Quantifying annual cycles of macronutrient fluxes and net effect of transformations in an estuary: their responses to stochastic storm-driven events

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Estuaries are more than simply an area of mud and marsh that represents the transition zone between rivers and the ocean. They play a vital role in our economy as sites of leisure and commercial activities, such as fishing and boating. In addition, they are important nursery grounds for many species of economically important fish that later migrate to the open sea. As approximately 40% of the world's population live within 100 km of the coast, estuaries are also some of the most vulnerable sites for impact from man's activities. Not only can they suffer from activities occurring within the estuary itself, but they also mark the point where pollutants gathered by rivers from large areas of the interior can accumulate.One of the major pollution concerns in estuaries arises from the excess river borne concentrations of phosphate and nitrate. These can be derived from a variety of sources, such as run off from fertilised fields and discharge (accidental or purposeful) from sewage treatment plants, but regardless of their source they can cause severe problems, such as stimulating the growth of excess algal growth that can deplete the water in oxygen and causing widespread fish kills, or causing the growth of poisonous algal species (red tides) that cause shell fish fisheries to be closed.. Although this problem has been recognised for some time, and monitoring activities by bodies such as the Environment Agency and water companies play an important role in keeping pollution in check, there are still major gaps in our knowledge. In particular, it is apparent that a large proportion of the flux of nitrate and phosphate are delivered to estuaries by sudden storm events, but most monitoring takes place at fixed times that are spaced too far apart to capture these events. This is a major gap in our knowledge that will become more important as the intensity and frequency of storms are likely to increase due to climate change. Additionally, the phosphate and nitrate load of rivers can take many forms - dissolved and particulate, organic and inorganic - and relatively little is known about the concentrations of these different forms varies throughout the seasons and during storm events. Only if we are able to fully understand these processes will we be able to take the necessary steps to identify and control polluting sources of nitrate and phosphate to estuaries.Our research seeks to address this gap in our knowledge by carrying out detailed monitoring of the many forms of phosphate and nitrate that enter Christchurch Harbour estuary (Dorset) from both the rivers and the sea over the course of a year. We will be using state-of-the-art technology (much of it developed by ourselves) that will allow us to monitor they key parameters at intervals of every 30 minutes. Hence, we will be able to capture the effects of sudden and short-lived storms that have eluded previous studies and routine monitoring practices. We will then use the results of our study to carry examine how these sudden storm events affect the distribution of phosphate and nitrate within the estuary. In particular, we will examine what happens when sediments are stirred up in the estuary by storms - do they remove or add phosphate and nitrate to the system? We will also examine the effects of these sudden storms on the biological activity in the estuary. Again, do they increase or decrease the growth of algae, and what is the difference if the storm happens in the summer or the winter?The various threads of our study will be drawn together into a powerful statistical model that will allow us to better understand the transfer of phosphate and nitrate from rivers, through estuaries and into the coastal seas, and the role that storms play in this process. Our results will then allow policy makers to make more informed decisions about how we can seek to reduce pollution of estuaries by nitrate and phosphate.