Paleotemperature reconstruction in tropical Africa using fossil Chironomidae (Insecta: Diptera)

Fossil assemblages of chironomid larvae (non-biting midges) preserved in lake sediments are well-established paleothermometers in north-temperate and boreal regions, but their potential for temperature reconstruction in tropical regions has never before been assessed. In this study, we surveyed sub-fossil chironomid assemblages in the surface sediments of 65 lakes and permanent pools in southwestern Uganda (including the Rwenzori Mountains) and central and southern Kenya (including Mount Kenya) to document the modern distribution of African chironomid communities along the regional temperature gradient covered by lakes situated between 489 and 4,575 m above sea level (a.s.l). We then combined these faunal data with linked Surface-Water Temperature (SWTemp: range 2.1–28.1°C) and Mean Annual Air Temperature (MATemp: range 1.1–24.9°C) data to develop inference models for quantitative paleotemperature reconstruction. Here we compare and discuss the performance of models based on different numerical techniques [weighted-averaging (WA), weighted-averaging partial-least-squares (WA-PLS) and a weighted modern analogue technique (WMAT)], and on subsets of lakes with varying gradient lengths of temperature and other environmental variables. All inference models calibrated against MATemp have a high coefficient of determination ( r_\textjack² r_{\text{jack}}^{2}  = 0.81–0.97), low maximum bias (0.84–2.59°C), and low root-mean-squared error of prediction (RMSEP = 0.61–1.50°C). The statistical power of SWTemp models is generally weaker ( r_\textjack² r_{\text{jack}}^{2}  = 0.77–0.95; maximum bias 1.55–3.73°C; RMSEP = 1.39–1.98°C), likely because the surface-water temperature data are spot measurements failing to catch significant daily and seasonal variation. Models based on calibration over the full temperature gradient suffer slightly from the limited number of study sites at intermediate elevation (2,000–3,000 m), and from the presence of morphologically indistinguishable but ecologically distinct taxa. Calibration confined to high-elevation sites (>3,000 m) has poorer error statistics, but is less susceptible to biogeographical and taxonomic complexities. Our results compare favourably with chironomid-based temperature inferences in temperate regions, indicating that chironomid-based temperature reconstruction in tropical Africa can be achieved.     

Historical variability of subfossil chironomids (Diptera: Chironomidae) in three lakes impacted by natural and anthropogenic disturbances

In the eastern boreal forest of Quebec, Canada, harvesting strategies try to mimic the effects of fire on forest ecosystems, assuming that both disturbances have similar impacts. However impacts of both types of perturbations on lacustrine ecosystems, especially on chironomids (non-biting midges), are still poorly understood. The objectives of this study were to determine if logging and fire resulted in chironomid assemblages significantly different than pre-disturbance states and to see if the harvesting strategy (careful logging around advanced growth (CLAAG) and buffer zones) protect lakes from logging effects in the boreal forest. Three statistical tests were used to study the difference between pre- and post-disturbance assemblages: a principal component analysis (PCA), analysis of similarity (ANOSIM) and a non-metric multi-dimensional scaling (MDS) ordination. All statistical analyses suggested that fire did not have any effects on chironomid assemblages. The PCA analysis showed that two logging events in Lac aux Huards created chironomid assemblages slightly outside the pre-disturbance variability. However, ANOSIM showed that these differences were not significant at the 0.5% level of significance. These results suggest that the presence of a buffer zone probably limited the impacts of logging on lakes in this area.     

