Potential for using high frequency turbidity as a proxy for total phosphorus in Sävjaån

Transport of particles carrying nutrients and contaminants from land to sea is a challenge to monitor due to the high temporal variability in concentrations. Phosphorus is a particle associated nutrient, largely affecting the state of waters due to its effects on eutrophication. When using traditional monitoring methods, there is a prevailing risk of misjudging the state of water and transport of phosphorus due to lack of data. Therefore, this study aimed to evaluate the potential use of continuous high frequency turbidity as a proxy for total phosphorus concentration. An in situ sensor monitoring turbidity every 10th minute was deployed from 2012-2015 in Sävjaån, a river draining a mixed land use catchment in central Sweden. The sub-catchment is an agricultural area dominated by clay soil close to Uppsala in Sweden. The results from measuring high frequency turbidity with the sensor were compared to traditional monthly grab sampling. A significant information loss could be observed when performing grab sampling, the turbidity from the sensor varied more and showed higher maximum values (9-15 times). The correlation between the different parameters was evaluated by linear regression. The results show very high correlation between turbidity and total phosphorus (r2= 0.79) and high correlation between turbidity and total suspended solids (r2= 0.67). The relationships seemed to be affected by calibration of the sensor, spatial variation and the proportion of phosphate and total phosphorus in Sävjaån. The phosphorus load was calculated from the high frequency data and compared to linear interpolation and piecewise constant interpolation of grab samples. Loads calculated from high frequency data was during two years (2012 and 2015) 31% and 17% larger than when using linear interpolation. However, the timing and the instant flow at the time of grab sampling had large impact on the estimated load when using linear interpolation (2013 and 2014). It could be concluded that most P was transported when high discharge and high concentrations coincided. When comparing the calculations of ecological quality ratios from grab sampling and high frequency data the difference was modest.Kontinuerligt rapporteras det i svenska medier om algblomning och övergödning i ytvatten och i Östersjön. Ökat antal algplankton och bakterier skapar en grön och grynig vattenmassa. Det leder även till potentiell syrebrist i vattnet och störda ekosystem. Ur ett historiskt perspektiv har mängden näringsämnen som transporteras till Östersjön ökat. Idag är det främst jordbruk, vattenreningsverk, industrier, privata avlopp och dagvatten som bidrar till problemet. Fosfor är ett av näringsämnena som till stor del påverkar övergödningsproblematiken. För att kunna hantera övergödningsproblematiken behöver vi veta hur det är ställt i svenska sjöar och vattendrag. Vanligtvis tas månatliga vattenprover som analyseras i ett laboratorium, tiden mellan vattenproverna estimeras med hjälp av olika metoder. Fosforhalten i vattnet varierar dock avsevärt i tid och rum. På grund av det är den årliga transporten fosfor från ett vattendrag svår att uppskatta på ett trovärdigt sätt. I den här studien har en ny metod för att beskriva förhållandena i Sävjaån testats och utvärderats. En sensor som mäter grumlighet i vatten (turbiditet) var 10:e minut har monterats i Sävjaån i närheten av Uppsala under perioden 2012-2015. Fosfor transporteras ofta tillsammans med partiklar och dessa bidrar till grumlighet i vattnet. Därför har möjligheten att använda turbiditet som ett substitut för fosformätningar undersökts. Det visade sig finnas ett väldigt starkt samband mellan turbiditet och fosfor i Sävjaån. Ett starkt samband kunde även observeras mellan turbiditet och mängd vattenburna partiklar (suspenderat material/slamhalt). När förhållandena i vattnet övervakades med hjälp av sensorn var det tydligt att mycket information saknades när endast månatliga vattenprover togs. När de två metoderna jämfördes varierade grumligheten mer och 9-15 gånger högre maximala värden uppmättes. Den totala mängden transporterat fosfor per år visade sig vara 31% and 17% (2012 och 2015) större när den beräknades med hjälp av informationen från sensorn i jämförelse med den vanligen använda metoden. När höga vattenflöden inträffade samtidigt med höga fosforkoncentrationer transporterades störst mängd fosfor. Även om det innebär en osäkerhet att använda grumlighet som ett mått för fosfor finns stora möjligheter till bättre uppskattningar av fosfortransport. Med en välskött sensor och noggrant kontrollerad data finns potential för mer representativa resultat som kan hjälpa samhället att hantera övergödningsproblematiken på ett bättre sätt

