Riverine Sites Research Articles

Tidal Freshwater Zones as Hotspots for Biogeochemical Cycling: Sediment Organic Matter Decomposition in the Lower Reaches of Two South Texas Rivers

While organic and inorganic nutrient inputs from land are recognized as a major driver of primary production in estuaries, remarkably little is known about how processes within the tidal freshwater zones (TFZs) of rivers modify these inputs. This study quantifies organic matter (OM) decomposition rates in surface sediment layers in the lower reaches of two south Texas river channels and identifies key parameters that influence sediment decomposition rates. Sediment cores were collected from non-tidal and tidal freshwater sites in the Mission and Aransas rivers during two summers (June 2015 and June 2016) and two winters (February 2016, January 2017). We measured oxygen consumption rates, organic carbon and nitrogen content, stable isotope ratios (δ13C and δ15N of OM), and sediment porosity. O2 consumption rates in TFZ sediments were 385 ± 88 μmol O2 m−2 h−1 (summer) and 349 ± 87 μmol O2 m−2 h−1 (winter) in the Aransas River and 767 ± 153 μmol O2 m−2 h−1 (summer) and 691 ± 95 μmol O2 m−2 h−1 (winter) in the Mission River. These rates in TFZs were similar to rates in estuaries and higher than rates at non-tidal riverine sites. Rates of sediment O2 consumption were primarily controlled by OM content and temperature. Sediment OM was dominated by algal biomass from in situ production in both TFZs. We hypothesize that algal production and sinking within TFZs is a major pathway for translocation of watershed-derived nutrients from the water column to the sediments within TFZs. Further work is needed to quantify linkages between decomposition, nutrient remineralization, and potential removal through processes such as denitrification.

Threshold responses of riverine fish communities to land use conversion across regions of the world.

The growing human enterprise has sparked greater interest in identifying ecological thresholds in land use conversion beyond which populations or communities demonstrate abrupt nonlinear or substantive change in species composition. Such knowledge remains fundamental to understanding ecosystem resilience to environmental degradation and informing land use planning into the future. Confronting this challenge has been largely limited to inferring thresholds in univariate metrics of species richness and indices of biotic integrity and has largely ignored how land use legacies of the past may shape community responses of today. By leveraging data for 13,069 riverine sites from temperate, subtropical, and boreal climate zones on four continents, we characterize patterns of community change along diverse gradients of urbanization and agricultural land use, and identity threshold values beyond which significant alterations in species composition exists. Our results demonstrate the apparent universality by which freshwater fish communities are sensitive to even low levels of watershed urbanization (range of threshold values: 1%-12%), but consistently higher (and more variable) levels of agricultural development (2%-37%). We demonstrated that fish community compositional thresholds occurred, in general, at lower levels of watershed urbanization and agriculture when compared to threshold responses in species richness. This supports the notion that aggregated taxon-specific responses may better reflect the complexity of assemblage responses to land use development. We further revealed that the ghost of land use past plays an important role in moderating how current-day fish communities respond to land use intensification. Subbasins of the United States experiencing greater rates of past land use change demonstrated higher current-day thresholds. Threshold responses of community composition, such as those identified in our study, illustrate the need for globally coordinated efforts to prioritize country-specific management and policy initiatives that ensure that freshwater fish diversity is not inevitably lost in the future.

Potential Benefits of Acanthocephalan Parasites for Chub Hosts in Polluted Environments.

Some parasites are expected to have beneficial impacts on wild populations in polluted environments because of their bioaccumulation potential of pollutants from their hosts. The fate of organic micropollutants in host-parasite systems and the combined effect of parasitism and pollution were investigated in chub Squalius cephalus, a freshwater fish, infected (n = 73) or uninfected (n = 45) by acanthocephalan parasites Pomphorhynchus sp. from differently contaminated riverine sites. Several ubiquitous pollutants (polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl-ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), phthalates, insecticides, pyrethroids, and N,N-diethyl-meta-toluamide (DEET)) and some of their metabolites were characterized for the first time in parasites and various fish matrices (muscle, liver, and stomach content). Most organic pollutants reached higher levels in parasites than in chub matrices. In contrast, metabolite levels were lower in parasite tissues compared to fish matrices. Infected and uninfected chub exhibited no significant differences in their pollutant load. Body condition, organo-somatic indices, and immunity were not affected by parasitism, and few correlations were found with chemical pollution. Interestingly, infected chub exhibited lower oxidative damage compared to uninfected fish, irrespective of their pollutant load. In light of these results, this correlative study supports the hypothesis that acanthocephalan parasites could bring benefits to their hosts to cope with organic pollution.

