| Autor: |
Bowes, M.J.1 mibo@ceh.ac.uk, Ings, N.L.1,2, McCall, S.J.1, Warwick, A.1, Barrett, C.1, Wickham, H.D.1, Harman, S.A.1, Armstrong, L.K.1, Scarlett, P.M.1, Roberts, C.1, Lehmann, K.1, Singer, A.C.1 |
| Předmět: |
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| Zdroj: |
Science of the Total Environment. Sep2012, Vol. 434, p201-212. 12p. |
| Abstrakt: |
Abstract: Soluble reactive phosphorus (SRP) concentrations in the River Thames, south east England, have significantly decreased from an annual maximum of 2100μgl−1 in 1997 to 344 in 2010, primarily due to the introduction of phosphorus (P) removal at sewage treatment works within the catchment. However, despite this improvement in water quality, phytoplankton biomass in the River Thames has greatly increased in recent years, with peak chlorophyll concentrations increasing from 87μgl−1 in the period 1997 to 2002, to 328μgl−1 in 2009. A series of within-river flume mesocosm experiments were performed to determine the effect of changing nutrient concentrations and light levels on periphyton biomass accrual. Nutrient enrichment experiments showed that phosphorus, nitrogen and silicon were not limiting or co-limiting periphyton growth in the Thames at the time of the experiment (August–September 2010). Decreasing ambient SRP concentration from 225μgl−1 to 173μgl−1 had no effect on periphyton biomass accrual rate or diatom assemblage. Phosphorus limitation became apparent at 83μg SRP l−1, at which point a 25% reduction in periphyton biomass was observed. Diatom assemblage significantly changed when the SRP concentration was reduced to 30μgl−1. Such stringent phosphorus targets are costly and difficult to achieve for the River Thames, due to the high population density and intensive agriculture within the Thames basin. Reducing light levels by shading reduced the periphyton accrual rate by 50%. Providing shading along the River Thames by planting riparian tree cover could be an effective measure to reduce the risk of excessive algal growth. If the ecology of the Thames is to reach the WFD''s “good ecological status”, then both SRP concentration reductions (probably to below 100μgl−1) and increased shading will be required. [Copyright &y& Elsevier] |
| Databáze: |
GreenFILE |
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Full Text from ScienceDirect