Effekt av klima og jordbruk på hydrologi og vannkvalitet : en studie av små jordbruksdominerte nedbørfelt

Eutrophication and degradation of water quality are global problems and affect many freshwater and coastal systems. Agricultural areas are major contributors of nutrients and soil particles in streams and lakes. The objectives of this study were to discuss the impacts on water quality and quantity of expected land use changes due to a transition to bioeconomy (the green shift) in Norwegian agricultural catchments; to detect trends in climate and hydrology; and to describe and understand catchment processes related to runoff, soil and nutrient losses. The study has been carried out in seven Norwegian small headwater catchments and has included analyses of long-term data series (26 years) as well as collection of new data, in particular high-frequency sensor data on turbidity and water samples for a stable water isotope (18O, 2H) analysis. Moreover, data from a network of Nordic catchments (69 sites in total) have been included in the study. Analysis for the thesis was done using latest statistical and time series analytical methods. Pressures on deterioration of water quality related to bioeconomy activities have been discussed based on data from 69 Nordic catchments. A green shift in Nordic agriculture might imply more intensive land use or clearing of new land. Our study showed that agricultural sites show the highest concentration and fluxes of total nitrogen and phosphorus compared to forestry-impacted and natural catchments. In addition, pressures from climate change (droughts and heavy rainfalls) and their combined effects can pose severe threats to water quality in Nordic regions. The analysis for seven Norwegian catchments revealed changes in meteorological inputs and hydrological responses. The annual mean temperature increased significantly during 26 years of observations in six of the seven studied catchments. This increase in temperature affected evaporation, the hydrological regime, the snow water equivalent, nutrient concentration, and the length of the growing season. In four of seven catchments the snow water equivalent decreased significantly during winter, and only one catchment showed an increase. The change in the snow regime affects the hydrology of the snow-dominated catchments (main runoff events due to snowmelt periods). Hydrological patterns varied between the seven catchments depending on whether they were located at the coast (rain-dominant) or inland (snow-dominant). In the rain-dominated catchments precipitation and discharge showed a strong coherence. Snow-dominated catchments showed a weaker coherence, because precipitation as snow is not immediately available for discharge. Snow precipitation does not translate to discharge until snowmelt occurs. Extreme conditions, as in 2010 (relative low average temperature) and 2018 (drought), seemed to decrease the coherence between runoff and variables such as precipitation, snow water equivalent, and soil water storage capacity in four of the catchments. Climatic and hydrological long-term changes could be best detected at the seasonal scale. Studied variables such as discharge, turbidity, field operations, crop factor, connectivity index, soil water storage capacity, and snow water equivalent showed a strong seasonality. In our study we also considered factors which impact the concentrations and losses of nutrients and sediments. We found that a prolonged growing season coincided with a decrease in nitrogen concentrations in cereal dominated catchments. However, this change in growing season length did not affect the farmers’ sowing time, nor did they harvest earlier, assumedly because soil moisture is in this case the determining factor for soil workability. Nutrient and sediment losses were closely linked to hydrological processes in study catchments. Results from the multivariate regression of two monitored catchments showed that discharge is one of the main drivers for sediment and particulate phosphorus concentration (explained 50% of the variation in turbidity). For nitrogen, an increase in discharge gave a dilution effect. High frequency turbidity sensor data revealed that the concentration-discharge patterns of runoff events were characterised by turbidity peaks before discharge peaks. This indicates a rapid mobilisation of suspended sediments and particulate phosphorus. Channel bed dynamics, including stream bank erosion and remobilisation of in-stream particles contribute to these patterns. A high-water discharge in a first storm event in general reduced the sediment transport in the following event, suggesting depletion of available in-stream/near-stream material. Detecting responses of agricultural management were challenging using sensor-data. In general, detecting responses of agricultural land management on stream water quality