An Approach to Reaeration Coefficient Modeling in Local Surface Water Quality Monitoring

Reaeration coefficient (k ₂) for River Atuwara, Ogun State, Nigeria was calculated from dissolved oxygen and biochemical oxygen demand data collected over period of 3 months covering the two prevailing climatic seasons in the country. Both the Akaike and Bayesian information criteria were used in the selection and analysis of ten models to identify the most suitable reaeration coefficient (k ₂) model for Atuwara River. Models that passed the confidence limit were subjected to model evaluation using measures of agreement between observed and predicted data such as percent bias, Nash–Sutcliffe efficiency, and root mean square observation standard deviation ratio. The used approach yield better results than empirical models developed for local conditions while it is also useful in conserving scarce resources.     

Hydrologic modelling for Lake Basaka: development and application of a conceptual water budget model

Quantification of fluxes of water into and out of terminal lakes like Basaka has fundamental challenges. This is due to the fact that accurate measurement and quantification of most of the parameters of a lake’s hydrologic cycle are difficult. Furthermore, quantitative understanding of the hydrologic systems and hence, the data-intensive modelling is difficult in developing countries like Ethiopia due to limitation of sufficient recorded data. Therefore, formulation of a conceptual water balance model is extremely important as it presents a convenient analytical tool with simplified assumptions to simulate the magnitude of unknown fluxes. In the current study, a conceptual lake water balance model was systematically formulated, solved, calibrated, and validated successfully. Then, the surface water and groundwater interaction was quantified, and a mathematical relationship developed. The overall agreement between the observed and simulated lake stage at monthly time step was confirmed based on the standard performance parameters (R ², MAE, RMSE, E _f). The result showed that hydrological water balance of the lake is dominated by the groundwater (GW) component. The net GW flux in recent period (post-2000s) accounts about 56 % of the total water inflow. Hence, GW plays a leading role in the hydrodynamics and existence of Lake Basaka and is mostly responsible for the expansion of the lake. Thus, identification of the potential sources/causes for the GW flux plays a leading role in order to limit the further expansion of the lake. Measurement of GW movement and exchange in the area is a high priority for future research.     

Regional status assessment of stony corals in the US Virgin Islands

States may protect coral reefs using biological water quality standards outlined by the Clean Water Act. This requires biological assessments with indicators sensitive to human disturbance and regional, probability-based survey designs. Stony coral condition was characterized on a regional scale for the first time in the nearshore waters of the US Virgin Islands (USVI). Coral composition, abundance, size, and health were assessed at 66 stations in the St. Croix region in fall 2007 and at 63 stations in the St. Thomas and St. John region in winter 2009. Indicators were chosen for their sensitivity to human disturbance. Both surveys were probability-based (random) designs with station locations preselected from areas covered by hardbottom and coral reef substrate. Taxa richness was as high as 21 species but more than half the area of both regions exhibited taxa richness of <10 species in the 25 m² transect area. Coral density was as high as 5 colonies m^?2 but more than half the area of both regions had <2 colonies m^?2. Both regions showed similar dominant species based on frequency of occurrence and relative abundance. Because of large colony sizes, Montastrea annularis provided more total surface area and live surface area than more abundant species. The surveys establish baseline regional conditions and provide a foundation for long-term regional monitoring envisioned by the USVI Department of Planning and Natural Resources. The probabilistic sampling design assures the data can be used in Clean Water Act reporting.     

The New Bedford Harbor Superfund site long-term monitoring program (1993–2009)

New Bedford Harbor (NBH), located in southeastern Massachusetts, was designated as a marine Superfund site in 1983 due to sediment contamination by polychlorinated biphenyls (PCBs). Based on risks to human health and the environment, the first two phases of the site cleanup involved dredging PCB-contaminated sediments from the harbor. Therefore, a long-term monitoring program (LTM) was developed to measure spatial and temporal chemical and biological changes in sediment, water, and biota to assess the effects and effectiveness of the remedial activities. A systematic, probabilistic sampling design was used to select sediment sampling stations. This unbiased design allowed the three segments of the harbor to be compared spatially and temporally to quantify changes resulting from dredging the contaminated sediments. Sediment was collected at each station, and chemical (e.g., PCBs and metals), physical (e.g., grain size), and biological (e.g., benthic community) measurements were conducted on all samples. This paper describes the overall NBH-LTM approach and the results from the five rounds of sample collections. There is a decreasing spatial gradient in sediment PCB concentrations from the northern boundary (upper harbor) to the southern boundary (outer harbor) of the site. Along this same transect, there is an increase in biological condition (e.g., benthic community diversity). Temporally, the contaminant and biological gradients have been maintained since the 1993 baseline collection; however, since the onset of full-scale remediation, PCB concentrations have decreased throughout the site, and one of the benthic community indices has shown significant improvement in the lower and outer harbor areas.     

