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1.
This two-part study examined the benthic macrofaunal community in Delaware salt marsh impoundments having partial tidal restriction. The first part compared abundance, diversity, and taxonomic composition in three habitat types in impoundments—creeks, vegetated creek banks, and ponds—to those found in natural marshes. Impoundment effects were present but were habitat-specific. Abundances were higher in natural marsh creeks than in impoundment creeks, and diversities were higher in impoundment ponds than in natural marsh ponds. Vegetated bank communities in impoundments were about 50% insects and arachnids and 50% oligochaetes, while natural bank communities were primarily oligochaetes and the polychaeteManayunkia aestuarina. This is likely due to the decrease in flooding of the vegetated high marsh caused by partial impoundment. Pond and creek community composition also showed impoundment effects: in comparison with natural marshes, impoundments had higher proportions of the burrowing anemoneNematostella vectensis, nemerteans, andTubificoides sp. oligochaetes and lower proportions of the oligochaeteClitellio arenarius. The second part of the study compared benthic macrofauna in an impoundment before, during, and after the water level was lowered so that some bottom sediments were exposed and some covered with just a few centimeters of water for several weeks. During this event, macrofaunal abundances were reduced and the community shifted from being dominated by annelids, anemones, and nemerteans toward one dominated by annelids and insects. About 6 wk after reflooding, persistent effects of this disturbance were still suggested by greatly increased abundances and 96% dominance by one species of oligochaete,Paranais litoralis. Impoundment management plans calling for periods of sediment exposure or very low water may want to consider the potential for strong and persistent effects on the macrofaunal community.  相似文献   

2.
This study examined the effects of watershed development on macrobenthic communities in tidal creeks of Charleston Harbor, South Carolina, U.S. Two types of creeks were evaluated: upland creeks which drained watersheds consisting of at least 15% terrestrial land cover, and salt marsh creeks which drained no upland habitat (i.e., only intertidal habitat). Samples of macrobenthic organisms were taken along the longitudinal axis of twenty-three primary (first order) tidal creeks. Water and sediment quality data were also collected including measurements of dissolved oxygen, salinity, temperature, sediment characteristics, and toxic chemicals in the creek sediments. Hypoxic conditions occurred more than 15% of the time in both reference and developed creeks and were a natural attribute of these systems. The most severe and frequent hypoxia occurred in impacted salt marsh creeks. Salinity fluctuations were the greatest in developed upland creeks and salinity range was identified as a potentially reliable indicator of the degree to which watershed development has altered hydrodynamic processes. The creeks draining urban and industrial watersheds were degraded environments characterized by watersheds with high (>50%) levels of impervious surface, broad fluctuations in salinity, severe hypoxia, and potentially toxic levels of chemicals in the sediment. These creeks had low macrobenthic diversity and abundance and were numerically dominated by the oligochaeteMonopylephorus rubroniveus in mud sediments, and the polychaeteLaeoreis culveri in sand sediments. Suburban watersheds had 15–35% impervious surface and creeks draining them were exposed to frequent hypoxia and broad salinity fluctuations. The levels of chemical contaminants in sediments of suburban and impacted salt marsh creeks were generally not different from the levels in reference creeks. Macrobenthic diversity and abundance were higher for suburban and impacted salt marsh creeks than for urban and industrial creeks. However, suburban and salt marsh impacted creeks were numerically dominated by a few pollution indicative species including the oligochaetesM. rubroniveus andTubificoides brownae and the polychaeteL. culveri. These creeks appear to be exhibiting early signs of degradation (e.g., a simplified food web). Two promising community-level macrobenthic metrics for assessing environmental quality were identified: the proportional abundance of pollution indicative taxa, and the proportional abundance of pollution sensitive taxa. These indicators were significantly (p<0.05) correlated with the salinity range, the level of chemical contaminants in sediments, and amount of impervious surface in the watershed.  相似文献   

