Water-saving irrigation can mitigate climate change but entails negative side effects on biodiversity in rice paddy fields

Abstract

Tackling climate change while enhancing biodiversity without compromising production is a main goal in agricultural management. In rice farming, water-saving irrigation techniques alternative to permanent flooding have been globally adopted to face more severe and frequent droughts and have proven effective in reducing greenhouse gas emissions. Yet potential trade-offs with other global concerning environmental issues such as biodiversity conservation are often overlooked. Here we used a field-scale experiment to compare the effects of water management strategies representing a water use gradient (continuous flooding as the lowest intensity water use management; mid-season drainage (MSD) as medium intensity; and alternate wetting and drying (AWD) as the highest intensity management) on i) greenhouse gas emissions, ii) the abundance and diversity of freshwater biological communities, and iii) crop yield. While a positive climate change mitigation effect was observed under water-saving practices (92.5 % and 67.3 % methane emission decreases for AWD and MSD, respectively, when compared to continuous flooding), these resulted negative for biodiversity conservation. Even though AWD decreased species richness only at the richness peak, a strong negative effect was observed on the abundance of aquatic organisms (decapods, heteropterans, odonates and amphibians). Grain yield decreased 12.9 % with AWD management as opposed to continuous flooding but did not vary under MSD. Even though wider adoption of water-saving strategies might help achieving climate mitigation goals while maintaining yields, negative effects on biodiversity should be addressed to preserve highly diverse communities of aquatic organisms and the broad range of ecosystem services they provide. These results point towards marked trade-offs among different agri-environmental issues, therefore, we advocate for more integrative solutions that account for potential side effects when designing alternative water management plans.