Lakes and Watercourses

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Oxygen status and oxygen-consuming substances Introduction Dissolved oxygen is vital for respiration and many microbial and chemical processes in the ecosystem. The concentration may thus regulate the biological structure. Oxygen conditions vary, mainly due to changing production conditions and the organic load, including natural humic substances leaching from the catchment area. In the bottom water of stratified lakes (the hypolimnion), the oxygen situation is at its worst at the end of the stagnation period in summer, at which time conditions may become critical for many organisms. The end of the period when lakes and rivers are ice-covered is another crucial time. Oxygen conditions in watercourses may be poorest at times of low flow, particularly in polluted rivers. Significant variations in oxygen levels and oxygen saturation can occur from one day to the next in the surface waters of unstratified lakes and in rivers and streams. Oxygen concentration is prefered to saturation as a means of characterising oxygen status because the thresholds of tolerance of various organisms are usually expressed as concentrations. However, merely stating the oxygen concentration may give an incomplete picture of oxygen conditions, particularly in rivers and streams. This is due to variations in oxygen input and organic load. The presence of oxygenconsuming substances should therefore also be taken into account. The concentration of organic matter provides essential information about the risk of low oxygen levels occurring between the occasions on which oxygen concentrations are monitored. A high oxygen concentration or oxygen saturation is not always a sign of a ”healthy” environment. Assimilation by plants may result in saturation figures of over 100 per cent in eutrophic waters. Scales have only been given for assessing current conditions because of the difficulties of determining reference values. Assessment of current conditions Oxygen status is assessed in the bottom waters of stratified lakes and also in the circulating water column in unstratified lakes. Annual minimum values based on concentrations monitored during critical periods (late 29
winter/spring, i.e. ice-covered period, late summer/autumn) over three years are assessed for all lakes. Annual minimum values for watercourses are also assessed, although here assessment should be based on samples taken 12 times a year over three years. It may be necessary to monitor concentrations more frequently in small watercourses, particularly during the summer. TABLE 10. CURRENT CONDITIONS: oxygen concentration (mg O 2 /l) Class Description Annual minimum concentration 1 Oxygen-rich ≥ 7 2 Moderately oxygen-rich 5 – 7 3 Moderately oxygen-deficient 3 – 5 4 Oxygen-deficient 1 – 3 5 No or almost no oxygen ≤ 1 Note: The presence of hydrogen sulphide (H 2 S) is indicated by †† Samples from the deepest point in a stratified lake sometimes give a misleading picture of oxygen state if only a very small proportion of the total volume of the lake is deep water. To avoid this, a rule of thumb should be that readings taken from localities or sampling depths representing at least 10 per cent of the bottom area of the lake should be used to reflect the oxygen status of stratified lakes. TABLE 11. CURRENT CONDITIONS: organic matter (oxygen-consuming substances) Class Description Concentration as TOC or COD Mn (mg/l) 1 Very low concentration ≤ 4 2 Low concentration 4 – 8 3 Moderately high concentration 8 – 12 4 High concentration 12 – 16 5 Very high concentration > 16 30
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 and 20: (in Swedish with English summary).
Page 21 and 22: conditions for watercourse flora an
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: Comments Classifications must be ba
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 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 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
Page 98 and 99:
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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