DOI: 10.5061/dryad.5hqbzkh5t
title: Atmospheric pressure influencing ebullition and turbidity

description: Methane ebullition from lake sediment is an important source of
 atmospheric methane. Previous studies have suggested that temperature
 variations, water level changes, atmospheric pressure fluctuations and
 wind-induced current can affect ebullition. However, most of those studies
 were conducted during open-water season. There is a lack of observations
 during ice-cover, despite of the abundance of seasonally ice-covered
 lakes. In this dataset, we present high-frequency ebullition intensity
 data, atmospheric pressure data, bottom-water temperature data, and
 turbidite data from Base Mine Lake (57° 1' N, 111° 37' W in
 Alberta, Canada) during ice cover. During the study period, the water
 level in the lake is stable. Also, due to the ice cover, the impact of
 wind-induced current is negligible. The dataset shows that ebullition
 during ice cover is regulated by atmospheric pressure variations; the
 stable bottom-water temperature has on correlation with the ebullition.
 The dataset also shows that turbidity at depth in the lake increases
 during ebullition events.
description: The ebullition intensity data is collected using a single-beam
 echosounder (Echologger EA400), which is mounted beneath ice. Bursts of 50
 pings over 25 seconds (2Hz) are logged once every hour.
 The turbidity is collected at 30-minute intervals using a RBRDuo
 logger with a Seapoint turbidity sensor attached to a mooring chain. The
 instrument was calibrated by the manufacturer (RBR). To remove spikes, for
 example, a three-point median can be applied to the raw data .
 Water temperature data is collected every 10 seconds using a
 RBRSolo logger, attached to the same mooring chain as turbidity
 logger. The instrument was calibrated by the manufacturer (RBR). To smooth
 the short-term variations, for example, a 10-minute moving average can be
 applied to the raw data. Atmospheric pressure data is
 collected at the center of lake. The pressure data has been compared with
 the atmospheric pressure at a nearby airport,. The variations in
 atmospheric pressure at these two stations were nearly identical, except a
 constant pressure offset. Notes for echo-sounding
 data: The echo-sounding data is used to derive the ebullition intensity.
 The echosounder records the full profiles of the water column beneath
 it. Every hour, a burst of 50 pings over 25 seconds is set to record the
 ebullition activities through the water column. Each burst of 50 pings
 produces an echogram. In the echogram, there are several common elements:
 rising bubbles, floating reflectors, random noises, a blank after transmit
 region at the top and the lakebed at the bottom. A filtering  methode
 discribed below is used to remove the interference while preserving the
 signal from the rising bubbles. This filtering method
 is designed with consideration of the two main features of the echograms:
 1) In each echogram, the rising bubbles are diagonal lines and in general
 have much higher backscattering intensity than the background noise and
 the average row intensity. 2) the floating reflectors are time invariant
 and therefore their intensities are similar to the depth specific time
 average. The filtering method has three steps. Firstly, a certain range of
 depth (5.2 m to 8.5 m) is chosen to exclude the depths with interference
 close to the instrument and to exclude the lakebed. Secondly, the
 influence of the system noise is excluded, i.e. if the intensity of each
 element is less than the noise it is set to zero. Thirdly, in every row of
 the echogram, if the value of each element is less than one fifth the time
 averaged value, it is set to zero. After applying a filtering method, the
 intensity of the rising bubbles in the individual echogram is averaged and
 used to represent the ebullition intensity at that hour. 
description: There are five sheets in the Excel, including ebullition
 intensity, atmospheric pressure, temperature and turbidity data. The
 missing data is stored as NaN. There is also an associated
 README.txt.