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1.
Internal loading of phosphorus from sediments of Lake Pontchartrain (Louisiana,USA) with implications for eutrophication 总被引:1,自引:0,他引:1
Diffusive flux of bioavailable soluble reactive phosphorus (SRP) across the sediment–water interface is one mechanism by which
sediments can be a source of phosphorus to the water column in aquatic systems and contribute to primary productivity. This
process is dependent on sediment biogeochemistry and SRP concentration gradients at the sediment–water interface. In systems
subjected to episodic external pulses of nutrient-rich water, SRP concentration gradients can have potential implications
for diffusive flux. In this study, we sought to investigate two hypotheses: (1) diffusive flux of SRP from sediments is a
significant source of SRP in the annual budget for the oligohaline Lake Pontchartrain estuary and (2) under SRP-depleted water
column conditions following large episodic, external pulses of nitrogen-rich Mississippi River water to the estuary, internal
SRP loading by diffusive flux can regenerate SRP in the water column to previously observed levels rapidly. Our specific objectives
were to: (i) determine sediment, water column, and phytoplankton characteristics at multiple locations in the estuary, (ii)
measure rates of SRP diffusive flux from sediments using intact cores under aerobic and anaerobic incubations, (iii) estimate
the potential for water column SRP regeneration by diffusive flux under SRP-depleted conditions using a simple model, and
(iv) estimate the annual load of SRP from the sediments by diffusive flux. Results indicate that diffusive flux of SRP from
Lake Pontchartrain sediments likely contributes ~30–44% of the annual SRP load to the estuary. Further, internal SRP loading
by diffusion has the potential to regenerate SRP in SRP-depleted waters to previously observed concentrations in <60 days.
Our findings suggest that a sequence of events is feasible where external pulses of nitrogen-rich water produce phosphorus-limited
conditions, followed by an internal pulse of SRP from sediments to restore nitrogen-limited conditions. This internal SRP
load may be an important contributor in promoting blooms of nitrogen-fixing harmful algae under summertime low-nutrient conditions. 相似文献
2.
Wet and dry atmospheric fluxes of total phosphorus (TP) and soluble reactive phosphorus (SRP) measured at four sites over a 12-month period were used to estimate lake-wide atmospheric phosphorus (P) deposition to Lake Victoria, East Africa. Atmospheric samples were collected in plastic buckets with top diameter of 25.5 cm by 30 cm deep. The highest P loading rates of 2.7 (TP) and 0.8 (SRP) kg ha–2 year–1 were measured at Mwanza compared to less than 1.9 (TP) and 0.65 (SRP) kg ha–2 year–1 measured in other three sites. By applying these loading rates to the lake surface, it was estimated that 13.5 ktons (13.5 × 103 kg) of TP were deposited annually into the lake from the atmosphere. Thirty-two percent of the total was found to be in the SRP form. Dryfall, a component ignored in previous studies exceeded wet deposition by contributing 75% of the total P input. However, materials deposited by dryfall made a lesser contribution to soluble form of phosphorus, as SRP concentrations in the wet samples were 2–3 times higher than SRP concentrations in dry samples. The annual fluxes of phosphorus measured on the south and western shores of Lake Victoria (1.8–2.7 kg ha–2 year–1) are near the upper range of similar fluxes measured in the tropics. In comparison with the existing estimates of municipal and runoff P inputs from other studies, it is estimated that atmospheric deposition represent 55% of the total phosphorus input to the Lake Victoria. The four sampling sites were fairly clustered and wet and dry P deposition data were collected from shore/land stations and applied to open lake areas to estimate lake-wide P deposition. In this regard, the estimates determined here should be viewed as a first order approximation of actual P load deposited into the lake. 相似文献
3.
Phosphorus (P) dynamics in the agriculturally-dominated Minnesota River (USA) were examined in the lower 40 mile reach in
relation to hydrology, loading sources, suspended sediment, and chlorophyll to identify potential biotic and abiotic controls
over concentrations of soluble P and the recycling potential of particulate P during transport to the Upper Mississippi River.
