H Bennion

A diatom-phosphorus transfer function for shallow, eutrophic ponds in southeast England

Shallow ponds in southeast England are often eutrophic with high phosphorus concentrations. The aim of this study was to develop a diatom-phosphorus ‘transfer function’ to enable past phosphorus levels in such waters to be inferred from the sediment record. A water chemistry survey of 123 randomly chosen, shallow, artificial ponds in southeast England was carried out. Principal components analysis (PCA) revealed that phosphorus was an important environmental variable. A subset of 31 sites was selected along a total phosphorus (TP) gradient (winter TP range 7–1123 µg 1-1), in order to explore the relationship between the surface-sediment diatom assemblages and the contemporary water chemistry using canonical correspondence analysis (CCA). Annual mean TP was the most significant variable in explaining the variance in the diatom species data.

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.

Sedimentary evidence for changes in the pollution status of Taihu in the Jiangsu region of eastern China

As part of a study using lake sediments to determine the extent and causes of human impacts to lakes along an east–west transect following the Yangtse River, sediment cores were taken from Taihu in eastern China. Previous studies have focussed on the impacts of direct inputs of pollutants from municipal and industrial wastewater but little work has been undertaken on trends in atmospheric deposition from the many industrial sources surrounding the lake. Analysis of the Taihu sediment cores for atmospheric pollutant indicators such as trace metals, magnetic parameters and spheroidal carbonaceous particles (SCPs) show the lake has become increasingly contaminated over the last 40–50 years. Sediment levels of atmospherically deposited pollutants are currently similar to some of the more contaminated lakes in Europe. Further, sediment nitrogen, phosphorus and geochemical analyses confirm the dramatic increase in eutrophication at the site and periods of recent soil erosion in the catchment.

SURFACE-SEDIMENT DIATOM ASSEMBLAGES IN SHALLOW, ARTIFICIAL, ENRICHED PONDS, AND IMPLICATIONS FOR RECONSTRUCTING TROPHIC STATUS

This paper examines the surface-sediment diatom assemblages of 31 shallow, artificial, enriched ponds in southeast England lying along a total phosphorus (TP) gradient (annual mean TP 25-646 μg 1−1), with respect to their species composition, and the role of such waters in generating diatom-chemistry training sets for reconstructing lake nutrient status. Detrended Correspondence Analysis (DCA) was used to explore the major patterns within the species data and revealed that there are principally two axes, a nutrient axis and a life-form axis. Consequently, there are two major types of diatom assemblage, one dominated by centric taxa of the genera Stephanodiscus and Cyclostephanos, associated with the most nutrient-rich waters, and the other dominated by non-planktonic taxa of the genera Fragilaria and Achnanthes, associated with the shallowest waters. The small, shallow, artificial nature of these water-bodies with relatively uniform water depth and well-mixed water columns increases the likelihood that th...

Recommendations for sampling littoral diatoms in lakes for ecological status assessments

This review summarises the existing literature and outlines the theoretical basis for using standard methods for sampling diatoms from rivers to sample littoral diatoms and other phytobenthos from standing waters. The European Unions Water Framework Directive has created a statutory obligation for EU Member States to monitor macrophytes and phytobenthos in lakes. Although there has been a considerable amount of work using phytobenthos (especially diatoms) to monitor river water quality in Europe, there are fewer studies on the use of phytobenthos for monitoring in lakes. European standard methods for sampling diatoms from rivers should be suitable, with only minor modifications, for sampling littoral diatoms from lakes and other standing water bodies. These recommendations should be applicable to all temperate regions.

Uncertainty in ecological status assessments of lakes and rivers using diatoms

The EU’s Water Framework Directive requires all surface water bodies to be classified according to their ecological status. As biological communities show both spatial and temporal heterogeneity, expressions of ecological status will, inevitably, have an element of uncertainty associated with them. A consequence of this environmental heterogeneity is that there is a risk that status inferred from one or more samples is different to the true status of that water body. In order to quantify the scale of temporal uncertainty associated with benthic diatoms, replicate samples were collected from sites across the ecological status gradient in lakes and rivers in the UK. Variability (expressed as standard deviation of temporal replicate samples from a single site) could be described using a polynomial function and this was then used to calculate the risk of placing a water body in the wrong ecological status class. This risk varied depending on the distance from the class boundaries and the number of replicates. Based on these data, we recommend that ecological status is determined from a number of samples collected from a site over a period of time.

