Nitrogen loss in a nitrifying rotating contactor treating ammonium rich leachate without organic carbon

Extended loss (up to 70%) of nitrogen is observed in a nitrifying rotating biological contactor (RBC) treating ammonium - rich leachate of a hazardous waste landfill. Due to pretreatment (flocculation, BOD-removal, activated carbon) DOC was less than 20 mg/l so heterotrophic denitrification can be excluded. The nitrification rate reaches 3-4 g NH₄-N m⁻² d⁻¹ at a pH of 7-7.3 in the first two of three RBC compartments. An increasing partial pressure of oxygen and ammonium concentration favor nitrogen removal over ammonium oxidation. The reduction of nitrite produced in the aerobic biofilm layer close to the surface might therefore be coupled with ammonium oxidation and takes place in the deeper or temporarily anoxic layer of the biofilm.     

Effects of pulsed flows on nuisance periphyton growths in rivers: a mesocosm study

Rivers regulated by dams are typically characterized by altered biotic communities and habitat structure in downstream reaches. In the Jackson River (Alleghany Co., VA), a relatively constant flow regime below Gathright Dam and anthropogenic nutrient loading have apparently contributed to nuisance levels of periphyton (>300 mg chlorophyll a m^?2). These nuisance growths cause low dissolved oxygen concentrations in the water column and altered benthic habitats in the Jackson River. The use of periodic pulsed flows has been suggested as a restoration practice that could potentially reduce periphyton biomass. We investigated the effects of increased flow on periphyton chlorophyll a (chl a), ash‐free dry mass (AFDM), % organic matter (%OM) using streamside channels in which periphyton‐colonized tiles were subjected to near‐bed velocities ranging from 20 (control) to 240 cm s^?1. Analysis of variance (ANOVA) and regression were used to examine periphyton responses to velocity treatments. There was a significant decrease in chl a and AFDM, and significant increase in %OM in velocity treatments of 150, 180 and 240 cm s^?1 (p < 0.001), but not in lower velocity channels. Regression analyses showed a significant positive relationship with %OM (r² = 0.88) and significant negative relationship with chl a (r² = 0.77) and AFDM (r² = 0.63). Algal taxa were dominated by Cladophora glomerata, Melosira varians and Pleurosira laevis. There was a significant positive relationship between treatment velocity and % C. glomerata (p = 0.007, r² = 0.87) as diatoms were differentially removed with increasing treatment velocity. Our results demonstrate that pulsed flows can reduce periphyton standing crops in the Jackson River, but the discharge required to achieve this reduction would probably need to produce near‐bed velocities >100 cm s^?1. Further study is needed to establish specific flow targets and evaluate the direct and indirect effects of pulsed flows on ecological conditions in the Jackson River. Copyright © 2009 John Wiley & Sons, Ltd.     

Nitrogen processing by biofilms along a lowland river continuum

While numerous studies have examined N dynamics along a river continuum, few have specifically examined the role of biofilms. Nitrogen dynamics and microbial community structure were determined on biofilms at six sites along a 120 km stretch of the lowland Ovens River, South Eastern Australia using artificial substrates. Terminal restriction fragment length polymorphism (T‐RFLP), chlorophyll a and protein analyses were used to assess biofilm microbial community composition. N dynamics was determined on the biofilms using the acetylene (C₂H₂) block technique and assessing changes in NH, NO_x and N₂O. Unlike microbial community structure, N dynamics were spatially heterogeneous. Nitrification, determined from the difference in accumulation of NH before and after addition of C₂H₂, occurred mostly in the upper sites with rates up to 1.4 × 10^?5 mol m^?2 h^?1. The highest rates of denitrification occurred in the mid‐reaches of the river (with rates up to 1 × 10^?5 mol m^?2 h^?1) but denitrification was not detected in the lower reaches. At the very most, only 50% of the observed uptake of NO_x by the biofilms following addition of C₂H₂ could be accounted for by denitrification. Copyright © 2005 John Wiley & Sons, Ltd.     

