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Dissolved organic carbon and its potential predictors in eutrophic lakes
Abstract
Understanding of the true role of lakes in the global carbon cycle requires reliable estimates of dissolved organic carbon (DOC) and there is a strong need to develop remote sensing methods for mapping lake carbon content at larger regional and global scales. Part of DOC is optically inactive. Therefore, lake DOC content cannot be mapped directly. The objectives of the current study were to estimate the relationships of DOC and other water and environmental variables in order to find the best proxy for remote sensing mapping of lake DOC. The Boosted Regression Trees approach was used to clarify in which relative proportions different water and environmental variables determine DOC. In a studied large and shallow eutrophic lake the concentrations of DOC and coloured dissolved organic matter (CDOM) were rather high while the seasonal and interannual variability of DOC concentrations was small. The relationships between DOC and other water and environmental variables varied seasonally and interannually and it was challenging to find proxies for describing seasonal cycle of DOC. Chlorophyll a (Chl a), total suspended matter and Secchi depth were correlated with DOC and therefore are possible proxies for remote sensing of seasonal changes of DOC in ice free period, while for long term interannual changes transparency-related variables are relevant as DOC proxies. CDOM did not appear to be a good predictor of the seasonality of DOC concentration in Lake Võrtsjärv since the CDOM–DOC coupling varied seasonally. However, combining the data from Võrtsjärv with the published data from six other eutrophic lakes in the world showed that CDOM was the most powerful predictor of DOC and can be used in remote sensing of DOC concentrations in eutrophic lakes.
... Colored dissolved organic matter (CDOM), also known as yellow matter, is the colored portion of dissolved organic matter (DOM) and accounts for more than half of the dissolved organic carbon (DOC) [1,2]. CDOM is the main light-absorbing substance in the water column and has relatively homogeneous optical properties; it mainly exhibits absorptive properties in water, and its scattering is negligible [3]. ...
... In addition, the composition of CDOM is complex and is composed mainly of fulvic acid, humus, aromatic polymers and other substances, and its source, nature and spatial distribution are significantly different in different water bodies. The spectral absorption properties of CDOM are effective in interpreting the composition and origin of substances and provide some indication of the pollution status of a water body [2,3]. Therefore, the study of the optical properties of CDOM can reflect the ecological environment of water bodies well and plays an important role in water color remote sensing inversion [5]. ...
... The results are expressed as the means of replicates or three analyses with a coefficient of variation and standard deviation of ≤2%. The absorption coefficient of the CDOM is obtained via equation (1), and the calculated results are subsequently corrected for scattering effects via equation (2) to obtain the corrected absorption coefficient: * ( ) = 2.303( )/ ...
Colored dissolved organic matter (CDOM), which is a type of dissolved organic matter (DOM) in water bodies with color-carrying optical properties and is also the main component of dissolved organic carbon (DOC), is an important component of optically active substances in water bodies. Remote sensing monitoring of its concentration is scientifically important for understanding the carbon cycle of water bodies and understanding the distribution of organic matter. In this study, two field sampling and experimental analyses were conducted in April and July 2024 in the Pingzhai Reservoir, a karst reservoir in Southwest China, to study the CDOM concentration and absorption spectral characteristics. The inverse model of the CDOM concentration was established on the basis of Sentinel-2B/MSI remote sensing data and the machine learning random forest method, and the inverse model of the DOC concentration was developed by combining the strong correlations between the CDOM and DOC concentrations, after which the water body DOC concentration was estimated. The effects of water quality parameters and meteorological factors on CDOM and DOC concentrations were subsequently explored. The results revealed that (1) the CDOM of the Pingzhai Reservoir could be well inverted on the basis of measured data, Sentinel-2B/MSI remote sensing data and a random forest model; (2) the CDOM of the Pingzhai Reservoir had a good correlation with the DOC, and the accuracy of the inversion model of the DOC was high (R ² = 0.72, MAE = 0.33, RMSE = 0.44); (3) the Pingzhai Reservoir SUVA 254 (ratio of the absorption coefficient of the CDOM at a wavelength of 254 nm to the DOC concentration) values were relatively high, and the M values (ratio of the absorption coefficient of the CDOM at wavelengths of 250 nm and 365 nm) were relatively small, which indicated that the CDOM of the Pingzhai Reservoir tended to be input from land-based sources and had a relatively high content of humus; and (4) the results of the redundancy analyses indicated that water quality parameters such as the chlorophyll a (Chl-a), total suspended matter (TSM), turbidity (Tur), and dissolved oxygen (DO) had important effects on the CDOM concentration. This study contributes to the understanding of the changes in CDOM and DOC concentrations in the Pingzhai Reservoir and provides a reference basis for water ecological environmental protection and water resource management.
... In addition, none of these ocean color sensors was designed for the purpose of water quality monitoring. Thus, Ocean and Land Color Instrument (OLCI), a follow-up project and an imaging spectrometer for the monitoring of open, coastal and inland waters (Toming, Kutser, Tuvikene, Viik, & Nõges, 2016;van der Woerd & Wernand, 2015) was designed to be specialized in ocean color remote sensing (Wang, Ling, Yao, Liu, & Xu, 2019). OLCI is attached on Sentinel-3A and Sentinel-3B satellites launched on the 16 th of February, 2016 and 25 th of April, 2018 respectively by European Space Agency (ESA). ...
... The swath width and the spatial resolution of OLCI is 1200 km and 300 m, respectively and it has 21 spectral bands with a wide range, from optical to near-infrared wavelengths (Donlon et al., 2012;Petus et al., 2019;Wang et al., 2019). Since the design of the OLCI spectral bands was performed considering its specific aims, the images obtained via Sentinel-3 OLCI sensor are able to be used in mapping the parameters of the water quality (Toming et al., 2016;Wang et al., 2019). ...
... The majority of the CDOM consists of humic and fulvic acids. Generally, CDOM is assigned as a measure of dissolved organic matter (Brezonik, Olmanson, Finlay, & Bauer, 2015;Toming et al., 2016). However, the sources of CDOM can be both indigenous and exogenous. ...
Detection of biological, physical and chemical parameters is needed for the determination of water quality. Some of these water quality parameters such as turbidity, chlorophyll-a, harmful algae, suspended sedi-ment, submerged habitat and temperature, can be derived directly via the satellite remote sensing facilities, particu-larly through the ocean color sensors. The competitiveness of satellite remote sensing comes from its capability of extensive geographical range and temporal coverage. Thus, changes and trends in water quality can be monitored and assessed to a greater degree, especially under the dynamic conditions of coastal zones. This study focuses on the water quality parameters in the vicinity of Green Ports of Turkey located in the Marmara Sea. There are 12 certified Green Ports in Turkey, located mostly in the Marmara Sea. Marmara Sea is a semi-enclosed inland sea and a passageway, which connects the Black Sea to the Mediterranean. There are 7 cities surrounding the Marmara Sea, representing the different anthropogenic aspects of civilization: Population, industry and agriculture. These aspects affect the water quality of the coastal zones in the Marmara Sea in different scales. Briefly, the aim of this study is to monitor and assess the impact of the Green Ports in the Marmara Sea region, in terms of water quality parameters detected via the Earth Observation System. Consequently, it is concluded that remote sensing capabilities of the contemporary Earth Observation Systems provide reliable results of water quality parameters when coupled with the field measurements in order to use in further decision-making mechanisms.
... Comme l'illustre le Tableau 9, la concentration en COD dans les plans d'eau eutrophes évoluent au cours des saisons. Nord (Evans et al., 2005 ;Monteith et al., 2007 ;Clark et al., 2010 ;Delpla, 2011 ; Filella et Rodrigues-Murillo, 2014 ;Toming et al., 2016). Un manque de données dans les pays de l'hémisphère sud ne permet cependant pas de généraliser le phénomène (Filella et Rodrigues- Murillo, 2014). ...
... La MO est divisée en deux fractions : MO particulaire (MOP) et MO dissoute (MOD), en fonction du diamètre des particules. La MOD représente la fraction la plus abondante (90 -95 % d'après Thurman, 1985 ;Toming et al., 2016 ;Song et al., 2018), retrouvée après filtration à 0,45 µm (McDonald et al., 2004). Elle englobe les molécules de dégradation d'organismes morts ainsi que les molécules excrétées. ...
... De nombreuses études ont montré que la concentration moyenne en COD dans les eaux de surface augmente depuis les années 1980 en Europe du Nord (entre 1990 et 2004, jusqu'à > 0,15 mg C.L -1 .an -1 ), dans le centre de l'Europe et en Amérique du Nord (Evans et al., 2005 ;Monteith et al., 2007 ;Clark et al., 2010 ;Delpla, 2011 ;Filella et Rodrigues-Murillo, 2014 ;Toming et al., 2016). Un manque de données dans les pays de l'hémisphère sud ne permet cependant pas de généraliser le phénomène (Filella et Rodrigues- Murillo, 2014). ...
Les phénomènes d’eutrophisation caractérisés par la prolifération de phytoplancton sont à l’origine d‘impacts négatifs sur les écosystèmes aquatiques et les usages de la ressource en eau. Lors de son développement, le phytoplancton génère de la Matière Organique Algale (MOA) qui augmente la concentration et modifie les caractéristiques et la réactivité de la Matière Organique Naturelle (MON) du plan d’eau. Des cyanotoxines peuvent également être générées si des cyanobactéries productrices sont présentes. Le climat futur, prévu par les experts, vient soutenir ces proliférations et en aggraver les conséquences. L’optimisation d’une méthode d’identification et de quantification des microcystines (MCs) extracellulaires par HPLC-UV/PDA après concentration par SPE permet l’analyse à des concentrations jusqu’à 0,1 μg.L-1. Cependant, un pH basique et une charge organique dans l’échantillon surestiment la concentration. La croissance cellulaire et la production de MOA et de MCs sous différents couples température/pluviométrie sont étudiées sur des cultures mono-spécifiques d’algue et de cyanobactérie. Les variations climatiques impactent le développement cellulaire, la quantité et la répartition des fractions hydrophobes de la MOA, la concentration totale en MCs et la proportion de la fraction extracellulaire. L’étude in-situ menée pendant 21 mois sur le plan d’eau hypereutrophe de Pigeard (87) est comparée au suivi de 18 mois de 2012-2013. Les apports récurrents de MOA perturbent annuellement et durablement la dynamique de la MON du plan d’eau, en modifiant ses caractéristiques et augmentant la charge organique et la part de composés hydrophiles. Les évolutions observées pour des ressources en eau sous des climats différents (Suède et Togo) corroborent les observations au laboratoire. Ces évolutions quantitatives et qualitatives de la MON affectent l’efficacité des procédés de traitement des eaux et notamment l’adsorption sur CAP. Les performances du procédé sont diminuées en présence de composés hydrophiles. Un bon rendement a été observé pour l’élimination des MCs malgré une diminution par compétition avec la MO.
... CDOM is the optically active component of dissolved organic carbon (DOC). It is often considered as an indicator for DOC (Brezonik et al. 2015;Toming et al. 2016) which in turn is an important response variable of lakes to climate change (Adrian et al. 2009). Statistical relationships between DOC and CDOM can vary within a lake in space and time due to the variability of external inputs from the catchment or of lake internal production from phytoplankton or macrophytes (Hestir et al. 2015). ...
... Several studies found a strong correlation between DOC and CDOM, e.g. Brezonik et al. (2015), Toming et al. (2016), although seasonal and local variations have to be considered (Hestir et al. 2015). At Lake Kummerow, in situ DOC and MERIS CDOM showed a similar seasonal behaviour during spring/early summer (Fig. 9c). ...
... DOC and, therefore, CDOM originate from lake internal sources, i.e. macrophytes and phytoplankton (autochthonous production), or from soil organic matter and plants from the catchment (allochthonous production; Brezonik et al. 2015). Autochthonous DOC mainly consists of non-humic substances which have lower absorption properties, i.e. a lower influence on CDOM; allochthonous DOC mainly is composed of highly absorbing humic substances and has a high influence on CDOM (Thurman 1985;Toming et al. 2016). Peat bogs and swamps (allochthonous source) bordering the lake may, therefore, explain the relatively high CDOM values, e.g. ...
Monitoring water constituents of lakes using satellites is gaining increasing importance. Image archives of historic satellites represent valuable data sources to analyse the development of constituent concentrations over time and to derive trends. This study presents an analysis of the MERIS archive (2003–2011) using a neural network algorithm (FUB/WeW) to retrieve concentrations of Chlorophyll-a, total suspended matter and absorption by coloured dissolved organic matter (440 nm) at Lake Kummerow. All three constituents showed a clear seasonality: Chlorophyll-a (0.3–45.8 mg/m³) exhibited a spring bloom and multiple blooms during summer. Total suspended matter (0.1–10.0 g/m³) and coloured dissolved organic matter (0.01–0.94 1/m) revealed highest values during summer and lower values during autumn/winter. While total suspended matter (− 1.3 g/m³) and chlorophyll-a (− 3.4 mg/m³) showed a decreasing tendency from 2003 to 2011, coloured dissolved organic matter showed no clear trend. Chlorophyll-a retrieved from MERIS was around 20% higher than in situ measurements. The other constituents (total suspended matter and coloured dissolved organic matter) were obtained by qualitative analysis due to the absence of in situ measurements. This analysis provides a first multi-year time series on these constituents over the whole lake and all seasons. Both, its size and its form, make Lake Kummerow a suitable lake for remote sensing validation activities. Recent and upcoming satellites, especially of the Sentinel missions, will provide further valuable information for integrating remote sensing into lake monitoring.
