Diel surface temperature range scales with lake size

Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at Diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of Diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface Diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer Diel ranges in their near-surface temperatures of between 4 and 7°C. Large Diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored

Appendix: supplementary figures and tables from Established rodent community delays recovery of dominant competitor following experimental disturbance

Human activities alter processes that control local biodiversity, causing changes in the abundance and identity of species in ecosystems. However, restoring biodiversity to a previous state is rarely as simple as reintroducing lost species or restoring processes to their pre-disturbance state. Theory suggests that established species can impede shifts in species composition via a variety of mechanisms, including direct interference, preempting resources or habitat alteration. These mechanisms can create transitory dynamics that delay convergence to an expected end state. We use an experimental manipulation of a desert rodent community to examine differences in recolonization dynamics of a dominant competitor (kangaroo rats of the genus Dipodomys) when patches were already occupied by an existing rodent community relative to when patches were empty. Recovery of kangaroo rat populations was slow on plots with an established community, taking approximately 2 years, in contrast with rapid recovery on empty plots with no established residents (approx. three months). These results demonstrate that the presence of an established alternate community inhibits recolonization by new species, even those that should be dominant in the community. This has important implications for understanding how biodiversity may change in the future, and what processes may slow or prevent this change

Hierarchical Generalized Additive Models: an introduction with mgcv

This repository includes the code, data, documentation, metadata and figure source files that accompany this research

Hierarchical Generalized Additive Models: an introduction with mgcv

This repository includes the code, data, documentation, metadata and figure source files that accompany this research

DataSheet1_Seasonal variability of CO2, CH4, and N2O content and fluxes in small agricultural reservoirs of the northern Great Plains.docx

Inland waters are important global sources, and occasional sinks, of CO2, CH4, and N2O to the atmosphere, but relatively little is known about the contribution of GHGs of constructed waterbodies, particularly small sites in agricultural regions that receive large amounts of nutrients (carbon, nitrogen, phosphorus). Here, we quantify the magnitude and controls of diffusive CO2, CH4, and N2O fluxes from 20 agricultural reservoirs on seasonal and diel timescales. All gases exhibited consistent seasonal trends, with CO2 concentrations highest in spring and fall and lowest in mid-summer, CH4 highest in mid-summer, and N2O elevated in spring following ice-off. No discernible diel trends were observed for GHG content. Analyses of GHG covariance with potential regulatory factors were conducted using generalized additive models (GAMs) that revealed CO2 concentrations were affected primarily by factors related to benthic respiration, including dissolved oxygen (DO), dissolved inorganic nitrogen (DIN), dissolved organic carbon (DOC), stratification strength, and water source (as δ18Owater). In contrast, variation in CH4 content was correlated positively with factors that favoured methanogenesis, and so varied inversely with DO, soluble reactive phosphorus (SRP), and conductivity (a proxy for sulfate content), and positively with DIN, DOC, and temperature. Finally, N2O concentrations were driven mainly by variation in reservoir mixing (as buoyancy frequency), and were correlated positively with DO, SRP, and DIN levels and negatively with pH and stratification strength. Estimates of mean CO2-eq flux during the open-water period ranged from 5,520 mmol m−2 year1 (using GAM-predictions) to 10,445 mmol m−2 year−1 (using interpolations of seasonal data) reflecting how extreme values were extrapolated, with true annual flux rates likely falling between these two estimates.</p

Spatial variations in snowpack chemistry, isotopic composition of NO3−and nitrogen deposition from the ice sheet margin to the coast of western Greenland

