Locations In Lake Research Articles

Survival of cabomba (Cabomba caroliniana) during lake drawdown within mounds of stranded vegetation

Control of submerged aquatic vegetation during drawdown is known to be hindered by mounds of stranded vegetation that protect underlying stems from desiccation. This study investigated the viability of stranded cabomba (Cabomba caroliniana) during a winter drawdown of Lake Benalla, Victoria, Australia. The viability of stems and crowns, determined by their ability to generate new shoots, was related to substrate exposure status, location in lake, mound height, and soil moisture, at 34 and 69 days after exposure (DAE). Stem viability at 34 and 69 DAE was most closely associated with exposure status, where ∼20% of stems under mounds on relatively dry substrate were viable, compared to ∼95% of stems under mounds on saturated substrate, and 92% of unexposed stems. Stem viability was similar when collected 34 and 69 DAE and was similar under naturally occurring mounds of differing thickness. In contrast, viability of exposed crowns was usually 40% or less, compared to 72% for unexposed crowns, and their viability was not influenced by substrate moisture. Instead, their viability was influenced by location in the lake and was proportional to mound thickness. Like stems, viability of crowns did not decrease over the duration of the drawdown. We concluded that for drawdown to be effective in minimizing viable stems, the substrate below them needs to dry out. Even then, viable crowns may be a source of recolonization.

Simulating the growth of supraglacial lakes at the western margin of the Greenland ice sheet

Abstract. We present a new method of modelling the growth of supraglacial lakes at the western margin of the Greenland ice sheet, based on routing runoff estimated by a regional climate model across a digital elevation model (DEM) of the ice sheet surface. Using data acquired during the 2003 melt season, we demonstrate that the model is 19 times more likely to correctly predict the presence (or absence) of lakes than it is to make incorrect predictions, within an elevation range of 1100 to 1700 metres above sea level (m a.s.l.), when compared with MODIS satellite imagery. Of the 66% of observed lake locations which the model correctly reproduces, the simulated lake onset day is found to be correlated with that observed with a Pearson correlation coefficient of 0.76. Our model accurately simulates maximum cumulative lake area with only a 1.5% overestimate. However, because our model does not simulate processes leading to lake stagnation or decay, such as refreezing or drainage, at present we do not simulate absolute daily lake area. We find that the maximum potential lake-covered ice sheet area is limited by topography to 6.4%. We estimate that this corresponds to a volume of 1.49 km3, 12% of the runoff produced in 2003. This can be taken as an upper bound given uncertainty in the DEM. This study has proved a good first step towards capturing the variability of supraglacial lake evolution with a numerical model. These initial results are promising and suggest that the model is a useful tool for use in analysing the behaviour of supraglacial lakes on the Greenland ice sheet in the present day and potentially beyond.

Low Prevalence of Cyprinid Herpesvirus 3 Found in Common Carp (Cyprinus carpio carpio) Collected from Nine Locations in the Great Lakes

Cyprinid herpesvirus 3 (CyHV3) is a viral disease of fish first detected in the United States in 1998. Since that time, mortality events in common carp (Cyprinus carpio carpio) have occurred in several locations within the Great Lakes basin, but not within the Great Lakes themselves. We sampled 675 carp from 20 sites across the Great Lakes and Lake St. Clair, Michigan, USA, between 19 July and 26 September 2010. We tested the gill and a pooled internal organ sample from each fish for CyHV3 with the use of a quantitative polymerase chain reaction (qPCR) assay. Virus was detected in 18 fish from nine sites in four lakes (Lakes Michigan, Huron, St. Clair, and Ontario). Tissues from these 18 fish were also tested for CyHV3 with the use of the PCR assay recommended by the World Organization for Animal Health; amplification was achieved from two fish and confirmation by sequencing of CyHV3 from one fish collected in Lake St. Clair. The results of this study suggest that CyHV3 is present in the Great Lakes.

