Natural drama under the surface of the Broads

Hickling Broad: The ecosystem of the broads depends on the health of its underwater environment. Pic

Hickling Broad: The ecosystem of the broads depends on the health of its underwater environment. Picture: Richard Osbourne/NWT - Credit: Archant

There's something worrying going on under the surface of the Broads, as Kevin Hart of Norfolk Wildlife Trust explains.

Chara virgata (stonewort) and Potamogeton friesii. Picture: Eilish Rothney

Chara virgata (stonewort) and Potamogeton friesii. Picture: Eilish Rothney - Credit: Archant

Norfolk is rich in habitats and wildlife, with the Broads a shining jewel in the crown, a tranquil and beautiful lowland landscape of interconnected shallow lakes, rivers and dyke networks, buffered and surrounded by reedbeds, fens, grazing marshes and wet woodlands.

There is much biodiversity (many different species) and bioabundance (amount of wildlife) here and much to celebrate - but in many places something important is missing.

The underwater eco-system across the Broads National Park is in a parlous state. Imagine the broadland landscape above water bare of all vegetation bar the odd clump here and there, just lifeless dirt. This is unthinkable and yet that is exactly what has happened over a great deal of the subaquatic system. For the last 50 years or so almost all our broads and rivers have been enriched with nutrients from a variety of human activities resulting in disastrous consequences for underwater and marginal plant communities.

The nutrient enrichment means high phytoplankton production – huge amounts of microscopic algae creating turbid murky water stopping sunlight reaching through to any other plants resulting eventually in a complete loss of aquatic plant cover and diversity. The knock-on effects are significant. Imagine a forest landscape where all the trees are destroyed, all the creatures associated specifically with the trees are lost, the species that use the trees for food are lost and other prey species with nowhere to hide or shelter are eaten by predators. A subsequent shift occurs in the whole food web and ecosystem with a dramatic loss of biodiversity.

A few notable exceptions give a glimpse of the condition our broads and rivers could be in. The River Thurne in its upper reaches at NWT Martham Broad is incredible - gin-clear water with a host of different water plants including a key group that are internationally rare: the stoneworts. Evidence shows that pre-1900, stoneworts were common in the low nutrient Broads system. This group of plants play a key role in the health of our wetland networks and although plant-like in appearance, they are actually classified as green algae and are ancient ancestors of primitive terrestrial plants. There are a number of species found in the Broads, all of which have suffered major decline in this country and beyond due to pollution and poor water quality. This makes many of them internationally threatened and of great importance to protect from further loss.

To find further examples of healthy, clear water conditions with established plant communities one must look to waterbodies and dyke systems not connected to the main river systems. Places such as the Trinity Broads (Ormesby, Rollesby and Filby) and Upton Broad have been isolated to a large degree from enrichment, sometimes through good fortune and sometimes by conservation design (dams and catch dykes have been used to prevent poor quality river water entering sensitive waterbodies).

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As well as being a wildlife haven and internationally-recognised wetland system for biodiversity, broadland is rightly revered for its cultural significance and recreational opportunities, particularly sailing, boating and fishing. It is clear that the essential water plant populations needed for good ecological condition in shallow lakes can cause problems to powered boats and sailing boats with stabilisation boards projecting below the hull getting caught up in the plant mass.

At locations such as NWT Hickling Broad National Nature Reserve, we are working closely with the Broads Authority and Natural England to protect these rare and essential plants whilst attempting to maintain the space necessary for recreation.

The first of ongoing trial cuts to stonewort beds took place last year in an effort to better understand how stoneworts and other water plants can be managed to thrive while making space for the important water-based recreational activities that many Broads provide. Healthy water plant communities and crystal-clear water throughout the Broads will benefit biodiversity, tourism, and all water-based recreation – a truly win / win scenario that we are committed to pursuing.

Discover the Norfolk Broads for wildlife:

Kevin Hart is Head of Nature Reserves at Norfolk Wildlife Trust.