4.4. Monitoring of surface water acidification

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Surface water quality monitoring

4.4 Monitoring of surface water acidification

Acidification of surface waters is found in areas where acidic deposition is high and the catchment soil and bedrock are poor in limestone and other easily weatherable minerals. During the last century, acidic deposition in Europe has increased markedly as a consequence of increased atmospheric emission of oxides of sulphur and nitrogen, in particular from the burning of fossil fuels. The southern parts of Finland, Sweden and Norway are the areas most affected by surface water acidification. Most surface waters in western and central Europe are not affected by acidification. However, acidification has been observed in a number of areas, including high altitude lakes in some mountain regions, lakes and streams in some forest areas in central Europe, surface waters in acidic soil areas of Scotland, northern England and Wales and small seepage lakes in north-western Europe.

Monitoring of acidification effects is coordinated internationally in an ECE programme, the International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes, arising from the Convention on Long-range Transboundary Air Pollution. Participants are 12 European countries, Canada and USA. The member countries report chemical and biological variables to the programme centre.

The national acidification monitoring programmes are restricted to the countries affected by surface water acidification (Table 4.4.1 & 4.4.2). Finland, Norway and Sweden have, for instance, a long tradition of assessment of surface water acidification. The acidification monitoring programmes can be divided into: (1) nation-wide surveys to assess the extent of acidification and (2) monitoring programmes involving detailed studies of a few catchments with the purpose of understanding the process of acidification and analyzing trends. In the following the two types of monitoring programmes are described.

National acidification surveys

Norway, Finland and Sweden each have nation-wide surveys with the purpose of assessing the extent of acidification (NO-L2, SE-L1; Table 4.4.1). The surveys include national sampling of more than 1,000 lakes and are generally performed at intervals of five to ten years. In 1995 a coordinated lake acidification survey will be performed in each of the three countries.

The countries also take annual samples in a reduced number of lakes, ie. 176 lakes in Finland (FI-L4), 100 lakes in Norway (NO-L2) and 85 lakes in Sweden (SE-L2); in addition, a number of small streams are sampled. The annual programmes are used for analyses of acidification trends.

Table 4.4.1: National surface water acidification survey programmes.

No.	Name	Variables	Period of operation & Sampling Frequency (SF)	Geographical coverage
Acidification surveys
FI-L4	Acidification monitoring of surface waters	Water TEMPW, COND, PH, ALK, OX, OXSAT, TURB, CNR, COD_MN, PTOT, NTOT, NO3N, NH4N, FE, MN, SIO2, K, Ca, MG, NA, SO4, CL, F, AL-fract., TOC	since 1987: SF: National, 1/yr Lapland, 1/2-3 yr	National, 176 lakes; Lapland, 200 lakes
NO-L2	1000- Lake survey	Water PH, COND, CA, MG, NA, K, SO4, CL, ALK, NO3N, TOC, AL Biota Zoobenthos, fish	since 1986 (1005 lakes) full survey approximately every 10 year 100 lakes sampled annually (1/yr)	Nation-wide survey including 1005 lakes yearly 100 lakes,
NO-L4/R9	Monitoring of acidification & heavy metals in surface waters in the Norwegian-Russian border areas	Water PH, COND, CA, MG, NA, K, SO4, CL, ALK, NO3N, TOC, CU, AL, NI, PTOT, CHLA, COLIFAEC Biota Zoobenthos, phytoplankton, zooplankton, fish, Sediment CU, NI; CD, CO, PB, ZN, HG	Start year 1986 26 lakes and 3 rivers have been sampled since the late 1980s lakes; 1/yr rivers; weekly or monthly	40-50 sampling sites in each country In Norway: 26 lakes and 3 rivers plus 20 lakes only sampled twice
NO-L8/R13	Monitoring the effects of acidification on fish stock in Norwegian inland waters.	Fish: species composition and abundance	since 1980 SF: lakes - every 2-5 years rivers - 1/year	Nation-wide 140 river stations and 100 lake stations
NO-R13	Monitoring of invertebrates in Norway. To assess the development of acidification by use of indicator species	INVERT, species list, Acidification index (Raddum-index)	since 1981 SF: 2/year	Western Norway 15-20 stations in 8 river systems
SE-L1/R1	National lake & stream survey Multi-purpose monitoring programme also including assessment of acidification	Water TEMPW, CL, CHLA, NH4N, NO23N, NORG, NTOT, PO4P, PRES, PTOT, COND, TOC, SIO2, SDT, ABS, PH, ANC, ALK, CA, MG, NA, K, SO4, FE, MN, AL Biota macroinvertebrates	since 1972; SF: every five year	National - randomly selected 1000 lakes, 300 streams
SE-L2/R2	National time-series in reference lakes & streams Multi-purpose monitoring programme also including assessment of acidification.	Water TEMPW, CL, CHLA, NH4N, NO23N, NORG, NTOT, PO4P, PRES, PTOT, COND, TOC, SIO2, SDT, ABS, PH, ANC, ALK, CA, MG, NA, K, SO4, FE, MN, AL Biota macroinvertebrates, periphyton, phytoplankton, fish paleoreconstruction Sediment Sediment chemistry in lakes	Some stations have time series from the 1960s, others from the 1980s and others are new. Lake water chemistry 4/yr, Stream water chemistry 12/yr, Biota 1/yr except fish 1/3 yr and paleoreconstruction once sediment 1/10 yr	National - 85 lakes, 35 streams. Subjectively selected sites representing different eco-regions, different types of lakes and streams.