© Author(s) 2018. The relative roles of anthropogenic nitrogen (N) deposition and climate change in causing ecological change in remote Arctic ecosystems, especially lakes, have been the subject of debate over the last decade. Some palaeoecological studies have cited isotopic signals (δ( 15 N)) preserved in lake sediments as evidence linking N deposition with ecological change, but a key limitation has been the lack of co-located data on both deposition input fluxes and isotopic composition of deposited nitrate (NO - 3 /. In Arctic lakes, including those in western Greenland, previous palaeolimnological studies have indicated a spatial variation in (δ 15 N) trends in lake sediments but data are lacking for deposition chemistry, input fluxes and stable isotope composition of NO - 3 . In the present study, snowpack chemistry, NO - 3 stable isotopes and net deposition fluxes for the largest ice-free region in Greenland were investigated to determine whether there are spatial gradients from the ice sheet margin to the coast linked to a gradient in precipitation. Late-season snowpack was sampled in March 2011 at eight locations within three lake catchments in each of three regions (ice sheet margin in the east, the central area near Kelly Ville and the coastal zone to the west). At the coast, snowpack accumulation averaged 181mm snow water equivalent (SWE) compared with 36mm SWE by the ice sheet. Coastal snowpack showed significantly greater concentrations of marine salts (NaC, Cl-, other major cations), ammonium (NH + 4 ; regional means 1.4.2.7 μmol L -1 ), total and non-sea-salt sulfate (SO 2- 4 ; total 1.8.7.7, non-sea-salt 1.0.1.8 μmol L -1 /than the two inland regions. Nitrate (1.5. 2.4 μmol L -1 /showed significantly lower concentrations at the coast. Despite lower concentrations, higher precipitation at the coast results in greater net deposition for NO - 3 as well as NH + 4 and non-sea-salt sulfate (nss-SO 2- 4 /relative to the inland regions (lowest at Kelly Ville 6, 4 and 3; highest at coast 9, 17 and 11 mol ha-1 a-1 of NO - 3 , NH + 4 and nss-SO 2- 4 respectively). The (δ 15 N) of snowpack NO - 3 shows a significant decrease from inland regions (-5.7‰ at Kelly Ville) to the coast (-11.3 ‰). We attribute the spatial patterns of (δ 15 N) in western Greenland to post-depositional processing rather than differing sources because of (1) spatial relationships with precipitation and sublimation, (2) withincatchment isotopic differences between terrestrial snowpack and lake ice snowpack, and (3) similarities between fresh snow (rather than accumulated snowpack) at Kelly Ville and the coast. Hence the (δ 15 N) of coastal snowpack is most representative of snowfall in western Greenland, but after deposition the effects of photolysis, volatilization and sublimation lead to enrichment of the remaining snowpack with the greatest effect in inland areas of low precipitation and high sublimation losses

Regional variability in the atmospheric nitrogen deposition signal and its transfer to the sediment record in Greenland lakes

Disruption of the nitrogen cycle is a major component of global environmental change. δ15N in lake sediments is increasingly used as a measure of reactive nitrogen input but problematically, the characteristic depleted δ15N signal is not recorded at all sites. We used a regionally replicated sampling strategy along a precipitation and N‐deposition gradient in SW Greenland to assess the factors determining the strength of δ15N signal in lake sediment cores. Analyses of snowpack N and δ15N‐NO3 and water chemistry were coupled with bulk sediment δ15N. Study sites cover a gradient of snowpack δ15N (ice sheet: −6‰; coast urn:x-wiley:00243590:media:lno10936:lno10936-math-000110‰), atmospheric N deposition (ice sheet margin: ∼ 0.2 kg ha−1 yr−1; coast: 0.4 kg ha−1 yr−1) and limnology. Three 210Pb‐dated sediment cores from coastal lakes showed a decline in δ15N of ca. urn:x-wiley:00243590:media:lno10936:lno10936-math-00021‰ from ∼ 1860, reflecting the strongly depleted δ15N of snowpack N, lower in‐lake total N (TN) concentration (∼ 300 μg N L−1) and a higher TN‐load. Coastal lakes have 3.7–7.1× more snowpack input of nitrate than inland sites, while for total deposition the values are 1.7–3.6× greater for lake and whole catchment deposition. At inland sites and lakes close to the ice‐sheet margin, a lower atmospheric N deposition rate and larger in‐lake TN pool resulted in greater reliance on N‐fixation and recycling (mean sediment δ15N is 0.5–2.5‰ in most inland lakes; n = 6). The primary control of the transfer of the atmospheric δ15N deposition signal to lake sediments is the magnitude of external N inputs relative to the in‐lake N‐pool

Variance and Rate-of-Change as Early Warning Signals for a Critical Transition in an Aquatic Ecosystem State: A Test Case From Tasmania, Australia