3.
This study provides new insights in the relative role of tidal creeks and the marsh edge in supplying water and sediments to and from tidal marshes for a wide range of tidal inundation cycles with different high water levels and for marsh zones of different developmental stage. Net import or export of water and its constituents (sediments, nutrients, pollutants) to or from tidal marshes has been traditionally estimated based on discharge measurements through a tidal creek. Complementary to this traditional calculation of water and sediment balances based on creek fluxes, we present novel methods to calculate water balances based on digital elevation modeling and sediment balances based on spatial modeling of surface sedimentation measurements. In contrast with spatial interpolation, the presented approach of spatial modeling accounts for the spatial scales at which sedimentation rates vary within tidal marshes. This study shows that for an old, high marsh platform, dissected by a well-developed creek network with adjoining levees and basins, flow paths are different for tidal inundation cycles with different high water levels: during shallow inundation cycles (high water level <0.2 m above the creek banks) almost all water is supplied via the creek system, while during higher inundation cycles (high water level >0.2 m) the percentage of water directly supplied via the marsh edge increases with increasing high water level. This flow pattern is in accordance with the observed decrease in sedimentation rates with increasing distance from creeks and from the marsh edge. On a young, low marsh, characterized by a gently seaward sloping topography, material exchange does not take place predominantly via creeks but the marsh is progressively flooded starting from the marsh edge. As a consequence, the spatial sedimentation pattern is most related to elevation differences and distance from the marsh edge. Our results imply that the traditional measurement of tidal creek fluxes may lead in many cases to incorrect estimations of net sediment or nutrient budgets.  相似文献   

4.
Associations between macrobenthic communities, measures of water column and sediment exposure, and measures of anthropogenic activities throughout the watershed were examined for the Chesapeake Bay, U.S. The condition of the macrobenthic communities was indicated by a multimetric benthic index of biotic integrity (B-IBI) that compares deviation of community metrics from values at reference sites assumed to be minimally altered by anthropogenic sources of stress. Correlation analysis was used to examine associations between sites with poor benthic condition and measures of pollution exposure in the water column and sediment. Low dissolved oxygen events were spatially extensive and strongly correlated with benthic community condition, explaining 42% of the variation in the B-IBI. Sediment contamination was spatially limited to a few specific locations including Baltimore Harbor and the Southern Branch of the Elizabeth River and explained about 10% of the variation in the B-IBI. After removing the effects of low dissolved oxygen events, the residual variation in benthic community condition was weakly correlated with surrogates for eutrophication—water column concentrations of total nitrogen, total phosphorus, and chlorophylla. Associations between benthic conditions and anthropogenic inputs and activities in the watershed were also studied by correlation analysis. Benthic condition was negatively correlated with measures of urbanization (i.e., population density, point source loadings, and total nitrogen loadings) and positively correlated with watershed forestation. Significant correlations were observed with population density and nitrogen loading below the fall line, but not above it, suggesting that near-field activities have a greater effect on benthic condition than activities in the upper watershed. At the tributary level, the frequency of low dissolved oxygen events and levels of sediment contaminants were positively correlated with population density and percent of urban land use. Sediment contaminants were also positively correlated with point source nutrient loadings. Water column total nitrogen concentrations were positively correlated with nonpoint nutrient loadings and agricultural land use while total phosphorus concentrations were not correlated with land use or nutrient loadings. Chlorophylla concentrations were positively correlated with nitrogen and phosphorus concentrations in the water column and with agricultural land use but were not correlated with nutrient loads.  相似文献   