The Dynamics of Chironomidae (Insecta: Diptera) Assemblages in Response to Environmental Change during the past 700 years on Svalbard

The impact of recent natural and human-induced environmental change on chironomid faunas on Svalbard has been investigated. The modern chironomid fauna was studied from surface-sediment samples collected from 23 lakes in western Svalbard. A total of 18 taxa was found, of which three had not been recorded previously from Svalbard. The influence of water chemistry and physical variables on the distribution and abundance of the modern chironomid assemblages was investigated using correspondence analysis and multiple regression. The chironomid assemblages fall into four groups, which are primarily influenced by pH, nutrient concentrations, water temperature, and water depth. Sediment cores were taken from three lakes to investigate changes in chironomid assemblages over the last 700 years. At two of the sites there is evidence for a response to regional climatic change occurring about 200 years ago and may have been associated with the ‘Little Ice Age’. At the third site there is a response to local catchment changes, probably brought about, initially, by the establishment of a human settlement close to the lake 70 years ago, and subsequently, as a result of the abandonment of this settlement in 1988.     

A protocol for preparing subfossil chironomid head capsules (Diptera: Chironomidae) for stable isotope analysis in paleoclimate reconstruction and considerations of contamination sources

Several techniques are available to examine the isotopic composition of historic lake waters, providing data that can subsequently be used to examine environmental changes. A recently-developed technique is the stable oxygen isotope analysis of subfossil chironomid (Diptera: Chironomidae) head capsules (mostly chitin) preserved in lake sediments. This technique involves a high Temperature Conversion Elemental Analyzer (TC/EA), which has been a relatively recent addition to the suite of online peripherals for analyzing the stable isotopic composition of organic samples. The highly precise and accurate ¹⁸O/¹⁶O and D/H measurements obtainable using the TC/EA with samples in the microgram range make this instrumentation suitable for studying geochemical and biological processes. Preparation of organic samples for isotopic analysis typically requires first weighing each sample into silver/tin capsules. These capsules can introduce oxygen and hydrogen contamination (a “blank effect”), which is especially problematic for analysis of small organic samples (e.g. less than 100 μg). Here we tested tin and silver capsules from two manufacturers and a range of sizes to assess contamination to small organic samples on the TC/EA. We also assessed how a method for cleaning silver capsules affected our analysis of commercial chitin. In general, capsules made of silver have less detectible oxygen than those made of tin, and capsules from the two manufacturers varied in their detectible oxygen. There was no detectable H contamination from silver capsules. In addition to our empirical findings, we present a model demonstrating the influence that contaminant oxygen can have on the δ¹⁸O of small organic samples. Sample mass becomes an important issue for such analyses. In light of our findings, we recommend a minimum sample mass ≥50 μg (approximately 120 whole chironomid head capsules) on a TC/EA-IRMS (Delta^plus XP system). Finally, we present a detailed protocol for preparing and transferring chironomid head capsules into silver capsules that minimizes the influence of contaminant oxygen. This protocol provides the paleo-community with another potential method for reconstructing paleoenvironments.     

Surface sediment Chironomidae (Insecta: Diptera) distributions along an ecotonal transect in subarctic Fennoscandia: developing a tool for palaeotemperature reconstructions

We used multivariate statistical techniques to analyse the distributions of surface sediment chironomid assemblages with respect to surface-water temperature, and an additional set of 27 environmental variables, in 30 freshwater lakes of northern Fennoscandia. Our study transect spans boreal coniferous forest to subarctic tundra and includes a steep temperature gradient. Canonical correspondence analysis (CCA) with forward selection and associated Monte Carlo permutation tests revealed that there were statistically significant (P<0.05) relationships between chironomid distributions and two environmental variables, namely lakewater temperature and maximum lake depth. A constrained CCA with temperature as the only predictor variable suggested that the relationship between lakewater temperature and chironomid composition was sufficiently robust for developing a weighted-averaging (WA) based quantitative inference model that will allow palaeotemperature reconstructions using subfossil chironomid remains preserved in lake sediments.     

Chironomidae (Diptera) remains in surficial lake sediments from the Canadian Cordillera: analysis of the fauna across an altitudinal gradient

The altitudinal distribution of Chironomidae (Diptera) in the southern Canadian Cordillera was analyzed by means of head capsules preserved in surficial sediments of 30 lakes. Taxa characteristic of late-glacial deposits of southern, coastal British Columbia are extant at high elevations, particularly in the Rocky Mountains, and in large, deep, low-elevation lakes. Many chironomid taxa common at low elevations in the southern Canadian Cordillera were not found in alpine and upper subalpine lakes. These faunal differences are probably climatically related. The differences in fauna between high and low-elevation lakes parallel differences between arctic and temperate lakes.     

