No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Do organic matter metrics included in lake surveillance monitoring in Europe provide a broad picture of brownification and enrichment with oxygen consuming substances?
Abstract and Figures
Organic matter (OM) has numerous geochemical and ecological functions in inland waters and can affect water quality. Different parameters of aquatic OM are measured with various methods as no single analytical tool can provide definitive structural or functional information about it. In the present paper we review different OM metrics used in the European Union (EU) lake surveillance monitoring programmes and assess their suitability to provide sufficient data about the brownification and enrichment with oxygen consuming substances in European lakes. In the EU Water Framework Directive (WFD), metrics of OM are not mandatory physico-chemical parameters, but only recommended parameters to characterize water transparency, oxygenation conditions or acidification status. Our analysis shows that, as lake OM is monitored under the WFD in only 14 countries, no Europe-wide conclusions on the situation regarding brownification and organic enrichment can be drawn based on these data. Applied parameters in lake surveillance monitoring programmes are biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), dissolved organic carbon (DOC), water colour (WCol), and yellow substance. Different national OM metrics used avoid getting a broad picture of lake OM concentration changes in Europe over the last decades. Furthermore, our results demonstrate that the possibilities to convert different OM parameters to each other are limited because empirical relationships between them are region-specific. OM sensors for continuous measurements and remote sensing surveys could improve the effectiveness of lake OM monitoring, especially its temporal and spatial representativeness. It would be highly suggested to include in lake monitoring programmes also methods (e.g. absorbance or fluorescence spectroscopy) allowing to characterize the composition of OM as it influences strongly the biogeochemical role of OM in lakes.
Figures - uploaded by Toomas Kõiv
Author content
All figure content in this area was uploaded by Toomas Kõiv
Content may be subject to copyright.
... [6][7][8] These techniques differ in the mechanisms for the measurement of DOM and the organic fractions targeted. 6,8,9 DOC is the carbon component of DOM and thereby accurately quantifies the total DOM. 10 DOC is determined by high-temperature combustion or chemical oxidation methods followed by the detection of CO 2 . 9 Similar to the DOC method, COD is the measure of oxygen consumed during the oxidation of oxidizable matter by a strong chemical oxidant such as potassium permanganate (potassium permanganate index, COD Mn ). ...
... 6,8,9 DOC is the carbon component of DOM and thereby accurately quantifies the total DOM. 10 DOC is determined by high-temperature combustion or chemical oxidation methods followed by the detection of CO 2 . 9 Similar to the DOC method, COD is the measure of oxygen consumed during the oxidation of oxidizable matter by a strong chemical oxidant such as potassium permanganate (potassium permanganate index, COD Mn ). 11 In water monitoring, COD is used to collectively represent the organic pollution level of a sample. ...
... 11 In water monitoring, COD is used to collectively represent the organic pollution level of a sample. 9 Both DOC and COD analyses are widely used tools for monitoring DOM 7,9 and have also been adopted as official standard methods for DOM measurement of surface water and drinking water in China (GB/T 5750. , but they are quantitative, not qualitative methods. ...
Dissolved organic matter (DOM) has detrimental effects on drinking water treatment, distribution water quality and human health. In this study, four methods (dissolved organic carbon (DOC), potassium permanganate index (CODMn),...
... The rapid development of human society has led to the accumulation of anthropogenic organic carbon (OC) in aquatic environments, which has caused many environmental problems [1,2]. OC has complex effects on water quality and aquatic life, and measuring its composition, content, and activity is important for exploring the carbon cycle and environmental pollution [3]. As OC accumulates in water, it is decomposed by microbes, which release carbon dioxide (CO 2 ) and consume oxygen [4]. ...
... This, in turn, causes acidification and hypoxia in the water body and subsequently affects aquatic species [5]. Thus, indicators correlated with the OC content and composition are crucial for assessing water quality [3]. The chemical oxygen demand (COD) is a commonly used indicator of the amount of reduced organic compounds derived from human activities and autochthonous OC produced by primary production [6]. ...
The chemical oxygen demand (COD) is an essential indicator of organic pollution that represents the amount of bulk carbon in water. COD is strongly correlated with nutrient cycles and other pollutants in the environment, but it has a limited ability to quantify the amount of organic carbon (OC), of which a large proportion is made up of refractory dissolved organic carbon (RDOC) and is a potential carbon sink. Moreover, the biodegradability of OC in terms of its fate and destination should be explored, as well as how this is reflected by COD. Methods based on particle size, spectroscopy, and isotopic tracing are expected to help with deciphering the bioavailability of COD-responsive OC and explore the processes of biogeochemical cycles. As the pressure on the environment from anthropogenic inputs increases, understanding the bioavailability of OC associated with COD will help with developing more precise scientific indicators for environmental monitoring and identifying how new tools will increase knowledge of the carbon cycle. In this review, we discuss the application, scope, means, and advances of COD measurement. Based on data in the literature, we estimate the global RDOC stock and assess the impact of anthropogenic RDOC on the carbon cycle in offshore bays. This review presents new insights into the behavior of OC in aquatic environments and a potential pathway for ocean negative carbon emissions by expanding the role of RDOC as a carbon sink to offset the effect of anthropogenic carbon emissions.
... Optical sensors for high-frequency measurements can improve the effectiveness of lake organic matter monitoring, especially its temporal representativeness. To our knowledge, no European Union Member State is using high-frequency measurements of lake organic matter in their surveillance monitoring programs (Sepp et al. 2018). Usage of in situ optical sensors for high-frequency measurements should be coupled with discrete water sampling for direct calibration of optical properties used as proxies for DOM concentration . ...
... This equation has yielded good results for Estonian lakes and is also used in national monitoring programs (Sepp et al. 2018). In addition, the CDOM/DOC ratio was calculated from the respective concentrations. ...
Dissolved organic matter (DOM) plays an important role in biogeochemistry of lake ecosystems. Studies measuring DOM at short intervals in lakes are still rare, thus its short-term dynamics are largely unknown. We investigated DOM temporal variation in large and shallow eutrophic Lake Võrtsjärv (Estonia) during one growing season (May–September 2016) using field-deployable spectrometer In Situ Spectral Analyzer (GO Systemelektronik GmbH) to measure absorbance spectra (wavelength range 200–708 nm) at a 2-hour interval coupled with monthly discrete water sampling. Collected spectra were analyzed together with some in-lake variables, lake metabolic rates, and meteorological and hydrological data using Boosted Regression Tree (BRT) and Random Forest (RF) models. Different spectral parameters were used to assess total and allochthonous DOM quantity, and relative share of autochthonous DOM. All parameters, i.e., DOM quantity and quality, varied on a large scale. For example, dissolved organic carbon (DOC) concentrations ranged from 12.0 to 17.3 mg L-1. High levels of DOM were mainly of allochthonous origin; strong relationship with inflow indicated the same. Relative share of autochthonous DOM increased with rising air temperature as primary production rose in warm water; however, we did not find any direct relationships with gross primary production. RF and BRT models explained up to 38% and 63% of DOM temporal variability, respectively. Our results showed that monthly water samples did not capture large variation in DOM. Therefore, high-frequency measurements using in situ spectrometer improve temporal representativeness of DOM monitoring in lakes compared to traditional sampling methods.
... The monitoring of water colour, DOC and DIC is not mandatory under the EU WFD, with around half of EU MS monitoring one or more organic matter parameters in freshwaters (Sepp et al., 2018). Metrics that assess organic matter are also inconsistent across EU MS making it difficult to evaluate dystrophy on an EU level using existing datasets (Sepp et al., 2018). ...
... The monitoring of water colour, DOC and DIC is not mandatory under the EU WFD, with around half of EU MS monitoring one or more organic matter parameters in freshwaters (Sepp et al., 2018). Metrics that assess organic matter are also inconsistent across EU MS making it difficult to evaluate dystrophy on an EU level using existing datasets (Sepp et al., 2018). Secchi depth, a measure of water transparency, is routinely monitored however, and is primarily influenced by DOC, DIC and chlorophyll a concentrations. ...
Freshwater lakes and pools contained within peatlands are unique habitats that support rare and specialised species. Despite this, these ecosystems have been overlooked in conservation and management practices. One of these habitats, ‘3160 Natural dystrophic lakes and ponds’, is protected under the European Union (EU) Habitats Directive with a concerning proportion of these habitats having an “unfavourable-bad” or an “unfavourable-inadequate” conservation status across Europe. Our current understanding of the key physico-chemical and ecological features of this habitat is inadequate which is hindering the implementation of effective conservation measures. This review summarises the current knowledge of this protected lake habitat as defined under the EU Habitats Directive. With a focus on Ireland, we demonstrate how the current monitoring and assessment methods used to characterise and assess the structure and function and conservation status of this habitat, which relies largely on the use of macrophyte community composition and surrogate physico-chemical data collected under the EU Water Framework Directive, is ineffective. We propose the incorporation of further or alternative ecological metrics including, but not limited to, algae and macroinvertebrates which are needed to improve our understanding of the structure and function of this priority lake habitat. In addition, application of such data via ecological metrics would allow for the quantification of biodiversity and species rarity metrics which would aid in identifying sites of conservation importance.
... In France, 30% of the lakes may be affected by organic matter enrichment (Sepp et al., 2018); several studies have investigated DOM parameters in French streams, but no studies focused on browning have been carried out. Humic substances generally dominated DOM composition between 2010 and 2013 in a north-eastern French river, and the highest values of the SUVA 254 (an index for aromaticity) could not be explained (Assaad et al., 2015). ...
... Hence, the new availability of spectral and spatial resolutions for remote sensing data time series is opening up opportunities to monitor the impact of land-use and land cover changes on water quality at spatially explicit scales; remote sensing has thus high potential for evaluating control efforts to protect freshwater habitats (e.g., lakes, rivers, ponds, wetlands). Current monitoring data cannot provide a global picture of browning (Sepp et al., 2018). Nevertheless, several remote sensing analyses have focused on color, or DOC and DOM measurement parameters in recent years. ...
Water browning or brownification refers to increasing water color, often related to increasing dissolved organic matter (DOM) and carbon (DOC) content in freshwaters. Browning has been recognized as a significant physicochemical phenomenon altering boreal lakes, but our understanding of its ecological consequences in different freshwater habitats and regions is limited. Here, we review the consequences of browning on different freshwater habitats, food webs and aquatic-terrestrial habitat coupling. We examine global trends of browning and DOM/DOC, and the use of remote sensing as a tool to investigate browning from local to global scales. Studies have focused on lakes and rivers while seldom addressing effects at the catchment scale. Other freshwater habitats such as small and temporary waterbodies have been overlooked, making the study of the entire network of the catchment incomplete. While past research investigated the response of primary producers, aquatic invertebrates and fishes, the effects of browning on macrophytes, invasive species, and food webs have been understudied. Research has focused on freshwater habitats without considering the fluxes between aquatic and terrestrial habitats. We highlight the importance of understanding how the changes in one habitat may cascade to another. Browning is a broader phenomenon than the heretofore concentration on the boreal region. Overall, we propose that future studies improve the ecological understanding of browning through the following research actions: 1) increasing our knowledge of ecological processes of browning in other wetland types than lakes and rivers, 2) assessing the impact of browning on aquatic food webs at multiple scales, 3) examining the effects of browning on aquatic-terrestrial habitat coupling, 4) expanding our knowledge of browning from the local to global scale, and 5) using remote sensing to examine browning and its ecological consequences.
... Hence, the prediction of changes in phytoplankton communities in lakes is very difficult because many different parameters can affect phytoplankton composition and biomass, especially in an unpredictable world (Lürling and De Senerpont Domis, 2013). Nevertheless, Sepp et al. (2018) recently showed a trend in consecutive changes in water color (water brownification) associated with an increase in organic matter input to European lakes. Such changes can affect the development of primary producers, and thus affect the assessment of lake ecological status in each country belonging to the European Union (EU). ...