Within this reach, wastewater treatment plant (WWTP) contributions as soluble reactive P (SRP) were greatest during very low
discharge and declined with increasing discharge and nonpoint source P loading. Concentrations of SRP declined during low
discharge in conjunction with increases in chlorophyll, suggesting biotic transformation to particulate P via phytoplankton
uptake. During higher discharge periods, SRP was constant at ~0.115 mg l−1 and coincided with an independently measured equilibrium P concentration (EPC) for suspended sediment in the river, suggesting
abiotic control over SRP via phosphate buffering. Particulate P (PP) accounted for 66% of the annual total P load. Redox-sensitive
PP, estimated using extraction procedures, represented 43% of the PP. Recycling potential of this load via diffusive sediment
P flux under anoxic conditions was conservatively estimated as ~17 mg m−2 d−1 using published regression equations. The reactive nature and high P recycling potential of suspended sediment loads in the
Minnesota River has important consequences for eutrophication of the Upper Mississippi River. 相似文献
4.
Tiia Pedusaar Ilkka Sammalkorpi Arto Hautala Jaana Salujõe Ain Järvalt Margus Pihlak 《Hydrobiologia》2010,649(1):95-106
Lake ülemiste, the drinking water reservoir of Estonia’s capital city Tallinn, was biomanipulated by manual removal of cyprinids
in 2004–2006 and its impact on water quality in the vegetation period was studied. A total biomass of 156 tonnes corresponding
to 160 kg ha−1 of fish, predominantly cyprinids, were removed. A decline in the unit catches of fishing was observed. The removed fish biomass
versus phosphorus concentration of the lake was considered sufficient to reduce the impact of cyprinids on water quality.
The phosphorus removed within fish biomass corresponded to 38 μg l−1 and 21% of the external phosphorus load of the fishing period. The mean total phosphorus concentration dropped from >50 to
≤36 μg l−1. However, the densities of planktivorous young-of-the-year percids remained high and the role of zooplankton grazing in improving
water quality was found non-significant or transient. The cladocerans biomass decreased and the small-sized Daphnia cucullata remained almost the only daphnid in Lake ülemiste during and after the manipulation. Predomination of filamentous cyanobacteria
was replaced by a more diverse phytoplankton composition and co-domination of micro- and pico-sized colonial cyanobacteria
during summer. Mean phytoplankton biomass decreased from 15 to 6 mg l−1 primarily as a result of decreased in-lake TP availability. The Secchi disc transparency increased only in May 2005–2007.
The effects of coincidental events, a decline of external loading of phosphorus and a simultaneous flushing induced by heavy
rainfall, on lake water quality are discussed with some implications to the future management of the reservoir. 相似文献
5.
L. Xie R. R. Rediske Y. Hong J. O’Keefe N. D. Gillett J. Dyble A. D. Steinman 《Hydrobiologia》2012,691(1):255-268
We evaluated the variability of cyanotoxins, water chemistry, and cyanobacteria communities in two hypereutrophic drowned river mouth lakes (Spring Lake and Mona Lake; summer 2006) in west Michigan, USA. Even with considerable geographical and watershed similarity, local variations in nutrient concentrations and environmental factors were found to influence the differences observed in cyanobacteria assemblages and cyanotoxins levels between the two lakes. Limnothrix sp. dominated the phytoplankton community in Spring Lake (82% of biovolume) and was negatively correlated with total phosphorus (TP) concentrations. Although Spring Lake was treated with alum during the previous year, Limnothrix sp. was able to bloom in the lower P environment. In contrast, the N2-fixing cyanobacterium, Anabaena flos-aquae, dominated the phytoplankton in Mona Lake (64% of biovolume). N2-fixing cyanobacteria dominance in Mona Lake was correlated with higher TP lower dissolved nitrogen levels. Cylindrospermopsis raciborskii was found in both systems; however, the toxin-producing polyketide synthetase gene was not present in either population. The higher TP in Mona Lake appeared to account for the 3-fold increase in cyanobacteria biovolume. Restoration plans for both lakes should include assessments of internal loading and continued phytoplankton monitoring to track the temporal distribution of cyanobacteria species and cyanotoxin concentrations. 相似文献
6.
