• Login
• Admin

Markham, Hannah (2025) Investigation of the impact of elevated phosphorus concentrations on the different life phases of two species of Ephemeroptera. PhD thesis, University of Nottingham.

PDF (Thesis - as examined) - Repository staff only until 25 July 2027. Subsequently available to Anyone - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader Available under Licence Creative Commons Attribution. Download (31MB)

Abstract

Freshwaters are persistently threatened by anthropogenic activities that disrupt the chemistry and ecology of the ecosystem. In England, despite notable improvements in surface water quality since the 1990s, nutrient pollution -particularly elevated phosphorus concentrations - remains a significant obstacle to achieving the “good ecological status” outlined by the Water Framework Directive. Poor water quality has led to a decline in the abundance and diversity of pollution-sensitive aquatic insects such as the Ephemeroptera (mayflies) across many English rivers. As a bioindicator of aquatic environment health, mayflies provide critical insights into ecosystem change. However, while the link between phosphorus and freshwater eutrophication is well documented, declining mayfly populations have also been observed in river systems impacted by nutrient pollution but not classified as eutrophic.

Research on nutrient pollution in relation to mayflies has previously predominantly focused on the eutrophic effects on the nymph life phase. Therefore, there remains limited understanding of three critical aspects: (1) the specific effect of elevated phosphorus concentrations on the egg stage of mayflies which are particularly vulnerable due to their inability to evade polluted environments: (2) how phosphorus enrichment directly impacts mayflies across all life-stages in non-eutrophic conditions; and (3) how nutrient pollution affects aquatic fungal growth and the reciprocal interactions between fungal communities and mayflies from the moment their eggs are deposited.

The body of work presented here aimed to address these knowledge gaps through a series of mesocosm experiments and a year-long field study. For the mesocosm trials, a reductionist approach was taken to isolate the effects of elevated phosphorus concentrations on the fitness and hatching success of eggs from the mayfly species, Ecdyonurus venosus and Ephemera danica, captured from field sites in spring 2022 and 2023, respectively. Adult mayflies were encouraged to lay eggs in synthetic water in which all elements and pH were kept constant, apart from phosphorus. In addition, the direct effects of an elevated phosphorus concentration of 0.75 mg P L-1 on the nymph stages of the same species, while holding all other environmental factors constant, were evaluated.

For analysis of egg hatching, a Python programme was designed, written and implemented to aid in counting eggs. Egg and nymph survival data, and nymph growth and emergence values, showed that low concentrations of phosphorus (0.1 mg L-1) were required for physiological development and that elevated concentrations had no detrimental effect on either life stage of the species studied. Therefore, under controlled conditions, enhanced phosphorus concentrations did not detrimentally affect the eggs or nymphs of Ecdyonurus venosus and Ephemera danica when all other factors remained constant.

These data suggest that the observed (published and anecdotal) negative effects of phosphorus on mayflies under field conditions are likely to be more complicated than the negative effects of a single nutrient in isolation. To determine whether these findings would also be observed in the field, a river impacted by the treated discharge from a sewage outfall pipe was selected to evaluate mayfly populations and other invertebrates above, at, and below, the ingress point. The river was a chalk stream in Buckinghamshire – the River Chess. Biologically available phosphorus was consistently higher in the water near the outfall (> 2 mg L-1) relative to the upstream site (< 0.3 mg L-1) depending on season. Potassium and nitrogen concentrations were also higher at the outfall site; it was not possible to differentiate between the effects of phosphorus, other elements, or whether any effects were additive. However, pollution sensitive mayfly (e.g. Heptageniidae, Ephemeridae, Ephemerellidae) were absent from the outfall site, but were present elsewhere in the river. Other pollution-sensitive taxa in general were absent from samples taken from the outfall site across all seasons, whilst sensitive indicator species were observed in samples both above and below the outfall site in all seasons. More pollution-tolerant taxa were collected from the outfall site (e.g. Asellidae, Annelida, Sphaeriidae) than at other sites. There was evidence of ecological recovery by 830 m downstream of the outfall pipe although water nutrient concentrations were higher than at the site above the outfall pipe, although lower than at the outfall. During the laboratory-based mesocosms trials, an incidental observation of filamentous fungal hyphal entrapment of nymphs emerging from eggs and leading to their death, prompted further investigation into the effects of elevated nutrient concentrations on aquatic fungi and potential links between invertebrate and fungal populations. By subsequently analysing fungal taxa derived from DNA extracted from sediment at the three sites in the River Chess, differences in fungal community composition between sites were observed. Ascomycota and Basidiomycota abundance decreased significantly at the outfall site while Rozellomycota increased, relative to the upstream and downstream sites. Seasonal interactions complicated the overall picture, but multidimensional scaling ordinations showed that elevated nutrient concentrations, particularly phosphorus, were a key driver of the observed changes in fungal community composition. The fungal component of the river system is vital for ecosystem functions and any imbalance between ecosystem engineers (e.g. members of the Ascomycota and Basidiomycota) and potential parasites (e.g. Rozellomycota) could directly or indirectly affect invertebrate survival. Given that invertebrate health and population stability are closely tied to microbial communities, it is clear that the impacts of the outfall in the studied river were both widespread and significant.

The content and findings of this study provide valuable insights into the impact of nutrient pollution on freshwater ecosystems, particularly in relation to microbial and invertebrate communities. By identifying phosphorus as a key driver of community change, this research highlights the need for more nuanced water quality monitoring that includes microbial communities as indicators of ecosystem health. Incorporating these findings into policy could inform more targeted nutrient management strategies ensuring that even sub-eutrophic conditions are effectively addressed.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Johnson, Matthew F. West, Helen M.
Keywords:	Ephemeroptera; mayfly; aquatic fungi; phosphate, nutrient; pollution
Subjects:	Q Science > QH Natural history. Biology
Faculties/Schools:	UK Campuses > Faculty of Social Sciences, Law and Education > School of Geography
Item ID:	80341
Depositing User:	Markham, Hannah
Date Deposited:	25 Jul 2025 04:40
Last Modified:	25 Jul 2025 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/80341

Actions (Archive Staff Only)

Edit View