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1.
Holly L. Menninger Margaret A. Palmer Laura S. Craig David C. Richardson 《Ecosystems》2008,11(8):1306-1317
The emergence of 17-year periodical cicadas in Maryland, USA, in 2004 provided a unique opportunity to study the effect of
a large, but temporally limited, resource pulse of arthropod detritus on stream ecosystem function. Cicada emergence was quantified
in the forests adjacent to two small streams with different histories of riparian disturbance (Intact and Disturbed sites).
We estimated the input of cicada detritus to the streams, described its retention and breakdown dynamics, and measured whole-stream
respiration over the cicada flight season (May–July). Average emergence density was significantly greater at the Intact site,
but average cicada detritus input rates were greater at the Disturbed site. Cicada detritus was locally retained within both
streams and rapidly broke down. Daily whole-stream respiration (CR24) at both sites responded dramatically to the cicada pulse, with CR24 doubling pre-cicada measurements following the period of greatest cicada input (Intact: 12.82 → 23.78 g O2 m−2 d−1; Disturbed: 2.76 → 5.77 g O2 m−2 d−1). CR24 returned to baseline levels when cicada input decreased at the Intact site, but more than doubled again at the Disturbed
site (13.14 g O2 m−2 d−1), despite a decline in cicada input rate. Differences in respiration response may be a function of differences in cicada
input rates as well as differences in microbial community activity. The strong effects on stream ecosystem function exerted
by a short but intense input of periodical cicada detritus may provide insights regarding the response of streams to other
irregular resource pulses.
HM, MP, LC, and DR conceived and designed study; HM, LC, and DR performed research; HM, LC, and DR analyzed data; HM, MP,
LC, and DR wrote the paper. 相似文献
2.
Headwater streams are key sites of nutrient and organic matter processing and retention, but little is known about temporal
variability in gross primary production (GPP) and ecosystem respiration (ER) rates as a result of the short duration of most
metabolism measurements in lotic ecosystems. We examined temporal variability and controls on ecosystem metabolism by measuring
daily rates continuously for 2 years in Walker Branch, a first-order deciduous forest stream. Four important scales of temporal
variability in ecosystem metabolism rates were identified: (1) seasonal, (2) day-to-day, (3) episodic (storm-related), and
(4) inter-annual. Seasonal patterns were largely controlled by the leaf phenology and productivity of the deciduous riparian
forest. Walker Branch was strongly net heterotrophic throughout the year with the exception of the open-canopy spring when
GPP and ER rates were co-equal. Day-to-day variability in weather conditions influenced light reaching the streambed, resulting
in high day-to-day variability in GPP particularly during spring (daily light levels explained 84% of the variance in daily
GPP in April). Episodic storms depressed GPP for several days in spring, but increased GPP in autumn by removing leaves shading
the streambed. Storms depressed ER initially, but then stimulated ER to 2–3 times pre-storm levels for several days. Walker
Branch was strongly net heterotrophic in both years of the study, with annual GPP being similar (488 and 519 g O2 m−2 y−1 or 183 and 195 g C m−2 y−1) but annual ER being higher in 2004 than 2005 (−1,645 vs. −1,292 g O2 m−2 y−1 or −617 and −485 g C m−2 y−1). Inter-annual variability in ecosystem metabolism (assessed by comparing 2004 and 2005 rates with previous measurements)
was the result of the storm frequency and timing and the size of the spring macroalgal bloom. Changes in local climate can
have substantial impacts on stream ecosystem metabolism rates and ultimately influence the carbon source and sink properties
of these important ecosystems. 相似文献
3.
