Effects of oil/gas field produced water on the macrobenthic community in a small gradient estuary

Little is known about how climatic events (i.e., drought) inhibit or enhance movement of petroleum hydrocarbon laden sediments in estuarine systems and how this in turn effects the macrobenthic populations exposed to these sediments. Seventeen collection stations were established and monitored at New Bayou, Texas, a small gradient estuary which receives petroleum products via oil/gas field produced water discharge. Hydrographic, geologic and biotic samples were taken monthly from each station during a period of reduced rainfall. Both temperature and dissolved oxygen data taken during the study followed patterns typical for the area. Salinity values increased into the polyhaline range at near-bay stations during the reduced rain period, while upper bayou stations remained within the oligohaline range. Sediment grain sizes along the bayou were generally in the silty-clay range. Sediment hydrocarbon concentrations were highest (11.4 mg g⁻¹ dry sediment) around the produced water discharge site and lowest at near-bay stations (0.2 mg g⁻¹ dry sediment). Ninety-six macrobenthic species were collected during the study. General effects from produced water discharge on macrobenthic populations followed the classical pattern outlined by other research in shallow bay systems. A sediment hydrocarbon concentration of 2.5 mg g⁻¹ dry sediment was found to reflect the average value needed to depress population abundances. Both abundance and diversity values were lowest at central stations near the discharge site. This zone of depressed macrobenthic populations extended from the discharge site at least 107 m downstream and 46 m upstream. The zone of stimulated macrobenthic populations occurred 1486 m downstream and 381 m upstream from the discharge site.     

Spatial and temporal patterns of intertidal macrobenthic populations in the Oosterschelde: are they influenced by the construction of the storm-surge barrier?

The construction of a storm-surge barrier in the mouth of the Oosterschelde caused important hydrodynamical and morphological changes that could influence the macrobenthic populations. This paper is one in a series of five all dealing with the effects of the storm-surge barrier on macrozoobenthos and analyses the spatial and temporal distribution of macrozoobenthos in the Oosterschelde and its relationship with some environmental parameters, based on two large scale sampling campaigns, one before and one after the completion of the barrier.The sediment of the sampling stations was fine, well sorted sand, with an average mud content of about 2.5 %. Only in the Krabbenkreek the sediment was coarser in 1989. The tidal elevation of the sampling sites decreased significantly in 1989.The density of macrozoobenthos was significantly lower, the biomass higher in 1989. The density was dominated by deposit feeders, the biomass by filter feeders. The difference in biomass between both years was mainly due to a substantial increase of the biomass of filter feeders in 1989. The number of species per station was significantly smaller in 1989 than in 1985. Between 1985 and 1989, frequency of occurrence decreased in 34 versus 13 which increased, density increased in 13 species and decreased in 34 species, biomass increased in 18 species and decreased in 29 species.Based on TWINSPAN several clusters of stations, each with a different faunal composition, were identified. These clusters did not form distinct zones on the tidal flats but were dispersed widely.The relationship between density and biomass of different trophic groups and the mud content of the sediment and the depth was analysed. This relationship sometimes differed clearly between years. The correlation coefficient of a multiple regression between density and biomass of individual species and environmental factors, although significant in most cases, was very low, indicating that only a small proportion of the species variability was explained. The relationship between benthos and environmental factors was further analysed by canonical correlation analysis and multivariate discriminant analysis that gave different results for the 1985 and 1989 data. This is probably due to the broad tolerance of the species to the range of the environmental variables found in our study area. From a TWINSPAN of the density data of 1985 and 1989 together we could conclude that, although the environmental parameters in a group of stations, showing a large faunal similarity in one year, did not change, the faunal composition did. This indicates that faunal changes are not necessarily linked to changes in the measured environmental parameters.In the discussion the different factors affecting macrobenthic populations are situated and it is suggested that the macrobenthic populations are probably more towards the nonequilibrium end of the continuum between nonequilibrium and equilibrium communities as defined by Wiens (1984).Although the impact of the construction of the barrier on the macrobenthic community seems at present to be rather small this does not mean that on the long-term there will be no effect.     