... This approach includes the role of the catchment area, but does not consider the type of catchment as a source of colored substances delivered to the lake. In general, for the typology of Polish lakes, this approach is sufficient; however, in the context of increasing water color of many European lakes (Sepp et al., 2018), it seems to be insufficient for appropriately determining the ecological status of a lake such as Lake Rogóźno. Similarly, the assessment of the ecological status of Lake Rogóźno based on the German index (PSI) seems to be insufficient. ...
During the 11-year period covered by this study (2003–2013), high precipitation events increased the water level in the deep hardwater of Lake Rogóźno (Eastern Poland), causing its water to become browner. We investigated the effect of a change in water color on the physical, chemical, and biological parameters of the lake. The concentration of total phosphorus and nitrogen decreased, whereas the total phytoplankton biomass, coupled with a high biomass of flagellate species, increased, with the increase in water color intensity. Such changes had an effect on the determination of ecological status, based on selected phytoplankton metrics (i.e., Polish, German, and Estonian) as well as the trophic status of Lake Rogóźno. The decrease of phosphorus concentration associated with an increase in water color intensity improved the trophic status of the lake based on Carlson's Trophic State Index. The changes in the phytoplankton community caused the deterioration of the ecological status of the lake when using the Polish and German indices adopted for clear water lakes. The use of the Estonian index, which is adapted to colored lakes, suggested that, despite the increase in water color intensity, the good ecological status of the lake was maintained or even improved. Our findings suggest that, in the event of a transformation like the one that occurred in the lake studied here, the use of only one index, adapted by state environmental monitoring programs in individual European countries, may be insufficient for the appropriate assessment of the ecological status of European lakes.
... Water temperature and biological oxygen demand (BOD) were sampled within streams and lakes to represent warming and enrichment variables. BOD measures the loss of dissolved oxygen (mg/L) due to the degradation of organic matter by the ambient microbial community, and is commonly used to assess organic matter content in continental and coastal aquatic environments (Lv et al., 2022;Sepp et al., 2018). We found positive correlations between BOD, total phosphorus and total nitrogen in both streams and lakes (Appendix A, Figure S2), confirming that organic enrichment often results from inorganic enrichment, which can lead to eutrophication (Fitch & Crowe, 2012;O'Gorman et al., 2012). ...
Nutrient enrichment and climate warming threaten freshwater systems. Metabolic theory and the paradox of enrichment predict that both stressors independently can lead to simpler food‐webs having fewer nodes, shorter food‐chains and lower connectance, but cancel each other's effects when simultaneously present. Yet, these theoretical predictions remain untested in complex natural systems. We inferred the food‐web structure of 256 lakes and 373 streams from standardized fish community samplings in France. Contrary to theoretical predictions, we found that warming shortens fish food‐chain length and that this effect was magnified in enriched streams and lakes. Additionally, lakes experiencing enrichment exhibit lower connectance in their fish food‐webs. Our study suggests that warming and enrichment interact to magnify food‐web simplification in nature, raising further concerns about the fate of freshwater systems as climate change effects will dramatically increase in the coming decades.
... Learning media developed based on validation by material and language experts (Rawindaran et al., 2021), validation of learning media experts, validation of expert learning practitioners and the results of trials by teachers and student responses to media used in learning (Sepp et al., 2018), and around the shape of the flat, which is an interesting media image and will be made into an e-comic with the aim that it will be easier for students to understand, the concepts can improve problem-solving skills which will be interviewed to students to better understand the storyline and to apply (Ahmad et al., 2021), it was stated that it was appropriate to use comic media learning in the form of distributing questionnaires on comic learning media with this research giving the result that JETE | Vol. 1 | No. 1 | 2023 e-comic media can assist teachers in overcoming problems in delivering a material. Balancing (Побиванцева, 2021). ...
Background. Nowadays, education requires ways to improve the quality of students. In improving and developing the quality of students, teachers must innovate in making learning media, one of which is learning media in the form of e-comic media. Purpose. this is to find out how the benefits of e-comics in learning. Method. using quantitative methods, data obtained through interviews and distributing questionnaires to students by utilizing the google form. Results. explained that learning media using e-comics can improve student learning outcomes. From the results of the interviews, it was obtained that these students felt an attraction and were motivated in learning by using e-comics. Students feel that learning by using e-comic media, grades and learning outcomes are increasing. e-comics is also one of the learning media that is easily understood by students. Conclusion. explained that this e-comic learning media really helps teachers to see students' skills in learning. e-comics is one of the learning media that is easily understood and liked by students as well as an effective learning media to use in learning.
... It seems that browni cation has an in uence on water quality and, consequently, on waterbirds (Hansson et al. 2010, Blanchet et al. 2022). COD has traditionally been considered as a parameter for the estimation of organic matter in water (Sepp et al. 2018). ...
Brownification of freshwater is a global issue with many implications. The high accumulation of organic matter causing the darkening of freshwater is explained by numerous factors including climate and land use. One example of this alteration can be found in the population of waterbirds (fish eaters, diving and dabbling ducks and other species) in lakes Kukkia and Rautajärvi in Finland, where the number of waterbirds has decreased by 40% since the mid-1980s. We run Generalized Linear Mixed Models to determine how climatic, water chemistry and land use factors are interacting with one another and how those interactions impact waterbird density. Our results showed the significance of brownification and climatic factors, as COD (chemical oxygen demand) and turbidity of the water body and wind speed were the most relevant in explaining the decline of waterbirds.
... To incorporate browning in EBM and the WFD, there is a need to reach an agreement among EU member states on the browning-related variables to be regularly measured in European water-monitoring programs (Sepp et al., 2018). Whether humic content should be considered in the WFD as a quality measure rather than an inherent character of aquatic ecosystems is a policy issue based on both the biological impacts of water browning and the public perceptions of water quality. ...
Browning of surface waters, also known as brownification, is a process of decreasing water transparency, particularly in boreal lakes surrounded by intensively managed forests and wetlands. In this paper, we review the ecological consequences and ecosystem‐based management (EBM) of browning through a systematic review approach and adopt an interdisciplinary approach to formulating new governance of this complex phenomenon. To understand the effects of browning on the recreational value of freshwaters, we present primary survey data on public perceptions of recreational fishing tourists on water quality in Finland. We identify a need to develop EBM beyond the EU's Water Framework Directive (WFD) to fully account for the extensive implications of browning. We also highlight the need for a better understanding of the within‐lake microbial processes to estimate the browning‐associated changes in the greenhouse gas balance of lakes. Tourist perceptions of the quality of waterbodies in Finland were largely in agreement with the general proportion of waterbodies classified in a good or excellent ecological status class, but these perceptions may be detached from biological quality assessment criteria. Consequently, we suggest that the EBM of inland waters should improve the utilization of information on not only biogeochemical processes but also users' perspectives on aquatic ecosystems beyond the EU WFD.
... To incorporate browning in EBM and the WFD, there is a need to reach an agreement among EU member states on the browning-related variables to be regularly measured in European water-monitoring programs (Sepp et al., 2018). Whether humic content should be considered in the WFD as a quality measure rather than an inherent character of aquatic ecosystems is a policy issue based on both the biological impacts of water browning and the public perceptions of water quality. ...
... Many treatment facilities depend on the UV absorbance of a sample at 254 nm normalized to the DOC concentration (e.g., SUVA) to assess the character of NOM in source and coagulated waters, where a SUVA >4 indicates mainly hydrophobic and aromatic material (Edzwald and Tobiason, 1999;Weishaar et al., 2003). Sepp et al. (2018) evaluated different traditional metrics for monitoring NOM (e.g., TOC, DOC, colour, chemical oxygen demand) and highlighted the importance of absorbance and fluorescence spectroscopy as key sensors to include in brownification monitoring programs. ...
Reduced atmospheric acid deposition has given rise to recovery from acidification – defined as increasing pH, acid neutralization capacity (ANC), or alkalinity in surface waters. Strong evidence of recovery has been reported across North America and Europe, driving chemical responses. The primary chemical responses identified in this review were increasing concentration and changing character of natural organic matter (NOM) towards predominantly hydrophobic nature. The concentration of NOM also influenced trace metal cycling as many browning surface waters also reported increases in Fe and Al. Further, climate change and other factors (e.g., changing land use) act in concert with reductions in atmospheric deposition to contribute to widespread browning and will have a more pronounced effect as deposition stabilizes. The observed water quality trends have presented challenges for drinking water treatment (e.g., increased chemical dosing, poor filter operations, formation of disinfection by-products) and many facilities may be under designed as a result. This comprehensive review has identified key research areas to be addressed, including 1) a need for comprehensive monitoring programs (e.g., larger timescales; consistency in measurements) to assess climate change impacts on recovery responses and NOM dynamics, and 2) a better understanding of drinking water treatment vulnerabilities and the transition towards robust treatment technologies and solutions that can adapt to climate change and other drivers of changing water quality.
... mg/L in endemic fisheries respectively, showing no significant changes. In lake ecosystems, the biodegradable portion of the dissolved organic carbon average of the biodegradable DOC (BDOC) is about 14% of the total pool [26]. However, Sepp stated that the high concentration of oxidisable organic matter in anthropogenic effluent is a significant threat to the oxygen regime of surface waters. ...
This study aims to determine the self-purification of Lake Maninjau based on the depth stratification. Sampling was carried out at the locations where there was lake water use, namely in the middle, domestically, in the hydropower area, in the endemic fisheries and at the aquaculture cages under SNI 6989.57: 2008. The measured parameters were BOD and the environmental parameters of pH, DO, and temperature were used to determine the lake stratification. Lake Maninjau's self-purification was determined by comparing the deoxygenation (K1) and reaeration (K2) coefficients. Based on the pH, DO, and temperature profiles, the epilimnion layer was found at 0-22 m depth and the hypolimnion layer started at a depth of 22 m. The BOD concentrations obtained did not meet the Government Regulation quality standards of 21.87-47 mg/L. The deoxygenation coefficient K1 in the epilimnion layer ranged from 0.04-1.49/day while in the hypolimnion layer it ranged from 0.08-0.54/day. The reaeration coefficient K2 in the epilimnion layer ranged from 0.04 to 0.57/day while in the hypolimnion layer, it ranged from 0.005 to 0.04/day. Wind speed and depth play a significant role in determining the lake's self-purification capacity. The self-purification of the lake was still held mainly in the epilimnion layer at depths of 0-9 m while in the hypolimnion layer deeper than 22 m, its ability begins to diminish. This indicates that most of the lake waters have a significantly decreased natural self-purification capacity.
... The increase in inputs has led to the darkening of the water color, also known as water "brownification." Brownification is observed most often in northern latitudes (Haaland et al. 2010;Sepp et al. 2018), notably in Scandinavian countries (Solomon et al. 2015), and is predicted to become more common in the upcoming centuries (Larsen et al. 2011;de Wit et al. 2016). Brownification, by increasing humic organic substance concentrations in the water column, alters not only the light conditions but also the availability of organic and inorganic matter (Karlsson et al. 2009;Kritzberg et al. 2020). ...
