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

Area of Science:

• Marine Ecology
• Environmental Chemistry
• Bioindicators

Background:

• Anthropogenic nitrogen loading poses a threat to UK coastal ecosystems.
• Macroalgae are underutilized as bioindicators for nitrogen pollution.
• Sewerage infrastructure significantly influences coastal nitrogen levels.

Purpose of the Study:

• To compare nitrogen loading in two island systems with different sewerage infrastructure: Jersey and St. Mary's (Isles of Scilly).
• To assess the effectiveness of macroalgae, specifically Fucus vesiculosus and Ulva sp., as bioindicators of nitrogen pollution.
• To investigate the impact of sewerage treatment works (STW) and effluent outflow on coastal nitrogen isotope ratios (δ¹⁵N).

Main Methods:

• Analysis of nitrogen isotopes (δ¹⁵N) in 831 macroalgae samples (Fucus vesiculosus and Ulva sp.).
• Comparison of δ¹⁵N values between Jersey and St. Mary's, considering their respective sewerage systems.
• Creation of δ¹⁵N isoplot maps to visualize nitrogen diffusion patterns in coastal areas.

Main Results:

• Elevated δ¹⁵N values (>9‰) were observed in St. Aubin's Bay, Jersey, linked to the Bellozanne STW outflow.
• Low nitrogen diffusion was indicated in St. Aubin's Bay, suggesting localized pollution impacts.
• St. Mary's showed varied δ¹⁵N values, generally lower than Jersey, attributed to a smaller population and less efficient STW, with localized pollution hotspots near effluent outflows.

Conclusions:

• Macroalgae, particularly Fucus vesiculosus and Ulva sp., are reliable bioindicators of anthropogenic nitrogen loading in coastal environments.
• Differing sewerage infrastructure significantly impacts nitrogen loading, with advanced STWs reducing widespread pollution compared to less efficient systems and septic tanks.
• Island systems require improved sewerage development and upgrades to mitigate effluent environmental issues and protect marine ecosystems.