Mean Total Phosphorus Research Articles

Effects of water temperature on summer periphyton biomass in shallow lakes: a pan-European mesocosm experiment

Periphyton communities play an important role in shallow lakes and are controlled by direct forces such as temperature, light, nutrients, and invertebrate grazing, but also indirectly by planktivorous fish predation. We performed a pan-European lake mesocosm experiment on periphyton colonization covering five countries along a north/south geographical/temperature gradient (Estonia, Germany, Czech Republic, Turkey, and Greece). Periphyton biomass on artificial polypropylene strips exposed at 50 cm water depth at low and high nutrient regimes (with mean total phosphorus concentration of 20 and 65 µg L−1, respectively) was compared during mid-summer. No significant effect of nutrient loading on periphyton biomass was observed as nutrient concentrations in the mesocosms were generally above limiting values. Water temperature significantly enhanced summer periphyton biomass development. Additionally, direct and indirect top-down control of snails and fish emerged as a significant factor in periphyton biomass control.

Removal efficiencies of vegetation-specific filter strips on nonpoint source pollutants

A field experiment was conducted to examine the removal efficiencies of different autochthonous vegetation-specific filter strips on nonpoint source pollutants (NPSPs) and to identify their major influencing factors under various conditions. Furthermore, the effects of five major influencing factors on the removal efficiencies were analyzed. We found that the removal efficiencies in total suspended solid (SS), total nitrogen (TN) and total phosphorus (TP) of the grass vegetation filter strip were significantly higher than those of the seabuckthorn bushy vegetation filter strip. The averaged SS concentration and mass removal efficiencies of the VFS were commonly above 90%, respectively. The TN concentration removal efficiency ranged from 50 to 70%, and the mean TN mass removal efficiency ranged from 70 to 90%. The mean concentration and mass removal efficiencies in particulate nitrogen (PN) were approximately 85 and 95%, respectively. However, the concentration and mass efficiencies in dissolved nitrogen (DN) were lower. The TP concentration removal efficiency averaged 86%, and the mean TP mass removal efficiency was about 94%. The mean concentration and mass removal efficiencies in particulate phosphorus (PP) were approximately 88 and 96%, respectively. Moreover, the concentration and mass efficiencies in dissolved phosphorus (DP) were not significantly high. This suggests that PN is the main loss form of N and PP is the major loss form of P. Overall, the mass removal efficiencies of various species of VFS on nonpoint source pollutants in various forms were higher than the concentration removal efficiencies. Additionally, the removal efficiencies of VFS on nonpoint source pollutants were subject to many factors such as vegetation coverage, initial soil water content, width of VFS, inflow discharge and inflow concentration. However, the most important influencing factors are vegetation coverage, width of VFS and inflow concentration. The width of VFS plays an essential role in N and P removal efficiencies, in that even though the width of VFS is longer, the removal efficiency of VFS is not really better. Additionally, the removal of SS should be firstly considered during the course of the application of VFS due to the SS correlating well linearly with TN and TP. Nevertheless, routine maintenance is also quite necessary to keep in good removal performance of VFS.

Predicting the Distribution of Naturally Occurring Phosphatic Soils across a Countywide Landscape, Florida, USA

We used a GIS approach to test a conceptual soil-landscape model which integrates topographic, geologic and soil information for predicting the distribution of phosphatic soils. The hypothesis was that phosphatic soils occur on erosional landscapes where phosphatic geologic materials are exposed at or near land surface. Areas of high (scarp), medium (plain), and low (plateau) likelihood of such exposure were delineated based on topographic and geologic information. An initial predictive phosphatic soils map was created and validated by field sampling. Samples were taken at two depths: upper (0–25 cm) and lower (100–125 cm); and the total phosphorus (TP) was determined. Mean TP concentration for the lower depth was 6195 mg kg−1 for the scarp, 2485 mg kg−1 for the plain, and 193 mg kg−1 for the plateau. The initial map was revised to show that the probability of finding a phosphatic soil was highest for the scarp region (73%), medium for the plain region (33%), and lowest for the plateau region (7%).

Nutrient concentrations and fluxes in the upper catchment of the Miyun Reservoir, China, and potential nutrient reduction strategies.