Benthic community metabolism in four temperate stream systems: An inter-biome comparison and evaluation of the river continuum concept 总被引:7,自引:3,他引:4
T. L. Bott J. T. Brock C. S. Dunn R. J. Naiman R. W. Ovink R. C. Petersen 《Hydrobiologia》1985,123(1):3-45
Benthic community metabolism was studied on four stream systems located in different biomes in the United States: the eastern deciduous forest (Pennsylvania, PA, and Michigan, MI), the high desert (Idaho, ID), and the coniferous forest (Oregon, OR). Studies were designed to test the hypothesis advanced within the River Continuum Concept that a transition in community metabolism will occur from a predominance of heterotrophy in headwaters to a predominance of autotrophy in mid-sized reaches, with a return to heterotrophy further downstream. Both gross primary productivity (GPP) and community respiration (CR24) increased with downstream direction on all systems. Net daily metabolism (NDM, or GPP – CR24) shifted from heterotrophy (–NDM, GPP < CR24) to autotrophy (+NDM, GPP > CR24) with downstream direction at all sites, supporting the hypothesis. Annual metabolism in the most upstream reach of all sites was dominated by respiration; however, the farthest downstream reach was not necessarily the most autotrophic. Site-specific factors affected manifestation of the trend. Photosynthesis predominated annual metabolism in reaches (designated 1–4 in order of increasing size) 2–4 in ID, 3 and 4 in OR, and 4 in MI. In PA annual photosynthesis was slightly greater than respiration only at Station 3. Photosynthesis was predominant most consistently in ID and respiration most often in PA. About half the reaches that were heterotrophic annually were autotrophic at one or more seasons. Annual means of benthic GPP, CR24 and NDM ranged from 0.16 to 3.37, 0.36 to 2.88 and –0.73 to 0.50 g O2 · m2 · d1, respectively. Metabolic rates were usually high in PA and MI (and sometimes ID) and almost always lowest in OR. Parameters accounting for most variance in multiple linear regression analyses of the combined metabolism data from all sites were indicators of stream size, photosynthetically active radiation, temperature, and chlorophyll a concentration. 相似文献
4.
Flow extremes and benthic organic matter shape the metabolism of a headwater Mediterranean stream 总被引:8,自引:0,他引:8
Vicenç Acuña Adonis Giorgi Isabel Muñoz Urs Uehlinger Sergi Sabater 《Freshwater Biology》2004,49(7):960-971
1. Single‐station diel oxygen curves were used to monitor the oxygen metabolism of an intermittent, forested third‐order stream (Fuirosos) in the Mediterranean area, over a period of 22 months. Ecosystem respiration (ER) and gross primary production (GPP) were estimated and related to organic matter inputs and photosynthetically active radiation (PAR) in order to understand the effect of the riparian forest on stream metabolism. 2. Annual ER was 1690 g O2 m?2 year?1 and annual GPP was 275 g O2 m?2 year?1. Fuirosos was therefore a heterotrophic stream, with P : R ratios averaging 0.16. 3. GPP rates were relatively low, ranging from 0.05 to 1.9 g O2 m?2 day?1. The maximum values of GPP occurred during a few weeks in spring, and ended when the riparian canopy was fully closed. The phenology of the riparian vegetation was an important determinant of light availability, and consequently, of GPP. 4. On a daily scale, light and temperature were the most important factors governing the shape of photosynthesis–irradiance (P–I) curves. Several patterns could be generalised in the P–I relationships. Hysteresis‐type curves were characteristic of late autumn and winter. Light saturation responses (that occurred at irradiances higher than 90 μE m?2 s?1) were characteristic of early spring. Linear responses occurred during late spring, summer and early autumn when there was no evidence of light saturation. 5. Rates of ER were high when compared with analogous streams, ranging from 0.4 to 32 g O2 m?2 day?1. ER was highest in autumn 2001, when organic matter accumulations on the streambed were extremely high. By contrast, the higher discharge in autumn 2002 prevented these accumulations and caused lower ER. The Mediterranean climate, and in its effect the hydrological regime, were mainly responsible for the temporal variation in benthic organic matter, and consequently of ER. 相似文献
5.
V. I. Kolmakov O. V. Anishchenko E. A. Ivanova M. I. Gladyshev N. N. Sushchik 《Journal of applied phycology》2008,20(3):289-297
Periphyton (epilithon) gross primary production (GPP) was estimated using the DCMU-fluorescence method in the Yenisei River.
