Effects of sunlight on the production of dissolved organic and inorganic nutrients from resuspended sediments

A series of laboratory-based and field experiments was conducted to address the effects of sunlight-exposed resuspended sediments on dissolved nutrient fluxes in two different water bodies. In suspensions of tidal creek sediments in 0.2 μm-filtered creek water, measurable increases in dissolved nutrients occurred after only 2 h of exposure to simulated sunlight. During a 6-h irradiation, nutrient release rates for total dissolved nitrogen (TDN) and phosphate were 2.2 ± 0.5 (standard error; S.E.) μmol g^?1 h^?1 and 0.09 ± 0.005 μmol g^?1 h^?1 (S.E.), compared to no significant changes in dark controls. The majority of nitrogen was released as dissolved organic nitrogen (87% on average) with lesser amounts of ammonium (13%). Continental shelf sediments resuspended in unfiltered seawater also released phosphate and TDN when exposed to sunlight, suggesting that this process can occur in a variety of marine and estuarine environments. The source material for inorganic nutrients appears to be associated with sediments rather than dissolved organic matter, as no significant changes in nutrient concentrations occurred in experiments with 0.2 μm-filtered creek water or seawater alone. Results suggest that photoproduction of dissolved nutrients from resuspended sediments could be an episodically significant and previously unrecognized source of dissolved organic and inorganic nutrients to coastal ecosystems. This process may be especially important for continental margins where episodic resuspension events occur, as well as in regions experiencing high riverine sediment fluxes resulting from erosion associated with deforestation and desertification.     

Photobleaching Response of Different Sources of Chromophoric Dissolved Organic Matter Exposed to Natural Solar Radiation Using Absorption and Excitation–Emission Matrix Spectra

CDOM biogeochemical cycle is driven by several physical and biological processes such as river input, biogeneration and photobleaching that act as primary sinks and sources of CDOM. Watershed-derived allochthonous (WDA) and phytoplankton-derived autochthonous (PDA) CDOM were exposed to 9 days of natural solar radiation to assess the photobleaching response of different CDOM sources, using absorption and fluorescence (excitation-emission matrix) spectroscopy. Our results showed a marked decrease in total dissolved nitrogen (TDN) concentration under natural sunlight exposure for both WDA and PDA CDOM, indicating photoproduction of ammonium from TDN. In contrast, photobleaching caused a marked increase in total dissolved phosphorus (TDP) concentration for both WDA and PDA CDOM. Thus TDN∶TDP ratios decreased significantly both for WDA and PDA CDOM, which partially explained the seasonal dynamic of TDN∶TDP ratio in Lake Taihu. Photobleaching rate of CDOM absorption a(254), was 0.032 m/MJ for WDA CDOM and 0.051 m/MJ for PDA CDOM from days 0–9, indicating that phototransformations were initially more rapid for the newly produced CDOM from phytoplankton than for the river CDOM. Extrapolation of these values to the field indicated that 3.9%–5.1% CDOM at the water surface was photobleached and mineralized every day in summer in Lake Taihu. Photobleaching caused the increase of spectral slope, spectral slope ratio and molecular size, indicating the CDOM mean molecular weight decrease which was favorable to further microbial degradation of mineralization. Three fluorescent components were validated in parallel factor analysis models calculated separately for WDA and PDA CDOM. Our study suggests that the humic-like fluorescence materials could be rapidly and easily photobleached for WDA and PDA CDOM, but the protein-like fluorescence materials was not photobleached and even increased from the transformation of the humic-like fluorescence substance to the protein-like fluorescence substance. Photobleaching was an important driver of CDOM and nutrients biogeochemistry in lake water.     

