Factors affecting diatom distribution in floodplain lakes of the southeast Murray Basin,Australia and implications for palaeolimnological studies

Diatom assemblages of surface sediments in 46 billabongs from four river floodplains in the southeast Murray-Darling Basin, Australia were sampled to investigate drivers of species distribution. The principal purpose of the study was to derive information to aid interpretation of diatom-based palaeoecological studies of these systems and of floodplain lakes more generally. Patterns in billabong diatom assemblages in relation to river reach, hydrology and farming intensity on surrounding land were examined, as were correlations with water quality variables. Seasonal variation in billabong water quality was high relative to spatial variation, and spatial patterns in billabong water quality were weak. In contrast, strong patterns were evident in diatom assemblages. Three main patterns were observed: (1) a distinction between billabongs dominated by planktonic diatoms from those dominated by benthic and attached forms; (2) differences in diatom assemblages in billabongs on different river reaches; and (3) differences in assemblages in billabongs with different hydrology. Of all water quality variables tested, total phosphorus (TP), total nitrogen (TN) and pH exerted the strongest independent influence on diatom distribution; however, only TP remained an important variable when species variation due to river reach, hydrology, and aquatic plant cover was taken into account. The weak influence of water quality on diatom distribution is interpreted as reflecting the dichotomy between plankton and non-plankton-dominated billabongs, the influence of hydrology and biogeography, the lack of strong spatial water quality gradients and the high degree of temporal variability in water quality. The findings show that diatom records from billabong sediments can provide evidence of long-term changes in the abundance of aquatic macrophytes and hydrology. They also suggest that merging calibration data sets across regions for the purpose of improving diatom transfer functions for water quality reconstruction is of limited value for floodplain lakes, and that performance is more likely to be gained by boosting site numbers within regions.     

Palaeolimnological evidence for submerged plant loss in a floodplain lake associated with accelerated catchment soil erosion (Murray River,Australia)

Shallow lakes have been described as existing in two alternative equilibrium states, dominated by either submerged plants or phytoplankton. Causes of, often catastrophic, shifts between these states have been widely debated but may often result from displacement of the dominant community by stochastic influence. In Australian cut-off river meanders (also known as ‘billabongs’), anecdotal and palaeolimnological evidence suggests widespread loss of aquatic macrophytes since European occupation of the region c. post-1800. Our detailed and high-resolution stratigraphic study of a sediment core from Hogan’s Billabong (Murray River, Australia) seeks to identify the causes of the loss of aquatic macrophytes. Little direct evidence of the past extent and composition of submerged macrophyte communities was recovered. Nevertheless, results derived from other sediment proxies, including declines in the abundance of epiphytic diatoms and in plant-associated invertebrates, provide further indirect evidence of macrophyte disappearance. Despite limitations with radiometric dating, the sequence of events in the derived record suggests that a period of high abiotic turbidity, leading to a critical reduction in water transparency and caused by widespread erosion during the late 19th century, is the most likely factor contributing to loss of submerged vegetation from this billabong.     

The pollen record from El’gygytgyn Lake: implications for vegetation and climate histories of northern Chukotka since the late middle Pleistocene

Three types of pollen assemblages (shrub-dominated, mixed herb- and shrub-dominated, and herb-dominated) characterize the ~ 300,000 year palynological record from El’gygytgyn Lake. Despite major changes in global climatic forcings, all pollen spectra, with a few isolated exceptions, have strong to possible analogs in the modern plant communities of Northeast Siberia and Alaska. Paleoclimatic reconstructions based on squared chord-distance analog analyses indicate two periods (~8600–10,700 ¹⁴C year B.P. and OIS 5e) when summers were perhaps ~2 to 4°C warmer than modern. January temperatures were also warmer than present, and both July and January were wetter than today. Palynological data remain inconclusive as to the establishment of forests near El’gygytgyn Lake at these times. The wettest Julys occurred during OIS 5 d. July temperatures were near modern, and Januarys were colder and drier than now. January temperatures, even into the Middle Pleistocene, generally show little variability, suggesting that the suppression of arboreal taxa during glaciations was likely caused by cool summers with low effective moisture and not by frigid winters. Because age schemes that correlate magnetic susceptibility to variations in summer insolation or ∂¹⁸O have cool plant taxa persisting in warm times (and vice versa), we propose an alternative age model based on the palynological data. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . This is the first in a series of eleven papers published in this special issue dedicated to initial studies of El’gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.     

