Assessing nutrient and sediment transport for Water Framework Directive purposes using the SWAT model - a case study in SW Finland

The ecological status of lake Pyhäjärvi, located in south-western Finland, may be classified as moderate due to its elevated nutrient concentrations and algal biomass production. Thus, the Yläneenjoki river basin, accounting for >50% of the total phosphorus loading to the lake, was chosen as the Finnish test catchment in the Benchmark models for the Water Framework Directive project. One aim of the project was to test the suitability of models like the catchment scale model SWAT for the assessment of nutrient and sediment transport and management options needed to meet the surface water quality requirements

Assessment of hydrology, sediment and particulate organic carbon yield in a large agricultural catchment using the SWAT model

The Soil and Water Assessment Tool (SWAT, 2005) was used to simulate discharge and sediment transport at daily time steps within the intensively farmed Save catchment in south-west France (1110 km2). The SWAT model was applied to evaluate catchment hydrology and sediment and associated particulate organic carbon yield using historical flow and meteorological data for a 10-years (January 1999–March 2009). Daily data on sediment (27 months, January 2007–March 2009) and particular organic carbon (15 months, January 2008–March 2009) were used to calibrate the model. Data on management practices (crop rotation, planting date, fertiliser quantity and irrigation) were included in the model during the simulation period of 10 years. Simulated daily discharge, sediment and particulate carbon values matched the observed values satisfactorily. The model predicted that mean annual catchment precipitation for the total study period (726 mm) was partitioned into evapotranspiration (78.3%), percolation/groundwater recharge (14.1%) and abstraction losses (0.5%), yielding 7.1% surface runoff. Simulated mean total water yield for the whole simulation period amounted to 138 mm, comparable to the observed value of 136 mm. Simulated annual sediment yield ranged from 4.3 t km−2 y−1 to 110 t km−2 y−1 (annual mean of 48 t km−2 y−1). Annual yield of particulate organic carbon ranged from 0.1 t km−2 y−1 to 2.8 t km−2 y−1 (annual mean of 1.2 t km−2 y−1). Thus, the highest annual sediment and particulate carbon yield represented 25 times the minimum annual yield. However, the highest annual water yield represented five times the minimum (222 mm and 51 mm, respectively). An empirical correlation between annual water yield and annual sediment and organic carbon yield was developed for this agricultural catchment. Potential source areas of erosion were also identified with the model. The range of the annual contributing erosive zones varied spatially from 0.1 to 6 t ha−1 according to the slope and agricultural practices at the catchment scale

From a test case to a trusted tool: Lithuania’s evolving SWAT system for water and agricultural management

Lithuania’s development of the river modelling system (RMS) exemplifies an institutional development and application of integrated modelling for water and agricultural management. What started as a test case, continued to develop focusing on environmental compliance with the EU regulations. Currently, the RMS is a part of decision-making. By incorporating the soil and water assessment tool (SWAT) model and comprehensive data sources, the system facilitates in-depth analysis and policy formulation. Applications in water management plans, pollution assessments, and climate change studies demonstrate the reliability of RMS. Despite data quality and skill retention challenges, institutional commitment and collaboration ensure the RMS’s persistence. This experience emphasizes the value of sustained investment in integrated modelling systems for achieving sustainable environmental governance and signifies Lithuania’s shift towards data driven green transition practices

Assessment of Optional Sediment Transport Functions via the Complex Watershed Simulation Model SWAT

The Soil and Water Assessment Tool 2012 (SWAT2012) offers four sediment routing methods as optional alternatives to the default simplified Bagnold method. Previous studies compared only one of these alternative sediment routing methods with the default method. The proposed study evaluated the impacts of all four alternative sediment transport methods on sediment predictions: the modified Bagnold equation, the Kodoatie equation, the Molinas and Wu equation, and the Yang equation. The Arroyo Colorado Watershed, Texas, USA, was first calibrated for daily flow. The sediment parameters were then calibrated to monthly sediment loads, using each of the four sediment routing equations. An automatic calibration tool—Integrated Parameter Estimation and Uncertainty Analysis Tool (IPEAT)—was used to fit model parameters. The four sediment routing equations yielded substantially different sediment sources and sinks. The Yang equation performed best, followed by Kodoatie, Bagnold, and Molinas and Wu equations, according to greater model goodness-of-fit (represented by higher Nash–Sutcliffe Efficiency coefficient and percent bias closer to 0) as well as lower model uncertainty (represented by inclusion of observed data within 95% confidence interval). Since the default method (Bagnold) does not guarantee the best results, modelers should carefully evaluate the selection of alternative methods before conducting relevant studies or engineering projects

Aerial thermal infrared imaging and baseflow filtering analysis for river baseflow estimation in Lake Pyhäjärvi catchment, SW Finland

