Phosphate Testing

Over the last few months Friends of the Rib & Quin have introduced a water testing regime at several of our Riverfly monitoring sites, specifically looking at phosphate levels. This work was initially funded thanks to TeaTime Talks in Standon and recently expanded through a grant from the Hertfordshire Community Foundation, which allowed the purchase of the testing equipment.

Why test for for phosphate? I’ll leave that to Charles Rangeley-Wilson to explain, through extracts from his personal blog article from January 2021……

Phosphate: to those like me who answered their Chemistry O level multiple choice by rolling a pencil down the desk because that way they tended to get higher marks, phosphate is just another chemical. But in terms of river ecology in general and chalk stream ecology in particular, phosphate is very, very important.

Source: BBC

Phosphorous is the key chemical that drives nutrient enrichment of chalk streams. That enrichment has a number of deleterious effects on a river’s ecology which increase in line with increasing P enrichment. All plants need P to grow, but different plants and plants communities either thrive or conversely suffer and are out-competed at differing levels of P concentration.

Higher order and important chalk stream plants like Ranunculus thrive at very low, background natural P concentrations. The first effect of P enrichment is actually an increase in the growth-rate of the higher order plants, but with commensurate weakening in root growth – making the plants vulnerable in high flows. As P levels increase further the river’s ecology shifts towards a dominance of the higher order plants that are most tolerant of nutrient enrichment, and that leads to a reduction in the overall bio-diversity of the plant community. 

Finally, if P concentrations keep on rising, the river’s ecology will switch over to an algal-dominated plant community. Benthic algae smothers the river bed and the interstices in the gravel in which many insect species live and epiphytic algae cloaks the leaves and stems of the higher order plants, reducing their ability to photosynthesise. The prevalence of algae will also cause extreme diurnal variations in dissolved oxygen levels, with really low oxygen levels at night and in the early morning, which stresses fish and insects alike. There comes a point where, if the P is very concentrated, the river turns into an anoxic soup and nothing much survives.

P is very limited in a natural chalk stream system. But P is contained in human sewage (treated and raw) and animal slurry, as well as in agricultural fertilisers. There are other diverse sources of P: our drinking water is dosed with P, for example. Consequently there is much more P in our anthropogenically impacted river systems than might be considered natural. Relatively modest increases in P can cause the ecological changes outlined above. Any reduction in P will benefit the ecology of a chalk stream, but if P levels are high, or there’s loads of it still washing around the system, you might have to reduce P by an awful lot before you start noticing the difference.

Charles Rangeley-Wilson
– To Remove P or not to Remove P, that is the Question

FORQ chose to adopt the Hanna HI713 Phosphate Colorimeters to test samples – a hand held device commonly used by river campaigners to gain indicative levels of phosphate in water bodies. We have been using them at a growing number of our Riverfly monitoring sites across our catchment and are expanding our dataset.

Phosphate level records from RFM sites on the Rib & Quin

Analysis of our first few months testing results began to suggest a pattern to the phosphate levels. Test results below the sewage treatment works in Buntingford were above the maximum reading level of the Phosphate Colorimeter, with lower results at Standon and all points south of there (though still well above natural levels), yet the Quin, at Braughing, indicated lower levels still.

New samples were needed, at new locations, to give a clearer picture. A days testing was conducted, in early July, at chosen sites on the Rib between Buntingford and Wadesmill. Results were recorded and plotted into the table and graph below, to which we have added some annotations.

Our first test site, at Buntingford Watermill on Luynes Rise, is above the Thames Water Sewage Treatment Works, gave a reading of 0.52ppm. This is approximately 7X what might be expected in a ‘natural’ chalk stream. Our next testing point, at Aspenden Road, is below the STW, and triggers the colorimeter to ‘max out’ at its highest level, 2.50ppm. This means the water there has well in excess of 30X the level of phosphate present compared to that expected in a chalk stream.

The next three sites, at Westmill North Bridge, A10 Hay Street Bridge and Hamel’s Mead, all produced the same reading of greater than 2.50ppm. It wasn’t until a test taken from water at Braughing Railway Bridge that phosphate levels fell back to within the parameters of the Colorimeter, with 1.56ppm. Here the Rib has been diluted by the River Quin with its lower phosphate levels.

After the test site in Standon, the River Rib is diluted by discharges from Standon STW which we believe has phosphate stripping infrastructure) and possibly other springs, at this lower elevation to register it’s lowest phosphate level of 1.26ppm in these tests above Latchford, before rising again to 1.69ppm at Barwick Ford, where private sewage treatment discharges at Latchford, Hanging Wood and Barwick will likely have contributed phosphate. A fall again in the test result at Cold Christmas they rise again at Wadesmill.

Chalk Stream Restoration Strategy appendices

The data collected in this snapshot test, and our ongoing testing regime provides evidence by ‘our own hands’ of a story of phosphate pollution. It also replicates the findings of EA testing and demonstrates one of the main reasons why the river classification, according to the Water Framework Directive and presented in the Chalk stream Restoration Strategy, is poor.

Indeed, as documented by the EA in their 2004 report for Defra – The State of England’s Chalk Rivers, the Upper Rib has been polluted by extremely high levels of phosphate since at least 1999 and no doubt for a long time before.

Phosphate concentrations in Chalk rivers 1999 – 2001. Source: Environment Agency

It must also be remembered that these levels of phosphate are due to the inadequate processing and removal of sewage at the treatment works under normal operation.

Chalk Stream Restoration Strategy appendix, showing only Standon STW as possibly having phosphate stripping.

Equally alarming and environmentally damaging (as well as a rising risk to public health) are the levels of raw sewage being discharged into both the Rib and Quin from Thames Water Sewage Treatment Works (STWs). Failing infrastructure and processing capacity issues at STWs across the catchment are strongly indicated by the rising number and quantity of raw sewage spills, evidenced in the table below and sourced from The Rivers Trust data. This is further discussed in our State of Our Rivers article.

201920202021
RIVER RIB
Therfield0273243
Buntingford166154
Standon0310
Chapmore End805762
RIVER QUIN
Barkway175547734
Braughing000
TOTAL2719611103
Raw sewage spills in the Rib & Quin catchment (duration – hours) 2019 – 2021

We are left with the following questions for Thames Water, to which we will be seeking answers over the coming weeks and months;

We ask of Thames Water when Phosphate Stripping processes will be in place at all our STWs and in particular at Buntingford, where the phosphate released has, and is having, a direct damaging impact on the chalk stream environment?

Why the Therfield STW had no spills in 2019, yet spilled raw sewage for 274 hours in 2020 and 243 hours in 2021?

Why Barkway STW’s record of raw sewage spills shows increases from 175 hours in 2019 to 548 in 2020 and then 734 hours (equivalent to a whole month) in 2021?

Whether proposed new housing development at Barkway will further increase these raw sewage spills and when infrastructure and capacity improvements will be made here?

Whether the proposed new housing development, of 400 houses, in Buntingford is within the capabilities of the infrastructure at Buntingford STW and whether we should expect to see an increase in spills from there into the future?


Historic and current information on the ecological and chemical health of our rivers is available through Environment Agency’s Catchment Data Explorer, which gives access to testing and analysis data on a wide range of measures. Links to the individual pages for our catchment can be found on our Links page here.

The quality of the water in the River Rib and River Quin remains a significant, continuing and deteriorating problem, alongside the abstraction of the groundwater that feeds them. Friends of the Rib & Quin will continue to campaign on this issue alongside employing increased water quality monitoring, adding further data and weight to the case for improved water infrastructure in parallel to development and measures to directly protect our precious chalk streams.