Midges of the genus Pseudodiamesa Goetghebuer (Diptera, Chironomidae): current knowledge and palaeoecological perspective

Larvae of the genus Pseudodiamesa Goetghebuer, which includes 12 described valid species and is divided by Makarchenko and Makarchenko (1999) into two species groups, Pseudodiamesa branickii group and Pseudodiamesa nivosa group, are widespread in lakes and running waters of cold, high-latitude and high-altitude areas of the Northern Hemisphere. Larval remains of the genus are often found in subfossil assemblages from these cold regions, but intra-genus morphotypes usually are not distinguished by palaeoecologists. Current knowledge of the ecology of the species indicates that the Pseudodiamesa nivosa group is more cold-adapted than the Pseudodiamesa branickii group and, therefore, these two intra-genus morphotypes cannot be amalgamated into a larger taxonomic unit without losing substantial information. Here we present the morphological characters of head capsules of Pseudodiamesa larvae attributed to the different species-group morphotypes, which are clearly visible in subfossil specimens. The information summarized in this paper will help provide more reliable chironomid-based palaeoclimatic inferences from lake sediment records covering colder phases through the late Quaternary in the Northern Hemisphere.     

Reconstructing recent environmental changes using non-biting midges (Diptera: Chironomidae) in two high mountain lakes from northern Patagonia,Argentina

Remote lakes of northern Patagonia are ideal sites for examining climate- and non-climate-driven changes in aquatic ecosystems because there is little evidence of human influence and there is no detailed information on recent environmental trends in the region (i.e. the last 200 years). Subfossil chironomids (Diptera: Chironomidae) are useful paleoindicators due to their specific response to numerous environmental factors. Here, we analyze the chironomid subfossil assemblages from two remote lakes located in different environmental settings in Nahuel Huapi National Park of northern Patagonia, Argentina. Chironomids combined with sedimentary pigments (chlorophyll derivatives and total carotenoids) and organic matter provided information on the environmental history of the lakes for the last ca. 200 years. The ²¹⁰Pb chronology and tephra layers are used to establish the chronology of changes in the chironomid assemblages associated to different environmental factors that impacted the area during the period covered by the study. The deposition of volcanic ash affected the abundance and composition of chironomid assemblage throughout the record of both lakes. However, changing climate conditions and human activities are also responsible for chironomid changes in the last 50 years.     

The modern distribution of chironomid sub-fossils (Insecta: Diptera) in the Sierra Nevada, California: Potential for paleoclimatic reconstructions

Surface lake sediment was recovered from 57 lakes along an elevation gradient in the central, eastern Sierra Nevada of California. The surface sediment was analysed for subfossil chironomid remains in order to assess the modern distribution of chironomids in the region. The lakes sampled for the calibration dataset were between 2.0 and 40.0 m in depth, spanned an altitudinal gradient of 1360 m and a surface water temperature gradient of approximately 14 °C. Redundancy analysis (RDA) identified that five of the measured environmental variables – surface water temperature, elevation, depth, strontium, particulate organic carbon – accounted for a statistically significant amount of the variance in chironomid community composition. Quantitative transfer functions, based on weighted-averaging (WA), partial least squares (PLS) and weighted-averaging partial least squares (WA-PLS), were developed to estimate surface water temperature from the chironomid assemblages. The best model was a WA model with classical deshrinking, which had a relatively high coefficient of determination (r² = 0.73), low root mean square error of prediction (RMSEP = 1.2 °C) and a low maximum bias (0.90 °C). The results from this study suggest that robust quantitative estimates of past surface water temperature can be derived from the application of these models to fossil chironomid assemblages preserved in late-Quaternary lake sediment in this region.     

