Habitat suitability modelling to improve understanding of seagrass loss and recovery and to guide decisions in relation to coastal discharge.

Habitat suitability modelling was used to test the relationship between coastal discharges and seagrass occurrence based on data from Adelaide (South Australia). Seven variables (benthic light including epiphyte shading, temperature, salinity, substrate, wave exposure, currents and tidal exposure) were simulated using a coupled hydrodynamic-biogeochemical model and interrogated against literature-derived thresholds for nine local seagrass species. Light availability was the most critical driver across the study area but wave exposure played a key role in shallow nearshore areas. Model validation against seagrass mapping data showed 86 % goodness-of-fit. Comparison against later mapping data suggested that modelling could predict ~745 ha of seagrass recovery in areas previously classified as 'false positives'. These results suggest that habitat suitability modelling is reliable to test scenarios and predict seagrass response to reduction of land-based loads, providing a useful tool to guide (investment) decisions to prevent loss and promote recovery of seagrasses.

Landsat historical records reveal large-scale dynamics and enduring recovery of seagrasses in an impacted seascape.

Seagrasses are considered indicators of anthropogenic impact but surprisingly little is known about their temporal and spatial dynamics in impacted seascapes. In this study, we used three decades of Landsat imagery (1988-2018) off the coast of Adelaide, South Australia, to investigate how seagrass cover over 501 km2 responds to changes in land-based inputs, including breakpoints in system trajectory and associated timelags, and the identification of vulnerable meadows. Field data was used to help train benthic classification of summer imagery and define its accuracy. Temporal dynamics of seagrass cover were investigated in relation to annual and multi-year nitrogen and suspended solids loads. Spatial dynamics were inferred from maps of benthic cover persistence and trajectory for each decade. The region experienced a net regrowth of some 11,000 ha of seagrasses since the early 2000s, with the initial large-scale recruitment visible in the imagery 6 years after the closure of sludge outfalls. Seagrass expansion occurred primarily in deeper waters (>10 m) of the central coast and at the seaward edge of the distribution. Recovery continued until 2011 assisted by a window of opportunity created by a decade-long drought and further reductions in nitrogen loads from wastewater treatment plants and industry. Localized seagrass losses however continued to be observed as a result of either permanent or transient increases in suspended solids loads. Seagrass area in the central coast was well correlated (r2 = 0.88) with 5-year running averages of nitrogen and suspended solids loads. Meadows particularly vulnerable to changes in land-based discharges were located at the edges of the distribution, along erosional scarps and at depths >10 m south of the Torrens River. These areas were identified as useful indicators of seagrass status. Overall, seagrass persistence expanded from 48 to 69% of the mapped area, with the region now mostly covered by stable seagrasses.

Using hyperspectral imagery to investigate large-scale seagrass cover and genus distribution in a temperate coast.

Seagrasses are regarded as indicators and first line of impact for anthropogenic activities affecting the coasts. The underlying mechanisms driving seagrass cover however have been mostly studied on small scales, making it difficult to establish the connection to seagrass dynamics in an impacted seascape. In this study, hyperspectral airborne imagery, trained from field surveys, was used to investigate broadscale seagrass cover and genus distribution along the coast of Adelaide, South Australia. Overall mapping accuracy was high for both seagrass cover (98%, Kappa = 0.93), and genus level classification (85%, Kappa = 0.76). Spectral separability allowed confident genus mapping in waters up to 10 m depth, revealing a 3.5 ratio between the cover of the dominant Posidonia and Amphibolis. The work identified the absence of Amphibolis in areas historically affected by anthropogenic discharges, which occasionally contained Posidonia and might be recovering. The results suggest hyperspectral imagery as a useful tool to investigate the interplay between seagrass cover and genus distribution at large spatial scales.

Bioconcentration of triclosan and methyl-triclosan in marine mussels (Mytilus galloprovincialis) under laboratory conditions and in metropolitan waters of Gulf St Vincent, South Australia.

The anti-microbial agent triclosan (TCS), and its derivative methyl-triclosan (Me-TCS), are discharged with treated effluents from wastewater treatment plants to receiving environments. We investigated the bioconcentration of TCS and Me-TCS in mussels (Mytilus galloprovincialis) exposed to TCS (100 ng L(-1)) for 30 days in seawater aquaria (19±2°C) with fresh phytoplankton as a food source. Bioconcentration increased with time reaching a steady-state around 24-30 days. The bioconcentration factor (log BCF) for TCS were 2.81 L kg(-1) (dry weight) and 4.13 L kg(-1), when lipid normalised concentrations were used. Mussels were also deployed in cages at four marine locations receiving effluents from WWTPs. The mean (±SD) TCS and Me-TCS concentrations for mussels from these sites were 9.87 (±1.34) and 6.99 (±2.44) µg kg(-1). The study showed that mussels can be a useful tool for monitoring pollution of TCS and Me-TCS in marine and estuarine environments.

Poly-aromatic hydrocarbon (PAH) inputs from the Rhône River to the Mediterranean Sea in relation with the hydrological cycle: impact of floods.

The concentrations of dissolved and particulate polycyclic aromatic hydrocarbons (PAHs) were monitored in waters of the Rhône River (France) every fortnight for a full calendar year, from June 1994 to May 1995. All flood events occurring over the course of the experiment were sampled at higher frequency to better quantify the impact of these extreme hydrological episodes on the annual export of PAHs to the Mediterranean Sea. This time-series indicates that more than 90% of the annual load of particulate PAHs is transported during flood episodes, with 77% discharged during the course of only one extreme flood event occurring in November 1994. During these intense events, riverine particles are depleted in PAHs while at low river discharge particles are PAH-enriched. Dissolved PAHs were less variable and less abundant than adsorbed PAHs, consistently with the low solubility of these compounds.