Potential effects of leaf litter on water quality in urban watersheds

Leaf litter plays a critical role in regulating ecological functions in headwater forest streams, whereas the effects of leaves on water quality in urbanized streams are not fully understood. This study examined the potential importance of leaf litter for the release and transformations of organic carbon and nutrients in urban streams, and compared the effects with other types of natural organic substrates (periphyton and stream sediment). Nutrients and organic carbon were leached from senescent leaves of 6 tree species in the laboratory with deionized water, and maximal releases, leaching rate constants, composition and bioavailability of the leached dissolved organic carbon (DOC) were determined. Stream substrates (leaf debris, rocks with periphyton, and sediment) were seasonally collected from urban and forest reference streams of the NSF Baltimore Long-term Ecological Research Site and incubated with overlying stream water to estimate areal fluxes of DOC and nitrogen. Leaf litter leaching showed large ranges in maximal releases of DOC (7.0–131 mg g^?1), dissolved organic nitrogen (DON; 0.07–1.39 mg g^?1) and total dissolved phosphorus (TDP; 0.14–0.70 mg g^?1) among tree species. DOC leaching rate constants, carbon to nitrogen ratios, and DOC bioavailability were all correlated with organic matter quality indicated by fluorescence spectroscopy. Results from substrate incubation experiments showed far higher DOC and DON release and nitrate retention with leaf debris than with sediment, or rocks with periphyton. DOC release from leaf debris was positively correlated with stream nitrate retention at residential and urban sites, with the highest values observed during the fall and lowest during the summer. This study suggests the potential importance of leaf litter quantity and quality on fostering DOC and nutrient release and transformations in urban streams. It also suggests that species-specific impacts of leaves should be considered in riparian buffer and stream restoration strategies.     

Relationship between cardiac performance and environment across populations of Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>): a common garden experiment implicates local adaptation

Cardiac performance in fishes is predicted to be shaped by environmental factors such as temperature and river flow rate through natural selection for local adaptations, but few studies have explored these relationships. Using a common garden breeding design, we collected heart rate data from three populations of Atlantic salmon (Salmo salar) to measure peak heart rate and estimate optimal and upper critical temperatures for cardiac performance. We found that peak heart rate across populations matched the variation in natural river flow rates, such that the population that experienced the highest flow rate had the highest peak heart rate. Moreover, all populations showed evidence of local adaptation to summer water temperatures, with optimal temperatures (inferred from the Arrhenius breakpoint temperature) consistently falling 2.2–3.8 °C below the water temperature averaged for the summer months for each population. Also, upper critical temperatures (inferred from the temperature at which heart rates became arrhythmic) were nearly identical to peak summer water temperatures (0–0.3 °C above the peak). These results are consistent with heritable differences in cardiac performance among populations and suggest local adaptation to temperature and river flow.     

Enhanced hyporheic exchange flow around woody debris does not increase nitrate reduction in a sandy streambed

Anthropogenic nitrogen pollution is a critical problem in freshwaters. Although riverbeds are known to attenuate nitrate, it is not known if large woody debris (LWD) can increase this ecosystem service through enhanced hyporheic exchange and streambed residence time. Over a year, we monitored the surface water and pore water chemistry at 200 points along a ~ 50 m reach of a lowland sandy stream with three natural LWD structures. We directly injected ¹⁵N-nitrate at 108 locations within the top 1.5 m of the streambed to quantify in situ denitrification, anammox and dissimilatory nitrate reduction to ammonia, which, on average, contributed 85, 10 and 5% of total nitrate reduction, respectively. Total nitrate reducing activity ranged from 0 to 16 µM h^?1 and was highest in the top 30 cm of the stream bed. Depth, ambient nitrate and water residence time explained 44% of the observed variation in nitrate reduction; fastest rates were associated with slow flow and shallow depths. In autumn, when the river was in spate, nitrate reduction (in situ and laboratory measures) was enhanced around the LWD compared with non-woody areas, but this was not seen in the spring and summer. Overall, there was no significant effect of LWD on nitrate reduction rates in surrounding streambed sediments, but higher pore water nitrate concentrations and shorter residence times, close to LWD, indicated enhanced delivery of surface water into the streambed under high flow. When hyporheic exchange is too strong, overall nitrate reduction is inhibited due to short flow-paths and associated high oxygen concentrations.     

The effects of environmental factors on the migratory movement patterns of Sacramento River yearling late-fall run Chinook salmon (Oncorhynchus tshawytscha)