渤海中、南部大型底栖动物物种多样性的研究

以1997年 6月、1998年9月和1999年4月共3个航次,覆盖渤海中、南部大部分海区的大型底栖动物丰度、生物量和生产力的研究为基础,进一步对其物种多样性进行了分析。结果表明：研究海域的大型底栖动物物种多样性没有明显的平面分布规律;物种多样性指数与沉积物因子的相关性高于其与底层水因子的相关性;沉积物中污染物含量的确会对大型底栖动物的多样性造成影响。通过对3个航次中3个相同站位的比较,发现不同年份之3个季节的平均Shannon Wiener指数无显著差异（P>0.05）;而1998年9月和1999年4月2个航次中20个相同站位的平均Shannon Wiener指数同样也未表现出明显的差异（P>0.05）。此外,渤海的物种数量要明显地高于胶州湾。     

Macrobenthic Distribution within the Sediment along an Estuarine Salinity Gradient

The distribution of the macrobenthic infaunal community within the upper 25 cm of the sediment was studied at 16 stations in the lower Chesapeake Bay. Stations were located from the tidal freshwater to the polyhaline zone of major tributaries (James, York and Rappahannock Rivers) and in the polyhaline portion of the lower bay mainstem. Profiles for total number of individuals, total ash-free dry weight biomass and species encountered with depth were calculated. Except for the deep dwelling bivalve, Macoma balthica, tributary macrobenthic communities had a shallow depth distribution compared to the mainstem sites which were found in generally coarser sediments in the higher salinity region of the estuary.     

海蜇养殖对池塘底泥营养盐和大型底栖动物群落结构的影响

2009年5-9月,对荣成靖海湾大型养殖池塘海蜇(Rhopilema esculentum Kishinouye)养殖期间与养殖期前后底泥营养盐及大型底栖动物群落结构变化进行了研究。结果表明,7月份海蜇养殖期间,由于海蜇的避光性而产生的上下浮动的行为特征造成了对水体的扰动作用, 与海蜇的生物沉积作用共同导致养殖海区(实验点)与邻近非养殖海区(对照点)之间各项底泥营养盐指标均存在显著性差异,其中,实验点氨氮(NH₄-N)、硝氮(NO₃-N)和沉降速率(sedimentation rate, SR)显著高于对照点,实验点叶绿素a(Chla)、总有机物(TOM)和总有机碳(TOC)含量显著低于对照点。多变量聚类分析结果表明,海蜇养殖对养殖池塘的大型底栖动物群落结构产生显著影响,并且7月份实验点大型底栖动物生物多样性指数(H')和均匀度指数(J) 随海蜇放养显著增大,并显著高于对照点。大型底栖动物群落多样性指数与沉降速率(SR)和底泥TOM含量分别表现出显著正相关和负相关,而与其他营养盐指标无显著相关性。     

长江口潮下带春季大型底栖动物的群落结构

2005年4月对长江口全区域潮下带共10个采样站位的大型底栖动物进行了调查。调查采获大型底栖动物38种,分属5个生态类型,种类数较少,河口外缘站位种类数多于口内站位。各站位大型底栖动物的平均丰度为32.9个/m2、平均生物量为5.035g/m2(湿重);与20世纪七八十年代相比,平均生物量显著降低;口外缘站位的总丰度和总生物量均高于口内站位。环境因子相关分析表明,盐度是决定长江口大型底栖动物种类分布最重要的环境因子。群落聚类、标序分析显示,春季长江口潮下带大型底栖动物群落结构空间分异明显,完全符合目前长江口支、港、槽“三级分汊”的空间格局。其中,北支的大型底栖动物以混合高盐水种类为主,而南支则以淡水和半咸水种类为主。南支的南北槽分界处内外站位的群落差异也由盐度决定,因为靠近口内的群落均受长江冲淡水影响较大;而口外站位群落则受咸淡水影响。南支的南北港分界点内外的群落差异则主要受长江来水的影响,原因在于处在港分界点以内的群落所在区域,直接受长江来水的冲刷,底质环境极不稳定;而港、槽分界点之间的群落所在区域由于河口上段的诸多明暗沙体的阻挡,水势较为稳定,所以底质环境较稳定,从而使得港、槽分界点之间的群落出现了更多的沙蚕等底质环境类型种类。     