The Miyun Reservoir is Beijing's main drinking water source. Increased nutrient levels in the reservoir have resulted in an increased risk of harmful algal blooms. One hundred ten water samples were collected at a range of spatial scales in the upper catchment of the Miyun Reservoir and were analyzed for total nitrogen (TN), nitrate (NO3 (-)-N), ammonium (NH4 (+)-N), total phosphorus (TP), and the potassium permanganate index (CODMn). Empirical equations were developed from relationships between nutrient concentrations and the main controls on nutrient, and were used to identify parts of the catchment that should be targeted with nutrient load reduction measures. Cropland was the main source of sediment for the streams, and much of the phosphorus was associated with sediment. The annual mean TP concentrations were closely correlated with both the annual mean suspended sediment concentrations and the ratio of the cropland area to the total basin area. There was a linear relationship between the annual mean TN concentration and the population density in the basins. Soil conservation may play an important role in reducing TP concentrations in the upper reaches of the Chao and Bai Rivers. It may be useful to (1) construct natural riparian buffers and vegetated buffers along croplands close to the watercourses, (2) implement management strategies to reduce nitrogen (N) fertilizer applications, and (3) construct additional wetlands to reduce nutrient loads in the study area.

Vertical distribution and retention mechanism of nitrogen and phosphorus in soils with different macrophytes of a natural river mouth wetland

Wetland vegetation can improve water quality through several processes including direct assimilation and the indirect effects of sedimentation and mineralization. This research takes the Zhucao River mouth of Daxi reservoir as a study case to investigate the vertical distribution of nitrogen and phosphorus in the soil of a natural wetland covered by different plants prior to any restoration action. There are four native emergent macrophytes (Typha latifolia L., Polygonum hydropiper L., Juncus effuses L., Phragmites communis L.) in the wetland. The total nitrogen (TN) and nitrate contents decreased with the soil depth for all vegetation types, and the mean TN and nitrate concentrations were higher in vegetative soil than in bare ground. The maximum TN concentration was found in the surface soil (0-2cm) covered by P. communis. Ammonium decreased with the soil depth in vegetative areas, while it increased with soil depth in bare ground. The rank order of P fractions was organic P (OP) > P associated with Ca (Ca-P) > P associated with Fe/Al (Fe/Al-P). Total phosphorus (TP) and OP showed vertical profiles similar to that of TN. The mean concentrations of TP, Ca-P and Fe/Al-P were higher in vegetative soil than in bare ground. The maximum mean TP was also found in soil covered by P. communis. Loss on ignition (LOI) was significantly correlated with TN and TP (P < 0.05). Organic matter accumulation may be the main pathway to retain nitrogen and phosphorus in the wetland. Nitrogen and phosphorus sequestration in P. communis soil was the highest of the four dominant plants. The results could support the restoration of other degraded river mouth wetlands of the reservoir.

Effects of nitrogen and phosphorus load reduction on benthic phosphorus release in a riverine lake

The Lower Havel in Berlin is a polymictic riverine lake, thermally stratified for some days or weeks in summer. It is characterized by a relatively high mean total phosphorus concentration (145 µg l−1) and frequent cyanobacteria mass development in summer. We quantified the potentially mobile P pool in sediments, determined P fluxes based on conventional dialysis sampler-, gel probe- and benthic chamber measurements, and combined this with column experiments and P budget calculations to evaluate whether a) a reduction of P loading would be counterbalanced by P release from sediment, and b) release of redox sensitive P would even increase with reduction of nitrogen loading. The potentially mobile P pool was relatively small (228 t) compared to mean annual external load (190 t a−1) and gross P release (1.2–36 mg m−2 day−1), and was thus of little relevance for long-term P availability. Despite 38 % of P in the sediment being redox sensitive, the seasonal course of P gross release was mainly driven by redox independent organic matter mineralization of diagenetically young surface sediment. Under anoxic conditions, P release was higher than under oxic conditions and to some extent controlled by nitrate under laboratory conditions. However, ambient nitrate availability was too low to affect P release which was more dependent on mineralization and Fe availability than on redox. Therefore, the Lower Havel would benefit from P load reduction but internal P loading would be largely unaffected from further N load reduction.

Biomass accumulation and nutrient uptake of 16 riparian woody plant species in Northeast China

Our research focused on eutrophication control and species screening for riparian zone vegetation restoration in the upstream reach of the Hun River. We studied 16 hardwood plant species to investigate nutrient concentrations and nitrogen and phosphorus accumulations. After about 120 days of growth in pots, these 16 species varied in dry matter biomass, ranging from 15.13 to 637.16 g. Total nitrogen (TN) and total phosphorus (TP) concentrations and distribution in roots, stems and foliage differed both within and between tested species. Mean TN and TP accumulation ranged from 0.167 to 14.730 g per plant and from 0.016 to 1.20 g, respectively. All 16 species, but especially Lespedeza bicolor, Robinia pseudoacacia and Sorbaria sorbifolia had strong potential to remove TN and TP from soil and could be widely utilized for the restoration of destroyed riparian zones in northeast China.