FI: Finland; NO: Norway; SE: Sweden;

One sample is taken from each waterbody both in the survey programme and in the annual programme, and it is then analyzed for general acidification variables. The common variables for all the monitoring programmes are pH (PH), conductivity (COND), alkalinity (ALK), total organic carbon (TOC), nitrate (NO3N), the four major cations: potassium (K), calcium (CA), magnesium (MG), and sodium (NA), and the anions: sulphate (SO4) and chloride (CL), and various aluminium fractions (AL-frac). Some monitoring programmes also include measurements of total phosphorus (PTOT), total nitrogen (NTOT), and ammonical nitrogen (NH4N). The extent of acidification is also assessed using of various biological indicators such as zoobenthos, phytoplankton, and fish.

Acidification studies in specific catchments

Seven integrated acidification monitoring programmes are in operation in five countries: Norway, Sweden, Finland, the UK, and Ireland (Table 4.4.2). Generally the programmes include extensive investigations of a limited number of waterbodies or catchments areas involving frequent sampling and determination of many variables. Chemical analyses of surface water samples are made and in some cases also of precipitation and groundwater samples. Water samples are analyzed for all the previously mentioned acidification variables. In some of the programmes detailed studies of the biological communities are also performed, examples being studies of macroinvertebrates in streams and the littoral zone of lakes, as well as studies of phytoplankton, macrophytes and fish. In some lakes the record of acidification is reconstructed by use of palaeolimnogical indicators (primarily diatoms).

Table 4.4.2: National surface water acidification monitoring programmes including detailed investigations of few waterbodies or catchment areas

No.	Name	Variables	Period of operation & Sampling Frequency (SF)	Geographical coverage
Monitoring of specific catchments
FI-R2	Transport of suspended & soluble material from land areas. Multi-purpose monitoring programme also including assessment of acidification.	TEMPW, COND; PH, TURB, ALK, SM, PTOT, NTOT, NO3N, NH4N, K, CA, MG, NA, SO4, CL, TOC, CNR, COD_MN, FE, MN, AL-fract., F,	Since 1962: Automatic sampling during peaks of flow, manual sampling once a week (52/yr)	13 small watersheds
NO-R2	Monitoring of 20 rivers in East, South & Western Norway To provide long-term data for revealing trends in acidification	PH, COND, CA, MG, NA, K, SO4, ALK, NO3N; TOC, AL-fract., Q	since 1980 SF: weekly-monthly	20 rivers in eastern, southern and western Norway
NO-R8	Transport & dynamics of acid compounds in calibrated catchments	Water chemistry on surface water, groundwater, and deposition PH, COND, CA, MG, NA, K, SO4, ALK, NO3N, TOC, AL, Q,	since 1973 SF: weekly	Nation-wide 5 catchments in regions with different levels of air-transported pollution of acid compounds
NO-L9/R12	Monitoring of liming projects in Norway. Chemical and biological effects of liming in acidified rivers and lakes	Water: COND, TURB, PH, ALK, SO4, NO3N, NA, K, CL, AL Biological: MAPHYT, INVERT, FISH	Start one year before liming is initiated. Variable sampling frequency.	Twelve liming projects, varying number of stations, but at least one reference station.
SE-L3/R3	National intensive time-series in reference lakes & streams Multi-purpose monitoring programme also including assessment of acidification.	Water TEMPW, CL, CHLA, NH4N, NO23N, NORG, NTOT, PO4P, PRES, PTOT, COND, TOC, SIO2, SDT, ABS, PH, ANC, ALK, CA, MG, NA, K, SO4, FE, MN, AL, HG, CD, PB, CU, ZN Biota macroinvertebrates, periphyton, phytoplankton, zooplankton, fish, contaminants of fish, paleoreconstruction Sediment Sediment chemistry in lakes	Some stations have time series from the 1960s, other from the 1980s and some are new. Lake water chemistry 7/yr, Stream water chemistry 12/yr, Biota Phyto- & zooplankton 6/yr macroinvertebrates, periphyton, fish, contaminants in fish 1/yr macrophytes 1/3 yr and palaeoreconstruction once sediment 1/10 yr	Nation-wide 15 lakes, 15 streams Subjectively selected sites representing different eco-regions, different types of lakes and streams
UK-	UK Acid Water Monitoring Network	Water PH, ALK, COND, CA, CL, SO4, NTOT, AL_D, DOC, Q Biota Fish, macroinvertebrates, macrophytes, diatoms,	Since 1988 Water: lakes 4/yr streams 12/yr, and continuous registration of pH and flow in 6 streams Biota 1/yr	11 lakes and 11 streams in areas considered to be sensitive to acidification
IE-	Acid Sensitive Surface Waters in Ireland	Water chemistry on precipitation, lake water, stream water Water OX, TEMPW, SDT, PH, COND, CNR, PO4P, NO23N, NH4N, ALK, CHLA, SO4, NA, CA, MG, CL, MN, AL-fract. Biota macroinvertebrates, phytoplankton, zooplankton, fish, paleolimnologi studies	Period 1987-90 Water: lakes 10/yr streams 10/yr, Biota 2/yr	5 lake catchments in acid sensitive areas Sampling of lake water and 12 inflowing streams, in addition 4 mountain streams were sampled. An acidification survey was conducted in 129 lakes.