In recent decades, the increase in terrestrial inputs to freshwater and coastal ecosystems, especially occurring at northern latitudes, has led to a process of water color darkening known as "brownification." To assess how brownification affects plankton community composition and functioning in northern coastal areas, an in situ mesocosm experiment using a highly colored humic substance to simulate a brownification event was performed in a North Atlantic bay (Hopavågen, Norway) in August 2019. Manual sampling for analyses of nutrient concentrations, phytoplankton pigments and zooplankton abundances was combined with high-frequency (every 15 min) monitoring of key environmental variables to investigate the response of the plankton community in terms of oxygen metabolism and community composition. In response to brownification, the oxygen gross primary production (GPP) and community respiration (R) slowed down significantly, by almost one-third. However, GPP and R both decreased to the same extent; thus, the oxygen metabolic balance was not affected. Moreover, the chlorophyll-a concentration significantly decreased under brownification, by 9% on average, and the chemotaxonomic pigment composition of the phytoplankton changed, indicating their acclimation to the reduced light availability. In addition, brownification seemed to favor appendicularians, the dominant mesozooplankton group in the mesocosms, which potentially contributed to lowering the phytoplankton bio-mass. In conclusion, the results of this in situ mesocosm experiment suggest that brownification could induce significant changes in phytoplankton and zooplankton community composition and significantly alter the overall oxygen metabolism of plankton communities in a northern Atlantic bay.
... With the development of human society, the content of DOM in water will inevitably increase (Sepp et al., 2018), and if DOM is removed indiscriminately, carbon will be emitted to the atmosphere, aggravating climate change. With the improvement of wastewater treatment technology, more organic matter will be removed to meet the COD standard. ...
Chemical oxygen demand (COD) is widely used as an organic pollution indicator in wastewater treatment plants. Large amounts of organic matter are removed during treatment processes to meet environmental standards, and consequently, substantial greenhouse gases (GHGs) such as methane (CH 4 ) are released. However, the COD indicator covers a great amount of refractory organic matter that is not a pollutant and could be a potential carbon sink. Here, we collected and analysed COD data from 86 worldwide municipal wastewater treatment plants (WWTPs) and applied a model published by the Intergovernmental Panel on Climate Change to estimate the emission of CH 4 due to recalcitrant organic compound processing in China’s municipal wastewater treatment systems Our results showed that the average contribution of refractory COD to total COD removal was 55% in 86 WWTPs. The amount of CH 4 released from the treatment of recalcitrant organic matter in 2018 could have been as high as 38.22 million tons of carbon dioxide equivalent, which amounts to the annual carbon sequestered by China’s wetlands. This suggests that the use of COD as an indicator for organic pollution is undue and needs to be revised to reduce the emission of GHG. In fact, leaving nontoxic recalcitrant organic matter in the wastewater may create a significant carbon sink and will save energy during the treatment process, aiming at carbon neutrality in the wastewater treatment industry.
... It can also create a positive feedback between climate change and greenhouse gas emission from lakes (Kumar and Sharma 2014) and have major implications for drinking water treatment (Rook 1974, Lavonen et al. 2013. However, about ½ of the European Union Member States do not measure DOM in their lake monitoring programs, which inhibits understanding of the causes and effects of brownification in Europe (Sepp et al. 2018). ...
Allochthonous supply of dissolved organic matter (DOM) and nutrients from the catchment have a substantial
impact on the physical and chemical properties of lake water. Transport of DOM and nutrients is affected
by different catchment characteristics, e.g., catchment area, soil and land cover, and population density. The aim of
this study was to relate geological, hydrological, land-cover, and soil characteristics of 52 temperate catchments in
Estonia to variability in DOM (measured as dissolved organic carbon [DOC]), total organic nitrogen (TON), and
total phosphorus (TP) in lakes and to assess the relative importance of different land-cover and soil types as sources
of these substances. DOC, TON, and TP were very diverse in the studied lakes. Strong positive correlation between
DOC and TON indicated that these substances had similar concentration patterns and sources. Catchment soil cover
was the best predictor of DOC, TON, and TP levels in lakes, explaining up to 43.8% of their variabilities. This observation
can partly be explained by different soil organic carbon (SOC) content: soils with higher SOC were associated
with higher lakeDOC and TON, whereas soils with low SOC corresponded to lower DOC and TON. Similar to other
temperate lakes, bogs and peat soils were a major source of DOM in our studied lakes. DOC, TON, and color were
positively associated with percentages of peat soils in the catchment. On the other hand, TP increased with the proportion
of urban areas in the catchments, indicating the importance of human impact on its concentration. Understanding
the impact of different catchment characteristics on DOC, TON, and TP in temperate lakes is crucial for
developing transportmodels used for predicting future levels of DOMand nutrients under changing climate and land
use.
... Klante et al. 2021). Brownification has been observed in a large number of lakes in the Northern Hemisphere and the factors behind the phenomenon are being intensively discussed (Evans et al., 2005;Roulet and Moore, 2006;Weyhenmeyer et al., 2016;Sepp et al., 2018). Additionally, we examine if ditching influences the water color:DOC ratio of lakes. ...
We studied the connections between lake water quality and the density of artificial ditching in lake catchments. Water color and the concentrations of dissolved organic carbon (DOC) and iron (Fe) in lake water increased with increasing ditch density. Additionally, the water color:DOC ratio increased along a ditch density gradient because ditching had a stronger effect on color than on DOC. This was mainly due to the positive effect of ditching on the Fe concentration in lakes. Color:DOC ratio was strongly dependent on Fe up to Fe concentrations of 1-1.5 mg L-1. Thus, the water color of lakes with Fe concentrations < 1 mg L-1 will respond especially strongly to the effects of catchment ditching. The effects of ditching were strongest in catchments with high peatland coverage due to their high ditch density and high storage of organic carbon and Fe. The long-lasting effects of ditching should be taken into account when studying the factors governing lake brownification.
... observations of increased water colour in Ireland (Sepp et al., 2018), there has been limited long-term monitoring of trends in DOC concentration. The International Cooperative Waters Programme found there was a significant increase in DOC for three lakes in Ireland between 1990 and 2001 (Skjelkvåle et al., 2005). ...
This report is part of a detailed scoping study to:
-Provide an in depth literature review of peatlands in Ireland covering the following topics: 1) rewetting degraded peatlands; 2) carbon sequestration; 3) social value of peatlands; 4) alternative management options.
-Provide strategic guidance and identify resources for future integrated management of peatlands.
This project was produced for and funded by Fóram Uisce (The Irish Water Forum).
the report can also be found here: https://mail.thewaterforum.ie/app/uploads/2021/03/Peatlands_Full_Report_Final_Feb2021.pdf
... Most in situ studies and observations to date have focused on a gradual and incremental upward trend in DOC concentrations in freshwater ecosystems, a trend that is widely referred to as brownification (e.g. Evans et al. 2006;Sepp et al., 2018;Williamsen et al. 2015). Nonetheless, DOC inputs and concentrations can also fluctuate significantly on shorter timescales. ...
• Terrestrial loads of dissolved organic carbon (DOC) have increased in recent years in many north temperate lakes, leading to widespread brownification. This process can profoundly alter the relative strength of planktonic and benthic primary production in lakes due to changes in light and nutrient availability. While most existing in situ studies of brownification focus on gradual decadal trends, short‐term flooding can induce rather sudden natural browning events in lakes.
• We investigated the recovery of a small, temperate, groundwater‐fed shallow lake from a strong natural flooding‐induced browning and nutrient loading event. We hypothesised that along with a return to pre‐flood lake water levels, DOC concentrations would return to pre‐flood concentrations due to bacterial and photolytic mineralisation and flocculation, while total phosphorus (TP) concentrations would show a delayed and potentially incomplete recovery due to sustaining effects of phytoplankton dominance on nutrient dynamics in the lake. Phytoplankton gross primary production (GPP), which surged in response to higher nutrient concentrations and a compressed mixing depth, was expected to follow the same recovery pattern as TP. Benthic periphyton GPP was expected to recover in tandem with improving light conditions.
• We measured post‐flood water levels, water chemistry, and summer pelagic and benthic GPP. The lake water level declined gradually, returning to pre‐flood levels within 4 years. As hypothesised, DOC concentrations initially declined rapidly, but remained 1.5‐fold higher (c. 22 mg/L) than pre‐flood values 3 years after peak browning. TP concentrations fluctuated greatly between seasons but remained generally elevated in subsequent years, being roughly double pre‐browning values (c. 130 µg/L) 3 years post‐flood. Measurements taken in 2019, 7 years after the initial browning event, showed both DOC and TP concentrations remaining at these elevated levels.
• Across the intensive study period 3 years before and after peak browning (2010–2015), TP concentrations were positively correlated to summer phytoplankton biomass, while DOC and TP concentrations were negatively correlated to summer periphyton biomass and GPP. Accordingly, the lake's recovery period exhibited a decline of pelagic GPP and a partial recovery of summer periphyton biomass and production, although a full return to pre‐flood values was not recorded in either case. Whole‐lake areal summertime GPP increased due to browning and remained higher than before the browning event.
• This study provides a rare examination of differences in response rates between DOC, TP, and autotrophic structure in a shallow, temperate lake following a natural flood‐induced extreme browning event. The available data provide compelling evidence that browning events can produce lasting changes in the water chemistry, trophic status, and productive pathways of a lake, persisting beyond the lake's return to pre‐flood water levels. Such delayed or incomplete recoveries from flooding‐induced browning and nutrient loading may have consequences for regional and long‐term temporal trends in lake biogeochemistry, potentially contributing to the widespread phenomenon of incremental brownification.
... In particular, mitigation methods to decrease nutrient loads originating from diffuse sources have been inadequate (Hering et al., 2010;Tattari et al., 2017). Several factors linked to climate change have counteracted mitigation measures targeted at reducing nutrient loads (Räike et al., 2020), and studies in northern Europe imply that water bodies across the entire landscape are browning Sepp et al., 2018). Brownification is closely related to increased leaching of dissolved organic carbon (DOC) and linked to climate change. ...
Brownification, caused by increasing dissolved organic carbon (DOC) concentrations is a threat to aquatic ecosystems over large areas in Europe. The increasing concentrations of DOC in northern boreal streams and lakes have attracted considerable attention with proposed important drivers such as climate, deposition and land-use, and complex interactions between them. Changes in total organic N (TON) concentrations have received less attention, even though carbon and nitrogen losses are highly related to each other. We used long-term (1990−2019) monitoring records of 12 small data-rich headwater forested catchments in a large gradient of climate and deposition. We found that total organic carbon (TOC) concentrations were significantly increasing in almost all study catchments. The mean air temperature and change in sulphate concentrations both had a strong, significant correlation to TOC change-%. Both explained, alone, more than 65% of the change in TOC concentrations, and, together, up to 83% of the variation. Sulphur deposition has already decreased to low levels, our results indicate that its importance as a driver of TOC leaching has decreased but is still clearly detected, while the impact of climate warming as a driver of TOC leaching will be even more pronounced in the future. A positive correlation was found between drainage-% and increases in TON, suggesting also importance of land management. TON trends were tightly connected to changes in TOC, but not directly linked to decreasing S deposition.
... Under the pressure of industrialization and urbanization, large amounts of COD, NH 4 þ -N, and sulfate are discharged into rivers. These oxygen-depleting substances can rapidly consume DO in the water (Sepp et al., 2018;Zhang et al., 2015), thereby reducing the DO concentration to zero at the SWI, which results in a significant reducing environment . An increase in the sulfate concentration stimulates S reduction, resulting in S 2À accumulation in water and sediments (Yu et al., 2013). ...