Dissolved organic nutrient uptake by riverine phytoplankton varies along a gradient of nutrient enrichment

The concentration of dissolved organic matter (DOM) in freshwaters is increasing in large areas of the world. In addition to carbon, DOM contains nitrogen and phosphorus and there is growing concern that these organic nutrients may be bioavailable and contribute to eutrophication. However, relatively few studies have assessed the potential for dissolved organic nitrogen (DON) or dissolved organic phosphorus (DOP) compounds to be bioavailable to natural river phytoplankton communities at different locations or times. Temporal and spatial variations in uptake, relative to environmental characteristics were examined at six riverine sites in two contrasting catchments in the UK. This study also examined how the uptake by riverine phytoplankton of four DON and four DOP compounds commonly found in rivers, varied with concentration. Total nitrogen (TN) and phosphorus (TP) concentrations, the proportion of inorganic nutrient species, and nutrient limitation varied temporally and spatially, as did the potential for DON and DOP uptake. All eight of the DOM compounds tested were bioavailable, but to different extents. Organic nutrient use depended on the concentration of the organic compound supplied, with simple compounds (urea and glucose-6-phosphate) supporting algal growth even at very low concentrations. DON use was negatively correlated with the TN and ammonia concentration and DOP use was negatively correlated with soluble reactive phosphorus (SRP) and dissolved organic carbon (DOC) concentration. The evidence indicates that DOM in rivers has been overlooked as a potential source of nutrients to phytoplankton and therefore as an agent of eutrophication.

Geochemistry of Bivalve Shells As Indicator of Shore Position of the 2<sup>nd</sup> Century BC

In an area named Mermian (municipality of Agde, South of France), a significant amount of fragmented italic amphorae from the 2nd century BC was discovered, located at a depth of 6 to 8 meters under the bed of the Hérault river. As no ship wreck was found in the vicinity, the reason of the presence of these amphora fragments, whose faces present a large accumulation of oyster shells, is unknown. Reconstructed geomorphological maps of the area present Mermian as a riverine site already at this period, and several hypothetical explanations on the role of these amphorae exist (landfill linked to a neighbouring habitat, bank reinforcement linked to a ford crossing, river landing, etc.). In order to define whether the amphorae were transported to this location and from where, we analysed the stable carbon and oxygen isotopes of the oyster shells. The δ13C and δ18O indicate that all oysters lived in the same environment, refuting a potential transport during the oyster accumulation. Moreover, the analysis of Mytilaster sp. shells in the sediment around the oyster shells also reported a marine origin, suggesting that these oysters were also buried in a marine deposit. Transport to Mermian from a coastal locality is unlikely but may still have happened, although no trace of human handling were observed on the fragments. Still, the presence of other marine or brackish molluscs in the sediment discards the interpretation of Mermian being a continental locality.

Benthic archaeal community structure and carbon metabolic profiling of heterotrophic microbial communities in brackish sediments

Benthic Archaea play a crucial role in the biogeochemical cycles and food webs, however, their spatiotemporal distribution and environmental drivers are not well investigated in brackish sediments. The composition and abundances of benthic archaeal communities were examined from a coastal lagoon; Chilika (India) which is experiencing an intense pressure from anthropogenic and natural factors. High-throughput sequencing of 16S rRNA genes revealed that sediment (n = 96) archaeal communities were largely composed of Crenarchaeota (18.76%), Euryarchaeota (18.34%), Thaumarchaeota (13.45%), Woesearchaeota (10.05%), and Pacearchaeota (4.21%). Archaeal taxa affiliated to methanogens, sulfate-reducers, and ammonia-oxidizers were detected suggesting that carbon, sulfur, and nitrogen cycles might be prominent in benthic sediments. Salinity, total organic carbon, available nitrogen, available phosphorus, macrophyte (Phragmites karka) and inter-taxa relationships between community members and with bacterial communities played steering roles in structuring the archaeal communities. Marine sites with mesohaline-polyhaline regime were dominated by Nitrosopumilus and Thaumarchaeota. In contrast, riverine sites with oligohaline regime demonstrated a higher abundance of Thermoprotei. Macrophyte dominated zones were enriched in Methanomicrobia and Methanobacteria in their rhizosphere sediments, whereas, bulk (un-vegetated) sediments were dominated by Nitrosopumilus. Spatial patterns in archaeal communities demonstrated ‘distance-decay’ patterns which were correlated with changes in physicochemical factors over geographical distances. Heterotrophic microbial communities showed much higher metabolic diversity and activity in their carbon utilization profiles in rhizosphere sediments than the bulk sediments. This baseline information on benthic archaea and their environmental drivers would be useful to assess the impact of anthropogenic and natural pressures on these communities and associated biogeochemical cycles.

