Water Total Phosphorus Concentrations Research Articles

Changes in the spatial distribution of total phosphorus in sediment and water column of a shallow subtropical lake

Julian PJ II, Schafer T, Cohen MJ, Jones P, Osborne TZ. 2023. Changes in the spatial distribution of total phosphorus in sediment and water column of a shallow subtropical lake. Lake Reserv Manage. 39:213–230. In shallow lakes, interactions between bed sediment and the water column strongly influence the availability and transport of nutrients. Lake Okeechobee, in South Florida, is a eutrophic, shallow, polymictic lake that exhibits frequent mixing of the water column and resuspension of unconsolidated sediments. The objective of this study was to evaluate the temporal and spatial patterns of water and sediment characteristics and evaluate the linkage of sediment and water column total phosphorus (TP) concentrations. Spatiotemporal generalized additive models identified key periods during which both surface water total suspended solids (TSS) and TP increased, corresponding to hurricane and tropical storm activity. Our models identified regions with persistently greater water column concentrations than the lake average, indicating potential hot spots in resuspension processes and/or internal loading. Sediment bulk density (BD) and TP were inversely correlated, indicating that light, less dense sediments have greater TP concentrations, potentially contributing to the redistribution of sediments and P. An integrated evaluation of surface water and sediment characteristics using a generalized additive model revealed that sediment TP strongly influences water column TP concentrations, potentially explaining the spatial distribution of surface water TP concentrations. The area of the lake with sediment TP concentration ≤500 mg/kg is increasing while the low bulk density sediments area is decreasing, marking a potential improvement in sediment conditions. If this trend persists, it indicates that the lake is increasingly storing P in sediments that can resist entrainment, with significant implications for assessing the trajectory of lake restoration.

Determination of total phosphorus concentration in water by using visible-near-infrared spectroscopy with machine learning algorithm.

Total phosphorus (TP) content is a crucial evaluation parameter for surface water quality assessment, which is one of the primary causes of eutrophication. High-accuracy, fast-speed approach for the determination of low-concentration TP in water is important. We proposed a rapid, highly sensitive, and pollution-free approach that combines spectroscopy with a machine learning algorithm we improved called synergy interval Extra-Trees regression (siETR) to determine TP concentration in water. Results show that the prediction model based on siETR can get a high coefficient of determination of prediction ([Formula: see text] = 0.9444) and low root mean square error of prediction (RMSEP = 0.0731), which performs well on the prediction of TP concentration. Furthermore, the statistical analysis results further prove that the model based on siETR is superior to other models we studied both in prediction accuracy and robustness. What is more, the prediction model we established with only 140 characteristic wavelengths has the potential for the development of miniature spectral detection instruments, which is expected to achieve in situ determination of TP concentration. These results indicate that Vis-NIR spectroscopy combined with siETR is a promising approach for the determination of TP concentration in water.

Remote sensing monitoring of total nitrogen and total phosphorus concentrations in the water around Chaohu Lake based on geographical division

Remote sensing is useful for quantifying water-quality parameters for managing inland water systems. However, the single water-quality retrieval model usually has poor applicability in large regions. To solve the issue of low retrieval accuracy of water-quality parameters in inland water, the study area herein is geographically divided into rural water and urban water according to the proportion of land-use types in the riparian zones. Furthermore, the machine-learning regression algorithms are used to construct the retrieval models suitable for the total nitrogen (TN) and total phosphorus (TP) concentrations based on the measured water-quality data and the simultaneous Sentinel-2 Multispectral Imager (MSI) images. Additionally, the optical retrieval models are applied to the MSI images acquired on different dates to analyze the variations of TN and TP concentrations in the water around Chaohu Lake of China. The results show that the three accuracy indices of determination coefficient (R2), mean square error (MSE), and mean absolute percentage error (MAPE) of the TN concentration retrieval models for rural water and urban water were 0.67, 0.37 mg/L, and 36.81%, and 0.78, 0.34 mg/L, and 8.34%, respectively, while those of the TP concentration retrieval model for rural water and urban water reached 0.46, 0.0034 mg/L, and 38.60%, and 0.58, 0.018 mg/L, and 37.57%, respectively. The accuracy of the TN and TP concentration retrieval model constructed using geographical division is significantly better than that which does not use geographical division. According to the retrieval results from MSI images, the TN and TP concentrations in urban water are higher than those in rural water. TN and TP concentrations in urban water are stable throughout the year and peak in December, while those of rural water are highest in March and lowest in November. The method proposed in this study can provide a new idea for improving the retrieval accuracy of water-quality parameters in different water bodies in a large-scale region, and the relevant conclusion can provide a theoretical basis for water pollution control and prevention strategies in agricultural basins.

