Biological and physico-chemical characterization of shallow lakes in Spain’s Sierra Nevada

Study Extent

The dataset corresponds to the simultaneous sampling (carried out by multidisciplinary groups of researchers, citizen volunteers and environmental agents) of a set of 55 and 48 high mountain shallow lakes in the Spanish’s Sierra Nevada during the years 2020 and 2022, respectively. The year 2022 corresponded to a relatively anomalous year in which Sierra Nevada was subjected to a massive influx of aerosols from the Sahara. See exact location of the shallow lakes in https://lagunasdesierranevada.es/lagunas/

Sampling

1. Sampling: field samples were taken during the ice-free period when there was maximum biological activity in July or early August. In the smaller shallow lakes (ca. 1 meter or less), water samples were taken aleatory around the perimeter using a pole-mounted buckets. For larger lakes, water samples were taken at the deepest part of the lake using an integrating water sampler of the upper waters (ca. 1.2 m). Water was mixed in a container and subsamples taken for the quantitative assessment of bacteria, zooplankton, macronutrients (total and dissolved nutrients), major cations and anions, and alkalinity. 2. Physico-chemical characterization: temperature was measured in situ using precision portable thermometers. Turbidity, pH, dissolved oxygen, redox potential, NTU, conductivity and salinity were determined within three 3 hours after sampled using a YSI ProDSS probe. 3. Nutrients, major cations/anions, and alkalinity: total nitrogen and total phosphorus samples were persulfate digested and measured as nitrate and as soluble reactive phosphorus, respectively, by means of standard spectrophotometric methods (APHA, 1998). These methods were also used to measure total dissolved nitrogen and total dissolved phosphorus after filtration through Whatman GF/F filters. Major cations and anions were measured in ion chromatography. Total alkalinity was measured by the acid tritation method (APHA, 1998). 4. Bacteria and zooplankton: for the quantification of bacteria aliquots were fixed with paraformaldehyde, stained with SYBR Green I DNA and determined using a Becton Dickinson FACScan flow cytometer and Yellow-green-1 µm beads (Lozano et al. 2022). Zooplankton were identified and counted with the aid of an inverted microscope. 5. Chlorophyll-a (chl-a) sampling and analysis: water samples were filtered through pre-combusted glass fibre filters (Whatman GF/F, pore size = 0.7 µm). Filters were frozen at -20ºC until the analysis. For analysis, chl-a was extracted with 7 ml 99% absolute ethanol for analysis during 24 h in refrigerated and dark conditions. Chl-a concentration was determined spectrophotometrically using a Perkin Elmer UV-Vis 25 spectrophotometer with 5-cm path-length cuvettes (Jeffrey & Humphrey, 1975; Ritchie, 2006).

Quality Control

1. Sampling: the multidisciplinary teams (composed of citizen volunteers and environmental agents) have been led and supervised and researchers. 2. Digitalisation: all data has been revised by experts before their introduction in the dataset. 3. Storage: data is stored in Linaria (https://linaria.obsnev.es/), the institutional data repository of the Sierra Nevada Global-Change Observatory. Linaria is a normalised database focused on ecology and biodiversity related-data and it is developed in a PostgreSQL/PostGIS relational database management system (RDBMS). 4. Taxonomic validation: scientific names were reviewed by experts and were checked with the GBIF backbone taxonomy using the species matching tool (https://www.gbif.org/tools/species-lookup). 5. Coordinates validation: the sampling event’ coordinates are the same as those that locate the lakes on this official website https://lagunasdesierranevada.es/lagunas/. 6. Standardisation: the standardisation to Darwin Core was done according to the practices recommended by the TDWG guidelines (https://dwc.tdwg.org/terms/).

Method steps

1. 1. Field sampling, measurement of environmental variables (see Sampling Description section). 2. Sampling processing in the laboratory (see Sampling Description section). 3. Data storage in Linaria (https://linaria.obsnev.es/), the institutional data repository of the Sierra Nevada Global-Change Observatory. 4. Standardisation to the Darwin Core structure (De Pooter et al., 2017) as sampling event data. It contains, specifically: 102 events, 2,649 occurrences, and 2,071 records of associated measurements (23 variables). The Darwin Core elements included in the Event Core are: eventID, modified, language, institutionCode, ownerInstitutionCode, datasetName, license, eventDate, year, month, day, continent, country, countryCode, highergeography, waterBody, minimumElevationInMeters, maximumElevationInMeters, samplingProtocol, decimalLatitude, decimalLongitude, geodeticDatum. For the Occurrence Extension are: occurrenceID, catalogNumber, collectionCode, eventID, eventDate, organismQuantity, organismQuantityType, basisOfRecord, scientificName, taxonRank, kingdom, phylum, class, order, family, genus, specificEpithet, scientificNameAuthorship, occurrenceStatus. For the Measurement or Fact Extension table, the Darwin Core elements included are: measurementID, eventID, measurementType, measurementValue, measurementUnit, measurementMethod. In the eventDate element the local time zone (Europe/Brussels) is indicated as an offset from UTC (conforming to ISO 8601). Special values in the measurementValue element: “BDL” (Below Detection Limit). 5. The resulting dataset was published through the Integrated Publishing Toolkit of the Spanish node of the Global Biodiversity Information Facility (GBIF) (http://ipt.gbif.es).

This dataset includes a total of 2,649 occurrence records of bacteria and zooplankton, the latter represented by 14 families, 20 genera and 19 species.

1. Bacteria
   rank: kingdom
2. Arthropoda
   rank: phylum
3. Rotifera
   rank: phylum

Sierra Nevada, situated in the southern part of the Iberian Peninsula within Spain, spans the provinces of Granada and Almería. This mountain range extends over 2,273 square km and reaches its highest point at 3,479 meters a.s.l. at the Mulhacén summit. Due to its southern European location, proximity to the Mediterranean Sea, and considerable elevation, Sierra Nevada boasts a diverse range of climatic conditions, encompassing five of the six bioclimatic zones found in the Mediterranean region, ranging from the thermo-mediterranean to the crioro-mediterranean. The Sierra Nevada Natural Area boasts an extensive hydrographic network, comprised of rivers, streams, and high mountain lakes, primarily nourished by the snowmelt from its towering peaks. This dataset covers high elevations shallow lakes of glacial origin located between 2,700 and 3,100 meters a.s.l., on small catchment areas above treeline characterised by metamorphic siliceous bedrocks, poorly developed soils and steep topographic gradients.