Comparing efficacy of different taxonomic resolutions and surrogates in detecting changes in soft bottom assemblages due to coastal defence structures

Sandy shores on the West coast of the North Adriatic Sea are extensively protected by different types of defence structures to prevent coastal erosion. Coastal defence schemes modify the hydrodynamic regime, the sediment structure and composition thus affecting the benthic assemblages. This study examines the effectiveness in detecting changes in soft bottom assemblages caused by coastal defence structures by using different levels of taxonomic resolution, polychaetes and/or bivalves as surrogates and different data transformations. A synoptic analyses of three datasets of subtidal benthic macrofauna used in studies aimed at assessing the impact of breakwaters along the North Adriatic coast has been done. Analyses of similarities and correlations between distance matrices were done using matrices with different levels of taxonomic resolution, and with polychaetes or bivalves data alone. Lentidium mediterraneum was the most abundant species in all datasets. Its abundance was not consistently related to the presence of defence structures. Moreover, distribution patterns of L. mediterraneum were masking the structure of the whole macrofaunal assemblages. Removal of L. mediterraneum from the datasets allowed the detection of changes in benthic assemblages due to coastal defences. Analyses on different levels of taxonomic resolution showed that the level of family maintained sufficient information to detect the impacts of coastal defence structures on benthic assemblages. Moreover, the outcomes depended on the transformation used. Patterns of distribution of bivalves, used as surrogates, showed low correlations with the patterns of the total macrofaunal species assemblages. Patterns of polychaetes, if identified to the species or genus level showed higher correlations with the whole dataset. However, the identification of polychaetes to species and genus level is as costly as the identification of all macrobenthic taxa at family level.This study provided additional evidences that taxonomic sufficiency is a useful tool in environmental monitoring, also in investigations on the impacts of coastal defence structures on subtidal macrofauna. The use of coarser taxonomic level, being time-efficient, would allow improving sampling designs of monitoring programs by increasing replication in space and time and by allowing long term monitoring studies.     

Using sediment rating parameters to evaluate the changes in sediment transport regimes in the middle Yellow River basin,China

This study analyses the changes in sediment transport regimes in the middle Yellow River basin (MYRB) using sediment rating parameters. Daily streamflow and suspended sediment concentration data were collected at 35 hydrological stations from the 1950s to 2016, which can be divided into three periods based on the type and intensity of human activities: the base stage before 1970, the restraining stage from 1971 to 1989, and the restoration stage after 2002. Data within each period were fitted by log‐linear sediment rating curves and the sediment rating parameters were utilized to analyse the spatial and temporal variations in sediment transport regimes. The results show that sediment rating parameters are indicative of sediment transport regimes. In the base stage and the restraining stage, the hydrological stations can be categorized into four groups based on their locations on the rating parameter plot. The stations with small drainage basins were characterized by the highest sediment transport regime, followed by those located in the coarse‐particle zone, the loess zone, and the mountainous/forest zone. In the restoration stage, the difference in sediment transport regimes between different geomorphic zones became less distinguishable than in previous stages. During the transition from the base stage to the restraining stage, sediment rating parameters showed no significant changes in sediment transport regimes in all four geomorphic groups. During the transition from the restraining stage to the restoration stage, significant changes were observed in the coarse‐particle zone and the mountain/forest zone, indicating that the revegetation programme and large reservoirs imposed a stronger influence on sediment transport regimes in these two zones than in the rest of the MYRB. This study provides theoretical support for evaluating sediment transport regimes with sediment rating parameters.     

An assessment of the pollutant status of surficial sediment in Cork Harbour in the South East of Ireland with particular reference to polycyclic aromatic hydrocarbons

Surface sediment from three polluted sites within Cork Harbour, Ireland, and from a relatively clean reference site were collected and analysed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), brominated flame retardants (BFRs), organotins (OTs), and heavy metals. PAHs were determined to be the most abundant class of contaminant. Concentrations of the sum (Sigma) of the 21 PAHs measured from the Harbour sites (2877.70 ng g(-1), 1000.7 ng g(-1) and 924.40 ng g(-1) dry weight respectively) were significantly higher than that of the sediment from the reference site (528.30 ng g(-1) dry weight). An inner harbour site, Douglas being the more contaminated of the three harbour sites. A similar pattern was observed with the other contaminants however, these compounds, with the exception of the heavy metals, all tended to be detected at concentrations on or below detection limits.     

Calibration and identifiability analysis of a water quality model to evaluate the contribution of different processes to the short-term dynamics of suspended sediment and dissolved nutrients in the surface water of a rural catchment

A method that combines calibration and identifiability analysis of a dynamic water quality model to evaluate the relative importance of various processes affecting the dynamic aspects of water composition is illustrated by a study of the response of suspended sediment and dissolved nutrients to a flood hydrograph in a rural catchment area in the Netherlands. Since the water quality model simulates the observed concentrations of suspended sediment and dissolved nutrients reasonably well, the most important processes during the observed flood hydrograph could be determined. These were erosion, exchange between dissolved phase and bed sediments and denitrification. It is concluded that the method is very useful for identifying the most significant model parameters and processes that are essential for water quality modelling. © 1998 John Wiley & Sons, Ltd.     