Ecological status assessment of clay rivers with naturally enhanced water phosphorus concentrations

• Water P and the PIT index were higher in unimpacted clay than non-clay rivers. • Water TP was less bioavailable in unimpacted clay rivers than in non-clay rivers. • Natural water TP increases with catchment clay cover. • The PIT good/moderate class boundary increases with catchment clay cover. The species composition of benthic algae changes as water phosphorus concentrations increase, and these changes can be used for ecological status assessment according to the Water Framework Directive. Natural background phosphorus concentrations in rivers and streams that are unaffected by anthropogenic impacts are usually low. Running waters draining catchments with deposits of marine clay, however, may have enhanced phosphorus concentrations, because the clay is naturally rich in apatite. Almost all clay rich areas have been cultivated for centuries, however, and fertilization has increased the soil phosphorus levels. It has, therefore, been difficult to disentangle natural from anthropogenically enhanced phosphorus in streams draining clay rich areas. We compared water phosphorus concentrations, and the Periphyton Index of Trophic Status PIT, between clay and non-clay, impacted and unimpacted rivers in Norway. We found that water phosphorus concentrations and the PIT index were higher in unimpacted clay rivers than in unimpacted non-clay rivers, indicating that natural phosphorus concentrations in clay rivers are indeed enhanced compared to rivers without deposits of marine clay. In addition, phosphate-P contributed 18–23% to total phosphorus in unimpacted clay rivers, but 33–37% in unimpacted and impacted non-clay rivers and clay rivers affected by agriculture. This indicates that the total phosphorus in unimpacted clay rivers is less bioavailable than in non-clay rivers and in impacted clay rivers. Water total phosphorus concentrations in unimpacted clay rivers significantly increased with catchment clay cover. Based on these findings, we derived new status class boundaries for the PIT index in clay rivers. Clay rivers are suggested to be assessed in only two status classes, i.e., “good or better” or “moderate or worse”, respectively. The good/moderate status class boundary for the PIT index was shown to increase with increasing catchment clay cover. .

Internal phosphorus loading and its driving factors in the dry period of Brazilian semiarid reservoirs

This study investigated the relationships between physical, limnological and climatic drivers with the internal total phosphorus (TP) loading produced over the dry period in 30 water supply reservoirs of the Brazilian semiarid. Improvements in the understanding of sedimentary TP fluxes in reservoirs of dryland regions are pressing as they usually have serious water quality related issues, remaining mostly eutrophic especially under frequent drought events. Gross daily fluxes and net seasonal average release rates were calculated from mass balance and regression equations considering water and sediment TP concentrations, anoxic duration, water temperature and fish contribution. Additionally, the ratio of wind speed to reservoir volume was proposed as a new surrogate and then applied as explanatory variable to predictive models. The results indicated TP release rates higher than reported for non-semiarid lakes/reservoirs with average gross fluxes ranging from 17.64 to 35.99 mg m−2 day−1. This may be attributed to the enriched sediments (1029.49 ± 552.49 mg kg−1) allied with warmer water temperature, high trophic state, and prolonged anoxic periods (average duration of about 60 days). The average release rates were negatively correlated with water transparency and water depth, and positively correlated with Chl-a, wind speed and trophic state. The release rates increased across the trophic gradient (p < 0.05), about 10-fold higher under hypertrophic conditions than in oligotrophic ones. As anoxia is linked with eutrophication, phosphorus release is more likely in eutrophic ecosystems. Regarding the new surrogate, a strong predictive ability for TP release (R2: 0.26–0.93) was observed. Similarly, the proposed models presented a physically consistent behavior with a stabilizing releasing pattern suggesting the achievement of equilibrium in nutrient exchange between sediment-water interface. This research advanced by combining and proposing methods to assess and quantify sedimentary fluxes in data-scarce regions balancing accuracy and transferability, in order to be replicable to other dryland environments globally.

