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1.
Modeled Effects of Dissolved Organic Carbon and Solar Spectra on Photobleaching in Lake Ecosystems 总被引:1,自引:0,他引:1
Dissolved organic matter (DOM) contains molecules that absorb light at various wavelengths. This chromophoric DOM (CDOM) influences
the transmission of both visible and ultraviolet energy through water. The absorption of light by CDOM often causes structural
changes that reduce its capacity to further absorb light, a process termed ‘photobleaching‘. A model was designed to assess
photobleaching through the entire water column of lake ecosystems. The model uses lake morphometry and dissolved organic carbon
(DOC) concentration in conjunction with a defined solar spectrum and experimentally measured photobleaching rates to compute
the total water columm photobleaching. The model was initially applied to a theoretical ‘average‘ lake using solar spectra
for both the north (N) and south (S) temperate western hemispheres and variable DOC from 0.3 to 30 mg L−1. The consequences of varying waveband-specific photobleaching coefficients and lake morphometry were explored in a second
set of simulations. Finally, the model was also applied to four temperate northern lakes for which we had prior measurements
of CDOM photobleaching rates. The model demonstrates that all three wavebands of solar radiation (UVB, UVA, and PAR) contribute
significantly to total water column photobleaching, with UVA being most important. The relative contributions of the three
wavebands were invariant for DOC more than 3 mg L−1. Total water column photobleaching at 440 nm was three to five times faster under the UV-enriched solar spectrum of the southern
hemisphere. Increasing the lake’s mean depth (from 0.37 to 9.39 m) resulted in five- or 15-fold slower rates of total water
column photobleaching for DOC concentrations of 1 or 10 mg L−1, respectively. Varying the waveband-specific photobleaching coefficients by 10-fold resulted in a similar change in total
water column photobleaching rates. Applying the model to four specific lakes revealed that photobleaching for the entire water
column would reduce CDOM light absorption by 50% in 18–44 days under summer conditions.
Received 17 November 1998; accepted 27 June 2000. 相似文献
2.
The movement of dissolved organic carbon (DOC) through soils is an important process for the transport of carbon within ecosystems
and the formation of soil organic matter. In some cases, DOC fluxes may also contribute to the carbon balance of terrestrial
ecosystems; in most ecosystems, they are an important source of energy, carbon, and nutrient transfers from terrestrial to
aquatic ecosystems. Despite their importance for terrestrial and aquatic biogeochemistry, these fluxes are rarely represented
in conceptual or numerical models of terrestrial biogeochemistry. In part, this is due to the lack of a comprehensive understanding
of the suite of processes that control DOC dynamics in soils. In this article, we synthesize information on the geochemical
and biological factors that control DOC fluxes through soils. We focus on conceptual issues and quantitative evaluations of
key process rates to present a general numerical model of DOC dynamics. We then test the sensitivity of the model to variation
in the controlling parameters to highlight both the significance of DOC fluxes to terrestrial carbon processes and the key
uncertainties that require additional experiments and data. Simulation model results indicate the importance of representing
both root carbon inputs and soluble carbon fluxes to predict the quantity and distribution of soil carbon in soil layers.
For a test case in a temperate forest, DOC contributed 25% of the total soil profile carbon, whereas roots provided the remainder.
The analysis also shows that physical factors—most notably, sorption dynamics and hydrology—play the dominant role in regulating
DOC losses from terrestrial ecosystems but that interactions between hydrology and microbial–DOC relationships are important
in regulating the fluxes of DOC in the litter and surface soil horizons. The model also indicates that DOC fluxes to deeper
soil layers can support a large fraction (up to 30%) of microbial activity below 40 cm.
Received 14 January 2000; accepted 6 September 2000 相似文献
3.
