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1.
Short-term sedimentation patterns were evaluated from August 1992 to May 1993 in different wetland habitats characteristic of the Rhône Delta, including impounded and seasonally-dry saline Arthrocnemum marshes, brackish Juncus, Phragmites, and Scirpus riverine wetlands directly connected to the Rhône River, and Arthrocnemum-dominated marine marshes influenced by the Mediterranean. Short-term sedimentation was measured as sediment accumulation on paper filters which had been placed on the soil surface for several weeks. Total sedimentation and material lost on ignition was significantly related to individual sampling periods, reflecting the importance of short-term processes. High sedimentation at riverine sites (up to 22 g m?2 d?1) was related to a combination of river stage and wind events. Marine and impounded wetlands of the Rhône Delta experienced low sedimentation throughout the period of study. Sedimentation rates averaged over the study period were 0.8 g m?2 d?1, 1.8 g m?2 d?1, and 5.4 g m?2 d?1 for marine, impounded, and riverine sites, respectively. Percent material lost on ignition was low in all habitats (average 15%) and followed a seasonal trend with a minimum in late fall and winter (1%). Soil percent organic matter was also low in the top several centimeters (13%), suggesting that inorganic sedimentation is very important for accretion on these wetland surfaces. Coastal flooding was not a significant mechanism for sedimentation in the marine sites during the period of study. Sedimentation is an important factor in elevation change, and this study shows that impounded habitats, the most common “natural environment“ left in the delta, may become vulnerable to sea-level rise in the future if management practices continue to isolate these wetlands from riverine sources of sediment.  相似文献   

2.
Submersed macrophytes are important in nutrient cycling in marine and lacustrine systems, although their in nutrient exchange in tidally-influenced riverine systems is not well studied. In the laboratory, plants significantly lowered porewater nutrient pools of riverine sediments compared with bare controls. Deep-rootedVallisneria americana lowered the porewater nutrients to a greater extent than the shallow-rootedPotamogeton pectinatus. V. americana showed significantly higher tissue nutrient content (N in roots, P in leaves) thanP. pectinatus. porewater nutrients in the river increased from spring to summer (1995) when vegetation was at its peak (for porewater PO4-P, p<0.05). In 1996, porewater nutrients were higher during peak plant biomass in the summer than in the fall (for porewater PO4-P, p<0.05). In the summer (1995) vegetated patches had significantly greater porewater PO4-P than bare patches. We hypothesize that the concentrating of particulates in riverine grassbeds and subsequent microbial processing may provide an indirect source of nutrients for submersed macrophytes. In tidally-influenced riverine systems, biological mechanisms such as root uptake of nutrients and lateral oxygen release may be masked by the interaction of physical forces (i.e., tides, currents) with the structure of the grassbeds.  相似文献   

3.
Urban and artificial structures are increasingly added to the world’s coasts during a time in which changing climate is forecast to drive shifts in naturally occurring habitats. We ask whether the role of artificial structures as marine habitats will increase in importance relative to their natural counterparts, particularly as natural habitats are negatively affected by ocean warming and acidification. To evaluate this model, we contrasted use of natural (kelp forest and turfing algae) and artificial habitat (plastic pier-piling) by a nest-building amphipod (Cymadusa pemptos) under current and future climate conditions of CO2 and temperature. Under future conditions, amphipod populations in mesocosms increased, but this did not lead to greater proportional colonization of kelp and turf. Instead, colonization doubled in artificial habitats, and there was increasing production and occupation of nests on artificial habitats relative to natural habitats. In an age when human modification of natural substrata is increasingly cited as an agent of wildlife decline, understanding the future role of artificial habitats as replacement dwellings for natural habitats is critical. We pioneer an understanding of the future role of natural and artificial habitats, identifying the possibility that the role of urban structures as marine habitats may only increase.  相似文献   