Assessment of Avifaunal Diversity in Riverine and Urban Areas of Layyah along the River Indus, Punjab-Pakistan

Layyah City is located along the River Indus and provides rich habitat for a wide range of resident and migratory bird species. The present study documents for the first time the avifaunal diversity and abundance of urban and riverine sites of Layyah. Potential habitats around the city were identified and three study sites were selected, one in each of the main habitat types. A total of 223 species was recorded: 92 residents, 87 winter visitors, 42 passage migrants and two new records from the area. A Shannon Wiener Index of 4.36 indicates that the area has a high level of biodiversity. Of the species recorded, 16 are included in the IUCN Red list as vulnerable (N=6), near threatened (N=9) or endangered (N=1). The most abundant species were House Crow Corvus splendens, House Sparrow Passer domesticus, Common Myna Acridotheres tristis and Common Starling Sturnus vulgaris. Two species, Houbara or McQueen's Bustard Chlamydotis macqueenii and Black-headed Ibis Threskiornis melanocephalus were recorded for the first time from the area. Potential threats to the avian diversity of the area are hunting, habitat loss, and pollution.

Phylogenetic diversity of larval Chironomidae (Diptera) in lowland rivers as a potential tool in assessment of environmental quality

Different components of biological diversity of larval Chironomidae, typically the most abundant and the most diverse of all lotic zoo-benthos, were assessed to determine their suitability in prediction of the environmental quality. Animals were collected as 73 samples at 62 riverine sites on the territory of Poland and identified morphologically. The analysis of nonlinear regression was used to compare the suitability of the seven indices of diversity. Traditional indices of taxonomic diversity (taxonomic richness, Margalef and Shannon indices) and indices of taxonomic distinctness were found to be unsuitable for this purpose because of the unimodal type of response of their values along with the gradient of the environmental quality. Contrary to them, values of two measures of phylogenetic diversity monotonically increased along with the values of environmental quality measured by official index MMI (Multimetric Macroinvertebrate Index) and were considered highly useful. The best fitted functions estimating relationships between MMI and both indices of phylogenetic diversity (total phylogenetic distance and quadratic entropy) were statistically highly significant and have high values of the fit-accuracy parameters. Original index of phylogenetic diversity ChiPDi based on total phylogenetic diversity, quadratic entropy and taxonomic richness has been presented as well as the proposal of related procedure using barcoding methods.

Whooping crane use of riverine stopover sites.