Exploring watershed effects on nutrient concentrations in shallow lakes through stable isotope analysis

Biogeochemistry patterns in shallow lakes are influenced by both in-lake factors such as ecosystem state as well as watershed-level factors such as land use, but the relative importance of in-lake versus watershed factors is poorly known. This knowledge gap makes it difficult for lake mangers to prioritize efforts on watershed versus in-lake strategies for stabilizing the clear-water state. We studied 48 shallow lakes in Minnesota, USA to assess the relative influence of lake size, land use in watersheds, and ecosystem state (turbid versus clear) on water column total nitrogen (TN) and total phosphorus (TP), as well as δ15N and δ13C in three species of fish. Our land use categories included natural areas, row crop agriculture, and all agriculture (row crops plus alfalfa). A model selection approach revealed different control mechanisms on the behavior of stable isotopes and nutrients. δ13C ratios in fish were most strongly influenced by lake size, while δ15N ratios were influenced by all agriculture in watersheds. In contrast, water column TN and TP concentrations were influenced by the in-lake factor of ecosystem state, with both nutrients lower in the clear state. We detected no effects of land use on TN or TP concentrations, likely due to strong effects of ecosystem state masking watershed effects. However, the strong relationship between agriculture and δ15N in fish indicated that watersheds did influence nutrient processing in shallow lakes, and that effects are not a legacy from past watershed events. Collectively, these observations indicate that lake managers should minimize agricultural intensity in shallow lake watersheds to facilitate the clear-water state, which will, in turn reduce water-column TN and TP relative to the turbid state.

Phosphorus cycle and its influencing factors in different areas of Lake Taihu

为进一步了解人类活动及环境因子对太湖磷污染的贡献，揭示磷在太湖不同介质中的迁移转化规律，本文以太湖主要入湖湖区竺山湖、西部沿岸区、南部沿岸区和主要出湖湖区东太湖为对象，调查了表层水、上覆水、间隙水和沉积物中总磷(TP)分布的概况，分析了不同介质中磷的交换特征及其影响因素. 结果表明，表层水和上覆水TP浓度基本相当，平均值均为0.10 mg/L，上覆水和间隙水TP差异较大，间隙水平均浓度约为上覆水的7倍，表层沉积物TP含量为474~2160 mg/kg. 在本研究水域中，TP具有较强的沉积物吸附特性，沉积物作为“汇”的特征明显强于其“源”的特征，且磷的留存能力高度依赖于铁浓度. 空间分布上，入湖湖区磷污染程度明显高于出湖湖区，竺山湖和西部沿岸区存在较大的底泥污染释放风险，但竺山湖外源污染影响较内源污染更加突出，应列为当前太湖磷治理重点关注的区域，建议以控源截污作为竺山湖周边区域的治理重点. 西部沿岸区需注重外源和内源污染同步控制. 南部沿岸区周边区域需妥善处理好未来经济发展与废水排放负荷的关系.;This paper explores the influences of human activities and environmental factors to phosphorus (P) loadings in Lake Taihu, and further reveals the migration and transformation patterns of P across different mediums. To this end, the total phosphorus (TP) distribution characteristics were firstly investigated in surface water, overlying water, pore water and sediments, and further, the TP exchange characteristics and its influencing factors were analyzed, taking the main inlet-lake-areas such as the Zhushan Bay, the western coastal area, the southern coastal area, and the main outlet-lake-area of East Lake Taihu as study objects. The TP concentrations in surface water and overlying water was basically equivalent in those study areas, with an average concentration of 0.10 mg/L. Whereas, TP concentrations between the overlying water and the pore water showed large differences: the average TP concentration in pore water reached seven times of that in the overlying water. The TP content of surface sediment was about 474-2160 mg/kg. In those study areas, TP tended to be adsorbed into sediments rather than to be released from sediments, and the characteristics of sediments as sink were obviously stronger than those as source. Also, the P retention capacity was found highly dependent on iron concentrations. Spatially, the degree of P pollution in the inlet-lake-areas was significantly higher than that in the outlet-lake-areas. Main inlet-lake-areas, e.g., Lake Zhushan and the western coastal area showed greater potential risks of TP release from the sediments. However, external P input was still more prominent than that of internal P loading for Lake Zhushan; thus, measures such as source control and pollution interception should be highlighted for those areas. Whilst, for the western coastal area, apart from the external P loading reduction, the potential risks of internal P loadings should also be concentrated. Additionally, for the surrounding region of the southern area, the relationship between future economic development and wastewater discharge loading should be comprehensively considered and properly handled.

