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1.
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
2.
Nitrogen Export from Forested Watersheds in the Oregon Coast Range: The Role of N<Subscript>2</Subscript>-fixing Red Alder 总被引:5,自引:2,他引:3
Variations in plant community composition across the landscape can influence nutrient retention and loss at the watershed scale. A striking example of plant species importance is the influence of N2-fixing red alder (Alnus rubra) on nutrient cycling in the forests of the Pacific Northwest. To understand the influence of red alder on watershed nutrient export, we studied the chemistry of 26 small watershed streams within the Salmon River basin of the Oregon Coast Range. Nitrate and dissolved organic nitrogen (DON) concentrations were positively related to broadleaf cover (dominated by red alder: 94% of basal area), particularly when near-coastal sites were excluded (r
2 = 0.65 and 0.68 for nitrate-N and DON, respectively). Nitrate and DON concentrations were more strongly related to broadleaf cover within entire watersheds than broadleaf cover within the riparian area alone, which indicates that leaching from upland alder stands plays an important role in watershed nitrogen (N) export. Nitrate dominated over DON in hydrologic export (92% of total dissolved N), and nitrate and DON concentrations were strongly correlated. Annual N export was highly variable among watersheds (2.4–30.8 kg N ha–1 y–1), described by a multiple linear regression combining broadleaf and mixed broadleaf–conifer cover (r2 = 0.74). Base cation concentrations were positively related to nitrate concentrations, which suggests that nitrate leaching increases cation losses. Our findings provide evidence for strong control of ecosystem function by a single plant species, where leaching from N saturated red alder stands is a major control on N export from these coastal watersheds. 相似文献
3.
Does Anthropogenic Nitrogen Enrichment Increase Organic Nitrogen Concentrations in Runoff from Forested and Human-dominated Watersheds? 总被引:1,自引:0,他引:1
Although the effects of anthropogenic nitrogen (N) inputs on the dynamics of inorganic N in watersheds have been studied extensively,
“the influence of N enrichment on organic N loss” is not as well understood. We compiled and synthesized data on surface water
N concentrations from 348 forested and human-dominated watersheds with a range of N loads (from less than 100 to 7,100 kg
N km−2 y−1) to evaluate the effects of N loading via atmospheric deposition, fertilization, and wastewater on dissolved organic N (DON)
concentrations. Our results indicate that, on average, DON accounts for half of the total dissolved N (TDN) concentrations
from forested watersheds, but it accounts for a smaller fraction of TDN in runoff from urban and agricultural watersheds with
higher N loading. A significant but weak correlation (r
2 = 0.06) suggests that N loading has little influence on DON concentrations in forested watersheds. This result contrasts
with observations from some plot-scale N fertilization studies and suggests that variability in watershed characteristics
and climate among forested watersheds may be a more important control on DON losses than N loading from atmospheric sources.
Mean DON concentrations were positively correlated, however, with N load across the entire land-use gradient (r
2 = 0.37, P < 0.01), with the highest concentrations found in agricultural and urban watersheds. We hypothesize that both direct contributions
of DON from wastewater and agricultural amendments and indirect transformations of inorganic N to organic N represent important
sources of DON to surface waters in human-dominated watersheds. We conclude that DON is an important component of N loss in
surface waters draining forested and human-dominated watersheds and suggest several research priorities that may be useful
in elucidating the role of N enrichment in watershed DON dynamics. 相似文献
4.