... At present, studies of the optical properties of DOC increasingly include the specific UV absorbance (SUVA 254 ), the ratio of absorption at 250-365 nm (E 250:365 ), the spectral slopes (S CDOM ), which allow tracing of its source, chemical composition, and molecular weight (De Haan and De Boer 1987;Helms et al. 2008;McKnight et al. 2001;Weishaar et al. 2003). Optical properties of DOC are also widely utilized as proxies of DOC concentration by measuring the fluorescence or absorption coefficients (Rochelle-Newall et al. 2014;Toming et al. 2016;Wen et al. 2016b). We show that although in some lakes DOC concentration can be estimated using CDOM fluorescence or absorption with little error, this is not the case in all lake systems (Rochelle-Newall et al. 2014;Toming et al. 2016;Ylostalo et al. 2014;Zhang et al. 2010;Zhou et al. 2015). ...
... Optical properties of DOC are also widely utilized as proxies of DOC concentration by measuring the fluorescence or absorption coefficients (Rochelle-Newall et al. 2014;Toming et al. 2016;Wen et al. 2016b). We show that although in some lakes DOC concentration can be estimated using CDOM fluorescence or absorption with little error, this is not the case in all lake systems (Rochelle-Newall et al. 2014;Toming et al. 2016;Ylostalo et al. 2014;Zhang et al. 2010;Zhou et al. 2015). ...
... Lots of terrigenous DOM, derived from withered grass, rotten leaves, and vascular plant, would import to the lakes by rain, runoff and flooding. These allochthonous DOM consisted mainly of humic substances, and was refractory to decomposition (Toming et al. 2016), which may be another reason for the higher DOC levels in oligotrophic lakes. However, some studies showed that eutrophic lakes tended to have higher DOC values than meso-and oligotrophic lakes (Sugiyama et al. 2004;Williamson et al. 1999;Yoshioka et al. 2002), because the eutrophic lakes indicated that during phytoplankton blooms, the phytoplankton cell burst could contribute carbohydrates to autochthonous DOC (Ye et al. 2015(Ye et al. , 2010. ...
In limnological environments, most organic carbon is present in the dissolved form. Dissolved organic carbon (DOC) is the main source of energy for microbial metabolism and biosynthesis, and also affects photosynthetic radiation level and the attenuation of ultraviolet irradiation to protect aquatic organisms. There are large differences in DOC concentration, source, and characteristics due to regional variations in water quality and basin characteristics. Reliable estimates of DOC and analysis of optical characteristics are crucial to understand the true role of lakes in the global carbon cycle. In this article, the distribution of DOC across 30 lakes in semi-arid areas of Northern China is reported. The data shows that saline lakes exhibited higher DOC concentrations than freshwater lakes, and the positive relationship between salinity and DOC was established (R² = 0.42, p < 0.01, n = 196). The mean DOC concentration in eutrophic lakes was lower than in mesotrophic and oligotrophic lakes. Analysis of optical characteristics of CDOM indicated that saline lakes in this semi-arid regions contained abundant fulvic acid, and greater levels of autochthonous dissolved organic matter (DOM) with a lower molecular mass than fresh waters. The total suspended matter (TSM) is the main factor influencing on SUVA254 in both freshwater and saline lakes with a negative correlation. SUVA254 was negatively correlated with the salinity only in freshwater lakes, and with pH only in saline lakes. The result suggests that it was doubtful whether CDOM or SUVA254 alone can be a predictor of DOC concentration and other water quality parameters, especially in different types of lakes with different optical and physicochemical characteristics.
... (3) BOD and COD, which indicate OM contents using oxygen consumption through biological and chemical oxidation, respectively (Geerdink et al., 2017;Jiao et al., 2021). (4) Water environment variables such as Chlorophyll-a (Chl-a) and suspended matter concentrations, which are usually correlated with DOC and/or POC contents (Liu et al., 2020a;Toming et al., 2016). ...
... (2) Directly calculating OM from routinely monitored COD using the correlation between OM and COD (Liu et al., 2022a;Virro et al., 2021). (3) Qualitatively indicating OM level using water quality indicators, such as TP, transparency, or trophic state index (Liu et al., 2020b;Toming et al., 2016). ...
... The practical application of remote sensing technology has been demonstrated to be a useful tool for recognizing the physical characteristics of water bodies. Researchers have used various remote sensing platforms, such as satellites, to study water bodies, including lakes, rivers, and reservoirs [8][9][10]. ...
... The reflection coefficient R is defined as the ratio of the water surface radiation to the descending stream radiation directly above the water surface. This feature describes the absorption of light, the associated optical properties of the surface, as well as the scattering properties of the components in the water, as well as the albedo of the bottom and depth [8]. In the process of obtaining bathymetry using satellite observations, the fundamental physical principle is based on the phenomena of light extinction in a water column, as well as bottom reflection and dispersion. ...
... EEM spectra combined with parallel factor analysis of components (PARAFAC) enables quantification of DOC and characterisation (and therefore source delineation) of the constituent molecules 121 . For example, this approach distinguishes humic-like, soil-derived material from autochthonous algae-derived DOC, which is characterised by a higher proportion of amino acids 122 . In soil leachates, the strong relationship between humic-like fluorescence and DOC concentrations is wellknown 123 , and has been used to assess DOC concentrations in alpine lake waters 124 , speleothems 42 , and lake sediments 56 . ...
Despite decades of research, the influence of climate on the export of dissolved organic carbon (DOC) from soil remains poorly constrained, adding uncertainty to global carbon models. The limited temporal range of contemporary monitoring data, ongoing climate reorganisation and confounding anthropogenic activities muddy the waters further. Here, we reconstruct DOC leaching over the last ~14,000 years using alpine environmental archives (two speleothems and one lake sediment core) across 4° of latitude from Te Waipounamu/South Island of Aotearoa New Zealand. We selected broadly comparable palaeoenvironmental archives in mountainous catchments, free of anthropogenically-induced landscape changes prior to ~1200 C.E. We show that warmer temperatures resulted in increased allochthonous DOC export through the Holocene, most notably during the Holocene Climatic Optimum (HCO), which was some 1.5–2.5 °C warmer than the late pre-industrial period—then decreased during the cooler mid-Holocene. We propose that temperature exerted the key control on the observed doubling to tripling of soil DOC export during the HCO, presumably via temperature-mediated changes in vegetative soil C inputs and microbial degradation rates. Future warming may accelerate DOC export from mountainous catchments, with implications for the global carbon cycle and water quality.
... Low values of CDOM/DOC and DOC and CDOM concentrations coincided with high values of A 250 /A 365 , which also indicated a higher share of DOM with low molecular weight and low aromaticity (i.e., autochthonous DOM). In May and July, only half the DOM was allochthonous; however, in late September, almost all the DOM was terrestrially derived, confirming the finding by Toming et al. (2016) that CDOM-DOC coupling varies seasonally in Võrtsjärv. ...
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 general relationship (R 2 =0.61) reported by Massicotte et al. (2017) was across many lakes and a wide DOC range (100-10,000 μmol L -1 ), but significant variability was evident. Studies have shown that the a g (λ)-DOC relationship varies significantly temporally and/or among lakes (Erlandsson et al., 2012;Hestir et al., 2015;Liu et al., 2021;Molot and Dillon, 1997;Toming et al., 2016;Fig. 4B). ...
... Our results show that inter-annual wet-dry periods cause much of the observed inter-annual variability in lake DOC characteristics. The inter-annual variability of lake DOC characteristics observed in the study lakes was larger than studies from northern temperate regions (Sepp et al., 2019;Toming et al., 2016). Although there are many similarities in landscape characteristics of the Boreal Plains ecozone and northern temperate regions, the climate of temperate regions is generally wetter, thereby stabilizing lake water residence times resulting in less inter-annual variability in lake DOC characteristics. ...
Concentration and chemical composition of dissolved organic carbon (DOC) influence several lake functions; greenhouse gas exchange, nutrient cycling, food webs, and water treatability. To assess spatial and inter‐annual controls on DOC characteristics, 34 lakes were sampled annually for 8 years on the Boreal Plains, Western Canada—a region with heterogeneous surficial geology, and a sub‐humid climate with pronounced inter‐annual wet‐dry periods. Large spatial variability in long‐term average DOC concentration (10–49 mg C L⁻¹) and aromaticity (SUVA254: 1.2–3.9 L mg⁻¹ C m⁻¹) among lakes was found. Higher DOC concentrations and aromaticity were associated with lakes in watersheds with fine‐textured surficial geology and with relatively large contributions through shallow, organic‐rich flow paths. Lake DOC aromaticity was also higher in lakes with lower evaporative enrichment, regardless of surficial geology, indicating shorter lake water residence times and less within‐lake degradation of allochthonous DOC. High inter‐annual variability for both DOC and aromaticity was observed, with coefficients of variation at 10.9 ± 4.6% and 11.1 ± 2.5% among lakes, respectively. Inter‐annual variability in DOC concentrations had low synchronicity among lakes, with patterns of variability linked to surficial geology and primarily responsive to short‐term cumulative precipitation. Conversely, inter‐annual variability in aromaticity had high synchronicity among lakes, driven by longer‐term cumulative precipitation and shifts in lake water residence times. Our study shows it is necessary to consider lake hydrogeomorphic setting and climate to understand spatial and inter‐annual variability in lake DOC characteristics and associated lake functions, and that Boreal Plains lakes have high climate sensitivity.
... The predominantly mineral soil is usually a DOC-sorption and mineralisation environment, where DOC might become the soil organic matter (SOM) performing such important pedoecological functions as nutrient cycling, complexation and immobilisation of metals, formation of aggregates, and cation retention (Bäumler and Zech 1997;Flores-Céspedes et al. 2002;Bezerra et al. 2009;Abdolalahi et al. 2014;Liu et al. 2020). Regarding water bodies, a big part of the current environmental problems is linked to increases in DOC-arriving, bringing nutrients that cause eutrophication and affecting limnic ecosystems and water potability (Duan et al. 2014;Seekell et al. 2015;Ye et al. 2015;Mitrovic and Baldwin 2016;Toming et al. 2016). ...
Dissolved organic carbon (DOC) fluxes between environmental compartments are an important component of the global carbon balance and pedoecological processes. Tropical forests are the world’s most productive ecosystems and the forest floor is the main DOC-source in these environments. This study aimed to compare DOC concentrations under the forest floor with different litter-decomposition rates. Four study plots were established along a hillslope profile where heterogeneity was observed in previous studies: drainage divide (DRD); upper-hillslope (UHS); lowerhillslope
(LHS); and valley bottom (VLB). Inversely proportional to the decomposition rates, the litter storage in this profile was as follows: DRD > UHS ≅ LHS > VLB. The bulk precipitation was a DOC source statistically similar to canopy-washing, and DOC concentrations in throughfall were statistically similar among the hillslope positions. There was some dilution effect in the interevent modulation, mainly in throughfall and associated with the rainfall maximum intensity. The
DOC concentrations under the forest floor were related in a non-linear manner with the litter storage: thin stocks in VLB showed lower DOC concentrations, but the thicker stocks in DRD did not materialise in the highest concentrations; the litter storage in UHS and LHS showed higher DOC-concentrations as a result of a balance between maintaining the DOC-source and making new soluble byproducts available that favoured the DOC-release to water.
... Accurate monitoring and understanding of city water quality are vital for scientists, engineers, and policy-makers for efficient decision-making and appropriate engineering interventions (Jayson-Quashigah et al., 2019). Satellite remote sensing has been increasingly applied for the monitoring of inland water quality at large scales and long periods (Li et al., 2017;Toming et al., 2016). For water quality monitoring, turbidity is usually an essential parameter to be retrieved (Nechad et al., 2010). ...
Understanding of turbidity, an indicator of water quality, is of great importance in cities and can have significant implications for human society. Many users are interested in mapping turbidity using remote sensing tools for long-term and large-scale monitoring. This study aims to derive turbidity maps in an urbanizing city and to identify the driving factors for better decision-making and water quality management. Taking Wuhan, the most rapidly urbanizing metropolis in central China, as an instance, the water turbidity is monitored using Landsat observations from 1987 to 2019, and the relationships of turbidity and climatic/human factors are examined. Climatic factors are represented by meteorological conditions (rainfall, wind speed, temperature, and water vapor pressure) and human factors are characterized by the normalized difference vegetation index (NDVI) and impervious surface area (ISA). The results demonstrated that: (1) the seasonal mean turbidity increased from spring to summer (34.28 NTU to 36.27 NTU), decreased in autumn (25.04 NTU), and increased again in winter (37.20 NTU), and the variations were related to changes in rainfall; and (2) the annual mean turbidity was fluctuatingly stable during 1987–2004 and decreased by 1 NTU/yr. since 2005. The decline of water turbidity was highly correlated to the increase of NDVI and ISA with p values <0.01. The study indicates that meteorological conditions affect seasonal variations in turbidity, while human factors have long-term impacts. A cautious approach to human activities during urbanization is needed to achieve a balance between water quality protection and the city’s developments.
