IntroductIon
Natural resources provide the goods on which our economies and healthy existence depend. Regrettably our planet has limited natural resources to adequately meet the ever-increasing demands of the human societies for their economical development which makes sustainable development probably the greatest challenge facing us [1]. Exploitation of natural resources causes numero-us environmental problems which influence all ecosystems and the ecosystem services they provide [2]. Transformation of na-tural ecosystems into cropland and grazing area, urbanization, introduction of alien species and xenobiotics into environment and changes in the rate and amount of material cycling between various parts of the biosphere are some of the more prominent environmental problems with globally significant effects. The-se problems have already disturbed natural ecological procesThe-ses with harmful consequences on biogeochemical cycling of ele-ments and species richness of biological communities [3].
Human societies obtain and trade many commodities such as seafood, wild game, timber, bio-fuels, and many pharmaceutical and industrial products from nature [4]. Marketable goods are not the only benefits we obtain from nature, there is another group of benefits that can be grouped under the name of vital ecosy-stem services or life support syecosy-stems without which life would not exist, as we know it. These include provision of clean water and air, soil formation, maintenance of soil fertility, regulation of global climate, pollination, decomposition of wastes, nutrient cycling, generation and conservation of biodiversity and natural
pest control [5]. Thus it is quite clear that human beings would not survive without the benefits nature provides for them. The damage we are making on nature not only diminishes the benefits we obtain from it but it also puts our own existence in jeopardy [1]. Agriculture is among the most conspicuous anthropogenic activities with global scale influences [2] and together with fo-restry is one of the most transformative powers on natural ecosy-stems [6]. The foremost environmental impacts of agriculture include; (i) conversion of natural ecosystems into croplands, (ii) release of pesticides, and limiting nutrients, namely nitrogen and phosphorus into soil and aquatic environment, (iv) changes in hydrological cycle [7, 8]. The presence of freshwater shortage problem in many parts of the world and the increase in the world population, per capita production and consumption prompt water quantity and quality related problems as the most prominent type of problem to deal with among the other environmental impacts of agriculture. In this review it is aimed to provide a brief overvi-ew of agricultural impacts on world’s freshwater resources.
Quantitative effects of agriculture on freshwater resources Humans have transformed a large proportion of world sur-face mainly through conversion of natural ecosystems into agri-ecosystems [6]. Agricultural lands (croplands and pasturelands) cover almost 40 % of the total land’s surface area [9, 10] and they use and fragment 45 % of the world’s major nature reserves [7]. Globally, clearing and draining of wetlands for conversion into cropland is the chief cause of wetland loss [11]. Since wetlands filter and assimilate waste their loss means an increase in the amount of pollutants and sediments carried into rivers, lakes and coastal seas.
Food And Clean Water: Two Conflicting Necessities of Life
Esra KOÇUM
Çanakkale Onsekiz Mart Üniversitesi Fen-Edebiyat Fakültesi, Biyoloji Bölümü, Ekoloji ABD, Çanakkale.
Abstract
Human societies depend on limited natural resources of our planet for their existence and economic development. Rise in human population and per capita consumption increases the human share of natural resources. In particular development in agriculture to meet the escalating demand for food has resulted in various environmental problems. The share of agriculture in water use represents the 70 % of the global total making water quantity and quality related problems foremost impacts of agriculture on the environment. In this brief review environmental costs of agriculture on our limited freshwater resources have been summarized to draw attention to this critical issue.
Keywords: agriculture, environment, freshwater, impact.
Besin ve Temiz Su: Birbiri Lle Çatişan İki Yaşamsal Gereksinim
Özet
İnsan toplumları kendi varlıkları ve ekonomik gelişimleri için gezegenimizin sınırlı doğal kaynaklarına bağımlıdırlar. İnsan nüfusu ve kişi başına düşen tüketimdeki artış insanların doğal kaynaklardan aldıkları payı artırmaktadır. Özellikle gittikçe artan gıda gereksinimini karşılamak için tarımda meydana gelen gelişim çeşitli çevre sorunlarına yol açmıştır. Tarımda kullanılan suyun küresel toplamın % 70 ini oluşturması su ile ilgili nicel ve nitel sorunları tarımın çevre üzerinde önde gelen etkisi kılmaktadır. Bu kısa derlemede sınırlı tatlı su kaynakları üzerinde tarımdan kaynaklanan zararlar bu önemli konuya dikkat çekmek için özetlenmiştir.
Anahtar kelimeler: Tarım, çevre, tatlı su, etki.