Simultaneous nitrification/denitrification in an aerobic biofilm system

In the biological pretreatment of landfill leachate in Mechemich (Germany) a loss of inorganic nitrogen of up to 90% was observed in the nitrification step (rotating biological contactor) under low DO conditions. Ammonia was removed but only small amounts of nitrate were produced. Nitrite accumulation did not occur. In aerobic batch tests nitrogen loss was confirmed without any addition of organic substrate, even when homogenizing the biofilm mechanically to destroy possible anoxic microzones. N₂ was measured as the gaseous end product of the process. From results presented it can be assumed that a largely autotrophic microorganism population performed this aerobic nitrification/denitrification.     

Periphyton contribution to nitrogen dynamics in the discharge from a wastewater treatment plant

To evaluate the importance of periphyton to nitrogen dynamics in the discharge from wastewater treatment plants (WWTPs), we examined changes in total and inorganic nitrogen content downstream from a WWTP on the Kurose River in Hiroshima Prefecture, Japan. At 0.7 km downstream of the WWTP (point A), NH₄⁺?N was the dominant form of inorganic nitrogen, but concentrations decreased rapidly to 5 km downstream (point B). In contrast, no significant change in the [NO₂^?+ + NO₃^?]?N concentration was observed between the two points. Total nitrogen (TN) load decreased significantly between the two points, suggesting that sorption and/or denitrification occurred in the river channel. Potential rates of nitrogen sorption and transformation by periphyton were determined in a loboratory experiment in which changes in the nitrogen content of river water were examined in an acrylic chamber with periphyton. Nitrification and nitrogen removal occurred mainly in the periphyton. The contributions of periphyton activity to TN and NH₄⁺?N decrease in the field, as estimated from the results of the laboratory experiments, were 6–18% and 23–72%, respectively. These results suggest that periphyton plays an important role in decreasing NH₄⁺?N concentration in the discharge from wastewater treatment plants.     

Population dynamics and biofilm composition in a new three-phase circulating bed reactor

The biofilm characteristics of a novel three-phase reactor, the circulating bed reactor (CBR), were studied using industrial prototype fed with primary and secondary settled effluent in conditions of tertiary N and secondary C+N nitrification. The results showed a high nitrification rate close to the intrinsic values for N and C+N conditions: up to 2 and 0.6 kgN-NH₄ m^-3 d^-1, or 1.88±0.26 and 0.22±0.07 gN g^-1 PR d^-1, respectively. The application of an integrated approach for biofilm analysis enabled the better understanding of biofihn dynamics. The biofilm remained relatively thin, below 100 μm, indicating an effective control of the biofilm development. Protein, measured by the conventional colometric method and pyrolysis-GCMS, was the major fraction accounting for up to 35% of the biomass dry weight and 58% of the biopolymer content. The polysaccharide's fraction remained very low (<3%). The ribosomal RNA probes analysis confirmed the predominance of bacterial cells in the CBR biofilm (80–86% of bacteria versus the universal probe) showing a high proportion of nitrifying bacteria accounting for up to 50% and 27% in the N and C+N removal respectively. Nitrosomonas predominated in tertiary nitrification whereas carbon input led to the appearance of other ammonia oxidizers. This particular composition was characterized by a high state of oxidation of the biomass, expressed by the low COD/DW ratio of about 0.85. In conclusion, it can be stated that this new three-phase bioreactor ensures a high nitrification rate through an effective biofilm control promoting the development of bacterial cells, especially nitrifying bacteria, and minimizing exopolysaccharides production.     

Serial discontinuities in a Rocky mountain river. I. Distribution and abundance of plecoptera

Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m^?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m^?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m^?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m^?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m^?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river.     