Human activities have greatly increased the input of biologically available nitrogen (N) from land-based sources to aquatic
ecosystems; yet few studies have examined how human actions influence N export in regions with a strong seasonality in water
availability. In this study, we quantified N inputs and outputs for 23 California watersheds and examined how climate, hydrology,
and land use practices influenced watershed N export. N inputs ranged from 581 to 11,234 kg N km−2 year−1 among watersheds, with 80% of total input for the region originating from agriculture (inorganic fertilizer, manure, and
legumes). Of the potential N sources examined, mean annual concentrations of dissolved organic N and dissolved inorganic N
in study rivers correlated most strongly with manure N input (r
2 = 0.54 and 0.53, respectively). Seasonal N export varied by basin and was correlated with climate, anthropogenic N inputs,
and reservoir releases. Fractional export of watershed N inputs by study rivers annually was small (median of 8%) and scaled
exponentially with runoff (r = 0.66). Collectively, our results show that anthropogenic activities have altered both the magnitude and timing of watershed
N export in California and suggest that targeted management in specific locations and times of the year could reduce N export
to downstream systems in the region. 相似文献
5.
This study examined impacts of succession on N export from 20 headwater stream systems in the west central Cascades of Oregon,
a region of low anthropogenic N inputs. The seasonal and successional patterns of nitrate (NO3−N) concentrations drove differences in total dissolved N concentrations because ammonium (NH4−N) concentrations were very low (usually < 0.005 mg L−1) and mean dissolved organic nitrogen (DON) concentrations were less variable than nitrate concentrations. In contrast to
studies suggesting that DON levels strongly dominate in pristine watersheds, DON accounted for 24, 52, and 51% of the overall
mean TDN concentration of our young (defined as predominantly in stand initiation and stem exclusion phases), middle-aged
(defined as mixes of mostly understory reinitiation and older phases) and old-growth watersheds, respectively. Although other
studies of cutting in unpolluted forests have suggested a harvest effect lasting 5 years or less, our young successional watersheds
that were all older than 10 years still lost significantly more N, primarily as NO3−N, than did watersheds containing more mature forests, even though all forest floor and mineral soil C:N ratios were well
above levels reported in the literature for leaching of dissolved inorganic nitrogen. The influence of alder may contribute
to these patterns, although hardwood cover was quite low in all watersheds; it is possible that in forested ecosystems with
very low anthropogenic N inputs, even very low alder cover in riparian zones can cause elevated N exports. Only the youngest
watersheds, with the highest nitrate losses, exhibited seasonal patterns of increased summer uptake by vegetation as well
as flushing at the onset of fall freshets. Older watersheds with lower N losses did not exhibit seasonal patterns for any
N species. The results, taken together, suggest a role for both vegetation and hydrology in N retention and loss, and add
to our understanding of N cycling by successional forest ecosystems influenced by disturbance at various spatial and temporal
scales in a region of relatively low anthropogenic N input. 相似文献
6.
Megan E. Moore Fred A. Goetz Donald M. Van Doornik Eugene P. Tezak Thomas P. Quinn Jose J. Reyes-Tomassini Barry A. Berejikian 《PloS one》2010,5(9)
Background
Hybridization between coastal cutthroat trout (Oncorhynchus clarki clarki) and steelhead or rainbow trout (Oncorhynchus mykiss) has been documented in several streams along the North American west coast. The two species occupy similar freshwater habitats but the anadromous forms differ greatly in the duration of marine residence and migration patterns at sea. Intermediate morphological, physiological, and performance traits have been reported for hybrids but little information has been published comparing the behavior of hybrids to the pure species.Methodology/Principal Findings
This study used acoustic telemetry to record the movements of 52 cutthroat, 42 steelhead x cutthroat hybrids, and 89 steelhead smolts, all wild, that migrated from Big Beef Creek into Hood Canal (Puget Sound, Washington). Various spatial and temporal metrics were used to compare the behavior of the pure species to their hybrids. Median hybrid residence time, estuary time, and tortuosity values were intermediate compared to the pure species. The median total track distance was greater for hybrids than for either cutthroat or steelhead. At the end of each track, most steelhead (80%) were located near or north of the Hood Canal, as expected for this seaward migrating species, whereas most cutthroat (89%) were within 8 kilometers of the estuary. Most hybrids (70%) were detected leaving Hood Canal, though a substantial percentage (20%) remained near the Big Beef Creek estuary. More hybrids (7.5%) than pure cutthroat (4.5%) or steelhead (0.0%) were last detected in the southern reaches of Hood Canal.Conclusions/Significance
Given the similarity in freshwater ecology between the species, differences in marine ecology may play an important role in maintaining species integrity in areas of sympatry. 相似文献7.
