Invasive alien plants increase CH4 emissions from a subtropical tidal estuarine wetland

Methane (CH₄) is an important greenhouse gas whose emission from the largest source, wetlands is controlled by a number of environmental variables amongst which temperature, water-table, the availability of substrates and the CH₄ transport properties of plants are most prominent and well characterised. Coastal wetland ecosystems are vulnerable to invasion by alien plant species which can make a significant local contribution to altering their species composition. However the effect of these changes in species composition on CH₄ flux is rarely examined and so is poorly understood. Spartina alterniflora, a perennial grass native to North America, has spread rapidly along the south-east coast of China since its introduction in 1979. From 2002, this rapid invasion has extended to the tidal marshes of the Min River estuary, an area that, prior to invasion was dominated by the native plant Cyperus malaccensis. Here, we compare CH₄ flux from the exotic invasive plant S. alterniflora with measurements from the aggressive native species Phragmites australis and the native species C. malaccensis following 3-years of monitoring. CH₄ emissions were measured over entire tidal cycles. Soil CH₄ production potentials were estimated for stands of each of above plants both in situ and in laboratory incubations. Mean annual CH₄ fluxes from S. alterniflora, P. australis and C. malaccensis dominated stands over the 3 years were 95.7 (±18.7), 38.9 (±3.26) and 10.9 (±5.26) g m^?2 year^?1, respectively. Our results demonstrate that recent invasion of the exotic species S. alterniflora and the increasing presence of the native plant P. australis has significantly increased CH₄ emission from marshes that were previously dominated by the native species C. malaccensis. We also conclude that higher above ground biomass, higher CH₄ production and more effective plant CH₄ transport of S. alterniflora collectively contribute to its higher CH₄ emission in the Min River estuary.     

A review of methodologies and success indicators for coastal wetland restoration

Coastal wetlands are considered to be amongst the most productive ecosystems and can provide invaluable ecological services. However, coastal wetlands are listed amongst the most threatened ecosystems suffering from anthropogenic activities. The loss or degradation of coastal wetlands has drawn a high level of attention to wetland restoration. Improvement of the structure and function of degraded, damaged and destroyed wetlands may be achieved through ecological restoration. Large numbers of restoration projects have been conducted worldwide based on different restoration goals and different methods. It is undoubtedly important to evaluate whether coastal wetland restoration is successful. However, coastal wetland restoration assessment has become challenging because of current disagreement on definitions and concepts of restoration evaluation. We reviewed the methodology of coastal wetland restoration and criteria for success evaluation, and then summarized the issues for current wetland restoration and success evaluation based on literature review. Moreover, we used an estuarine wetland affected by urbanization as a sample to demonstrate how to establish a success indicator system for guiding wetland restoration and evaluating the success of wetland restoration.     

Diatoms as indicators of isolated herbaceous wetland condition in Florida,USA

Benthic, epiphytic, and phytoplanktonic diatoms, as well as soil and water physical–chemical parameters, were sampled from 70 small (average 0.86 ha) isolated depressional herbaceous wetlands located along a gradient of human disturbance in peninsular Florida to (1) compare diatom assemblage structure between algal types; (2) develop biological indicators of wetland condition; (3) examine synecological relationships between diatom structure and environmental variables, with the ultimate goal of developing an index of biological integrity using a single assemblage. Collected diatom samples were enumerated to 250 valves and identified to species or subspecies. An assessment of wetland condition was made using a landscape-scale human disturbance score (Landscape Development Intensity index, LDI), calculated for each site using land use maps and GIS.Assemblages from both impaired and reference sites were compared using blocked multi-response permutation procedures, the percent similarity index, and visually examined using non-metric multidimensional scaling (NMDS). No ecologically significant compositional differences were found within sites. Mantel's test (Mantel's r = 0.29, p < 0.0001) and NMDS (stress: 14.52, variance: 78.5%) identified epiphytic diatoms as the most responsive to human disturbance. Strong significant correlations (|r_s| > 0.50, p < 0.05) were found between epiphytic NMDS site scores and soil pH, specific conductivity, water total phosphorous, and LDI, while soil pH, water color, soil TP, and turbidity were also significantly correlated (p < 0.05).Metrics to assess wetland condition were developed using epiphytic abundance data. Epiphytic taxa sensitive or tolerant to human landscape modification were identified using Indicator Species Analysis, and autecological indices relating diatom sensitivity to nutrients, pH, dissolved oxygen levels, saprobity, salinity, and trophic status were calculated. Fourteen final metrics were identified, scored on an ordinal scale, and combined into the Diatom Index of Wetland Condition (DIWC). The DIWC was highly correlated with the disturbance score (Spearman's r_s = −0.71, p < 0.0001), although the results need to be validated.     

