Working with water
How the Watercress Company works with 50 million litres of
water per day and what are we asked to achieve by the EA
Watercress is a truly unique crop, and the vital ingredient for growing watercress is, of course, water – pure, mineral-rich spring water, from which this peppery leaf derives its power house of nutrients.
We use this water to grow our crops and then return it to the river system. It is our aim to do this with as little effect on water quality as possible.
Each farm has its own abstraction licence and discharge permit, issued and
The two main considerations in our discharge waters are suspended solids (from bed cleaning) and phosphate (from fertiliser applications).
Our farms in Hampshire discharge through settlement ponds into the River Itchen, a chalk river which has been designated as a Special Area of Conservation (SAC) under the EU Habitats Directive. This means that the targets for water quality are much more stringent than the Water Framework Directive targets which need to be met by watercress farms in other areas.
Because of this legislation, the Environment Agency (EA) has set limits for phosphate levels in watercress discharge water for any watercress growers discharging into an SAC. These limits were set in 2014 and came into force in September 2016 and are very low, set typically at around 40 µg/l above base levels (which are the natural levels found in our spring water). As well as limits on phosphate, a limit was also set for ammoniacal nitrogen at 0.5mg/l which came into force immediately when the permits were first issued in 2014.
How do we reduce Fertiliser use, manage
effluent and reduce suspended solids ....…
Suspended solids are created when we clean out a watercress bed so that we can re-drill with a new crop. In order to reduce the level of suspended solids, these ponds are designed to slow the flow down so that the solids are able to settle out. The ponds are cleaned out on average once per year to allow their efficient operation. Since 2017 we have reduced the number of times a bed is cleaned out and relanted as this vastly reduces the ammount of suspeneded solids produced, with the aim for 2018 to only drill twice in each bed. This reduces the loading on the ponds and helps protect the downstream environment.
Another by-product of the cleaning out process is a mix of watercress waste and gravel. We have recently redeveloped our composting area for this material, and it is now stored on a concrete pad. All the liquid effluent is collected in a tank. The aim is to use this liquid as an additional nutrient source.
Fertiliser reduction has been enabled by establishing plants in the beds based on densities that allow the crop to take up as much of the freely available nutrition within the water without addition. Its worth noting that for the majority of the year there is no fertiliser added and during the summer growing period, fertiliser is only needed for a period of less that 4% of its growing life.As the permit limits for both phosphate and ammoniacal nitrogen set by the EA are so low, we have had to trial various methods for reducing the quantity and type of fertiliser we use to meet the new standards.
Phosphate is a more complicated issue, as phosphate deficiency can lead to an unmarketable crop, particularly during the flowering period. Between 2007 and 2017 we have managed to reduce the quantity of phosphate being used on our farms by 87.5%, although this has not been achieved easily. We are seeing increased levels of flowers and purple stems, together with an increase in the growing time, but our compliance monitoring results (based on samples taken by the EA) for the first year since the permits came into force were compliant with the new limits. These results are below.
How we monitor ourselves with testing of
water and calculating annualised averages
In addition to the EA monitoring of our discharges, we also deploy our autosamplers (ISCO 3700s) on each farm and monitor phosphate discharges for 24 hour periods after a fertiliser application has taken place. From these figures, and known information about the periods when we do not apply fertiliser (there is evidence that in winter, watercress actually removes a certain amount of phosphate from the incoming water, so discharge levels are lower than the inlet levels although this effect cannot be used in the calculations) we are able to calculate an annualised average based on a larger number of samples than taken by the EA. We know that there are still peaks in the levels of phosphate after a fertiliser application, but these peaks are short lived and when averaged out, the discharge levels are below permit levels.
In 2018, we carried out some intensive monitoring on the discharge from one of our farms, a site 1km downstream and another 3.3km downstream from our discharge point. We timed this testing to ensure that we were testing after multiple fertiliser applications during the time period. Although there were some peaks in our discharge, no affect was seen 1km & 3.3km downstream, and based on those taken from our discharge (without even adding in the period of the year when we don’t apply any additional nutrients) the average level detected was well below the level required by our permit.
In 2016, we asked an independent freshwater ecologist (Aquilina Environmental) to carry out an invertebrate survey at one of our discharge points.
Following the standard EA sampling protocol, aquatic macroinvertebrates were collected using a standard size FBA D-frame pond net from the major habitats along the stream (stands of different wetland plants, distinctive substrates, tree roots etc.). All the different habitats present were allocated a proportion of the overall sampling time (3 minutes) and different areas of the same mesohabitat were subsampled to ensure that as great a range as possible was sampled.
Each location was also searched for an additional minute looking for surface dwelling animals such as water skaters and whirligig beetles and inspecting submerged habitats such as logs and larger stones for attached animals.
We imagined that our discharge points would be fairly similar, as the water quality is the same at each farm. However each of the surveys gave quite different results, in the main because each of the discharge points had different habitats present, some with more shading, some with steep banks, some with a silty substrate, some with a gravel base, some fast flowing and some slower flowing. It seems that these environmental characteristics have a very significant effect on biodiversity when water quality is the same.
We have repeated that survey again this year and seen an improvement in biodiversity, and we also sampled at two other discharge points this year. The report is below.
This type of survey work will be carried out on a regular basis now that we have established some baseline levels, and any improvements can be recorded.
Why we are under pressure and what we have
done to try and engage with local groups
There has been significant pressure from the fishing community and local environmental groups, both on the watercress industry to reduce the levels of phosphate in the discharge water, and on the EA to regulate effectively.
We have met with Salmon and Trout Conservation UK and with local landowners to tell them what we have been doing to reduce our discharge levels.
We also have representatives who attend meetings of the Upper Itchen Initiative, a group that has been meeting for 10 years, concerned with the protection of the Upper Itchen river catchment and its tributaries. The group comprises of statutory bodies, riparian landowners, business interests and local stakeholders. This group is kept informed on our progress at each meeting.
We also attend meetings of the Test and Itchen Catchment Partnership which brings together local people and organisations to plan and deliver positive actions that will improve our water environment and are a supporter of their lottery funded Watercress and Winterbournes project.
Over the past few years we have been working closely with the EA to formulate an action plan and to report to them on our progress. This successful working relationship has contributed to the success we have had with permit compliance in the first year of monitoring.
Macroinvertebrate Survey of Manor Farm outflow, Old Alresford , Hants
Report prepared by Robert Aquilina MSc MCIEEM
Macroinvertebrate Survey of three watercress farm outflows, Alresford , Hants
Report prepared by Robert Aquilina MSc MCIEEM
Watercress farming, A new era - by Ollie Bedford