The Pawcatuck River watershed (764 km2) is a mainly forested drainage basin with a low population density (80 people km−2) that discharges to a shallow estuary, Little Narragansett Bay (RI and CT, USA). In order to quantify the nitrogen (N) and
phosphorus (P) flux to the estuary, we measured all forms of nitrogen and phosphorus, as well as suspended solids at the mouth
of the river above tidal influence, on more than 80 occasions over an annual cycle. The annual export of total nitrogen, total
phosphorus, and total suspended solids amounted to 16.0×106 mol y−1, 0.97×106 mol y−1, and 1.4×106 kg y−1, respectively. Nitrogen export was equally divided between dissolved inorganic (83% NO3−) and organic forms, with particulate nitrogen comprising 17% of the total flux. Phosphorus export was dominated by particulate
forms (67%), with dissolved inorganic phosphate contributing 30% and dissolved organic phosphorus contributing 8% of the annual
flux. Preliminary nutrient budgets for the Pawcatuck watershed suggest that only about 10% of the nitrogen and phosphorus
inputs are exported from the system. Strong regressions between water discharge and TN enabled us to extrapolate the data
collected during the relatively dry study period to a long term average discharge year. Under normal river discharge conditions,
the N flux would be approximately 26.0×106 mol y−1 or about 20% of the nitrogen inputs to the watershed. This value is very close to the N flux predicted by a regression developed
by others from a wide range of larger watersheds. The relatively large size of the Pawcatuck watershed relative to the estuary
(9.6 km2), makes Little Narragansett Bay one of the most intensively nitrogen loaded estuaries on the Atlantic coast in spite of the
dominant forest cover of the watershed. 相似文献
8.
Simon J. Ussher Andrew J. Manning Alan D. Tappin Mark F. Fitzsimons 《Hydrobiologia》2011,672(1):69-77
Previous measurements of the benthic nitrogen (N) flux from resuspended estuarine particles in the Thames Estuary appeared
to underestimate benthic inputs. This study attempted to address experimental limitations by using a mini-annular flume. The
flume has a 45 l capacity and was prepared in order to facilitate trace chemical analysis of N. Sediment (S1) and suspended
particulate material (SPM; S2) were collected from the Tamar Estuary, UK, and added to prepared, low-N, freshwater and seawater
solutions to give a final particle concentration of 500 mg l−1. Two tidal cycles were simulated and SPM and total dissolved N (TDN) were measured at a range of turbulent shear stresses
(0.06–0.9 Pa) representative of the sampling sites. A large increase in TDN concentration was measured after particle addition
and initial mixing, due to release of loosely bound particulate N (PN). The TDN concentration increased as the experiment
progressed (up to 12 μM), but did not appear to be systematically linked to either salinity or SPM concentration. The flume
system and experimental protocol provided reproducible physical data and low detection limits for TDN, which demonstrates
its potential for studying relationships between estuarine particle transport and macronutrient cycles. 相似文献
9.
