Land Manager Assessments – Credits

This work package has two main parts,

1. The first part sought to define and understand the problems within the Milford Haven and Cleddau Catchment in order to understand what the required load reduction targets within the waterbodies would be.
2. The second part was designed to identify where the land management opportunities are within the catchment areas in order to achieve the required nutrient loading reduction.

In order to ensure the end scheme is based on sound data we collated and reviewed all available information on the catchments including; nutrient loads, SAC condition, known pollution sources and data on nutrient load analysis. Subsequently this information has been analysed to better understand the local nutrient reduction requirements and how these might be delivered by initiatives across the catchment.

Due to the absence of a known threshold to which the initiative could work towards, additional work has been undertaken to identify potential thresholds and identify, based on the data, which are the most appropriate to use.

In addition, the second element of work for this work package sought to identify potential buyers and sellers within the catchment. This has been established by utilising “Farmscoper” to undertake land management assessments, from which to identify opportunities for land to enter the nutrient offsetting programme.

There is significant concern that many of the Pembrokeshire Marine Special Area of Conservation (PMSAC) features are in unfavourable conservation status and nutrient loading into the Milford Haven has been identified as a key priority action. Existing actions within the PMSAC management scheme adopted in 2008, are not in themselves adequate to address this loading and the ecological impacts this has on the ecosystems.

Between 2002 and 2006 a review of all Environment Agency Wales (EAW) regulated discharges, potentially impacting on the Pembrokeshire Marine Special Area of Conservation (SAC) was carried out under the EU Habitats Regulations. The Regulations require that Agency-licensed activities must not adversely affect the integrity of any Natura 2000 site.

Since the Review of Consents in 2006, increasing concern has been expressed about the occurrence of opportunistic macroalgae on inter-tidal mudflats and sandflats within sheltered bays and inlets in the waterway. Although there appeared to be little evidence linking increasing macroalgae growth to nutrient inputs to the waterway, the concerns around this increase prompted further investigations and more rigorous assessment of new discharges.

Currently, NRW consider that due to the level of nutrient loading within the waterway it should be considered as “full” with no headroom in the Milford Haven catchment for additional loading. This is seen as presenting a significant barrier to development and therefore a robust solution is required.

SAC Information

The Pembrokeshire Marine SAC covers an area of 138,069 ha. The site extends from near Abereiddy to Manorbier and includes the coast of the islands of Ramsey, Skomer, Grassholm, Skokholm, the Bishops and Clerks, and The Smalls (21 miles offshore). It also encompasses almost the entire Milford Haven Waterway. The landward boundary of the SAC mostly follows the extreme high water mark.

Pembrokeshire Marine SAC is a multiple interest site that has been selected for the presence of eight marine habitat types and associated wildlife (Habitats Directive Annex I habitat types) and seven Annex II species (Habitats Directive Annex II species).

It is considered that the potential impacts arising from nutrient enrichment could affect all but two of the designated habitat features. The features likely to be impacted include:

• Estuaries
• Large shallow inlets and bays
• Coastal lagoons
• Mudflats and sandflats not covered by seawater at low tide
• Atlantic salt meadows (Glauco-puccinellietalia maritimae)

 

Impact of Nutrient Loading on SAC Features

The designated features described above can be negatively impacted by diffuse pollution causing a worsening in the quality of the water. These effects are largely due to the potential impacts upon the physical and chemical factors impacting upon the feature habitats and therefore the species they support.

A 2009 CCW report[1] stated that the coastal waters are considered to have raised levels of nutrients, predominantly as a consequence of diffuse agricultural sources. It does note that nutrient and contaminant levels are also variable and often contaminant levels are below detectable limits because of the highly dynamic water movement within Milford Haven and the Daugleddau estuary. However, the report clearly concludes that the issue is likely to be more pronounced in the sheltered low energy areas within the marine system which are likely to experience much greater impacts as a result of nutrification.