Sampling strategy to describe the temporal hydrochemical characteristics of an alpine proglacial stream

A hierarchical sampling programme (including continuous monitoring, twice-daily sampling and sampling at hourly intervals over selected 24 hour periods) was devised to support hydrochemical and hydrological research programmes on an alpine proglacial stream. The rationale for the research and for the sampling programme are explained and the hydrochemical time series generated over an ablation season are analysed to assess the degree to which they support the study aims. It appears that there is no satisfactory substitute for the chemical analysis of at least two water samples taken at approximately maximum and minimum discharge every day, if seasonal variations in meltwater chemistry are to be effectively characterized. Such time series data can be used to estimate Box-Jenkins transfer function-noise models between particular solutes (SO²⁻₄, Ca²⁺, Mg²⁺, Na⁺ and possibly K⁺) and either discharge or electrical conductivity, which can then be used to fill any short gaps in the data. This approach is not satisfactory even for filling short gaps in the twice-daily determinations of pH, HCO⁻₃ and NO⁻₃. At the diurnal time-scale (based on hourly determinations over 24 hour periods) electrical conductivity seems to provide a good surrogate for most of the solutes studied. HCO⁻₃, SO²⁻₄, Ca²⁺ and Mg²⁺ were found to be particularly strongly related to electrical conductivity and there was little if any significant serial autocorrelation in the residuals from all of the simple linear regression relationships that were estimated between individual species and conductivity. It is concluded that the hierarchical sampling design was suitable for the purposes of the study, and that the continuous monitoring of electrical conductivity provides excellent supporting information to the chemical analysis of water samples if it is used carefully as a means of short term calibration and interpolation of the solute record.     

A probabilistic framework to evaluate the uncertainty of design hydrograph: case study of Swannanoa River watershed

ABSTRACT

This study presents a probabilistic framework to evaluate the impact of uncertainty of design rainfall depth and temporal pattern as well as antecedent moisture condition (AMC) on design hydrograph attributes – peak, time to peak, duration and volume, as well as falling and rising limb slopes – using an event-based hydrological model in the Swannanoa River watershed in North Carolina, USA. Of the six hydrograph attributes, falling limb slope is the most sensitive to the aforementioned uncertainties, while duration is the least sensitive. In general, the uncertainty of hydrograph attributes decreases in higher recurrence intervals. Our multivariate analysis revealed that in most of the return periods, AMC is the most important driver for peak, duration and volume, while time to peak and falling limb slope are most influenced by rainfall pattern. In higher return periods, the importance of rainfall depth and pattern increases, while the importance of AMC decreases.     

Spatio-temporal variability of phytoplankton assemblages in the Pearl River estuary, with special reference to the influence of turbidity and temperature

The Pearl River Estuary is among the largest estuaries in the subtropical areas of the world. Along the salinity and turbidity gradient between the freshwater reach of the Pearl River and the marine water of the South China Sea, the spatial and temporal composition and abundance of phytoplankton was examined in relation to physic-chemical variables during the dry and wet seasons of 2009. Water samples for phytoplankton and environmental parameters were collected from 18 stations during two seasons along a transect from upper estuary to estuarine and marine sectors. A total of 162 species belonging to 7 phyla were identified, with diatoms dominated in both seasons while dinoflagellates proliferated in autumn. Two main clusters and three sub-clades under each main cluster corresponding to seasons and water sectors were defined with multivariate analysis (cluster and nMDS). Based on the species composition and abundance of phytoplankton, both seasonal and spatial variability were observed at a significant level (ANOSIM: season effect, R=0.896, P<0.01; station effect, R=0.463, P<0.01). The correlation analysis between biotic and abiotic variables indicated that instead of the “proverbial” anthropogenic nutrients loading and salinity gradient, the best 2-variable combination (temperature and turbidity) showed a significant effect on the pattern of phytoplankton assemblages (ρ_w=0.49, BIOENV analysis) between wet and dry seasons in the Pearl River Estuary. This result suggests that physical disturbance either natural or manmade is a more important factor in regulating the phytoplankton community structure within the hydrologically distinct zone of estuaries.     