5.
This paper examines how perennial Aster tripolium and annual Salicornia procumbens salt marshes alter the biomass, density, taxon diversity, and community structure of benthic macrofauna, and also examines the role of elevation, sediment grain size, plant cover, and marsh age. Core samples were collected on a fixed grid on an intertidal flat in the Westerschelde estuary (51.4° N, 4.1° E) over 5 years (2004–2008) of salt marsh development. In unvegetated areas, macrobenthic biomass, density, and taxon diversity were highest when elevation was highest, benthic diatoms were most abundant, and sediment median grain size was smallest. In contrast, in salt marsh areas, macrobenthic biomass and taxon diversity increased with median grain size, while the effects of elevation and diatom abundance on macrobenthic biomass, density, and diversity were not significant. In fine sediments, macrofaunal community structure in the salt marsh was particularly affected; common polychaetes such as Nereis diversicolor, Heteromastus filiformis, and Pygospio elegans had low abundance and oligochaetes had high abundance. Marsh age had a negative influence on the density of macrofauna, and A. tripolium stands had lower macrofaunal densities than the younger S. procumbens stands. There were no significant effects of marsh age, plant cover, and vegetation type on macrobenthic biomass, taxon diversity, and community structure. The results highlight that ecosystem engineering effects of salt marsh plants on macrofauna are conditional. Organic enrichment of the sediment and mechanical hindering of macrofaunal activity by plant roots are proposed as plausible mechanisms for the influence of the salt marsh plants on macrofauna.  相似文献   

6.
Benthic microalgal biomass is an important fraction of the primary producer community in shallow water ecosystems, and the factors controlling benthic microalgal biomass are complex. One possible controlling factor is sediment grain-size distribution. Benthic microalgal biomass was sampled in sediments collected from two sets of North Carolina estuaries Massachusetts and Cape Cod bays, and Manukau Harbour in New Zealand. Comparisons of benthic microalgal biomass and sediment grain-size distributions in these coastal and estuarine ecosystems frequently showed a negative relationship between the proportion of fine-grained sediments and benthic microalgal biomass measured as chlorophylla. The highest sedimentary chlorophylla levels generally occurred in sediments with lower percentages of fine particles (diameter <125 mm). A negative relationship between the proportion of fine sediments and benthic microalgal biomass suggests anthropogenic loadings of fine sediment may reduce the biological productivity of shallow-water ecosystems.  相似文献   

7.
Quarterly field sampling was conducted to characterize variations in water column and sediment nutrients in a eutrophic southern California estuary with a history of frequent macroalgal blooms. Water column and sediment nutrient measures demonstrated that Upper Newport Bay (UNB) is a highly enriched estuary. High nitrate (NO3 −) loads from the river entered the estuary at all sampling times with a rainy season (winter) maximum estimated at 2,419 mol h−1. This resulted in water NO3 − concentration in the estuary near the river mouth at least one order of magnitude above all other sampling locations during every seasons; maximum mean water NO3 − concentration was 800 μM during springer 1997. Phosphorus (P)-loading was high year round (5.7–90.4 mol h−1) with no seasonal pattern. Sediment nitrogen (N)-content showed a seasonal pattern with a spring maximum declining through fall. sediment and water nutrients, as well as percent cover of three dominant macroalgae, varied between the main channel and tidal creeks. During all seasons, water column NO3 − concentrations were higher in the main channel than in tidal creeks while tidal creeks had higher levels of sediment total Kjeldhal nitrogen (TKN) and P. During each of the four sampling periods, percent cover ofEntermorpha intestinalis andCeramium spp. was higher in tidal creeks than in the main channel, while percent cover ofUlva expansa was always higher in the main channel. Decreases in sediment N in both creek and channel habitats were concurrent with increases in macroalgal cover, possibly reflecting use of stored sediment TKN by macroalgae. Our data suggest a shift in primary nutrient sources for macroalgae in UNB from riverine input during winter and spring to recycling from sediments duirng summer and fall.  相似文献   