Understanding smolt migration dynamics is a critical step in the preservation and conservation of imperiled salmonids in California’s Sacramento River system. Late-fall run Chinook salmon yearling smolts were acoustically tagged and tracked during their outmigration through California’s Sacramento River and San Francisco Estuary during 2007–2009. Migration rates were 14.3 km·day^-1 (± 1.3 S.E.) to 23.5 km?day^-1 (± 3.6 S.E.), similar to rates published for other West Coast yearling Chinook salmon smolt emigrations. Region-specific movement rates were fastest through the upper river regions, and slowest in the Sacramento/San Joaquin River Delta. River travel times were recorded for smolts travelling through a series of ten monitor-delimited reaches. Using these, a smolt travel time model determined by two parameters (movement rate and rate of population spreading) was then used to determine the influence of different factors on the model’s fit, using model selection with Akaike’s Information Criterion. The model that allowed for both year and reach to be expressed additively for both travel time and population spreading rate estimates, while accounting for a “release” effect, was the best supported model. Finally, several models incorporated environmental data as a linear predictor of movement rates. The addition of the environmental variables, in order of importance, river width to depth ratio, river flow, water turbidity, river flow to mean river flow ratio, and water velocity all resulted in improved model fit. Water temperature did not improve model fit. These environmental associations are discussed and potential improvements on the travel time model are suggested.     

Concentrations and controls of dissolved organic matter in a constricted-channel region of the Ohio River

A 12-month study was conducted to measure the concentrations ofdissolved organic matter (DOC, TDN, TDP) in four sites within a119 km long reach of the Ohio River, near Louisville, KY. In thisstudy we test whether specific geomorphological and biologicalfactors influenced variations in dissolved organic matter.Concentrations of DOC in the river averaged 1200mol/L, and varied by nearly two orders of magnitudeseasonally (mean DOC during base flow 620 mol/L).Peak periods for DOC at all sites were during April–May. Thesite nearest a navigation dam (deeper, lower current velocities)had significantly lower concentrations of TDN and greater C:Nratios than upstream sites. The largest tributary entering thisreach (Kentucky River) had no significant effect on levels of DOMin the main river, despite having significantly greaterconcentrations of TDN and lower levels of DOC during most monthsof the year. Concentrations of DOC, TDN, and TDP were notsignificantly different in littoral and pelagic habitats at allsites studied, suggesting little floodplain influence on DOM inthis constricted-channel section of the Ohio River. C:N ratios ofDOM in the Ohio were significantly different among seasons; C:Nexceeded or equaled Redfield ratios in summer and fall (6 to 10),but were below Redfield (1.8 to 3.0) during winter and spring.Regression models suggest that total phytoplankton densities andflow conditions are the two most important factors regulating DOMin this very large river.     

Trace elements influenced by environmental changes in Lake Biwa: (II) Chemical variations in the hypolimnion over the last half-century

The history of the deep north basin of Lake Biwa extends over 430,000 years. Although it has probably been oxic and oligotrophic since its formation, human impacts have been changing lake conditions. In this paper, we discuss long-term changes in the chemistry of bottom water by compiling literature and through our own data over the last half-century. Long-term records show an increase in temperature, decrease in dissolved oxygen (DO), and increase in nutrients in bottom water. The stoichiometry among oxygen and nutrients indicates that changes are basically consistent with aerobic decomposition of organic matter. These changes are most likely the result of global warming and local eutrophication. Of particular note, yearly minimum DO concentrations <50 µmol kg^?1 have started to occur frequently at ~90 m depth since 1999. Manganese (Mn) concentrations in bottom water are at their minimum during the turnover period and at a maximum during the late stratification period each year. Yearly minimum Mn concentration has been within a narrow range over the last 30 years (0.25 ± 0.07 µmol kg^?1, n = 12). However, abnormally high Mn concentrations (up to 9.3 µmol kg^?1) were observed in 2007, caused by reductive release of a substantial amount of Mn from suboxic sediments and subsequent oxidation in bottom water. The concentration of arsenic (As) has gradually increased over the last 20 years in a similar manner, with a homologous element of phosphorus (P), resulting in an observed range of 17–29 nmol kg^?1 in 2010. The accumulation rate was ~0.8 nmol kg^?1 year^?1 for As and ~6 nmol kg^?1 year^?1 for P.     

