Lake Sanabria ecosystem regime shift (1986-2019)
Data files
Aug 30, 2024 version files 439.32 KB
Abstract
This dataset has been used to study the ecosystem regime shifts of Lake Sanabria, the largest natural glacial lake in Spain, in a situation of climate change that may affect compliance with ecological quality objectives, even with no significant water quality pressures. It comprises basic data from long-term (1986-2017) and intensive short-term (2015-2017) limnological monitoring of a few relevant state variables related to nutrients balance, primary production of phytoplankton and thermal structure of the water column. Data about recent history of the lake productivity, reconstructed by high-resolution palaeolimnological analysis of a surface sediment core, is provided. Time series analysis over several decades has detected significant conditional heteroscedasticity in the concentrations of parameters such as chlorophyll and oxygen in recent years in relation to lake turnover rates, coinciding with exceptional episodic single-species blooms of some planktonic diatoms. We include precipitation data, inflow measurements and land use modeling data that indicate how external nutrient loadings have declined during the last decades, with reduced precipitation and progressive afforestation of the catchment, but the lake is shifting to a more productive regime enhancing the relevance of internal loading and processes.
README
Lake Sanabria ecosystem regime shift (1986-2019)
DESCRIPTION OF FILES STRUCTURE AND CONTENTS
We have submitted our lake chemistry data from long-term monitoring 1986-2018 of lake water column (Lake-Sanabria_water-chemistry_1986-2018.csv) and biannual intensive monitoring 2015-2017 of lake inlet and outlet (Lake-Sanabria_water-chemistry_2015-2017.csv), the biovolume data of the different phytoplankton groups for the period 2015-2017 (Lake-Sanabria_phytoplankton_Biovolumen_2015-2017.csv), the chemistry data of a recent sediment core (Lake-Sanabria_sediment-core-chemistry_2018.csv), the monthly precipitation for the period 1963-2017 (Lake-Sanabria_meteorology_1963-2017.csv), and the data type used in the MapShed model (Lake-Sanabria_TN-TP-modelling_2015-2017.csv).
Descriptions:
Lake-Sanabria_water-chemistry_1986-2018.csv
- Date of sampling: date on which water samples were collected (YYYY-MM-DD) with monthly periodicity.
- Lake depth sampling: water column depth of sampling (m: meters). Water sample was collected using a hydrographic bottle at 2.5-m intervals from surface to 50-m depth.
- Lake station code: D02 is the code for the sampling site on the surface of the lake, located in the eastern sub-basin of the lake.
- Dissolved oxygen concentration: percent (%) saturation of dissolved oxygen of water at the depth of sampling measured with a multiprobe sonde.
- Water temperature: water sample temperature (°C) at the depth of sampling measured with a multiprobe sonde.
- Soluble Reactive Phosphorus: soluble reactive phosphorus (P-PO4) concentration (µ/L) in the water sample, determined in the laboratory by ion chromatography (940 Professional IC Vario TWO/SeS/PP Metrohm following EPA 300.1 method).
- Nitrates: nitrates (N-NO3) concentration (µ/L) in the water sample, determined in the laboratory by ion chromatography (940 Professional IC Vario TWO/SeS/PP Metrohm following EPA 300.1 method).
- Chlorophyll “a”: chlorophyll “a” concentration (µ/L) in the water sample, determined using Whatman® GF/F fiberglass filters, acetone extraction (90%), spectrometry, and calculated according to Jeffrey et al. (1975).
Lake-Sanabria_water-chemistry_2015-2017.csv
- Date of sampling: date on which water samples were collected (YYYY-MM-DD) with monthly periodicity.
- Lake station code: I02 is the code for the sampling site at the inlet into the lake of the river Tera, and O01 is the code for the sampling site on lake outlet to the river Tera.
- Total nitrogen: total nitrogen (N) concentration (mg/L) in the water sample, determined in the laboratory by segment microflow AutoaNALIZER AA3.
- Nitrates: nitrates (N-NO3) concentration (µ/L) in the water sample, determined in the laboratory by ion chromatography (940 Professional IC Vario TWO/SeS/PP Metrohm following EPA 300.1 method).
- Total Phosphorus: total phosphorus (P) concentration (µ /L) in the water sample, determined in the laboratory by segment microflow AutoaNALIZER AA3.
Lake-Sanabria_phytoplankton_Biovolumen_2015-2017.csv
- Date of sampling: date on which water samples for the analyses of phytoplankton were collected (YYYY-MM-DD) with monthly periodicity.
- Lake station code: D02 is the code for the sampling site on the surface of the lake, located in the eastern sub-basin of the lake.
- Lake depth sampling: water column depth of sampling (m: meters). Water sample for phytoplankton was collected using a hydrographic bottle at 0, 2, 15 and 45 m depth during the water column mixing period, and at 0, 2, 5, 10, 15, 20 and 45 m depth during the stratification period. Phytoplankton samples were fixed with Lugol's solution.