Brenda K. Rone Alexandre N. Zerbini Erin A. Falcone Erin L. Keene Gregory S. Schorr 《The Journal of wildlife management》2024,88(3):e22543
Harbor porpoises (Phocoena phocoena) are the only cetaceans routinely sighted in Hood Canal, a narrow fjord that comprises the western edge of Puget Sound, Washington, USA. Harbor porpoises are sensitive to anthropogenic sounds, including noise from recreational and commercial vessel traffic, and the United States Navy, which conducts military training and testing within Hood Canal that can include underwater sound sources. This study was funded as part of the Navy monitoring program to assess potential impacts of naval activities on cetaceans. We conducted vessel-based line-transect surveys for harbor porpoises in Hood Canal in 2022–2023 to derive seasonal estimates of abundance and density. We carried out surveys over 37 days and surveyed the entire canal twice per season totaling 2,176 km of on-effort track line. We recorded 809 on-effort harbor porpoise groups and 1,385 individuals. Seasonal abundance estimates were lowest in winter (308 animals, 95% CI = 189–503) and gradually increased through spring and summer to a peak of 1,336 animals (95% CI = 826–2,160) in fall. Overall porpoise density was highest in central Hood Canal, an area that includes a designated United States Navy training range, though porpoise sightings were notably absent in a 21-km2 area adjacent to the naval submarine base within this otherwise high-density region. Though we collected only a single year of data, these results suggest that harbor porpoise abundance in Hood Canal increased significantly since it was last estimated (2013–2015). The notable seasonal fluctuation of harbor porpoise abundance suggests Hood Canal may host a larger percentage of the overall Washington Inland Waters stock during the fall season, raising important management considerations. 相似文献
10.
Jeffrey M. Klopatek 《Plant Ecology》2008,196(1):123-133
Litterfall and its subsequent decomposition are important feedback mechanisms in the intrasystem cycling of nutrients in forest
ecosystems. The amount of litterfall and the rate of decomposition are expected to vary with stand age and climate. Over a
2-year period, decomposition of five litter types were measured in two second-growth forest stands and one old-growth stand
in the Cascade Mountains of southern Washington state, USA. Both second-growth stands were dominated by Douglas-fir [Pseudotsuga menziesii (Mirb.,) Franco] but one had a significant proportion of red alder (Alnus rubra Bong.), a nitrogen (N) fixer. The old-growth stand was dominated by Douglas-fir and western hemlock [Tsuga heterophylla (Raf.) Sarg.]. All stands had a relatively shallow layer of forest floor mass. The five litter types were placed in each
stand to evaluate decomposition patterns. Despite significant differences in stand age, microclimate and mean residence times
for carbon (C) and N, the rates of litter mass loss varied only slightly between sites. The relative order of species litter
mass loss was: vine maple ≫ salal = western hemlock > Douglas-fir (from the youngest stand) > Douglas-fir (from the N rich
stand with red alder). The initial litter lignin concentration, not lignin:N, was the primary determinant of decomposition
rates, although the initial N concentration was the predictor for mass loss after 2 years in the N rich Douglas-fir-alder
stand. All litter types showed immobilization of N for nearly 2 years. Data for Douglas-fir litter suggest that higher levels
of N may retard decomposition of tissues with greater amounts of lignified material. The retention of N by the litter appeared
influenced by the nutrient capital of the stands as well as the forest floor C:N ratio. Decomposition was minimal during the
cold winter months, but displayed a definitive peak period during early Fall with wet weather, warm soils, and fungal activity.
Thus, long-term climatic change effects on forest floor C storage may depend more on changes in seasonality of precipitation
changes than just temperature changes. 相似文献
11.
Tuoping Hu Congjie Zhang Fude Ren Jun Ren Wenhong Jia 《Journal of molecular modeling》2009,15(2):157-163
The structures and electronic properties of the triatomic molecules containing Al, P, X atoms (X = B, Al, Ga; C, Si, Ge; N,
P, As; O, S and Se) and their anions are investigated at the B3LYP/cc-PVTZ and the B3LYP/aug-cc-PVTZ levels. The results show
that the most stable structures of the anions are AlXP− (X = B, C, N) and PAlX− (X = S, Se), while for the neutral molecules, the most stable structures are PXAl (X = C, N and O). The order of the VDEs
of the anions molecules and the AEAs of the neutral species are C < N < O < Si ≈ Ge < P ≈ As < Al = Ga < B < S ≈ Se and C
< O < N < Si ≈ Ge < P ≈ As < B < Al ≈ Ga < S ≈ Se, respectively. 相似文献
12.