ISSN:1308-3961, www.nobel.gen.tr
Sorumlu Yazar Geliş Tarihi : 16 Şubat 2009
The estimated human share of the terrestrial biologi-cal production is 40 % of the total [12] and humans use more than > 50 % of the accessible freshwater resources [13]. The projected 50 % increase [14] in world’s popu-lation by the year 2050 is going to increase the demand for both food and freshwater. In response to this pressure the total area of agricultural land is expected to be larger than the present by 18 % in 2050 [15]. This projection includes a 45 million hectare increase in the area of irri-gated land in developing countries which does not only represents a change in total area of agricultural land but also a 14 % increase in total agricultural water use by the year 2030 [16] which already claims 70 % of the global freshwater use [17]. The share of agriculture in water use may rise up to 95 % of the total of in developing countri-es [18] whose economicountri-es primarily depend on agricultu-re. All these figures implicate once again the crucial need for a sound management of water use in the agricultural sector.
A rather indirect effect of water use in agriculture is through alternation of natural water flow regimes which both quantitatively and qualitatively increases the risk of catastrophic changes in the structure and functioning of lotic ecosystems [8]. Reservoir building dredging, nelization, canalization and construction of levees chan-ge river channel morphology and flow regime with con-sequent changes in material flow [19]. The presence of dam reservoirs exerts the greatest pressure on the health of lotic ecosystems. There are ~ 40 000 dams exceeding 15 m in height [20] and 75 % of them are used for irri-gation and power generation or for both purposes [21]. Nearly 40 % of the large riverine ecosystems have been fragmented by dams and other structures on them [11]. While serving food production through storing water for the irrigation of crop lands, dams change the timing and the amount of natural flow regime and causes detrimental changes in lotic ecosystems such as deterioration of wa-ter quality, loss of biodiversity [22] and reduction in the amount of sediment transport to the coast.
Quantitative effects of agriculture on water resources is not limited to the surface waters. 20 % of the water used for irrigation comes from the groundwater reso-urces, this fraction is much higher for arid regions. For example, Saudi Arabia obtains almost 100 % of its irri-gation water from groundwater resources [11]. These fi-gures clearly show overuse of groundwater resources for irrigation. Considering the facts that almost half of the world’s population depend on groundwater as a source of safe drinking water, the extremely slow replenishment time of aquifers and pollution related problems they are subjected to [23], sustainable use of groundwater resour-ces becomes a vital task.
Qualitative effects of agriculture on world’s freshwa-ter resources
Agriculture does not only affect quantity of water re-sources through consumption but also has a great poten-tial to affect quality of water resources [23]. Soil erosion, pesticide and nutrient pollution are the dominant forms of pollution originating from agricultural activities [24]. Agriculture increases sediment load through intensifica-tion of soil erosion [25] and leaching of pesticides and nutrients into water resources. Globally, almost 40 % of croplands experience soil erosion [6] which creates prob-lems in croplands and surface waters. Transport of soil organic matter and plant nutrients from croplands to sur-face waters globally cause most pervasive water quality related problems [26]. The fact that erosion is generally more severe in semi-arid regions [27] where freshwater resources are already limited makes the problem even more critical. There has been a 2.3 ± 0.6 billion metric tons of annual increase in the amount of sediments carri-ed by rivers due to human causcarri-ed soil erosion [28]. Incre-ased sediment load in rivers deteriorates the light climate for photosynthetic organisms due to increased turbidity of water and fine sediment particles covering benthos which results in destruction of spawning habitats for fish [29]. Within sediment particles inorganic (ex.; plant nutrients) and organic matter and pesticides also enter receiving water bodies [27] and increase their pollutant loads.
Intensive agriculture has brought about an increase in the variety and number of the pests and in the occurrence of crop disease, which has led a rise in the global pesti-cide use. Pestipesti-cides are intensively used in many parts of the world [16], with developing countries using the gre-ater part. Our grave depence on pesticides goes back to post Worl War II era when they were first applied to cont-rol vector borne diseases. At that time noone knew about the real extent of the dangers of pesticide use on human health and environment [30]. The publication of Rachel Carson’s seminal book Silent Spring in 1962 stimulated a first-time public interest on the potential dangers of pes-ticide use which eventually led declaration of a national ban on the use of DDT in USA and in industrial countries and had a great impact on environmental movement [31] though DDT is still used in developing countries [24].