Migratory birds like endangered whooping cranes (Grus americana) require suitable nocturnal roost sites during twice annual migrations. Whooping cranes primarily roost in shallow surface water wetlands, ponds, and rivers. All these features have been greatly impacted by human activities, which present threats to the continued recovery of the species. A portion of one such river, the central Platte River, has been identified as critical habitat for the survival of the endangered whooping crane. Management intervention is now underway to rehabilitate habitat form and function on the central Platte River to increase use and thereby contribute to the survival of whooping cranes. The goal of our analyses was to develop habitat selection models that could be used to direct riverine habitat management activities (i.e., channel widening, tree removal, flow augmentation, etc.) along the central Platte River and throughout the species’ range. As such, we focused our analyses on two robust sets of whooping crane observations and habitat metrics the Platte River Recovery Implementation Program (Program or PRRIP) and other such organizations could influence. This included channel characteristics such as total channel width, the width of channel unobstructed by dense vegetation, and distance of forest from the edge of the channel and flow-related metrics like wetted width and unit discharge (flow volume per linear meter of wetted channel width) that could be influenced by flow augmentation or reductions during migration. We used 17 years of systematic monitoring data in a discrete-choice framework to evaluate the influence these various metrics have on the relative probability of whooping crane use and found the width of channel unobstructed by dense vegetation and distance to the nearest forest were the best predictors of whooping crane use. Secondly, we used telemetry data obtained from a sample of 38 birds of all ages over the course of seven years, 2010–2016, to evaluate whooping crane use of riverine habitat within the North-central Great Plains, USA. For this second analysis, we focused on the two metrics found to be important predictors of whooping crane use along the central Platte River, unobstructed channel width and distance to nearest forest or wooded area. Our findings indicate resource managers, such as the Program, have the potential to influence whooping crane use of the central Platte River through removal of in-channel vegetation to increase the unobstructed width of narrow channels and through removal of trees along the bank line to increase unforested corridor widths. Results of both analyses also indicated that increases in relative probability of use by whooping cranes did not appreciably increase with unobstructed views ≥200 m wide and unforested corridor widths that were ≥330 m. Therefore, managing riverine sites for channels widths >200 m and removing trees beyond 165 m from the channel’s edge would increase costs associated with implementing management actions such as channel and bank-line disking, removing trees, augmenting flow, etc. without necessarily realizing an additional appreciable increase in use by migrating whooping cranes.

Spatial and temporal heterogeneity in the structure and function of sediment bacterial communities of a tropical mangrove forest.

Bacterial communities of mangrove sediments are well appreciated for their role in nutrient cycling. However, spatiotemporal variability in these communities over large geographical scale remains understudied. We investigated sediment bacterial communities and their metabolic potential in an intertidal mangrove forest of India, Bhitarkanika, using high-throughput sequencing of 16S rRNA genes and community-level physiological profiling. Bulk surface sediments from five different locations representing riverine and bay sites were collected over three seasons. Seasonality largely explained the variation in the structural and metabolic patterns of the sediment bacterial communities. Freshwater Actinobacteria were more abundant in monsoon, whereas γ-Proteobacteria demonstrated higher abundance in summer. Distinct differences in the bacterial community composition were noted between riverine and bay sites. For example, salt-loving marine bacteria affiliated to Oceanospirillales were more prominent in the bay sites than the riverine sites. L-asparagine, N-acetyl-D-glucosamine, and D-mannitol were the preferentially utilized carbon sources by bacterial communities. Bacterial community composition was largely governed by salinity and organic carbon content of the sediments. Modeling analysis revealed that the abundance of δ-Proteobacteria increased with salinity, whereas β-Proteobacteria displayed an opposite trend. Metabolic mapping of taxonomic data predicted biogeochemical functions such as xylan and chitin degradation, ammonia oxidation, nitrite reduction, and sulfate reduction in the bacterial communities suggesting their role in carbon, nitrogen, and sulfur cycling in mangrove sediments. This study has provided valuable clues about spatiotemporal heterogeneity in the structural and metabolic patterns of bacterial communities and their environmental determinants in a tropical mangrove forest.

The role of sleeping sites in the predator-prey dynamics of leopards and olive baboons.

Predation is widely recognized as an important selective pressure on prey animals such as baboons (Papio spp.), which face high leopard (Panthera pardus) predation risk, particularly at night. Baboons regularly sleep on cliff faces and in trees at night, ostensibly to avoid such predators. Despite retreating to such "refuges," baboons are most often killed by leopards at or near their sleeping sites. Because of the challenges of studying nocturnal behavior and human-averse predators, few systematic data exist to reveal how leopard ranging near baboon sleeping sites influences baboons' selection of sites and behavior at those sites. To investigate leopard-baboon dynamics at sleeping sites we deployed GPS/VHF radio collars on six representatives of four baboon groups and four leopards during a 14-month field study in Kenya. We used locations recorded every 15 min to identify baboons' cliffside and riverine sleeping sites, the frequency and duration of leopard visits to these sites, and baboons' adjustments in site use after leopard visits. Collared leopards visited riverine sites more frequently than cliffside sites, whereas most baboon groups strongly preferred cliffside sites, suggesting that leopard visits were often due to factors other than baboon presence, and that baboons used cliffside sites to reduce their risk of leopard predation. Regardless of type, collared leopards remained near baboon-occupied sleeping sites longer than vacant ones, indicating interest in hunting baboons then. Baboons at riverine sites departed later on mornings after leopard visits. Baboon groups occasionally shared sleeping sites simultaneously, possibly reducing risk through dilution. However, they did not reduce risk by frequently changing sleeping sites, minimizing detection at sleeping sites, or after leopard visits, arriving earlier the next evening or moving to a different site. Future research should explore if baboons readily detect nocturnal leopard presence and if predation-related changes in sleeping site use have cascading ecological effects.

