Low Total Phosphorus Concentrations Research Articles

Total nitrogen and pH are key variables for functional structure of zooplanktonic communities in an agropastoral landscape

Changes in land use are one of the main impacts on aquatic ecosystems. The conversion of natural areas into agropastoral, such as pasture or monocultures, can affect the limnological characteristics of the water that in turn influence the structure of aquatic communities. But the impact is still unclear, particularly on zooplankton communities. The objective of this study was to evaluate the effect of water parameters from eight reservoirs inserted in an agropastoral landscape on the functional structure of zooplankton. The functional characterization of the zooplankton community was based on four traits: body size, feeding type, habitat type, and trophic group. Functional diversity indices (FRic FEve and FDiv) were estimated and modeled water parameters, using generalized additive mixed models (GAAM). The water parameters investigated were total nitrogen (TN) and total phosphorus (TP), dissolved oxygen (OD), temperature and pH. Moreover, we used RDA to analyze the influence of these environmental variables on the sharing of traits among the sample sites. FRic was high in the reservoirs with low TN concentration and low pH values. FEve was also high in low pH and high TP concentration. FDiv was high with unsharp increases of pH and high concentrations of TN and DO. Our analyses showed pH as a key variable for functional diversity, since it was related to the variation in all indices. Data also pointed out changes in diversity functional with small pH changes. The big and medium size, raptorial-cop and filtration-clad functional traits were positively associated with high concentrations of TN and alkaline pH. The small size and filtration-rot were negatively associated with high concentrations of TN and alkaline pH. Density of filtration-rot was lower in pasture landscapes. In conclusion, our study indicated that pH and TN are key variables for the functional structure of zooplanktonic communities in an agropastoral landscape.

Drying of Chinese medicine residues (CMR) by hot air for potential utilization as renewable fuels: drying behaviors, effective moisture diffusivity, and pollutant emissions.

The online version contains supplementary material available at 10.1007/s13399-022-03722-4.

Aquatic ecosystem responds differently to press and pulse nutrient disturbances as revealed by a microcosm experiment.

Due to climate change and increasing anthropogenic activities, lakes are disturbed frequently, usually by press (e.g., diffused pollution, rising temperatures) or pulse (e.g., storms, rainfall, pollution events) disturbances. Both press and pulse disturbances can affect abiotic and biotic environments, changing the structure of ecosystems and affecting ecosystem services. To confront with the effects of climate change and increasing anthropogenic activities, understanding the different effects of press and pulse disturbances on lake ecosystems is essential. This study assessed the effect of press and pulse disturbances of phosphorus on a microcosmic aquatic ecosystem by measuring the total phosphorus (TP), algae density, and physiological indicators of submerged macrophytes. We found that the microcosmic aquatic ecosystem responded differently to press and pulse disturbances. Our results suggested that it had a lower resistance to pulse phosphorus disturbances than to press phosphorus disturbances. There were significantly higher nutrient concentrations and algal densities in the pulse treatment than in the press treatment. Positive feedback was found between the biomass of submerged macrophytes and the water quality. There was a higher submerged macrophytes biomass at low TP concentration and algal density. In the context of climate change, press and pulse disturbances could have severe impacts on lake ecosystems. Our findings will provide some insight for further research and lake management.

Enhanced phosphate removal by coral reef-like flocs: Coagulation performance and mechanisms

In order to meet stricter phosphorus discharge standards for wastewater treatment plant effluent and better protect natural aquatic environments, this study investigated the coagulation performance and mechanisms of coral reef-like flocs formed in a continuous dosing coagulation (CDC) process. The CDC process exhibited enhanced phosphorus removal compared to the conventional coagulation (CC) process. To meet the 0.3 mg/L total phosphorus discharge standard, the CDC dosage (2 mg Al/L) was half the CC dosage (4 mg Al/L). Furthermore, at 4 mg Al/L, the CDC process obtained a very low total phosphorus concentration (0.035 mg/L). The CDC process had better phosphate removal performance when the initial pH was 6 or 5, and exhibited steady phosphate removal in the presence of organics and various ions. The CDC process enhanced phosphate removal in the following two ways. First, the “low pH and low Al3+ concentration” environment in the early stage benefited the co-precipitation of monomeric Al species and phosphate to form insoluble AlPO4 particles. Second, the coral reef-like flocs formed in the continuous dosing process had a stronger positive charge (2.3 mV) and larger specific surface area (264.11 m2/g). The enhanced absorption ability towards undissolved AlPO4 particles and dissolved phosphate anions promoted the overall phosphate removal of the CDC process. The coral reef-like flocs formed by a continuous dosing method provided new insights into the advanced treatment of dissolved contaminants in wastewater.

