Methane Emissions in Spanish Saline Lakes: Current Rates, Temperature and Salinity Responses, and Evolution under Different Climate Change Scenarios

Antonio Camacho,Antonio Picazo,Anna Santamans,Daniel Morant,Javier Miralles-Lorenzo,Andreu Castillo-Escrivà,Carlos Rochera

doi:10.3390/w9090659

Abstract

Wetlands are among the most biologically active ecosystems on Earth, playing an important role in the global carbon cycle. Methane production in wetlands, resulting from anaerobic respiration of organic matter, accounts for an important part of natural sources of methane. In this work, we have evaluated the methane release rates of saline shallow lakes located in Central Spain, some of which maintain natural conditions, whereas others are hydrologically altered, with lowered salinity, or even presenting trophic alterations. We used sediment core plus water incubations to determine the release of methane from the studied lakes to the atmosphere, integrating both diffusion and ebullition processes, as well as the effects of temperature and salinity on methane production. The studied hypersaline lakes released methane at rates within the lowest range reported for temperate lakes and wetlands, whereas in hydrologically altered lakes that have dropped their salinity these rates were markedly higher. Models built with the specific response of methane release rates to temperature regarding the temperature changes expected according to the RCP climate scenarios predicted significant increases of these rates for the future, which could almost double current methane release for some of the studied lakes under the most pessimistic mitigation scenario (RCP8.5).

Highlights

Anthropogenic emissions of greenhouse gases (GHG) due to human activity are increasing global average surface air temperatures, disrupting weather patterns [1,2]
Chlorophyll-a, N and P data show that the lakes are mesotrophic, except Lake Manjavacas, which receives treated wastewater inputs and shows a higher trophic status. These inputs extend the flooding period and drop the salinity compared to the natural conditions of these saline lakes
Through Europe, the Iberian Peninsula is one of the territories presenting a greater amount of saline lakes and, within Spain, the lake district of “La Mancha Húmeda

Summary

Introduction

Anthropogenic emissions of greenhouse gases (GHG) due to human activity are increasing global average surface air temperatures, disrupting weather patterns [1,2]. The main biological processes involved in the carbon cycle within aquatic ecosystems are inorganic carbon fixation (primary productivity) as well as those releasing carbon as CO2 or methane (aerobic respiration, and methanogenesis, the latter among other anaerobic respirations) [3]. The balance of these processes is closely related with the natural emissions of greenhouse gases (GHG), with lakes and wetlands being relevant [4]. Inland aquatic ecosystems can make a disproportionately large contribution to GHG emissions and to carbon burial [5,6], with shallow lakes being particular hotspots. The balance of CH4 and CO2 exchange can provide an index of lakes and wetland’s greenhouse gas (carbon) contribution to the atmosphere [8]

Methods

Results

Conclusion