East Cambridgeshire District Council Water Cycle Study Detailed ...

Stage 2 Water Cycle Study: Final Report
Sept 2011
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Cambridgeshire Horizons
East Cambridgeshire – Detailed WCS
The communities of Wicken Lode have relatively few floating-leaved species and an
abundance of submerged, slender-leaved species. At present they are best placed somewhere
in the Potamogeton pectinatus - Myriophyllum spicatum community (Fennel-leaved Pondweed,
Spiked Water Milfoil) There are also scarce plants including flat‐stalked pondweed
(Potamogeton friesii) and long‐stalked Pondweed (Potamogeton praelongus), both ‘RDB near
threatened’ species and the rare species Nitella tenusissima which has been recorded in turf
diggings and, in 1992, in Wicken Lode. Wicken Lode also contains a diverse invertebrate
assemblage including the rare Depressed River Mussel Pseudanodonta complanata, also an
SSSI interest feature.
There is a general assumption (used for example in the Environment Agency Review of
Consents) that pollution and/or excessive nutrients, particularly phosphorus, may cause
damage or undesirable change to the other features. Therefore, phosphorus is the main focus
for the assessment of water quality discharges. The target of 0.1mg/litre Soluble Reactive
Phosphorus (annual average) is used as a provisional “threshold value” for river water in and
adjacent to the site as per the EA RoC and JNCC Common Standards Monitoring guidance.
Wicken Lode, where the spined loach is found, is the main source of water for Wicken Fen,
both during normal flow conditions and during floods. The only other sources of water are
rainfall, and drainage from agricultural land to the north of the Fen into Drainer’s Dyke (this
dyke is isolated from other dykes on the fen because of water quality concerns but there are no
consented discharges implicated here). Therefore, for the purposes of this assessment, if the
water in Wicken Lode meets the 0.1mg/litre SRP as an annual average, no further assessment
of water quality discharge consents will be required.
There is no routine water quality sample point on Wicken Lode but there is one upstream on
New River which feeds Wicken Lode. According to the Review of Consents work, SRP has
never been above 0.033mg/litre during the whole of this survey period, which is well below the
0.1mg/litre Favourable Condition Table required standard.
Burwell WwTW discharges to the Catchwater Drain which itself drains to Burwell Lode. Wicken
Lode flows into Burwell Lode at the south-west corner of Wicken Fen. It is theoretically
possible for water to backflow from Burwell Lode into Wicken Lode, but the EA in their RoC
considered this a sufficiently low eventuality that they did not consider backflow of water from
Burwell Lode into Wicken Lode further (stating that ‘there is currently no connectivity between
… Wicken Fen and the water in Burwell and Reach Lodes’) other than to state that if any
proposal to abstract water from the southern end of Wicken Lode to back up the fen came
forward a detailed investigation to determine whether Burwell Lode does backup Wicken Lode
would be required.
This is supported by Harding et al (2005) 32 which states that ‘Wicken Lode does not appear to
be degraded by eutrophic water backing up from Reach Lode’ [Reach Lode merges with
Burwell Lode before it reaches Wicken Lode].
This being the case, there is no evidence on which to conclude that discharges to Burwell Lode
associated with the increase in discharges from Burwell WwTW as described in this Detailed
WCS will have any impact on Wicken Lode or Wicken Fen with regard to any of its ecological
features, based on extrapolation of historic trends/information.
32
Cook A. and Harding M. (2005) An evapotranspiration groundwater water balance for Wicken Fen. Ecology, Land
and People (elp) on behalf of the National Trust
Harding M., Smith K. And Williamson B. (2005) The ecohydrology of Wicken Fen and a Water Level Management
Strategy. Ecology, Land and People (elp) on behalf of the National Trust