Problems with the application of diatom‐total phosphorus transfer functions: examples from a shallow English lake

Abstract

1. A diatom‐total phosphorus transfer function has been applied to a sedimentary diatom sequence from Groby Pool, a small shallow lake in Leicestershire, U.K. 2. Extensive aquatic plant records exist for Groby Pool dating back over two centuries. These records, in conjunction with selected aquatic pollen and herbarium diatom data, provide independent, qualitative evidence for the progression of eutrophication and its effects on aquatic plant communities and habitat structure. 3. Before 1800, Groby Pool was probably mesotrophic with clear water and a diverse submerged macrophyte community, but subsequently it experienced considerable nutrient enrichment. Key evidence for this includes: (i) historical plant records indicating the loss of species associated with mesotrophic waters and their replacement by others typical of eutrophic conditions, (ii) a significant increase in the percentage of planktonic diatoms in the lake sediment record (particularly Cyclostephanos dubius) after 1890, and (iii) increases in percentages of Stephanodiscus parvus and Cocconeis placentula in the second half of the twentieth century. 4. Diatom‐inferred total phosphorus (DI‐TP) estimates were inconsistent with the qualitative evidence for eutrophication at Groby Pool. In particular the DI‐TP profile was thought to overestimate phosphorus during the period of dominance by small Fragilaria spp. before 1890, and to misjudge the timing and direction of subsequent changes in nutrient loading. 5. This study highlights some of the problems associated with the application of diatom‐TP transfer functions to sedimentary diatom sequences from shallow lakes. The major problem relates to the frequent dominance of non‐planktonic diatoms in the sediments of these systems, many species of which (particularly small Fragilaria spp.) appear to be more sensitive to changes in habitat availability than to phosphorus. Potential ways of improving diatom‐TP models via altered approaches to sampling are suggested.

Palaeolimnological evidence for recent climatic change in lakes from the northern Urals, arctic Russia

“…The wide TP-tolerance range of these taxa reduces their utility as indicator species of TP. Sayer (2001) found that these taxa were more sensitive to habitat availability than to phosphorus in shallow lakes. It is more likely, therefore, that the decrease in Fragilaria taxa in Mitrofanovskoe Lake is caused by habitat changes (e.g., change in water level) or interspecific competition.…”

Assessing degradation and recovery pathways in lakes impacted by eutrophication using the sediment record

“…However, several studies have highlighted the shortcomings of the transfer function technique in certain situations, and this is particularly well documented for shallow lakes where non-planktonic taxa dominate the diatom assemblages. Problems include the influence of factors such as light, substrate, and top-down factors in addition to water chemistry on the distribution of these taxa and their wide tolerance to nutrient concentrations, making them poor indicators of lake trophic status (e.g., Anderson et al, 1993;Bennion, 1995;Bennion et al, 2001;Sayer, 2001;Juggins et al, 2013). Nonetheless, in the absence of other techniques for hindcasting nutrient concentrations, inference models are likely to remain a valuable part of the lake manager's toolkit (SaulnierTalbot, 2015).…”

“…Furthermore, one has to allow for a good deal of approximation in the models and fits, accepting that the model will interpolate between adjacent time points and the strength of the fitted trend at any point is dependent upon the pattern in the data both prior and subsequent to any particular time point of interest. Caution must also be exercised when interpreting changes seen in surface sediment samples (upper 0-1 cm) in terms of recovery as the reduced period of decomposition experienced by recently deposited diatoms can result in these being over-represented (Sayer, 2001). Varved sequences, offering an annual resolution, lend themselves particularly well to studies of degradation and recovery (e.g., Chandler Rowell et al, 2015).…”

Extending the timescale and range of ecosystem services through paleoenvironmental analyses, exemplified in the lower Yangtze basin

“…Transfer functions based on modern-day relationships between a proxy, such as the distribution of diatoms, and an environmental variable, such as aquatic P concentration, are common techniques used to produce quantitative estimates of past changes. However, care is needed to exclude or disentangle the effects of strongly correlating variables on the response function (115,143,144).…”