Wetland management maintains nitrogen (N) removal capacity in mature and overgrown constructed wetlands (CWs). We evaluated whether CW management by macrophyte harvesting, and subsequent installation of woodchips-based floating beds (WFBs) planted with Glyceria maxima and Filipendula ulmaria improved N removal. In sixteen heavily overgrown experimental CWs, we applied four treatments: i) only macrophyte harvesting, ii) 5% of the harvested-CW surface covered with WFBs, iii) 20% WFBs cover, and iv) a control treatment (heavily overgrown). N removal was determined in all wetlands at nine occasions. Plant biomass accrual, N assimilation, and denitrification genes nirS, nirK, nosZI and nosZII on plant roots and woodchips from WFBs were estimated. Macrophyte harvesting improved N removal of heavily overgrown CWs, whereas subsequent WFB installation only sometimes improved N removal. Mean N removal efficiencies (± standard deviation) overall were 41 ± 15 %, 45 ± 20 %, 46 ± 16 % and 27 ± 8.3 % for treatments i to iv, respectively. Relative biomass production, root length and root surface area for G. maxima (mean ± standard deviation: 234 ± 114 %, 40 ± 6.5 cm, 6308 ± 1059 cm2g-1, respectively) were higher than those for F. ulmaria (63 ± 86 %, 28 ± 12 cm, 3131 ± 535 cm2g-1, respectively) whereas biomass N assimilation was higher for F. ulmaria (1.8 ± 0.9 gNm−2 of WFB) than for G. maxima (1.3 ± 0.5 gNm−2 of WFB). Denitrification gene abundance was higher on plant roots than on woodchips while G. maxima hosted higher root denitrification gene abundance than F. ulmaria. We conclude that macrophyte harvesting improves N removal in heavily overgrown CWs. WFBs installation has the potential to support plant growth and denitrification in surface-flow constructed wetlands. Further studies need to evaluate the long-term effects of macrophyte harvesting and WFB installation on N removal in CWs. © 2024 The Authors

Wetlands in agricultural areas mitigate eutrophication by intercepting nutrient transports from land to sea. The role of wetlands for nutrient removal may become even more important in the future because of the expected increase in agricultural runoff due to climate change. Because denitrification is temperature dependent, wetland nitrogen (N) removal usually peaks during the warm summer. However, climate change scenarios for the northern temperate zone predict decreased summer and increased winter flows. Future wetlands may therefore shift towards lower hydraulic loading rate and N load during summer. We hypothesised that low summer N loads would decrease annual wetland N removal and tested this by examining 1.5–3 years of continuous N removal data from created agricultural wetlands in two regions in southern Sweden (East and West) during different periods. West wetlands showed relatively stable hydraulic loads throughout the year, whereas East wetlands had pronounced no-flow periods during summer. We compared East and West wetlands and tested the effects of several variables (e.g., N concentration, N load, hydraulic load, depth, vegetation cover, hydraulic shape) on annual absolute and relative N removal. We found no difference in annual N removal between East and West wetlands, even though summer N loads were lower in East than in West wetlands. A possible explanation is that stagnant water conditions in East wetlands suppressed decomposition of organic matter during summer, making more organic matter available for denitrification during winter. Absolute N removal in all wetlands was best explained by N load and hydraulic shape, whereas relative N removal was best explained by emergent vegetation cover and hydraulic shape. This study highlights the importance of design and location of agricultural wetlands for high N removal, and we conclude that wetlands in a future climate may remove N from agricultural runoff as efficiently as today. © 2023 The Authors

With increasing temperatures and precipitation, as well as land use changes in boreal regions, waterbodies are receiving larger inputs of coloured terrestrial humic substances. At the same time, nutrient inputs are increasing. This brownificationin combination with increasing nutrient levels has consequences for the aquatic food web in terms of species composition and energy transfer efficiency. In Lake Bolmen, Sweden’s 7ths largest lake, brownification additionally creates problems for drinkingwater production, since this lake is an important drinking water reservoir of southern Sweden. Lake monitoring data show a clear pattern of increasing brownification in Lake Bolmen over the preceding decades. To understand the consequences ofincreased browning and of increased nutrient inputs for Lake Bolmen’s food web on bacterial production, and phytoplankton and zooplankton species community composition and abundance, we conducted a 6-week mesocosm experiment during summer 2021. Brownification and nutrient ratios were manipulated. Measures of algal pigment concentrations show that browning has strong effects on algal pigment composition and thus probably on algal taxonomic composition. Our results suggest that brownification affects basic producer community composition in lakes, thus possibly changing community composition and biomass of higher trophic levels of the aquatic food web in boreal regions.

