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

copyright Springer Science+Business Media B.V. 2007Diatoms 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).John Tibby, Peter A. Gell, Jennie Fluin and Ian R. K. Sluite

Assessing eutrophication and reference conditions for Scottish freshwater lochs using subfossil diatoms

The definitive version is available at www.blackwell-synergy.com1. The European Council Water Framework Directive requires reference conditions to be determined for all water body types including lakes. We examined the role of palaeolimnology, specifically the diatom record, as a tool for assessing eutrophication and for defining lake reference conditions and ecological status. 2. Sediment cores (representing c.1850 to present day) were taken from 26 Scottish freshwater loch basins. Radiometric dating techniques (210Pb and 137Cs) established a chronology for each core. Two levels of diatom analysis were employed: a relatively high resolution (15–20 samples) at 21 lochs considered of high interest, and a lower resolution (four to five samples) at the remaining sites. 3. Detrended correspondence analysis and dissimilarity measures were applied to the core top (present day) and bottom (reference state, c.1850) samples to assess floristic change at each site. Significant floristic change, indicative of nutrient enrichment, occurred in 18 lochs along a broad trophic gradient. 4. Two-way indicator species analysis (TWINSPAN) was applied to the bottom (c.1850) samples to classify the ‘reference’ diatom assemblages and thereby characterize the reference floras of the different lake types. TWINSPAN identified four site end-groups, each with a characteristic diatom assemblage, although there was some overlap in the taxa present in the four groups. Water depth and productivity were key factors that explained the groupings. 5. Diatom transfer functions that reconstructed total phosphorus (TP) concentrations were used to evaluate eutrophication. Nineteen lochs had increases in diatom-inferred (DI) TP of > 5{micro}g l-1 (five of these > 20{micro}g l-1), six lochs had no change or negligible increases in DI-TP (< 2{micro}g l-1), and there was evidence of a decline in DI-TP in one loch over the period represented by the sediment cores. The inferred increases were significant at 12 lochs. 6. Synthesis and applications . Our data indicate that it may be difficult to find minimally impacted waters to act as reference sites, particularly for shallow, lowland lake types, in the current population. The derivation of site-specific reference conditions from the sediment record is a particularly valuable approach in such cases. Ordination, clustering and dissimilarity measures applied to palaeodata, combined with transfer functions, offer powerful techniques for characterizing lake types, defining ecological and chemical reference conditions, and assessing deviation from the reference state.Helen Bennion, Jennie Fluin and Gavin L. Simpso

Seasonal and interannual variations in diatom assemblages in Murray River connected wetlands in north-west Victoria, Australia

© CSIRO PublishingEpipelic diatom assemblages collected from three wetlands connected to the Murray River displayed considerable variation in response to flooding and drying phases. Murray River water input usually generated diatom assemblages dominated by Aulacoseira species. After isolation, the diatom flora of two wetlands shifted to assemblages of small Fragilariaceae forms. Elevated nutrient levels corresponded with the appearance of eutraphentic taxa such as Cyclotella meneghiniana, Eolimna subminuscula, Luticola mutica and Nitzschia palea. Further evapoconcentration induced shifts to taxa tolerant of elevated salinity levels including Amphora coffeaeformis, Navicula incertata, Staurophora salina and Tryblionella hungarica. Ordination analyses reveal a strong chemical control on the diatom taxa present in the wetlands, in accordance with known ecological preferences for salinity and nutrients. The influence of nitrogen and phosphorus concentrations in controlling diatom assemblages was subordinate to salinity once conductivity values exceeded 1400 μS cm–1. The results of such biomonitoring provide a means of interpreting wetland history from fossil assemblages contained in sediment sequences.Peter A. Gell, Ian R. Sluiter and Jennie Flui

Multiproxy palaeoeology reconstruction of the mid-Holocene to present salinity, marine incursions and flow regime of Lake Alexandrina and the Goolwa channel, South Australia.

