Though relatively small and unassuming, the Test and Itchen headwaters - the uppermost tributaries of those famous rivers - are some of our county's most vibrant habitats. This is why they are the focus of the Watercress and Winterbournes scheme, in which the Trust is a lead partner. As part of the scheme, we monitor nine headwater sites through the SmartRivers initiative, which is co-ordinated by our scheme partner WildFish.

The SmartRivers methodology assesses water quality by measuring invertebrate populations. The larvae of mayflies, stoneflies, and caddisflies are particularly indicative, but beetles, molluscs, freshwater shrimp (Gammarus pulex), and other invertebrates are also counted. As different species are sensitive to different pollutants, their presence or absence can help us to identify issues in the area.

Samples are taken from each site twice a year, and preserved so that the invertebrates can be identified to species level. This makes SmartRivers a great complement to the Riverfly Monitoring Initiative (RMI or ARMI) methodology, which can be used monthly but groups the invertebrate species into broader categories. Our brilliant volunteers use both methods to assess the health of the headwaters.

The in-depth nature of SmartRivers monitoring means that it takes time to process and analyse the data. Our most recent results, for example, are from samples taken in the spring of 2023. They are nonetheless immensely valuable for spotting potential problems at the nine monitoring sites, which are:

• The Upper Anton (two sites)
• The Upper Test (two sites)
• The Bourne Rivulet (two sites)
• The Pillhill Brook (one site)
• The River Arle (one site)
• The Candover Brook (one site)

In our most recent results, all of the nine sites showed stress from excess sediment. This can be caused when bank erosion, or rain running over bare soil, causes sediment to be washed into the stream. This sediment then covers up the stream bed, limiting the insect population and suffocating the eggs of the fish that make their nests in the gravel, like brown trout and grayling.

Eight of the sites had elevated levels of phosphorus, which can come from fertilisers, livestock manure, and sewage pollution. As a powerful fertiliser, this mineral boosts the growth of algae, which form large “blooms” in the water. These blooms block out the sunlight, and their rapid growth uses up the water's dissolved oxygen. This can be very harmful for many chalk stream species.

Seven of the sites exhibited signs of “organic loading”. In river ecosystems, various plants, fungi, and bacteria break down dead organic matter by digesting it for energy. If these organisms aren’t present in large enough numbers, or if there is an excess of dead matter – from wastewater discharges and livestock farms, for example – it can affect animals that have a low tolerance for such conditions.

Seven of the sites also showed evidence of a reduced flow rate. While chalk streams are relatively "low energy" compared to more powerful rivers, they enjoy a fairly constant flow because they are fed by an underground aquifer. But this can change if their water levels are lowered by abstraction, impoundment, or channel modification (e.g. bank erosion making them overly wide).

Finally, two of the sites were impacted by pesticide pollution. Often used on gardens and agricultural land to remove certain species, these chemicals can end up in the streams and harm the resident invertebrates. As a key link in various food webs, invertebrates are crucial to the health of these ecosystems - if their numbers are lowered, then many larger animals will be affected.

Overall, the latest results show that the nine headwater sites are not in terrible condition, but could be healthier. As they face mounting pressure from threats like sewage pollution and climate change, we must improve their condition so that they can face whatever the future holds. This could mean restoring habitats, tackling invasive species, or preserving endangered ones.

This kind of monitoring becomes more accurate as you build an unbroken, long-term data record. A baseline can be established, and it becomes easier to know whether an outlying result is a cause for concern. We are now in our fifth year of SmartRivers and Riverfly Monitoring Initiative for the headwaters, and we recently began testing for nitrate, phosphate, and ammonia.

All of this is made possible by our wonderful volunteers, who show incredible dedication in taking care of our chalk streams. If you'd like to join them in becoming a Chalk Stream Champion, you can contact the scheme team by emailing winterbournes@hiwwt.org.uk. There are lots of different tasks to try, from performing water vole surveys to supporting youth education sessions.

Learn more about SmartRivers

Learn more about Watercress and Winterbournes