faroe Islands (cold; 6.5 ± 2.8 °C annual average (SD) and the Azores Islands (warm; 17.3 ± 2.9 °C)). As for mainland lakes, mean body size of fish in the warmer lakes were smaller overall, and phytoplankton per unit of phosphorus higher. The δ13C carbon range for basal organisms, and for the whole food web, appeared wider in colder lakes. In contrast to previous works in continental fresh waters, Layman metrics of the fish food web were similar between the two climatic regions. Our results from insular systems provide further evidence that ambient temperatures, at least partially, drive the changes in fish size structure and the cascading effects found along latitude gradients in lakes