Biogeochemical and microbial community responses to anthropogenic nutrient inputs into the Solent

Given their pivotal role in providing essential ecosystem services, understanding the dynamics of coastal waters and their responses to disturbances such as climate change and nutrient pollution is imperative. In this study, we conducted year-long monitoring (May 2021 to May 2022) of the pico- and nanoplanktonic community driving biogeochemical cycling in waters of the Solent on the south coast of the UK. Our investigation revealed that the Solent receives excess nutrient influxes year-round, attributable to sewage spills transported through the intertidal Langstone Harbour, amounting 45.4 ± 14.8 t NO3− and 2.5 ± 0.5 t PO43− per year. However, these, and sub-annual environmental fluctuations appear not to impede phytoplanktonic succession and associated ecosystem functioning, with observed planktonic blooms in spring (2.46–5.96 μg L−1 chlorophyll a) and late summer (3.85 μg L−1 chlorophyll a), despite a warming event in July 2021. These results underscore the importance of continuous monitoring of point sources of nutrient pollution to discern long-term trends and interannual variability of ecosystem functioning in the Solent.