8.
In a large (8 ha) salt marsh restoration site, we tested the effects of excavating tidal creeks patterned after reference systems. Our purposes were to enhance understanding of tidal creek networks and to test the need to excavate creeks during salt marsh restoration. We compared geomorphic changes in areas with and without creek networks (n = 3; each area 1.3 ha) and monitored creek cross-sectional areas, creek lengths, vertical accretion, and marsh surface elevations for 5 yr that included multiple sedimentation events. We hypothesized that cells with creeks would develop different marsh surface and creek network characteristics (i.e., surface elevation change, sedimentation rate, creek cross-sectional area, length, and drainage density). Marsh surface vertical accretion averaged 1.3 cm yr−1 with large storm inputs, providing the opportunity to assess the response of the drainage network to extreme sedimentation rates. The constructed creeks initially filled due to high accretion rates but stabilized at cross-sectional areas matching, or on a trajectory toward, equilibrium values predicted by regional regression equations. Sedimentation on the marsh surface was greatest in low elevation areas and was not directly influenced by creeks. Time required for cross-sectional area stabilization ranged from 0 to > 5 yr, depending on creek order. First-order constructed creeks lengthened rapidly (mean rate of 1.3 m yr−1) in areas of low elevation and low vegetation cover. New (volunteer) creeks formed rapidly in cells without creeks in areas with low elevation, low vegetation cover, and high elevation gradient (mean rate of 6.2 m yr−1). After 5 yr, volunteer creeks were, at most, one-fourth the area of constructed creeks and had not yet reached the upper marsh plain. In just 4 yr, the site’s drainage density expanded from 0.018 to reference levels of 0.022 m m−2. Pools also formed on the marsh plain due to sediment resuspension associated with wind-driven waves. We conclude that excavated creeks jump-started the development of drainage density and creek and channel dimensions, and that the tidal prism became similar to those of the reference site in 4–5 yr.  相似文献   

9.
Surface films on marsh creeks form water-air interfaces of high biological activity. The development, movement, deposition, and breakup of the tidal creek surface film in a naturalSpartima alterniflora-dominated salt marsh in Delaware were followed seasonally over tidal cycles. The metabolic activity, i.e., photosynthesis and respiration, of the surface film and underlying water were determined in the field at the time of peak film formation, just prior to high tide, and the particulate material and chlorophylla were quantified over the tidal cycles. The quantities of organic and inorganic components of the particulate material were all significantly higher in the surface film than in the underlying water (on a volume basis). Numbers of algal cells and quantities of chlorophyll were orders of magnitude greater in the surface film than in the water column. Photosynthesis and respiration were significantly higher in the surface film than in the underlying water. The spectrum of fatty acids was more diverse and their total content was significantly greater in the surface film than in the water column, indicating a concentrated food source contributed by the film as well as a biological richness of the film. When water in the creek flooded the marsh plain at high tide, film deposition was greatest on simulated creek bankS. alterniflora stems, compared to stems along rivulets in the marsh and those in the marsh plain. Using surface film dry weight measurements on an areal basis and film velocity in the creek, both measured throughout a tidal cycle during the summer, it was determined that approximately 12 kg (dry weight) of particulate material moved on the creek surface (2 m wide) past a given point on the flood tide, and 14 kg moved in the opposite direction on the ebb tide. The biological and physical data collected in this study illuminate the contribution of the surface film to the biological (food web) and physical (sediment transport and deposition) functions of a salt marsh.  相似文献   

10.
Coastal systems serve many human uses and as a result are susceptible to anthropogenic activities such as nutrient loading and overfishing. In soft sediments, infauna frequently serve as key indicators of such activities. To use infauna effectively as bioindicators, it is important to understand how infaunal abundances and community patterns vary naturally within ecosystems. We examined the spatial and temporal dynamics of infaunal annelids in four tidal creeks of the Plum Island Estuary, Massachusetts, USA, from June to October 2003, sampling along a tidal inundation gradient that crossed five distinct habitats from creek bottoms to the vegetated high marsh platform. Annelids comprised 97% of the total number of macroinfauna. Highest densities were found in creek wall habitats (33,418–65,535 individuals m−2), and lowest densities (2,421–10,668 individuals m−2) were found inSpartina patens habitats. Five numerically abundant species comprised 87% of the annelid assemblage and three species,Manayunkia aestuarina (Polychaeta),Paranais litoralis (Oligochaeta), andCernosvitoviella immota (Oligochaeta), were broadly distributed across the marsh landscape.Streblospio benedicti (Polychaeta) andFabricia sabella (Polychaeta) were abundant only in mudflat and creek wall habitats, respectively.P. litoralis experienced a summer decline in all habitats, whereasM. aestuarina abundance increased 4–5 fold, in October relative to June in creek wall and tall-formSpartina alterniflora habitats. Hierarchical spatial, analysis revealed that >90% of the variability in annelid abundances was found at the mesospatial scale (<50 m). Variation among the four creeks, (>1 km) was relatively small.  相似文献   