Recruitment of Heliozoa, rhizopods and rotifers from the sediments of an extremely acidic lake during spring and early summer

The goal of this study was to investigate the recruitment of zooplankton from the littoral sediment of Lake 111, an acidic lake in north‐east Germany, in April (spring) and June (early summer), and its role in coupling the benthos and the pelagic. Maximum heliozoan and rhizopod recruitment occurred in early summer from sediment cores incubated at ambient water temperatures (20°C). Conversely, recruitment of the rotifer Cephalodella sp. was highest in spring at ambient spring temperatures of 12°C. A combination of passive and active recruitment processes is likely responsible. The seasonal abiotic and biotic sediment characteristics were relatively constant and therefore not likely responsible for the observed temporal recruitment pattern. The sediment water and carbon content ranged from 20 to 50% (mean = 29 ± 6% standard deviation) and 2–12% (mean = 5 ± 2% standard deviation), respectively. Similarly, there was little variation in the chlorophyll‐a (mean = 0.2 ± 0.2 µg Chl‐a g^?1 dry weight ≡ 6.1 ± 3.9 mg Chl‐a m^?2). The in situ sediment bacterial density (0.82 × 10⁹ ± 0.26 × 10⁹ g^?1 dry weight ≡ 1.01 × 10⁹ ± 0.34 × 10⁹ cells cm^?3) was high. In contrast, the abundance of zoobenthos and their resting stages was low (< 25 individuals cm^?3, and mean of 90 ± 75 cysts cm^?3, respectively), with no temporal pattern being observed. Temperature was the only abiotic factor influencing recruitment. This study suggests that, even in relatively young, chemically extreme lakes, the benthos can play an important role in whole lake microbial processes and zooplankton community composition. Such benthic repositories of resting stages potentially provide protection against adverse environmental changes.     

Colorado river benthic ecology in Grand Canyon,Arizona, USA: dam,tributary and geomorphological influences

The serial discontinuity concept (SDC; Ward and Stanford, in Ecology of River Systems, 1983) predicts that recovery of large regulated rivers over distance downstream from a dam is limited by relative tributary size; however, channel geomorphology may also influence the recovery process. We examined the spatial variation in water quality, benthic composition and ash-free dry standing biomass (AFDM) among the bedrock-defined geomorphological reaches in three turbidity segments of the Colorado River between Glen Canyon Dam and Diamond Creek, Arizona, including most of the Grand Canyon. This 387-km long study area supported virtually no Ephemeroptera, Plecoptera or Trichoptera, probably because cold, stenothermic, hypolimnetic releases limited maximum aestival warming to 17·1°C. The benthos displayed abrupt, physically related decreases in AFDM over distance from the dam and in the varial zone. The 26-km long clear water segment between the dam and the Paria River supported a depauperate Cladophora glomerata/epiphyte/chironomid/Gammarus lacustris/lumbricine/Physella sp. assemblage, and ooze-dwelling oligochaetes. This segment contained 6·9% of the aquatic habitat below the 140 m³/s (normal minimum) discharge stage of the Colorado River study area, but supported 63·5% of the benthic primary producer AFDM and 87% of the benthic consumer AFDM in the entire study area. Turbidity increased and light penetration decreased immediately downstream from the confluence of the small, turbid Paria River, and further downstream from the Little Colorado River confluence. The benthos downstream from the Paria River was abruptly replaced by an Oscillatoria/Simuliium assemblage with a mean AFDM of <0·12 g C/m². Dam-related effects on water clarity, varial flow and water temperature overrode geomorphological influences on habitat availability. These results generally support the SDC, in that recovery of the benthos did not take place over distance in this large river ecosystem; however, geomorphological differences in substratum availability between reaches mediated dam and tributary effects on water clarity and benthic AFDM. Interactions between flow regulation and geomorphology produce a pattern of circuitous recovery of some physical river ecosystem characteristics over distance from the dam, but not of the benthos. Improving discharge management for endangered native fish populations requires detailed understanding of existing and potential benthic development, and trophic interactions, throughout the geomorphological reaches and turbidity segments in this river. © 1997 John Wiley & Sons, Ltd.     