The cycling of phosphorus (P), iron (Fe) and sulfur (S) in sediments has been previously investigated, but its impacts on the formation of black-odorous waterbodies remains unclear. Here, high-resolution simultaneous measurements of P (2 mm), Fe (2 mm), and S (0.042 mm in 2D presentation) profiles in river sediments based on the diffusive gradients in thin-films (DGT) technique were conducted in the Pearl River Delta region, South China. Similar distribution trends and significant positive correlations (R = 0.67‒0.93, p < 0.01) were observed between Fe and P. Considering the high diffusion fluxes of Fe and P together, it revealed that P release was promoted by the Fe reduction. The labile S profiles showed that their concentrations in sediments were higher by factors of 1.6-20 than those in overlying water. The minor diffusion fluxes of S and the accumulation of acid volatile sulfide (AVS) indicated that S2- combining with Fe2+ occurred prior to diffusion. Furthermore, the formation mechanisms of black-odorous waterbodies were explored in this study: (i) oxygen depletion by COD and NH4+‒N and large amounts of sulfate input were the main exogenous driving factors. (ii) reduction of Fe and S to form ferrous sulfide accompanied with P release in sediments were the dominant endogenous causes. These observations together with mechanism analysis can provide a basis for the governance of black-odorous rivers.
... Identifying strategies to counteract these negative effects of climate change is challenging, particularly since the transfer of OM from catchments to lakes, as well as the effects of climate change on soil carbon stores, is still poorly understood. Thus, more research and monitoring, as well as the use of similar metrics (Sepp et al., 2018), is needed to identify the factors responsible for increases in OM within aquatic ecosystems and to evaluate possible land use changes in catchments with high OM discharge. Improved management is particularly important for sites where peat is removed as well as sites undergoing land use changes and afforestation which can lead to DOM export into lakes (Haddaway et al., 2018;Kritzberg, 2017). ...
An increase of dissolved organic carbon (DOC)in inland waters has been reported across the northern temperate region but the effects of this on whole lake ecosystems, often combined with other anthropogenic stressors like nutrient inputs and warming, are poorly known. The effects of these changes on different component of the ecosystem were assessed in an experiment using twenty-four large (3000L)outdoor mesocosms simulating shallow lakes. Two different temperature regimes (ambient and ambient +4 °C)combined with three levels of organic matter (OM, added as filtered peaty water), simulating the DOC increase that is predicted to take place over the next 4 to 21 years were used. Neither temperature nor OM had significant effects on net ecosystem production, respiration or gross primary production. Phytoplankton chlorophyll a concentration was not significantly affected by warming, however in summer, autumn and winter it was significantly higher in mesocosms receiving intermediate OM levels (July–Feb DOC concentrations 2–6 mg L ⁻¹ ). Summer cyanobacterial blooms were highest in intermediate, and lowest in the highest OM treatments. OM concentration also influenced total macroinvertebrate abundance which was greater in spring and summer in mesocosms with intermediate and high OM. Fish abundance was not significantly affected by OM concentration, but abundance was greater in ambient (55 fish subsample ⁻¹ )compared to heated mesocosms (17 fish subsample ⁻¹ )and maximum abundance occurred two weeks later compared to heated mesocosms. The results suggest that changes in OM may have a greater effect on shallow lakes than temperature and that phytoplankton, especially cyanobacteria, benefit from intermediate OM concentrations, therefore, nuisance algal blooms might increase in relatively clear shallow eutrophic lakes where DOC concentrations increase.
... The bioavailability of DOM (the fraction of DOM pool available for rapid microbial degradation) 4 2000), aims at improving the ecological status of all European surface waters and thus obligates monitoring, planning and control of water quality. However, about half of the EU countries do not measure lake OM in their surveillance monitoring programmes (Sepp et al., 2018). WFD stipulates inter alia estimation of land use patterns to provide information about the type and magnitude of the significant anthropogenic pressures on surface water bodies (EC, 2000). ...
Dissolved organic matter (DOM) is a critical component in freshwater ecosystem functioning. The main sources of DOM in lakes are allochthonous inputs from the catchment and autochthonous in-lake production. This study focused on the role of catchment characteristics on the qualitative and quantitative properties of DOM in small temperate lakes along a gradient of alkalinity. We examined DOM properties based on the optical absorbance and fluorescence measurements of water from 34 Estonian lakes. The content and composition of DOM were highly diverse in the lakes studied, e.g. the dissolved organic carbon (DOC) concentrations varied from 3.2 to 53.0 mg L⁻¹. Land cover, soil, and catchment hydrology and geology had substantial effects on DOM in lakes. Stock of soil organic carbon (SOC) in the catchment and water exchange rate (a descriptor of catchment hydrology, reciprocal of water residence time) had major positive effects on DOC concentrations. The aromaticity and molecular weight of DOM, i.e. the relative abundance of humic substances, and the dominance of allochthonous DOM increased with the drainage ratio (catchment area/lake area) and the percentages of bogs, and Dystric and Fibric Histosols (peat soils in transitional mires and bogs, respectively) in the catchments. Dominance of non-humic over humic substances and autochthonous over allochthonous DOM in lakes corresponded to calcareous catchments and higher percentages of Gleyic Rendzinas (thin soils on calcareous rock), Sapric Histosols (peat soils in mires) and open spaces (areas with little vegetation). Our results showed that soil variables had in general a greater effect than land cover and were more informative for describing the role of catchment characteristics on DOM in lakes. Patterns in DOM quantity and quality found in our study were similar to patterns found in other temperate lakes; therefore, our results have important implications for understanding catchment-lake interactions across the temperate region.
... As an important source of energy and nutrient, organic matter (OM) has great impact on the biological activities of phytoplankton and bacteria in aquatic ecosystems (Wu et al. 2010). First, organic matter, rich in carbon, nitrogen, phosphorus, and other biogenic elements, has numerous geochemical and ecological functions in all kinds of water bodies, which is highly valued in ecological studies of both marine and inland environments (Margot et al. 2018). Second, the formation, transformation, and fate of OM and its accompanying nutrient regeneration process are key links in the biogeochemical cycling of nutrients in aquatic ecosystems. ...
Organic matter (OM), a complex entity with diverse functional groups and molecular sizes, has important effects on aquatic systems. We studied the optical compositions and sources of dissolved organic matter (DOM) and particulate organic matter (POM) in Lake Taihu, a large, shallow and eutrophic lake in China. Significant differences in optical compositions and sources occurred between the POM and DOM. The temporal–spatial distribution of the fluorescence indices suggested that the POM in Lake Taihu was mainly from autochthonous sources, but more exogenous characteristics were shown in POM in the river mouths compared with other regions. The chromophoric DOM in Lake Taihu mainly displayed autochthonous characteristics. The POM–DOM PARAFAC model was used to examine OM optical composition and five components were identified, which contained three protein-like components (C1, C2, and C5), a microbial humic-like component (C3), and a terrestrial humic-like component (C4). The POM was dominated by C5 in summer and autumn and C3 in winter and spring, and the DOM was dominated by protein-like components (C1, C2, and C5) through the entire year. The algae-dominated region had a relative higher contribution of tryptophan-like components of POM compared with the macrophyte-dominated region. A conceptual model based on the theory of “four phases of cyanobacteria bloom development” was proposed to fully describe the relationship between POM–DOM exchanges and cyanobacteria bloom development.
... The role of humic substances in regulating ecosystem functioning is a topical issue because the increasing load of dissolved organic matter from the catchments along the climate change causes worldwide water brownification of lakes (Sepp, Kõiv, Nõges, & Nõges, 2018;Solomon et al., 2015;Weyhenmeyer, Muller, Norman, & Tranvik, 2016). To clarify the mechanisms, through which water brownification can affect predator prey interactions, we examined the daytime depth of chaoborid larvae in relation to the availability of oxygen and light in two lakes differing in water color. ...
To clarify the effect of brownification on the functioning of lake ecosystems, the utilization of daytime refuges by chaoborids was examined in two lakes having different water colour. It was hypothesized that with high water colour, oxygen concentration plays a smaller role for the behavior of chaoborids than with lower water colour. It was also expected that the depth distribution of chaoborids is associated with light intensity at 680–700 nm. This could decrease their visibility to predators. In Lake Iso Valkjärvi with 50 mg L−1 Pt water colour, chaoborids occurred below 5 m depth, where the oxygen concentration was 0.4 mg L−1. Supporting the first hypothesis, in Lake Majajärvi with 200 mg L‐ 1 Pt colour, the leading edge of the population was at 3 m with 3.5 mg L−1 oxygen concentration. In Majajärvi, chaoborids remained in a layer where planktivorous fish could feed, explained by the low light intensity that decreased the potential predation pressure of fish. In Iso Valkjärvi with higher light intensity, chaoborids inhabited only the layers where oxygen concentration was too low for fish. Supporting the second hypothesis, the intensity of 693 nm light in the two lakes was similar at the depth of the leading edge of the chaoborid population. This wavelength represents the wavelengths that chaoborids reflect most effectively and is beyond the sensitivity peak of their main predator perch. The results suggested that combined effects of oxygen and water colour are potential explanatory mechanisms of the observed patterns in the behavior of chaoborids. The results thus suggested that along the worldwide brownification of lakes, the role of oxygen as a regulator of invertebrate predators may change. Because invertebrate predators are important components of lake food webs, such effects may be reflected to the whole ecosystem and further studies on the subject are encouraged.
The spatial and temporal variation of Nuphar lutea chlorophyll content was studied in 12 small lakes in Finland to clarify the bioindicator potential of N. lutea chlorophyll content for monitoring lake brownification. Significant in-lake variation in water colour and total phosphorus concentration was observed in a few study lakes. At highest, the in-lake variation for water colour was 13% and for total phosphorus concentration 27%. However, the in-lake variation in water quality did not coincide with significant in-lake variation of N. lutea chlorophyll content. The total chlorophyll concentration (chlorophyll a + b) varied in a few lakes, but the chlorophyll a and b ratio (chlorophyll a:b) did not change within the lakes. The chlorophyll a:b, however, varied between lakes and decreased significantly with increasing water colour and total phosphorus concentration in Nuphar lutea individuals collected near the lake outflow. The chlorophyll content of N. lutea did not show significant temporal variation during the one-week sampling period despite variable weather conditions. Chlorophyll a:b of N. lutea seems to be a possible bioindicator for monitoring brownification, as it can differentiate lakes from each other based on a small difference in water colour but does not react to short-term in-lake variations in the water quality.
Total organic carbon (TOC) analysis with accurate determination of particulate organic carbon (POC) content in suspended solids (SS) containing water is critical for evaluating the environmental impact of particulate organic pollutants in water and calculating the carbon cycle mass balance. TOC analysis is divided into the non-purgeable organic carbon (NPOC) and differential (known as TC-TIC) methods; although the selection of method is greatly affected by the sample matrix characteristics of SS, no studies have investigated this. This study quantitatively evaluates the effect of SS containing inorganic carbon (IC) and purgeable organic carbon (PuOC), as well as that of sample pretreatment, on the accuracy and precision of TOC measurement in both methods for various environmental water sample types (12 wastewater influents and effluents and 12 types of stream water). For influent and stream water with high SS, the TC-TIC method expressed 110-200 % higher TOC recovery than that for the NPOC method due to POC component losses in SS owing to its conversion into PuOC during sample pretreatment (using ultrasonic) and subsequent loss in the NPOC purging process. Correlation analysis confirmed that particulated organic matter (POM, mg/L) content in SS directly affected this difference (r > 0.74, p < 0.01, n = 24); for POC water samples (those containing >10 mg/L of POM) featuring purgeable dissolved organic matter, TC-TIC was appropriate in securing TOC measurement accuracy. In constrast, in effluent and stream water with low SS (i.e., < ~5 mg/L) and high IC (> 70 %) contents, the TOC measurement ratios (TC-TIC/NPOC) of both methods were similar, between 0.96 and 1.08, suggesting that NPOC is appropriate for improving precision. Our results provide useful basic data to establish the most reliable TOC analysis method considering SS contents and its properties along with the matrix characteristics of the sample.
