Fromdarkness

tolight

the restoration ofBarton Broad

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2

Map 2

Introduction 3

The restoration of Barton Broad 4

Project objectives 5

Methodology and results 6Suction dredgingLower phosphorus levels in the sedimentLower phosphorus levels in the waterChange in the algaeSecuring water space for recreation

Biomanipulation 12Creating clear waterReducing wave energyRe-growth of aquatic plants

Reed margin restoration 16

Additional restoration work 17

Visiting Barton Broad 18

What happens next? 19

Glossary 19

More reading 20

Contents

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BartonBroad

Neatishead

BartonTurf

PleasureIsland

car park fordisabled people

viewingplatform

Fish barriers

Boardwalk

Rive

r Ant

TurkeyBroad

Irstead

Herons' Carrvery wetwoodland

toilets and car parkfor solar boat tripand for the Herons' Carrboardwalk withviewing platform

0.5 km

1/2 mile

0

0

TheHeater

North

River

Ant

Gay's staithe andRa solar boat trip

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Introduction

Clear Water 2000 was the Broads Authority’smillennium project to restore the clear water andlandscape of Barton Broad, encourage back thewildlife, and improve and expand access to thisbeautiful broad. Barton Broad is owned by theNorfolk Wildlife Trust and is the second largest ofthe broads. It is a national treasure, as a NationalNature Reserve and international site for wildlifeconservation, and as an important site for boatingand sailing for many local people and visitors.

Research and monitoring has formed an essentialpart of the Barton Broad restoration project, andthis document sets out its results. Investigation ofnutrient budgets, sediment nutrient release andcreation of clear water areas were part of theresearch programme, which informed the project’sinception, development and success.

The restoration of Barton Broad

Since the 1950s the underwater ecosystem in thebroads and rivers has changed from onecharacterised by abundant and diverse aquatic lifeto one dominated by algae, as a result of nutrientenrichment from sewage treatment works andagriculture.The algal growth blocked out sunlight,with the result that underwater plants and thehabitats they provide were lost. Barton Broad wasan example of these degraded ecosystems. By the1970s its turbid waters had no aquatic plants, apoor fish community and summer blue-greenalgal blooms.

Lake restoration began on Barton Broad in thelate 1970s when improvements to sewagetreatment works meant less phosphorus wasdischarged into the River Ant, upstream of BartonBroad.This resulted in considerable water qualityimprovements, however vast quantities of nutrientremained locked in the sediment at the bottom ofthe broad, which had also become too shallow forboats.The £3 million Clear Water 2000 projectset about restoring the silted up Barton Broad toecological health, with sufficient water space andwater depth to make it navigable for allBroads craft.

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Project objectives were to:

1 Improve water quality;

2 Increase water depth and area of water open for navigation;

3 Create clear water areas to facilitatere-growth of water plants;

4 Create a better habitat for wildlife in and around the margin of the broad;

5 Improve accessibility and facilities for visitors by land and on water; and

6 Interpret the science for the benefit of visitors.

Top to bottom: stonewort, sailing onBarton, water lily, reed warbler,Herons’ Carr Boardwalk, interpretationboard for Barton Broad.

Methodology and results

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Two techniques were principally employed atBarton: suction dredging to remove phosphorusand biomanipulation to encourage the return ofclear water and wildlife.

Suction dredgingDredging was vital to achieving the first threeobjectives. It had two purposes - to reducenutrient leaking from the sediment into the water,which fuels algal growth, and to increase waterdepth to safeguard navigation for all Broads craft.

Dredging took six years (1996-2001), removingover 305,000 m3 of sediment, equivalent to 160Olympic size swimming pools.This sediment waspumped into specially constructed settlementlagoons on adjacent agricultural land, with topsoilforming bunds to contain the liquid sediment as itdried out. After drying the lagoons hadapproximately 1m depth of sediment.Therestoration of the sediment disposal site back toagricultural land involved mixing dredgings withsubsoil, re-covering with topsoil and planting witha conditioning crop of oil seed rape or wheat,before returning to commercial agricultural use.

Left to right:suction dredging,mud pumped intosediment lagoon,sediment lagoons

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Aerial view of Barton Broad inrelation to the sediment lagoons(bottom right)

After incorporation of the dredged silt the soilhad a higher organic matter and nutrient contentcompared to the original soil.This resulted inimproved moisture retentive capacity of the soiland a lower requirement for additionalartificial fertiliser.