Deoxygenation potential of the Richmond River Estuary floodplain,northern NSW,Australia

Periodic deoxygenation events (DO < 1 mg/L) occur in the Richmond River Estuary on the east coast of Australia following flooding and these events may be accompanied by total fish mortality. This study describes the deoxygenation potential of different types of floodplain vegetation in the lower Richmond River catchment and provides a catchment scale estimate of the relative contribution of floodplain vegetation decomposition to deoxygenation of floodwaters. Of the major vegetation types on the floodplain slashed pasture was initially (first 5 to 7 h) the most oxygen demanding vegetation type after inundation (268 ± mg O₂ m^?2 h^?1), followed by dropped tea tree cuttings (195 ± 18 mg O₂ m^?2 h^?1) and harvested cane trash (110 ± 8 mg O₂ m^?2 h^?1). However, 10 h after inundation the oxygen consumption rates of slashed pasture (105 ± 5 mg O₂ m^?2 h^?1) and tea tree cuttings (59 ± 7 mg O₂ m^?2 h^?1) had decreased to a rate less than the harvested cane trash (110 ± 8 mg O₂ m^?2 h^?1). The oxygen demands of the different floodplain vegetation types when inundated were highly correlated with their nitrogen content (r² = 0.77) and molar C:N ratio (r² = 0.82) reflecting the dependence of oxygen demand of vegetation types on their labile carbon content. The floodplain of the lower Richmond River (as flooded in February 2001) has the potential to deoxygenate about 12.5 × 10³ mL of saturated freshwater at 25°C per day which is sufficient to completely deoxygenate floodwater stored on the floodplain with 3 to 4 days. In addition, oxidation of Fe²⁺ mobilized during the decomposition of floodplain vegetation via iron reduction and discharged from groundwater and surface runoff in acid sulfate soil environments could account for about 10% of the deoxygenation of floodwater stored on the floodplain. Management options to reduce floodplain deoxygenation include removing cuttings from slashed pasture and transporting off‐site, reducing slashed pasture windrow loads by using comb‐type mowers, returning areas of the floodplain to wetlands to allow the establishment of inundation tolerant vegetation and retaining deoxygenated floodwaters in low lying areas of the floodplain to allow oxygen consumption process to be completed before releasing this water back to the estuary. Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of residence time on summer nitrate uptake in mississippi river flow‐regulated backwaters

Nitrate uptake may be improved in regulated floodplain rivers by increasing hydrological connectivity to backwaters. We examined summer nitrate uptake in a series of morphologically similar backwaters on the Upper Mississippi River receiving flow‐regulated nitrate loads via gated culverts. Flows into individual backwaters were held constant over a summer period but varied in the summers of 2003 and 2004 to provide a range of hydraulic loads and residence times (τ). The objectives were to determine optimum loading and τ for maximum summer uptake. Higher flow adjustment led to increased loading but lower τ and contact time for uptake. For highest flows, τ was less than 1 day resulting in lower uptake rates (U_net < 300 mg m^?2 day^?1), low uptake efficiency (U% < 20%) and a long uptake length (S_net > 4000 m). For low flows, τ was greater than 5 days and U% approached 100%, but U_net was 200 mg m^?2 day^?1. S_net was < half the length of the backwaters under these conditions indicating that most of the load was assimilated in the upper reaches, leading to limited delivery to lower portions. U_net was maximal (384–629 mg m^?2 day^?1) for intermediate flows and τ ranging between 1 and 1.5 days. Longer S_net (2000–4000 m) and lower U% (20–40%) reflected limitation of uptake in upper reaches by contact time, leading to transport to lower reaches for additional uptake. Uptake by ～10 000 ha of reconnected backwaters along the Upper Mississippi River (13% of the total backwater surface area) at a U_net of ～630 mg m^?2 day^?1 would be the equivalent of ～40% of the summer nitrate load (155 mg day^?1) discharged from Lock and Dam 4. These results indicate that backwater nitrate uptake can play an important role in reducing nitrate loading to the Gulf of Mexico. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of dissolved oxygen on nitrification kinetics in a circulating bed reactor

The influence of dissolved oxygen concentration in nitrification kinetics was studied in a new biofilm reactor, the circulating bed reactor (CBR). The study was carried out partly at laboratory scale with synthetic water containing inorganic carbon and nitrogen compounds, and partly at pilot scale for secondary and tertiary nitrification of municipal wastewater.The experimental results showed that either the ammonia or the oxygen concentration could be limiting for the nitrification rate. The transition from ammonia to oxygen limiting conditions occurred for an oxygen to ammonia concentration ratio of about 1.5 - 2 gO₂/gN-NH₄⁺ for both laboratory- and pilot-scale reactors. The nitrification kinetics of the laboratory-scale reactor was close to a half order function of the oxygen concentration, when oxygen was the rate limiting substrate.     

