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1.
In-situ measurements of benthic fluxes of oxygen and nutrients were made in the subtidal region of the Mandovi estuary during premonsoon and monsoon seasons to understand the role of sediment–water exchange processes in the estuarine ecosystem. The Mandovi estuary is a shallow, highly dynamic, macrotidal estuary which experiences marine condition in the premonsoon season and nearly fresh water condition in the monsoon season. The benthic flux of nutrients exhibited strong seasonality, being higher in the premonsoon compared to the monsoon season which explains the higher ecosystem productivity in the dry season in spite of negligible riverine nutrient input. NH4+ was the major form of released N comprising 70–100% of DIN flux. The benthic respiration rate varied from −98.91 to −35.13 mmol m−2 d−1, NH4+ flux from 5.15 to 0.836 mmol m−2 d−1, NO3− + NO2− from 0.06 to −1.06 mmol m−2 d−1, DIP from 0.12 to 0.23 mmol m−2 d−1 and SiO44− from 5.78 to 0.41 mmol m−2 d−1 between premonsoon to monsoon period. The estuarine sediment acted as a net source of DIN in the premonsoon season, but changed to a net sink in the monsoon season. Variation in salinity seemed to control NH4+ flux considerably. Macrofaunal activities, especially bioturbation, enhanced the fluxes 2–25 times. The estuarine sediment was observed to be a huge reservoir of NH4+, PO43− and SiO44− and acted as a net sink of combined N because of the high rate of benthic denitrification as it could remove 22% of riverine DIN influx thereby protecting the eco system from eutrophication and consequent degradation. The estuarine sediment was responsible for ∼30–50% of the total community respiration in the estuary. The benthic supply of DIN, PO43− and SiO44− can potentially meet 49%, 25% and 55% of algal N, P and Si demand, respectively, in the estuary. Based on these observations we hypothesize that it is mainly benthic NH4+ efflux that sustains high estuarine productivity in the NO3− depleted dry season.  相似文献   

2.
“Biolog” plates were used to study the changes in the metabolic capabilities of bacterioplankton over a complete tidal cycle in a tropical ecosystem (Cochin Estuary) along southwest coast of India. The pattern of utilization of carbon sources showed a definite shift in the community metabolism along a salinity gradient. Multivariate statistical analysis revealed two communities, namely allochthonous bacterioplankton sensitive to salinity and autochthonous bacterioplankton, which are tolerant to wide salinity fluctuations. Regression analysis showed salinity as the most important parameter influencing the physiological profile of bacterioplankton, irrespective of tide. Apart from salinity, limno-tolerant retrievable counts and halo-tolerant retrievable counts also accounted for the metabolic variation of bacterioplankton during low and high tides, respectively. The shift in the substrate utilization from carbohydrates to amino acids appears to be due to the physiological adaptation or nitrogen limitation of bacterial community with increasing salinity.  相似文献   

3.
Spatial and temporal variations in particle-bound pesticide contamination, natural environmental variables, and benthic abundance were measured during the dry summer season within a temporarily open estuary (Lourens River). This study focused on the effect of particle-associated pesticides on the dynamics of the benthic community (including epi-benthic, hyper-benthic, and demersal organisms) by comparing two runoff events, differing in their change in pesticide concentration and environmental variables. The two chosen sites were situated within the upper and middle reaches of the estuary and differ significantly in salinity (p = 0.001), flow (p = 0.5), temperature (p < 0.001) and particulate organic carbon in the sediment (p < 0.001). Generally higher particle-bound pesticides were found in the upper reaches.  相似文献   