Andrew P. Stubblefield Marisa I. Escobar Eric W. Larsen 《Wetlands Ecology and Management》2006,14(4):287-302
The Upper Truckee River and Trout Creek, two major tributaries inflowing to Lake Tahoe, join to form what was historically
the largest wetland in the Sierra Nevada mountain range that separates California and Nevada (USA). In the 1950s the delta
floodplain of the Upper Truckee River was greatly reduced in area (38%) by urban development and the diversion of the river
into a single excavated channel. Conversely, Trout Creek still flows through a wide marsh system with significant overbank
flooding before entering Lake Tahoe. This study hypothesized that river channel reaches that are not incised within the delta
floodplain retain more sediment and nutrients as a result of greater floodplain connectivity, compared to more incised and
excavated reaches. Suspended sediment (SS) and total phosphorus (TP) load data from the delta formed by the Upper Truckee
River and Trout Creek were collected using flow stage sensors, turbidometers and depth-integrated samples. During the spring
snowmelt flow events monitored in 2003, SS load was reduced by 13–41% for the Upper Truckee River and by 68–90% for Trout
Creek. Similar reductions in TP load were observed: 13–32% for the Upper Truckee River and 61–84% for Trout Creek. Monitoring
of Trout Creek indicated a reduction in load per unit volume of 20–34% in a moderately incised reach versus a reduction of
51–77% in a non-incised marsh reach containing lagoons, braided channels and backwater areas created by a beaver dam. Smaller
particle sizes, <10 μm, were retained in the lower marsh reach with similar efficiencies as larger particle sizes. If retention
rates from the Trout Creek portion of the marsh are applied to the Upper Truckee River, sediment loading to Lake Tahoe for
2003 would have been reduced by 917 tons of SS. 相似文献
7.
Benthic nutrient fluxes in a eutrophic,polymictic lake 总被引:2,自引:0,他引:2
Sediment release rates of soluble reactive phosphorus (SRP) and ammonium (NH4) were determined seasonally at three sites (water depth 7, 14 and 20 m) in Lake Rotorua using in situ benthic chamber incubations.
Rates of release of SRP ranged from 2.2 to 85.6 mg P m−2 d−1 and were largely independent of dissolved oxygen (DO) concentration. Two phases of NH4 release were observed in the chamber incubations; high initial rates of up to 2,200 mg N m−2 d−1 in the first 12 h of deployment followed by lower rates of up to 270 mg N m−2 d−1 in the remaining 36 h of deployment. Releases of SRP and NH4 were highest in summer and at the deepest of the three sites. High organic matter supply rates to the sediments may be important
for sustaining high rates of sediment nutrient release. A nutrient budget of Lake Rotorua indicates that internal nutrient
sources derived from benthic fluxes are more important than external nutrient sources to the lake. 相似文献
8.
Lake Okaro is a small, warm monomictic lake in central North Island, New Zealand, which progressed from oligotrophic to eutrophic through the 1960s. Trends in phosphorus (P) concentrations in the lake are linked to multiple restoration efforts over a 5-year period (2003–2008). The restoration procedures include a 2.3 ha constructed wetland established in February 2006 and riparian margin protection to reduce external loading, as well as an Alum application in December 2003 and sediment capping using modified zeolite in September 2008 to reduce internal loading. The annual average total phosphorus (TP) concentration in the lake decreased by 41% from 2004–2005 to 2007–2008. Two predictive models based on external P loading data generally underestimated the measured TP concentrations in the water column due to internal P loading. The relatively rapid response of TP concentrations after reduction of the internal loading using modified zeolite suggests that this technique can effect a rapid decrease in lake water TP concentrations though the trophic state of Lake Okaro showed high resilience to the reduced P loading. It is concluded that the combined effect of all restoration procedures resulted in a relatively rapid decrease in TP concentrations in Lake Okaro, which may be prolonged by continued external load reduction. 相似文献
9.
Sediment phosphorus cycling in a large shallow lake: spatio-temporal variation in phosphorus pools and release 总被引:12,自引:0,他引:12
Bryan M. Spears Laurence Carvalho Rupert Perkins Alex Kirika David M. Paterson 《Hydrobiologia》2007,584(1):37-48
Sediment and water column phosphorus fractions were recorded monthly for one year (April 2004–April 2005) in a shallow lake
recovering from nutrient pollution (Loch Leven, Scotland). Equilibrium phosphate concentration (EPC0) and gross sediment phosphorus
(P) release rates were estimated from laboratory experiments. Pore water and organic P pools were lowest during warm water
periods whereas bottom water P was lowest during cold water periods. Reductant-soluble, organic, metal oxide-adsorbed, residual
and sediment total phosphorus pools all varied significantly with overlying water depth. Short-term, high magnitude, redox
initiated P release events occurred in late summer and winter as a result of anoxic sediment conditions. Lower magnitude long-term
release conditions were maintained for most of the year, most likely as a result of organic P cycling and maintenance of high
concentration gradients between the pore and bottom water P pools. Estimates of summer P uptake/release rates, across an intact
sediment-water interface, suggested that maximum gross internal release was ~12 mg SRP m−2 lake surface area d−1 with EPC0 values ranging between 180 and 270 μg P L−1. This study highlights the biological mediation of internal loading in shallow eutrophic lakes, and in particular, the role
of sediment algae in decreasing, and sediment bacteria in enhancing, sediment P release. 相似文献
10.