The Interplay between Environmental Conditions and Filamentous Algae Mat Formation in Two Agricultural Influenced South African Rivers

The regulation of nutrient inputs into rivers dominated by agriculture land use activities is an important aspect of ecological resilience of aquatic systems and the management of river eutrophication. The overabundance of benthic filamentous algae mats in river systems due to nutrient enrichment can modify the habitats of macroinvertebrate and fish communities as well as clogging irrigation crop sprayers of downstream water users. The current study examined over a period of 2 years (2013–2014) the interplay between physical and chemical river characteristics and epilithic filamentous algae biomass in two South African agricultural influenced rivers. The study area consisted of the Touw and Duiwe Rivers, which run into a proclaimed Ramsar site, namely, the Wilderness Lake System. A strong positive correlation was observed between the maximum filamentous algae biomass (97 chl‐a mg m^?2) observed during the dry season and the average water column alkalinity >30 mg l^?1. The benthic trophic status of the nine sampling sites during the dry seasons indicated the highest benthic algae biomass with mesotrophic (1.7–21 chl‐a mg m^?2) to hypertrophic (>84 chl‐a mg m^?2) conditions. During the dry season, only three sampling sites were below the suggested guideline value (35 µg l^?1) for total phosphorus (TP), while four sampling sites were below the total nitrogen guideline of 252 µg l^?1. In the wet season, two sites were below TP values with five sites below total nitrogen guideline values. From the data gathered, it was evident that water column alkalinity and hardness were the main drivers for the formation or absence of benthic filamentous algae mats in the two river systems and that nitrogen and/or phosphorus concentrations was overshadowed by the physical and chemical characteristics of the river systems at certain sites. Nutrient results for the river bottom sediments revealed that the sediment qualities were variable at the different sampling sites, but more specifically along the longitudinal paths of flow. It was apparent that the high TP concentrations in the water column and bottom sediment, which were lowest during the dry season, were associated with the highest epilithic filamentous algae mat formation. The outcome of the current study shows that a more holistic approach must be followed for the development of future eutrophication guidelines and nutrient thresholds in South African rivers influenced by agriculture land use activities. Copyright © 2016 John Wiley & Sons, Ltd.     

Seasonal dynamics of light absorption by suspended particulate matter and CDOM in highly turbid inland rivers on the Loess Plateau,China

The spectral characteristics of optically active constituents in water are key parameters in bio‐optical modelling. Light absorption by phytoplankton [a_ph(λ)], nonalgal particles (NAPs) [a_NAP(λ)], and chromophoric dissolved organic matter (CDOM) [a_CDOM(λ)] was investigated at 28 sites in the Wuding River (WDR) during the abundant river flow period (AP) in July 2017 and the normal river flow period (NP) in May 2018. The water quality parameters in the WDR substantially differed between the AP and NP. The dissolved organic carbon and turbidity were high in the NP, and chlorophyll a (Chl‐a), total suspended matter (TSM), dissolved oxygen concentrations and electrical conductivity were low in the AP. a_p(675) and Chl‐a were more strongly correlated in the NP (r=0.96) than in the AP (r=0.41). a_NAP(440) and a_NAP(675) were strongly correlated with TSM (r=0.98 and 0.97) in the AP but weakly correlated in the NP. Moreover, a_ph(λ) was positively correlated with Chl‐a in both the AP and NP. In addition, a_CDOM(440) was significantly correlated with Chl‐a (r=0.62, p<.001) in the NP but not the AP. TSM was weakly correlated with a_CDOM(440) in both the AP and NP. The S_275‐295 values in the NP (0.0147‐0.020 nm^‐1) were lower than those in the AP, demonstrating that the molecular weights were higher in the AP than in the NP. The photosynthetically active radiation absorption of most samples was dominated by the NAPs and CDOM, implying a crucial role in light attenuation in highly turbid inland rivers on the Loess Plateau.     

