An assessment of the annual mass balance of carbon,nitrogen, and phosphorus in Narragansett Bay

Narragansett Bay is a relatively well-mixed, high salinity coastal embayment and estuary complex in southern New England (USA). Much of the shoreline is urban and the watershed is densely developed. We have combined our data on C, N, and P inputs to this system, on C, N, and P accumulation in the sediments, and on denitrification with extensive work by others to develop approximate annual mass balances for these elements. The results show that primary production within the bay is the major source of organic carbon (4 times greater than other sources), that land drainage and upstream sewage and fertilizer are the major sources of N, and that landward flowing bottom water from offshore may be a major source of dissolved inorganic phosphorus. Most of the nutrients entering the bay arrive in dissolved inorganic form, though DON is a significant component of the N carried by the rivers. About 40% of the DIN in the rivers is in the form of ammonia. Sedimentation rates are low in most of Narragansett Bay, and it appears that less than 20% of the total annual input of each of these elements is retained within the system. A very small amount of C, N, and P is removed in fisheries landings, denitrification in the sediments removes perhaps 10–25% of the N input, and most of the carbon fixed in the system is respired within it. Stoichiometric calculations suggest that some 10–20% of the organic matter formed in the bay is exported to offshore and that Narragansett Bay is an autotrophic system. Most of the N and P that enters the bay is, however, exported to offshore waters in dissolved inorganic form. This assessment of the overall biogeochemical behavior of C, N, and P in the bay is consistent with more rigorously constrained mass balances obtained using large living models or mesocosms of the bay at the Marine Ecosystem Research Laboratory (MERL).     

Nutrient enrichment weakens the stabilizing effect of species richness

With global freshwater biodiversity declining at an even faster rate than in the most disturbed terrestrial ecosystems, understanding the effects of changing environmental conditions on relationships between biodiversity and the variability of community and population processes in aquatic ecosystems is of significant interest. Evidence is accumulating that biodiversity loss results in more variable communities; however, the mechanisms underlying this effect have been the subject of considerable debate. We manipulated species richness and nutrients in outdoor aquatic microcosms composed of naturally occurring assemblages of zooplankton and benthic invertebrates to determine how the relationship between species richness and variability might change under different nutrient conditions. Temporal variability of populations and communities decreased with increasing species richness in low nutrient microcosms. In contrast, we found no relationship between species richness and either population or community variability in nutrient enriched microcosms. Of the different mechanisms we investigated (e.g. overyielding, statistical averaging, insurance effects, and the stabilizing effect of species richness on populations) the only one that was consistent with our results was that increases in species richness led to more stable community abundances through the stabilizing effect of species richness on the component populations. While we cannot conclusively determine the mechanism(s) by which species richness stabilized populations, our results suggest that more complete resource-use in the more species-rich low nutrient communities may have dampened population fluctuations.     

The determination of fresh organic carbon weight from formaldehyde preserved macrofaunal samples

Methodologies are presented whereby the fresh organic carbon weight of formaldehyde preserved macrofaunal samples may be estimated. Length-organic carbon weight regressions were determined for the four numerically dominant bivalves in Narragansett Bay, Rhode Island (Nucula annulata, Yoldia limatula, Mulinia lateralis, and Pandora gouldiana) and one commercially important, but less abundant species (Mercenaria mercenaria). Constants were determined to convert the dry weight of preserved softbodied organisms (polychaetes, oligochaetes, amphipods, etc.) to fresh (unpreserved) organic carbon weight. These results can be used by investigators studying the energetics of benthic communities similar to those in Narragansett Bay.     