Our study examines the relative importance of the causal linkages between exogenous total phosphorus (TP) loading and internal nutrient recycling with the water quality conditions in Lake Simcoe, Ontario, Canada. We enhance the mechanistic foundation of a simple TP mass-balance model, originally developed to guide the eutrophication management in the system. The structural improvements include the incorporation of macrophyte dynamics, the explicit representation of the role of dreissenids in the system, and the improved portrayal of the interplay between water column and sediments. Our model provides good agreement with the observed TP variability in the system during the study period (1999–2007). Consistent with empirical evidence, our model predicts that macrophyte uptake from the interstitial waters is responsible for a significant loss of P from the sediments. Our model also suggests that dreissenids filter a considerable amount of particulate P from the water column, but the effective clearance rate is significantly lower with a substantial amount of the filtered particles (> 85%) returned into the water column as faeces, pseudofeces or other metabolic excreta. P diffusive fluxes from the sediments account for about 30–35% of the exogenous P loading in Lake Simcoe. The sediments in the main basin are mostly driven by fast diagenetic processes of settling organic matter from the epilimnion, suggesting an internal P loading of 9.2 tonnes yr− 1. Finally, our study attempts to explain the lack of distinct decreasing trends in ice-free TP concentrations after the invasion of dreissenid mussels, suggesting that the presence of active nutrient recycling pathways, potentially magnified by the particular morphological features and hydrodynamic patterns of Lake Simcoe, could counterbalance the direct effects of dreissenid filtration. 相似文献
11.
Influence of suspended clay on phosphorus uptake by periphyton 总被引:1,自引:0,他引:1
We investigated the effect of suspended clay upon the phosphorus uptake rate exhibited by lotic periphyton communities. Suspended
inorganic clays and periphyton are common to aquatic environments, and both can strongly influence physical and chemical water
conditions. We used replicated artificial stream channels to test the prediction that suspended clay particles would affect
the uptake of soluble reactive phosphorus (SRP) by periphyton. Commercially available kaolinite and bentonite clays were characterized
for their aqueous suspension behavior and affinities for SRP. Periphyton was grown in a recirculating stream system and subjected
to simultaneous suspended clay and SRP additions. SRP removal from solution, both in the presence and absence of suspended
clays, was used to quantify SRP uptake parameters by periphyton. Clay type and concentrations of 20, 80, and 200 mg l−1 had no significant effect upon SRP uptake rate exhibited by periphyton during three 90-min experiments. Less than 1% of SRP
removal was attributable to the suspended clay load or artificial stream construction materials, based on clay isotherm data
and material sorption studies, indicating that 99% of SRP removal was attributable to biotic uptake. Removal of SRP (as KH2PO4) was described by a first-order equation with rate constants ranging between 0.02 and 0.14 min−1. Our results suggest that high turbidity conditions caused by suspended mineral clays have little immediate effect upon SRP
removal from the water column by periphyton.
Handling editor: D. Ryder 相似文献
12.
Lake Taihu suffers from eutrophication caused by riverine nutrient inputs and air deposition. To characterize wet deposition
of phosphorus (P) and nitrogen (N) to the lake, precipitation collection and measurements of total phosphorus (TP) and total
nitrogen (TN) and other components at five cities around Lake Taihu were made from July 2002 to June 2003. TP and TN concentrations
and deposition rates exhibited strong spatial variation in the whole catchment. An inverse correlation between station-averaged
TP and TN concentrations and precipitation amount was found. Maximal TP concentration in rainfall was found in Suzhou, and
maximal TN in Wuxi. However, highest wet deposition rates of TP and TN were found in Suzhou, which suggests that atmospheric
nutrients are mostly from the east and northwest area of Lake Taihu. Mean TP and TN deposition rates were 0.03 and 2.0 t km−2 year−1 respectively in Lake Taihu, which are greater than reported values in other areas by comparision. Total N and P contributed
to the lake by wet deposition were 75 and 4720 t per year, respectively, which represent about 7.3% and 16.5% of total annual
N and P inputs via inflow rivers. Wet deposition, especially N, could have significant effects on eutrophication in the lake,
which shows that air deposition should be taken into account while reducing the external nutrients in the lake. 相似文献
13.