Habitat use by fishes after tidal reconnection of an impounded estuarine wetland in the Indian River Lagoon,Florida (USA)

Most of the wetlands located along the Indian River Lagoon (IRL) ineast-central Florida (USA) have been impounded since the 1950's and1960's to reduce mosquito reproduction. Impounded marsh (i.e.,impoundment) dikes physically separate the wetlands from the estuary toallow artificial flooding of the impoundments during the mosquito breedingperiod (May to October). Presently, Rotational ImpoundmentManagement (RIM) is the preferred impoundment management techniquein the IRL. Impoundments maintained under RIM have culverts installedthrough the dikes which are kept closed during the mosquito breedingseason (to control mosquitos) and are allowed to remain open for theremainder of the year (to allow tidal flow). A 24.3 ha impoundment8 km north of Sebastian Inlet that had been isolated from the IRL for over39 years was studied for 12 months to determine habitat use by fishes aftertidal reconnection and the implementation of RIM. Fish sampling wasconducted with a seine in the perimeter ditch and with clover and minnowtraps in the upper marsh and tidal creek areas of the impoundment. Waterlevel, impoundment bottom topography, and the seasonal nursery functionof the impoundment were factors that contributed to observed patterns offish habitat use during the study. Within the first 15 weeks of perimeterditch sampling, an increase from 9 to 40 species was observed. Transientspecies used the perimeter ditch almost exclusively and entered theimpoundment primarily during the spring open period. Juvenile Pogonias cromis (Linnaeus), Elops saurus Linnaeus, Centropomusundecimalis (Bloch), and Megalops atlanticus Valenciennes were themost abundant recreationally important species, respectively. Habitat useby the most abundant resident species (Gambusia holbrooki Girard,Poecilia latipinna (Lesueur), Cyprinodon variegatus Lacepède, andFundulus confluentus Goode & Bean) was influenced primarily bywater level fluctuations. Resident species used the upper marsh and tidalcreek habitats during summer flooded periods and the cyprinodontids leftthe interior surface of the impoundment last as water levels decreased. Thisstudy is the first to document the recovery of fish populations in areconnected impoundment north of Sebastian Inlet using both active andpassive sampling techniques.     

Plants as indicators of wetland water source

At the local scale, plant species distribution is determined primarily by the environmental characteristics of a site. In a wetland, water chemistry and hydroperiod are two of the most important of these environmental characteristics. Both are functions of water source. In central Pennsylvania, groundwater input tends to be continuous, while surface water may be permanent or seasonal. The chemistry of groundwater and surface water differs since groundwater is influenced by the substrate through which it flows. Because of these differences, and because of their effects on plant species distribution, it is possible to use vegetation as an indicator of the dominant water source of a site. Plots within 28 wetlands in central Pennsylvania were sampled, and the plots were classified by water source. The three hydrologic categories were groundwater, seasonal surface water, and permanent surface water. The core of the study was the analysis of half of the plots to identify species that were associated with a particular water source. Several groups of indicator species were identified. Some species, including Nyssa sylvatica, were strongly associated with the presence of groundwater. Others, such as Symplocarpus foetidus, were strongly associated with the presence of seasonal surface water. Several aquatic species were associated with permanent surface water. The remainder of the plots were used to test the predictive ability of the indicator species identified. The vegetation of a wetland plot predicted its hydrologic category with 72% accuracy. The identification of more indicator species could lead to the development of a useful tool for wetland research and management, since monitoring hydrology is often both expensive and time-consuming.     