Relating environmental pressures to littoral biological water quality indicators in Western Balkan lakes: Can we fill the largest gaps?

Along six transects in each of six lakes across the Western Balkans, we collected data for three groups of littoral biological water quality indicators: epilithic diatoms, macrophytes, and benthic invertebrates. We assessed the relationships between them and three environmental pressures: nutrient load (eutrophication), hydro-morphological alteration of the shoreline, and water level variation, separating the effect of individual lakes and continuous explanatory variables. Lake water total phosphorus concentration (TP) showed substantial variation but was not related to any of the tested biological indicators, nor to any of the tested pressures. We suggest that this may be due to feedback processes such as P removal in the lake littoral zone. Instead, we found that a gradient in surrounding land-use towards increasing urbanization, and a land-use-based estimate of P run-off, served as a better descriptor of eutrophication. Overall, eutrophication and water level fluctuation were most important for explaining variation in the assessed indicators, whereas shoreline hydro-morphological alteration was less important. Diatom indicators were most responsive to all three pressures, whereas macrophyte biomass and species number responded only to water level fluctuation. The Trophic Diatom Index for Lakes (TDIL) was negatively related to urbanization and wave exposure. This indicates that it is a suitable indicator for pressures related to urbanization, although a confounding effect of wave exposure is possible. Invertebrate abundance responded strongly to eutrophication, but the indicator based on taxonomic composition (Average Score Per Taxon) did not. Our results suggest that our metrics can be applied in Western Balkan lakes, despite the high number of endemic species present in some of these lakes. We argue that local water management should focus on abating the causes of eutrophication and water level fluctuation, whilst preserving sufficient lengths of undeveloped shoreline to ensure good water quality in the long run.

A method for reconstructing past lake water phosphorus concentrations using\xa0sediment geochemical records

An existing steady state model of lake phosphorus (P) budgets has been adapted to allow reconstruction of long-term average historic lake water total phosphorus (TP) concentrations using lake sediment records of P burial. This model can be applied without site-specific parameterisation, thus potentially having universal application. In principle, it is applicable at any site where there is both a sediment P burial record and knowledge of the current water budget, although we advise caution applying it to problematic sediment records. Tested at six published case study sites, modelled lake water TP concentrations agree well with water-quality monitoring data, and limited testing finds good agreement with wholly independent diatom inferred lake water TP. Our findings, together with a review of the literature, suggest that well preserved lake sediments can usefully record a long-term average P burial rate from which the long-term mean lake water TP can be reliably estimated. These lake water TP reconstructions can provide meaningful site-specific reference values to support decision making in lake eutrophication management, including establishing targets for lake restoration.

Distribution of TN and TP in Dongchang Lake from Sediment and Non-sediment Water Recharge Based on MIKE21

With the continuous increase of urban population, the eutrophication of urban lakes is becoming more and more serious. It is necessary to improve the ecological environment of lakes by water supplement. In this study, TN (total nitrogen) and TP (total phosphorus) of Dongchang Lake before and after water replenishment were sampled and measured, and the hydrodynamic, water quality and sediment MIKE21 models of Dongchang Lake were established. Finally, the variation trend of TN and TP of Dongchang Lake before and after water replenishment of sediment and non-sediment water were simulated, and the following conclusions are drawn: During water replenishment, the TP concentration of each point will rise, and the TP concentration of non-sediment water is higher. After the completion of the water replenishment process, the TP concentration at each point decreases in turn. Under the two water replenishment modes, the difference of TP concentration gradually become narrower, but the TP concentration in non-sediment water is higher. The change trend of TN is similar to that of TP, but after the increase of TN concentration caused by water supply, the concentration of TN remains high in the next few days. This study provides an empirical basis for the development of lake water environment improvement strategies.