Temporal declines in Wadden Sea phytoplankton cell volumes observed within and across species

AbstractCell size is a master trait in the functional ecology of phytoplankton correlating with numerous morphological, physiological, and life‐cycle characteristics of species that constrain their nutrient use, growth, and edibility. In contrast to well‐known spatial patterns in cell size at macroecological scales or temporal changes in experimental contexts, few data sets allow testing temporal changes in cell sizes within ecosystems. To analyze the temporal changes of intraspecific and community‐wide cell size, we use the phytoplankton data derived from the Lower Saxony Wadden Sea monitoring program, which comprises sample‐ and species‐specific measurements of cell volume from 1710 samples collected over 14 yr. We find significant reductions in both the cell volume of most species and the weighted mean cell size of communities. Mainly diatoms showed this decline, whereas the size of dinoflagellates seemed to be less responsive. The magnitude of the trend indicates that cell volumes are about 30% smaller now than a decade ago. This interannual trend is overlayed by seasonal cycles with smaller cells typically observed in summer. In the subset of samples including environmental conditions, small community cell size was strongly related to high temperatures and low total phosphorus concentration. We conclude that cell size captures ongoing changes in phytoplankton communities beyond the changes in species composition. In addition, based on the changes in species biovolumes revealed by our analysis, we warn that using standard cell size values in phytoplankton assessment will not only miss temporal changes in size, but also lead to systematic errors in biomass estimates over time.

Under-ice environmental conditions, planktonic communities and ichthyofauna in dystrophic lakes

High content of humic substances and low pH values are factors limiting the species richness and abundance of some organisms in dystrophic lakes. Unfavourable winter conditions (i.e. low water temperature, poor light conditions, ice/snow cover) may additionally restrict their development. The aim of this study was to compare ice-on (winter) and ice-off (summer) abiotic (organic carbon, total phosphorus and nitrogen) and biotic (chlorophyll a, phytoplankton, ciliates, rotifers, crustaceans, fish) parameters in five dystrophic lakes of the Wigry National Park (north-east Poland). We tested the hypothesis that the abundance and diversity of planktonic organisms in dystrophic lakes could be lower in winter than in summer. Our results showed that the winter period, with ice and snow cover, was characterised by clearly higher oxygen concentrations, pH values and conductivity, but lower total phosphorus concentrations, species richness of phytoplankton, ciliates, rotifers and crustaceans, and phytoplankton to zooplankton biomass ratios in comparison to the summer. All of the studied groups of organisms, except rotifers, reached relatively high abundances and biomasses in both seasons and, in some lakes, they were higher in winter than in summer. Our results suggest that fish composition and abundance did not play an important role in structuring plankton communities. The small dystrophic lakes, although located close to one another, differed in terms of abiotic parameters and had specific species compositions of phyto- and zooplankton. Warmer winters, which are the result of climate change, may favour the intensive development of planktonic communities under the ice in dystrophic lakes of temperate climatic zones.

Does differential phosphorus processing by plankton influence the ecological state of shallow lakes?

Shallow lakes have a tendency to settle into turbid or clear-water states, the latter having lower concentrations of total phosphorus (TP). However, how P-cycling is affected by and perhaps contributes to maintaining the different states is not well understood, in part because quantifying the processes involved by traditional methods is difficult. To elucidate these processes, we conducted experiments using 32P-PO4 as a tracer on samples collected from the unrestored, unvegetated sections of Huizhou West Lake where turbid water prevails as well as the restored, clear-water, macrophyte-rich waters of the lake. We measured PO4 uptake rates, 32P-PO4 accumulation by various plankton size-fractions (picoplankton (0.2–2 μm), nanoplankton (2–20 μm) and microplankton (>20 μm)) as well as release rates of 32P-PO4 by labelled plankton. Our results revealed slow PO4 uptake in the turbid state due to low PO4 concentration, slow recycling of the high particulate P, and high levels of particulate 32P which may allow for continuous high growth and biomass of phytoplankton. In contrast, in the clear water state, the uptake of PO4 was rapid due to a higher PO4 concentration, the recycling rates of particulate 32P were high and the levels of particulate 32P were low, potentially constraining the phytoplankton growth. A greater proportion of particulate 32P was in the microplankton fraction in clear waters, suggesting that grazing by microplankton may play an important role in the rapid P recycling in clear-waters. Our results provide some evidence for a reinforcement of the turbid conditions (low recycling rate) when the lake is in a turbid state and vice versa when in the clear water state. The results add new knowledge to the understanding of P cycling in shallow lakes and illustrate the utility of using P-kinetics in contrasting states in plankton communities.

