We studied patterns of production and loss of four different extracellular polymeric substance (EPS) fractionscolloidal carbohydrates, colloidal EPS (cEPS), hot water (HW)-extracted and hot bicarbonate (HB)-extracted fractions-and community profiles of active (RNA) bacterial communities by use of Terminal-Restriction Fragment Length Polymorphism (T-RFLP) analysis of reverse transcription-polymerase chain reaction amplified 16S rRNA in mudflats in the Colne Estuary, United Kingdom, over two tidal emersion-immersion cycles. Colloidal carbohydrates and intracellular storage carbohydrate (HW) increased during tidal emersion and declined during tidal cover. The dynamics of cEPS and uronic acid content were closely coupled, as were the HB fraction and HB uronic acids. Changes in monosaccharide profiles of HW and HB fractions occurred during the diel period, with some similarity between cEPS and HB fractions. Increasing enzymatic release rates of reducing sugars and increased reducing sugar content were correlated with increased concentrations of colloidal carbohydrate and cEPS during the illuminated emersion period, and with the amount of HB-extracted uronic acids (the most refractory EPS fraction measured). Loss of reducing sugars was high, with sediment concentrations far below those predicted by the measured in situ release rates. T-RFLP analysis revealed no significant shifts in the overall taxonomic composition of the active bacterial community. However, 12 of the 59 terminal restriction fragments identified showed significant changes in relative abundance during the tidal cycle. Changes in the relative abundance of three particular terminal restriction fragments (bacterial taxa) were positively correlated to the rate of extracellular hydrolysis. Losses of chlorophyll a and colloidal and cEPS (up to 50-60%) occurred mainly in the first 30 min after tidal cover. About half of this may be owing to in situ degradation, with ''wash away'' into the water column accounting for the remainder.Microphytobenthic biofilms in intertidal sediments play an important role in the ecology of estuarine systems (Under-1 Corresponding author (gjcu@essex.ac.uk).

An experiment in >1000 river and riparian sites found spatial patterns and controls of carbon processing at the global scale.

Benthic microalgae (microphytobenthos) are the dominant group of primary producers in many marine intertidal and subtidal habitats. Estuarine mudflat diatoms are thought to be major contributors of extracellular polymeric substances (EPS), which are important for sediment stabilization and in benthic food chains. Biofilms from 6 sites in the Colne estuary, UK, were fractionated to isolate biopolymers (colloidal, colloidal EPS [cEPS], low molecular weight [LMW] carbohydrates, hot water [HW] and hot bicarbonate [HB] soluble) and the same techniques were applied to diatoms cultured from these sediments. At sites dominated by benthic diatoms, colloidal carbohydrate concentration and chlorophyll a were closely related. With increasing biomass, the proportion of cEPS within the colloidal fraction decreased from 60 to 20%. Carbohydrate analysis revealed significant differences in monosaccharide and uronic acid composition of different carbohydrate fractions. Principal component analysis (PCA) of monosaccharide composition of HB polymers from both field and culture samples grouped closely along fucose and rhamnose vectors and formed 2 distinct clusters. HW and LMW fractions grouped along the glucose vector and cEPS polymers along the galactose and arabinose vectors. These data indicate that the simple relationship between colloidal carbohydrate concentration and microphytobenthic biomass in biofilms masks a high degree of potential complexity within the sediment carbohydrate pool and in the different proportions of polymeric and nonpolymeric material between different biofilms. Comparing monosaccharide composition of extracts generated using the same protocol, natural assemblages showed close relationships with unialgal cultures, confirming the important role of diatom-derived polymers in mudflat ecology. KEY WORDS: Diatoms · Biofilms · Microphytobenthos · EPS · Monosaccharide distribution · Uronic acids · Biopolymers · Fractionation Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 38: [169][170][171][172][173][174][175][176][177][178][179][180] 2005 1993, . Many benthic diatoms exhibit patterns of vertical migration which allow cells to move into the narrow photic zone present in the top few millimeters of sediment, and this diatom motility is closely linked to EPS production (Lind et al. 1997. The postulated role of EPS in the ecosystem includes biostabilisation of sediments (Paterson 1986), a carbon source for benthic and planktonic species (Decho 1990, Underwood & Smith 1998a, and in mediating species interactions (Hoagland et al. 1993).Correlations have been measured between algal biomass (chlorophyll a [chl a] concentration) and colloidal (water-soluble) carbohydrate concentrations in estuarine sediments (Underwood & Paterson 1993, Underwood & Smith 1998b. These observations led to the publication of a model describing the relationship between sediment chl a and colloidal carbohydrate concentrations, developed using data from a number of European estuar...

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Diatoms are frequently used as indicators of eutrophication in temperate systems, but little is known about their application to impacted African tropical systems. Five streams located within Gombe Stream National Park and five streams supporting human settlements draining into Lake Tanganyika, East Africa, were investigated for species composition, richness and diversity of epilithic algae. In addition, a trophic diatom index (TDI) developed for monitoring European rivers was applied to these tropical systems. 54 specific and infraspecific diatom taxa representing 20 genera were identified for all sites with Achnanthes s.l., Gomphonema and Navicula s.l. being the most common genera. Species richness varied between 10 and 21 in disturbed streams and 13 and 19 in undisturbed streams. Nutrients were significantly enriched in streams draining the deforested watersheds but indices of diversity and evenness (Shannon H, J and Simpson-Yule D, E) did not show any significant differences between streams in forested and deforested watersheds. Significant differences were observed between pooled data for the TDI between forested and deforested watersheds. Analysis of percent pollution tolerant diatom taxa indicates that organic pollution of streams in deforested watersheds may be contributing to eutrophication. This study shows that African diatoms, cosmopolitan or resembling well-known North American and European taxa, allows for trophic indices tailored to the autecological preferences of species to be applied to new regions, although intensive studies on these African taxa will lead to more accurate results. Measures of species-richness and diversity, historically used to describe the state of an ecosystem, may not be suitable to evaluate streams which are not grossly polluted.