4.
Leaf wax components of terrestrial plants are an important source of biomass in the geological records of soils, lakes and marine sediments. Relevant to the emerging use of plant wax derived biomarkers as proxies for past vegetation composition this study provides key data for C3 plants of tropical and subtropical Africa. We present analytical results for 45 savanna species and 24 rain forest plants sampled in their natural habitats. Contents and distribution patterns of long chain n-alkanes (n-C25 to n-C35) and n-alkan-1-ols (n-C24 to n-C34) as well as bulk and molecular carbon isotopic data are presented. The variations of the analysed parameters among different growth forms (herb, shrub, liana and tree) are small within the vegetation zones, whereas characteristic differences occur between the signatures of rain forest and savanna plants. Therefore, we provide averaged histogram representations for rain forest and savanna C3 plants.The findings were compared to previously published data of typical C4 grass waxes of tropical and subtropical Africa. Generally, trends to longer n-alkane chains and less negative carbon isotopic values are evident from rain forest over C3 savanna to C4 vegetation. For n-alkanols of rain forest plants the maximum of the averaged distribution pattern is between those of C3 savanna plants and C4 grasses. The averaged presentations for tropical and subtropical vegetation and their characteristics may constitute useful biomarker proxies for studies analysing the expansion and contraction of African vegetation zones.  相似文献   

5.

If the photosynthetic organisms assimilated only CO2 in the Archean atmosphere, hydroxide ion in the Archean seawater would not increase. If plants would not consume bicarbonate as a direct substrate during photosynthesis, it is difficult to explain the evolution of Earth's environment. To date, it is generally accepted that photosynthetic O2 evolution of plants come from water photolysis. However, it should be debated by evaluating the effect of bicarbonate in photosynthetic O2 evolution, analyzing the role of carbonic anhydrase (CA) in photosynthetic O2 evolution, and the relationship between thylakoid CA and photosynthetic O2 evolution. In the paper, I propose that bicarbonate is directly used as substrate to participate in photosynthetic O2 evolution. The rationality of bicarbonate photolysis of plants is discussed from the thermodynamics and evolution of Earth's environment. The isotopic evidence that bicarbonate is not the direct substrate of photosynthetic O2 release is reexamined, and the new explanation of bicarbonate photolysis in photosynthetic O2 evolution is proposed.

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6.
Two piston cores, one located far from the continents (The North Pacific Ocean: ES core), and another located comparatively closer to the continents (The Bering Sea: BOW-8a core) were investigated to reconstruct environmental changes on source land areas. The results show significant contribution of terrestrial organic matter to sediments in both cores. The δ13C values of n-C27, n-C29, and n-C31 alkanes in sediments from the North Pacific ES core show significant glacial to interglacial variation whereas those from the Bering Sea core do not. Variations of δ13C values of land plant n-alkanes are related to the environmental or vegetational changes in the source land areas. Environmental changes, especially, aridity, rainfall, and pCO2 during glacial/interglacial transitional periods can affect vegetation, and therefore C3 / C4 plant ratios, resulting in δ13C changes in the preserved land plant biomarkers. Maximum values of δ13C as well as maximum average chain length values of long chain n-alkanes in the ES core occur mostly at the interglacial to glacial transition zones reflecting a time lag related to incorporation of living organic matter into soil and transportation into ocean basins via wind and/or ability of C4 plants to adapt for a longer period before being replaced by C3 plants when subjected to gradual climatic changes. Irregular variations with no clear glacial to interglacial trends in the BOW-8a core may result from complex mixture of aerosols from westerly winds and riverine organic matter from the Bering Sea catchments. In addition, terrestrial organic matter entering the Bering Sea could originate from multiple pathways including eolian, riverine, and ice rafted debris, and possibly be disturbed by turbidity and other local currents which can induce re-suspension and re-sedimentation causing an obliterated time relation in the Bering Sea biomarker records.  相似文献   

7.
Temperature acclimation influenced the desiccation tolerance of the marine snail Ilyanassa obsoleta (Nassarius obsoletus). I. obsoleta acclimated to 35‰ seawater at 18°C could survive for 116 hours, and tolerate a 57% loss of body water when desiccated at 15 °C in air with a relative humidity of 35%. In contrast, I. obsoleta acclimated to 3°C seawater survived for only 76 hours, and could not tolerate more than a 37% loss of body water. These results were used to support the proposition that freezing and desiccation tolerance are closely related in I. obsoleta.  相似文献   