4.
Size-fractionated bacterial production, abundance and α- and β- glucosidase enzyme activities were studied with respect to changes in hydrography, total suspended matter (TSM), chlorophyll a, particulate organic carbon and nitrogen ratio (POC:PON), 1.5 M NaCl-soluble and 10 mM EDTA-soluble carbohydrates (Sal-PCHO and CPCHO) and transparent exopolymeric particles (TEP) in the surface waters from July 1999–2000 at a shallow coastal station in Dona Paula Bay, west coast of India. The bulk of the total bacterial production and glucosidase activity were associated with particles (75% and >80%, respectively). Total bacterial production was linearly correlated to chlorophyll a (r = 0.513; p < 0.05) whereas enzyme activity was significantly correlated to TSM (α-glucosidase: r = 0.721 (p < 0.001); β-glucosidase: r = 0.596 (p < 0.01)). Both α-glucosidase (r = 0.514; p < 0.05) and β-glucosidase enzymes (r = 0.598; p < 0.01) appeared to be involved in the degradation of CPCHO and Sal-PCHO, respectively. Changes in α-glucosidase/β-glucosidase ratios highlighted the varying composition of particulate organic matter. The bacterial uptake of 14C-labeled bacterial extracellular carbohydrate measured over 11 days showed a strong linear correlation between 14C-uptake and bacterial production using tritiated thymidine. The turnover rate of 14C-labeled carbohydrate-C was 0.52 d−1, higher than the estimated annual mean potential carbohydrate carbon turnover rate of 0.33 ± 0.2 d−1. Our study suggests that carbohydrates derived from sediments may serve as an important alternative carbon source sustaining the bacterial carbon demand in the surface waters of Dona Paula Bay.  相似文献   

5.
To assess the potential of stable isotope ratios as an indicator of fish migration within estuaries, stable isotope ratios in important zooplankton species were analyzed in relation to estuarine salinity gradients. Gut contents from migratory juveniles of the euryhaline marine fish Lateolabrax japonicus were examined along the Chikugo River estuary of the Ariake Sea, which has the most developed estuarine turbidity maximum (ETM) in Japan. Early juveniles in March and April preyed primarily on two copepod species; Sinocalanus sinensis at lower salinities and Acartia omorii at higher salinities. Late juveniles (standard length > 40 mm) at lower salinities preyed exclusively on the mysid Acanthomysis longirostris until July and complementarily on the decapod Acetes japonicus in August. These prey species were collected along the estuary during the spring–summer seasons of 2003 and 2004, and their carbon and nitrogen stable isotope ratios (δ13C and δ15N) were evaluated. The δ13C values of prey species were distinct from each other and were primarily depleted within and in close proximity to the ETM (salinity < 10); S. sinensis (−26.6‰) < Acanthomysis longirostris (−23.3‰) < Acartia omorii (−21.1‰) < Acetes japonicus (−18.5‰). The overall gradient of δ13C with salinity occurred for all prey species and showed minor temporal fluctuations, while it was not directly influenced by the δ13C values in particulate organic matter along the estuary. In contrast to δ13C, the δ15N values of prey species did not exhibit any clear relationship with salinity. The present study demonstrated that δ13C has the potential for application as a tracer of fish migration into lower salinity areas including the ETM.  相似文献   

6.
Phytoplankton community composition, productivity and biomass characteristics of the mesohaline lower Neuse River estuary were assessed monthly from May 1988 to February 1990. An incubation method which considered water-column mixing and variable light exposure was used to determine phytoplankton primary productivity. The summer productivity peaks in this shallow estuary were stimulated by increases in irradiance and temperature. However, dissolved inorganic nitrogen loading was the major factor controlling ultimate yearly production. Dynamic, unpredictable rainfall events determined magnitudes of seasonal production pulses through nitrogen loading, and helped determine phytoplankton species composition. Dinoflagellates occasionally bloomed but were otherwise present in moderate numbers; rainfall events produced large pulses of cryptomonads, and dry seasons and subsequent higher salinity led to dominance by small centric diatoms. Daily production was strongly correlated (r = 0·82) with nitrate concentration and inversely correlated (r = −0·73) with salinity, while nitrate and salinity were inversely correlated (r = −0·71), emphasizing the importance of freshwater input as a nutrient-loading source to the lower estuary. During 1989 mean daily areal phytoplankton production was 938 mgC m−2, mean chlorophyll a was 11·8 mg m−3, and mean phytoplankton density was 1·56 × 103 cells ml−1. Estimated 1989 annual areal phytoplankton production for the lower estuary was 343 gC m−2.  相似文献   