Turbidity-discharge hysteresis in a meso-scale catchment: The importance of intermediate scale events

In-situ sensors for riverine water quality monitoring are a powerful tool to describe temporal variations when efficient and informative analyses are applied to the large quantities of data collected. Concentration-discharge hysteresis patterns observed during storm events give insights into headwater catchment processes. However, the applicability of this approach to larger catchments is less well known. Here, we evaluate the potential for high-frequency turbidity-discharge (Q) hysteresis patterns to give insights into processes operating in a meso-scale (722 km(2)) northern mixed land use catchment. As existing event identification methods did not work, we developed a new, objective method based on hydrograph characteristics and identified 76 events for further analysis. Qualitative event analysis identified three recurring patterns. Events with low mean Q (= 15 m(3)/s) were often associated with spring flood or snowmelt, and showed a disconnection between turbidity and Q. Intermediate Q events (mean Q: 2-11 m(3)/s) were the most informative when applying hysteresis indexes, since changes in turbidity and Q were actually connected. Hysteresis indexes could be calculated on a subset of 60 events, which showed heterogeneous responses: 38% had a clockwise response, 12% anticlockwise, 12% figure eight (clockwise-anticlockwise), 10% reverse figure eight (anticlockwise-clockwise) and 28% showed a complex response. Clockwise hysteresis responses were associated with the wetter winter and spring seasons. Generally, changes in Q and turbidity were small during anticlockwise hysteresis events. Precipitation often influenced figure-eight patterns, while complex patterns often occurred during summer low flows. Analysis of intermediate Q events can improve process understanding of meso-scale catchments and possibly aid in choosing appropriate management actions for targeting a specific observed pattern

In-situ sensorers användning i nationell miljöövervakning

Övervakning med in-situ sensorer ger ett värdefullt komplement till den nuvarande miljöövervakningen med labanalyser av stickprov. Även om det än så länge endast är möjligt att mäta vissa variabler, som i vissa fall innebär indirekt mätning, ger högfrekventa mätningar ny och värdefull kunskap om hur vattenkvaliteten varierar i olika tidsskalor. Mätningarna bidrar därigenom till att uppfylla kraven på den kontrollerande övervakningen i EU:s ramdirektiv för vatten. Det gäller både att ge underlag för att utforma effektiva mätprogram och att följa långsiktiga förändringar i naturliga förhållanden och effekter av storskalig påverkan. På institutionen för vatten och miljö, SLU, har vi under tio år arbetat med in-situ sensorer. Vi har idag sensorer utplacerade i tio olika vattendrag som övervakar variationen i vattenkemi var 15:e minut. Metoder för installation av sonder i vattendrag, datahantering och kvalitetssäkring har utvecklats. Inledningsvis var arbetet inriktat på att förbättra transportberäkningar av total fosfor (TP) och slamhalt (TSS) baserat på turbiditetsmätningar samt att mäta halten organiskt material i råvattenintag för dricksvatten. Andra användningsområden är att bevaka erosionsbenägna vattendrag, fånga viktiga episoder/perioder (exempelvis algblomning, lågt pH), användning vid övervakning av dagvatten, adaptiv provtagning för att fånga perioder med höga/låga koncentrationer, utvärdering av åtgärder samt fånga variation med korta tidsskalor (exempelvis dygnscykler). Vi föreslår att mätningarna med sensorer i den nationella miljöövervakningen permanentas och om möjligt utökas. Det skulle ge möjlighet att bygga upp tidsserier med högfrekventa data samt att testa nya typer av mätutrustning i takt med att de utvecklas. Det kommer även att ge ny värdefull kunskap kring den kortsiktiga variationen av vattenkemiska parametrar, vilket tillför ett viktigt komplement till den idag långsiktiga beskrivningen av tillståndet i Sveriges vattenmiljö

Water quality in a large complex catchment: Significant effects of land use and soil type but limited ability to detect trends

Globally, significant societal resources are devoted to mitigating negative effects of eutrophication from excessive phosphorus (P) and nitrogen (N) loading. Potential effectiveness of mitigation measures and possible confounding factors are often assessed using studies conducted in headwater catchments. However, success is often evaluated based on trends in river mouth water chemistry. It is not clear how transferrable insights from headwater catchments are to larger rivers. Here, relationships between P and suspended solids (SS) identified in small agricultural headwater catchments were applied to 30 larger, mixed land use catchments draining into Malaren, ¨ a Swedish great lake. Relationships identified in headwater streams between SS concentration, catchment agricultural land percentage and arable land clay content were corroborated for the larger catchments (R2 = 0.59, p-valu