Nutrient enrichment that results in major ecological changes has the potential to disrupt ecosystems including the delicate balance between invertebrate populations, biomass, waterfowl populations, sediment flats and salt marsh structure, function and community structure. The Atlantic salt meadows feature is at particular risk as increased nutrients may cause algal mats or blooms of green algae to form, smothering their normal functioning.

A 2014 NRW Report[2] suggests that nutrient loading can have direct or indirect impacts on the wider site designated features including:

• Where algal mats are sufficiently dense, the salt marsh vegetation and other communities including cockle, mussel, polychaete worm and amphipod communities beneath could potentially die. This would result in increased microbial decomposition of organic matter and increased oxygen demand.
• Increased nutrients can cause increased above-ground growth of vegetation, while also causing reduced root growth; this can then cause banks and sediments to become less stable.
• Reduction in salt marsh species diversity or change in species composition in favour of more nitrogen loving species.
• Loss of habitat for overwintering wildfowl
• Reduction in salt marsh species will impact upon the invertebrate communities present.
• Loss of salt marsh habitat resulting in exposed substrates, destabilized sediments causing sedimentation, increased turbidity and further habitat erosion.
• Loss or change of geomorphological features resulting from reduced geomorphic stability can change species communities, species composition and increased sediments.
• Algal blooms can also reduce water clarity or cause smothering effects, which to varying degrees will affect the distribution and species composition of the mosaic of habitats in the other features of the site.
• Cefas was commissioned by Environment Agency Wales in 2011 to model the impact of nutrient inputs to the Milford Haven waterway and the likely effectiveness of nutrient removal scenarios in controlling macroalgal and phytoplankton growth (Aldridge et al, 2011)[3]. The main conclusions from the model outputs were as follows:
• For nitrogen, direct loadings from rivers and sewage treatment works (STWs) are the dominant sources.
• Changes of ±25% to direct nutrient loadings of nitrogen (N) and phosphorus (P) were predicted to give rise to relative changes in average summer chlorophyll concentrations in the range ±6% and to relative changes in average summer macroalgal biomass in the range ±9%.
• For phytoplankton, natural light was predicted to be the limiting factor during spring, autumn and winter.
• An analysis of summer nutrient concentrations was not able to establish clear evidence for nitrogen limitation, nor did it suggest regular phosphorus limitation.

Summary

There remains some uncertainty over whether the nutrient loading within the Milford Haven and Cleddau waterbodies is of a significant enough level to prevent the SAC achieving favourable conservation status. The water quality data shows that there are elevated levels of nutrients, however there is little robust evidence to show that this is impacting on the SAC via hyper-eutrophication and the growth of macro-algae.

Further surveying has taken place in 2014/2015 and the results of this are due to be published soon. Anecdotal evidence suggests that this may contain sufficient robust data to confirm what the current situation is and show the impacts of nutrification on the SAC features.

[1] Countryside Council for Wales (2009). Milford Haven Waterway, Pembrokeshire, Water Quality Issues – Ecological Indicators and photographic Evidence of Excess Nutrients.

[2] NRW (2014), Environmental Pressures on Milford Haven Waterway

[3] Aldridge, J. and Painting, S. (2012) Milford Haven: Modelling Assessment. CEFAS Report Commissioned by Environment Agency Wales.

 

Figure 3: Location of Annex 1 Habitats

Figure 2: Location of Annex 1 Habitats

Introduction

The overarching purpose of the project is to reduce the nutrient loading within Milford Haven, with the assumption being that this is best achieved through reducing nitrogen inputs onto catchment land.   In order to establish the scale of the issue, define the scale of the remedial measures required and to test the success of the approach it is necessary to define the scale of the nitrogen problem.  To date a detailed review of available water quality data (both provided by NRW / Welsh Government and from other sources such as NRW reports) has been completed. This has supported a clearer understanding of the current position, likely future increases and the levels to which nutrient loading should be reduced in order to deliver habitat improvements.

