Chromophoric Dissolved Organic Matter and Dissolved Organic Carbon in Lakes Across an Elevational Gradient From the Mountains to the Sea

Dissolved organic matter (DOM) in lakes across elevation gradients is a complex function of topography, climate, vegetation coverage, land use, and lake properties. To examine sources and processing of DOM from sea level to mountain lakes (3–1,574 m), we measured dissolved organic carbon (DOC) concentrations and chromophoric dissolved organic matter (CDOM) optical properties, lake characteristics, and water quality parameters in 62 freshwater lakes in the Pacific Northwest, USA. Higher elevation lakes had lower DOC concentrations and absorbance. These lakes had higher forest cover and minimal wetlands in their watershed, in addition to low nutrients, water temperatures, and chlorophyll a in the lake itself. Two humic-like and one protein-like fluorescent component were identified from excitation-emission matrix spectroscopy. The index of recent autochthonous contribution (BIX), fluorescence index (FIX), and SR optical indices showed that most lakes were dominated by terrestrially derived material. The humification index (HIX) and specific ultra-violet absorbance (SUVA254) were consistent with more aromatic humic CDOM at lower elevations. The lower fluorescence of humic-like components at higher elevation was attributed to lower inputs from vegetation. The relative contribution of the protein-like component increased at higher elevation. This may be due to reduced allochthonous terrestrial inputs relative to in situ production of autochthonous material or increased photochemical/biological degradation of allochthonous material. Differences in optical characteristics associated with the amount and source of CDOM were observed across the elevational gradient. These differences were driven by characteristics at both within-lake and watershed scales

Supporting Information for Chromophoric Dissolved Organic Matter (CDOM) Across an Elevational Gradient from Sea Level to Mountain Lakes in the Pacific Northwest

This dataset is in support of Juetten et al., which has been submitted to the Journal of Geophysical Research Biogeosciences for consideration for publication. Chromophoric dissolved organic matter (CDOM) in lakes across elevation gradients is a complex function of topography, climate, vegetation coverage, land use, and lake properties. To examine sources and processing of CDOM from sea level to mountain lakes (3 to 1574 m), we measured CDOM optical properties, lake characteristics, and water quality parameters in 62 freshwater lakes in the Pacific Northwest, USA. Higher elevation lakes had lower dissolved organic carbon (DOC) and absorbance. These lakes had higher forest cover, minimal wetlands or crops, low nutrients, cooler water temperatures, and low chlorophyll a. Two humic-like and one protein-like fluorescent component were identified from excitation-emission matrix spectroscopy (EEMs). The index of recent autochthonous contribution (BIX), fluorescence index (FIX) and SR optical indices indicated that most lakes were dominated by terrestrially-derived material. The humification index (HIX) and specific ultra-violet absorbance (SUVA) were consistent with more aromatic humic CDOM at lower elevations. Fluorescence of humic-like components was lower at higher elevation, indicating reduced amounts of CDOM, attributed to lower inputs from vegetation. The relative contribution of the protein-like component increased at higher elevation, because allochthonous terrestrial inputs are reduced relative to in situ production of autochthonous material or higher photochemical and biological degradation of allochthonous material. Differences in optical characteristics associated with CDOM levels and some characteristics associated with CDOM source and quality were observed across the elevational gradient. These differences were driven by characteristics at both within-lake and watershed scales, suggesting a more complete understanding of CDOM patterns can be gained by examining factors at multiple spatial scales. The dataset available below is supplementary information to the paper in a Word file format. This includes: a figure corresponding to the RDA Figure 6 in the manuscript giving the lake names; a table giving sampling dates, elevations, locations and watershed characteristics for the lakes; a table comparing water quality parameters for deep vs, surface water samples from Lake Padden in 2011; and a table giving the measured water quality parameters for the lakes from summer 2018

Impact of the Macrophyte Nymphaea odorata (Lily Pads) on Dissolved Organic Matter (DOM) in a Lake

(Files are available for download below.) Macrophytes are a potential source of dissolved organic matter (DOM) in lakes. To probe the contribution of Nymphaea odorata (lily pads), dissolved organic carbon concentrations (DOC) and optical properties of chromophoric DOM were measured in a lake in the Pacific Northwest, United States over a year. Lily pads are prevalent around the shoreline during summer, dying back in fall. Indices of recent autochthonous contribution (BIX), fluorescence (FIX) and SR showed the lake was dominated by terrestrially-derived material. DOC concentrations were not correlated with rainfall, but were positively correlated with absorption coefficients. Values were highest in the summer dry season and decreased in the winter wet season, suggesting a source in the lake being diluted by precipitation rather than a dominant source from watershed runoff. Humic-like and protein-like fluorescent components were identified from excitation-emission matrix spectroscopy in lake waters and lily pad leachates. The protein-like component was highest during the summer, indicative of an in situ autochthonous source. Lily pad leachates had BIX, FIX, and SR values characteristic of terrestrial material and lake samples. However, leachates had lower humification index (HIX), specific ultraviolet absorbance (SUVA), flu/abs ratios and spectral slope (S) values. Higher absorption coefficients and DOC concentrations in the lake in summer were correlated with lower HIX, SUVA, flu/abs and S values, consistent with material leaching from lily pads. Seasonal trends in optical indices, absorption coefficients and DOC concentrations are consistent with lily pads being a significant DOM source in the lake, particularly in the summer dry season with low watershed runoff. This is for the supporting data for the paper in Limnology and Oceanography, specifically the absorbance and fluorescence spectra of the Lake Louise water samples (taken weekly over the course of a year). These files include large spreadsheets with raw and corrected absorbance and fluorescence intensity data as a function of wavelength, as well as the raw and corrected absorbance and fluorescence 3D excitation-emission matrix spectra (EEMs). These files are in .opj format, which is readable with commercially available Origin graphing software. Data includes tables with optical parameters and indices for absorbance and fluorescence for the weekly lake water samples, and spreadsheets with raw and corrected absorbance and fluorescence intensity data as a function of wavelength, as well as raw and corrected absorbance and fluorescence 3D excitation-emission matrix spectra (EEMs)