Bastidas Navarro Marcela Schenone Luca Martyniuk Nicols Vega Evelyn Modenutti Beatriz Balseiro Esteban 《Ecosystems》2022,25(4):795-811
Ecosystems - Dissolved organic matter (DOM) dynamics influence aquatic ecosystem metabolism with ecological and biogeochemical effects. During microbial degradation, certain DOM molecules... 相似文献
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Kelly J. Benoit-Bird Brian C. Battaile Scott A. Heppell Brian Hoover David Irons Nathan Jones Kathy J. Kuletz Chad A. Nordstrom Rosana Paredes Robert M. Suryan Chad M. Waluk Andrew W. Trites 《PloS one》2013,8(1)
Spatial coherence between predators and prey has rarely been observed in pelagic marine ecosystems. We used measures of the environment, prey abundance, prey quality, and prey distribution to explain the observed distributions of three co-occurring predator species breeding on islands in the southeastern Bering Sea: black-legged kittiwakes (Rissa tridactyla), thick-billed murres (Uria lomvia), and northern fur seals (Callorhinus ursinus). Predictions of statistical models were tested using movement patterns obtained from satellite-tracked individual animals. With the most commonly used measures to quantify prey distributions - areal biomass, density, and numerical abundance - we were unable to find a spatial relationship between predators and their prey. We instead found that habitat use by all three predators was predicted most strongly by prey patch characteristics such as depth and local density within spatial aggregations. Additional prey patch characteristics and physical habitat also contributed significantly to characterizing predator patterns. Our results indicate that the small-scale prey patch characteristics are critical to how predators perceive the quality of their food supply and the mechanisms they use to exploit it, regardless of time of day, sampling year, or source colony. The three focal predator species had different constraints and employed different foraging strategies – a shallow diver that makes trips of moderate distance (kittiwakes), a deep diver that makes trip of short distances (murres), and a deep diver that makes extensive trips (fur seals). However, all three were similarly linked by patchiness of prey rather than by the distribution of overall biomass. This supports the hypothesis that patchiness may be critical for understanding predator-prey relationships in pelagic marine systems more generally. 相似文献
6.
Whole-Lake Sugar Addition Demonstrates Trophic Transfer of Dissolved Organic Carbon to Top Consumers
Roger I. Jones Paula Kankaala Hannu Nykänen Sari Peura Martti Rask Sami Vesala 《Ecosystems》2018,21(3):495-506
Terrestrial dissolved organic carbon (DOC) provides an external carbon source to lake ecosystems. However, there is ongoing debate about whether external DOC that enters a lake can pass up the food web to support top consumers. We show, from experimental manipulation of a whole lake, that externally loaded DOC can contribute appreciably to fish biomass. Monthly additions of cane sugar with a distinct carbon stable isotope value during 2 years rapidly enriched the 13C content of zooplankton and macroinvertebrates, with a more gradual 13C enrichment of fish. After sugar addition stopped, the 13C content of consumers reverted towards original values. A simple isotope mixing model indicated that by the end of the sugar addition almost 20% of fish carbon in the lake was derived from the added sugar. Our results provide the first direct experimental demonstration at relevant ecological spatial and temporal scales that externally loaded DOC to lakes can indeed transfer to top consumers. 相似文献
7.
During the unstratified (winter) and stratified (summer) periods of 1999 and 2000, we examined carbon (C) dynamics in the
upper water column of southern Lake Michigan. We found that (a) bacterial respiration (BR) and planktonic respiration (PR)
were major sinks for C, (b) C flux through bacteria (CFTB) was diminished in winter because of reduced bacterial production
(BP) and increased bacterial growth efficiency (BGE) at colder temperatures, and (c) PR exceeded primary production (PP) during
the spring–summer transition. Drawdown of dissolved organic C (DOC), resuspended organic matter from the lake floor, and riverine
organic matter likely provided organic C to compensate for this temporal deficit. DOC in the water column decreased between
winter and summer (29–91 mg C m2 d−1) and accounted for 20%–53% of CFTB and 11%–33% of PR. Sediment resuspension events supported elevated winter heterotrophy
in the years that they occurred with greatest intensities (1998 and 2000) and may be important to interannual variability
in C dynamics. Further, riverine discharge, containing elevated DOC (5×) and dissolved P (10×) relative to lake water, peaked
in the winter–spring season in southern Lake Michigan. Collectively, terrigenous inputs (river, stream, and groundwater discharges;
storm water runoff; and atmospheric precipitation) may support approximately 10%–20% of annual in-lake heterotrophy as well
as autotrophy. Terrestrial subsidies likely play a key role in the C balance of even very large lakes, representing a critical
linkage between terrestrial and aquatic ecosystems.
Received 11 June 2001; Accepted 14 December 2001. 相似文献
8.
Photochemical transformation of dissolved organic matter (DOM) has been studied for more than two decades. Usually, laboratory or “in-situ” experiments are used to determine photodegradation variables. A common problem with these experiments is that the photodegradation experiments are done at higher than ambient temperature. Five laboratory experiments were done to determine the effect of temperature on photochemical degradation of DOM. Experimental results showed strong dependence of photodegradation on temperature. Mathematical modeling of processes revealed that two different pathways engaged in photochemical transformation of DOM to dissolved inorganic carbon (DIC) strongly depend on temperature. Direct oxidation of DOM to DIC dominated at low temperatures while conversion of DOM to intermediate particulate organic carbon (POC) prior to oxidation to DIC dominated at high temperatures. It is necessary to consider this strong dependence when the results of laboratory experiments are interpreted in regard to natural processes. Photodegradation experiments done at higher than ambient temperature will necessitate correction of rate constants. 相似文献
9.
