Spatial variability of methane (CH₄) ebullition in a tropical hypereutrophic reservoir: silted areas as a bubble hot spot

Abstract

De Mello NAST, Brighenti LS, Barbosa FAR, Staehr PA, Bezarra Neto JF. 2017. Spatial variability of methane (CH ₄) ebullition in a tropical hypereutrophic reservoir: silted areas as a bubble hot spot. Lake Reserv Manage. 35:105—114. The concentration of methane (CH ₄) has doubled in the atmosphere over the last 200 yr, raising the need to understand emissions of this potent greenhouse gas from inland waters. CH ₄ ebullition is the dominant pathway in shallow aquatic environments and is difficult to quantify due to its episodic nature and heterogeneous spatial distribution. We investigated the temporal and spatial variability of CH ₄ ebullition during 2013 in a shallow hypereutrophic urban reservoir, in Belo Horizonte City, Brazil. The average emission measured during summer was 780 mg CH ₄/m ²/d, ranging from 1 to 3070 (n = 75). During winter, the average emission was 316 mg CH ₄/m ²/d, ranging from 4 to 1253 (n = 75). A strong spatial variation (P < 0.001) was observed across the reservoir in both seasons. Several folds higher (39—58% of the total) emissions were recorded at the mouth of the main tributaries, which therefore was considered to be a hot spot ebullition zone. This was expected due to its shallow area (mean depth 1.30 m) with low hydrostatic pressure and 2 to 6 C (winter and summer, respectively) higher sediment temperatures, which is aggravated by the intense siltation process resulting from insufficient management of the sewage water entering the reservoir. In this article we demonstrate the consequence of siltation as an enhancing factor for CH ₄ emission from the hot spots ebullition zones.