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Nutrient overenrichment has led to dramatic increases in harmful cyanobacterial blooms, creating serious threats to drinking water supplies, ecological and economic sustainability of freshwater ecosystems. Nutrient-cyanobacterial bloom interactions were examined in eutrophic Lake Taihu, China. In situ microcosm nutrient dilution bioassays and mesocosm nutrient addition experiments were conducted to determine nitrogen (N) and phosphorus (P) concentration and load thresholds needed to control cyanobacterial bloom formation. Blooms were dominated by toxic, non N2 fixing Microcystis spp, from May to December. Dilution bioassays showed seasonality in nutrient limitation, with P-availability controlling prebloom spring conditions and N-availability controlling summer-fall blooms. Nutrient dilution and enrichment bioassays indicated that total nitrogen (TN) and total phosphorus (TP) concentration thresholds should be targeted at below 0.80 mg L(–1) and 0.05 mg L(–1), respectively, to limit intrinsic growth rates of Microcystis dominated blooms. Based on estimates of nutrient loading and observed stoichiometry of phytoplankton biomass, 61–71% TN and 20–46% TP reduction are necessary to bring Taihu’s phytoplankton biomass to “acceptable” sub-bloom conditions of less than 20 μg L(–1) chlorophyll a.

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Coastal North Carolina (USA) has experienced 35 tropical cyclones over the past 2 decades; the frequency of these events is expected to continue in the foreseeable future. Individual storms had unique and, at times, significant hydrologic, nutrient-, and carbon (C)-loading impacts on biogeochemical cycling and phytoplankton responses in a large estuarine complex, the Pamlico Sound (PS) and Neuse River Estuary (NRE). Major storms caused up to a doubling of annual nitrogen and tripling of phosphorus loading compared to non-storm years; magnitudes of loading depended on storm tracks, forward speed, and precipitation in NRE-PS watersheds. With regard to C cycling, NRE-PS was a sink for atmospheric CO 2 during dry, storm-free years and a significant source of CO 2 in years with at least one storm, although responses were storm-specific. Hurricane Irene (2011) mobilized large amounts of previously-accumulated terrigenous C in the watershed, mainly as dissolved organic carbon, and extreme winds rapidly released CO 2 to the atmosphere. Historic flooding after Hurricanes Joaquin (2015) and Matthew (2016) provided large inputs of C from the watershed, modifying the annual C balance of NRE-PS and leading to sustained CO 2 efflux for months. Storm type affected biogeochemical responses as C-enriched

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