Freshwater reservoirs are an important type of inland waterbody. However, they can suffer from oxygen-consuming pollution, which can seriously threaten drinking water safety and negatively impact the health of aquatic ecosystems. Oxygen-consuming pollutants originate from both allochthonous and autochthonous sources, and have temporally and spatially heterogeneous drivers. Datanggang Reservoir, China, is located in a small agricultural watershed; it is controlled by multiple sluice gates. Anomalously high oxygen consumption indicators were observed in this reservoir in March 2021. Here, it was hypothesized that autochthonous sources were the primary drivers of oxygen-consuming pollution in the reservoir under drought conditions. Datasets of water quality, precipitation, primary productivity, and sediment were used to analyze water quality trends in the reservoir and inflow rivers, demonstrating the effects of allochthonous inputs and autochthonous pollution. No correlation was found between reservoir oxygen consumption indicators and allochthonous inputs; reservoir oxygen consumption indicators and chlorophyll-a concentration were significantly positively correlated (p < 0.05). Substantially lower precipitation and higher water temperature and pH (compared to historical levels) were also observed before the pollution event. Therefore, during this period the hydrological conditions, water temperature, pH, and other variables caused by short-term drought conditions may have facilitated phytoplankton growth in the reservoir. This contributed to a large increase in autochthonous oxygen-consuming pollutants, as reflected by the abnormally high indicators. Sediments contaminated with organic matter may also have been an important contributor. As the effects of environmental management and pollution control continue to emerge, exogenous pollutants imported from the land to reservoirs are currently effectively controlled. However, endogenous pollutants driven by a variety of factors, such as meteorology and hydrology, will likely become the main drivers of short-term changes in oxygen-consuming pollution in freshwater reservoirs in the foreseeable future.
Indicators related to organic matter are important when assessing aquatic environment quality. The chemical oxygen demand (COD) is widely used as a water quality reference. However, oxidizing agents used to determine the COD can oxidize refractory organic matter that is not pollutant and can persist in the ocean for thousands of years. This means the COD can misrepresent the water quality. The actual water quality can be indicated better by the biochemical oxygen demand (BOD) than the COD, but determining the BOD is time-consuming and gives variable results. In this study, the optical properties of dissolved organic matter in water samples from the Chinese coast that had been incubated for a long time or directly oxidized using COD oxidant were analyzed. The results indicated that the oxidizing agent rapidly oxidized 22.93% ± 4.96% of refractory dissolved organic matter (RDOM) that was resistant to microbial degradation, implying that RDOM made a marked contribution to the COD. Meanwhile, size-fractional fluorescence spectroscopy and COD measurements indicated that the COD of the >0.7 μm fraction and the fluorescence intensity of the protein-like component significantly positively correlated with the BOD of the bulk sample. This indicated that, for monitoring organic pollutants in coastal waters, the COD of the >0.7 μm fraction could be used as a proxy for the standard COD and that the fluorescence intensity of the protein-like component could be used as a convenient proxy for the BOD. The method can help retain recalcitrant organic matter in seawater to act as a carbon sink.
The purpose of this study was to analyze the organic content of Lake Maninjau based on depth stratification and its organics carrying capacity. Sampling was carried out at the location of lake utilization, namely in the lake center, settlement, hydropower, endemic fisheries, and fish cage following Indonesian National Standard SNI 6989.57: 2008. The parameters measured were BOD5, COD and environmental condition such as pH, DO and temperatures. Lake Maninjau generally is polluted, especially for organic pollutants characterized by the BOD5 and COD values that did not meet the quality standard of Government regulations the Republic of Indonesia Number 82 the year 2001 class 2 according to its designation namely 21.87-47 mg BOD/L and 35.2-74 mg COD/L. Using one-way analysis of variance (ANOVA) at 0.05% level of significance both BOD5 and COD has a strong correlation with depth of the lake, at hydropower and endemic fisheries. At the shallow
lake depths, water is easy to mix so that the organic matter distributed vertically. Fish cage has the highest contribution to the contamination of organic matter in the lake.
This study assessed the water quality in Lake Wydmińskie (Warmińsko-Mazurskie Voivodeship) based on the content of both organic and inorganic pollutants flowing into the lake with water from drainage systems. The study demonstrated that the water flowing into the lake through drainage ditches that drain the improved part of the catchment area of the lake, was a potential source of diffuse pollutants and excess chemical components were deposited in the lake which could lead to its degradation. The most polluted water was found in the main tributary and the lake bay fed by its water. For this reason, it was concluded that the greatest problem was the area-wide sources of pollutants outgoing from agricultural areas. It was also found that water flowing out of the lake was of a considerably better quality than water flowing into the lake through the ditches. This clearly indicates the accumulative role of the lake on the route of pollutant migration from agricultural sources.
We assessed the allochthonous organic carbon (OC) budgets for thirteen hemiboreal lakes using a simple equilibrium model coupled with a Bayesian framework for estimating parameter distribution and uncertainty. Model inputs consisted of hydrological, bathymetric and chemical data that are easily measurable at the lake and basin scale. Among the model outputs were mean OC loads (5–123 g m⁻² y⁻¹), exports (1.10⁻³–108 g m⁻² y⁻¹), mineralization (3–12 g m⁻² y⁻¹), and sedimentation (2–6 g m⁻² y⁻¹). “Active” lake-catchment systems received and emitted the largest amounts of allochthonous OC, whereas lakes depending mostly on atmospheric inputs exhibited much more modest OC fluxes. Simulated organic carbon retention varied accordingly from 12% in some drainage lakes to 99% in seepage lakes. Lake allochthonous OC loads and exports were strongly correlated to drainage ratio (catchment area/lake area, R²: 0.89 and 0.92, respectively) and to forest ratio (catchment forested area/lake area, R²: 0.86 and 0.89), but not to wetland ratio. The simplicity of the model makes it easily transposable to a large variety of lakes. For a better insight into carbon processing, we suggest to follow a more integrative approach accounting for interactions between lake hydrology and catchment land cover.
Graphical Abstract
The effect of long-term changes in total precipitation on physical and chemical parameters of the water and the structure of phytoplankton community during a year were studied in a deep hard water lake. With respect to total precipitation, two different periods were distinguished: dry and wet. In the wet period, the water level rose and caused an increase in the water colour and a decrease in the electrolytic conductivity and concentration of nutrients. These changes were reflected in the composition and amount of phytoplankton. Certain phytoplankton groups, e.g. Cryptophyceae, Dinophyceae, Chrysophyceae, Bacillariophyceae and Chlorophyta/Charophyta, were positively affected by the environmental changes; instead, these effects were not observed in Cyanobacteria and Euglenophyta. The development of flagellates, such as Cryptomonas curvata, Plagioselmis nannoplanctica and Ceratium hirundinella, was enhanced during the wet period, whereas the dry period favoured non-flagellates, such as Planktothrix agardhii, Planktothrix rubescens and Limnothrix planctonica. Hence, the long-term variability in total precipitation can be a switch from non-flagellate- to flagellate-dominated phytoplankton in lakes. Moreover, a short time of ice cover duration in winter linked with the wet period promoted phytoplankton groups typical for spring and autumn, e.g. Cryptophyceae and Bacillariophyceae.
Increased concentrations of dissolved organic carbon (DOC), often labelled “browning”, is a current trend in northern, particularly boreal, freshwaters. The browning has been attributed to the recent reduction in sulphate (S) deposition during the last 2 to 3 decades. Over the last century, climate and land use change have also caused an increasing trend in vegetation cover (“greening”), and this terrestrially fixed carbon represents another potential source for export of organic carbon to lakes and rivers. The impact of this greening on the observed browning of lakes and rivers on decadal time scales remains poorly investigated, however. Here, we explore time-series both on water chemistry and catchment vegetation cover (using NDVI as proxy) from 70 Norwegian lakes and catchments over a 30-year period. We show that the increase in terrestrial vegetation as well as temperature and runoff significantly adds to the reduced SO4-deposition as a driver of freshwater DOC concentration. Over extended periods (centuries), climate mediated changes in vegetation cover may cause major browning of northern surface waters, with severe impact on ecosystem productivity and functioning.
The importance of lakes and reservoirs leads to the high need for monitoring lake water
quality both at local and global scales. The aim of the study was to test suitability of Sentinel-2 Multispectral Imager’s (MSI) data for mapping different lake water quality parameters. In situ data of chlorophyll a (Chl a), water color, colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) from nine small and two large lakes were compared with band ratio algorithms derived from Sentinel-2 Level-1C and atmospherically corrected (Sen2cor) Level-2A images. The height of the 705 nm peak was used for estimating Chl a. The suitability of the commonly used green to red band ratio was tested for estimating the CDOM, DOC and water color. Concurrent
reflectance measurements were not available. Therefore, we were not able to validate the performance of Sen2cor atmospheric correction available in the Sentinel-2 Toolbox. The shape and magnitude of water reflectance were consistent with our field measurements from previous years. However, the atmospheric correction reduced the correlation between the band ratio algorithms and water quality parameters indicating the need in better atmospheric correction. We were able to show that there is good correlation between band ratio algorithms calculated from Sentinel-2 MSI data and lake water parameters like Chl a (R2 = 0.83), CDOM (R2 = 0.72) and DOC (R2 = 0.92) concentrations as well as water color (R2 = 0.52). The in situ dataset was limited in number, but covered a reasonably wide range of optical water properties. These preliminary results allow us to assume that Sentinel-2 will be a valuable tool for lake monitoring and research, especially taking into account that the data will be
available routinely for many years, the imagery will be frequent, and free of charge.
Over the past 15 years, an increasing number of studies in limnology have been using data from high-frequency measurements (HFM). This new technology offers scientists a chance to investigate lakes at time scales that were not possible earlier and in places where regular sampling would be complicated or even dangerous. This has allowed capturing the effects of episodic or extreme events, such as typhoons on lakes. In the present paper we review the various fields of limnology, such as monitoring, studying highly dynamic processes, lake metabolism studies, and budget calculations, where HFM has been applied, and which have benefitted most from the application. Our meta-analysis showed that more than half of the high-frequency studies from lakes were made in North America and Europe. The main field of application has been lake ecology (monitoring, lake metabolism) followed by physical limnology. Water temperature and dissolved oxygen have been the most universal and commonly measured parameters and we review the various study purposes for which these measurements have been used. Although a considerable challenge for the future, our review highlights that broadening the spatial scale of HFM would substantially broaden the applicability of these data across a spectrum of different fields.
Many boreal waters are currently becoming browner with effects on biodiversity, fish production, biogeochemical processes and drinking water quality. The question arises whether and at which speed this browning will continue under future climate change. To answer the question we predicted the absorbance (a420) in 6347 lakes and streams of the boreal region under future climate change. For the prediction we modified a numerical model for a420 spatial variation which we tested on a temporal scale by simulating a420 inter-annual variation in 48 out of the 6347 Swedish waters. We observed that inter-annual a420 variation is strongly driven by precipitation that controls the water flushing through the landscape. Using the predicted worst case climate scenario for Sweden until 2030, i.e., a 32 % precipitation increase, and assuming a 10 % increase in imports of colored substances into headwaters but no change in land-cover, we predict that a420 in the 6347 lakes and streams will, in the worst case, increase by factors between 1.1 and 7.6 with a median of 1.3. This increase implies that a420 will rise from the present 0.1–86 m−1 (median: 7.3 m−1) in the 6347 waters to 0.1–154 m−1 (median: 10.1 m−1), which can cause problems for the preparation of drinking water in a variety of waters. Our model approach clearly demonstrates that a homogenous precipitation increase results in very heterogeneous a420 changes, where lakes with a long-term mean landscape water retention time between 1 and 3 years are particularly vulnerable to climate change induced browning. Since these lake types are quite often used as drinking water resources, preparedness is needed for such waters.
