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1.
Protected areas will more efficiently protect biodiversity if threats to the persistence of populations are addressed. Seagrass meadows are globally regarded as critical habitats because of their ecosystem services, human use values, and their diminishing extent. While selecting priority areas for conservation of seagrass meadows is largely aimed at maximizing the protection of their biodiversity, little attention is paid to consider simultaneously the representation of biodiversity and the minimization of threats. This study developed and tested an approach for integrating vulnerability of seagrass meadows to anthropogenic disturbance with the selection of estuarine-protected areas. Vulnerability was measured by data on different land use types in subcatchments. Conservation value was measured by irreplaceability, diversity indices, and rarity of macroinvertebrate species in seagrass meadows. Vulnerability was incorporated into conservation planning by plotting grid cell scores for conservation value versus their scores for vulnerability. The results showed that the performance of the model for the integration of vulnerability into estuarine conservation planning was sensitive to the data treatment. The vulnerability of seagrass meadows and accordingly the arrangement of priority areas for conservation and management attention may change if more information is incorporated into the measurement of vulnerability. 相似文献
2.
Rikke Jeppesen Miguel Rodriguez Jenna Rinde John Haskins Brent Hughes Laura Mehner Kerstin Wasson 《Estuaries and Coasts》2018,41(1):89-98
Human land use activities around estuaries can result in high levels of eutrophication. At Elkhorn Slough estuary, a highly eutrophic California estuary, we investigated the effects of impaired water quality on two stress-tolerant estuarine species, a common fish, the staghorn sculpin, Leptocottus armatus and a foundational invertebrate, the Olympia oyster, Ostrea lurida. We caged the two indicator species at six wetlands with different levels of water quality impairment, four of which had restricted tidal flow. We also recorded water quality parameters simultaneously at all sites using YSI sondes, and sampled nutrients and chlorophyll-a monthly, building on the National Estuarine Research Reserve System-wide Monitoring Program. We found that the monitored environmental variables predicted ecological responses by the indicator species. In particular, we found that the duration and severity of hypoxia were negatively correlated with fish survival and oyster growth. Further, our results corroborate previous studies that artificial tidal restriction leads to increased hypoxia stress. We conclude that large diurnal fluctuations in dissolved oxygen and extended nighttime hypoxia can have lethal and sub-lethal effects even on stress-tolerant organisms in the estuary. While laboratory experiments have often shown such effects, it is relatively rare to demonstrate negative effects of oxygen variation with in situ experiments, which provide stakeholders with concrete evidence for impaired water quality at local wetlands. Tidally restricted sites, which experience the largest fluctuations in dissolved oxygen and longest periods of hypoxia, harbor conditions harmful to vertebrates and invertebrates in the estuary. Reversing the anthropogenically induced low oxygen levels, by restoring more natural tidal exchange and by decreasing agricultural runoff, could improve the survival and growth of important estuarine organisms. 相似文献
3.
The hydrodynamic characteristics of small, intertidal perimeter habitats make flushing and residence times in these environments difficult to quantify using conventional approaches. The flooding and draining of intertidal shallows surrounding small perimeter sloughs result in large volume changes relative to total system volume during each tidal cycle. In such environments, an Eulerian framework of flushing and residence time may not be the best approach for quantifying tidal exchange; thus, alternative approaches should be considered in analyzing hydrodynamic exchange in small perimeter habitats. In this study, the results of applying such an approach to a small intertidal perimeter slough in South San Francisco Bay are presented. Previous work has shown that hydrodynamic exchange in an estuarine system can be analyzed by making Eulerian measurements of hydrodynamic fluxes and binning them according to salinity and temperature classes, thus providing a quasi-Lagrangian method of analyzing exchange and transport in an estuarine system. We apply a method which uses this approach to estimate the volumetric exchange ratio M, which is used to estimate the tidal exchange within an estuary during each tidal cycle. We find that the estimation of volumetric exchange ratios and the calculation of hydrodynamic residence times in estuarine systems can be complicated by mixing conditions associated with very strong tidal forcing, particularly in small-volume systems such as small perimeter sloughs, where the tidal prism can be on the scale of or greater than the total system volume. 相似文献
4.