Application of Bayesian model and discriminant function analysis to the estimation of sediment source contributions

Bayesian and discriminant function analysis (DFA) models have recently been used as tools to estimate sediment source contributions. Unlike existing multivariate mixing models, the accuracy of these two models remains unclear. In the current study, four well-distinguished source samples were used to create artificial mixtures to test the performance of Bayesian and DFA models. These models were tested against the Walling-Collins model, a credible model used in estimation of sediment source contributions estimation, as a reference. The artificial mixtures were divided into five groups, with each group consisting of five samples with known source percentages. The relative contributions of the sediment sources to the individual and grouped samples were calculated using each of the models. The mean absolute error (MAE) and standard error of (SE) MAE were used to test the accuracy of each model and the robustness of the optimized solutions. For the individual sediment samples, the calculated source contributions obtained with the Bayesian (MAE = 7.4%, SE = 0.6%) and Walling-Collins (MAE = 7.5%, SE = 0.7%) models produced results which were closest to the actual percentages of the source contributions to the sediment mixtures. The DFA model produced the worst estimates (MAE = 18.4%, SE = 1.4%). For the grouped sediment samples, the Walling-Collins model (MAE = 5.4%) was the best predictor, closely followed by the Bayesian model (MAE = 5.9%). The results obtained with the DFA model were similar to the values for the individual sediment samples, with the accuracy of the source contribution value being the poorest obtained with any of the models (MAE = 18.5%). An increase in sample size improved the accuracies of the Walling-Collins and Bayesian models, but the DFA model produced similarly inaccurate results for both the individual and grouped sediment samples. Generally, the accuracy of the Walling-Collins and Bayesian models was similar (p > 0.01), while there were significant differences (p < 0.01) between the DFA model and the other models. This study demonstrated that the Bayesian model could provide a credible estimation of sediment source contributions and has great practical potential, while the accuracy of the DFA model still requires considerable improvement.     

福建省山仔水库沉积物磷对水体磷浓度贡献的估算

为掌握白洋淀浮游植物的群落特征,于2006年4月至10月间对其进行了5次采样调查,经显微镜检,共鉴定出浮游植物155种（属）,浮游植物的密度范围在55．5&#215;10^4-1704．8&#215;10^4cells／L之间,群落组成以蓝藻、隐藻和绿藻为主应用CANOCO4．5软件对获得的浮游植物数据和环境因子数据进行典范相关分析（CCA）,作出物种与环境因子关系的二维排序图．结果表明,水体中的pH值及总磷浓度是影响这一区域物种分布格局重要因素,除此之外,生物需氧量和溶氧量也对浮游植物的分布有较大影响．CCA排序图较好的说明了浮游植物物种分布和环境因子之间的关系．     

Appraisal of the carbon to nitrogen(C/N)ratio in the bed sediment of the Betwa River,Peninsular India

Bed sediment carbon to nitrogen(C/N) ratio is one of the essential variables reflecting sources of organic matter in river basins.In order to explore the spatial variability in sources of sediment C/N ratios,and the influence of land use and land cover(LULC) changes on the Betwa River basin in Peninsular India,51 river bed sediment samples were collected in December 2016.The coefficient of variation(CV) was35%indicating highly variable biogeochemical parameters.The sediment C/N ratio varied from 2.94 to 10.09.3.21-56.40,and 6.50-76.97 in upstream,mid-stream,and downstream regions,respectively,indicating a progressive change in sources of organic matter and depositional environment.The positive correlation between total carbon(TC) and C/N ratio was increasing in the downstream direction [upstream(+0.560) mid-stream(+0.603) downstream(+0.838)],which is an indication of high deposition and slow decomposition of sedimentary terrigenous organic matter distant from the regions of urban pollution.The LULC change analysis done by remote sensing and Geographic Information System(GIS)methods revealed an adverse change for the forests and barren land and a positive change for the agricultural land and built-up areas.The sediment C/N ratio mapping showed the impact of LULC changes on the sediment quality.The spatial distribution of bed sediment C/N ratio in the Betwa River basin has important reference value for managing organic matter transport in the downstream Yamuna River and Ganga River basin.     

Analysis of foraminifera assemblages and sediment geochemical properties to characterise the environment near Araçá and Saco da Capela domestic sewage submarine outfalls of São Sebastião Channel, São Paulo State, Brazil

Superficial bottom samples were collected near diffusers of domestic sewage submarine outfalls at Araçá and Saco da Capela, São Sebastião Channel, Brazil. The goal of this study was to investigate the distribution and composition of live benthic foraminifera assemblages and integrate the results obtained with geochemical analyses to assess human-induced changes. According to the results obtained no environmental stress was observed near the Saco da Capela submarine outfall diffusers. The foraminifera assemblage is characterised by species typical of highly hydrodynamic environments, with well-oxygenated bottom waters and low nutrient contents. In contrast, near Araçá submarine outfall, organic enrichment was denoted by high phosphorus, sulphur and, to a lesser extent, total organic carbon content. Harmful influences on foraminifera could be identified by low richness and specific diversity, as well as the predominance of detritivore feeder species, which are associated with higher organic matter flux and low oxygen in the interstitial pore water.