Inshore

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Inshore

Introduction

The Tamar estuary consists of the main river Tamar and two tributaries, river Tavy and river Lynher. Rivers provide nutrients to the estuary and ultimately the open sea and their concentrations have a fundamental influence on the growth of phytoplankton, together with ecological factors and mechanical phenomenon (Mommaerts, 1969). The temporal and spatial variability in phytoplankton species composition influences in turn the entire food chain since it is at its base. Nutrients concentration and behaviour along the estuary are regulated by processes and self-regulated mechanisms including river run off, estuarine residence time, biological nutrient uptake and many others (Morris et al., 1981).

Aim

The aims of the inshore surveys were to investigate the behaviour of nutrients (silicate, nitrate and phosphate) along the entire estuary, the distribution and composition of the phytoplankton and zooplankton communities along the entire estuary and the water column structure along the lower estuary.

Methods section

On the 03/07/19 two RIBs, Porky Pig and Flying Pig, and the RV Falcon Spirit surveyed the upper estuary and the lower estuary respectively. Porky Pig and Flying Pig sampled at intervals of 2 salinity from Calstock pier to past Tamar Bridge near Saltash, while Falcon Spirit sampled at established locations from the Tavy confluence to the Eastern Channel. Each of the RIBs collected nutrient (silicate, nitrate and phosphate), chlorophyll, phytoplankton samples and Porky Pig sampled for zooplankton as well. Falcon Spirit also sampled for dissolved oxygen at various salinities and collected CTD and ADCP data, the latter was collected both at stations and across transects of the estuary.

Water was passed through a 25mm GFF filter and stored for subsequent lab analysis for silicate, nitrate and phosphate. In order to collect chlorophyll samples, water was passed through GFF filters that were placed in tubes containing 90% acetone. Samples were collected from NISKIN bottles and fixed using manganese chloride and alkaline iodide for dissolved oxygen. Phytoplankton sample where collected and stored with lugol as preservative. Zooplankton samples were collected through a zooplankton net and fixed with 10% formaldehyde solution. All water samples and filters were stored in a dark, cool box.

References

- Mommaerts J.P. (1969). On the distribution of major nutrients and phytoplankton in the Tamar estuary. Journal of the Marine Biological Association of the United Kingdom, 49,749-765.

- Morris A.W., Bale A.J., Howland R.J.M. (1981). Nutrient distributions in an estuary: evidence of chemical precipitation of dissolved silicate and phosphate. Estuarine, Coastal and Shelf Science, 12 (2), 205-216.