Biogeochemical processes at the sediment–water interface, Bombah Broadwater, Myall Lakes

Myall Lakes has experienced algal blooms in recent years which threaten water quality. Biomarkers, benthic fluxes measured with chambers, and pore water metabolites were used to identify the nature and reactivity of organic matter (OM) in the sediments of Bombah Broadwater (BB), and the processes controlling sediment-nutrient release into the overlying waters. The OM in the sediments was principally from algal sources although terrestrial OM was found near the Myall River. Terrestrial faecal matter was identified in muddy sediments and was probably sourced via runoff from farm lands. The reactive OM which released nutrients into the overlying waters was from diatoms, dinoflagellates and probably cyanobacteria. Microcystis filaments were observed in surface sediments. OM degradation rates varied between 5.3 and 47.1 mmol m^?2 day^?1 (64–565 mg m^?2 day^?1), were highest in the muddy sediments and sulphate reduction rates accounted for 20–40% of the OM degraded. Diatoms, being heavy sink rapidly, and are an important vector to transport catchment N and P to sites of denitrification and P-trapping in the sediments. Denitrification rates (mean ～4 mmol N m^?2 day^?1), up to 7 mmol N m^?2 day^?1 (105 mg N m^?2 day^?1) were measured, and denitrification efficiencies were highest (mean = 86 ± 4%) in the sandy sediments (～20% of the area of BB), but lower in the muddy sediments (mean = 63 ± 15%). These differences probably result from higher OM loads and anaerobic respiration in muddy sediments. Most DIP (>70%) from OM degradation was not released into overlying waters but remained trapped in surface sediments. Biophysical (advective) processes were responsible for the measured metabolite (O₂, CO₂, DSi, DIN and DIP) fluxes across the sediment–water interface.     

Nitrogen removal in coastal sediments of the German Wadden Sea

Although sediments of the German Wadden Sea are suspected to eliminate a considerable share of nitrate delivered to the SE North Sea, their denitrification rates have not been systematically assessed. We determined N₂ production rates over seasonal cycles (February 2009–April 2010) at two locations with two sediments types each, the first site (Meldorf Bight) receiving nitrate during all seasons from the Elbe river plume, and a second site on the island of Sylt, where nitrate is depleted during summer months. In sediments from the Sylt site, N₂ production ranged from 15 to 32 μmol N₂ m^?2 h^?1 in the fine sand station and from 7 to 13 μmol N₂ m^?2 h^?1 in the coarse sand station; N₂ production was not detected when nitrate was depleted in May and July of 2009. N₂ production in the Meldorf Bight sediments were consistently detected at higher rates (58–130 μmol N₂ m^?2 h^?1 in the very fine sand station and between 14 and 30 μmol N₂ m^?2 h^?1 in the medium sand station). Analysis of ancillary parameters suggests that major factors controlling N₂ production in coastal sediments of the German Wadden Sea are the nitrate concentrations in the overlying water, the ambient temperature, and the organic matter content of the sediment. Extrapolating our spot measurements to the zone of nitrate availability and sediment types, we estimate an annual nitrogen removal rate around 16 kt N year^?1 for the entire northern sector of the German Wadden Sea area. This corresponds to 14% of the annual Elbe river nitrogen load.     

Dissolved organic carbon in streams from artificially drained and intensively farmed watersheds in Indiana, USA

Dissolved organic carbon (DOC) in streams draining hydrologically modified and intensively farmed watersheds has not been well examined, despite the importance of these watersheds to water quality issues and the potential of agricultural soils to sequester carbon. We investigated the dynamics of DOC for 14 months during 2006 and 2007 in 6 headwater streams in a heavily agricultural and tile-drained landscape in the midwestern US. We also monitored total dissolved nitrogen (TDN) in the streams and tile drains. The concentrations of DOC in the streams and tile drains ranged from approximately 1–6 mg L^?1, while concentrations of TDN, the composition of which averaged >94% nitrate, ranged from <1 to >10 mg L^?1. Tile drains transported both DOC and TDN to the streams, but tile inputs of dissolved N were diluted by stream water, whereas DOC concentrations were generally greater in the streams than in tile drains. Filamentous algae were dense during summer base flow periods, but did not appear to contribute to the bulk DOC pool in the streams, based on diel monitoring. Short-term laboratory assays indicated that DOC in the streams was of low bioavailability, although DOC from tile drains in summer had bioavailability of 27%. We suggest that these nutrient-rich agricultural streams are well-suited for examining how increased inputs of DOC, a potential result of carbon sequestration in agricultural soils, could influence ecosystem processes.     