Reduction of bacterial integrity associated with dam construction: A quantitative assessment using an index of biotic integrity improved by stability analysis

Rivers are extensively regulated by damming, yet the effects of such interruption on bacterial communities have not been assessed quantitatively. To fill this gap, we proposed a bacteria-based index of biotic integrity (Ba-IBI) by using bacterial community dataset collected from the Three Gorges Reservoir and its upper reaches. Stability analysis based on bacterial resistance (RS) and resilience (RL) to external disturbance was conducted to improve the performance of the index. Four core metrics, i.e. the ratio of Bacilli, Bacteroidetes and Clostridia to Alphaproteobacteria (BBC/A), Oxalobacteraceae, Methanotrophs and Thermophiles were selected after range, responsive and redundancy tests. The improved Ba-IBI, ranging from 1.04 to 4.10, was better at distinguishing sites with or without direct dam effects compared with the unimproved one. The index values maintained high in the riverine sites while reducing in the reservoir, demonstrating the negative influence of dam construction on bacterial integrity. Based on the assessment results, 23.1%, 46.2% and 30.8% sampling sites were large, moderately and little affected by damming, respectively. A Random Forest (RF) regression model was trained and tested, offering a valid prediction of the input Ba-IBI and environmental parameters. Sensitivity analysis revealed the significant contributions of flow velocity towards the predicting process performance, indicating the importance of hydrodynamic conditions on determining the spatial variability of bacterial communities. This study provides not only a first quantitative insight for assessing bacterial response to damming, but also a guideline for applying the improved index in the dam regulation and ecological protection.

Environmentally relevant chemical mixtures of concern in waters of United States tributaries to the Great Lakes.

The North American Great Lakes are a vital natural resource that provide fish and wildlife habitat, as well as drinking water and waste assimilation services for millions of people. Tributaries to the Great Lakes receive chemical inputs from various point and nonpoint sources, and thus are expected to have complex mixtures of chemicals. However, our understanding of the co-occurrence of specific chemicals in complex mixtures is limited. To better understand the occurrence of specific chemical mixtures in the US Great Lakes Basin, surface water from 24 US tributaries to the Laurentian Great Lakes was collected and analyzed for diverse suites of organic chemicals, primarily focused on chemicals of concern (e.g., pharmaceuticals, personal care products, fragrances). A total of 181 samples and 21 chemical classes were assessed for mixture compositions. Basin wide, 1664 mixtures occurred in at least 25% of sites. The most complex mixtures identified comprised 9 chemical classes and occurred in 58% of sampled tributaries. Pharmaceuticals typically occurred in complex mixtures, reflecting pharmaceutical-use patterns and wastewater facility outfall influences. Fewer mixtures were identified at lake or lake-influenced sites than at riverine sites. As mixture complexity increased, the probability of a specific mixture occurring more often than by chance greatly increased, highlighting the importance of understanding source contributions to the environment. This empirically based analysis of mixture composition and occurrence may be used to focus future sampling efforts or mixture toxicity assessments. Integr Environ Assess Manag 2018;14:509-518. © 2018 SETAC.

Dissolved organic matter dynamics in Mediterranean lagoons: The relationship between DOC and CDOM

