John Tibby

Late Quaternary palaeoecology, palynology and palaeolimnology of a tropical lowland swamp: Rawa Danau, West-Java, Indonesia

Abstract Sedimentological, limnological and palynological analyses of a sediment core from a lowland site in West-Java, Indonesia, provide a detailed palaeoenvironmental record for the Late Glacial and the Holocene. The record suggests open vegetation under inferred drier climatic conditions for the Late Glacial. However, there is no unequivocal evidence for cooler conditions at this time. The onset of the Holocene coincides with a change to more humid climatic conditions, with the development of a fern-rich closed forest vegetation type. Dramatic changes in diatom community composition provide a striking record of habitat change associated with lake shallowing, but this process appears to be a result of basin in-filling rather than variations in precipitation/evaporation balance associated with climatic fluctuations. Evidence for human impact on the vegetation development is restricted to the last few hundred years.

Holocene environmental change in southwest Turkey: a palaeoecological record of lake and catchment-related changes

Percentage, concentration and accumulation pollen data together with diatom and non-siliceous microfossil data are presented for the site of Go‹ lhisar Go ‹l u‹ (37i8@N, 29i36@E; elevation 930 m), a small intramontane lake in Burdur Province, southwest Turkey. Microfossil assemblages from the longest sediment core (GHA: 813 cm) record changes in local and regional vegetation and lake productivity over the last &9500 years. Pollen spectra indicate that vegetation progressed from an open landscape with an increase in arboreal pollen occurring &8500 BP to mixed forest comprising oak, pine and juniper until around 3000 BP (Cal &1240 BC) when a human occupation phase becomes discernible from the pollen spectra. This occurs shortly after the deposition of a volcanic tephra layer which originated from the Minoan eruption of Santorini (Thera) and radiocarbon dated to 3330

EFFECTS OF DEPTH, SALINITY, AND SUBSTRATE ON THE INVERTEBRATE COMMUNITY OF A FLUCTUATING TROPICAL LAKE

70 yr BP (Cal &1600 BC). This human occupation phase is comparable to the Beys,ehir Occupation phase recorded at other sites in southwest Turkey and involved forest clearance and the cultivation of fruit trees such as Olea, Juglans, Castanea and »itis together with arable cereal growing and pastoralism. The presence of pollen types associated with the Beys,ehir Occupation phase in deposits above the Santorini tephra layer confirms a Late Bronze Age/early Anatolian Dark Age date for its commencement. Since &3000 BP notable changes in aquatic ecology associated with tephra deposition and subsequent nutrient and sediment flux from the lake catchment are recorded. The Beys,ehir Occupation phase at Go‹ lhisar Go ‹l u‹ came to an end around 1300 BP (Cla AD &700) when pine appears to have become the dominant forest tree. ( 1999 Elsevier Science Ltd. All rights reserved.

A model for inferring past conductivity in low salinity waters derived from Murray River (Australia) diatom plankton

Salinity is generally considered to be the dominant environmental factor regulating aquatic community structure in hydrologically closed lakes and wetlands, but it is not well known whether community response to long-term trends in hydrological balance is driven primarily by the direct physiological effect of salinity stress or by the habitat restructuring that accompanies changes in lake level and salinity. Attempts to separate the effects of various environmental factors on invertebrate populations in shallow fluctuating lakes through field study are hampered by the typically large temporal and spatial variation in species abundances and the long time scale of climate-driven habitat restructuring relative to the period of study. We used paleolimnological techniques to document long-term dynamics of the benthic invertebrate community inhabiting a shallow fluctuating lake in Kenya where during the period ∼1870–1991 lake depth fluctuated between 4 and 19 m, and lakewater conductivity between ∼250 and 14000...

Diatoms as indicators of environmental change in shallow lakes.

Detecting human-induced salinisation in rivers and wetlands of the Murray-Darling Basin has proved problematic. A diatom-based model that permits the estimation of past electrical conductivity (EC) from sedimentary diatom sequences has been developed from Murray River planktonic diatoms. Canonical Correspondence Analysis indicates that EC explains the greatest amount of variance in Murray River planktonic diatoms and that its influence is partially independent of that associated with velocity, turbidity, pH and nutrients. A weighted-averaging based model for inferring past EC was therefore derived from the relationship between diatom composition and EC in Murray River plankton samples. The model works well when comparisons are made between measured and diatom-inferred EC determined by jackknifing based leave-one-out computer resampling (r2jack = 0.71, root-mean-square-error of prediction = 115 μS cm−1). Application of the model will enhance understanding of the nature of pre-European variability in electrical conductivity and permit detection of changes in conductivity through the period of European occupation at key sites. Such reconstructions will provide a firm empirical basis for assessing European impact on aquatic ecosystems and a means by which to assess restoration efforts.

