Translocation of isotopically distinct macroalgae: A route to low-cost biomonitoring?

Diffuse and concentrated nitrogen sewage pollution in island environments with differing treatment systems

Macroalgae is an under-utilised tool as a bioindicator of anthropogenic nitrogen loading to the coastal environment in the UK. This study compared two island systems-Jersey (Channel Islands) and St Mary's (Isles of Scilly) to assess how differing sewerage infrastructure affects nitrogen loading. A total of 831 macroalgae samples of Fucus vesiculosus and Ulva sp. were analysed for nitrogen isotopes (δ¹⁵N). Elevated δ¹⁵N values were recorded for Jersey (> 9‰) in St Aubin's Bay-caused by the outflow of the Bellozanne Sewerage Treatment Works (STW). δ¹⁵N isoplots maps indicate low diffusion of nitrogen out of St Aubin's Bay. St Mary's produced a varied δ¹⁵N isoplot map in comparison. δ¹⁵N was typically lower and is attributed to a smaller population and inefficient STW. Outflow of sewage/effluent at Morning Point, Hugh Town and Old Town produced elevated δ¹⁵N values in comparison to the island average. St Mary's inefficient sewerage treatment and reliance on septic tanks/soakaways complicates δ¹⁵N interpretation although it still indicates that nitrogen pollution is an island-wide issue. Future sewerage development and upgrades on islands are required to prevent similar effluent environmental issues as recorded in St Aubin's Bay. This study advocates the use of macroalgae as a bioindicator of nitrogen effluent in the marine environment.

Biomass and nutrient dynamics of major green tides in Ireland: Implications for biomonitoring

The control of macroalgal bloom development is central for protecting estuarine ecosystems. The identification of the nutrients limiting the development of macroalgal blooms, and their most likely sources is crucial for management strategies. Three Irish estuaries (Argideen, Clonakilty and Tolka) affected by green tides were monitored from June 2016 to August 2017. During each sampling occasion, biomass abundances, tissue N and P contents, and δ¹⁵N were determined for tubular and laminar morphologies of Ulva. All estuaries showed maximum biomass during summer and minimum during winter. Tissue nutrient contents revealed P rather than N limitation. The δ¹⁵N during the peak bloom indicated agriculture as the most likely source of nitrogen in the Argideen and Clonakilty, and urban wastewaters in the Tolka. No differences in the δ¹⁵N, and the tissue nutrients content were observed between morphologies. The period between May and July is most suitable for bioassessment of green tides.

Effects of marine biofertilisation on Celtic bean carbon, nitrogen and sulphur isotopes: Implications for reconstructing past diet and farming practices

RATIONALE

The application of fertilisers to crops can be monitored and assessed using stable isotope ratios. However, the application of marine biofertilisers (e.g., fish, macroalgae/seaweed) on crop stable isotope ratios has been rarely studied, despite widespread archaeological and historical evidence for the use of marine resources as a soil amendment.

METHODS

A heritage variety of Celtic bean, similar in size and shape to archaeobotanical macrofossils of Vicia faba L., was grown in three 1 × 0.5 m outdoor plots under three soil conditions: natural soil (control); natural soil mixed with macroalgae (seaweed); and 15 cm of natural soil placed on a layer of fish carcasses (Atlantic cod). These experiments were performed over two growing seasons in the same plots. At the end of each growing season, the plants were sampled, measured and analysed for carbon, nitrogen and sulphur stable isotope ratios (δ¹³ C, δ¹⁵ N, δ³⁴ S).

RESULTS

The bean plants freely uptake the newly bioavailable nutrients (nitrogen and sulphur) and incorporate a marine isotopic ratio into all tissues. The bean δ¹⁵ N values ranged between 0.8‰ and 1.0‰ in the control experiment compared with 2‰ to 3‰ in the macroalgae crop and 8‰ to 17‰ in the cod fish experiment. Their δ³⁴ S values ranged between 5‰ and 7‰ in the control compared with 15‰ to 16‰ in the macroalgae crop and 9‰ to 12‰ in the cod fish crop. The beans became more ¹³ C-depleted (δ¹³ C values: 1-1.5‰ lower) due to crop management practices.