Nicola A. McEnroe Clayton J. Williams Marguerite A. Xenopoulos Petr Porcal Paul C. Frost 《PloS one》2013,8(11)
Urbanization has the potential to dramatically alter the biogeochemistry of receiving freshwater ecosystems. We examined the optical chemistry of dissolved organic matter (DOM) in forty-five urban ponds across southern Ontario, Canada to examine whether optical characteristics in these relatively new ecosystems are distinct from other freshwater systems. Dissolved organic carbon (DOC) concentrations ranged from 2 to 16 mg C L-1 across the ponds with an average value of 5.3 mg C L-1. Excitation-emission matrix (EEM) spectroscopy and parallel factor analysis (PARAFAC) modelling showed urban pond DOM to be characterized by microbial-like and, less importantly, by terrestrial derived humic-like components. The relatively transparent, non-humic DOM in urban ponds was more similar to that found in open water, lake ecosystems than to rivers or wetlands. After irradiation equivalent to 1.7 days of natural solar radiation, DOC concentrations, on average, decreased by 38% and UV absorbance decreased by 25%. Irradiation decreased the relative abundances of terrestrial humic-like components and increased protein-like aspects of the DOM pool. These findings suggest that high internal production and/or prolonged exposure to sunlight exerts a distinct and significant influence on the chemistry of urban pond DOM, which likely reduces its chemical similarity with upstream sources. These properties of urban pond DOM may alter its biogeochemical role in these relatively novel aquatic ecosystems. 相似文献
10.
陆地生态系统中水溶性有机质的环境效应 总被引:43,自引:3,他引:40
目前水溶性有机质(Dissolved Organic Matter)已逐步成为陆地生态系统中的一个研究热点。系统地评述了陆地生态系统中DOM的组成特点及其环境效应。尽管关于陆地生态系统中DOM的研究还不完善,至今对其性质,组成和分类方法等问题看法不一,但现有结果已经表明DOM是一种十分活跃的重要化学组分,它对陆地生态系统中污染物质的溶解,吸附,解吸,吸收,迁移和生物毒性,微生物活动以及土壤形成过程等均有显著的影响。影响DOM在地生态系统中的环境效应的主要因素包括:DOM与污染物的络合作用,污染物溶解/沉淀作用,土壤对DOM的吸附作用,土壤质地,酸碱缓冲作用等。 相似文献
11.
Dynamics of a Boreal Lake Ecosystem during a Long-Term Manipulation of Top Predators 总被引:1,自引:0,他引:1
David L. Findlay Michael J. Vanni Michael Paterson Kenneth H. Mills Susan E.M. Kasian Willie J. Findlay Alex G. Salki 《Ecosystems》2005,8(6):603-618
We assessed the long-term (16 years) effects of introducing piscivores (northern pike) into a small, boreal lake (Lake 221,
Experimental Lakes Area) containing abundant populations of two planktivorous fish species. After the introduction, pearl
dace were extirpated and yellow perch abundance was greatly reduced. Daphnia species shifted from D. galeata mendota to larger bodied Daphnia catawba, but the total zooplankton biomass did not increase, nor did the biomass of large grazers such as Daphnia. Phytoplankton biomass decreased after the northern pike introduction, but increased when northern pike were partially removed
from the lake. Phosphorus (P) excretion by fish was ∼0.18 mg P m−2 d−1 before pike addition, declined rapidly to approximately 0.03–0.10 as planktivorous perch and dace populations were reduced
by pike, and increased back to premanipulation levels after the pike were partially removed and the perch population recovered.
When perch were abundant, P excretion by fish supported about 30% of the P demand by primary producers, decreasing to 6–14%
when pike were abundant. Changes in phytoplankton abundance in Lake 221 appear to be driven by changes in P cycling by yellow
perch, whose abundance was controlled by the addition and removal of pike. These results confirm the role of nutrient cycling
in mediating trophic cascades and are consistent with previous enclosure experiments conducted in the same lake. 相似文献
12.