Globallly, pesticide use has risen at least ten-fold wit-hin the second half of the 20th century and another 270 % increase is anticipated to take place by the year 2050 [15]. The effects of pesticide use on human health depend on the degree of their persistence and accumulation in the environment and on the degree of exposure. Estimates show that only 0.1 % of the pesticides applied actually reach the pests and the remaining amount stays in the environment or on the food [32]. Pesticides can also re-ach surface and groundwaters from point source
(conta-mination through accidental release) and from non-point sources (agricultural lands). Pesticides pollute freshwater resources rendering them impotable and due to their per-sistence some of them can accumulate in food chains [7]. Detection of pesticides in environmental samples requi-res expensive chemical analysis therefore in many parts of the world surface and ground waters have not been analysed for the presence of pesticides [33] hindering an accurate estimate of the real extent of the problem. Ac-cording to the data gathered by US Geological Survey [34] 80 % of the monitored rivers and 60 of the sampled wells in agricultural regions of USA contaminated by at least one kind of pesticide. The situation is similar in Europe. A survey on the presence of pesticides in gro-undwater samples in several European countries revealed that in a substantial number of sampling points pesticide concentrations were above 0.1 mg L-1 which is the
ma-ximum admissible concentration of pesticides set by EU Drinking Water Directive [35].
The increases in fertilizier use and in the area of land converted into agricultural and grazing land have re-sulted in the disruption of nitrogen [2] and phosphorus cycles [36]. Annual application of N and P in fertilizers is equivalent to 242 % and 83 % respectively of the annual global riverine inputs [37] and predicted to double by the middle of this century [38]. The amount of industrially fixed nitrogen in fertilizers is ca.80 Tg per year and is the largest human contribution of new nitrogen to global N cycle [39]. When nitrogen from cropping of legume plants and fossil fuel burning is taken into account, ca.140 Tg of new nitrogen is annually added into terrestrial ecosy-stems [39]. The amount of phosphorus input in fertilizers to surface soils was estimated to be ca. 18.5 Tg yr-1 and
intense fertilizer use is leading to more phosphorus build up in soils increasing the potential for phosphorus run-off to aquatic ecosystems [36]. In a study on human impact on erodable phosphorus and eutrophication Bennett et al. [36] estimated a 75 % increase in net phosphorus storage in terrestrial and freshwater ecosystems compared to the pre-industrial levels using a global budget approach. As a result more phosphorus reaches the sea compared to the pre-industrial levels. The amount of P carried by the world’s rivers to the sea is estimated to be 22 Tg yr-1 [40]
and estimates suggest that 2/3 of the nitrogen and 1/3 of the phosphorus entering into surface waters have an agri-cultural origin [33].
Enrichment of waters with plant nutrients stimula-tes primary production and disturbs the balance betwe-en the production and consumption of organic matter in these ecosystems. Enrichment of aquatic ecosystems with plant nutrients or the so-called eutrophication has different definitions. It has been defined in the European Commission (EC) Urban Waste Water Treatment
Direc-tive (UWWTD) as “the enrichment of water by nutrients, especially nitrogen and/or phosphorus, causing an acce-lerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of or-ganisms present in the water and to the quality of water concerned” [41]. According to the EC Nitrates Directi-ve, eutrophication has been defined as “the enrichment of water by nitrogen compounds causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of water concer-ned” [42]. The difference between two definitons of eut-rophication is in the latter definition nitrogen is the main culprit while the former points both or either of N and P as the major cause of the problem. Nixon’s (1995) defini-tion of eutrophicadefini-tion as “an increase in the rate of supply of organic matter to an ecosystem” describes eutrophica-tion as a process rather then a trophic state [43].
Agriculture has been identified as the largest source of excess nitrogen and phosphorus entering waterbodi-es [44, 36] and as an disrupting factor for all frwaterbodi-eshwater ecosystems [45]. Together with global climate change the problem of nutrient enrichment of aquatic ecosystems re-ceives a great deal of attention from the scientific com-munity owing to its global occurrence and significance [46], its harmful consequences on biodiversity, element cycling and more noticeable problems such as colo-ur and odocolo-ur changes in water, harmful algal blooms, hypoxia and associated fish kills. Eutrophication prob-lem has also socio-economic dimensions due to direct and indirect costs arising from monitoring and treatment of water bodies, decreased value of water resources for consumptive, recreational and touristic uses, health costs associated with food poisonings caused by algal derived toxins, decreased ecological value of the effected water bodies due to loss of biodiversity and species composi-tion changes [47, 48]. Therefore enrichment of natural water bodies with nitrogen and phosphorus deserves spe-cial consideration among the other impacts of agriculture on freshwaters.