8.
An isobathic transect of marine surface sediments from 1°N to 28°S off southwest Africa was used to further evaluate the potential of the chain length distribution and carbon stable isotope composition of higher plant n-alkanes as proxies for continental vegetation and climate conditions. We found a strong increase in the n-C29–33 weighted mean average δ13C values from −33‰ near the equator to around −26‰ further south. Additionally, C25–35 n-alkanes reveal a southward trend of increasing average chain length from 30.0 to 30.5. The data reflect the changing contribution of plants employing different photosynthetic pathways (C3 and C4) and/or being differently influenced by the environmental conditions of their habitat. The C4 plant proportions calculated from the data (ca. 20% for rivers draining the rainforest, to ca. 70% at higher latitude) correspond to the C4 plant abundance in continental catchment areas postulated by considering prevailing wind systems and river outflows. Furthermore, the C4 plant contribution to the sediments correlates with the mean annual precipitation and aridity at selected continental locations in the postulated catchment areas, suggesting that the C4 plant fraction in marine sediments can be used to assess these environmental parameters.  相似文献   

9.
Coastal ecosystems are exposed to changes in physical-chemical properties, such as those occurring in upwelling and freshwater-influenced areas. In these areas, inorganic carbon can influence seawater properties that may affect organisms and populations inhabiting benthic habitats such as the intertidal mussel Perumytilus purpuratus. Feeding and metabolic responses were measured in adult mussels from two geographic regions (central and southern Chile) and two local habitats (river-influenced and non-river-influenced) and three pCO2 levels (380, 750, and 1200 μatm pCO2 in seawater). The feeding rates of mussels tend to increase at high pCO2 levels in seawater; however this response was variable across regions and local habitats. In contrast, there was no difference in the respiratory rate of mussels between geographic areas, but there was a significant reduction of oxygen consumption at intermediate and high levels of pCO2. The results indicate that river-influenced organisms compensate for reductions in metabolic cost at elevated pCO2 levels by having their energy demands met, in contrast with non-river-influenced organisms. The lack of regional-scale variability in the physiological performance of mussels may indicate physiological homogeneity across populations and thus potential for local adaptation. However, the local-scale influences of river- and non-river-influenced habitats may counterbalance this regional response promoting intra-population variability and phenotypic plasticity in P. purpuratus. The plasticity may be an important mechanism that allows mussels to confront the challenges of projected ocean acidification scenarios.  相似文献   

10.
The supply and accumulation of silica in the marine environment   总被引：4，自引：0，他引：4  
Rivers and submarine hydrothermal emanations supply 6.1 × 1014g SiO2/yr to the marine environment. Approximately two-thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep-sea deposits. Siliceous deep-sea sediments located beneath the Antarctic Polar Front (Convergence) account for over a fourth (1.6 × 1014g SiO2/yr) of the silica supplied to the oceans. Deep-sea sediment accumulation rates beneath the Polar Front are highest in the South Atlantic with values as large as 53cm/kyr during the last 18.000 yr. Siliceous sediments in the Bering Sea, Sea of Okhotsk, and Subarctic North Pacific accumulate 0.6 × 1014g SiO2/yr or 10% of the dissolved silica input to the oceans. The accumulation of biogenic silica in estuarine deposits removes a maximum of 0.8 × 1014g SiO2/yr. Although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters, the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters. Siliceous sediments from continental margin upwelling areas (e.g. Gulf of California, Walvis Bay, or Peru-Chile coast) have the highest biogenic silica accumulation rates in the marine environment (69 g SiO2 cm2/kyr). Despite the rapid accumulation of biogenic silica, upwelling areas account for less than 5% of the silica supplied to the marine environment because they are confined laterally to such small areas.  相似文献   

11.
Shallow estuarine habitats often support large populations of small nekton (fishes and decapod crustaceans), but unique characteristics of these habitats make sampling these nekton populations difficult. We discuss development of sampling designs and evaluate some commonly used devices for quantitatively sampling nekton populations. Important considerations of the sampling design include the size and number of samples, their distribution in time and space, and control of tide level. High, stable catch efficiency should be the most important grear characteristic considered when selecting a sampling device to quantify nekton densities. However, the most commonly used gears in studies of estuarine habitats (trawls and seines) have low, variable catch efficiency. Problems with consistently low catch efficiency can be corrected, but large unpredictable variations in this gear characteristic pose a much more difficult challenge. Study results may be bised if the varibility in catch efficiency is related to the treatments or habitat characteristics being measured in the sampling design. Enclosure devices, such as throw traps and drop samplers, have fewer variables influencing catch efficiency than do towed nets (i.e., trawls and seines); and the catch efficiency of these enclosure samplers does not appear to vary substantially with habitat characteristics typical of shallow estuarine areas (e.g., presence of vegetation). The area enclosed by these samplers is often small, but increasing the sample number can generally compensate for this limitation. We recommend using enclosure samplers for estimating densities of small nekton in shallow estuarine habitats because these samplers provide the most reliable quantitative data, and the results of studies using these samplers should be comparable. Many kinds of enclosure samplers are now available, and specific requirements of a project will distate which gear should be selected.  相似文献   