In the unshaded littoral zone, chlorophyll a concentration (Chl a) and GPP value varied from 0.83 to 973.74 mg m−2and 2–304,425 O2 m−2 day−1 (0.64–95 133 mg C m−2 day−1), respectively. Positive significant correlation (r = 0.8) between daily GPP and periphyton Chl a was found. Average ratio GPP:Chl a for periphyton was 36.36 mg C mg Chl a m−2 day−1. The obtained GPP values for the Yenisei River have a high significant correlation with values predicted by a conventional
empirical model for stream periphyton. We concluded that the DCMU-fluorescence method can be successfully used for measuring
of gross primary production of stream phytoperiphyton at least as another useful tool for such studies. 相似文献
6.
Jes Jessen Rasmussen Annette Baattrup-Pedersen Tenna Riis Nikolai Friberg 《Aquatic Ecology》2011,45(2):231-242
We surveyed macrophyte community structure and measured community metabolism and nutrient uptake along a temperature gradient
(9.7–17.4°C) in four Icelandic streams influenced by geothermal heating. The study streams are part of the geothermal area
in Hengill that is uniquely characterised by streams with comparable water chemistry despite the geothermal influence. Stream
metabolism was studied applying the diurnal upstream–downstream dissolved oxygen change technique. Nutrient uptake was studied
by adding solutions of nitrogen and phosphorus together with a conservative tracer. Rates of primary production (GPP) and
uptake of nitrate–N and phosphate-P increased with increasing stream temperature. GPP was 20 times higher (up to 12.99 g O2 m−2 day−1) and rates of nutrient uptake were up to 30-times higher (up to 22.99, 13.31 and 7.94 mg m−2 h−1 for ammonium, nitrate and phosphate, respectively) in the warmest streams compared with the coldest. Furthermore, macrophytes,
when present, were strongly controlling ecosystem processes. Our study implies that temperature may affect stream ecosystem
processes both directly (i.e. physiologically) and indirectly (i.e. by changing other structural parameters). 相似文献
7.
8.
9.
Spatial variability in hydrological flowpaths and nitrate-removal processes complicates the overall assessment of riparian
buffer zone functioning in terms of water quality improvement as well as enhancement of the greenhouse effect by N2O emissions. In this study, we evaluated denitrification and nitrous oxide emission in winter and summer along two groundwater
flowpaths in a nitrate-loaded forested riparian buffer zone and related the variability in these processes to controlling
soil factors. Denitrification and emissions of N2O were measured using flux chambers and incubation experiments. In winter, N2O emissions were significantly higher (12.4 mg N m−2 d−1) along the flowpath with high nitrate removal compared with the flowpath with low nitrate removal (2.58 mg N m−2 d−1). In summer a reverse pattern was observed, with higher N2O emissions (13.6 mg N m−2 d−1) from the flowpath with low nitrate-removal efficiencies. Distinct spatial patterns of denitrification and N2O emission were observed along the high nitrate-removal transect compared to no clear pattern along the low nitrate-removal
transect, where denitrification activity was very low. Results from this study indicate that spots with high nitrate-removal
efficiency also contribute significantly to an increased N2O emission from riparian zones. Furthermore, we conclude that high variability in N2O:N2 ratio and weak relationships with environmental conditions limit the value of this ratio as a proxy to evaluate the environmental
consequences of riparian buffer zones. 相似文献
10.
The effects of seasonality and dilution stress on the functioning of Rambla Salada, a hypersaline Mediterranean stream in
SE Spain, were evaluated. The stream is subject to diffuse freshwater inputs from the drainage of intensively irrigated agriculture
in the catchment and periodic losses of water through an irrigation channel. Metabolic rates and the biomass of primary producers
and consumers were estimated over a 2-year period. During the first year several dilution events occurred, while during the
second year the salinity recovery reached predisturbance levels. Functional indicators were compared in the disturbance and
recovery salinity periods. Primary production and respiration rates in the Rambla Salada ranged between 0.07–21.05 and 0.19–17.39 g
O2 m−2 day−1, respectively. The mean values for these variables were 7.35 and 5.48 g O2 m−2 day−1, respectively. Mean net daily metabolism rate was 1.87 ± 0.52 g O2 m−2 day−1 and mean production/respiration ratio was 2.48 ± 1.1, reflecting autotrophic metabolism. The metabolic rates showed the typical
seasonal pattern of Mediterranean open canopy streams. Therefore, gross primary production (GPP) and ecosystem respiration
(ER) registered maximum values in summer, intermediate values in spring and autumn and minimum values in winter. The metabolic
rates and biomass of consumers were greater in the disturbance period than in the recovery period. However, they did not show
significant differences between periods due to their important dependence on seasonal cycle. Seasonality accounted for much
of the temporal variability in GPP and ER (76% and 83% in the multiregression models, respectively). Light availability seems
to be the most important factor for GPP and ER in the Rambla Salada. Autotrophic biomass responded more to variations in discharge
and conductivity than to seasonal variations. In fact, it was severely affected by freshwater inputs after which the epipelic
biomass decreased significantly and Cladophora glomerata proliferated rapidly. Epipelic algal biomass was the most sensitive parameter to dilution disturbance.