Eutrophication is clearly a prime manifestation of human intervention of N and P cycles. So how does it manifest it-self in the waterbody it occurs? It causes various symptoms ranging from increase in phytoplankton biomass and pro-duction, blooming of toxin producing algal species, hypo-xia, changes in the structure of food webs, element cycling and energy flow to economic losses associated with reduced fisheries [49]. Fertilization of aquatic ecosystems with previ-ously scarce plant nutrient elements stimulates primary pro-duction by both microscopic and macroscopic plant forms [50]. Since phytoplankton can grow much faster than the larger plants they benefit more from the increase in the amount of nutrients. Amplified phytoplankton biomass
makes water column more turbid preventing penetration of light to bottom dwelling macroscopic plants. This sha-ding effect damages the submerged plant communities such as seagrass beds, reducing their areal cover and/or stimulates nuisance seaweeds [46] and since they provi-de food, shelter, spawning and nursery area for various marine animals their degradation effects animal diversity as well. The increase in the organic matter content as phytoplankton increase in abundance leads formation of hypoxia and/or anoxia creating an unsuitable habitat for fish, shelfish and for other aerobic organisms. According to UNEP [51] there are 146 “dead zones” in the oceans where marine life could not exist due to oxygen depleti-on. The effects of eutrophication are not simply increa-sed production and lowered oxygen levels; it also leads to changes in the ecological structure of benthic fauna and flora and in the species composition of phytoplank-ton. Relative availability of nitrogen and phosphorus is crucial for the occurrence of these changes in phytop-lankton species composition through selection of domi-nant types [52]. Silicate also influences phytoplankton species composition and eutrophication decreases the relative availability of it through increasing amount of nitrogen and phosphorus eventually leading to a chan-ge in phytoplankton community from silica requiring forms to non-siliceous forms [53, 54]. Such changes in phytoplankton community may lead to bloom forma-tions by non-diatom species some of which are toxic such as members of dinoflagellate genus Gymnodinium
spp. [47], Pfiesteria piscicida [55], Dinophysis norvegi-ca and D. acuminata and Prorocentrum minimum [56].
Eutrophication of freshwater ecosystems
Eutrophication of lakes has been recognized as a problem since the early days of the 19th the century in Europe. Botanist
Candolle reported change of colour in the waters of Lake Mur-ten in Switzerland by the presence of Oscillatoria rubescens in 1820. Since then eutrophication in all types of freshwaters, estuaries and coastal waters has been reported [50] though it was not until the middle of the 20th century when it has been
recognized as a familiar problem first among those living clo-se to the lakes which exhibited very visible symptoms like algal scums and fish kills. The scientific discovery of the con-nection between algal blooms and nutrient enrichment as a result of anthropogenic activities in the catchments of lakes were made in 1960s [57]. Since then freshwater eutrophicati-on has been a growing problem causing impairment of water quality in lakes, reservoirs and lotic systems around the world interfering with their use for drinking and for other purposes. Today nearly 50 % of the lakes in Europe, Asia, North and South America have been reported as eutrophic [51]. Eutrop-hication of lotic ecosystems has been overlooked due to the common consensus that these ecosystems were insensitive to the nutrient enrichment owing to their hydrological
cha-racteristics. This view is no longer plausible as there are se-veral studies showing the vulnerability of these ecosystems to the anthropogenic inputs of nitrogen and phosphorus [49, 58]. There are also several studies showing that phytoplank-ton biomass and benthic algal biomass increase as a response to increased phosphorus in lotic ecosystems [59, 60, 61, 62, 63]. Catchment scale processes are the main culprits of river eutrophication. The annual rate of nitrogen and phosphorus loading into freshwater ecosystems has increased by 6-50 fold through anthropogenic activities in the catchments [44].