12.
《Organic Geochemistry》1987,11(4):291-302
Normal alkanes (n-C13n-C36), isoprenoid hydrocarbons (i-C15, i-C16, i-C18, i-C19, and i-C20) triterpanes (C27C32), and (C27C29) are present in low concentrations offshore Antarctica in near-surface, Quaternary sediment of the Wilkes Land continental margin and of the western Ross Sea. The distributions of these hydrocarbons are interpreted relative to possible sources and processes. The hydrocarbons appear to be mixtures of primary and recycled material from marine and terrigenous sources. The n-alkanes are most abundant and are characterized by two distinct populations, one of probable marine origin and the other likely from terrigenous, vascular plant sources. Because the continent of Antarctica today is devoid of higher plants, the plant-derived hydrocarbons in these offshore sediments probably came from wind-blown material and recycled Antarctic sediment that contains land-plant remains from an earlier period of time. Isoprenoid hydrocarbons are partially recycled and mainly of marine origin; the dominance of pristane over phytane suggests oxic paleoenvironmental conditions. Both modern and ancient triterpanes and steranes are present, and the distribution of these indicates a mixture of primary and recycled bacterial, algal, and possible higher-plant materials. Although the sampled sediments were deposited during the Quaternary, they apparently contain a significant component of hydrocarbons of pre-Quaternary age.  相似文献   

13.
The presence of the C30 sterol gorgosterol (22,23-methylene-23,24-dimethylcholest-5-en-3ß-ol) and its analogues in some marine and freshwater environments is generally associated with invertebrate animals or dinoflagellates since there have been no reports of them in other microalgal classes. Here we show that two unialgal cultures of different species of the marine diatom Delphineis contain gorgosterol in addition to sterols more commonly found in diatoms. Our findings suggest that some reports of gorgosterol in seawater and marine sediments may well have an origin, at least in part, from diatoms.  相似文献   

14.
While it is critical to accurately understand the sources and transformation of sulfate based on time-series analysis, there are limited studies on temporal variation of sulfate in rivers and on rock weathering by sulfuric acids. We conducted a monthly sampling campaign in the Beipan, Nanpan, and Hongshui Rivers over the course of one hydrological year. This study examined seasonal variations in riverine sulfate impacted by the monsoon climate in the upper reaches of the Xijiang River basin. In general, the SO4 2? contents in these rivers dropped from relatively high levels to low values during the high-flow season, in response to increasing discharge. The sulfate was generally enriched in heavy isotopes during the low-flow season compared to the high-flow season. The calculated results indicate that the riverine sulfate was mainly derived from sulfide oxidation, but that evaporite dissolution could be an important source during the low-flow season, based on isotopic evidence. Mine drainage is likely an important source of sulfate to these rivers during the high-flow season due to contributions from fast surface flow, which responds to frequent heavy rain in monsoonal climate regions. A relatively high proportion of HCO3 ? was found to be derived from rock weathering by sulfuric acid during the high-flow season when compared to that observed during the low-flow season. The results suggest that approximately one quarter of the HCO3 ? in the Hongshui River originated from carbonate weathering by sulfuric acid derived from the oxidation of sulfide. Such information on the specific dual isotopic characteristics of riverine sulfate throughout a hydrological year can provide unique evidence for understanding the temporal variability of sulfate concentrations and weathering processes in rivers.  相似文献   