Säkylän Pyhäjärven kahden laskujoen, Pyhäjoen ja Yläneenjoen, pohjavirtaamaa arvioitiin infrapunakuvauksen (TIR) ja Baseflow- analyysin avulla. Heinäkuussa 2011 tehdyssä helikopteriavusteisessa TIR-kuvauksessa jokisysteemeissä ja niiden varsilla havaittiin yhteensä lähes 200 pohjaveden purkautumiskohtaa. Pohjaveden purkautumiseen liittyvät lämpötila-anomaliat jaettiin viiteen eri luokkaan, jotka olivat 1) lähde/ lähteiköt, 2) kylmä sivu-uoma, 3) diffuusi purkaus jokiuomaan, 4) kosteikko/ tihkupinta, 5) tunnistamaton anomalia. Tutkituista joista tehtiin myös lämpötila-analyysi, jossa havaittiin, että molemmissa jokisysteemeissä vesi lämpenee yläjuoksulta alajuoksulle. Pohjavirtaamaan osuutta arvioitiin myös Baseflow- ohjelmiston avulla. Ohjelmisto erottaa joen virtaamasta pohjavirtaaman osuuden signaalin prosessointiin perustuvan silmukoivan filtteröinnin avulla. Vuosien 2010-2013 pohjavirtaaman keskimääräiseksi osuudeksi saatiin Baseflow- ohjelmistolla 70 % Pyhäjoelle ja 54 % Yläneenjoelle. Samankaltaisia tutkimustuloksia on esitetty myös aiemmin julkaistuissa Pyhäjoen ja Yläneenjoen pohjavesiosuuksia käsittelevissä tutkimuksissa. Suurempi pohjavirtaama, pienempi jokiveden lämpötila ja laaja-alaiset pohjaveden purkautumisanomaliat osoittavat, että pohjaveden osuus Pyhäjoessa on suurempi kuin Yläneenjoessa. TIR- tutkimuksen tuloksia sekä pohjavirtaamalle laskettuja osuuksia on syytä tarkastella kriittisesti. TIR- aineistoista saadut tulokset kuvaavat vain hetkellisiä olosuhteita ja havaitut pohjaveden purkautumispaikat perustuvat kuva-aineiston tulkintaan. TIR- aineistosta tehtyyn lämpötila-analyysiin ja pohjaveden purkautumispaikkojen havainnointiin liittyy myös paljon epävarmuustekijöitä. Pohjavirtaama-analyysin tuloksia täytyy tulkita varoen, sillä pohjavirtaaman suodattaminen virtaama-aineistosta perustuu puhtaasti signaalien prosessointiin. Lämpökamera-aineiston tulokset ja pohjavirtaaman arvioinnista saadut tulokset osoittavat kuitenkin, että pohjaveden vaikutus on havaittavissa sekä Pyhäjoessa että Yläneenjoessa. Pohjaveden vaikutus tutkituissa joissa on erilainen. Pohjaveden suurempi osuus (70 %) Pyhäjoessa liittyy Pyhäjoen valuma-alueen karkearakeisempaan maaperään. Infrapuna-aineiston perusteella pohjaveden osuutta Pyhäjoessa lisää erityisesti kaksi suurta yläjuoksun lähdettä: Myllylähde ja Kankaanranta, jotka liittyvät Säkylä-Virttaankankaan harjukompleksiin. Yläneenjoella, missä pohjaveden osuus oli arvioitu pienemmäksi (54 %) ja pohjaveden purkautumisanomaliat pistemmäisemmiksi, joen lähellä on vain kaksi pienempää moreenivaltaista pohjavesialuetta. Lisäksi Yläneenjoen maaperässä on enemmän hienorakeisempia sedimenttejä kuin Pyhäjoella.The two input rivers of Säkylä’s Lake Pyhäjärvi: Pyhäjoki and Yläneenjoki, were studied with aerial thermal infrared imaging (TIR) analysis and baseflow program, in order to estimate the baseflow in the two rivers. From the helicopter- assisted TIR survey made in July 2011, almost 200 groundwater discharge sites were located in the two studied rivers. The groundwater discharge anomalies were categorized in 5 different classes: 1) spring/springs, 2) cold channel connected to the main channel, 3) diffuse discharge to river, 4) wetland/ wide seepage, 5) unknown anomaly. In addition, a temperature analysis was performed from the studied rivers. In both rivers, pattern of increasing river water temperature from headwaters towards river outlet were discovered with temperature analysis. The baseflow share estimate was made with baseflow filtering program which uses recursive digital filter for signal processing. Mean baseflow share estimation from four years: 2010-2013, were 70 % for River Pyhäjoki and 54 %, for River Yläneenjoki. Larger baseflow portion, lower river water temperature and wide diffuse discharge areas of River Pyhäjoki indicate that Pyhäjoki is more groundwater contributed than River Yläneenjoki. Previous studies made from the Lake Pyhäjärvi catchment have signs of higher groundwater share in River Pyhäjoki catchment, as well. However, TIR and baseflow estimation results of this study have to be dealt with caution. TIR results represent momentary circumstances and GWD locations are interpretations. There are also many factors increasing the uncertainty of the temperature analysis and observations of GWD anomalies. The results of baseflow analysis has to be interpreted carefully too because baseflow filtering is pure signal processing. However, this study shows that River Pyhäjoki and River Yläneenjoki have groundwater contribution. There is a difference in groundwater share in the two studied rivers. In River Pyhäjoki the larger groundwater share (70 %) is related to coarser grained glacial deposits in the river catchment. In TIR results, the influence of headwaters of the River Pyhäjoki, fed by two large springs: Myllylähde and Kankaanranta were emphasized. The two feeding springs are connected to the Säkylä-Virttaankangas esker complex. In River Yläneenjoki catchment, where GW portion was estimated to be smaller (54 %) and GW anomalies where mostly discrete, there are only two little till groundwater areas near the river channel and the catchment is characterized by finer sediments than River Pyhäjoki catchment

