Research and Development s14

DEPARTMENT for ENVIRONMENT, FOOD and RURAL AFFAIRS CSG 15 Research and Development Final Project Report (Not to be used for LINK projects)

Two hard copies of this form should be returned to: Research Policy and International Division, Final Reports Unit DEFRA, Area 301 Cromwell House, Dean Stanley Street, London, SW1P 3JH. An electronic version should be e-mailed to [email protected]

Project title Transport and fate of UK nutrient input to the southern North Sea

DEFRA project code AE1221

Contractor organisation CEFAS, and location Pakefield Road, Lowestoft, NR33 0HT

Total DEFRA project costs £ 800,892

Project start date 04/01/99 Project end date 31/03/02

Executive summary (maximum 2 sides A4)

There are international concerns about the management of enclosed coastal seas like the North Sea with debate not only about how to identify the impacts (especially the more subtle ecological changes) but also about the significance of land-based sources of input. Resolving these issues depends on a good scientific evidence base and a good understanding of how the complex marine ecosystem functions. The purpose of this project was to build scientific consensus concerning the transport and fate of nutrients in the southern North Sea. The work was required because of concerns about the contribution made by UK inputs to the eutrophication symptoms evident in the North Sea. A programme of marine observations was undertaken to resolve key uncertainties in transport, sediment climate and the factors controlling phytoplankton/nutrient interaction in the region between East Anglia and the Netherlands. The project concluded with an international workshop which brought together scientists from around the globe to assess the state of knowledge on phytoplankton response to nutrient enrichment (the direct output of the workshop will be reported separately). The project built on previous work carried out inter alia by the JoNuS programme which has examined the transport and fate of nutrients as they pass from land to sea. This project has moved the story outside the coastal regions and was designed to provide an up to date understanding of the physical mechanisms of transport but also the influence of biological processes on the fate of the nutrients. The strong observational programme builds on the well developed use of a variety of modern oceanographic techniques that have been developed by CEFAS and UEA. An interesting dimension was added to the work through collaboration with scientists working for the Netherlands government who had developed a hypothesis to explain their perception of high primary productivity at the Frisian Front to the north of Holland. The hypothesis (given the title of ‘English River’) implicated a strong input of nutrients derived from the UK in fuelling this phytoplankton growth. In concluding both this project and the equivalent Netherlands project we have developed a good dialogue but agree to differ on aspects of interpretation of the common data-set.

CSG 15 (9/01) 1 Project Transport and fate of UK nutrient input to the southern DEFRA AE1221 title North Sea project code

The principal findings of the project were

 The underlying transport of the water mass off East Anglia is around 3.5 km day-1, it is more variable in winter, when strong winds are more prevalent and drive additional flow. There is no direct link between the region of high suspended load as observed in satellite imagery and the zone of lowest salinity water.  Sediment concentration is primarily controlled by wind activity in winter with a low background due to tidal resuspension in summer and a transitionary period in spring. However, the tides in UK waters are still sufficiently strong that organic matter (including phytoplankton) is not able to settle.  The light levels in winter limit phytoplankton growth, due the reduced incident light and the increased light attenuation due to higher suspendeed load caused by storms. In summer light is available and nutrients limit growth. In spring there is a transitory phase where light is available but storms may increase the suspended load and locally retard the spring bloom for the duration of the storm. However, observations show the timing of the spring bloom in the Southern Bight of the North Sea is the same over the entire area.  After the spring bloom the majority of phytoplankton growth is driven by regenerative production, that is production fuelled by ammonium, a product of plant decay. The importance of this regenerative mechanism had not previously been adequately quantified in this area.  The nitrogen transport budgets derived for these phytoplankton uptake rates and continuous nutrient measurements from moorings showed that in winter nitrate dominates the transport of nitrogen across the southern North Sea. By contrast, in summer the overall transport falls by a factor of 2 and is dominated by the transport of particulate organic nitrogen (PON) derived from phytoplankton growth. This is potentially available to settle out in regions of low tidal stress which often become stratified.  In summer light levels do not inhibit growth and most of the nitrate within the UK coastal region is utilized for plant growth, subsequently the small amounts of DIN (Dissolved inorganic nitrogen) that are transported are insufficient to promote summer blooms at the Frisian Front. However, transport of particulate nitrogen may contribute, through regeneration, to further growth at this possible sedimentation site. Curretnly, there is no direct observational data to confirm such a hypothesis.  We have established and quantified the overall transport of nitrogen ex UK waters into the wider North Sea and determined the variability of the flow. The contribution of UK land-based sources is between 10% and 20% of the total flux across this section of the North Sea but this estimate is based on a number of assumptions and has been calculated in ways that maximise the contribution.  A state of the art coupled physical and ecosystem model was not able to resolve the features of the system that were studied by the project. This limitation points to the need for further work on such models if they are to be of value in helping to understand and manage our impacts on the sea.

Scientific report (maximum 20 sides A4) Introduction

The North Sea is the focus of concern regarding the impact of nutrients on the health of the marine ecosystem (Anon, 1995). Clearly, all bordering states make a contribution to the nutrient load of the North Sea, but there is a continuing debate concerning how different sources might contribute to identified problems, largely in Dutch and German waters. Numerical models have been used to help resolve the issue, but none of the established models is based on a modern understanding of the physical nature of the North Sea nor is there sufficient observational data at relevant time and space scales to achieve adequate validation. For example, OSPAR ASMO organised an intercomparison of different models which showed that no matter what assumptions had been made in specific models they all produced similar answers (ASMO 96). While this may be good news and we have a common understanding of the system, it is a worrying result given the known inadequacies of, and differences between, all of the models.

The context for this project was brought into focus in a report about the “green curtain” in Dutch waters which alleged that a large proportion of the productivity associated with the Frisian Front was derived from nutrients originating directly from the UK (Baars et al., 1991; Baars, 1998; Baars, 1999). It was postulated that limited light availability due to high turbidity (Visser, 1969) restricts phytoplankton growth in UK coastal waters allowing the undiminished transport of nutrients to an area off the Netherlands coast. Here, as sediment settled out of the water in a lower tidal energy environment and the light climate improved, algal blooms were said to form leading to an undesirable disturbance. The phrase ‘English River’ has been coined to encapsulate this view of the general flow regime.

The potential fate of all nutrients is to fuel plant growth which if in large quantities, or the wrong type (nuisance or harmful algae), or in the wrong place, can lead to an undesirable disturbance and require action to be taken. However, there are other environmental factors that may be as, or more important than nutrients in determining the fate of nutrients. For example, ambient light determines the timing of phytoplankton growth and a view has emerged that it may also play a role in nuisance bloom formation (Peperzak et al., 1998). A critical light level may act as the ‘switch’ to promote blooms of flagellates (e.g. Phaeocystis sp) rather than the more commonly held view that it is depletion of silicate which reduces the prevalence of diatoms competing for nutrients. Uncertainty exists concerning the importance of light and turbidity on the expression of algal growth in estuary/offshore and turbid/non turbid gradients in the North Sea.