... In regression trees, decision rules are set according to the relationship between the input and output variables (Mousavi et al., 2017). Although the general procedure of the BT is complex, it can be applied to various simulation/prediction problems and have better simulation/prediction accuracy than the most conventional models (Elith et al., 2008;Toming et al., 2016). For detailed information about the basic theory of the BT, see Freidman et al. (2000) and França and Cabral (2015). ...
Due to the lack of lysimetric data in many regions, the standard Penman‐Monteith equation adopted FAO (FAO56‐PM model) is usually used for calculating the reference evapotranspiration (ETo). However, as this model needs lots of meteorological parameters that cannot be easily obtained in many regions, other simple models along with the soft computing models are used for obtaining ETo values. The current paper presents a comprehensive comparison of 12 soft computing models, gene expression programming (GEP), neuro fuzzy with grid partitioning (NF‐GP), neuro fuzzy with sub‐clustering (NF‐SC), multi‐variate adaptive regression spline (MARS), boosted regression tree (BT), random forest (RF), model tree (MT), support vector machine (SVM), SVM‐firefly algorithm (SVM‐FA), extreme learning machine (ELM), neural network‐particle swarm optimization (NN‐PSO) and neural network‐differential evolution (NN‐DE), for estimating daily ETo values in humid regions. So, daily meteorological data from two weather stations (during a 12‐years period) were used to assess the models. The obtained results revealed that a very good efficiency was obtained from all the applied methods. The temperature‐based SVM‐FA (root mean square error, RMSE = 0.324 mm and Nash‐Sutcliffe coefficient, NS = 0.960) and NF‐GP (RMSE = 0.272 mm and NS = 0.974) models generally provided the best accuracy in estimating ETo of Sari and Bablosar, respectively. The accuracy ranks of the other models (from the best to worst) were found as NN‐PSO, NF‐SC, ELM, NN‐DE, MARS, GEP, RF, SVM, BT and MT. Among the radiation‐based models, the NF‐GP provided the best accuracy in estimating ETo of both stations. The other models were ranked as ELM, SVM‐FA, NN‐DE, NN‐PSO, MARS, RF, BT, NF‐SC, SVM and MT, respectively. This article is protected by copyright. All rights reserved.
... À dinâmica de COD associa-se, por exemplo, a qualidade química e estrutura/dinâmica trófica da água de lagos (Ye et al., 2015;Toming et al., 2016) e reservatórios para o abastecimento humano afetados diretamente pela sua presença excessiva (Hestir, et al., 2015;Massicote et al., 2017). Também há a influência indireta pelo controle exercido sobre mobilidade espacial de contaminantes, em virtude da competição entre ambas pelos sítios de sorção à superfície das partículas minerais do solo (Céspedes et al., 2002;Marques et al., 2017;Favorito et al., 2018). ...
O fluxo de matéria orgânica é um componente importante da dinâmica de ecossistemas e dos impactos ambientais. A água da chuva, ao percolar os ambientes terrestres, transporta partículas orgânicas das quais as menores têm maior mobilidade espacial e são mais ativas do ponto de vista ecológico, sendo chamadas de dissolvidas quando menores que 0,45 µm na maioria dos estudos recentes. A dinâmica de carbono orgânico dissolvido (COD) inclui entradas atmosféricas de moléculas alóctones, tanto pela deposição úmida vinculada à chegada direta via chuva e que pode ser observada pela concentração de COD na precipitação inicial, quanto pela deposição seca originada pela lavagem da biomassa viva onde se acumulam poeiras orgânicas de origem atmosférica, a qual pode ser observada na precipitação atravessada. Nesta segunda, também há a presença de COD originado por exsudatos solúveis secretados pela própria vegetação. Nas deposições úmida e seca, é mais relevante a condição atmosférica vinculada à influência de atividades industriais e centros urbanos, do que a produtividade dos ecossistemas em si. Ao percolar e lixiviar os estoques de serrapilheira a água da chuva atinge as maiores concentrações de COD, onde a dinâmica de produtividade e decomposição de cada ecossistema torna-se preponderante. Quando infiltra o horizonte mineral do solo o COD pode adsorver-se às partículas minerais, reduzindo sua concentração na solução do solo gradativamente com o aumento da profundidade. Quando ocorrem escoamentos superficiais, ficam reduzidas as oportunidades de adsorção do COD ao solo, resultando em aumento das transferências dos ecossistemas terrestres para os aquáticos. A B S T R A C T The flows of organic matter are an important part of the ecosystem dynamics and environmental impacts. Rainwater, when percolating through terrestrial environments, transports organic particles, of which the smallest ones have greater spatial mobility and are more ecologically active. These particles are considered dissolved when smaller than 0.45 μm in most recent studies. The dynamics of dissolved organic carbon (DOC) involves the atmospheric input of allochthonous molecules, due to the wet deposition associated with rainfall, which can be observed in the DOC concentration in the initial precipitation, as well as by the dry deposition caused by the washing of living biomass where organic dust of atmospheric origin accumulates, which can be observed in the throughfall fluxes. In the later, there is also the presence of DOC originated by soluble exudates secreted by the vegetation itself. About wet and dry depositions, the atmospheric condition associated with the influence of industrial activities and urban centers is more relevant than the productivity of the ecosystems themselves. When percolating and leaching the litter stocks, rainwater reaches the highest concentrations of DOC, where the dynamics of productivity and decomposition of each ecosystem becomes preponderant. When it infiltrates the soil mineral horizon the DOC can adsorb to the mineral particles, reducing its concentration in the soil solution gradually as the depth increases. With the occurrence of surface runoff, opportunities for adsorption of DOC to the soil are reduced, resulting in increased transfer from terrestrial to aquatic ecosystems. Key-words: Dissolved organic carbon; forest leaching; geoecology
... A number of previous studies have analyzed the impacts of the mixing processes of shallow lakes or reservoirs on certain water constituents [17][18][19][20][21]; however, they were often confined to short periods of time or based on relatively low-frequency measurements. With regards specifically to DOM, previous studies relied on laboratory measurements of its chemical and optical properties [22][23][24]. Typically, these rely on manual field water sampling, which for the location of this study, are undertaken on a monthly basis. ...
A good understanding of the physical processes of lakes or reservoirs, especially of those providing drinking water to residents, plays a vital role in water management. In this study, the water circulation and mixing processes occurring in the shallow, subtropical Tingalpa Reservoir in Australia have been investigated. Bathymetrical, meteorological, chemical and physical data collected from field measurements, laboratory analysis of water sampling and an in-situ Vertical Profile System (VPS) were analysed. Based on the high-frequency VPS dataset, a 1D model was developed to provide information for vertical transport and mixing processes. The results show that persistent high air temperature and stable reservoir water depth lead to a prolonged thermal stratification. Analysis indicates that heavy rainfalls have a significant impact on water quality when the dam level is low. The peak value of Dissolved Organic Carbon (DOC) concentration occurred in the wet season, while the specific UV absorbance (SUVA) value decreased when solar radiation increased from spring to summer. The study aims to provide a comprehensive approach for understanding and modelling the water mixing processes in similar lakes with high-frequency data from VPS’s or other monitoring systems.
... CDOM is the colored (optically active) fraction of the dissolved organic matter (DOM) of waters, consisting mostly of humic and fulvic acids. Although CDOM is considered as an indicator of DOM [10,11], its origin can vary, as the amount of CDOM is affected by external factors and diffuse sources from the catchment. CDOM in waters is autochtonous, i.e., coming from degradation of algae or macrophytes in the given water body, and/or allochtonous, i.e., coming from the catchment area. ...
The Ocean and Land Color Instrument (OLCI) onboard Sentinel 3A satellite was launched in February 2016. Level 2 (L2) products have been available for the public since July 2017. OLCI provides the possibility to monitor aquatic environments on 300 m spatial resolution on 9 spectral bands, which allows to retrieve detailed information about the water quality of various type of waters. It has only been a short time since L2 data became accessible, therefore validation of these products from different aquatic environments are required. In this work we study the possibility to use S3 OLCI L2 products to monitor an optically highly complex shallow lake. We test S3 OLCI-derived Chlorophyll-a (Chl-a), Colored Dissolved Organic Matter (CDOM) and Total Suspended Matter (TSM) for complex waters against in situ measurements over Lake Balaton in 2017. In addition, we tested the machine learning Gaussian process regression model, trained locally as a potential candidate to retrieve water quality parameters. We applied the automatic model selection algorithm to select the combination and number of spectral bands for the given water quality parameter to train the Gaussian Process Regression model. Lake Balaton represents different types of aquatic environments (eutrophic, mesotrophic and oligotrophic), hence being able to establish a model to monitor water quality by using S3 OLCI products might allow the generalization of the methodology.
... Chichester Reservoir, during the fieldwork period. A possible reason for this result may be that the relationship between absorbance indices and DOC largely depends on basin morphology, and therefore could only be applied in large-scale studies among basins (Toming et al., 2016). The watershed size and structure largely affects the hydrologic residence time (HRT) and organic carbon degradation processes in the waterbody. ...
... In Taihu Lake (Mao et al., 2008), the temporal variations of the eutrophication dynamics are significantly influenced by the meteorological forcing, which played an important role in the spatial distribution of the algae blooms. The same results are found in other studies (Lamote et al., 2012;Kaire et al., 2016). ...
It is pressing to investigate the influence factors of eutrophication in Dongting Lake, which is the second largest freshwater lake in China and is faced with more and more serious eutrophication problems by natural and man-made factors in recent years. In this study, a new multivariate analysis approach integrating the maximum likelihood estimation structural equation modelling (ML-SEM) with neural network method is proposed. Twenty-seven variables indicating water quality from 2005 to 2012 were derived from the Dongting Lake Ecological Environment Monitoring Center of Hunan Province. The results showed that: (1) temperature (T) and hydraulic gradient (HG) had the most positive influence on chlorophyll-a (Chl-a) with a sensitivity ratio of 1.218 and 1.039, respectively, (2) transparency (SD) had the most negative effect on Chl-a concentration and (3) Chl-a increased quickly and reached the highest level when total phosphorus (TP) levels were from 0.08 mg/L to 0.12 mg/L. These results would provide guidance for eutrophication control strategies for Dongting Lake. By combining ML-SEM with artificial intelligence technique such as neural network, this study examined the causal and nonlinear relationships involved in the eutrophication process.
... In Taihu Lake (Mao et al., 2008), the temporal variations of the eutrophication dynamics are significantly influenced by the meteorological forcing, which played an important role in the spatial distribution of the algae blooms. The same results are found in other studies (Lamote et al., 2012;Kaire et al., 2016). ...
... The photolysis of organic matter was shown to supply CH 4 to the surface waters at relatively low rates in Saguenay River (4.36 × 10 −6 mol m −2 yr −1 ) 53 . Such a process would directly relate to the trophic state (i.e., clarity) 54 . In Lake Hallwil, this seems supported by the light penetration/CH 4 production curve relationship ( Fig. 7; Supplementary Fig. 5a). ...
Oxic lake surface waters are frequently oversaturated with methane (CH 4). The contribution to the global CH 4 cycle is significant, thus leading to an increasing number of studies and stimulating debates. Here we show, using a mass balance, on a temperate, mesotrophic lake, that ~90% of CH 4 emissions to the atmosphere is due to CH 4 produced within the oxic surface mixed layer (SML) during the stratified period, while the often observed CH 4 maximum at the thermocline represents only a physically driven accumulation. Negligible surface CH 4 oxidation suggests that the produced 110 ± 60 nmol CH 4 L −1 d −1 efficiently escapes to the atmosphere. Stable carbon isotope ratios indicate that CH 4 in the SML is distinct from sedimentary CH 4 production, suggesting alternative pathways and precursors. Our approach reveals CH 4 production in the epilimnion that is currently overlooked, and that research on possible mechanisms behind the methane paradox should additionally focus on the lake surface layer.
... However, unlike previous studies ( Vantrepotte et al., 2015Fichot et al., 2011, the relationship between DOC and a CDOM is invalid (DOC = 0.32 * a CDOM + 3.42, R 2 = 0.31, Fig. 7A). This may be because the optically active matter (CDOM) in DOC is not the primary component of DOC or the DOC includes a large amount of bleached CDOM (Zhang et al., 2006;Hestir et al., 2015;Tominga et al., 2016). R rs (λ) is highly correlated to DOC levels; the positive correlation coefficient reached 0.4 (700 nm) in August of 2014 and the negative correlation coefficient reached −0.72 (440 nm) in October of 2014 (Fig. 7B). ...