7.
Marine sponges are key players in the transfer of carbon from the pelagic microbial food web into the benthos. Selective uptake of prokaryotic picoplankton (<2 μm) by a demosponge (Callyspongia sp.), and carbon flux through this process, were examined for the first time in the oligotrophic coastal waters of southwestern Australia, where sponge abundance and biodiversity ranks among the highest in the world. Water sampling and flow rate measurements were conducted over five sampling occasions following the InEx method of Yahel et al. (2005), with heterotrophic bacteria and autotrophic Synechococcus cyanobacteria identified and enumerated by flow cytometry. Callyspongia sp. demonstrated high filtration efficiencies, particularly for high DNA (HDNA) bacteria (up to 85.3% in summer 2008) and Synechococcus (up to 91.1% in autumn 2007), however efficiency varied non-uniformly with time and food type (p < 0.01). Overall filtration efficiency for Synechococcus (86.6 ± 6.3%; mean ± s.d.) was always significantly higher (p < 0.05) than for low DNA (LDNA) bacteria (40 ± 17.2%), except during winter 2007 (p = 0.14) when ambient Synechococcus concentrations were lowest. When compared to ambient abundances of the different food types, Callyspongia sp. exhibited consistently negative selectivity for LDNA bacteria and positive selectivity for Synechococcus, while HDNA bacteria was generally a neutral or positive selection. The total carbon removal rate (sum of all prokaryotic picoplankton cells), calculated on a per unit area basis, varied significantly with time (p < 0.01), with lowest rates recorded during the winter (0.5 ± 0.4–0.6 ± 0.8 mg C m−2 d−1) and highest values recorded in summer (3.5 ± 1.9 mg C m−2 d−1). These flux estimates quantify the role of a demosponge species in the ultimate fate of prokaryotic picoplankton within the nearshore food webs of southwestern Australia, and support the conclusion that sponges actively select food particles that optimise their nutritional intake.  相似文献   

8.
The influence of prolonged mouth closure on the population dynamics of the caridian shrimp, Palaemon peringueyi and the estuarine isopod, Exosphaeroma hylocoetes, in the littoral zone of temporarily open/closed Kasouga Estuary located on the south-eastern coastline of southern Africa was assessed monthly over the period October 2007 to September 2008. Prolonged mouth closure of the estuary contributed to hypersaline conditions (psu > 35) prevailing throughout the estuary for the last four months of the study. The high salinities coincided with a decrease in the areal extent (up to 80%) of the submerged macrophytes, mainly Ruppia maritima, within the littoral zone of the estuary. Total abundance and biomass values of the shrimp and isopod over the period of investigation ranged from 0 to 14.6 ind m−2, from 0 to 13.3 mg dwt m−2, from 12 to 1540 ind m−2 and from 0.1 to 2.16 mg dwt m−2, respectively. Maximum values of both the shrimp and isopod were recorded in the upper reaches of the estuary in close association with R. maritima. Over the course of the investigation, both the abundance and biomass values of the shrimp decreased significantly (P < 0.05 in both cases) which could be related to reduced habitat availability, R. maritima, that acts as a refuge against fish predation. Additionally, the decrease in abundance and biomass values could be attributed to reduced recruitment opportunities for the shrimp and the cessation of reproduction in the estuarine isopod. The establishment of a link to the marine environment following an overtopping event in September 2008 contributed to a decrease in salinity within the system although no recruitment of either the isopod or shrimp was recorded.  相似文献   