Data Analysis

The current River Basin Management Plan identifies the estuarine transitional waters of Milford Haven as being of WFD “Moderate status due to the Dissolved Inorganic Nitrogen (DIN) level, although all other elements are classified as at least of “Good status” (Natural Resources Wales, 2014[1]). In addition:

• WFD investigations have concluded that agricultural and rural land use practices are likely to be the primary diffuse pollutant sources to Milford Haven, particularly DIN
• Environmental Permitting Regulated installations only have limited DIN input and insignificant Dissolved Inorganic Phosphorus (DIP) inputs
• STWs discharging into the estuary account for 5% of total DIN and 34% of total DIP

In order to implement a trading scheme for nutrients within the Milford Haven catchment, the nutrient contribution for DIN needs to be understood at least at the catchment scale and a threshold target established. This can then be used to guide reductions in nutrient loadings to the estuary and contribute towards improving the current condition of the estuary and the ecology that it supports.

The key steps required to identify nutrient thresholds and reduction targets are outlined below:

1. 1. Produce a detailed source apportionment of both DIN^[2] and Dissolved Inorganic Phosphorous (DIP) within the catchment from point and diffuse sources.
   2. Analysis of all long term river, estuary and marine water quality data, river flow data and STW and industrial effluent discharge data. Specify the annual reduction target for DIN and DIP using this analysis.
   3. Calculate the DIN and DIP loading from all catchment sources.
   4. Identify impacts of future population growth in DIN and DIP loadings for each STW.
   5. Determine reductions in nitrogen leaching from agricultural land required to meet annual reduction target and identify range of measures to accomplish this target.
   6. Identify mitigation measures to ensure neutral impact of future development on nitrate and phosphorus loading.
   7. Undertake a Cost-Benefit Analysis of mitigation measures suggested for agriculture and future development in the catchment.

Understanding the Nutrient Loading Problem

Although it is accepted by stakeholders that the Milford Haven catchment is suffering from hyper-eutrophication it has been difficult to identify robust publicly available data to confirm this and the true situation is still unclear.

The latest publicly available report on the environmental pressures of Milford Haven (NRW 2014) states that there is an opportunistic macroalgae issue within the Milford Haven Inner water body, with large algal mats covering areas of available intertidal habitat (AIH).

This is based on surveys carried out for WFD monitoring purposes in Milford Haven Inner water body during 2009 and 2011 (using a ‘true colour’ technique) and 2012 (using a more accurate high intensity Compact Airborne Spectral Imager (CASI) technique but over a smaller area). Aerial imagery was gathered and ground truthing quadrat surveys carried out to obtain information on biomass, extent, percentage cover and entrainment of opportunistic macroalgae.

The survey results varied due to the techniques used but essentially they suggested that opportunistic macroalgae fell within the WFD Moderate class  with an Ecological Quality Ratio score of 0.5 – 0.53, depending on the technique used to gather the information[3]. In percentage terms the two survey techniques suggested a cover of AIH of between 12.7% and 40.8%. This latter figure was extrapolated from a smaller survey area but is considered to be more accurate than the lower figures obtained from the ‘true colour’ technique.

The situation for the outer Haven is less of a concern with surveys undertaken in 2011 and 2013 demonstrating that there is no ecological effect in this area caused by the elevated DIN. Macroalgae extent in the outer Haven extended to 8.7% (well below the 15% threshold) of the AIH and the biomass was well below the 500gm² threshold.

In addition a seasonal biomass survey has been established at two sample stations in Pembroke River and one at Cosheston Pill. The survey gathers biomass and percentage cover estimations being gathered for alternating months for a minimum of three years. This survey commenced in September 2012. UKTAG Guidance (2007) states that ‘consistent algae cover over the winter months in excess of 50g/m² would trigger concern’. Available data from 2013 found average biomass values did not exceed this threshold.