The location of the fields was adjacent to thebroad.This meant that any water that ran off theagricultural fields carried nutrients directly backinto the broad.Therefore it would have beendesirable (but proved impossible here) to site thesediment lagoons and their outflow downstreamfrom the broad.

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Lower phosphorus levels in the sedimentPhosphorus is a key aquatic nutrient that can eitherlimit algal growth or allow algae to bloom. Suctiondredging removed 50 tonnes of phosphorus fromthe sediment in Barton Broad.The nutrientreduction is equal to approximately 20 years ofphosphorus inputs from theRiver Ant catchment.

Immediately after dredging the sedimentphosphorus concentration was lowered to 50% ofits original level (Figure 1). Phosphorusconcentration at 3 to 20 cm depth in the sedimentremained significantly lower (approximately 50%) inthe dredged areas for a period of five years afterdredging. However, phosphorus levels of thesurface sediment, at 1 cm depth, rapidly increasedafter dredging, to reach a similar concentration tothat of the undredged surface sediment.Thisincrease is probably a result of phosphorus richalgal material settling and reaching a state ofre-equilibrium with the water.

Sediment phosphorus mg g-1

Depth cm

0.5 10 1.5

2

6

4

8

10

12

14

16

18

20

0

Dredged

Undredged

Algae

Figure 1Graph to comparephosphorousconcentrationin dredged andundredged sediment

Lower phosphorus levels in the waterDuring the six-year dredging operation theaverage annual phosphorus concentrationdecreased each year.This encouraging trend issupported by longer clear water periods in thespring, with lower algal populations. Experimentsshowed 50% decrease in phosphorus release fromthe sediment after dredging.Therefore dredginghas contributed towards lower phosphorus levelsand fewer algae in the water (Figure 2).

0.35

0.3

0.25

0.15

0.1

0.05

0

0.2

350

300

250

200

150

100

50

0

1979

1980

1981

1998

1999

2000

2001

2002

2003

2004

Before phosphorusremoval

Afterphosphorusremoval

Total phosphorusChlorophyll-a

Tot

al p

hosp

horu

s m

g-1

Chl

orop

hyll-

a µg

-1

10

Figure 2Annual average totalphosphorus and algal(Chlorophyll-a)concentration inBarton Broad beforeand after phosphorusremoval from sewagetreatment works.

(Data source:Environment Agency)

Daphnia

Diatoms and algae

Change in the algaeSince the late 1970s the algal population hasshifted from domination by diatoms andpotentially toxic blue-green algae, to small greenalgae and fewer blue-green algae.This change inthe algal community is thought to be a responseto the lower phosphorus concentration in thewater, rather than being influenced by Daphnia(zooplankton) grazing.The Daphnia population hasdecreased each year from 1996 to 2000, probably

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resulting from the clearer water allowing fish toprey on them more effectively (see table below).However in 2005 large blue-green algae wereobvious in the relatively clear water, indicating thatgrazing Daphnia were removing small algal cellsand leaving the large cells as they are unable tocope with them.

These improvements in water quality may not betotally related to the sediment removal for twomain reasons. Firstly, the improvement is part of ageneral trend in water quality improvements in theBroads, such as those seen in Wroxham Broad onthe River Bure. Secondly, improved phosphorusstripping at sewage treatment works upstream ofBarton Broad coincided with the start of thedredging programme. However the 50% decreasein nutrient release certainly has improved waterquality.

1995 pre-dredging

2000 post-dredgingMain Broad

2000 post-dredgingExclosures

Water depth 1.2m 1.7m 1.5m

Total Phosphorus mg /1-1(a) 0.121±0.015 0.06±0.005 0.06±0.005

Chlorophyll-a µg/l-1(*a) 70±14 50±8.9 16.4±4.8

Daphnia individuals/l-1(a) 45±16 7±4 91±16

Conditions before and after dredging in BartonBroad (mean ± standard errors).

* Chlorophyll-a is a measure of the amount of algal pigmentsin the water and is used to indicate the total algal population.

a Source: Environment Agency

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Sailing regatta onBarton Broad

Securing water space for recreationDredging has increased the water depth by anaverage of 0.43 m, resulting in a sailing depth ofaround 2 m in the winter and over 1.5 m in thesummer. In addition to the depth increase, thenavigable area has increased as a result ofdredging the shallow margins, which werepreviously inaccessible to many craft. Over onethird of the broad (or 28 ha) has been reopenedas good navigable water space as a result of theClear Water 2000 project, benefiting racing sailorsand novices alike. Since dredging the annual sailingregatta has celebrated the increased water spaceby extension of racing courses to include an areaof Turkey Broad at the southern end ofBarton Broad.

