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The justification for nutrient-enrichment being a transboundary problem is that once in the Sea, nutrients are cycled throughout the whole system as a result of dissolved materials being transported in water currents and by sequestration by phytoplankton which are also transported in currents. However, it is not only the problem of eutrophication which are shared by the surrounding countries, the causes of this problem are also shared. All discharge nutrients into the Sea both directly (industrial/municipal discharges), through river flows into the Sea, and indirectly via atmospheric emissions containing nitrogen oxides that contribute to atmospheric deposition. into the Sea. In addition to sharing the same types of nutrient sources, the same causal chain analysis can be applied on a regional and/or national basis.
The Black Sea is particularly prone to eutrophication because of its enclosed (land-locked) nature. During cold winters, relatively nutrient-rich water from the northern continental slope and shelf probably feeds the cold intermediate layer (CIL) that extends over much of the Black Sea and has a residence time of about 5.5 years (Stanev et al., 2003). Vertical mixing from the CIL may feed productivity over large areas of the Black Sea, and thus variations in winter temperatures on the shelf could have a profound effect over offshore primary production in the summer. Satellite data have also revealed significant winter phytoplankton blooms in the southern part of the sea, presumably as a result of mixing of deeper waters. This winter production may make a greater overall contribution to offshore primary production in the Black Sea than eutrophication-fuelled summer growth (Sorokin, 2002). The “natural” conditions of the Black Sea remain unknown (Mee et al, 2005).
Nutrient enrichment by itself is not a cause of concern, since there are no toxicity or other health-related issues associated with nutrient enrichment of the Sea to current or historical levels (albeit that unıonısed ammonia is very toxic). Rather, it is the biological response to nutrient enrichment that is the problem.
The biological response occurs through a number of different mechanisms. Higher nutrient concentrations in the water column result in higher phytoplankton standing crops, with consequences higher up the food chain (see Section 4.2.3). The higher phytoplankton density decreases light penetration to submerged macroalgae, which can then only receive sufficient light to continue to grow in shallower waters. In addition, growth of epiphytic algae (those growing on the thalli/fronds of seaweeds attached to the sea floor) is also stimulated, further reducing light availability to their hosts, and so further the reducing the depth at which such species/communities can survive. The most famous of these seaweeds is the red alga Phyllophora, which once formed a huge meadow covering much of the Northwest shelf, but which is now to confined to a mere fraction of its former area.
However, when the increased amount of biological matter living in the sea begins to die, the sediment becomes organically-enriched and the microbiological decomposition of this organic matter strips oxygen out of the water in previously highly oxygenated areas of the NW shelf. The resulting hypoxia can result in the death of fish, although fish are usually mobile and aware enough to escape such unfavourable conditions, but the greatest impact is on those invertebrates living on/in the sediment. Thus, a single hypoxic event, even if it lasts for only a single day, has the potential to devastate the sediment faunal community for years to come. This includes shellfisheries. Odessa Bay, once nicknamed the “Kingdom of Mussels”, has some distance to go before it can resume that title, since in extensive areas of the NW Shelf, mussels have been replaced by other invertebrates (albeit belonging to the same functional group, ie. filter-feeders), notably ascidians.
Even if hypoxic conditions do not occur in the water column, the organic enrichment of both water and sediment results in ecological changes, e.g. heterotrophic phytoplankton (notably Noctiluca spp.) increase greatly in number and biomass and there is a shift to sediment fauna which are more tolerant of low oxygen conditions away from those requiring higher dissolved oxygen levels. |
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Eutrophication favours the dominance of some species over others, in fish, benthic zooplankton, phytoplankton and macroalgal communities. In Zernov’s Phyllophora field, Phyllophora nervosa had previously existed in such large quantities that it was exploited commercially as a source of alginates. However, preliminary results from the July/August 2006 BSERP research cruise show that while Phyllophora brodiaei is present, it is rarely the dominant species. At shallow depths, the filamentous red alga Polysiphonia sp. becomes increasingly prevalent, sometimes growing as an epiphyte on Phyllophora. Huge numbers of ascidians (sea squirts; primitive filter-feeding invertebrates) are also found in deeper parts of the former Phyllophora field (abundances as large as 300 individuals/m2), benefiting from the organically-enriched environment.
In other parts of the former field, Phyllophora has been replaced by filamentous red (Polysiphonia)andgreen (Ectocarpus confervodes and Desmarestia viridis) algae; species indicative of nutrient-enriched conditions. Excessive growth of Cladophora sp, another filamentous green alga indicative of nutrient-enrichment, is also reported in both western and eastern parts of the Black Sea (e.g. Karkinitsky Bay and Anapa bay, respectively).
Thus, the NW Shelf has not returned to its former (1960s) state, dominated by Phyllophora nervosa, but is instead now dominated by opportunistic filamentous algae, with very smaller areas of Phyllophora. This is not necessarily bad, since the opportunistic seaweeds may well be an intermediate step towards a more stable system. However, they still represent eutrophic conditions, albeit less serious than those represented by the monospecific phytoplankton blooms of the 1980s. Indeed the fact that there are fairly abundant benthic algae shows that transparency of the water column is sufficient to allow Phyllophora to re-establish, providing the level of nutrient enrichment can be reduced.