9.
Eurytemora americana has been only reported as invader in Bahía Blanca Estuary, Argentina within the South Hemisphere. There are a few experimental researches under laboratory conditions done with this species and its reproductive behaviour around the world is very scarce. Consequently, it is still not possible to completely understand its population dynamics. In the present study, E. americana reproductive temporal behaviour and relationships among abundance, female size, egg production and hatching success were examined in the Bahía Blanca Estuary, during 2007 pulse. In order to determine the potential relationships between these variables and the environmental variables, experimental incubations were conducted in the laboratory simulating natural conditions. Spearman’s rank correlation was used to analyze the relationships among all variables. Temporal change of biotic and environmental variables was corroborated by a Mann–Whitney/Kruskal–Wallis non-parametric tests, with significant differences (p ? 0.01) in all variables throughout the study. Abundance population results showed very high values in relation to those recorded in recent years in Bahía Blanca Estuary. This response could be due to the unusual combination of environmental factors (polar wave with temperatures ≤6 °C and a drought period with high salinities, 32.7–36.6) recorded during the studied winter period. Significant positive correlations between abundance and salinity (p < 0.01, n = 226), and hatching success (p < 0.01, n = 25) as well as a significant negative correlation between abundance and chlorophyll a (p < 0.01, n = 226) were found. Although E. americana shows a k-strategy within its annual pulse, it presented two markedly distinct behaviours depending on temporal environmental variability. From July to early september, when the estuary evidenced high salinity, low temperature and high food availability, E. Americana showed large females, large clutch size and high hatching success. When environmental conditions became unfavorable from September to October, small females, small clutch size and very low hatching success were observed. The latter is associated with diapause egg laying which ensures population recruitment. According to our findings the particular combination of low temperatures, high salinities and high available food (i.e. variables which each year modulate its pulse) during 2007 winter–spring, favored the great development of E. americana. This invading species in its opportunistic role has managed to exploit a vacant niche in the estuary, developing two different behaviours within the k-strategy depending on change in environmental conditions.  相似文献   

10.
Temporal and spatial variations in Synechococcus abundance were investigated over an annual cycle (February'10–January'11) along a salinity gradient (0–35) in the tropical Zuari estuary, influenced by south-west monsoons. Synechococcus exhibited salinity preferences with phycoerythrin-rich cells at salinities >2 (Synechococcus-PEI), >20 (Synechococcus-PEII) and <1 (Synechococcus-PEIII) whereas phycocyanin-rich (Synechococcus-PC) dominant at lower salinities. Downstream stratification during monsoon caused Synechococcus group segregation in the surface and near-bottom waters. During monsoon-break and non-monsoon period stabilized waters, increased salinity, temperature, solar radiation and low rainfall favored high Synechococcus abundance whereas unstable waters, increased turbidity and low solar radiation during active monsoon lowered abundance. SYN-PC positively co-related with nitrate and phosphate and SYN-PEI with phosphate. Synechococcus contribution to phytoplankton carbon biomass ranged from 9 to 29%. In monsoonal estuaries, rainfall intensity regulates freshwater runoff which modulates the estuarine environment, creating temporal–spatial niche segregation of Synechococcus groups thereby serving as indicator organisms of the estuarine hydrodynamics.  相似文献   

11.
Ecosystem management and decision making process are dependent of a good knowledge of ecosystem functioning. Conceptual models allow knowledge organization through representation of relationships between variables and processes, facilitating management decisions. In this study, spatial and temporal characterization of key environmental variables, as well as relationships between them, was studied aiming the design of a conceptual model of the Douro estuary. This temperate mesotidal estuary is limited upstream by a hydroelectric power dam that controls freshwater inflow and prevents the propagation of the tide upstream, which, in turn, influences water circulation and biogeochemical dynamics of the system. During one year, from December 2002 to December 2003, water column data were collected monthly at 10 stations along the estuary, during ebb and flood tides. Spatial and temporal variability of water column salinity, temperature, nutrients, phytoplankton biomass, total particulate matter (TPM), phytoplankton primary production (PP), faecal coliform bacteria (FC) and community respiration (CR) were analysed. Salinity stratification was assessed by means of the Estuary Number (Ne) and variation of this index as well as other key characteristics with river flow was analysed. Freshwater discharge controlled salinity stratification and freshwater residence time. Ne indicated that the Douro was stratified for river flows <300 m3 s−1, and freshwater residence time was >1 day for the same conditions. A decaying exponential relationship between PP and river flow was found, whereas nitrate and TPM increased logarithmically and linearly, respectively, with river flow. Regarding spatial distribution, nitrate and PP decreased downstream, showing that the river was a source of nutrients and phytoplankton, while the opposite trend was found for TPM, FC, ammonium and CR. The latter increase was probably due to untreated sewage discharge in the urbanized middle and lower estuarine stretches. Reduction of nitrate coming from the watershed and of bacterial contamination in the urban stretches of this highly modified water body, according to the European Water Framework Directive, emerges as the main water quality issues for this estuarine ecosystem.  相似文献   

