May, Linda

English

NERC Open Research Archive

Loch Leven: understanding environmental changeContact: Linda May lmay@ceh.ac.ukStakeholders:• CEH• SEPA• SE• East of Scotland Water• SNH• RSPB• Perth & Kinross Council• Scottish Agricultural College• NFUS• United Distillers& many othersDetecting changeDuring the 1970s and 1980s:• nutrient inputs and concentrations increased• ecosystem structure and function changed• toxic algal blooms became more frequentDetecting changeProviding solutionsIdentifying causes68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84μg chlorophyll a l-105010015020025030085 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01μg chlorophyll a l-1050100150200250300Algae (µg chlal-1)Algae (µg chlal-1)         BackgroundLoch Leven is a shallow eutrophic loch in south east Scotland. It has international recognition for its conservation value and is an important part of the local economy.Long term monitoringNERC has been monitoring the loch on a fortnightly basis for over 40 years. The data collected span 150 biological, chemical and physical variables. Cause of increased algal bloomsBetween 1968 and 1985, increases in algal abundance were closely related to increased phosphorus (P) availability in the loch.Cause of increased P availabilityOur catchment data show that the supply of P to the lake had increased by 400% over this period, due to growth in agriculture, industry and population.Climate changeOur physical data show evidence of warmer water and less wind induced mixing in recent years. The impact of these on species interactions, nutrient cycling and algal blooms are still being investigated.Future workWhen P inputs were reduced, P released from the sediment delayed recovery by 10-15 years. We are investigating the factors that control this phenomenon to find ways of accelerating lake recovery processes.Setting restoration targetsWater quality restoration targets were set, based on CEH science, and a catchment management plan implemented. P inputs from sewage, industry and farms fell by about 60%. This cost more than £4.2M.Evidence of recoveryAs a result, water quality improved significantly. P concentrations fell and algal blooms became less frequent. Underwater plants began to thrive in deeper water as the water became clearer.02040608010040 50 60 70 80 90 100 110Annual mean TP conc. (mg m-3)Annual mean chlorophyllconc.(mg m-3)Data: 1968 - 1985Data: 1968 - 1985Annual meanalgalabundance(µg chla l-1)Annual mea  phosphorus concentration (µg P l-1)4040 50 60 70 80 90 100 1104020681000Soluble reactive P (µg l-1)6 8 6 9 7 0 7 1 7 2 7 3 7 4 7 5 7 6 7 7 7 8 7 9 8 0 8 1 8 2 8 3 8 4μ g soluble reactive P l-102 55 07 51 0 01 2 51 5 08 5 8 6 8 7 8 8 8 9 9 0 9 1 9 2 9 3 9 4 9 5 9 6 9 7 9 8 9 9 0 0 0 1μ g soluble reactive P l-102 55 07 51 0 01 2 51 5 012341. Reduction of woollen mill effluent2. External P inputs halved 3. Prolonged recovery4. Recovery05101520251850 1900 1950 2000(y)Annual Pinputto lake(tonnes)20195190185060% reduction in P loadWind mixed depth (m)Average water temperature (oC)1980 1990 2000y = 0.033x + 8.78.08.59.09.510.010.511.0Watertemperature(ºC)1970811091975 1980 1985 1990 1995 2000 2005 2010Variatoin from mean (m)-0.6-0.4-0.20.00.20.40.6S1 S2S3 S4 S5 S6-0.-0.20.40.20.6-0.1980 1990 2000 2010R2 = 0.807301234560 5 10 15 20 25Macrophytegrowingdepth(m)Annual P input to lake (tonnes)1993199019861979200520041999200619091972nnual P input to lake (tonnes)Macrophytegrowingdepth(m)

Loch Leven: understanding environmental change

http://nora.nerc.ac.uk/3627/1/NERC_May.pdf

Loch Leven: understanding environmental change

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