Occurrence and mass development of Mougeotia spp. (Zygnemataceae) in large, deep lakes

Over the last decades, mass developments by the filamentous conjugating green alga Mougeotia have been followed in three large peri-alpine lakes (Lake Geneva, Lake Garda, Lake Maggiore) and in the sub-tropical Lake Kinneret. The aim of this study is to highlight annual and interannual patterns of Mougeotia biomass in the studied lakes and select key environmental parameters that may favour and maintain its mass development. Our results confirm former studies that planktic Mougeotia favours meso-oligotrophic conditions and becomes dominant when annual mean total phosphorus concentrations in the epilimnion fall below 20 µg l−1. This triggering factor has effect with interactions of other environmental circumstances such as the water column stability. Physiological and morphological features of the taxon make it a successful competitor under stratified conditions. Results also showed that in three out of the four studied lakes, the annual peak was higher when the annual population development started earlier. Focusing on Lake Geneva, depth and strength of the thermocline, as well as wind speed in the beginning of summer that can cause nutrient replenishment and mix the epilimnion are key factors in the blooming of the taxon.

Eutrophic urban ponds suffer from cyanobacterial blooms: Dutch examples.

Ponds play an important role in urban areas. However, cyanobacterial blooms counteract the societal need for a good water quality and pose serious health risks for citizens and pets. To provide insight into the extent and possible causes of cyanobacterial problems in urban ponds, we conducted a survey on cyanobacterial blooms and studied three ponds in detail. Among 3,500 urban ponds in the urbanized Dutch province of North Brabant, 125 showed cyanobacterial blooms in the period 2009-2012. This covered 79% of all locations registered for cyanobacterial blooms, despite the fact that urban ponds comprise only 11% of the area of surface water in North Brabant. Dominant bloom-forming genera in urban ponds were Microcystis, Anabaena and Planktothrix. In the three ponds selected for further study, the microcystin concentration of the water peaked at 77 μg l(-1) and in scums at 64,000 μg l(-1), which is considered highly toxic. Microcystin-RR and microcystin-LR were the most prevalent variants in these waters and in scums. Cyanobacterial chlorophyll-a peaked in August with concentrations up to 962 μg l(-1) outside of scums. The ponds were highly eutrophic with mean total phosphorus concentrations between 0.16 and 0.44 mg l(-1), and the sediments were rich in potential releasable phosphorus. High fish stocks dominated by carp lead to bioturbation, which also favours blooms. As urban ponds in North Brabant, and likely in other regions, regularly suffer from cyanobacterial blooms and citizens may easily have contact with the water and may ingest cyanobacterial material during recreational activities, particularly swimming, control of health risk is of importance. Monitoring of cyanobacteria and cyanobacterial toxins in urban ponds is a first step to control health risks. Mitigation strategies should focus on external sources of eutrophication and consider the effect of sediment P release and bioturbation by fish.

Comparison of digestion methods for determination of total phosphorus in river sediments

AbstractIn this study, four digestion methods used to determine total phosphorus in river sediments, including Na2CO3 fusion, the H2SO4 and H2SO4 + H2O2 methods and the SMT protocol were investigated. Interference effects of iron, calcium and organic matter in river sediments, and the substances contained in the digestion agents on the photometric determination of the phosphates were analysed. The digestion methods were tested on ten river sediment samples. Statistical analysis of the results showed significant differences between sample treatments relating to the mean total phosphorus concentration.