Current opinion is that too many niches have been filled by opportunistic and/or invasive species to make it likely that the Black Sea will ever recover to exactly how it was in the 1960s. The question therefore is whether or not the Black Sea ecosystem is ‘healthier’ than it was during the ‘dark’ years of the 1980s. There appears greater transparency of the water and this is leading to renewed growth of benthic algae, albeit species that may have been regarded as a nuisance at other times (but under the current circumstances have an important function). Dissolved oxygen concentrations in bottom waters are not as great a cause of concern as they once were, since hypoxic conditions no longer equate to ‘dead zones’. Gelatinous organisms continue to abound in the water column, including the common jellyfish Aurelia aurita (just above the sea floor), the invasive comb jellies Mnemiopsis leydi and Beroe ovata,and benthic tunicates. Heterotrophic phytoplankton continue to form intense blooms, notably at the outer edges of riverine influence, but overall there appears to be a trend away from dense monospecific phytoplankton blooms to a more diverse phytoplankton community in many areas.
The NW shelf now appears to contain a heavily altered but relatively functional ecosystem when compared to the 1960s. Nevertheless, symptoms of dysfunction are still evident, such as the inability of the system to recycle the high load of organic material it receives/produces in some areas, and the continuing dominance of monospecific phytoplankton blooms in other areas. At this stage the Black Sea is a long way removed from being ‘totally recovered’ and requires further protection from human pressure as it adapts to the new reality and the new species that have settled in it.
Fisheries productivity almost certainly increased as a consequence of eutrophication, due to the additional energy provided by increased phytoplankton growth being transported up the food chain, so is likely to decrease as trophic status falls. The implications of this for the fishing industry, however, are not clear, since the improved oxygen status of much of the NW shelf is likely to have had a stimulatory effect on fisheries generally in terms of the expansion of available spawning nursery areas, but an even more favourable effect on demersal fish species in particular because of the greater area available for living and feeding.
The impact of improved trophic status on the existing shellfish industry is likely to have been great in the NW Shelf area because of the much greater area for shellfish production, but of lesser importance in other parts of the Black Sea. However, it is essential that bacterial pollution is tackled in shallow coastal water ecosystems if future benefits are to be accrued, that environmentally sustainable aquaculture methods are utilised and that non-destructive harvesting methods are employed. Only then will the potential socio-economic benefits be fully realised.
Available data do not provide clear evidence of whether there has been an impact on the tourist trade, but the growth of filamentous green algal beds along some shores is unlikely to have been conducive in persuading tourists to return to coastal hotels/resorts. Improved biodiversity in coastal waters and fringe wetland ecosystems as a result of reduced trophic status is likely to result in increased numbers of tourists, albeit a more specialised sub-sector of tourists than those which the Black Sea has attracted during much of the last 20-30 years. Eco-tourism advertising, whether directed at single issue customers or as a compenent of wider rest/relaxation packages, has the potential to generate a small but increasing funding stream for coastal communities.
The socio-economic impacts of changing agricultural management to control nutrient status of the Black Sea have probably had a greater impact than the changes which have occurred in any other economic sector. They therefore require special attention. Change in farmıng practices resulted in worsening trophic status during the mid-1970s to 1980s, after which a very abrupt reversal of those practices occurred. The overall result, pre- and post-1990, has been a huge population shift and major changes in rural community demographics.
Increased mechanisation/industrialisation of farming during the 1970s and 1980s required fewer workers, resulting in a large-scale migration of predominantly young male workers from rural to urban areas. This trend was exacerbated by the economic collapse of the late 80s, its bequest to the 1990s and its continuing impact. Thus, a rural-urban migration trend still continues, albeit one which has slowed in many countries. This has left a high percentage of female and older residents in rural villages. One national example of how this pattern has evolved is shown in Table 4.2 for Romania where, since 1960, the proportion of the population relying on employment within the agricultural sector has halved.
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Nutrient over-enrichment/eutrophication in the Black Sea is closely linked to the transboundary problems of changes in marine living resources (Section 4.3), chemical pollution (Section 4.4) and biodiversity/habitat changes (Section 4.5). For chemical pollution, the explanation is simple: nutrient and (other) chemical share many of thethe same causes and sources. However, the links between nutrient enrichment and changes in marine living resources/ biodiversity are more complex.
In general terms, zooplankton feed on phytoplankton, and young fish/larvae feed on zooplankton, which are themselves eaten by other fish. Phytoplankton biomass in the 1970s and 1980s was far greater than in the 1960s, with a decreasing trend since 1990.
However, during the 1970s and 1980s, there should not only have been an increase in the standing crop of phytoplankton as nutrient levels increased, there should also have been an increase in the standing crop of zooplankton and fish, as the energy from the increased biomass of phytoplankton was carried up through the food chain. The problem with such simple explanations is that nutrient enrichment/eutrophication does not operate in isolation as an environmental problem. For example, the plankton results presented in Section 3.3.2 clearly show that invasive species impact on trophic status indicators such as phytoplankton and zooplankton biomass. In Section 4.5.4.3 it is noted that eutrophication has been underestimated as a threat to biodiversity in the Black Sea because of misunderstandings of how different factors interact to impact on biota. The Mnemiopsis invasion in the 1980s (Section 3.3.2) brought with it a decrease in fishery productivity, since fewer fish larvae survived to grow into adults and there was less food available for those fish that did survive.
Whilst eutrophication is considered to be the result of nutrient-enrichment, one of its most severe effects is the development of hypoxic conditions as a result of the production and breakdown of organic matter. A consequence of this is dramatically reduced benthic biodiversity. Organic matter is produced primarily as a result of photosynthesis by phytoplankton, but organic (BOD5 and total organic carbon) loads from land, discharged to the Sea via rivers and outfalls, also exacerbate the problem.