Coastal lagoons are highly vulnerable to climate change-related pressures, such as floods and increasing temperatures, which lead to higher oxygen consumption, anaerobic metabolism and dystrophic events. Although these factors have a significant impact on the carbon cycle, the dynamics of dissolved organic matter (DOM) in these systems have not been extensively investigated. DOM can be analytically determined from the concentration of dissolved organic carbon (DOC) and/or from the spectral properties of chromophoric dissolved organic matter (CDOM), which is the light-absorbing fraction of DOM. In the present study, we investigated the spatio-temporal distribution of surface water trophic variables (Chl a and DOC) and CDOM in two Mediterranean lagoon systems, the Oristano Lagoon-Gulf system (OLG) and the Varano Lagoon (VL), in order to provide quantitative information on the dynamics of DOM in these systems. Furthermore, we assessed the value of CDOM-related indices (i.e. absorption coefficients, spectral slopes and Specific UV Absorbance at 254 nm [SUVA254]) as tools for describing the dynamics of DOM in coastal lagoons, irrespective of geographical settings, environmental conditions and anthropogenic pressures. In OLG, spatial heterogeneity and compartmentalization, with salinity varying from <1 (riverine sites) to >50 (Mistras Lagoon), affected the distribution of DOC and CDOM, with the lowest values on the south side and at sites far from riverine input. In OLG, the highest DOC and CDOM values were found in the sediment pore-water of the organic-rich Cabras Lagoon, where they were nearly double those of the water column. In VL, salinity was homogeneously distributed throughout the lagoon, which indicated a mixing of freshwater with marine waters. DOC and CDOM values were on average lower in VL than in OLG. However, in VL, DOC and CDOM showed strong peaks following a flood (September 2014) and a dystrophic event (July 2015), demonstrating the quick response of the system to environmental perturbation. In OLG, absorption coefficients at 280 nm and 350 nm were slightly negatively correlated with salinity, which indicated the influence of terrigenous inputs at riverine sites. In contrast, in VL, CDOM varied linearly and positively with salinity as a result of the in situ input of organic matter from phytoplankton during the dry season. Segment analysis showed that besides the differences between the two investigated systems, the trophic variables and optical parameters analyzed in the present study shared a common relationship. These results suggest that CDOM indices can be good predictors for the estimation of DOM. Overall, the present study provides insight into the dynamics of DOC and CDOM in little-studied Mediterranean lagoons and demonstrates that the CDOM indices can be a valuable, cost-effective and simple tool for describing the trophic conditions of these systems.

Life histories and ecotype conservation in an adaptive vertebrate: Genetic constitution of piscivorous brown trout covaries with habitat stability.

Ecotype variation in species exhibiting different life history strategies may reflect heritable adaptations to optimize reproductive success, and potential for speciation. Traditionally, ecotypes have, however, been defined by morphometrics and life history characteristics, which may be confounded with individual plasticity. Here, we use the widely distributed and polytypic freshwater fish species brown trout (Salmo trutta) as a model to study piscivorous life history and its genetic characteristics in environmentally contrasting habitats; a large lake ecosystem with one major large and stable tributary, and several small tributaries. Data from 550 fish and 13 polymorphic microsatellites (H e = 0.67) indicated ecotype‐specific genetic differentiation (θ = 0.0170, p < .0001) among Bayesian assigned small riverine resident and large, lake migrating brown trout (>35 cm), but only in the large tributary. In contrast, large trout did not constitute a distinct genetic group in small tributaries, or across riverine sites. Whereas life history data suggest a small, river resident and a large migratory piscivorous ecotype in all studied tributaries, genetic data indicated that a genetically distinct piscivorous ecotype is more likely to evolve in the large and relatively more stable river habitat. In the smaller tributaries, ecotypes apparently resulted from individual plasticity. Whether different life histories and ecotypes result from individual plasticity or define different genetic types, have important consequence for conservation strategies.

CO2 dynamics on three habitats of mangrove ecosystem in Bintan Island, Indonesia

Atmospheric carbon dioxide (CO2) has increased over time, implied on global warming and climate change. Blue carbon is one of interesting options to reduce CO2 concentration in the atmosphere. Indonesia has the largest mangrove area in the world which would be potential to mitigate elevated CO2 concentrations. A quantitative study on CO2 dynamic was conducted in the habitat-variable and pristine mangrove of Bintan island. The study was aimed to estimate CO2 flux on three different mangrove habitats, i.e., lagoon, oceanic and riverine. Even though all habitats were dominated by Rhizophora sp, they were significantly differed one another by species composition, density, and soil characteristics. Averagely, CO2 dynamics had the positive budget by ∼0.668 Mmol/ha (82.47%) which consisted of sequestration, decomposition, and soil efflux at 0.810 Mmol/ha/y, -0.125 Mmol/ha/y and -0.017 Mmol/ha/y, respectively. The study found that the fringing habitat had the highest CO2 capturing rate and the lowest rate of litter decomposition which was contrast to the riverine site. Therefore, oceanic mangrove was more efficient in controlling CO2 dynamics due to higher carbon storage on their biomass. A recent study also found that soil density and organic matter had a significant impact on CO2 dynamics.