Field measurements of dissolved organic carbon (DOC) concentration and remote-sensing reflectance were conducted to develop a regional, empirical red-blue algorithm to retrieve surface DOC from Geostationary Ocean Color Imager (GOCI) data for Lake Taihu, China. The auxiliary data (in-situ observations of the optical properties and water quality, buoy measurements of hydrodynamic data and water chemical parameters) were used to investigate the spatial and temporal variations in DOC. GOCI was shown to be capable of successfully obtaining hourly variations in DOC, with a root mean square error percentage (RMSP) of 17.29% (RMSE = 0.69 mg/L) for the match-up data. The GOCI-derived DOC in Lake Taihu confirms that the highest DOC concentration is in northwest Lake Taihu, followed by Meiliang Bay, Gonghu Bay and northeast Lake Taihu. Hourly DOC variation is significant and presents a different trend for each lake segment due to the variety of influencing factors. Discharge of DOC from surrounding rivers is an important factor to the variation of DOC in northeast Lake Taihu. However, organic products of algae will be the primary contributor to DOC when algal bloom occurred. During the period of algal bloom, high DOC levels in Lake Taihu can lead to hypoxia when coupled with high temperatures and low disturbance.
... Fitting numerous trees in BT defeats the greatest disadvantage (poor prediction accuracy) of single tree models. In spite of the fact that BRT is complex, it can be outlined in ways that provide powerful ecological understanding, and its prediction accuracy is better than the most conventional modelling approaches (Elith et al., 2008;Toming et al., 2016). As a recently created class of analytical calculation, BT has not yet observed broad application the hydrological sciences, in spite of the fact that uses of this data intensive strategy have expanded in the last decade (e.g., Tisseuil et al., 2010;Erdal and Karakurt, 2013;Rice et al., 2015;Rice et al., 2016). ...
Soil bulk density (BD) is very important factor in land drainage and reclamation, irrigation scheduling (for estimating the soil volumetric water content), and assessing soil carbon and nutrient stock as well as determining the pollutant mass balance in soils. Numerous pedotransfer functions have been suggested so far to relate the soil BD values to soil parameters (e.g. soil separates, carbon content, etc). The present paper aims at simulating soil BD using easily measured soil variables through heuristic gene expression programming (GEP), neural networks (NN), random forest (RF), support vector machine (SVM), and boosted regression trees (BT) techniques. The statistical Gamma test was utilized to identify the most influential soil parameters on BD. The applied models were assessed through k-fold testing where all the available data patterns were involved in the both training and testing stages, which provide an accurate assessment of the models accuracy. Some existing pedotransfer functions were also applied and compared with the heuristic models. The obtained results revealed that the heuristic GEP model outperformed the other applied models globally and per test stage. Nevertheless, the performance accuracy of the applied heuristic models was much better than those of the applied pedotransfer functions. Using k-fold testing provides a more-in-detail judgment of the models.
... According to Toming et al. (2013), there is a lack of data about the DOC-CDOM relationship in eutrophic inland waters, where autochthonous DOC may form a considerable fraction of the total DOC pool when compared to allochthonous DOC. Autochthonous DOC is produced by phytoplankton and other photosynthetic organisms and the allochthonous from vascular plants and soil organic matter of the catchment area (Toming et al. 2016). ...
Through exchange of heat between the water and the atmosphere inland waters affect climate at the regional scale and play an important role in the global carbon cycle. Therefore, there is a need to develop methods and models for mapping inland water carbon content to understand the role of lakes in the global carbon cycle. The colored dissolved organic matter (CDOM) has a strong correlation with dissolved organic carbon (DOC) and can be studied using remote sensed images. In this work, we developed an empirical model to estimate the DOC concentration by using the absorption coefficient of CDOM (aCDOM). The aCDOM was estimated through band ratio index and validated with in situ data. The empirically adjusted model to estimate the DOC was applied to a series of OLI/Landsat-8 images. The results showed a good relationship between the aCDOM at 412 nm (aCDOM412) and the ratio between OLI band 1 and OLI band 3, but the validation results showed a normalized root mean square error (NRMSE) of about 37.89%. The aCDOM412 obtained in laboratory was used to establish a relationship between aCDOM412 and DOC. The DOC spatial distribution was then obtained and the concentration varied from 22 to 52 mg.l⁻¹ during the year of 2014.
... The DOC concentration during the spring freshet and summer discharge is markedly higher, but is lower in autumn [20,24]. In addition, Toming et al. found that CDOM did not appear to be a good predictor of the seasonality of the DOC concentration in large boreal lakes since the CDOM-DOC coupling varied seasonally [25]. Hestir et al. studied six manmade reservoirs in Australia along a temperate to tropical gradient and did not find a good correlation between the CDOM and DOC [26]. ...
Spectral characteristics of CDOM (Chromophoric dissolved organic matter) in water columns are a key parameter for bio-optical modeling. Knowledge of CDOM optical properties and spatial discrepancy based on the relationship between water quality and spectral parameters in the Yinma River watershed with in situ data collected from highly polluted waters are exhibited in this study. Based on the comprehensive index method, the riverine waters showed serious contamination; especially the chemical oxygen demand (COD), iron (Fe), manganese (Mn), mercury (Hg) and dissolved oxygen (DO) were out of range of the contamination warning. Dissolved organic carbon (DOC) and total suspended matter (TSM) with prominent non-homogenizing were significantly high in the riverine waters, but chlorophyll-a (Chl-a) was the opposite. The ternary phase diagram showed that non-algal particle absorption played an important role in total non-water light absorption (>5 0%) in most sampling locations, and mean contributions of CDOM were 13% and 22% in the summer and autumn, respectively. The analysis of the ratio of absorption at 250-365 nm (E250:365) and the spectral slope (S275-295) indicated that CDOM had higher aromaticity and molecular weight in autumn than in summer, which is consistent with the results of water quality and the CDOM relative contribution rate. Redundancy analysis (RDA) indicated that the environmental variables OSM (Organic suspended matter) had a strong correlation with CDOM absorption, followed by heavy metals, e.g., Mn, Hg and Cr⁶⁺. However, for the specific UV absorbance (SUVA254), the seasonal values showed opposite results compared with the reported literature. The potential reasons were that more UDOM (uncolored dissolved organic matter) from human sources (wastewater effluent) existed in the waters. Terrigenous inputs simultaneously are in relation to the aCDOM(440)-DOC relationship with the correlation coefficient of 0.90 in the summer (two-tailed, p < 0.01), and 0.58 in the autumn (two-tailed, p < 0.05). Spatial distribution of the CDOM parameters exhibited that the downstream regions focused on dry land have high CDOM molecular weight and aromatic hydrocarbon. Partial sampling locations around the cities or countries generally showed abnormal values due to terrigenous inputs. As a bio-optical model parameter, the spectral characteristic of CDOM is helpful in adjusting the derived algorithms in highly polluted environments. The study on organic carbon and pollutants in highly polluted waters had an important contribution to global carbon balance estimation and water environment protection.
... Therefore , appropriate quantitative and qualitative descriptions of the optical properties of CDOM are crucial for the ocean color remote sensing of aquatic environments. The CDOM absorption coefficient is a very reliable predictor of the dissolved organic carbon concentration in fresh and estuarine waters (Brezonik et al., 2015; Kutser et al., 2015; Toming et al., 2016 ), and therefore this optical parameter could be easily applied to various aspects of organic carbon biogeochemistry. Ocean color remote sensing offers new operational satellite missions based on medium ground resolution (of the order of 250 m) sensors, like the European Earth Observation Copernicus program Sentinel- 3 Ocean and Land Colour Instrument (OLCI) mission, and the US Joint Polar Satellite System program Visible Infrared Imaging Radiometer Suite (VIIRS) sensors. ...
This study presents three alternative models for estimating the absorption properties of Chromophoric Dissolved Organic Matter aCDOM(). For this analysis we used a database containing 556 absorption spectra measured in 2006 – 2009 in different regions of the Baltic Sea (open and coastal waters, the Gulf of Gdańsk and the Pomeranian Bay), at river mouths, in the Szczecin Lagoon and also in three lakes in Pomerania (Poland) – Obłęskie, Łebsko and Chotkowskie. The variability range of the CDOM absorption coefficient at 400 nm, aCDOM(400), lay within 0.15 – 8.85 m-1. The variability in aCDOM() was parameterized with respect to the variability over three orders of magnitude in the chlorophyll a concentration Chla (0.7 – 119 mg m-3). The chlorophyll a concentration and aCDOM(400) were correlated, and a statistically significant, non-linear empirical relationship between these parameters was derived (R2=0.83). On the basis of the co-variance between these parameters, we derived two empirical mathematical models that enabled to design the CDOM absorption coefficient dynamics in natural waters and reconstruct the complete CDOM absorption spectrum in the UV and visible spectral domains. The input variable in the first model was the chlorophyll a concentration, and in the second one it was aCDOM(400). Both models were fitted to a power function, and a second-order polynomial function was used as the exponent. Regression coefficients for these formulas were determined for wavelengths from 240 to 700 nm at 5 nm intervals. Both approximations reflected the real shape of the absorption spectra with a low level of uncertainty. Comparison of these approximations with other models of light absorption by CDOM demonstrated that our parameterizations were superior (bias from -1.45% to 62%, RSME from 22% to 220%) for estimating CDOM absorption in the optically complex waters of the Baltic Sea and Pomeranian lakes.
... Surprisingly, the correlation with DOC was even higher (R 2 = 0.92) than with CDOM. If in many lakes the correlation between DOC and its colored component is very strong [38,45,46] then in Estonian lakes the relationship is varying seasonally [47,48]. Moreover, it has been shown [49] that iron bound to carbon molecules absorbs light in a similar way like CDOM and variable carbon to iron ratio makes remote sensing mapping of lake DOC more complicated. ...
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.
... Our results, which are based on Landsat 8 data, field data based algorithms assessment by Zhu et al. (2014), and other CDOM remote sensing studies , Kutser, Pierson, Tranvik, et al. 2005Del Castillo and Miller 2008;Ficek, Zapadka, and Dera 2011), suggest that global mapping of lake CDOM with a simple green-red band ratio calculated from multispectral satellites (such as Landsat 8) data is plausible. Many studies have shown that there is often good correlation between lake a CDOM (400) and C DOC (Tranvik 1990;Kallio 1999;Brezonik et al. 2015;Kutser, Verpoorter, et al. 2015;Toming et al., forthcoming), even if this is not the case for a single lake. This suggests that mapping of global lake carbon content using CDOM as a proxy is possible. ...
Landsat 8 is the first Earth observation satellite with sufficient radiometric and spatial resolution to allow global mapping of lake CDOM and DOC (coloured dissolved organic matter and dissolved organic carbon, respectively) content. Landsat 8 is a multispectral sensor however, the number of potentially usable band ratios, or more sophisticated indices, is limited. In order to test the suitability of the ratio most commonly used in lake carbon content mapping, the green–red band ratio, we carried out fieldwork in Estonian and Brazilian lakes. Several atmospheric correction methods were also tested in order to use image data where the image-to-image variability due to illumination conditions would be minimal. None of the four atmospheric correction methods tested, produced reflec-tance spectra that matched well with in situ measured reflec-tance. Nevertheless, the green–red band ratio calculated from the reflectance data was in correlation with measured CDOM values. In situ data show that there is a strong correlation between CDOM and DOC concentrations in Estonian and Brazilian lakes. Thus, mapping the global CDOM and DOC content from Landsat 8 is plausible but more data from different parts of the world are needed before decisions can be made about the accuracy of such global estimation.
Lakes play a crucial role in the global biogeochemical cycles through the transport, storage, and transformation of different biogeochemical compounds. Their regulatory service appears to be disproportionately important relative to their small areal extent, necessitating continuous monitoring. This study leverages the potential of optical remote sensing sensors, specifically Sentinel-2 Multispectral Imagery (MSI), to monitor and predict water quality parameters in lakes. Optically active parameters, such as chlorophyll a (CHL), total suspended matter (TSM), and colored dissolved matter (CDOM), can be directly detected using optical remote sensing sensors. However, the challenge lies in detecting non-optically active substances, which lack direct spectral characteristics. The capabilities of artificial intelligence applications can be used in the identification of optically non-active compounds from remote sensing data. This study aims to employ a machine learning approach (combining the Genetic Algorithm (GA) and Extreme Gradient Boost (XGBoost)) and in situ and Sentinel-2 Multispectral Imagery data to construct inversion models for 16 physical and biogeochemical water quality parameters including CHL, CDOM, TSM, total nitrogen (TN), total phosphorus (TP), phosphate (PO4), sulphate, ammonium nitrogen, 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), and the biomasses of phytoplankton and cyanobacteria, pH, dissolved oxygen (O2), water temperature (WT) and transparency (SD). GA_XGBoost exhibited strong predictive capabilities and it was able to accurately predict 10 biogeochemical and 2 physical water quality parameters. Additionally, this study provides a practical demonstration of the developed inversion models, illustrating their applicability in estimating various water quality parameters simultaneously across multiple lakes on five different dates. The study highlights the need for ongoing research and refinement of machine learning methodologies in environmental monitoring, particularly in remote sensing applications for water quality assessment. Results emphasize the need for broader temporal scopes, longer-term datasets, and enhanced model selection strategies to improve the robustness and generalizability of these models. In general, the outcomes of this study provide the basis for a better understanding of the role of lakes in the biogeochemical cycle and will allow the formulation of reliable recommendations for various applications used in the studies of ecology, water quality, the climate, and the carbon cycle.
