The color of freshwaters, often measured as absorbance, influences a number of ecosystem services including biodiversity, fish production, and drinking water quality. Many countries have recently ...reported on increasing trends of water color in freshwaters, for which drivers are still not fully understood. We show here with more than 58000 water samples from the boreal and hemiboreal region of Sweden and Canada that absorbance of filtered water (a₄₂₀) co-varied with dissolved organic carbon (DOC) concentrations (R² = 0.85, P<0.0001), but that a₄₂₀ relative to DOC is increased by the presence of iron (Fe). We found that concentrations of Fe significantly declined with increasing water retention in the landscape, resulting in significantly lower Fe concentrations in lakes compared to running waters. The Fe loss along the aquatic continuum corresponded to a proportional loss in a₄₂₀, suggesting a tight biogeochemical coupling between colored dissolved organic matter and Fe. Since water is being flushed at increasing rates due to enhanced runoff in the studied regions, diminished loss of Fe along the aquatic continuum may be one reason for observed trends in a₄₂₀, and in particular in a₄₂₀/DOC increases. If trends of increased Fe concentrations in freshwaters continue, water color will further increase with various effects on ecosystem services and biogeochemical cycles.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Inland waters transport large amounts of dissolved organic matter (DOM) from terrestrial environments to the oceans, but DOM also reacts en route, with substantial water column losses by ...mineralization and sedimentation. For DOM transformations along the aquatic continuum, lakes play an important role as they retain waters in the landscape allowing for more time to alter DOM. We know DOM losses are significant at the global scale, yet little is known about how the reactivity of DOM varies across landscapes and climates. DOM reactivity is inherently linked to its chemical composition. We used fluorescence spectroscopy to explore DOM quality from 560 lakes distributed across Sweden and encompassed a wide climatic gradient typical of the boreal ecozone. Six fluorescence components were identified using parallel factor analysis (PARAFAC). The intensity and relative abundance of these components were analyzed in relation to lake chemistry, catchment, and climate characteristics. Land cover, particularly the percentage of water in the catchment, was a primary factor explaining variability in PARAFAC components. Likewise, lake water retention time influenced DOM quality. These results suggest that processes occurring in upstream water bodies, in addition to the lake itself, have a dominant influence on DOM quality. PARAFAC components with longer emission wavelengths, or red‐shifted components, were most reactive. In contrast, protein‐like components were most persistent within lakes. Generalized characteristics of PARAFAC components based on emission wavelength could ease future interpretation of fluorescence spectra. An important secondary influence on DOM quality was mean annual temperature, which ranged between −6.2 and +7.5 °C. These results suggest that DOM reactivity depends more heavily on the duration of time taken to pass through the landscape, rather than temperature. Projected increases in runoff in the boreal region may force lake DOM toward a higher overall amount and proportion of humic‐like substances.
Recent increases in concentrations of dissolved organic carbon (DOC) in lakes and rivers over large regions have been related to both changes in the climate and in atmospheric deposition chemistry. ...Using a data set of 1041 boreal lakes along a 13° latitudinal gradient, sampled in 1995, 2000, and 2005, and an additional data set of 90 lakes along a 1000-m altitudinal gradient at 68°N, we show that DOC concentrations increase in a nonlinear way along a latitudinal and altitudinal temperature gradient. The nonlinear relation of DOC to increasing temperatures was consistent over space and time. Out of 14 meteorological, catchment, morphometric, and atmospheric deposition variables tested, the variable best explaining this kind of nonlinear pattern was the number of days when air temperatures exceeded 0°C, i.e., the duration of the main growing and runoff season (
$D_{T>0}$
). Using
$D_{T>0}$
as an input variable, we were able to predict the nonlinear temperature response of DOC concentrations, both spatially (R² = 0.90, p < 0.0001) and temporally (R² = 0.90, p < 0.0001).
$D_{T>0}$
has an advantage over other variables because it includes the time factor, which is decisive for the duration that biogeochemical processes can take place. We suggest that DOC concentrations in lakes are influenced by climate change and that present temperature increases over Sweden result in an accelerated DOC increase toward warmer geographical regions.
Lakes as Sentinels of Climate Change Adrian, Rita; O'Reilly, Catherine M.; Zagarese, Horacio ...
Limnology and oceanography,
November 2009, Letnik:
54, Številka:
6
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as ...indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate. However, the efficacy of the different indicators is affected by regional response to climate change, characteristics of the catchment, and lake mixing regimes. Thus, particular indicators or combinations of indicators are more effective for different lake types and geographic regions. The extraction of climate signals can be further complicated by the influence of other environmental changes, such as eutrophication or acidification, and the equivalent reverse phenomena, in addition to other land-use influences. In many cases, however, confounding factors can be addressed through analytical tools such as detrending or filtering. Lakes are effective sentinels for climate change because they are sensitive to climate, respond rapidly to change, and integrate information about changes in the catchment.