There are some risks to human and animal health associa-ted with the extraction of drinking water from eutrophic fresh-waters. One prominent risk arises from the fact that common occurrence of algae and cyanobacteria blooms in eutrophic waters. Cyanobacteria blooms in freshwaters have been in-tensively studied due to their wide-spread occurrence and po-tentials for toxin production [64]. Hepatotoxins, neurotoxins, cytotoxins and endotoxins are the main groups of cyanobac-terial toxins with several numbers of structural variants and various modes of toxicity [65]. Microcystins are hepatotoxins which are the most common type of cyanobacterial toxins and may cause liver injury and are reported to be tumour pro-moters in animal tests. In China long term epidemiological studies suggested a link between the presence of microsystin in drinking water and primary liver cancer [66]. Neurotoxins have a less widespread occurrence though they cause sudden deaths in mice and birds through respiratory arrest. Hepatitis and gastro-intestinal problems such as gastro-enteritis are also among the public health problems associated with the use of eutrophicated water for drinking purpose [64]. High nitrate le-vels in drinking water cause great concern as they have adver-se effects on human health. Nitrate pollution is a global envi-ronmental problem for surface waters and the most common contamination problem for groundwaters [23]. High nitrate levels in drinking water causes a kind of anemia known as methemoglobineia, or blue baby syndrome in infants. The to-xicity of nitrate to humans is ascribed to its reduction to nitrite in the gastro-intestinal system. Nitrite ions bind hemoglobin and form methemoglobin which can no more carry oxygen. This condition may lead to brain damage and in extreme ca-ses death [39]. The low pH of the infant stomach accelerates reduction of nitrate to nitrite. The concern over nitrate in drin-king water is also related to its suspected carsinogenic effect. Nitrate reacts with amines and amides in the stomach to form various N-nitroso compounds which are potent animal car-cinogens [67]. There are several evidences from epidemio-logical studies pointing the relation between nitrate levels in drinking water and risk of specific cancers and reproductive problems [68]. Necessiated by the widespread nitrate conta-mination of drinking water resources and its adverse effects on public health there are regulatory limits on nitrate concent-rations in drinking water. World Health Organization’s limit of 50 mg NO3- L-1 in drinking water has been reaffirmed by
European Union while in the USA Environmental Protection Agency (USEPA) has set the nitrate limit in drinking water at 45 mg NO3- L-1 [68]. A synthesis report prepared by
Europe-an Community (EC) through gathering Europe-and Europe-analysing of data on nitrogen pollution from agricultural sources in the member states has shown that in 20% of EU groundwater quality mo-nitoring stations, nitrate concentrations exceeded the 50 mg NO3- L-1 while in 40% of them it exceeded 25 mg NO3- L-1
[69]. The picture is quite similar in other countries including Turkey, Senegal, Mexico, Botswana, China [70] and in Eas-tern European countries where nitrate levels in well waters are high and in some instances exceed the limit set by World Health Organization [71].
The goal of adequately nourishing the crowded world po-pulation puts pressure on the use of more fertilizier to increase the yield per unit of cultivated land which brings about certa-in environmental damages. The ever- certa-increascerta-ing demand for food preclude attempts to put a limit on fertilizer use. Nevert-heless more efficient use of fertilizers through correct nutrient management practices aiming to decrease their lost from the soil does not interfere with food production and is therefore quite appropriate to apply.
conclusion
Invention of agriculture enabled humans to increase and manage the amount of food they obtain from nature yet there is no such invention with the same results on world’s water resources. This creates a clear dilemna on the use of water for producing food and protection of precious freshwater reso-urces. The technological transfer of agriculture, the so called “Green Revolution” caused a 2.5 fold increase in global grain production during the period between 1950 and early 1990s [7]. This increase in agriculture coupled with a 3.48 and 6.87 fold increases in the amount of phosphorus and nitrogen con-taining fertilizers, respectively and 1.68 fold increase in the area of irrigated cropland [72] made agriculture a major driver of global environmental change. Tilman et al. [15] argues that the task of feeding 9 billion people that is predicted to be the size of the world population in the year 2050 [73] calls for another Green Revolution with its inevitable environmental costs. Based upon the simple linear extension of past trends it is projected that a further doubling of agricultural produc-tion requires an 18 % increase in the amount of agricultural land, doubling of the area of irrigated land, 3- fold increases in the annual rates of both nitrogen and phosphorus fertiliza-tion [72]. Based on this predicfertiliza-tions, there is no doubt that the environmental impacts of agriculture will intensify especially on aquatic ecosystems through higher rates of nitrogen and phosphorus run-off from agricultural lands. Both food and water are indispensable to life thus it is not possible to sac-rifice one for the other. This means that agricultural practices should be modified in a way that maximize the water use ef-ficiency in crop production through scientific solutions aimed
to strike a balance between demand for food and available water supplies.
LITERATURE CITED
[1] Cairns J Jr. (2004) Future of life on Earth. Ethics in Science and Environmental Politics: 1-2.
[2] Vitousek PM, Money HA, Lubchenco J, Melillo JM (1997a) Human domination of Earth’s ecosystems. Science 277, 494–499.
