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.

In order to better understand the potential effects of climate change on the Peregrine Falcon, we investigated the relationship between extreme weather events and Peregrines’ breeding success in South Greenland. We defined three variables – number of days with extremely low temperatures, extreme precipitation, consecutive rainy days – and an additive variable, total days with extreme weather, and tested their relationship with Peregrines’ breeding success (measured as young per site and nest success) over a 33 year study period. Breeding success was negatively influenced by the number of days with extreme weather and extremely low temperature. The strongest relationship found was total days with extreme weather in the entire breeding season, which explained 22% and 27% of the variation in nest success and young per site, respectively. The number of days with extreme weather in our study related to fluctuations in the North Atlantic Oscillation (NAO). Thus, with a strengthening of the NAO, linked to climate change, more extreme weather may occur in the Arctic and induce increased variation in Peregrines’ breeding success. Our data did not allow us to pinpoint when in the breeding cycle inclement weather was particularly harmful, and we recommend finer-scale research (e.g. automated nest cameras) to better monitor the species-specific effects of rapidly changing climate.

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

1. Phosphorus (P) often limits the biomass of primary producers in freshwater lakes. However, in unproductive northern lakes, where anthropogenic nitrogen (N) deposition is low, N instead of P can limit primary producers. In addition, light can be limiting to primary producers at high concentrations of coloured dissolved organic matter (cDOM), as cDOM is the major determinant of light penetration in these lakes.

2. To address resource limitation of epilithic algal biomass, we repeatedly sampled epilithon (periphyton on stony substrata) in 20 lakes covering a large, correlated cDOM and N-deposition gradient across boreal and subarctic Sweden. Across these lakes, pelagic total N (TN) and total P (TP) were positively correlated, and benthic light supply was negatively correlated, with cDOM. Microscopically determined algal biovolume and epilithic carbon (C), N and P were subsequently regressed against benthic light supply and pelagic TN and TP.

3. Patterns in epilithic biovolume were driven by N₂-fixing cyanobacteria, which accounted for 2%–90% of total epilithic biovolume. Averaged over the growing season, epilithic algal biovolume, C and N were negatively related to TP and positively to TN, and were highest in the clearest, most phosphorus-poor lakes, where epilithon was heavily dominated by potentially N2-fixing cyanobacteria.

4. A structural equation model supports the hypothesis that cDOM had two counteracting effects on total epilithic algal biovolume: a positive one by providing N to algae that depend on dissolved N for growth, and a negative one by shading N₂-fixing cyanobacteria, with the negative effect being somewhat stronger.

5. Together, these findings suggest that (1) light and N are the main resources limiting epilithic algal biomass in boreal to subarctic Swedish lakes, (2) epilithic cyanobacteria are more competitive in high-light and low-nitrogen environments, where their N₂-fixing ability allows them to reach high biomass, and (3) epilithic N increases with N₂ fixer biomass and is—seemingly paradoxically—highest in the most oligotrophic lakes. © 2018 John Wiley & Sons Ltd

This survey of literature on substratum-associated microbiota from 2016 includes highlights of research findings associated with algae, cyanobacteria, and bacteria from a variety of aquatic environments, but primarily freshwaters. It covers topics of relevance to the Water Environment Federation along with those of emerging or recent interest such as nuisance, bloom forming and harmful algae, fossil fuel related contamination, and other environmental pollutants like nanoparticles. Additional interesting findings reported on include general ecology, method development, multistressor interactions, nutrient cycling, taxonomy and systematics, trophic interactions, and biomonitoring, bioassessment, and bioremediation.  © 2017 Water Environment Federation

This survey of 2018 literature on substratum‐associated microbiota presents brief highlights on research findings from primarily freshwaters, but includes those froma variety of aquatic ecosystems. Coverage of topics associated with benthic algae andcyanobacteria, though not comprehensive, includes new methods, taxa new to science, nutrient dynamics, trophic interactions, herbicides and other pollutants, metalcontaminants, nuisance, bloom‐forming and harmful algae, bioassessment, andbioremediation. Coverage of bacteria, also not comprehensive, focused on methylation of mercury, metal contamination, toxins, and other environmental pollutants, including oil, as well as the use of benthic bacteria as bioindicators, in bioassessment tools and in biomonitoring. Additionally, we cover trends in recent and emerging topics on substratum‐associated microbiota of relevance to the Water Environment Federation. © 2019 Water Environment Federation.

This review briefly highlights findings from a survey of 2017 literature on substratum-associated microbiota from a variety of aquatic environments, but primarily freshwaters. Centered on algae, cyanobacteria, and bacteria, topics covered include those of relevance to the Water Environment Federation, along with those of recent and emerging interest such as new or updated methods, new and interesting taxa, general ecology, trophic interactions, biogeochemical cycling, aquatic pollutants like herbicides and heavy metals, and nuisance, bloom-forming, or harmful algae. Additional coverage includes studies on bioremediation, bioassessment, biomonitoring and quantification of benthic microbiota.  © 2018 Water Environment Federation

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.

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.

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.