12.
Recurrent coastal upwelling is recognized as one of the main factors promoting the exceptionally high productivity of the Humboldt Current System. Herein, we study time series data of gross primary production (2003-2006) and its fluctuation in relation to seasonal changes in the light and nutrient field of the Concepción upwelling ecosystem. Concurrent measurements of gross primary production, community respiration, bacterial secondary production, and sedimentation rates allowed a characterization of the main carbon fluxes and pathways in the study area. The integrated values of gross primary production were higher during the upwelling period (>1 g C m−2 d−1; October-April; that is, early spring to early austral fall). Seasonal changes in the system were also reflected in community respiration, organic matter sedimentation, and bacterial production rates, which varied along with the gross primary production. The significant correlation between gross primary production and community respiration (Spearman, r = 0.7; p < 0.05; n = 18) reflected an important degree of coupling between organic matter formation and its usage by the microplanktonic community during periods when gross primary production/community respiration were highly similar. Higher gross primary production values (>6 g C m−2 d−1) were consistently associated with maximum biomass levels of Skeletonema costatum and Thalassiosira subtilis. We observed a positive correlation between gross primary production and the sedimentation of intact diatom cells (Spearman, r = 0.5, p < 0.05, n = 17). Our data suggest that, in the Concepción upwelling ecosystem, bacteria utilize an important fraction of the gross primary production. If our interpretations are correct, they leave unanswered the question of how the system supports the extremely high fish biomass levels, therein pointing out the system’s limited capacity to buffer the evasion of CO2 following upwelling.  相似文献   

13.
From January 2003 to December 2004 microphytobenthic primary production was estimated both from in situ (MPPs) and in the laboratory (MPPp) 14C-incubation of slurries collected in a coastal site of the Gulf of Trieste (northern Adriatic Sea). MPPs values varied from −7.54 ± 3.12 to 34.59 ± 7.66 mg C m−2 h−1 over the whole period. The lowest MPPs were observed in November 2003 and August 2004, while the highest MPPs in July 2003 and May 2004, in correspondence with high PAR at the bottom. Significant correlations between MPPs and the microphytobenthic biomass (BIOM) (r = 0.75, p < 0.001), between MPPs and PAR at the bottom (r = 0.54, p < 0.01) and between MPPs and OXY (r = 0.50, p < 0.05) were revealed. MPPp values were higher than MPPs ones in 15 out of 23 observations, with the highest MPPp recorded in July 2003. At 17 m depth a seasonal pattern of sampling months was revealed by the cluster analysis. The role of abiotic parameters in determining this seasonal pattern was highlighted by the PCA, with the first axis correlated with MPPs and PAR, and the second one with temperature. Applying the fuzzy sets it resulted that spring months showed a higher degree of membership with MPPs, summer months with temperature and autumn–winter months with OXY. The microphytobenthic community did not seem to be photosynthetically active throughout the study period. From August–September to December low or negative MPPs values were recorded. We infer that during these months a shift from the autotrophic to heterotrophic metabolism of the benthic microalgae occurred in correspondence with low PAR and/or high temperature at the bottom. Despite the progressive lowering of the trophy of the study area occurred during the last 20 years, we found higher primary production values than those estimated two decades earlier.  相似文献   

14.
A survey within the French National Programme of Ecotoxicology was carried out in 2002, 2003 and 2004 to study the response of Nereis diversicolor populations (Polychaeta, Nereididae) to the impact of pollution in the Authie estuary (non-contaminated site) and in the Seine estuary (contaminated site). In the period studied, the density varied from 672 ind. m−2 to 3584 ind. m−2 in the Authie estuary and from 80 ind. m−2 to 920 ind. m−2 in the Seine estuary. Biomass varied from 3.94 g m−2 (dry weight) in February 2004 to 38.0 g m−2 in August 2003 in the Authie estuary and from 3.4 g m−2 in February 2002 to 0.6 g m−2 in February 2004 in the Seine estuary. Density and biomass of the populations of N. diversicolor were consistently lower in the Seine estuary than in the Authie estuary. Size frequency histograms permit the analysis of the cohorts as well as the elaboration of the growth curves. For the individuals from the Authie estuary, the relation between dry weight (DW) and length L3 (prostomium, peristomium and chaetiger 1) was DW = 4.2205 L32.9832. For those from the Seine estuary, the relation between dry weight and L3 was DW = 0.4697e1.7209L3. The individuals of N. diversicolor should belong to eight cohorts in Authie estuary (two cohorts each year) instead of six cohorts for those from the Seine estuary. These differences can be attributed to the effect of pollution on the population of N. diversicolor.  相似文献   