Controlling eutrophication by combined bloom precipitation and sediment phosphorus inactivation

The hypothesis that the combination of the flocculent polyaluminium chloride (PAC) with the lanthanum-modified bentonite Phoslock® (Flock & Lock) could sink effectively a water bloom of cyanobacteria and could shift a turbid, cyanobacteria infested lake to a clear water lake was tested in a controlled laboratory experiment and a whole lake experiment. In the laboratory, a relatively low dose of the flocculent PAC (2.2 and 4.4 mg Al l−1) was insufficient to sediment positively buoyant cyanobacteria (Microcystis aeruginosa). Similarly, the lanthanum modified clay (dosed at 390 mg l−1) was insufficient to sediment the positively buoyant cyanobacteria. However, the combination of PAC and Phoslock® effectively sedimented cyanobacteria flocks. Likewise, a combined treatment of 2 tons PAC and 18 tons Phoslock® in Lake Rauwbraken in April 2008 effectively sedimented a developing cyanobacteria bloom of Aphanizomenon flos-aquae. The average chlorophyll-a concentration in the two years prior to this Flock & Lock treatment was 19.5 (±36.5) μg l−1, while it was as low as 3.7 (±4.5) μg l−1 in the years following the treatment. The combined treatment effectively reduced the amount of total phosphorus (TP) in the water column from on average 169 (±126) μg P l−1 before the application to 14 (±15) μg P l−1 after the treatment. Based on mean summer chlorophyll-a and TP concentrations, the lake was shifted from a eutrophic/hypertrophic state to an oligo/mesotrophic state. From directly after treatment in April 2008 until and including 2013, Lake Rauwbraken remained in an oligo-mesotrophic clear water state with TP reduced to less than 10% of the pre-treatment. This result shows that eutrophication in relatively small, isolated, stratifying lakes can be restored by targeting both water column and sediment P using a combination of flocculent and solid phase P-sorbent.

Temporal and spatial variability of phytoplankton in Lake Poyang: The largest freshwater lake in China

The composition and both the temporal and spatial distribution of phytoplankton were studied in Lake Poyang; samples were collected every 3months from January 2009 to October 2011 at 15 sites. The phytoplankton community was found to belong to seven groups, with Bacillariophyta dominating. No significant difference was observed in the phytoplankton community structure at any of the sites (p=0.2371), except one site; however, the structure was significantly different with regard to annual and seasonal trends (p=0.0001 and p<0.0001, respectively). Aulacoseira granulata, Synedra acus, Fragilaria virescens, and Cryptomonas erosa were the main contributors to the dissimilarity in temporal distribution. Although the nutrient concentrations for 3years combined were relatively high (mean total nitrogen was 1.719mgL−1 and mean total phosphorus was 0.090mgL−1), phytoplankton biomass was low (mean total biomass of 0.203mgL−1). The underwater light condition, as indicated by the Secchi depth, was shown to be the principal limiting factor in regulating the growth of phytoplankton, and the transparency coincided with biomass variation on a seasonal level. The effect of nutrients on phytoplankton may be concealed by the water level, which varied over a wide range among different seasons. However, the annual trend for the biomass was associated with the nutrient concentration, which increased yearly and initiated the development of phytoplankton. The biomass is high in the south and low in the north, which may be the result of greater underwater light climate and high nutrient concentrations in the southern area.

Assessment of Car Wash Runoff Treatment Using Bioretention Mesocosms

Car wash runoff is known to be a pollution source to surface water bodies. Many groups hold car-washing fundraisers unaware of pollution issues associated with car wash runoff. This preliminary study investigated whether rain gardens are an appropriate management practice for reducing car wash pollutants, specifically surfactants. The concentrations of total phosphorus (TP), total suspended solids (TSS), and surfactants were measured in car wash runoff before and after treatment in three rain garden mesocosms. Mean TSS and surfactant effluent concentrations were significantly lower than the car wash runoff with TSS reductions ranging from 84 to 95% and surfactant reductions ranging from 89 to 96%. The removal efficiencies for surfactants were not enough to reduce concentrations below literature-based values for aquatic toxicity. Mean TP effluent concentrations were higher than the car wash runoff with increases ranging from 197 to 388%, although the increase was not statistically significant. This project demonstrates the potential for using bioretention to reduce pollutants associated with car wash runoff and using car wash events to educate the public about watershed protection.

