Climate Change and the European Water Dimension - Agri ...

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Figure IV.C.5. Time series of winter mean wind speed (December to March) over the North Sea for 1958 to 1997, derived from NCEP re-analysis (solid line), and the winter NAO index (dashed line). The trends for both time series are calculated by linear regression. (Source: Siegismund and Schrum, 2001) The combined effect of climate change on the precipitation / river runoff on the one hand, and the intensification of North Atlantic input, on the other hand, could explain that no trends in salinity have been observed over 120 years in the North Sea (Laane et al. 1996). In opposition to the northern regions, the latest IPCC report (2001) indicates that the Southern mid-latitudes, including the Mediterranean regions, are already experiencing decreases in precipitation and stream flow. Future projection of this trend will reduce drastically water supplies in these areas, affecting considerably the population and economy of the Mediterranean countries (Trigo et al. 2004). As for higher precipitation in the north, seasonal trends to lower stream flow is linked to an increasing NAO index, which can be felt as far as the Middle East (Cullen et al. 2002). In addition, differences in sea surface temperature across the Pacific resulting from an unusually-long cold phase of ENSO (La Niña) would have triggered the 1998-2002 drought seasonal period over the southern United States, merging its effect with the positive anomaly of the NAO index to propagate the drought in the western Europe –Mediterranean regions (Hoerling and Kumar 2003; Pal et al. 2004). IV.C.3. Nutrients- Eutrophication Changes in the water cycle and river discharges have multiple effects on the nutrient composition of coastal waters. Of major importance to the entire ecosystem, the process of eutrophication represents the biogeochemical response to heavy nutrient loading (Cloern 2001), and is typically a regional issue, which occurs worldwide. It reflects both natural processes affecting the hydrological cycle in the catchment basin, but also human modifications of nutrient delivery due to agricultural practices (systematic use of fertilizers) and pollution from urban areas. Under increased precipitation and run-off in northern latitudes, heavy water discharges would decrease the residence time in the main estuarine channels, transferring nutrients 88
and organic material more rapidly to the coastal waters. Accordingly, the total dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) loadings can be scaled directly to functions of the population density and runoff magnitude (Smith et al. 2003). This provides global estimates of the present DIN and DIP fluxes to coastal waters that have doubled or even tripled during the past several decades (Mackenzie et al. 2002, Smith et al. 2003). Future projection adopting business-as-usual scenarios with sustained perturbation on land from human activities and from increasing global temperature will maintain the trends in the same direction with increasing delivery of reactive nitrogen and phosphorus to the global coastal margins (Mackenzie et al. 2002). At regional scales, observations are giving some credit to the global model results. The export of nitrate by the Mississippi river to the Gulf of Mexico has tripled since the 1950s, owing to an increase in agricultural fertilizer application and hydrological changes (Donner et al. 2002, Justic et al. 2003). The combination of meteorological forcing and human activities has not only changed the load of material to the coastal systems, but also the chemical speciation and elemental stoichiometry of the water. Unlike N and P, silica (Si) is little affected by human pollution and results mostly from the weathering or dissolution of silicate minerals. Consequently, the Si to N and Si to P ratios are significantly decreasing in coastal waters, even though higher precipitation and runoff must enhance the erosion of rock minerals and Si loads in the aquatic system. In coastal waters, the lack of Si with respect to other macronutrients would affect the phytoplankton assemblage and the entire ecosystem. On the other hand, the loading ratio of DIN and DIP remain relatively stable over time in spite of having very different chemical transformation pathways. Using a data set of 165 globally-distributed sites, Smith et al. (2003) describe the tight coupling between DIN and DIP with a loading ratio of 18:1, very close to Meybeck’s (1982) observations made several decades earlier on a much smaller data set, although the concentration of these nutrients were three times less. Note that the DIN:DIP ratio is also very close to the well-known Redfield ratio of 16:1 for oceanic waters published earlier (Redfield 1958). Anomalies from this ratio occur systematically on regional and temporal scales according to the dominant chemical and ecological processes (nitrification, denitrification, mineralization, uptake) controlling the nutrient cycling. For example, the riverine N:P ratio for the East China Sea is 111 (Chen et al. 2003), much different than the average ratio of 16. This ‘excess nitrate’ still remains, although at lower values, in the adjacent coastal waters, making the ecosystem Plimited rather N-limited. Inversely, higher runoff increases both the delivery of nutrients in coastal waters and the water column stratification, thereby increasing the probability of a sub-surface oxygen-depleted layer and favoring denitrification processes with the release of N2O into the atmosphere and a decrease in the N:P ratio. Over an extended area on the Indian continental shelf, Naqvi et al. (2000) observed an intensification of the denitrification process resulting from increasing runoff of nutrients from land and water stratification, producing anoxic conditions in coastal sub-layers, and reducing considerably the N:P ratio when compared with the value of 16 (i.e. Redfield ratio) observed in oxygenated waters. Although anthropogenic nutrient inputs are mostly responsible for this situation, the influence of climatic factors such as an intensification of the summer monsoon due to global warming can be significant (Naqvi et al. 2000). According to Seitzinger and Kroese (1998), ca. 21 TgN.yr -1 is exported from rivers to estuaries and coastal zones, i.e. twice the value estimated earlier by Meybeck (1982). Inputs to the enclosed and semi-enclosed European Seas account for 12% (2.5TgN.yr -1 ) of the world river N export. A large part (75%) of this N input results from anthropogenic activities and as expected displays a significant north-south 89
