Boreal Environment Research 20: 431–454 © 2015 ISSN 1239-6095 (print)  ISSN 1797-2469 (online) H elsinki 28 August 2015 Preface to the special issue on integrated research of atmosphere, ecosystems and environment at Pallas Annalea Lohila1), Timo Penttilä2), Sinikka Jortikka3), Tuula Aalto1), Pia Anttila1), Eija Asmi1), Mika Aurela1), Juha Hatakka1), Heidi Hellén1), Heikki Henttonen2), Pekka Hänninen4), Juho Kilkki1), Katriina Kyllönen1), Tuomas Laurila1), Ahti Lepistö5), Heikki Lihavainen1), Ulla Makkonen1), Jussi Paatero1), Martti Rask6), Raimo Sutinen7), Juha-Pekka Tuovinen1), Jussi Vuorenmaa5) and Yrjö Viisanen1) 1) Finnish Meteorological Institute (FMI), P.O. Box 503, FI-00101 Helsinki, Finland 2) Natural Resources Institute Finland (LUKE), P.O. Box 18, FI-01301 Vantaa, Finland 3) Natural Resources Institute Finland (LUKE), Eteläranta 55, FI-96300 Rovaniemi, Finland 4) Geological Survey of Finland (GTK), P.O. Box 96, FI-02151 Espoo, Finland 5) Finnish Environment Institute (SYKE), P.O. Box 140, FI-00251 Helsinki, Finland 6) Natural Resources Insititute Finland (LUKE), Survontie 9 A, FI-40500 Jyväskylä, Finland 7) Geological Survey of Finland (GTK), P.O. Box 77, FI-96101 Rovaniemi, Finland Lohila A., Penttilä T., Jortikka S., Aalto T., Anttila P., Asmi E., Aurela M., Hatakka J., Hellén H., Hent- tonen H., Hänninen P., Kilkki J., Kyllönen K., Laurila T., Lepistö A., Lihavainen H., Makkonen U., Paatero J., Rask M., Sutinen R., Tuovinen J.-P., Vuorenmaa J. & Viisanen Y. 2015: Preface to the spe- cial issue on integrated research of atmosphere, ecosystems and environment at Pallas. Boreal Env. Res. 20: 431–454. The Pallas area in northern Finland has served as a meteorological monitoring site for 80 years and, more recently, as a platform for atmospheric, ecological and hydrological research. Currently, Pallas comprises one of the most important research infrastructures in Finland and in the wider circumpolar region. Moreover, it is a successful example of the benefits obtained from scientific cooperation and integration among disciplines. This paper is an introduction to a special issue that collates studies related to greenhouse gas fluxes and concentrations, atmospheric aerosols and air pollutants, which were presented at the Fourth Pallas Symposium held in 2013. We give an overview of the historical and current research activities within the Pallas area, outline the most important infrastructure projects and list the recent literature that has originated from the various scientific programs and projects. The results of these activities are illustrated in this paper with examples of long- term data sets on variations in soil, lake and river water, air quality and greenhouse gas concentrations. Pallas area as a meeting point of nature heritage and top science The Pallas fells, located approximately 170 km north of the Arctic Circle, rise to an elevation of 500–800 m above sea level (a.s.l.); the high- est summit, Taivaskero, reaches 809 m a.s.l. The fells belong to the 50-km-long fell chain of Pallas–Ounastunturit (the Finnish word tunturi, used here as a suffix, means “fell”). Pallasjärvi 432 Lohila et al.  •  Boreal Env. Res. V ol. 20 is the largest lake within the area, has an area of 17.3 km² and drains to the Baltic Sea via the rivers Ounasjoki and Kemijoki (the Finnish words järvi and joki, used here as suffixes, mean “lake” and “river”, respectively). The mean and maximum depths of Pallasjärvi are 9 and 36 m, respectively. The Keimiötunturi, Sammaltunturi and Pallastunturi are composed of mafic volca- nic rock types, thus giving rise to nutrient rich soil conditions on the fell slopes. The treeline conifer species is the Norway spruce, which is found at 457 m a.s.l. on the Lommoltunturi and at 530–548 m a.s.l. on Keimiötunturi. In contrast, the treeline conifer on the nutrient-poor, felsic Ounastunturi is the Scots pine at 360 m a.s.l. (Sutinen et al. 2011). As a consequence of the warming climate in the region since the 1920s, a significant shift of spruce has occurred such that the tree line has extended in elevation by 55 m in 60 years (Sutinen et al. 2012). According to the Köppen climate classifica- tion, the Pallas region is located at the edge of the northern-boreal and subarctic climatic zones. The winters are cold and the summers short and cool with long-term monthly mean temperatures of –14 °C and +14 °C in January and July, respectively. The long-term annual mean tem- perature (1981–2010) measured at the Alamuo- nio weather station located ca. 35 km west of Pallas is –1.0 °C (Pirinen et al. 2012). The aver- age peak snow depth reaches 73 cm and is typ- ically observed during the latter half of March. Pallas can be considered to also lie on the border of anthropogenic influences: to the south there is densely populated, continental Europe, while to the east and north there are mainly large, sparse- ly-populated areas dominated by tundra and the Arctic Ocean, respectively. Although the first air quality measurements at Pallas were moti- vated by the industrial emissions from the Kola Peninsula (Russia), the area is one of the least polluted parts of continental Europe and thus the data from the Pallas sites are often considered to represent “background conditions”. The Pallastunturit area was designated as a National Park in 1938. While the National Park initially covered the Pallas-Ounastunturi region, in 2005 it was expanded to include the southern fell area of Yllästunturit as well. The Pallas-Yllästunturi National Park currently covers an area of 1020 km2. On 6 July 1952, the Olympic flame ignition for the Helsinki Olympic Games took place at the summit of the Taivaskero fell. The Finnish Meteorological Institute (FMI; Finnish Meteorological Office before 1968) has a long history of atmospheric monitoring at Pallas. The first weather station “Pallasjärvi” (site 6c in Fig. 1) was established near Pallasjärvi in 1935 with three daily weather observations (Fig. 2a). The operation of this station ceased in 1972, four years after the retirement of Mr. Viljo Pakasmaa, the station manager and the park ranger of the Pallas-Ounastunturi National Park (Fig. 2b). The only significant gap in the observation records between 1935 and 1972 was from the autumn of 1944 to the winter of 1946 as the residence of the park ranger at Pallasjärvi was destroyed in the final stages of World War II (Keränen and Väisälä 1938, Hiilivirta and Hiilivirta 2011). The weather station was in operation again from 1996 until 2002, thereafter the measurements were moved to the newly established Kenttärova station. The Pallas research infrastructure has been extensively instrumented for modern and versa- tile monitoring of the environment since the start of continuous monitoring of atmospheric sulphur dioxide (SO2) and ozone (O3) concentrations at Sammaltunturi in September 1991, and with the setup of the Global Atmosphere Watch (GAW) station in 1994. The measurement sites have contributed to numerous European and global research programs and research infrastructures (Table 1). In 2009, the Academy of Finland recognized Pallas (together with the FMI Arctic research Centre at Sodankylä) as one of the most significant national research infrastructures in Finland. Since 2015, the measurements of greenhouse gas (GHG) concentrations and eco- system-atmosphere fluxes have been part of the Integrated Carbon Observation System (ICOS). Pallas has also been nominated as a strong can- didate for the European-wide ecosystem exper- imentation infrastructure (AnAEE). Thus Pallas is unquestionably one of the most important cli- mate and ecosystem research stations in northern Europe and within the wider circumpolar region. This special issue of Boreal