Observations of Titan’s Northern lakes at 5 μm: Implications for the organic cycle and geology

Since Titan entered Northern spring in August 2009, the North Pole has been illuminated allowing observations at optical wavelengths. On June 5, 2010 the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft observed the Northern Pole area with a pixel size from 3 to 7km. Since, as we demonstrate, little of the solar flux at 5μm is scattered by the atmosphere, these observations were obtained at relatively large incidence angles and allowed us to build a mosaic covering an area of more than 500,000km2 that overlaps and complements observations made by the Synthetic Aperture Radar (SAR) in 2007. We find that there is an excellent correlation between the shape of the radar dark area, known as Ligeia Mare and the VIMS 5-μm dark unit. Matching most of the radar shoreline, the 2010 VIMS observations suggest that the 125,000-km2 surface area of Ligeia Mare measured by RADAR in 2007 has not significantly changed. The VIMS observations complement the radar observations to the west of Ligeia Mare and suggest that Ligeia Mare is connected to Kraken Mare by either a diffuse network similar to a swamp area, or by well-defined, sub-pixel rivers. Considering the results of recent evaporation models of methane, our preferred interpretation of the relative constancy in surface area of Ligeia is that it is principally composed of ethane although we cannot rule out the possibility that methane evaporation is balanced with replenishment by either precipitation or underground seepage. There is also strong correlation between the location of the small radar lakes and the small VIMS 5-μm dark patches. The geographic location of the small lakes are within a VIMS pixel of the SAR location, suggesting that the non-synchronous component of Titan’s spin rate, if it exists, was less than 2.3×10−4deg/day between 2007 and 2010 in agreement with the recent T64 radar observations. These observations question the existence of non-synchronous rotation. Two radar-bright features appear dark at 5-μm. The simplest interpretation is that these are very shallow lakes, less than one meter deep. Three new small lakes, named Freeman, Cardiel, and Towada by the IAU, are found outside of the area mapped with the SAR. A single-scattering model describing reflection of sunlight at 5-μm suggests that the lake surface is mirror-like and that the albedo of the solid surfaces surrounding the lakes is about 8%. These observations together with information of the haze aerosols allow us to show that Titan’s lakes, atmospheric ethane and aerosol haze are smaller carbon reservoirs than Titan’s sand dunes and atmospheric methane. A simple model involving an outburst of methane a few hundreds of Myr ago followed by the dissociation of methane in the atmosphere leading to the formation of the haze particles that constitute the dune fields would be consistent with both the present observations and recent measurements of isotopic ratios in atmospheric methane (Mandt, K.E. et al. [2012]. Astrophys. J. 749(160), 14).

Assessment of chemical and mineralogical characteristics of airborne dust in the Sistan region, Iran

Windblown transport and deposition of dust is widely recognized as an important physical and chemical concern to climate, human health and ecosystems. Sistan is a region located in southeast Iran with extensive wind erosion, severe desertification and intense dust storms, which cause adverse effects in regional air quality and human health. To mitigate the impact of these phenomena, it is vital to ascertain the physical and chemical characteristics of airborne and soil dust. This paper examines for the first time, the mineralogical and chemical properties of dust over Sistan by collecting aerosol samples at two stations established close to a dry-bed lake dust source region, from August 2009 to August 2010. Furthermore, soil samples were collected from topsoil (0–5cm depth) at several locations in the dry-bed Hamoun lakes and downwind areas. These data were analyzed to investigate the chemical and mineralogical characteristics of dust, relevance of inferred sources and contributions to air pollution. X-ray Diffraction (XRD) analysis of airborne and soil dust samples shows that the dust mineralogy is dominated mainly by quartz (30–40%), calcite (18–23%), muscovite (10–17%), plagioclase (9–12%), chlorite (∼6%) and enstatite (∼3%), with minor components of dolomite, microcline, halite and gypsum. X-ray Fluorescence (XRF) analyses of all the samples indicate that the most important oxide compositions of the airborne and soil dust are SiO2, CaO, Al2O3, Na2O, MgO and Fe2O3, exhibiting similar percentages for both stations and soil samples. Estimates of Enrichment Factors (EFs) for all studied elements show that all of them have very low EF values, suggesting natural origin from local materials. The results suggest that a common dust source region can be inferred, which is the eroded sedimentary environment in the extensive Hamoun dry lakes lying to the north of Sistan.