Using algal metrics and biomass to evaluate multiple ways of defining concentration-based nutrient criteria in streams and their ecological relevance

We examined the utility of nutrient criteria derived solely from total phosphorus (TP) concentrations in streams (regression models and percentile distributions) and evaluated their ecological relevance to diatom and algal biomass responses. We used a variety of statistics to characterize ecological responses and to develop concentration-based nutrient criteria (derived from ecological effects) for streams in Connecticut, USA, where urbanization is the primary cause of watershed alteration. Mean background TP concentration in the absence of anthropogenic land cover was predicted to be 0.017mg/l, which was similar to the 25th percentile of all study sites. Increased TP concentrations were significantly correlated with altered diatom community structure, decreased percent low P diatoms and diatoms sensitive to impervious cover, and increased percent high P diatoms, diatoms that increase with greater impervious cover, and chlorophyll a (P<0.01). Variance partitioning models showed that shared effects of anthropogenic land cover and chemistry (i.e., chemistry affected by land cover) represented the majority of explained variation in diatom metrics and chlorophyll a. Bootstrapped regression trees, threshold indicator taxa analysis, and boosted regression trees identified TP concentrations at which strong responses of diatom metrics and communities occurred, but these values varied among analyses. When considering ecological responses, scientifically defensible and ecologically relevant TP criteria were identified at (1) 0.020mg/l for designating highest quality streams and restoration targets, above which sensitive taxa steeply declined, tolerant taxa increased, and community structure changed, (2) 0.040mg/l, at which community level change points began to occur and sensitive diatoms were greatly reduced, (3) 0.065mg/l, above which most sensitive diatoms were lost and tolerant diatoms steeply increased to their maxima, and (4) 0.082mg/l, which appeared to be a saturated threshold, beyond which substantially altered community structure was sustained. These criteria can inform anti-degradation policies for high quality streams, discharge permit decisions, and future strategies for watershed development and managment. Our results indicated that management practices and decisions at the watershed scale will likely be important for improving degraded streams and conserving high quality streams. Results also emphasized the importance of incorporating ecological responses and considering the body of evidence from multiple conceptual approaches and statistical analyses for developing nutrient criteria, because solely relying on one approach could lead to misdirected decisions and resources.

Evaluation of floating treatment wetlands as retrofits to existing stormwater retention ponds

Thousands of existing wet retention ponds have been built across the United States, primarily for the mitigation of peak flow and removal of sediment. These systems struggle to mitigate soluble nutrient loads from urban watersheds. A simple retrofit for improvement of pond performance for nitrogen and phosphorus removal could become popular. Floating treatment wetlands (FTWs), one such retrofit, are a hydroponic system that provides a growing medium for hydrophytic vegetation, which obtain nutrients from the stormwater pond. Installation of FTWs does not require earth moving, eliminates the need for additional land to be dedicated to treatment, and does not detract from the required storage volume for wet ponds (because they float). To test whether FTWs reduce nutrients and sediment, two ponds in Durham, NC, were monitored pre- and post-FTW installation. At least 16 events were collected from each pond during both monitoring periods. The distinguishing characteristic between the two ponds post-retrofit was the fraction of pond surface covered by FTWs; the DOT pond and Museum ponds had 9% and 18%, respectively, of their surface area covered by FTWs. A very small fraction of N and P was taken up by wetland plants, with less than 2% and 0.2%, respectively, of plant biomass as N and P. Temperature measurements at three depths below FTWs and at the same depths in open water showed no significant difference in mean daily temperatures, suggesting little shading benefit from FTWs. The two ponds produced effluent temperatures that exceeded trout health thresholds. Both the pre- and post-FTW retrofit ponds performed well from a pollutant removal perspective. One pond had extremely low total nitrogen (TN) effluent concentrations (0.41mg/L and 0.43mg/L) during both pre- and post-FTW retrofit periods, respectively. Floating treatment wetlands tended to improve pollutant capture within both ponds, but not always significantly. Mean effluent concentrations of TN were reduced at the DOT pond from 1.05mg/L to 0.61mg/L from pre- to post-retrofit. Mean total phosphorus (TP) effluent concentrations were reduced at both wet ponds from pre- to post-retrofit [0.17mg/L to 0.12mg/L (DOT pond) and 0.11mg/L to 0.05mg/L (Museum pond)]. The post-retrofit effluent concentrations were similar to those observed for bioretention cells and constructed stormwater wetlands in North Carolina. The DOT pond showed no significant differences between pre- and post-retrofit effluent concentrations for all nine analytes. The Museum pond had a statistically significant improvement post-retrofit (when compared to the pre-retrofit period) for both TP and total suspended solids (TSS). Wetland plant root length was measured to be approximately 0.75m, which had the benefit of stilling water flow, thereby increasing sedimentation. Results suggested that greater percent coverage of FTWs produced improved pollutant removal.