Worldwide estuaries have been subject to multiple and escalating anthropogenic impacts which have resulted in the loss of many ecosystem goods and services including: commercial activities, navigation and marine transportation, recreational and landscape values, and flood control and biodiversity support. An example of these losses is provided in an urban-industrial region of an estuary in northern Tasmania, Australia, where excessive silt deposition has resulted in almost complete loss of the channel at low tide. The causes of siltation have long been attributed to poor watershed management and high concentrations of flocculated and suspended sediments transported upstream by asymmetrical tides. However, historical analysis of anthropogenic changes in estuarine and riverine processes revealed different stressors. These included the decrease in the tidal prism and hence regime equilibrium, brought about by channel infilling and draining of tidal wetlands to create dry land for urban and agricultural uses, and the reduction and redirection of freshwater inflows for the generation of hydroelectricity. Watershed sediment loads exerted a relatively minor role in the estuarine equilibrium, which is solely dependent on tidal flows and river discharges for maintenance of stable cross-sectional areas. Sustainable remediation measures include increasing the tidal prism through the restoration of dynamic river flows and reconnection and restoration of tidal wetlands. However, the former will not be achievable without changes in major provisioning services, particularly the use of water to generate hydroelectricity. This study emphasises the importance of identifying stressors as the basis for examining the potential to reduce the trade-offs between the multiple ecosystem services provided by an estuary and its tributaries, particularly between provisioning and cultural ecosystem services, within a rehabilitation context. 相似文献
5.
Renato Gerdol Lisa Brancaleoni Lorenzo Lastrucci Giovanni Nobili Mauro Pellizzari Michele Ravaglioli Daniele Viciani 《Estuaries and Coasts》2018,41(7):2079-2091
Wetlands are important centers of biodiversity. Coastal wetlands are subject to anthropogenic threats that can lead to biodiversity loss and consequent negative effects on nature conservation. We investigated relationships between wetland vegetation and habitat conditions in a coastal Nature Reserve in Northern Italy that has undergone seawater intrusion and eutrophication for several decades. The wetland vegetation in the Nature Reserve consisted of nine communities of hygrophytic and helophytic vegetation and five communities of waterplant vegetation. The hygrophytic and helophytic communities were arranged according to a salinity gradient, from salt-free habitats to strongly saline habitats. The saline habitats had high nutrient levels, due to the influx of nitrate-rich saltwater from an adjacent lagoon. The waterplant communities were all typical of freshwater habitats. Water-table depth and concentration of dissolved nutrients in the water were the main factors structuring waterplant vegetation. The main driver of future changes in the wetland vegetation of the Nature Reserve is the ongoing increase in salinity levels which may enhance expansion of halophilic species and communities, thus outcompeting locally rare freshwater species. If nutrient, especially nitrate, load further increases in the next future, this may exert negative effects on wetland species and communities preferring nutrient-poor habitats. 相似文献
6.
We describe the tidal circulation and salinity regime of a coastal plain estuary that connects to the ocean through a flood
tide delta. The delta acts as a sill, and we examine the mechanisms through which the sill affects exchange of estuarine water
with the ocean. Given enough buoyancy, the dynamics of tidal intrusion fronts across the sill and selective withdrawal (aspiration)
in the deeper channel landward appear to control the exchange of seawater with estuarine water. Comparison of currents on
the sill and stratification in the channel reveals aspiration depths smaller than channel depth during neap tide. During neap
tide and strong vertical stratification, seawater plunges beneath the less dense estuarine water somewhere on the sill. Turbulence
in the intruding bottom layer on the sill promotes entrainment of fluid from the surface layer, and the seawater along the
sill bottom is diluted with estuarine water. During ebb flow, salt is effectively trapped landward of the sill in a stagnant
zone between the aspiration depth and the bottom where it can be advected farther upstream by flood currents. During spring
tide, the plunge point moves landward and off the sill, stratification is weakened in the deep channel, and aspiration during
ebb extends to the bottom. This prevents the formation of stagnant water near the bottom, and the estuary is flooded with
high salinity water far inland. The neapspring cycle of tidal intrusion fronts on flood coupled with aspiration during ebb
interacts with the sill to play an important role in the transport and retention of salt within the estuary. 相似文献
7.