This study provides an overview of the techniques, shortcomings, and strengths of remote sensing (RS) applications in the effective retrieval and monitoring of water quality parameters (WQPs) such as chlorophyll-a concentration, turbidity, total suspended solids, colored dissolved organic matter, total dissolved solids among others. To be effectively retrieved by RS, these WQPs are categorized as optically active or inactive based on their influence on the optical characteristics measured by RS sensors. RS applications offer the opportunity for decisionmakers to quantify and monitor WQPs on a spatiotemporal scale effectively. The use of RS for water quality monitoring has been explored in many studies using empirical, analytical, semi-empirical, and machine-learning algorithms. RS spectral signatures have been applied for the estimation of WQPs using two categories of RS, namely, microwave and optical sensors. Optical RS, which has been heavily applied in the estimation of WQPs, is further grouped as spaceborne and airborne sensors based on the platform they are on board. The choice of a particular sensor to be used in any RS application depends on various factors including cost, and spatial, spectral, and temporal resolutions of the images. Some of the known satellite sensors used in the literature and reviewed in this paper include the Multispectral Instrument aboard Sentinel-2A/B, Moderate Resolution Imaging Spectroradiometer, Landsat Thematic Mapper, Enhanced Thematic Mapper, and Operational Land Imager.
MODIS surface reflectance product (R_land) has been used to monitor waters due to its free availability and higher spatial resolution than MODIS ocean bands. However, its applicability in aquatic remote sensing has not been sufficiently assessed. Some fundamental questions such as the following need to be addressed: How does the R_land product perform in global inland and coastal waters? What water color parameters can be mapped using R_land? This study provided a comprehensive evaluation of the performance of MODIS R_land products against a field optical dataset containing 4143 reflectance spectra, 2320 chlorophyll-a (Chla) samples, and 1467 suspended particulate matter (SPM) samples across global nearshore coastal and inland waters. The results showed that R_land significantly overestimated remote sensing reflectance, particularly in the bands of 469 nm and 859 nm. The noticeable negative values and patchiness were found in the R_land imagery, and existing algorithms did not estimate satisfactory Chla and SPM from R_land across the global inland and coastal waters. Furthermore, we tested popular machine-learning approaches, such as random forest (RF), support vector machine, XGBoost, and deep neural networks, to examine the potential of the R_land product in estimating SPM and Chla. Machine learning models were found to outperform the state-of-the-art algorithms for SPM retrievals from R_land. Specifically, RF and XGBoost showed the best performance with mean absolute errors of ~25.0% and mean absolute percentage error of ~23% for a broad SPM range of 10–500 mg L⁻¹. Yet, machine learning models cannot retrieve reliable Chla from R_land with approximately 55% uncertainty due to the limited spectral information and uncertainty of R_land products. This implicated that R_land might be able to quantify the parameters that are closely related to SPM (e.g., water clarity and extinction coefficients) in most waters; however, it is challenging to quantify pigments like Chla in waters from R_land. We conclude that R_land might not be an optimal data source for monitoring inland and coastal waters, despite the ease of using this product and its higher spatial resolution than the MODIS ocean bands.
Dissolved organic matter (DOM) is an abundant and mobile part of the aquatic environment and plays important roles in aquatic biogeochemical cycles and the global carbon cycle. Recently, eutrophication has become an important environmental issue in global lakes, but how eutrophication drives changes in the molecular composition of DOM along trophic gradients remains poorly understood. We thus characterized 67 DOM isolates from 11 lakes along a trophic gradient in China by using a combined approach including absorption spectroscopy, excitation-emission matrix fluorescence and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Our results indicated that dissolved organic carbon and absorption coefficients at 350 nm increased with increasing trophic status index. The ultraviolet absorbance at 254 nm and fluorescence intensity of all fluorescent components were higher in eutrophic lakes than in oligotrophic lakes. DOM in high trophic state lakes tended to be dominated by higher molecular weight, unsaturation degree, greater abundance of S-containing compounds, and condensed or polycyclic aromatic compounds than oligotrophic lakes. Additionally, autochthonous DOM characterized by more aliphatic compounds increased with the increasing trophic state. We concluded that nutrient input along with allochthonous DOM favors the lake eutrophication and subsequently increases the release and accumulation of autochthonous DOM. Consequently, eutrophication modifies the structure of the organic matter into more complex materials with increased input of allochthonous DOM and increased release of autochthonous DOM, which could accelerate global carbon cycle processes. Our results here have potential to contribute significantly to future studies of DOM dynamics in eutrophic lakes.
Dissolved organic carbon (DOC) is an important fraction of organic carbon (OC) that together with colored dissolved organic matter (CDOM) plays a key role in the carbon cycling of lakes. Lake Võrtsjärv is a large and shallow eutrophic lake where water quality measurements have been carried out for a long time. The monthly characteristics of DOC and CDOM in Võrtsjärv and its input/output rivers were traced in 5-years observations. We attempted to link the hydro-morphological indices as lake area (A), water level (WL) and volume variations (Qc) with lake DOC fluxes and CDOM-DOC relationships to improve understanding of carbon fluxes in a very shallow, large and highly eutrophic lake, as well as of the possibility to estimate DOC fluxes by CDOM via remote sensing. The research questions were: how the properties and quantity of DOC, its fluxes and CDOM-DOC relationship in a very shallow, large and highly eutrophic lake are responding to 1) variable proportions of allochthonous and autochthonous processes and 2) changing hydrological conditions. The increased lake volume variation in spring caused the higher level of CDOM, signifying the terrestrial (allochthonous) DOC (DOCAlloch) domination in Lake Võrtsjärv. The proportion of DOCAlloch increased together with increasing WL, A and CDOM concentration. Although the generally high proportion of DOCAlloch in Võrtsjärv, the autochthonous DOC determines the water color (CDOM/DOC) in this highly productive ecosystem with short residence time (280-365 days). Our study on DOC flux revealed that the internal carbon sources, driven by hydrological factors, contribute significantly to the role of large and shallow lakes in global carbon cycling. The further development of water color remote sensing could provide novel directions for understand the feedbacks of lake DOC flux and changing hydrology.
Dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) in rivers and reservoirs on the western Loess Plateau, which is an area of severe soil erosion, were investigated in September 2017 to analyze the CDOM characteristics and composition, DOC distribution and influence of environmental factors on these parameters. Great differences of water parameters were exhibited between different groups based on the analysis of variance (p < 0.01). The results indicated that rivers exhibited higher DOC concentrations (mean: 3.70 mg/L) than reservoir waters (mean: 2.04 mg/L). Artificial and agricultural lands exert a large influence on DOC concentrations, which verifies the hypothesis that intense anthropogenic activity results in high DOC concentrations. The CDOM absorption at 350 nm [aCDOM(350)] of tributary water samples was 2.73 m−1, which was higher than that in the Yellow River (1.71 m−1) and reservoir waters (1.33 m−1). The effects of DOC, TC and Tur on CDOM are positive and significant (p < 0.05) according to the multiple linear regressions. An analysis of the optical characteristics of CDOM indicated that waters on the Loess Plateau contained abundant humic acid and higher levels of allochthonous DOM with a higher molecular weight (MW) based on the spectral slopes (S) and specific UV absorbance (SUVA254) values.
The spectral characteristics of optically active constituents in water are key parameters in bio‐optical modelling. Light absorption by phytoplankton [aph(λ)], nonalgal particles (NAPs) [aNAP(λ)], and chromophoric dissolved organic matter (CDOM) [aCDOM(λ)] was investigated at 28 sites in the Wuding River (WDR) during the abundant river flow period (AP) in July 2017 and the normal river flow period (NP) in May 2018. The water quality parameters in the WDR substantially differed between the AP and NP. The dissolved organic carbon and turbidity were high in the NP, and chlorophyll a (Chl‐a), total suspended matter (TSM), dissolved oxygen concentrations and electrical conductivity were low in the AP. ap(675) and Chl‐a were more strongly correlated in the NP (r=0.96) than in the AP (r=0.41). aNAP(440) and aNAP(675) were strongly correlated with TSM (r=0.98 and 0.97) in the AP but weakly correlated in the NP. Moreover, aph(λ) was positively correlated with Chl‐a in both the AP and NP. In addition, aCDOM(440) was significantly correlated with Chl‐a (r=0.62, p<.001) in the NP but not the AP. TSM was weakly correlated with aCDOM(440) in both the AP and NP. The S275‐295 values in the NP (0.0147‐0.020 nm‐1) were lower than those in the AP, demonstrating that the molecular weights were higher in the AP than in the NP. The photosynthetically active radiation absorption of most samples was dominated by the NAPs and CDOM, implying a crucial role in light attenuation in highly turbid inland rivers on the Loess Plateau.
This paper discusses raw water quality results for the raw water from Vaalkop dam reservoir in South Africa. A time series analysis was conducted for various parameters over a prolonged period of time. The analysis indicates that apart from conductivity and coliform counts, most parameters were below their recommended threshold levels for the greatest part of the study period.
Recent studies indicate that inland waters play a very important role in the global carbon cycle. Inland water bodies are the main source of drinking water in many parts of the world and important resource for aquaculture and tourism. Neither determining the true role of lakes in the global carbon cycle nor monitoring lake water quality in real time are possible without using remote sensing. The optically active part of carbon that can be detected by remote sensing is colored dissolved organic matter (CDOM). This chapter discusses the importance of carbon in inland waters, its optical properties, and the performance of different empirical and model based approaches in retrieval of the amount of CDOM.
This paper discusses raw water quality results for the raw water from Bospoort dam in South Africa. A time series analysis was conducted for various parameters over a prolonged period of time. It was revealed that apart from conductivity, hardness, and high coliform counts, most parameters were below their recommended threshold levels for the greatest part of the study period.
Temporal variation in dissolved organic carbon (DOC) and water color (light absorption at 440 nm) was measured in 20 lakes in northern Michigan that varied in DOC, pH, morphometry, and relative productivity as indicated by chlorophyll and total phosphorus (TP). Monthly observations during May-August over 6 yr revealed that DOC and color varied by 6- and 28-fold among lakes and varied substantially through time within lakes. The pattern of temporal variation differed among years but was synchronous among lakes. Of the 190 possible correlations among lake time series, most were positive for DOC (158) and color (160), and 50% of the positive correlations were significant (P < 0.05). Other variables, such as total phosphorus, chlorophyll, and pH, were less synchronous and had fewer significant positive correlations (13-25%). Temporal dynamics in DOC and color were related to ice-out date as well as spring and summer precipitation. Years of late ice-out and high spring rain were associated with high DOC and color in spring. A summer drought in one year lead to declines in color (up to 40%;) and DOC (up to 38%) in nearly all of the lakes. The common temporal dynamics of DOC and color were most likely the result of climatic conditions that affected loading of allochthonous carbon as well as losses due to photodegradation. The variations in DOC were sufficient to cause large changes in light penetration, standing stocks of carbon, and ecosystem metabolism.
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.
Lake Taihu, high-molecular-weight dissolved organic matter (HMW-DOM), with sizes between 1 kDa and 0.2 mu m, were collected using cross-flow ultrafiltration, from three different eutrophic regions. The DOC, and HMW-DOC concentrations, as well as environmental factors, including water temperature, nitrate, phosphate, and Chlorophyll-a (Chl-a), were analyzed. A significant negative relationship was observed between Chl-a and nitrate concentration, suggesting that cyanobacterial bloom was limited by nitrate. The high phosphate concentration can probably be attributed to phosphorus released from the sediment or can be a result of the accumulation of bloom. Furthermore, DOC concentration significantly increased with water temperature, and was negatively related to nitrate concentration, indicating that these two environmental factors are well correlated to DOC dynamics. DOC concentration did not significantly corresponded with the Chl-a concentration in Lake Taihu. Moreover, the relationship between HMW-DOC and Chl-a concentration was only observed in Gonghu Bay, suggesting that DOC and HMW-DOC are not solely derived from cyanobacterial bloom. Other organic carbon origins, such as terrestrial input, were also assumed to play an important role in Lake Taihu.
