INNSENDTE ARTIKLER Water chemistry and acidification recovery in Rogaland County By Espen Enge Espen Enge is senior engineer, Environmental Division, County Governor of Rogaland. Sammendrag Introduction Redusert forsuring av fjellvann i Rogaland Due to exceptionally slow weathering bedrock, fylke. Her bearbeides resultater fra i alt 1144 the concentrations of ions in river and lake water prøver fra 2002, 2007 og 2012. Tre ulike forsurings­ in the mountain areas of southern Norway are modeller antydet at forsuringen i fjellområdene i generally very low (Wright and Henriksen 1978). Rogaland (>500 m) i dag er begrenset, og at In Rogaland, 12% of the surveyed lakes in 1974­ vannkvaliteten trolig er nær en opprinnelig ufor­ 1979 (Sevaldrud and Muniz 1980) had conduc­ suret vannkvalitet. Mange lavereliggende inn­ tivity of <10 µS/cm, and the minimum value was sjøer var tilsynelatende fortsatt forsuret, men 4.2 µS/cm. disse estimatene kan være forbundet med usik­ Dilute, weakly buffered water is highly sensi­ kerhet. Ioneinnholdet i vannet i fjellområdene er tive to acidification. Thus, as early as the 1870s ekstremt lavt, noe som i seg selv trolig utgjør en the brown trout population (Salmo trutta) in begrensning for utbredelsen av aure. Sandvatn in Hunnedalsheiene declined close to extinction (Huitfeldt­Kaas 1922), possibly due to Summary emerging acidification (Qvenild et al. 2007). In The current study compiles data from 1144 water the 1920s massive fish kills due to acidic water samples from three large regional water chemical were observed in the salmon rivers Dirdal, Fra­ surveys, performed in 2002, 2007 and 2012. fjord and Espedal (Huitfeldt­Kaas 1922). Coin­ Three different models suggested that the acidi­ cidentally, mass death of brown trout was fication of the mountain lakes in Rogaland (>500 observed in some of the mountain lakes, e.g. in m) has declined to a minimum, and subsequently Månavatn (Huitfeldt­Kaas 1922). In the follo­ that the water chemistry is close to “pre­acidifi­ wing decades the acidification problems increa­ cation” conditions. Many low altitude lakes were sed (Hesthagen et al. 1999), and in 1970­1980 as apparently still acidified, but these estimates were much as 41% of the county area was severely associated with somewhat uncertainty. The con­ affected by acidification (Sevaldrud and Muniz ductivity of the water in the mountain areas is 1980). extremely low, and is possibly restricting the dis­ Several large regional water chemical surveys tribution of brown trout. have documented the water chemical effects of the acidification in Norway. The most important of these surveys were the comprehensive samp­ 78 VANN I 01 2013 INNSENDTE ARTIKLER Sandvatn (altitude 910 m). In these remote, barren mountain areas the water is extremely dilute. According to Huitfeldt-Kaas (1922) the brown trout population in Sandvatn was close to extinction as early as the 1870s (Photo: Anne E. Carlsen). ling of 700 lakes in southern Norway in 1974­ Material and methods 1975 (Wright and Snekvik 1978), the “1000 lakes The sampling included lakes from all over Roga­ survey” in 1986 (Lien et al. 1987) and the regional land County, from sea level up to an altitude of survey of 1500 lakes in 1995 (Skjelkvåle et al. 1324 m. To assure a convenient map overlap to 1996). the neighboring counties in the east (Aust­ and Due to several international emission control Vest­Agder), a few samples from these two coun­ agreements (unece.org 2013), the acid deposition ties, located along the border, were also included. over Norway have been considerably reduced The intention was to sample the same lakes over the last 2­3 decades. Sulfate in surface water all three years (2002, 2007 and 2012), but minor has decreased by 43­86% throughout 1980­2010, changes in the selection were, however, unavoid­ and a distinct increase in pH and ANC has been able (will be discussed later). Primarily, lake observed (Skjelkvåle 2011). In 14 lakes in “Sør­ locations were sampled, but occasionally rivers Vestlandet”, including Rogaland, a 74% decrease and streams were sampled too. Water was sampled in non­marine sulfate has been observed bet­ at the lake outlets, but in some lakes, however, ween 1986 and 2010 (Skjelkvåle 2011). the samples had to be collected as surface Over the last decade, the County Governor of samples along the shoreline of the lakes. In 2002 Rogaland has performed several large scale the water was sampled in new 125 ml HDPE water chemical surveys. In the current study this bottles (“Nalgene”), in 2007 in 250 ml PE bottles data set has been used to update the acidification (“Assistent”) and in 2012 in 150 ml HDPE bottles status in the county and predict the remaining (“Mellerud Plast”). recovery potential. Sampling was performed by local environ­ VANN I 01 2013 79 INNSENDTE ARTIKLER mental authorities (“kommuner”), landowners meter and Metrohm ion selective electrodes and landowners associations, power companies, (ISE), according to the