Three and a half years of hydrographic, velocity, and meteorological observations are used to examine the dynamics of upper Elkhorn Slough, a seasonally inverse, shallow, mesotidal estuary in central California. The long-term observations revealed that residual circulation in Elkhorn Slough is seasonally variable, with classic estuarine circulation in the winter and inverse estuarine circulation in the summer. The strength of this exchange flow varied both within years and between years, driven by the annual cycle of dry summers and wet winters. Subtidal circulation is a combination of both tidal and density-driven mechanisms. The subtidal magnitude and reversal of the exchange flows is controlled primarily by the density gradient despite the significant tidal energy. As the density gradient weakens, the underlying tidal processes generate vertically sheared exchange flows with the same sign as that expected for an inverse density gradient. The inverse density gradient may then further strengthen this inverse circulation. These data were collected as part of the Land/Ocean Biogeochemical Observatory and demonstrate the utility of long-term in situ measurements in a coastal system, as consideration of such a wide range of forcing conditions would not have been possible with a less comprehensive data set. 相似文献
8.
E. C. Milbrandt J. M. Greenawalt-Boswell P. D. Sokoloff S. A. Bortone 《Estuaries and Coasts》2006,29(6):979-984
Although hurricane disturbance is a natural occurrence in mangrove forests, the effect of widespread human alterations on
the resiliency of estuarine habitats is unknown. The resiliency of mangrove forests in southwest Florida to the 2004 hurricane
season was evaluated by determining the immediate response of mangroves to a catastrophic hurricane in areas with restricted
and unrestricted tidal connections. The landfall of Hurricane Charley, a category 4 storm, left pronounced disturbances to
mangrove forests on southwest Florida barrier islands. A significant and negative relationship between canopy loss and distance
from the eyewall was observed. While a species-specific response to the hurricane was expected, no significant differences
were found among species in the size of severely impacted trees. In the region farthest from the eyewall, increases in canopy
density indicated that refoliation and recovery occurred relatively quickly. There were no increases or decreases in canopy
density in regions closer to the eyewall where there were complete losses of crown structures. In pre-hurricane surveys, plots
located in areas of management concern (i.e., restricted connection) had significantly lower stem diameter at breast height
and higher stem densities than plots with unrestricted connection. These differences partially dictated the severity of effect
from the hurricane. There were also significantly lower red mangrove (Rhizophora mangle) seedling densities in plots with restricted connections. These observations suggest that delays in forest recovery are possible
in severely impacted areas if either the delivery of propagules or the production of seedlings is reduced by habitat fragmentation. 相似文献
9.
A. Chakrabarti 《Journal of Earth System Science》2005,114(3):353-368
Sedimentary structures of some coastal tropical tidal flats of the east coast of India, and inner estuarine tidal point bars
located at 30 to 50 kilometers inland from the coast, have been extensively studied under varying seasonal conditions. The
results reveal that physical features such as flaser bedding, herringbone cross-bedding, lenticular bedding, and mud/silt
couplets are common to both the environments. In fact, flaser bedding and lenticular bedding are more common in the point
bar facies during the monsoon months than in the coastal tidal flat environments. Interference ripples, though common in both
the environments, show different architectural patterns for different environmental domains. Interference ripples with thread-like
secondary set overriding the earlier ripple-form, resembling wrinkle marks, are the typical features in estuarine point bars
near the high water region. Because structures which are so far considered as key structures for near-coastal tidal flats
are common to both the environments, caution should be exercised for deciphering palaeo-environments, particularly for Proterozoic
rocks, where one has to depend only on physical sedimentary structures. 相似文献
10.
杭州城市供水85%取自钱塘江河口段,取水水质在枯水大潮期都不同程度地受到盐水入侵的威胁,分析钱塘江河口盐水入侵时空变化及研制二维数值预测模型对保障城市供水安全十分必要。根据钱塘江河口段实测水文氯度资料,分析了强潮作用下盐水入侵的时空变化特征;据此构建考虑斜压作用的二维水流、盐度输移的耦合数学模型,计算格式采用守恒性较好的有限体积法;在模型验证的基础上,数值分析了径流和潮汐对钱塘江河口段盐水入侵的影响,结果表明河口段的盐水入侵明显地受径流和潮汐的影响,据此可通过增大上游新安江水库的下泄流量抑制盐水入侵上溯以减小取水口氯度及超标时间,确保用水安全。 相似文献
11.