Handling editor: Luigi Naselli-Flores 相似文献
11.
Stream export of nitrogen (N) as nitrate (NO3−; the most mobile form of N) from forest ecosystems is thought to be controlled largely by plant uptake of inorganic N, such
that reduced demand for plant N during the non-growing season and following disturbances results in increased stream NO3− export. The roles of microbes and soils in ecosystem N retention are less clear, but are the dominant controls on N export
when plant uptake is low. We used a mass balance approach to investigate soil N retention during winter (December through
March) at the Hubbard Brook Experimental Forest by comparing NO3− inputs (atmospheric deposition), internal production (soil microbial nitrification), and stream output. We focused on months
when plant N uptake is nearly zero and the potential for N export is high. Although winter months accounted for only 10–15%
of annual net nitrification, soil NO3− production (0.8–1.0 g N m−2 winter−1) was much greater than stream export (0.03–0.19 N m−2 winter−1). Soil NO3− retention in two consecutive winters was high (96% of combined NO3− deposition and soil production; year 1) even following severe plant disturbance caused by an ice-storm (84%; year 2) We show
that soil NO3− retention is surprisingly high even when N demand by plants is low. Our study highlights the need to better understand mechanisms
of N retention during the non-growing season to predict how ecosystems will respond to high inputs of atmospheric N, disturbance,
and climate change. 相似文献
12.
Mitsuru Hirota Pengcheng Zhang Song Gu Haihua Shen Takeo Kuriyama Yingnian Li Yanhong Tang 《Journal of plant research》2010,123(4):531-541
Characterizing the spatial variation in the CO2 flux at both large and small scales is essential for precise estimation of an ecosystem’s CO2 sink strength. However, little is known about small-scale CO2 flux variations in an ecosystem. We explored these variations in a Kobresia meadow ecosystem on the Qinghai-Tibetan plateau in relation to spatial variability in species composition and biomass. We
established 14 points and measured net ecosystem production (NEP), gross primary production (GPP), and ecosystem respiration
(Re) in relation to vegetation biomass, species richness, and environmental variables at each point, using an automated chamber
system during the 2005 growing season. Mean light-saturated NEP and GPP were 30.3 and 40.5 μmol CO2 m−2 s−1 [coefficient of variation (CV), 42.7 and 29.4], respectively. Mean Re at 20°C soil temperature, Re20, was −10.9 μmol CO2 m−2 s−1 (CV, 27.3). Re20 was positively correlated with vegetation biomass. GPPmax was positively correlated with species richness, but 2 of the 14 points were outliers. Vegetation biomass was the main determinant
of spatial variation of Re, whereas species richness mainly affected that of GPP, probably reflecting the complexity of canopy
structure and light partitioning in this small grassland patch. 相似文献
13.