Establishing a Reduction Target

Typically when a Natura 2000 site is concerned the reduction target would allow for the site (in this case the Pembroke Marine SAC) to achieve “favourable condition”. However, the SAC Conservation Objectives state[4]: “flow regime, water quality, and physical habitat should be maintained in, or restored as far as possible to, a near natural state”. At the time of writing there is no information publicly available that details what a “natural state” should look like in terms of nutrient loading. Given the vital importance of defining clear measurable objectives to be achieved for a PES scheme, alternative measures have therefore been identified.

There are no WFD standards for nitrogen in rivers, however there are standards for Transitional and Coastal (TRAC) Waters (essentially estuaries) and Coastal waters. Coastal waters are defined as being located within 1-3 nautical miles off the coast or having a salinity of 30-34.5ppt. TRAC waters have a salinity of less than 30ppt. Only one site in Milford Haven is classified as a Coastal water, namely Mid Channel Angle Peninsular, the rest are TRACs.

The most appropriate standard measure identified was the UK Technical Advisory Group (UK TAG) on the Water Framework Directive. This body has set thresholds, outlined in the UK Environmental Standards and Conditions 2008, for nitrogen loading within Transitional and Coastal (TRAC) waters. The threshold value for the boundary between WFD “High” and “Good” status of both coastal and transitional was chosen as the concentration figure to which any nutrient trading scheme would ultimately aim to achieve.

Whilst the WFD requires that waterbodies meet at least Good status the choice to use the boundary between High and Good was chosen (rather than Good to Moderate) because it was felt that the scheme should be aiming to deliver the greatest environmental benefit and this could only be achieved by choosing the more stringent threshold. In addition, the relative difference between the two thresholds, when considering nutrient loading and required reductions is not sufficiently large to make a material difference in the reduction targets. Consequently, the decision was made to keep the more challenging target at the outset.

Figure 5: WFD Coastal Waters

Figure 6: WFD TRAC Waters

For TRACs, the DIN standard threshold for High/Good quality is 20µmol/l, whilst for the Good to Moderate threshold this is 30µmol/l (both for winter mean values from December to February). The coastal water DIN standards for High/Good quality are 12µmol/l, whilst for the Good to Moderate threshold this is 18µmol/l (again, for winter mean values).

Findings

As the aim of the project is to manage diffuse catchment nitrogen inputs into Milford Haven, an understanding of current nitrogen loads and a required target for reduction is required.  This has been calculated using two key steps: identifying current nitrogen loadings to the estuary from the catchment using water quality data; and determining a reduction target using these data.

Existing NRW water quality monitoring data recorded between 2010 – 2015 has been used to calculate; Dissolved Inorganic Nitrogen (DIN) in the Eastern Cleddau, Western Cleddau and Milford Haven. In late June 2015, NRW provided further water quality monitoring data as far back as 1990 for some sites. This data has been analysed and does not indicate any significant change in condition between 1990 and 2015. It is particularly difficult to analyse this data as it is incomplete for some monitoring points and switches between monitored determinands at others. Consequently, there appears to be no reason why the 2010 – 2015 data cannot be the main source of data used for this work.

The location of the water monitoring points is shown in Figure 5.

Figure 7: Water Quality Monitoring Points

Data Analysis

The data (see Table 1) show that average DIN levels in the Eastern and Western Cleddau where these rivers flow into Milford Haven is 153.6µmol/l and 252.0µmol/l respectively. At the top of Milford Haven (UWWTD Milford Haven Beggars Reach), this declines to 48.2µmol/l and continues to decline to 14.4µmol/l at the mouth of Milford Haven (Mid channel Angle Peninsular). Based on the WFD standard, most of the winter mean statistics for the estuary samples fall within the WFD Moderate and Poor standards.