Referring back to Section 3.3.2, organic enrichment has resulted in the development of large populations of non-phytoplankton eating Noctiluca along the Western edge of the Black Sea. This planktonic organism has to a large extent occupied the ecological niche formerly occupied by phytoplankton-eating zooplankton. Thus, remote-sensing imagery of chlorophyll-like substances indicate higher levels of phytoplankton in this area than in other shallow areas of the Black Sea, .e.g. Fig. 4.1.
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Figure 4.1 Chlorophyll-like substance concentrations in the Black Sea, May 2004  |
All ecological communities demonstrate a resistance to change, resilience, as external pressures on them change. These pressures come in all sorts of forms, such as invasive species, nutrient and organic enrichment, toxic pollutants, changes in climatic conditions, etc. Resilience does have its limits, however, and the collapse of the benthic ecosystem in huge areas of the NW Shelf throughout the 1970s-early 1990s clearly demonstrated this. |
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Fig. 4.2 shows the results of a causal chain analysis of nutrient enrichment of the Black Sea. The results of this analysis are described in Sections 4.2.4.1-4.2.4.10 and 4.2.5.
The immediate causes of nutrient enrichment are changes (increases) in the nutrient loads from different sources. Nutrients are derived from a variety of sources (Table 4.3):
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Figure 4.2 Causal chain analysis for nutrient enrichment |
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Coastal development has been recognised as a cause of environmental degradation throughout Western Europe, with the recent publication of a report by the European Environment Agency (EEA, 2006) highlighting this issue as a common European concern. This is regarded as an underlying or immediate cause of coastal habitat destruction, nutrient and toxic substance export to the sea, and therefore a contributory factor to changes in the patterns of fish/shellfish production and harvests.
A brief tour around the coast of the Sea illustrates the scale of coastal development. Existing towns are sprawling further along the coast and new small communities are being built. In the future these may form the seeds of new villages or merge into the suburbs of expanding towns. With summer populations in resorts being typically 3 times greater than winter resident populations, there is a need to build sewerage systems and treatment works that can cope with the peak seasonal demands placed on them.
The vast majority of industrial plants are connected to municipal sewerage systems, so the nutrient exported are included within the nutrient loads measured for sewage treatment works discharging to the sea. Relatively few industrial plants discharge directly to the Sea and, of these, data were requested only for major industrial discharges – those with an average discharge in excess of 1000 m3/day. Likewise, data were requested from national experts only for municipal sewage treatment works/sewerage system discharges –serving a population of at least 5000 people (i.e. with a dry weather discharge of approximately 1000 m3/day). Summary results of these are shown in Table 4.4. In the case of industry, perhaps, these results are not surprising, since a manufacturing/processing plant producing that volume of wastewater is likely to be a large facility and industrial discharge data were not provided by two countries. However, the load from sewage treatment works/municipal discharges probably represents the great majority of the load from all coastal sewerage systems, and these values appear to be relatively low. To put the calculated municipal nutrient loads into perspective, they represent the expected loads of a population of only about 1 million people, compared to a coastal population of some 7 million inhabitants that are actually connected to sewerage systems discharging directly into the Sea (Section 3.2.1). |
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In the 1960s the former Soviet countries developed cooperative agricultural farming practices, containing relatively small numbers of livestock, bred and maintained using ‘traditional’ animal husbandry systems. A large part of the manure/waste from these (a mixture of excreta, bedding and feed residues) was applied on cooperative land, as organic fertiliser for crops. However, during the 1970s and 1980s large stock-breeding farms were built, using industrial methods of operation. To give an extreme example of the scale of this agricultural industrialisation, a single Romanian farm contained over 1.2 million pigs.
These intensive livestock farms were usually located close to rivers, into which the manure and waste was discharged. The role of livestock excreta as a valuable organic fertiliser was therefore transformed into one of being a problematic pollution source , particularly for nutrients and biodegradable organic matter, the breakdown of which strips oxygen out of fresh and marine waters..
During the 1970s and 1980s the increase of livestock numbers in state cooperative farms (except Turkey) was often combined with changes in farming practices from farmyard manure to slurry-based systems – producing more nutrient-rich and readily biodegradable waste. Manure/slurry which was not discharged to rivers, was disposed of to land without being used as fertiliser, and so remained as a potential source of pollution. At the same time soil nutrient testing was introduced and fertilization rates were first recommended both to meet the needs of crops and to re-establish soil reserves. However, this type of crop management was in its infancy, was economically (rather than environmentally) driven and mistakes were made. The result of these changing policies and practices was to increase nutrient losses to rivers draining the fields, to ground waters and to the Black Sea itself.
At about the same time, increasingly greater amounts of inorganic mineral fertilisers began to be used because they were more economic and easier to apply. Following the economic crisis, the collapse of the Soviet Union and birth of the independent countries of Bulgaria, Georgia, Romania, the Russian Federation and Ukraine in the early 1990s, a major increase in subsistence farming occurred, with the ex-Soviet farms reducing in both number and size. This occurred in parallel with an end to centralised state subsidies for the use of inorganic fertilisers.
