Nutrient limitation of periphyton growth in arctic lakes in south-west Greenland

Many arctic lakes are oligotrophic systems where phototrophic growth is controlled by nutrient supply. Recent anthropogenic nutrient loading is associated with biological and/or physico-chemical change in several lakes across the arctic. Shifts in nutrient limitation (nitrogen (N), phosphorus (P), or N ? P) and associated effects on the growth and composition of algal communities are commonly reported. The Kangerlussuaq region of south-west Greenland forms a major lake district which is considered to receive little direct anthropogenic disturbance. However, long-range transport of pollutant N is now reaching Greenland, and it was hypothesised that a precipitation gradient from the inland ice sheet margin to the coast might also deliver increased N deposition. In situ nutrient bioassays were deployed in three lakes across the region: ice sheet margin, inland (close to Kangerlussuaq) and the coast (near Sisimiut), to determine nutrient limitation of lakes and investigate any effects of nutrients on periphyton growth and community composition. Nutrient limitation differed amongst lakes: N limitation (ice sheet margin), N and P limitation (inland) and N ? P co-limitation (coast). Factors including variation in N supply, ice phenology, seasonal algal succession, community structure and physical limnology are explored as mechanisms to explain differences amongst lakes. Nutrient limitation of arctic lakes and associated ecological impacts are highly variable, even across small geographic areas. In this highly sensitive region, future environmental change scenarios carry a strong risk of significantly altering nutrient limitation; in turn, potentially severely impacting lake structure and function

Centennial clonal stability of asexual Daphnia in Greenland lakes despite climate variability

Climate and environmental condition drive biodiversity at many levels of biological organization, from populations to ecosystems. Combined with paleoecological reconstructions, palaeogenetic information on resident populations provides novel insights into evolutionary trajectories and genetic diversity driven by environmental variability. While temporal observations of changing genetic structure are often made of sexual populations, little is known about how environmental change affects the long‐term fate of asexual lineages. Here, we provide information on obligately asexual, triploid Daphnia populations from three Arctic lakes in West Greenland through the past 200–300 years to test the impact of environmental change on the temporal and spatial population genetic structure. The contrasting ecological state of the lakes, specifically regarding salinity and habitat structure may explain the observed lake‐specific clonal composition over time. Palaeolimnological reconstructions show considerable regional environmental fluctuations since 1,700 (the end of the Little Ice Age), but the population genetic structure in two lakes was almost unchanged with at most two clones per time period. Their local populations were strongly dominated by a single clone that has persisted for 250–300 years. We discuss possible explanations for the apparent population genetic stability: (a) persistent clones are general‐purpose genotypes that thrive under broad environmental conditions, (b) clonal lineages evolved subtle genotypic differences unresolved by microsatellite markers, or (c) epigenetic modifications allow for clonal adaptation to changing environmental conditions. Our results motivate research into the mechanisms of adaptation in these populations, as well as their evolutionary fate in the light of accelerating climate change in the polar regions

Lake eutrophication and its implications for organic carbon sequestration in Europe

The eutrophication of lowland lakes in Europe by excess nitrogen (N) and phosphorus (P) is severe because of the long history of land-cover change and agricultural intensification. The ecological and socio-economic effects of eutrophication are well understood but its effect on organic carbon (OC) sequestration by lakes and its change overtime has not been determined. Here, we compile data from ~90 culturally impacted European lakes [~60% are eutrophic, Total P (TP) >30 μg P l-1] and determine the extent to which OC burial rates have increased over the past 100-150 years. The average focussing corrected, OC accumulation rate (C ARFC) for the period 1950-1990 was ~60 g C m-2 yr-1, and for lakes with >100 μg TP l-1 the average was ~100 g C m-2 yr-1. The ratio of post-1950 to 1900-1950 C AR is low (~1.5) indicating that C accumulation rates have been high throughout the 20th century. Compared to background estimates of OC burial (~5-10 g C m-2 yr-1), contemporary rates have increased by at least four to fivefold. The statistical relationship between C ARFC and TP derived from this study (r2 = 0.5) can be used to estimate OC burial at sites lacking estimates of sediment C-burial. The implications of eutrophication, diagenesis, lake morphometry and sediment focussing as controls of OC burial rates are considered. A conservative interpretation of the results of the this study suggests that lowland European meso- to eutrophic lakes with >30 μg TP l-1 had OC burial rates in excess of 50 g C m-2 yr-1 over the past century, indicating that previous estimates of regional lake OC burial have seriously underestimated their contribution to European carbon sequestration. Enhanced OC burial by lakes is one positive side-effect of the otherwise negative impact of the anthropogenic disruption of nutrient cycles