11.
This study was designed to investigate seasonal changes on food available for benthic consumers in relation to tidal levels and sediment depth in an estuarine beach. The relationships between the biochemical characteristics of sedimentary organic matter and benthic macrofauna were analyzed quarterly over 2 years (from January 1997 to January 1999), in an estuarine soft intertidal zone from the NW coast of Spain (42°64′04″N, 8°88′36″W). Sediment samples were collected to provide a two-dimensional view of macroinfauna distribution in the intertidal zone and its relationship with the quantity and quality of the organic matter. The nutritional value of organic matter (i.e., lipid, protein, and carbohydrate) and the content of chlorophyll a of the sediment were measured. Macrofaunal assemblages and food availability in the sediment were studied at three tidal levels on the shore: two intertidal and one supratidal. Macroinfauna and biochemical compounds showed a clear vertical stratification with the highest macrofaunal abundance at the superficial layer of the sediment, where redox potential discontinuity was also observed. Crustaceans were found mainly inhabiting the supratidal level of the estuarine beach, while polychaetes and mollusks occupied the intertidal level. Food availability, measured as biopolymeric carbon, and also chlorophyll a from the sediment were better related to macroinfauna abundance, biomass, and abundance of main taxonomic groups. Macrofauna assemblages showed particular distribution in both vertical and horizontal ranges suggesting specific preferences to several abiotic factors. No clear seasonal pattern was found in macrofauna and sedimentary organic characteristics suggesting that macrofaunal assemblages are controlled by complex and unpredictable factors, including small-scale changes in substrate and hydrological characteristics.  相似文献   

12.
Spatial and temporal variations in the abundances and distributions of oligochaetes of a southwestern Louisiana estuary were examined as part of a long term study of community structure of benthic macroinvertebrates. Quantitative samples were collected at monthly intervals from nine stations for two years and an additional 17 stations were sampled once. A tubificid oligochaete,Tubificoides denouxi n. sp., is described from the five species collected. The two predominant oligochaetes,Tubificoides heterochaetus andT. denouxi, were congeneric and exhibited completely allopatric distributions. Two oligochaete species with-restricted distributions,Monopylephorus helobius andLimnodriloides sp., were sympatric withT. denouxi, whileThalassodrilides belli, although less abundant, was sympatric with bothT. denouxi andT. heterochaetus. Sexually mature specimens ofT. denouxi andT. belli were collected only in the summer,T. heterochaetus was sexually mature in both winter and summer collections, andMonopylephorus helobius was sexually mature in spring and summer collections. Many of the studies of Oligochaeta have concluded that correlation exists between sediment grain size and species demography. Our data demonstrate a strong relationship between salinity and the abundance and distribution of estuarine species.Tubificoides denouxi was found only within the salinity range of 14.8 to 22.0‰ salinity,T. heterochaetus was found only within the range of 2.3 to 14.1‰, andT. belli had a salinity distribution intermediate between the previous species. No relationship was found between sediment grain-size analysis, water depth or hydrographic variables and species distribution.  相似文献   

13.
Food habits of two species of dolichopodid fly larvae, from two Gulf Coast oligohaline tidal marshes, were analyzed from monthly collections taken between June 1979 and May 1980. Larvae ofPelastoneurus abbreviatus Loew andThinophilus frontalis Van Duzee, taken from aJuncus roemerianus Scheele dominated marsh, fed predominantly on oligochaetes and nematodes.Pelastoneurus abbreviatus, collected in a nearbySpartina cynosuroides (L.) Roth marsh, also fed on oligochaetes but consumed more polychaetes than nematodes. By being predators and prey in turn, these larvae serve in the transfer of energy between benthic, aquatic, and terrestrial components of the marsh, system.  相似文献   