Jakobs sjö, an electricity dam of the Nissan River system (Southwest Sweden) is contaminated with large microplastics sedimented out at its shores. In 2021 a field survey of microplastics was carried out in the Nissan River with the Lagan River asreference. We sampled three locations in each river (upstream, lake/dam and downstream). Four replicate bottom and shore sediment samples were taken at each location. Dried samples were fractionated into three size categories (> 2 mm; 2 – 0.9mm; 0.9 – 0.55 mm) and microplastics per area and weight were estimated. We found a higher concentration of large shore microplastics in Jacobs sjö and downstream from it than upstream in the Nissan River. We found no large shore microplastics in the Lagan River system. Smaller size fractions of microplastics were omnipresent in shore and bottom sediments of both rivers. However, the smallest size category tended to be proportionately more dominant at upstream than at downstream locations. This could be explained by biofilm-microplastic floc formation and sedimentation as particles travel downstream. Concentrations of toxicants such as heavy metals can increase thousandfold on the surface of microplastics and since the five heavy metals most likely to sorb to microplastics in a freshwater environment (Cd, Cu, Ni, Pb and Zn) were all present in Jacobs sjö, we conclude that the high concentrations of microplastics in Jacobs sjö may pose a threat to aquatic life.

Wetland nitrogen (N) removal is temperature dependent and therefore generally highest during summer in the northern temperate zone. However, climate change scenarios predict more frequent summer droughts in these regions, resulting in lowered N transports during summer to wetlands created for interception of agricultural runoff. This may adversely affect annual wetland N removal, thus reducing the mitigative effects wetlands have on eutrophication. In this study, continuous flow-proportional sampling was performed in six agricultural wetlands located on the east coast, and three on the west coast, of southern Sweden. These two regions represent different climate conditions, where precipitation is lower and summer temperatures are higher on the east coast. Our results showed a pronounced no-flow period during summer in east coast wetlands, but not in west coast wetlands. No-flow periods only decreased N load and removal rate during summer but had no effect on annual N removal. Annual N removal was instead best explained by multiple regression with annual N load and hydraulic efficiency as predictors. This indicates that low wetland N removal during drier summers may be compensated by higher N removal during other seasons. A possible explanation is that annual N removal through denitrification is determined by the amount of organic carbon provided by wetland vegetation, and that organic carbon not utilized during summer, due to lack of nitrate and oxygen under no-flow conditions, will be available for denitrification during other seasons. In conclusion, climate change might not have the anticipated decreasing effect on wetland N removal.

A multitude of anthropogenic pressures deteriorate the Baltic Sea, resulting in theneed to protect and restore its marine ecosystem. For an efficient conservation,comprehensive monitoring and assessment of all ecosystem elements is of fundamentalimportance. The Baltic Marine Environment Protection Commission HELCOMcoordinates conservation measures regulated by several European directives. However,this holistic assessment is hindered by gaps within the current monitoring schemes.Here, twenty-two novel methods with the potential to fill some of these gaps andimprove the monitoring of the Baltic marine environment are examined. We asked keystakeholders to point out methods likely to improve current Baltic Sea monitoring. Wethen described these methods in a comparable way and evaluated them based ontheir costs and applicability potential (i.e., possibility to make them operational). Twelvemethods require low to very low costs, while five require moderate and two high costs.Seventeen methods were rated with a high to very high applicability, whereas fourmethods had moderate and one low applicability for Baltic Sea monitoring. Methodswith both low costs and a high applicability include the Manta Trawl, Rocket, SedimentCorer, Argo Float, Artificial Substrates, Citizen Observation, Earth Observation, theHydroFIARpH system, DNA Metabarcoding and Stable Isotope Analysis. © 2020 Mack, Attila, Aylagas, Beermann, Borja, Hering, Kahlert, Leese, Lenz, Lehtiniemi, Liess, Lips, Mattila, Meissner, Pyhälahti, Setälä, Strehse, Uusitalo, Willstrand Wranne and Birk.