For reference the DIN standard threshold value for WFD High – Good in transitional waters is 20µmol/l, (the Good to Moderate threshold is 30µmol/l) whilst the same threshold value for coastal waters is 12µmol/l (Good to Moderate threshold is 18µmol/l)

Table 1           DIN measured in the Eastern and Western Cleddaus and Milford Haven (all data in µmol/l)

                    

Determining a Reduction Target

Using water quality data collected at the end of the Western and Eastern Cleddau rivers, DIN load was calculated using flow data measured at the Eastern Cleddau at Canaston Bridge flow gauge. No flow data were available for the Western Cleddau (although a flow gauge is located at Prendergast Mill).  In the absence of measured flow data on the Western Cleddau, the Eastern Cleddau flow data were scaled by the difference in catchment size (the Western Cleddau measuring 197.6km² at the flow gauge whilst the Eastern Cleddau is 183.1km² at the flow gauge).

This is considered an appropriate approximation in the absence of flow data since the catchments have similar hydrological properties and rainfall, although checks will be undertaken if flow data becomes available. DIN loads in the Western Cleddau were calculated using this scaled flow. Current DIN loading calculations for the Eastern and Western Cleddau catchments are presented in Table 2 and Table 3 respectively.

Nitrogen reduction targets were assessed by comparing the current loads to what is assessed, with respect to all available evidence, as the background nitrogen loading in the upper Eastern Cleddau (as measured at the Eastern Cleddau above Glandy water quality monitoring site). The catchment above this site is essentially moorland and woodland with some grassland, only a small proportion of which appears to be used for grazing.  Average DIN values at this site are around 0.7mg/l. From this value, loads were calculated for both the Eastern and Western Cleddau catchments and these were taken to represent background values in the absence of agricultural practices.  By subtraction of the current loads from the background loads, a target reduction load was established for both catchments. These are displayed in Table 2 and Table 3.

 

 

Results

In the Eastern Cleddau (Table 2), this method specifies a DIN reduction target of 311t/yr or 0.017t/ha/yr. In the Western Cleddau (Table 3), this method specifies a DIN reduction target of 768.3t/yr (or 0.039t/ha/yr). This equates to an average reduction of DIN for all catchments of 539.6t/yr.

This value has been taken as the target reduction for DIN within the Milford Haven catchment and represents the best balance between pragmatic techniques for N reduction and environmental benefits.

When plotted on a graph (see Figure 8), the data clearly show that at all water monitoring points (with the exception of one anomalous recording) the transitional waters significantly exceed the TRAC High/Good standard.

The situation in the coastal waters is slightly more encouraging with the data (Figure 9) showing that the TRAC standard is achieved, or is much closer to being achieved, throughout the year. This clearly indicates that the river catchments are the main source of N loading within the wider system and these are the areas that should be focussed on.

 

 

 

Potential Alternative Nutrient Reduction Targets

Due to the large difference between the WFD TRAC waterbody thresholds and the current nutrient loading within the Milford Haven and Cleddau rivers the EEP requested in early June 2015 that additional analysis was undertaken of the water quality data. This analysis attempted to identify what the condition of the waterbodies would be with a percentage reduction in nutrient inputs, rather than a reduction to the TRAC waterbody threshold.

Table 4 below illustrates what the reduction targets for inputs would be with a range of decreases from 5% to 100%, in 5% steps. The 0% reduction is the current level of loading whilst the yellow highlight represents a 20kg / ha reduction across the catchment. This figure has been chosen as it is generally considered to be the absolute upper limit of what the land management measures could deliver per hectare.

This figure suggests that for the Eastern Cleddau, if an average reduction of 20kg /ha was achieved, it would be possible to get approximately a 65% reduction in loading, whilst for the Western Cleddau a catchment wide 20 kg /ha reduction would deliver a 35% saving. Whilst these would appear to be achievable targets it indicates the level of problem within the catchments as such reductions do not get the waterbodies close to the WFD TRAC threshold.

In late June 2015 NRW provided additional water quality data for the catchments extending back to 1990. This data did not cover all the monitoring points but was considered to be of interest because it provided an opportunity to try and identify and understand what the conditions were like in the catchment pre-SAC designation.