The environmental history of a mountain lake (Lago Paione Superiore, Central Alps, Italy) for the last c. 100 years: a multidisciplinary, palaeolimnological study

A palaeoecological study of an oligotrophic alpine lake, Paione Superiore (Italy), provided a record of historical changes in water quality. Historical trends in lake acidification were reconstructed by means of calibration and regression equations from diatoms, chrysophycean scales and pigment ratios. The historical pH was inferred by using two different diatom calibration data sets, one specific to the alpine region. These pH trends, together with the record of sedimentary carbonaceous particles and chironomid remains, indicate a recent acidification of this low alkalinity lake.Concentration of total organic matter, organic carbon, nitrogen, biogenic silica (BSiO₂), chlorophyll derivatives (CD), fucoxanthin, diatom cell concentration and number of chironomid head capsules increased during the last 2–3 decades. When expressed as accumulation rates, most of these parameters tended to decrease from the past century to c. 1950, then all except P increased to the present day. A marked increase in sedimentary nitrogen may be related to atmospheric pollution and to the general increases in output of N in Europe. High C/N ratios indicate a prevailing allochthonous source of organic matter.Finally, the increase in measured air temperature from the mid-1800's appeared to be related to lake water pH before industrialization: cold periods generally led to lower pH and vice-versa. The more recent phenomenon of anthropogenic acidification has apparently decoupled this climatic-water chemistry relationship.     

A Holocene record of allochthonous, aeolian mineral grains in an Australian alpine lake; implications for the history of climate change in southeastern Australia

A radiocarbon-dated core, NC, taken in the alpine Blue Lake in the Snowy Mountains of southeastern Australia provides a Holocene record of sedimentation that consists mainly of organic clays. Two types of quartz grains are recovered from 81 samples from the core. One type consists of angular grains, with frequently shattered faces, which originates from granitic lithologies present within the small catchment area of the lake. The other type is characteristically rounded to subrounded, often textured with frequent silica coating and is considered to have been deposited within the lake and its catchment by aeolian processes. These aeolian grains are thought to have been transported along the main dust path that ferries aeolian dust from the Mallee region, west of the Snowy Mountains, as far as the southeastern Tasman Sea. Aeolian grains with the largest size occur over approximately the last 1.6 ka of the Holocene and this indicates an increase of climatic instability, with arid phases that commenced about 3.5 ka. At 2 ka, a wet period in southeastern Australia coincided with low aeolian input at Blue Lake. The period of consistent reduced aeolian activity spans the 7.6 to 5.5 ka interval at Blue Lake.     

Burial/exhumation histories for the Cooper–Eromanga Basins and implications for hydrocarbon exploration, Eastern Australia