Legislations and commitments regulate Baltic Sea status assessments and monitoring. These assessments suffer from monitoring gaps that need prioritization. We used three sources of information; scientific articles, projectreports and a stakeholder survey to identify gaps in relation to requirements set by the HELCOM's Baltic SeaAction Plan, the Marine Strategy Framework Directive and the Water Framework Directive. The most frequentlymentioned gap was that key requirements are not sufficiently monitored in space and time. Biodiversity monitoringwas the category containing most gaps. However, whereas more than half of the gaps in reports related tobiodiversity, scientific articles pointed out many gaps in the monitoring of pollution and water quality. Animportant finding was that the three sources differed notably with respect to which gaps were mentioned mostoften. Thus, conclusions about gap prioritization for management should be drawn after carefully consideringthe different viewpoints of scientists and stakeholders. © 2020 The Authors. Published by Elsevier Ltd.

Restored and constructed semi-natural wetlands are increasingly used in the agricultural landscape to intercept nutrients from surface waters. Vegetated surface-flow wetlands remove more nitrogen (N) than those without vegetation. However, changes in N removal over time as differently vegetated wetlands progress from early successional stages to mature systems are less investigated. We monitored three different types of initial planting over the course of 12 years, with the aim to examine how planting of newly constructed wetlands affects long-term N removal. All our data were collected in an experimental wetland facility in south-western Sweden. The facility consists of 18 identical small (ca. 25 m²) surface-flow wetlands, simulating semi-natural wetlands in an agricultural landscape. Initially, the 18 wetlands were randomly divided into three treatments (vegetation types) with six replicates each and planted with (1) emergent vegetation, (2) submerged vegetation and (3) no vegetation for free development. Vegetation succession afterwards progressed uninhibited in all wetlands. Emergent vegetation wetlands initially removed more N than both submerged vegetation and free development wetlands. We found that N removal in submerged vegetation and free development wetlands increased with ecosystem age, whereas N removal in emergent vegetation wetlands did not. N removal in all three vegetation types converged when the wetlands reached a more mature state, around 8 years after wetland construction. However, although all wetlands contained emergent vegetation in year 8, the proportion of emergent vegetation cover and vegetation composition still differed substantially between wetland types. Our study indicates that it is not the cover of emergent vegetation per se which promotes higher N removal in more mature wetlands, but the maturation process itself; mature wetlands despite differing emergent vegetation coverage achieved equally high N removal. In conclusion, once wetlands reach maturity, beneficial effects of initial planting on N removal disappear. © 2020 The Authors. Published by Elsevier B.V.

I den här studien beräknades kväve- och fosforavskiljningen utifrån automatiserad flödesproportionell provtagning i fem anlagda våtmarker i Kalmar län under tre års tid samt i ett anlagt fosfordike i länet under två år (fortsättningsvis benämns alla sex studieobjekt som våtmarker). Syftet med studien var att utvärdera funktionen av våtmarker i Kalmar län för avskiljning av kväve och fosfor. I rapporten presenteras även nya beräkningsmetoder som tagits fram för att hantera de osäkerheter som oundvikligen följer av denna typ av situ-studier. Denna rapport bör kunna bidra till förbättrade mätmetoder och analyser i framtida våtmarksstudier.

De våtmarker som ingår i studien är lokaliserade i fem olika kommuner i Kalmar län. Våtmarkerna som studerats är Hanåsa (Högsby kommun), Resmo (Mörbylånga kommun), Påboda (Torsås kommun), Grisbäck (Torsås kommun), Hossmo (Kalmar kommun) och Häckenstad (Västerviks kommun). Urvalet av våtmarker är gjort av Länsstyrelsen med målsättningen att få ett representativt urval av våtmarker i Kalmar län. Våtmarkerna i studien skiljer sig därför från varandra både i utformning och i vilken omgivning de är anlagda. De flesta av våtmarkerna är cirka en halv hektar stora, men den största våtmarkens area är 2,5 hektar och den minsta har en area på endast 220 kvadratmeter. Några av våtmarkerna har mycket hög andel åkermark i tillrinningsområdet, medan andra våtmarker främst har skog i sitt tillrinningsområde.

Flödesproportionell provtagning har kontinuerligt genomförts vid in- och utlopp i fem våtmarker från november 2016 till och med december 2019, och i en våtmark från maj 2018 till och med december 2019. I tre av våtmarkerna mättes flöde både vid inlopp och utlopp, och i tre av våtmarkerna mättes flöde endast vid utlopp. Flödesmätning gjordes en gång per minut, och varje vecka hämtades vattenprover från våtmarkerna för att analyseras för bland annat innehåll av näringsämnen. Den data som samlats in har sedan bearbetats, beräknats och korrigerats för att kunna användas i bedömningen av våtmarkernas näringsavskiljning.