15.
The supply of nutrients from surface and subsurface water flow into the root zone was measured in a developing barrier island marsh in Virginia. We hypothesize that high production of tall-formSpartina alterniflora in the lower intertidal zone is due to a greater nitrogen input supplied by a larger subsurface flux. Individual nitrogen inputs to the tall-form and short-formS. alterniflora root zones were calculated from water flow rates into the root zone and the nutrient concentration corresponding to the source of the flow. Total dissolved inorganic nitrogen (DIN) input (as ammonium and nitrate) was then calculated using a summation of the hourly nutrient inputs to the root zone over the entire tidal cycle based on hydrologic and nutrient data collected throughout the growing season (April–August) of 1993 and 1994. Additionally, horizontal water flow into the lower intertidal marsh was reduced experimentally to determine its effects on nutrient input and plant growth. Total ammonium (NH4 +) input to the tall-formS. alterniflora root zone (168 μmoles 6 h?1) was significantly greater relative to the short-form (45 μmoles 6 h?1) during flood tide. Total NH4 + input was not significantly different between growth forms during ebb tide, and total nitrate (NO3 ?) and total DIN input were not significantly different between growth forms during either tidal stage. During tidal flooding, vertical flow from below the root zone accounted for 71% and horizontal flow from the adjacent mudflat accounted for 19% of the total NH4 + input to the tall-formS. alterniflora root zone. Infiltration of flooding water accounted for 15% more of the total NO3 ? input relative to the total NH4 + input at both zones on flood tide. During ebb tide, vertical flow from below the root zone still accounted for the majority of NH4 + and NO3 ? input to both growth forms. After vertical flow, horizontal subsurface flow from upgradient accounted for the next largest percentages of NH4 + and NO3 ? input to both growth forms during ebb tide. After 2 yr of interrupted subsurface horizontal flow to the tall-formS. alterniflora root zone, height and nitrogen content of leaf tissue of treatment plants were only slightly, but significantly, lower than control plants. The results suggest that a dynamic supply of DIN (as influenced by subsurface water flows) is a more accurate depiction of nutrient supply to macrophytes in this developing marsh, relative to standing stock nutrient concentrations. The dynamic subsurface supply of DIN may play a role in spatial patterns of abovegroundS. alterniflora production, but determination of additional nitrogen inputs and the role of belowground production on nitrogen demand need to also be considered.  相似文献   

16.
Long-term trends of waterfowl populations in Chesapeake Bay demonstrate the importance of shallow-water habitats for waterfowl species. Although recent increases in field feeding by geese and swans lessened the importance of shallow-water areas for these species, most duck species depend almost exclusively on shallow-water habitats. Many factors influenced the distribution and abundance of waterfowl in shallow-water habitats. Habitat degradation resulted in the decline in numbers of most duck species and a change in distribution of some species. Increased numbers of mallards (Anas platyrhynchos) in recent decades probably resulted from release programs conducted by the Maryland Department of Natural Resources and private individuals. Studies of food habits since 1885 showed a decline in submerged-aquatic vegetation in the diet of some species, such as the canvasback (Aythya valisineria), and an increase in the proportions of invertebrates in the diet. Diversity of food organisms for many waterfowl species has declined. Surveys of vegetation and invertebrates in the Chesapeake Bay generally reflect a degradation of shallow-water habitat. Human population increases in the Chesapeake Bay watershed directly and indirectly affected waterfowl distribution and abundance. The increase of exotic plant and invertebrate species in the bay, in most cases, benefited waterfowl populations. Increased contaminants have reduced the quality and quantity of habitat, although serious attempts to reverse this trend are underway. The use of shallow-water habitats by humans for fishing, hunting, boating, and other recreational and commercial uses reduced the use of shallow-water habitats by waterfowl. Humans can lessen the adverse influences on the valuable shallow-water habitats by restricting human population growth near these habitats and improving the water quality of the bay tributaries. Other affirmative actions that will improve these areas for waterfowl include greater restrictions on boat traffic in shallow-water habitats and establishing more sanctuaries in shallow-water areas that have complete protection from human disturbance. *** DIRECT SUPPORT *** A01BY074 00013  相似文献   

17.
In this work, we use Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (13C NMR) data to quantify the changes of major chemical compound classes (carboxylic acid, amide, ester, aliphatic, aromatic and carbohydrate) in high molecular weight (HMW, >1 kDa) dissolved organic matter (DOM) isolated along a transect through the Elizabeth River/Chesapeake Bay system to the coastal Atlantic Ocean off Virginia, USA. Results show that carboxylic acids and aromatic compounds are lost along the transect, while HMW DOC becomes enriched in carbohydrate moieties that could have a mid-transect source, perhaps the intensive red tide bloom (Choclodinium polykrikoides) which occurred during our sampling period. Taking the second derivative of the FTIR spectra resolved three pools of de-protonated carboxylic acids at our Dismal Swamp site (used to represent terrestrial organic matter in this area): one carboxylic acid pool, complexed with iron, seems to be lost between the Dismal Swamp and river sites; the second appears biogeochemically active throughout the riverine transect, disappearing in the coastal ocean sample; the third seems refractory, with the potential to be transported to and to accumulate within the open ocean. Five-member ring esters (γ-lactones) were the major ester form in the Dismal Swamp; aliphatic and acetate esters were the dominant esters in the estuary/marine DOM. No amide groups were detectable in Dismal Swamp DOM; secondary amides were present at the estuarine/marine sites. Coupling FTIR with 13C NMR provides new insights into the biogeochemical roles of carboxylic acid, amide and ester compounds in aquatic ecosystems.  相似文献   

