DOI: 10.5285/50f4344e-a79a-4e1f-a9ee-e7985ed847cd
title: Biogeochemistry and phytoplankton data from Loch Etive, Scotland, October 2022

description: This dataset contains biogeochemical measurements of surface water, sampled across Loch Etive, Scotland, between the 3rd and 7th of October 2022. The dataset encompasses 23 locations including nine open loch stations, four fish-farm adjacent loch sites, six river inflows, and four process experiment river sites, enabling a comparison of water chemistry across marine, freshwater, and anthropogenically influenced environments.

Surface water samples were collected and analysed for an extensive range of biogeochemical parameters. In-field measurements included water temperature, pH, dissolved oxygen, and specific conductivity. Laboratory analyses comprised:
-  Alkalinity
- Major nutrients, including nitrate, nitrite, ammonium, soluble reactive phosphorus (SRP), and silica
- Dissolved and total organic and inorganic carbon and nitrogen (DOC, TIC, TDN)
- Trace elements and rare earth elements (REEs), including lithium, barium, aluminium, and a full suite of lanthanides
- Stable isotope composition of oxygen (δ18O), determined via isotope ratio mass spectrometry
- Chromophoric and fluorescent dissolved organic matter (CDOM/FDOM), with derived indices such as fluorescence index (FI), biological index (BIX), and humification index (HIX)

In addition to water chemistry, particulate samples were collected and analysed for total suspended solids (TSS), particulate organic matter (POM), particulate inorganic matter (PIM), chlorophyll-a concentration, and particulate organic carbon/nitrogen (POC/PON). Phytoplankton community composition was assessed by flow cytometry, quantifying major groups including diatoms, pico- and nano-chlorophytes, cryptophytes, and cyanobacteria.

This comprehensive dataset is intended to inform biogeochemical process understanding in polar analogue environments and to validate analytical workflows and inter-institutional protocols.
description: Surface water was collected via grab sampling at 23 sites across loch, river, and fish farm locations. In situ parameters were measured immediately using a HACH HQ4300 multimeter with calibrated pH, conductivity, and dissolved oxygen probes. Vacuum filtration units and portable pumps were used for sample processing. Samples were transported to the lab within 6 hours for processing.

Nutrient concentrations were measured using segmented flow analysis; DOC, TIC, and TDN by thermal oxidation and chemiluminescence; metals and REEs by ICP-MS and ICP-OES; δ18O via isotope mass spectrometry. Phytoplankton were quantified using flow cytometry; particulate analyses followed gravimetric and spectrophotometric methods.

Units include:
Temperature (°C), pH (unitless), DO (mg/L, % saturation), conductivity (mS/cm)
Nutrients: µmol/L or µg/L (e.g. nitrate, phosphate)
DOC/TIC/TDN: mg/L
Metals: µg/L or ppm
Particulates: mg/L
Phytoplankton: cells/mL
CFDOM indices: Raman units or unitless indices (FI, HIX, BIX)

Raw readings were calibrated and corrected; fluorescence data were processed in R; compiled data include site metadata and documented exclusions.
Calibrations, reference standards, replicates, blanks, and internal controls were used. Analytical QA procedures were followed across all labs. Some data are missing due to instrument errors or lost samples. Not all parameters were measured at all sites.