Nutrient optimization has been proposed as a way to increase boreal forest production, and involves chronic additions of liquid fertilizer with amounts of micro- and macro-nutrients adjusted annually to match tree nutritional requirements. We used a short-term (maintained since 2007) and a long-term (maintained since 1987) fertilization experiment in northern Sweden, in order to understand nutrient optimization effects on soil microbiota and mesofauna, and to explore the relationships between plant litter and microbial elemental stoichiometry. Soil microbes, soil fauna, and aboveground litter were collected from the control plots, and short- and long-term nutrient optimization plots. Correlation analyses revealed no relationships between microbial biomass and litter nutrient ratios. Litter C:N, C:P and N:P ratios declined in response to both optimization treatments; while only microbial C:P ratios declined in response to long-term nutrient optimization. Further, we found that both short- and long-term optimization treatments decreased total microbial, fungal, and bacterial PLFA biomass and shifted the microbial community structure towards a lower fungi:bacterial ratio. In contrast, abundances of most fungal- and bacterial-feeding soil biota were little affected by the nutrient optimization treatments. However, abundance of hemi-edaphic Collembola declined in response to the long-term nutrient optimization treatment. The relative abundances (%) of fungal-feeding and plant-feeding nematodes, respectively, declined and increased in response to both short-term and long-term treatments; bacterial-feeding nematodes increased relative to fungal feeders. Overall, our results demonstrate that long-term nutrient optimization aiming to increase forest production decreases litter C:N, C:P and N:P ratios, microbial C:P ratios and fungal biomass, whereas higher trophic levels are less affected. © 2018 Elsevier B.V.

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.

Climate change predictions indicate that coastal and estuarine environments will receive increased terrestrial runoff via increased river discharge. This discharge transports allochthonous material, containing bioavailable nutrients and light attenuating matter. Since light and nutrients are important drivers ofbasal production, their relative and absolute availability have important consequences for the base of the aquatic food web, with potential ramifications for higher trophic levels. Here, we investigated the effects of shifts in terrestrial organic matter and light availability on basal producers and their grazers. In twelve Baltic Sea mesocosms, we simulated the effects of increased river runoff alone and in combination. We manipulated light (clear/shade) and carbon (added/not added) in a fully factorial design, with three replicates. We assessed microzooplankton grazing preferences in each treatment to assess whether increased terrestrial organic matter input would: (1) decrease the phytoplankton to bacterial biomass ratio, (2) shift microzooplanlcton diet from phytoplankton to bacteria, and (3) affect microzooplankton biomass. We found that carbon addition, but not reduced light levels per se resulted in lower phytoplanlcton to bacteria biomass ratios. Microzooplankton generally showed a strong feeding preference for phytoplanlcton over bacteria, but, in carbon-amended mesocosms which favored bacteria, microzooplankton shifted their diet towards bacteria. Furthermore, low total prey availability corresponded with low microzooplankton biomass and the highest bacteria/phytoplankton ratio. Overall our results suggest that in shallow coastal waters, modified with allochthonous matter from river discharge, light attenuation may be inconsequential for the basal producer balance, whereas increased allochthonous carbon, especially if readily bioavailable, favors bacteria over phytoplankton. We conclude that climate change induced shifts at the base of the food web may alter energy mobilization to and thebiomass of microzooplankton grazers. (C) 2017 Elsevier Ltd. All rights reserved.

Initial planting of created wetlands is common practice in order to, for instance, improve nitrogen (N) removal. It has been shown that vegetated surface-flow wetlands remove more N than non-vegetated surface-flow wetlands. However, changes in N removal as differently vegetated wetlands progress from an early successional stage to a mature system are less investigated.

In our study, we followed three different wetland types of initial planting over the course of 12 years, with the aim to examine how planting of newly created wetlands affects long-term N removal. All our data were collected in the experimental wetland facility near Halmstad in south-western Sweden. The facility consist of 18 small (ca. 25 m²) surface-flow wetlands, equal in age, shape and size. At the time of creation, the 18 wetlands were randomly divided into three types. One type was then planted with emergent vegetation, one was planted with submerged vegetation and the last type was left unplanted for free development. Succession of vegetation was thereafter allowed to progress uninhibited in all wetlands.

Our results confirmed that emergent vegetation wetlands initially removed more N than submerged vegetation and free development wetlands. In addition, our results showed 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 wetland vegetation types converged when the wetlands reached a more mature state, around year 9 after wetland creation. However, although all wetlands contained emergent vegetation in year 9, proportion cover of emergent vegetation and vegetation composition still differed substantially between wetland types.

We therefore conclude planting of created surface-flow wetlands with emergent vegetation will have a positive effect on N removal, but only during an early successional stage. Our study indicates it is not the emergent vegetation per se which results in higher N removal in more mature wetlands, but the maturation process in itself, since mature wetlands with different emergent vegetation cover achieved similar N removal. Initial planting will not result in higher N removal once the system has reached maturity.

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. 

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

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.

Setting numeric in-stream objectives (limits, criteria) to inform limits on catchment loads for major land-use stressors is a promising policy instrument to prevent ecosystem degradation. Management objectives can be informed by thresholds identified from stressor–response shapes of ecological indicators based on field survey data. Use of multiple structural and functional indicators and different organism groups provides multiple lines of evidence to make objectives more robust. We measured a suite of ecological indicators during a regional field survey in New Zealand. We built flexible boosted regression tree (BRT) models with a predictor set consisting of nutrient, sediment, and environmental variables and investigated the fitted functions for different types of thresholds across each stressor gradient. Congruence of impact initiation (II) thresholds for N among macroinvertebrate metrics and 2 periphyton indicators provided multiple lines of evidence for ecosystem change with small increases in N concentrations above background levels. Impact cessation (IC) on macroinvertebrate metrics at total N = ~0.5 mg/L (below N concentrations that saturate important ecosystem processes) highlighted sensitivity of macroinvertebrate communities to eutrophication. We found few stressor–response relationships for sediment. We suggest use of sediment-specific macroinvertebrate metrics and a reliable measure of deposited fine sediment in the future. Few indicators responded to phosphorus (P) concentration. Limited information for setting P objectives highlights the need to develop alternative indicators of P loading. Statistical analysis based on single-stressor inferential threshold models suggested that these models carry high risk of identifying spurious thresholds and are less suitable for setting management objectives. II and IC thresholds of multiple ecological indicators can be used to set robust objectives aimed at different levels of protection of ecosystem health.