Impacts of soil use and management on water quality in agricultural watersheds in Southern Brazil

AbstractWorldwide, agriculture is considered one of the main activities that influence water quality. The objective of this work was to evaluate the influence of soil use and management on water quality at the small watershed scale, in Southern Brazil. One watershed is characterized by production of annual crop seeds under no‐tillage (zero tillage), with crop rotation and with terraces (Sarandi watershed—SW), while the other is characterized by production of grains in the summer and pasture with grazing in the winter, under no‐tillage, without crop rotation and without terraces (Coxilha watershed—CW). Flow and climatic data were measured during 2 years. Water samples were manually taken at precipitation events and base flow over 1 year for laboratory analysis. During events of high volume, most of the rainfall was converted to base flow in SW, while in CW, most of the rainfall was transformed into overland flow. Overall, higher concentrations and losses of sediments and nutrients occurred in the CW, mainly during precipitation events in the winter crops season. Of the total nitrogen concentration in water, approximately 3% was ammonium‐N and 58% was nitrate‐N, on average, in both watersheds. For total phosphorus concentration in water, more than 75% was particulate in both watersheds, however, the bioavailable phosphorus accounted for 70% of the total phosphorus in the SW and for 35% in the CW. The higher concentration of bioavailable phosphorus in the SW indicates a short‐term pollution potential, but in both watersheds, the water quality was impaired by the high concentrations of total phosphorus. In general, even with no‐tillage, the results highlight the importance of best management practices as terracing, riparian vegetation, crop rotation, better crop systems and fertilizer management to avoid degradation of water resources.

Establishing an empirical equation for the relationship between total suspended solids and total phosphorus concentrations in the downstream Red river water

Recently, the Asian rivers have faced the strong reduction of riverine total suspended solids (TSS) flux due to numerous dam/reservoir impoundment. The Red river system is a typical example of the Southeast Asian rivers that has been strongly impacted by reservoir impoundment in both China and Vietnam, especially in the recent period. It is known that the reduction in total suspended solids may lead to the decrease of some associated elements, including nutrients (N, P, Si) which may affect coastal ecosystems. In this paper, we establish the empirical relationship between total suspended solids and total phosphorus concentrations in water environment of the Red river in its downstream section from Hanoi city to the Ba Lat estuary based on the sampling campaigns conducted in the dry and wet seasons in 2017, 2018 and 2019. The results show a clear relationship with significant coefficient between total suspended solids and total phosphorus in the downstream Red river. It is expressed by a simple equation y = 0.0226x0.3867 where x and y stand for total suspended solids and total phosphorus concentrations (mg/l) respectively with the r2 value of 0.757. This equation enables a reasonable prediction of total phosphorus concentrations of the downstream Red river when the observed data of total suspended solids concentrations are available. Thus, this work opens up the way for further studies on the calculation of the total phosphorus over longer timescales using daily available total suspended solids values.

Effects of a rainbow trout stocking moratorium on the Daphnia species composition and water quality of Square Lake (Minnesota)

Hembre, LK. 2019. Effects of a rainbow trout stocking moratorium on the Daphnia species composition and water quality of Square Lake (Minnesota). Lake Reserv Manage. 35:127–139.Square Lake is among the clearest lakes in the Minneapolis–St. Paul (Minnesota) metropolitan area, but its water clarity has decreased over the past several decades despite levels of total phosphorus (TP) remaining relatively stable. Predation by zooplanktivorous rainbow trout annually stocked since the early 1980s was hypothesized to be the cause for this eutrophication trend. To evaluate this hypothesis, a 3-year moratorium on trout stocking was imposed by the Minnesota Department of Natural Resources (MNDNR) and water quality and zooplankton monitoring data from 2 years prior to the moratorium (2010 and 2012) were compared to data from the 3 moratorium years (2013–2015). Significant changes observed during the moratorium years that support the hypothesis include (1) an increase in biomass concentrations of the large-bodied Daphnia pulicaria, (2) a coincident decrease in biomass concentrations of the smaller bodied D. mendotae, and (3) more pronounced spring clear-water phases when D. pulicaria reached peak densities. In addition, the volume of hypoxic water (dissolved oxygen [DO] < 1 mg/L) that developed in deep water was less in moratorium years compared to the premoratorium years. Unexpectedly, surface water TP concentrations were significantly lower during the moratorium years than in premoratorium years. Greater sequestration of P in the biomass of Daphnia during the moratorium years is the likely cause for the decrease in surface water TP levels in those years. Natural resource managers from the MNDNR have extended the moratorium and are using the conclusions from this study to determine the future fisheries management plan for Square Lake.