Environment Research covers a wide spectrum of research that takes place at Pallas. It was conceived in Septem- Boreal Env. Res. V ol. 20  •  Research of atmosphere, ecosystems and environment at Pallas 433 Fig. 1. Map of the Pallas area showing the mea- surement stations. Expla- nations are provided in Tables 2 and 3, except for sites 6a, b and c which are the Laukukero weather station, Pallas- järvi automatic weather station (1996–2002) and Pallasjärvi manual weather station (1935– 1972), respectively. Red circles, upward triangles and downward triangles represent FMI, SYKE and GTK measurement sites and sampling points, respectively. The main study sites for small-mam- mal research around Pal- lasjärvi are indicated as follows: black circles and ovals indicate the long- term, continuous monitor- ing sites (since 1970), and gray rectangles indicate various experimental sites with live-trapping pro- grams. Other, more irreg- ular mammal sampling sites are not shown. Fig. 2. (a) Mrs. Esteri Pakasmaa (née Kotakorva) making meteorological observations at the Pallasjärvi weather station in 1963. Local school children are following the procedure. (b) Mr. Viljo Pakasmaa beside the instrument shelter at Pallasjärvi in 1965. The shelter contains a thermometer to measure the ambient temperature, a wet-bulb thermometer for obtaining the dew point of the air, and a minimum–maximum thermometer for daily minimum and maximum temperatures. Photos: Ms. Sofia Pyykönen’s family album via Pallastunturi Nature Centre. ber 2013 during the Fourth Pallas Symposium, which was organized at Hotel Jeris, Muonio, in the inspiring surroundings of Jerisjärvi, which is adjacent to the Pallas-Yllästunturi National Park. The symposium brought together 45 scientists from different disciplines, which included e.g. geology, environmental science, atmospheric sci- ence, hydrology and biology. The earlier Pallas a b 434 Lohila et al.  •  Boreal Env. Res. V ol. 20 Symposia in 1988, 1996 and 1998 dealt mainly with the role of research within nature reserves. In 1988, the first symposium examined recent and current studies in nature conservation areas around the country. The topics of the first sympo- sium ranged from basic cartography in the natu- ral sciences to environmental economics (http:// www.metla.fi/tapahtumat/2013/pallas-sympo- sium/folia-forestalia-736.pdf). The second sym- posium in 1996 was still focused mainly on the role of the Pallas-Ounastunturi National Park in monitoring global environmental changes, although topics related to climate change were already emerging (http://www.metla.fi/julkaisut/ mt/623/index.htm). The topics of the third sym- posium were concentrated on the role of the National Park in literature and visual arts (http:// www.metla.fi/julkaisut/mt/735/index.htm). As an outcome of this meeting, a book entitled “Pal- las-Ounas” was published (http://www.metla.fi/ julkaisut/muut/annanpalo.htm). The key topic of the Fourth Symposium was the interactions between northern ecosystems and the various needs of human society with the main focus on recent trends and ecosystem functioning, and on the responses of northern ecosystems to chang- Table 1. International measurement programs and research infrastructures to which the Pallas sites contribute. Program/Infrastrucutre A cronym S ites included R esponsible institutes Global Atmosphere Watch GAW S ammaltunturi FMI Aerosols, Clouds, and Trace gases Research ACTRIS -2 S ammaltunturi, Matorova FMI Infrastructure International Arctic Systems for Observing IASOA S ammaltunturi FMI the Atmosphere Arctic Monitoring and Assessment AMA P S ammaltunturi, Matorova FMI, SYKE, Programme Pallasjärvi IVL The European Monitoring and Evaluation EME P S ammaltunturi, Matorova FMI, IVL Programme International Co-operative Programme on IC P M atorova L UKE Assessment and Monitoring of Air Pollution Forests Effects on Forests International Co-operative Programme on IC P IM Pallasjärvi and its catchment S YKE, FMI, Integrated Monitoring of Air Pollution Effects L UKE on Ecosystems Finnish Long-Term Socio-Ecological FinLTSER Pallasjärvi and its catchment S YKE, FMI, Research network L UKE Integrated Carbon Observation System ICOS L ompolojänkkä, Sammaltunturi FMI European Long-Term Ecosystem Research LTER - Pallasjärvi and its catchment S YKE, FMI, Network E urope L UKE International Long-Term Ecological Research ILTER Pallasjärvi and its catchment S YKE, FMI, Network L UKE EU Water Framework Directive WFD Keimiöjärvi, Pallasjärvi, S YKE, LUKE Pallasjoki Pan-Eurasian Experiment PEEX S ammaltunturi, Matorova FMI Global Mercury Observation System GMOS M atorova FMI, IVL Analysis and Experimentation in Ecosystems A naEE candidates: Lompolojänkkä, FMI (under construction) Kenttärova Boreal Env. Res. V ol. 20  •  Research of atmosphere, ecosystems and environment at Pallas 435 ing environment. Seven of the presentations of the symposium were expanded to full scientific papers presented in this special issue. This intro- ductory paper gives an overview of the wide spectrum of research conducted at Pallas, and lists the most recent published literature. Overview of the research sites and topics A wide range of environmental research is con- ducted within the Pallas area by the FMI, the Natural Resources Institute Finland (LUKE), the Finnish Environment Institute (SYKE) and the Geological Survey of Finland (GTK). The main research topics include GHG concentrations and ecosystem–atmosphere fluxes, the climate effects of atmospheric aerosols, aerosol–cloud interactions and air quality (FMI), the effects of air pollution on ecosystems, climate effects on both hydrology and physical, chemical and biological chracteristics of surface waters, and the deposition of persistent organic pollutants (POPs) (SYKE). At the aquatic sites — Pallas- järvi, Keimiöjärvi and Pallasjoki — LUKE is responsible for collecting fish status data for sur- veillance monitoring and ecological classification according to the EU Water Framework Directive. LUKE also monitors population dynamics, para- sites and pathogens of small rodents, forest con- dition (ICP Forests), dynamics of natural forests and timberline forests, and the timing of spring and autumn phenophases. GTK is currently studying soil hydrological changes with a par- ticular interest in snow accumulation, snowmelt and soil freezing mechanisms, which are related to treeline dynamics. Pallas also serves as one of the sites of the Finnish network for monitoring the concentrations of mercury and other heavy metals, benzo(a)pyrene, O3 and other air pollut- ants as required by the European legislation on ambient air quality assessment and management. In addition to the engagement of several national institutes, there is active cooperation with foreign institutes and universities, such as the Swedish Environmental Research Institute (IVL), the US National Oceanic and Atmo- spheric Administration (NOAA), and Royal Hol- loway University of London, UK. There are several research stations and mea- surement sites established within the area, the most prominent of which is the log cabin con- structed by the former Finnish Forest Research Institute (METLA, now part of LUKE) and the FMI at the summit of the Sammaltunturi (Fig. 1). Other measurement sites, typically smaller log or fiberglass cabins and shelters, or just sample-col- lection instruments, are spread over a relatively small area mainly south of Pallasjärvi. The Pallas area comprises five official FMI weather stations: Matorova (established in 1995), Laukukero (1996), Sammaltunturi (1996), Kenttärova (2002) and Lompolonvuoma (2013). The latter is actually situated on the Lompolo- jänkkä mire on the premises of the GHG flux station, but