The Cooper–Eromanga Basins of South Australia and Queensland are not at their maximum burial depth due to Late Cretaceous–Tertiary, and Late Triassic–Early Jurassic exhumation. Apparent exhumation (maximum burial depth–present burial depth) for the Cooper Basin has been quantified using the compaction methodology. The results show that exhumation of the Cooper Basin for the majority of the wells is greater than the exhumation of the Eromanga Basin. Using the compaction methodology, apparent exhumation of Early to Middle Triassic age Arrabury and Tinchoo Formatios has been quantified. Both units yield similar results and do not support that the Arrabury/Tinchoo boundary represents the Cooper–Eromanga boundary. Hence, the Cooper Basin is believed to have reached its maximum burial depth in Late Triassic times. Sonic log data are not available for the units overlying the Late Cretaceous Winton Formation; thus, it is not possible to date exhumation beyond the Late Cretaceous–Tertiary using the compaction methodology. Tertiary sequences as are preserved are relatively thin and separated by marked unconformities and weathered surfaces; hence, exhumation rather than sedimentation dominated the Tertiary, and in exhumed areas, maximum burial depth was attained in Late Cretaceous times. The burial/exhumation history of representative wells was synthesized using sediment decompaction and establishing porosity/depth relations for the Cooper–Eromanga units. Considering the relative significance of the major periods of exhumation in the Cooper/Eromanga Basins, three broad types of burial/exhumation histories can be distinguished. Maximum burial depth of the Cooper Basin sequence was attained before the deposition of the Eromanga Basin sequence, i.e. Late Triassic–Early Jurassic times; maximum burial depth of the Cooper and Eromanga Basin sequences attained in Late Cretaceous times; and Cooper and Eromanga Basin sequences are currently at maximum burial‐depth. Incorporation of exhumation into burial history has major implications for hydrocarbon exploration.     

Reconstructing nutrient histories in the Norfolk Broads, UK: implications for the role of diatom-total phosphorus transfer functions in shallow lake management

The fossil diatom records preserved in radiometrically dated sediment cores from four shallow lakes in the Norfolk Broads, UK (Barton Broad, Rollesby Broad, Wroxham Broad and Upton Broad) were analysed. A weighted-averaging partial least squares (WA-PLS) diatom-total phosphorus (TP) transfer function, based on a training set of 152 mostly shallow (maximum depth < 3 m) lakes in northwest Europe, was applied to the full diatom dataset for each core to reconstruct the past TP concentrations of the lakes. Owing to the dominance of non-planktonic Staurosira, Pseudostaurosira and Staurosirella spp. (formerly classified in the genus Fragilaria) throughout the diatom records, the quantitative diatom inferred TP (DI-TP) concentrations did not adequately reflect the changes that occurred in the lakes as indicated by shifts in the other diatom taxa, or as reported in the literature. This was most apparent at Barton Broad and Rollesby Broad, where there was a marked increase in the importance of planktonic taxa associated with highly nutrient-rich waters but no increase in DI-TP. The modern and fossil data were thus square-root transformed to downweight the dominant taxa and the new transfer function was applied to the cores. An improvement was seen only in the reconstruction for Barton Broad. Finally, the Staurosira, Pseudostaurosira and Staurosirella spp. were removed from the modern and fossil diatom data, and the transfer function was re-applied. The trends in DI-TP became less clear, particularly for Upton Broad and Barton Broad, owing to a paucity of data for calibration once these taxa were deleted from the counts data. The problems associated with reconstructing trophic status and determining TP targets for restoration from fossil diatom assemblages in these systems are discussed.     

Central‐Auckland rainfall, 1853–2020: Sites histories and implications for developing a long‐term rainfall record

Previous work related to central‐Auckland site Albert Park showed that sparse site histories for inner‐city weather stations can be usefully supplemented by mining searchable online historical archives (Papers Past, DigitalNZ), at least as far back as 1909. Assessment of potential is extended here back to 1853, within the context of developing a long‐term rainfall record for Auckland. Although late 19th century sources are thinner and of poorer quality, much useful information could be gleaned about the locations and exposures of early sites. Hypothesised implications for the rainfall record suggest that all early site data need to be adjusted upwards.     

The late Pleistocene ostracod record of the crater lake sediments from Lago di Albano (Central Italy): changes in trophic status, water level and climate