First occurrence of the Ponto-Caspian amphipod Echinogammarus trichiatus (Martynov, 1932) (Crustacea: Gammaridae) in Belgium

The Ponto-Caspian amphipod species Echinogammarus trichiatus (Martynov, 1932) was found in Belgium for the first time in June 2009 at two different locations in an artificial lake bordered by two large canals. Adults as well as juveniles were found in small numbers and occurred together with several other Ponto-Caspian species such as Dikerogammarus villosus (Sowinsky, 1894) and Dreissena polymorpha (Pallas, 1771). An identification key to the genus Echinogammarus of inland waters in Western Europe is provided. This first record of yet another new amphipod invader in Belgium demonstrates the continuous introduction of alien species into West European waters.

High Bacterial Diversity in Epilithic Biofilms of Oligotrophic Mountain Lakes

Benthic microbial biofilms attached to rocks (epilithic) are major sites of carbon cycling and can dominate ecosystem primary production in oligotrophic lakes. We studied the bacterial community composition of littoral epilithic biofilms in five connected oligotrophic high mountain lakes located at different altitudes by genetic fingerprinting and clone libraries of the 16S rRNA gene. Different intra-lake samples were analyzed, and consistent changes in community structure (chlorophyll a and organic matter contents, and bacterial community composition) were observed along the altitudinal gradient, particularly related with the location of the lake above or below the treeline. Epilithic biofilm genetic fingerprints were both more diverse among lakes than within lakes and significantly different between montane (below the tree line) and alpine lakes (above the tree line). The genetic richness in the epilithic biofilm was much higher than in the plankton of the same lacustrine area studied in previous works, with significantly idiosyncratic phylogenetic composition (specifically distinct from lake plankton or mountain soils). Data suggest the coexistence of aerobic, anaerobic, phototrophic, and chemotrophic microorganisms in the biofilm, Bacteroidetes and Cyanobacteria being the most important bacterial taxa, followed by Alpha-, Beta-, Gamma-, and Deltaproteobacteria, Chlorobi, Planctomycetes, and Verrucomicrobia. The degree of novelty was especially high for epilithic Bacteroidetes, and up to 50% of the sequences formed monophyletic clusters distantly related to any previously reported sequence. More than 35% of the total sequences matched at <95% identity to any previously reported 16S rRNA gene, indicating that alpine epilithic biofilms are unexplored habitats that contain a substantial degree of novelty within a short geographical distance. Further research is needed to determine whether these communities are involved in more biogeochemical pathways than previously thought.

Vertical and temporal variability in concentration and distribution of thaumarchaeotal tetraether lipids in Lake Superior and the implications for the application of the TEX86 temperature proxy

This study investigated the vertical and temporal distribution of Thaumarchaeota derived core isoprenoid glycerol dialkyl glycerol tetraether (GDGT) lipids through sampling and analysis of both suspended particulate matter from the water column at different times in the annual cycle and a 3year long record of settling particles in two sediment traps at different depths at an open lake location in Lake Superior. Results from these analyses suggest that Thaumarchaeota were present throughout the water column during times of overturning, but mainly resided below the depth of the thermocline (20–40m) during the period of thermal stratification. Fluxes of thaumarchaeotal produced GDGTs were highly periodic and mainly occurred during two periods of the annual cycle (winter and late spring/early summer). A covariance of both branched and isoprenoid GDGT fluxes with the mass accumulation flux combined with the observation that those periods of maximum fluxes were associated with increased BIT index values, however, suggest that these two periods of elevated fluxes may be related to an influx of resuspended particles transported from shallower near shore regions of Lake Superior. During all sampling periods TEX86 inferred temperatures from SPM were in good agreement with in situ water temperatures of the depths at which the SPM was sampled. The observed range of TEX86 inferred temperatures in 3years of settling particles is relatively small and does not show significantly higher inferred temperatures during the thermally stratified period, indicating that the sedimentary TEX86 signal during the summer thermally stratified period mainly originated from depths below the relatively shallow thermocline. Additionally, TEX86 values during the winter period of increased fluxes did not capture the decrease in water temperatures observed throughout the water column during this period, and thus may be a further indication that the thaumarchaeotal lipid flux was the result of sediment focusing. Flux-weighted TEX86 inferred temperatures from both sediment traps were in good agreement with TEX86 temperatures from surface sediments from the same location in Lake Superior. Both flux weighted TEX86 temperatures from the sediment traps and average TEX86 temperatures from surface sediments were similar to averaged measured water temperatures at below ∼40m depth within the error of the lacustrine TEX86 calibration. Based on the observed depths of Thaumarchaeota in the water column, TEX86 values in sediments of Lake Superior likely reflect a combination of mixed-season and sub-thermocline temperatures. This is effectively the same as the annual averaged water temperature observed at depths below 40m in Lake Superior. Thus, trends in TEX86 inferred temperatures in sediment records of Lake Superior, and similar lakes, are likely to reflect subsurface temperature variability rather than that of surface temperatures.