14.
Ten years (1985–1994) of data were analyzed to investigate general patterns of phytoplankton and nutrient dynamics, and to identify major factors controlling those dynamics in the York River Estuary, Virginia. Algal blooms were observed during winter-spring followed by smaller summer blooms. Peak phytoplankton biomass during the winter-spring blooms occurred in the mid reach of the mesohaline zone whereas peak phytoplankton biomass during the summer bloom occurred in the tidal fresh-mesohaline transition zone. River discharge appears to be the major factor controlling the location and timing of the winter-spring blooms and the relative degree of potential N and P limitation. Phytoplankton biomass in tidal fresh water regions was limited by high flushing rates. Water residence time was less than cell doubling time during high flow seasons. Positive correlations between PAR at 1 m depth and chlorophylla suggested light limitation of phytoplankton in the tidal fresh-mesohaline transition zone. Relationships of salinity difference between surface and bottom water with chlorophylla distribution suggested the importance of tidal mixing for phytoplankton dynamics in the mesohaline zone. Accumulation of phytoplankton biomass in the mesohaline zone was generally controlled by N with the nutrient supply provided by benthic or bottom water remineralization.  相似文献   

15.
Analysis of 75 vibracores from the backbarrier region of Kiawah Island, South Carolina reveals a complex association of three distinct stratigraphic sequences. Beach ridge progradation and orientation-controlled backbarrier development during the evolution of Kiawah Island, and resulted in deposition of: (1) a mud-rich central backbarrier sequence consisting of low marsh overlying fine-grained, tidal flat/lagoonal mud; (2) a sandy beach-ridge swale sequence consisting of high and low marsh overlying tidal creek channel and point bar sand, and foreshore/shoreface; and (3) a regressive sequence of sandy, mixed, and muddy tidal flats capped by salt marsh that occurs on the updrift end of the island. Central backbarrier deposits formed as a result of the development of the initial beach ridge on Kiawah Island. Formation of this beach ridge created a backbarrier lagoon in which fine-grained estuarine and tidal flat mud accumulated. Washovers, oyster mounds, and tidal creek deposits form isolated sand and/or shell-rich lenses in the lagoon. Spartina alterniflora low marsh prograded into the lagoon as the tidal flats aggraded. Barrier progradation and sediment bar-bypassing at Stono Inlet created digitate beach ridges on the northeast end of Kiawah Island. Within the beach-ridge swales, tidal flats were disconformably deposited on shoreface and foreshore sand of the older beach ridges. Tidal creek drainage systems evolved to drain the swales. These rapidly migrating creeks reworked the tidal flat, foreshore, and shoreface sediments while redepositing a fining-upward sequence of channel lag and point bar deposits, which served as a substrate for salt marsh colonization. This resultant regressive sedimentary package marks the culmination of barrier island development and estuary infilling. Given enough time and sedimentation, the backbarrier sequence will ultimately prograde over the barrier island, reworking dune, beach, and foreshore sediments to form the upper sand-rich bounding surface of the barrier lithosome. Preservation of the regressive sequence is dependent upon sediment supply and the relative rate of sea-level rise, but the reworking of barrier islands by tidal inlets and migrating tidal creeks greatly alter and complicate the stratigraphic sequence.  相似文献   

16.
为研究潮沟发育演变动力机制,建立了以江苏中部粉砂淤泥质潮滩-潮沟系统为原型的降比尺物理模型,模拟在潮汐作用下,潮沟系统从平坦滩面逐渐形成、发育演变至动态平衡状态的过程,并分析了潮沟系统在不同阶段的形态特征。研究结果表明:潮沟系统发育速率先快后慢,最终达到动态平衡状态。采用潮沟发育各阶段潮沟系统的总长度与终态潮沟总长度的比值以及潮沟及其相邻处潮滩的高程变化速率两种方法,均可以衡量潮沟系统的发育程度。潮沟系统发育达到动态平衡后,各级潮沟个数占潮沟总数量的比例基本固定。潮沟的宽度、深度、宽深比均符合对数正态分布。潮沟的宽度与宽深比、深度与宽深比之间均具有幂函数关系。  相似文献   

