Eutrophication ME-1

Anthropogenic eutrophication is usually caused by nitrogen and/or phosphate compounds either dumped at sea, discharged through pipes, or lost to the marine environment via the atmosphere or run off from land. These nutrients act as "food" for phytoplankton (plant cells in the water column), capable of multiplying at an enormous rate, given sufficient food and light. This in turn causes a change in the plankton population, a general increase in water turbidity and greater fluctutations in oxygen levels. As light is prevented from penetrating down, other organisms such as sea weeds (algae) and sea grass such as the Posidonia beds in the Mediter ranean ( Zostera beds in northern countries ) can be adversely effected. Finally with little water movement and a high plankton mass, deoxygenation and mass death of organisms in the affected area may be observed.

Unit of measurement: input of total nitrogen in tonnes per annum and input of total phosphate in tonnes per annum (see below on alternatives) . Often the measure used is the total oxidised nitrogen, made up of nitrate (NO₃) plus nitrogen dioxide (NO ₂). Total nitrogen = oxidised nitrogen, ammonia, plus organically bound nitrogen. For phosphate the present measure is usually total phosphorus, or ortho-phosphate - commonly described as the available phosphate (i.e. usable directly by plants for growth, rather than being bound) . We propose that total P be used where at all possible (see limitations). The area measure may be defined as a sea - North Sea, Black Sea etc. - or sub -systems such as a bay, or estuary.

Chapter 17 : Protection of the oceans, all kinds of seas and coastal areas. No specific targets agreed but under the management-related activities heading it states : Promoting controls over anthropogenic inputs of nitrogen and phosphorus that enter coastal waters where problems, such as eutrophication threaten the marine environment or its resources ” (p . 143).

Monitoring in several other water directives required, of interest for sea water is the Bathing Water Directive but only in so far as sampling is to be carried out where there are grounds for believing that there has been a deterioration in water quality. (NB : new framework Water Directive likely to be introduced) .

The new Integrated Pollution Control Directive about to be adopted foresee s limit values to be set by Council for Annex III Substances including “substances which contribute to eutrophication ” (Water point 11) .

In the Ministerial Agreements on the North Sea ( Esbjerg Declaration,1995), the Baltic, the Med iterranean Action Plan ( Blue Plan ) and the Black Sea, nutrient load reductions have been agreed with concrete time scales in both Baltic and North Sea.

The indicator expressed as nutrient input or eutrophication ranked in first position as core indicator and on analytical soundness. On policy relevance it was pushed by overfishing into second position and on responsiveness i t only came 10th.

The indicator gives a measure of sewage, agricultural (including forestry) , industrial and traffic nutrient input to the marine environment. Testing of oxidised nitrogen in particular is simple and inexpensive. Thus the indicator complex lends itself to wide public understanding and as yet almost unharnessed participation in monitoring and control.

A marked increase in nutrient input and hence eutrophication problem has been noted in most regional seas. Some of the problems such as increased algal blooms including toxic blooms are of concern to the coastal public at large. The Dobris Assessment estimates that Baltic Sea nitrogen inputs have increased four fold and phosphate eight fold since the beginning of this century. Chief contributors to the nutrient load are artificial fertilisers and animal slurry, sewage and occasional point sources of food industry. That is accidental loss of fertiliser the farmer has paid for and would like to reduce if possible on the one hand and the wilful disposal of waste on the other. Both need to be better controlled if we are to achieve sustainable use of our coastal ecosystems.

In the A ir Pollution policy field, this indicator is directly linked to AP-2: Emissions of VOC, AP-4: Emissions of particles, which are related to nitrogen compounds; it is also indirectly linked to AP-3: Emissions of SO ₂, AP-1: Emissions of NO _x, AP-9: Use of pesticides for agricultural purposes, AP-5: Consumption of gasoline & diesel oil by road vehicles, AP-9: Use of pesticides for agricultural purposes which deal with product consumption and waste formation with N or P production.

In the Loss of Biodiversity policy field, it is related to LB-3: Agriculture intensity and LB-6: Change in traditional land-use practice, that is indicators dealing with fertiliser and N input, and finally to LB-2: Wetland loss through drainage.

Finally, in Water Pollution & Water Resources, it is linked to WP-3: Pesticides used per hectare of utilised agriculture area, which deals with eutrophication and WP-1: Nutrient (N+P) use.

The Nitrate Directive has three key targets: to ensure nitrate concentration in all water is below 50 mg/l and euthrophication is prevented; to identify vulnerable areas and prepare action programmes for these and to limit nitrogen input (animal manure only) to a max of 170 kg/ha in the first action programme 1995-1999.

The assumption is that a certain nutrient load, put into a known marine system with known weather conditions has a predictable eutrophication effect, which in turn has a range of predictable detrimental effects on the flora and fauna of the receiving waters. The nutrient input can be estimated in time and space given enough measurements of concentration in known input routes and/or indirectly in a given sector by for example sales of fertiliser in a given area. Most countries have national limits for licensed operations, but aerial inputs and diffuse source agric ulture inputs require a different approach.

Nutrient load is calculated from N and P inputs in a given time. The routes normally considered are riverine, industrial discharges and estimates of aerial inputs. Additionally, direct run-off from land and dredge spoil/sewage sludge may be important.

There is no single unit of measurement combining N + P. Additionally there is great confusion about results expressed as “mg/l P”. Some researchers mean all forms of phosphorus, while others take it as unit of measurement for orthophosphate (PO ₄).

There are two principal limitations, one on clarity of meaning, the other on trust in data obtained. The significance of both could be reduced if one agreed internationally to standardise and integrate work of different bodies. A note on each:

“Nutrient input ” is a composit indicator, first of N and P and then the different forms of each. Hence there is room for argument as to measurement and significance in a given area. For example, in the Baltic as a whole, it is thought that nitrogen is the limiting factor. But in the Bothnian bay subsystem, phosphates are thought to be the nutrient which , if reduced, would cause a significant improvement in the situation. For this and pin pointing source reduction reasons, it would be ideal if apart from one overall figure for the nutrient load pressure in a given area, one could d isaggregate the figure on demand into N and P.

In practise, the calculation of input in all except industrial and sewage discharges contains a large margin of error. Even with information as detailed as x kg of a fertiliser applied per hect ar of crop y, the actual quantity of nitrogen and phosphate lost to surface waters in a specific place may vary six fold, due to overriding effects of weather after spreading the fertiliser and in the case of phosphate, the existing phosphate levels in the soil. Comparisons between sites are difficult too, unless umpteen extra parameters, particularly existence of a rough vegetation or reedbed buffer between the land and water drain can be included in the calculation. Thus only when you have a very large sample size, overcoming local or regional weather etc. factors, can the trends become apparent. Once this is set up though, a reduction of nutrient input in a sector - like farming - can be monitored and feedback of information can be fast.

Eutrophication as indicator may be expressed as state: nutrient concentration of a given system, or as pressure at two levels: input of N and P into a given marine area, or eutrophication pressure (measured as oxygen levels, chlorophyll a etc.) on key components of a coastal ecosystem. To avoid this confusion in the audience, it may be preferable to change our indicator to “nutrient loading ”.