Coastal managers and policy-makers are concerned with tracking improvements to water quality linked to management changes.
Long-term water quality data acquired from two wetland areas in the upper reaches of the Elkhorn Slough estuary in central
California were analyzed for signatures of land restoration or water control structure management. Post-restoration averaged
NO3, NH3, and PO4 concentrations were 50–70% less than before-restoration concentrations. Assessment of watershed-scale effects revealed that
proximity of restoration to sampling locations had almost as strong an effect on water quality as the percentage of land restored
relative to watershed size. Results also suggest that restoration of even 1% of an agriculturally intensive watershed such
as that of the Elkhorn Slough may result in improvements to water quality. Finally, results indicate that tide gate function
can dominate water quality in managed wetlands and must be carefully tracked and managed in the context of estuarine conservation
targets. 相似文献
12.
We investigated the historical ecology of Elkhorn Slough, a 1,200 ha tidal wetland system in central California. The goal of this study was to identify patterns of change in the extent and distribution of wetland habitats during a 150-yr period and to investigate the causes of these changes. Using a geographic information system (GIS), we interpreted historic maps, charts, and aerial photographs. We created a series of summary maps to illustrate and quantify changes in tidal flow and habitat types at six representative historical periods. With the aid of custom software tools, we performed semi-automated spatial analysis of historic aerial photographs to quantify changes in marsh cover at fixed quadrats and tidal creek width at fixed cross sections. Our multiscale analysis documents dramatic shifts in the distribution of habitat types resulting from anthropogenic modifications to the hydrology of the slough. More than half of the marshlands were diked, and more than two thirds have either degraded or been converted to other habitat types. The construction of an artificial mouth abruptly transformed the wetland system from depositional to highly erosional, enlarging channels, widening creeks, and converting marsh to intertidal mudflat or open water. Increased tidal amplitude and velocity are the likely causes. In recent decades, levee failure and intentional breaching have restored the acreage under tidal influence to nearly historic levels, but recolonization of former wetlands by salt marsh vegetation has been minimal. Degraded former marshland and unvegetated mudflat are now the dominant habitat types at Elkhorn Slough. The rate of habitat change remains high, suggesting that a new equilibrium may not be reached for many decades. This study can help tidal wetland managers identify patterns and mechanisms of habitat change and set appropriate conservation and restoration goals. 相似文献
13.
Aaron T. David Pascale A. L. Goertler Stuart H. Munsch Brittany R. Jones Charles A. Simenstad Jason D. Toft Jeffery R. Cordell Emily R. Howe Ayesha Gray Michael P. Hannam William Matsubu Erin E. Morgan 《Estuaries and Coasts》2016,39(5):1491-1504
Compared to benthic and water-column invertebrate assemblages, considerably less is known about terrestrial arthropods inhabiting estuarine wetlands despite their importance to tidal wetland biodiversity and productivity. We also need to know more about how human modification of estuaries, including efforts to restore estuarine wetlands, affects these assemblages. To address this knowledge gap, we assembled data from multiple studies on terrestrial arthropod assemblages from 87 intertidal wetland sites in 13 estuaries along the west coast of North America. Arthropods were sampled between 1998 and 2013 with fallout traps deployed in wetlands for 1 to 3 days at a time. We describe patterns in the abundance and taxonomic composition of terrestrial arthropods and evaluate the relative ability of natural and anthropogenic factors to explain variation in abundance and composition. Arthropod abundance was highly variable. Vegetation assemblage, precipitation, and temperature best explained variation in arthropod abundance, while river discharge, latitude, and developed and agricultural land cover surrounding sampling sites were less important. Arthropod abundance rapidly achieved levels of reference wetlands after the restoration of tidal influence to leveed wetlands, regardless of surrounding land cover. However, arthropod assemblage composition was affected by the amount of developed land cover as well as restoration age. These results suggest that restoration of tidal influence to leveed wetlands can rapidly restore some components of estuarine wetland ecosystems but that recovery of other components will take longer and may depend on the extent of anthropogenic modification in the surrounding landscape. 相似文献
14.