17.
为研究潮汐作用下潮沟网络形成、演变规律,结合江苏沿海粉砂淤泥质潮滩实际情况,建立试验室物理模型,模拟具有一定坡度的潮滩在潮汐作用下的地形演变,分析了潮沟发育演变中的水沙运动规律,研究了潮差对于潮沟发育的影响。研究表明,潮沟发育过程受到床面坡度变化的影响,坡度均一的潮滩上,潮沟系统通过相邻小潮沟相互连接而形成,没有明显的潮沟头部溯源侵蚀现象;在潮汐作用下,涨潮初期和落潮后期水流流速较快,泥沙运动主要出现在这一阶段,在潮滩中部泥沙运动最为剧烈;潮差对于潮沟系统形态和结构的影响较小,潮滩排水路径长度与子流域面积呈幂函数分布,潮差越大则潮沟系统越早达到动态平衡,且具有更大的拓宽潮沟的作用。  相似文献   

18.
Epiphytic microbial biomass (as chlorophylla) was measured monthly in North Inlet Estuary, South Carolina, for 16 months on spatially distinct stem sections (bottom and middle) of dead and livingSpartina alterniflora growth forms (tall, medium, and short) exposed at low tide. The highest biomass was located on the bottom section of tall plants, presumably due to their relatively longer contact with creek water and associated phytoplankton, and their closer proximity to marsh sediments with associated benthic microalgae, both recruitment sources for epiphytes. Dead plants left standing from the previous year’s growth cycle had higher epiphytic biomass than living plants, which occurred mostly in late spring through fall. Epiphytic biomass was highest in the winter (mean of 1.77 mg chla (m2 marsh)−1) and lowest in the summer (mean of 0.34 mg chla (m2 marsh)−1). Because phytoplankton andSpartina production are lowest in the winter, the results emphasize the relative importance of epiphytes to growth of herbivores in this season.  相似文献   

19.
Macrotidal estuaries (mean tidal range >2m) generally exhibit a tolerance to pollution with nitrogen-containing nutrients despite high loadings originating from freshwater outflows. These systems, which are characterized by high tidal energy, generally exhibit lower levels of chlorophylla than systems with lower tidal energy. A comparative analysis of data from 40 microtidal and macrotidal estuaries shows that mean annual chlorophylla levels are significantly lower in systems with high tidal energy even when nitrogen concentrations are equal to nitrogen levels in the microtidal systems. Tidal range and associated processes (e.g., tidal mixing, current velocity, light penetration, and sediment resuspension) influence phytoplankton biomass in some estuaries.  相似文献   

20.
In the tidal Potomac River, high river discharges during the spring are associated with high chlorophylla concentrations in the following in the following summer, assuming that summertime light and temperature conditions are favorable. Spring floods deliver large loads of particulate N and P to the tidal river. This particulate N and P could be mineralized by bacteria to inorganic N and P and released to the water column where it is available for phytoplankton use during summertime. However, during the study period relatively low concentrations of chlorophylla (less than 50 μg l?1 occurred in the tidal river if average monthly discharge during July or August exceeded 200 m3s?1. Discharge and other conditions combined to produce conditions favorable for nuisance levels of chlorophylla (greater than 100 μg l?1 approximately one year out of four. Chlorophylla maxima occurred in the Potomac River transition zone and estuary during late winter (dinoflagellates) and spring (diatoms). Typical seasonal peak concentrations were achieved at discharges as high as 970 m3 s?1, but sustained discharges greater than 1,100 m3 s?1 retarded development. Optimum growth conditions occurred following runoff events of 10 to 15 d duration which produced transit times to the transition zone of 7 to 10 d. Wet years with numerous moderate-sized runoff events, such as 1980, tend to produce greater biomass in the transition zone and estuary than do dry years such as 1981.  相似文献   

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