DOI: 10.5061/dryad.3j9kd51q2
title: Lake Sanabria ecosystem regime shift (1986-2019)

description: 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.
description: Analytical methods are described in more detail in the associated
 publications.  1.       Description of the
 methodology used to generate the dataset.
 1.1   <em>Site</em>: ·        
 Lake Sanabria, of glacial origin, is the largest natural lake in the
 Iberian Peninsula (maximum depth 50 m, area 3.536
 km<sup>2</sup>, volume 99.114 hm<sup>3</sup>,
 watershed 122.16 km<sup>2</sup>) 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  
 <em>Meteorological stations</em>: ·        
 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) <em>1.3   </em><em>Lake
 physico-chemical and biological data:</em>
 ·         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.
 <em>1.4   </em><em>Hydrological and external
 load modelling: </em> ·         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. <em>1.5  
 </em><em>Lake trends analyses:</em>
 ·         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.
description: Microsoft Excel Microsoft
 Word
description: **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.