Seasonal variability of meio- and macrobenthic standing stocks and diversity in an Arctic fjord (Adventfjorden, Spitsbergen)

Strong environmental seasonality is a basic feature of the Arctic system, still there are few published records of the seasonal variability of the Arctic marine biota. This study examined the year-round seasonal changes of soft bottom macro- and meiobenthic standing stocks and diversity on a station located in an Arctic fjord (Adventfjorden, Spitsbergen). The seasonality observed in benthic biota was related to the pelagic processes, primarily the seasonal fluxes of organic and inorganic particles. The highest abundance, biomass and richness of benthic fauna occurred in the spring after the phytoplankton bloom. During the summer, when a high load of glacial mineral material was transported to the fiord, the number of both meio- and macrobenthic individuals decreased remarkably. The strong inorganic sedimentation in summer was accompanied by a decline in macrobenthic species richness, but had no effects on evenness. Redundancy analysis (RDA) pointed to granulometric composition of sediments (depended on mineral sedimentation) and organic fluxes as factors best related to meio- and macrobenthic taxonomic composition, but no clear seasonal trend could be observed on the nMDS plots based on meiobenthic higher taxa or macrobenthic species abundances in the samples. This study addresses the possible effects of changes in the winter ice cover on the fjordic benthic systems because it was performed in a year with no ice cover on the fjord.     

Functional Role of Large Organisms in Intertidal Communities: Community Effects and Ecosystem Function

In marine soft sediments, large organisms are potentially important players in the nonlinear interactions that occur among animals, their food, and their chemical environment, all of which influence the contribution of benthos to ecosystem function. We investigated the consequences of removing large individuals of two functionally contrasting benthic communities on nutrient regeneration, microphyte standing stock, and macrobenthic community composition. The experiment was conducted at two adjacent sites that were physically similar but biologically different, one dominated by large deposit feeders and the other by large suspension feeders. Chemical fluxes were measured in experimental plots, and sediments were sampled to assess changes in macrofauna, sediment grain size, organic content, and microphyte standing stock. Our results demonstrate that the removal of large suspension feeders or deposit feeders influenced the flux of nitrogen and oxygen, surficial sediment characteristics, and community composition. In the deposit-feeder community, interactions between nutrient regeneration and grazing highlight important feedbacks between large macrofauna and biogeochemical processes and production by microphytes, indicating that the loss of large infauna driven by increased rates of anthropogenic disturbance may lead to functional extinction and cause shifts in community structure and ecosystem performance.     

Quantification of biogenic 3-D structures in marine sediments

Burrow and tube structures of marine infauna were quantified in sediments from cores obtained at 3 depths (75, 95 and 118 m) at 3 occasions over a 1-year period. The benthic communities at the two deeper stations were re-establishing subsequent to re-oxygenation after hypoxic conditions; the shallow station was a reference station unaffected by hypoxia. The benthic macrofauna was simultaneously quantified from sieved grab samples. The sediment cores were frozen and later sliced with a plane in horizontal layers. Biogenic structures in these sections were digitally analysed for numbers, area and volume. Number of tubes and burrows showed a general decline with depth in the sediment. The biogenic structures in the sediment at the reference station increased the sediment-water interface about 1.5 times compared to the surface area. The surface areas of burrows and tubes were 2 to 3 times larger at the reference station than at the deeper stations. The benthic fauna at the 95-m and 118-m stations showed a temporal increase in density and number of species. In contrast, development of biogenic surface areas in the sediment at these stations showed no significant temporal trend during the benthic faunal succession. Relic tubes of Melinna cristata were found throughout the sampling period at the 118-m station. The ecological importance of bioirrigation for biogeochemical processes is discussed.     