[3] Gorshkov VG, Makarieva AM, Gorshkov VV (2004) Revising the fundamentals of ecological knowledge: the biota–environment interaction. Ecological Complexity 1: 17–36
[4] Daily G.C, Alexander S, Ehrlich PR, Goulder L, Lubchenco J, Matson PA, Money HA, Postel S, Schneider SH, Tilman D, Wooodwell GM (1997) Ecosystem Services: Benefits Supplied to Human Societies by Natural Ecosystems. Issues in Ecology, Number 2. Ecological Society of America. [5] Lubchenco L (2007) Entering the century of the environment:
a new social contract for science. Science 279: 491-497. [6] Foley JA, Monfreda C, Ramankutty N, Zaks D (2007) Our
share of the planetary pie. PNAS 104(31):12585–12586 (www.pnas.org_cgi_doi_10.1073_pnas.0705190104). [7] Laurance WF (2001) Future shock: forecasting a grim fate
for the Earth. Trends in Ecology and Evolution 16(10): 531-533
[8] Gordon LJ, Peterson GD, Bennett EM (2008) Agricultural modifications of hydrological flows create ecological surprises. Trends in Ecology and Evolution 23(4): 211-219. [9] Ramankutty N, Foley JA (1999) Estimating historical
changes in global land cover: croplands from 1700 to 1992. Global Biogeochemical Cycles 13(4): 997-1027.
[10] Asner GP, Elmore AJ, Olander LP, Martin RE, Harris AT (2004) Grazing systems, ecosystem responses, and global change. Annual Review of Environment and Resources 29: 261-299.
[11] Scholes R, Hassan R, Ash NJ (2005). Summary: Ecosystems and their services around the year 2000. In R Hassan, R
Scholes, N Ash (eds). Ecosystems and human well-being : current state and trends. Millenium Ecosystem Assessment Series, Volume 1.
[12] Vitousek PM, Ehrlich PR, Ehrlich AH, Matson PA (1986) Human Appropriation of the Products of Photosynthesis. BioScience 36(6): 368-373.
[13] Jackson RB, Carpenter SR, Dahm CN, McKnight DM, Naiman RJ, Postel SL, Running SW (2001) Water in a Changing World Issues in Ecology Number 9, Ecological Society of America.
[14] FAO (2007) The State of Food and Agriculture. FAO Agriculture Series No.38 ISSN 0081-4539 Food and Agriculture Organization of the United Nations, Rome. [15] Tilman D, Fargione J, Wolff B, D’Antonio C, Dobson A,
Howarth R, Schindler D, Schlesinger WH, Simberloff D, Swackhamer D (2001) Forecasting Agriculturally Driven Global Environmental Change. Science 292:281-284.
[16] FAO (2002) World agriculture: towards 2015/2030 Summary Report. ISBN 92-5-104761-8 Food and Agriculture Organization of the United Nations, Rome.
[17] FAO (2003) Agriculture Food and Water. A contribution to the World Water Development Report (92-5-104943-2). Food and Agriculture Organization of the United Nations, Rome.
[18] FAO (2007) The State of Food and Agriculture. FAO Agriculture Series No.38 ISSN 0081-4539 Food and Agriculture Organization of the United Nations, Rome. [19] Meybeck M (2003) Global analysis of river systems: from
Earth system controls to Anthropocene syndromes. Phil. Trans. R. Soc. Lond. B 358: 1935–1955.
[20] Avakyan AB, Iakovleva VB (1998) Status of global reservoirs: the positioning in the late twentieth century. Lakes Estuaries Research and Management 3: 45–52. [21] Berkamp G, McCartney M, Dugan P, McNeely J, Acreman
M (2000). Dams, ecosystem functions and environmental restoration. Thematic Review II. Prepared as an input to the World Commission on Dams, Cape Town.
[22] Bunn SE, Arthington A (2002) Basic Principles and Ecological Consequences of Altered Flow Regimes for Aquatic Biodiversity. Environmental Management 30 (4): 492–507 (DOI: 10.1007/s00267-002-2737-0.
[23] UNESCO (2007) Groundwater Resources Sustainability Indicators. I H P - VI Series on Groundwater No. 14. [24] Bos R, Caudill C, Chilton J, Douglas EM, Meybeck M,
Prager D (2005) Fresh Water. In R HR Scholes, N Ash (2005). Ecosystems and human well-being: current state and trends. Millenum Ecosystem Assessment Series Vol. 1. [25] Lal R (2002) Soil erosion and the global carbon budget.
Environment International 29:437-450.
[26] Lenzi Ma, Di Luzio M (1997) Surface runoff, soil erosion and water quality modelling in the Alpone watershed using AGNPS integrated with a Geographic Information System. European
[27] Lal R (1998) Soil erosion impact on agronomic productivity and environment quality. Critical Reviews in Plant Sciences 17(4):319 — 464.
[28] Syvitski JPM, Vörösmarty CJ, Kettner AJ, Gren P (2005). Impact of humans on the flux of terrestrial sediment to the global coastal ocean. Science 308 (5720): 376 - 380. [29] Ongley ED (1996) Control of water pollution from
agriculture. FAO irrigation and drainage paper 55. ISBN 92-5-103875-9 (http://www.fao.org/docrep/W2598E, accessed on 02.02.2009 at 13.00).