Wetland Flowpaths Mediate Nitrogen and Phosphorus Concentrations across the Upper Mississippi River Basin.

Eutrophication, harmful algal blooms, and human health impacts are critical environmental challenges resulting from excess nitrogen and phosphorus in surface waters. Yet we have limited information regarding how wetland characteristics mediate water quality across watershed scales. We developed a large, novel set of spatial variables characterizing hydrological flowpaths from wetlands to streams, that is, "wetland hydrological transport variables," to explore how wetlands statistically explain the variability in total nitrogen (TN) and total phosphorus (TP) concentrations across the Upper Mississippi River Basin (UMRB) in the United States. We found that wetland flowpath variables improved landscape-to-aquatic nutrient multilinear regression models (from R2 = 0.89 to 0.91 for TN; R2 = 0.53 to 0.84 for TP) and provided insights into potential processes governing how wetlands influence watershed-scale TN and TP concentrations. Specifically, flowpath variables describing flow-attenuating environments, for example, subsurface transport compared to overland flowpaths, were related to lower TN and TP concentrations. Frequent hydrological connections from wetlands to streams were also linked to low TP concentrations, which likely suggests a nutrient source limitation in some areas of the UMRB. Consideration of wetland flowpaths could inform management and conservation activities designed to reduce nutrient export to downstream waters.

Glacier recession alters stream water quality characteristics facilitating bloom formation in the benthic diatom Didymosphenia geminata

Glaciers provide cold, turbid runoff to many mountain streams in the late summer and buffer against years with low snowfall. The input of glacial meltwater to streams maintains unique habitats and support a diversity of stream flora and fauna. In western Canada, glaciers are anticipated to retreat by 60–80% by the end of the century, and this retreat will invoke widespread changes in mountain ecosystems. We used a space-for-time substitution along a gradient of glacierization in western Canada to develop insights into changes that may occur in glaciated regions over the coming decades. Here we report on observed changes in physical (temperature, turbidity), and chemical (dissolved and total nutrients) characteristics of mountain streams and the associated shifts in their diatom communities during de-glacierization. Shifts in habitat characteristics across gradients include changes in nutrient concentrations, light penetration, temperatures, and flow, all of which have led to distinct changes in diatom community composition. Importantly, glacial-fed rivers were 3–5 °C cooler than rivers without glacial contributions. Declines in glacial meltwater contribution to streams resulted in shifts in the timing of nutrient fluxes and lower concentrations of total phosphorus (TP), soluble reactive phosphorus (SRP), and higher dissolved inorganic nitrogen (DIN) and light penetration. The above set of conditions were linked to the overgrowth of the benthic diatom Didymosphenia geminata. These changes in stream condition and D. geminata colony development primarily occurred in streams with marginal (2–5%) to no glacier cover. Our data support a hypothesis that climate-induced changes in river hydrochemistry and physical condition lead to a phenological mismatch that favors D. geminata bloom development.