Högfrekvent data i modellering : användning, utmaningar och nytta vid modellering av flöde- och vattenkemi

Användning av in-situ sensorer för insamling av data med hög frekvens (exempelvis var 15:e min) kan ge bättre förståelse för biogeokemiska och hydrologiska processer i specifika vattendrag. I denna rapport har beskrivits tre olika sätt att med fördjupad analys av sensordata generalisera och skala upp resultaten från mätningarna.I det första exemplet används vattennivå, som exempelvis kan mätas med sensorer, i modellen PERSiST för att ta fram tidsserier för vattenföring. Genom modellen skapas en ”syntetisk avbördningskurva” utan tidsödande manuella mätningar och kostsamma installationer. Detta kan göras med hög frekvens (exempelvis per timme) då tillgänglig nederbörds- och temperaturdata finns, men alternativet finns även att använda ett dagligt tidssteg. Kvaliteten på nederbörds- och temperaturdata hade stor betydelse för resultatet, men metoden verkar lovande. Hur väl detta fungerar i olika typer av vattendrag och under olika förhållanden behöver undersökas ytterligare.I det andra exemplet analyseras sensordata tillsammans med vattenföringsdata (C-Q analys) för att skapa en bättre förståelse för processer i vattendragen, exempelvis erosion av suspenderat material. Genom att undersöka dynamiken i turbiditet under episoder med högre vattenföring, kan vi se att de fyra undersökta vattendragen rea-gerar på olika sätt på ökat flöde. När klimatdata läggs till i analysen, exempelvis regn/snö, snösmältning, markfuktighet, kan responsen i vattendragen kopplas till olika processer och säsonger. Resultaten kan användas som stöd för val av åtgärder mot näringsförluster från jordbruksmark och även visa vilka vattendrag som är mest känsliga för ökad förekomst av extrem nederbörd och snabba flödesförändringar till följd av klimatförändringen.Vidare har högfrekvent data använts i vattenkvalitetsmodellering. Den betydande variationen i högfrekvent kalibreringsdata gjorde det svårare att uppnå hög samstäm-mighet mellan modellerade och observerade värden. Användning av den högfre-kventa datan i modellen gav generellt både högre koncentrationer (mg/l) och belast-ning (kg/dag ) av suspenderat material och totalfosfor (kg/dag) i jämförelse med den lågfrekventa datan. I takt med att kunskapen om användningen av högfrekvent data i modeller ökar kommer det visa sig i vilken mån de kommer kunna användas i förvaltningen.Vi har här gett några exempel på hur olika typer av fördjupad analys av sensordata kan öka användningen, med potential att ge underlag för vattenförvaltningen så att värdet av datan ökar ytterligare. Arbetet med att skala upp användning av data från in-situ sensorer är dock ännu i ett tidigt skede, och mycket arbete kvarstår innan applikationer kan användas direkt i förvaltningen

Metabolic processes control carbon dioxide dynamics in a boreal forest ditch affected by clear-cut forestry

Boreal watercourses are large emitters of carbon dioxide (CO2) to the atmosphere. For forestry intensive areas of the Nordic and Baltic countries, a high share of these watercourses are man-made ditches, created to improve drainage and increase forest productivity. Previous studies have suggested that terrestrial sources sustain the CO2 in these ditches and variability in hydrology is the main temporal control. However, few studies have explored ditch CO2 dynamics and its associated controls in catchments being exposed to forest harvest. An altered hydrology, increased nutrient export and light availability following forest harvest are all factors that potentially can change both levels, dynamics, and source controls of ditch CO2. Here, high-frequency (30 min) CO2 concentration dynamics together with other hydrochemical variables were studied in a forest ditch draining a fully harvested catchment in the Trollberget Experimental Area, northern Sweden. We collected data during the snow-free season from May to October. Ditch CO2 concentrations displayed a clear seasonal pattern with higher CO2 concentrations during summer than in spring and autumn. Concentrations ranged from 1.8 to 3.5 mg C L−1 (median: 2.4 mg C L−1 , IQR = 0.5 mg C L−1 ). Strong diel cycles in CO2 developed during early summer, with daily amplitudes in CO2 reaching up to 1.1 mg C L−1 . These pronounced daily cycles in CO2 were closely related to the daily sum of shortwave radiation and water temperature. Variations in hydrology had generally a low impact on the CO2 dynamics but did vary among seasons and between individual hydrological events. It was evident from our study that growing season CO2 concentrations in a forest ditch aected by clearcut harvest were highly variable and mainly controlled by light and temperature induced metabolism. These high dynamics and the associated controls need to be considered when scaling up ditch CO2 emissions across boreal landscapes aected by intensive fores