► Characteristics of drug sources control their detection frequency and concentrations. ► A high caffeine/carbamazepine might be an indicative of raw sewage discharge in rivers. ► Caffeine ...concentrations and fecal coliforms were correlated in four rivers (R2=0.45). ► Caffeine is a promising indicator of recent urban fecal contaminations. ► Carbamazepine is a good indicator of cumulative persistent compounds.
We surveyed four different river systems in the Greater Montreal region, upstream and downstream of entry points of contamination, from April 2007 to January 2009. The studied compounds belong to three different groups: PPCPs (caffeine, carbamazepine, naproxen, gemfibrozil, and trimethoprim), hormones (progesterone, estrone, and estradiol), and triazine herbicides and their metabolites (atrazine, deethylatrazine, deisopropylatrazine, simazine, and cyanazine). In the system A, B, and C having low flow rate and high TOC, we observed the highest detection frequencies and mass flows of PPCPs compared to the other compounds, reflecting discharge of urban contaminations through WWTPs and CSOs. However, in River D, having high flow rate and low TOC, comparable frequency of detection of triazine and their by-products and PPCPs, reflecting cumulative loads of these compounds from the Great Lakes as well as persistency against natural attenuation processes. Considering large differences in the removal efficiencies of caffeine and carbamazepine, a high ratio of caffeine/carbamazepine might be an indicative of a greater proportion of raw sewage versus treated wastewater in surface waters. In addition, caffeine appeared to be a promising indicator of recent urban fecal contaminations, as shown by the significant correlation with FC (R2=0.45), while carbamazepine is a good indicator of cumulative persistence compounds.
Annual maximum lake surface temperature influences ecosystem structure and function and, in particular, the rates of metabolic activities, species survival and biogeography. Here, we evaluated ...50 years of observational data, from 1966 to 2015, for ten European lakes to quantify changes in the annual maximum surface temperature and the duration above a potentially critical temperature of 20 °C. Our results show that annual maximum lake surface temperature has increased at an average rate of +0.58 °C decade
−1
(95% confidence interval 0.18), which is similar to the observed increase in annual maximum air temperature of +0.42 °C decade
−1
(95% confidence interval 0.28) over the same period. Increments in lake maximum temperature among the ten lakes range from +0.1 in the west to +1.9 °C decade
−1
in the east. Absolute maximum lake surface water temperatures were reached in Wörthersee, 27.5 °C, and Neusiedler See, 31.7 °C. Periods exceeding a critical temperature of 20 °C each year became two to six times longer than the respective average (6 to 93). The depth at which water temperature exceeded 20 °C increased from less than 1 to more than 6 m in Mondsee, Austria, over the 50 years studied. As a consequence, the habitable environment became increasingly restricted for many organisms that are adapted to historic conditions.
Many boreal waters are currently becoming browner with effects on biodiversity, fish production, biogeochemical processes and drinking water quality. The question arises whether and at which speed ...this browning will continue under future climate change. To answer the question we predicted the absorbance (a₄₂₀) in 6347 lakes and streams of the boreal region under future climate change. For the prediction we modified a numerical model for a₄₂₀ spatial variation which we tested on a temporal scale by simulating a₄₂₀ inter-annual variation in 48 out of the 6347 Swedish waters. We observed that inter-annual a₄₂₀ variation is strongly driven by precipitation that controls the water flushing through the landscape. Using the predicted worst case climate scenario for Sweden until 2030, i.e., a 32 % precipitation increase, and assuming a 10 % increase in imports of colored substances into headwaters but no change in land-cover, we predict that a₄₂₀ in the 6347 lakes and streams will, in the worst case, increase by factors between 1.1 and 7.6 with a median of 1.3. This increase implies that a₄₂₀ will rise from the present 0.1–86 m⁻¹ (median: 7.3 m⁻¹) in the 6347 waters to 0.1–154 m⁻¹ (median: 10.1 m⁻¹), which can cause problems for the preparation of drinking water in a variety of waters. Our model approach clearly demonstrates that a homogenous precipitation increase results in very heterogeneous a₄₂₀ changes, where lakes with a long-term mean landscape water retention time between 1 and 3 years are particularly vulnerable to climate change induced browning. Since these lake types are quite often used as drinking water resources, preparedness is needed for such waters.