象山港大型底栖动物生物多样性现状

2006年7月至2008年8月对象山港13个站位进行了8个航次的大型底栖动物采样调查.研究了该海域大型底栖动物群落的优势种组成, 大型底栖动物的丰度、生物量、次级生产力和P/B值,并采用物种丰富度指数、物种均匀度指数和物种多样性指数分析大型底栖动物物种的多样性.调查共获得大型底栖动物123种,其中软体动物48种,甲壳类33种,鱼类和环节动物多毛类各12种,棘皮动物8种,还包括一些腔肠动物、线虫等.群落中优势种较为集中,且优势度指数较高.该海域大型底栖生物年次级生产力平均值为16.70 ·m^-2·a^-1,平均P/B值为0.60.对物种丰富度指数(d)、均匀度指数( J )、辛普森多样性指数(D)和香农多样性指数(H)进行双因素方差分析表明,不同站位之间4种指数的差异均高度显著(P<0.01),周年之间4种指数的差异除均匀度指数不显著外(P>0.05),均高度显著(P<0.01).     

Trophic structure of macrobenthos in the Tagus estuary and adjacent coastal shelf

The trophic structure of benthic communities in the Tagus estuary and adjacent coastal shelf was characterized according to a functional guild approach, based on sampling surveys conducted between 1987 and 2000. Macrobenthic organisms were assigned to seven distinct trophic groups (herbivorous, filter feeders, surface deposit feeders, subsurface deposit feeders, carnivores, filter feeders/detritivores, carnivores/detritivores) and the dominance of these groups was related to environmental variables using multivariate ordination techniques. Surface-deposit feeders were numerically dominant in the Tagus estuary, making up 52% of the benthic communities, while in the adjacent coastal shelf the assemblage was dominated by both surface-deposit feeders and filter feeders (37% and 33%, respectively). When biomass was considered, filter feeders and filter feeders/detritivores were the dominant groups in the estuary, while for the adjacent coastal shelf filter feeders represented 83% of the total biomass. Salinity, depth and sediment composition were the main factors structuring spatial distribution. Surface-deposit feeders were the most abundant macrobenthos of the upper estuary. Surface deposit feeders also dominated the middle and the lower estuary but the proportion of filter feeders as well as other trophic groups increased with salinity. Generally, a more even distribution of trophic structure was found at stations with high salinity. In the adjacent coastal shelf, the trophic diversity decreased with depth. The trophic structure revealed that filter feeders dominated in abundance and biomass in shallow sandy sediments (<25 m), while in deeper sandy mud and muddy habitats (>50 m to 260 m), deposit feeders and carnivores were the most important groups in abundance and biomass, respectively.     

Bionomy of Macrobenthic Polychaetes in the Evros Delta (North Aegean Sea)

The composition and distribution of the macrobenthic polychaete fauna in the Evros Delta (North Aegean Sea) have been investigated by means of 4 replicate quantitative samples collected at 35 sites. 10 species were found and, in additional qualitative samples, the sedentary species Ficopomatus enigmaticus was collected. On the basis of the similarity in distribution among stations, 3 groups of species have been distinguished. One of these groups includes the species Spio decoratus and Hediste diversicolor which were both dominant and present at almost all stations. The distribution of species in the study area seems to depend on factors such as salinity, granulometric composition and organic matter of the sediment and interspecific competition, but mainly on the degree of “confinement”, namely the degree of exchange with the open sea. At the most isolated stations, the lowest number of species and the highest values of abundance and biomass were recorded.     

Natural and man-caused factors affecting the abundance and cycling of dissolved organic substances in precambrian shield lakes