Research of total phosphorus concentration in Hefei Ring River based on landsat-8 satellite image data

Total phosphorus (TP) in water is an important indicator reflecting water environment and water ecology. If the concentration exceeds the standard, it will directly lead to eutrophication. The daily monitoring of total phosphorus in water bodies has already mentioned the important agenda of environmental protection, while the routine testing has a large workload and heavy tasks. We used satellite remote sensing technology to extract image data and establish a mathematical models, what was used to invert the total phosphorus concentration in water. Taking the Ring River as an example, we selected different time nodes to sample and measure the TP value, and use the landsat-8 image data to establish a semi-empirical regression model. The model structure, the calculation results found that the error with the measured data is within the controllable range. The method is simple in operation, saves resources, manpower and financial resources, and can accurately reflect the actual situation of the water body TP.

Análise espacial e temporal do índice de estado trófico da água em diferentes sub-bacias do rio Verruga no trecho Vitória da Conquista-Itambé, Bahia

Este trabalho teve como objetivo analisar a variabilidade espacial e temporal do Índice de Estado Trófico (IET) em sete pontos de amostragem e em diferentes sub-bacias do rio Verruga, localizado entre os municípios de Vitória da Conquista e Itambé, região sudoeste da Bahia, durante o período de 10 meses de monitoramento, em escala de tempo mensal. A determinação da concentração de fósforo total na água foi feita de acordo as recomendações da APHA (2005). Com base nos resultados obtidos, conclui-se que as águas do rio Verruga apresentam estado hipereutrófico.

Evaluation of Storm Water Surface Runoff and Road Debris as Sources of Water Pollution

Street sweeping is regularly performed within cities and residential communities to reduce roadway debris and ensure properly functioning storm water management systems. Given removal of plant and soil debris, street sweeping may also reduce nonpoint source pollution through removal of leachate source material. To assess the influence of street sweeping on storm water pollutants, 36 storm water collection devices were installed within six residential communities in Central Florida and subjected to varying municipal sweeping regimes. Additionally, precipitation and storm water retention pond leachate samplers were installed to quantify pollutant sources that may enter and leave selected urban communities. Despite high variability in percentage of impervious surfaces, population density, and volume of road debris among communities, no significant (P ≤ 0.05) differences were observed for total Kjeldahl nitrogen (TKN), nitrate + nitrite (NOx), and total phosphorus (TP) concentrations in storm water among communities or between swept and unswept areas of roadways. Similarly, no significant differences were observed for TKN, NOx, and TP concentrations in precipitation and storm water. Significant differences in orthophosphate (ortho-P), however, were observed between communities and precipitation. Additionally, storm water TP concentrations were greater than discharge estimated to originate from communities within the study area. Although street sweeping may be effective at reducing volume of roadway debris, our data did not find it reduced N or P in storm water.

Temporal and spatial variability of in situ nitrogen fixation activities associated with the Mediterranean seagrass Posidonia oceanica meadows

AbstractThis study provides the first extensive data on in situ rates of N2 fixation in minimally disturbed Posidonia oceanica meadows and their temporal and spatial variability along the Mallorcan coasts in the Mediterranean Sea. Benthic bell‐jar chambers were deployed underwater enclosing (1) natural P. oceanica shoots, (2) matted sediment of P. oceanica with the leaves carefully removed by clipping to assess the contribution of N2 fixation associated with leaves, and (3) adjacent unvegetated sediment to assess the contribution of N2 fixation by the sediment. In all of the chambers, N2 fixation varied seasonally, with highest rates during summer and lowest in winter. Average N2 fixation rates in chambers enclosing natural P. oceanica shoots ranged from 0.06 mg N m−2 d−1 to 1.51 mg N m−2 d−1 (0.004–0.107 mmol N m−2 d−1) in summer. Careful removal of leaves generally reduced N2 fixation rates by 16–89%. The N2 fixation rates in unvegetated sediments ranging from 0.01 mg N m−2 d−1 to 1.99 to mg N m−2 d−1 (7.1 × 10−4–0.14 mmol N m−2 d−1) have similar magnitudes in sediments with P. oceanica. This suggests that these sediments are “hot spots” for N2 fixation. Exploratory analyses of environmental factors that may influence N2 fixation rates highlight temperature and pore water total phosphorus concentrations as important factors.