Impact of N-Saturated Upland Forests on Downstream N Pollution in the Tatara River Basin, Japan 总被引:1,自引:0,他引:1
This study evaluated whether nitrogen (N) saturated upland forests can degrade downstream water quality in the Tatara River
Basin, northern Kyushu, western Japan. Our hypothesis is that elevated atmospheric N deposition degrades downstream water
quality in a watershed containing N-saturated forests because a considerable amount of atmospherically deposited N passes
into the streams without being retained. Synoptic stream water samplings were conducted at 23 sites across a wide range of
land-use categories in the basin over 1 year. A long-term temporal analysis of downstream water quality over the last 30 years
(1977–2007) was conducted and compared with long-term trends in related factors such as urban/agricultural activity, sewage
wastewater treatment, atmospheric N deposition, and forest condition. The results showed that atmospherically deposited N
to N-saturated forests can be a large enough non-point source of N leaving the watershed to impact downstream water quality.
This was highlighted by the reduction in pollutant exports derived from urban/agricultural activities, an increase in atmospheric
N deposition, and the maturation of coniferous plantation forests in the past 30 years. These have led to reductions in total
phosphorus and organic nitrogen concentrations in downstream water, whereas downstream nitrate (NO3
−) concentrations increased over the last 30 years. The consequent increase in the downstream N:P ratio indicated P limitation.
Reducing the NO3
− exports from N-saturated upland forests is suggested as a strategy to improve regional downstream NO3
− pollution, but involves intercontinental-scale action in reducing atmospheric N emissions. 相似文献
13.
Wilfred M. Wollheim Brian A. Pellerin Charles J. Vörösmarty Charles S. Hopkinson 《Ecosystems》2005,8(8):871-884
Urbanization can potentially alter watershed nitrogen (N) retention via combined changes in N loading, water runoff, and N
processing potential. We examined N export and retention for two headwater catchments (∼4 km2) of contrasting land use (16% vs. 79% urban) in the Plum Island Ecosystem (PIE-LTER) watershed, MA. The study period included
a dry year (2001–2002 water year) and a wet year (2002–2003 water year). We generalized results by comparing dissolved inorganic
nitrogen (DIN) concentrations from 16 additional headwater catchments (0.6–4.2 km2) across a range of urbanization (6–90%). Water runoff was 25–40% higher in the urban compared to the forested catchment,
corresponding with an increased proportion of impervious surfaces (25% vs. 8%). Estimated N loading was 45% higher and N flux
6.5 times higher in the urban than in the forested catchment. N retention (1 − measured stream export / estimated loading)
was 65–85% in the urban site and 93–97% in the forested site, with lower retention rates during the wetter year. The mechanisms
by which N retention stays relatively high in urban systems are poorly known. We show that N retention is related to the amount
of impervious surface in a catchment because of associated changes in N loading (maximized at moderate levels of imperviousness),
runoff (which continues to increase with imperviousness), and biological processes that retain N. Continued declines in N
retention due to urbanization have important negative implications for downstream aquatic systems including the coastal zone. 相似文献
14.
Nitrogen export by surface runoff from a small agricultural watershed in southeast China: seasonal pattern and primary mechanism 总被引:1,自引:0,他引:1
The seasonal pattern and primary mechanism of nitrogen (N) export by surface runoff from the Wuchuan subwatershed (WCW), an
agricultural upper watershed (1.88 km2) located in southeast China, were investigated based on extensive streamwater measurements in 2004–2005 under subtropical
climatic conditions. The results disclosed a highly variable but strong linkage between hydrological and anthropogenic controls
and N export. N export via surface runoff presented a significant seasonal pattern caused by changes in rainfall and watershed
N input. Approximately 75% of the annual N export (67 kg ha−1) was flushed by those storm runoff mainly occurred during the wet season (March through September). The WCW dataset of N
concentrations and loads during both baseflow and stormflow implied an interactive effects of anthropogenetic N input and
hydrology conditions: N export was flush-driven in late spring, summer and autumn (wet season), but highly related with soil
N in winter and early spring. Compared to undisturbed watersheds under similar rainfall conditions, WCW exported a considerable
amount of N due to intensive fertilizer application (a mean of 690 kg N ha−1 year−1, commonly as surface applications). This work provides a first characterization of a small agricultural Chinese catchment
under subtropical climates and its associated N export behavior. 相似文献
15.