潮滩剖面形态与多组分泥沙分选是海岸动力学与河口、海岸地貌学的重要研究内容,对保持生物多样性、研究沉积历史和沿海工程评估等具有重要的实际意义。从现场观测、理论解析和数值模拟等方面,归纳了在潮滩剖面形态特征与多组分泥沙分选方面研究的主要进展。回顾了潮滩剖面形态分别在潮流和波浪主导下的经典理论解析解,剖析了包括潮流、波浪泥沙来源及特性等主要影响因子以及植被、海平面上升、围垦工程等其他影响因子对潮滩剖面形态水平向、垂向泥沙分选过程的作用机理,同时提出了考虑水动力、生物作用、人类活动等多因子耦合作用下潮滩演变研究以及定量化预测方向的若干亟待解决的科学问题。 相似文献
15.
Research Advance in Air-Water CO2 Exchange of Estuaries 总被引：1，自引：0，他引：1
Estuary holds a key position in linking the four geo-spheres, i.e., atmosphere, lithosphere, hydrosphere and biosphere. Figuring out the transfer mechanisms of estuarine carbon, especially the exchange ofCO2 at the air water interface is conducive to understanding the carbon pattern in coastal oceans. To date, many fruitful studies have been conducted on the control mechanism towards the partial pressure of CO2 (pCO2) in different estuarine areas around the world. By a thorough research on the latest studies of estuarineCO2 exchange with the atmosphere, it is concluded as follows: ①A common pattern is found on the spatial distribution of pCO2in different estuarine areas. However, the concrete seasonal change of pCO2 shows great differences, and the corresponding control factors also vary considerably. ②Estuaries are believed to be large sources ofCO2 to the atmosphere. It is estimated that the global estuarineCO2 degassing fluxes, although the global surface area of estuariesis small, are up to 0.25×1015~0.50×1015g C/a; and about 1/3 of riverine carbon is released into the atmosphere during the estuarine transit. ③Degradation of organic matter, lateral transfer of marsh derivedCO2 , mineral deposits in water and turbulence in the liquid phase are the main factors that are responsible for the emission of estuarineCO2 . At present, this estimate of estuarineCO2 exchange with the atmosphere is based on limited spatial data, therefore problems such as the limitation in the depth and scope of studies still exist. There are also varieties of uncertainties in the estimation of gas transfer velocity and the whole areas of global estuaries, all of them make it difficult to reach an accurate evaluation ofCO2 fluxes at the air water interface. It is difficult to predict the future trend of theCO2 exchange at the air-water interface due to the complexities of the driving forces and feedback mechanisms in estuarine carbon cycle and the intense anthropogenic disturbance. Investigating the mechanism of pCO2 in estuarine areas, improving the accuracy of evaluation ofCO2 fluxes and comparing studies of different estuaries would be new scopes in the future researches on the exchange ofCO2 at the air-water interface in estuaries. 相似文献
16.
María Recio Bárbara Ondiviela Araceli Puente Cristina Galván Aina G. Gómez Jose A. Juanes 《Estuaries and Coasts》2013,36(5):997-1005
Estuaries are one of the most threatened ecosystems, with a great number of stressors related to pollution, hydromorphological changes, and invasive species. However, the response of the biological indicators proposed for their ecological status assessment is not always well established. When using estuarine vegetation (saltmarshes and seagrasses) as an indicator, there are several theoretical concepts regarding the relationships between the variations of this indicator and hydromorphological stressors. It is precisely these relationships which are presented in this work. To carry out this objective, based on the first intercalibration process, a set of metrics for saltmarsh and seagrass taxonomic compositions (e.g., loss of number of taxa and richness) and abundance (e.g., relative coverage and relative extent) have been selected and applied to different estuaries located in Northern Spain. Additionally, a methodology for the hydromorphological status assessment, based on the analysis of the anthropogenic changes in the hydrodynamic and morphological estuarine characteristics (e.g., the extension of land claim areas or changes in the estuarine perimeter), has been developed and applied to these transitional water bodies in order to find a gradient of pressured sites in which we seek correlations between the vegetation metrics and hydromorphological stressors. As a result, the response of the different vegetation indicators is variable. In some cases, a negative correlation of the indicator with the pressure degree exists, whereas in other cases, the relationship is not as clear. Nonetheless, according to the results, it can be suggested that the placing of anthropogenic structures diminishes the quality of the estuarine vegetation. Therefore, to maintain a suitable environment for the estuarine vegetation seems necessary in order to reduce the number of the hydrodynamic structures which are no longer in use. 相似文献
17.