15.
Large Zostera marina meadows (covering 13.6 km2) existed in the Nakdong River estuary on the south coast of Korea until the mid-1980s, but these Z. marina beds nearly disappeared due to reclamation of adjacent mud flats for the construction of a port and industrial complex during the late 1980s. Partial recovery of Z. marina meadows occurred recently, and Z. marina coverage of about 0.3 km2 was observed in this estuary. In this study, shoot morphology, density, biomass, productivity, and tissue nutrient content were measured to evaluate the current status of the Z. marina meadows by comparing these data to those for persistent seagrass meadows in similar geographical areas. Additionally, we examined the ecological roles of Z. marina in this estuary after recovery from the large-scale disturbance. Shoot density (151 shoots m−2) and total biomass (141 g DW m−2) in the estuary were similar to those reported from other Z. marina meadows in Korea. Annual leaf production (1726 g DW m−2 y−1) was higher than generally observed for Z. marina in other geographical areas. These results imply that the existing Z. marina meadows in this estuary have adjusted to local environmental conditions that changed after large-scale reclamation. Estimated annual whole plant carbon (C) and nitrogen (N) incorporations based on shoot production and tissue C and N content were 810.0 g C m−2 y−1 and 59.7 g N m−2 y−1, respectively. These values were equivalent to 2.4 × 105 kg C y−1 and 1.8 × 104 kg N y−1 for all Z. marina beds in the Nakdong River estuary. This high C and N incorporation into Z. marina tissues suggests that existing Z. marina meadows play important roles in C and N cycles in this estuary. Although the currently existing Z. marina beds in this estuary are persisting and play an important ecological role, anthropogenic factors that cause seagrass declines still affect the estuary. Thus, effective management and monitoring of Z. marina beds and environmental factors are critical to protecting and conserving this invaluable component of the Nakdong River estuary.  相似文献   

16.
Cadmium and copper in the dissolved and particulate phase and in zooplankton were determined in the Bahía Blanca estuary during six surveys from March to December 2005. Temperature, pH, salinity, dissolved oxygen, suspended particulate matter, particulate organic matter and chlorophyll-a were also considered. Dissolved Cd was below the detection limit (0.2 μg L−1) for almost the entire study period whereas Cu concentrations (0.5–2.4 μg L−1) indicated a continuous dissolved Cu input. Particulate Cd concentrations ranged from below the detection limit (<0.01) to 28.6 μg g−1 d.w. while particulate Cu ranged from below the detection limit (<0.04) to 53.5 μg g−1 d.w. Cd in mesozooplankton ranged from below the detection limit (<0.01) to 37.4 μg g−1 d.w. Some of the Cd levels were higher than those reported for other aquatic ecosystems. Cu in the mesozooplankton ranged from 1.3 to 89.3 μg g−1 d.w., values which were within the reported values or higher than other studies. The log of the partition coefficients (log (Kd)) of Cd was 0.04, while log (Kd) for Cu ranged from −0.39 to 2.79. These values were lower than both those calculated for other estuaries and the typical coefficients for marine environments. The log of the bioconcentration factor (log BCF) of Cd was 1.78, indicating that Cd concentration was higher in the zooplankton than in the dissolved phase. Log BCF of Cu ranged from 1.15 to 3. The logs of the biomagnification factors (log BMF) of Cd were low, with a range between −3.45 and 2.21 and those for Cu ranged from −0.1 to 3.35. Positive values indicate biomagnification while negative values indicate biodiminution. In general, no significant dissolved Cd concentration appeared to be present in the Bahía Blanca estuary and Cu values did not indicate a critical environmental status. The particulate phase seemed to be the major carrier for Cd and Cu and TPCu values were within the normal values for an anthropogenically stressed estuary but not for a strongly polluted system. This fraction was the most important metal source for the mesozooplankton. Moreover, the highest metal concentrations were in the mesozooplankton since most of the bioconcentration and biomagnification factors were positive, especially for Cu.  相似文献   