Surveys of the North Sea (Visser, 1969; Lee & Folkard, 1969; Eisma, 1981; Howarth et al., 1994) reveal a region of high suspended load extending south from the Holderness coast and eastward from Norfolk toward Dutch waters. Dramatic images (Fig. 1) derived from remote sensing (Sundermann, 1993; van Raaphorst et al., 1998; Hoogenboom, 2001) also show an area of high reflectance (characterised as suspended load) extending eastwards from the shallow sandbanks off Norfolk showing something of the underlying geology and structure of the North Sea basin. This region coincides with an area of lower salinity water (ICES, 1962). Diagrams (or cartoons) of the long term mean circulation derived from modelling studies (Prandle, 1984; Lee and Ramster, 1981) and tracer distributions (Kautsky, 1973) reinforce the impression that the observed distribution of suspended sediment reflects an underlying coherent transport of turbid water eastward from the UK. Mean speeds are characterised as being of the order of 4 cm s -1 (approx. 3.5 km per day) and, on the basis of models and sparse monthly measurements, it was estimated that the annual flux of suspended load from the UK was 6.6 million tonnes. Much of the transport depends critically on the wind, as 71% occurred in two months when winds were particularly strong from the south-west (Howarth et al., 1994).

The view that the ‘plume’ represents water travelling directly from UK into continental waters may be simplistic. The region coincides with a large area of sand ridges up to 55 km long, 5 km wide and rising up to 35 m above the surrounding seabed and running parallel to the coast (Huntley et al., 1994). Some reach within 5 m of the sea surface. The strong tides and shallow water of the region mean that highly reflective sand is readily kept in suspension and even moderate winds and associated waves readily disturb the bed. During periods of low wind in the summer months the distribution of suspended sediment (van Raaphorst et al., 1998) indicates that the ‘plume’ is greatly reduced or non- existent. The residual circulation (Howarth & Huthnance, 1984) around each linear feature runs strongly north- west/south-east maintaining the banks. In models of the North Sea from which mean circulations are derived this complicated topography is inadequately resolved, placing uncertainty over estimates of mean eastward flow. A further complication is introduced by seasonal thermal stratification of the water column in the weaker tidal regime towards the continental coast. A distinct boundary (front) develops between UK and Dutch coastal waters (van Aken et al., 1987) and it is conceivable that the breakdown of stratification may be linked to blooms at the Frisian Front. CSG 15 (9/01) 3 Project Transport and fate of UK nutrient input to the southern DEFRA AE1221 title North Sea project code

The aim of the project was to improve the scientific basis for understanding the transport of nutrients in a critical area of the North Sea and to understand the fate of nutrients, particularly, the factors that affect the growth of phytoplankton and the extent of recycling of nutrients. The work builds on the ‘gradient’ philosophy of the JoNuS programme; JoNuS 1 developed an understanding concerning the inputs of nutrients to the sea through estuaries and JoNuS 2 dealt with the impact defined inputs have on the ecosystem in the coastal regions. The programme was designed to make observations at appropriate time and space scales to quantify transport, determine fate and support the future application of state-of- the-art models as well as interacting with scientists from Europe to develop a clearer common understanding of the science.

The project will provide evidence that can be used by inter alia the Eutrophication Task Group of OSPAR and the European Commission to support the debate about eutrophication status and links between cause and effect that underpin decisions about effective delivery of various eutrophication control strategies. The project will also aid progress in improving, and targetting, the monitoring of eutrophication status of UK coastal waters by providing a better picture of how nutrients interact with the ecosystem.

The scientific objectives of this project were:

1. To build international scientific consensus about the transport and fate of nutrients in the southern North Sea. 2. To clarify the uncertainty in transport rates, sources and fate of nutrients in the southern North Sea between East Anglia and the Frisian Front. 3. To determine the spatial and temporal variability in factors (nutrients, light levels, grazing) controlling phytoplankton growth in the southern North Sea between East Anglia and the Frisian Front. 4. To use the best available physical and ecosystem models to explore the transport and fate of nutrients in the southern North Sea. 5. To evaluate the factors responsible for suppressing non-diatom production in the outflow of the Thames and by experimental work. 6. To explore the use of regional scale biogeochemical models for large sectors of the North Sea.

Methods

In order to address the questions concerning the mechanisms involved in the transport and fate of UK nutrient input into the North Sea a series of six cruises were undertaken using the RV Corystes, covering periods (January – September 2000) which could be characterised as winter, spring and summer. Efforts were focused on the UK coastal region from the Thames to the Wash and eastwards to the Frisian Islands (Fig. 2). The aim was to establish the spatial and temporal variability in transport rates of water, nutrients and fine sediment. A combination of surveys and moored instruments were used, employing a range of sophisticated multi-disciplinary observational techniques developed by CEFAS and UEA. Techniques included towed undulating CTD (Scanfish) giving profiles of water column parameters; ship mounted acoustic Doppler current profilers (ADCP); drogued satellite tracked drifting buoys; conventional CTD’s; and current meter moorings. The techniques are summarised below. More detailed information can be found in Fernand (1999). The spatial distribution of nutrients, phytoplankton, suspended load, temperature and salinity were determined during the cruises. At critical locations the temporal changes were monitored by ‘Smart Buoy’ giving light climate and phytoplankton production and a bottom lander (Minipod) was utilised to understand the processes governing suspended sediment dynamics. Estimates of carbon uptake, nitrate and ammonium assimilation were undertaken to calculate total, new and regenerated primary productivity, respectively. Scanfish sections were performed at 3.0 - 4.5 m s-1, with the instrument nominally set to profile between 4 m below the surface to within 5 m of the sea bed. Separation of profiles was equivalent to conventional CTD profiles of approximately 100 - 350 metres, the latter largely dependent on bottom depth. The Scanfish vehicle and a conventional profiling CTD/rosette package were both fitted with a Falmouth Scientific Inc. Integrated (FSI) CTD. Calibration of the temperature sensor was performed pre- and post cruise in the laboratory, and values were found to be accurate to ±0.001ºC. Salinity calibration of the Scanfish CTD was undertaken at sea. Water samples were drawn hourly from a pumped ship board system, with the inlet at 4 m, and salinities determined using a Guildline Portasal. Comparisons were CSG 15 (9/01) 4 Project Transport and fate of UK nutrient input to the southern DEFRA AE1221 title North Sea project code

then made with values from the FSI CTD as it reached the top of its profile at approximately 4 m depth. By allowing for the distance of the instrument behind the ship and the residence time of the ship board sample in the ship's pipe work, derived salinities were determined with a standard deviation of ±0.007. Salinity and density were calculated according to international standard procedures for seawater (UNESCO, 1981). All salinities quoted hereafter were determined using the practical salinity scale (UNESCO, 1978).