D. A. Jay R. J. Uncles J. Largeir W. R. Geyer J. Vallino W. R. Boynton 《Estuaries and Coasts》1997,20(2):262-280
The purpose of this contribution is to review recent developments in calculation of estuarine scalar fluxes, to suggest avenues for future improvement, and to place the idea of flux calculation in a broader physical and biogeochemical context. A scalar flux through an estuarine cross section is the product of normal velocity and scalar concentration, sectionally integrated and tidally averaged. These may vary on interannual, reasonal, tidal monthly, and event time scales. Formulation of scalar fluxes in terms of an integral scalar conservation expression shows that they may be determined either through “direct” means (measurement of velocity and concentration) or by “indirect” inference (from changes in scalar, inventory and source/sink terms). Direct determination of net flux at a cross section has a long and generally discouraging history in estuarine oceanography. It has proven difficult to extract statistically significant net (tidally averaged) fluxes from much larger flood and ebb transports, and the best mathematical representation of flux mechanisms is unclear. Observations further suggest that both lateral and vertical variations in scalar transport through estuarine cross sections are large, while estuarine circulation theory has focused on two-dimensional analyses that treatment either vertical or lateral variations but not both. Indirect estimates of net fluxes by determination of the other relevant terms in an integral scalar conservation balance may be the best means of determining scalar import-export in systems with residence times long relative to periods of tidal monthly fluctuations. But this method offers, little insight into the interaction of circulation modes and scalar fluxes, little help in verifying predictive models, and may also be difficult to apply in some circumstances. Thus, the need to understand, measure, and predict anthropogenic influences on transport or carbon, nutrient, suspended matter, trace metals, and other substances across the land-margin brings a renewed urgency to the issue of how to best carry out estuarine scalar flux determination. An interdisciplinary experiment is suggested to test present understanding, available instrument, and numerical models. 相似文献
18.
Anning Suo Dongzhi Zhao Fengshou Zhang Huaru Wang Fengqiao Liu 《Frontiers of Earth Science》2010,4(1):51-58
Estuaries, which lie at the end of rivers, belong to the interlocking area between marine ecosystems and terrestrial ecosystems.
In the estuary region, there are plenty of biological resources that carry many important ecosystem services. However, severe
degradation of the estuary ecosystem in northern China has been caused by anthropogenic disturbances, including water pollution
from upstream area, change of marine environmental dynamics, animal habitat loss, and unreasonable exploitation in the estuary
region. In order to provide scientific evidence for restoration and conservation of the estuary ecosystem, we collected data
from published literature to analyze the ecological problems in several main estuary regions in northern China, such as the
Yellow River estuary, Liaohe River estuary, Haihe River estuary, Yalu River estuary, and some others. The main ecological
problems in the estuary region of northern China include the input decrease of fresh water from rivers, the change of the
sediment input from rivers, the destruction of the estuary wetland ecosystem, the environmental pollution in the estuary region,
the erosion in the estuary region, seawater encroachment, the biodiversity decline of the estuary region, and the depletion
of the fish resources in the estuary region. Meanwhile, the driving forces for these ecological problems in the estuary region
were also assessed. Based on the analysis of these driving forces, we propose several pieces of advice for integrated estuary
management in northern China, including the creation of a management system for estuary conservation, improvement of the means
and strength of the environmental law execution, increased investment on scientific research in the estuary ecosystem, improvement
of public participation on the conservation for the estuary environment and biodiversity, and construction of a monitoring
system for the estuary environment. 相似文献
19.