Many articles published in the last few years start with the assumption that the past decades have seen an increase in dissolved organic carbon (DOC) concentrations in the rivers and lakes of the Northern Hemisphere. This study analyses whether the existing evidence supports this claim. With this aim, we have collected published studies where long series of organic carbon concentrations (i.e., longer than 10 years) were analyzed for existing trends and have carefully evaluated the 63 articles found. Information has been collated in a comprehensive and comparable way, allowing readers to easily access it. The two main aspects considered in our analysis have been the analytical methods used and the data treatment methods applied. Both are sensitive issues because, on the one hand, the difficulties associated with correctly determining organic carbon concentrations in surface waters are well known, while, on the other, dealing with real environmental data (i.e., lack of normality, censoring, missing values, etc.) is an extremely intricate matter. Other issues such as data reporting and the geographical location of the systems studied are also discussed. In conclusion, it is clear that organic carbon concentrations have increased in some surface waters in the Northern Hemisphere since the 1990s. However, due to a lack of data in many parts of the world, it is not known whether this phenomenon is general and, more importantly, in the areas for which such data do exist, the reporting and methodological problems in the published studies prevent any conclusion on the existence of a general temporal behavior of organic carbon from being drawn.
Over the past several decades, dissolved organic carbon (DOC) in inland natural water systems has been a popular research topic to a variety of scientific disciplines. Part of the attention has been due to observed changes in DOC concentrations in many of the water systems of the Northern Hemisphere. Shifts in DOC levels, and changes in its composition, are of concern due to its significance in aquatic ecosystem functioning and its potential and realized negative effects on waters that might be treated for drinking purposes. While it may not be possible to establish sound cause and effect relationships using a limited number of drivers, through long-term DOC monitoring studies and a variety of laboratory/field experiments, several explanations for increasing DOC trends have been proposed, including two key mechanisms: decreased atmospheric acid deposition and the increasing impact of climate change agents. The purpose of this review is three-fold: to outline frequently discussed conceptual mechanisms used to explain DOC increases (especially under a changing climate), to discuss the structure of DOC and the impact of higher levels of DOC on drinking water resources, and to provide renewed/sustained interest in DOC research that can encourage interdisciplinary collaboration. Understanding the cycling of carbon from terrestrial ecosystems into natural waters is necessary in the face of a variable and changing climate, as climate change-related mechanisms may become increasingly responsible for variations in the inputs of allochthonous DOC concentrations in water.
Lake ecosystems and the services that they provide to people are profoundly influenced by dissolved organic matter derived from terrestrial plant tissues. These terrestrial dissolved organic matter (tDOM) inputs to lakes have changed substantially in recent decades, and will likely continue to change. In this paper, we first briefly review the substantial literature describing tDOM effects on lakes and ongoing changes in tDOM inputs. We then identify and provide examples of four major challenges which limit predictions about the implications of tDOM change for lakes, as follows: First, it is currently difficult to forecast future tDOM inputs for particular lakes or lake regions. Second, tDOM influences ecosystems via complex, interacting , physical-chemical-biological effects and our holistic understanding of those effects is still rudimentary. Third, non-linearities and thresholds in relationships between tDOM inputs and ecosystem processes have not been well described. Fourth, much understanding of tDOM effects is built on comparative studies across space that may not capture likely responses through time. We conclude by identifying research approaches that may be important for overcoming those challenges in order to provide policy-and management-relevant predictions about the implications of changing tDOM inputs for lakes.
For more than 50 years, scientific insights from surface water monitoring have supported Swedish evidence-based environmental management. Efforts to understand and control eutrophication in the 1960s led to construction of wastewater treatment plants with phosphorus retention, while acid rain research in the 1970s contributed to international legislation curbing emissions. By the 1990s, long-time series were being used to infer climate effects on surface water chemistry and biology. Monitoring data play a key role in implementing the EU Water Framework Directive and other legislation and have been used to show beneficial effects of agricultural management on Baltic Sea eutrophication. The Swedish experience demonstrates that well-designed and financially supported surface water monitoring can be used to understand and manage a range of stressors and societal concerns. Using scientifically sound adaptive monitoring principles to balance continuity and change has ensured long-time series and the capability to address new questions over time.
The invasive and nuisance microalga Gonyostomum semen has recently expanded its geographical distribution and increased its biomass in Sweden and Finland. Temperatures, total organic carbon (TOC), water colour and phosphorous are main factors suggested as drivers for its success. Already in the 1980s there were indications of the same patterns also in Norway, and in this study we further examine these observations based on the hypotheses that (1) G. semen has continued its increase in abundance in Norway since then, (2) after settling in a lake, G. semen may increase its biomass, provided a simultaneous change in climatic factors. We use existing data from Norwegian monitoring databases for the study and additional water samples to investigate distribution. G. semen was detected by microscopy and quantitative PCR, while trends over time in G. semen biomass and possible explanatory variables were analysed by simple regression. We show that G. semen has increased its distribution in Norway since the 1980s, geographically and to new lakes. In eight of the nine lakes studied, the proportion of G. semen biomass in lake phytoplankton has increased with time. These changes seem to be explained only to some degree by temperature, TOC, water colour and phosphorous.
Organic carbon (OC) can be classified into three main categories: labile, semi labile and refractory. The area of research is primarily focused on the labile organic carbon (LOC) as it is considered highly reactive indicator of green house gas (GHG) emission from reservoirs and lakes. The CO 2 or CH 4 release from sediment OC depends on its source and temperature of the reservoirs. The several analytical methods are available to determine and evaluate LOC based on physical, chemical and biochemical methods. A review of the advantages and disadvantages of each technique has indicated that none of the methods can be used to determine LOC precisely either because a part of the LOC is not involved or its further characterization is apparently missing. The approach is an omnipotent tool for the measurement of LOC. The present paper reviews the methodologies for estimating LOC and other types of organic carbon like LOC which plays crucial role in estimating the GHG emissions from reservoirs /lakes and lays the emphasis only on LOC (DOC, DIC and POC) due to its rapid degradation for the release of GHG compared to other "C" types.
Browning of inland waters has been noted over large parts of the
Northern Hemisphere and is a phenomenon with both ecological and
societal consequences. The increase in water color is generally ascribed
to increasing amounts of dissolved organic matter of terrestrial origin.
However, oftentimes the increase in water color is larger than that of
organic matter, implying that changes in the amount of organic matter
alone cannot explain the enhanced water color. Water color is known to
be affected also by the quality of organic matter and the prevalence of
iron. Here we investigated trends in water color, organic matter and
iron between 1972 and 2010 in 30 rivers draining into the Swedish cost,
and peformed a laboratory iron addition experiment to natural waters, to
evaluate the role of iron and organic matter in determining water color.
By comparing the effect of iron additions on water color in the
experiment, to variation in water color and iron concentration in the
monitoring data, we show that iron can explain a significant share of
the variation in water color (on average 25%), especially in the rivers
in the north of Sweden (up to 74%). Further more, positive trends for
iron are seen in 27 of 30 rivers (21-468%) and the increase in iron is
larger than that of organic matter, indicating that iron and organic
matter concentrations are controlled by similar but not identical
processes. We speculate that increasing iron concentrations can be
caused by changes in redox conditions, that mean that more anoxic water
with high concentrations of soluble FeII are feeding into the surface
waters. More studies are needed about why iron is increasing so
strongly, since both causes and consequences are partly different from
those of increasing organic matter content.
Increased color in surface waters, or browning, can alter lake ecological function, lake thermal stratification and pose difficulties for drinking water treatment. Mechanisms suggested to cause browning include increased dissolved organic carbon (DOC) and iron concentrations, as well as a shift to more colored DOC. While browning of surface waters is widespread and well documented, little is known about why some lakes resist it. Here, we present a comprehensive study of Mälaren, the third largest lake in Sweden. In Mälaren, the vast majority of water and DOC enters a western lake basin, and after approximately 2.8 years, drains from an eastern basin. Despite 40 years of increased terrestrial inputs of colored substances to western lake basins, the eastern basin has resisted browning over this time period. Here we find the half-life of iron was far shorter (0.6 years) than colored organic matter (A420 ; 1.7 years) and DOC as a whole (6.1 years). We found changes in filtered iron concentrations relate strongly to the observed loss of color in the western basins. In addition, we observed a substantial shift from colored DOC of terrestrial origin, to less colored autochthonous sources, with a substantial decrease in aromaticity (-17%) across the lake. We suggest that rapid losses of iron and colored DOC caused the limited browning observed in eastern lake basins. Across a wider dataset of 69 Swedish lakes, we observed greatest browning in acidic lakes with shorter retention times (< 1.5 years). These findings suggest that water residence time, along with iron, pH and colored DOC may be of central importance when modeling and projecting changes in brownification on broader spatial scales.
The utilization of dissolved organic carbon (DOG) by bacteria in grazer-free cultures can be used to measure the concentration of labile DOC (DOCL). A database of 126 measurements was used to test whether or not the concentration of DOCL is positively related to total DOG. A positive and significant correlation between DOCL and DOC was found for the entire database as well as for lakes, rivers and seawater. An average response of about 0.17 mu mol DOCL mu mol(-1) DOC could be calculated and 60% of the variance was explained by DOG. The DOCL concentration averaged 14, 19, and 19% of the total DOC pool in lakes, rivers and seawater, respectively; however, the median value of 25% for rivers was about twice the values for lakes and seawater. The high relative amount of DOCL in half the rivers was explained by anthropogenic influence. The control of DOCL concentrations was analyzed according to models of bacterial and substrate interactions applying Michaelis-Menten-Monod kinetics. It is suggested that the higher concentrations of DOCL in eutrophic as opposed to oligotrophic systems may be explained by a higher 'theoretical community half-saturation constant' (K-s) in eutrophic systems. The consequence of a higher K-s will be a higher steady-state concentration of labile substrate, as was found. Other possible explanations were analyzed, but rejected as major causes for the cross-system difference.
Humic acids have been widely studied in the literature as a representative to natural organic matter (NOM) in drinking water supplies due to their composite heterogeneous nature comprising a variety of different molecular weight compounds. However, humic acids are difficult to isolate from water primarily due to their low concentration, resulting in time-consuming and laborious processes for their isolation and purification. In this study the applicability of surrogate parameters such as E250/E365, E254/E436, E365/E465 and E465/E665, which are widely used in the literature for NOM characterization, were investigated in relation to aquatic and terrestrial model humic acids and a natural water sample. Molecular size fractionation of the samples was employed in an approach to understand the UV-vis properties of each size fraction. The specified ratios for both aquatic and terrestrial humic acids do not exhibit any significant differences up to 30 kDa. Lower molecular size fractions are differentiated in comparison to the natural water sample. E254/E436 and E250/E365 ratios exhibit a molecular size specific distribution with respect to the type of humic acids. The ratio of E254/E436 was proposed to assess the composition of altered NOM provided that the total removal of color-forming moieties is not required. Under conditions of total decolorization, the use of E250/E365 is also recommended relevant to the spectroscopic changes acquired during treatment.