Palaeoenvironmental evolution of Cenote Aktun Ha (Carwash) on the Yucatan Peninsula,Mexico and its response to Holocene sea-level rise

A 61-cm core was obtained from 4 m below the water table in Cenote Aktun Ha, on the Yucatan Peninsula, Mexico. The cenote is 8.6 km from the Caribbean coast and its formation and evolution have been largely affected by sea-level change. The base of the core dates to 6,940–6,740 cal year BP and overlying sediments were deposited rapidly over the subsequent ~200 years. The pollen record shows that the cenote evolved from a marsh dominated by red mangrove (Rhizophora mangle) and fern (Polypodiaceae) to an open-water system. These vegetation changes were controlled by water level and salinity and are thus useful indicators of past sea level. At the base, the δ¹³C_org isotopic ratios reveal the influence of terrestrial vegetation (−29‰ VPDB), but shift to more negative values up-core (−33‰), indicating an influence from particulate matter in the flooded cenote pool. Although microfossil populations were nearly absent through most of the core, the microfossil assemblage in the upper 6 cm of the core is dominated by the juvenile foraminifer Ammonia tepida and the thecamoebian genus Centropyxis. These populations indicate open-water conditions in the cenote and a major environmental shift around 6,600 cal year BP, which is related to sea-level rise in the Caribbean basin. These data fit well with previously established sea-level curves for the Caribbean Sea. Our reconstruction of the environmental history of Cenote Aktun Ha helps elucidate the floral and hydrological history of the region, and highlights the utility of cenote sediments for studying the Holocene sea-level history of the Caribbean Sea.     

Seed-like hydroptilid larval cases (Insecta: Trichoptera) from Holocene freshwater deposits

The seed-like larval cases of hydroptilid caddis flies may be mistaken for plant remains in subfossil studies. However, being correctly identified, they may be important for the interpretation of former freshwater environments. Two such subfossil caddis fly remains from Holocene lake sediments and river deposits are described morphologically and their palaeoecological significance interpreted.     

Mass occurance and sporadic distribution of Corynocera ambigua Zetterstedt (Diptera, Chironomidae) in Danish lakes. Neo- and palaeolimnological records

The chironomid Corynocera ambigua (Tanytarsini) is commonly reported as a cold-stenothermal species living in shallow lakes in arctic and subarctic regions. In palaeoecological studies of temperate lakes, larval remains of C. ambigua are usually found in late-glacial sediments from the Allerød and Younger Dryas periods, and often in association with subfossil Chara oospores. During a surface sampling program of chironomid head-capsules in 41 Danish temperate lakes, C. ambigua was found to comprise 25% of the chironomid assemblages in two lakes, and was sporadically found in 8 other lakes (0.5-10%). A 70 cm palaeo-stratigraphy from the shallow (max depth 1.2 m) and eutrophic (total phosphorus = 150 g P l^-1) Lake Stigsholm showed that C. ambigua has been abundant in the last 4-5 centuries. At a sediment level of 25 cm (~year 1925, ²¹⁰Pb dating), C. ambigua began to decrease in frequency while Chironomus plumosus, Procladius sp., Cladotanytarsus gr. mancus and Tanytarsus spp. increased, suggesting an increased nutrient loading and an approach to eutrophic conditions. In 1995 C. ambigua was still very abundant in Lake Stigsholm but in early March 1997 no living larvae were found. An extremely heavy growth of Elodea, Enteromorpha and filamentous algae in the summers of 1995 and 1996, with following degradation in the fall, might have influenced the invertebrate population dynamics. No significant distinguishing characteristics were found for the lakes supporting C. ambigua. Its occurrence in warm (~20°C) Danish lakes brings into question the perception of the species as being cold-stenothermal.     