Monitoring rapid vegetation succession in estuarine wetland using time series MODIS-based indicators: An application in the Yangtze River Delta area

Frequent and continuous time series is required for the detection of plant phenology and vegetation succession. The launch of novel remote sensor MODIS (moderate resolution imaging spectroradiometer) provided us with an opportunity to make a new trial of studying the rapid vegetation succession in estuarine wetlands. In this study, the spatiotemporal variations of vegetation cover and tidal flat elevation along a transect (covering 6 pixels of MODIS) of an estuarine wetland at Dongtan, Chongming Island, in Yangtze River estuary, China were investigated to assess its rapid vegetation succession and physical conditions. By combining the field data collected, the time series of MODIS-based VIs (vegetation indices), including NDVI (normalized difference vegetation index), EVI (enhanced vegetation index) and MSAVI (modified soil adjusted vegetation index), and a water index, LSWI (land surface water index) were utilized to characterize the rapid vegetation succession between 2001 and 2006. We found that NDVI, EVI and MSAVI exhibited significant spatial and temporal correlations with vegetation succession, while LSWI behaved in a positive manner with surface water and soil moisture along with the successional stages. In order to take the advantages of both VIs and water index, a composite index of VWR (vegetation water ratio) combining LSWI and EVI or MSAVI was proposed in this paper. This index facilitates the identification of vegetation succession by simply comparing the values of VWR at different stages, and therefore it could track vegetation succession and estimate community spread rate. Additionally, this study presented an attempt of using MODIS datasets to monitor the change of tidal flat elevation, which demonstrated a potential remote sensing application in geodesy of coastal and estuarine areas.     

Water use patterns of estuarine vegetation in a tidal creek system

Water availability is a key determinant of the zonation patterns in estuarine vegetation, but water availability and the use of different water sources over space and time are not well understood. We have determined the seasonal water use patterns of riparian vegetation over an estuarine ecotone. Our aim was to investigate how the water use patterns of estuarine vegetation respond to variations in the availability of tidal creek water and rain-derived freshwater. The levels of natural stable isotopes of oxygen and hydrogen were assessed in the stem of the mangrove Avicennia marina (tall and scrub growth forms), Casuarina glauca and Melaleuca quinquenervia that were distributed along transects from river/creek-front towards inland habitats. The isotopic composition of plant tissues and the potential water sources were assessed in both the wet season, when freshwater from rainfall is present, and the dry season, when mangrove trees are expected to be more dependent on tidal water, and when Casuarina and Melaleuca are expected to be dependent on groundwater. Our results indicate that rainwater during the wet season contributes significantly to estuarine vegetation, even to creek-side mangroves which are inundated by tidal creek water daily, and that estuarine vegetation depends primarily on freshwater throughout the year. In contrast, high intertidal scrub mangroves were found to use the greatest proportion of tidal creek water, supplemented by groundwater in the dry season. Contrary to prediction, inland trees C. glauca and M. quinquenervia were found also to rely predominantly on rainwater—even in the dry season. The results of this study reveal a high level of complexity in vegetation water use in estuarine settings.     