H. N. McKellar D. L. Tufford M. C. Alford P. Saroprayogi B. J. Kelley J. T. Morris 《Estuaries and Coasts》2007,30(6):989-1006
Tidal freshwater sections of the Cooper River Estuary (South Carolina) include extensive wetlands, which were formerly impounded
for rice culture during the 1,700s and 1,800s. Most of these former rice fields are now open to tidal exchange and have developed
into productive wetlands that vary in bottom topography, tidal hydrography and vegetation dominants. The purpose of this project
was to quantify nitrogen (N) transport via tidal exchange between the main estuarine channel and representative wetland types
and to relate exchange patterns to the succession of vegetation dominants. We examined N concentration and mass exchange at
the main tidal inlets for the three representative wetland types (submerged aquatic vegetation [SAV], floating leaf vegetation,
and intertidal emergent marsh) over 18-21 tidal cycles (July 1998–August 2000). Nitrate + nitrite concentrations were significantly
lower during ebb flow at all study sites, suggesting potential patterns of uptake by all wetland types. The magnitude of nitrate
decline during ebb flow was negatively correlated with oxygen concentration, reflecting the potential importance of denitrification
and nitrate reduction within hypoxic wetland waters and sediments. The net tidal exchange of nitrate + nitrite was particularly
consistent for the intertidal emergent marsh, where flow-weighted ebb concentrations were usually 18–40% lower than during
flood tides. Seasonal patterns for the emergent marsh indicated higher rates of nitrate + nitrite uptake during the spring
and summer (> 400 μmol N m-2 tide-1) with an annual mean uptake of 248 ± 162 μmol m–2 tide–1. The emergent marsh also removed ammonium through most of the year (207 ± 109 μmol m–2 tide–1), and exported dissolved organic nitrogen (DON) in the fall (1,690 ± 793 μmol m–2 tide–1), suggesting an approximate annual balance between the dissolved inorganic N uptake and DON export. The other wetland types
(SAV and floating leaf vegetation) were less consistent in magnitude and direction of N exchange. Since the emergent marsh
site had the highest bottom elevation and the highest relative cover of intertidal habitat, these results suggest that the
nature of N exchange between the estuarine waters and bordering wetlands is affected by wetland morphometry, tidal hydrography,
and corresponding vegetation dominants. With the recent diversion of river discharge, water levels in the upper Cooper estuary
have dropped more than 10 cm, leading to a succession of wetland communities from subtidal habitats toward more intertidal
habitats. Results of this study suggest that current trends of wetland succession in the upper Cooper River may result in
higher rates of system-wide inorganic N removal and DON inputs by the growing distributions of intertidal emergent marshes. 相似文献
20.
Douglas W. Bell Susan Denham Erik M. Smith Claudia R. Benitez-Nelson 《Estuaries and Coasts》2018,41(8):2223-2239
Across the coastal zone, rates of carbon and nutrient exchange are defined by the spatiotemporal heterogeneity of individual estuarine systems. Elemental stoichiometry provides a mechanism for simplifying overlapping physical, chemical, and biological drivers into proxies that can be used to compare and monitor estuarine biogeochemistry. To this end, the seasonal and tidal variability of estuarine stoichiometry was examined over an annual cycle in North Inlet (NI), South Carolina. Surface samples for dissolved and particulate carbon (C), nitrogen (N), and phosphorus (P) were collected every 20 days (August 2014 to August 2015) over a semi-diurnal tidal cycle. Dissolved nutrient flux estimates of an individual tidal creek were also made. Overall, the results demonstrated the dominance of seasonal versus tidal forcing on water column C:N:P stoichiometry. This seasonal behavior mediated the relative exchange of N and P into and out of the tidal creek and influenced the nutrient status index (NSI) of NI plankton communities. These communities were largely N deficient with the magnitude of this deficiency impacted by assumptions of inorganic versus organic plankton P demand and nutrient supply. Persistent N deficiency appeared to help drive the net import of N, while temporary P surplus likely drives its seasonal export. Combined, these results indicate that material delivery must be considered on seasonal time frames, as net annual fluxes do not reflect the short-term deliveries of C and nutrients into nearshore ecosystems. 相似文献