A long-term (1986-2010) phytoplankton dataset from the LTER-Italy site Lake Candia

Study Extent

Phytoplankton integrated samples in the whole euphotic zone were gathered approximately monthly, at the station of lake maximum depth (7.7 m). They were then analysed in the lab through the inverted microscope, estimating abundance and biovolume of each taxa from March 1986 to December 2010.
A total of 266 sampling events, from March 1986 to December 2010, with 10120 georeferenced occurrence records at the species level or higher rank have been uploaded to the GBIF repository

Sampling

Phytoplankton data were collected monthly from 1986 to 2010, at the point of lake maximum depth (7.7 m) as integrated samples of the euphotic water column.
Phytoplankton determinations were carried out on subsamples of the integrated sample preserved in acetic Lugol’s solution. Phytoplankton organisms were counted using the Utermöhl technique (Utermöhl, 1958), classifying the taxa to the species level, whenever possible, using a Zeiss Axiovert 10 inverted microscope at 200x and 400x until 400 cells for the most important taxa were counted. Biomass of each taxa in the sample was estimated from abundance data and original measurements of cell volume (Smayda, 1978; Hillebrand et al., 1999; Sun and Liu, 2003). Finally, total biovolume was calculated from the sum of the biovolumes of each taxon in the sample (cell number x specific cell volume).
All records are validated to the currently accepted nomenclature using the taxonomic backbone of GBIF, Algaebase: Listing of World’s Algae (Guiry and Guiry, 2022), and World Register of Marine Species WoRMS (Ahyong et al., 2022). Life Science Identifiers (LSIDs) are used to identify univocally the taxon and to facilitate data integration and interoperability.
Taxon specialists: Martina Austoni, Radiana Cozza, Giuseppe Morabito, Alessandro Oggioni, Pierisa Panzani, Alessandra Pugnetti, Teresa Ruffoni, Delio Ruggiu, Karin Sparber.

Quality Control

Quality control for geographic data: Reliability of coordinates was checked with open source Geographic Information System (Quantum GIS – http://www.qgis.org/) to identify the correctness of sampling station position. Geographic coordinate format and the absence of anomalous ASCII characters in the dataset were also double checked.
Quality control for taxonomic data: Nomenclature validation and cleaning were based on the global algal database AlgaeBase (Guiry and Guiry, 2022), World Register of Marine Species WoRMS (Ahyong et al., 2022) and on the taxonomic backbone of GBIF. To check the taxonomic classification and to fill the information about taxa, taxon rank, occurrences status, and taxonomic status we used ReLTER R package (Oggioni, et al. 2022).

Method steps

1. Dataset includes 10120 georeferenced occurrences related to 545 taxa. During this 25-year period the lake underwent profound modifications mainly related to the lake biomanipulation activities addressed to the management of aquatic macrophyte and to the evolution of the trophic condition. Making available this dataset represents also a contribution to the current activities of the LTER networks, aiming on accessibility of the time series of the LTER sites, in order to reconstruct trends and dynamics and to identify and compare reliable trends.
2. The dataset was structured based on the Darwin Core standard (DwC, Wieczorek et al., 2012), with each row containing a record of the occurrence of a taxon from a sample. The columns report taxonomical (e.g. scientificName, scientificNameID, taxonRank), geographic (e.g. decimalLatitude, decimalLongitude, geodeticDatum) information, along with density and biovolume for each taxon recognised in the sample.

General description: dataset covers phytoplankton assemblages and counts. Phytoplankton counting are based on inverted microscopy following Uthermöl method (Uthermöl, 1958) and biomass of each taxa was estimated from abundance data and original measurements of cell volume (Hillebrand et al., 1999; Sun and Liu, 2003). The dataset covers Cyanobacteria with 1660 occurrences; Plantae with 1302 occurrences (28.1% of Plantae occurrences) of Charophyta and 3324 occurrences (71.8%) of Chlorophyta; Protozoa (426 occurrences); and Chromista with Ochrophyta (1736 occurrences), Cryptophyta (1213 occurrences), Myzozoa (345 occurrences), and Haptophyta (108 occurrences).

1. Bacillariophyceae
   rank: class
2. Cyanobacteria
   rank: phylum

Lake Candia belongs to the Italian, European and International Long-Term Ecological Research (LTER) Networks: Candia (https://deims.org/c7fe4203-24b1-4d11-a573-99b99204fede). Data are georeferenced according to WGS 84 datum (EPSG:4326, https://epsg.io/4326.wkt).
Habitat type: Pelagic of lake, water column.
Biogeographic region: Within the Palearctic realm, according to the definitions of the European Environmental Agency (2017), the dataset covers the Alpine European biogeographical regions.
Country: Italy.