Table 4.5 shows that huge changes in livestock numbers have occurred in Black Sea coastal countries since 1960. For this table, attention should be diverted away from the actual values themselves, because of problems involved in obtaining data for the entire national coastal country Black Sea sub-basins (see footnotes to table). However, percentage changes in livestock numbers presented in the table can be used as a good indicator of change during the 1960-2003 period. For example, livestock numbers reached a clear maximum in 1988, just prior to the economic collapse, falling sharply to the situation in 1997, since when numbers of cattle, pigs, sheep and goats continued to fall further until 2003 (by 33, 26 and 31%, respectively). Only numbers of poultry increased (by 23% over the same period). Comparing the 1988-2003 period, numbers of cattle fell by by 64%, pigs by 62%, sheep and goats by 67% and poultry by 21%. The 2003 situation shows a major decrease in mammalian livestock numbers (44-67%) compared with the 1960 values.
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| * Russian Federeatiion data for 1998 were not available, the values shown therefore include Russian Federation data from 1990 |
The increasing costs of sheep production in particular have resulted in lower consumer demand for lamb products. The number of poultry has increased dramatically since 1960 due to the adoption of more intensive and cheaper production practices, bringing with them increasing demand.
When compared to the livestock figures (Table 4.5), similarly dramatic changes have happened with regard to the use of inorganic fertilisers in arable farming. This is shown dramatically by Romanian data (Table 4.6). In 1960 only very low levels of inorganic fertilisers were applied, but by 1988 the amount of inorganic nitrogen fertiliser had increased 27-fold and inorganic phosphorus fertiliser 7-fold. Following the economic collapse and independence of Romania, fertiliser application rates fell to below the levels applied in 1970, with a continuing decrease still evident in 2003. Levels applied in 2003 were about one third of those applied in 1988.
Statistics from the 2005 World Bank World Development Indicators
database show that during the early 2000s fertiliser application rates were substantially higher in Turkey than in other Black Sea countries. Bulgaria, Georgia and Romania formed a middle group and lowest fertiliser application rates were found in the Russian Federation and Ukraine (Fig. 4.3). Although these data were provided by national governments to the World Bank and can, therefore, be recognised as official, there is some concern over their accuracy. For example, the Turkish and Georgian values appear to be higher than expected, while the Russian values may not be applicable for the country’s Black Sea sub-catchment, bearing in mind the national importance of Krasnodar Krai as an agricultural region. However, the data presented could also reflect the relative importance of different crops in individual countries and the varying nutrient requirements of those crops.
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Figure 4.3 Fertliser application rates per hectare of arable land |
An assessment of fertiliser application rates for Black Sea coastal administrative areas is effectively impossible to make because only three countries provided any information (Georgia, Romania and Russia). Even amongst these datasets there were differences in the manner in which data were reported, crop types and years for which data were available and differences in how organic/inorganic fertiliser data were combined. Nevertheless, it appears that between 1997 and 2004, inorganic fertiliser application rates have increased for cereal, oilseed and leguminous (bean and pea) crop production. So, although based on a weak data set, and with the need to develop robust arable farming indicators for use by all coastal countries, the decline in arable productivity may now be reversing. If this is true, then improved regulation of arable agriculture would be an important step in future environmental management.
In terms of nutrient pollution, livestock farming probably represents a higher priority to tackle than arable farming. Nutrients need to be applied to land when crops are able to utilise them, so over-winter storage facilities for livestock manure/slurry is essential if this source of nutrients is to be tackled. In effect, this requires farms to have storage facilities for at least 6 months of manure/slurry production.
However, changed nutrient applications to land are not generally mirrored by spontaneous parallel changes in nutrient export from land to rivers, groundwater and the Sea. Changed application rates are reflected in emissions only after a lag period, as excess nutrients present in the soil are gradually “flushed out” of the terrestrial system or taken up by crops. Fig. 4.4 suggests that much of the excess phosphorus in soils would probably have been exported from land in surface water runoff within a few years.
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Figure 4.4 River Danube annual inorganic nitrogen and total phosphorus loads (corrected for annual discharge) to the Black Sea (1989-2005) |
However, the far greater solubility of nitrogenous salts (which do not adsorb onto soil/geological substrates) has meant that much of the organic/inorganic nitrogen applied to land has leached to groundwater, rather than exported directly to surface waters (rivers, lakes and the Sea itself). Thus, the contribution of groundwater to river flows and direct submarine discharges implies that even decades after being applied to land, nitrogen from this original source could still make a large contribution to the nitrogen budget of the Sea.
Even if agricultural management practices are revised, the lengthy delay period introduced by ‘storage’ of inorganic nitrogen in groundwater before improvements in emissions can be realised make this a difficult source to tackle, particularly from a political viewpoint, since costs and benefits are usually assessed over a much shorter timescale. However, this is essential if eutrophication of the Black is to be tackled seriously by Regional governments. |
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The majority of the human population in the 6 national Black Sea sub-catchments is probably connected to sewerage systems (see Section 3.2 for statistics on coastal administrative areas), but the proportion will obviously vary from country to country, depending on the ratio of rural:urban population numbers, topography and capital investments.
The vast majority of phosphorus in the wastes of unsewered population will be retained in soils, since the waste is buried and the phosphate binds to the soil. However, where the population overlies unconfined aquifers, a relatively large proportion of the nitrogen will be released into interstitial water within the soil and can migrate to groundwaters. Groundwater acts as both a storage and transport system for inorganic nitrogen; so, once in an aquifer, it is likely that the nitrogen (or a large proportion of it) will eventually be transported to river or discharged directly to the sea. However natural denitrification in aquifers can vary greatly, meaning that the proportion of nitrate entering an aquifer to that is exported to surface waters can range from less than 70% to almost 100%. As with submarine discharges (Section 4.2.4.9) no estimates can be made of this contribution to the nutrient budget (Section 4.2.4.10), other than the unsewered population contribution to in-river loads discussed in Section 4.2.4.8).