Satellite-tracked drifters were tracked via Service Argos. The instruments were fitted with holey sock drogues 5.5 m long and 1.5 m diameter and centred at typically 20 m depth. Position fixes during the deployments were obtained at a rate of 8 - 12 per day with a standard deviation in the position estimate of between 150 m and 1000 m, dependent on the quality of the signal received at the satellite. The drag area ratio of the system was greater than 50 which restricts wind slip to less than 1 cm s-1 for winds of 10 m s-1 (Niiler et al., 1995). Drifter trajectories were determined by using linear interpolation to transform latitude and longitude on to a uniform 3-hour time series, and applying a lowpass filter (Horsburgh, 1999; Horsburgh et al., 2000) to remove the semidiurnal tidal signal and ‘noise’ introduced by inaccuracy in position fixes. Zonal (u) and meridional (v) residual velocities were obtained from central spatial differences of the filtered time series over 24 hours.

Moored current meters, both ADCP’s and Aanderaa’s, were deployed to characterise the variability in transport and fluxes of material through the region (Figure 2). In conjunction with the drifter observations, the measurements represent the first co-ordinated attempt to monitor and resolve the forcing mechanisms that govern the eastward flux of water through the region. In order to determine quantitatively the effect of wind forcing on the flow variability of each drifter and each current meter, wind and current variability were correlated after the data were lowpass filtered and the mean removed. The applied technique is adapted from that described by Brown and Gmitrowicz (1995). The wind velocity W

at some angle w anticlockwise of the flow direction forces a current C, which at time t is given by

C(t) = RW(t - L),

where R is the regression coefficient between wind and current, and L is the time lag of current response to forcing. Flows were resolved along the east (u) and north (v) components of current variability at each current meter and drifter

and w and L were varied to maximise the correlation between wind and current.

In order to characterise the suspended sediment climate a Minipod was deployed at the centre of the mooring array. The instrument measured at high frequency (5 Hz) the three axis of turbulent flow using a Nortek Vector Acoustic Doppler Velocimeter, the suspended load field by means of optical backscatter sensors (at 1 Hz) and dual frequency acoustic backscatter sensors (at 1 and 4.7 M Hz). Also at this location and at the outer Thames (Figure 2) a ‘Smart buoy’ was deployed to measure dissolved nutrients (ToxN & silicate), phytoplankton fluorescence, sediment concentration, light climate, salinity and temperature. In order to calibrate the instruments water samples were collected regularly from an onboard water sampler and, when in the vicinity, from research vessels.

On the six cruises measurements were made of the spatial nutrients, phytoplankton, suspended load, salinity and temperature fields. Analysis of nitrate, nitrite, phosphate and ammonia was undertaken using an autoanalyser (Kirkwood, 1996). At primary productivity stations ammonia was also measured using a new high sensitivity method to enable accurate measurements of the ammonium uptake (Aminot et al., 1995) At critical locations, estimates of primary productivity, new production and regenerated production were undertaken using 13C, 15N-nitrate and 15N ammonium uptake experiments, respectively, in temperature controlled light gradient incubators on board ship. Seawater samples were collected from one or more depths, filtered to remove mesozooplantkon and spiked with (radio-) tracer/stable isotope and incubated for 24 hours. At the end of the incubation water samples were filtered and the amount of tracer incorporated into the phytoplankton measured and the value used to derive carbon fixation rates normalised to chlorophyll.

A number of ways have been used to calculate fluxes to ensure that we achieved the best possible estimates. The flow has been estimated from the current meter array using the conventional hydrographic method of assigning cross sectional areas associated with similar characteristics to the individual current records, other statistical approaches have been used to determine the error of this approach. The estimates of UK origin are derived on the basis of salinity from the sectional data. The lower limit was derived from an examination of the sections and calculation of the content of water of a salinity associated with UK coastal water. This was ascribed as being UK origin and associated with what would usually be described as the width of the ‘plume’, i.e. 10 or 15 km. However, due to mixing there is no hard boundary between UK coastal water and the off shore component, in practise there is a continuum of mixing elements between the coastal water

at salinity of 33 (at the Warp site; Figure 2) and English Channel (>34.5) and northern North Sea water (>34.5). The upper limit has been derived by calculation of the salinity deficit in a section as if it had been all Channel water and the amount of English coastal water that must have mixed with it in order to generate the observed salinity field. The exact value used for the Channel water varies through the year and is derived from observations at the outer Gabbard site.

Continuous values of ToxN and chlorophyll were recorded by the Smart Buoy at the central mooring site. In combination with the mooring array, fluxes of nutrients have been derived. Typically this site was in or near to the centre of the lowest salinity water and consequently sampled the highest nutrient water. To account for variability in salinity and associated dissolved nutrients across the section a relationship between this site and the rest of the section was derived from the six cruise periods. Additionally, to derive complete DIN estimates from ToxN an assessment was made of the relationship between ammonia and ToxN concentrations using the cruise data.

The nitrate flux has been derived, using the observed daily residuals and adjusted daily concentrations, the upper and lower bounds express the relationship of the point measurement to the section as a whole. From process measurements undertaken on the cruises a relationship between PON and chlorophyll has been derived enabling utilisation of the calibrated fluorometer from the Smart Bouy. Again a relationship has been derived from the Smart Bouy site to the section as a whole. The derivation of the UK element of nutrient transport comes from two methods. One limit is given by the salinity % that is from UK coastal water derived in the section taking the average value from the salinity method calculated before. The other method is again by consideration of mixing. The element of nutrients in the section above that which can be ascribed to English Channel or northern North Sea water is calculated. This surplus is then of UK origin. An element of this input will be non UK but this will act as an upper limit.

Results OBSERVATIONS OF THE FLOW FIELD

The current meter deployments can be characterised as winter (late January to late March), spring (late March to late May) and summer (late May to August). Overall, the pattern of flow measured at each location was essentially similar with little difference between the seasons (e.g. speeds of 4.5 - 7.0 cm s-1 in winter, 4.6 cm s-1 in spring and 3.0 – 7.0 cm s-1 in summer; see Figure 3). The net direction of flow was also similar, at approximately 45º relative to true north. However, during winter and spring the variability in the east/west and north/south flow was 100% greater than summer. This reflected the lower storm activity during summer when flow is comparable to estimates due to tidal residuals alone, as derived from hydrodynamic models simulations of the region (e.g. Otto et al., 1990; Heinbucher et al., 1987). However, during winter and spring the wind forces additional water movement. It so happened that during 2000 the net wind influence was such that easterly and westerly transport events were essentially equivalent in magnitude. In other years a predominance of westward winds would reduce the net long-term eastward flux, or alternatively eastward winds boost the eastward flux.

