Changes to chronic nitrogen loading from sewage discharges modify standing stocks of coastal phytoplankton.

Nutrient delivery in subtropical coastal systems is predominantly via acute episodic high flow events. However, continuous nutrient discharges from point sources alter these natural fluctuations in nutrient delivery, and are therefore likely to lead to different ecosystem responses. The aim of this study was to assess how a reduction in chronic sewage nutrient inputs affected chlorophyll a (chl a) concentrations in a subtropical bay, in the context of seasonal fluctuations in riverine nutrient inflows. Reduced nutrient inputs from a large sewage treatment plant (STP) resulted in lower mean dissolved inorganic nitrogen and phytoplankton chl a concentrations during both the austral summer wet and winter dry season. This was measurable within 10 y of nutrient reductions and despite the confounding effects of nutrient inflow events. Our study demonstrates that reductions in STP inputs can have significant effects on phytoplankton biomass despite confounding factors over relatively short time frames.

[1]  Bradley D. Eyre,et al.  Regional evaluation of nutrient transformation and phytoplankton growth in nine river-dominated sub-tropical east Australian estuaries , 2000 .

[2]  T. Malone,et al.  Influences of river flow on the dynamics of phytoplankton production in a partially stratified estuary , 1988 .

[3]  M. Burford,et al.  Effect of sewage nutrients on algal production, biomass and pigments in tropical tidal creeks. , 2012, Marine pollution bulletin.

[4]  B. Eyre,et al.  Carbon, nitrogen, and phosphorus budgets for a shallow subtropical coastal embayment (Moreton Bay, Australia) , 2002 .

[5]  K. O’Brien,et al.  Sources and fate of nutrients in a subtropical reservoir , 2011, Aquatic Sciences.

[6]  W. Dennison,et al.  Nitrogen, phosphorus, silica, and carbon in Moreton Bay, Queensland, Australia: Differential limitation of phytoplankton biomass and production , 2006 .

[7]  C. Gallegos,et al.  Event-scale response of phytoplankton to watershed inputs in a subestuary: Timing, magnitude and location of blooms , 1992 .

[8]  K. O’Brien,et al.  Flow events drive patterns of phytoplankton distribution along a river)estuary)bay continuum , 2013 .

[9]  W. Junk.  The flood pulse concept in river-floodplain systems , 1989 .

[10]  B. Eyre,et al.  Nitrogen versus phosphorus limitation in a subtropical coastal embayment (Moreton Bay; Australia): Implications for management , 2011 .

[11]  N. Loneragan,et al.  River flows and estuarine ecosystems: Implications for coastal fisheries from a review and a case study of the Logan River, southeast Queensland , 1999 .

[12]  H. Paerl,et al.  Controlling Eutrophication: Nitrogen and Phosphorus , 2009, Science.

[13]  I. Suthers,et al.  Plankton dynamics due to rainfall, eutrophication, dilution, grazing and assimilation in an urbanized coastal lagoon , 2009 .

[14]  Shahadat Hossain,et al.  A Suspended Sediment Budget for the Modified Subtropical Brisbane River Estuary, Australia , 1998 .

[15]  Eva Abal,et al.  Moreton Bay Study: A scientific basis for the healthy waterways campaign , 1999 .

[16]  Bradley D. Eyre,et al.  Impact of a flood event on benthic and pelagic coupling in a sub-tropical east Australian estuary (Brunswick) , 2006 .

[17]  J. Stewart.  Benefits and limitations of current approaches to whole of catchment modelling , 2009 .

[18]  B. Gillanders,et al.  Impact of changes in flow of freshwater on estuarine and open coastal habitats and the associated organisms , 2002 .

[19]  A. E. Greenberg,et al.  Standard methods for the examination of water and wastewater : supplement to the sixteenth edition , 1988 .

[20]  J. Cloern.  Our evolving conceptual model of the coastal eutrophication problem , 2001 .

[21]  H. Paerl,et al.  Regulation of estuarine primary production by watershed rainfall and river flow , 1993 .

[22]  W. Dennison,et al.  Utilization of nitrogen and carbon by phytoplankton in Moreton Bay, Australia , 2000 .

[23]  W. Richard,et al.  TEMPERATURE AND PHYTOPLANKTON GROWTH IN THE SEA , 1972 .

[24]  H. Greening,et al.  Toward Reversal of Eutrophic Conditions in a Subtropical Estuary: Water Quality and Seagrass Response to Nitrogen Loading Reductions in Tampa Bay, Florida, USA , 2006, Environmental management.

[25]  J. Carstensen,et al.  Return to Neverland: Shifting Baselines Affect Eutrophication Restoration Targets , 2009 .

[26]  You‐Gan Wang,et al.  Spatial and temporal distribution of tropical phytoplankton species and biomass in the Gulf of Carpentaria, Australia , 1995 .

[27]  D. Boesch.  Challenges and opportunities for science in reducing nutrient over-enrichment of coastal ecosystems , 2002 .

[28]  S. Carpenter.  Phosphorus control is critical to mitigating eutrophication , 2008, Proceedings of the National Academy of Sciences.

[29]  Michael R. Roman,et al.  Eutrophication of Chesapeake Bay: historical trends and ecological interactions , 2005 .

[30]  David Pont,et al.  Intra- and inter-annual variability in the different forms of diffuse nitrogen and phosphorus delivered to seven sub-tropical east Australian estuaries , 2003 .

[31]  A. Ram,et al.  Seasonal shift in net ecosystem production in a tropical estuary , 2003 .

[32]  S. Costanzo,et al.  Using nitrogen stable isotope ratios (delta 15N) of macroalgae to determine the effectiveness of sewage upgrades: changes in the extent of sewage plumes over four years in Moreton Bay, Australia. , 2005, Marine pollution bulletin.

[33]  A. Gabric,et al.  Water quality and phytoplankton dynamics in Moreton Bay, south-eastern Queensland. II. Mathematical modelling. , 1998 .

[34]  M. D. Kumar,et al.  Influence of river discharge on plankton metabolic rates in the tropical monsoon driven Godavari estuary, India , 2009 .

[35]  H. Paerl,et al.  Long‐term temporal and spatial trends in phytoplankton biomass and class‐level taxonomic composition in the hydrologically variable Neuse‐Pamlico estuarine continuum, North Carolina, U.S.A. , 2006 .

[36]  M. O'donohue,et al.  Phytoplankton productivity response to nutrient concentrations, light availability and temperature along an Australian estuarine gradient , 1997 .

[37]  Janet K. Thompson,et al.  A cold phase of the East Pacific triggers new phytoplankton blooms in San Francisco Bay , 2007, Proceedings of the National Academy of Sciences.

[38]  S. Biswas,et al.  Ecology of Phytoplankton of the Volta Lake , 1972, Hydrobiologia.