Sub-fossil Chironomidae from East Africa. 2. Chironominae (Chironomini and Tanytarsini)

This paper and a companion article present illustrated guides to the identification of sub-fossil chironomid larvae (Insecta: Diptera: Chironomidae) preserved in the sediments of low- and mid-elevation lakes in East Africa. They are based on analysis of surface-sediment death assemblages from 61 lakes located in the humid to semi-arid environments in equatorial East Africa (Uganda, Kenya, Tanzania), supplemented with similar surface-sediment samples from 12 lakes in the Horn of Africa (Ethiopia), and sub-recent core samples from six lakes in Kenya and two in Uganda. We analyzed about 11,000 specimens and identified 98.4% of these to species, species group, genus, or tribe level, depending on current -taxonomic knowledge of the various considered genera and the taxonomic resolution of preserved diagnostic features. We distinguished 90 different sub-fossil morphotypes, of which 16 are Tanypodinae, 19 are Orthocladiinae, and 55 are Chironominae. In this paper we focus on the subfamily Chironominae (tribes Chironomini and Tanytarsini). The diagnostic characters distinguishing these morphotypes from each other resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our morphotypes equivalent to morphological species or groups of closely related species. Given that core samples yielded only seven morphotypes not also found in the surface-sediment samples, the current inventory of 90 taxa likely represents the large majority of distinct sub-fossil chironomid larval types to be found in East African lakes, excluding the few very large Rift lakes, cold-water lakes above treeline, and special standing-water environments such as fens and bogs. Consistent use of a single set of morphological characters to identify both fossil and living chironomid larvae would ensure exchangeability of information between modem and paleoenvironmental studies on aquatic invertebrate communities in African lakes, and increase the relevance of paleoenvironmental reconstructions to water-quality evaluations aimed at sustainable management of scarce, fluctuating surface-water resources in tropical East Africa.     

Morphology and sedimentary systems in the Central Bransfield Basin, Antarctic Peninsula: sedimentary dynamics from shelf to basin

A detailed regional characterization of the physiography, morphology and sedimentary systems of the Central Bransfield Basin (CBB) was carried out using swath bathymetry and high‐ and very high‐resolution seismic profiles. The basin margins show continental shelves with numerous glacial troughs, and continental slopes where relatively wide and flat slope platforms represent the middle domain in an atypical physiographic scenario in glaciated margins. Although the CBB is tectonically active, most of the morphologic features are sedimentary in origin, and can be classified into four sedimentary systems: (1) glacial‐glaciomarine, composed of erosional surfaces, glacial troughs, furrows and draping sheets; (2) slope‐basin, formed by trough mouth fans, slope aprons, the Gebra‐Magia instability complex and turbidity systems; (3) seabed fluid outflow system composed of pockmark fields; and (4) contourite, composed of drifts and moats. The sedimentary systems show a clear zonation from shelf to basin and their dynamics reflects the complex interplay among glacial, glaciomarine, marine and oceanographic processes involved in the entire shelf‐to‐basin sediment distribution. The CBB morphology is primarily controlled by glacial/interglacial cyclicity and physiography and to a lesser extent by tectonics and oceanography. These factors have affected the South Shetland Islands (SSI) and Antarctic Peninsula (AP) margins differently, creating a relatively starved SSI margin and a more constructional AP margin. They have also created two entire sediment‐dispersal domains: the shelf‐to‐slope, which records the glaciation history of the CBB; and the lower slope‐to‐basin, which records the imprint of local factors. This study provides a ‘source‐to‐sink’ sedimentary scheme for glaciated margins, which may be applied to the basin research in other margins, based on the characterization of sedimentary systems, their boundaries and the linkages among them. This approach proves to be adequate for the identification of global and local factors governing the CBB and may therefore be applied to other study areas.     