Low dissolved ions may limit secondary invasion of inland waters by exotic round gobies and dreissenid mussels in North America

Round gobies and dreissenid mussels, exotic species in the North American Great Lakes basin, are euryhaline organisms whose geographic spread and ecological impacts in freshwaters may be limited by low levels of dissolved ions such as calcium (Ca). We measured source populations of these exotics in the St. Lawrence River and found population densities of dreissenids (range of ~1,000–6,400 individuals m−2) and round gobies (6–32 individuals m−2) similar to those in other Great Lake locations from which they have spread inland. However, we found little evidence for their secondary invasion of inland tributary rivers and lakes of northern New York State. Using natural waters collected from inland ecosystems, we ran laboratory bioassays of reproduction, growth, and survival of several life stages of zebra and quagga mussels as well as the round goby. We found little difference in the responses of zebra and quagga mussels, with each species showing moderate reproductive success, growth, and survival at Ca concentrations > 13 mg L−1 and dramatic improvements at >18 mg L−1. Round gobies showed moderate survival in waters with Ca concentrations > 8 mg L−1 and high survival > 18 mg L−1. These bioassays are the first such experiments for quagga mussels and round gobies and show how all three species may be similarly restricted in their ability to invade and permanently colonize significant geographic regions of New York State and perhaps the US.

K 0-prompt gamma ray activation analysis for estimation of boron and cadmium in aqueous solutions

K 0-PGAA (prompt gamma activation analysis) has been used to estimate boron and cadmium contents in industrial and environmental materials from some different local areas as well as, samples from different locations in Burullus and Qarun Lakes. A high efficiency Compton background suppression gamma-ray spectrometry by anti-coincidence counting with a NaI(Tl) shield around a central HPGe detector for in beam PGAA using a 252Cf neutron source has been calibrated and described in this paper. The facility is principally designed for measurement of the prompt gamma-ray spectra obtained due to thermal neutron capture using 1951.14 keV gamma line of 35Cl as the internal mono-standard comparator. A calibration curves were developed in which a set of boron and cadmium standards were tested and the count rate to boron and cadmium mass curves were determined. This set of boron and cadmium measurements was compared with a method for determining composition using K 0-PGAA. Conventional prompt neutrons capture Gamma-ray results were in a good agreement with the data obtained by K 0-PGAA method. Detection limits and self-shielding study are presented.

Rapid climate change from north Andean Lake Fúquene pollen records driven by obliquity: implications for a basin-wide biostratigraphic zonation for the last 284 ka

This paper compares a new super-high resolution pollen record from a central location in Lake Fúquene (4°N) with 3 pollen records from marginal sites from the same lake basin, located at 2540 m elevation in the Eastern Cordillera of Colombia. We harmonized the pollen sum of all records, and provided previously published records of climate change with an improved age model using a new approach for long continental pollen records. We dissociated from subjective curve matching and applied a more objective procedure including radiocarbon ages, cyclostratigraphy, and orbital tuning using the new 284 ka long Fúquene Basin Composite record (Fq-BC) as the backbone ( Groot et al., 2011). We showed that a common ∼9 m cycle in the arboreal pollen percentage (AP%) records reflects obliquity forcing and drives vegetational and climatic change. The AP% records were tuned to the 41 kyr component filtered from standard benthic δ 18O LR04 record. Changes in sediment supply to the lake are reflected in concert by the four records making frequency analysis in the depth domain an adequate method to compare records from the same basin. We calibrated the original 14C ages and used where necessary biostratigraphic correlation, i.e. for records shorter than one obliquity cycle. Pollen records from the periphery of the lake showed changes in the abundance of Alnus and Weinmannia forests more clearly while centrally located record Fq-9C shows a more integrated signal of regional vegetation change. The revised age models show that core Fq-2 reflects the last 44 ka and composite record Fq-7C the last 85.5 ka. Marginally located core Fq-3 has an age of 133 ka at 32 m core depth and the lowermost 11 m of sediments appear of older but unknown age. The longest record Fq-BC shows ∼60 yr resolution over the period of 284-27 ka. All pollen records are in support of a common regional vegetation development leading to a robust reconstruction of long series of submillennial climate oscillations reflecting Dansgaard–Oeschger (DO) cycles. Reconstructed climate variability in the tropical Andes since marine isotope stage (MIS) 8 compares well with NGRIP (δ 18O based), Epica Dome C (δD based) and the Mediterranean sea surface temperature record MD01-2443/44 (U K′37 based) underpinning the global significance of the climate record from this tropical Andean lake. A basin-wide biostratigraphy is presented and we concluded although with varying robustness that each core is representative of regional vegetational and climatic change.

