UNC Inst of Marine Sci.
http://www.unc.edu/ims/paerllab/
Mitigating global proliferation of harmful cyanobacterial blooms in the face of nutrient over-enrichment and climate change
12 PM
AHF 153 (Torrey Webb Room)
Abstract: Harmful (toxic, hypoxia-generating, food web altering) cyanobacterial blooms (CyanoHABs) are proliferating globally and represent one of the most serious threats to the use and sustainability of freshwater, estuarine and coastal resources. Managing these blooms (CyanoHABs) has historically focused on reducing phosphorus (P) inputs, based on the assumption that nitrogen (N) fixation will supply ecosystem N needs. Much has changed in terms of human nutrient inputs to and climatic alterations of bloom-sensitive waters since this paradigm was introduced. Recent studies indicate that cyanobacteria flourish in response to combined N and P loading, or even N enrichment. Non N2 fixing, toxic CyanoHAB genera (e.g., Microcystis, Planktothrix) often dominates under these conditions. Members of these genera require combined N sources to support growth. Despite decades of P loading controls in the Baltic Sea and North American Great Lakes basin and elsewhere, these CyanoHABs are proliferating worldwide, threatening drinking water supplies, fishing, tourism and overall sustainability of impacted systems. Burgeoning usage of N fertilizers, urban and agricultural N wastes, atmospheric N deposition and groundwater N inputs have increased bioavailable N in receiving waters. N occurs in gaseous forms, unlike P, and is “lost” to the atmosphere via denitrification and other N sinks, perpetuating N-limitation. In-system N2 fixation does not appear to compensate for N loss, so external N input is a key driver of eutrophication. Furthermore, there is mounting evidence and concern that N availability is linked to CyanoHAB toxicity; further justification for controlling growing N inputs. Lastly, freshwater and marine ecosystems are hydrologically interconnected; single nutrient (e.g., P only) reductions upstream may not necessarily reduce HABs impacts downstream. Reducing both N and P inputs is the only viable long-term solution for long-term control of HAB proliferation along the freshwater to marine continuum. Managers now face the additional effects of climate change, including rising temperatures and changes in precipitation patterns and amounts, on watershed hydrologic and nutrient loading dynamics, internal nutrient cycling, thermal stratification, hydraulic flushing rates and other factors. Those changes generally favor CyanoHABs over other phytoplankton and could influence the efficacy of nutrient control measures; thus requiring setting new nutrient input reduction targets and establishing nutrient-bloom thresholds for impacted waters. The “P-only” management paradigm should be updated to incorporate controls on external N inputs and be adaptive to increasing human population pressure and climate change.
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