Carbon Dioxide Variation in a Hardwood Forest Stream: An Integrative Measure of Whole Catchment Soil Respiration 总被引:8,自引:3,他引:5
The concentration of CO2 in stream water is a product of not only instream metabolism but also upland, riparian, and groundwater processes and as
such can provide an integrative measure of whole catchment soil respiration. Using a 5-year dataset of pH, alkalinity, Ca2+, and Mg2+ in surface water of the West Fork of Walker Branch in eastern Tennessee in conjunction with a hydrological flowpath chemistry
model, we investigated how CO2 concentrations and respiration rates in stream, bedrock, and soil environments vary seasonally and interannually. Dissolved
inorganic carbon concentration was highest in summer and autumn (P < 0.05) although the proportion as free CO2 (pCO2) did not vary seasonally (P > 0.05). Over the 5 years, pCO2 was always supersaturated with respect to the atmosphere ranging from 374 to 3626 ppmv (1.0- to 10.1-fold greater than atmospheric
equilibrium), and CO2 evasion from the stream to the atmosphere ranged from 146 to 353 mmol m−2 d−1. Whereas pCO2 in surface water exhibited little intra-annual or interannual variation, distinct seasonal patterns in soil and bedrock pCO2 were revealed by the catchment CO2 model. Seasonally, soil pCO2 increased from a winter low of 8167 ppmv to a summer high of 27,068 ppmv. Driven by the seasonal variation in gas levels,
evasion of CO2 from soils to the atmosphere ranged from 83 mmol m−2 d−1 in winter to 287 mmol m−2 d−1 in summer. The seasonal variation in soil CO2 tracked soil temperature (r
2= 0.46, P < 0.001) and model-derived estimates of CO2 evasion rate from soils agreed with previously reported fluxes measured using chambers (Pearson correlation coefficient =
0.62, P < 0.05) supporting the model assumptions. Although rates of CO2 evasion were similar between the stream and soils, the overall rate of evasion from the channel was only 0.4% of the 70,752
mol/d that evaded from soils due to the vastly different areas of the two subsystems. Our model provides a means to assess
whole catchment CO2 dynamics from easily collected and measured stream-water samples and an approach to study catchment scale variation in soil
ecosystem respiration.
Received 24 July 1997; accepted 14 November 1997. 相似文献
14.
Primary production rates, chlorophyll and phytoplankton biovolume were measured monthly from April 2003 to November 2004 in
Lake Tana, a large tropical lake in the highlands of Ethiopia. The lake is characterised by low nutrient concentrations, and
a low water transparency due to high silt load of the inflowing rivers during the rainy seasons (May–November) and daily resuspension
of sediments in the inshore zone. The mean chlorophyll-a concentrations varied seasonally and ranged from 2.6 mg m−3 to 8.5 mg m−3 (mean: 4.5 mg m−3) in the offshore zone. Primary production was measured using the light–dark bottles technique. We incubated only at three
depths, i.e. 0.6, 1.2 and 1.8 m. Therefore, we may have missed a substantial part of the depth production profile and probably
also frequently missed P
max. Gross primary production in the openwater averaged 2.43 g O2 m−2 d−1 and ranged between 0.03 g O2 m−2 d−1 and 10.2 g O2 m−2 d−1; production was significantly higher in the inshore zone. The highest production rates were observed in the post-rainy season
(Oct–Nov), which coincided with a bloom of Microcystis and higher chlorophyll levels. This seasonal high production is probably caused by a relatively high nutrient availability
in combination with favourable light conditions. The gross primary production rates of L. Tana are among the lowest compared
with other tropical lakes. This will be partly the result of our underestimation of gross primary production by often missing
P
max. Another cause is the oligotrophic nature of the lake in combination with its relatively low water transparency. The gross
primary production per unit chlorophyll in the openwater zone was in the same range as in 30 other tropical lakes and reservoirs.
The higher primary production in the inshore zone is probably the result of the daily water column mixing (Z
mix ≥ Z
t) in this area, enhancing nutrient recycling. A large proportion of the annual primary production is realised in one of the
four seasons only. This productive post-rainy season is relatively short (2 months) and therefore efficiency of transfer of
matter between the first and second trophic level of the Lake ecosystem will be poor. 相似文献
15.
Annual cycle of gross primary production and respiration in the Viroin River (Belgium) 总被引:1,自引:1,他引:0
Gross primary production, community respiration and reaeration coefficient were determined during an annual cycle on the Viroin
River (South Belgium), based on the daily variations of dissolved oxygen concentration.