This study presents results from field surveys performed over various seasons in a large, eutrophic, shallow lake (Lake Taihu, China) using an in situ chromophoric dissolved organic matter (CDOM) fluorescence sensor as a surrogate for other water quality parameters. These measurements identified highly significant empirical relationships between CDOM concentration measured using the in situ fluorescence sensor and CDOM absorption, fluorescence, dissolved organic carbon (DOC), chemical oxygen demand (COD) and total phosphorus (TP) concentrations. CDOM concentration expressed in quinine sulfate equivalent units, was highly correlated with the CDOM absorption coefficient (r2 = 0.80, p < 0.001), fluorescence intensities (Ex./Em. 370/460 nm) (r2 = 0.91, p < 0.001), the fluorescence index (r2 = 0.88, p < 0.001) and the humification index (r2 = 0.78, p < 0.001), suggesting that CDOM concentration measured using the in situ fluorescence sensor could act as a substitute for the CDOM absorption coefficient and fluorescence measured in the laboratory. Similarly, CDOM concentration was highly correlated with DOC concentration (r2 = 0.68, p < 0.001), indicating that in situ CDOM fluorescence sensor measurements could be a proxy for DOC concentration. In addition, significant positive correlations were found between laboratory CDOM absorption coefficients and COD (r2 = 0.83, p < 0.001), TP (r2 = 0.82, p < 0.001) concentrations, suggesting a potential further application for the real-time monitoring of water quality using an in situ CDOM fluorescence sensor.
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.
Dissolved organic carbon (DOC) was collected in six rivers that transect the coastal plain of Georgia in July 1999 and February 2000. DOC concentrations ranged from 4.9 to 40.7 g m-3 and from 7.1 to 40.5 g m-3, respectively. The absorption coefficient at 440 nm was highly correlated with DOC concentration, suggesting that the optical parameter may be utilized for rapid estimation of DOC in these waters. The isolated DOC was separated into fractions of operationally defined molecular size, using an ultrafiltration technique that yielded three fractions: 50 ("large") kilodalton. The smallest fraction was the most abundant (>50%) in 4 rivers in July and in all rivers in February, and considerably more abundant than in previous years. The wavelength-dependent absorption of the total DOC and its fractions showed approximately uniform shape of a curve declining expo- nentially with the increase of wavelength. The average slope of logarithmically transformed curves was 0.0151 and 0.0159 nm-1, for the material collected in July and February, respectively and showed a dependence on DOC molecular size. In unfractionated DOC samples, the mass-specific light absorption determined at 440 nm was on average 0.33 m2 g-1 in July, and 0.26 m2 g-1 in February. The mass-specific absorption coefficient in all fractions ranged between 0.085 and 1.347 m2 g-1 in July and between 0.085 and 1.877 m2 g-1 in February, and was positively correlated with the molecular size of the measured samples. The results of the reported study clearly suggest that the specific absorption coefficient of the yellow substance is an outcome of the relative contribution of its differ- ent size fractions.
Optical approaches were developed to examine the relationship between the optically active and the optically inactive fractions of dissolved organic carbon in inland waters. A multiple linear regression model was developed on the basis of an extensive dataset from Taihu Lake, and validated employing data from another large shallow eutrophic lake (Chaohu Lake) in southern China. The model was used to estimate the concentration of dissolved organic matter (n = 191) using the absorption characteristics of its chromophoric fraction with a high correlation coefficient (R2 = 0.62) and a low root mean squared error (RMSE = 9.67%). This intra-ecosystem validity allows us to improve our understanding of carbon dynamics using optical remote sensing approaches for these optically complex lakes, where multiple sources and sinks of dissolved organic matter were present.
Temporal variation in dissolved organic carbon (DOC) and water color (light absorption at 440 nm) was measured in 20 lakes in northern Michigan that varied in DOC, pH, morphometry, and relative productivity as indicated by chlorophyll and total phosphorus (TP). Monthly observations during May-August over 6 yr revealed that DOC and color varied by 6- and 28-fold among lakes and varied substantially through time within lakes. The pattern of temporal variation differed among years but was synchronous among lakes. Of the 190 possible correlations among lake time series, most were positive for DOC (158) and color (160), and 50% of the positive correlations were significant (P , 0.05). Other variables, such as total phosphorus, chlorophyll, and pH, were less synchronous and had fewer significant positive correlations (13-25%). Temporal dynamics in DOC and color were related to ice-out date as well as spring and summer precipitation. Years of late ice-out and high spring rain were associated with high DOC and color in spring. A summer drought in one year lead to declines in color (up to 40%) and DOC (up to 38%) in nearly all of the lakes. The common temporal dynamics of DOC and color were most likely the result of climatic conditions that affected loading of allochthonous carbon as well as losses due to photodegradation. The variations in DOC were sufficient to cause large changes in light penetration, standing stocks of carbon, and ecosystem metabolism.
There have been major improvements in our understanding of the role of lakes and impoundments in global carbon cycle. Estimating the true role of lakes as sentinels, regulators and integrators of climate change requires analyzing carbon content of vast number of lakes. This is not realistic without using remote sensing methods. There are no satellite sensors at the moment that provide full global coverage and at the same time have spatial and radiometric resolutions suitable for lake color dissolved organic matter (CDOM) mapping. Therefore, the global study has to be performed using more sensitive sensors to create regional lake CDOM statistics for as many sites as possible and extrapolating the results on global lake map that can be created from less sensitive sensor data with full global coverage (Landsat). As a first step towards the global lake carbon mapping we show that the Advanced Land Imager (ALI) allows to study regional variations in lake CDOM content and consequently estimate closely correlated DOC (dissolved organic carbon) and CO2 saturation values. The results show also that there may be regional differences in lake CDOM content even if the study sites are geographically relatively close to each other and occupying zones with similar land cover and annual runoff. In one occasion the difference can be explained with human impact that has caused acidification of lakes but the other occasion needs further studies.
A significant increase in the content of natural organic matter (NOM) has been observed in several surface water sources in Norway during the past 10-12 years. Similar observations are reported also from test sites in Europe and North America. Water works in the southern part of Norway have experienced a doubling and in some cases even a tripling of source water color levels during the last decade. Other important characteristics of NOM, e.g. the specific UV absorption (SUVA), have changed as well. The change in raw water quality increases the required NOM removal capacity in water treatment, and significantly affects treatment process selection, design and operation. However, the operational impacts on water treatment processes are poorly quantified. This paper addresses the observed NOM increase in parts of Europe and North America. Although the reasons are not fully understood or identified, possible causes are presented and discussed. Factors like climate change or variability, especially alteration in precipitation patterns and land-use, as well as reductions in anthropogenic sulfur loadings seem relevant. From pilot testing on relevant raw waters, major operational impacts of increasing NOM and SUVA levels on coagulation-contact filtration processes are identified and quantified. As an illustration, an increase in raw water color from 20 to 35 mg Pt L-1 increased the required coagulant dose, sludge production, number of backwashes per day and residual TOC by 64%, 64%, 87%, and 26%, respectively. In addition, hydraulic capacity and filter run time decreased by 10% and 47%, respectively.
Colour and dissolved organic carbon (DOC) concentrations and mass balances were measured for seven unproductive lakes and 20 tributary streams between June 1980 and May 1992. Individual observations of colour, which measures an unknown DOC fraction assumed to be principally humic, were not good predictors of discrete DOC concentrations for any of the study sites. Long-term mean colour was, however, strongly correlated with long-term mean DOC concentrations in streams and lakes. Colour behaved differently from the total DOC pool in lakes. Lake retention and loss coefficients for colour were always higher than corresponding values for the total DOC pool, and the mean annual colour/DOC ratios in lake outflows were always less than the corresponding ratios in lake inputs, indicating that the coloured fraction was preferentially removed or photooxidized. A steady-state mass balance model was used to estimate the upper bound for the average coloured fraction of DOC in each lake. The upper bound for the seven lakes ranged from 34 to 88%, increasing with increasing colour, DOC, and total phosphorus.
This study experimentally determined the contribution of ferric iron (Fe(III)) associated with humic substances (HS) to the light absorption by chromophoric dissolved organic matter (CDOM). The associations between Fe(III) and HS (HS-Fe) were generated by mixing HS standards with Fe(III) in acidic conditions and adjusting pH to 8. HS-associated Fe was separated from the total Fe by filtering (0.7 m and 0.2 m filters) and by removing the free Fe ions by cation exchange chromatography. The maximum Fe-binding capacity (at pH 8) of Suwannee River humic acid, Suwannee River fulvic acid and Pony Lake (Antarctica) fulvic acid were 13.0, 13.5, and 7.64 mol Fe [mg C]-1, respectively, indicating that the wetland-derived HS had a higher Fe-binding capacity than plankton-derived HS. HS-associated Fe increased the absorption coefficient of CDOM by up to several folds at the visible range of spectrum and reduced the spectral slope coefficient of CDOM. The Fe-induced increase in light absorption was spectrally similar among different HS examined. The Fe-specific absorption coefficient spectrum for HS-associated Fe (a,Fe*) was calculated from the Fe-induced increase in light absorption by normalizing it with the concentration of Fe in HS pool. The a,Fe* was adopted in estimation the contribution of HS-associated Fe to light absorption by CDOM in thirteen circum neutral natural waters collected from a spring, ten major rivers, a lake and a coastal area. The HS-associated Fe was calculated to be responsible for from 0.6% (Mississippi River) to 56.4% (Löytynlähde spring) of light absorption by CDOM at wavelength of 410 nm.This study shows that HS-associated Fe can be an important component in the light absorption by CDOM and influence also the spectral slope coefficient of CDOM.
Ultraviolet/visible (UV/Vis) absorbance spectroscopy is a commonly used technique for characterizing dissolved organic matter (DOM). We present an analysis of UV/Vis absorbance spectra from 983 lakes throughout Sweden, sampled during autumn 2009. Metrics included both specific absorbances (i.e. absorbance per mass unit of organic carbon), and descriptions of spectral shape. Overall, we found three factors to which all spectral metrics were similarly related: acidity, retention-time, and latitude. In general, alkaline lakes with a long retention time in northern Sweden have lower specific absorbance and steeper spectral slope than acidic lakes with a short retention time in southern Sweden. Relative to the specific absorbance measured at 254 nm (SUVA), commonly used as a measure of DOM aromaticity, the specific absorbance at longer wavelengths and metrics of spectral shape were more sensitive to acidity and less sensitive to latitude. Although different spectral metrics are hypothesized to reflect different properties of DOM, UV/Vis absorbance spectroscopy may not be useful for more refined characterization of organic matter because of the strong inter-correlation between metrics. Nevertheless, it remains useful as a quick, cheap and reliable method of estimating DOM quantity and describing quality. We suggest that the most informative range to measure absorbance is between approximately 250 and 360 nm, where the between-lake variability is largest and absorbance can, in general, be precisely measured.
Prediction of species’ distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species’ distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species’ occurrence data. Presence-only data were effective for modelling species’ distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.
We analysed long-term changes in phytoplankton composition in relation to hydrological, meteorological and nutrient loading
data in the large (270km2) shallow (mean depth 2.8m) Lake Võrtsjärv. Nutrient loads to the lake were heavy in the 1970s and 1980s and decreased considerably
thereafter. The average nutrient concentrations for 1985–2004 (1.6mgl−1 of total nitrogen and 53μgl−1 of total phosphorus) characterize the lake as a eutrophic water body. All four calculated taxonomic indices showed a unidirectional
deterioration of the lake’s ecological status, despite reduced concentrations of nutrients. We focused our analysis on the
PTSI index, which revealed a stepwise change between the years 1977 and 1979 that coincided with a large increase in water
level, but also with a change of investigator. After correcting input data for possible investigator-induced differences,
the step change remained because it was caused by major changes in the whole phytoplankton community. The previous dominant
Planktolyngbyalimnetica was replaced by two species of seasonally altering Limnothrix. Among phytoplankton functional groups, there was a decrease in all groups comprising small-sized phytoplankton species,
such as X1, E, F, J, N and an increase in S1 and H1, both represented by filamentous cyanobacteria. Our results suggest a non-linear response of phytoplankton to changing nutrient
loadings, and that the change observed between 1977 and 1979 was a regime shift triggered by water level change. High shade
tolerance of the new dominants, and their ability to create shade, obviously stabilized the new status making it resistant
to restoration efforts.
KeywordsRegime shift-Lake water level-Nutrient loading-Trophic index-Phytoplankton functional groups
Given the importance of colored dissolved organic matter (CDOM) for the structure and function of lake ecosystems, a method that could estimate the amount of CDOM in lake waters over large geographic areas would be highly desirable. Satellite remote sensing has the potential to resolve this problem. We carried out model simulations to evaluate the suitability of different satellite sensors (Landsat, IKONOS, and the Advanced land Imager [ALI]) to map the amount of CDOM in concentration ranges that occur in boreal lakes of the Nordic countries. The results showed that the 8-bit radiometric resolution of Landsat 7 is not adequate when absorption by CDOM at 420 nm is higher than 3 m−1. On the other hand, the 16-bit radiometric resolution of ALI, a prototype of the next generation of Landsat, is suitable for mapping CDOM in a wider range of concentrations. An ALI image of southern Finland was acquired on 14, July 2002 and in situ measurements were carried out in 15 lakes (18 stations). The results showed that there is a high correlation (R
2 = 0.84) between the 565 nm/660 nm ALI band ratio and the CDOM absorption coefficient in lakes. Analysis of 245 lakes in the acquired satellite image showed a normal distribution of CDOM concentration among the lakes. However, the size distribution of lakes was highly skewed toward small lakes, resulting in the CDOM concentration per unit lake area being skewed toward high values. We showed that remote sensing enables synoptic monitoring of the CDOM concentration in a large number of lakes and thus enables scaling up to the level of large ecosystems and biomes.
