The impact of petroleum hydrocarbons (diesel) on periphyton in an impacted tropical estuary based on in situ microcosms

The distribution of petroleum hydrocarbons and their effects on the periphytic algal biomass using in situ microcosms were investigated in Ponggol estuary located on the northeastern coast of Singapore. Dissolved or dispersed petroleum hydrocarbon (DDPH) concentrations in the surface and bottom waters and absorbed or adsorbed petroleum hydrocarbon (AAPH) concentrations in sediments were monitored from July 1999 to June 2000. Results showed concentrations ranging from 4.42 to 248.94 μg l⁻¹, from 0.35 to 1099.65 μg l⁻¹, and from 20.55 to 541.01 mg kg⁻¹ for DDPH in surface and bottom waters and AAPH in sediments, respectively. Accidental spillages of fuel from dredgers operating in the estuary, fuel and engine oil from recreational boats, shipping operations in the adjacent strait, and runoff monsoon drains in the vicinity were some of the possible sources of petroleum hydrocarbons in the estuary. An assessment of environmentally realistic concentrations of petroleum hydrocarbons on periphytic algal biomass using in situ microcosms revealed signs of acute toxicity. A reduction in periphytic algal biomass (with respect to controls) of 68-93% was observed for various treatments exposed to diesel.     

Larval trematode infections and spatial distributions of snails

Abstract. The hypothesis that infecting trematodes influence the spatial distribution of the estuarine snail Ilyanassa obsoleta was tested. This work was conducted in the Savages Ditch habitat, Rehoboth Bay, DE, USA, which has an essentially flat, sandy-mud bottom bordered by saltmarsh shorelines and many infected snails. In 1996, two groups of snails were individually marked and released from one location after being screened for trematode infections. One group, transplanted from sites where snails tended not to be infected, consisted of snails that tested as uninfected. The other group consisted of snails native to Savages Ditch. Species of trematode carried by each snail was recorded. Marked snails were found and their positions were recorded until 2001. Snails were in five infection categories: (1) not infected, and infected with (2) Himasthla quissetensis , or (3) Lepocreadium setiferoides or (4) Zoogonus rubellus , or (5) with both H. quissetensis and Z. rubellus . The results show that the spatial distributions of snails depended on whether or not they were infected and, if infected, on which trematode species they carried. To complete life cycles, these parasites must accomplish transmission from the first (the snail) to the second intermediate hosts by short-lived, swimming cercariae. These data do not allow resolution of why snails distributed as they did, but sighting distributions of infected snails can be related to distributions of second hosts and it is proposed that parasites engender host snail distributions that improve chances of transmission.     

Nitrogen loading into an urban estuary: Lake Pontchartrain (Louisiana,U.S.A.)

We constructed a nitrogen loading budget for the Lake Pontchartrain watershed located north of New Orleans, Louisiana (U.S.A.). Water quality measurements, discharge estimates, and literature values were used to establish the annual and seasonal variations in loading rates for total nitrogen and nitrate. The relatively stable annual loadings (million kg N) are about 10× that of the pre-settlement nitrogen loading, and come from atmosphere (1.3), the watershed (7.8), pumped urban runoff from New Orleans (1.0), and leakage through the Bonnet Carré flood control structure (0.5–0.9). Relatively minor additional amounts come from nitrogen fixation in the Lake. Occasional openings of the Bonnet Carré Spillway (for flood protection) could triple the annual average loading within 1–2 months. Proposed smaller diversions (for wetland restoration) could raise present N loadings by 50%. The results of water quality management, flood protection and wetland restoration may thus have conflicting effects on the Lake's phytoplankton community, which is primarily nitrogen limited. Lowering the total nitrogen loading, however, seems quite possible, especially given that the present loadings are almost all reducible through existing technology, especially sewerage treatment. The analysis demonstrates that the consequences of ecosystem restoration efforts, continued population growth and flood protection to estuarine nitrogen budgets are intertwined with each other, have a seasonal component, and are changing as policies evolve.     