Streamflow and Nutrients from a Karst Watershed with a Downstream Embayment: Chapel Branch Creek

Understanding sources of streamflow and nutrient concentrations are fundamental for the assessment of pollutant loadings that can lead to water quality impairments. The objective of this study was to evaluate the discharge of three main tributaries, draining different land uses with karst features, as well as their combined influences on total nitrogen (TN) and total phosphorus (TP) levels in reservoir-like embayment (R-E) on a stream entering Lake Marion, South Carolina. From 2007-2009, hydrology, TN, and TP data were collected from the 1,555-ha Chapel Branch Creek (CBC) watershed. In general, monthly streamflow in all tributaries was found to be �10% of rainfall, and as little as 0.1% in the smallest tributary. The third tributary flowed into a cave system and discharged via a cave spring (CS) into the embayment while gaining a sustained groundwater flow from a second cave (GW) system. The CS flow was substantially larger than the flow measured in the other tributaries. The small amount of rainfall that became surface flow and the large flow at the cave spring indicated a significant water loss from the surface watershed to subsurface flow or a groundwater source area substantially larger than the surface watershed. Nutrient concentrations in flows from tributaries draining various land uses were not significantly different (α ¼ 0.05) for most of the locations. A simple water balance was developed to estimate the R-E outflow to Lake Marion using measured discharges from three tributaries, change in storage computed using a bathymetric survey, daily lake level changes, rainfall, and computed evaporation. Mean monthly TN and TP concentrations in the embayment were substantially lower than the observed means from the two tributary outlets and the CS into the embay- ment, indicating a loss in the embayment. The second cave system at CS, representing an unknown subsurface drainage area, was the source of nearly 50% of TP loading, over 50% of flow, and over 70% of TN loading to CBC. These results may have implications in water quality management of the CBC watershed. DOI: 10.1061/(ASCE)HE.1943-5584.0000794. © 2014 American Society of Civil Engineers.

Variation in chlorophyll a to total phosphorus ratio across 94 UK and Irish lakes: Implications for lake management

Eutrophication is the most widespread pressure impacting on lakes worldwide and, in general, its control is underpinned by the premise that algal biomass is regulated by phosphorus availability. This paper aims to demonstrate that not all lakes will conform to the underlying principle of the Chl:TP relationships using variables collected widely in lake monitoring programmes across the world (i.e. total phosphorus (TP) and chlorophyll a (Chl) concentrations). The ratio of annual mean Chl and TP concentrations in 94 lakes (2007 and 2008) was used as a measure of the efficiency with which TP is transferred into algal biomass (i.e. as an indicator of P limitation) to investigate the validity of the phosphorus reduction approach. Chl:TP ratios ranged from 0.02 to 0.84 in 2007 and from 0.03 to 0.96 in 2008. Chl and TP values were positively correlated (p < 0.05) with alkalinity, and negatively correlated with depth and surface area, in both years. In general, mean annual Chl and TP concentrations increased as alkalinity increased and depth decreased. However, Chl:TP ratio was highest in high alkalinity lakes in 2007, and moderate alkalinity lakes in 2008. Our results indicate that the use of TP water quality targets alone is insufficient to accurately manage eutrophication pressures at the lake specific scale, and that a wider range of ecological and ecosystem service evaluation targets would provide a more comprehensive assessment of management needs. The wide range of Chl:TP ratio values reported in this study suggests that, although reducing TP concentrations in lakes is undoubtedly a sensible approach to eutrophication management in many cases, TP reductions alone may not result in the expected reductions in phytoplankton biomass in all lakes.

Meiobenthic community patterns of oligotrophic and deep Lake Constance in relation to water depth and nutrients

Between February and April 2004, 48 sites in Lake Constance (Germany) were investigated to determine the distribution of the meiobenthic community, including 16 sites from the sub-littoral (13 -30 m water depth), 16 sites from the profundal (31-99 m) and 16 sites from the deep profundal (100-250 m). Lake-wide analysis showed no simple distribution pattern, but rather a heterogenic meiobenthic community composition, with nematodes representing the dominant group (48.7 %), followed by rotifers (27.7 %), harpacticoids (7.7 %), copepods (5.0 %), oligochaetes (3.7 %), ostracods (3.1 %), nauplii (1.9 %) and tardigrades (1.2 %). The relative abundances of all other investigated meiobenthic groups (cladocerans, chironomids, arachnids, gastrotrichs) were below 1 %. The densities of meiobenthic organisms varied greatly between sites, with nematodes reaching up to 3,336,676 and rotifers up to 6,357,008 individuals per m(2). The abundances of most organisms varied significantly between the different water zones. Nematodes, copepods, nauplii and cladocerans, however, were equally distributed between sub-littoral and the profundal zones. Organisms showed their highest levels of abundance in the sub-littoral zone, with the exception of harpacticoids and ostracods, which were most abundant in the profundal and deep profundal respectively. A multivariate statistical analysis revealed that besides Chl-a explaining 47 % of the variance degenerated algae, water depth, mean grain size, organic carbon, C/N ratio and total phosphorus were significantly correlated with lake-wide community structure. In the sub-littoral, mean grain size was the most important parameter explaining 25.4 % of the variance, while in the profundal Chl-a (29.4 %) and in the deep profundal algae pigments (38.6 %) were the most important parameters for meiofaunal distribution and environmental variables.

