Global change is modifying meteorological and hydrological factors that influence the thermal regime of water bodies. These modifications can lead to longer stratification periods with enlarged hypolimnetic anoxic periods, which can promote heterotrophic anaerobic processes and alter reservoir carbon cycling. Here, we quantified aerobic and anaerobic heterotrophic processes (aerobic respiration, denitrification, iron and manganese reduction, sulfate reduction, and methanogenesis) on dissolved inorganic carbon (DIC) production in the hypolimnion of a Mediterranean reservoir (El Gergal, Spain) under two contrasting hydrological conditions: a wet year with heavy direct rainfall and frequent water inputs from upstream reservoirs, and a dry year with scarce rainfall and negligible water inputs. During the wet year, water inputs and rainfall induced low water column thermal stability and earlier turnover. By contrast, thermal stratification was longer and more stable during the dry year. During wet conditions, we observed lower DIC accumulation in the hypolimnion, mainly due to weaker sulfate reduction and methanogenesis. By contrast, longer stratification during the dry year promoted higher hypolimnetic DIC accumulation, resulting from enhanced methanogenesis and sulfate reduction, thus increasing methane emissions and impairing reservoir water quality. Aerobic respiration, denitrification and metal reduction produced a similar amount of DIC in the hypolimnion during the two studied years. All in all, biological and geochemical (calcite dissolution) processes explained most of hypolimnetic DIC accumulation during stratification regardless of the hydrological conditions, but there is still ~ 30% of hypolimnetic DIC production that cannot be explained by the processes contemplated in this study and the assumptions made.

全球变化正在改变影响水体热状况的气象和水文因素。这些修改可以导致更长的分层期和扩大的低水缺氧期，这可以促进异养厌氧过程并改变储层碳循环。在这里，我们量化了地中海水库（西班牙埃尔热格尔）低温下溶解无机碳 (DIC) 生产的需氧和厌氧异养过程（需氧呼吸、反硝化、铁和锰还原、硫酸盐还原和产甲烷）在两种对比下水文条件：雨年有大量直接降雨和上游水库频繁的水输入，旱年降雨稀少和水输入可忽略不计。在雨季，水输入和降雨导致低水柱热稳定性和更早的周转。相比之下，干旱年份的热分层时间更长、更稳定。在潮湿的条件下，我们观察到低盐沼中的 DIC 积累较低，这主要是由于较弱的硫酸盐还原和产甲烷作用。相比之下，干旱年份较长的分层促进了较高的低浓度 DIC 积累，这是由于产甲烷作用增强和硫酸盐减少所致，从而增加了甲烷排放并损害了水库水质。在研究的两年中，有氧呼吸、反硝化和金属还原在低温环境中产生了相似量的 DIC。总而言之，