Eutrophication has long been an environmental concern for the world's lakes, oceans, river, reservoirs and wetlands (Smith, 2003). During the life cycle of every body of water, it will be inevitable that it will, at some stage, receive an influx of chemicals or nutrients, the volumes and nature of which will determine whether the potential effects are detrimental to the ecology of the water system.
Eutrophication is the enrichment of a water body by the addition of nutrients which accelerates the biological productivity. This process occurs in the natural environment but can also be accelerated by human activities (USDA, 2003) which add to the natural levels of nutrients and chemicals. They are characterised by the increased growth of algal species with the marked reduction in the diversity of species (Scholten, 2005).
Natural Causes of Eutrophication
Water will naturally contain nutrients that it picks up from the erosion of terrigenous sediments as it flows over the land surface. This mass movement is key in the transporting of Carbon, Phosphorus, Nitrogen, Potassium, Zinc, Copper and Calcium (Dekov et al, 1998) which all contribute to the natural enrichment of global water systems.
Anthropogenic Sources of Eutrophication
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As stated above, eutrophication does occur without the impact of human sources but the addition of anthropogenic sources rapidly amplifies the effects. The pressures of an ever increasing population have meant the globe has been dramatically altered to cope with these needs. The strain of urbanisation, industrialization, forestry and the clearing of land for residential purposes have meant hydrological cycles have radically changed (Smith, 1999). Nitrogen and Phosphorus are the two main contributors to Eutrophication. Human activity has almost doubled the amount of Nitrogen that is currently in the N cycle and that figure is still set to rise as demand for fossil fuels increases (Smith, 1999). Excess Nitrogen is introduced into the system through atmospheric precipitation and agricultural processes. Atmospheric nitrogen in the form of Nitrous Oxide (NO) is returned to the terrestrial environment as both wet and dry precipitation which then flows into the water system. It is also applied in agriculture as a component of fertiliser. Nitrogen in this form is easily leachable as it's not well retained by soils (Scholten, 2005) and so can filter down into the groundwater as well as enter the surface waters and flow overland.
Phosphorus is found also in many commonly used fertilisers and therefore follows a similar pathway to that of Nitrogen. P, in the form of polyphosphates, is a component of detergents used in the commercial cleaning industry although due to governmental efforts, since the 1950's the contribution made by this source is now minimal (Newton et al, 2003). Domestic and industrial wastes contain phosphorous in its organic form so it's therefore naturally present due to biological processes.
Effects of Eutrophication
A number of direct and indirect effects can be observed. Excessive nutrient influx rapidly accelerates the primary productivity, which in most cases are algal species. These grow rapidly in mass until either the nutrients are depleted or the mass becomes so much that some begin to die. Decomposition of these ‘blooms' uses dissolved oxygen within the water which deprives other organisms co-inhabiting of oxygen they need. This can lead to a reduction in biodiversity as fish and other organisms die.
Eutrophication of the Baltic Sea
The Baltic Sea has long been a large region of ocean with oligotrophic waters (HELCOM 2006). Low nutrient levels along with low productivity meant for a long period of time eutrophication was never an issue. The Baltic Sea is one of the world's vastest expanses of brackish water with steep gradients in climate, topography and hydrography (Lundberg, 2005).
The Baltic is currently subject to severe anthropogenic stresses with 16 million people living on the coast with another 85 million in the catchment.
The prevalence of cyanobacterial algal blooms has increased since the 1960's which presents an issue due to the nitrogen fixing nature of these organisms (HELCOM 2006) and in the report brought out by the Helsinki Commission (HELCOM) only 13 out of the 189 sites tested were ‘non eutrophic problem areas' (HELCOM 116b).
The Baltic is particularly prone to the effects of eutrophication due to the minimal seawater renewal it receives. This lack of major replenishment means many of the deeper basins within the sea don't get a renewed supply of oxygen leading to stagnation of the bottom waters (HELCOM 2009a). It's because of this that some areas are more eutrophicated than others (Bonsdorff et al, 2009)
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Nutrients enter the sea from 3 main identified sources; atmospheric diffusion, rivers and discharges from numerous sources located along the coastlines. (HELCOM, 2006). Lundberg, 2005 states that” In the year 2000, about 28,000 tons of phosphorous and 660,000 tons of nitrogen were brought to the Baltic Sea by rivers”. This accounts for nearly 75% of the total nitrogen received by the Baltic compared to Phosphorous of which over 95% is attributed to waterborne inputs (HELCOM, 2009a) Figure 3.11 shows the input figures of both Nitrogen and Phosphorous over the last 16 years with the target figures indicated within the BSAP.
Atmospheric and Direct Sources
Airborne emissions account for approximately 25% of Nitrogen inputs and between 1-5% of Phosphorous inputs, the sources of these come from shipping, agriculture combustion and transportation (HELCOM 2006). Nitrogen is emitted as either Nitrogen Oxides or Ammonia.