CONCLUSIONS

Humans and animals consuming plants grown with marine biofertilisers will incorporate a marine signature. Isotopic enrichment in nitrogen and sulphur using marine resources has significant implications when reconstructing diets and farming practices in archaeological populations.

Isotopically labelled macroalgae: A new method for determining sources of excess nitrogen pollution

RATIONALE

Stable nitrogen isotope ratios (δ15 N) can be used to discern sources of excess nitrogen pollution in water. The δ15 N values of nitrate in water often do not reflect the true δ15 N source value owing to high temporal variation, and there are high analytical costs associated with obtaining δ15 N values from water nitrate. To find alternative solutions, we isotopically labelled macroalgae (i.e. seaweed) beyond natural variation as a new method for determining sources of excess nitrogen pollution in seawater.

METHODS

Fucus vesiculosus (bladder wrack) non-fertile tips were collected from Easington Colliery, County Durham, UK, and cultured in two isotopically enriched solutions containing ammonium sulphate with δ15 N values of 170 ± 5‰ and -60 ± 3‰ for a period of 19 days. The macroalgae were cultured in separate opened glass jars in an incubator with set temperature (11°C) and light (125 μmol photons m-2 s-2 on a light/dark rhythm of 16 h/8 h). The oven-dried tips were analysed for δ15 N over the 19-day experiment.

RESULTS

The macroalgal tips incorporated the isotopically enriched solutions rapidly, reaching 50% of the isotopically enriched seawater after ca 11 days for the 15 N-enriched solution and ca 15 days for the 14 N-enriched solution. δ15 N values were incorporated more into the torn base of the macroalgal tips than into the middle and apex regions.

CONCLUSIONS

F. vesiculosus rapidly incorporates the isotopic ratio of the artificial seawater solution to which it is translocated. The laboratory-developed isotopically labelled macroalgae can be manufactured to generate 'unnatural' δ15 N values for translocation into coastal environments. This approach can provide an efficient, low-cost alternative to current analytical methods for determining and monitoring nitrogen pollution.

δ15N in deployed macroalgae as a tool to monitor nutrient input driven by tourism activities in Mediterranean islands

Mediterranean Sea is among the world's leading tourist destinations; however, the sharp increase in tourists during the high season may affect coastal seawater. The main aim of this study was to evaluate the occurrence and temporal variation of anthropogenic nutrients in coastal seawater in relation to tourist flows in three Mediterranean islands (Cyprus, Sicily and Rhodes), through short-term macroalgae deployments, coupled with δ¹⁵N analysis and GIS mapping. In all islands, an overall increase in macroalgae δ¹⁵N occurred over the deployment carried out in August in the tourist sites, suggesting the presence of anthropogenic nutrients. Decreasing δ¹⁵N values occurred at increasing distance from the coastline in two out of the three islands (Cyprus and Sicily). This study revealed the usefulness of the approach used in the assessment of tourism impact in terms of trophic enrichment and its potential to support competent authorities for the development of sustainable coastal management plans.

Biomonitoring coastal environments with transplanted macroalgae: A methodological review

The use of macroalgae transplants is a recent technique used in pollution biomonitoring studies in marine ecosystems. Only 60 articles published between 1978 and 2017 reported the use of this environmental tool for the active biomonitoring of inorganic pollutants and nutrients worldwide. In this review paper, we evaluated studies on this topic in relation to the development of methodological aspects of the technique and the degree of standardization of the protocols used. On the basis of findings of this review, we conclude that the technique is not yet standardized and that uniformisation of protocols is required to enable comparison of the results of different studies. We propose a new protocol for applying the technique, in which each suggestion has been carefully and rigorously compared with the relevant findings reported in the available literature.