The trajectories of the satellite tracked drifters deployed for up to 120 days during January (19 – 26), March (24 – 30) and May (18 – 25) indicated the principal pathways of flow through the region (Figure 4). Overall, the mean movement was eastward (Figure 4), with water from the coastal region to the north of East Anglia being transported south and then east. Water from the Thames and English Channel was also transported east. Again, the data were consistent with traditional diagrams of the overall mean regional circulation, but within this there was considerable variability imposed by wind forcing. Analysis showed that in eleven of the fourteen drifters, movement was significantly correlated (at 95%) with the wind. Those uncorrelated where in the region of high tidal residuals in the vicinity of East Anglia. In winter approximately 75% of the flow had an eastward component (25% westward), whilst in summer the figure was >90% eastward. Mean velocities for the period January to June were similar to those derived for the current meters (Figure 3).

SEDIMENT AND RESUSPENSION

Laser-derived particle size distributions of seabed sediment within the ‘plume’ region indicated largely fine to medium sands (grain diameter 125-500 m), with a dominant sand mode of approximately 300 m. Abundance of gravel was minimal (<2 %), whilst the proportion of silt/clay-sized material was generally <5 %, although on occasion reached 10 %.

During the Minipod deployments from January to August at the centre of the mooring array (Figure 2) wave conditions were highly variable and dependent on wind strength. In general, the more extreme wave heights and periods prevailed during winter. Throughout the deployments significant wave height was <6 m, with mean values of 1 m in winter (and 0.6 m in summer), and wave period was <17 s with a mean value of 9 s. Intuitively, it is not surprising that waves resulting from winter storm activity have a profound effect on sediment dynamics in this shallow region. However, this study has enabled us to quantify the monthly differences in the wave climate and understand the relative contributions of waves and tidal currents in determining the sediment climate (Bunt et al., 2002), information not available in previous studies (e.g. Lee and Folkard, 1969; Jago et al., 1994).

Concentrations of sediment are periodic depending on current magnitude, with four peaks and four minima per day, as previously reported by Jago et al. (1994). During maximum tidal currents (spring tides) there was always bed material in resuspension, with maximum particle size of 100 and 1200 m at slack and peak tide, respectively. During weak tides (neaps) resuspension was very much reduced with corresponding maximum particles size of 50 and 600 m. During summer the tides dominate resuspension, whilst episodic winter storms wave activity may resuspend material > 2000 m (2 mm). The importance of storm activity as a contributor to the sediment flux across the southern North Sea has been inferred by previous researchers (e.g. Dyer and Moffat, 1998). For the dominant material in bed sediments (i.e. 300 m) wave induced resuspension occurs for 50% of the time in January, but for only 5% in July. Tides resuspend such material for 50% every month. Fine silt sized (< 100 m) material is resuspended for > 90% of the time. As a consequence, very little fine material entering the region from the cliffs of East Anglia, for example, is able to settle.

High concentrations of suspended sediment persist for several days following a storm, effectively maintaining the elevated background values in winter when compared to summer. For example, near bed concentrations of 60 mg l -1 can persist for up to four days following a storm, when peak values may reach 250 mg l -1. The overall mean winter concentration was of the order 30 mg l-1, as compared to a typical summer value of 3 mg l-1.

A semi-quantitative estimate of the effect of changes in sediment concentration on light climate was gained from comparison of the near-bed (Minipod) and surface (Smart Buoy) sediment estimates with surface light attenuation measured on the smart buoy. During winter and spring the surface light climate was well-correlated with surface suspended load, and although not quite as strong there was a distinct correlation between near-bed suspended sediment and surface light attenuation. A weaker correlation in terms of the bed is to be expected, as generally larger particles do not reach the surface and instruments were separated in the horizontal by 300 m. Interestingly, in summer neither near- surface nor near-bed estimates of suspended load correlate with surface light attenuation. Overall these results emphasize the role of the episodic winds/wave resuspension in determining the light climate and explain the absence of a ‘plume’ signature in satellite imagery during summer.

SPATIAL AND TEMPORAL VARIATIONS

Observations of the flow field serve to quantify water movement, but data derived from towed undulating CTD (Scanfish) and associated process studies provide information to assess the dynamics of the nutrient and phytoplankton interaction within the region. For example, the Scanfish sections across the line of the moorings (Figure 2) in January, March, May and August (e.g. Figure 5.1(b) & 5.2(b)) clearly illustrated a region of lower salinity water that had originated from the UK coast. To the south and north were regions of higher salinity water characteristic of that entering from the English Channel and that in the central North Sea, respectively. During March the highest concentrations of ToxN (total oxidised nitrogen) (Figure 5.1(c)) were associated with the lowest salinity water, whilst concentrations to the north were relatively depressed by phytoplankton growth. The suspended load (Figure 5.1(d)) clearly indicated a region of relatively higher concentrations apparently associated with the shallower topography and commensurate with the location of the ‘plume’ as defined by satellite imagery (Figure 1). During August the lowest salinity was in approximately the same location (Figure 5.2(b)), but to the north was a distinct frontal region (Figure 5.2(a & b)) marking the transition from the well mixed to thermally stratified (during summer) region of the central North Sea. To the south was the distinctive signature of higher salinity English Channel water. Throughout the section, chlorophyll concentrations (typically 1.5 –2.5 g l-1) indicated a source of primary production despite the low levels of ToxN (Figure 5.2(c)). Again, suspended load was comparatively elevated in the shallower central section (Figure 5.2(d)). In both transects of suspended load the peak coincides with strongest tidal flow (e.g. Figure 5.1(d); position 15 – 35 km). Overall, the fixed point Minipod measurements and transects suggest that the majority of suspended sediment comes from local resuspension through the action of tides and wind/wave induced turbulence.

Surface samples collected during 19 - 25 May have been combined in Figure 6 to illustrate surface distributions of salinity, suspended load, chlorophyll and nutrients (ToxN, silicate and ammonia). For example, in salinity (Figure 6a) fresher (<34.2) English coastal water is clearly seen adjacent to the English coast and stretches toward the north-east. Between this and the fresher (<32.0) continental coastal water were regions of more saline English Channel water (>34.6). The continental water clearly extended up to 35 km from the coast in the eastern most portion of the survey. Suspended load (Figure 6b) was highest in the shallower northern part of the region and along the English coast. Chlorophyll concentrations (Figure 6c) coincided with locations where ToxN was elevated (Figure 6d). In the UK coastal water this represented water from the Thames. In the centre of the region it is unclear whether the water originated from the continental or UK coast, whilst in the north-east the enhanced chlorophyll (> 8 μg l-1) was evidently associated with continental coastal water.