Evaluation of RUSLE and spatial assessment of agricultural soil erosion in Finland

Agricultural soil erosion has negative effects on surface water quality and aquatic ecosystems. A major impediment to agricultural erosion management in Finland has been the lack of high-resolution country-scale data on the spatial distribution of erosion. As a result, erosion mitigation measures have been targeted with limited information. Therefore, we evaluated the performance of the widely used RUSLE model against measurements from experimental fields, used the model to produce a two-metre resolution crop and management independent erosion estimate for all agricultural lands of Finland, and analysed erosion over different spatial scales. RUSLE showed skill (R2 = 0.76, NSE = 0.72) in estimating the observed erosion at experimental fields (55–2100 kg ha−1 yr−1) but with large errors (mean: −134 kg ha−1 yr−1, 90% range: −711 and 218 kg ha−1 yr−1). The evaluation, however, suggests that RUSLE performs similarly in Finland as elsewhere. The analysis of the developed country-scale data, in turn, revealed high erosion regions, and it showed how erosion varies between sub-catchment and between and within field parcels. For example, high-erosion areas concentrated in the proximity of water bodies were identified at the sub-catchment and within-field parcel scales. Altogether, the results demonstrate the predictive skill of RUSLE in high-latitude conditions, fill the earlier data gap in country-scale erosion, provide information for targeting erosion mitigation measures, and considerably improve the understanding of the spatial distribution of erosion in Finland

Long-term nutrient load management and lake restoration: Case of Säkylän Pyhäjärvi (SW Finland)

