Groundwater affects the provision of ecosystem services (ES) such as food production, freshwater supply, and climate regulation by altering critical zone ecohydrological and biogeochemical processes. Previous research has demonstrated significant and nonlinear impacts of shallow groundwater on a wide range of ES at the field- to watershed-scale. However, it remains unclear how groundwater affects ES at the global scale, and how such effects respond to environmental factors such as climate, land use, soil, and human management. In this research, we investigate the global patterns of groundwater effects on multiple food, water, and biogeochemical-related ES, and analyze the underlying mechanisms that drive groundwater influences. We synthesized a large amount of high spatial-resolution (1 km) datasets to characterize water table depth (WTD) and quantify indicators of multiple ES (e.g., net primary productivity - NPP, soil carbon storage, biodiversity, runoffs etc.). We used a fine-resolution delineation of basin as the spatial scale of analysis (N=57646) and calculated the basin-scale Spearman’s correlations between WTD and each ES indicator. We also performed generalized linear models to test how selected predictors affect the WTD-ES relationships.
Results/Conclusions
Our preliminary results showed significant correlations between WTD and ES indicators (i.e., NPP and soil carbon) in >54.9% of all basins globally. Focusing on shallow groundwater regions, correlations ranged from -0.86 to 0.91, with substantial spatial variations. For example, mean NPP were significantly correlated with WTD, with positive correlations in 65.4% of basins primarily in high northern latitudes and negative correlations in 34.6% located in the Midwestern USA and the Indian sub-continent. Groundwater was also strongly correlated with soil carbon (0-15cm layer: 46.2% positive relationships, 53.8% negative; 0-200cm layer: 29.1% positive, 70.9% negative). Negative correlations were primarily located in the Midwestern USA and Europe, and positive correlations in northeastern American and southeastern Asia. Given consistent correlations between NPP and soil carbon vs. WTD found in the Midwestern USA and Europe, but divergent correlations in northern Eurasia and southeastern Asia, our results indicate spatially-explicit ES tradeoffs and synergies that can be driven by groundwater. Climate, land-use, soil type and human factors such as irrigation extent all showed as significant predictors that affect basin-scale ES-WTD correlations. Our findings demonstrate that groundwater effects are spatially heterogeneous and ES-dependent, and provide mechanistic understanding on human and environmental factors that mediate groundwater effects on ES.