Flödena i våtmarkerna följde vanligen tydliga säsongsmönster där sommarflöden var låga och flödestoppar skedde under höst, vinter och vår. Resmo, på Öland, hade längre torrperioder än övriga våtmarker i studien. Näringskoncentrationerna vid de olika våtmarkernas inlopp var i genomsnitt under studien mellan 1,7 och 9,9 mg kväve per liter och mellan 64 och 157 µg fosfor per liter. Kvävet var huvudsakligen i form av nitratkväve, och fosforn var i huvudsak partikelbunden fosfor. Både kväve- och fosforavskiljning i våtmarkerna ökade med ökad belastning. Den genomsnittliga årliga kväve- och fosforavskiljningen per hektar vattenyta skiljde sig stort mellan våtmarkerna. Den varierade från negativ avskiljning i den största våtmarken till över 1 000 kg per hektar vattenyta och år för både kväve och fosfor i den minsta våtmarken (tabell 1). Angivet i procent avskildes i genomsnitt upp till 14 % av den årliga kvävebelastningen och upp till 70 % av den årliga fosforbelastningen. Jämfört med tidigare modellerad kväve- och fosforavskiljning för våtmarker i Kalmar län och andra delar av Sverige var avskiljningen i våtmarkerna i denna studie generellt högre.

_{Tabell 1. Genomsnittlig kväve- och fosforavskiljning angivet per hektar vattenyta och år och i procent av den årliga belastningen i de sex våtmarkerna i studien. På grund av mätosäkerheter anges avskiljningen i vissa av våtmarkerna som ett intervall.} 

                     Kväveavskiljning                   Fosforavskiljning

Våtmark       kg ha^-1 år^-1   %                     kg ha^-1 år^-1    %

Hanåsa          -351               -37                   -49                  -91

Resmo           407                3,8                   19                    31

Påboda          845 – 1 013    12 – 14             20 – 28            22 – 29

Grisbäck        523 – 899       7,2 – 12            113 – 153        45 – 54

Hossmo         346 – 965       2,7 – 7,3           -1,1 – 14         -4,4 – 13

Häckenstad    1 471             4,3                    1 688              70

Resultaten i denna studie visar att våtmarker i Kalmar län kan uppnå hög näringsavskiljning, men att skillnaderna mellan olika våtmarker är stora. Resultaten visar också att hög kväve- och fosforavskiljning kan uppnås i våtmarker med relativt låg andel åkermark i tillrinningsområdet, och att mycket hög fosforavskiljning kan uppnås i små våtmarker även utan en djuphåla. Projektet bidrar till en bättre bild av vilken avskiljning av kväve och fosfor som kan uppnås i anlagda våtmarker i södra Sverige. Resultat från projektet kan tillsammans med tidigare mätningar utgöra en grund för säkrare modellberäkningar av kväve- och fosforavskiljning, vilka kan användas för att på ett enklare sätt undersöka avskiljningen i ett större antal våtmarker eller för att prediktera vad som kan uppnås i planerade våtmarksprogram. 

This report presents the results of a review on gaps in Baltic Sea monitoring based on two different information sources: peer-reviewed scientific articles, and BONUS and HELCOM project reports. The reviews are part of the BONUS project FUMARI. Our main questions are:

(1)    does the current monitoring of the Baltic Sea sufficiently address the requirements set by the Marine Strategy Framework Directive, the Water Framework Directive and the HELCOM´s Baltic Sea Action Plan?

(2)    what are the most critical shortcomings (gaps) in the current Baltic Sea monitoring programs?

We found that scientific articles dealing with Baltic Sea monitoring present a view on main monitoring gap occurrence, that differs from the view presented in reports dealing with the same topic. Both scientific articles and reports agreed that many thematic assessment categories are not monitored sufficiently, often due to insufficient spatial coverage. However, whereas articles often highlight both that a category is not sufficiently monitored, and that there is a lack of indicators, the reports focused more on gaps in data storage or handling, coordination of monitoring, or highlighted plans for new but non-operational indicators. Articles mainly mentioned gaps in relation to Eutrophication, Contaminants, Biodiversity, Commercial fish and shellfish, Food webs, Hydrographical conditions, and No alien species. Reports however indicated primarily Biodiversity gaps, followed by Contaminants and Healthy wildlife, Marine litter, and Sea-floor integrity. Our review also showed that certain categories are underrepresented in the scientific literature, i.e. with few scientists developing indicators or assessing data related to them, potentially indicating a knowledge gap in these fields.