Multiproxy palaeoecology techniques are used to reconstruct the mid-Holocene to present salinity, marine incursions and flow regime of Lake Alexandrina and the Goolwa channel, South Australia. Microfossils (foraminiferal, ostracoda and diatoms) are analysed in three sediment cores. Foraminiferal remains are used to reconstruct the frequency, duration, and spatial extent of marine incursions upstream through the Goolwa channel to Lake Alexandrina. Diatom analysis provides a quantitative reconstruction of salinity, while the ostracoda analysis is currently exploratory. Three C-14 AMS radiocarbon dates and eight Pb-210 dates for each of the three cores have been submitted for analysis. To support the flow-regime-reconstruction with quantitative data, grain size analysis is included. Preliminary data from the foraminiferal assemblage of core RS1 (taken from just above the Goolwa barrage) illustrates a substantial change in both grain size and presence of foraminifera at a core depth of 130 cm. This may represent a sedimentation rate of 2 cm/yr, since the placement of the Goolwa barrage in 1939. At depths between 130 cm and 0 cm the sediment is barren of foraminifera. Below 130 cm foraminifera are abundant; inner-shelf marine species, especially Elphidium crispum, are dominant from 130 cm to the bottom of the core (216 cm). Only three increments (140-144 cm; 164-168 cm; 174-182 cm) have very low foraminiferal counts (<100). The sediment at these depths is of a much finer grain size. For a majority of the time, it is likely that pre-river-regulation-flow rates of the Murray River were high enough to maintain an open mouth, allowing the mixing of marine and estuarine waters.International Union for Quaternary Researc

Diatom and foraminifera relationships to water quality in The Coorong, South Australia, and the development of a diatom-based salinity transfer function

The Ramsar-listed Coorong lagoon lies at the terminus of the Murray-Darling River system in South Australia. Diatom and foraminifera relationships with water quality were characterised in order to develop diatom- and foraminifera-based models with the potential to infer water column salinity. Seventy-four samples were collected during 2007, a year of continuing drought in the catchment, and of no discharges at the Murray Mouth. The sample sites had a salinity gradient of 1. 8-190 g l-1 total dissolved solids. The diatom data set comprised 215 taxa, while there were only eight taxa in the foraminiferal data set. Canonical correspondence analysis of diatom species-environment relationships showed that salinity explained the largest proportion of diatom variance. Hence, a diatom-based salinity transfer function with reasonable predictive power (measured vs. diatom-inferred salinity rjack2 = 0. 82; Root Mean Squared Error of Prediction = 16 g l-1) was developed. Application of the transfer function to fossil diatom assemblages from The Coorong suggested that pre-European salinity values were generally >50 g l-1 and that salinity declined following settlement. These results, however, contradict the recent history of The Coorong where there have been substantial lagoon-wide salinity increases. The pre-impact diatom flora has no analogue in the modern data set, highlighting the degree of departure from past conditions. CCA of the foraminiferal data set identified salinity and total nitrogen as the variables with the greatest explanatory power. However, accurate predictive models could not be developed using either variable due to low foraminiferal abundance and species richness. These factors may have been a consequence of diminished foraminiferal recruitment rates over successive years, an artefact of reduced marine water input to The Coorong. Future attempts to generate predictive models from this region would benefit from the inclusion of data from distant locations, since suitable analogue sites do not exist in close proximity. The study has generated useful insights to the apparently broad salinity tolerances for several cosmopolitan diatom and foraminifera species, and has identified a number of diatom and foraminifera taxa that may prove useful in the qualitative interpretation of down-core trends in The Coorong and the lower Murray River region. © 2011 Springer Science+Business Media B.V.D. Haynes, R. Skinner, J. Tibby, J. Cann and J. Flui

Assessing long-term pH change in an Australian river catchment using monitoring and palaeolimnological data

Copyright © 2003 American Chemical SocietyReviews of stream monitoring data suggest that there has been significant acidification (>1.0 pH unit at some sites) of Victorian streamwaters over the past 3 decades. To assess whether these declines are within the range of natural variability, we developed a diatom model for inferring past pH and applied it to a ca. 3500-yr diatom record from a flood plain lake, Callemondah 1 Billabong, on the Goulburn River, which has among the most substantial observed pH declines. The model has a jackkniffed r 2 between diatom inferred and measured pH of 0.77 and a root mean square error of prediction of 0.35 pH units. In the pre-European period, pH was stable (range 6.5-6.7) for approximately 3000 yr. Since European settlement around 160 yr ago, diatom-inferred billabong pH has increased significantly by >0.5 units. We hypothesize that this increase in pH is related to processes associated with land clearance (e.g., increased base cation load and decreased organic acid load). There is no evidence of the recent monitored declines in the Callemondah record, which may indicate that that flood plain lakes and the main stream are experiencing divergent pH trends or that the temporal resolution in the billabong sediment record is insufficient to register recent declines.John Tibby, Michael A. Reid, Jennie Fluin, Barry T. Hart, and A. Peter Kersha