and quantity at catchment scale proved to be challenging due to spatial variations in field management, topography, soil, hydrology, and vegetation. Therefore, it is important to continue monitoring programs, especially where long-term datasets exist. Responses of climate, hydrology and land management on water quality were different from catchment to catchment, which is why it is important to apply land management and mitigation measures adapted and tailored to the local conditions.Eutrofiering og forringet vannkvalitet er globale problemer som påvirker mange ferskvanns- og kystsystemer. Jordbruk er en av de sektorene som bidrar mest med næringsstoffer og jordpartikler i bekker, elver og innsjøer. Hensikten med denne studien har vært å diskutere effekter på vannkvalitet og hydrologi som følge av en overgang til bioøkonomi (det grønne skiftet); å oppdage trender innen klima og hydrologi; og å beskrive og forstå nedbørfeltprosesser knyttet til avrenning, tap av jord og næringsstoffer. Studien har blitt utført i syv norske nedbørfelt og inkluderte analyser av lange dataserier (26 år) samt innsamling av nye data, spesielt høyfrekvente sensordata av turbiditet, og vannprøver for en stabil vannisotopanalyse (18O, 2H). Videre er data fra et nettverk av nordiske nedbørfelt (totalt 69 felt) inkludert i studien. Dataene ble analysert med forskjellige statistiske metoder: Mann-Kendall trendanalyse, lineær blandet modell, multivariat regresjon og en såkalt wavelet coherence analyse. Utfordringer for vannkvalitet knyttet til innføring av bioøkonomi har blitt diskutert basert på data fra 69 nordiske nedbørfelt. Et grønt skifte kan innebære mer intensiv arealbruk eller rydding av nytt land for oppdyrking. Dataene viser at jordbruksbekker allerede i dag har de høyeste konsentrasjoner og tilførsler av totalnitrogen og fosfor sammenlignet med bekker i skogbruksområder og naturlige nedbørfelt. I tillegg kommer klimaendringer (tørke og store nedbørsmengder), og den kombinerte effekten kan være en alvorlig trussel mot vannkvaliteten. Den årlige gjennomsnittstemperaturen økte betydelig i løpet av 26 års observasjoner i alle de syv undersøkte nedbørfeltene, bortsett fra ett. Denne temperaturøkningen påvirket fordampning, det hydrologiske regimet, snøvannets ekvivalent, næringsstoffkonsentrasjon og lengden på vekstsesongen. I fire av sju nedbørfelt ble snøvanns-ekvivalenten betydelig redusert om vinteren, og bare ett nedbørfelt hadde en økning. Denne endringen i snøregimet påvirker hydrologien i snødominerte nedbørfelt, dvs. der avrenningsmønster er sterkt preget av snøsmelting. Hydrologiske mønstre varierte mellom de syv nedbørfeltene, avhengig av om det var regn- eller snø-dominert, noe som igjen hang sammen med geografisk plassering (innland eller kyst). I regn-dominerte nedbørfelt var det en tydelig sammenheng mellom nedbør og avrenning. Snø-dominerte nedbørfeltfelt viste ikke en sterk sammenheng, fordi nedbør som snø først gir økt avrenning under snøsmelting. Ekstremår som i 2010 (relativ lav gjennomsnittstemperatur) og 2018 (tørke) så ut til å redusere sammenhengen mellom avrenning og variabler som nedbør, snøvanns-ekvivalent og lagringskapasitet i jord i fire av nedbørfeltene. Klimatiske og hydrologiske langsiktige endringer kan best oppdages på sesongskalaen. Studerte variabler som avrenning, turbiditet, dyrkingspraksis, avlingsfaktor, konnektivitet, lagringskapasitet for jordvann og snøvannekvivalenter hadde en sterk sesongavhengighet. En forlenget vekstsesong samvarierte med reduserte nitrogenkonsentrasjoner i korndominerte nedbørfelt. En endring i vekstsesongens lengde påvirket ikke bøndenes såtid eller høstetid, antagelig fordi jordfuktighet i dette tilfellet er den avgjørende faktoren for når jorda er laglig for bearbeiding. Næringsstoff- og sedimenttap er nært knyttet til hydrologi. Resultatene fra den multivariate regresjonen viste at avrenningen er en av hovedårsakene for sediment- og partikkelbundet fosforkonsentrasjon (forklarte 50% av variasjonen i turbiditet). For nitrogen ga en økning i avrenning en fortynningseffekt. Turbiditet-sensordata viste at turbiditet kulminerer før avrenningen. Dette indikerer en rask mobilisering av suspenderte sedimenter og partikkelbundet fosfor. Dynamikken i bekkene, som erosjon og remobilisering av partikler, samt størrelsen av tidligere avrenningsepisoder spilte også en viktig rolle for transport av sediment. Det er utfordrende å finne sammenhenger mellom jordbruksaktivitet og vannkvalitet og hydrologi i nedbørfelt på grunn av romlige variasjoner i topografi, jord, hydrologi, driftspraksis og vegetasjon. Derfor er det viktig å fortsette med overvåkningsprogrammer, spesielt der det finnes lange dataserier. Responsene på vannkvalitet av klima, hydrologi og jordbruk var forskjellige fra nedbørfelt til nedbørfelt, og derfor er det viktig at arealforvaltning og tiltak er tilpasset lokale forhold