Considerable progress is being made in some countries in terms of the proportion of the population connected to sewerage systems, and inevitably this values falls behind the proportion of population served by WWT plants. In Romania and Bulgara, all populations of >2,000 people will need to be sewered and served by WWTPs in compliance with the EU UWWT Directive. In the Turkish Western Black Sea Region, the proportion of the municipal population connected to sewer increased from 83 to 90% between 1998 and 2004, while the proportion served by WWTPs increased from 4 to 15%. Over the same time period in the Turkish Eastern Black Sea Region, the proportion connected to sewer increased from 66 to 71%, and the number served by WWTPs rose from 10 to 18% (TSI, 2004). While the proportions served by WWTPs may appear low, the costs of building sewerage systems are many times those of building the WWTPs to serve them, so these values represent huge national financial investments. |
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Some export of nutrients from land is natural, but no estimates of this are known to have been made for the Black Sea region. However, workers in Western Europe have identified what they judge to be ‘quasi-pristine’ rivers, calculated the instream phosphorus loads and expressed these as export coefficients. The values cited may include some contribution from a limited number of small point sources as well as from anthopogenically-derived diffuse sources in the catchment.
The larger the drainage basin, the lower the proportion of nutrients that are eventually transported to seas, so for Black Sea, real natural export coefficients will almost certainly be lower than those discussed in the footnote below. If natural export coefficients of 0.025 kg PO4-P/ha and 0.25 kg DIN/ha are selected and multiplied by the catchment area of the Sea (drainage area minus the surface area of the Sea itself), natural annual loads are approximately 3,630 tonnes PO4-P and 36,300 tonnes DIN can be estimated, the vast majority of which are already accounted for in river loads (Section 4.2.4.8). These values represent approximately 20% of the calculated river-borne P load and 10% of the river-borne DIN load. These results can be compared with the more complex modelling methodology employed by Kroiss et al (2005), who estimated natural sources of N and P to represent 8% of total nutrient emissions to the Danube River.
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Atmospheric deposition is a substantial source of nitrogen (deriving principally from the combustion of fossil fuels [vehicles, power generation, etc] and from agricultural atmospheric emissions), but not of phosphorus. Previous monitoring studies have suggested a wide range of atmospheric nitrogen deposition rates for the Black Sea, with modelling studies also intimating that a broad range of nitrogen deposition rates could be applicable throughout the region and over the Black Sea itself.
A recent nutrient budget for the NW shelf (Mee et al, 2005), indicated nitrogen deposition rates of 4.8-10.2 kg N/ha, based on data provided by Sofief et al (1994). Multiplying these values up from the 50,000 km2 of the NW Shelf as used by Mee et al to the 423,000 km2 surface area of the whole Black Sea (excluding the Sea of Azov) provides an air-borne load estimate of 203,040–431,460 tonnes N/year. |
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Nutrients may enter the Black Sea from both authorized landfills and illegal dumping of solid waste near to the shore. Nutrients from this source could enter the Sea either in overland runoff or via groundwater discharges. However, it has not been possible to make an estimate of nutrient loads entering the Sea from such sources, since the loads from individual sites differ enormously, depending on the design criteria of authorized landfills, local topography, geology, precipitation statistics, mass/volume and type of waste dumped, etc. |
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Once in rivers and the Sea itself, during periods of elevated nutrient loading, huge reservoirs of nitrogen and phosphorus build up in the sediment and form a source for years to come. In the marine environment there is no “rule of thumb” to estimate how long this period will be, but in lakes which undergo a large sudden decrease in phosphorus loadings, a useful estimate is that it takes in the order of 5 years for sediments to switch from being a net source to a net sink of phosphorus (Sas, 1989), but for estuarine and coastal systems, and for nitrogen, the situation is more complex.
From recent (2006) measurements of sediment-water fluxes in the NW Shelf (Friedrich, 2007) the state of the benthic system along the Romanian and Ukrainian coast of the Black Sea has improved as the bottom water is now more oxygenated than about 10 years ago. However, benthic nutrient fluxes resulting from the decomposition of organic matter within the sediment are still at levels comparable with those from the mid 1990s. The release of nutrients from the sediments continues to fuel productivity within the Sea itself. Parts of the Phyllophora field appear to be recovering. A healthy benthic ecosystem with plants and animals in balance releases less organic and inorganic nutrients to the overlaying water than a disturbed system without macrobenthic life. Phyllophora (and other benthic macroalgae) play an important role in taking up nutrients released from the sediments and supplying the benthic system with oxygen (Friedrich, 2007).
Benthic nutrient recycling is a significant internal nutrient source for the pelagic system of the NW shelf, sustaining high productivity by the release of nutrients from the sediment. For phosphorus this sediment→water flux is of the same order of magnitude as river inputs, albeit that the sediment→water flux of nitrogen is only about 10% of the river-borne load (Mee et al, 2005). However, in 2006 only a very low phosphorus flux from the sediment to the water column was observed in front of the Dniester mouth, on this occasion/site at least, since phosphate appeared to be adsorbed by the ferric hydroxides visible at the sediment surface (Friedrich, 2007).