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

Michael Reid, Jennie Fluin, Ralph Ogden, John Tibby, Peter Kersha

Diatom-water quality thresholds in South Australian streams indicate a need for more stringent water quality guidelines

Water quality guidelines are an important tool that guide stream protection. In South Australia, as in other Australian states, guidelines have been set using statistical properties of physical and chemical stressors in reference streams. Given that water quality guidelines are designed to protect ecosystems, biologically based guidelines are more desirable. In this context, we investigated diatom–water quality relationships in South Australian streams. Our analysis focused on electrical conductivity (EC) and total phosphorus (TP), which explained significant variance in diatom assemblages. Threshold indicator taxa analysis was conducted to determine thresholds of diatom community change along EC and TP gradients. There were significant declines in the relative abundance of sensitive species at an EC of ~280 μS cm⁻¹ and a TP concentration of 30 μg L⁻¹. The TP threshold is considerably lower than the trigger value in South Australia’s guidelines (100 μg TP L⁻¹). The change in species composition in relation to EC is considerably lower than the upper limit of the water quality guidelines (which range from 100 to 5000 μS cm⁻¹). Hence, particularly in the case of TP, but also for EC, the current water quality guideline trigger values are too high in South Australia, and indeed in other temperate Australian states.J. Tibby, J. Richards, J.J. Tyler, C. Barr, J. Fluin and P. Goona

Palaeoenvironmental developments in the Lake Tondano area (N. Sulawesi, Indonesia) since 33,000yr B.P.

Copyright © 2001 Elsevier Science B.V. All rights reserved.Geo(morpho)logical, sedimentological and ecological developments in the Lake Tondano area since ±33,000 yr B.P., and limnological changes in the moderately-sized lake situated at 680 m asl in the northern part of Sulawesi, Indonesia are discussed. First, the environmental setting of the lake is presented. Study of the regional distribution of lacustrine sediments, and a detailed analysis of their sedimentary facies (texture, organic matter content) suggest major changes in size and depth of the lake and in past sedimentation. Insight into the long-term development of the lake (sedimentation processes) is highly relevant for sustainable use of the present lake. Analysis of diatom assemblages provides further detail of the changing aquatic settings of the lake; lake levels rise quickly around 33,000 and 12,000 yr B.P., fall dramatically between ±30,000 and 13,000 yr B.P. and are lowered gradually since approximately 6000 yr B.P., following Early Holocene high lake levels. Drainage of the lake is affected by both volcanic depositional events and regional climatic events. Palynological analysis is indicative of local palaeoecological settings in the lake area and regional climatic change; a distinct, Late Pleistocene phase, with lower precipitation and lowered mean temperatures is inferred. Furthermore, progressive deforestation of the Tondano uplands is evident, as well as diffuse anthropogenic/volcanic vegetation disturbance from the early Mid Holocene onwards. Information from sedimentary facies, diatom assemblages and local palaeoecology (pollen) are integrated to reconstruct palaeoenvironmental settings and processes in the lake area. This record of environmental change as well as the pollen-based record of regional vegetation and climate change corroborates other palaeoenvironmental data derived from the few terrestrial sites in the region. The data attribute a greater magnitude of temperature and precipitation change in the region than is commonly deduced in studies based on marine faunal and sedimentary records. The Lake Tondano sedimentary record is highly suitable for further analysis aimed at determining the exact timing and amplitudes of environmental change in the SE Asian equatorial region.Rien A. C. Dam, Jennie Fluin, Papay Suparan and Sander van der Kaarshttp://www.elsevier.com/wps/find/journaldescription.cws_home/503355/description#descriptio