Environmental conditions and human activities play a significant role in structuring novel assemblages of native and non-native species. Ongoing and future climatic change may alter the performance of native and non-native species and their biotic interactions. In the northern hemisphere, expected climate changes include warmer temperatures and higher precipitation, the latter of which may increase dissolved organic carbon (humic) concentrations, resulting in browner water in aquatic ecosystems (brownification). We tested the effects of elevated temperature (3 °C) and brownification on native and non-native aquatic plant production in mesocosms over 56 days. Elodea canadensis, an aquatic invasive plant, had higher relative growth rate in terms of both length and weight, as well as higher weight to length ratio when grown in brown versus clear water; E. canadensis did not respond to temperature treatments. Different functional groups of native producers (phytoplankton, periphyton, macrophytes) showed different relationships to temperature and brownification treatments, with the macrophyte response being most notable because it was opposite to that of E. canadensis. Native macrophytes decreased in biomass in browner water, where they represented about 40 % of total biomass compared to 85 % in clear water. In regression analyses, E. canadensis length RGR was best predicted only by water color treatment, but biomass RGR and biomass per length were inversely correlated with native macrophyte biomass, which is consistent with competition. Our results unexpectedly showed water brownification to have more influence on lake invasion than climate warming at this temperature regime. Two pathways emerged for climate to interact with biological invasions in structuring novel communities: directly, if non-native species respond positively to climate change, and indirectly through species interactions, for instance, because water brownification impairs growth of native macrophytes and reduces biotic resistance to invasion. © 2012 Springer Science+Business Media B.V.
Dissolved organic matter (DOM) in aquatic systems originates from a range of sources. Some is allochthonous, transported from the surrounding landscape to the water body, and is derived from and influenced by the geology, land use and hydrology of its origin. Some is created in situ through microbial activity, which may provide an independent source of organic matter, or a recycling mechanism for that which has been transported into the water body. The relative contribution of each source depends upon the location and environmental conditions within and without the water body. Human activity is also a source of DOM, much of which is believed to be labile, which can enter the aquatic system through direct point discharges, diffuse leaching and aerial dispersal. Fluorescence spectroscopy can provide an excellent tool to source DOM fractions, and to monitor and understand DOM transformations in aquatic systems, as much DOM has an intrinsic fluorescence. In particular, recent advances in optical technology, enabling rapid investigation of shorter wavelengths, have enabled more detailed characterization of organic material and its reactions in water. In this article, we review the use of fluorescence spectroscopic techniques to measure the intrinsic fluorescence of organic matter and the application of fluorescent DOM analysis in marine waters, freshwaters and wastewaters. Copyright © 2007 John Wiley & Sons, Ltd.
Recent increases in dissolved organic carbon (DOC) concentrations in surface waters across both Europe and North America have
focused attention on the factors controlling the export of DOC compounds from catchments. Waters containing high concentrations
of DOC generally have a characteristic brown colour and are associated with the presence of highly organic soils. Catchments
dominated by these soils typically export between 10 and 300kg DOC ha−1 year−1 (Billett et al., 2004; Laudon et al., 2004; Jonsson et al., 2006). A portion of this DOC is mineralised in streams and lakes
to CO2, while the remainder is transported to the sea (Jonsson et al., 2006). Organic matter accumulates in soils when decomposition
rates are restricted either by low temperatures or water-logged conditions. In Europe organic soils are found mainly in colder,
wetter
We sampled small (0.03 to 3.3 km ² surface area) forest lakes in southern Sweden during two summers to investigate how concentration of dissolved organic carbon (DOC) and lake size influence epilimnion depth ( z e ) and light conditions in the epilimnion. z e increased with increasing fetch (square root of lake area) but did not decrease with increasing DOC concentration. This suggests greater importance of wind mixing in our study area than in areas with more continental climate, i.e., epilimnion‐deepening wind mixing overrides the tendency for epilimnion depth to decrease with increasing DOC concentration. Extinction of photosynthetically active radiation was mainly caused by DOC. The euphotic zone was shallower in the first year than in the second, probably because of higher precipitation and lower solar irradiance in 2007, which together led to higher water color. Mean epilimnetic irradiance was low, especially in 2007, mainly because the increase in DOC did not lead to shallower epilimnia. Browning of lakes in southern Sweden, in combination with a predicted increase in the number of storm events, may lead to more severe light limitation of phytoplankton in small, nutrient‐poor lakes, since it may not be accompanied by a compensatory shallowing of the epilimnion. As a consequence, lake ecosystems will become more heterotrophic, CO 2 ‐evasion to the atmosphere will increase, and fish production decrease.
Colored dissolved organic matter (CDOM) has become increasingly valuable as a proxy for dissolved organic carbon and as a tracer for biogeochemical and physical processes in the ocean. A variety of benchtop and in situ instruments are available for CDOM measurement both by absorption (color) and fluorescence; however, several precautions are required for accurate measurement, especially for hyperspectral techniques.
The biochemical composition of dissolved organic matter (DOM) strongly influences its biogeochemical role in freshwater ecosystems, yet DOM composition measurements are not routinely incorporated into ecological studies. To date, the majority of studies of freshwater ecosystems have relied on bulk analyses of dissolved organic carbon and nitrogen to obtain information about DOM cycling. The problem with this approach is that the biogeochemical significance of DOM can only partially be elucidated using bulk analyses alone because bulk measures cannot detect most carbon and nitrogen transformations. Advances in fluorescence spectroscopy provide an alternative to traditional approaches for characterizing aquatic DOM, and allow for the rapid and precise characterization of DOM necessary to more comprehensively trace DOM dynamics. It is within this context that we discuss the use of fluorescence spectroscopy to provide a novel approach to tackling a long-standing problem: understanding the dynamics and biogeochemical role of DOM. We highlight the utility of fluorescence characterization of DOM and provide examples of the potential range of applications for incorporating DOM fluorescence into ecological studies in the hope that this rapidly evolving technique will further our understanding of the biogeochemical role of DOM in freshwater ecosystems.
We sampled small (0.03 to 3.3 km2 surface area) forest lakes in southern Sweden during two summers to investigate how concentration of dissolved organic carbon (DOC) and lake size influence epilimnion depth (ze) and light conditions in the epilimnion. ze increased with increasing fetch (square root of lake area) but did not decrease with increasing DOC concentration. This suggests greater importance of wind mixing in our study area than in areas with more continental climate, i.e., epilimnion-deepening wind mixing overrides the tendency for epilimnion depth to decrease with increasing DOC concentration. Extinction of photosynthetically active radiation was mainly caused by DOC. The euphotic zone was shallower in the first year than in the second, probably because of higher precipitation and lower solar irradiance in 2007, which together led to higher water color. Mean epilimnetic irradiance was low, especially in 2007, mainly because the increase in DOC did not lead to shallower epilimnia. Browning of lakes in southern Sweden, in combination with a predicted increase in the number of storm events, may lead to more severe light limitation of phytoplankton in small, nutrient-poor lakes, since it may not be accompanied by a compensatory shallowing of the epilimnion. As a consequence, lake ecosystems will become more heterotrophic, CO2-evasion to the atmosphere will increase, and fish production decrease. © 2010, by the American Society of Limnology and Oceanography, Inc.
A noteworthy increase in the organic matter concentration and export, as well as water colour, in the
catchments of the Salaca River has been observed during the last decades. This study investigates
factors behind this increase: the impact of climate, land use and human loading changes on the
concentrations and export of the organic matter in the Salaca River/Lake Burtnieks catchments.
Proportion of wetlands in the river basin, type of land use, and runoff regime can be considered as
the main factors influencing the organic carbon loadings. Despite a steady overall tendency of
increase, considerable oscillations of organic matter loadings influenced by the changes in the river
discharge regime were observed for extended periods of time.
We evaluated MERIS spectral inversion processors in the estimation of chlorophyll a (Chl-a), total suspended matter (TSM), absorption of colored dissolved organic matter (aCDOM at 443 nm) and Secchi disk transparency (ZSD) in four lakes located in southern Finland. The lakes represent oligotrophic, mesotrophic and humic (high aCDOM, low TSM) lake types. Our validation data was extensive, consisting of remote sensing reflectance (Rrs) measured in the field, detailed measurements of (specific) inherent optical properties ((S)IOP) and water quality measurements. Validation measurements were collected at stations and as spatially intensive transects. The tested processors were Boreal lakes (BOR) and Free University of Berlin WeW WATER processor (FUB). In the case of BOR we included two versions, the original one available in 2008 and the most recent version. The processing chains of these versions differed in terms of MERIS archive reprocessing (2nd reprocessing (RP2) and 3rd reprocessing (RP3) were used), version of adjacency effect correction (ICOL) and rectification method. However, all these had only minor effect on the estimated Rrs when compared to the effect caused by the differences in the atmospheric correction versions. The use of ICOL improved the estimation of Rrs and therefore all IOP and water quality validations were made with ICOL pre-processed data. Rrs was best estimated with RP2 BOR, although it somewhat overestimated Rrs in blue in the humic lake. RP3 BOR greatly overestimated the Rrs in blue. FUB was outside its aCDOM training range in most of the studied lakes. RP2 BOR estimated water quality with the best accuracy in mesotrophic lakes, but failed in humic and clear water lakes. BOR overestimated Chl-a, particularly with RP3. The best TSM correlation was for RP2 BOR. All processors underestimated aCDOM. The SIOP measurements showed that overestimation of Chl-a was not due to incorrect conversion factors, and that underestimation of TSM was to some extent explained by lower average conversion factor than that measured in the validation lakes. The inaccuracies in Chl-a and aCDOM(443) estimation were related to the partition of atot to phytoplankton and CDOM absorption, which emphasizes the importance of including IOP measurements in the validation studies. ZSD was best estimated on the basis of atot and btot, which were separately calculated from BOR output and the bio-optical model assumed in the processor. For the needs of transparency estimation the processors should produce atot and btot for all MERIS bands as standard output. Atmospheric correction over humic lakes is another problem to be solved in future versions of the processors. The 2008 version of BOR provided better atmospheric correction results in humic lakes and is thus more applicable in the boreal zone where these lakes are common. This suggests that before a new processor version is published it should be validated with existing in situ data.
This paper presents an application of a physic-based method that relies on spectral inversion procedures to simultaneously estimate concentrations of water constituents, water column heights (cH) and benthic substrate types in Lake Trasimeno (Italy) from airborne imaging spectrometry. Complex waters of this lake are challenging due to the coexistence of optically-deep turbid waters and of optically-shallow waters, mostly characterised by dense submerged aquatic vegetation (SAV) beds. Airborne data acquired on 12 May 2009 by Multispectral Infrared and Visible Imaging Spectrometer (MIVIS) were converted into remote sensing reflectance Rrs(λ) with the atmospheric correction code ATCOR. A spectral inversion procedure implementing a bio-optical model (namely BOMBER), parameterised with in situ data, was firstly run to retrieve concentrations of suspended particulate matter (SPM), chlorophyll-a (chl-a) and coloured dissolved organic matter (i.e. aCDOM(440)) in the optically-deep waters. The areas where the retrieved optimisation error was higher than 10% were instead assumed as optically-shallow. In these areas two maps depicting the linear unmixing of three substrate types (i.e., silty-clay, Chara ssp. and other hydrophyte) and the water column heights were produced. The MIVIS-derived products were validated with field data providing a reliable estimation of SPM, chl-a, aCDOM(440) and cH (determination coefficients always R2 > 0.7). SPM concentrations were also similar to a 5.4-km long transect of flow-through turbidity data, and the SAV map was comparable to in situ observations. Generally, the colonisation patterns of SAV were reflecting the spatial distribution of SPM concentrations. In particular, the positive role of Chara on keeping SPM concentrations low was observed. Future research should extend this application to remote sensing data acquired in other seasons to trace the dynamics of SAV and its effect on spatial water clarity.