Eutrophication caused by anthropogenic nutrient pollution has become one of the most severe threats to water bodies. Nutrients enter water bodies from atmospheric precipitation, industrial and domestic wastewaters and surface runoff from agricultural and forest areas. As point pollution has been significantly reduced in developed countries in recent decades, agricultural non-point sources have been increasingly identified as the largest source of nutrient loading in water bodies. In this study, Lake Säkylän Pyhäjärvi and its catchment are studied as an example of a long-term, voluntary-based, co-operative model of lake and catchment management. Lake Pyhäjärvi is located in the centre of an intensive agricultural area in southwestern Finland. More than 20 professional fishermen operate in the lake area, and the lake is used as a drinking water source and for various recreational activities. Lake Pyhäjärvi is a good example of a large and shallow lake that suffers from eutrophication and is subject to measures to improve this undesired state under changing conditions. Climate change is one of the most important challenges faced by Lake Pyhäjärvi and other water bodies. The results show that climatic variation affects the amounts of runoff and nutrient loading and their timing during the year. The findings from the study area concerning warm winters and their influences on nutrient loading are in accordance with the IPCC scenarios of future climate change. In addition to nutrient reduction measures, the restoration of food chains (biomanipulation) is a key method in water quality management. The food-web structure in Lake Pyhäjärvi has, however, become disturbed due to mild winters, short ice cover and low fish catch. Ice cover that enables winter seining is extremely important to the water quality and ecosystem of Lake Pyhäjärvi, as the vendace stock is one of the key factors affecting the food web and the state of the lake. New methods for the reduction of nutrient loading and the treatment of runoff waters from agriculture, such as sand filters, were tested in field conditions. The results confirm that the filter technique is an applicable method for nutrient reduction, but further development is needed. The ability of sand filters to absorb nutrients can be improved with nutrient binding compounds, such as lime. Long-term hydrological, chemical and biological research and monitoring data on Lake Pyhäjärvi and its catchment provide a basis for water protection measures and improve our understanding of the complicated physical, chemical and biological interactions between the terrestrial and aquatic realms. In addition to measurements carried out in field conditions, Lake Pyhäjärvi and its catchment were studied using various modelling methods. In the calibration and validation of models, long-term and wide-ranging time series data proved to be valuable. Collaboration between researchers, modellers and local water managers further improves the reliability and usefulness of models. Lake Pyhäjärvi and its catchment can also be regarded as a good research laboratory from the point of view of the Baltic Sea. The main problem in both of them is eutrophication caused by excess nutrients, and nutrient loading has to be reduced – especially from agriculture. Mitigation measures are also similar in both cases.Ihmisen aiheuttamasta ravinnekuormituksesta johtuva rehevöityminen on yksi pahimmista vesistöjä uhkaavista ilmiöistä. Ravinteet kulkeutuvat vesiin ilmalaskeumana, teollisuuden ja yhdyskuntien jätevesissä sekä maatalous- ja metsäalueilta tulevissa valumavesissä. Kehittyneissä maissa pistekuormitus on merkittävästi vähentynyt viime vuosikymmeninä, ja hajakuormituksen, erityisesti maatalouden, on todettu olevan merkittävin vesistöjen ravinnekuormittaja. Tässä tutkimuksessa Säkylän Pyhäjärveä ja sen valuma-aluetta käytetään esimerkkinä pitkäjänteisestä, vapaaehtoisuuteen perustuvasta yhteistyömallista järven ja valuma-alueen vesien tilan parantamiseksi. Pyhäjärvi sijaitsee Lounais-Suomen intensiivisesti viljellyllä alueella. Järvellä toimii yli 20 ammattikalastajaa, sen vettä käytetään raakavetenä ja myös virkistyskäyttö on monipuolista ja intensiivistä. Pyhäjärvi on erinomainen esimerkki isosta, matalasta rehevöitymisen oireista kärsivästä järvestä, jonka tilaa pyritään määrätietoisesti parantamaan muuttuvissa olosuhteissa. Ilmastonmuutos on yksi suurimmista vesiensuojelun haasteista niin Pyhäjärvellä kuin muissakin vesistöissä. Tulokset osoittavat, että ilmastollinen vaihtelu vaikuttaa valunnan ja ravinnekuormituksen määriin sekä niiden vuodenaikaisuuksiin. Havainnot tutkimusalueelta koskien lämpimien talvien vaikutusta ravinnekuormitukseen ovat linjassa IPCC:n ilmastonmuutosskenaarioiden kanssa. Paitsi ravinnekuormituksen vähentäminen, myös ravintoketjukunnostus (biomanipulaatio) on keskeinen keino veden laadun hallinnassa. Ravintoketjun rakenne on kuitenkin häiriintynyt leutojen talvien, lyhyen jääpeiteajan ja vähäisen kalansaaliin vuoksi. Talvinuottauksen mahdollistavalla jääpeitteellä ja sen pituudella on suuri merkitys Pyhäjärven veden laadun ja ekosysteemin kannalta, sillä muikkukanta on yksi ravintoketjua ja järven tilaa säätelevistä tekijöistä. Ravinnekuormituksen vähentämiseksi ja maatalouden valumavesien käsittelemiseksi kehitettyjä uusia menetelmiä, esimerkiksi hiekkasuodattimia, on testattu kenttäolosuhteissa. Suodatintekniikka osoittautui käyttökelpoiseksi menetelmäksi ravinteiden vähentämiseksi, mutta kehitystyötä on edelleen jatkettava. Hiekkasuodattimien ravinteiden poistoa voidaan tehostaa erilaisilla ravinteita sitovilla yhdisteillä, esimerkiksi kalkkipohjaisilla materiaaleilla. Pyhäjärven ja sen valuma-alueen pitkäkestoiset hydrologiset, kemialliset ja biologiset seuranta- ja tutkimusaikasarjat ovat vesiensuojelun perusta ja niiden avulla lisätään ymmärrystä monimutkaisista järven ja valuma-alueen fysikaalisista, kemiallisista ja ekologisista vuorovaikutussuhteista. Kenttäolosuhteissa tehtyjen mittausten lisäksi Pyhäjärveä ja sen valuma-aluetta on tutkittu erilaisilla mallinnusmenetelmillä. Mallien kalibroinnissa ja validoinnissa pitkät ja monipuoliset aikasarjat osoittautuivat arvokkaiksi. Mallintajien, tutkijoiden ja käytännön vesiensuojelun toteuttajien yhteistyöllä voidaan edelleen parantaa mallien luotettavuutta ja hyödynnettävyyttä. Pyhäjärveä valuma-alueineen voidaan tarkastella myös Itämeren kaltaisena luonnonlaboratoriona. Ylimääräisten ravinteiden aiheuttama rehevöityminen on molempien ongelma, ja ravinnekuormitusta on molemmissa tapauksissa vähennettävä – erityisesti maataloudesta. Vähentämismenetelmät ovat niin ikään samoja.Siirretty Doriast