It was felt that analysis of this data might provide an alternative loading threshold to that provided by the WFD. As discussed above the threshold for TRAC waterbodies, even when including a background load, is prohibitively high which may prevent a scheme ever achieving its main aim. If the older data provided an alternative threshold value, especially if this was lower than the WFD threshold, this might be more achievable via the land management mechanisms available. It would also help define, in terms of nutrient loading, what favourable conservation status is for the Pembrokeshire Marine SAC.

Unfortunately however, after extensive analysis the data has not provided us with the necessary information to either identify the load at SAC designation or an alternative threshold. Consequently, the WFD threshold for TRAC waterbodies will continue to be used.

 

 

[1] NRW (2014) Environmental Pressures on the Milford Haven Waterway: Report A&R/SW/14/1

[2] For the purposes of this study DIN is taken as equivalent to Dissolved Available Inorganic Nitrogen (DAIN). Where DAIN = Total Oxidised Nitrogen (TON = nitrate + nitrite) + NH4 (ammonium).

[3] When carrying out a WFD biological assessment, each biological quality element defined in the WFD is required to give a statistically robust definition of the ‘health’ of that element in the sampled water body. The ‘health’ of the element is assessed by comparing the measured conditions (observed value) against that described for reference conditions (minimally disturbed). This is reported as an (EQR).

[4] Countryside Council for Wales (2009) Pembrokeshire Marine European Marine Site: Advice Provided By The Countryside Council For Wales In Fulfilment Of Regulation 33 Of The Conservation (Natural Habitats, &C.) Regulations 1994

Agriculture

Agricultural nitrate loads for the Cleddau catchments are taken from Anthony et al (2012), who developed a spatially explicit modelling framework to calculate emissions for a suite of pollutants in order to determine the impacts of the Welsh Agri-Environment schemes. The framework was stratified by robust farm type and reported emissions separately for each of the Water Framework Directive river catchments in Wales.

The modelling framework used a combination of process based and inventory models, with nitrate losses calculated using the N-CYCLE, NITCAT and MANNER models (Scholefield et al., 1991; Lord, 1992; Chambers et al., 1999). The results of Anthony et al (2012) are based upon livestock and cropping from the 2004 June Agricultural Census, along with farm management data (fertiliser practice, livestock management etc.) based upon recent survey data, and reflecting both conventional and organic management.

The calculated total nitrate load from agriculture being delivered to watercourses was 2.4 kT N per year. This works out at an average nitrate load of 35 kg ha^-1 per year. Figure 10 shows how this varies footprint varies across the Cleddau catchments, with greatest loads (over 40 kg ha^-1) found in the north and centre of the catchment, where farming is dominated by dairying, and the lowest loads (under 25 kg ha^-1) where the catchments are dominated by rough grazing and the National Park to the North East.

Sector Apportionment

Anthony et al (2012) also calculated the nitrate losses from non-agricultural sectors, allowing for an assessment on the importance of the agricultural load. Figure 11 shows that the other sectors are small in comparison to agriculture, which contributes over 95% of the total load. Note that this data does not include sewage treatment works discharging directly to the sea or the impacts of any within stream retention, although this would not significantly change the relative importance of agriculture. Figure 12 shows that, even at waterbody scale, agriculture is always the dominant source, with only a few catchments where the agricultural component of the total load is less than 90%.

 

Housing and Development

In contrast to the figures above, existing and projected housing would appear to have little impact on the condition of the watercourses.

The review of consents study undertaken by EAW showed that approximately 61% of the dissolved inorganic phosphorus (DIP) load could be accounted for by Stage 3 continuous discharges from the following Dwr Cymru Welsh Water sources: Milford Haven sewage treatment works (STW), Pembroke Dock STW, Merlin’s Bridge STW, Neyland STW, and Narberth STW. In contrast, approximately 95% of the dissolved inorganic nitrogen (DIN) load to the Milford Haven waterway came from sources other than the Stage 3 continuous discharges. Consequently, NRW (2014) estimates that only 5% of the DIN loading can be attributed to DCWW sewage treatment works (STW) as a result of existing housing stock.