杭州湾内外海域秋季浮游动物群落的比较

本文比较了杭州湾湾外海域(122.10°-122.58° E, 30.54°-30.93° N)和湾内不同海域(北岸东侧: 121.67°- 121.87° E, 30.68°-30.83° N; 南岸东侧: 121.60°-121.85° E, 29.95°-30.24° N; 北岸西侧: 121.31°-121.56° E, 30.58°- 30.77° N)秋季浮游动物的群落组成、累积优势度曲线以及多样性指数(H')等群落结构特征, 并进行了差异性分析。结果表明: 湾外海域的群落组成与湾内海域的3个群落之间均有较大的差异。湾外海域的群落I是以中华假磷虾(Pseudeuphausia sinica)等近海种、背针胸刺水蚤(Centropages dorsispinatus)等沿岸低盐种为主, 其次是外海种。湾内南岸东侧海域的群落II主要以左突唇角水蚤(Labidocera sinilobata)等沿岸低盐种为主, 近海种次之。湾内北岸东侧海域的群落III是以真刺唇角水蚤(Labidocera euchaeta)等沿岸低盐种、虫肢歪水蚤(Tortanus vermiculus)等河口半咸水种组成的混合群落。湾内北岸西侧海域群落IV是以虫肢歪水蚤为代表的河口半咸水种为主的群落。总的说来, 这一水域向西和向北方向出现更低盐度适应性的群落。从累积优势度曲线来看, 湾外海域群落I与湾内北岸东侧群落III的累积优势度上升趋势均相对平缓, 但群落III的初始累积优势度略高于群落I; 而与群落I相比, 湾内南岸东侧的群落II与北岸西侧的群落IV的初始累积优势度均很高。湾外海域群落I的初始累积优势度较低, 显示出群落I的优势种较多, 而单一优势种优势度低于湾内3个群落。方差分析结果表明: 湾外海域的浮游动物多样性指数与湾内3个海域均有极显著差异(P < 0.01), 而湾内各海域之间均无显著性差异(P > 0.05)。说明湾外浮游动物群落的多样性高于湾内海域。湾内外海域浮游动物群落特征之间有较大差异, 其主要原因是影响各自群落的主导水团明显不同。     

Variable responses within epiphytic and benthic microalgal communities to nutrient enrichment

We evaluated how changes in nutrient supply altered the composition of epiphytic and benthic microalgal communities in a Thalassia testudinum (turtle grass) bed in Florida Bay. We established study plots at four sites in the bay and added nitrogen (N) and phosphorus (P) to the sediments in a factorial design. After 18, 24, and 30 months of fertilization we measured the pigment concentrations in the epiphytic and benthic microalgal assemblages using high performance liquid chromatography. Overall, the epiphytic assemblage was P-limited in the eastern portion of the bay, but each phototrophic group displayed unique spatial and temporal responses to N and P addition. Epiphytic chlorophyll a, an indicator of total microalgal load, and epiphytic fucoxanthin, an indicator of diatoms, increased in response to P addition at one eastern bay site, decreased at another eastern bay site, and were not affected by P or N addition at two western bay sites. Epiphytic zeaxanthin, an indicator of the cyanobacterial/coralline red algae complex, and epiphytic chlorophyll b, an indicator of green algae, generally increased in response to P addition at both eastern bay sites but did not respond to P or N addition in the western bay. Benthic chlorophyll a, chlorophyll b, fucoxanthin, and zeaxanthin showed complex responses to N and P addition in the eastern bay, suggesting that the benthic assemblage is limited by both N and P. Benthic assemblages in the western bay were variable over time and displayed few responses to N or P addition. The contrasting nutrient limitation patterns between the epiphytic and benthic communities in the eastern bay suggest that altering nutrient input to the bay, as might occur during Everglades restoration, can shift microalgal community structure, which may subsequently alter food web support for upper trophic levels.     