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Biomanipulation

Left to right:installing a fish curtain,electro fishing,pike (a piscivore)

Biomanipulation is a technique often used tomanage degraded shallow lakes. It involves thetemporary removal of selected fish species toincrease the number of grazer zooplankton,particularly Daphnia species.This in turn effects achange in the ecosystem, in this case gaining clearwater and plant re-growth.

In shallow lakes without aquatic plants, fish that eatzooplankton (zooplanktivores) often predominate,reducing the number of zooplankton that mightotherwise suppress algal growth. Reducing thenumbers of these fish by removal or by addingpiscivores (fish that eat other fish) is an establishedtechnique to create clear conditions. Clear watergives aquatic plants a chance to re-grow; these actas refuges for zooplankton which in turn sustainclear water without the need to continuallyremove the fish.

In Barton Broad it was difficult to remove fishbecause a wide channel has to remain open toenable free navigation.Thus fish were removedfrom isolated bays or ‘exclosures’, which wereseparated from the main lake by ‘fish curtains’(Figure 3).

Using a technique called ‘electrofishing’, fish werecaptured in nets, whilst they were temporarilystunned.They were then gently transferred into

Floats

Chain

Sedimentsurface Polyester

curtain

Mesh

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the main broad where they soon recovered.Many previous rigid barrier constructions havefailed as a result of being under-cut due tounequal tidal fluctuations in water levels inside andoutside the barrier.The barriers installed in BartonBroad were designed to overcome this problemby being flexible, consisting of a heavy polyestercurtain coated in PVC.The bottom edge wasweighted into the soft sediment with a heavychain.The top consisted of two rows of polyethyl-ene floats, with a section of mesh runningbetween them.Water was able to transfer overthe top of the barrier.

Figure 3

View along a fishbarrier.You can see thecalmer water insidethe barrier

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Creating clear waterBiomanipulation resulted in lower fish numbers;zooplankton began to thrive and significantlyreduced the algae population inside theexclosures, creating clear water. However, whenfish got into the exclosures clear water was lostrapidly, often for the whole summer season.Where the water remained clear submergedplants grew in the exclosures, while there wasalmost total absence of submerged plantsthroughout the other areas of the broad. Plantspecies that have grown within three years sincebiomanipulation include:

Pondweeds (Potomogeton crispus, P. pectinatus,P. pusillus)Stoneworts (Chara vulgaris, C. virgata, C. hispida) Water-crowfoot (Ranunculus circinatus) Canadian pondweed (Elodea candensis) Holly leaved naiad (Najas marina) Hornwort (Ceratophyllum demersum)

It is possible that ancient seeds, exposed afterdredging, germinated.This is the firstbiomanipulation project in the Broads that hasresulted in such a rapid re-establishment of adiverse range of aquatic plants.

Pond-weed(Potomogeton)

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Reducing wave energy The barriers significantly lowered the amount ofsuspended sediment in the water column. Suspendedmaterial in shallow waters, such as Barton Broad, ishighly influenced by wind and boats.The fetchdistance, or distance waves travel, was reduced from1000 m to 50 m on Barton by installation of thebarriers perpendicular to the predominant winddirection.This fetch reduction creates calmer waterwhere plants are protected from burial and uprooting.

Re-growth of aquatic plantsYellow lilies (Nupha lutea) appeared in anon-biomanipulated exclosure, suggesting thatinstalling barriers, which reduce wave energy, may aidthe re-growth of submerged plants. Howeverexclosures also reduce the circulation of water andthis can lead to the build up of high algal populations,therefore effective fish removal is essential for gainingclear water.This is proved by the fact that exclosuresthat have had the fish successfully removed haveexcellent re-growth of plants, with over 11 plantspecies recorded during 2000 and 2004. In 2005, forthe first time in over 30 years aquatic plants grewoutside the clear water areas, without the help ofbiomanipulation, we hope this natural recoverywill continue.

Left to right:stonewort (Chara),water-crowfoot(Ranunculus circinatus),yellow water lily(Nupha lutea)

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Around Barton Broad scrub encroachmentaccounted for the loss of the reed swamp (reedthat grows in permanent standing water) thatoccurred in the 1800s. However, since the1950sremanant reed swamp has also been lost by bankerosion. Reed swamp was therefore lost fromboth sides and was limited to a narrow marginaround the broad or had completely disappeared.