A test of vegetation-related indicators of wetland quality in the prairie pothole region

This study was part of an effort by the U.S. Environmental Protection Agency to quantitatively assess the environmental quality or health of wetland resources on regional and national scales. During a two-year pilot study, we tested selected indicators of wetland quality in the U.S. portion of the prairie pothole region (PPR). We assumed that the amount of cropland versus non-cropland (mostly grassland) in the plots containing these basins was a proxy for their quality. We then tested indicators by their ability to discriminate between wetlands at the extremes of that proxy. Amounts of standing dead vegetation were greater in zones of greater water permanence. Depth of litter was greater in zones of greater water permanence and in zones of basins in poor-quality watersheds. Amounts of unvegetated bottom were greater in basins in poor-quality watersheds; lesser amounts occurred in all wetlands during a wetter year. Greater amounts of open water occurred during a wetter year and in zones of greater water permanence. When unadjusted for areas (ha) of communities, plant taxon richness was higher in wet-meadow and shallow-marsh zones in good-quality watersheds than in similar zones in poor-quality watersheds. Wet-meadow zones in good-quality watersheds had greater numbers of native perennials than those in poor-quality watersheds. This relation held when we eliminated all communities in good-quality watersheds larger than the largest commnities in poor-quality watersheds from the data set. We conclude that although amounts of unvegetated bottom and plant taxon richness in wet-meadow zones were useful indicators of wetland quality during our study, the search for additional such indicators should continue. The value of these indicators may change with the notoriously unstable hydrological conditions in the PPR. Most valuable would be indicators that could be photographed or otherwise remotely sensed and would remain relatively stable under various hydrological conditions. An ideal set of indicators could detect the absence of stressors, as well as the presence of structures or functions, of known value to major groups of organisms.     

A review of wetland inventory and classification in Australia

Studies of wetlands in Australia, as in other countries, have taken a wide variety of approaches to defining, surveying and classifying these environments. Past and current approaches in Australia are reviewed for each of the States and Territories which provide the context for much of the natural resource investigation in the country. While there are obvious advantages of national, and perhaps international, agreement on definition and types of wetlands, a variety of approaches to inventory and classification will always be necessary for particular purposes. More fundamental than general agreement on approaches is the need for wetland scientists and managers to maximise the accuracy of survey information, to test the assumptions involved in the use of classifications, and to ensure that the classifications they use are the most appropriate for their purposes. The issue of a global wetland classification scheme is discussed on the basis of a representative range of views by Australian wetland workers.     

Isotopic indicators of environmental change in a subtropical wetland

The δ¹⁵N and δ¹³C signatures of major organic matter (OM) pools were measured across chemical and hydrologic gradients in a large (58,800 ha) subtropical wetland to evaluate whether stable isotopes were useful indicators of environmental change. Once a rainfall-driven wetland, the Loxahatchee National Wildlife Refuge in the Florida Everglades now receives agricultural and urban drainage that has increased phosphorus (P) and mineral loads around the wetland perimeter. Additionally, water impoundment at the southern end has produced a latitudinal hydrologic gradient, with extended hydroperiods in the south and overdrained conditions in the north.Detritus (?4.8‰ to 8.6‰), floc (?1.4‰ to 3.6‰), and metaphyton (?6.6‰ to +7.4‰) δ¹⁵N declined southward with changes in hydrology as indicated by water depth. This pattern was attributed to higher mineralization rates under shorter hydroperiods. These signatures were also strongly correlated with increased nutrient and mineral loading. Rooted macrophyte δ¹⁵N, by contrast, appeared more responsive to soil nutrient pools. Cattail (?8.9‰ to +7.7‰) was restricted to the wetland perimeter and had the widest δ¹⁵N range, which was positively correlated with soil P. Sawgrass (?5.3‰ to +7.7‰) occurred across most of the wetland, but its δ¹⁵N was not strongly correlated to any gradient. Patterns for δ¹³C were more strongly related to chemical gradients caused by canal intrusion than to latitude or hydrology. Again, metaphyton and detrital signatures were more sensitive to water chemistry changes than macrophytes. This pattern is consistent with their locations at the soil–water (detritus-floc), and air–water (metaphyton) interface. Metaphyton δ¹³C (?36.1‰ to ?21.5‰) which had the broadest range, was affected by DIC source and pool size. In contrast, cattail δ¹³C (?28.7‰ to ?26.4‰) was more closely related to soil P and sawgrass δ¹³C (?30.1‰ to ?24.5‰) was not related to any environmental gradient except latitude. There was no correlation between the two isotopes for any OM pool except cattail.These results indicate that isotopic signatures of microbial (metaphyton and detrital) pools are more responsive to changes in wetland hydrology and water chemistry while those of rooted macrophytes respond only to the extent that soil chemistry is altered. Rooted macrophytes also differ in the sensitivity of their isotopic signatures to environmental change. The selection of OM pools for isotopic analysis will, therefore, affect the sensitivity of the analysis and the resulting patterns. Furthermore, δ¹⁵N may be more robust and interpretable than δ¹³C as an indicator of ecosystem change in wetlands exposed to multiple or complex anthropogenic gradients.     