Paddy soil nutrients and stoichiometric ratios as affected by anthropogenic activities during long-term tillage process in Chengdu Plain

Being the most widespread soil in the Chengdu Plain in Sichuan Basin, China, paddy soil has a great importance in agriculture and ecology. Anthropogenic activities alter the concentrations and stoichiometric ratios (C:N, C:P, and N:P) of carbon (C), nitrogen (N), and phosphorus (P) in paddy soil. This study aims to investigate whether the cycling of C, N, and P in paddy soil is influenced by cropping system and pedogenic process (the subtype of paddy soil). In this study, we collected 1080 soil samples at 0–20 cm from five cropping systems (rice monoculture (RM), vegetable monoculture (VM), rice and vegetable rotation (RVR), rice and wheat rotation (RWR), rice and oilseed rape rotation (ROR)) and six subtypes (bleached paddy soil (BPS), gleyed paddy soil (GPS), percogenic paddy soil (PPS), degleyed paddy soil (DPS), submergienc paddy soil (SPS), and hydromorphic paddy soil (HPS)) of paddy soil in Chengdu. Soil organic carbon (SOC), soil total nitrogen (TN), and soil total phosphorus (TP) concentrations were determined to calculate the stoichiometric ratios. Our results indicated that the concentrations of SOC, TN, and TP of paddy soil were higher than those of cropland on a global scale. There are similar stoichiometric ratios between paddy soil in Chengdu Plain and the cropland in the global scale. The cropping system and subtype significantly altered the soil nutrient concentrations and stoichiometric ratios. The concentrations of soil TN under rotation systems (RV, RW, and RO) were significantly higher than those of VM. The soil with the subtypes of BPS and GPS were related to low TP concentration. The cropping system of VM showed soil N consumption compared with the traditional cropping system (rotation systems, such as RV, RW, and RO). In addition, subtype also significantly influenced the element balance in paddy soil. The balance of soil C, N, and P is mainly affected by fertilizer application of N and P.

Effect of dam construction on nutrient deposition from a small agricultural karst catchment

Abstract Assessing the effects of dam construction on nutrient deposition in small catchments is important to our understanding of the influence of dam interception on downstream nutrient transport as well as of the link between nutrient loss from sloping land and the eutrophic status of large rivers. This study investigates the effect of dam construction on nutrient deposition from a small agricultural karst catchment over the past 50 years by examining the nutrients preserved in reservoir sediments. A new method is proposed to determine the historical nutrient deposition rate ( NDR ) in a small man-made reservoir. We analyzed the concentrations of total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) in three sediment cores retrieved from the reservoir, and estimated the mean annual NDRs across the whole reservoir for five depth ranges represented deposition over the periods 1959–1962, 1963–1972, 1973–1985, 1986–1997, and 1998–2012. The relatively low TN, TP, and TOC concentrations below about 30 cm in the three cores reflect the small contribution from anthropogenic nutrient inputs prior to the 1990s. In contrast, the rapid up-core increases in TN, TP, and TOC above 30 cm reflect the increasing supply of anthropogenic nutrients since the 1990s. Natural nutrients were the main contributor to nutrient deposition in the reservoir over the past 50 years. The lack of coupling between sedimentation rates ( SRs ) and nutrient concentrations suggests that the sediment yield has had little influence on the changing pattern of nutrient concentrations preserved within the reservoir deposits, and this provides a new insight into the relationship between sediment yield and nutrient concentration in reservoir sediments. The deposition rates of TN, TP, and TOC over the past 50 years show similar patterns; i.e., they decreased between 1959 and 1972, and then generally increased thereafter. The temporal patterns of these deposition rates were controlled mainly by the sediment yield over the first four periods, whereas anthropogenic nutrient sources (e.g., fertilizer application) were the main cause of the increased NDRs during the final period. These results provide an improved understanding of the environmental factors controlling changes in NDRs . Overall, the profiles of TN, TP, and TOC concentrations, and the NDRs estimated from the three cores, reflect the processes of nutrient loss from the catchment and enrichment in the reservoir in light of environmental change influenced by human activity, and indicate the effect of dam construction on nutrient deposition in the catchment over the past 50 years. This is the first study to document historical NDRs in a small dam reservoir, and the newly proposed method could be applied to other reservoirs in karst and non-karst areas.