Reviewing Local Development Plans and population forecasts, it has been calculated that by 2021 an additional 10.65t N will enter the catchment (or approximately 1t per year) as a result of potential new housing development. In addition, by 2035 this increases to 16.58t N, or an average of 0.83t per year. These calculations are based on the projected increase in population (8800 between 2011 and 2021; and 13,700 between 2011 and 2031), multiplied by the assumed average nitrate loading per population equivalent (PE). This is generally accepted to be 1.21kg/N/Yr/PE and is derived from the average load that is discharged to rivers based on STW operation and permit conditions. In the absence of alternative figures, this is considered to be appropriate for the Milford Haven and Cleddau catchments.

Additional calculations were completed based on development rates and typical house sizes and extended to cover a 50 year period, in order to account for continued long term reductions in N loading. The basic calculation used to identify the long term impact of housing on N loading is:

S x A x Q x T where; S is the size of development i.e. number of houses, A is the average number of bedrooms[1], Q is the accepted multiplier per population equivalent[2] and T is the time period over which the reduction is to be delivered.

In the 100 unit example this would equate to an additional 18,150kg of N over 50 years (100 X 3 X 1.21 X 50 = 18,150kg). This equates to 181.5 kg per house or 3.63kg per house per year. These figures are insignificant when compared against the 454.7 tonnes average loading in the Eastern Cleddau and 923.4 in the Western Cleddau and illustrate the size of the problem when trying to reduce nutrient loading via development.

The relatively low level impact of existing housing and new development may also cause complications if developers are viewed as “buyers” in any PES scheme and seen as a source of income to offset the impacts of agriculture. It is likely that asking people, who have limited impact on the problem, to pay for those who have a significantly larger impact to change their practices will not be popular and may limit the attractiveness of the scheme.

It may be possible to engage developers, through this process, in order to deliver nitrate neutral developments within the catchment areas. This would depend however, on the likely increase in construction cost (and hence sale price) of each unit as a result of such an initiative, and this cannot be accurately determined at this time. It is recommended therefore that developers are considered key stakeholders and they should be contacted and engaged as early as possible to identify what might be achievable via an offsetting scheme.

Other Sources

There is little evidence to suggest that alternative sources of nutrient enrichment exist within the catchment. Whilst there is significant amounts of industry within the catchment areas ADAS estimated that only 9737 kg N/year or <0.5% of the total estimated load in the waterbodies. It is considered unlikely that this would materially change in the short term and if another source of nutrients applied for planning permission or permits these are likely to only be agreed if nutrient loading did not increase.

[1] According to the Office for National Statistics (ONS) the average house has 3 bedrooms so this is the figure used here. For individual housing developments this number could be amended to provide the actual average figure based on the planning application.

http://www.ons.gov.uk/ons/rel/census/2011-census/detailed-characteristics-on-housing-for-local-authorities-in-england-and-wales/short-story-on-detailed-characteristics.html

[2] It has been assumed for the purposes of this example that each bedroom would be occupied by one person (i.e. one population equivalent). Whilst a relatively crude simplification of housing dynamics it is sufficient to help demonstrate the gap between what new housing would likely contribute to the problem vs. diffuse rural pollution. If required (for example if the scheme was trying to achieve nitrate neutral developments), a more detailed calculation could be completed based on the specifics of an individual development

Introduction

The main aim of this work package was to identify the potential opportunities, within the catchment, for delivering the load reduction requirements via farm based measures. This work was undertaken by ADAS using their Farmscoper tool and used a range of data to model the potential contribution from the ‘average farm’ types for this area of Pembrokeshire.

Data Analysis and Modelling

In order to achieve this analysis three datasets were obtained from Welsh Government to allow the Farmscoper tool to be applied to the Milford Haven and Cleddau catchments.