At the centre of the mooring array and at the comparatively inshore Gabbard site (Figure 2) a CEFAS Smart Buoy recorded timeseries of chlorophyll fluorescence and ToxN from January to September (Figure 7a). The short term variability within the chlorophyll and nutrient data, recorded at respective sampling intervals of half hourly and hourly, reflects the tidal addiction of water and provides a measure of the local gradients. At times these were as great as 10 µmol l-1 for ToxN and 2 µg l-1 for chlorophyll. There was considerable variability in the winter (up to the end of April) concentrations of ToxN, indicative of variability in water masses and changing coastal inputs which are largely driven by episodic rainfall/run-off events.

The onset of the spring bloom was clearly evident in the increased chlorophyll fluorescence at the end of April. The chlorophyll signature at the Gabbard exhibits the classical spring bloom cycle with a rapid increase in chlorophyll fluorescence corresponding to almost complete depletion of ToxN within 4 days from a peak level of approximately 20 µmol l-1. The bloom persisted for roughly three weeks, but with the latter phase representing residual chlorophyll fluorescence associated with largely decaying phytoplankton. Following this was a gradual ‘recovery’ in ToxN by the beginning of July, but only to a level of 1.5 µmol l-1 whereupon the mooring was removed by a fishing vessel.

At the central mooring the bloom was more erratic, with evidence of an increase in production and depletion of ToxN approximately 4 days before that at the Gabbard site. This was followed by a series of peaks and troughs in chlorophyll and ToxN. Unfortunately, technical problems meant that there was no measure of fluorescence at the central station after April or ToxN from May – July, therefore the peak in the cycle was not characterised. Nevertheless, daily samples from the water sampler on the buoy showed that ToxN at both sites was rapidly depleted. Following this, chlorophyll at the Gabbard site gradually increased until July. Whilst a measure of chlorophyll was unavailable at the central site, the data indicate that ToxN increased to a mean level of approximately 3 µmol l-1.

Overall, the patterns of nutrient/chlorophyll cycling at the two stations were not dissimilar and the timing of increased production at both sites was essentially the same. The comparatively uneven pattern of production at the central mooring site as compared to the Gabbard was not inconsistent with the variability in water masses in the region (Figure 6).

The situation at the stations in UK waters strongly contrasts with that observed at a further Smart Buoy station approximately 10 km offshore in Dutch coastal waters (Figure 7b) , (Mills et al., 2001b). Here, ToxN concentrations during March 2000 in water of salinity 25 - 30 were 60 – 70 µmol l-1 and they gradually declined to approximately 1 µmol l-1 by mid-July before oscillating between this value and 25 µmol l-1 until late September. At the end of April there was a distinctive spring bloom with chlorophyll concentrations peaking at > 60 μg l-1. This was followed by continuing production, characterised by a series of peaks in chlorophyll > 30 µg l-1 until September, in response to the persistent supply of nutrients.

BIOMASS PRODUCTIVITY AND NUTRIENT TURNOVER

Nutrient levels in the southern North Sea reach a maximum prior to the spring phytoplankton bloom when light limits growth. Following the peak in biomass during the bloom, dissolved nutrients remain low throughout the summer. However, low concentrations of nutrients do not necessarily imply low rates of primary productivity. It is possible that regenerated production during zooplankton grazing of phytoplankton and the bacterial remineralisation of organic matter (e.g. Dugdale and Goering, 1967) supplies sufficient nitrogen for primary production to continue. In order to explore this, a series of stations (Figure 2; stations A-E) were sampled between March and August along the axis of the ‘plume’ at approximately monthly intervals for nitrate and ammonium uptake rates and estimates of primary productivity. Additional stations were also sampled on cruises in July and September in collaboration with the Netherlands Institute of Sea Research (NIOZ) and in the Thames plume in February.

Dissolved nitrate and ammonium concentrations developed in contrasting ways with nitrate concentrations declining from ~25 µmol l-1 in the Thames embayment to <2 µmol l-1 for May - September, whereas ammonium steadily increased from <0.2 µmol l-1 in February to 1-2 µmol l-1 during July - September. As the year progressed water column integrated 13 primary productivity, calculated from shipboard NaH CO3 incubations at a range of light levels, increased to a maximum of 3.7 gC m-2 d-1 in August, with rates between March and September in the range 0.5-1.5 gC m -2 d-1. In conjunction with these measurements 15N-nitrate and 15N-ammonium incubations were conducted. February showed no detectable ammonium uptake and very low productivity and nitrate uptake rates, after which nitrate uptake rates remained low (generally 0 - 25 mgN m-2 d-1 from March to September) relative to ammonium uptake rates. The latter increased consistently from an average of 60 mgN m-2 d-1 in March to a maximum of 268 mgN m-2 d-1 in August. This study is the first time these rates have been measured in the context of nitrogen transport across the North Sea. Ammonium and nitrate turnover times (i.e. the total ammonium and nitrate in the water column divided by uptake rate) were derived to estimate the time theoretically taken for the phytoplankton population to remove all nitrate or ammonium if no additional nutrient inputs were available. Nitrate turnover times decreased exponentially from order 30 years in February to 1-5 days in August. Ammonium turnover was considerably more rapid, varying between 15 days in March to typically 1-5 days in August/September. Average ammonium turnovers during summer (May – September) were 6 days as compared to nitrate at 102 days.

Nitrate uptake rates decreased relative to ammonium uptake rates across the sampling area towards the continental coast. The higher rates of ammonium uptake relative to nitrate were possibly due to ammonium build up above ~1.5 µmol l-1 (e.g. Wheeler and Kokkinakis, 1990). As a result, almost all production was regenerated, i.e. based on ammonium uptake in preference to nitrate, as has been previously shown (Dortch, 1990). Below this threshold the relative uptakes rates were more variable due to the changes in the preference of the phytoplankton for nitrate and ammonium. In the context of UK riverine nitrate uptake, this switch to ammonium uptake implies no uptake of the remaining nitrate.

CONTROLS ON PHYTOPLANKTON GROWTH IN THE OUTFLOW OF THE THAMES

Water samples were collected in the Thames estuary at the Warp (Figure 2) site in order to investigate controls on primary productivity and phytoplankton community structure and specifically the flagellate alga Phaeocystis spp. blooms in the region. A variety of laboratory-based incubations were performed to study the relationship of phytoplankton with respect to nutrients, light and microzooplankton grazing were carried out between June and November. Primary productivity rates were similar to previous studies (JoNuS II) however in-situ nutrient concentrations fell to lower levels than in JoNuS II with phytoplankton >5µm still dominant.

