Multiple element limitation of primary producer communities across ecosystems and contribution of leaf litter to nutrient export during winter months in an urban residential watershed

Abstract

Human alteration of global macronutrient availability is well documented. Compared to pre-industrial levels, anthropogenic creation of biologically reactive nitrogen (N) has increased twelve fold and phosphorous (P) inputs to terrestrial systems have doubled. Additionally, it is well understood that N and P limit primary productivity globally across ecosystems, and recent meta-analyses have demonstrated that primary producer response to nutrient manipulation most frequently supports co-limitation by N and P. However, the role of resource availability in driving nutrient limitation of aquatic primary producer communities remains unclear, especially in freshwater ecosystems subject to human perturbation. To address this knowledge gap, we determined how resource availability influences nutrient limitation by N and P of phytoplankton primary production in aquatic communities across 12 lakes in Minnesota. Despite large differences in land use (agricultural, urban, and suburban) and water column N and P availability, planktonic algal community response to nutrient manipulation was consistently characterized by co-limitation by N and P across years and months. Higher lake primary production was associated with a stronger, positive response to N+P addition. These results support the emerging body of literature on co-limitation. However, few studies have explored beyond a two-nutrient approach to assess effects of other nutrients (e.g. K, Si, Ca) in limiting primary productivity. We performed a meta-analysis using 120 fertilization studies that tested the effects of N, P, and “other” nutrients (anything other than N and P) additions on primary productivity. We found that additions of other nutrients significantly increased primary production when added with N and P, and additions of two other nutrients significantly increased primary production compared to additions of one other nutrient. These results demonstrate that co-limitation by other nutrients is more prevalent across ecosystems than previously assumed. Taken together, these chapters of my dissertation research further supports the emerging paradigm shift towards co-limitation of primary production across ecosystems, especially in freshwaters.