The fluorescence of dissolved organic matter (DOM) is suppressed by a phenomenon of self‐quenching known as the inner filter effect (IFE). Despite widespread use of fluorescence to characterize DOM ...in surface waters, the advantages and constraints of IFE correction are poorly defined. We assessed the effectiveness of a commonly used absorbance‐based approach (ABA), and a recently proposed controlled dilution approach (CDA) to correct for IFE. Linearity between corrected fluorescence and total absorbance (ATotal; the sum of absorbance at excitation and emission wavelengths) across the full excitation‐emission matrix (EEM) in dilution series of four samples indicated both ABA and CDA were effective to an absorbance of at least 1.5 in a 1 cm cell, regardless of wavelength positioning. In regions of the EEMs where signal to background noise (S/N) was low, CDA correction resulted in more variability than ABA correction. From the ABA algorithm, the onset of significant IFE (>5%) occurs when absorbance exceeds 0.042. In these cases, IFE correction is required, which was the case for the vast majority (97%) of lakes in a nationwide survey (n= 554). For highly absorbing samples, undesirably large dilution factors would be necessary to reduce absorbance below 0.042. For rare EEMs with ATotal > 1.5 (3.0% of the lakes in the Swedish survey), a 2‐fold dilution is recommended followed by ABA or CDA correction. This study shows that for the vast majority of natural DOM samples the most commonly applied ABA algorithm provides adequate correction without prior dilution.
The emissions of carbon dioxide (CO2) from inland waters are substantial on a global scale. Yet the fundamental question remains open which proportion of these CO2 emissions is induced by sunlight ...via photochemical mineralization of dissolved organic carbon (DOC), rather than by microbial respiration during DOC decomposition. Also, it is unknown on larger spatial and temporal scales how photochemical mineralization compares to other C fluxes in the inland water C cycle. We combined field and laboratory data with atmospheric radiative transfer modeling to parameterize a photochemical rate model for each day of the year 2009, for 1086 lakes situated between latitudes from 55°N to 69°N in Sweden. The sunlight‐induced production of dissolved inorganic carbon (DIC) averaged 3.8 ± 0.04 g C m−2 yr−1, which is a flux comparable in size to the organic carbon burial in the lake sediments. Countrywide, 151 ± 1 kt C yr−1 was produced by photochemical mineralization, corresponding to about 12% of total annual mean CO2 emissions from Swedish lakes. With a median depth of 3.2 m, the lakes were generally deep enough that incoming, photochemically active photons were absorbed in the water column. This resulted in a linear positive relationship between DIC photoproduction and the incoming photon flux, which corresponds to the absorbed photons. Therefore, the slope of the regression line represents the wavelength‐ and depth‐integrated apparent quantum yield of DIC photoproduction. We used this relationship to obtain a first estimate of DIC photoproduction in lakes and reservoirs worldwide. Global DIC photoproduction amounted to 13 and 35 Mt C yr−1 under overcast and clear sky, respectively. Consequently, these directly sunlight‐induced CO2 emissions contribute up to about one tenth to the global CO2 emissions from lakes and reservoirs, corroborating that microbial respiration contributes a substantially larger share than formerly thought, and generate annual C fluxes similar in magnitude to the C burial in natural lake sediments worldwide.
Key Points
Approximately 12% of the CO2 emissions from Swedish lakes are directly sunlight inducedThis carbon flux is similar in size to the OC burial in the sedimentsUp to 10% of the global CO2 emissions from inland waters are sunlight induced
Climate change studies have long focused on effects of increasing temperatures, often without considering other simultaneously occurring environmental changes, such as browning of waters. Resolving ...how the combination of warming and browning of aquatic ecosystems affects fish biomass production is essential for future ecosystem functioning, fisheries, and food security. In this study, we analyzed individual‐ and population‐level fish data from 52 temperate and boreal lakes in Northern Europe, covering large gradients in water temperature and color (absorbance, 420 nm). We show that fish (Eurasian perch, Perca fluviatilis) biomass production decreased with both high water temperatures and brown water color, being lowest in warm and brown lakes. However, while both high temperature and brown water decreased fish biomass production, the mechanisms behind the decrease differed: temperature affected the fish biomass production mainly through a decrease in population standing stock biomass, and through shifts in size‐ and age‐distributions toward a higher proportion of young and small individuals in warm lakes; brown water color, on the other hand, mainly influenced fish biomass production through negative effects on individual body growth and length‐at‐age. In addition to these findings, we observed that the effects of temperature and brown water color on individual‐level processes varied over ontogeny. Body growth only responded positively to higher temperatures among young perch, and brown water color had a stronger negative effect on body growth of old than on young individuals. Thus, to better understand and predict future fish biomass production, it is necessary to integrate both individual‐ and population‐level responses and to acknowledge within‐species variation. Our results suggest that global climate change, leading to browner and warmer waters, may negatively affect fish biomass production, and this effect may be stronger than caused by increased temperature or water color alone.
As lakes get warmer and browner, fish biomass production decreases through different pathways. Warming reduces population biomass and induces a shift toward smaller and younger individuals, whereas browning leads to slower body growth. Our study shows that it is necessary to study multiple climate stressors and both individual‐ and population‐level responses to understand and predict shifts in fish biomass production in a changing climate.
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