To identify the controls on dissolved organic carbon (DOC) production, we incubated soils from 18 sites, a mixture of 52 forest
floor and peats and 41 upper mineral soil samples, at three temperatures (3, 10, and 22°C) for over a year and measured DOC
concentration in the leachate and carbon dioxide (CO2) production from the samples. Concentrations of DOC in the leachate were in the range encountered in field soils (<2 to >50 mg l−1). There was a decline in DOC production during the incubation, with initial rates averaging 0.03–0.06 mg DOC g−1 soil C day−1, falling to averages of 0.01 mg g−1 soil C day−1; the rate of decline was not strongly related to temperature. Cumulative DOC production rates over the 395 days ranged from
less than 0.01 to 0.12 mg g−1 soil C day−1 (0.5–47.6 mg g−1 soil C), with an average of 0.021 mg g−1 soil C day−1 (8.2 mg g−1 soil C). DOC production rate was weakly related to temperature, equivalent to Q10 values of 0.9 to 1.2 for mineral samples and 1.2 to 1.9 for organic samples. Rates of DOC production in the organic samples
were correlated with cellulose (positively) and lignin (negatively) proportion in the organic matter, whereas in the mineral
samples C and nitrogen (N) provided positive correlations. The partitioning of C released into CO2–C and DOC showed a quotient (CO2–C:DOC) that varied widely among the samples, from 1 to 146. The regression coefficient of CO2–C:DOC production (log10 transformed) ranged from 0.3 to 0.7, all significantly less than 1. At high rates of DOC production, a smaller proportion
of CO2 is produced. The CO2–C:DOC quotient was dependent on incubation temperature: in the organic soil samples, the CO2–C:DOC quotient rose from an average of 6 at 3 to 16 at 22°C and in the mineral samples the rise was from 7 to 27. The CO2–C:DOC quotient was related to soil pH in the organic samples and C and N forms in the mineral samples. 相似文献
13.
Vertical and seasonal distributions of dissolved organic carbon (DOC) were investigated in a deep reservoir by considering the biodegradability and optical properties of DOC from three different layers during the stratified season. DOC in the epilimnion was characterized by relatively labile compounds that may have originated from phytoplankton. DOC in the metalimnion was variable in its composi<\h>tion and was possibly affected by turbid water inputs to the reservoir during the summer monsoon season. DOC in the hypolimnion always showed refractory characteristics, with low decomposition rates and high ultraviolet (UV) absorption. 相似文献
14.
The Role of Dissolved Organic Carbon, Dissolved Organic Nitrogen, and Dissolved Inorganic Nitrogen in a Tropical Wet Forest Ecosystem 总被引:3,自引:0,他引:3
Although tropical wet forests play an important role in the global carbon (C) and nitrogen (N) cycles, little is known about the origin, composition, and fate of dissolved organic C (DOC) and N (DON) in these ecosystems. We quantified and characterized fluxes of DOC, DON, and dissolved inorganic N (DIN) in throughfall, litter leachate, and soil solution of an old-growth tropical wet forest to assess their contribution to C stabilization (DOC) and to N export (DON and DIN) from this ecosystem. We found that the forest canopy was a major source of DOC (232 kg C ha–1 y–1). Dissolved organic C fluxes decreased with soil depth from 277 kg C ha–1 y–1 below the litter layer to around 50 kg C kg C ha–1 y–1 between 0.75 and 3.5m depth. Laboratory experiments to quantify biodegradable DOC and DON and to estimate the DOC sorption capacity of the soil, combined with chemical analyses of DOC, revealed that sorption was the dominant process controlling the observed DOC profiles in the soil. This sorption of DOC by the soil matrix has probably led to large soil organic C stores, especially below the rooting zone. Dissolved N fluxes in all strata were dominated by mineral N (mainly NO3−). The dominance of NO3– relative to the total amount nitrate of N leaching from the soil shows that NO3– is dominant not only in forest ecosystems receiving large anthropogenic nitrogen inputs but also in this old-growth forest ecosystem, which is not N-limited. 相似文献
15.
