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Effectiveness according to development targets of measure

The specific target for Welwick was to create intertidal habitat to compensate for that lost through ABP port development on the Humber Estuary. Early discussion with stakeholders was highly beneficial throughout the whole process, including the selection of a potentially suitable site, design issues, the EIA and subsequent implementation of the scheme. An environmental steering committee also met at regular intervals to discuss issues relating to the site.

Although there was no planned timetable, it took considerably longer than anticipated to get all of the required approvals from the regulatory bodies, including the Environment Agency and Local Authorities.

The scheme was breached in June 2006 and appears to be performing as predicted at this early stage with saltmarsh development and bird usage already evident. In the medium to long term, the monitoring results will be compared with the objectives of the site to determine the success of the scheme.

Habitat Area

The specific targets of the Welwick Scheme were to create the following habitats:

• Between 7ha and 37ha of intertidal mudflat (and maintain this area in the long-term, over the 10 year period);
• Between 8 ha and 32ha of saltmarsh (and maintain in the long-term, over the 10 year period);
• Between 9 ha and 15ha of supralittoral grassland (which at least 50% of which should support natural plant communities comparable to local reference areas within 5 years of construction);
• 100m2 area of stone parsley (and maintain this area in the long-term, over the 10 year period0; and
• Two saline pools within the grassland area in the north east corner of the site. Within 5 years of creation the pools should support a fauna and flora comparable to local reference pools.

Welwick has had to overcome problems relating to saline pool development and an important lesson to learn from the monitoring of saline pools was to ensure that the position of the habitat is at the right elevation with respect to the tidal frame, in order to allow specialist fauna to colonise, which also includes ensuring contractors follow exact design details. No such specialist fauna has colonised at Welwick and so the pools have continued to be monitored post the initial 5 year review period.

Habitat quality

Within 5 years of realignment, the mudflat created should support an invertebrate assemblage of similar species, population abundance and biomass to local reference sites.

In particular, it was hoped to be able to support the following key species:

• Ragworm (Hediste diversicolor);
• Bristle Worm (Pygospio elegans);
• Mud Shrimp (Corophium volutator); and
• Baltic tellin (Clam) (Macoma balthica).
• Laver Spire Shell (Hydrobia ulvae); and
• Worm (Streblospio shrubsolii).

It was also hoped that invertebrate quality would be maintained over the area of mudflat in the long-term.

Monitoring the success of habitat quality was proposed to be undertaken by including descriptions of the size distribution of individuals (adult/juvenile), tidal height and sediment properties, where samples were taken, in order to determine options for remedial action, if required.

It was also hoped that within 10 years of realignment, the saltmarsh created would show a similar zonation and species composition to existing adjacent saltmarsh, which locally include species such as red fescue, sea plantain, lesser sea spurrey, sea lavender, glassworts, sea purslane, sea aster and sea couch vegetation.

With regards to the intensity of the actual monitoring that has been undertaken at Welwick, it was felt that little had been gained from the intensive invertebrate monitoring post breach. It was identified that invertebrate monitoring every year post inundation did not provide any more valuable information than would have been achieved at a less regular frequency.

Bird Usage

One of the targets of the Welwick scheme was for the creation of intertidal habitats with the ability to provide feeding habitat for in excess of 800 (peak mean over 5 years) feeding water birds with typical species in the following relative proportions:

• 60% dunlin;
• 20% black-tailed godwit;
• 10% redshank; and
• 10% other bird species.

Within ten years of realignment, it was hoped that the mudflat would be regularly used by approximately 607 overwintering waterfowl (peak) (166 average) based on the following species:

• Golden plover;
• Lapwing;
• Dunlin;
• Redshank;
• Black tailed godwit;
• Ringed plover;
• Curlew; and
• Shelduck.

This estimate was based on the assumption that waterfowl would use the realignment area pro rata to the adjacent bird count sector (ISE1). This usage should be maintained in the long-term, taking account of the natural variability through comparison with relevant WeBS data.

Grassland habitat to support a range of farmland bird species including reed bunting, skylark and yellow wagtail was also created and the saltmarsh is used by breeding waterbirds and passerines, with the area behind being important for breeding Marsh Harrier.

Fish

Attempts to value the utilisation of managed realignment by commercial fish species have been successful elsewhere in the UK (see for example Colclough et al., 2005; Fonseca, 2009), and an initial attempt to value the fish species at the Welwick managed realignment was made by Burdon et al., (2011). This latter study provided the first evidence of the fish species using the Welwick managed realignment site and this information was linked to the potential value of commercial species landed in the North Sea (see Table 2). This data shows that the fish species found within the Humber Estuary, and within the Welwick managed realignment site, may contribute value to the demersal and pelagic commercial fishing sectors of the North Sea (Burdon et al.,, 2011). It is unlikely that the market price will change given the marginal impact of these landings in relation to the overall landings.

Table 2: North Sea landings (quantity and value) by UK vessels (in UK and abroad) in 2010 (MMO, 2011)

Species	Northern North Sea (IVa)		Central North Sea (IVb)		Southern North Sea (IVc)		Average Price per Tonne
	Quantity (tonnes)	Value (£’000)	Quantity (tonnes)	Value (£’000)	Quantity (tonnes)	Value (£’000)
Sea Bass	-	-	17	99	134	842	£9,029
Plaice	562	413	13,576	15,961	651	673	£2,255
Saithe	11,527	10,609	360	316	-	-	£1,359
Herring	21,095	8,927	2,381	665	78	32	£838
European Flounder	-	-	41	13	46	19	£534

Information regarding utilisation of the managed realignment sites by fish species is currently being assessed by IECS on behalf of the Environment Agency. This research will provide a greater insight into the fish species present at Welwick and will give an indication of what commercial species are currently using this site.

A recent study undertaken by Burdon et al., (2011) focussed specifically on the value that saltmarsh present in the Welwick managed realignment site in the Humber Estuary provides with respect to the fish species present. Unfortunately, insufficient data was available to undertake the full analysis, however the study did provide an insight into the fish community found within the site and provided a list of data requirements in order to complete a more comprehensive site-specific analysis in the future.

Carbon Sequestration

Site specific benthic biomass data from mudflats can be used as an indicator of carbon sequestration in the estuarine environment, providing an underestimate of biomass given that it does not include any mobile fish and shellfish species within the area. In order to evaluate the consequences of managed realignment for CO2 emissions, the change in value of carbon associated with the newly created managed realignment site would need to be compared with the established mudflats outside of the site. This would enable the net gain/loss of the realignment to be measured in terms of carbon sequestration alone.

An example is presented below (Table 3) which shows that at present carbon sequestration at Welwick is much greater outside of the site than inside the site, and this equates to a carbon value of £4,252 per km2 outside the site and £408 per km2 inside the site.

Table 3: Conversions of benthic biomass (ash free dry weight) to the value of carbon (using the 2010 traded price of £14.10) inside and outside of the Welwick managed realignment site (benthic biomass data supplied by ABPmer)

	Inside Welwick	Outside Welwick
Mean Biomass (per core)	0.147	1.529
Total Biomass (g AFDW m-2)	18.320	191.085
Carbon (g m-2)	7.877	82.167
CO2e (g m-2)	28.910	301.551
Cost of Carbon  (£ km-2)	407.633	4,251.872

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