Four cores (ranging between ca. 9 and ca. 14 m in length) from Lago di Albano in Central Italy were studied for their ostracod content, as well as algal and bacterial pigments, CaCO3 and concentration of organic matter. Cores PALB 94 1E and PALB 94 1C from Site 1, located at the bottom of a steep slope at 70 m water depth, where oxygen concentration is below 6 mg l-1, spans the Holocene and the late Pleistocene until 28 kyr B.P. (calibrated age). The other cores, PALB 94 6A and PALB 94 6B taken at a depth of 30 m, where oxygen is 7--11 mg l-1, represent mainly Pleistocene deposits.Ostracod valves were found in the lowermost ca. 3 m of the sequence at Site 1, dated to ca. 28--24 kyr B.P., and throughout the sequence from Site 6 which represents the interval 23--17 kyr B.P.Candona neglecta is the dominant species in most of the levels at Site 1, whereas both C. neglecta and Cyclocypris sp. dominate during different biostratigraphic zones at Site 6. The influx of springs entering the lake at Site 1 was inferred on the basis of species of the genus Potamocypris and Ilyocypris bradyi present in the record. Wide fluctuations in species abundance and assemblages in both coring sites indicate lake-water level oscillations between 28 to 17 kyr B.P. In particular, a strong rise in water level of the order of 40 m occurred between 24 and 23 kyr B.P. Fluctuations in productivity, oxygen availability and water temperature at both sites were also reconstructed on the basis of the ostracod assemblages and the algal and bacterial pigment concentrations. The environmental reconstruction reached using ostracod remains and pigments was verified with other proxy records published elsewhere such as invertebrate remains, diatoms, magnetic properties, etc. A synthesis of climatic reconstructions for Central and Southern Italy for the late Full Glacial is attempted on the basis of previous studies on hydrology, lithostratigraphy and palynology. Sharp fluctuations in lake palaeoproductivity/palaeoclimate recorded by invertebrate and pigment remains at both sites from Lago di Albano might be related to similar events reported in North Atlantic Full-Glacial records from marine and ice cores.     

Geochemical assessment of an annually laminated lake sediment record from northern Sweden: a multi-core,multi-element approach

We used seven annually laminated (varved) sediment cores from Nylandssjön, a lake in northern Sweden, to assess between-core variation and diagenetic changes at annual resolution. By using several cores, multiple elements and employing principal components analysis (PCA), we also studied how the geochemical composition changed over time, and assessed to what extent these changes were related to variations in the weather. There are between-core differences for aluminum, silica, lead, titanium, zirconium and dry-mass accumulation rate. Diagenesis causes a decrease in bromine, as well as carbon, nitrogen and varve thickness, as reported in previous publications. In spite of anoxic bottom waters phosphorus is not lost from the sediment. In fact, there is an increase in phosphorus concentrations with time. The PCA identified four principal components (PCs). PC-1 accounts for the relative content of mineral and organic material; PC-2 represents mineral-particle grain size; PC-3 reflects phosphorus loading and PC-4 reflects atmospheric pollution. Variations in the weather partly explain the temporal patterns in PC-1 and PC-2: cold winters, i.e. more accumulation of snow, resulted in more mineral than organic matter (i.e. higher PC-1 scores), and increased the relative amount of coarse-grained mineral particles in the sediment (i.e. lower PC-2 scores). Increased spring precipitation had a weak positive effect on the PC-2 scores by promoting the transport of fine-grained material. However, the influence of weather is weak, explaining at most 30 % of the variance, and hence, other factors, e.g. land use and its effect on soil erosion, seem to be more important for the sediment geochemical composition. The importance of land use is also exemplified by an increase in PC-3 scores in the late 1970s, which can be attributed to a shift in agricultural practices that resulted in increased phosphorus loading to the lake. In summary, our findings show that down-core trends are reproducible between cores, but between-core variability and diagenesis need to be considered when interpreting some elements. We also conclude that there is a need to constrain temporal changes in land use before using lake sediments to study changes in weather or climate.     