Influence of forest management changes and reuse of peat production areas on water quality in a northern river

In Northern Finland, the most significant land use challenges are related to bioenergy production from peat extraction and forest biomass. Increasing societal demand for bioenergy may increase production rates. However, environmental impacts of peat extraction are of increasing concern, which has led to a decline in production, thereby freeing up these areas for other uses. Using storylines for different societal futures and process-based models (PERSiST and INCA), we simulated the effect of simultaneous land use change and climate change on water quality (phosphorus, nitrogen and suspended sediments concentration). Conversion of peat extraction areas to arable land, together with climate change, may pose a risk for deterioration of ecological status. On the other hand, continuous forestry may have positive impacts on water quality. Suspended sediment concentrations in the river do not exceed water quality requirements for salmonids, but nitrogen concentrations may exceed threshold values especially during high flows. A storyline emphasizing sustainable development in energy pro-duction led to the best outcome in terms of water protection

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

Phosphorus transport in the landscape – Integrating high-frequency monitoring, phosphorus geochemistry and modelling to improve water management

Eutrophication is one of today’s most challenging water quality issues, despite considerable efforts to reduce phosphorus (P) input to surface waters. We need to explore new tools and techniques to improve the nutrient status of our waters and facilitate the management of catchment-scale P transport. This thesis includes research on P stored in lake and streambed sediment, timing and delivery of P in the system, processes influencing this transport and predictions by water quality modelling. The results show that significant amounts of P are stored in the catchment sediments, with some streams showing comparable concentrations to lakes. Phosphorus fractions are influenced by land cover and stream order. Some fractions could be important P sources during low flows when there is a significant risk of eutrophication associated with small increases in concentration. High-frequency (HF) monitoring is an important tool to increase understanding of catchment-scale P dynamics. Especially during intermediate and high flow events, the finer temporal resolution of HF data is essential for load calculations. Also, these events showed a dominant clockwise C-Q hysteresis response that suggests fast mobilisation of particles from the streambed and riparian areas. HF data was valuable in water quality modelling to describe temporal patterns but was challenging to calibrate and evaluate with standard performance statistics. Further work is needed on efficient and transferrable methods to analyse HF data. With an improved knowledge of P stores and the use of HF data, better-informed management decisions can be made to ensure water management that reduces catchment-scale P transport

Drained land and nutrient transport in the river Svärtaå catchment

Land use changes such as lowering of lakes, draining of wetlands and channelizing of streams have affected the hydrological environment in many catchment areas. Numerous studies report that these changes affect the nutrient retention. The river Svärtaå catchment, near Nyköping is identified as one of the areas in Sweden that transport most phosphorus and nitrogen to the Baltic Sea per unit area. The aim of this study was therefore to analyse to which extent land use changes such as lowering of lakes, draining of wetlands and channelizing of streams have affected the nutrient transport to the Baltic Sea. Land use changes were to a large extent performed between the years 1880 and 1930 inSweden, historical maps from the late 19th century have therefore been studied. An application based on the concept of a Geographical Information System (GIS) has been used in order to compare the district map from late 19th century and the terrain map from today. To address the nutrient transport retention coefficients have been found in the literature and implemented on the changes in water area.  Changes in the hydrological environment reached totally1068 ha,964 hawere decreasing water areas and104 haincreasing water areas. Wet areas totally decreased with 28 % when the historical setting was compared with the contemporary environment. The loss in wet area represents860 ha. Watercourses with riparian zones have decreased with 54 %, bogs with 53 %, wetlands with 43 % and lakes with 13 %. The loss in retained mass regarding phosphorus was, based on calculations involving retention coefficients, 7,18 – 146 tonnes, and regarding nitrogen 37,9 – 941 tonnes. The changes in the catchment are probably connected to measures like lowering of lakes, draining of wetlands and channelizing of streams. The assumed lost retained masses shows to be high compared to the measured output from the catchment. This leads to questioning of the retention coefficients and the vast range between them, as well as questioning of other assumptions in the method. The consequences of the hydrological changes are therefore difficult to evaluate