Brandon K. Swan James M. Watts Kristen M. Reifel Stuart H. Hurlbert 《Hydrobiologia》2007,576(1):111-125
The Salton Sea currently suffers from several well-documented water quality problems associated with high nutrient loading.
However, the importance of phosphorus regeneration from sediments has not been established. Sediment phosphorus regeneration
rates may be affected by benthic macroinvertebrate activity (e.g. bioturbation and excretion). The polychaete Neanthes
succinea (Frey and Leuckart) is the dominant benthic macroinvertebrate in the Salton Sea. It is widely distributed during periods
of mixing (winter and spring), and inhabits only shallow water areas following development of anoxia in summer. The contribution
of N. succinea to sediment phosphorus regeneration was investigated using laboratory incubations of cores under lake temperatures and dissolved
oxygen concentrations typical of the Salton Sea. Regeneration rates of soluble reactive phosphorus (SRP) were lowest (−0.23–1.03
mg P m−2 day−1) under saturated oxygen conditions, and highest (1.23–4.67 mg P m−2 day−1) under reduced oxygen levels. N. succinea most likely stimulated phosphorus regeneration under reduced oxygen levels via increased burrow ventilation rates. Phosphorus
excretion rates by N. succinea were 60–70% more rapid under reduced oxygen levels than under saturated or hypoxic conditions. SRP accounted for 71–80% of
the dissolved phosphorus excreted under all conditions. Whole-lake SRP regeneration rates predicted from N. succinea biomass densities are highest in early spring, when the lake is mixing frequently and mid-lake phytoplankton populations
are maximal. Thus, any additional phosphorus regenerated from the sediments at that time has potential for contributing to
the overall production of the lake.
Guest Editor: John M. Melack
Saline Water and their Biota 相似文献
14.
Seigen Tsukuda Masahito Sugiyama Yunosuke Harita Kazuo Nishimura 《Biogeochemistry》2006,77(1):117-138
Atmospheric bulk depositions of soluble reactive phosphorus (SRP), soluble unreactive phosphorus (SUP), particulate inorganic
phosphorus (PIP), particulate organic phosphorus (POP), total phosphorus (TP) and some other dissolved and particulate components
were monitored for 3 years in Ashiu, Central Japan. The mean bulk depositions of SRP, SUP, PIP, POP, TP, dissolved components
(Na, Mg, nss-Ca, K, V, Mo, nss-SO4) and particulate components (Al, Fe, Ti, Ca, Mg, Mn, Ba, Sr, Zn) were 175, 76, 136, 397, 783, 156,000, 10,900, 7450, 5470,
10.3, 1.52, 40,100, 13,200, 3590, 2630, 576, 624, 42.3, 30.2, 17.4, 8.2 μmol m−2 year−1, respectively. The value for TP deposition was in the lower range of previous literature. The low P deposition probably reflected
the method applied to reduce the contribution of local particles, including (1) placement of samplers off the ground surface,
(2) installation of multiple samplers, and (3) rejection of contaminated samples. Al data suggested that 15 ± 5% of TP was
brought by lithogenic dust from East Eurasia. Nss-SO4 and Mo data and air-mass backward trajectories suggested that 39 ± 4% of TP was derived from coal combustion in China. It
was speculated that the rest (47 ± 6%) of the TP deposition might be predominantly attributed to the contribution of local
biogenic particles. Net atmospheric TP input (lithogenic dust and fossil fuel combustion) was almost equal to the TP outflow
from Japanese forests on granitic soils. 相似文献
15.
