Nitrogen pollution in rivers and coastal environments

Coastal and estuarine eutrophication is a widespread problem across the United Kingdom and often has multiple sources. The Environment Agency use macroalgae extent and biomass as an indicator of eutrophication; there are quite a number of UK estuaries that fail to meet Water Framework Directive standards due to excessive macroalgae growth. Macroalgae blooms have numerous deleterious effects on coastal environments; for example, smothering delicate intertidal seagrass habitats and saltmarsh environments causing bleaching and plant die back, which ultimately leads to coastal erosion. Tracking nitrogenous pollution sources, transport and sinks in dynamic coastal and estuarine waters presents a significant challenge, conventionally requiring significant water sample collection and understanding of complex flow patterns. Stable isotope ratios are an excellent tool to discern, or ascertain, biological, ecological and environmental processes. The modern nitrogen cycle has been heavily influenced by human activity. Waste products, such as sewage and fish farm effluent, are normally more enriched in 15N than seawater (Vizzini and Mazzola, 2004), whereas agricultural waste products are normally more depleted in 15N (Heaton, 1986). This has led to the application of using nitrogen isotope ratios of marine sediments, marine organisms and macroalgae to monitor nitrogen pollution/contamination (e.g., Savage 2005). Nitrogen isotope ratios can also be measured in dissolved inorganic nitrogen isotopes taken directly from the water (Deutsch et al. 2006; Korth et al. 2014). However, dissolved inorganic nitrogen isotopes is analytically more time-consuming and costly. To address this difficulty, nitrogen isotope ratios in macroalgal tissues have been utilized to discern sources of excess nutrients (Costanzo et al. 2001, 2005; Dailer et al. 2012). Gröcke et al. (2017) and Bailes and Gröcke (2020) have shown that the translocation of macroalgae with isotopically distinct signatures could be used as a rapid, cost-efficient method for nitrogen biomonitoring in estuarine environments. Understanding the type of nitrogenous pollution sources is only one part of the problem. Tracing the source of that pollution can be used by riverine water analysis and/or the nitrogen isotope analysis of freshwater macrophytes. A nitrogen isoscape (isotope contour map) of the hydrological basin being investigated will provide a basis from which to pinpoint sources and sinks in the nitrogen isotope cycle.

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Image Captions

Seaweed love heart with a sampling hole.


The student will learn fieldwork and laboratory techniques associated with seawater and macroalgae analysis related to water quality and environmental analysis. Stable isotope analysis is fundamental to this project and will be completed in the Stable Isotope Biogeochemistry Laboratory (SIBL) at Durham University under the supervision of Dr Gröcke. Macroalgae photophysiology will be monitored using imaging pulse amplitude modulated fluorometry at Newcastle University. Experimental work will be conducted both at Durham and Newcastle University. Field experiments will be conducted in the north-east of England.

Project Timeline

Year 1

Fieldwork will be undertaken in the first 4-6 months of the studentship to generate a modern collection of macroalgae from around the north-east coast of England during the winter months. The student will learn sampling and analytical techniques in this period. This will consist of multiple relatively short duration fieldtrips (e.g. days to 1 week). The macroalgae will be analysed in SIBL at Durham University, with photophysiology and biochemical data collected at Newcastle University. This will be repeated again in the Spring and Summer months to generate a annual record of nitrogen isotope patterns.

Year 2

Experimental studies will be conducted at Newcastle University and will involve the collection and incubation of macroalgae growing tips in different environmental conditions and seawater compositions. In addition, nitrate and ammonia uptake experiments will be conducted with macroalgae and macrophytes. During this year, the site/s of specific interest will be selected for environmental monitoring using the translocation of isotopically-labelled macroalgae and macrophytes. The publication process will be started in this year, as the PhD will consist of a series of manuscripts.

Year 3

Final experimentation and fieldwork will be conducted in this year. Isoscape maps and isotope modelling will be presented at conferences and to stakeholders in the region. Manuscripts will be written and submitted for publication. Reports and outreach to local stakeholders will also be conducted.

Year 3.5

If required, the student will be finishing off papers related to their PhD and fine-tuning any reports and/or policy documents for local stakeholders.

& Skills

Stable isotope analysis, stable isotope mass spectrometry, analytical chemical, environmental growth chambers, field experimentation.

References & further reading

Bailes, I., Gröcke, D.R., 2020. Rapid Communications in Mass Spectrometry 34:e8951.
Costanzo, S.D., O’Donohue, M.J., Dennison, W.C., Loneragan, N.R., Thomas, M., 2001. Marine Pollution Bulletin 42:149–156.
Costanzo, S.D., Udy, J., Longstaff, B., Jones, A., 2005. Marine Pollution Bulletin 51:212–217.
Dailer, M.L., Smith, J.E., Smith, C.M., 2012. Harmful Algae 17:111–125.
Deutsch, B., Mewes, M., Liskow, I., Voss, M., 2006. Organic Geochemistry 37:1333–1342.
Gröcke, D.R., Racionero Gómez, B., Marschalek, J.W., Greenwell, H.C., 2017. Chemosphere 184:1175–1185.
Heaton, T.H.E., 1986. Chemical Geology 59:87–102.
Korth, F., Deutsch, B., Frey, C., Moros, C., Voss, M., 2014. Biogeosciences 11:4913–4924.
Savage, C., 2005. Ambio 34:145–150.
Vizzini, S., Mazzola, A., 2004. Marine Pollution 49:61–70.

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