Impacts of cage fish farms in a large reservoir on water and sediment chemistry

The Keban Reservoir, which is the second man-made waterbody in Turkey, has the biggest rainbow trout production in the country. In this study, the impacts of rainbow trout farms on water and sediment chemistry were investigated. Water and sediment samples were taken at distances of 0, 10, 25, 50 and 100 m from the edge of the cages at the three fish farms, and at the respective reference stations. Samples were also taken at 0 m stations and reference stations in the late August when there were no fish in the cages. Physico-chemical variables and trace metals were analysed in all samples. Due to likely high dilution rates and recycling processes in the water column of the reservoir, little changes in the water quality parameters associated with wastes of the fish farms were noticed. When compared with those in the sediment samples at the stations near the edge of cages, the lower concentrations of total phosphorus (TP), total nitrogen (TN), organic matter (OM), total carbon (TC), sulfide (S2−), arsenic (As), cobalt (Co), copper (Cu), manganese (Mn) and zinc (Zn), and higher values of redox potential (Eh) were found at the reference stations. According to organic enrichment classification based on S2− and Eh values, sediments of the three fish farms in the period when there were fish in the cages fell into the oxic category, whereas sediments in the August (no fish farming activity) fell into the normal category. Also, it was found in the August that most of sediment quality parameters at the 0 m stations had close values to those at the reference stations. These results revealed that a three-month period when there were no fish in the cages allows for sediments to return to reference station conditions.

Bayesian chemistry-assisted hydrograph separation (BACH) and nutrient load partitioning from monthly stream phosphorus and nitrogen concentrations

A Bayesian chemistry-assisted hydrograph separation (BACH) approach was developed, based on calibration of a three-component recursive digital filter, that requires monthly water quality data only. This enables BACH to be applied to the large number of rural catchments for which continuous flow records and monthly water chemistry time series exist from ‘state of environment’ monitoring programmes, but little supplementary data required for more sophisticated analysis techniques. As well as estimating fast, medium, and slow flow components, BACH also estimates for each flow component a time-invariant concentration of the chemical tracers chosen, allowing flow path-specific loads to be calculated. The method was demonstrated using 15 years of total phosphorus (TP) and total nitrogen (TN) data from eight mesoscale catchments in the Waikato region of New Zealand’s North Island. Calibration was done separately for three 5-year data periods, and validated against data from the following 5-year period. Flow path separation and concentration predictions were consistent between data periods, indicating that the TP–TN combination contained sufficient information to reliably identify three flow paths in each catchment; an event-response near-surface flow path with high concentrations of both phosphorus and nitrogen, a seasonal shallow groundwater flow path with lower concentrations of TP but high concentrations of TN, and a deeper slower groundwater flow path characterised by generally low concentrations of both TP and TN. Based on this analysis, the catchments were able to be grouped in three hydro-types. This shows that commonly available water quality data can support robust, objective flow separation and nutrient load apportionment, even in the absence of other supporting data, provided appropriate modelling methods are used.

Study of the impacts of process changes of a pulp and paper mill on aerated stabilization basin (ASB) performance

A laboratory scale (LS) and a field-based pilot plant (PP), designed to simulate aerobic stabilization basin (ASB) operation, were utilized to assess the potential impacts of changes in pulp and paper (P&P) mill operations on full-scale (FS) ASB performance. Two stages of investigation were conducted. The first was undertaken to determine the potential of pre-alum treatment of pulp mill wastewaters on ASB performance. The second investigation was conducted to assess ASB performance where wastewaters transitioned from being coagulated pulp and paper mill wastewaters to paper mill wastewaters only. Simulation ASB performance was assessed based on removals of BOD5, colour, UV@254 nm and nutrients [total phosphorus (TP) and nitrogen compounds (TN)]. Pre-alum treatment of pulp mill wastewaters with subsequent ASB treatment following mixing with paper mill wastewaters showed high percentage removals of BOD5. Despite low TP concentrations (≤0.05 mg/L) and low nutrient to BOD5 ratios of wastewaters in the LS-ASB trial, the high % BOD5 removal indicated recycling of nutrients from sludge [sourced from the FS-ASB]. Despite coagulation of pulp mill wastewater being performed using a very high alum dose (∼2000 mg/L) to remove colour and its precursors, colour formation remained high throughout the simulated ASB trials. Simulation of discontinuation of pulping indicated that colour would reduce rapidly to low levels in ASB wastewaters, but that TP and TN concentrations would persist for longer periods of time and decline slowly. Survey data of water qualities of the FS-ASB system obtained before, during and 2 years after discontinuation of pulping are presented.