The Land Parcel Information System (LPIS) provided the individual field boundaries for all fields in the project area, along with a unique identifier for the farm that they belong to. For each of these fields, the crop type was taken from the Integrated Agricultural Control System (IACS) records, and for each of the farms, the farm type (according to the Robust Farm Type (RFT) definitions) and livestock counts were available from the June Agricultural Census. These data make it possible to determine an average farm type, in terms of crop areas and livestock counts, for each of the RFTs.

The nitrate losses for each of these average RFT farms was calculated using Farmscoper, for each of the climate and soil types recognised by the tool that are found within the Cleddau catchments. Other farm practices (e.g. manure management) were based upon the default assumptions within Farmscoper.

The calculated nitrate losses are expressed in terms of kilograms lost per hectare, and these unit area losses were then be mapped back on to the LPIS field boundary data, based upon farm type, using the results for the soil and climate most representative for that field. The data was then used to calculate the overall load (this is a “baseline load” in the absence of mitigation) per measure / activity.

Any mitigation method which resulted in a reduction of over 0.1% on at least 1 farm was included in the analysis though please note that not all methods impact on each farm type.

The farm types were based on the 9 farm types previously used by ADAS for catchment modelling, which had been derived from the census data. Additional farm types were also added, primarily to allow for more variation in livestock. This has allowed us to be incredibly detailed and meant we can include information for an upland farm with cattle and sheep (the typical upland farm type), as well as one with just cattle and one with just sheep. Further additions include farms without livestock but where manure was being imported again to reflect the situation on the ground as closely as possible. However, even with 20 different farm types we are unable to reflect the wide variation of farm types in Pembrokeshire.

Results

Due to the complexity and size of the modelling undertaken for this work package it is not possible to present all of the findings of this work in this section. However, what the work has shown is that depending on a number of factors (farm type, rainfall, soil type, fertilizer application rates etc.) the available land management measures are capable of delivering between a 17% reduction and a 4% increase in N loading[1]. It is unlikely that this would be sufficient to reduce loadings to the level required by the WFD threshold however; it will deliver substantial savings which will deliver headroom in the catchment.

One point to note is that as more mitigation methods are implemented on individual farms or areas of catchment there is a tendency to achieve diminishing beneficial returns as the measures, though different, are trying to control the same sources. As a result, the total impact of a collection of methods is generally less than the sum of their individual impacts.

Appendix 4 includes the outputs from the modelling detailing the likely percentage reduction in nitrogen loading from the 100 or so measures available. Please note this Appendix is over 280 Pages long and is an MS Excel table with important cell functionality included. Consequently it is recommended that this is only viewed electronically and not printed.

Though there remains some uncertainty over the impact of nutrient loading within the Milford Haven and Cleddau Catchments there is no uncertainty over the challenge to reduce nitrates to an accepted level under WFD. The work undertaken for this Work Package demonstrates the level of the problem and suggests a threshold level with which to measure success. This threshold is challenging and the initial modelling suggests a purely land management approach is unlikely to deliver sufficient savings.

The following Work Packages detail the potential structure of a nutrient trading toolkit however, it may be necessary to consider additional measures in order to reduce the loading sufficiently. A specific measure that might be beneficial is encouraging farms to reduce stock numbers in order to reduce the amount of fertilizer required as well as the quantity of farmyard manure and faecal matter which are currently a major contributor to N loading.

Destocking has not been explored in great detail as part of this work as it is very difficult to assign a robust value to the amount of N that would be reduced due to the number of variables involved. However, it may be something that is taken into account if a Nitrate Vulnerable Zone (NVZ) is put in place in these catchments. An NVZ designation is likely to be relatively onerous for farmers and to meet the thresholds destocking might have to be an option. It is probably more acceptable if a requirement for reducing stock numbers is driven by a legal requirement rather than this scheme. The benefits however, should not be ignored and are likely to assist the loading reduce closer to the WFD threshold than would be possible via this scheme alone. The likely impact of the NVZ as well as reducing stock numbers should be explored in any further work phases.