Mercury and other heavy metals in free-ranging mink of the lower Great Lakes basin, Canada, 1998–2006

Mercury concentrations were examined in livers of free-ranging mink (Neovison vison) trapped in the lower Great Lakes basin from 1998 to 2006. Significant geographic variation in total mercury levels was found in mink from 13 Great Lakes locations, many of which are within Great Lakes Areas of Concern (AOCs). Total mercury levels in mink from these locations were generally low to moderate, with means (±SE) ranging from 0.99 (±0.36) μg/g dry weight in mink from inland Lake Erie to 7.31 (±1.52) μg/g in mink from Walpole Island in the St. Clair River AOC. Overall, mercury exposure was highest in mink trapped in locations associated with large riverine wetlands. Total mercury concentrations were negatively related to the percentage of mercury present as methylmercury and positively related to selenium concentrations, consistent with increasing demethylation of methylmercury with increasing total mercury concentrations. One-year old mink had significantly higher levels of mercury and selenium than mink under 1 year but similar to mink 2 years of age and older. Mercury levels were below those associated with mercury toxicity. Concentrations of cadmium, lead and arsenic were low and largely associated with environmental background levels. Significant age and sex effects were found for cadmium. Lead levels were significantly lower in mink infected by the lung nematode parasite compared to uninfected animals. Further studies of biomagnification of methylmercury in wetland environments, where top predators such as mink may be an increased risk of exposure, are warranted.

Improved prediction of vegetation composition in NW European softwater lakes by combining location, water and sediment chemistry

Isoetids, as indicators of near-pristine softwater lakes, have a high priority in national and international (European Water Directive Framework) assessments of ecological lake quality. Our main goal was to identify the most important environmental factors that influence the composition of plant communities and specifically determine the presence and abundance of the isoetid Lobelia dortmanna in NW European softwater lakes. Geographical position and composition of surface water, porewater, sediment and plant communities were examined in 39 lakes in four regions (The Netherlands, Denmark, West Norway and East Norway) distributed over a 1,200-km long distance. We confirmed that lake location was accompanied by significant changes in environmental variables between NW European lakes. Lake location was the single most important determinant of vegetation composition and it had significant individual contributions independent of the coupling to environmental variables. This influence of location was supported by a significant decline of community similarity with geographical distance between pairs of lakes at regional, inter-regional and international scales. Combining the geographical position with environmental variables for surface water, porewater and sediment significantly improved prediction of vegetation composition. Specifically, the combination of latitude, surface water alkalinity, porewater phosphate and redox potential offered the highest correlation (BIO ENV correlation 0.66) to vegetation composition. This complex analysis can also account for high sediment variability in the littoral zone of individual lakes, by using site-specific physico-chemical sediment factors, and offer better predictions of vegetation composition when lake water chemistry is relatively homogeneous among lakes within regions.