Metal concentrations and metallothionein levels in Mytilus galloprovincialis from Elefsis bay (Saronikos gulf, Greece)

Spatial and temporal variability of Cd, Cu, Cr, Ni, Zn, Fe and Mn and metallothionein (MT) concentrations were determined in mussels Mytilus galloprovincialis from Elefsis bay (Saronikos gulf, Greece). Higher concentrations of both metal concentrations and MTs were recorded in mussels inhabiting industrial locations (steelworks and shipyard), indicating a markedly higher metal bioavailability. However at these sites, located at the eastern part of the bay, mussel metal concentrations were not always correlated with both seawater metal concentrations and MTs possibly due to different time scales of integration of the metal sources into mussels and/or the participation of other metal regulatory mechanisms except MT induction. The pattern of the temporal variation of mussel metal concentrations and the MT levels was similar among stations with higher values during the winter–spring season and lower during the summer–autumn period. The inverse relationship of flesh condition index with mussel metal concentrations was attributed to the influence of mussel annual reproductive cycle.     

Characterizing the intrinsic bioremediation potential of 1,4-dioxane and trichloroethene using innovative environmental diagnostic tools

An intrinsic biodegradation study involving the design and implementation of innovative environmental diagnostic tools was conducted to evaluate whether monitored natural attenuation (MNA) could be considered as part of the remedial strategy to treat an aerobic aquifer contaminated with 1,4-dioxane and trichloroethene (TCE). In this study, advanced molecular biological and stable isotopic tools were applied to confirm in situ intrinsic biodegradation of 1,4-dioxane and TCE. Analyses of Bio-Trap? samplers and groundwater samples collected from monitoring wells verified the abundance of bacteria and enzymes capable of aerobically degrading TCE and 1,4-dioxane. Furthermore, phospholipid fatty acid analysis with stable isotope probes (PLFA-SIP) of the microbial community validated the ability for microbial degradation of TCE and 1,4-dioxane. Compound specific isotope analysis (CSIA) of groundwater samples for TCE resulted in δ(13)C values that indicated likely biodegradation of TCE in three of the four monitoring wells sampled. Results of the MNA evaluation showed that enzymes capable of aerobically degrading TCE and 1,4-dioxane were present, abundant, and active in the aquifer. Taken together, these results provide direct evidence of the occurrence of TCE and 1,4-dioxane biodegradation at the study site, supporting the selection of MNA as part of the final remedy at some point in the future.     

Utilizing pyrosequencing and quantitative PCR to characterize fungal populations among house dust samples

Molecular techniques are an alternative to culturing and counting methods in quantifying indoor fungal contamination. Pyrosequencing offers the possibility of identifying unexpected indoor fungi. In this study, 50 house dust samples were collected from homes in the Yakima Valley, WA. Each sample was analyzed by quantitative PCR (QPCR) for 36 common fungi and by fungal tag-encoded flexible (FLX) amplicon pyrosequencing (fTEFAP) for these and additional fungi. Only 24 of the samples yielded amplified results using fTEFAP but QPCR successfully amplified all 50 samples. Over 450 fungal species were detected by fTEFAP but most were rare. Twenty-two fungi were found by fTEFAP to occur with at least an average of ≥0.5% relative occurrence. Many of these fungi seem to be associated with plants, soil or human skin. Combining fTEFAP and QPCR can enhance studies of fungal contamination in homes.     

Sand as a relevant fraction in geochemical studies in intertidal environments

Soil and sediment samples from several intertidal environment exposed to different types of contamination were studied to investigate the importance of grain size in relation to the capacity of the substrates to retain trace metals. The unfractionated samples (referred to as bulk samples) were separated into the following grain/size fractions: fine–coarse sand (2?0.100 mm), very fine sand (0.100?0.050 mm), silt (0.050?0.002 mm), and clay (0.002 mm). The sample into its fractions was carried out was in a glove box under high-purity N₂ atmosphere in order to minimize any alterations to the samples. The bulk samples were characterized in terms of physicochemical properties such as pH, redox potential, and grain size. The total organic carbon (TOC), total sulfur (S), iron (Fe) pyrite, Fe, and manganese (Mn), and trace metals lead (Pb), mercury (Hg), chromium (Cr), and nickel (Ni) were analyzed in the bulk samples and in each fraction. The sand fractions were also examined by scanning electron microscopy (SEM). Comparisons of the above parameters were made between fractions and between each fraction and the corresponding bulk sample. The fine–coarse sand fraction contained high levels of the primary elements of the geochemical processes that occur in marine sedimentary environments such as TOC, total Fe, Mn, and S. The net concentrations of these four elements were higher in the fine-coarse sand fraction than in the very fine sand fraction and were similar to the net concentrations in the silt and clay fractions. Detailed SEM analysis of the sand coarse fraction revealed the presence of Fe and aluminum oxyhydroxide coatings in the oxic layers, whereas the framboidal pyrites and coatings observed in the anoxic layers were Fe sulfides. The presence of the various coatings explains why the trace metal concentrations in the sand fine–coarse fraction were similar to those in the clay fraction and higher than those in the very fine sand fraction. The present results highlight the importance of the sand fraction, which is generally disregarded in geochemical and environmental studies of sedimentary layers.