Physicochemical characteristics of Lake IRAD, an artificial lake in Wakwa region, Cameroon

Wakwa is a region in north Cameroon characterized by intensive cattle production. This study evaluated the physicochemical characteristics of the waters in Lake IRAD, located near Wakwa, which is the main water source for cattle grazing in this area. Water samples were collected at four sampling sites during the rainy and dry seasons (April, July, October and February). The chemical composition of the water samples was analysed for various constituents, including nitrate (NO₃^–), chloride (Cl^?), phosphate (PO₄^3?), bicarbonate (HCO₃^?), calcium (Ca), magnesium (Mg), manganese (Mn), aluminium (Al), zinc (Zn), copper (Cu), iron (Fe), nickel (Ni), cadmium (Cd), ammonia–nitrogen (NH₄–N) and organic matter (OM). The mineral composition varied significantly (P < 0.05) with the sampling period. High concentrations of zinc (0.96 mg L^?1) and dissolved iron (1.23 mg L^?l) were observed during the dry season. Total iron (3.25 mg L^?1), OM (15.4 mg of O₂ L^?1), nitrate (28.82 mg L^?1) and NH₄–N (1.05 mg L^?1) concentrations were highest during the rainy season. The iron, OM and NH₄–N concentrations were higher than the USEPA‐recommended values (0.2 mg L^?1, 4 mg of O₂ L^?1 and 0.5 mg L^?1, respectively). The phosphate, copper, nickel and cadmium concentrations, considered as the polluting substances, were present in negligible concentrations, being below the detection limits of the analytical techniques used to measure them. The high iron, OM and nitrogen concentrations were attributed to water‐leached soil run‐off, as well as the activity of animals in the lake. Sampling sites 1 and 2, which were used mostly by cattle, were observed to have the highest concentrations of NH₄–N, compared with sites 3 and S (exit point). It will be necessary to delimit cattle access points to the lake to reduce this type of contamination of drinking water.     

Nitrogen Dynamics in Sandy Freshwater Sediments (Saginaw Bay,Lake Huron)

Sediment-water nitrogen fluxes and transformations were examined at two sites in Saginaw Bay, Lake Huron, as a model for sandy freshwater sediments. Substantial ammonium release rates (74 to 350 μmole NH₄⁺/m²/h¹) were observed in flow-through cores and in situ benthic chamber experiments. Sediment-water ammonium fluxes were similar at the inner and outer bay stations even though inner bay waters are enriched with nutrients from the Saginaw River. The high net flux of remineralized ammonium into the overlying water from these sandy sediments resembles typical data for marine systems (11 to 470 μmole NH₄⁺/m²/h¹) but were higher than those reported for depositional freshwater sediments (0 to 15 μmole NH₄⁺/m²/h¹; Seitzinger 1988). Addition of montmorillonite clay (ca. 1 kg dry weight/m²) to the top of the sandy cores reduced ammonium flux. Mean “steady-state” ammonium flux following clay addition was 46 ± 2 (SE) % of the initial rates as compared to 81 ± 8% of the initial rates without clay addition. Zebra mussel excretion dominanted ammonium regeneration in the inner bay where the bivalve was abundant, but addition of zebra mussel feces/psuedofeces (3.0 g dw/m²) to sediments did not increase ammonium or nitrate flux. Partial nitrification of ammonium at the sediment-water interface was suggested by removal of added ¹⁵NH₄⁺ from lake water passing over dark sediment cores. Sediment-water fluxes of nitrogen obtained from flow-through sediment cores resembled those from in situ benthic chambers. However, extended static incubations in gas-tight denitrification chambers caused more of the regenerated nitrogen to be nitrified and denitrified than occurred with the other two measurement systems.     