it is named according to the adja- cent wetland west of Lompolojänkkä. The main meteorological variables recorded at these sta- tions are air temperature, relative humidity, wind speed and wind direction. In addition, soil tem- perature and moisture, air pressure, snow depth, precipitation and solar radiation are measured at Kenttärova and Lompolojänkkä (for details see tables 2 and 3 in Aurela et al. 2015). While the Laukukero station (site 6a in Fig. 1) mainly provides meteorological outputs with occasional measurement campaigns for other variables, the other stations host a wide spectrum of different research activities. Four GHG flux stations at Pallas are partly co-located with the weather stations: Kenttärova spruce forest (GHG flux measurements established in 2003), Lom- polojänkkä wetland (2005), Pallaslompolonniemi at Pallasjärvi (2014) and Sammaltunturi (2013). Measurements at these sites include the exchange of carbon dioxide (CO2), water vapor and energy between the atmosphere and the local ecosystem. At some stations, methane (CH4) exchange is also measured. These data make it possible to quan- tify the GHG balances of the major ecosystems within the area (Aurela et al. 2015). In addition to GHG fluxes, many additional meteorological and hydrological measurements are conducted to facilitate the interpretation of the flux data. These measurements are detailed in table 2 of Aurela et al. (2015). The Sammaltunturi station (site 1 in Fig. 1) is located at an elevation of 565 m a.s.l. at the summit of the second southernmost fell along 436 Lohila et al.  •  Boreal Env. Res. V ol. 20 the 50-km-long north–south chain of fells. The station resides ca. 100 m above the treeline. The vegetation around the station consists mainly of low vascular plants, mosses and lichen. Moni- toring activities at Sammaltunturi began in 1991 in a building that originally served the Finnish Broadcasting Company. The new, 102-m2 station opened in July 2001. Since 1994, Sammaltunturi has been a node of the Pallas–Sodankylä supersite that contributes to the GAW program of the World Meteorological Organization. The GAW measure- ments at Sammaltunturi focus on tropospheric air composition and meteorology, while upper-air ozone soundings and measurements of aerosol optical depth and spectral UV, for example, are operated by the FMI Arctic Research Centre at Sodankylä (125 km SE from Pallas). As the Pallas area has no significant local or regional air pollu- tion sources, Sammaltunturi provides an excellent location for the monitoring of the background air composition in northern Europe. The measure- ments conducted at Sammaltunturi and other sites are detailed in Table 2. The Matorova station (site 2 in Fig. 1) lies 6 km ENE of Sammaltunturi at an elevation of 340 m a.s.l. The station is mainly used to col- lect deposition, gas and aerosol samples. Special attention is paid to minimize contamination of the samples collected for trace metal, mercury and POP analyses. This extends to the selection of the materials for the station building and to the wooden walking trails constructed to prevent wind-driven erosion. In addition, usage of motor vehicles close to the station is limited as much as possible. A Level II intensive monitoring site of the International Co-operative Programme on the Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests, site 9) is located in the close vicinity of the Matorova station. The Kenttärova station (site 3a in Fig. 1), which includes a 20-m high measurement tower, was established in 2002 to study atmosphere– biosphere interactions above a Norway spruce forest. For synergy, the FMI Observation Ser- vices moved the old Pallasjärvi weather station, located 5 km to the northwest, onto the premises of Kenttärova. The Kenttärova station lies on a hilltop plateau, 1.4 km south of the Matorova station, ca. 60 m above the surrounding plains. Kenttärova is well known for often having the thickest snow cover among the Finnish weather stations. A more detailed description of the site is given in Aurela et al. (2015). The Lompolojänkkä (site 4 in Fig. 1) flux station was built in 2005 to measure CO2 and CH4 exchange between the wetland and the atmosphere (Aurela et al. 2015). It is located on a treeless open mire through which the waters from the Kenttärova catchment discharge to Pal- lasjärvi. This aapa mire is characterized by a relatively high water level, with almost the entire peat profile being water-saturated throughout the year (Aurela et al. 2009, Lohila et al. 2010). The maximum peat thickness is 3 m. Peat cores and their macrofossil and radiocarbon analyses have revealed that peatlands started to develop imme- diately after the retreat of the ice about 10 000 years ago. Since then, the mire has been growing both horizontally and vertically (Mathijssen et al. 2014). In 2008, a drying and warming exper- iment was set up at Lompolojänkkä by LUKE to quantify the effects of the predicted climate change, i.e. warming, water-level drawdown and their interactions, on the functioning of the fen ecosystem (Pearson et al. 2015). The Pallaslompolonniemi (site 5 in Fig. 1) flux station was established in order to measure gas and energy fluxes between Pallasjärvi and the atmosphere. A 2-m-tall steel mast was erected in June 2012 at the tip of a small spit, a beautiful site which is also known as an ancient hunting and fishing site of the Sami people. The spit is part of an esker gravel ridge that is partly located underwater. The ridge divides the area into a shallow and sheltered inlet (through which the surface waters from the Pallaslompolo catchment are discharged), and a deeper lake. The mean depths of the lake are approx. 1.5 and 5 m in the inlet and in the deeper parts, respectively. In addi- tion to GHG fluxes, basic meteorological data and water temperature and level are measured at this site (Lohila et al. 2015, Aurela et al. 2015). Pallasjärvi with its catchment (sites 7a–f in Fig. 1). SYKE conducts hydrological, chem- ical and biological monitoring at seven stations, including four main inlet streams, two lakes and a river. Keimiöjärvi (site 7g in Fig. 1) is located outside the catchment ca. 5 km south of Pallasjärvi. The main studies utilizing these measurements include air pollution effects on Boreal Env. Res. V ol. 20  •  Research of atmosphere, ecosystems and environment at Pallas 437 Ta bl e 2. M ai n va ria bl es m ea su re d at th e di ffe re nt P al la s su bs ite s. T he s ite lo ca tio n is s ho w n ac co rd in g to th e W G S- 84 c oo rd in at es . N um be rs in b ol d de pi ct c or re sp on di ng si te s in F ig . 