Organism growth and reproduction are often limited by nutrient availability in freshwater ecosystems where, in some cases,
food webs are primarily supported by allochthonous organic matter. Therefore, we hypothesized that the composition of riparian
vegetation would influence the variability of N, P, and fatty acid content of in-stream consumers. Specifically, we predicted
that organisms living in alder streams would have higher levels of N, P, and polyunsaturated fatty acids than organisms in
coniferous streams. To determine this, we sampled fresh and aged leaf litter, periphyton, invertebrates, and cutthroat trout
(Oncorhynchus clarki) from 6 streams in western Washington state: 3 streams had high densities of nitrogen-fixing red alder (Alnus rubra) in the riparian zone, whereas 3 had high densities of conifers. We found fresh alder litter had twice the total polyunsaturated
fatty acid concentrations of hemlock vegetation while there were few statistical differences among aged alder and aged hemlock
vegetation. Multidimensional plots showed fatty acid profiles were unique to vegetation and fish while periphyton and invertebrates
shared the same multidimensional space. We used a mixed model to determine the relative importance of vegetation type (fixed
factor: conifer or alder), trophic levels (fixed factor: periphyton, primary consumer, or fish), and streams (random factor)
on individual fatty acid concentrations. Total polyunsaturated fatty acids, 16:0, 20:1, 20:3n6 and total n3 were the only
fatty acids influenced by stream vegetation (vegetation + stream model or full model). 67% of the fatty acids were best supported
by the trophic + stream model. Nitrogen, P, Ca, Fe, C:N, N:P, and C:N:P were all best supported by the trophic level + stream
model, and Zn was the only nutrient supported best by the full model. Correlations of n3 and n6 fatty acid concentrations
between periphyton and primary consumers, and primary consumers with trout indicated several fatty acid metrics, such as n3:n6,
showed food resources may affect relative fatty acid abundances of consumers. Although vegetation type did not influence relative
fatty acids of stream organisms, the importance of trophic level likely indicates organisms have different physical requirements
for fatty acids. The significance of a random factor, ‘stream,’ suggests that the relative abundances of fatty acids in periphyton,
invertebrates, and trout are stream-specific and are responding to local environmental or communal variables. 相似文献
16.
《Harmful algae》2017
Nutrient enrichment is a significant global-scale driver of change in coastal waters, contributing to an array of problems in coastal ecosystems. The St. Lucie Estuary (SLE) in southeast Florida has received national attention as a result of its poor water quality (elevated nutrient concentrations and fecal bacteria counts), recurring toxic Microcystis aeruginosa blooms, and its proximity to the northern boundary of tropical coral species in the United States. The SLE has an artificially large watershed comprised of a network of drainage canals, one of which (C-44) is used to lower the water level in Lake Okeechobee. Public attention has primarily been directed at nutrient inputs originating from the lake, but recent concern over the importance of local watershed impacts prompted a one-year watershed study designed to investigate the interactions between on-site sewage treatment and disposal systems (OSTDS or septic systems), groundwaters, and surface waters in the SLE and nearshore reefs. Results provided multiple lines of evidence of OSTDS contamination of the SLE and its watershed: 1) dissolved nutrients in groundwaters and surface waters were most concentrated adjacent to two older (pre-1978) residential communities and the primary canals, and 2) sucralose was present in groundwater at residential sites (up to 32.0 μg/L) and adjacent surface waters (up to 5.5 μg/L), and 3) δ15N values in surface water (+7.5 o/oo), macroalgae (+4.4 o/oo) and phytoplankton (+5.0 o/oo) were within the published range (>+3 o/oo) for sewage N and similar to values in OSTDS-contaminated groundwaters. Measured δ15N values in M. aeruginosa became increasingly enriched during transport from the C-44 canal (∼5.8 o/oo) into the mid-estuary (∼8.0 o/oo), indicating uptake and growth on sewage N sources within the urbanized estuary. Consequently, there is a need to reduce N and P loading, as well as fecal loading, from the SLE watershed via septic-to-sewer conversion projects and to minimize the frequency and intensity of the releases from Lake Okeechobee to the SLE via additional water storage north of the lake. These enhancements would improve water quality in both the SLE and Lake Okeechobee, reduce the occurrence of toxic harmful algal blooms in the linked systems, and improve overall ecosystem health in the SLE and downstream reefs. 相似文献
17.