A study on nutrient regeneration processes and a measure of their fluxes at the sediment-water interface was carried out in two different stations of a shallow lagoon of the Po delta river (Italy). A few parameters on the solid fraction (grain-size, porosity, C, N) and pore water profiles of o-P, NH₃, NO _inf3 ^sup– , SiO₂, Tot-CO₂, SO _inf4 ^sup2– , Fe, Mn, Ca, Mg, pH, Eh were determined. At both stations the results were typical for fine sediments rich in organic matter. The ratio of variations of sulphate (SO _inf4 ^sup2– ) to total carbonate demonstrates the main role sulphate reduction plays on the organic matter decay. The use of the ratios of variations of sulphate (SO _inf4 ^sup2– ) to ammonia (NH₃) and of sulphate (SO _inf4 ^sup2– ) to phosphate (o-P) in pore waters enabled us to calculate the C/N/P of the decomposing organic matter. Obtained C/N/P indicated an enrichment of N and P with regard to C/N/P ratios of the solid fraction, due to the selective stripping of N and P during organic matter mineralization. This phenomenon decreases with depth, where organic matter becomes more refractory. Calculations on saturation degrees have shown the possibility of authigenic calcite, apatite and rhodochrosite precipitation in sediments. Nutrient fluxes were estimated for SiO₂, NH₃ and o-P by means of benthic chambers and modelling the pore water profiles. The model used for the calculation of fluxes allowed us to account for the bioturbation-irrigation influence near the interface, by means of a cumulative diffusion coefficient. Directly measured fluxes proved to be always significantly greater than the theoretical ones. These differences seem to be due to surface processes which do not affect pore water concentrations (degradation of fresh materials at the interface; micro-bioturbation by small gasteropoda such as Hydrobia ventrosa) and/or to the different concept of the two methods in time and space. Number, size and biomass of macrobenthic species living in the sediment underneath the benthic chambers were determined. The comparison between data on macrobenthic populations and flux values showed a good relationship between the number of organisms and benthic fluxes within each station. However, flux variations between stations are to be attributed mainly to the different arrangement of the tubes of the polychaetes Polydora ciliata in the sediment.     

Effects of Sewage Dumping on Macrobenthic Invertebrates in the Jordan Gulf of Aqaba,Red Sea

There are two sewage outfalls along the Jordanian coastline in the Gulf of Aqaba. During 1982 and 1983 a total of 328 core samples (0.01 m² to a depth of 15 cm) were collected from the two outfalls, two control stations which resemble the outfalls in depth and sediment texture, and from two stations 100 m on both sides of each outfall. Faunal analysis revealed that the total number of individuals, number of species, species richness, and faunal similarities of macrobenthic invertebrates were lower at the sewage outfall near the phosphate loading port than the control station during both collections. At the 100 m stations, the numbers of individuals were generally higher than the sewage and control stations. The number of species, however, was highest at the control station and lowest at the sewage outfall. At the other sewage outfall, where the sewage effluent is discharged sporadically, no measurable effects on macrobenthic invertebrates were found.     

The biodiversity of macrobenthos from Jiaozhou Bay

The current situation of the animal species biodiversity of macrobenthic fauna in the Jiaozhou Bay (South Shandong Peninsula, Yellow Sea) is reported in the present paper, based on the data from 15 investigation cruises carried out from February 1998 to November 2001. In analyzing the data, the Shannon-Wiener index, and species evenness and richness indices were used to study the trends of variation of the community structure, the species assemblages in the macrobenthic community, the dominant species, and the abundance of macrobenthic fauna in Jiaozhou Bay. A total of 322 species of macrobenthic animals were found in the bay, of which 133 species belong to 44 families of Polychaeta, while 92 species belong to 42 families of Crustacea. The average number of species per sample station ranged from 8 to 26. The Shannon-Wiener indices were very different among the samples, with the highest being recorded from Station 8 in November 2001, and the lowest from Station 9 in August 2001. The number of species, the Shannon-Wiener indices, and the species richness indices from Stations 7 and 9 were generally lower than those from other stations. This is because both the stations are situated at areas with a strong current and where the sediment is coarse sand. Although the richness index of species and the Shannon-Wiener index were high in Station 3, the Pielou evenness index was the lowest of all the sampling stations. This is because the station is located near the culture area of Ruditapes philippinarum, where a high abundance of clams caused low evenness. The results also revealed that the number of species and abundance greatly affected the biodiversity, and some environmental factors such as temperature, salinity, and primary productivity were also closely interrelated with biodiversity. Pollution and overexploitation caused by human activities were very important factors affecting macrobenthic biodiversity. In order to find the best way to enhance and protect living marine resources, the relationship between human activities and the biodiversity of macrobenthos in the Jiaozhou Bay should be studied further.     