A diatom-based Holocene record of human impact from a coastal environment: Tuckean Swamp, eastern Australia

Diatom-based paleolimnological studies are being increasingly used to track anthropogenic change in estuaries. Little is known, however, about the direction and nature of long-term environmental changes in Australian estuaries. In this study, shifts in diatom assemblages preserved in a ²¹⁰Pb and C¹⁴ AMS dated sediment core from Tuckean Swamp were analysed to determine environmental changes that had taken place as a result of changing land-use practices. Prior to European impact, the diatom assemblage remained relatively stable and was dominated by Actinocyclus normanii and Diploneis smithii. An increasing dominance of Cyclotella meneghiniana correlates well with changed land use activities in the catchment area and indicates an increase of freshwater influence in the swamp’s environment. A major shift in species composition began ∼1970, Eunotia flexuosa becoming dominant. The assemblage shifts recorded at this site appear to be consistent with environmental changes triggered by human activities such as vegetation clearance, drainage and the construction of a barrage. This study demonstrates the use of paleolimnoology in an estuarine environment to provide pre-impact data necessary for management of the aquatic environment.     

The Relationship between Geomorphic River Structure and Coarse Particulate Organic Matter (CPOM) Storage along the Kangaroo River,New South Wales,Australia

Fluvial landforms provide a physical template upon which to appraise biophysical relationships along river courses. In this study, the spatial pattern of organic matter storage along the Kangaroo River, NSW, is related to geomorphic controls that operate at a range of scales within a nested hierarchy. This snapshot study of CPOM storage found that at the catchment scale the longitudinal pattern of coarse particulate organic matter (CPOM) storage is dependent on the type and downstream pattern of River Styles. At the reach scale, CPOM storage is dependent on the geomorphic unit structure and physical heterogeneity of the river, and associated energy conditions along the reach. At the geomorphic unit scale, CPOM storage capacity is related to the position of geomorphic units relative to the thalweg (i.e. flow characteristics) and associated roughness attributes. At the hydraulic unit scale, CPOM storage capacity is related to local flow velocity and substrate characteristics (clast size and distribution).     

Tectonic and climatic controls on historical landscape modifications: The avulsion of the lower Cecina River (Tuscany, central Italy)

Integration of geomorphology, stratigraphy, sedimentology and morphotectonics in the analysis of the lower Cecina River reach, coastal Tuscany, reveals an undocumented historical channel avulsion. Geomorphological evidence and radiocarbon dating support that, from the Last Glacial Maximum until the end of the 16th century, the Cecina River flowed north of the present course and formed a well-developed cuspate delta. Two concurrent factors, active tectonics as a preparing factor and discharge regime as an activation factor, are thus inferred to have favored the avulsion of Cecina River. Fragmentary archaeological and historical records indicate that the late Holocene Cecina River plain was virtually unpopulated until the latest 16th century. This seems the main reason why high-magnitude hydrological events and prominent river channel avulsions were not reported in historical chronicles. From this perspective, geomorphological data may provide important knowledge and understanding of recent dynamics of environmental change when historical record is lacking or missing.     

Spatially irregular sedimentation in a small, morphologically complex lake: implications for paleoenvironmental studies

A sub-bottom acoustic survey of Devil Lake on the Canadian Shield in southern Ontario reveals three acoustic facies: (I) a moderately acoustically transparent, laminated sequence interpreted as a glacilacustrine deposit in glacial Lake Iroquois or a subsequent phase in water depths up to 200 m greater than at present, (II) a transitional more transparent, less layered facies interpreted as being deposited in a more distal glacial lake from erosion of sediment in the watershed exposed by the failure of the ice dam and lowering of the glacial lake before stabilization by the development of forests, and (III) an acoustically transparent facies with similar transmissivity to the water column, interpreted as Holocene gyttja. Each is spatially variable in extent and thickness in response to those processes. There is only a very weak relation between sediment thickness and the water depth in which it was deposited. Wave processes prevent deposition in water depths less than about 6 m and evidence of erosion to the greatest depths of the lake (>40 m) is pervasive. The data demonstrate the value of acoustic survey in assessing lacustrine processes and the history of lakes, and the significance of such documentation in planning a coring program and in interpreting the results.     

The biota of lake abalakh (Yakutia,eastern Siberia,Russia Federation)

The fauna and flora of Lake Abalakh, a saline lake in Yakutia, eastern Siberia, Russian Federation, is described from a collection made in July, 1990. The fauna comprisedMoina mongolica, Metadiaptomus asiaticus, Brachionus plicatilis and larval ceratopogonids. The flora was much more diverse. It contained 82 taxa most of which were cyanophytes, bacillariophytes, and chlorophytes. Also present were cryptophytes (1 taxon), xanthophytes (5) and euglenoids (1).     