EFFECTS OF NUTRIENT ENRICHMENT ON NATURAL POPULATIONS OF THE BROWN TIDE PHYTOPLANKTON AUREOCOCCUS ANOPHAGEFFERENS (CHRYSOPHYCEAE)1

The brown tide picoalga Aureococcus anophagefferens Hargraves et Sieburth was present in approximately equal numbers in 12 large scale (13,000 L) mesocosms at the start of a nutrient addition experiment in June 1985. Increases in abundance in untreated systems mimicked the pattern of bloom development in Narragansett Bay, Rhode Island, the seawater source for the experiment. Aureococcus increased to maximal values of 2.6 × 10⁹ cells. L^?1 and persisted at high numbers (10⁸ cells·L^?1) for 7–8 weeks. In nutrient addition tanks, the picoalgae bloomed briefly (1–3 weeks) but rapidly declined to the usual level (～10⁷ cells·L^?1) for eukaryotic algae in Narragansett Bay. The decline in picoalgae abundance was followed by an increase in total diatoms in all nutrient treated tanks. Mean picoalgae abundance in the mesocosms and the bay was significantly (P < 0.05) and inversely correlated (r =–0.93) with mean concentration of dissolved inorganic nitrogen. The persistence of the brown tide species in control mesocosms and Narragansett Bay appears related to its ability to grow at very low concentrations of dissolved inorganic nitrogen, levels previously shown to limit diatom growth.     

Effects of domestic pollution in Izmir Bay (Turkey)

The untreated domestic sewage of 650,000 people and wastes from industries and ships are discharged into the inner Bay of Izmir daily. Since May 1977 physico-chemical and biological effects of pollution in the bay have been examined at 10 stations. The hydrographic studies included measurements of temperature, transparency, seston, salinity, nitrate, phosphorus and dissolved oxygen. The benthic animals collected belong to 108 species; most of them were polychaetes. Comparison of the stations reveals that species richness increases from very polluted regions towards cleaner waters.     

Microcosm and Experimental Pond Evaluation of Microbial Community Response to Synthetic Oil Contamination in Freshwater Sediments

A multivariate approach was used to evaluate the significance of synthetic oil-induced perturbations in the functional activity of sediment microbial communities. Total viable cell densities, ATP-biomass, alkaline phosphatase and dehydrogenase activity, and mineralization rates of glucose, protein, oleic acid, starch, naphthalene, and phenanthrene were monitored on a periodic basis in microcosms and experimental ponds for 11 months, both before and after exposure to synthetic oil. All variables contributed to significant discrimination between sediment microbial responses in control communities and communities exposed to a gradient of synthetic oil contamination. At high synthetic oil concentrations (4,000 ml/12 m³), a transient reduction in sediment ATP concentrations and increased rates of oleic acid mineralization were demonstrated within 1 week of exposure. These transient effects were followed within 1 month by a significant increase in rates of naphthalene and phenanthrene mineralization. After initial construction, both control and synthetic oil-exposed microbial communities demonstrated wide variability in community activity. All experimental microbial communities approached equilibrium and demonstrated good replication. However, synthetic oil perturbation was demonstrated by wide transient variability in community activity. This variability was primarily the result of the stimulation of polyaromatic hydrocarbon mineralization rates. In general, microcosms and pond communities demonstrated sufficient resiliency to recover from the effects of synthetic oil exposure within 3 months, although polyaromatic hydrocarbon mineralization rates remained significantly elevated.     

The combined effects of treated sewage discharge and land use on rivers

Freshwater ecosystems are increasingly threatened by multiple anthropogenic stressors. Release of treated sewage effluent and pollution from agricultural or urban sources can independently reduce water quality with implications for ecological communities. However, our knowledge of the combined effects of these stressors is limited. We performed a field study to quantify the combined effect of treated sewage discharge and land use on nutrient concentrations, sewage fungus presence and communities of macroinvertebrates and benthic algae. Over three seasons in four rivers we found that a model which included an interaction between sewage pollution and time of the year (i.e. months) was the best predictor of nutrient concentrations and the abundance of algae and sewage fungus. Both macroinvertebrate and algae communities shifted downstream of sewage input. Specifically, more tolerant groups, such as cyanobacteria and oligochaetes, were more abundant. The EPT (Ephemeroptera, Plecoptera and Tricoptera) water quality score was best explained by an interaction between month and agriculture in the surrounding landscape. Overall, our results show that sewage discharge has a significant impact on water quality and benthic riverine communities, regardless of the surrounding land uses. Agricultural inputs, however, could be more important than treated sewage discharge in reducing the abundance of sensitive invertebrate taxa. We need both improvements to wastewater treatment processes and reductions in agricultural pollution to reduce threats to vulnerable freshwater communities.     