Phosphorus (P) dynamics in large shallow lakes are greatly influenced by physical processes such as wind-driven sediment resuspension,
at times scales from hours to years. Results from long-term (30 year) research on Lake Okeechobee, Florida (area 1,730 km2, mean depth 2.7 m) illustrate key features of these P dynamics. Variations in wind velocity result in changes in water column
transparency, suspended solids, and total P (TP). In summer there are diurnal changes in TP associated with afternoon winds,
and in winter, when strong winds occur for multiple days, monthly average TP remains high compared to summer. The magnitude
of daily and seasonal TP changes can exceed 100 μg l−1. Hurricanes and tropical storms also cause extreme changes in TP that are superimposed on seasonal dynamics. When a hurricane
passed 80 km south of the lake in October 1999, mean pelagic TP increased from 88 to 222 μg l−1. During large resuspension events, light attenuation is substantially increased, and this influences the biomass and spatial
extent of submerged plants, as well as water column TP. In Lake Okeechobee, TP concentrations typically are ∼20 μg l−1 when submerged plants are dense, and soluble reactive P concentrations are reduced below detection, perhaps by the periphyton
and plant uptake and by precipitation with calcium at high pH. In contrast, TP exceeds 50 μg l−1 when submerged plants and periphyton are absent due to prolonged deep water, and phytoplankton biomass and algal bloom frequency
both are increased. In Lake Okeechobee and other large shallow lakes, complex models that explicitly consider wind-wave energy,
hydrodynamics, and sediment resuspension, transport, and key biological processes are needed to accurately predict how lake
water TP will respond to different management options. 相似文献
16.
Hiroshi Kamiya Hitoshi Ohshiro Yu Tabayashi Yoshihiro Kano Koji Mishima Toshiyuki Godo Masumi Yamamuro Osamu Mitamura Yu Ishitobi 《Landscape and Ecological Engineering》2011,7(1):53-64
In situ phosphorus release rates in three contiguous shallow brackish lakes were calculated by considering the amount of water
inflow, changes in salinity and phosphorus stock, and loading from phosphorus inflow based on monthly data. The annual amount
of sedimental phosphorus relative to that of phosphorus inflow was different for each of the three water bodies: 16% for Lake
Shinji, 3% for the Honjo area, and −8% for Lake Nakaumi, as estimated in a 10-year period from January 1993 to December 2002.
During the warm season, the quantity of phosphorus released surpassed sedimentation in these three water bodies. The low annual
sedimentation ratio in Lake Nakaumi is related to a large seawater backflow resulting in phosphorus removal, in addition to
a stable stratified structure promoting phosphorus release from sediment due to oxygen depletion in the lower layer. In Lake
Nakaumi, field data shows that if dissolved oxygen at the sediment surface falls below 2.54 mg L−1, phosphorus release from the sediment begins to be accelerated. 相似文献
17.
This article reviews historical changes in the total phosphorus (TP) inputs to Loch Leven, Scotland, UK. Data derived from
palaeolimnological records suggest that inputs in the early 1900s were about 6 t TP year−1 (0.45 g TP m−2 year−1). By 1985, this had risen to about 20 t TP year−1 (1.5 g TP m−2 year−1) due to increases in runoff from agricultural land and discharges from point sources. By the late 1970s, increased TP inputs
were causing serious degradation of lake water quality. Most noticeably, there had been an increase in cyanobacterial blooms.
A catchment management plan was implemented in the early 1990s. This resulted in a 60% reduction in the annual TP input between
1985 (20 t TP year−1/1.5 g TP m−2 year−1) and 1995 (8 t TP year−1/0.6 g TP m−2 year−1). The main reduction was associated with better control of point source discharges, but attempts were also made to reduce
inputs from diffuse sources. The reduction in external TP loading to the lake led to a marked decline in TP retention by the
lake each year. 相似文献
18.