Farming the Iveragh uplands: A tale of humans and nature

The rugged beauty of the Iveragh peninsula has fascinated many a passing visitor and never fails to make some of us linger or stay for good. For those who need proof of the area’s uniqueness, a variety of national and European designations provide ample attestation of the splendour of Iveragh’s scenery, the diversity of its landscape and its heritage. Being surrounded on three sides by the Atlantic, Iveragh is the largest and most geographically isolated peninsula in Ireland whose western extremity, the Great Skellig, forms the westernmost point of Europe. Despite its maritime location, Iveragh’s character is fundamentally determined by the mountains, valleys and streams that form the peninsula’s interior—the bequest of a landscape sculpted by ice thousands of years ago (Crowley and Sheehan, 2009). Distinctive mountain scene in the Bridia Valley, Glencar Perhaps most distinctive, however, are the extensive blanket bogs and upland heather moorlands that cover most of the peninsula and captivate the imagination with the wild and austere appeal of an area where life did not change much for man and beast until relatively recently. Having come into existence in the wake of woodland clearances, the cutting of vegetation for fuel and the harvesting of crops for food and fiber by Neolithic farmers in the first and second millennium BC, this unique cultural landscape continues to be managed by traditional farmers and their animals to the present day. The value of areas such as Iveragh as repositories of a unique flora and fauna has long been recognized, but they have entered a period of major transformation as the agricultural economy that lay behind them no longer exists (Webb, 1998). The single largest danger is that farming communities may not survive the present discussion of how competitive European agriculture should be, as under present market conditions they are unable to compete without fundamentally changing their way of farming (Luick, 1998). The last 10 years have seen a growing debate over the future of areas like the Iveragh peninsula that may be ‘marginal’ in agricultural terms, but that are quite essential to life in Europe as we know and cherish it. Upland farmed landscapes provide clean water, maintain a rich plant and animal life and help to keep families in regions that offer few alternative employment opportunities – at the same time as attracting millions of tourists each year. The Caragh in Glencar—one of Europe’s cleanest rivers. Such areas, also termed high nature value farmland, cover about 25% of all agricultural land in Ireland and include, besides Iveragh, other parts of Kerry, Connemara, Mayo, Donegal, the Comeraghs, Wicklow, the Burren and the offshore Islands. The farming systems of these areas are characterised by extensive mixed livestock grazing and little agro-chemical inputs combined with labour-intensive management practices. Without dedicated farmers and their families, the character of these areas would change completely leading to the disappearance of unique cultural landscapes with effects such as rural depopulation and the loss of local communities. Already farming systems have changed substantially with livestock being concentrated on better quality land while marginal areas are being abandoned. Along with this, there are changes in the animals being farmed. The traditional Scotch Blackface sheep are increasingly crossed with or replaced by lowland breeds to satisfy market demands for heavy lamb. This has led to a softening in sheep and the fear among farmers that the traditional grazers of the uplands may be extinct in years to come. Going, too, is the use of the native rustic Kerry cow that grazed the rough Farming the Iveragh Uplands grasses, bracken, gorse and soft rushes in the winter - growth that sheep cannot control. Unsurprisingly, this disruption over a relatively short time, in what was formerly a sustainable relationship between farming and nature, will have implications for the area’s flora and fauna. Some of the repercussions are obvious; others need to be researched in more depth if appropriate solutions are to be formulated. It is now a stated objective of EU environment and rural development policy to maintain and conserve traditional farming systems like the one practised on Iveragh. Beyond acknowledging the importance of traditional farming for nature conservation and local livelihoods, it is necessary to understand how such farming systems function and to determine how the inevitable process of change can be redirected to provide a way of life that is socially and economically rewarding for farm families while preserving the farming practices necessary for Iveragh’s unique landscape to persist into the future. In this light, University College Cork (UCC) in conjunction with the Environmental Research Institute (ERI) and funded by Science Foundation Ireland (SFI) initiated BioUp, a 3 year research programme to investigate the upland farming system and rich biodiversity associated with it. Managing rural change in the uplands calls for the active involvement of many stakeholders, including farmers and agricultural advisory groups, land owners, conservation groups, forestry, tourism, and local authorities. In the BioUp project, researchers and stakeholders worked closely together. It is hoped that this will help to obtain a better understanding of the social, economic and environmental challenges facing Iveragh and promote greater public appreciation of the indispensable contributions made by farm families to maintaining our unique heritage - a service that has gone unappreciated too long

The influence of climate change on the restoration trajectory of a nutrient-rich deep lake

