Owing to poor water exchange in many lagoons or parts of lagoons, by the time a change in biota of conservation importance is detected, and the change is attributed to changes in nutrient inputs, it may well be too late for biological interests of the site to recover within the sort of time frame employed in management planning, e.g. five to twenty five years. This is because responses to nutrient enrichment in other systems similar to lagoons have been found to be self-perpetuating, i.e. once they begin to occur they create conditions which further create deterioration, and the few studies from lagoons support this. Lagoons, such as isolated lagoons, or parts of lagoons such as the head end of lagoonal inlets where flushing is poor, are likely to be most susceptible to this. Stratification of the water column, if it occurs, will also affect what happens in terms of nutrient recycling within any lagoon.

As a consequence, it is recommended that a precautionary approach should be adopted for relevant lagoon sites, or parts of sites, taking account of the conservation objectives for the site, i.e. that proportionate management measures should be considered even where there is only limited evidence of an impact. In deciding upon management measures, it should be noted that the later these are initiated the more costly they may become.

In addition to evidence from the site, the recommendations for management measures in the Fleet take account of the importance and sensitivity of the biological communities and species concerned, e.g. environmental requirements of charophytes, and studies from elsewhere, e.g. nutrient recycling within other partially enclosed systems. In summary:

• There is (only) limited evidence for impacts on features of nature conservation importance from nutrient enrichment
• Several features of nature conservation importance in the Fleet are sensitive to impacts from nutrient enrichment.
• There is circumstantial evidence that nutrient inputs have increased over the last few decades.
• There is therefore a potential risk that the impact to which features are sensitive will be realised, i.e. features of conservation importance are vulnerable
• Studies elsewhere suggest that there is a low potential for recovery should such impacts occur and, indeed, that such impacts may be sustained in the long-term.

Taking these points together, particularly the latter, it is appropriate to act on the precautionary principle and recommend reducing inputs of nutrients. Given this precautionary approach, the cost of any management actions will need to be proportionate to the benefits gained.

Management strategies will depend on the conservation objectives for the site, financial resources, and the findings of the historical and baseline surveys. Some measures may need to be introduced before data collection is completed, depending on the findings of the surveys.

Management strategies are likely to involve various agencies and groups for different aspects. Ideally, they should therefore be coordinated by a single group. On European marine sites, this function would sensibly fall to the management group and be outlined in the management scheme document for the site. Management, monitoring and collection of additional baseline data will be closely interrelated and will feed back to each other. Regular reviews of management practices against monitoring data should be carried out, and both modified as appropriate depending on the findings of the reviews. Ad hoc reviews should also be undertaken as appropriate, as extraordinary events dictate (e.g. particular development pressures arise, or unusual meteorological events may affect monitoring data).

Where excessive growth of macrophytes appears to be affecting features of conservation interest, including the system as a whole, consideration may be given to physically removing this material, as done in several cases (e.g. see Hodgkin and Birch 1986; semi-enclosed Cuckmere estuary in Sussex (Curzon pers. comm.)). Such an option should be assessed very carefully to determine that it will not cause other, potentially greater, impacts than the presence of the material being removed. Physical cropping will not address excessive growth of phytoplankton. More importantly, it only addresses a symptom and does nothing to tackle cause(s) of the problem.

Where it is concluded that nutrients are or may be adversely affecting saline lagoon features of interest, there are a number of management measures that could be considered depending on the causal activity. These include:

Agriculture: options range from voluntary to statutory mechanisms. Voluntary measures should be explored as a preference. In all cases, the success of proposed measures should be developed and implemented in close cooperation with the local (farming) community. Mainstone et al (2000) and Hodgkin and Hamilton (1993) provide overviews of tackling agricultural sources of nutrient loading and the latter discussed community involvement. Options include:

• better Management Practices (BMPs) for farming to retain nutrients on fields and reduce inputs to water courses or directly into the site; note that such an approach is consistent with codes of practice advocated for farming practice anyway, including both application of nutrients (see MAFF 1998) and soil erosion (MAFF 1999). The economic benefits of more effective fertiliser use should be highlighted;
• in England and Wales, identification of contribution from agricultural sources of diffuse pollution within Local Environment Agency Plans (LEAPs);
• considering the potential for adopting measures as part of an Environmentally Sensitive Area (ESA) status requirement, or, locally (and more readily), under Countryside Stewardship, e.g. use of buffer zones along field margins;
• identifying the catchment as a Nitrate Vulnerable Zone under UK legislation in fulfilment of the EC Nitrates Directive. Note, this measure does not address phosphates;
• other statutory mechanisms are potentially available and may merit investigation, such as the use of Water Protection Zones under the 1991 Water Resources Act.