Despite there being quantitative estimates of sediment-water nutrient fluxes for the NW shelf, similar estimates are not available for other shelf areas around the Black Sea coast and no information is available on fluxes from deep sediments in the main body of the Black Sea. Consequently no estimates of sediment-water nutrient exchange can be produced for the Sea as a whole for comparison with other sources in Section 4.2.4.10. |
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Because of missing flow (See Section 3.1.5) and/or concentration data from some years, only data from a 3-year period (2003-2005) are provided to present a regional overview of nutrient loads to the Black Sea. This is the period for which most information exists, although data are still missing for some rivers. For Georgian rivers the flow data used are long-term averages measured prior to 1993, and flow monitoring of the Tuapse River, Russia was discontinued in 1996 (Table 3.3). Loads from other rivers are based on very few concentration data and, worryingly, estimates for other rivers (e.g. the Supsa and Khobi) are are absent. However, these are relatively small rivers and therefore likely to contribute comparatively small loads.
To present data for as many rivers as possible , PO4-P loads for Russian rivers are shown as half of total P loads. Total P is the preferred parameter for estimating phosphorus loads to the Sea, but total P data were available for a smaller number of rivers than were PO4-P data. Nevertheless, Table 4.7 shows the Danube to be by far the largest riverine contributor of nutrients to the Black Sea, responsible for about 50% of the total river-borne phosphate load and approaching 90% of the total river-borne DIN load.
Considering the emphasis placed on river and strait nutrient loads in the 1996 TDA and SAP, it is unfortunate that substantially improved data were not provided by all countries for this analysis.
To assess trends in river-borne nutrient loads to the Black Sea since the last TDA was produced, Fig. 4.5 shows the total river loads of nutrients in those rivers for which annual load data are avaılable for every year from 1996 to 2005. For PO4-P, this includes the rivers Rioni, Tchorokhi, Danube, Sakarya, Dniepro, Southern Bug and Dniester; and for inorganic nitrogen the rivers Rioni, Tchorokhi, Danube, Sakarya, Dnipro, Southern Bug and Dniester. Assuming that the same pattern of change has applied to all rivers draining into the Black Sea, a linear regression through these combined annual loads suggests that there has been little change in river-borne DIN loads to the.Sea, with a moderate (15%) decrease in river-borne PO4-P loads over the same period. However, the level of confidence associated with the PO4-P load decrease is very low, due to the large inter-annual variability.
Considering that the Danube is such a major pathway of nutrient input to the Black Sea and that phosphorus emissions to the Danube are estimated to have fallen by approaching 50% between 1990 and 2000, and nitrogen emissions by about 20% between 1985 and 2000 (http://danubs.tuwien.at/), this may appear to be disappointing result. However, reductions in nutrient loads/concentrations in the upper and middle reaches of the Danube have been observed since 2000, and these improvements are expected to continue downstream in future years (Anon 2006).
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Figure 4.5 Trends in river nutrient loads to the Black Sea, 1996-2005 |
The Istanbul Strait effectively consists of two layers: an upper stratum flowing out of the Black Sea and a lower, denser layer flowing into the Sea. According to the Master Plan and Investment Strategy for the Marmara Basin project results; the total nitrogen load from the Black Sea to the Sea of Marmara is 79 ktonnes/year and the nitrogen load from Sea of Marmara to the Black Sea is about 58 ktonnes/year. The total phosphorus load from the Black Sea to the Sea of Marmara is 13 ktonnes/year and phosphorus load from Sea of Marmara to the Black Sea is about 12 ktonnes/year. This makes the Istanbul Strait the second largest input of nutrients to the Black Sea, with phosphorus inputs that in recent years have been lower than those from the Danube, but which during 2000-2001 were of a similar level. However, nitrogen loads to the Black Sea via the Istanbul Strait have been very much lower than those via the Danube.
Nutrient (and other chemical) inputs to the Black Sea via the Istanbul Strait are “discharged” below the themocline/halocline, with monitoring results suggesting that this pollution load has little impact on surface water quality around the Black Sea entrance to the Strait. However, once in the lower waters/sediment of the Sea, a considerable proportion of these nutrients are likely to be recycled into surface waters via upwelling currents.
The absence of data for the Kerch Strait represent a major gap in our knowledge of the Region. This information is collected, but has not been provided.
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No estimate of submarine groundwater discharges of nitrogen are known to have been undertaken. However, such discharges would be included in diffusive sediment-water fluxes, as discussed in Section 4.2.4.7 |
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Table 4.8 shows a comparison of nutrient loads to the Black Sea from four major sources. The river loads include sub-loads from a variety of land-based sources (agriculture, sewered/unsewred populations, direct industrial discharges to rivers). The contribution of natural background export from land is not possible to estimate without a validated and calibrated model. Nevertheless, the table indicates a huge contribution of nitrogen from atmospheric deposition, albeit that there is considerable uncertainty about this estimate (Section 4.2.4.5).
However, a nutrient source apportionment study using the MONERIS model for the entire Danube basin (Kroiss et al, 2005) provides interesting results. These show that in the Danube (which provides about 70% of the freshwater inflow to the Black Sea), 45% of the N and 33% of the P are derived from agriculture (both arable and livestock farming); 32% of N and 56% of P are derived from urban settlements (both sewered and unsewered settlements): 8% of both N and P emissions are considered to be of natural origin; and 16% of N and 3% P are derived from other diffuse sources (e.g. forestry and small unsewered communities). |
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The underlying socio-economic drivers for nutrient enrichment can be divided into funding and policy development/enforcement of the major sectoral groups responsible for nutrient production and export to the sea. These can be largely grouped into two categories corresponding to point sources (industry and urbanisation; Section 4.2.5.1) and diffuse sources (agriculture, atmospheric deposition, internal loading from sediments; Section 4.2.5.2).