Effects and Remediation
With the Baltic Sea being such a vast expanse of water it's immediately clear that there were spatial and temporal variations within the distribution of nutrients. The nutrient content rose rapidly until the 1980's but all areas around the Baltic are showing evidence of decline (HELCOM, 2009a). Despite this the effects of eutrophication are still very evident at the present time. The water transparency has declined in all areas of the Baltic which suggests visible eutrophication in both coastal and open waters although Figure 3.2.1 suggests that the transparency is lower in the coastal regions. This would be expected as the majority of nutrient inputs will come from the coastlines.
Eutrophication within the Baltic has caused some significant changes to the ecosystems that thrive within it. Seagrass and perennial macroalgal communities are rich in diversity and “harbour the highest biodiversity in coastal, shallow-water ecosystems” according to the 2009 HELCOM report. The limiting of water transparency has prevented the growth of these vegetation species at depth. (HELCOM 2009a, 2006). This means there is less space to colonise and so certain species within these communities are in serious decline (Lundberg, 2005).
Oxygen depletion has been long known as a prominent effect of eutrophication. All basins bar the Gulf of Bothnia suffered from seasonal or permanent hypoxia up until 2007due to the decomposition of the algal blooms. (HELCOM 2006, HELCOM 2009)(Figure 3.2.2). This has had a subsequent effect on the biodiversity of the benthic organism's species which have disappeared in the deep waters of the Baltic Proper (HELCOM, 2009). Certain regions undergo seasonal oxygen depletion which has seen benthic and macro benthic species reduced in numbers and certain communities being unable to fully develop (HELCOM 2007, HELCOM 2009)
All bordering countries met on the 15th November 2007 so discuss how best to remediate all areas of pollution with major emphasis on eutrophication. The outcome was a document known as the ‘Baltic Sea Action Plan' (Stockholm University, 2008). Each major region was given a maximum allowance on nutrient input calculated on current inputs and the level of eutrophication. Some areas like Bothnian Bay required no changes to be made whereas the Baltic Proper needed to reduce Nitrogen inputs by 94,000 tonnes (BSAP, 2007) Overall the required reduction of Phosphorous and Nitrogen was 15,250 and 135,000 tonnes respectively (BSAP, 2007) The new levels of maximum inputs were to be reached by 2016 for Riverine and 2021 for airborne inputs (Stockholm University). Each bordering country was also assigned its own nutrient reduction requirements (BSAP, 2009). It was also agreed that countries must include into their programme the River Basin Management Plans of the EU Water Framework Directive. (BSAP, 2007)
All countries were also required to adopt two recommendations made by HELCOM for the treatment of their wastewater. These were
- HELCOM RECOMMENDATION 28E/5 - This calls for a bigger clamp down on the removal of phosphorous from the larger treatment plants as well as introducing requirements for the smaller treatment plans
- HELCOM RECOMMENDATION 28E/6 - Improved treatment of domestic waste from households and small businesses.
- HELCOM RECOMMENDATION 28E/7 - The substitution of polyphosphates in detergents to aid with the reduction of phosphates in the water (BSAP, 2007)(http://www.helcom.fi)
For the reduction of airborne inputs it was decided that each contributing country is to strengthen its targets under the EU National Emissions Ceilings Directive (which is to include the emissions released from the shipping industry) and for the 1999 Gothenburg Protocol under the UNECE Convention for Long-Range Transboundary Air Pollution (BSAP 2007). It was also agreed to identify the hot spots where the most stringent action needed to be taken. A subsequent illustration (Fig 3.2.3) has been released demonstrating this. (HELCOM, 2009a)
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It's clear that the current level of eutrophication in the Baltic Sea is at an unacceptable level. Much is being done to reverse the effects of the over enriching that took place in the 1980's and 90's and its evident that its slowly working although there is a long way to go before the waters are back to the oligotrophic state that they once were. The level of pollution is very spatial with some areas being almost clean with others having lost huge amounts of biodiversity. This means that the approach needs to be very specific to each region to ensure the whole of the Baltic is remediated effectively. The control of eutrophication also needs to be considered with relation to the other environmental problems that are currently going on such as erosion, over-fishing and toxic waste dumping (Lundberg, 2005). A combination of small scale operation combined with national objectives and measures is the key to sorting this serious problem.
- Smith - Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems - 1999
- Scholten - Eutrophication management and ecotoxicology - 2005
- HELCOM 2006
- HELCOM 2009a
- Baltic Sea Action Plan - 2007
- Lundberg - Eutrophication in the Baltic Sea - 2005
- www.environment.fi - Eutrophication in the Baltic
- Smith - Eutrophication - 2003
- Lundberg et al - The spreading of eutrophicationnext term in the eastern coast of the Gulf of Bothnia, northern previous termBaltic Seanext term - An analysis in time and space - 2009