The relationship between chlorophyll a (Chl) and primary productivity in the uppermost water layer and the water column-based (0-15 m) integral values of those variables were examined using measurements taken in Lake Kinneret, Israel from 1990 to 2003. In 81% of all chlorophyll a profiles examined the distribution was fairly uniform within the entire 0-15 m water column, and in 12.3% of instances showed a prominent subsurface maximum, when the lake phytoplankton was dominated by the dinoflagellate Peridinium gatunense . Chl can be reliably estimated by remote sensing techniques in the productive and turbid water of Lake Kinneret, since Chl concentration at surface layers can be extrapolated to the entire water column. Light vertical attenuation coefficient average for wavelengths from 400 to 700 nm, K<SUB>d</SUB>, ranged from 0.203 to 1.954 m-1, and showed high degree of temporal variation. The maximal rate of photosynthetic efficiency, P<SUB>B</SUB>opt , average was 3.16 (±1.50), ranged from 0.25 to 8.85 mg C m-3 h-1 mg Chl-1. Using measured data of Chl, P<SUB>B</SUB>opt, and light as an input, a simple depth-integrated primary productivity model allowed plausible simulation of primary productivity. However, a lack of correlation between photosynthetic activity and temperature (or other variable with remotely sensed potential) renders the use of models which require input of photosynthetic efficiency to calculate integrated primary productivity of little value in the case of the productive and turbid Lake Kinneret.
Decomposition of natural populations of Lake Mendota phytoplankton dominated by blue-green algae (cyanobacteria) was monitored by using oxygen uptake and disappearance of chlorophyll, algal volume (fluorescence microscopy), particulate protein, particulate organic carbon, and photosynthetic ability (CO(2) up-take). In some experiments, decomposition of C-labeled axenic cultures of Anabaena sp. was also measured. In addition to decomposition, mineralization of inorganic nitrogen and phosphorus were followed in some experiments. Decomposition could be described as a first-order process, and the rate of decomposition was similar to that found by others using pure cultures of eucaryotic algae. Nitrogen and phosphorus never limited the decomposition process, even when the lake water was severely limited in soluble forms of these nutrients. This suggests that the bacteria responsible for decomposition can obtain all of their key nutrients for growth from the blue-green algal cells. Filtration of lake water through plankton netting that removed up to 90% of the algal biomass usually did not cause a similar decrease in oxygen demand, suggesting that most of the particulate organic matter used for respiration of the decomposing bacteria was in a small-particle fraction. Short-term oxygen demand correlated well with the particulate chlorophyll concentration of the sample, and a relationship was derived that could be used to predict community respiration of the lake from chlorophyll concentration. Kinetic analysis showed that not all analyzed components disappeared at the same rate during the decomposition process. The relative rates of decrease of the measured parameters were as follows: photosynthetic ability > algal volume > particulate chlorophyll > particulate protein. Decomposition of C-labeled Anabaena occurred at similar rates with aerobic epilimnetic water and with anaerobic sediment, but was considerably slower with anaerobic hypolimnetic water. Of the various genera present in the lake, Aphanizomenon and Anabaena were more sensitive to decomposition than was Microcystis. In addition to providing a general picture of the decomposition process, the present work relates to other work on sedimentation to provide a detailed picture of the fate of blue-green algal biomass in a eutrophic lake ecosystem.
Estimates were made of the biomass and production of heterotrophic bacteria in the epilimnion of Lake Mendota, Wis. Cell counts were done with epifluorescence microscopy and varied from 3 x 10 bacteria per ml in winter to 3 x 10 bacteria per ml in summer. Cell volumes were measured in scanning electron micrographs. The average cell volume was 0.159 mum. Annual variations and depth distribution were studied. Production was estimated from the frequency of dividing cells and from dark radioactive sulfate uptake. Annual productivity and daily average productivity were very close with both methods: 107 to 205 g of C per m per year for sulfate and 89 to 117 g of C per m per year for frequency of dividing cells. Zooplankton feeding removed 2 to 10% of the bacterial net production annually. When compared with biomass changes and losses due to zooplankton feeding, production values were very high. Therefore, it was suggested that other loss factors have to be more important than zooplankton feeding in controlling the bacterial population. Bacterial heterotrophic production was about 50% of gross primary production.
Fauna and flora oflakes are an integrative result of regional past history and present environmental factors. In the Lake Kinneret area where Prehistoric Man witnessed the last tectonic readj ustments of the Rift Valley, geological events do not belong only to the remote past but still strongly affect the lacustrine environment. It is therefore necessary to give a detailed picture of the regional background and limnological features of the lake (Parts I and II) before describing its planktic and benthic com munities (Parts III and IV) and the Vertebrate fauna of the lake and its surroundings (Part V). The trophic relationships between communities are beyond the scope of a Monograph and have consequently not been studied in detail but only mentioned occasionally. It is intentional that Man and his penetration into the Kinneret area have been treated on a purely zoological basis. It underlines the fact that Man, as any other living organism, is part of the ecosystem and ruled by its laws and that his activities have an automatic feed back on his environment. However, in contrast with other living organisms, Man is able to 'utilize' the lakes and their watersheds for his benefit if, by appropriate management, he minimizes the damaging influence of his activities. This is the main purpose of the research carried out presently on Lake Kinneret and its watershed and briefly described in Part VI.
Penetration of total PAR was measured in 14 small forest lakes during early August at the time of most intense stratification of the water columns. The lakes were chosen to cover the widest possible range of water colour (5–335 mg Pt · l⁻¹). The extinction coefficient of total PAR, and hence the depth of the euphotic zone, was strongly correlated with water colour, which provided a better prediction of €PAR than either dissolved organic carbon or absorbance at 260 nm. Chlorophyll a concentration in the lakes had no significant influence on €PAR. The depth of the mixed layer showed a strong inverse relationship to water colour so that the effective light climate experienced by phytoplankton was much less variable between lakes than might be expected from the variability of water colour and €PAR. Most of the lakes contained a very high proportion of motile or buoyant forms in their phytoplankton, but there was no evidence for any trend of increasing representation of flagellated phytoplankton with increasing water colour. In these small lakes the lack of turbulence is probably of more importance in promoting the development of populations of motile phytoplankton.
The main objective of the present study is to test various methods for describing the absorption spectra of coloured dissolved organic matter (CDOM) and to determine the numerical values of some optical parameters of CDOM in lakes with diverse water quality. First, the parameters of an exponential model in different spectral intervals were determined. In addition, the suitability of some other models for the approximation of CDOM spectra was estimated. Specific absorption coefficients of CDOM were calculated from the absorption coefficients and dissolved organic carbon (DOC) concentrations. The experimental initial data were differences between spectral attenuation coefficients of filtered and distilled water. Two datasets were used: 1) for 13 Estonian and 7 Finnish lakes (altogether 404 spectra between 350 and 700 nm) measured by the Estonian Marine Institute (EMI); 2) for 10 Finnish lakes (73 spectra) measured by the Finnish Environment Institute (FEI).
The spectra of CDOM absorption coefficients (aCDOM) were calculated from experimental data taking into account the correction due to scattering properties of colloids in the filtered water. The total content of CDOM in natural waters of Estonian and Finnish lakes was expressed by means of aCDOM at the wavelength of 380 nm. It varied significantly, from 0.71 to 19.5 m−1, the mean value (of all the investigated lakes) being around 6.6 m−1. Slopes of the exponential approximation varied widely, from 0.006 to 0.03 nm−1. Averaged over all lakes values of slope for the interval 380-500 nm obtained from the EMI dataset are close to those obtained from the FEI dataset: from 0.014 nm−1 (without correction) to 0.016-0.017 nm-1 (with different types of correction). These results are in good correspondence with most published data.
Attempts to describe the spectra in the region of 350-700 nm by means of hyperexponential functions (∽ exp(-αλη)) show that: (1) η < 1 (in the case of traditional exponential approximation η = 1); (2) a promising idea is to seek the best fit only for wavelengths λ > λ1, where λ1 will be chosen taking into account the real shape of aCDOM spectra.
The mean value of the specific absorption coefficient (a*CDOM) at the wavelength 380 nm obtained in this study (0.44 L mg−1 m−1) is close to the values published in the literature, if we assume that a*CDOM (380) is calculated using the data of dissolved organic matter (DOM). The optically non-active fraction of DOM in our study was high and therefore a*CDOM (380) was considerably higher (1.01 L mg−1 m−1) than a*CDOM (380).
The results of the present work could be used in the modeling of underwater light field as well as in the interpretation of radiation measurements and optical remote sensing results.
This chapter discusses the role of autochthonous sources of Dissolved Organic Matter (DOM) in surface waters. Microalgae are important sources of organic matter in most aquatic systems, because they transform solar energy into reduced carbon compounds. It is clear that autochthonous DOM of algal and macrophyte origin is an important contributor to the total pool of organic matter in most aquatic environments. Production of DOM from aquatic algae and macrophytes occurs by several different mechanisms: predatory grazing, cell death and senescence, viral lysis, and extracellular release. Both algae and macrophytes release a significant proportion of their net primary production as dissolved organic matter during active growth. More in-depth assessment of the functional links between heterotrophic microorganisms and aquatic primary producers including: kinetic studies of DOM release, transformation and uptake, as well as population level coupling between primary producers and heterotrophic microorganisms, may help in understanding the influence of autochthonously produced DOM on aquatic ecosystems.
The purpose of this chapter is to acquaint the reader with the importance of biochemical processes in organic geochemistry. Unfortunately, it is not possible to explain in detail all of the biochemical processes that affect organic solutes. Therefore, this chapter introduces basic concepts of biochemical processes. First, the chapter discusses the general decomposition of organic carbon, which is a major biogeochemical pathway in natural systems. The chemical processes of life put together amino acids, carbohydrates, and fatty acids to build specific compounds, such as proteins, polysaccharides, and lipids. When the death of an organism occurs, then the biochemical processes of decay and decomposition take over, and an entirely different suite of fragmented compounds occur. The general decomposition of organic carbon is a broad view of this complicated process.
There is a strong need to develop remote sensing methods for mapping lake carbon content on regional to global scales. The use of in situ methods is impractical for monitoring lake water quality over large geographical areas, which is a fundamental requirement to understand the true role of lakes in the global carbon cycle. The coloured component of dissolved organic carbon (DOC), called CDOM, absorbs light strongly in the blue part of the visible spectrum and can be used as a proxy for mapping lake DOC with remote sensing. However, iron associated to organic matter can cause extra browning of waters. Consequently, the remote sensing signal we interpret as DOC may partially be attributed to the presence of iron associated to organic matter, potentially hampering our ability to estimate carbon concentrations.
A spectrophotometric study was made of the absorption of light by yellow substance (gilvin, gelbstofl) in 12 freshwater lakes of diverse optical and biochemical character in which concen- trations of yellow substance ranged 50-fold. The shapes of the spectra of yellow substance absorp- tion, g,, suitably corrected for residual light scattering in the spectrophotometer, were well described by an exponential function of wavelength, X, at near-UV to visible wavelengths: in which R is a reference wavelength and S is the characteristic exponential slope parameter. The average value of S was 0.0 187 nm- I, somewhat higher than previous workers have found in seawaters and other freshwaters. Absorption coefficients of yellow substance at reference-visible wavelengths (e.g. 440 nm) can be predicted within about f 15% from near-UV absorption mea- surements with the exponential model of spectral shape.
A method has been developed for measuring the absorption spectra, and calculating the in situ absorption coefficients, of the particulate fraction (tripton/phytoplankton) of natural waters. The procedure involves concentrating the particulate fraction by filtration followed by resuspension in a smaller volume, and measuring the absorption spectrum with the help of an integrating sphere to minimize the effects of light scattering. The method has been applied to seven inland water bodies in the southern tablelands of New South Wales and the Australian Capital Territory. For comparative purposes the absorption spectra. and in situ absorption coefficients, of the soluble colouring matter (gilvin, gelbstoff) have also been measured. The absorption coefficients have been used to calculate what part of the total absorbed photosynthetically active radiation (PAR) is captured by each of the three major absorbing components. In clear but rather coloured waters, gilvin absorbs most of the quanta, followed by water itself. In two waters with fairly high phytoplankton levels, the particulate fraction absorbs as much PAR as the water, but gilvin still absorbs rather more than either. In highly turbid waters, the particulate fraction (consisting mainly of tripton) absorbs most of the quanta. The data show that tripton has an absorption spectrum in the visible region. which rises steadily with decreasing wavelength: this is attributed to humic materials. It is clear that in turbid waters the inanimate particulate fraction (tripton) is a major light absorber, in addition to being the most important light scatterer.