Sorption of 17beta-estradiol onto selected soil minerals.

Sorption of the endocrine-disrupting chemical 17beta-estradiol (E(2)) from aqueous solutions to goethite, an iron oxide, and the clay minerals kaolinite, illite, and montmorillonite (K and Ca forms) was measured at 25 degrees C. The clay minerals sorbed more E(2) than the oxide, with sorption capacity increasing in the order goethite

Characterization of carbonaceous combustion residues: II. Nonpolar organic compounds.

Aromatic and aliphatic fractions of black carbon (BC) solvent extracts were examined by gas chromatography/mass spectrometry to determine how differences in broad chemical and physical features are correlated with the load, composition, "extractability" and bioavailability of organic compounds. Diesel soot, urban dust and chimney soot had concentrations of n-alkanes >20 microg/g and of carcinogenic polycyclic aromatic hydrocarbons (PAHs)>8 microg/g. These high levels of solvent-extractable compounds were interpreted as resulting from combustion at temperatures below optimum values for BC formation. PAH concentrations normalized to the amount of soot carbon in chimney soot were close to values for diesel soot. However, the high proportion of polar amorphous organic matter in chimney soot suggests a higher bioavailability for associated PAHs. Carbon black, vegetation fire residues, and straw and wood charcoals had only residual concentrations of n-alkanes (<9 microg/g) and PAHs (<0.2 microg/g). PAH distributions were mostly unspecific, while the overall signature of the aliphatic fraction varied with BC origin. Molecular markers among plant-derived BC included steroid and sesquiterpenoid hydrocarbons. Molecular fingerprints suggest that compounds associated with fossil BC might be more refractory than those associated with plant-derived BC.

Characterization of carbonaceous combustion residues. I. Morphological, elemental and spectroscopic features.

Scanning electron microscopy, surface area determination, elemental analysis, organic matter extraction and solid-state cross polarization/magic angle spinning and Bloch decay/magic angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy were used to investigate distinctive features among carbonaceous combustion residues. Black carbon (BC) samples included diesel soot, urban dust, carbon black, chimney soot, vegetation fire residues, wood and straw charcoals. Particles varied from small spheres (<50 nm) in fossil BC (>100 m(2)/g), to large layered structures in plant-derived BC (generally <8 m(2)/g). Chimney soot also included large (>1 micrometer) liquid-like structures, while spherules >100 nm were unique to urban dust. The ratios of amorphous to soot carbon (SC) (isolated by thermal degradation) were not necessarily correlated with the degree of aromaticity estimated from H/C ratios. In particular, values of SC in diesel soot were clearly overestimated. Solvent-extractable organic matter (SEOM) was <2% for charcoals and carbon black, but >13% for urban dust, chimney and diesel soot. SEOM is thought to clog pores or to form large waxy globules, hence reducing surface areas. The ratio of polar/nonpolar SEOM was generally <7 for fossil BC, but >30 for plant-derived BC. NMR analysis revealed essentially one chemical shift in the aromatic C region of charcoals, while diesel soot also showed important aliphatic contributions. Aliphatic and oxygenated C predominated over aryl C in urban dust and chimney soot. These morphological and chemical characteristics of the BC samples are discussed in terms of their environmental implications.

Atmospheric BTX and polyaromatic hydrocarbons in Rio de Janeiro, Brazil.

Polycyclic aromatic and monoaromatic (benzene, toluene and xylene, or BTX) hydrocarbons were monitored in Rio de Janeiro, Brazil, during the summer of 1998/1999. The levels of these aromatic chemicals decreased with distance from main roads, indicating mobile sources are the main pollutant emitters in this Latin American city. Benzo[ghi]perylene/indeno[1,2,3-cd]pyrene and benzene/toluene ratios corroborate this idea. However, higher benzene/toluene ratios at one of the major access routes into the city suggest pollutant inputs from a nearby refinery. Literature data were reviewed in order to outline differences and similarities among sources and levels of aromatic pollutants in large urban agglomerations worldwide. Concentrations of benzo[a]pyrene and benzene, which are well-known carcinogenic chemicals, were relatively low in Rio de Janeiro. This fact was attributed to specific atmospheric conditions during the tropical summer and differences in vehicle fuel composition.

The sorption of anthracene onto goethite and kaolinite in the presence of some benzene carboxylic acids.

The uptake of anthracene from dilute aqueous solutions onto goethite and kaolinite was investigated at 25 degrees C, first in the absence and then in the presence of three benzene carboxylic acids: phthalic acid (benzene-1,2-dicarboxylic acid), trimesic acid (-1,3,5-), and mellitic acid (-1,2,3,4,5,6-). Carboxylic acid concentrations were 0.20, 0.10, and 0.05 mM. Anthracene (0.20 microM) did not adsorb strongly onto the pure mineral surfaces, but in the presence of phthalic acid a substantial increase in anthracene uptake was observed, particularly for the goethite systems. Trimesic and mellitic acids did not enhance anthracene uptake. Phthalate and proton adsorption data have been used to model phthalate adsorption onto the mineral surfaces using an extended constant capacitance surface complexation model. This model was then successfully adapted to account for the observed increase in anthracene uptake, where anthracene molecules were assumed to interact with adsorbed phthalate. We propose that the enhancement of anthracene adsorption in the presence of phthalic acid is due to an increase in the hydrophobicity of the mineral surface once phthalic acid molecules adsorb. The same effect was not observed for the other benzene carboxylates because of their greater polarity.