Reaeration coefficient remains remarkably constant (0.26 h−1) during the year in spite of discharge variations. The autotrophic community is dominated by ‘Ranunculus fluitans’. Primary production parallels the variations of total solar radiations. It ranges from 0 in winter to 8 g O2 m−2 d−1 in summer. In spring and summer, respiration variations parallel those of primary production (average value: 10 g O2 m−2 d−1); in the dry autumn, decomposition of dying macrophytes considerably enhances the community respiration (15 g O2 m−2 d−1).
A P/R diagram is used to characterize the trophic state of the Viroin. 相似文献
16.
The metabolism of organic matter in the hyporheic zone of a mountain stream, and its spatial distribution 总被引:6,自引:1,他引:5
Martin Pusch 《Hydrobiologia》1996,323(2):107-118
Community respiration in hyporheic sediments (HCR) was studied in a characteristic riffle-pool-sequence of a mountain stream.
HCR activity at the riffle site strongly exceeded that at the corresponding pool site with a mean ratio of 5.3. The vertical
distribution of HCR activity was homogeneous in the pool, while there was a distinct maximum in the uppermost layer in the
riffle. Similarly, the spatial distribution of certain fractions of particulate organic matter (POM), and their turnover,
was largely determined by stream morphology. Mean annual HCR per unit area of stream bed was estimated as 1.71 g O2 m−2 d−1. Hence, HCR contributes significantly to total heterotrophic activity in streams, thus enhancing the relative importance
of heterotrophic processes in running waters containing hyporheic zones. 相似文献
17.
Contribution of root to soil respiration and carbon balance in disturbed and undisturbed grassland communities, northeast China 总被引:1,自引:0,他引:1
Changes in the composition of plant species induced by grassland degradation may alter soil respiration rates and decrease
carbon sequestration; however, few studies in this area have been conducted. We used net primary productivity (NPP), microbial
biomass carbon (MBC), and soil organic carbon (SOC) to examine the changes in soil respiration and carbon balance in two Chinese
temperate grassland communities dominated by Leymus chinensis (undisturbed community; Community 1) and Puccinellia tenuiflora (degraded community; Community 2), respectively. Soil respiration varied from 2.5 to 11.9 g CO2 m−2 d−1 and from 1.5 to 9.3 g CO2 m−2 d−1, and the contribution of root respiration to total soil respiration from 38% to 76% and from 25% to 72% in Communities 1
and 2, respectively. During the growing season (May–September), soil respiration, shoot biomass, live root biomass, MBC and
SOC in Community 2 decreased by 28%, 39%, 45%, 55% and 29%, respectively, compared to those in Community 1. The considerably
lower net ecosystem productivity in Community 2 than in Community 1 (104.56 vs. 224.73 g C m−2 yr−1) suggests that the degradation has significantly decreased carbon sequestration of the ecosystems. 相似文献
18.
Microphytobenthic oxygen production was studied in the Gulf of Fos (French Mediterranean coast) during 1991/1992 using transparent
and dark benthic chambers. Nine stations were chosen in depths ranging from 0.5 to 13 m, which represents more than 60% of
bottoms in the Gulf. Positive net microphytobenthic oxygen production was seasonally detected down to 13 m; the maximum value
attained was 60 mg O2 m−2 h−1 (0.7–0.8 g O2 m−2 d−1) in sediments at 0.5 m depth during spring and winter. Respiration rates were maximum in the sediments located at the mussel
farm (5 m), in the center of the Gulf, with 135 mg O2 m−2 h−1 in spring (3.2 g O2 m−2 d−1); in the other locations, it ranged from 3.3 to 58.2 mg O2 m−2 h−1 (0.08–1.4 g O2 m−2 d−1).
Compared to phytoplankton, microphytobenthos production was higher only in the bottoms < 1 m depth. In deeper bottom waters,
phytoplankton production could be absent due to light limitation, while microphytobenthos was still productive. Phytoplankton
production m−2 was generally higher than microphytobenthic production. Microphytobenthic biomass, higher than phytoplanktonic, varied from
27 to 379 mg Chl a m−2, the maximum in the mussel farm sediments, with the minimum in sandy shallow bottoms. Pigment analysis showed that microphytobenthos
consisted mainly of diatoms (Chl c and fucoxanthin) but other algal groups containing Chl b could become seasonally important. A Principal Component Analysis suggested that the main statistical factors explaining
the distribution of our observations may be interpreted in terms of enrichment in phaeopigments and light; the role of Chl
a appearing paradoxically as secondary in benthic production rates. Phaeopigments are mainly constituted by phaeophorbides,
which indicate grazing processes. The influence of the mussel farm on the oxygen balance is noticeable in the whole Gulf. 相似文献
19.