Comparing in situ turbidity sensor measurements as a proxy for suspended sediments in North-Western European streams

Climate change in combination with land use alterations may lead to significant changes in soil erosion and sediment fluxes in streams. Optical turbidity sensors can monitor with high frequency and can be used as a proxy for suspended sediment concentration (SSC) provided there is an acceptable calibration curve for turbidity measured by sensors and SSC from water samples. This study used such calibration data from 31 streams in 11 different research projects or monitoring programmes in six Northern European countries. The aim was to find patterns in the turbidity-SSC correlations based on stream characteristics such as mean and maximum turbidity and SSC, catchment area, land use, hydrology, soil type, topography, and the number and representativeness of the data that are used for the calibration. There were large variations, but the best correlations between turbidity and SSC were found in streams with a mean and maximum SSC of >30-200 mg/l, and a mean and maximum turbidity above 60-200 NTU/FNU, respectively. Streams draining agricultural areas with fine-grained soils had better correlations than forested streams draining more coarse-grained soils. However, the study also revealed considerable differences in methodological approaches, including analytical methods to determine SSC, water sampling strategies, quality control procedures, and the use of sensors based on different measuring principles. Relatively few national monitoring programmes in the six countries involved in the study included optical turbidity sensors, which may partly explain this lack of methodological harmonisation. Given the risk of future changes in soil erosion and sediment fluxes, increased harmonisation is highly recommended, so that turbidity data from optical sensors can be better evaluated and intercalibrated across streams in comparable geographical regions

Climate effects on land management and stream nitrogen concentrations in small agricultural catchments in Norway

Land use and climate change can impact water quality in agricultural catchments. The objectives were to assess long-term monitoring data to quantify changes to the thermal growing season length, investigate farmer adaptations to this and examine these and other factors in relation to total nitrogen and nitrate water concentrations. Data (1991–2017) from seven small Norwegian agricultural catchments were analysed using Mann–Kendall Trend Tests, Pearson correlation and a linear mixed model. The growing season length increased significantly in four of seven catchments. In catchments with cereal production, the increased growing season length corresponded to a reduction in nitrogen concentrations, but there was no such relationship in grassland catchments. In one cereal catchment, a significant correlation was found between the start of sowing and start of the thermal growing season. Understanding the role of the growing season and other factors can provide additional insight into processes and land use choices taking place in agricultural catchments.publishedVersio

Climate effects on land management and stream nitrogen concentrations in small agricultural catchments in Norway

Land use and climate change can impact water quality in agricultural catchments. The objectives were to assess long-term monitoring data to quantify changes to the thermal growing season length, investigate farmer adaptations to this and examine these and other factors in relation to total nitrogen and nitrate water concentrations. Data (1991–2017) from seven small Norwegian agricultural catchments were analysed using Mann–Kendall Trend Tests, Pearson correlation and a linear mixed model. The growing season length increased significantly in four of seven catchments. In catchments with cereal production, the increased growing season length corresponded to a reduction in nitrogen concentrations, but there was no such relationship in grassland catchments. In one cereal catchment, a significant correlation was found between the start of sowing and start of the thermal growing season. Understanding the role of the growing season and other factors can provide additional insight into processes and land use choices taking place in agricultural catchments

Hydrology under change: Long-term annual and seasonal changes in small agricultural catchments in Norway

In agricultural catchments, hydrological processes are highly linked to particle and nutrient loss and can lead to a degradation of the ecological status of the water. Global warming and land use changes influence the hydrological regime. This effect is especially strong in cold regions. In this study, we used long-term hydrological monitoring data (22–26 years) from small agricultural catchments in Norway. We applied a Mann–Kendall trend and wavelet coherence analysis to detect annual and seasonal changes and to evaluate the coupling between runoff, climate, and water sources. The trend analysis showed a significant increase in the annual and seasonal mean air temperature. In all sites, hydrological changes were more difficult to detect. Discharge increased in autumn and winter, but this trend did not hold for all catchments. We found a strong coherence between discharge and precipitation, between discharge and snow water equivalent and discharge and soil water storage capacity. We detected different hydrological regimes of rain and snow-dominated catchments. The catchments responded differently to changes due to their location and inherent characteristics. Our results highlight the importance of studying local annual and seasonal changes in hydrological regimes to understand the effect of climate and the importance for site-specific management plans

Climate effects on land management and stream nitrogen concentrations in small agricultural catchments in Norway

Land use and climate change can impact water quality in agricultural catchments. The objectives were to assess long-term monitoring data to quantify changes to the thermal growing season length, investigate farmer adaptations to this and examine these and other factors in relation to total nitrogen and nitrate water concentrations. Data (1991–2017) from seven small Norwegian agricultural catchments were analysed using Mann–Kendall Trend Tests, Pearson correlation and a linear mixed model. The growing season length increased significantly in four of seven catchments. In catchments with cereal production, the increased growing season length corresponded to a reduction in nitrogen concentrations, but there was no such relationship in grassland catchments. In one cereal catchment, a significant correlation was found between the start of sowing and start of the thermal growing season. Understanding the role of the growing season and other factors can provide additional insight into processes and land use choices taking place in agricultural catchments

