Lakes and Watercourses

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Nutrients / eutrophication Introduction Elevated nutrient levels, known as eutrophication, result from an increased influx or increased availability of plant nutrients in lakes and watercourses. Eutrophication leads to increased production and plant and animal biomass, increased turbidity, greater oxygen demand resulting from the decomposition or organic matter and a change in species composition and diversity of plant and animal communities. In most cases the nutrients governing vegetative growth in fresh water are phosphorus (P) and, in a few cases, nitrogen (N). Total phosphorus, total nitrogen and the phosphorus/nitrogen ratio are parameters used to assess lakes. Total phosphorus has been chosen even though this includes phosphorus fixed in minerals and humus, which is not directly available to plants. This is due to the need for an indicator that is analytically straightforward and generally used. The relative importance of phosphorus and nitrogen is proportional to the quantities in which they occur, here described as the weight ratio between the concentration of total nitrogen and that of total phosphorus. This indicates a deficit or surplus of the two elements and shows the potential for nitrogen fixation and for accumulation of nitrogen-fixing cyanobacteria (”blue-green algae”). The concentration of total phosphorus, like the N/P ratio, can be clearly linked to biological and biochemical effects. Unlike the N/P ratio, the scale for total nitrogen concentrations, which is also given, does not measure the effects of nitrogen on production; it is intended to differentiate between various typical concentrations in Swedish lakes. The area-specific loss of nitrogen and phosphorus, respectively, is used when assessing watercourses. Although this indicator, in principle, mainly belongs to the criteria for the Agricultural Landscape and the Forest Landscape, it has been included here since monitoring and calculation of these losses are a normal and increasingly important part of the environmental water monitoring programme and since area-specific losses and discharge of plant nutrients are of importance to the pollution burden on lakes and marine areas. Area-specific losses are also an indirect predictor of production 19
conditions for watercourse flora and fauna. No specific scales are given for assessing concentrations of nitrogen or phosphorus in watercourses; it is expected that these will be evaluated having been converted in areaspecific losses. Instructions for conversion are given with the scales in question. High concentrations of nitrate in drinking water can constitute a health problem and the National Food Administration defines drinking water as ”fully fit for consumption” when nitrate concentrations are below 10 mg NO3-N/l. Assessment scales for nitrate are not given here, however. Ammonium is converted into molecular ammoniac in an equilibrium reaction at high pH levels. The risk of fish and other aquatic organisms being poisoned rises rapidly at high ammonium concentrations at pH level exceeding about 8. Calculation methods and criteria for toxicity to fish and other aquatic organisms have been published (see references). Assessment scales for ammoniac are not given here. Assessment of current conditions TABLE 2. CURRENT CONDITIONS: concentration of total phosphorus in lakes (µg/l) Class Description Concentration Concentration May – October August 1 Low concentrations ≤ 12.5 ≤ 12.5 2 Moderately high concentrations 12.5 – 25 12.5 – 23 3 High concentrations 25 – 50 23 – 45 4 Very high concentrations 50 – 100 45 – 96 5 Extremely high concentrations > 100 Not defined Concentrations are given as seasonal mean (May – October) over one year based on monthly readings taken in the epilimnion or, if only one sample is taken, surface water (0.5 m). The concentration of total phosphorus displays little seasonal variation at lower concentration ranges and an assessment can also be made of concentrations recorded in August as shown above, although it should then be assessed as a mean figure over three years. Late summer concentrations vary enormously at extremely high concentrations and seasonal mean figures should be used to make an assessment. The classes relate to various production levels long used by limnologists, principally determined by the phosphorus 20
Page 1 and 2: Environmental Quality Criteria - La
Page 3 and 4: TO ORDER Swedish Environmental Prot
Page 5 and 6: Reference Group Mats Bengtsson, Swe
Page 7 and 8: Summary This report on lakes and wa
Page 11 and 12: included. In addition to a large nu
Page 13 and 14: ased estimates are used. Given that
Page 15 and 16: TABLE 1. SUMMARY of parameters incl
Page 17 and 18: 16 The current conditions scale in
Page 19: (in Swedish with English summary).
Page 23 and 24: show the availability of nitrogen i
Page 25 and 26: Mean concentration of total phospho
Page 27 and 28: TABLE 9. DEVIATION from reference v
Page 29 and 30: Comments Classifications must be ba
Page 31 and 32: winter/spring, i.e. ice-covered per
Page 33 and 34: Light conditions Introduction Light
Page 35 and 36: TABLE 13. CURRENT CONDITIONS: turbi
Page 37 and 38: Acidity / acidification Introductio
Page 39 and 40: industrial pH). The change in acidi
Page 41 and 42: The pre-industrial concentration of
Page 43 and 44: very high degree of reliability and
Page 45 and 46: TABLE 19. CURRENT CONDITIONS: metal
Page 47 and 48: TABLE 22. DEVIATION from reference
Page 49 and 50: TABLE 24. (continued) Cu Zn Cd Pb C
Page 51 and 52: Swedish EPA (1993): Metals and the
Page 53 and 54: Assessment of current conditions TA
Page 55 and 56: TABLE 29. CURRENT CONDITIONS: poten
Page 57 and 58: TABLE 32. DEVIATION from reference
Page 59 and 60: References Cronberg, G., Lindmark,
Page 61 and 62: (see Appendix 1). If submerged and
Page 63 and 64: References Andersson, B. (1998): Va
Page 65 and 66: The genera in question and their tr
Page 67 and 68: Benthic fauna Introduction Benthic
Page 69 and 70: TABLE 41. CURRENT CONDITIONS: botto
Page 71 and 72:
Comments The assessment must be bas
Page 73 and 74:
has yielded better results than did
Page 75 and 76:
TABLE 45. CURRENT CONDITIONS: fish,
Page 77 and 78:
TABLE 46. DEVIATION from reference
Page 79 and 80:
TABLE 48. DEVIATION from reference
Page 81 and 82:
TABLE 48. (Contd.) Proportion of al
Page 84 and 85:
Presentation of data When using the
Page 86 and 87:
APPENDIX 1 Ceratophyllum demersum 1
Page 88 and 89:
APPENDIX 2 Calculation of index and
Page 90 and 91:
APPENDIX 2 Table 1b. Indicator gene
Page 92 and 93:
Genus Indicator value -------------
Page 94 and 95:
APPENDIX 2 45 Planorbis sp. 46 Anis
Page 96 and 97:
APPENDIX 2 214 Leuctra hippopus 215
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APPENDIX 2 384 Tinodes waeneri 385
Page 100 and 101:
APPENDIX 2 (6) O/C index (Wiederhol
Page 102 and 103:
APPENDIX 3 Dace Stäm Leuciscus leu
Page 106:
REPORT 5050 Environmental Quality C
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Lakes and Watercourses

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