18.
Angiosperms began to colonise riparian habitats very soon in their evolutionary history, probably already in the Aptian, but it is still poorly known when flowering plants finally dominated entirely these kind of communities as they do in the present. A new fossil plant locality (Molí del Baró-1) from the upper Maastrichtian of the Southern Pyrenees is described in which meandering river facies represent one of the first riparian communities formed only by angiosperms. The fossil assemblage consists of abundant leaves, seeds, logs and sporomorphs. Angiosperms remains dominate in all these cases and the leaf sample is mostly composed of a new eudicot willow-like species, Saliciphyllum gaetei sp. nov., the palm Sabalites longirhachis and an helophytic monocot. Pollen remains suggest that the later belonged to Typhaceae. Most of these plant remains were parautochthonous and deposited in a pond formed in the accretional part of a meander loop. The locality of Molí del Baró-1 represents an unique plant fossil assemblage in the uppermost Cretaceous of southern Europe. It clearly differs from those reported in other Maastrichtian localities of the Pyrenees (Fumanya and South Isona) and from the Campanian-Maastrichtian of Austria and Romania. In addition, it reflects a surprisingly modern physiognomy for a Late Cretaceous riverine plant assemblage that was built up with willow-like plants, palms and reeds.  相似文献   

19.
The amount of bicarbonate utilised by plants is usually ignored because of limited measurement methods. Accordingly, this study quantified the photosynthetic assimilation of inorganic carbon (CO2 and HCO3 ?) by plants. The net photosynthetic CO2 assimilation (P N), the photosynthetic assimilation of CO2 and bicarbonate (P N’), the proportion of increased leaf area (f LA) and the stable carbon isotope composition (δ13C) of Orychophragmus violaceus (Ov) and Brassica juncea (Bj) under three bicarbonate levels (5, 10 and 15 mm NaHCO3) were examined to determine the relationship among P N, P N’ and f LA. P N’, not P N, changed synchronously with f LA. Moreover, the proportions of exogenous bicarbonate and total bicarbonate (including exogenous bicarbonate and dissolved CO2-generated bicarbonate) utilised by Ov were 2.27 % and 5.28 % at 5 mm bicarbonate, 7.06 % and 13.28 % at 10 mm bicarbonate, and 8.55 % and 17.31 % at 15 mm bicarbonate, respectively. Meanwhile, the proportions of exogenous bicarbonate and total bicarbonate utilised by Bj were 1.77 % and 3.28 % at 5 mm bicarbonate, 2.11 % and 3.10 % at 10 mm bicarbonate, and 2.36 % and 3.09 % at 15 mm bicarbonate, respectively. Therefore, the dissolved CO2-generated bicarbonate and exogenous bicarbonate are important sources of inorganic carbon for plants.  相似文献   

20.
Land-based eutrophication is often associated with blooms of green macroalgae, resulting in negative impacts on seagrasses. The generality of this interaction has not been studied in upwelling-influenced estuaries where oceanic nutrients dominate seasonally. We conducted an observational and experimental study with Zostera marina L. and ulvoid macroalgae across an estuarine gradient in Coos Bay, Oregon. We found a gradient in mean summer macroalgal biomass from 56.1 g dw 0.25 m−2 at the marine site to 0.3 g dw 0.25 m−2 at the riverine site. Despite large macroalgal blooms at the marine site, eelgrass biomass exhibited no seasonal or interannual declines. Through experimental manipulations, we found that pulsed additions of macroalgae biomass (+4,000 mL) did not affect eelgrass in marine areas, but it had negative effects in riverine areas. In upwelling-influenced estuaries, the negative effects of macroalgal blooms are context dependent, affecting the management of seagrass habitats subject to nutrient inputs from both land and sea.  相似文献   

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