Quantification of methane bubbles in shallow freshwaters using horizontal hydroacoustical observations

0443155 - BC 2016 RIV US eng J - Článek v odborném periodiku
Frouzová, Jaroslava - Tušer, Michal - Stanovský, Petr
Quantification of methane bubbles in shallow freshwaters using horizontal hydroacoustical observations.
LIMNOLOGY AND OCEANOGRAPHY-METHODS. Roč. 13, č. 11 (2015), s. 609-616. ISSN 1541-5856. E-ISSN 1541-5856
Grant CEP: GA ČR(CZ) GAP504/12/1186
Institucionální podpora: RVO:60077344 ; RVO:67985858
Klíčová slova: methane ebullition * freshwaters * sonar
Kód oboru RIV: DA - Hydrologie a limnologie
Impakt faktor: 2.008, rok: 2015

Methane represents an important greenhouse gas, and its ebullition is a significant method of releasing the gas from bottom sediments of shallow waters to the atmosphere. Detecting methane bubbles is complicated because of high spatiotemporal variability; however, hydroacoustical surveys represent an effective method for quantifying ebullitive emissions. Vertical and horizontal hydroacoustical observations performed in shallow waters are presented in this work, with an emphasis on horizontal observations. Bubbles of various sizes, ranging from 2.5 to 907.2 μl, were artificially prepared using a bubble generator and released from a depth of 6 m in a freshwater lake. The acoustic target strength (TS) of these bubbles was observed using both the vertical and horizontal beams of 120-kHz frequency sonar. The recorded TS of the bubbles in vertical mode varied from -61 dB to -43 dB. These values were significantly stronger than those of the bubbles observed in horizontal mode, which ranged from 62 dB to -48 dB. The TS obtained in both the vertical and horizontal modes increased with increasing bubble size. Additionally, the TS of the smallest sizes in vertical mode increased as the bubbles rose to the surface. For other sizes of bubbles and in horizontal mode, the bubble TS either decreased or did not change significantly when the bubbles traveled upwards. Based on these results, we suggest elimination of the depth correction for volume in studying methane bubbles in shallow waters. Furthermore, we developed equations that can determine bubble volume from bubble TS in both the vertical and horizontal planes.
Trvalý link: http://hdl.handle.net/11104/0252457