Eutrophication of lakes in urbanized areas: The case of Yaounde Municipal Lake in Cameroon, Central Africa

A 1 year qualitative and quantitative evaluation of phytoplankton and chlorophyll‐a, as well as some physicochemical parameters, was recorded in a shallow tropical lake in Cameroon: the Yaounde Municipal Lake. Physicochemical measurements also were regularly made in its main tributary (Mingoa Stream). These analyses aimed to assess the lake's trophic status and to propose measures for controlling its degradation process. The Secchi disk transparency was low and rarely exceeded 100 cm. Conductivity was higher near the lake bottom. The oxygen deficiency, and sometimes anoxia, recorded from a 2.5 m depth leads to high quantities of ammonium‐nitrogen. The total phosphorus concentrations varied from 80–2290 µg P L^?1 and the total Kjeldhal nitrogen concentrations fluctuated between 3 and 15 mg  L^?1. Upstream to the lake, in the Mingoa Stream, total phosphorus concentrations ranged from 0.6–3.8 mg P L^?1 and total Kjeldhal nitrogen concentrations ranged from 10–22 mg  L^?1. There are up to 102 phytoplankton‐specific taxa, with Euglenophyta and Chlorophyta particularly more diversified. The phytoplankton biomass and chlorophyll‐a concentrations reached 225 µg mL^?1 and 566 mg m^?3, respectively. The analyses pointed out the allogenic nature of the functioning of this ecosystem as a result of bad waste management in the surrounding landscape. Urgent actions need to be undertaken in order to rehabilitate this lake, which rapidly shifted to a hypertrophic status.     

Response of phytoplankton from the metalimnetic chlorophyll maximum to macro- and micro-nutrients amendments in Lake Geneva

Despite re-oligotrophication and low trace elements concentrations, direct determination of limiting nutrient(s) of the phytoplankton community in Lake Geneva is still missing. Incubation experiments were carried out with either addition of phosphate (+P), nitrate (+N), reactive silica (+Si), iron (+Fe), nickel (+Ni) and molybdenum (+Mo) to surface water collected between 9 and 12?m, during seasonal fieldtrips in 2015. Macro- and micro-nutrients, dissolved concentrations, temperature and irradiance as well as chlorophyll a (Chl a) levels, Chl a:POC ratios, POP:POC ratios and Chl a variable fluorescence parameters were quantified. The rapid phosphorus consumption, elevated inorganic nitrogen to phosphorus ratios and increased Chl a, Chl a:POC and POP:POC, in response to P additions, all indicated a phosphorus limitation in phytoplankton. Moreover, none of the measured parameters differed significantly from the control in the other treatments. These results were also confirmed by the response of Chl a variable fluorescence. The effective photosystem II quantum yield in ambient light, the absolute electron transfer rate and the connectivity, under 53?μmol photons/m²/s illumination, significantly increased while the non-photochemical quenching decreased in the +P treatment. Phytoplankton cells supplemented with phosphate were thus more efficient to capture photons and to drive them into photochemistry at light levels close to in situ levels. This is the first study to demonstrate directly a phosphorus limitation in Lake Geneva, pointing towards the success of its re-oligotrophication process.     

HIGH RATES OF PRIMARY PRODUCTIVITY IN A SEMI‐ARID TAILWATER: IMPLICATIONS FOR SELF‐REGULATED PRODUCTION

Reservoir‐river systems in desert environments may provide the optimal combination of environmental conditions (e.g. light, nutrients, temperature, and flow) that maximizes primary production in downstream reaches. Stream metabolism was measured using an open‐system approach each month during spring‐summer in a semi‐arid tailwater (South Fork Humboldt River) in the central Great Basin, USA. Spatial and temporal differences in metabolic rates were evident despite tailwater reaches sustaining comparable standing stocks of periphyton (>10 µg chla cm^?2) during this growing season. Primary productivity was highest (15 to 36 g O₂ m^?2 day^?1) in July, supporting previous studies that have described arid regulated/unregulated streams as ultra‐productive. Substrate availability when combined with self‐shading and hypoxic conditions created a system that was likely near the maximal productivity that stream systems can achieve because of the self‐regulating attributes that thick periphyton mats impose upon themselves as they reach high biomass and maximal production rates. Copyright © 2011 John Wiley & Sons, Ltd.