Age, Growth, Maturity, and Fecundity of Yellowstone Lake Cutthroat Trout

Abstract Demographic data are sparse for Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri; YCT). Data for YCT in the spawning run (spring; 29 years) of a Yellowstone Lake tributary or caught in gill nets set (fall; 30 years) at established lake locations between 1977 and 2007 were examined. Female proportion in runs averaged 0.61 but was 0.48 among gillnetted “prespawner” YCT (i.e., mature fish whose excised gonads indicated the fish would have spawned the next year). Maturity proportion-total length (TL) relationships for gillnetted female and male YCT were logistic-shaped and similar in their inflection points; maturity onset occurred at 200–250 mm TL; ∼95% of YCT ≥ 400 mm TL were mature and ∼70% were prespawners. Fecundity was positively associated with YCT TL. Accuracy of scale-based YCT ages was affected by a frequently overlooked scale annulus and an inability to unequivocally identify fish of a single cohort on the basis of scale characteristics using associated, recognized ageing criteri...

Distribution and morphometry of shallow lakes in a temperate zone (Buenos Aires Province, Argentina)

We have developed a database of water bodies to characterise and assess the distribution and morphometry ofPampean shallow lakes and reservoirs in a temperate zone (Buenos Aires Province, Argentina). In the study area, there are over 2000 shallow lakes with a mean area <1 km2. The spatial variation in the shallow lakes studied is related to alternating periods of different hydrological conditions and the flatness of the Pampean landscape. The aim of this research is both to establish a cJassification system for the shallow lakes in the studied area and to evaluate the influence of rainfall regime on their morphometry. This classification system will provide a typological reference against which the ecological state of waters can be assessed. The spatial distribution, morphometry and changes in the size of the shallow lakes in southern Buenos Aires were studied during two periods: a normal (a year with average rainfaJl) and a wet year. A Geographic Information System (GIS) as well as satellite imaging and Digital Elevation Model (DEM) data were used to caJculate the morphometry of the shaJlow lakes and observe changes over time. Based on c1imatic criteria, geomorphology, soils and hydrology, four groups of lakes were identified: 1) plain and plateau lakes (constituting the highest proportion of circular shallow lakes), 2) artificial lakes (a category constituted solely of the only water reservo ir in the studied area), 3) coastal plain lakes characterised by a Coastal Line Development (CLD) 2. In the last two cases, geomorphology determines the morphometry and location of these shalJow lakes. The development of numerous water bodies with areas <1 km2 caused a significant increase in the number of water bodies during the wet year. The areal coverage and density of lakes is lowest in the western plateau zones, low near the hiJls, moderate in the centre of the study area and high in the eastern plains.

The impact of environmental change on medieval settlement structure in Transdanubia

The large-scale archaeological excavations of the past years yielded a rapid increase of archaeological finds and observations. This large amount of new evidence enabled the observation of wider environmental archaeological relationships. In the study we reconstruct certain environmental and settlement pattern changes from the 13th to the 18th centuries based on archaeological data from the southern shore of Lake Balaton and the cities of the Danube Bend region. The settlements on the shore of Lake Balaton and along the Danube reacted similarly, but with a temporal lag. Hydroclimatic changes caused a shift in the location and structure of lake- and riverside settlements, which was of a horizontal character in the case of Lake Balaton, and of a vertical character in the case of the Danube Bend region.

Assessing the toxicity of ingested Taihu Lake water on mice via hepatic histopathology and matrix metalloproteinase expression

Water from Taihu Lake (China) is used as a drinking source. The frequency of contamination in Taihu Lake has increased over the past decade and the bloom-forming cyanobacteria are the dominant species during eutrophication. Cyanobacteria can produce various harmful secondary substances including microcystins capable of endangering human health and ecological safety. This study investigated toxicity of ingested Taihu Lake water on mice via hepatic histopathology and matrix metalloproteinase (MMP) expression. Water was sampled from four Taihu Lake locations, Meiliang Bay 2 group (M2), Meiliang Bay 1 group (M1), Lake Center (H) and Xukou Bay (X), along a gradient of decreasing degree of eutrophication. The experimental design consists of five groups of male mice (Mus musculus, ICR): one control and four groups ingesting water from the four sampling sites for 90 days. Compared to control, M1 and M2 mice showed hepatic histopathological changes including swollen, vacuolar degeneration or inflammatory. Immunohistochemical staining demonstrated a higher expression of MMP-2 proteins in M2 group and a lower expression of MMP-9 in M1. Enzyme-linked immunosorbent assay indicated that MMP-9 concentration was significantly reduced from 0.55 to 0.28 ng/g liver weight in M2 (p < 0.05). Real time PCR revealed a down-regulation of MMP-9 mRNA by 2.2 fold in M1 and an up-regulation of MMP-2 mRNA by 1.73 fold in H. Using this mouse model as a gauge of water toxicity, our results revealed that potential health risks induced by Taihu Lake water might arise from the use of this source water by local resident.