Diatom-salinity relationships in wetlands: assessing the influence of salinity variability on the development of inference models

© Cambridge University Press 1999, 2010. Introduction Historically, limnological and paleolimnological research has focused on large and typically deep lakes but in the last two decades there has been a growing interest in smaller and shallower water bodies. Shallow lakes are justifiably considered as a separate lake type, distinguished physically from deeper waters by the fact that they are permanently mixed (polymictic) with a consequent lack of stratification of temperature or oxygen and with increased potential for nutrient recycling and redistribution of seston by physical water circulation patterns (Carrick et al., 1994). Whilst this is a useful distinction, there is no single definition of a shallow lake (Padisak & Reynolds, 2003). Scheffer (1998), in his classic text book, acknowledged a fundamental difference in the behavior, ecological functioning, and biotic communities of shallow waters and arbitrarily selected a mean depth of less than 3 m to define shallowness. For the purposes of this chapter we have chosen to adopt this definition and thereby to focus on lakes where, under a favorable light climate, benthic algae and/or rooted submerged macrophytes may occupy the majority of the lakebed (see also Jeppesen et al., 1997). Under enriched conditions, however, the mechanisms that stabilize the macrophyte communities of shallow lakes may often break down and a transition to pelagic production with phytoplankton dominance occurs (Scheffer et al., 1993; Vadeboncoeur et al., 2003). Importantly, because of these characteristics, shallow lakes are, for the most part, more vulnerable to a given pollutant load than large lakes.

Explaining lake and catchment change using sediment derived and written histories: an Australian perspective.

Diatoms are among the most widely used indicators of human and climate induced wetland salinity history in the world. This is particularly as a result of the development of diatom-based models for inferring past salinity. These models have primarily been developed from relationships between diatoms and salinity measured at the time of sampling or during the preceding year. Although within site variation in salinity has the potential to reduce the efficacy of such models, its influence has been rarely considered. Hence, diatom–conductivity relationships in eight seasonally monitored wetlands have been investigated. In developing a diatom–conductivity transfer function from these sites, we sought to assess the influence of conductivity variation on diatom inference model performance. Our sites were characterised by variability in conductivity that was not correlated to its range and thus were well suited to an investigation of this type. We found, contrary to expectations, that short-term (seasonal) changes in conductivity which were often dramatic did not result in unduly reduced transfer function performance. By contrast, sites that were more variable in the medium term (5–6 years) tended to have larger model errors. In addition, we identified a secondary ecological gradient in the diatom data which could not be related to any measured variable (including pH, turbidity or nutrient concentrations).

Climate-water quality relationships in three Western Victorian (Australia) lakes 1984-2000

Palaeolimnological records can be powerfully combined with documentary data to explain the impact of modern industry and agriculture on lake systems and their catchments. Such an approach is highly appropriate in Australia since modern society was imposed on a continent until recently populated solely by hunter-gatherers and because there is a wealth of historical data to draw upon. Confounding factors such as the influence of climate change, depopulation of the indigenous community and non-linear responses to human impact must be considered in analysis of the relative importance of various land use changes upon lake pollution.

Long-term perspectives on human impacts on floodplain-river ecosystems, Murray-Darling Basin, Australia

To achieve robust simulations of past and future climate and their effect on aquatic biota, it is desirable to integrate results from palaeolimnology, contemporary monitoring and process modelling. Here we analyse over 15 years of water quality monitoring data from three lakes, Purrumbete, Colac and Bullen Merri from Western Victoria, Australia and their relationship to climate. In the context of a large number of limnological and palaeoenvironmental studies from the region, we seek to refine understanding of the primary forcing mechanisms that explain present, past and potentially future water quality variability in the lakes. Our analysis shows that there are strong relationships between climate and water quality in these lakes of varied size and salinity (average conductivity range 740–14,000 μS cm−1). The strongest climate–water quality relationship exists between air and water temperature, particular during the colder months. Strong relationships also exist with air temperature and other parameters, most notably nutrient concentrations. Effective precipitation also appears to exert a strong influence on water quality in these lakes. This influence is, by contrast with the influence of air temperature, less direct. Nevertheless, these lakes of varying salt concentration exhibit a coherent pattern of conductivity response to variation in effective precipitation, particularly during times of high moisture stress.

Diatoms as indicators of sedimentary processes in Burrinjuck reservoir, New South Wales, Australia

Australian aquatic ecosystems are characteristically subject to high temporal variability at scales that range from seasonal to more than decadal yet few ecological studies extend beyond 3 years (WESTOBY 1991). lt is widely accepted that the clearance o f native vegetation, agriculture and river regulation have caused dramatic changes in aquatic ecosystems yet there are precious few real data documenting changes to these ecosystems. Such knowledge gaps can be addressed by palaeolimnological study of aquatic environments. In this paper the manner by which palaeolimnology can aid understanding of the changes that have occurred in the aquatic ecosystems of the Murray-Darling Basin (MDB) is discussed, with reference to ongoing studies that focus on developing lake histories that track changes associated with h uman activities over the last 200 years.