Fen Management Handbook - Scottish Natural Heritage

68
Water chemistry – key terms
Base-poor Having few base ions (Ca, Mg) and generally more acidic (pH 5.5). Water
source typically minerotrophic and nutrient status typically ogliotrophic or
mesotrophic.
Electrical
conductivity
(EC)
A measure of the total concentration of chemical ions in solution, easily measured
by a meter in Siemens/m (S m -1 ) or micro-Siemens/cm (μS cm -1 ). Higher values
indicate higher concentrations of ions.
Redox potential The potential for a reduction-oxidation chemical reaction occurring, gives an
indication as to whether the environment is oxygenating or reducing. Measured in
volts (V), millivolts (mV) or Eh (where 1 Eh = 1mV) by an electrode. More positive
values indicate oxygenating environments, negative values indicate reducing
environments.
Ion exchange Process by which chemical ions move between the soil/plant surface and solution.
This process leads to the acidification of bogs and fens by the release of hydrogen
ions (H + ) from the peat.
pH Measure of the acidity of a solution.
4.5 Assessing fen nutrient regimes
An assessment of a fen’s nutrient regime would evaluate:
– the nutrient inputs and outputs;
– the total concentration of different nutrients within the system;
– the availability of these nutrients for biological uptake;
– the cycling of these nutrients within the fen system.
Assessing all of these aspects is costly and in a conservation context generally
unrealistic. A small number of indirect measures of nutrients can usually supply
enough information for effective management decisions and/or to decide whether
further investigation is required. However, in order to understand how to interpret
these measures and how this can guide fen management, it is important to
understand what factors influence nutrient status in fen habitats, and the range of
nutrient regimes that might be considered ‘typical’ across the UK.
Identifying the symptoms and cause(s) of enrichment is both difficult and expensive,
but useful information can be gleaned using simple walk-over surveys, especially
where coupled with relevant survey or monitoring information. In all cases,
managers should start with the following stage 1 assessment. More detailed
guidance on measuring and monitoring nutrient enrichment is provided in Section
10: Monitoring to Inform Fen Management.