[30] Farah J (1994) Pesticide policies in developing countries: do they encourage excessive use? World Bank Discussion Papers 238. World Bank Washington DC. ISBN 0-8213-2830-1
[31] Wilkinson C (2002) Silent spring revisited – the main contribution of the book was environmental rather than human health-related. Pesticide Outlook – October. (DOI: 10.1039/b209420g)
[32] Nugent R, Drescher A (2006) Understanding the links between agriculture and health for food, agriculture, and the environment. Agriculture, Environment, and Health: Toward Sustainable Solutions. International Food Policy Research Institute, Focus 13, Brief 14 of 16.
[33] OECD (2001). Environmental indicators for Agriculture. Volume 3. Methods and Results. Agriculture and Food. OECD Publications Service, France.
[34] USGS (United States Geological Survey) (1999). The quality of our nation’s waters – nutrients and pesticides. USGS Circular 1225, Washington DC, United States. [35] EEA (1998). Europe’s Environment: The Second
Assessment, Office of Official Publications of the European Communities, Luxembourg. http://reports.eea.europa.eu/92-828-3351-8/en (accessed on 31.10.2008 at 14.54).
[36] Bennett EM, Carpenter SR, Caraco NF (2001) Human Impact on Erodable Phosphorus and Eutrophication: A Global Perspective.. BioScience 51(3): 227-234.
[37] Schlessinger WH (1991) Biogeochemistry 2nd ed. An Analysis of Global Change. Academic Press, New York. [38] Turner RE, Rabalais NN, Justic D, Dortch Q (2003) Future
aquatic nutrient limitations. Marine Pollution Bulletin 46: 1032–1034.
[39] Vitousek, PM, Aber J, Howarth RW, Likens GE, Matson PA, Schindler DW, Schlesinger WH, Tilman GD (1997b). Human alteration of the global nitrogen cycle: causes and consequences. Issues in Ecology Number 1: 1-16. Ecological Society of America.
[40] Howarth RW, Jensen HS, Marino R, Postma H (1995) Transport to and processing of P in near-shore and oceanic waters. p: 323–345 in Tiessen H (ed.) Phosphorus in the Global Environment: Transfers, Cycles, and Management. New York: John Wiley and Sons.
[41] Anonymous (1991a). Council Directive of 21 May 1991 concerning urban waste water treatment (91/271/EEC). Official Journal L 135.
[42] Anonymous (1991b). Council Directive 91/676/EEC of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources. Official Journal L 375.
[43] Andersen JH, Schlüter L, Ertebjerg G (2006) Coastal eutrophication: recent developments in definitions and implications for monitoring strategies. Journal of Plankton Research 288(7): 621–628.
[44] Carpenter SR, Caraco NF, Correll DL, Howarth RW, Sharpley AN, Smith VH (1998). Nonpoint pollution of surface waters with phosphorous and nitrogen. Ecological Applications 8:559–568.
[45] Moss B (2007) Water pollution by agriculture. Phil. Trans. R. Soc. B 363: 659–666 (doi:10.1098/rstb.2007.2176). [46] Howarth R, Anderson D, Cloern J, Elfring C, Hopkinson C,
Lapointe B, Malone T, Marcus N, McGlathery K, Sharpley A, Walker D (2000) Nutrient Pollution of Coastal Rivers, Bays, and Seas. Issues in Ecology 7. Ecological Society of America.
[47] Cloern JE (2001) Our evolving conceptual model of the coastal eutrophication problem. Marine Ecology Progress Series 210:223-253.
[48] Pretty J, Brett C, Gee D, Hine R, Mason C, Morison J, Rayments M, Van der Bijl G, Dobbd T (2001) Policy challenges and priorities for internalising the externalities of modern agriculture. Journal of Environmental Planning and Management 44 (2): 263-283
[49] Smith VH, Tilman GD, Nekola JC (1999) Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems. Environmental Pollution 100: 179-196.
[50] Vollenweider RA (1992) Coastal marine eutrophication: principles and control. In Marine Coastal Eutrophication. RA Vollenweider, R Marchetti, R Vicviani (eds.) pp. 1-20. Elsevier, Amsterdam.
[51] UNEP (2003) Global Environmental Outlook Year Book 2003. United Nations Environmental Program. GEO Section, PO Box 30552, Nairobi, Kenya.
[52] NRC (2000) Clean coastal waters: Understanding and reducing the effects of nutrient pollution. National Academies Press.