electrode manuals. Ca tourist associations and other volunteers. The was measured with Radiometer electrode sampling period was set to June, July and ISE25Ca according to Enge et al. (in prep.). Non August. Sampling beyond this period was also marine fractions of ions (notation: *) were cal­ accepted, e.g. sampling in September/October culated by subtracting the marine fractions, for lakes in remote high altitude areas having estimated from Cl, from the measured concen­ snowmelt throughout the entire summer. The trations (Skartveit 1980). H+ adjusted conducti­ samples were stored cold, and sent to the labo­ vity was calculated by subtracting 0.35 µS/cm ratory within a few days after sampling. per µeq/l H+. The median time between sampling and the The chemical measurements were subject to samples being received at the laboratory, was 3 internal and external quality assurance. Partici­ days. The median time further to analysis of pH, pation at “SIFF­Ringtest” in 2002, demonstrated conductivity, color and alkalinity was 1 day results comfortably within the acceptance limits (2012). The other three parameters accept a cer­ for all parameters and test samples. tain storage time (Eaton et al. 1995), but were Several advanced water chemical models for anyhow analyzed within a few days. assessing acidification have been developed, e.g. pH, conductivity, color and Ca were measu­ the frequently used “MAGIC” model (Cosby et red on all samples in all years, and alkalinity, Na al. 1985). Such models are, however, highly and Cl in 2012 only. There have been some demanding with respect to both water chemical minor changes in analytical equipment through­ and catchment input data. Thus, three simpler out the years, but except for the determinations models were applied at the current data material: of color, the instrumentation are comparable. pH was measured with pH­meters Radiometer 1. A general evaluation of the acidification was PHM92 and VWR “pHenomenal”. Calibration performed with the classical “Henriksen was performed with standard buffers (pH=4.01 acidification indicator” (Henriksen 1978). and 6.86/7.00). The applied electrodes were 2. Acidification was also estimated as loss of Metrohm “Aquatrode” (2002), Radiometer alkalinity (Henriksen 1978). Due to the lack GK2401C (2007&2012) and Radiometer of Mg­data, the original alkalinity (“ALK0”) pHC2001 (2012), all excellent for low conducti­ was estimated using non marine Ca only, vity water measurements. Intercalibration of the according to Henriksen (1980): electrodes showed agreement in the range of ALK0=1.21Ca*. Henriksen (1978) suggests a ±0.02 pH. The conductometers used, Petracourt “background acidification” of 10­20 µeq/l in PCM1 (2002), HACH CO150 (2002), Amber granitic areas in southern Norway. Thus, the Science mod. 1056 (2007&2012) and Cyberscan lakes that had an alkalinity loss >20 µeq/l PC300 (2007&2012) were calibrated with stan­ were considered as “acidified”, while those dard KCl­solutions. Intercalibration of the con­ with a loss of <10 µeq/l were considered as ductometers showed agreement to ±0.5 µS/cm in “not acidified”. the current measuring range. Color was measu­ 3. Estimated pre­acidification pH­values red with comparator HACH CO­1 (2002&2007) (pH0), according to Hindar and Wright and photometric (445 nm) without filtration (2002), were compared to observed pH. (2012). Thus, the color results are not directly pCO2 was set to 4x the atmospheric partial comparable between 2002/2007 and 2012. Alka­ pressure (Enge 2009). linity was titrated with sulfuric acid to fixed endpoint pH=4.50, and equivalence alkalinity Estimations of pre­acidification pH require (“ALKe”) was calculated according to Henriksen analysis of all major constituents in water. The (1982a). Na and Cl were measured with Radio­ “1000­lakes survey” in 1986 (Lien et al. 1987) is 80 VANN I 01 2013 INNSENDTE ARTIKLER one of the few large regional surveys meeting causing pollution and possibly other severe this requirement. The 32 lakes included in both water chemical interferences. Pollution may also the 1000­lakes survey and the current study, directly affect the ISE­measurements (Ion were used. Select ive Electrodes). Mapping was performed with ArcGIS/Arc­ The water chemistry showed distinct geo­ Info (v.10.1). The Thiessen polygon method was graphic gradients, figure 1 and figure 2. Most applied for map presentations. A “redraw” of an apparent was the decreasing conductivity, Ca old map of pH­values in the lakes in Rogaland and color along a southwest to northeast gradient, from the mid 1980s (Enge and Lura 2003) has while pH decreased along a northwest to south­ been included in the current study. Originally, east gradient. this map was drawn by hand, but due to the The marine exposure was highly correlated requirement of an objective basis for compari­ to geographic parameters. Multiple regression of son, this map was redrawn by using Thiessen log{Cl} against UTM­East, UTM­North and polygons.