The biodiversity of macrobenthos from Jiaozhou Bay

The current situation of the animal species biodiversity of macrobenthic fauna in the Jiaozhou Bay (South Shandong Peninsula, Yellow Sea) is reported in the present paper, based on the data from 15 investigation cruises carried out from February 1998 to November 2001. In analyzing the data, the Shannon-Wiener index, and species evenness and richness indices were used to study the trends of variation of the community structure, the species assemblages in the macrobenthic community, the dominant species, and the abundance of macrobenthic fauna in Jiaozhou Bay. A total of 322 species of macrobenthic animals were found in the bay, of which 133 species belong to 44 families of Polychaeta, while 92 species belong to 42 families of Crustacea. The average number of species per sample station ranged from 8 to 26. The Shannon-Wiener indices were very different among the samples, with the highest being recorded from Station 8 in November 2001, and the lowest from Station 9 in August 2001. The number of species, the Shannon-Wiener indices, and the species richness indices from Stations 7 and 9 were generally lower than those from other stations. This is because both the stations are situated at areas with a strong current and where the sediment is coarse sand. Although the richness index of species and the Shannon-Wiener index were high in Station 3, the Pielou evenness index was the lowest of all the sampling stations. This is because the station is located near the culture area of Ruditapes philippinarum, where a high abundance of clams caused low evenness. The results also revealed that the number of species and abundance greatly affected the biodiversity, and some environmental factors such as temperature, salinity, and primary productivity were also closely interrelated with biodiversity. Pollution and overexploitation caused by human activities were very important factors affecting macrobenthic biodiversity. In order to find the best way to enhance and protect living marine resources, the relationship between human activities and the biodiversity of macrobenthos in the Jiaozhou Bay should be studied further.     

Ingestion by deposit-feeding macro-zoobenthos in the aphotic zone does not affect the pool of live pelagic diatoms in the sediment

The ability of deposit feeders to utilise the pool of live planktonic diatoms in the sediment was investigated after the spring bloom in 2001 and 2002 at four sediment sites in the aphotic zone in the Kattegat. Seven species of deposit-feeding bivalves, gastropods and polychaetes were allowed to defecate in containers with filtered seawater. A total of 22 containers were set up holding between 3 and 32 animals, grouped by station and taxa. When defecation was completed, the animals were re-introduced to different stocks of homogenised sediment which were manipulated by addition of luminophores and spores of the diatom Chaetoceros diadema, and the faeces again collected and analysed. Our analysis included the number of germinable planktonic diatoms, measured by the dilution extinction method, and the concentrations of the algae pigments fucoxanthin and chl a, in the faeces samples, in the sediment stocks and in the sediment at the sampling location. Comparison between the sediment composition at the sampling locations, and the composition of the corresponding faeces, showed that the concentration of germinable diatoms averaged about 50,000 g⁻¹ dry weight (DW) in the surface sediment as well as in the faeces in 2001, while in 2002, the average concentration was about 390,000 g⁻¹ DW in both faeces and in the sediment. A similar comparison in the second part of the experiments also showed that the diatoms in the sediment were unaffected by gut passage and the added spores of C. diadema germinated in the same quantity in the faeces as in the sediment. The taxonomic composition of the diatoms in the faeces matched the composition at the respective stations and sediment stocks. Finally, the concentration of pigments did not change significantly during gut passage. The biomass of live planktonic diatoms in the area of study was estimated to be 2-10 g DW/m² or 0.2-5% of the total organic content in the top 3 cm of the sediment. It is concluded that this pool of diatoms is largely unaffected by deposit feeders and seems to be unimportant as a food source. It is hypothesised that the input of the spring bloom should be considered as composed of two fractions playing different roles for the benthic ecosystem. One fraction of dead organic material may be utilised immediately, while the fraction of live planktonic diatoms serve as a stable food buffer, which gradually become available to deposit feeders after the diatoms die and degradation starts.     

Structural and trophic alterations in macrobenthic communities downstream from a fish farm outlet