We traced the origin of dissolved organic matter (DOM) in the large, shallow, eutrophic Lake Võrtsjärv in
Estonia. Allochthonous DOM (Al-DOM) had higher d13C values than autochthonous DOM (Au-DOM). The
d13C of inflow DOM varied from 228.2% to 225.4% (mean 226.7%) and in-lake DOM varied from 228.4% to
226.1% (mean 227.2%). Low stable isotope (SI) signatures of Au-DOM were caused by relatively 13C-depleted values of its precursors (mainly phytoplankton) with mean d13C of 228.9%. SI signatures of dissolved inorganic carbon (DIC) in the inflows and in the lake were also relatively low (from 215.1% to 23.28%). SI values of DOM were lower during the active growing season from May to September and higher from October to April, with the corresponding estimated average proportions of Al-DOM 68% and 81%. The proportion of Al-DOM decreased with increasing water temperature, chlorophyll a, and pH and increased with increasing water level and concentration of yellow substances and DIC. The high proportion of Al-DOM in Võrtsjärv shows that, even in this highly productive ecosystem, the labile Au-DOM produced is rapidly utilized and degraded by microorganisms and thus makes a relatively small contribution to the instantaneous in-lake DOM pool.
We investigated the use of ocean color remote sensing to measure the transport of dissolved organic carbon (DOC) by the Mississippi River to the Gulf of Mexico. From 2000 to 2005 we recorded surface measurements of DOC, colored dissolved organic matter (CDOM), salinity, and water-leaving radiances during five cruises to the Mississippi River Plume. These measurements were used to develop empirical relationships to derive DOC, CDOM, and salinity from monthly composites of SeaWiFS imagery collected from 1998 through 2005. We compared our remote sensing estimates of river flow and DOC transport with data collected by the United States Geological Survey (USGS) from 1998 through 2005. Our remote sensing estimates of river flow and DOC transport correlated well (r 2 ∼ 0.70) with the USGS data. Our remote sensing estimates and USGS field data showed low variability in DOC concentrations in the river end-member (7–11%), and high seasonal variability in river flow (∼ 50%). Therefore, changes in river flow control the variability in DOC transport, indicating that the remote sensing estimate of river flow is the most critical element of our DOC transport measurement. We concluded that it is possible to use this method to estimate DOC transport by other large rivers if there are data on the relationship between CDOM, DOC, and salinity in the river plume.
1. We used first-order kinetic parameters of biological oxygen demand (BOD), the constant of aerobic decomposition (k) and the asymptotic value of BOD (BODult), to characterise the lability of organic carbon pools in six lakes of different trophic state: L. Naroch, L. Miastro and L. Batorino (Belarus), L. Kinneret (Israel), L. Ladoga (Russia) and L. Mendota (U.S.A.). The relative contributions of labile and refractory organic carbon fractions to the pool of total organic carbon (TOC) in these lakes were quantified. We also determined the amounts of labile organic carbon within the dissolved and particulate TOC pools in the three Belarus lakes.
2. Mean annual chlorophyll concentrations (used as a proxy for lake trophic state) ranged from 2.3 to 50.6 μg L−1, labile organic carbon (OCL = 0.3BODult) from 0.75 to 2.95 mg C L−1 and k from 0.044 to 0.14 day−1.
3. Our data showed that there were greater concentrations of OCL but lower k values in more productive lakes.
4. In all cases, the DOC fraction dominated the TOC pool. OCL was a minor component of the TOC pool averaging about 20%, irrespective of lake trophic state.
5. In all the lakes, most (c. 85%) of the DOC pool was refractory, corresponding with published data based on measurements of bacterial production and DOC depletion. In contrast, a larger fraction (27–55%) of the particulate organic carbon (POC) pool was labile. The relative amount of POC in the TOC pool tended to increase with increasing lake productivity.
6. Long-term BOD incubations can be valuable in quantifying the rates of breakdown of the combined particulate and dissolved organic carbon pools and in characterising the relative proportions of the labile and recalcitrant fractions of these pools. If verified from a larger number of lakes our results could have important general implications.
Aim To examine the relationship between diadromy and dispersal ability in New Zealand’s freshwater fish fauna, and how this affects the current environmental and geographic distributions of both diadromous and non-diadromous species.
Location New Zealand.
Methods Capture data for 15 diadromous and 15 non-diadromous fish species from 13,369 sites throughout New Zealand were analysed to establish features of their geographic ranges. Statistical models were used to determine the main environmental correlates of species’ distributions, and to establish the environmental conditions preferred by each species. Environmental predictors, chosen for their functional relevance, were derived from an extensive GIS database describing New Zealand’s river and stream network.
Results In terms of geography, most diadromous species occur in a scattered fashion throughout extensive geographic ranges, and occupy large numbers of catchments of widely varying size. By contrast, most non-diadromous species show relatively high levels of occupancy of smaller geographic ranges, and most are restricted to a few large catchments, particularly in the eastern South Island. In terms of environment, there is marked separation of diadromous from non-diadromous species, with diadromous species generally caught most frequently in low-gradient coastal rivers and streams with warm, maritime climates. With a few notable exceptions, most diadromous species have lower occurrence in river segments that are located above obstacles to upstream migration. Non-diadromous species are usually caught in inland rivers and streams with cool, strongly seasonal climates, typified by a low frequency of high-intensity rainfall events.
Main conclusions We interpret the contrasting biogeographies of New Zealand’s diadromous and non-diadromous species as reflecting interaction between their marked differences in dispersal ability and a landscape that is subject to recurrent, often large-scale, natural disturbance. While both groups are likely to be equally susceptible to local, disturbance-driven extinction, the much greater dispersal ability of diadromous species has allowed them to persist over wide geographic ranges. By contrast, the distributions of most non-diadromous species are concentrated in a few large catchments, mostly in regions where less intense natural disturbance regimes are likely to have favoured their survival.
Dynamics of dissolved organic carbon concentration (DOC) and capacity toabsorb light (color) are determined by in-lake and external properties andprocesses. In this study, the influence of external factors such as rainfallandsolar radiation on DOC and color dynamics was assessed for a small forestedlake. DOC and absorption coefficients at 440 nm (a440)ranged 4-fold from 0.46 to 1.62 mM and from 3.4 to 14.8m–1, respectively. DOC and a440 variedsynchronously, but an important percentage of the variability (26%) ina440 was not explained by DOC. The resulting twofold variation inthemolar absorption coefficient of DOC suggested significant seasonal changes inchromophoric content. Both DOC and a440 were positive andsignificantly related to cumulative rainfall. Solar radiation, however, onlyappeared to influence a440 dynamics. This influence was mediated byphotobleaching. Photobleaching coefficients (kb) were higher in falland spring relative to the summer. This seasonal variability in kbvalues was related to monthly rainfall. The influence of photobleaching ona440 dynamics was evaluated by comparing the half life ofa440 in the water column with water residence time (WRT). For thestudy lake, photobleaching contributed notably to a440 dynamicsduring the dry periods when WRT was longer than the a440 half life .DOC dynamics, however, were not related to solar radiation becausephotomineralization was considerably slower than photobleaching.
Humic substances (HS) are the main constituent of the organic carbon pool in stained aquatic ecosystems. HS absorb visible
and ultraviolet (UV) light, have acid-base properties and metal and nutrient binding abilities. Based on these characteristics,
UV irradiation, pH and the trophic status of aquatic ecosystems will influence the impact of HS on element cycling in surface
waters. With climatic change and environmental pollution, UV irradiance, acidification and eutrophication may increase further.
In this paper impacts of UV irradiation, pH and eutrophication on the structure, properties and biodegradation of aquatic
HS are discussed.
The biological availability of dissolved organic carbon (DOC) was experimentally studied in water samples collected at the
mouth of the River Zala and in the western and eastern basin of Lake Balaton (Hungary) in four seasons. The water samples
were filter-sterilized and inoculated with the in situ bacterial population. The concentration of fulvic and humic acids were
analyzed at the beginning of the experiment. The bacterioplankton biomass and DOC concentration were measured on day 0 and
28. The decrease in the DOC concentration and the ratio of the bacterial C/initial DOC concentration showed the microbial
utilization of DOC. No seasonal changes in DOC availability were found at any of the sampling stations. The DOC bioavailability
was higher in the river than in the lake water. A strong positive correlation was found between the bioavailability and the
humic properties of DOC. The observed changes in the organic matter composition of Lake Balaton support the view that much
of the not readily utilizable ‘refractory’ DOM resides in the non-humic pool in standing waters.
Substantial evidence exists that allochthonous dissolved organic matter (DOM) can provide an important carbon source for pelagic
bacteria. On the other hand, it is implicit in the concept of the ‘microbial loop’ that the degradation of recalcitrant, allochthonous
DOM should be retarded in the pelagic environment, as bacteria able to utilize recalcitrant DOM compounds for slow growth
would be outcompeted by faster-growing bacteria utilizing more labile DOM compounds. Several possible solutions of this apparent
paradox are suggested in this paper, including formation of labile DOM from recalcitrant DOM by e.g. photochemical reactions,
and mechanisms enabling the maintenance of a metabolically diverse bacterioplankton. These mechanisms include an explanation
analogous to Hutchinson's classical solution to the ‘paradox of plankton’, and differential mortality of different populations
within the bacterioplankton enabled by selective grazing, infections by bacteriophages and predatory bacteria, and spatial
micropatchiness.
Absorption measurements from chromophoric dissolved organic matter (CDOM) and their relationships with dissolved organic carbon (DOC) and fluorescence were studied in Lake Taihu, a large, shallow, subtropical lake in China. Absorption spectra of lake water samples were measured from 240 nm to 800 nm. Highest values of a(λ), DOC and F
n(355) occurred near the river inflow to Meiliang Bay and decreased towards the central lake basin. A significant spatial difference was found between Meiliang Bay and the central lake basin in absorption coefficient, DOC-specific absorption coefficient, exponential slope coefficient, DOC concentration and fluorescence value. The spatial distribution of CDOM suggested that a major part of CDOM in the lake was from river input. CDOM absorption coefficients were correlated with DOC over the wavelength range 280–500 nm, and a(355) was also correlated with F
n(355), which showed that CDOM absorption could be inferred from DOC and fluorescence measurement. The coefficient of variation between a(λ) and DOC concentration decreased with increase in wavelength from 240 nm to 800 nm. Furthermore, a significant negative linear relationship was recorded between S value and CDOM absorption coefficient, as well as DOC-specific absorption coefficient. S value and DOC-specific absorption coefficient were used as a proxy for CDOM composition and source. Accurate CDOM absorption measurements are very useful in explaining UV attenuation and in developing, validating remote sensing model of water quality in Lake Taihu.
We analysed relationships between demersal fish species richness, environment and trawl characteristics using an extensive collection of trawl data from the oceans around New Zealand. Analyses were carried out using both generalised additive models and boosted regression trees (sometimes referred to as 'stochastic gradient boosting'). Depth was the single most important environmental predictor of variation in species richness, with highest richness occurring at depths of 900 to 1000 m, and with a broad plateau of moderately high richness between 400 and 1100 m. Richness was higher both in waters with high surface concentrations of chlorophyll a and in zones of mixing of water bodies of contrasting origins. Local variation in temperature was also important, with lower richness occurring in waters that were cooler than expected given their depth. Variables describing trawl length, trawl speed, and cod-end mesh size made a substantial contribution to analysis outcomes, even though functions fitted for trawl distance and cod-end mesh size were constrained to reflect the known performance of trawl gear. Species richness declined with increasing cod-end mesh size and increasing trawl speed, but increased with increasing trawl distance, reaching a plateau once trawl distances exceed about 3 nautical miles. Boosted regression trees provided a powerful analysis tool, giving substantially superior predictive performance to generalized additive models, despite the fitting of interaction terms in the latter.
Concentrations of dissolved organic carbon have increased in many, but not all, surface waters across acid impacted areas of Europe and North America over the last two decades. Over the last eight years several hypotheses have been put forward to explain these increases, but none are yet accepted universally. Research in this area appears to have reached a stalemate between those favouring declining atmospheric deposition, climate change or land management as the key driver of long-term DOC trends. While it is clear that many of these factors influence DOC dynamics in soil and stream waters, their effect varies over different temporal and spatial scales. We argue that regional differences in acid deposition loading may account for the apparent discrepancies between studies. DOC has shown strong monotonic increases in areas which have experienced strong downward trends in pollutant sulphur and/or seasalt deposition. Elsewhere climatic factors, that strongly influence seasonality, have also dominated inter-annual variability, and here long-term monotonic DOC trends are often difficult to detect. Furthermore, in areas receiving similar acid loadings, different catchment characteristics could have affected the site specific sensitivity to changes in acidity and therefore the magnitude of DOC release in response to changes in sulphur deposition. We suggest that confusion over these temporal and spatial scales of investigation has contributed unnecessarily to the disagreement over the main regional driver(s) of DOC trends, and that the data behind the majority of these studies is more compatible than is often conveyed.
Baltic Marine Biologists. Publication ; 5 Pages: 38 p.