Dinophysis spp. abundance and toxicity events in South Cornwall, U.K.: Interannual variability and environmental drivers at three coastal sites.

Dinophysis is a genus of dinoflagellates with the potential to cause diarrhoeic Shellfish Poisoning (DSP) in humans. The lipophilic toxins produced by some species of Dinophysis spp. can accumulate within shellfish flesh even at low cell abundances, and this may result in the closure of a shellfish farm if toxins exceed the recommended upper limit. Over the period 2014 to 2020 inclusive there were several toxic events along the South West coast of U.K. related to Dinophysis spp. The Food Standards Agency (FSA) monitoring programme measure Dinophysis cell abundances and toxin concentration within shellfish flesh around the coasts of England and Wales, but there are few schemes routinely measuring the environmental parameters that may be important drivers for these Harmful Algal Blooms (HABs). This study uses retrospective data from the FSA monitoring at three sites on the south Cornwall coast as well as environmental data from some novel platforms such as coastal WaveRider buoys to investigate potential drivers and explore whether either blooms or toxic events at these sites can be predicted from environmental data. Wind direction was found to be important in determining whether a bloom develops at these sites, and low air temperature in June was associated with low toxicity in the shellfish flesh. Using real time data from local platforms may help shellfish farmers predict future toxic events and minimise financial loss.

The impact of rainfall events, catchment characteristics and estuarine processes on the export of dissolved organic matter from two lowland rivers and their shared estuary.

Terrestrially-derived dissolved organic carbon (DOC) and nitrogen (DON) transported by rivers have been recognised as contributors to aquatic nutrient burdens, and can be of importance in rivers and estuaries already impacted by anthropogenic inorganic nutrient discharges. The concentration of DOC and DON and the flux of both to the estuary and ultimately the coastal zone is dependent upon many factors including rainfall, catchment land use, and biological processes. DOC and DON concentrations together with nitrate plus nitrite and ammonium concentrations were measured in the anthropogenically-impacted estuary Christchurch Harbour (UK) and at sites in the lower reaches of its two source rivers, the Hampshire Avon and the Stour, at weekly intervals for a year during which time several extreme rainfall events occurred. A series of transects along the estuary were also performed after weekly sampling was completed. DOC concentrations were correlated between both rivers and the estuary and were positively related to increases in river flow, but DON concentrations revealed a more complicated picture. Peak instantaneous fluxes of DOC and DON exceeded 60,000 kg C d-1 and 7000 kg N d-1 respectively both in the Stour and the estuary during high flow periods. The sources of both and routes by which they enter the aquatic system may account for the differences in dynamics, with flushing of superficial soils being a key source of DOC and point sources such as sewage treatment works being proposed as sources of DON. Removal processes within the estuary were also of importance for DON concentrations whilst DOC behaved more conservatively with some evidence of local production within the estuary. Estimated annual loads of DON and DOC to the coastal zone from Christchurch Harbour were 118 kg N km-2 y-1 and 2296 kg C km-2 y-1.

Modelling macronutrient dynamics in the Hampshire Avon river: A Bayesian approach to estimate seasonal variability and total flux.

The macronutrients nitrate and phosphate are aquatic pollutants that arise naturally, however, in excess concentrations they can be harmful to human health and ecosystems. These pollutants are driven by river currents and show dynamics that are affected by weather patterns and extreme rainfall events. As a result, the nutrient budget in the receiving estuaries and coasts can change suddenly and seasonally, causing ecological damage to resident wildlife and fish populations. In this paper, we propose a statistical change-point model with interactions between time and river flow, to capture the macronutrient dynamics and their responses to river flow threshold behaviour. It also accounts for the nonlinear effect of water quality properties via nonparametric penalised splines. This model enables us to estimate the daily levels of riverine macronutrient fluxes and their seasonal and annual totals. In particular, we present a study of macronutrient dynamics on the Hampshire Avon River, which flows to the southern coast of the UK through the Christchurch Harbour estuary. We model daily data for more than a year during 2013-14 in which period there were multiple severe meteorological conditions leading to localised flooding. Adopting a Bayesian inference framework, we have quantified riverine macronutrient fluxes based on input river flow values. Out of sample empirical validation methods justify our approach, which captures also the dependencies of macronutrient concentrations with water body characteristics.