Lake eutrophication and its implications for organic carbon sequestration in Europe

The eutrophication of lowland lakes in Europe by excess nitrogen (N) and phosphorus (P) is severe because of the long history of land-cover change and agricultural intensification. The ecological and socio-economic effects of eutrophication are well understood but its effect on organic carbon (OC) sequestration by lakes and its change overtime has not been determined. Here, we compile data from ~90 culturally impacted European lakes [~60% are eutrophic, Total P (TP) >30 μg P l(-1) ] and determine the extent to which OC burial rates have increased over the past 100-150 years. The average focussing corrected, OC accumulation rate (C ARFC ) for the period 1950-1990 was ~60 g C m(-2) yr(-1) , and for lakes with >100 μg TP l(-1) the average was ~100 g C m(-2) yr(-1) . The ratio of post-1950 to 1900-1950 C AR is low (~1.5) indicating that C accumulation rates have been high throughout the 20th century. Compared to background estimates of OC burial (~5-10 g C m(-2) yr(-1) ), contemporary rates have increased by at least four to fivefold. The statistical relationship between C ARFC and TP derived from this study (r(2) = 0.5) can be used to estimate OC burial at sites lacking estimates of sediment C-burial. The implications of eutrophication, diagenesis, lake morphometry and sediment focussing as controls of OC burial rates are considered. A conservative interpretation of the results of the this study suggests that lowland European meso- to eutrophic lakes with >30 μg TP l(-1) had OC burial rates in excess of 50 g C m(-2) yr(-1) over the past century, indicating that previous estimates of regional lake OC burial have seriously underestimated their contribution to European carbon sequestration. Enhanced OC burial by lakes is one positive side-effect of the otherwise negative impact of the anthropogenic disruption of nutrient cycles.

Climate change and the future of freshwater biodiversity in Europe: a primer for policy-makers.

Abstract Earths climate is changing, and by the end of the 21st century in Europe, average temperatures are likely to have risen by at least 2 °C, and more likely 4 °C with associated effects on patterns of precipitation and the frequency of extreme weather events. Attention among policy-makers is divided about how to minimise the change, how to mitigate its effects, how to maintain the natural resources on which societies depend and how to adapt human societies to the changes. Natural systems are still seen, through a long tradition of conservation management that is largely species-based, as amenable to adaptive management, and biodiversity, mostly perceived as the richness of plant and vertebrate communities, often forms a focus for planning. We argue that prediction of particular species changes will be possible only in a minority of cases but that prediction of trends in general structure and operation of four generic freshwater ecosystems (erosive rivers, depositional floodplain rivers, shallow lakes and deep lakes) in three broad zones of Europe (Mediterranean, Central and Arctic-Boreal) is practicable. Maintenance and rehabilitation of ecological structures and operations will inevitably and incidentally embrace restoration of appropriate levels of species biodiversity. Using expert judgement, based on an extensive literature, we have outlined, primarily for lay policy makers, the pristine features of these systems, their states under current human impacts, how these states are likely to alter with a warming of 2 °C to 4 °C and what might be done to mitigate this. We have avoided technical terms in the interests of communication, and although we have included full referencing as in academic papers, we have eliminated degrees of detail that could confuse broad policy-making.

Recent histories of six productive lakes in the Irish Ecoregion based on multiproxy palaeolimnological evidence

Palaeolimnological data from six mesotrophic, eutrophic and hypertrophic lakes in the Irish Ecoregion, in the form of microfossil (cladocera, diatoms and pollen) and sediment chemistry data from radiometrically dated sediment cores, were used to reconstruct past variations in lake water quality and catchment conditions. Basal sediments from sediment cores from the six sites ranged in age from the late 18th century to the early 20th century. A weighted averaging partial least squares regression model was developed to reconstruct past epilimnetic total phosphorus concentrations. The results indicate that all but one of the study sites currently are in a far more productive state compared with the beginning of the sediment core record and that those same five lakes have experienced accelerated enrichment post c. 1980. Two of the sites demonstrated long-term enrichment, in one case beginning in the late 19th century, while both eutrophication and oligotrophication have occurred at three sites. The results highlight the difficulties in applying a general temporal end-point for reference conditions and demonstrate that productive lakes in the Irish Ecoregion have complex, locally specific and often long histories of enrichment. These may not be responsive to reduced external loadings of phosphorus and, as a result, restoration could prove particularly challenging. The results also provide evidence of the ways in which palaeolimnological techniques can assist implementation of the EU Water Framework Directive.

Environmental Impacts in the Jianghan Plain: Evidence from Lake Sediments

There is growing concern about the environmental impact of rapid economic growth in China. The problem is compounded by the scarcity of baseline data on the state of Chinas natural environment. As a step towards solving this problem, palaeolimnological methods have been applied to seven lakes in the Jianghan Plain, China, to evaluate recent changes in human impact. Lake sediment cores show enhanced concentrations of fossil fuel derived spheroidal carbonaceous particles (SCP) and Pb at all sites across the Jianghan Plain. The distribution of these industrial contaminants shows the overwhelming influence of the industrial cities. Wuhan dominates the fossil fuel derived pollution, while the copper smelter at Daye dominates the heavy metal pollution. Analysis of sediment diatom assemblages indicates mean total phosphorus concentrations of greater than 40 μg L-1 P in the lakes of the more intensely agricultural western part of the Jianghan Plain. The sediment concentration profiles for biogenic elements at these sites indicates a post-1960 eutrophication. Evidence for eutrophication in the eastern lakes is much weaker, though some evidence is present at all sites. The tracers of industrial pollution (Pb and SCP) correlate with Mn in the many of the lake sediments. This is compatible with both soil acidification, and soil gleyification due to intensified rice production.