Blood hormone profiles,physiological variables,and behavioral criteria in Corriedale ewes fed different TMR moisture levels during thermal–humidity exposure

In this study, blood hormone profiles, physiological variables, and behavioral criteria in Corriedale ewes fed total mixed ration (TMR) at different moisture levels during thermal–humidity exposure were evaluated. Nine non-pregnant Corriedale ewes (ave. BW = 41 ± 3.5 kg) were individually fed diets based on maintenance requirements in metabolic crates. Ewes were assigned to three treatment groups according to a 3 × 3 Latin Square design for 3 periods of 21 days duration each (9 ewes per treatment). Treatments were TMR (CP (crude protein) = 16.1, TDN (total digestible nutrients) = 69.1%) moisture levels at 40, 50, and 60%. No differences were found in blood hormone profiles including cortisol (μg/dL), immunoglobulin G (mg/dL), triiodothyronine (ng/mL), thyroxin (μg/dL), growth hormone (ng/mL), prolactin (ng/mL), insulin (μU/mL), insulin-like growth factor 1 (ng/mL), aldostrone (ng/dL), antidiuretic hormone (pg/mL), and creatinine (mg/dL) among all treatment groups (p > 0.05). Measurements of physiological variables indicated that heart rate (number of beats/min) in the afternoon was higher in 50 and 60% TMR group than in the 40% group (p < 0.05). No differences were observed in respiratory rate (number/min), panting score, and fecal score among the groups (p > 0.05). The behavior criteria including urine excretion frequency (number/d), fecal excretion frequency (number/d), standing frequency (number/d), resting frequency (number/d), standing duration (min/d), and resting duration (min/d) showed no differences among the treatment groups (p > 0.05). Conclusions drawn indicate the minor impacts of TMR moisture levels up to 60% on behavioral criterions of Corriedale ewes during thermal–humidity exposure, but help smooth down the intensified heat stress conditions over physiological variables and endocrine system.     

Vertical distribution and release characteristics of nitrogen fractions in sediments in the estuaries of Dianchi Lake,China

Columnar sediment samples were collected from five representative estuaries of Dianchi Lake, China. And the vertical distribution of each fraction of nitrogen (IEF-N, CF-N, IMOF-N, OSF-N) were tested. The results showed that the TN content in sediments from areas A, B, C, D and E gradually decreased with depth between 0 and 15 cm, then sharply decreased with depth between 15 and 30 cm and stabilized at depth below 30 cm, indicating the exogenous input of N in these areas has not been controlled effectively. The proportion of TN occupied by various N fractions in the sediments ranked as follows: OSF-N > IMOF > CF-N > IEF-N. Correlation analysis results showed both IEF-N and IMOF-N were significantly correlated with the content of TFe₂O₃ + MnO + Al₂O₃ in deeper sediments, while no correlation in superficial sediments. The areas A and B have extremely high release risks for N in superficial sediments. However, the N in the sediments of areas C, D and E were in relative equilibrium with the overlying water, indicating release potential risk was relatively low.     

Potamoplankton and primary productivity in the River Danube

Autochthonous production of potamoplankton has recently attracted greater interest as it was incorporated into expanded river concepts such as the flow pulse concept or the riverine productivity model (RPM). This review assembles data on primary production from the River Danube to evaluate the importance of productivity in large rivers. Results indicate positive net production in the middle reach of the river and in impoundments. These sections are characterised by favourable conditions for algal growth. Reduction in flow, reduced concentrations of suspended solids and improved under-water light result in significant increase in plankton biomass. Maximum chlorophyll concentrations were below 20 mg m^?3 in 2007 but concentrations up to 130 mg m^?3 have been recorded in the past. Since nutrients are not limiting, as in most large rivers, net primary production is largely controlled by availability of photosynthetic active radiation under water, chlorophyll-a, water depth and discharge. Hourly carbon uptake rates of 3–130 mg C m^?3 h^?1 observed in the Danube are well within the range of 0–790 mg C m^?3 h^?1 for large rivers of the world. Autochthonous autotrophic production must be regarded as an important feature of large rivers supporting the RPM concept.     