1 . Su bs ite V a ria bl es M ea su re m en t m et ho ds R ef er en ce Sa m m al tu nt ur i ( fe ll to p) , s ite 1 (6 7° 58 .4 00 ´N , 2 4° 06 .9 39 ´E , 5 65 m a .s .l. ) FMI At m os ph er ic CO 2, CH 4, N 2O , O 3, O n- si te a na ly ze rs H at ak ka e t a l. 20 03 , K ilk ki e t a l. SO 2, NO +NO y, SF 6, CO , H 2 20 15 , R uo ho -A iro la e t a l. 20 15 , T s ur ut a et a l. 20 15 NOAA , U S A t m os ph er ic CO 2, CH 4, CO , H 2, W ee kl y fla sk s am pl es ht tp :// w w w. es rl. no aa .g ov /g m d/ N 2O , S F 6, δ1 3 C (CO 2), δ 18 O cc gg /fl as k. ph p (CO 2) R oy al H ol lo w ay A t m os ph er ic d el ta 13 C (CH 4) W ee kl y ba g sa m pl es S r is ka nt ha ra ja h et a l. 20 12 U ni ve rs ity o f Lo nd on , U K FMI A t m os ph er ic VOC O n- lin e G C H el lé n et a l. 20 15 FMI T o ta l a nd c lo ud in te rs tit ia l a er os ol 2 ¥ C PC , 2 ¥ D M PS Ko m pp ul a et a l. 20 03 , K iv ek äs nu m be r c on ce nt ra tio n an d si ze et a l. 20 09 di st rib ut io n (7 –5 00 n m ) FMI L a rg er a er os ol s iz e di st rib ut io n (0 .5 –1 0 µm ) A P S FMI I o n an d ne ut ra l p ar tic le s iz e di st rib ut io ns NAIS L i ha va in en e t a l. 20 07 , M an ni ne n (0 .4 –4 0 nm ) et a l. 20 10 FMI A e ro so l h yg ro sc op ic ity H -T D MA A n tti la e t a l. 20 09 FMI A e ro so l b la ck c ar bo n, s ca tte rin g an d A e th al om et er , A a lto ne n et a l. 20 06 , L ih av ai ne n ab so rp tio n co ef fic ie nt s N ep he lo m et er , M AA P et a l. 20 15 FMI PM 10 a er os ol m as s Be ta g au ge FMI 22 2 R n T o ta l b et a ac tiv ity Pa at er o et a l. 19 94 FMI CO 2, H 2O , s en si bl e he at , m om en tu m fl ux es Ed dy c ov ar ia nc e Au re la e t a l. 20 15 FMI Ph en ol og y, cl ou di ne ss D ig ita l p ho to gr ap hy K en ttä ro va (s pr uc e fo re st ), si te 3 a (6 7° 59 .2 37 ´N , 2 4° 14 .5 79 ´E , 3 47 m a .s .l. ) FMI At m os ph er ic CO 2, CH 4, H 2O O n- si te a na ly ze r co nc en tra tio n pr ofi le in th e ca no py FMI CO 2, H 2O , s en si bl e he at , m om en tu m fl ux es Ed dy c ov ar ia nc e Au re la e t a l. 20 15 FMI So il CH 4, N 2O fl ux es M an ua l c ha m be rs FMI C lo ud b as e he ig ht C ei lo m et er FMI Ph en ol og y D ig ita l p ho to gr ap hy co nt in ue d 438 Lohila et al.  •  Boreal Env. Res. V ol. 20 Ta bl e 2. C on tin ue d. Su bs ite V a ria bl es M ea su re m en t m et ho ds R ef er en ce Lo m po lo jä nk kä (w et la nd ), si te 4 (6 7° 59 .8 35 ’N , 2 4° 12 .5 46 ’E , 2 69 m a .s .l. ) FMI CO 2, CH 4, H 2O , s en si bl e he at , E d dy c ov ar ia nc e Au re la e t a l. 20 09 , 2 01 5 m om en tu m fl ux es FMI CO 2, CH 4 fl ux es (N 2O fl ux es 2 00 6– 2 01 0) Au to m at ic c ha m be rs Lo hi la e t a l. 20 10 FMI , LU KE CO 2, CH 4, N 2O fl ux es M an ua l c ha m be rs Lo hi la e t a l. 20 10 , P ea rs on e t a l. 20 15 FMI CO 2, CH 4, co nc en tra tio ns in a ir (1 a nd 3 m ) O n- si te a na ly ze r an d in p ea t ( 0. 15 m b el ow th e su rfa ce ) FMI O 3 c on ce nt ra tio ns in a ir A u to m at ic a na ly ze r FMI Ph en ol og y D ig ita l p ho to gr ap hy Pa lla sj är vi (l ak e) (6 8° 0. 28 0´ N , 2 4° 12 .2 54 ´E , 2 67 m a .s .l. ) FMI ( si te 5 ) CO 2, H 2O , s en si bl e he at , m om en tu m fl ux es Ed dy c ov ar ia nc e Lo hi la e t a l. 20 15 SY KE (s ite 7 a) L a ke w at er c he m is try (h ig h nu m be r M an ua l s am pl in g, L o hi la e t a l. 20 15 of v ar ia bl es in cl ud in g m aj or io ns , au to m at ic nu tri en ts , o rg an ic m at te r, tra ce m ea su re m en ts m et al s1) ) a nd b io lo gy 5) . W at er le ve l an d te m pe ra tu re o f l ak e LU KE (s ite 7 a) Fi sh p ar am et er s fo r a ss es si ng th e CEN s ta nd ar di ze d S a ira ne n an d R uu hi jä rv i 2 01 4 ec ol og ic al s ta tu s6) sa m pl in g w ith NOR D IC g illn et s C at ch m en t o f P al la sj är vi SY KE (s ite s 7a –f ) S t re am w at er c he m is try 1) o f t he fo ur in le t M an ua l s am pl in g, st re am s an d th e ou tle t r iv er o f P al as jä rv i au to m at ic (P al la sj ok i). B io lo gi ca l m on ito rin g7) . m ea su re m en ts D is ch ar ge o f l ak e in le t a nd o ut le t. LU KE (s ite 7 f) Pa lla sj ok i. Fi sh p ar am et er s fo r CEN s ta nd ar di ze d ec ol og ic al s ta tu s8) . el ec tro fis hi ng U ni ve rs ity o f O ul u (s ite s 3b –c , 4 , 7 e) 18 O in p re ci pi ta tio n an d st re am w at er M an ua l s am pl in g FMI ( si te s 3b –c ) S t re am w at er c he m is try M an ua l s am pl in g K ei m iö jä rv i ( la ke ), si te 7 g (6 7° 57 .1 98 ´N , 2 4° 9. 53 4´ E, 3 32 m a .s .l. ) SY KE L a ke w at er c he m is try (h ig h nu m be r M an ua l s am pl in g of v ar ia bl es in cl ud in g m aj or io ns , nu tri en ts , o rg an ic m at te r, tra ce m et al s1) ) a nd b io lo gy 5) . LU KE Fi sh p ar am et er s fo r a ss es si ng th e CEN s ta nd ar di ze d S a ira ne n an d R uu hi jä rv i 2 01 4 ec ol og ic al s ta tu s6) sa m pl in g w ith NOR D IC g illn et s M at or ov a, s ite 2 (6 7° 59 .9 91 ´N , 2 4° 14 .3 99 ´E , 3 40 m a .s .l. ) FMI PM 10 P AH , P M 10 tr ac e m et al s4) , P M 2. 5 m aj or Fi lte r s am pl in g Pa at er o et a l. 20 09 , R uo ho -A iro la e t a l. io ns 2) , m aj or io ns a nd g as es 3) 20 15 FMI D ep os iti on s am pl es : p H , c on du ct iv ity , Bu lk c ol le ct or s Ky llö ne n et a l. 20 09 , C ap e et a l. m aj or io ns 2) , m er cu ry , t ra ce m et al s4) , P AH 20 12 , R uo ho -A iro la e t a l. 20 15 FMI G as eo us m er cu ry A n al yz er W än gb er g et a l. 20 10 IVL , S w ed en PO Ps Fi lte r s am pl in g an d bu lk c ol le ct or s H un g et a l. 20 08 IVL , S w ed en T o ta l g as eo us a nd to ta l p ar tic ul at e m er cu ry G ol d tra ps W än gb er g et a l. 20 10 IVL , S w ed en M er cu ry d ep os iti on Bu lk c ol le ct or W än gb er g et a l. 20 10 SY KE PO Ps Bu lk c ol le ct or s Ko rh on en e t a l. 19 98 , M an ni o et a l. 20 02 FMI PM 2. 5 a er os ol m as s Be ta g au ge FMI E l em en ta l/o rg an ic c ar bo n (EC /OC ) T h er m o- op tic a na ly ze r LU KE (s ite 9 ) Fo re st c on di tio n (IC P Fo re st ) L i nd ro os e t a l. 20 06 , 2 00 8, M er ilä a nd D er om e 20 08 , U ko nm aa na ho e t a l. 20 08 So il/ w at er s ta tio ns a t S am m al tu nt ur i, Lo m m ol tu nt ur i an d H an ga sk ur un oj a, (s ite s 8a –f ) G TK S o il w at er c on te nt , s oi l/a ir/ sn ow Fi ve a ut om at ic a nd S u tin en e t a l. 20 09 , 2 01 1, L iw at a et a l. te m pe ra tu re , s no w pa ck th ic kn es s, te le m et ric (C am pb el l/D ec ag on ) 20 14 sn ow w at er , p re ci pi ta tio n; st at io ns s in ce 2 00 7. st re am w at er p H , r ed ox , T h e ol de st s oi l s ta tio n co nd uc tiv ity , t em pe ra tu re ; es ta bl is he d in 1 99 8, ot he rs : s tre am w at er c he m is try up da te d in 2 00 3. Ec ol og ic al m on ito rin g in th e Pa lla s re gi on LU KE (s ite s 10 a– c, 1 1a –c ) D yn am ic s of n at ur al fo re st s an d S e pp än en a nd N or ok or pi 1 99 8, tim be rli ne fo re st s V a rm ol a et a l. 20 01 LU KE (s ite s 12 a– c) S p rin g an d au tu m n ph en op ha se s of tr ee s Ku bi n et a l. 20 06 an d sh ru bs , m on ito rin g of s ee d pr od uc tio n an d lit te rfa ll of fo re st tr ee s LU KE (c irc le s D yn am ic s of s m al l r od en t p op ul at io ns . M an y H en tto ne n et a l. 19 87 , H en tto ne n 20 00 an d re ct an gl es in lo ng -te rm m on ito rin g si te s in d iff er en t h ab ita ts Fi g. 1 ) ar ou nd th e Pa lla sj är vi –L om m ol tu nt ur i– H an hi vu om a– M at or ov a ar ea 1) T em pe ra tu re , c on du ct iv ity , p H , a lk al in ity , a bs or ba nc e, O 2 c on ce nt ra tio n, O 2 p er ce nt ag e, tu rb id ity , c ol ou r, ch em ic al o xy ge n de m an d (CO D M n) , t ot al P , P O 4-P , t ot al N ,   NO 3-N , NH 4-N , A l, Fe , M n, S iO 2, K, C a, M g, N a, SO 4, C l, F, TOC , TIC , A s, B a, C d, C o, C r, C u, N i, Pb , P d, P t, Se , S r, Ti , Z n, V , H g. 2) SO 4, NO 3, C l, N a, K , C a, M g, NH 4. 3) SO 2, SO 4, NO 3 + HNO 3, C l, N a, K , C a, M g, NH 4 + NH 3 ( EM EP 3 -s ta ge fi lte r s am pl in g) . 4) A l, As , C d, C o, C r, C u, F e, M n, N i, Pb , V , Z n. 5) C hl or op hy l a , p hy to pl an kt on , p er ip hy to n, b en th ic m ac ro in ve rte br at es , m ac ro ph yt es . 6) B PU E (to ta l w ei gh t o f fi sh /n et ), N PU E (to ta l n um be r o f fi sh /n et ), bi om as s pr op or tio n of c yp rin id fi sh es , o cc ur re nc e of in di ca to r s pe ci es . 7) P er ip hy to n, b en th ic m ac ro in ve rte br at es . 