DOI: 10.5061/dryad.905qftttj
title: Climate change and underwater light: Large-scale changes in UV transparency associated with intensifying wet-dry cycles

description: Ultraviolet radiation (UV) is the most energetic waveband of incident
 solar radiation and has wide-ranging effects in the aquatic environment.
 Our analysis of an 18-year record of underwater irradiance and related
 limnological variables in sub-alpine, ultra-oligotrophic Lake Tahoe
 revealed orders of magnitude changes in UV transparency associated with
 interannual climate perturbations. The largescale shifts between years
 were caused by pronounced changes in the loading of allochthonous
 particulate matter and colored dissolved organic matter (CDOM) associated
 with regional dry-wet cycles, while chlorophyll a combined with
 autochthonous CDOM controlled the seasonal variations in UV under average
 weather conditions. Water clarity in the photosynthetically available
 radiation (PAR) waveband showed less variation, resulting in large
 interannual differences in the UV:PAR ratio. Clear-water lakes are likely
 to experience increasingly large fluctuations in underwater UV and
 spectral irradiance due to ongoing climate change and precipitation
 extremes, with potential impacts on their ecosystem structure and
 function.
description: # Climate change and underwater light: large-scale changes in UV
 transparency associated with intensifying wet-dry cycles
 [https://doi.org/10.5061/dryad.905qftttj](https://doi.org/10.5061/dryad.905qftttj) The data set include all optical, limnological, and metrological data used in the manuscript "Climate change and underwater light: large-scale changes in UV transparency associated with intensifying wet-dry cycles" submitted to Limnology and Oceanography - Letters. The value "n/a" stands for not available (missing value = sample not collected or analysis failed). Description of the data and file structure ## 1. Tahoe\_UVPAR.csv Calculated attenuation coefficient values for all measured wavebands (305, 320, 380, and PAR). Col 1: Event_ID The ID number of the sampling event. Col 2: Date Date of sampling in YYYY-MM-DD Col 3: Kd305 The diffuse attenuation coefficient of downward irradiance at 305 nm in m^-1 Col 4: Kd320 The diffuse attenuation coefficient of downward irradiance at 320 nm in m^-1 Col 5: Kd380 The diffuse attenuation coefficient of downward irradiance at 380 nm in m^-1 Col 6: KdPAR The diffuse attenuation coefficient of downward irradiance for PAR in m^-1 Col 7: Flag Quality control Flag (T/F) Col 8: Note Comments ## 2. Tahoe\_Chl.csv Measured Chl a concentrations for discrete water samples. Col 1: Event_ID The ID number of the sampling event. Col 2: Date Date of sampling in YYYY-MM-DD Col 3: Depth Depth of sampling Col 4: Chla Concentrations of Chl a in ug L^-1 ## 3. Tahoe\_Particle.csv Measured concentrations of particulate matter for discrete water samples. Col 1: Event_ID The ID number of the sampling event. Col 2: Date Date of sampling in YYYY-MM-DD Col 3: Depth Depth of sampling Col 4: Particle Concentrations of Particulate matter in number of particles L^-1 ## 4. Tahoe\_Phyto\_Count.csv Measured concentrations of Cyclotella spp for discrete water samples. Col 1: Event_ID The ID number of the sampling event. Col 2: Date Date of sampling in YYYY-MM-DD Col 3: Depth Depth of sampling Col 4: Cyclotella_Num Concentrations of Cyclotella in number of cells L^-1 Col 5: Non_Cyclo_Num Concentrations of Non Cyclotella Phytoplankton in number of cells L^-1 For Col 4 & 5, n/a stands for Data not available due to unknown issues in analysis. ## 5. Tahoe\_CDOM.csv Measured absorption coefficient of colored dissolved organic matter (CDOM) for discrete water samples. Col 1: Event_ID The ID number of the sampling event. Col 2: Date Date of sampling in YYYY-MM-DD Col 3: Depth Depth of sampling Col 4: a305 Absorption coefficient of CDOM at 305nm m^-1 Col 5: a320 Absorption coefficient of CDOM at 320nm m^-1 Col 6: a380 Absorption coefficient of CDOM at 380nm m^-1 Col 7: a440 Absorption coefficient of CDOM at 440nm m^-1 ## 6. Tahoe\_Secchi.csv Secchi depth. This is a subset of an open access data repository available from the link below Watanabe, S. 2023. Lake Tahoe Historic Secchi depth. Environmental Data Initiative. [https://portal.edirepository.org/nis/mapbrowse?scope=edi&identifier=1340](https://portal.edirepository.org/nis/mapbrowse?scope=edi&identifier=1340) Col 1: Date_Time_Local Sampled date and time in local time (PSD/PDT) Col 2: Secchi Measured Secchi depth in m ## 7. Tahoe\_City\_Annual\_Precipitation.csv Annual precipitation at Tahoe City Meteorological Station (GHCND:USC00048758). Raw data were downloaded from Climate Data Online, National Oceanic and Atmospheric Administration ([https://www.ncei.noaa.gov/cdo-web/](https://www.ncei.noaa.gov/cdo-web/)) Col 1: Water_Year Water year Col 2: Annual_Prec Annual precipitation in inch. ## 8. Tahoe\_Drought\_Index.csv Drought Index in Lake Tahoe Basin (HUC: 16050101). Data were downloaded from the US Drought Monitor, droughtmonitor.unl.edu. Col 1: Week Week of observation Col 2: None % area classfied as Normal or wet conditions. Col 3: D0-D4 % area classfied as D0 (Abnormally Dry) to D4 (Exceptional Drought) Col 4: D1-D4 % area classfied as D1 (Moderate Drought) to D4 (Exceptional Drought) Col 5: D2-D4 % area classfied as D2 (Severe Drought) to D4 (Exceptional Drought) Col 6: D3-D4 % area classfied as D3 (Extreme Drought) to D4 (Exceptional Drought) Col 7: D4 % area classfied as D4 (Exceptional Drought)