First record of Branchinella spinosa (Milne-Edwards) (Crustacea: Branchiopodacolon; Anostraca) from Greece

As the result of a first screening of temporary inland water habitats,Branchinella spinosa is here recorded for the first time in Greece. This finding extends the circum-Mediterranean part of its vast distribution. The species was collected from a shallow astatic coastal salt-marsh that is mainly fed by rainwater, where it coexists but rarely co-occurs withArtemia parthenogenetica. Branchinella spinosa is only the fourth anostracan species currently known from Greece. The poor knowledge of anostracan richness and abundance is mainly due to limited sampling efforts in this area. As temporary aquatic habitats are threatened by several anthropogenic activities, especially agriculture and land clearing for urbanisation and tourism, there is an urgent necessity for further monitoring and protection of these precious habitats.     

A record of early to middle Holocene environmental change inferred from lake deposits beneath a sabkha sequence in the Central Sahara (Seggedim, NE Niger)

Seggedim is a remote site in NE Niger where previous studies demonstrated the presence of Holocene paleolake deposits beneath an existing sabkha. In 2005, we retrieved a 15-m core that contains a high-resolution record of early to middle Holocene environmental change. Mineralogical, chemical and petrographic data were used to infer paleoenvironmental conditions recorded by successive lake stages. An exceptionally stable lake regime existed from 10.6 to 7.3 cal ka BP. This regime, reflecting moist conditions, was characterized by deposition of continuously laminated diatomite with high organic matter content, formed under meromictic conditions, with very low detrital input. A lake regime shift occurred at 7.3 cal ka BP, interpreted as the beginning of a transition to arid conditions. This shift was initially marked by a change to predominantly clastic sedimentation, followed by increased sand input during later stages, culminating in the onset of the sabkha stage. Because of the presence of reworked organic material in the deposits, reliable radiocarbon dating of the succession of lake stages could not be achieved.     

Seasonal variability of Holocene climate: a palaeolimnological study on varved sediments in Lake Jues (Harz Mountains, Germany)

Studies combining sedimentological and biological evidence to reconstruct Holocene climate beyond the major changes, and especially seasonality, are rare in Europe, and are nearly completely absent in Germany. The present study tries to reconstruct changes of seasonality from evidence of annual algal successions within the framework of well-established pollen zonation and ¹⁴C-AMS dates from terrestrial plants. Laminated Holocene sediments in Lake Jues (10°20.7′ E, 51°39.3′ N, 241 m a.s.l.), located at the SW margin of the Harz Mountains, central Germany, were studied for sediment characteristics, pollen, diatoms and coccal green algae. An age model is based on 21 calibrated AMS radiocarbon dates from terrestrial plants. The sedimentary record covers the entire Holocene period. Trophic status and circulation/stagnation patterns of the lake were inferred from algal assemblages, the subannual structure of varves and the physico-chemical properties of the sediment. During the Holocene, mixing conditions alternated between di-, oligo- and meromictic depending on length and variability of spring and fall periods, and the stability of winter and summer weather. The trophic state was controlled by nutrient input, circulation patterns and the temperature-dependent rates of organic production and mineralization. Climate shifts, mainly in phase with those recorded from other European regions, are inferred from changing limnological conditions and terrestrial vegetation. Significant changes occurred at 11,600 cal. yr. BP (Preboreal warming), between 10,600 and 10,100 cal. yr. BP (Boreal cooling), and between 8,400 and 4,550 cal. yr. BP (warm and dry interval of the Atlantic). Since 4,550 cal. yr. BP the climate became gradually cooler, wetter and more oceanic. This trend was interrupted by warmer and dryer phases between 3,440 and 2,850 cal. yr. BP and, likely, between 2,500 and 2,250 cal. yr. BP.