To combat continuing scrub encroachment andresultant shading effect, the Norfolk Wildlife Trustremoved a 20 m strip of scrub from the broadedge. An actively growing reed swamp marginprovides valuable habitat for invertebrates such asdragonfly larvae and snails, refuges for Daphnia,and spawning sites for fish, as well as helping toresist erosion. It is important that reed swampgrowth is encouraged, however it is alsoimportant to consider the role of marginal scruband trees in providing summer shade for fish.

Reed margin restoration

A healthy reed fringe

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The Clear Water 2000 project has been built onby an English Nature Lake Restoration Project(2002/04).This work has extended the fishexclusion areas and created two further areas ofclear water and aquatic plant growth. In addition anovel floating reed swamp island has beeninstalled.The island provides refuges for fish in theopen water in addition to restoring some of thehover reed swamp that has been lost over recentyears.Water quality in the clear water areas andthe rest of the broad will continue to evolve andimprove over time. Monitoring will continue sothat we continue to learn from this project anddevelop plans for future projects.

Additional restoration work

Improving access for victors was an integral partof Clear Water 2000 - to enable people to see,enjoy and learn about Barton Broad. Aninnovative public boat trip is available on board Ra- Britain’s first solar-powered passenger boat,which is wheelchair accessible. A boarded walkwayalso takes visitors through ancient, wet ‘carr’woodland to a viewing platform on the edge ofthe broad.The boardwalk is accessible towheelchair users and an access pack is availablefor loan to make it more user-friendly for visitorswith sensory impairment. At the Norfolk BroadsStudy Centre at How Hill, just downstream fromBarton Broad, a new, ‘green’ building was providedto improve facilities for educational visits.The newbuilding won an Environment Award from NorthNorfolk District Council in 1999, and the wholeClear Water 2000 project received an award fromthe Campaign to Protect Rural England (TheNorfolk Society) in 2004.

Visiting Barton Broad

Left to rightRa (solar boat),boardwalk at Herons’ Carr,the boardwalk platform onBarton Regatta day

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The Broads Authority is working closely with localinterested parties and organisations to develop aWaterspace Management Plan.This plan, due forcompletion in 2006, records and values existinguses and landscape, prioritises future restorationworks, and provides a framework for continueddialogue with interested parties who havesupported the restoration works for over10 years.

What happens next?

Algae - A general term for photosynthetic aquaticorganisms, which range from microscopic floatingforms to large, rooted seaweeds. Hundreds ofspecies occur in the rivers and broads.

Biomanipulation - A technique often used torestore shallow lakes, which involves thetemporary removal of selected fish species toincrease the number of grazer zooplankton,particularly Daphnia species.This in turn effects achange in the ecosystem, in this case gaining clearwater and plant re-growth.

Daphnia - These belong to a larger group ofmicroscopic crustaceans called zooplankton, andthey graze on algae. Daphnia are some of themost effective grazers due to their largebody size.

Glossary

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Diatoms - These are a type of algae.They can turnthe water a brown colour in the early springwhen they tend to reach a peak in numbers.

Phosphorus - This is a plant nutrient found infertilisers, detergents and sewage effluent.Phosphorus stripping at sewage treatment worksis an effective way of reducing the addition ofphosphorus into the Broads, although a significantproportion comes from agriculture.

Sediment - A layer of mud, silt and dead organicmatter, which collects at the bottom of rivers andbroads..

More readingMoss B, Madgwick J, Phillips G (1996) A guide tothe restoration of nutrient-enriched shallow lakes.Environment Agency, Broads Authority, LIFE.(Available from the Broads Authority, price £5 pluspostage. Free to students.)Phillips G *1, Kelly A 2, Pitt J-P 1, Sanderson R 1 and

Taylor E 2 (2005) The recovery of a very shalloweutrophic lake, 20 years after the control ofeffluent derived phosphorus Freshwater Biology

For more information:about the project and visiting Barton Broad,please contact:Broads Authoritytel 01603 610734www.broads-authority.gov.ukNorfolk Wildlife Trusttel 01603 625540www.norfolkwildlifetrust.org.uk

about the Norfolk Broads Study Centre,please contact:How Hill Trusttel 01692 678555www.how-hill.org.uk