Long-term nitrate removal in a stream riparian zone

The long-term capacity of riparian zones in regulating groundwater nitrate fluxes is not well understood. This study analyses patterns of nitrate removal for the period 1994–2012 at two sites in a river floodplain that have received high groundwater nitrate loading from a large upland aquifer for over 32 years. During the study, mean NO₃ ^?–N concentrations entering the riparian zone varied between 20–30 and 30–42 mg/L at the upstream and downstream sites respectively, but did not show any clear inter-annual trend. A permeable sand layer in the riparian zone is underlain by a regional aquitard at a depth of 5–6 m and 4 m at the upstream site and downstream site respectively. Denitrification resulted in a decline in nitrate concentrations as lateral groundwater flow in the sand layer interacted with buried peat and channel bar deposits that range up to 3 m in depth at both riparian sites. This interaction was greater at the downstream site where the organic deposits extend down to <1 m from the aquitard in some locations. At the upstream site nitrate removal efficiency in the sand layer, at depths of 3–4 m ~20 m from the river bank, declined from 68 % in 1996–1998 to 42 % in 2009–2012. A smaller decline from 92 to 82 % occurred in the sand layer 10 m from the river bank during the study. In contrast, no clear pattern of change was evident at the downstream site where a nitrate removal efficiency of 98–100 % occurred at the river bank in most years between 1994 and 2012. These data suggest that the long-term nitrate removal performance of some riparian zones may decline if carbon availability for denitrification becomes limited as a result of variations in the quantity, quality and location of subsurface organic deposits that interact with deeper groundwater flowpaths.     

Organic matter accumulation in the bottom sediments and its regulatory aspects in the southern basin of Lake Biwa

Approximately 14 million people get their drinking and industrial water from the most southern part of Lake Biwa. This shallow region, however, has been eutrophicated severely from year to year by nutrients loading from both the surrounding inflowing rivers and the north basin. Sedimented solids of the surface layer of bottom sediments are stirred up very frequently by strong winds and waves in this shallow region. Moreover, the water quality has been deteriorated by the release of nutrients from the surface layer of bottom sediments in which organic matter has accumulated. For the period 1989 to 1990, the suspended solids content had a close correlation with the COD value, and the T-N and T-P concentrations in the water of inflowing rivers to the basin. T-N release rate from the surface layer of bottom sediments ranged from 6.3 to 213.8 mg m^-2 d^-1 and the release load was 936 kg d^-1 for the entire 58 km² of the south basin. On the other hand, T-P release rate ranted from 0.91 to 3.56 mg m^-2 d^-1 and the total release load was approximately 69 kg d^-1 in the basin. Suction dredging of organic matter rich sediments was carried out in the basin to improve the water quality. Removed sediments were used after processing for various kinds of construction materials, such as bricks for pavement, walls of domestic houses, and ornamental materials of public buildings.     

Critical moisture content for successful cryopreservation of embryonic axes of <Emphasis Type="Italic">Fortunella polyandra</Emphasis> determined by differential scanning calorimetry (DSC)

The relationships between water content of desiccated embryonic axes (using different methods of desiccation), the availability of water determined by differential scanning calorimetry (DSC) analysis and recovery percentage after liquid nitrogen (LN) exposure of Fortunella polyandra embryonic axes were investigated. The objectives were to understand thermal properties of desiccated embryonic axes during cryopreservation and to determine the critical moisture contents for successful cryopreservation of the embryonic axes. Excised embryonic axes were desiccated under laminar air flow (0, 10, 15, 30 and 45 min), over silica gel (0, 5, 15, 30 and 60 min), and ultra-rapidly (0, 5, 10, 20 and 25 min). Desiccation under laminar air flow resulted in an optimal water content of 0.150 gH₂O g^?1 dw and a survival of 50 % after cryopreservation, while the unfrozen water content (WC_u) was 0.126 gH₂O g^?1 dw. After drying over silica gel, the optimal water content was 0.190 gH₂O g^?1 dw, where the survival was 40 % after cryopreservation and the WC_u was determined as 0.177 gH₂O g^?1 dw. Using the flash-drying method, the optimal water content was found to be 0.145 gH₂O g^?1 dw, the survival was 50 % after cryopreservation and the WC_u was 0.133 gH₂O g^?1 dw. Embryonic axes of F. polyandra showed low-to-moderate tolerance to desiccation. The results of the freezing transitions for all the desiccation times and methods showed that the onset temperature and the peak of the mean enthalpy decreased in size with decreasing water content. DSC elucidated the critical moisture contents and the cooling and melt enthalpies for successful cryopreservation of F. polyandra embryonic axes.     