This study examines a natural, rapid, fivefold increase in dissolved organic carbon (DOC) concentrations in a temperate shallow lake, describing the processes by which increased DOC resulted in anoxic conditions and altered existing carbon cycling pathways. High precipitation for two consecutive years led to rising water levels and the flooding of adjacent degraded peatlands. Leaching from the flooded soils provided an initial increase in DOC concentrations (from a 2010 mean of 12.mg L-1 to a maximum concentration of 53 mg L-1 by June 2012). Increasing water levels, DOC, and phytoplankton concentrations reduced light reaching the sediment surface, eliminating most benthic primary production and promoting anoxia in the hypolimnion. From January
to June 2012 there was a sudden increase in total phosphorus (from 57 µg L-1 to 216 µg L-1), DOC (from 24.6 mg L-1 to 53 mg L-1), and iron (from 0.12 mg L-1 to 1.07 mg L-1) concentrations, without any further large fluxes in water levels. We suggest that anoxic conditions at the sediment surface and flooded soils produced a dramatic release of these chemicals that exacerbated brownification and eutrophication, creating anoxic
conditions that persisted roughly 6 months below a water depth of 1 m and extended periodically to the water surface. This anoxia resulted in a near-complete loss of macroinvertebrate and fish populations, and surface carbon dioxide (CO2) emissions increased by an order of magnitude relative to previous years. In short, a
brownification–anoxia feedback loop reduced benthic primary and secondary production and increased CO2 emissions in a shallow lake.
The microbial loop in flowing waters is dependent on allochthonous sources of carbon, which vary in quality. The proportion of dissolved organic carbon (DOC) that can be degraded ranges from <1 to over 50%, and the bioavailability of DOC (micrograms bacterial biomass produced per milligram DOC present) ranges over two orders of magnitude. Bioavailability of DOC is predictable from the ratio of H/C and O/C of the DOC, but further work is needed to develop simple predictors of bioavailability of DOC in a range of environments. Consumers of bacteria in streams range in size from protists to insect larvae, with highest rates of bacterial consumption found among the meiofauna and certain filter feeders and grazers. Because there appear to be fewer trophic transfers in the lotic microbial loop, it functions more as a link in flowing waters than it appears to do in the marine plankton.
The Water Framework Directive (WFD) establishes a new regulatory framework for the management of water bodies throughout the European Union. The Directive introduces new principles, importantly shifting policy towards Integrated Water Resource Management, and a more holistic approach to water quality comprising both ecological and chemical status. Owing to the emphasis the Directive places on it, monitoring plays an integral part in its success. In this paper the implications of implementing the WFD on monitoring requirements are reviewed and compared to previous arrangements in England and Wales. This paper demonstrates the challenge associated with making the transition from established monitoring networks to those that support a more integrated approach to water management. The need for integration of monitoring using ecological elements, the use of risk in the design of monitoring programmes, the collection of monitoring data to inform decision making and the active engagement with stakeholders are highlighted as some of the challenges of such a transition.
The adsorption of phosphorus on natural diagenetic iron (Feox) and manganese (Mnox) oxyhydroxides was studied in deep and littoral zone sediments of mesotrophic Lac Saint-Charles (46°56 N, 71°23 W), using a Teflon sheet technique for collecting diagenetically produced metal oxyhydroxides. Collected metal oxide amounts were greater at the deep-water station, relative to littoral zone stations reflecting sediment and local diagenetic differences. Two-layer surface complexation modeling on iron oxyhydroxide was consistent with the measured total P/Fe molar ratios except for the upper mixed Mn–Fe oxide layer from the littoral stations, where measured phosphorus exceeded the modeled phosphorus by more than fivefold. Soluble reactive phosphorus (SRP) exchange between oxyhydroxide samples and natural lake water in the laboratory revealed a labile phosphorus pool. Phosphorus determined on the Teflon sheets from the littoral zone stations appears to be related to a distinct non-humic organic carbon pool that readily exchanges SRP, while little exchange was observed from material collected from the deep-water station. We suggest that the enhanced SRP release from littoral zone sediments is due to an organic carbon and/or metal oxide-impoverished sediment matrix, limiting microbial oxide reduction and allowing phosphorus to be rapidly recycled at the sediment–water interface, instead of being slowly incorporated into humic material. The SRP fluxes revealed in our study, which originate from the solid phase at the sediment–water interface, would be difficult to resolve using interstitial pore-water samplers and might be a quantitatively important source of inorganic phosphorus in Shield lakes.
Recent studies indicate that lakes are regulators of carbon cycling and climate. Therefore, it is important to know how the lake carbon content has changed over the last decades. In situ long time data series about the amount of dissolved organic carbon (DOC) in lakes are rare. The only potential way to study retrospectively the changes in lake carbon over the last decades is by means of remote sensing data provided there are sensors that can provide data about coloured dissolved organic matter (CDOM) in lakes over long periods. Landsat data archive contains images from 1984 to nowadays and covers the whole Earth. Although the sensors were not designed for remote sensing of aquatic environments it is still tempting to utilise the long data series. Landsat 4, Landsat 5 and Landsat 7 imagery available in free Landsat image archive was compared with time series of CDOM in situ data from 19 sampling stations available in the Swedish University of Natural Sciences lake monitoring database. There was no correlation between the image and in situ data when all the above mentioned data were used. Low radiometric resolution of the sensor, small size of many lakes (= large adjacency effects) and high concentration of CDOM (negligible water leaving radiation) could be the reasons. The results were more promising (R2 = 0.62) when Lake Mälaren stations were analysed separately. The lake is sufficiently large and with variable, but not extremely high, CDOM content. The Lake Mälaren in situ data showed very different trends in CDOM concentrations in different basins of the lake over the last 45 years. Although the correlation between the image and in situ data was a bit low for accurate daily estimation of CDOM concentrations from Landsat data it could allow detecting general trends in lake CDOM content. Unfortunately, there is currently a gap in Landsat archive (for our study sites) between 1988 and 1998 which makes calculations of long time trends unreasonable for the time being.
The median TOC, colour, and chemical oxygen demand (CODMn) are 12 mg/L-1, 100 mg Pt.L-1, and 15 mg O2.L-1, respectively. TOC is significantly related to other water quality parameters including the following: CODMn(r2 = 0.92), colour (R2 = 0.86), total iron (r2 = 0.69), total nitrogen (r2 = 0.53), and total phosphorus (r2 = 0.41). TOC and nutrient concentrations are low in northern Finland compared with southern and central regions. The proportion of the catchment area covered by peatlands is the most important catchment variable determining TOC concentrations. In northern Finland, where catchment areas are less disturbed compared with southern regions, peatlands and latitude explain 63% of the variation in TOC. In the full set of lakes, latitude, catchment to lake area ratio, and the proportion of the catchment area covered by peatlands, upstream lakes, and fields explain 55% of the variation in TOC. -from Author
A semi-micro modification of the dichromate method for the determination of low concentrations (1–35 mg l–1) of the chemical oxygen demand is described. It is based on the experimentally established dependencies of the oxidation efficiency on the concentrations of H2SO4, K2Cr2O7 and Ag2SO4, and on the temperature and time of heating. The procedure involves increasing the concentration of H2SO4 and heating in closed test-tubes in a heating block at 170 °C for 40 min and the spectrophotometric determination of dichromate at 455 nm. The interfering effect of chloride, up to a concentration of 100 mg l–1, is masked by using a combination of HgSO4 and KCr(SO4)2. The modification has been tested on 30 samples of ground, tap, precipitation and surface waters and on 16 chemical compounds, and gives results comparable to those from a standard reflux method.
Natural organic matter (NOM) serve as precursors for disinfection by-products (DBPs) in drinking water production making NOM removal essential in pre-disinfection treatment processes. We identified molecular formulae of chlorinated DBPs after chlorination and chloramination in four Swedish surface water treatment plants (WTPs) using ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Chlorine-containing formulae were detected before and after disinfection and were therefore classified to identify DBPs. In total, 499 DBPs were detected, of which 230 have not been reported earlier. The by-products had, as a group, significantly lower ratio of hydrogen to carbon (H/C) and significantly higher average carbon oxidation state (COS ), double bond equivalents per carbon (DBE/C) and ratio of oxygen to carbon (O/C) compared to Cl-containing components present before disinfection and CHO formulae in samples taken both before and after disinfection. Electrophilic substitution, the proposed most significant reaction pathway for chlorination of NOM, results in carbon oxidation and lower H/C while O/C and DBE/C is left unchanged. Because the identified DBPs had significantly higher DBE/C and O/C than the CHO formulae we concluded that chlorination of NOM during disinfection is selective towards components with relatively high double bond equivalency and number of oxygen atoms per carbon. Furthermore, choice of disinfectant, dose and pre-disinfection treatment at the different WTPs resulted in distinct patterns in the occurrence of DBP formulae.
Spectral values of absorption of light by dissolved organic matter were measured in samples originating from diverse parts of the ocean, quite different with respect to pigment and par- ticle content. The use of llO-cm cells and then of lo-cm cells, with a highly sensitive spec- trophotometer, allowed measurement throughout the UV-visible range (200-700 nm) even for the low concentrations of yellow substance encountered in the open sea. The concentra- tion appears influenced predominantly by natural and industrial land discharges. In oceanic waters, it remains low and seems to be related to the biological activity averaged over a long period rather than to the local and temporary phytoplankton content. However, even at such low concentrations, yellow substance in the open sea may have an effect on absorption and hence on ocean color similar to that of low or moderate algal biomass. The spectral depen- dence law of absorption appears to vary within a restricted range, and an average law can be considered representative of rapid measurements at one selected wavelength.
This manual is designed for students involved in environmental education programs dealing with water pollution problems. By establishing a network of Environmental Monitoring Stations within the educational system, four steps toward the prevention, control, and abatement of water pollution are proposed. (1) Train students to recognize, monitor, and record information about water pollution problems within their own community; (2) Funnel the resulting information to proper agencies; (3) Develop an awareness of general and specific pollution problems; (4) Develop community action, support state and federal programs, and direct concerted efforts for the abatement of water pollution. Sections of the laboratory manual explain the research procedures for student monitors--surveying the water system; selecting the tests, sampling stations, and equipment; sampling methods; recording data and reporting results; and correcting water quality abuse. The appendix includes additional testing information, a glossary of terms, a bibliography of books, pamphlets, periodicals, and films, and a listing of citizen action questions, and a sample report of a preliminary water quality field study. (BL)
The suitability of the AISA airborne imaging spectrometer for monitoring lake water quality was tested in four surveys carried out in southern Finland in 1996-1998. Altogether, 11 lakes were surveyed and the total number of stations with concurrent remote sensing and limnological measurements was 127. The ranges of the water quality variables were: the sum of chlorophyll a and phaeophytin a 1-100 microg l(-1), turbidity 0.4-26 FNU, total suspended solids 0.7-32 mg l(-1), absorption coefficient of aquatic humus at 400 nm 1.2-14 m(-1) and secchi disc transparency 0.4-7 m. For the retrieval analyses, 24 AISA channels in the 450-786 nm range with a channel width of 6-14 nm were used. The agreement between estimated and observed water quality variables was generally good and R2 for the best algorithms was in the range of 0.72-0.90 over the whole dataset. The channels used for May were, in most cases, the same as those for August, but the empirical parameters of the algorithms were different. After seasonal grouping, R2 varied from 0.84 to 0.95. The use of apparent reflectance instead of radiance improved the estimation of water quality in the case of total suspended solids and turbidity. In the most humic lake, the empirical algorithms tested were suitable only for the interpretation of total suspended solids and turbidity.
A hyperspectral model was developed for the interpretation of remote sensing data collected above inland waters. Specific absorption and scattering coefficients proposed by other authors were not suitable for modelling of the irradiance reflectance in 12 studied lakes. Therefore, special studies were carried out to estimate absorption and scattering coefficients as well as backscattering probability of suspended matter in turbid waters. AC-9 and Li-1800UW results were used for these purposes. The algorithms obtained were used to improve the model, which was then tested in forward and inverse modes.