Impact Type: Deposition of pollutant
Key Concerns:
The slender naiad (Najas flexilis) is an aquatic plant occurring in clear, mesotrophic lowland lakes in Scotland and Ireland. It is vulnerable to eutrophication and has disappeared from a number of sites that have become enriched (e.g. Esthwaite Water - its only English record) (Preston & Croft 1997). Its current decline is believed to be due to restrictions on light penetration due to heavy weed growth and nutrient enrichment (Biodiversity Steering Group 1995). While agricultural run off and sewage/septic tank effluents may be a frequent cause of eutrophication, atmospheric nitrogen deposition may be important in some circumstances.
Additional Comments:
There is no published research on the effects of atmospheric nitrogen deposition in the UK on this species. Work by Knapton and Petrie (1999) in the US has shown a link between reduced turbidity and increased distribution of N. flexilis.
>P�s `Kp��ption leading to a loss of base cations or eutrophication. It also increases the demand for base cations and micronutrients. N additions have also been shown to affect fruit body production in young stands of Pinus sylvestris Termorshulzen (1990).
Additional Comments:
Of more concern is the effect of N deposition on the ground flora in Scots pine woodlands. Initial effects will probably increase tree growth which will immediately reduce light reaching the ground. Thereafter, increased litter fall will cover the ground flora and eutrophy the site. NH4+ ions will be bound by organic matter and mineralisation can be stimulated. On less acid sites nitrification may give rise to NO3- leaching of base cations.
| Critical Load/ Level |
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No comparable habitat with established critical load estimate available |