Hydrology under change: Long-term annual and seasonal changes in small agricultural catchments in Norway

In agricultural catchments, hydrological processes are highly linked to particle and nutrient loss and can lead to a degradation of the ecological status of the water. Global warming and land use changes influence the hydrological regime. This effect is especially strong in cold regions. In this study, we used long-term hydrological monitoring data (22–26 years) from small agricultural catchments in Norway. We applied a Mann–Kendall trend and wavelet coherence analysis to detect annual and seasonal changes and to evaluate the coupling between runoff, climate, and water sources. The trend analysis showed a significant increase in the annual and seasonal mean air temperature. In all sites, hydrological changes were more difficult to detect. Discharge increased in autumn and winter, but this trend did not hold for all catchments. We found a strong coherence between discharge and precipitation, between discharge and snow water equivalent and discharge and soil water storage capacity. We detected different hydrological regimes of rain and snow-dominated catchments. The catchments responded differently to changes due to their location and inherent characteristics. Our results highlight the importance of studying local annual and seasonal changes in hydrological regimes to understand the effect of climate and the importance for site-specific management plans.publishedVersio

Hydrology under change: Long-term annual and seasonal changes in small agricultural catchments in Norway

In agricultural catchments, hydrological processes are highly linked to particle and nutrient loss and can lead to a degradation of the ecological status of the water. Global warming and land use changes influence the hydrological regime. This effect is especially strong in cold regions. In this study, we used long-term hydrological monitoring data (22–26 years) from small agricultural catchments in Norway. We applied a Mann–Kendall trend and wavelet coherence analysis to detect annual and seasonal changes and to evaluate the coupling between runoff, climate, and water sources. The trend analysis showed a significant increase in the annual and seasonal mean air temperature. In all sites, hydrological changes were more difficult to detect. Discharge increased in autumn and winter, but this trend did not hold for all catchments. We found a strong coherence between discharge and precipitation, between discharge and snow water equivalent and discharge and soil water storage capacity. We detected different hydrological regimes of rain and snow-dominated catchments. The catchments responded differently to changes due to their location and inherent characteristics. Our results highlight the importance of studying local annual and seasonal changes in hydrological regimes to understand the effect of climate and the importance for site-specific management plans

Learning Science during Teatime : Using a Citizen Science Approach to Collect Data on Litter Decomposition in Sweden and Austria

The decay of organic material-litter decomposition-is a critical process for life on Earth and an essential part of the global carbon cycle. Yet, this basic process remains unknown to many citizens. The Tea Bag Index (TBI) measures decomposition in a standardized, measurable, achievable, climate-relevant, and time-relevant way by burying commercial tea bags in soil for three months and calculating proxies to characterize the decomposition process (expressed as decomposition rate (k) and stabilization factor (S)). We measured TBI at 8 cm soil depth with the help of school and farm citizen scientists in 2015 in Sweden and in 2016 in Austria. Questionnaires to the participating schools and farms enabled us to capture lessons learned from this participatory data collection. In total >5500 citizen scientists participated in the mass experiments, and approximately 50% of the tea bags sent out yielded successful results that fell well within previously reported ranges. The average decomposition rates (k) ranged from 0.008 to 0.012 g d(-1) in Sweden and from 0.012 to 0.015 g d(-1) in Austria. Stabilization factors (S) were up to four times higher in Sweden than Austria. Taking part in a global experiment was a great incentive for participants, and in future experiments the citizen scientists and TBI would benefit from having enhanced communication between the researchers and participants about the results gained

Learning science during teatime: Using a citizen science approach to collect data on litter decomposition in Sweden and Austria

The decay of organic material—litter decomposition—is a critical process for life on Earth and an essential part of the global carbon cycle. Yet, this basic process remains unknown to many citizens. The Tea Bag Index (TBI) measures decomposition in a standardized, measurable, achievable, climate-relevant, and time-relevant way by burying commercial tea bags in soil for three months and calculating proxies to characterize the decomposition process (expressed as decomposition rate (k) and stabilization factor (S)). We measured TBI at 8 cm soil depth with the help of school and farm citizen scientists in 2015 in Sweden and in 2016 in Austria. Questionnaires to the participating schools and farms enabled us to capture lessons learned from this participatory data collection. In total >5500 citizen scientists participated in the mass experiments, and approximately 50% of the tea bags sent out yielded successful results that fell well within previously reported ranges. The average decomposition rates (k) ranged from 0.008 to 0.012 g d−1 in Sweden and from 0.012 to 0.015 g d−1 in Austria. Stabilization factors (S) were up to four times higher in Sweden than Austria. Taking part in a global experiment was a great incentive for participants, and in future experiments the citizen scientists and TBI would benefit from having enhanced communication between the researchers and participants about the results gained