The incubations demonstrated size differential control of phytoplankton of the >5µm and <5µm communities in summer as has previously been shown in Dutch coastal waters (Reigman et al., 1993). Grazing rate was much greater as a proportion of the growth rate for <5µm fraction, mainly flagellates, implying control of flagellates by microzooplankton grazing. The phytoplankton >5µm, mainly diatoms, were however generally silicate limited in summer (Figure 3) and both fractions were light limited in winter

MODELLING

The project started with an aspiration to use the best physical and ecosystem models to explore the transport and fate of nutrients in the southern North Sea. The way we were going to achieve this, and partly support the development of international consensus, was through collaboration with the original ERSEM modelling group (Baretta-Bekker et al., 1995) part of the Netherlands ‘Plume and Bloom’ project and through a European Community Framework V programme. Neither aspect of the work received funding and could not therefore go ahead. This raises questions about how to ensure that science that focusses on specific policy sensitive questions can be succesfully promoted at a European scale.

We have used a much simpler, more robust and transparent approach to meet the specific needs of the project and this has allowed fluxes of nutrients and particulate nitrogen to be reliably estimated. The results from this box model are presented in the discussion. We have not been able to work with simulations of the ecosystem, but the technology may not yet be up to resolving the issues that have been addressed. For example, through informal collaboration with MUMM (Management Unit of Mathematical Models) in Belgium we have had access to the output of the state-of-the-art

COHERENS ecosystem model coupled to a physical transport model (Luytens, 1999) with a 4 km grid spacing and incorporating freshwater inputs. A simulation of the southern North Sea did not resolve the low salinity region between England and the Netherlands that we have studied even though it did resolve the hypernutrified Rhine ‘plume’, its extension to the Frisian Front and associated high chlorophyll levels in (modelled) June and July. The most recent comprehensive review (Moll & Radach, 2001) of 3-D ecological models (specifically for the North Sea) highlighted the strengths and weaknesses of different approaches and drew upon recent modelling inter-comparison exercises (ASMO, 1997; ASMO 1996; Proctor, 1995). The review concluded that a general weakness of the existing ecosystem models is their limited ability to address complex processes such as the succession of phytoplankton species. While this is theorectically possible given knowledge of, for example, the environmental and physiological demands of algal species or functional groups there is a complete lack of appropriate observations to test such models. There are, of course, developments which will allow such observations in the future.

Discussion and Summary

The underlying non-wind driven residual transport in the central southern North Sea carries water eastward at a mean speed of approximately 3.5 km day-1, this is regulated by the magnitude and direction of the wind forcing. For 2000, calculated volume fluxes through the mooring array (Table 1) indicate little seasonal variability. However, the figures mask considerable short term variability in flow direction which determine how the components of UK coastal, English Channel, Central North Sea and European coastal water impact the southern North Sea. Storm activity plays a strong role in regulating the suspended sediment climate between East Anglia and the continental coast. The cumulative effect of wind/wave induced resuspension and shallow topography during winter generates the region of high suspended load seen in satellite imagery, leading to what some interpret as a plume. Furthermore, the low salinity water mass associated with UK freshwater discharge (or ‘English River’) is not necessarily coincident with the highest suspended sediment. In actuality, the flux of material occurs over the entire region and the so-called ‘plume’ is not a reliable indicator of how and where material is transported.

Prior to the spring phytoplankton bloom light limits growth. The Smart Buoy time-series at the Gabbard, central mooring site and in the Dutch coastal zone suggest that the onset of the spring bloom occurs throughout the region at essentially the same time. This view was reinforced by the spatial surveys, revealing some patchiness in biomass and light climate, but the locations of such features were variable. Short-term resuspension events may briefly delay the onset of the bloom through a reduction in light levels. While attenuation of light is largely determined by suspended load, surface measurements may not provide a good measure of the depth integrated light climate. The amount of light that a phytoplankton receives in a mixed water column is governed by the depth of the water column and the degree by which light is attenuated. In a shallow turbid water column the amount of light a phytoplankton receives may be the same or greater than that in a deeper and clearer water column. Despite the disparity in suspended load conditions across the region the light climate is generally favourable for growth in the relatively turbid and clear waters alike.

Phytoplankton growth during the spring bloom is fuelled primarily by nitrate which is reduced during the spring bloom. Post bloom ammonium, produced by grazing and decomposition of organic matter, is the dominant nitrogen source for primary production in southern North Sea. As the summer progresses the rate of ammonium uptake increases in comparison to nitrate and may inhibit the uptake of nitrate. Both ammonium and nitrate therefore provides a source of nitrogen to be transported across the southern North Sea in summer.

This process should be viewed in the context of nitrate inputs. Aggregated data from the UK Harmonised Monitoring Scheme (HMS) for 1995-2000 indicates that between 55 and 70 % of the UK nitrate load enters the southern North Sea in the winter/spring (December – April, inclusive). Prior to the spring bloom this will be transported across the North Sea with little attenuation. Post bloom, the nitrate levels on the UK coast have been reduced from approximately 10-15 to 1-2 µmol l-1. Hence, although transport of dissolved nitrate is significantly reduced nitrogen will be transported in dissolved form as ammonium or as PON. Whilst winter nitrate controls the magnitude of the spring bloom, it is the processes that prevail in summer that determine biomass yield. The fate of this PON is be to remineralised or advected as the tidally energetic nature of the southern North Sea largely prevents sinking and loss of phytoplankton to the sediments.

To illustrate these processes, the production and transport data were integrated into a simple box model of nitrogen fluxes through the centre of the mooring array for one month in winter (March) and one month in summer (July) (Figures 8a & 8b). The model incorporates the nitrogen fluxes as ammonium measured on cruises, nitrate and nitrite (DIN) from the Smart Buoy and PON derived from Smart Buoy chlorophyll measurements. A section 10 km either side of the Smart Buoy was chosen, as that broadly representative of the water passing through the site. In order to characterise the

inputs/losses from the atmosphere and via exchange across the water column/sediment interface a box length of 80 km was chosen, this being the approximate distance of the mooring from the Frisian front and roughly the distance water might travel in a month.

On this basis the DIN and PON fluxes into the western end of the box during winter months were 15,840 and 2,190 tonnes, respectively. Estimates of atmospheric nitrogen input due to wet and dry deposition (Rendall et al., 1993) and nitrogen lost from the water column due to denitrification (Lohse et al., 1996) were 135 and 350 tonnes, respectively, and are approximately constant through out the year. Sedimentation and burial are assumed to be negligible which is consistent with the sand dominated nature of the seabed.