Absorption of solar ultraviolet radiation (UVR) in aquatic ecosystems is primarily controlled by dissolved organic carbon
(DOC). The role of iron (Fe) has also been suggested to contribute to UVR attenuation either directly or by interactions with
DOC. Here we present findings from three laboratory manipulations of Fe and DOC on changes to the dissolved UVR absorption
(ad,320) in a mid-latitude, dimictic, humic lake. In a laboratory simulation of lake turnover where anoxic, hypolimnetic water was
oxygenated ad,320 significantly increased from 23.3 to 81.7 m−1 (p<0.0001). In a second laboratory experiment, addition of ferrous Fe to deoxygenated lake water increased ad,320 upon reoxygenation up to a concentration of 1.0 mg l−1 Fe, where a solubility saturation threshold may have been reached. In situ lake experiments were designed to simulate release of UV absorbing substances from anoxic sediments by placing 20-l carboys
(open at the bottom, sealed at the top) onto the lake bottom. UV absorption at 320 nm increased over time for samples from
within the experimental carboys. Finally, samples from several lake profiles and sediment experiments were analyzed for ad,320, total Fe, and DOC. UV absorption of dissolved substances at 320 nm and total Fe concentration both increased with depth,
however DOC remained relatively constant over depth. Furthermore, total Fe and spectral slope showed tight coupling up to
1 mg l−1 total Fe in our survey analysis. Our results provide evidence for the importance of anoxic sediments as a source of ferrous
iron and UV absorbing substances and suggest a role for ferric iron in increasing UVR and PAR absorption in lake water. We
suggest that as this ferrous Fe oxidizes, its absorptive properties increase, and it may bind with dissolved organic matter,
enabling it to remain in solution and thus increasing the dissolved absorption of lake water for extended periods of time. 相似文献
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Trends in Dissolved Organic Carbon in UK Rivers and Lakes 总被引:11,自引:6,他引:5
Fred Worrall Ron Harriman Chris D. Evans Carol D. Watts John Adamson Colin Neal Ed Tipping Tim Burt Ian Grieve Don Monteith Pam S. Naden Tom Nisbet Brian Reynolds Paul Stevens 《Biogeochemistry》2004,70(3):369-402
Several studies have highlighted an increase in DOC concentration in streams and lakes of UK upland catchments though the causal mechanisms controlling the increase have yet to be fully explained. This study, compiles a comprehensive data set of DOC concentration records for UK catchments to evaluate trends and test whether observed increases are ubiquitous over time and space. The study analysed monthly DOC time series from 198 sites, including 29 lakes, 8 water supply reservoirs and 161 rivers. The records vary in length from 8 to 42 years going back as far as 1961. Of the 198 sites, 153 (77%) show an upward trend in DOC concentration significant at the 95% level, the remaining 45 (23%) show no significant trend and no sites show a significant decrease in DOC concentration. The average annual increase in DOC concentration was 0.17 mg C/l/year. The dataset shows: (i) a spatial consistent upward trend in the DOC concentration independent of regional effects of rainfall, acid and nitrogen deposition, and local effects of land-use change; (ii) a temporally consistent increase in DOC concentration for period back as far as the 1960s; (iii) the increase in DOC concentration means an estimated DOC flux from the UK as 0.86 Mt C for the year 2002 and is increasing at 0.02 Mt C/year. Possible reasons for the increasing DOC concentration are discussed. 相似文献
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We examined patterns of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) loading to a small urban stream
during baseflow and stormflow. We hypothesized that lower DOC and TDN contributions from impervious surfaces would dilute
natural hydrologic flowpath (i.e., riparian) contributions during storm events in an urban watershed, resulting in lower concentrations
of DOC and TDN during storms. We tested these hypotheses in a small urban watershed in Portland, Oregon, over a 3-month period
during the spring of 2003. We compared baseflow and stormflow chemistry using Mann–Whitney tests (significant at p<0.05). We also applied a mass balance to the stream to compare the relative significance of impervious surface contributions
versus riparian contributions of DOC and TDN. Results showed a significant increase in stream DOC concentrations during stormflows
(median baseflow DOC = 2.00 mg l−1 vs. median stormflow DOC = 3.46 mg l−1). TDN streamwater concentrations, however, significantly decreased with stormflow (median baseflow TDN = 0.75 mg l−1 vs. median stormflow TDN = 0.56 mg l−1). During storms, remnant riparian areas contributed 70–74% of DOC export and 38–35% of TDN export to the stream. The observed
pattern of increased DOC concentrations during stormflows in this urban watershed was similar to patterns found in previous
studies of forested watersheds. Results for TDN indicated that there were relatively high baseflow nitrogen concentrations
in the lower watershed that may have partially masked the remnant riparian signal during stormflows. Remnant riparian areas
were a major source of DOC and TDN to the stream during storms. These results suggest the importance of preserving near-stream
riparian areas in cities to maintain ambient carbon and nitrogen source contributions to urban streams. 相似文献