Critical transitions in ecosystem states are often sudden and unpredictable. Consequently, thereis a concerted effort to identify measurable early warning signals (EWS) for these important events. Aquaticecosystems provide an opportunity to observe critical transitions due to their high sensitivity and rapidresponse times. Using palaeoecological techniques, we can measure properties of time series data todetermine if critical transitions are preceded by any measurable ecosystem metrics, that is, identify EWS.Using a suite of palaeoenvironmental data spanning the last 2,400 years (diatoms, pollen, geochemistry, andcharcoal influx), we assess whether a critical transition in diatom community structure was preceded bymeasurable EWS. Lake Vera, in the temperate rain forest of western Tasmania, Australia, has a diatomcommunity dominated by Discostella stelligera and undergoes an abrupt compositional shift at ca. 820 cal yrBP that is concomitant with increased fire disturbance of the local vegetation. This shift is manifest as atransition from less oligotrophic acidic diatom flora (Achnanthidium minutissimum, Brachysira styriaca, andFragilaria capucina) to more oligotrophic acidic taxa (Frustulia elongatissima, Eunotia diodon, andGomphonema multiforme). We observe a marked increase in compositional variance and rate-of-change priorto this critical transition, revealing these metrics are useful EWS in this system. Interestingly, vegetationremains complacent to fire disturbance until after the shift in the diatom community. Disturbance taxa invadeand the vegetation system experiences an increase in both compositional variance and rate-of-change.These trends imply an approaching critical transition in the vegetation and the probable collapse of the localrain forest system.</p

Variance and Rate-of-Change as Early Warning Signals for a Critical Transition in an Aquatic Ecosystem State: A Test Case From Tasmania, Australia

Critical transitions in ecosystem states are often sudden and unpredictable. Consequently, thereis a concerted effort to identify measurable early warning signals (EWS) for these important events. Aquaticecosystems provide an opportunity to observe critical transitions due to their high sensitivity and rapidresponse times. Using palaeoecological techniques, we can measure properties of time series data todetermine if critical transitions are preceded by any measurable ecosystem metrics, that is, identify EWS.Using a suite of palaeoenvironmental data spanning the last 2,400 years (diatoms, pollen, geochemistry, andcharcoal influx), we assess whether a critical transition in diatom community structure was preceded bymeasurable EWS. Lake Vera, in the temperate rain forest of western Tasmania, Australia, has a diatomcommunity dominated by Discostella stelligera and undergoes an abrupt compositional shift at ca. 820 cal yrBP that is concomitant with increased fire disturbance of the local vegetation. This shift is manifest as atransition from less oligotrophic acidic diatom flora (Achnanthidium minutissimum, Brachysira styriaca, andFragilaria capucina) to more oligotrophic acidic taxa (Frustulia elongatissima, Eunotia diodon, andGomphonema multiforme). We observe a marked increase in compositional variance and rate-of-change priorto this critical transition, revealing these metrics are useful EWS in this system. Interestingly, vegetationremains complacent to fire disturbance until after the shift in the diatom community. Disturbance taxa invadeand the vegetation system experiences an increase in both compositional variance and rate-of-change.These trends imply an approaching critical transition in the vegetation and the probable collapse of the localrain forest system.</p

Data_Sheet_1_A westernized diet changed the colonic bacterial composition and metabolite concentration in a dextran sulfate sodium pig model for ulcerative colitis.docx

IntroductionUlcerative colitis (UC) is characterized by chronic inflammation in the colonic epithelium and has a blurred etiology. A western diet and microbial dysbiosis in the colon were reported to play a role in UC development. In this study, we investigated the effect of a westernized diet, i.e., increasing fat and protein content by including ground beef, on the colonic bacterial composition in a dextran sulfate sodium (DexSS) challenged pig study.MethodsThe experiment was carried out in three complete blocks following a 2×2 factorial design including 24 six-week old pigs, fed either a standard diet (CT) or the standard diet substituted with 15% ground beef to simulate a typical westernized diet (WD). Colitis was induced in half of the pigs on each dietary treatment by oral administration of DexSS (DSS and WD+DSS, respectively). Samples from proximal and distal colon and feces were collected.Results and discussionBacterial alpha diversity was unaffected by experimental block, and sample type. In proximal colon, WD group had similar alpha diversity to CT group and the WD+DSS group showed the lowest alpha diversity compared to the other treatment groups. There was a significant interaction between western diet and DexSS for beta diversity, based on Bray-Curtis dissimilarly. The westernized diet and DexSS resulted in three and seven differentially abundant phyla, 21 and 65 species, respectively, mainly associated with the Firmicutes and Bacteroidota phyla followed by Spirochaetota, Desulfobacterota, and Proteobacteria. The concentration of short-chain fatty acids (SCFA) was lowest in the distal colon. Treatment had a slight effect on the estimates for microbial metabolites that might have valuable biological relevance for future studies. The concentration of putrescine in the colon and feces and that of total biogenic amines was highest in the WD+DSS group. We conclude that a westernized diet could be a potential risk factor and an exacerbating agent for UC by reducing the abundance of SCFA-producing bacteria, increasing the abundance of pathogens such as Helicobacter trogontum, and by increasing the concentration of microbial proteolytic-derived metabolites in the colon.</p