Nutrient reduction in impacted lowland freshwater systems is ecologically and culturally important. Gaining a greater insight into how lakes respond to lowering nutrient loads and how climate-driven physical limnology affects present and future cycling of available nutrients is important for ecosystem resource management. This study examines the nutrient decline in a hypereutrophic freshwater lake (Rostherne Mere, Cheshire, UK) 25 years after sewage effluent diversion, a uniquely long-term analysis of a recovering nutrient-rich deep lake. Using nutrient, phytoplankton, climate and catchment hydrological monitoring, the contemporary lake system is compared to previous studies from 1990 to 2002. Nutrient change since point source load diversion showed annual average and maximum phosphorus (P) concentrations decreased significantly for the first 10 years (1992: ~ 600 µg P L−1; 2002: ~ 200 µg P L−1), but have since stabilised due to a substantial legacy sediment P internal load. Dissolved inorganic nitrogen (DIN) concentrations have not substantially changed since diversion, resulting in the alteration of the DIN/SRP ratio from a system characterised by N limitation (N:P ~ 5), to one predominantly P limited (N:P > 20). Nutrient changes over this time are shown to drive ecological change, especially in the cyanobacterial and algal communities. Furthermore, very high-resolution monitoring of lake inflow and outflow (every 5 min during 2016) shows that water residence time at this lake is significantly shorter than previously estimated (~ 0.8 years compared to previous estimates of ~ 1.6–2.4 years). Together with long-term data demonstrating that the stratification period at Rostherne Mere has increased by 40 days over the last ~ 50 years (due to later autumnal mixing), we show that a rapid rate of epilimnetic flushing together with a long stratification period substantially reduces the available epilimnetic P during the summer cyanobacterial bloom. This is of growing importance for many such lakes, given widespread climate-driven lengthening of stratification and a national trend of decreasing summer rainfall (decreasing seasonal flushing) but more intense summer storm events (resulting in short-term flushing events).</div

The landscape–atmosphere continuum determines ecological change in alpine lakes of SE Tibet

© 2017 Springer Science+Business Media, LLC Remote alpine regions were considered to be largely unimpacted by anthropogenic disturbance, but it is now clear these areas are changing rapidly. It is often difficult to identify the causal processes underpinning ecological change because the main drivers (direct and indirect climate forcing, land use change and atmospheric deposition) are acting simultaneously. In addition, alpine landscapes are morphometrically complex with strong local environmental gradients creating natural heterogeneity which acts as a variable filter to climate and anthropogenic forcing, emphasizing the need for analyzing responses at multiple sites. The eastern margin of Tibet is a hotspot of global biodiversity and is affected by both atmospheric N and dust deposition, whereas regional climate warming is comparatively recent. Here we use 210 Pb and 137 Cs dated sediment records from nine alpine lakes, and statistical measures of diatom ecological change (turnover and PCA axis 1 scores) to determine regional scale patterns in community response to global environmental change forcing over approximately the last 150 years. The study lakes showed contrasting ecological responses with increased nutrient input as the primary driver of change, mediated by lake morphology and catchment characteristics. Turnover rates of diatom composition, although low, are significantly associated with lake volume, lake area, altitude and DOC

The SDSS-2MASS-WISE Ten Dimensional Stellar Color Locus

We present the fiducial main sequence stellar locus traced by 10 photometric colors observed by SDSS, 2MASS, and WISE. Median colors are determined using 1,052,793 stars with r-band extinction less than 0.125. We use this locus to measure the dust extinction curve relative to the r-band, which is consistent with previous measurements in the SDSS and 2MASS bands. The WISE band extinction coefficients are larger than predicted by standard extinction models. Using 13 lines of sight, we find variations in the extinction curve in H, Ks, and WISE bandpasses. Relative extinction decreases towards Galactic anti-center, in agreement with prior studies. Relative extinction increases with Galactic latitude, in contrast to previous observations. This indicates a universal mid-IR extinction law does not exist due to variations in dust grain size and chemistry with Galactocentric position. A preliminary search for outliers due to warm circumstellar dust is also presented, using stars with high signal-to-noise in the W3-band. We find 199 such outliers, identified by excess emission in Ks-W3. Inspection of SDSS images for these outliers reveals a large number of contaminants due to nearby galaxies. Six sources appear to be genuine dust candidates, yielding a fraction of systems with infrared excess of 0.12$\pm$0.05%.Comment: 11 pages, 10 figures, MNRAS Accepted. Tables 1 and 2 available online: https://github.com/jradavenport/wise_locu

The historical dependency of organic carbon burial efficiency

Many studies have viewed lakes as quasi-static systems with regard to the rate of organic carbon (OC) burial, assuming that the dominant control on BE is sediment mineralization. However, in systems undergoing eutrophication or oligotrophication (i.e., altered nutrient loading), or climatic forcing, the changes in primary production will vary on both longer (> 10 yr) and shorter (seasonal) timescales, influencing the rate of OC accumulation and subsequent permanent burial. Here, we consider the extent to which permanent OC burial reflects changing production in a deep monomictic lake (Rostherne Mere, UK) that has been culturally eutrophied (present TP>200 μg L-1), but has undergone recent reductions in nutrient loading. We compare multi-year dynamics of OC fluxes using sediment traps to longer-term burial rates estimated from two 210Pb-dated sediment cores. The recent sediment record demonstrates that most of the autochthonous OC is preserved (∼95% of OC captured in the deep trap and 86% of the NEP in the contemporary system), contrary to widely held assumptions that this more labile, algal-dominated OC component is not well preserved in lake sediments. A revised method for calculating BE for lakes which have undergone changes in primary productivity in recent decades is developed, which reduces some of problems inherent in existing approaches using historical sediment records averaged over the last 25-150 yr. We suggest that an appreciation of lakes in all biomes as ecosystems responding dynamically to recent human impact and climate change (for example) can improve up-scaled regional and global estimates of lake OC burial