A fish-based index for the assessment of the ecological quality of temperate lakes

A fish – based index for the assessment of the ecological quality of natural temperate lakes was developed, in accordance to the requirements of the Water Framework Directive (WFD) 2000/60/EC. As a case study, 11 natural lakes located at northern and western Greece were selected. Fish surveys were conducted during mid summer to mid autumn in 2010, 2011 and 2012 using Nordic gillnets and electrofishing. Environmental parameters and anthropogenic pressures were assessed for each lake. Fish species richness, abundance, trophic, reproductive and habitat functional guilds were used for extracting a set of 107 metrics, meeting the requirements of the WFD. All metrics were initially tested as candidates for the index development. A stepwise linear regression of each metric against environmental parameters (lake area, altitude, maximum depth, alkalinity) and anthropogenic pressures (drainage area covered by non-natural land uses – NNLC, water total phosphorus concentrations – TP, Lake Habitat Modification Score – LHMS) was initially conducted for ensuring pressure-response relationships. Reference conditions for each lake were estimated by the hindcasting procedure and the ecological quality for each lake was expressed as the ecological quality ratio (EQR) by a value ranging from 0 (poor quality) to 1 (excellent quality). Two fish fauna metrics, the relative numerical abundance of introduced species (Introduceda) and the relative biomass of omnivorous species (OMNIb) were finally extracted as the most significant, responding to LHMS and TP, respectively. The final index was expressed as the mean values of the EQRs of these two metrics. The multimetric fish index presented herein could serve as a tool for assessing the ecological quality of natural lakes at broad geographical scale and generally, in the Mediterranean temperate lakes with similar hydromorphological characteristics.

Artificial destratification effects on nitrogen and phosphorus dynamics in a eutrophic impoundment in the northern Great Plains.

To determine the influence of artificial destratification on nutrient variations in a small eutrophic impoundment, field monitoring and laboratory analyses were conducted in three consecutive summers (2010, 2011, and 2012). The impact of aeration among sampling locations and across the water column of nutrient concentrations, including total and dissolved inorganic nitrogen (N) and phosphorus (P) and water temperature and dissolved oxygen (DO) was evaluated under aerated and non-aerated conditions. Aeration eliminated thermal stratification and DO concentrations of bottom waters increased. Nutrients including soluble reactive phosphorus (SRP), total phosphorus (TP), and total nitrogen (TN) concentrations across the water column did not change significantly during aeration. Nevertheless, under aerated conditions, dissolved inorganic nutrients, TN, TP, and temperature were homogenously distributed throughout the water column as an effect of aeration. Results indicated that artificial destratification resuspended nutrients throughout the water column; however, it did not have a significant effect on nutrient concentrations in the water column, but SRP, TN, and TP concentrations did not reach to the recommended limit as needed by the North Dakota Department of Health requirements. Therefore, alternative aeration methods, for instance, hypolimnetic oxygenation or hypolimnetic aeration are recommended to control nutrient redistribution and/or further releases by existing aeration system.

Effects of Controlled Irrigation and Drainage on Nitrogen and Phosphorus Concentrations in Paddy Water

Controlled irrigation and drainage (CID) has received attention for improving water quality. Under CID condition, water stress is frequently experienced in two contexts: first drought and then flooding (FDTF) and first flooding and then drought (FFTD). This study aimed to investigate the effects of FDTF and FFTD on nitrogen (N) and phosphorus (P) dynamics in paddy water at different growth stages. The effects of water stress on the migration and transformation of N and P were also investigated. Results showed that CID can decrease N and P concentrations in surface water.NH4+-Nwas the major form of N in surface drainage and percolation water. Mean total phosphorus (TP),NH4+-N, andNO3--Nconcentrations were significantly higher than in FFTD during the growth stage. MeanNH4+-N,NO3--N, and TP concentrations were significantly higher in percolation water under flooding stress than those under drought stress at growth stage, except for mean TP concentrations at milky stage (stage IV). Meanwhile, flooding can sharply increase theNH4+-N,NO3--N, and TP concentrations in percolation water after drought. Thus, without CID, the considerably highNH4+-N,NO3--N, and TP concentrations via runoff and leaching can be responsible for the eutrophication of water bodies in the vicinity of paddy fields during the rice growing season when water stress transforms from drought into flooding.