Fen Management Handbook - Scottish Natural Heritage
Fen Management Handbook - Scottish Natural Heritage
Fen Management Handbook - Scottish Natural Heritage
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4.2 Sources of nutrient input<br />
Water Table<br />
60<br />
Figure 4.1 External sources of nutrients<br />
<strong>Fen</strong><br />
Soil and rock saturated with water<br />
Groundwater (purple)<br />
<strong>Fen</strong><br />
Surface water (red) = overland flow and flood water from lake or river.<br />
Atmospheric (blue)<br />
Sources of fen nutrient enrichment – key points<br />
Groundwater<br />
inputs<br />
Surface water<br />
inputs<br />
Atmospheric<br />
inputs<br />
Rain (contains N from<br />
atmospheric inputs)<br />
Groundwater is an important source of nutrient enrichment in fens. It is linked to catchment land<br />
use and also affected by catchment geology. Nitrates (i.e. nitrogen in solution) entering a fen<br />
are a significant issue as N is one of the main nutrients which affects plant growth and therefore<br />
affects fen vegetation and habitat.<br />
Surface water which might enter fens via streams or other surface flow often carries nitrates<br />
and/or phosphorus. Soil erosion often leads to surface water transportation of phosphorus-rich<br />
sediments into a fen.<br />
Nitrous oxides and ammonia deposition are key pollutants of fens. Nitrous oxides are typically<br />
derived from fossil fuel burning (e.g. electricity generation, transport) while ammonia is<br />
associated with highly intensive agricultural systems (e.g. poultry farming, pig farming).<br />
Point sources Point sources of pollution or eutrophication are those where the nutrients can be traced back<br />
to a specific source, which might be a sewage works, a pollution incident, or discharge from a<br />
farm or industrial plant. Power stations and airports can be point-sources of air-borne nutrient<br />
pollutants.<br />
Diffuse sources Aerial and water borne nutrient enrichment attributable to more widespread or diffuse sources<br />
includes activities within the fen catchment (e.g. intensive agriculture) or further away (e.g. aerial<br />
pollution).<br />
Internal nutrient<br />
enrichment<br />
Nutrient cycling in fens typically involves relatively small amounts of plant-available inorganic<br />
nutrients, the availability of which are strongly affected by waterlogging. Changes to the fen<br />
habitat, especially drainage, can result in a peak of nutrients and also the conversion through<br />
oxidation of organically bound nutrients not normally available to most plants.<br />
Nutrient limitation When the availability of one plant nutrient prevents or limits the growth response of the<br />
vegetation to other nutrients, thus often keeping the effects of nutrient enrichment in check.
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