Ultrastructure of the ampullary organs of Plicofollis argyropleuron (Siluriformes: Ariidae)

The morphology of ampullary organs in Plicofollis argyropleuron, collected from a southeast Queensland estuary, was examined by light and electron microscopy to assess the morphological characteristics of teleost ampullary organs in environments with fluctuating salinities. This catfish possesses both macroampullae and microampullae. Both have the typical teleost arrangement of an ampullary pore linked by a canal to a single ampulla that is lined with receptor and supportive cells. The canal wall of macroampullae consists of a collagen sheath, a basement membrane, and two layers of squamous epithelial cells adjacent to the lumen, joined by desmosomes and tight junctions near the surface of the epithelium. Ampullary pore diameters are similar in range for both the macroampullae and the microampullae, with microampullae always arising from the larger pores within a single region of the head. Canal length of the macroampullae is longer than those of the microampullae. Macroampullae also contain approximately 10 times as many receptor cells compared with the microampullae. In both organs, these pear‐shaped receptor cells alternate with supportive cells along the entire luminal surface of the ampulla. The apical region of receptor cells extends into the lumen and bears numerous microvilli. The basal region of receptor cells adjoins to either individual or multiple unmyelinated neural terminals. The coexistence of two markedly different ampullary organ morphologies within a single species support theories concerning the possible multifunctionality of these sensory organs. J. Morphol., 276:1405–1411, 2015. © 2015 Wiley Periodicals, Inc.     

The role of suspended matter in the distribution of dissolved inorganic phosphate,iron and aluminium in the Ems estuary

In winter 1992/1993, a persistent local maximum in fluorescence, dissolved iron, dissolved aluminium and dissolved inorganic phosphate was found, upstream of the turbidity maximum in the freshwater zone of the Ems estuary (The Netherlands — Federal Republic Germany; western Europe). Upstream of this local maximum values ranged from 6 to 9 rel. units fluorescence, 0.9 to 2.4 μmol dm⁻³ iron, 0.5 to 0.7 μmol dm⁻³ aluminium and 0.6 to 2.3 μmol dm⁻³ dissolved inorganic phosphate. Within the maximum peak values of 24 rel. units fluorescence, 5.8 μmol dm⁻³ iron, 1.4 μmol dm⁻³ aluminium and 8.3 μmol dm⁻³ dissolved inorganic phosphate were observed. Downstream, fluorescence (indicator of dissolved organic carbon) showed conservative mixing with sea water, whereas dissolved iron, aluminium and dissolved inorganic phosphate did not. Dissolved aluminium and iron were quickly removed from solution to reach values of ∼100 nmol dm⁻³ aluminium and ∼0.3 μmol·dm⁻³ Fe at salinities of approximately 7 PSU. Further seaward iron concentrations gradually decreased to levels below 0.04 μmol dm⁻³. Dissolved aluminium first decreased to ∼20 nmol dm⁻³ at 29 PSU and increased again to concentrations of 30–44 nmol dm⁻³ at higher salinities. Dissolved inorganic phosphate, however, first decreased to upstream concentrations before reaching a secondary peak in the mid-estuarine reaches. At salinities >25 PSU dissolved inorganic phosphate mixed conservatively with sea water. It is hypothesized that adsorption-desorption equilibria are responsible for the local maximum values of fluorescence (DOC), iron, aluminium and dissolved inorganic phosphate. The similarity between the observed curves suggests a common underlying process, possibly related to the adjustment of new equilibria between suspended matter of marine and riverine origin.     

Primary production and biomass on a Dutch salt marsh: emphasis on the below-ground component

The primary production and below-ground biomass of angiosperms were measured in four almost monospecific vegetation stands situated on a salt marsh along the Oosterschelde estuary, The Netherlands. Maximum below-ground biomass values found for Spartina anglica, Elymus pycnanthus, Halimione portulacoides and Triglochin maritima, were very high relative to values reported from other European salt marshes: 12 586, 9 717, 17 737 and 16 121 g m^-2 respectively. These relatively high values may be due to the fineness of the sieve used, compared to other studies. The actual values are likely to be even higher because the sample treatment has probably caused loss of fine root material. Below-ground production estimates, based on the difference between maximum and minimum biomass, yielded: 6 044 g m^-2 yr^-1 for Spartina, 4 421 g m^-2 yr^-1 for Elymus, 7 799 g m^-2 yr^-1 for Halimione and 3 475 g m^-2 yr^-1 for Triglochin. This high production is mainly concentrated in the deeper layers of the root environment (20–60 cm). Although these production figures are considerably higher than those generally reported for comparable species or vegetation types in Europe, statistical evidence suggests that, for the first three species, they are real values rather than figures caused by random fluctuations.     