An effective method based on wet-heat treatment for the selective isolation of Micromonospora from estuarine sediments

Several methods for the isolation of Micromonospora from soil samples have been developed; however, it is unclear whether these methods are optimal for estuarine samples. In this study, we optimized the conditions of a wet-heat method for the selective isolation of Micromonospora from estuarine sediments. Sediments were collected from the Arakawa River (estuarine sediments) and Tokyo Bay (marine sediments). Sediment samples were wet-heated at 45, 55, or 65 °C for 30 min and then incubated at 27 °C for 3 weeks. After incubation, most of the actinomycete colonies were macroscopically determined to be of the genus Micromonospora or Streptomyces. In contrast to the treatment at 55 °C, treatment at 65 °C drastically reduced the number of Streptomyces colonies but increased the number of Micromonospora colonies from the estuarine sediments. This procedure allowed us to grow cultures that were composed of more than 90 % Micromonospora. In addition, treatment at 65 °C did not affect the diversity of Micromonospora species compared with treatment at 55 °C. These results indicate that the wet-heat method, which involves pre-treating the sediment at 65 °C for 30 min, is a very simple and effective method for the selective enrichment of a large number of diverse Micromonospora from estuarine sediments. Our results may lead to the isolation of new Micromonospora species, which produce novel bioactive compounds, from different estuarine sediments.     

Impact of resuspension of cohesive sediments at the Oyster Grounds (North Sea) on nutrient exchange across the sediment–water interface

Benthic-pelagic exchange processes are recognised as important nutrient sources in coastal areas, however, the relative impact of diffusion, resuspension and other processes such as bioturbation and bioirrigation are still relatively poorly understood. Experimental ship-based data are presented showing the effects of diffusion and resuspension on cohesive sediments at a temperate shelf location in the North Sea. Measurements of diffusive fluxes in both spring (1.76, 0.51, ?0.91, 17.6 μmol/m²/h) and late summer (8.53, ?0.03, ?1.12, 35.0 μmol/m²/h) for nitrate, nitrite, phosphate and dissolved silicon respectively, provided comparisons for measured resuspension fluxes. Increases in diffusive fluxes of nitrate and dissolved silicon to the water column in late summer coincided with decreases in bottom water oxygen concentrations and increases in temperature. Resuspension experiments using a ship board annular flume and intact box core allowed simultaneous measurement of suspended particulate matter, water velocity and sampling of nutrients in the water column during a step wise increase in bed shear velocity. The resuspension of benthic fluff led to small but significant releases of phosphate and nitrate to the water column with chamber concentration increasing from 0.70–0.76 and 1.84–2.22 μmol/L respectively. Resuspension of the sediment bed increased water column concentrations of dissolved silicon by as much as 125% (7.10–15.9 μmol/L) and nitrate and phosphate concentrations by up to 67% (1.84–3.08 μmol/L) and 66% (0.70–1.15 μmol/L) respectively. Mass balance calculations indicate that processes such as microbial activity or adsorption/desorption other than simple release of pore water nutrients must occur during resuspension to account for the increase. This study shows that resuspension is potentially an important pathway for resupplying the water column with nutrients before and during phytoplankton blooms and should therefore be considered along with diffusive fluxes in future ecosystem models.     

Influence of outbreak of macroalgal blooms on phosphorus release from the sediments in Swan Lake Wetland,China

Macroalgal blooms have occurred worldwide frequently in coastal areas in recent decades, which dramatically modify phosphorus (P) cycle in water column and the sediments. Rongcheng Swan Lake Wetland, a coastal wetland in China, is suffering from extensive macroalgal blooms. In order to verify the influence of macroalgal growth on sediment P release, the sediments and filamentous Chaetomorpha spp. were incubated in the laboratory to investigate the changes of water quality parameters, P levels in overlying water, and sediments during the growth period. In addition, algal biomass and tissue P concentration were determined. In general, Chaetomorpha biomasses were much higher in high P treatments than in low P treatments. Compared with algae+low P water treatment, the addition of sediments increased the algal growth rate and P accumulation amount. During the algal growth, water pH increased greatly, which showed significant correlation with algal biomass in treatments with high P (P < 0.05). P fractions in the sediments showed that Fe/Al–P and organic P concentrations declined during the algal growth, and great changes were observed in algae+low P water+sediment treatment for both. As a whole, the sediments can supply P for Chaetomorpha growth when water P level was low, and the probable mechanism was the release of Fe/Al–P at high pH condition induced by intensive Chaetomorpha blooms.