Evaluation of seven mulch treatments for erosion control and vegetation establishment on steep slopes

Soil erosion and sediment pollution in and around construction sites can result from land disturbing activities that leave areas of unprotected soil during construction. This study evaluated different types of hydromulch for erosion control and grass establishment in comparison to straw alone or straw plus an application of polyacrylamide (PAM) on steep slopes at five construction sites in North Carolina. One site was located in the Coastal Plain (CP) region, and another in the Mountain (M) region, with the remaining three in the Piedmont (P1 through P3). At each site, 20 plots (3 m [10 ft] wide by 6 to 9 m [20 to 30 ft] long) were established on a contiguous area. After applying grass seed, the erosion control treatments were as follows: wheat straw (<i>Triticum aestivum</i>) and wheat straw + 22.4 kg ha⁻¹ (20 lb ac⁻¹) of granular, linear, anionic PAM on all five sites; and hydromulches including flexible growth medium (FGM), stabilized mulch matrix (SMM), bonded fiber matrix (BFM), wood fiber/cellulosic blend (WCB), and wood fiber mulch (WFM) applied at three sites each. Runoff volumes, turbidity, eroded sediment, and nutrient concentration data were collected after natural rain events; grass growth and cover were also evaluated. At both the CP and M sites, there were no differences between treatments, most likely due to the sandy soil texture at CP and a combination of sandy soil texture and relatively light rainfall events at M. At P1, there was a trend of straw cover producing higher runoff volume, turbidity, total suspended solids (TSS), and in general higher concentrations and amount of nutrient loss compared to all hydromulch treatments. In contrast, at P2 and P3, hydromulches tended to have greater runoff volumes, turbidity, and TSS compared to straw. Also, on these sites, straw + PAM treatment had lower concentrations of total phosphorus (P) in runoff compared to WCB. The addition of PAM did not have an effect on runoff volumes at any site, but it reduced average turbidity on P2. Overall, there was no clear pattern of hydromulch advantages over straw as a mulch for reducing erosion or establishing grass on steep slopes.

Sensitivity of plankton indices to lake trophic conditions.

Herein, we report the response of indices based on phytoplankton and zooplankton and their combination to different nutrient concentrations in lakes. The study was carried out in ten lakes in northeastern Poland. Integrated samples were collected from the epilimnion during the summer of 2012–2013. Secchi disk visibility (SD), total phosphorus (TP), total nitrogen (TN), and chlorophyll a were used as proxies for eutrophication. We calculated 16 plankton indices: two phytoplankton indices, six crustacean indices, five rotiferan indices, two zooplankton diversity indices, and one combined phytoplankton and zooplankton index. Among them, nine indices with the strongest correlations with TP were selected: percentage share of Crustacean species indicative of high trophy in the indicative group’s numbers (IHTCRU), percentage share of Rotifera species indicative of high trophy in the indicative group’s numbers IHTROT, Crustacean ratio of biomass to numbers B/NCRU, phytoplankton trophic index (TITP+TN), Margalef’s index, percentage share of cyclopoid biomass in total biomass of Crustacea (CB), Rotifera numbers (NROT), biomass of Cyclopoida (BCY), and ratio of the cyclopoid biomass to the biomass of Cladocera (CY/CL). The sensitivity of the normalized values of these indices to proxies of eutrophication was tested. IHTCRU, IHTROT, and B/NCRU were the most sensitive and gave the strongest responses at lower TP concentrations (<35 μg/L). The phytoplankton trophic index, TITP+TN, together with the zooplankton-based Margalef’s index and CB were very sensitive in both low (<35 μg/L) and high (>60 μg/L) TP conditions. On the other hand, NROT, BCY, and CY/CL were slightly sensitive at low TP concentrations while their reaction was notable at high TP concentrations. A similar pattern of response was observed for TN concentration and SD visibility.

Numerical Response of Migratory Shorebirds to Prey Distribution in a Large Temperate Arid Wetland, China.