Frank Triska Catherine M. Pringle John H. Duff Ronald J. Avanzino Gary Zellweger 《Biogeochemistry》2006,81(2):145-157
Soluble reactive phosphorus (SRP) transport/retention was determined in two rain forest streams (Salto, Pantano) draining La Selva Biological Station, Costa Rica. There, SRP levels can be naturally high due to groundwater enriched by geothermal activity within the surfically dormant volcanic landscape, and subsequently discharged at ambient temperature. Combined field and laboratory approaches simulated high but natural geothermal SRP input with the objective of estimating the magnitude of amended SRP retention within high and low SRP settings and determining the underlying mechanisms of SRP retention. First, we examined short-term SRP retention/transport using combined SRP-conservative tracer additions at high natural in situ concentrations. Second, we attempted to observe a DIN response during SRP amendment as an indicator of biological uptake. Third, we determined SRP release/retention using laboratory sediment assays under control and biologically inhibited conditions. Short-term in situ tracer-SRP additions indicated retention in both naturally high and low SRP reaches. Retention of added SRP mass in Upper Salto (low SRP) was 17% (7.5 mg-P m−2 h−1), and 20% (10.9 mg-P m−2 h−1) in Lower Salto (high SRP). No DIN response in either nitrate or ammonium was observed. Laboratory assays using fresh Lower Salto sediments indicated SRP release (15.4 ± 5.9 μg-P g dry wt.−1 h−1), when incubated in filter sterilized Salto water at ambient P concentration, but retention when incubated in filter sterilized river water amended to 2.0 mg SRP l−1 (233.2 ± 5.8 μg-P g dry wt.−1 h−1). SRP uptake/release was similar in both control- and biocide-treated sediments indicating predominantly abiotic retention. High SRP retention even under biologically saturated conditions, absence of a DIN response to amendment, patterns of desorption following amendment, and similar patterns of retention and release under control and biologically inhibited conditions all indicated predominantly abiotic P flux. 相似文献
19.
Assessment of the importance of internal nutrient loading is essential for managing and restoring eutrophic shallow lakes.
To date, studies of internal loads have tended to focus on one of two abiotic processes, either molecular diffusion or sediment/nutrient
entrainment (resuspension). This study presents a new approach to determining the non-biological fluxes of nitrogen (N) and
phosphorus (P) from the sediment to the water column of shallow lakes. Three mutually exclusive flux processes: (i) molecular
diffusion, (ii) turbulent diffusion (eddy diffusivity) and (iii) wind-induced resuspension of N and P, were related to a gradient
of benthic shear stress. A model presented here allowed the durations and magnitudes of different non-biological fluxes to
be calculated over time, based on benthic shear stress. Two site-specific critical shear stress thresholds determined which
of the three flux processes dominated for any benthic shear stress value. The model was calibrated for a shallow lake and
the continuous flux of nutrient from the sediment to the overlying water generated by each process during that period was
calculated, enabling the estimation of the relative importance of each of the three flux processes over a one-year period.
Wind-induced resuspension dominated the internal nutrient flux, operating for 38% of the time and contributing 0.9 T P year−1 and 10.2 T N year−1 to the internal nutrient load. In contrast, molecular diffusion only contributed 0.01–0.02 T P year−1 and 0.12–0.20 T N year−1 to the water column, while turbulent diffusion provided up to 0.6 T P year−1 and 6.2 T N year−1. Our model suggests that turbulent diffusion is a neglected and potentially important process contributing to internal nutrient
loading in shallow lakes, whereas molecular diffusion appears to be relatively unimportant in lakes that experience turbulence
at the sediment–water interface.
Handling editor: L. Naselli-Flores 相似文献
20.
Spatial variability in nutrient concentration and biofilm nutrient limitation in an urban watershed 总被引:1,自引:0,他引:1
Nutrient enrichment threatens river ecosystem health in urban watersheds, but the influence of urbanization on spatial variation
in nutrient concentrations and nutrient limitation of biofilm activity are infrequently measured simultaneously. In summer
2009, we used synoptic sampling to measure spatial patterns of nitrate (NO3
−), ammonium (NH4
+), and soluble reactive phosphorus (SRP) concentration, flux, and instantaneous yield throughout the Bronx River watershed
within New York City and adjacent suburbs. We also quantified biofilm response to addition of NO3
−, phosphate (PO4
3−), and NO3
− + PO4
3− on organic and inorganic surfaces in the river mainstem and tributaries. Longitudinal variation in NO3
− was low and related to impervious surface cover across sub-watersheds, but spatial variation in NH4
+ and SRP was higher and unrelated to sub-watershed land-use. Biofilm respiration on organic surfaces was frequently limited
by PO4
3− or NO3
− + PO4
3−, while primary production on organic and inorganic surfaces was nutrient-limited at just one site. Infrequent NO3
− limitation and low spatial variability of NO3
− throughout the watershed suggested saturation of biological N demand. For P, both higher biological demand and point-sources
contributed to greater spatial variability. Finally, a comparison of our data to synoptic studies of forested, temperate watersheds
showed lower spatial variation of N and P in urban watersheds. Reduced spatial variation in nutrients as a result of biological
saturation may represent an overlooked effect of urbanization on watershed ecology, and may influence urban stream biota and
downstream environments. 相似文献