Reconstructing riverine paleo-flow regimes using subfossil insects (Coleoptera and Trichoptera): the application of the LIFE methodology to paleochannel sediments

Sub-fossil insect remains have the potential to characterise changing environmental conditions in both lentic and lotic water systems, however, relatively few studies have been undertaken in riverine environments. This paper uses sub-fossil caddisfly larvae (Trichoptera) and aquatic beetles (Coleoptera) to reconstruct river flow conditions for a large paleochannel (from multiple monoliths) using the Lotic invertebrate Index for Flow Evaluation (LIFE). Examination of the larval Trichoptera and Coleoptera remains indicated a marked change in the community and flow environment, as suggested by paleoLIFE scores within the profile of three of the monoliths examined. At the base of the channel the community was characterised by taxa indicative of high energy lotic habitats with predominantly mineral substrates (e.g. Trichoptera: Hydropsyche contubernalis and Brachycentrus subnubilis, Coleoptera: Elmis aenea and Esolus parallelepipedus). Within three of the monoliths there was a change in community composition to one indicative of a low energy backwater/lentic environment with abundant submerged and emergent vegetation (e.g. Trichoptera: Phryganea bipunctata and Limnephilus flavicornis, Coleoptera: Colymbetes fuscus and Hydrobius fuscipes). Detrended Correspondence Analysis (DCA) and loss of mass on ignition (LOI) indicated the presence of a strong environmental gradient within the data, associated with river flow. The utilisation of two aquatic insect orders provides clear evidence of temporal changes within the instream community and when combined with knowledge of ecological and habitat associations, allows differences between the two groups to be interpreted more clearly.     

Subfossil Chironomidae from Lake Tanganyika, East Africa. 2. Chironominae (Chironomini and Tanytarsini)

Analysis of subfossil remains of larval Chironomidae in 38 surface-sediment samples from between 53 and 189 meter depth in Lake Tanganyika (East Africa) yielded 77 morphotypes, among which 7 Tanypodinae, 19 Orthocladiinae, and 51 Chironominae. Character-state differences between these morphotypes resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our Lake Tanganyika morphotypes equivalent to morphological species. Individual morphotypes were identified to species, genus, or tribe level depending on current alpha-taxonomic knowledge on the larvae of the group concerned, and the taxonomic resolution of preserved diagnostic features. This paper presents taxon diagnoses and an illustrated key to the Chironominae (Chironomini and Tanytarsini) in this collection. As the living chironomid fauna of Lake Tanganyika has never been comprehensively studied, we also briefly discuss faunistic aspects, and the ecology of the recovered species and genera in relation to benthic habitat diversity in Lake Tanganyika.     

Heavy Oil and Oil (Tar) Sands in North America: An Overview & Summary of Contributions

As conventional oil and gas reservoirs become depleted other unconventional energy sources have to be recovered and produced. Four of the major unconventional resources that are strategic for North American interests are heavy oil, oil sands, oil shales, and coal-bed methane. Recent interest and activity in Canada’s vast oil sands are progressing rapidly as soaring oil prices are fueling a ‘gold rush’ in oil sands development in Alberta. This interest is evident by the record-number of oil sands and heavy oil presentations at Energy Minerals Division (EMD)-sponsored sessions at the 2004 and 2005 Annual Conventions of the American Association of Petroleum Geologists (AAPG), held in Dallas, TX and Calgary, AB.     

Midges (Chironomidae,Ceratopogonidae, Chaoboridae) as a temperature proxy: a training set from Tasmania,Australia

Chironomid and ceratopogonid head capsules, along with Chaoborus mandibles, were used to model mean temperature of the warmest quarter (TWARM) in Tasmania. Our transfer function is based on midge assemblages and 21 environmental variables sampled from 47 lakes. Canonical correspondence analysis (CCA) revealed seven variables that account for a significant (P ≤ 0.05) portion of the explainable variance. In order of explanatory power, these were pH, TWARM, annual radiation, magnesium, annual precipitation, SiO₂, and depth. TWARM was modeled using weighted averaging partial least squares (WA-PLS) and generated a model with and RMSEP = 0.94. Advances in chironomid paleoecology are progressing very quickly in the Southern Hemisphere. Chironomid identification guides and autecological data are available for many regions, highlighting the potential for developing midge-based quantitative models to address hemispheric and interhemispheric climate hypotheses.