Nitrogen dynamics in lower Narragansett Bay. II. Phytoplankton uptake, depletion rates of nitrogenous nutrient pools, and estimates of ecosystem remineralization

Phytoplankton nitrogen demand in lower Narragansett Bay, RhodeIsland, measured during the winter-spring of 1977–78 andsummers of 1978 and 1979, is compared with estimates of zooplanktonand the benthic nitrogen remineralization drawn from the resultsof ekperimental field studies. Measured uptake rates would generallylead to the depletion of available nitrogenous nutrient stockswithin hours, and usually exceeded estimates of benthic pluszooplankton remineralization. Additional estimates of nitrogeninputs from sewage and riverine sources appear insufficientto make up the difference. The discrepancy lends support tothe paradigm that water column remineralization by microheterotrophsmay supply much, if not most, of the nitrogen needs of coastalphytoplankton.     

An overview of the assessment of aquatic ecosystem health using benthic invertebrates

Community structure or species composition of benthic invertebrates has frequently been used in environmental monitoring and assessment of aquatic systems. Three general approaches have been taken: the saprobic approach, which requires detailed knowledge of taxonomy and is most effective in measuring impacts from sewage effluents; diversity indices, which do not require detailed knowledge of species requirements but ignore information provided by important species and tend to lose information; and biotic indices, which combine both approaches. In the past few years considerable advances have been made by applying multivariate statistical techniques to large data matrices and relating benthic community structure to key environmental variables. Using these techniques it is possible to establish reference communities for a set of environmental conditions, to predict the benthic community that should occur at new sites and thus measure deviation from an expected community type. This suggests that environmental criteria and objectives can be established based on biological variables as opposed to the more traditional chemical approach.Measurement of ecosystem health using functional attributes of benthic invertebrates is generally in the development stage. In the future, functional measures of ecosystem health, such as chronic measures of toxicity or stress, should be incorporated into any assessment process.     

山东半岛南部海湾底栖动物群落生态特征及其与水环境的关系

2006-2007年对山东半岛南部4个海湾(荣成湾、桑沟湾、靖海湾和五垒岛湾)19个站位的底栖动物群落结构特征进行了研究,并对14个环境因素和底栖动物群落生态特征分别进行主成分分析和Spearman相关分析。结果显示,荣成湾、桑沟湾和靖海湾的底栖动物种类中,多毛类所占比例最高,而五垒岛湾仅秋、冬季多毛类所占比例最高。根据聚类分析和非度量多维标度方法分析,4季底栖动物群落均可分为2个群落,春、冬季的第一聚群为靖海湾和五垒岛湾,第二聚群为荣成湾和桑沟湾。秋季荣成湾、桑沟湾、靖海湾组成第一聚群,第二聚群由五垒岛湾构成。夏季,底栖动物Shannon-Wiener多样性指数(H')与采样深度和总碱度呈显著正相关,与水温呈极显著的负相关关系。秋季,与硝酸盐呈负相关关系,说明富营养化对山东半岛南部4个海湾大型底栖动物群落产生了一定负面影响。ABC曲线法分析显示,荣成湾和桑沟湾底栖动物的丰度优势度曲线与生物量优势度曲线相交,表明荣成湾和桑沟湾大型底栖动物群落处于中度干扰状态,密集的养殖活动可能对其生态系统带来了巨大影响,加强海水养殖管理,强化生态健康养殖理念,合理利用海洋生物资源,对大型底栖动物群落的稳定性具有重要意义。     

Polar ecosystem dynamics: recovery of communities from organic enrichment in McMurdo Sound, Antarctica