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There are very few large direct discharges of industrial wastewater to the Black Sea, However, information on monitoring of and compliance with standards for the discharge of nutrients to sewer from industry has not been made available, so it is difficult to estimate the industrial contribution to municipal sewage treatment works effluent.
A wide variety of estimates have been made for domestic sewage treatment works around the world, but most of these methods rely on subtracting the assumed domestic loads (modelled using per capita nutrient export coefficients) from the load in raw sewerage entering sewage treatment works. Given that there is so much uncertainty over the selection of such export coefficients, with further uncertainties over the contribution of detergent-derived phosphate to domestic loads, as well as sewer leakage, a broad range of industry-derived nutrient load estimates is available. Alternative modelling approaches are also available, using industry-specific nutrient export coefficients. Indeed, one such method was used in the 1996 Black Sea TDA, but such approaches require detailed knowledge of all industrial operations/plants, which is rarely available.
Despite it not being possible to differentiate between the relative contributions of municipal and industrial discharges, the underlying causes for both remain similar:
- Poor understanding of the “carrying capacity” of receiving waters downstream of discharges.
- Either a low level of environmental awareness or low positioning of environmental quality on the political agenda, due to strong competition for funding from other ministries with more politically urgent requirements.
- Lack of consideration of the Sea itself as a receiving waterbody for municipal/industrial discharges to river.
- A lack of willingness to impose more stringent enforcement of legislation because of the socio-economic consequences (closure of factories, increased unemployment, etc.).
- Low penalties for failing to meet discharge standards, meaning that cost-benefit study results have been heavily weighted in favour of “no investment required” results
- For industrial discharges to sewer, poor regulation (monitoring and enforcement of existing norms) relating to nutrient loads to sewer and a lack of planning/enforcement
- Uncoordinated coastal development and associated tourism, leading to over-loaded sewage treatment facilities that are able offer only partial treatment of the effluent they receive.
- Poor financing of wastewater treatment facilities, either through low service charges to industrial or municipal users or through the re-direction of fees collected for other purposes.
- Poor investment in regulation/monitoring of discharges, meaning that quality-assured results to allow enforcement of existing legislation have often not been available.
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Historically, agricultural management bore little consideration to environmental impacts; cost-efficiency and socio-economic considerations (employment) were the major drivers behind decisions that were made at policy level. Thus, state subsidies for inorganic fertiliser application were available in five of the six Black Sea countries. The amount of fertiliser applied was, sensibly, based on crop nutrient balances, but the result was widescale over-fertilisation, leaving nutrient surpluses in soil that were just too great to be contained, so increasing amounts of nutrients were either leached or exported in surface run-off. The concept of best agricultural practice, encompassing both economic and environmental considerations had not been embraced at any level.
Even though some guidance was available to promote improved environmental management (e.g. on the construction of winter manure stores, to prevent the direct application of manure to frozen land, from where nutrients and organic waste would be washed off during snowmelt, if not before) this was often not followed and rarely enforced. The emphasis was often either on guidance or a failure to enforce legislation, meaning that penalties for non-compliance were scarcely introduced, thereby stimulating a culture of non-awareness of environmental consequences. The root causes are once again financial.
Mis-management of livestock farming meant that ever increasing numbers of livestock were concentrated on fewer major farms. A failure to enforce existing legislation resulted in the manure generated being insufficiently treated, and unwisely disposed of – often by collection and dumping of large manure piles on land or discharge to rivers. The result was that the main centres of livestock and arable production became increasingly isolated from each, and it became uneconomic to transport the huge manure surpluses generated in some areas to arable farms located large distances away. Because of economic considerations, there was also a move away from solid manure-based farming practices to slurry-based systems, which further increased the nutrient content of animal waste, due to changes in animal diet/size.
Then, with the economic collapse, break-up of the Soviet Union and an end to state-subsidies, the level of inorganic fertiliser usage plummeted, almost overnight. Large-scale livestock production units decreased in size or closed down completely as the market for meat products collapsed. Customers could no longer afford this level of “luxury”. Trends in GDP and GNI per capita statistics (Section 3.2) suggest more recent increase in personal wealth with which to purchase food, but the middle class in Black Sea countries tends be of a small size, with this increased personal wealth belonging predominantly to a very small but very wealthy upper class.
Small-scale subsistence farming (a few livestock per household) became increasingly important, and effectively impossible to regulate or manage. Many farmers on this scale lack the equipment (tractors) necessary to move the manure produced any distance and apply it to arable land where it would be useful, although many small farms do exist. The overall result has been one of diminished government control of farming. In addition to this, the manure from livestock kept in owners gardens – a common feature of urban life - is sometimes disposed of to sewer, helping to over-burden already struggling municipal sewage treatment works.
Large areas of once productive arable land were either left fallow or abandoned, with some begining to convert back naturally to scrubland. However, the new status of Bulgaria and Romania as EU Member States, combined with the low wages of agricultural workers is likely to stimulate foreign investment in the agricultural sectors of these countries to produce food for export.