The changes generated by a Spanish trout farm, located in the upper Río Tajuña (Central Spain), on benthic macroinvertebrates were studied by comparing biological characteristics of an upstream station (S-1) with those of three downstream sites placed 0.01 (S-2), 0.15 (S-3) and 1 (S-4) km below the fish farm outlet. In addition, a biological index is presented for estimating relative contributions (informative weights) of major macroinvertebrate groups to the macrobenthic community. Species richness and Shannon diversity were depressed downstream from the trout farm. However, density and biomass values were significantly higher at downstream stations during the summer, presumably due to an increase in water temperature and food supply. Amphipods, plecopterans and planarians were the macroinvertebrates most adversely affected by the fish farm effluent. Coleopterans, ephemeropterans and trichopterans were absent immediately below the outlet (S-2), but exhibited a partial downstream spatial recovery of their informative weights at S-3 and S-4. The abundance of tubificid worms, chironomids, simuliids and leeches increased below the trout farm, with dipterans predominating at all downstream sampling sites. The macrobenthic trophic structure was altered downstream from the trout farm by a significant increase in collectors (gathers and filter feeders) and predators, and a marked decrease in shredders and scrapers. The highest environmental impact was found just below the troutfarm outlet (S-2). It is concluded that the fish farm generates potamological effects on the functional structure of the macrobenthic community.     

Diagenetic stoichiometry and benthic nutrient fluxes at the sediment–water interface of Lake Illawarra, Australia

Benthic flux measurements of O₂, TCO₂ and inorganic nutrients were made at three stations (seagrass beds, shallow bare sand and deep mud) in Lake Illawarra (Australia) to compare the characteristics of diagenesis and benthic biogeochemical processes for different primary producers (seagrass or microphytobenthos, (MPB)) and/or sediment types (sand or mud).Seagrass beds exhibited the highest gross primary productivity while the lowest rates occurred at the deep mud station. At the shallow bare sand station only, the gross primary production (GPP) and respiration (R) were balanced, while at the other two stations, R exceeded GPP by as much as 2 fold, indicating more organic carbon was decomposed than produced at the time of sampling. In general, nutrient fluxes displayed typical diurnal variation.Organic carbon oxidation scenarios, evaluated by either calcium carbonate dissolution or sulfate reduction models, indicated that both models can represent organic matter mineralization. The difference of estimated total carbon oxidized in this lake using the two models was small, ranging from 0.2% at deep mud station to maximum of 21% at seagrass station. In addition, N₂ flux rates (net denitrification), estimated using carbon and nitrogen stoichiometry, were of similar magnitude as the rates estimated using LOICZ budget modeling or measured using the N₂/Ar technique.Finally, a comparison of calculated diffusive fluxes and measured fluxes using incubation cores indicated that the results were of similar magnitude at the deep mud station, but the incubation cores fluxes were much higher than the calculated diffusive fluxes at the other two stations. This may have been caused by bioturbation or bioirrigation.     

Benthic–pelagic coupling: a comparison of the community structure of benthic and planktonic heterotrophic protists in shallow inlets of the southern Baltic

1. The taxonomic composition, abundance and biomass of heterotrophic protists (ciliates, heterotrophic flagellates (HF), rhizopods and actinopods) in the sediment and water column of shallow inlets of the Southern Baltic was studied under a variety of environmental conditions during 1996–1997. A shallow, highly eutrophic station and a deeper, less eutrophic station were compared.
2. Community biomass ranged from 0.12 to 0.34 μg C cm?3 in the water column and from 1.5 to 105 μg C cm?3 in the sediment. Heterotrophic protists dominated zooplankton biomass at both stations (73% and 84% mean contribution), while they were of minor importance within the zoobenthos. Expressed per unit area, benthic biomass contributed a significant part (44% and 49%) to the total heterotrophic protistan community at both stations.
3. Although the methodology for counting ciliates and HF was focussed on a high taxonomic resolution, the results reveal some general trends in the distribution of heterotrophic protists: protozooplankton biomass was dominated by flagellates (80% mean biomass contribution) at the shallow station and by ciliates (73% mean biomass contribution) at the deep station. In the benthos at both stations, ciliates were the dominant protozoans, followed by the hitherto little‐studied rhizopods (25% and 35% mean biomass contribution) and flagellates.
4. The degree of benthic–pelagic coupling differed between taxonomic groups. Benthic and pelagic communities of ciliates showed little taxonomic overlap. In contrast, many heterotrophic flagellate species were found both in the benthos and in the pelagic. These benthic–pelagic species contributed significantly to the biomass of HF in the water column. The planktonic rhizopod community consisted of a subset of those species found in the benthos.
5. The abundance of benthic and pelagic protists was positively correlated at the shallow station, but taxonomic data indicate that the direct exchange between benthic and pelagic communities was only partly responsible.