Wuliangsuhai Lake provides important breeding and stopover habitats for shorebirds. The health of this wetland ecosystem is rapidly deteriorating due to eutrophication and water pollution and environmental management is urgently needed. To explore the connections among ecosystem health, prey density, and shorebird populations, we conducted surveys of both the benthic macroinvertebrates and shorebirds in the shorebird habitat of the wetland during the 2011 autumn migration season. The abundance of both shorebirds and benthic macroinvertebrates varied significantly in both space and time. Our data showed a clear association between shorebird populations and the density of benthic macroinvertebrates, which explained 53.63% of the variation in shorebird abundance. The prey density was strongly affected by environmental factors, including water and sediment quality. Chironomidae were mainly found at sites with higher total phosphorus, but with lower sediment concentrations of Cu. Lymnaeidae were mainly found at sites with a higher pH, lower salinity, and lower concentrations of total phosphorus and Cu. Habitats with very high concentrations of total phosphorus, heavy metals, or salinity were not suitable for benthic macroinvertebrates. Our findings suggest that the reductions of nutrient and heavy metal loadings are crucial in maintaining the ecological function of Wuliangsuhai as a stopover habitat for migratory shorebirds.

Chemical pollution in inland shallow lakes in the Mediterranean region (NW Spain): PAHs, insecticides and herbicides in water and sediments

The possible effect of land uses and human-related geographic patterns (presence of roads and urban settlements) on chemical pollution was evaluated in the waters and sediments of fifty-three Mediterranean shallow lakes. The presence of fifty-nine pollutants (belonging to PAHs, insecticides and herbicides groups) was analysed in these lakes by GC–MS. The studied lakes had similar pollutant concentrations to other lakes worldwide. The distribution of the compounds between water and sediment compartments was strongly influenced by log Kow values (an average of 3.61 for compounds found in water and of 4.69 for compounds found in sediments). A multivariate analysis suggested that the concentration of PAHs in water could be related to agricultural activities and not related to local road traffic. When assessing nutrient levels in the lakes, it was observed that eutrophicated lakes [>300μgL−1 total phosphorus (TP)] appeared in areas affected by urban or industrial use (at least 2% urban use in a 1-km radius around the lake), whilst lakes with lower TP concentrations were placed in forest areas (60% of forest use in a 1-km radius); in addition, the aqueous concentrations of Σ(PAH) were lower in lakes with higher TP concentrations (>150μgL−1 TP), which could be related to the adsorption capacity of PAHs onto suspended matter which is present in mesotrophic and eutrophic lakes, thus being removed from the aqueous phase.

An analysis of sampling programs to evaluate compliance with numerical standards: total phosphorus in Platte Lake, MI

Platte Lake has a numerical standard for total phosphorus mandated in 2000 following judicial proceedings that requires volume weighted total phosphorus to be below 8 mg/m3 95% of the time. Compliance has been evaluated using an extensive monitoring program that collects samples at roughly biweekly intervals. Analysis indicates that the lake has been and remains in violation of the numerical standard. This large dataset provides a unique opportunity to utilize statistical methods to evaluate compliance while controlling the Type I and Type II errors and to determine the minimum number of samples needed to detect changes in total phosphorus concentrations. Regression and analysis of variance were used to improve the sampling design. Similar techniques were used to design optimal monitoring programs for hypothetical lakes having a large range of total phosphorus concentrations and trophic conditions. Lakes with low total phosphorus concentrations require relatively few measurements during the year, but laboratory uncertainty necessitates multiple replicates. Lakes with higher total phosphorus concentrations require frequent sampling to obtain an acceptable estimate of the annual average concentration because large temporal and depth gradients are expected. Fewer replicates are indicated because laboratory measurements of higher concentrations are more reliable. A review of several national-scale studies indicates that few lakes have sufficient data to perform credible compliance evaluation or reliably detect changes in lake concentrations in response to shifts in watershed loads. Further, many laboratories have limited capability to measure the low concentrations of total phosphorus typically associated with oligotrophic lakes.

Macrophyte effects on algal turbidity in subtropical versus temperate lakes: a comment on Wanget al. (2014)

Summary A recent analysis of 30 lakes in the Yangtze basin found no effect of benthic macrophyte coverage on the relationship between chlorophyll a concentrations and total phosphorus (TP). While several recent studies have found the effects of macrophyte coverage to be weaker in subtropical versus temperate shallow lakes, in this case, the finding was due to a statistical error meaning that the comparison was effectively made for lakes with very low TP concentrations of just 1 μg L−1. Centring the data so that the comparison is made at a TP concentration where both vegetated and non‐vegetated lakes are found confirms a strong effect of macrophytes on the chlorophyll a to TP relationship. Thus, macrophyte effects for these subtropical lakes in the Yangtze basin are in fact similar to those found in temperate lakes.