Water hyacinth (Eichhornia crassipes) and water lettuce (Pistia stratiotes) in the Great Lakes: playing with fire?

The Laurentian Great Lakes have been successfully invaded by at least 182 nonindigenous species. Here we report on two new species, water hyacinth Eichhornia crassipes and water lettuce Pistia stratiotes, that were found at a number of locations in Lake St. Clair and Detroit River during autumn 2010. Both species are commonly sold in the water garden and aquarium trade in southern Ontario and elsewhere. While it is not clear whether these species are established or can establish in the Great Lakes, the historic assumption that neither of these subtropical to tropical plants pose an invasion risk must be questioned in the light of changing environmental conditions associated with climate warming that may render Great Lakes’ habitats more suitable for these species and increase the likelihood of their successful establishment.

The effect of a dynamic background albedo scheme on Sahel/Sahara precipitation during the mid-Holocene

Abstract. We have implemented a new albedo scheme that takes the dynamic behaviour of the surface below the canopy into account, into the land-surface scheme of the MPI-ESM. The standard (static) scheme calculates the seasonal canopy albedo as a function of leaf area index, whereas the background albedo is a gridbox constant derived from satellite measurements. The new (dynamic) scheme additionally models the background albedo as a slowly changing function of organic matter in the ground and of litter and standing dead biomass covering the ground. We use the two schemes to investigate the interactions between vegetation, albedo and precipitation in the Sahel/Sahara for two time-slices: pre-industrial and mid-Holocene. The dynamic scheme represents the seasonal cycle of albedo and the correspondence between annual mean albedo and vegetation cover in a more consistent way than the static scheme. It thus gives a better estimate of albedo change between the two time periods. With the introduction of the dynamic scheme, precipitation is increased by 30 mm yr−1 for the pre-industrial simulation and by about 80 mm yr−1 for the mid-Holocene simulation. The present-day dry bias in the Sahel of standard ECHAM5 is thus reduced and the sensitivity of precipitation to mid-Holocene external forcing is increased by around one third. The locations of mid-Holocene lakes, as estimated from reconstructions, lie south of the modelled desert border in both mid-Holocene simulations. The magnitude of simulated rainfall in this area is too low to fully sustain lakes, however it is captured better with the dynamic scheme. The dynamic scheme leads to increased vegetation variability in the remaining desert region, indicating a higher frequency of green spells, thus reaching a better agreement with the vegetation distribution as derived from pollen records.

Regional genetic subdivision in the Mohave ground squirrel: evidence of historic isolation and ongoing connectivity in a Mojave Desert endemic

AbstractThe Mojave Desert is characterized by a unique biodiversity and is an area of particular interest for the development of renewable energy facilities, which could impact habitat quality and population connectivity. To begin understanding current habitat connectivity in a Mojave Desert endemic, we examine population genetic characteristics of the Mohave ground squirrel, Xerospermophilus mohavensis. We use microsatellite and mitochondrial data to examine the spatial distribution of genetic variation and to infer regional demographic history and connectivity across the species' range. We also examine the demographic history of individual populations and assess the degree to which X. mohavensis may be hybridizing with its sister species, Xerospermophilus tereticaudus. We find that populations of X. mohavensis group into three regionally defined genetic clusters with admixture among the groups. Patterns of regional genetic subdivision and inferred patterns of colonization are consistent with what would be expected from the location and timing of the historic lake and river systems of the region. On a more recent timescale, most X. mohavensis populations do not appear to have experienced genetic bottlenecks, as would be expected from known population declines. Finally, we find that hybridization between X. mohavensis and X. tereticaudus is limited, and thus, not a source of introgression into the threatened species. The patterns of diversity and regional connectivity that we describe here for the Mohave ground squirrel are a first step in determining critical conservation areas for endemic Mojave Desert fauna.