Community structure and diversity are influenced by patterns of disturbance and input of food. In Antarctica, the marine ecosystem undergoes highly seasonal changes in availability of light and in primary production. Near research stations, organic input from human activities can disturb the regular productivity regime with a consistent input of sewage. McMurdo Sound has both high-productivity and low-productivity habitats, thereby providing an ideal test bed for community recovery dynamics under polar conditions. We used experimental manipulations of the subtidal communities to test the hypotheses that (1) benthic communities respond differently to disturbance from organic enrichment versus burial and (2) community response also varies in areas with different natural patterns of food supply. Both in low- and high-food habitats, the strongest community response was to organic enrichment and resulted in dominance of typical organic-enrichment specialists. In habitats with highly seasonal productivity, community response was predictable and recovery was rapid. In habitats with low productivity, community variability was high and caging treatments suggested that inconsistencies were due to patchy impacts by scavengers. In areas normally subject to regular organic enrichment, either from primary production or from further up the food web (defecation by marine mammals), recovery of benthic communities takes only years even in a polar system. However, a low-productivity regime is as common in near shore habitats around the continent; under these conditions, recovery of benthic communities from disturbance is likely to be much slower and follow a variable ecological trajectory.     

Changes in the planktonic copepod community in a landlocked bay in the subtropical coastal waters of Hong Kong during recovery from eutrophication

Tolo Harbour is a poorly flushed bay in the northeastern corner of Hong Kong. Eutrophication caused by discharge of untreated and secondarily treated sewage into the bay was first detected during the 1970s. Increased nutrient input led to a noticeable increase in algal biomass and algal bloom occurrences. Nutrient reduction measures, including the construction of a pipeline to export all sewage effluents from Tolo Harbour, were introduced during the late 1980s. Decline in nutrient levels and decrease in the number of algal blooms have been recorded since 1998 when all nutrient reduction measures became fully operational. Zooplankton samples collected during 2003–2004 revealed that Tolo Harbour still contained a higher density and lower diversity of planktonic copepods compared to Mirs Bay, a less-polluted sea area outside Tolo Harbour. A comparison between data collected in this study to those collected during 1988–1990, several years before nutrient reduction measures were to be fully implemented, showed a decrease in copepod densities and an increase in copepod diversity. Small copepods, notably species of Paracalanus and Oithona, dominated the copepod communities in both periods, but there was an increase in species evenness during 2003–2004, caused by an increase in the number of dominant species. These observations confirm that eutrophication may lead to increases in copepod densities accompanied by increased dominance of small species.     

VARIATION IN DCMU-ENHANCED FLUORESCENCE RELATIVE TO CHLOROPHYLL A: CORRELATION WITH THE BROWN TIDE BLOOM1

DCMU–enhanced fluorescence and extracted chlorophyll a were simultaneously measured in Narragansett Bay, Rhode Island and the MERL (Marine Ecosystems Research Laboratory) mesocosms during the 1985 brown tide bloom. Marked differences in the relationship between these variables were observed as the phytoplankton community shifted from dominance by picoalgae to diatoms. The fluorescence to chlorophyll a ratio was significantly (P< 0.05) higher in the mesocosms and the bay when the brown tide species (Aureococcus anophagefferens Hargraves et Sieburth) dominated the phytoplankton community compared with other taxa. Although several factors could have affected the relationship we believe the high ratios are related to the pigment composition and/or small size of the brown tide organism.     

NUTRIENT EFFECTS ON SEAGRASS EPIPHYTE COMMUNITY STRUCTURE IN FLORIDA BAY1

A field experiment was employed in Florida Bay investigating the response of seagrass epiphyte communities to nitrogen (N) and phosphorus (P) additions. While most of the variability in epiphyte community structure was related to uncontrolled temporal and spatial environmental heterogeneity, P additions increased the relative abundance of the red algae–cyanobacterial complex and green algae, with a concomitant decrease in diatoms. When N was added along with P, the observed changes to the diatoms and the red algae–cyanobacterial complex were in the same direction as P‐only treatments, but the responses were decreased in magnitude. Within the diatom community, species relative abundances, species richness, and diversity responded weakly to nutrient addition. P additions produced changes in diatom community structure that were limited to summer and were stronger in eastern Florida Bay than in the western bay. These changes were consistent with well‐established temporal and spatial patterns of P limitation. Despite the significant change in community structure resulting from P addition, diatom communities from the same site and time, regardless of nutrient treatment, remained more similar to one another than to the diatom communities subject to identical nutrient treatments from different sites and times. Overall, epiphyte communities exhibited responses to P addition that were most evident at the division level.     