8) P ro po rti on o f s en si tiv e sp ec ie s, p ro po rti on o f t ol er an t s pe ci es , d en si ty o f 0 + sa lm on id s, p ro po rti on o f c yp rin id s, n um be r o f s pe ci es . Boreal Env. Res. V ol. 20  •  Research of atmosphere, ecosystems and environment at Pallas 439 Ta bl e 2. C on tin ue d. Su bs ite V a ria bl es M ea su re m en t m et ho ds R ef er en ce Lo m po lo jä nk kä (w et la nd ), si te 4 (6 7° 59 .8 35 ’N , 2 4° 12 .5 46 ’E , 2 69 m a .s .l. ) FMI CO 2, CH 4, H 2O , s en si bl e he at , E d dy c ov ar ia nc e Au re la e t a l. 20 09 , 2 01 5 m om en tu m fl ux es FMI CO 2, CH 4 fl ux es (N 2O fl ux es 2 00 6– 2 01 0) Au to m at ic c ha m be rs Lo hi la e t a l. 20 10 FMI , LU KE CO 2, CH 4, N 2O fl ux es M an ua l c ha m be rs Lo hi la e t a l. 20 10 , P ea rs on e t a l. 20 15 FMI CO 2, CH 4, co nc en tra tio ns in a ir (1 a nd 3 m ) O n- si te a na ly ze r an d in p ea t ( 0. 15 m b el ow th e su rfa ce ) FMI O 3 c on ce nt ra tio ns in a ir A u to m at ic a na ly ze r FMI Ph en ol og y D ig ita l p ho to gr ap hy Pa lla sj är vi (l ak e) (6 8° 0. 28 0´ N , 2 4° 12 .2 54 ´E , 2 67 m a .s .l. ) FMI ( si te 5 ) CO 2, H 2O , s en si bl e he at , m om en tu m fl ux es Ed dy c ov ar ia nc e Lo hi la e t a l. 20 15 SY KE (s ite 7 a) L a ke w at er c he m is try (h ig h nu m be r M an ua l s am pl in g, L o hi la e t a l. 20 15 of v ar ia bl es in cl ud in g m aj or io ns , au to m at ic nu tri en ts , o rg an ic m at te r, tra ce m ea su re m en ts m et al s1) ) a nd b io lo gy 5) . W at er le ve l an d te m pe ra tu re o f l ak e LU KE (s ite 7 a) Fi sh p ar am et er s fo r a ss es si ng th e CEN s ta nd ar di ze d S a ira ne n an d R uu hi jä rv i 2 01 4 ec ol og ic al s ta tu s6) sa m pl in g w ith NOR D IC g illn et s C at ch m en t o f P al la sj är vi SY KE (s ite s 7a –f ) S t re am w at er c he m is try 1) o f t he fo ur in le t M an ua l s am pl in g, st re am s an d th e ou tle t r iv er o f P al as jä rv i au to m at ic (P al la sj ok i). B io lo gi ca l m on ito rin g7) . m ea su re m en ts D is ch ar ge o f l ak e in le t a nd o ut le t. LU KE (s ite 7 f) Pa lla sj ok i. Fi sh p ar am et er s fo r CEN s ta nd ar di ze d ec ol og ic al s ta tu s8) . el ec tro fis hi ng U ni ve rs ity o f O ul u (s ite s 3b –c , 4 , 7 e) 18 O in p re ci pi ta tio n an d st re am w at er M an ua l s am pl in g FMI ( si te s 3b –c ) S t re am w at er c he m is try M an ua l s am pl in g K ei m iö jä rv i ( la ke ), si te 7 g (6 7° 57 .1 98 ´N , 2 4° 9. 53 4´ E, 3 32 m a .s .l. ) SY KE L a ke w at er c he m is try (h ig h nu m be r M an ua l s am pl in g of v ar ia bl es in cl ud in g m aj or io ns , nu tri en ts , o rg an ic m at te r, tra ce m et al s1) ) a nd b io lo gy 5) . LU KE Fi sh p ar am et er s fo r a ss es si ng th e CEN s ta nd ar di ze d S a ira ne n an d R uu hi jä rv i 2 01 4 ec ol og ic al s ta tu s6) sa m pl in g w ith NOR D IC g illn et s M at or ov a, s ite 2 (6 7° 59 .9 91 ´N , 2 4° 14 .3 99 ´E , 3 40 m a .s .l. ) FMI PM 10 P AH , P M 10 tr ac e m et al s4) , P M 2. 5 m aj or Fi lte r s am pl in g Pa at er o et a l. 20 09 , R uo ho -A iro la e t a l. io ns 2) , m aj or io ns a nd g as es 3) 20 15 FMI D ep os iti on s am pl es : p H , c on du ct iv ity , Bu lk c ol le ct or s Ky llö ne n et a l. 20 09 , C ap e et a l. m aj or io ns 2) , m er cu ry , t ra ce m et al s4) , P AH 20 12 , R uo ho -A iro la e t a l. 20 15 FMI G as eo us m er cu ry A n al yz er W än gb er g et a l. 20 10 IVL , S w ed en PO Ps Fi lte r s am pl in g an d bu lk c ol le ct or s H un g et a l. 20 08 IVL , S w ed en T o ta l g as eo us a nd to ta l p ar tic ul at e m er cu ry G ol d tra ps W än gb er g et a l. 20 10 IVL , S w ed en M er cu ry d ep os iti on Bu lk c ol le ct or W än gb er g et a l. 20 10 SY KE PO Ps Bu lk c ol le ct or s Ko rh on en e t a l. 19 98 , M an ni o et a l. 20 02 FMI PM 2. 5 a er os ol m as s Be ta g au ge FMI E l em en ta l/o rg an ic c ar bo n (EC /OC ) T h er m o- op tic a na ly ze r LU KE (s ite 9 ) Fo re st c on di tio n (IC P Fo re st ) L i nd ro os e t a l. 20 06 , 2 00 8, M er ilä a nd D er om e 20 08 , U ko nm aa na ho e t a l. 20 08 So il/ w at er s ta tio ns a t S am m al tu nt ur i, Lo m m ol tu nt ur i an d H an ga sk ur un oj a, (s ite s 8a –f ) G TK S o il w at er c on te nt , s oi l/a ir/ sn ow Fi ve a ut om at ic a nd S u tin en e t a l. 20 09 , 2 01 1, L iw at a et a l. te m pe ra tu re , s no w pa ck th ic kn es s, te le m et ric (C am pb el l/D ec ag on ) 20 14 sn ow w at er , p re ci pi ta tio n; st at io ns s in ce 2 00 7. st re am w at er p H , r ed ox , T h e ol de st s oi l s ta tio n co nd uc tiv ity , t em pe ra tu re ; es ta bl is he d in 1 99 8, ot he rs : s tre am w at er c he m is try up da te d in 2 00 3. Ec ol og ic al m on ito rin g in th e Pa lla s re gi on LU KE (s ite s 10 a– c, 1 1a –c ) D yn am ic s of n at ur al fo re st s an d S e pp än en a nd N or ok or pi 1 99 8, tim be rli ne fo re st s V a rm ol a et a l. 20 01 LU KE (s ite s 12 a– c) S p rin g an d au tu m n ph en op ha se s of tr ee s Ku bi n et a l. 20 06 an d sh ru bs , m on ito rin g of s ee d pr od uc tio n an d lit te rfa ll of fo re st tr ee s LU KE (c irc le s D yn am ic s of s m al l r od en t p op ul at io ns . M an y H en tto ne n et a l. 19 87 , H en tto ne n 20 00 an d re ct an gl es in lo ng -te rm m on ito rin g si te s in d iff er en t h ab ita ts Fi g. 1 ) ar ou nd th e Pa lla sj är vi –L om m ol tu nt ur i– H an hi vu om a– M at or ov a ar ea 1) T em pe ra tu re , c on du ct iv ity , p H , a lk al in ity , a bs or ba nc e, O 2 c on ce nt ra tio n, O 2 p er ce nt ag e, tu rb id ity , c ol ou r, ch em ic al o xy ge n de m an d (CO D M n) , t ot al P , P O 4-P , t ot al N ,   NO 3-N , NH 4-N , A l, Fe , M n, S iO 2, K, C a, M g, N a, SO 4, C l, F, TOC , TIC , A s, B a, C d, C o, C r, C u, N i, Pb , P d, P t, Se , S r, Ti , Z n, V , H g. 2) SO 4, NO 3, C l, N a, K , C a, M g, NH 4. 3) SO 2, SO 4, NO 3 + HNO 3, C l, N a, K , C a, M g, NH 4 + NH 3 ( EM EP 3 -s ta ge fi lte r s am pl in g) . 4) A l, As , C d, C o, C r, C u, F e, M n, N i, Pb , V , Z n. 5) C hl or op hy l a , p hy to pl an kt on , p er ip hy to n, b en th ic m ac ro in ve rte br at es , m ac ro ph yt es . 6) B PU E (to ta l w ei gh t o f fi sh /n et ), N PU E (to ta l n um be r o f fi sh /n et ), bi om as s pr op or tio n of c yp rin id fi sh es , o cc ur re nc e of in di ca to r s pe ci es . 7) P er ip hy to n, b en th ic m ac ro in ve rte br at es . 8) P ro po rti on o f s en si tiv e sp ec ie s, p ro po rti on o f t ol er an t s pe ci es , d en si ty o f 0 + sa lm on id s, p ro po rti on o f c yp rin id s, n um be r o f s pe ci es . 440 Lohila et al.  •  Boreal Env. Res. V ol. 20 ecosystems, hydrological processes and climate change, and changes in leaching and material fluxes (C/N) in the catchment and the lake itself. In 2004, continuous water level and sur- face water temperature recordings commenced in Pallasjärvi, as did the monitoring of discharge in the main inlet stream Pyhäjoki and the outlet stream Pallasjoki. Since 2012, water temperature recording has been supplemented by automatic temperature measurements in the whole water profile in the deep-water area (1-m depth interval, 2 measurements per hour). In addition, a small drainage basin (with an overflow-measuring weir) for monitoring of the runoff water chem- istry and automatic runoff and dissolved organic matter (CDOM) recordings were established in Lompolojängänoja (site 7e) in 2013 and 2014, respectively, as part of the FMI’s Lompolojänkkä site. The stream drains the Lompolojänkkä fen and the upper parts of the sub-catchment (see Aurela et al. 2015). In 2008, quantitative moni- toring of the runoff flow from the Lompolojänkkä fen to Pallasjärvi was started by FMI and in 2013, SYKE upgraded the runoff measurement station by building a log cabin equipped with mains electricity. As part of the monitoring of hydrological processes, soil moisture recordings commenced in the Matorova area in 2014. METLA carried out extensive fish monitor- ing in Pallasjärvi in 1990. The results of this gill- net survey were utilized when METLA and the fishing