During 1999–2001 the chemical composition and fluxes were measured in rainfall, throughfall, soil solution and stream water
in a remote forested site in the Italian Alps. The analysis of temporal patterns revealed the differential behaviour of nitrogen
and sulphur and suggested that different mechanisms controlled their flux. No important changes in sulphate concentration
and fluxes emerged as the solution passed through the various components of the forest ecosystem, and temporal variations
of SO4 in the soil solution and stream were likely driven by the physical process of dilution. The availability of nitrate and ammonia,
by contrast, was drastically reduced as throughfall water entered the soil and passed through the mineral layers, irrespective
of season. The calculated hydrochemical budget based on throughfall and soil solution N fluxes revealed that ~80% N retention
in the forest soil, corresponding to 12 kg ha−1 yr−1, despite a relatively high N deposition loading (15 kg ha−1 yr−1). Most of the leached nitrogen (90%) was in the organic form. Indicators of the N status of this ecosystem, such as C/N ratio
in solid and solution phase of the soil and N foliage content as well as land use history were examined. Despite the strong
N retention in the forested part of the catchment, the stream water N–NO3 levels were consistently above 10 μg l−1 suggesting that the Val Masino catchment as a whole was less efficient in processing atmospheric N inputs. This contrasting
N behaviour illustrates the role of landscape features, such as the soil cover and vegetation type, that is characteristic
of an alpine catchment. 相似文献
20.
McCormick Paul V. Shuford III Robert B. E. Backus John G. Kennedy William C. 《Hydrobiologia》1997,362(1-3):185-210
We sampled periphyton in dominant habitats at oligotrophic and eutrophic sites in the northern Everglades during the wet and
the dryseasons to determine the effects of nutrient enrichment on periphytonbiomass, taxonomic composition, productivity,
and phosphorus storage. Arealbiomass was high (100–1600 g ash-free dry mass [AFDM]m−2) in oligotrophic sloughs and in stands of the emergentmacrophyte Eleocharis cellulosa, but was low in adjacent stands of
sawgrass,Cladium jamaicense (7–52 g AFDM m−2). Epipelon biomasswas high throughout the year at oligotrophic sites whereas epiphyton andmetaphyton biomass varied seasonally
and peaked during the wet season.Periphyton biomass was low (3–68 g AFDM m−2) and limitedto epiphyton and metaphyton in open-water habitats at eutrophic sites andwas undetectable in cattail stands (Typha
domingensis) that covered morethan 90% of the marsh in these areas. Oligotrophic periphytonassemblages exhibited strong seasonal
shifts in species composition and weredominated by cyanobacteria (e.g., Chroococcus turgidus, Scytonema hofmannii)during the
wet season and diatoms (e.g. Amphora lineolata, Mastogloiasmithii) during the dry season. Eutrophic assemblages were dominated
byCyanobacteria (e.g., Oscillatoria princeps) and green algae (e.g., Spirogyraspp.) and exhibited comparatively little seasonality.
Biomass-specific grossprimary productivity (GPP) of periphyton assemblages in eutrophic openwaters was higher than for comparable
slough assemblages, but areal GPP wassimilar in these eutrophic (0.9–9.1 g C m−2d−1) and oligotrophic (1.75–11.49 g C m−2d−1) habitats. On a habitat-weighted basis, areal periphytonGPP was 6- to 30-fold lower in eutrophic areas of the marsh due to
extensiveTypha stands that were devoid of periphyton. Periphyton at eutrophic siteshad higher P content and uptake rates than
the oligotrophic assemblage, butstored only 5% as much P because of the lower areal biomass.Eutrophication in the Everglades
has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity. These changesmay have
important implications for efforts to manage this wetland in asustainable manner.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献