Zooplankton in different types of estuaries (using Curonian and Vistula estuaries as an example)

Based upon the results of long-term monitoring of zooplankton in the Curonian and Vistula estuaries carried out by the author, specific features of the structure and functioning of the zooplankton communities are studied. It is shown that the zooplankton communities in the open (Vistula Bay) and closed (Curonina Bay) types of estuaries differ in the species structures, numbers, biomasses, and functioning. The similarity of the zooplankton communities of these estuaries has to do with the commonness of their trophic structure. The zooplankton community in the Vistula estuary is more affected by the gradient of abiotic factors than the Curonian bay community. The mechanism providing the stability of the zooplankton communities in the open-type estuaries is the energy flow through the omnivorous species and the increase in the number of facultative predators at the terminal links of the trophic chain. It is shown that the Vistula estuary zooplankton community has a higher specific productivity rate and a higher rate of its circulation and use.     

天津海域底栖线虫群落结构的多元统计分析

应用多元统计分析方法(等级聚类分析和非度量多维标度)研究了天津近岸海域的底栖线虫群落结构情况.结果表明,等级聚类分析和非度量多维标度分析的结果具有很好的一致性.15个取样站位的线虫群落存在差异,根据线虫种类组成和丰度不同,调查站位可以分为4组.中南部近岸海域多数站位的线虫种类组成相似,深水区域的底栖线虫种类变化最大,而北部湾顶海域的线虫组成近似,但与其他站位相差较大.     

Change in a lake benthic community over a century: evidence for alternative community states

Aquatic communities are one of the most studied systems where alternative states or regime shifts have been detected. We used data spanning a century of time to test whether the zoobenthic community of Lake Mendota, Wisconsin, USA, was relatively stable through time, variable, or whether there was any evidence of alternative community states. We used multivariate statistical analyses to test for community structure similarity and whether detected differences corresponded to major changes in the local environment. Surprisingly, the benthic community in Lake Mendota was not statistically different from the mid 1960s to the present. Similarly, the benthic community was not significantly different from 1914 to the 1950s. However, between the 1950s and mid 1960s there was a dramatic change in the zoobenthic community, including the loss of key taxa and a decrease in the diversity of several major taxa. This dramatic change cannot be attributed to any single environmental factor, and is correlated with multiple factors acting simultaneously, including increased urban development, human population density, intensive agriculture, and the introduction of a major invasive species, Eurasian watermilfoil. The long-term similarity in the benthic community before and after the shift suggests two alternative states that switched with the confluence of multiple stressors.     

兴化湾浮游动物群落季节变化和水平分布

兴化湾为福建北部最大的海湾,于2006年对该海湾浮游动物群落进行了四季9个站位的调查。共检出浮游动物及幼虫124种,其中春季42种,夏季89种,秋季71种,冬季20种;分属近岸暖温、近岸暖水和广布外海3个生态类群;优势种15种,春季以水母和桡足类占优势,夏季以水母占优势,秋季以水母、桡足类和箭虫占优势,冬季则以桡足类占优势。不同季节兴化湾浮游动物生物量湿重和丰度水平分布特征变化明显,并与温度和盐度呈显著相关。聚类分析显示兴化湾浮游动物群落夏季类群和秋季类群相似度较高;各季节水平分布基本可分为湾口区和湾内区两大类群。与20世纪80年代相比,尽管本次调查浮游动物群落没有表现出显著差异,但随着电厂等大规模工程的投产,兴化湾海域生态系统健康面临着极大威胁,其环境压力需引起持续关注。