Fen Management Handbook - Scottish Natural Heritage

4. Understanding Fen Nutrients
Nutrient levels have a significant effect on fen vegetation,
biodiversity and nature conservation value. Understanding
how and why nutrient regimes are subject to change, and the
problems which can arise as a result, is therefore critical to fen
management.
This section explains the basic principles of nutrient enrichment in
relation to fens and considers key factors which affect fen nutrient
regimes. It also outlines methods of identifying and monitoring
nutrient enrichment. Guidance on nutrient management is
summarised in Section 8: Managing Fen Nutrient Enrichment.
Key terminology used in relation to nutrients – glossary:
Nutrients The chemical building blocks of plants, the most significant of which are the macronutrients N
(nitrogen), P (phosphorus) and K (potassium).
Nutrient status
Nutrient enrichment
The amount of nutrients found in the fen.
When there are more nutrients than might be considered desirable for particular fen habitats or
features, also referred to as ‘eutrophication’. This is often caused by an increase in nutrient input
over a short period of time into the system. ‘Cultural eutrophication’ is the term used to describe
enrichment caused by human land management activities, typically intensive agriculture.
Nutrient regime Describes the way nutrients enter, are used within, and leave a fen. As water is the key carrier for
nutrients entering or leaving fens, the nutrient regime is closely linked to the hydrological regime,
and is influenced by catchment geology, shape and land use, all of which affect the chemistry of
water entering the fen.
Nutrient availability The amount of nutrients available to plants is governed by a range of microbial and redox
(reduction-oxidation) mediated processes in the soil. This means that the ‘plant-available’ pool of
nutrients may be different to (often much smaller than) the total pool in the soil, which will include
organically-bound forms less immediately available for plant uptake.
Nutrient cycling Fen plants take up nutrients during their life, which are then (partly) released when the plant, or
part of it, dies. The resulting nutrients are re-cycled by the soil microflora and re-used or re-cycled
by other plants.
Minerotrophic Wetlands receiving mineral inputs from groundwater, and/or surface runoff and/or over-bank
flooding, as well as rainfall.
Ombrotrophic Wetlands fed mainly by rainwater inputs (literally, fed by cloud inputs).
Oligotrophic Soils and fen waters which are infertile – i.e. with small pools of available macronutrients.
Mesotrophic
Eutrophic
Moderate fertility status.
High fertility status. Some fens can be naturally high in nutrients, but often this term suggests
some artificial enrichment.
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