It is unclear why such large changes in the agricultural sector have occurred in Turkey, when there never were such centralised state subsidies for agriculture and the population has continued to increase. The regional economic collapse would almost certainly have contributed to such changes, so once again changes in the import-export balance of agricultural products or changes in diet appear to be at the root of this change.
Currently, there is a lack of good agricultural management and poor awareness of good environmental practice. Bulgaria, Romania and Turkey intend to fully comply with the EU Nitrates Directive, requiring the introduction of Best Agricultural Practice, but the larger the number of farms and the smaller their size, the more difficult such legislation will be to enforce. The development of national soil monitoring programmes and improved advice to optimize inorganic and organic fertiliser application for arable crop production are required. |
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- No information is known on groundwater flows or direct groundwater loads of inorganic nitrogen loads to the Black Sea. In addition, the groundwater contribution to the Danube load is estimated to be 47% of the flow, but the contribution of groundwater to the loads of other rivers to the Black Sea has not been estimated. This is important to understanding the likely effectiveness of management options to control diffuse source-derived nitrogen.
- The contribution of industry-derived nutrient loads to municipal sewage treatment works loads is unknown. Based on available data, modeling of such loads is likely to produce very inaccurate results.
- It is not clear whether the perceived increased importance of subsistence farming in the region is adequately reflected in official livestock statistics.
- The contribution of different sources to river-borne nutrient loads for most rivers is unclear.
- Information on nutrient loads to/from the Black Sea via the Kerch Straits was not received for this report.
The river Danube is by far the single largest source of nutrients to the Black Sea, carrying some 50% of the river-borne PO4-P load and approaching 90% of the river-borne inorganic nitrogen load.
Major changes in livestock and arable farming have occurred throughout the Region since the late 1980s. There has been a major and continuous decrease in livestock numbers, and therefore in the production of livestock manure as a source of pollution. Agriculture is now much less intensive than it was in the late-1980s but some indicators suggest that the decline in arable agricultural productivity has bottomed-out and the region may be facing a renewed period of increasing inorganic fertiliser use.
The measured nutrient loads from coastal point sources (direct municipal and industrial discharges) are a tiny fraction of the load from rivers to the Sea, but these values are almost certainly under-estimates. Nevertheless, capital investments to upgrade coastal hot-spots are likely to have had a relatively small effect on transboundary nutrient pollution, particularly of nitrogen, even though local environmental improvements are likely to be much greater. This highlights a fundamental problem in the approach of the 1996 TDA, which focused heavily on direct marine discharges.
The Istanbul Strait effectively consists of two layers: an upper stratum flowing out of the Black Sea and a lower, denser layer flowing into the Sea. A substantial proportion of the wastewater effluent of Istanbul (a city of 15 million people) is discharged intoto the Strait contributing to it being the second largest source of nutrients to the Sea, and in some years rivalling the Danube as the largest phoshorus source to the Sea.
The environmental requirements for EU membership should result in substantial improvements in nutrient emissions from land based sources for Bulgaria and Romania within the next 15 years. Turkey has only recently started EU accession talks but its willingness to comply with the EU Water Framework Directive should also bring about substantial improvements.
However, EU accession/membership is not a one-sided issue in terms of eutrophication. The EU Urban Wastewater Treatment Directive requires all populations of 2,000 inhabitants or more to be connected to sewer systems. For currently unsewered populations of this size, this is likely to increase nutrient emissions to rivers and the Sea itself, since the nutrient removal efficiency of sewage treatment works (for phosphorus at least) is likely to be lower than that currently provided by soil/groundwater.
Capital investments and improved regulation of agriculture continue to be necessary. A shift in emphasis away from coastal sources/inputs of nutrients to an integrated basin-wide approach is required in the long-term to tackle the problem of nutrient-enrichment/eutrophication, as has been started in the Danube River Basin.
An emphasis of the original TDA in 1996 was on nutrient source apportionment and control, as was the 1996 SAP and the updated SAP in 2003. Efforts have been made to improve the understanding of this issue, but it is still important to collect and/or make available good quality data to quantify the various sources of nutrients in order to develop robust management plans.
The following recommendations are suggested in order to respond to the issue of nutrient overenrichment/eutrophication:
- Develop and gradually implement sanitation programmes in all coastal human settlements around the Black Sea.
- Construct and/or upgrade wastewater treatment plants for major industries.
- Phase out phosphate-containing detergents from the Black Sea region.
- Introduce and promote Integrated Prevention and Pollution Control principles to prevent atmospheric discharges from industrial sources.
- Introduce and/or disseminate principles and guidelines for best agriculture practice, including the compulsory requirement of storage facilities on farms, capable of holding 6 months manure production.
- Introduce environmentally sound regulations for the design and operation of large animal farms.
- Introduce and implement national regulations on manure and fertiliser handling and application.
- Develop and introduce national systems of economic incentives and disincentives for reducing nitrogen and phosphorous releases to the environment.
- Focus public awareness, educational and access to information campaigns on nutrient pollution, particularly from agriculture.
- Develop national nutrient pollution reduction programmes.
- Consider the Black Sea as a receiving waterbody when setting discharge standards for all municipal/industrial sources in the Black Sea Basin.
- Develop agreements with large river basin management structures to reduce the loads of nitrogen and phosphorous pollutants entering the Black Sea.
- Standardise and harmonise procedures for the quantification of river loads (as well as other pollution sources) to allow a more accurate comparison of loads entering the Black Sea from different sources.
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