- Biovolumen of Taxonomical group: Taxa were identified under 1000x light microscopy with a Nikon Eclipse Ti-S inverted microscope following Utermöhl's method. Counting and biovolume determination (mm3/L) followed European standards (EN 15204:2006, EN 16695:2015).
Lake-Sanabria_sediment-core-chemistry_2018.csv
- Date of sampling: date on which sediment core was collected (YYYY-MM-DD).
- Lake station code: D02 is the code for the sampling site on the surface of the lake, located in the eastern sub-basin of the lake.
- Core name: sediment core name consisting of a code, SAN18-D2-1, with the following meaning: SAN for Sanabria lake, 18 for the year of sampling 2018, D2 for the lake station D02, and 1 for the master core.
- Subsample level from sediment surface: depth (cm) of the sub-sample taken from the sediment core from the surface. The sediment core was laminated with a resolution of 2 mm.
- Density: dry weight of sediment per volume.
- Dry weight: percentage (%) of fresh sediment after drying at 105 degrees Celsius to constant mass.
- Total Organic Carbon: catalytic oxidation at 750-950 °C with Non-Dispersive InfraRed (NDIR) detection.
- Total Nitrogen: segmented microflow AutoaNALIZER AA3, quantified by a colorimetric method at a wavelength of 600 nm.
- Total Phosphorus: segmented microflow AutoaNALIZER AA3, quantified by a colorimetric method at a wavelength of 800 nm.
Lake-Sanabria_meteorology_1963-2017.csv
- Date: DD/MM/YYYY
- mm/month: total precipitation per month
- Hydrological year: e.g. the hydrological year 1964 runs from 1st October 1963 to 30th September 1964.
Lake-Sanabria_TN-TP-modelling_2015-2017.csv
- Data sources and critical parameters (with units and values) applied in the MapShed model.
Methods
Analytical methods are described in more detail in the associated publications.
1. Description of the methodology used to generate the dataset.
1.1 Site:
· Lake Sanabria, of glacial origin, is the largest natural lake in the Iberian Peninsula (maximum depth 50 m, area 3.536 km2, volume 99.114 hm3, watershed 122.16 km2) located at 1004 m a.s.l. on granitic bedrock. D02 sampling station coordinates: 42° 7' 12.2" N 6° 42' 27.9" W.
1.2 Meteorological stations:
· Puente Porto reservoir (M02 station, 42˚ 7' 1" N, 6º 49' 52" W, 1645 m a.s.l)
· Puebla de Sanabria (AEMET 2770B station, 42˚ 3' 15" N, 6º 38' 2" W, 960 m a.s.l)
1.3 Lake physico-chemical and biological data:
· Long-term lake monitoring (1986-2018) included monthly inlet and outlet samples and profiles in the eastern sub-basin (station D02) for temperature, conductivity, dissolved oxygen, Secchi disk depth, soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate, silica, and chlorophyll. Water samples were collected at 2.5-m intervals from surface to 50-m depth, and the same lab made measurements throughout the period. Additionally, there was a period (2015-2017) of more comprehensive sampling at both sub-basins, including phytoplankton samples and littoral points.
· Chemical parameters were analyzed according to standardized methods, as described in the associated publications.
· Phytoplankton taxa were identified and counted under light and SEM microscopy, and biovolume was determined followed European standards (EN 15204:2006, EN 16695:2015).
· The physical structure of the water column was studied following the methodology and resolution described in the associated publications.
· Cylindrical sediment traps were installed at three depths (6, 14, and 40 m) in the deepest area of the western sub-basin. Several surface sediment cores were obtained at the deepest area of the eastern sub-basin using a Glew-type gravity corer and were sliced at 2 mm intervals. Chemical and biological analyses were performed according to standardized methods, as described in the associated publications.
1.4 Hydrological and external load modelling:
· The water inflow and nutrient loads to the lake were assessed by dynamic modeling on a 5-m spatial resolution digital elevation model (CNIG, 2015) validated with an intensive biennial (2015-2017) sampling of catchment tributaries and atmospheric deposition. Details of the methodology used in the hydrological modelling and the calculation of external loads can be found in the associated publications.
1.5 Lake trends analyses:
· The Lagrange multiplier test for conditional heteroscedasticity (Seekell et al., 2012) was used to analyze lake ecosystem trends.
2. Procedures followed to ensure the quality of the data.
In the field sampling and laboratory analyses, official or standardized methodologies and protocols have been used or, failing that, those most widely accepted by the scientific community, adapting them to better meet the objectives of the work. The laboratories where the analyses have been carried out are certified for the ISO 9001 quality system for the design, development and performance of physical and chemical analyses using chromatography, spectrometry, spectrophotometry, elemental analysis, and toxicity analysis in inland waters.
Usage notes
- Microsoft Excel
- Microsoft Word