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Climate Change and the European Wat
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European Commission- Joint Research
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At the 2003 Rome Informal Meeting o
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Changes in the diurnal variation of
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Fugure I.2. (a) Maximum grid covera
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century. This corresponds to a sea
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Other causes Other causes of climat
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tropospheric ozone are photochemica
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Figure. I.4. Radiative forcings and
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There are two indirect effects of a
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The projected warming is not unifor
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water towards the west Pacific caus
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Aerosols and climate change in the
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precipitation intensities have been
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Chapter III. The Hydrologic Cycle I
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The quality class boundaries within
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An example of this kind of relation
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Regions 1 to 5 represent mainly a m
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een observed in southwestern countr
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Table V.D.2: Percentage area affect
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Lake Surface Temperature [°C] Desc
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Case Study: Esthwaite Water, Cumbri
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Residence time (days) Chlorophyll (
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Case Study: Lake Erken, Sweden ►
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TP (µg l -1 ) Modelling To analyse
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Data availability and investigation
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smaller volume of water. The warmer
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Chapter VI.B. Climate Change and th
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Concerning the flora of the lagoon
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Figure VI.B.2: Frequency of “bora
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Figure VI.C.2. Daily flows in Ebro
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Figure VI.C.4. Mean temperature inc
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factors including an appropriate su
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with the lower limit range indicate
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Chapter VI.C. The Effects of Climat
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the main carrier of nutrients to gr
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system pathway shows an increase of
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Table-VI.C.7: Main factors and cons
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Chapter VI.D. Climate Change and th
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Atmospheric deposition to marine wa
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Many studies during the 90’s have
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severe flooding were investigated (
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Table VI.E.1. Waterborne pathogens
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Chapter VI.F. Climate Change, Extre
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Areas behind the dikes broken in 20
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Second, the chemical is transported
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POPs exist in the atmosphere in the
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and ice have quite a low capacity t
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Table VI.F.1. Priority substances i
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22. Monteith, J.L., 1965. Evaporati
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31. Rodionov, S.N. 1994. Global and
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28. Dokulil, M.T., 2003. Algae as e
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63. Hejzlar, J., Dubrovský, M. Buc
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99. Melack, J.M., J. Dozier, C.R. G
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136. Straile, D. & Adrian, R. 2000.
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14. Blaas, M., Kerkhoven, D., and d
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60. McCleery, R. H. and Perrins, C.
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105. UNESCO 2003. The integrated st
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ecosystems and the landscape and de
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2. Carter, T.R., Saarikko, R.A., an
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24. Hydrographisches Zentralbüro 1
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European Coastal Lagoons: The Influ
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4. Bouma MJ, Sondrop HE, van der Ka
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variable trophic status: a paired l
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France GIANMARCO GIORDANI Departmen
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Chapter VI.E. Climate Change and Wa
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