[53] Conley DJ, Schelske CL, Stoermer EF (1993) Modification of silica biogeochemistry with eutrophication in aquatic systems. Marine Ecology Progress Series 101: 179–192. [54] Billen G, Garnier J (2007) River basin nutrient delivery to the
coastal sea: Assessing its potential to sustain new production of non-siliceous algae. Marine Chemistry 106:148–160 [55] Burkholder JM, Glasgow H. Jr. (1997) Pfiesteria piscicida
and other Pfiesteria-like dinofagellates: behavior, impacts, and environmental controls. Limnology and Oceanography 42: 1052-1075.
[56] Glibert PM, Seitzinger S, Heil CA, Burkholder JM, Parrow MW, Codispoti LA, Kelly V (2005). The Role of Eutrophication in the Global Proliferation of Harmful Algal Blooms New Perspectives and New Approaches. Oceanography 18(2): 198-209.
[57] Schindler DW (2006) Recent advances in the understanding and management of eutrophication. Limnol. Oceanogr. 51(1, part2): 356-363.
[58] Smith VH, Joye SB, Howarth RW (2006) Eutrophication of freshwater and marine ecosystems. Limnol. Oceanogr. 51(1, part2): 351-355.
[59] Basu BK, Pick FP (1996) Factors regulating phytoplankton and zooplankton biomass in temperate rivers. Limnology and Oceanography 41(7): 1572-1577.
[60] Van Nieuwenhuyse EE, Jones JR (1996) Phosphorus– chlorophyll relationship in temperate streams and its variation with stream catchment area. Can. J. Fish. Aquat. Sci. 53: 99–105.
[61] Lohman K, Jones JR (1999) Nutrient-sestonic chlorophyl relationships in northern Ozark streams. Canadian Journal of Fisheries and Aquatic Sciences 56(1): 124-130.
[62] Dodds WK, Smith VH, Lohman K (2002) Nitrogen and phosphorus relationships to benthic algal biomass in temperate streams. Can. J. Fish. Aquat. Sci. 59: 865–874
[66] Ueno Y, Satoshi Nagata1 S, Tsutsumi T, Hasegawa A, Watanabe MF, Park HD, Chen GC, Chen G, Yus SZ (1996) Detection of microcystins, a blue-green algal hepatotoxin, in drinking water sampled in Haimen and Fusui, endemic areas of primary liver cancer in China, by highly sensitive immunoassay. Carcinogenesis 17(6): 1317-1321.
[67] Tricker AR, Preussmann R (1991) Carcinogenic N-nitrosamines in the diet: occurrence, formation, mechanisms and carcinogenic potential. Mutation Research 259(3-4): 277-289.
[68] Ward MH, deKok TM, Levallois P, Brender J, Gullis G, Nolan BT, VanDerslice J (2005) Workgroup Report: Drinking-Water Nitrate and Health—Recent Findings and Research Needs. Environmental Health Perspectives 113(11).
[69] EC (2002b) Implementation of Council Directive 91/676/ EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources. Office for Official Publications of the European Communities, Luxembourg. ISBN: 92-894-4103-8. http://ec.europa.eu/ environment/water/water-nitrates/pdf/91_676_eec_en.pdf. (Accessed on 31.10.2008 at 14.35).
[70] WHO (2004). Nitrates and Nitrites in Drinking-Water. WHO/SDE/WSH/04.08/56. Rolling revision of the WHO guidelines for drinking-water quality. Draft for review and comments. (http://www.who.int/water_sanitation_health/ dwq/chemicals/en/nitratesfull.pdf (Accessed on 31. 10.2008 at 14.10)
[71] Jedrychowski W, Maugeri U, Bianchi I (1997) Environmental pollution in central and eastern European countries: a basis for cancer epidemiology. Rev. Environ. Health 12:1–23. [72] Tilman D (1999) Global environmental impacts of
agricultural expansion: The need for sustainable and efficient practices. Proc. Natl. Acad. Sci. USA 96 (5995–6000). [73] Anonymous (1999) World Population Prospects: the 1998
Revision, United Nations Dept of Economic and Social Affairs.
[63] Dodds WK (2006) Eutrophication and trophic state in rivers and streams. Limnology and Oceanography 51(1, part 2): 671–680.
[64] EC (2002a) Eutrophication and health. Luxembourg: Office for Official Publications of the European Communities. ISBN 92-894-4413-4. http://ec.europa.eu/environment/ water/water-nitrates/pdf/eutrophication.pdf (accessed on 31.10.2008 at 11.16)
[65] Codd G (2000). Cyanobacterial toxins, the perception of water quality, and the prioritisation of eutrophication control. Ecological Engineering 16: 51–60.