Variation in wetland seed banks across a tidal freshwater landscape

Almost nothing is known about landscape-level variation in seed bank composition across complexes of hydrologically connected wetlands. We examined species composition of seed and spore banks in three habitats of tidal freshwater wetlands (marshes, swamp hollows, and swamp hummocks) along 48 km of tributaries throughout the tidal freshwater portions of the Nanticoke River watershed (Maryland and Delaware). Taxa and seedling density decreased with increasing distance upstream in the swamp hollows and hummocks, but increased or remained constant proceeding upstream in the marshes. Species rarefaction curves indicated equal taxa richness (28) between marshes and swamp hummocks at 175 individuals, with lower richness in swamp hollows (19). However, communities in swamp hollows were patchier and had an estimated total taxa richness of 52, similar to the marshes (50) and higher than swamp hummocks (41). Coefficients of variation for seedling emergence densities (136-180%) were greater than those of published seed bank studies conducted at smaller spatial scales in tidal freshwater marshes (36-117%). Our literature searches suggest that ours is the first study to document significant spatial trends in seed bank diversity and density across a wetland landscape.     

Developing wetland inventories in southern Africa: A review

The status of wetland inventory effort and availability of maps and other data sources is reviewed for the ten countries of southern Africa: Angola, Bostwana, Lesotho, Malawi, Mozambique, Namibia, South Africa, Swaziland, Zambia and Zimbabwe. The aims and strategies for inventory are discussed and the main survey methods compared. Prior to commissioning new inventory work careful collation of existing maps and imagery is recommended together with targeting of strategic inventory at Province level, reserving high resolution effort only for certain important sites.     

我国湿地评价研究综述

湿地评价研究已成为新世纪湿地科学前沿研究领域的热点问题。近年来 ,随着对湿地认识的不断深入 ,我国湿地评价研究内容不断丰富 ,研究水平提高幅度较大 ,研究方法由过去仅局限于湿地特征描述的定性评价 ,发展到湿地价值评价、湿地生态系统健康评价、湿地环境影响评价以及湿地生态风险评价等方面 ,3S技术和数学方法在湿地评价研究中也得到了较为广泛的应用。今后我国湿地评价研究应侧重于湿地评价理论、湿地评价指标体系和模型、湿地对比评价研究、退化湿地评价研究、湿地与全球气候变化以及新技术和新方法应用等方面     

Six years of submerged plant community dynamics in a freshwater tidal wetland

1. The dynamics of a submerged plant community were studied for 6 years in a freshwater tidal wetland. The degree and nature of change at several spatial scales (quadrat, transect and overall community) was determined, and the implications for community stability were assessed. 2. A high degree of change was recorded in 1 m² quadrats, and this was reflected in 10 m² transects as well. In quadrats, mean species richness changed every year. Species richness changed in >60% of quadrats each year. Stem number changed by as many as several 100 stems per quadrat from one year to the next. 3. Richness varied more among quadrats than among transects and varied less at the community level than among either quadrats or transects. Greater stability at the spatial scale of the whole community was reflected in high scores on the Jaccard and Morasita–Horn indices and Kendall's coefficient of concordance. 4. Although most of the submerged species were perennials, persistence at the local scale was low, and 4‐year persistence exceeded 50% for only one species. Change in abundance was largely independent among the species. 5. In the face of great small‐scale changes, species remain in the community (and the community persists) because of high recruitment rates.     