17.
Mandovi estuary is a tropical estuary strongly influenced by the southwest monsoon. In order to understand, sources and fate of particulate organic nitrogen, suspended particulate matter (SPM) collected from various locations, was analyzed for particulate organic carbon (POC) and particulate organic nitrogen (PON), δ13CPOC, total hydrolysable amino acid enantiomers (l- and d- amino acids) concentration and composition. δ13CPOC values were depleted (−32 to −25‰) during the monsoon and enriched (−29.6 to −21‰) in the pre-monsoon season implying that OM was derived from terrestrial and marine sources during the former and latter season, respectively. The biological indicators such as C/N ratio, d-amino acids, THAA yields and degradation indices (DI) indicate that the particulate organic matter (POM) was relatively more degraded during the monsoon season. Conversely, during the pre-monsoon, the biological indicators indicated the presence of relatively fresh and labile POM derived from autochthonous sources. Amino acids such as alanine, aspartic acid, leucine, serine, arginine, and threonine in monsoon and glutamic acid, glycine, valine, lysine, and isoleucine in pre-monsoon were relatively abundant. Presence of bacterial biomarker, d-amino acids in the SPM of the estuary during both the seasons signifies important contribution of bacteria to the estuarine detrital ON pool. Based on d-amino acid yields, bacterial OM accounted for 16-34% (23.0 ± 6.7%) of POC and 29-75% (47.9 ± 18.7%) of PON in monsoon, and 30-78% (50.0 ± 15%) of POC and 34-79% (51.2 ± 13.3%) of the PON in pre-monsoon in the estuary. Substantial contribution of bacterial-N to PON indicates nitrogen (N) enrichment on terrestrial POM during the monsoon season. Transport of terrestrial POM enriched with bacterial OM to the coastal waters is expected to influence coastal productivity and ecosystem functioning during the monsoon season.  相似文献   

18.
Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates, and growth efficiencies were studied in the Northern region of the Cananéia–Iguape estuarine system, which has recently experienced an intense eutrophication due to anthropogenic causes. Two surveys were carried out during spring and neap tide periods of the dry season of 2005 and the rainy season of 2006. This region receives large freshwater inputs with organic seston and phosphate concentrations that reach as high as 1.0 mg l−1 and 20.0 μM, respectively. Strong decreasing gradients of seston and dissolved inorganic nutrients were observed from the river/estuary boundary to the estuary/coastal interface. Gradients were also observed in phytoplankton and bacterial production rates. The production rates of phytoplankton were 5.6-fold higher (mean 8.5 μg C l−1 h−1) during the dry season. Primary production rates (PP) positively correlated with salinity and euphotic depth, indicating that phytoplankton productivity was light-limited. On the other hand, bacterial biomass (BB) and production rates (BP) were 1.9- and 3.7-fold higher, respectively, during the rainy season, with mean values of up to 40.4 μg C l−1 and 7.9 μg C l−1 h−1, respectively. Despite such a high BP, bacterial abundance remained <2 × 106 cells ml−1, indicating that bacterial production and removal were coupled. Mean specific growth rates ranged between 0.9 and 5.5 d−1. BP was inversely correlated with salinity and positively correlated with temperature, organic matter, exopolymer particles, and particulate-attached bacteria; this last accounted for as much as 89.6% of the total abundance. During the rainy season, BP was generally much higher than PP, and values of BP/PP > 20 were registered during high freshwater input, suggesting that under these conditions, bacterial activity was predominantly supported by allochthonous inputs of organic carbon. In addition, BB probably represented the main pathway for the synthesis of high-quality (low C:N) biomass that may have been available to the heterotrophic components of the plankton food web, particularly nanoheterotrophs.  相似文献   