Our measurements of nitrogen uptake by phytoplankton of 3,650 tonnes was met by regenerated production and was assumed to be a closed system with no exchange to the north and south of the ‘plume’ and no net production of PON. The nitrate uptake was assumed to be all new production and gave an uptake of 475 tonnes. This can be thought of as being the upper limit for new production with the benthic nitrification rate (Lohse et al., 1993) being 125 tonnes per month. There is unlikely to be significant nitrate ammonification in the water column due to the rapid transformation of ammonium into phytoplankton. This leads to a resultant flux of 15,150 tonnes of N as DIN, with the majority of this being nitrate, and 2,665 tonnes as PON.

In July (summer) the same assumptions were made about new and regenerated production, rates of denitrification and Wet and dry deposition

+ 135 tonnes N NH4 uptake 3,650 tonnes N DIN DIN 15840 15150 NO - uptake tonnes N 3 tonnes N 475 tonnes N

PON PON 2,190 2,665 tonnes N tonnes N Denitrification 350 tonnes N

atmospheric input. The DIN input was 3,368 tonnes and 5,831 tonnes as PON. Again the regenerated production fuelled the bulk of primary productivity with an uptake of 5,500 tonnes. New production accounted for 325 tonnes of N resulting in the flux of 2828, tonnes of dissolved nitrogen and 6,156 tonnes as PON. In contrast to March, 35% of the DIN transport is as ammonium. To date, the latter has not generally incorporated into estimates of nitrogen flux across the North Sea due to methodological difficulties in its measurement.

Wet and dry deposition

+ 135 tonnes N NH4 uptake 5,500 tonnes N DIN DIN 3,368 2828 NO - uptake tonnes N 3 tonnes N 325 tonnes N

PON PON 5,831 6156 tonnes N tonnes N Denitrification 350 tonnes N These figures illustrate the large amounts of nitrogen uptake that are met through regenerated production, thought to be mainly due to the grazing and remineralisation of PON in the water column since benthic rates of ammonification are too low to sustain this production (Lohse et al., 1993). These mass balances indicate that total nitrogen transport through the box is twice as great in winter than in summer, while the element due to DIN is 5 times greater.

The nutrients present which are transported by the observed pathways are derived from a number of different sources including the Atlantic inflow, as modified during passage through the North Sea and the Channel, as well as inputs from land based sources. We have attempted to estimate the contribution of the UK input to the flux of nutrients in the southern North Sea. Two methods have been used. The first combines observed measurement of water flow with an estimate of the contribution of UK coastal water based on lowered salinity due to the freshwater contribution and the second is by consideration of the nutrients present in excess of that which would be expected if it were all English Channel or central North Sea water. Method details and the important assumptions that are made are in the methods section. The results are considered to give a good estimate of contribution and have been calculated in such a way as to maximise the result. The actual flux is therefore likely to be lower.

Table 1. Transport of Water and Nutrients through the mooring array

Season Date Water Mass Transport Nutrient Transport 000 tonnes Sv (106 m3 s-1) UK origin DIN PON UK origin % DIN Winter 26/1 - 25/3 0.19 10 – 15% 104 –154 17-22 15 – 29 Spring 26/3 - 19/5 0.13 12 – 18% 78 – 124 90-117 14 – 21 Summer 20/5 - 24/8 0.15 10 – 15% 39 - 53 51-68 5 – 16

Most nitrogen tranport occurs as disolved inorganic nitrogen (DIN) in winter. In spring, spanning the spring bloom period, nitrogen is transported in equivalent amounts by DIN and PON while in summer, nitrogen is transported as DIN and PON, but the DIN is dominated by ammonium rather than nitrate.

Overall land-based discharges of DIN from the UK (including Humber, Wash and Thames) account for around 15 – 25% of the total flux across the southern North Sea. However, it would not follow that a complete cessation of discharge would result in a proportionate reduction in the anthropogenic component of the flux as the connection between DIN input from land (some of which is retained in the coastal zone) and the flux of DIN and PON at any point in the sea is difficult to establish. This would be a role for the next generation of appropriate models. Even though the probable contribution of UK derived nutrients to the Frisian Front area is small it is worth considering what happens at the alleged site of impact. The Frisian Front is an area of organically enriched sea bed sediments resulting from temporary deposition of detritus. Summer phytoplankton blooms have been described in the literature (Baars, 1999) though they do not occur every year. The phytoplankton dynamics at the Frisian Front are complex and the explanation of the episodic appearance of summer phytoplankton blooms – termed by some the ‘green curtain’ – is not CSG 15 (9/01) 12 Project Transport and fate of UK nutrient input to the southern DEFRA AE1221 title North Sea project code

straightforward. The front is a natural feature of the way this part of the sea works and it is likely that higher production will occur here as a result of either, the intermittent breakdown of the front, through the physics of fronts or induced by wind, that will allow the cross frontal addition of nutrients or injection of nutrients from the ‘enriched’ seabed. The enrichment and retention story does not fit with other evidence that there is no long term storage of nitrogen in these sediments (van Raaphorst et al., 1992) nor the high intensity of trawling known to occur in this area which will encourage the rapid recycling of nitrogen and carbon. This does not mean that UK sourced nutrients do not contribute to the production at the Frisian Front, the transport of PON, particularly in summer, would suggest that there may well be a proportionate contribution. However, given the proximity of the front to the hypernutrified continental coastal waters (a much larger source than the UK coastal water), the known but poorly defined variability of offshore transport and the known variability in frontal processes, we cannot rule out a continental source for the additional nutrients fuelling the production at the Frisian Front. It is unclear whether the Netherlands regard the Frisian Front as eutrophication problem area. In summary, nitrate added to the North Sea in winter is transported in the general circulation across the North Sea. The spring bloom of phytoplankton rapidly reduces nitrate to low levels, but significant primary production can continue in the summer fed by ammonium derived from the decomposition of phyto-detritus and excretion of grazing animals. Despite the higher turbidity of the zone of East Anglia, the light climate in spring and summer is good and allows the growth of phytoplankton. Modulation of the light climate, rather than nutrient availability, can influence the type of plant that grows. The transport of nutrients occurs all year at rates reflecting the known mean circulation of the North Sea but is subject to considerable variabilty, rate and direction, depending on the incident wind. There is a significant difference between winter when transport of nutrients is dominantly of the dissolved form and in summer when it is partly dissolved and partly particulate. This has a bearing on the fate of the nutrients as particulate material may accumulate in areas of sediment deposition though the evidence for accumulation in the southern North Sea is limited as regeneration appears to be rapid (supporting new growth) and it is only in specific places, like the Frisian Front, that the physics would allow acumulation.