Constructed wetlands and denitrifying bioreactors for on-site and decentralised wastewater treatment: Comparison of five alternative configurations

The performance of five alternative treatment trains receiving primary domestic wastewaters was compared in side-by-side trials over an annual period after 2 years maturation. One of the systems was a passive horizontal-flow wetland. The other four hybrid systems comprised different configurations of subsurface horizontal- and/or intermittently-dosed (24/d) vertical-flow constructed wetlands (single pass or recirculating), and attached growth and carbonaceous (wood-chip and coconut husk) denitrifying bioreactors. The scale of the systems ranged from ∼20 to 40% of that required for a single household. Mean biochemical oxygen demand (BOD5) and total suspended solids (TSS) were reduced by over 94% in all systems. Mean ammonium-N (NH4-N) concentrations were reduced to between 0.05 and 0.20gm−3 (98–99.8% reduction) in the hybrid wetland and bioreactor systems, compared to ∼13gm−3 (61% reduction) in the horizontal-flow wetland. Mean total nitrogen (TN) removal ranged from 49% in the horizontal-flow wetland to between 58 and 95% in the hybrid systems. Apparent nitrification rates of 3.8–7.3gNm−2d−1 (based on ammonium reduction) were recorded in the vertical-flow wetlands and apparent denitrification rates of 2.8–12.4gNm−3d−1 (based on nitrate reduction) in linked denitrifying bioreactors and horizontal-flow wetlands. Mean total phosphorus (TP) removal ranged from 36 to 65%, while faecal indicator bacteria were reduced by 2.5–4.7log units in the different systems. The results of this study show that simple hybrid systems combining wetland and denitrifying bioreactor components are capable of achieving advanced effluent quality with low energy inputs. The areas required for these hybrid systems were generally half or less of those required for horizontal-flow wetlands.

Past and current trophic development in Lake Ammersee - Alterations in a normal range or possible signals of climate change?

In the past decades, nutrient concentrations in several pre-Alpine lakes in central Europe have increased due to human activity in the catchment area. Here, we examine whether this trend will continue in the future, through our analysis of the development of the trophic status, over a period of 25 years (1984 – 2009), of the pre-Alpine, dimictic tempered Lake Ammersee (South-Eastern Germany). The lake showed signs of an elevated eutrophic status until the 1990s. Immense management activities in the catchment area led to a reduction in the nutrient load in the tributaries. The study of dissolved oxygen, total phosphorus (TP) and chlorophyll-a revealed a substantial improvement in the trophic conditions of the lake. We identified a transition period in the development of trophic levels during the years 1996/1997. Therefore, our investigation is divided into two periods: 1984 –1996 and 1997– 2009. By comparing values during these two periods, we found that the annual mean TP concentrations of the complete water column declined from 18.2 μg l (1984 –1996) to 8.8 μg l (1997–2009). During this period the chlorophyll-a values are in relationship to other trophic variables such as TP, dissolved oxygen and sight depths (R between 0.41 and 0.56). At the same time, during the summer months, the surface temperature in the epilimnion increased (by about 0.8 K per decade), which was approximately in line with the thermal increase (about 0.6 K per decade) in the northern hemisphere (Pearson’s correlation coefficient, omitting 2006, of 0.81). In conclusion, in the case of Lake Ammersee, a decrease in nutrient input has led, most recently (1997– 2009), to a substantial improvement in the trophic state. This improvement is fundamentally a result of measures taken to correct any anthropogenic impact. Nevertheless, we show that the thermal stability of the lake reacts to climate-triggered alterations. Therefore it seems that the impact of recent climate change on trophic conditions will have to be monitored closely