The Long-term Effects of Disturbance on Organic and Inorganic Nitrogen Export in the White Mountains, New Hampshire 总被引:22,自引:8,他引:14
Traditional biogeochemical theories suggest that ecosystem nitrogen retention is controlled by biotic N limitation, that stream
N losses should increase with successional age, and that increasing N deposition will accelerate this process. These theories
ignore the role of dissolved organic nitrogen (DON) as a mechanism of N loss. We examined patterns of organic and inorganic
N export from sets of old-growth and historically (80–110 years ago) logged and burned watersheds in the northeastern US,
a region of moderate, elevated N deposition. Stream nitrate concentrations were strongly seasonal, and mean (± SD) nitrate
export from old-growth watersheds (1.4 ± 0.6 kg N ha−1 y−1) was four times greater than from disturbed watersheds (0.3 ± 0.3 kg N ha−1 y−1), suggesting that biotic control over nitrate loss can persist for a century. DON loss averaged 0.7 (± 0.2) kg N ha−1 y−1 and accounted for 28–87% of total dissolved N (TDN) export. DON concentrations did not vary seasonally or with successional
status, but correlated with dissolved organic carbon (DOC), which varied inversely with hardwood forest cover. The patterns
of DON loss did not follow expected differences in biotic N demand but instead were consistent with expected differences in
DOC production and sorption. Despite decades of moderate N deposition, TDN export was low, and even old-growth forests retained
at least 65% of N inputs. The reasons for this high N retention are unclear: if due to a large capacity for N storage or biological
removal, N saturation may require several decades to occur; if due to interannual climate variability, large losses of nitrate
may occur much sooner.
Received 27 April 1999; accepted 30 May 2000. 相似文献
18.
Summary Six stands of red alder (Alnus rubra Bong.) were sampled to assess the relationship between stand age and foliar chemical concentrations. The stands ranged in age from 9 to 45 years, and were located near Olympia, Washington, on sites of similar soil, aspect, and slope. Foliage was collected in July, and concentrations of most essential nutrients and aluminum were determined. Foliar concentrations of these elements varied among the different stands. Highest concentrations of N, P, Ca, S, Fe, and Al were found in trees of the youngest stand. Concentrations of N, P, S, and Fe were negatively correlated with stand age. The strongest correlation was obtained with P (r=–0.96,P<0.01), followed by N (r=–0.85,P=0.03). Results suggest that declining growth and deterioration of red alder stands with age may be related, at least in part, to limiting supplies of essential nutrients, especially P, N, and S. 相似文献
19.
