DOI: 10.5061/dryad.hmgqnk9cf
title: Data from: Sierra Nevada mountain lake microbial communities are structured by temperature, resources, and geographic location

description: Warming, eutrophication (nutrient fertilization) and brownification
 (increased loading of allochthonous organic matter) are three global
 trends impacting lake ecosystems. However, the independent and synergistic
 effects of resource addition and warming on autotrophic and heterotrophic
 microorganisms are largely unknown.  In this study, we
 investigate the independent and interactive effects of temperature,
 dissolved organic carbon (DOC, both allochthonous and autochthonous), and
 nitrogen (N) supply, in addition to the effect of spatial variables, on
 the composition, richness, and evenness of prokaryotic and eukaryotic
 microbial communities in lakes across elevation and N deposition gradients
 in the Sierra Nevada mountains of California, USA. We found that both
 prokaryotic and eukaryotic communities are structured by temperature,
 terrestrial (allochthonous) DOC and latitude. Prokaryotic communities are
 also influenced by total and aquatic (autochthonous) DOC, while eukaryotic
 communities are also structured by nitrate. Additionally, increasing N
 availability was associated with reduced richness of prokaryotic
 communities, and both lower richness and evenness of eukaryotes. We did
 not detect any synergistic or antagonistic effects as there were no
 interactions among temperature and resource variables. Together, our
 results suggest that (a) organic and inorganic resources, temperature, and
 geographic location (based on latitude and longitude) independently
 influence lake microbial communities; and (b) increasing N supply due to
 atmospheric N deposition may reduce richness of both prokaryotic and
 eukaryotic microbes, likely by reducing niche dimensionality.
  Our study provides insight into abiotic processes structuring
 microbial communities across environmental gradients and their potential
 roles in material and energy fluxes within and between ecosystems.
description: Between June and August 2015, thirty-four Sierra Nevada lakes
 containing fish were sampled across a 904 m elevation gradient (2433-3337
 m), encompassing lakes in the montane (below 2450 m), subalpine (2450-2900
 m) and alpine zones (2900 m and above). The lakes were also sampled across
 a latitudinal N deposition gradient spanning Yosemite National Park
 (YOSE), Inyo National Forest (INYO), and Sequoia National Park (SEKI).
 Latitude and Longitude data are provided in degrees and UTM, as well as
 Lake Chain Number (LCN), which indicates relative positioning of lakes
 connected by surface flow along a linear chain (ie. higher vs. lower in
 watershed) to account for connectivity between lakes sharing the same
 basin. The lakes encompassed a 10.2°C temperature gradient (8.7-18.9°C),
 805.7 μM DOC gradient (68.8-874.5 μM) and 2.6 μM
 NO<sub>3</sub><sup>-</sup> gradient (0.0044-2.6
 μM). The lakes ranged 0.5–21 hectares in surface area and 1.8 to 40.8 m in
 depth. All lakes were oligotrophic (chl-<em>a</em> ≤ 3.33 µg
 l<sup>−1</sup>) and have similar geologic and chemical
 characteristics as they are situated on granite and granodiorite
 bedrock. Water samples from the epilimnion (surface to
 1m depth) were collected at each lake for biological and chemical
 analyses. At the deepest point in each lake, in situ<i>
 </i>depth profiles of physico-chemical data were taken using a YSI
 probe (YSI Incorporated, Yellow Springs, Ohio, USA). However, pH data were
 not reliable due to a faulty pH probe and have been excluded from this
 study. Water samples were collected with a 1 m integrated tube sampler and
 filtered through 63 μm mesh to remove zooplankton, then processed for
 chlorophyll-a (chl-a); nitrogen and phosphorus in particulate organic
 matter (POM); total nitrogen (TN); total phosphorus (TP); dissolved
 nitrate (NO<sub>3</sub><sup>-</sup>); and
 dissolved organic carbon (DOC). From UV-vis absorbance
 and EEMs data, we calculated two indices of DOC quality: the freshness
 index (β:α) and specific UV absorption (SUVA). Freshness Index (FrI) is a
 ratio of emission intensity at 380 nm to that of the region between 420
 and 435 nm at an excitation of 310 nm and is reflective of recently
 produced algal organic matter (Parlanti et al., 2000). SUVA is a
 DOC-normalized index of aromaticity calculated as UV absorbance at 254
 nm/[(DOC(mg/L) x path length (0.01 m)] (Weishaar et al., 2003). Therefore,
 Freshness Index increases with autochthonous carbon production whereas
 SUVA increases with allochthonous carbon production.
description: There are missing values for TP because many samples were below
 detection limit (indicated as '&lt;detection') and missing
 values for NO<sub>3</sub><sup>- </sup>are
 indicated as 'NA'. Lakes higher in the basin have lower LCN
 values (eg. 1 is headwater lake), and LCN values of 0 indicate that lakes
 are not connected to others in the basin.