Riparian forest indicators of potential future stream condition

Large wood in streams can play an extraordinarily important role in influencing the physical structure of streams and in providing habitat for aquatic organisms. Since wood is continually lost from streams, predicting the future input of wood to streams from riparian forests is crucial to assessing or managing stream ecosystems. Unfortunately, regional monitoring protocols have no established capacity to provide this information. The goal of this research is to propose one or more methods that could meet this need. This goal is pursued by using stream wood delivery models to aid in the design of a monitoring method. Two questions are asked. First, does simpler data change model predictions of future contributions of wood from riparian ecosystems to the stream? The answers to this first question enable monitoring design to be tailored to details affecting estimates of future stream condition. These answers are important, because more detailed data is typically more costly. Second, which metrics, if any, correlate well with model predictions? If such metrics can be identified, then these measures can serve as effective indicators of ecosystem function directly, without using ecosystem models.These questions were addressed by collecting highly detailed field observations of riparian forests from 109 forested riparian sites in the Coast Range, Willamette Valley, and western Cascades of northwestern Oregon. Detailed and simplified versions of these data were used in models that forecast the potential of riparian forests to provide wood to the stream. Model predictions with less detailed data typically provided answers different than did predictions made with more detailed data. Thus, ecosystem assessments requiring these types of model predictions would benefit from more detailed data. In contrast, riparian metrics easily observed in the field (e.g. number of basal area of trees) or derived from remotely sensed imagery (e.g. number or height of canopy trees) were well correlated with model predictions of potential stream wood recruitment. When direct model predictions or model scenario analyses are not required, these metrics can serve as effective indicators of the potential of riparian forests to provide wood to the future stream network.     

闽江河口湿地土壤速效磷时空分布与来源

选取闽江河口潮滩湿地作为研究区,于2013年5、8和11月沿水文梯度采集不同深度土壤,测定其速效磷含量,研究闽江河口潮滩湿地土壤速效磷沿水文梯度的时空分布特征;并进一步测定土壤全磷(TP)、有机磷(Org-P)和无机磷(IP)分级,利用通径分析揭示土壤速效磷来源。结果表明:5月和8月土壤平均速效磷含量分别为3.53±1.15和3.23±1.15 mg·kg-1,显著高于11月(1.96±1.07 mg·kg-1)(P0.05);5、8和11月土壤速效磷空间分布格局相似,从高潮滩到中潮滩,其含量呈波动降低,并且表现为芦苇群落土壤速效磷含量显著高于短叶茳芏群落(P0.05);在垂直方向上,高潮滩土壤速效磷含量大都随深度增加而降低,中潮滩其垂直变化不显著;在植物生长初期(5月),土壤Org-P和闭蓄态磷(O-P)是速效磷的主要来源;在植物生长旺盛期(8月)和生长末期(11月),土壤Org-P和铁磷(Fe-P)是速效磷的主要来源。     

Nitrogen pools and soil characteristics of a temperate estuarine wetland in eastern Australia

The nitrogen status of the soil and plant components of an estuarine wetland near Sydney were investigated over 6 months to detect seasonal and spatial changes in nitrogen content. Organic carbon, organic nitrogen and inorganic nitrogen concentrations were measured in the soil at various depths in six vegetation zones across the wetland. Carbon and nitrogen content of the plant biomass were also determined in each of the zones. Soil redox potentials and pH were measured in situ and both were found to vary with depth and inundation frequency. Organic carbon, organic nitrogen and inorganic nitrogen in the soil decreased significantly from the fringe Casuarina forest (1391 g N m^?2) through to the Avicennia mangrove zone (133 g N m^?2). Exchangeable NH₄⁺, NO₃^? and NO₂^? concentrations from less than 1% of the soil nitrogen pool and vary seasonally. The distinctive feature of the mangrove zone is that the plant component of the total nitrogen pool is large (55%). This contrasts with the saltmarsh and fringe communities, where the plant pools are small (15%) in comparison with the soil. These findings are consistent with the hypothesis that mangroves export organic nutrients whereas the saltmarsh and fringe communities act as nutrient sinks.     