19.
Among tunicates, the small planktonic appendicularians generally comprise a significant fraction of the mesozooplankton of estuarine environments. However, no spatio-temporal studies nor estimation of some ecological parameters such as biomass or pellet production of these organisms have been previously reported in La Plata River estuary. We studied the species composition and abundance as well as biomass and pellet production, associated with the river plume variations using data collected during seven spring (October) cruises. Approximately 80 samples were collected in each cruise with a Pairovet net (200 μm mesh size) trawled vertically through the water column; CTD data profiles were also recorded. Three transects at the north, middle and south of the estuary were performed in order to compare the environmental gradients to the species distribution. The river's discharges varied between years and it was reflected on the salinity distribution. The salinity was the main factor driving species composition. Oikopleura dioica, Oikopleura fusiformis and Fritillaria borealis were found, O. dioica being the dominant one. We detected that O. fusiformis was more abundant in stratified waters between salinities of 31 and 33 mainly during 1994, 1995 and 1996. Fritillaria borealis was found only in salinities higher than 33 and in homogenous waters being more abundant in 1995. This year was singular in the sense that no river plume was observed at the middle transect, as it is shown by the homogenous salinity profiles. Oikopleura dioica was present in stratified waters at all salinity ranges. In 1993, it was more abundant at low salinities with temperatures between 12 and 16 °C and a predominance of juvenile animals was observed. The contribution in biomass and pellet production of O. dioica in the stratified waters of this front was very high (27.91–66.58 g C m−2 d−1) revealing their importance in the estuary's carbon cycle.  相似文献   

20.
This study shows results on litterfall dynamics and decay in mangrove stands of Avicennia germinans distributed along a latitudinal gradient (three forest sites) in the Gulf of California, in order to assess whether internal sources could support the observed mangrove ecosystem organic deficit in this arid tropic. Total mean annual litterfall production increased southward (712.6 ± 53.3, 1501.3 ± 145.1 and 1506.2 ± 280.5 g DW m−2 y−1, in the Yaqui, Mayo and Fuerte areas respectively), leaves being the main component of litter in all locations during the entire year, followed by fruits. The wet season (June–September) showed the highest litterfall rates through fruits. The temporal trend of litterfall production was significantly explained through mean air temperature (R2 = 68%) whilst total annual litter production in the entire region showed a statistically significant relationship with total soil phosphorus, salinity, total nitrogen, organic matter and tree height (R2 = 0.67). Throughout 117 days of the decomposition experiment, the litter lost 50% of its original dry weight in 5.8 days (average decay rate of 0.032 ± 0.04 g DW d−1) and there were not significant differences in the remaining mass after 6 days. The percentage of both C and P released from the litter correlated significantly with the ratio of tidal inundated days to total experiment days (R2 = 0.62, p = 0.03 and R2 = 0.67, p = 0.02, respectively); however, the frequency of tidal inundation only showed a significant increase in C release from Avicennia litter after 6 and above 48 days of decomposition. Whereas the total C content of litter bags decreased linearly over the decomposition to (% Total C = 5.52 − 0.46 days, R2 = 0.81, p = 0.0005), N content displayed an irregular pattern with a significant increase of decay between 48 and 76 days from the beginning of the experiment. The pattern for relative P content of litter revealed reductions of up to 99% of the original (%tot-P = −9.77 to 1.004 days, R2 = 0.72, p = 0.01) although most of the P reduction occurred between 17 and 34 days after the experiment started. Soil N and P contents, which exhibited significant differences in the course of the decomposition experiment, appeared to show significant differences between sampling sites, although they were not related to tidal influence, nor by leaf and nutrient leaching. In a global basis, C/N litter ratios decreased linearly (C/N = 32.86 − 0.1006 days, R2 = 0.62, p = 0.02), showing a strong and significant correlation with meteorological variables (R2 = 0.99, p = 0.01). C/P ratios of litter increased through an exponential function (C/P = 119.35e0.04day, R2 = 0.89, p < 0.001). Changes in the remaining percentage of litter mass during the experiment were significantly correlated with soil C/N ratio (R2 = 0.56, p = 0.03) as well as with the soil C/P ratio (R2 = 0.98, p < 0.001). Our results of litter decomposition dynamics in this mangrove support the fact of null net primary productivity of the arid mangrove wetlands: fast litter decomposition compensates the ecosystem organic deficit in order to sustain the mangrove productivity. Litter decomposition plays a key role in the ecosystem metabolism in mangroves of arid tropics.  相似文献   

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