R. Thomas James Wayne S. Gardner Mark J. McCarthy Stephen A. Carini 《Hydrobiologia》2011,669(1):199-212
Total nitrogen (TN) in Lake Okeechobee, a large, shallow, turbid lake in south Florida, has averaged between 90 and 150 μM
on an annual basis since 1983. No TN trends are evident, despite major storm events, droughts, and nutrient management changes
in the watershed. To understand the relative stability of TN, this study evaluates nitrogen (N) dynamics at three temporal/spatial
levels: (1) annual whole lake N budgets, (2) monthly in-lake water quality measurements in offshore and nearshore areas, and
(3) isotope addition experiments lasting 3 days and using 15N-ammonium (15NH4
+) and 15N-nitrate (15NO3
−) at two offshore locations. Budgets indicate that the lake is a net sink for N. TN concentrations were less variable than
net N loads, suggesting that in-lake processes moderate these net loads. Monthly NO3
− concentrations were higher in the offshore area and higher in winter for both offshore and nearshore areas. Negative relationships
between the percentage of samples classified as algal blooms (defined as chlorophyll a > 40 μg l−1) and inorganic N concentrations suggest N-limitation. Continuous-flow experiments over intact sediment cores measured net
fluxes (μmol N m−2 h−1) between 0 and 25 released from sediments for NH4
+, 0–60 removed by sediments for NO3
−, and 63–68 transformed by denitrification. Uptake rates in the water column (μmol N m−2 h−1) determined by isotope dilution experiments and normalized for water depth were 1,090–1,970 for NH4
+ and 59–119 for NO3
−. These fluxes are similar to previously reported results. Our work suggests that external N inputs are balanced in Lake Okeechobee
by denitrification. 相似文献
20.
Dissolved Nitrogen, Phosphorus, and Sulfur forms in the Ecosystem Fluxes of a Montane Forest in Ecuador 总被引:1,自引:0,他引:1
Rainer Goller Wolfgang Wilcke Katrin Fleischbein Carlos Valarezo Wolfgang Zech 《Biogeochemistry》2006,77(1):57-89
The N, P, and S cycles in pristine forests are assumed to differ from those of anthropogenically impacted areas, but there
are only a few studies to support this. Our objective was therefore to assess the controls of N, P, and S release, immobilization,
and transport in a remote tropical montane forest. The study forest is located on steep slopes of the northern Andes in Ecuador.
We determined the concentrations of NO3-N, NH4-N, dissolved organic N (DON), PO4-P, dissolved organic P (DOP), SO4-S, dissolved organic S (DOS), and dissolved organic C (DOC) in rainfall, throughfall, stemflow, lateral flow (in the organic
layer), litter leachate, mineral soil solution, and stream water of three 8–13 ha catchments (1900–2200 m a.s.l.). The organic
forms of N, P, and S contributed, on average, 55, 66, and 63% to the total N, P, and S concentrations in all ecosystem fluxes,
respectively. The organic layer was the largest source of all N, P, and S species except for inorganic P and S. Most PO4 was released in the canopy by leaching and most SO4 in the mineral soil by weathering. The mineral soil was a sink for all studied compounds except for SO4. Consequently, concentrations of dissolved inorganic and organic N and P were as low in stream water (TDN: 0.34–0.39 mg N l−1, P not detectable) as in rainfall (TDN: 0.39–0.48 mg N l−1, P not detectable), whereas total S concentrations were elevated (stream water: 0.04–0.15, rainfall: 0.01–0.07 mg S l−1). Dissolved N, P, and S forms were positively correlated with pH at the scale of soil peda except inorganic S. Soil drying
and rewetting promoted the release of dissolved inorganic N. High discharge levels following heavy rainstorms were associated
with increased DOC, DON, NO3-N and partly also NH4-N concentrations in stream water. Nitrate-N concentrations in the stream water were positively correlated with stream discharge
during the wetter period of the year. Our results demonstrate that the sources and sinks of N, P, and S were element-specific.
More than half of the cycling N, P, and S was organic. Soil pH and moisture were important controls of N, P, and S solubility
at the scale of individual soil peda whereas the flow regime influenced the export with stream water. 相似文献