association of Raattama negotiated the future fishing policies for the lake. Based on gill raker counts, there were several morphs of the whitefish in Pallasjärvi, reflecting both the orig- inal stock and several man-made introductions with other stocks (H. Henttonen unpubl. data). Fish status monitoring for the EU Water Framework Directive was commenced in Keimiöjärvi and Pallasjärvi in 2006 as part of the interregional project TRIWA (The River Torne International Watershed; Sairanen et al. 2008). Standard methods of CEN (European Commit- tee for Standardization) have been used in the sampling of the lakes (NORDIC gillnets) and the Pallasjoki (electrofishing). In test fishing of Pal- lasjärvi in 2013, the most abundant fish species were the vendace (Coregonus albula), whitefish (Coregonus lavaretus), grayling (Thymallus thy- mallus) and burbot (Lota lota). All these species, as well as the littoral species — the alpine bull- head (Cottus poecilopus) and the nine-spined stickleback (Pungitius pungitius) — are sensi- tive to environmental changes, which highlights the value of Pallasjärvi as a monitoring site of high ecological status. Similarly, the dominance of the grayling and bullhead (Cottus gobio) in the electrofishing catches from the Pallasjoki in 2012, supported by other biological quality parameters examined by SYKE, indicated the high ecological status of the river. The Pallasjärvi automatic weather station (site 6b) was in operation in 1996–2002. The station was located close to the northern shore of Palsijärvi (68°01´N, 24°10´E). The site also served as a platform for campaign-based meas- urements of radioactivity, for example (Paatero et al. 1998). Sammaltunturi–Lommoltunturi/Hangas- kurunoja (sites 8a–f). As a part of a national network, GTK established five automatic and telemetric soil monitoring stations in Sammal- tunturi–Lommoltunturi and one stream-water station at Hangaskurunoja in 2007. However, the oldest soil station on the northern slope of Sam- maltunturi was established in 1998 and updated in 2003. The focus of these sites is to follow the intra- and inter-annual soil hydrological changes with a particular interest in snow accumula- tion, snowmelt and soil freezing mechanisms. This is important for understanding the forest and treeline dynamics as well as for modeling the freeze-thaw effects on soil bearing capacity and infiltration in the watershed-scale (flooding) studies. The soil stations also provide informa- tion on spruce forest (south and north aspects), treeline and tundra conditions. In addition to the automatically recorded data, hydrological mod- eling requires input data on soil structure and texture down to a 1-m depth in the stratigraphic sequences. At the Hangaskurunoja station, the water cycle and the snowmelt effect on the water quality in particular are complemented by water chemistry analyses. Daily deposition samples for the main inor- ganic ion analyses were collected at the Särki- järvi frontier guard station (67°55´N, 23°56´E) in 1991–1999. These observations were later continued at Matorova with weekly sampling periods (Leinonen 2000). Boreal Env. Res. V ol. 20  •  Research of atmosphere, ecosystems and environment at Pallas 441 In addition to the permanent measurement stations, some of the ecological long-term monitoring studies take place at several sub- sites spread out around Pallas. One of the most famous of these is rodent monitoring (sites indi- cated with circles in Fig. 1), which makes use of the exceptionally diverse rodent fauna of the Pallas region: six vole and two lemming spe- cies are found sympatrically. In this respect, the Pallas region is of global interest. This diversity, observed in many animals and plant taxa, is attributed to the location of Pallas at the contact zone of many southern and northern elements. The Pallas rodent studies started in 1970 during the great lemming migration, and have contin- ued since then, allowing for detailed long-term studies on various aspects of mammalian popu- lation ecology. The research includes long-term permanent monitoring sites, as well as replicated shorter-term experimental sites. The main measured variables at the Pallas area (excluding meteorology which is detailed in Aurela et al. 2015) are listed in Tables 2 and 3. Trends in soil, water and atmospheric parameters In this section we present some examples of the long-term monitoring data collected at Pallas by the different institutes. While here we focus on the results from atmospheric and hydrological studies, there is a long list of papers on ecology, geology, microbiology and other subjects; most of which are listed in the references and the Appen- dix. Soil water content The Sammaltunturi soil stations provide intra- and inter-seasonal data to aid the understanding of soil freeze–thaw cycles and soil temperature variations along the elevation gradient (Sutinen et al. 2009). One of the recent observations indicates that — even though soil water con- tent varies seasonally — the spatial pattern of the soil water content does not change with time when the observations are ranked accord- ing to the magnitude of the soil water (Fig. 3). This time-stability concept holds for a diversity of soils throughout the boreal climatic zones, including Sammaltunturi forest and treeline soils (Liwata et al. 2014). Inflow and organic carbon in lakes and rivers In 2004, SYKE established the Pallasjärvi catch- ment research infrastructure for intensive hydro- logical, chemical and biological monitoring of the Pallasjärvi catchment. One of the findings of the monitoring was that total organic carbon Table 3. Chemical, hydrological and biological monitoring sites of SYKE and GTK and soil hydrological monitoring sites of GTK. LUKE conducts fish status monitoring at the biological monitoring sites. Sampling site C oordinates E nvironment C hemical H ydrological Biological monitoring monitoring monitoring Pallasjärvi, site 7a 68°1.812´N, 24°10.872´E L ake + + + Ylisenpäänoja, site 7b 68°3.714´N, 24°8.334´E I nlet stream + Pyhäjoki, site 7c 68°1.524´N, 24°9.318´E I nlet stream + + Lompolonoja, site 7d 68°0.15´N, 24°11.508´E I nlet stream + Lompolojängänoja, site 7e 68°0.024´N, 24°12.102´E I nlet stream + + Pallasjoki, site 7f 68°1.608´N, 24°17.202´E O utlet river + + + Keimiöjärvi, site 7g 67°57.198´N, 24°9.534´E L ake + + Sammaltunturi N, site 8a 67°59.982´N, 24°7.356´E Forest + Lommoltunturi, site 8b 68°0.132´N, 24°7.944´E Forest + Sammaltunturi S, site 8c 67°58.176´N, 24°5.7´E T reeline + Sammaltunturi S, site 8d 67°58.014´N, 24°4.968´E Forest + Sammaltunturi, site 8e 67°59.298´N, 24°6.87´E T undra + Hangaskurunoja, site 8f 68°0.102´N, 24°7.602´E I nlet stream + + 442 Lohila et al.  •  Boreal Env. Res. V ol. 20 (TOC) concentrations are highly variable in the inflow. However, their dynamics are obscured by many interacting in-lake processes, resulting in the smoothed concentrations measured in the (Fig. 4). Both mineralization and sedimentation control in-lake losses of TOC, as they also do in the larger Simojärvi (Lepistö et al. 2014). Greenhouse gas concentrations Atmospheric concentrations of CO2 and CH4 have been measured continuously at Sammaltun- turi since 1998 and 2004, respectively (Fig. 5). Marine signals represent the global atmospheric background levels, which were estimated by selecting non-local (consistent, well-mixed) hourly data that correspond to the air mass his- tory above the Atlantic and Arctic Oceans, using a routine described by Aalto et al. (2015). As a result, a “Keeling curve” emerges for CO2, which shows that it is possible to discriminate between different source areas, which are here determined using 5-day reanalysis-driven backward runs of the SILAM dispersion model (Sofiev et al. 2006). The CO2 and CH4 data from Sammaltun- turi have been actively used in modeling and data-oriented studies that address global and regional GHG sinks and sources, and the trans- port of GHG emissions in the atmosphere (Aalto et al. 2002, 2007, Eneroth et al. 2005, Geels et al. 2007, Peters et al. 2010, Ramonet et al. 2010, Chevallier et al. 2010, Bergamaschi et al. 2015, Tsuruta et al. 2015). Owing to the remote loca- tion, the tropospheric background data gathered at Sammaltunturi can be used for validation and site inter-comparisons for new monitoring tools, such as those observing total column concentra- tions at the surface or from space (e.g. Sepúlveda et al. 2014, Weaver et al. 2014). As the number of atmospheric stations and other monitoring tools has increased considerably during the years that Sammaltunturi has been in operation, the potential for accurately solving regional GHG balances by atmospheric inversion modeling has increased. However, existing background stations are still invaluable in constraining the emission estimates. In addition to CO2 and CH4, other long-lived atmospheric trace gases, such as nitrous oxide and hydrogen provide a means to increase the understanding of processes related to climate change. Measurements of these gases at Sammaltunturi have been used in a number of studies addressing surface sinks and sources (Lallo et al. 2009, Corazza et al. 2011, Yver et al. 2011, Thompson et al. 2014). Air quality FMI started air quality measurements at Sammal- tunturi in 1991 and at Matorova in 1995. In gen- S oi l w at er c on te nt (l m –3 ) 50 100 150 200 250 300 350 400 2004 2006 2008 2010 2012 Fig. 3. Long-term changes in the soil water content at the Norway spruce forest station on the northern slope of Sammaltunturi. Boreal Env. Res. V ol. 20  •  Research of atmosphere, ecosystems and environment at Pallas 443 eral, the air quality at Pallas has improved over the time of the measurements due to decreased emissions in Finland and elsewhere in Europe. For example, there has been a decreasing trend of –3.3% and –2.9% year–1 in the atmospheric concentrations of arsenic and nickel, respectively, at Matorova (Fig. 6a and b). For SO2 and trace elements, the decrease is likely to be due to the decreased emissions from the Kola Peninsula metal industry (about 300 km from Pallas). How- ever, nitrogen compounds have increased and nitrogen deposition at Pallas has been increasing since the mid-1990s (Ruoho-Airola et al. 2015), although it is still low compared with those at the other Finnish air quality measurement sites. Further enhancement of the nitrogen load to the ecosystems might be expected as shipping activities are expected to increase in the Arctic in the coming decades (Tuovinen et al. 2013). Furthermore, O3 and non-methane hydrocarbons (NMHC), which react in the air to form O3, have not decreased since the mid-1990s, although the emissions of NMHC in the European Union have decreased by over 60% in that time (Hellén et al. 2015). This may be due to increased concentra- tions in the air masses arriving from the east. Even though the Pallas area can, in general terms, be considered a clean environment, the dynamics of the SO2 concentration measured at Sammaltunturi exhibit wide variation generated In flo w (m 3 s –1 ) 0 2 4 6 8 10 a To ta l o rg an ic c ar bo n (m g l–1 ) 0 2 4 6 8 10 12 TOC inflow TOC lake b 2004 2006 2008 2010 2012 2014 Fig. 4. (a) Inflow from the Pyhäjoki and (b) total organic carbon (TOC) concentration in the Pyhä- joki and Pallasjärvi. 444 Lohila et al.  •  Boreal Env. Res. V ol. 20 a A tm os ph er ic A s co nc en tra tio n (n g m –3 ) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Monthly mean concentration Seasonal component and GLS-ARMA trend b 1996 2000 2004 2008 2012 A tm os ph er ic N i c on ce nt ra tio n (n g m –3 ) 0 1 2 3 Fig. 6. Atmospheric (a) arsenic (As) and (b) nickel (Ni) concentrations measured at Matorova in 1996–2013. The trend was calculated by General- ized Least-Squares (GLS) regression with classi- cal decomposition and AutoRegressive Moving Average (ARMA) errors applied for monthly mean values (see e.g. Anttila and Tuovinen 2010). Fig. 5. Hourly concentrations of atmospheric CO2 (1998–2015) and CH4 (2004–2015) at Sammaltunturi. Grey lines = all data; black lines = marine signal. by alternating air masses that pass the station. As SO2 is a primary pollutant with a short atmo- spheric lifetime of a day, its atmospheric concen- trations largely reflect nearby sources. However, distant emissions can be detected provided the source is sufficiently intense and meteorological conditions are favourable for the transportation of the pollution cloud without excessive dispersion. The first example of SO2 measurements depicts hourly data recorded soon after the establishment of the Sammaltunturi station and demonstrates how distinct pollution episodes are superimposed over a low background level (see Fig. 7a). During that period, northern Fin- Boreal Env. Res. V ol. 20  •  Research of atmosphere, ecosystems and environment at Pallas 445 land was frequently exposed to air pollution plumes that mainly originated from the indus- trial emissions in the Kola Peninsula (Tuovinen et al. 1993), evoking environmental concerns (Tikkanen 1995, Tikkanen and Niemelä 1995). Owing to subsequent emission reductions, such pollution episodes have become weaker and less frequent, as the data of November 2013 exempli- fies (Fig. 7b). On 5 September 2014, the SO2 concentra- tion time series took an anomalous turn (Fig. 7c), when large amounts of the SO2 emitted by a fissure eruption close to the Bárðarbunga volcano in Iceland (1800 km from Pallas) were transported to northern Finland (Ialongo et al. 2015). The highest hourly concentrations pro- duced from this volcanic plume were about 180 µg m–3, which clearly exceeds any previ- ous peaks attributed to anthropogenic emissions. While the concentration gradually decreased, SO2 of volcanic origin was observed at Pallas throughout that month. Aerosol measurements The first aerosol measurements of total particle number concentrations started at Sammaltunturi in 1996, making them one of the longest time series in the world (Fig. 8). Later, measurements were upgraded to cover a vast variety of aero- sol properties: particle number size distributions (in 2000), aerosol scattering coefficients (2000), total air inlet for cloud aerosol studies and aero- sol mass (2004), aerosol absorption coefficient (2005, 2007), size distribution of larger particles (2007) and ions (2008), and aerosol hygroscop- icity (2008). The Sammaltunturi station is also used to study the microphysical properties of clouds and aerosol cloud activation and chemis- try, since it is occasionally inside a cloud. For almost twenty years, Pallas has served as a unique site for studies of aerosol natural back- ground processes in an environment of minor anthropogenic influences. The process of sec- ondary particle formation and growth to potential cloud condensation nuclei has been extensively studied using measured aerosol size distributions (Komppula et al. 2003a, 2003b, Lihavainen et al. 2003, Komppula et al. 2006, Dal Maso et al. 2007, 2008, Asmi et al. 2011a). Using Pallas measurements, Kerminen et al. (2005) were the first to present solid experimental evidence of the in-cloud activation of these secondary parti- cles, suggesting they hold a significant potential for climate impacts also via clouds. Indeed, the aerosol–cloud interactions, aerosol cloud drop- let activation processes and induced direct and indirect climate impacts in Pallas have been a 1 8 15 22 29 S O 2 co nc en tra tio n (µ g m –3 ) S O 2 co nc en tra tio n (µ g m –3 ) S O 2 co nc en tra tio n (µ g m –3 ) 0 5 10 15 20 25 b 1 8 15 22 29 0 5 10 15 20 25 c Day of month 1 8 15 22 29 0 50 100 150 200 Fig. 7. Sulphur dioxide (SO2) concentration at Sammal- tunturi in (a) November 1991, (b) November 2013 and (c) September 2014. Note the different concentration scale in c. 446 Lohila et al.  •  Boreal Env. Res. V ol. 20 further studied by several groups (Lihavainen et al. 2003, Komppula et al. 2005, Lihavainen et al. 2010). The PaCE (Pallas Cloud Experiment) campaign which will be organized in autumn 2015 is the sixth in series since 2004. The PaCE campaigns focus on resolving the linkages between measured aerosol properties, in-cloud activation and cloud microphysics (Lihavainen et al. 2008, Kivekäs et al. 2009, Anttila et al. 2009, 2012, Jaatinen et al. 2014). Pallas data were also used in source area studies. Tunved et al. (2006) showed the high potential of natural emissions from boreal for- ests for increasing the aerosol mass in Pallas as well. The important role of biogenic emissions for secondary particle formation and growth and for aerosol climate impacts have since been confirmed in several studies (Lihavainen et al. 2009, Spracklen et al. 2010, Asmi et al. 2011a, Scott et al. 2014, Hermansson et al. 2014). The optical aerosol measurements have provided important knowledge on absorbing aerosol and black carbon concentrations and sources at this gateway to the high Arctic (Hienola et al. 2010, Hyvärinen et al. 2011, Lihavainen et al. 2015). Deposition of these airborne absorbing aero- sols into snow pack was studied in Pallas area by Svensson et al. (2013) and Forsström et al. (2013). The effect of long-range-transported bio- mass-burning plumes on aerosol properties was also observed at Pallas (Mielonen et al. 2013, Targino et al. 2013). Pallas aerosol measurements were part of different-scale integrating studies to understand the complexity and variation of aerosol and cloud condensation nuclei properties (Tunved et al. 2003, Laakso et al. 2003, Tomasi et al. 2007, Kerminen et al. 2010, 2012, Kulmala et al. 2011, Asmi et al. 2013, Collaud Coen et al. 2013). The long aerosol data series from Pallas has also enabled aerosol trend studies (Asmi et al. 2011b, 2013, Collaud Coen et al. 2013, Lihavainen et al. 2015), Lagrangian studies on aerosol parti- cle dynamics in the atmosphere (Komppula et al. 2006, Kivekäs et al. 2009, Väänänen et al. 2013, Beddows et al. 2014) and parametrization suggestions for climate models (Kivekäs et al. 2007, 2008). Rodent monitoring Northern Fennoscandia is famous for drastic population cycles of voles and lemmings, which are reflected at trophic levels below and above rodents. Multispecies rodent communities allow C on ce nt ra tio n (c m –3 ) 10 100 1000 10000 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 C on ce nt ra tio n (c m –3 ) 0 500 1000 1500 2000 Fig. 8. Time series of aerosol number concen- tration (> 10 nm) mea- sured at Sammaltunturi. Top and bottom figures show hourly and monthly averages, respectively. Boreal Env. Res. V ol. 20  •  Research of atmosphere, ecosystems and environment at Pallas 447 for the analyses of regulatory factors, either at the whole community or species level. To exemplify: if the population density of many species changes suddenly, it is probable that it can be explained by a single variable at the whole community level, particularly in the case of a collapse in population density. However, if species fluctuate non-syn- chronously, the regulating factors differ at the spe- cies level. Fluctuations of the bank vole (Myodes glareolus) and the field vole (Microtus agrestis) at Pallasjärvi (Fig. 9), presented here as an example, are characterized by four-year cycles with syn- chronous peaks and declines in the 1970s, and the nonsynchronous dynamics in the 1980s, 1990s and most of the 2000s. Recently, however, the cyclic pattern seems to have returned. The research has expanded from original mammalian population ecology to parasite and pathogen dynamics and evolution, for example. Pallasjärvi is currently one of the best-known global rodent research sites. Material from the project have been published in more than 100 peer-reviewed articles and in a host of other publications (for different approaches, see e.g. Henttonen 1987, 2000, Henttonen et al. 1987, Hanski & Henttonen 1996, 2002, Prévot-Julliard et al. 1999, Turchin et al. 2000, Yoccoz et al. 2001, Haukisalmi et al. 2008, 2009, 2010, Raz- zauti et al. 2009, Cornulier et al. 2013, Klemme et al. 2014). References 1) Papers presenting results of studies conducted at Pallas and including the site description. 2) Papers in which the data from the Pallas area were included, but which do not necessarily include the site description. 3) Publications not directly related to Pallas. 1Aalto T., Hatakka J. & Lallo M. 2007. Tropospheric meth- ane in northern Finland: seasonal variations, transport patterns and correlations with other trace gases. Tellus 59B: 251–259. 1Aalto T., Hatakka J., Kouznetsov R. & Stanislawska K. 2015. Background and anthropogenic influences on atmospheric CO2 concentrations measured at Pallas: Comparison of two models for tracing air mass history. Boreal Env. Res. 20: 213–226. 1Aalto T., Hatakka J., Paatero J., Tuovinen J.-P., Aurela M., Laurila T., Holmén K., Trivett N. & Viisanen Y. 2002. Tropospheric carbon dioxide concentrations at a north- ern boreal site in Finland: basic variations and source areas. Tellus 54B: 110–126. 1Aaltonen V., Lihavainen H., Kerminen V.-M., Komppula M., Hatakka J., Eneroth K., Kulmala M. & Viisanen Y. 2006. Measurements of optical properties of atmo- spheric aerosols in northern Finland. Atmos. Chem. Phys. 6: 1155–1164. 2Anttila P. & Tuovinen J.-P. 2010. Trends of primary and secondary pollutant concentrations in Finland in 1994– 2007. Atmos. Environ. 44: 30–41. 1Anttila T., Vaattovaara P., Komppula M., Hyvärinen A.-P., Lihavainen H., Kerminen V.-M. & Laaksonen A. 2009. Size-dependent activation of aerosols into cloud droplets at a subarctic background site during the second Pallas Cloud Experiment (2nd PaCE): method development 1970 1980 1990 2000 2010 V ol es p er 1 00 tr ap n ig ht s 0 5 10 15 20 25 30 35 Bank vole Field vole Bank vole Field vole Fig. 9. Population fluc- tuations of the bank vole (Myodes glareolus) and field vole (Microtus agrestis) at Pallasjärvi in 1970–2014. The curves are based on two annual samplings, in early June and September, allowing for differentiation of sea- sonal and multiannual variations. 448 Lohila et al.  •  Boreal Env. Res. V ol. 20 and data evaluation. Atmos. Chem. Phys. 9: 4841–4854. 1Anttila T., Brus D., Jaatinen A., Hyvärinen A.-P., Kivekäs N., Romakkaniemi S., Komppula M. & Lihavainen H. 2012. Relationships between particles, cloud conden- sation nuclei and cloud droplet activation during the third Pallas Cloud Experiment. Atmos. Chem. Phys. 12: 11435–11450. 1Asmi E., Kivekäs N., Kerminen V.-M., Komppula M., Hyvärinen A.-P., Hatakka J., Viisanen Y. & Lihavainen H. 2011a. Secondary new particle formation in northern Finland Pallas site between the years 2000 and 2010. Atmos. Chem. 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List of peer-reviewed papers and conference abstracts using data from Pallas area, and topics depicting the content of the papers. 1) Papers presenting results of studies conducted at Pallas and including the site description; 2) papers in which the data from the Pallas area were included, but which do not necessarily include the site description. Reference Topics 1Aalto T.,Hatakka J., Karstens U., Aurela M., Thum T. & Lohila A. 2006. Modeling atmospheric CO2 concentration profiles and fluxes above sloping terrain at a boreal sit