Estuarine nematodes as indicators of organic pollution; An example from the Ems estuary (The Netherlands)

A comparison is made of the structure and abundance of the nematode community of an intertidal, brackish-water mudflat in the Ems estuary under conditions of high (1980) and reduced (1987) organic waste input. Three stations, at different distances from the waste water inlet, were sampled monthly; nematodes were identified and counted in the upper 1 cm of the sediment. In 1987, numerical density of nematodes was lower, and species diversity was higher than in 1980. Diatom eating nematode species dominated in 1980, to decrease by 1987.Eudiplogaster pararmatus, an indicator of organic enrichment, also decreased strongly. The response of the nematode community to reduced organic waste input could be adequately described with the BONGERS' Maturity Index.     

Comparative study of the hyperbenthos of three European estuaries

The hyperbenthic fauna of the subtidal channels of the Eems (N. Netherlands), Westerschelde (S.W. Netherlands), and Gironde (S.W. France) estuaries was sampled within a 15-day period in summer 1991. In each estuary, quantitative samples were taken at regularly spaced stations covering the entire salinity gradient from marine conditions at the mouth to nearly freshwater conditions upstream. The diversity of the samples and the distribution of the species along the main estuarine gradients were assessed. Hyperbenthic communities were identified using different multivariate statistical techniques. The species composition and the density and biomass of the dominant species of each community were compared among communities.     

Bacteria and heterotrophic microflagellate production in the Santa Rosa Sound, Florida

Bacterial and microflagellate biomass and production and grazing onbacteria were compared weekly at a fixed station in Santa Rosa Sound,Florida, starting in February and ending in October. For bothpopulations the weekly variation in biomass and production was aslarge as the seasonal variation. Cycles for biomass and production ofthese organisms were generally out of phase, rendering it difficultto estimate the net grazing of bacteria by microflagellates atindividual time points. For evaluation of factors that control thefate of carbon cycled by bacterial, experiments were conducted toexamine bacterial growth rates in the absence of predators. Thisexamination resulted in low bacterial growth rates when biomass washigh, and rapid growth rates typically occurred near minimumpopulations. Further analysis suggested that microflagellatepredation was greater than bacterial production during minimumbacterial growth rates. With integration of production and grazingrates over the study period, factors controlling bacterial growthwere examined. Using this approach, 71% of the bacterial productionwas grazed by < 8.0µm predators. The microflagellate biomassproduction was 41% of the grazing rate on bacteria. The total amountof bacterial production assimilated into microflagellate biomass was29%. However, based on the variations in biomass and activity of themicrobial assemblages, it appears that substrate and predation exertalternating control on bacterial abundance and production.     

Settlement Dynamics of the Encrusting Epibenthic Macrofauna in Two Creeks of the Caeté Mangrove Estuary (North Brazil)

The epibenthic encrusting fauna of 2 creeks of the Caeté mangrove estuary, northern Brazil, was studied over a 13 month period using collectors fixed at 2.5 and 3.5 m above the creek bottom and in which upper and lower sides of ceramic and wooden panels were used as settlement substrates. The number of individuals of the most abundant organisms (barnacles, oysters and mussels) settling per panel was determined each month, for each substrate type, panel orientation and height above creek bottom. The barnacle, Fistulobalanus citerosum has a peak settlement period during the wet season whereas both peaks in the numbers of settlers of the oyster Crassostrea rhizophorae were recorded during the dry season and such discrete temporal patterns in settlement have also been observed for barnacles and oysters in other mangroves and estuaries. In contrast to other studies, settlement of the mussel Mytella falcata was generally low during the study period and may be related to over-exploitation of stocks in the region. Overall, settler density was usually greater on the underside of ceramic panels close to the creek bottom, similar to results of other studies of epibenthic settlement in diverse habitats.