Point discharges

• increased level of treatment at sewage works, e.g. tertiary treatment to remove phosphates or nitrates. In many cases, such as the Fleet, sewage works discharging to lagoons, or streams feeding the lagoons, are likely to be relatively small and this will therefore influence the chosen option for reducing inputs of phosphorus, e.g. phosphorus stripping is usually not recommended for small works for various reasons including difficulties in controlling the level of dosing (Bunting pers. comm.). See Mainstone et al (2000) for discussion of options for reducing phosphorus inputs from point sources;
• timing of discharge, eg to coincide with optimum flushing period during tidal cycle;
• relocation of discharges.

Other

• wildfowl: where these are managed through feeding, revise feeding regime to optimise food utilisation and minimise waste.

Monitoring is required to review and ensure the effectiveness of management measures and, in the case of statutory conservation sites, to report on the condition of features for which a site is designated. The actual monitoring programme will be site specific, depend on the resources available, and frequency will vary according to the attributes and parameters to be monitored. The above studies will highlight for any lagoon site those aspects of the environment which should be monitored, and give an indication of the frequency and extent of investigation required.

It is recommended that monitoring is undertaken to determine the condition of features of conservation interest including other biological features which indicate or affect these. Monitoring will also be required of relevant water quality parameters, both as an indication of attributes critical to the condition of conservation features, e.g. light attenuation, but particularly with respect to inputs where there is concern about these (some of which will be achieved by monitoring compliance with, for example, licensed discharges).

Guidance on methods for monitoring features of conservation interest are outlined in Hiscock (1998). Consideration should also be given to timing of monitoring surveys. For example, Lamprothamnium papulosum should be monitored in summer as it dies back in winter. Bamber et al (in prep.) discuss the required frequency of monitoring in detail. The requisite frequency of monitoring will partly depend on the sensitivity of different lagoons and/or species it supports, e.g. a small isolated lagoon is likely to be more sensitive to environmental impact than a large lagoonal inlet, the importance of the site, and site-specific aspects, e.g. is it exposed to a factor to which it is sensitive. Inevitably, funding will be another consideration and the monitoring programme will result from a compromise between this and other considerations. It is therefore important to provide guidance on a minimum standard for monitoring.

As a guide, for biological features, annual monitoring will certainly detect presence or absence, and may reveal changes in density or distribution, or species. More frequent (e.g. seasonal) monitoring may assist in understanding the life cycle of a species (for example timing of recruitment) and in identifying an optimum time(s) of year for monitoring, but the merit of the information gained would have to be balanced against the additional cost. In both cases any indication of a significant change would require a specific study to investigate cause and effect and help identify a management response.

It is suggested that for most biological features (with the exception of plankton studies), monitoring will need to be repeated at regular, but relatively infrequent intervals. On statutory nature conservation sites, including European marine sites, the minimum frequency is every 6 years (JNCC 1998). Where significant change is detected, or where the sensitivity or vulnerability of the sites merits it, the frequency may need to be greater.

A compromise option would be to take and preserve samples at additional times and archive them without sorting or analysis; then should a significant change be detected by less frequent monitoring, the archived samples can be retrospectively analysed to assist in determining cause and effect and its timing.

Depending on management issues, monitoring of water quality attributes will need to be carried out relatively frequently, and will need to take account of seasonal variation. For example, it is important to monitor for salinity conditions at times of highest and lowest salinity, normally late summer and mid-winter/early spring, respectively. It is recommended that, initially, monitoring is undertaken quarterly, and ideally monthly if possible, to build up a picture of the seasonal regime and to fully characterize the baseline for the site. Such monitoring should encompass both neap and spring tides. It is suggested that the scope of such surveys be reduced (i.e. select only a few sites to sample for only a few parameters), but that the frequency of sampling be maintained (e.g. monthly or weekly during summer, less frequently during winter). Periodic, more extensive surveys can then be coordinated with the less frequent biological monitoring surveys.

Guidance on methods for monitoring water quality parameters and/or modelling is provided in Scott et al 1999.

Hydrographical modelling, where undertaken, is likely to help determine effective location of sampling sites for monitoring of both biological features and water quality parameters.

For all aspects of lagoon systems, exceptional events (e.g. unusual meteorological conditions, or particular development pressures) or detected changes should trigger additional monitoring or baseline surveys, or may direct sampling to different areas or aspects of the lagoon system. Monitoring should be kept under regular review by the relevant management group.

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