The work described represents a substantial improvement in our understanding of the transport rates and the spatial and temporal variability of factors controlling phytoplankton growth and the fate of UK nutrient input to the southern North Sea. Workshops and Consensus

The work was undertaken with strong links to the Netherlands Institute of Oceanograhpic Research (NIOZ) and their “Plume and Bloom” project. Two workshops were conducted, one near the start of the project (January 2000) with the other towards the end (November 2001). Regular meetings were held between staff at both institutes and there was UK representation on some of the Plume and Bloom cruises. At the end of the project international ICES sponsored workshop co–funded by the Netherlands Rijkswaterstaat and DEFRA/CEFAS was held in the Netherlands in March 2002 entitled “Contrasting approaches to understanding eutrophication effects on phytoplankton”. Through these mechanisms we have attempted to develop scientific consensus about both the transport of nutrients and the fate of nutrients in causing changes to plankton communities. We have not reached complete consensus with our Netherlands colleagues on the interpretation of the transport of nutrients in the southern North Sea. However, such consensus as there is will be presented in a paper which is being developed jointly and further publications will, no doubt, describe the areas where there is no consensus. Recommendations for future work

The project has clearly demonstrated the importance of particulate nutrient transport and nutrient regeneration as a feature of the way that the shallow marine ecosystem works. This is important for both an understanding of the normal pattern of production in the sea from which we can assess deviations due to anthropogenic impact and in dealing with questions about impact in specific areas, especially where sedimentation occurs. Any future work on nutrient and carbon budgets needs to take close account of the particulate fraction, but detailed budget information will only be required if a particular problem of enrichment is first established.

There is a need for better information about the physics and biological response of the environment around frontal structures in the sea.

While this project has not taken the use of ecosystem models forward it is, nonetheless clear that there is a need to go beyond the present generation of models which are physically and chemically based to incorporate better understanding of the biology (at different levels) if we are to be able to adequately simulate ecosystems. This will be best achieved in CSG 15 (9/01) 13 Project Transport and fate of UK nutrient input to the southern DEFRA AE1221 title North Sea project code

concert with appropriately focussed observational programmes avoiding the mistakes of the past where modellers and observationalists have tended to work in isolation. CEFAS has a good track record of combining the two activities but the scale of the challenge is now such that single organisations cannot achieve what is required. There is a clear need to follow through with operational oceanography which combines good observational programmes (demonstrated through this project) with good modelling programmes. The importance of measurements at the right spatial and temporal scale is clear as well as ensuring that measurements are made both at the seabed and at the sea surface.

There is often a plea for the development of new and better models emerging from scientific projects. The plea here is for the effective use of ecosystem models that already exist but configured at a scale to address the issue of concern. However, there is also a clear need for a focus on the development of the biological component of ecosystem models if we are to have any chance of predicting the ecological consequences of managing nutrient inputs. This will become increasingly important for the effective management of biodiversity and ecosystem function in transitional and coastal waters supporting the Water Framework Directive and Habitats Directive, for example.

Actions resulting from the work

The results of the project need to be made available to both national and international bodies with an interest in assessing nutrient related environmental pressures and the consequences of specific management decisions on the quality of the marine environment. There is a clear need for OSPAR and the EC to use the outcome of this work as assessments are made about the eutrophication status of the OSPAR maritime area.

Collaborative Institutes and projects

Dr L. Spokes at UEA under EU project 'ANICE' (Atmospheric Nitrogen Inputs into Coastal Ecosystems) to estimate the impact of atmospheric nitrogen deposition on the primary productivity of the southern North Sea; Netherlands Institute of Oceanographic Research (NIOZ) and their Plume and Bloom project; links with other DEFRA projects AE1020, AE1021, AE1214 and AE1225.

Publications and other reports during the project

Bunt, J., Brown, J., Fernand, L. and Rees, J.M., 2002. Observations of the seasonal cycle of sediment resuspension in the southern North Sea. In prep for submission to Continental Shelf Research. Fernand, L.J., Medler K.J., Brown, J., Tinton, E. and Read, J.W., 2002. Observations of the transport and flow in the Southern North Sea during 2000. In prep for submission to Estuarine and Coastal Shelf Science. Fernand, L., Parker, R., Weston, K., Brown, J., Malcolm, S., Pearce, D., Mills, D., Medler, K. and Sivyer, D., 2001. Transport and fate of UK nutrient input to the southern North Sea. 16th Biennial conference of the Estuarine Research Federation. ERF 2001: An Estuarine Odyssey. University of Florida. Mills, D.K., Rees, J.M., Fernand, L and J. Brown, 1999. New developments in monitoring systems for detection of environmental change. In the proceedings of the 8th National Symposium on Environment, Kalpakkam, India June 22-25 1999, p 169-180. Mills, D.K., Sivyer, D.B., Malcolm, S., Pearce, D., Pearson, N., Brown, J. and Robinson, B., 2001a. Smart Buoy – A new data buoy for marine environmental monitoring. Detecting Environmental Change, Science and Society. University College, London. Mills, D.K., Laane, R., Sivyer, D., Suijlen, J., Rees. J., Roberti, J., Pearce, D., Hoogervoorst, R., Reeve, A., and Heins, C., 2001b. Scales of temporal variability of suspended matter, nitrate and phytoplankton in the Dutch coastal zone: preliminary results obtained with modern measuring techniques. International Scientific Symposium; Structuring Factors of Shallow Marine Coastal Communities, NIOZ, The Netherlands, Nov 2001. (abstract) Mills, D.K., Sivyer, D.B., Pearce, D., Read, J., Robinson, Platt, K. and Rawlinson, M., 2002. Multi-parameter buoy monitors coastal ecosystems. International Ocean Systems, 6(2); 23-27. Parker, R., Fernand, L., Brown, J., Malcolm, S.J., Mills, D., Sivyer, D., Tinton, E., Medler, K., Read, J., Jickells, T. and Weston K., 2000. Transport and fate of UK nutrient input to the southern North Sea. UK Marine Science 2000. University of East Anglia. Parker, R., Fernand, L., Weston, K., Brown, J., Malcolm, S.J., Mills, D.K., Medler, K.J. and Sivyer, D., 2002. Transport and fate of UK nutrient input to the southern North Sea. American Geophysical Union, Honolulu, Hawaii. Eos. Trans. AGU, 83(4) Ocean Sciences Meeting Supplement., Abstract OS22C-189. CSG 15 (9/01) 14 Project Transport and fate of UK nutrient input to the southern DEFRA AE1221 title North Sea project code

Weston, K. and Jickells, T., 2002. Plume and plankton: new and regenerated production in a North Sea silt plume. Phytoplankton productivity, Bangor, UK, March, 2002. Weston, K., Jickells, T., Parker, R., Fernand, L., Brown, J. and Malcolm, S.J., 2002. Nitrogen cycling in the southern North Sea: consequences for total nitrogen transport. In prep for submission to Estuarine Coastal and Shelf Sciences.

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CSG 15 (9/01) 17