A functional and morphological approach to evaluate the vertical migration of estuarine intertidal nematodes during a tidal cycle

We tested herein the hypothesis that exposure time significantly contributes to the vertical distribution profile of nematodes during a tidal cycle as a function of distinct feeding and locomotion behaviors, conditioned by body morphology. We showed that the vertical distribution profile of the slender with filiform tail, numerically dominant Terschellingia longicaudata is in fact significantly correlated with sediment changes induced by tidal variation. Conversely, none of the other nematode species showed unequivocal evidence of vertical migration. Horizontal spatial heterogeneity also influenced the vertical distribution of nematode associations, probably as a response to varying temperature and desiccation levels at the sediment surface. The resulting vertical profiles for individual or species groups are a trade-off among locomotory and feeding strategies and concordant morphological adaptations.     

Larval release rhythms and tidal exchange in the estuarine mudprawn, Upogebia africana

The mudprawn, Upogebia africana is common in intertidal regions of many South African estuaries. The life cycle is complex, incorporating a marine phase of development during the larval stages. Breeding peaks are in summer and first-stage larvae are released into the plankton at night. Maximum release activity and export to the marine environment follow a semi-lunar cycle synchronized to the time when high water in the estuary is crepuscular. This occurs after peak spring tidal amplitude. Estuarine reinvasion by postlarvae is also nocturnal, and maximum return occurs after neap's when low water at sea occurs around sunset. Rhythmic cycles of larval export and postlarval estuarine reinvasion are therefore asynchronous during the lunar cycle and are best explained by the timing of the change in light intensity relative to high and low water respectively. If maximum activity rhythms of Stage 1 and postlarvae are independent of tidal amplitude, then timing of maximum release and reinvasion during the lunar cycle would alter as the time of sunset shifts between solstices. Much of southern Africa experiences a semi-arid type climate and most estuaries close off from the sea for varying periods owing to sandbar development across tidal inlets. Larvae do not metamorphose if trapped in estuaries and recruitment ceases. Thus, mudprawn populations are directly affected by tidal inlet dynamics. In extreme cases populations become locally extinct if inlets remain closed for extended periods.     

Sorbitol-fermenting bifidobacteria as indicators of diffuse human faecal pollution in estuarine watersheds

Sorbitol fermenting bifidobacteria were evaluated as indicators of non-point source human faecal pollution to three sub-estuaries with elevated faecal coliform densities. Human-specific bifidobacteria correlated with identifiable human sanitary deficiencies in feeder streams to estuarine creeks in two of three watersheds examined, one rural and one moderately developed. Sorbitol-fermenting bifidobacteria were recovered at densities ranging from 1 to 90 colony-forming-units 100 ml-1 in 11 of 258 water samples but were undetected in sediment (n = 68) and scat from resident wildlife (deer, muskrat and raccoon, n = 20). Failure to detect sorbitol-fermenting bifidobacteria in water samples during the summer months was consistent with laboratory microcosm results showing non-recoverability of Bifidobacterium adolescentis after 5-9 d in membrane-filtered estuarine water at 23 and 30 degrees C, but persistence for 4 weeks at 10 degrees C. Persistence of sewage-derived bifidobacteria in membrane-filtered freshwater at 15 degrees C was also observed. Recovery of sorbitol-fermenting bifidobacteria was complicated by high background levels of Gram-positive rods and cocci. Use of propionic acid and reduced pH (pH = 5.0), or use of a two-step resuscitation protocol using non-selective and selective media, did not improve recovery. Although human specific bifidobacteria hold promise as indicators of diffuse faecal contamination, methodological constraints now limit its application to situations of gross contamination, or sampling potential sources during environmental conditions conducive to bifid persistence.