Calibration and field evaluation of the Chemcatcher® passive sampler for monitoring metaldehyde in surface water

Metaldehyde is a potent molluscicide. It is the active ingredient in most slug pellets used for crop protection. This polar compound is considered an emerging pollutant. Due to its environmental mobility, metaldehyde is frequently detected at impacted riverine sites, often at concentrations above the EU Drinking Water Directive limit of 0.1µgL−1 for an individual pesticide. This presents a problem when such waters are abstracted for use in the production of potable water supplies, as this chemical is difficult to remove using conventional treatment processes. Understanding the sources, transport and fate of this pollutant in river catchments is therefore important. We developed a new variant of the Chemcatcher® passive sampler for monitoring metaldehyde comprising a Horizon Atlantic™ HLB-L disk as the receiving phase overlaid with a polyethersulphone membrane. The sampler uptake rate (Rs) was measured in semi-static laboratory (Rs = 15.7mLday−1) and in-field (Rs = 17.8mLday−1) calibration experiments. Uptake of metaldehyde was linear over a two-week period, with no measurable lag phase. Field trials (five consecutive 14day periods) using the Chemcatcher® were undertaken in eastern England at three riverine sites (4th September-12th November 2015) known to be impacted by the seasonal agricultural use of metaldehyde. Spot samples of water were collected regularly during the deployments, with concentrations of metaldehyde varying widely (~ 0.03–2.90µgL−1) and often exceeding the regulatory limit. Time weighted average concentrations obtained using the Chemcatcher® increased over the duration of the trial corresponding to increasing stochastic inputs of metaldehyde into the catchment. Monitoring data obtained from these devices gives complementary information to that obtained by the use of infrequent spot sampling procedures. This information can be used to develop risk assessments and catchment management plans and to assess the effectiveness of any mitigation and remediation strategies.

An alternative method for interpreting JET erosion test (JET) data: Part 2. Application

AbstractThis paper reports the results of jet tester experiments on soil samples of uniform properties which allow quantitative application of the new theory proposed in part 1 of these publications. This theory explores the possibly that a more adequate indicator of soil erodibility may be obtained by using the mass (and so volume) of soil eroded by the jet and the depth of scour penetration, rather than by using penetration depth alone, as assumed in the commonly‐used data interpretation method. It is shown that scour geometry can be well described using a generalized form of the Gaussian function, defined by its standard deviation and maximum depth. Using a published expression for jet kinetic energy flux, the new theory divides this flux into that used to erode soil, and the remainder which is dissipated in a variety of ways. Jet experiments on a specially‐prepared uniform soil sample are reported which provide the key to determining the spatial variability in the profile resistance to erosion offered by field soils. This resistance is expressed in the work required to erode unit mass of soil, denoted as J (in J/kg). The paper also gives results obtained on the profile variation in J for jet tests carried out at riverine sites on the upper Brisbane River, Queensland, Australia. As expected in most natural soil profiles, the results show an increase in J with depth in the profile. The soil resistance (J) is compared to the traditional interpretation of soil erodibility, (kd). The graphical comparison of these two indicators illustrates the inverse type of relationship between them which is expected from their respective definitions, but this relationship is associated with significant scatter. Possible reasons for this scatter are given, together with comments on jet tester experience in a wide variety of soil types. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Taxonomy- or trait-based ecological assessment for tropical rivers? Case study on benthic diatoms in Mayotte island (France, Indian Ocean)

Diatom-based ecological quality assessment methods have been implemented and used regularly in the Water Framework Directive. These indices use the species' abundance profiles along a specific environmental gradient, which they aim to assess. However, this approach has several problematic issues including the unstable and fast-changing diatom taxonomy. The use of traits can be a solution if their responses to the environmental pressure are well-defined. Here, we developed taxonomy-based and trait-based diatom assemblage indices to assess the ecological status of riverine sites on a tropical island. The two indices are based on two sub-indices that measure the diatom assemblage response to a nutrient and organic matter/turbidity gradient. Both taxonomy- and trait-based indices correlated significantly with the selected environmental gradients of the test database, which was not used during index development. We showed that traits could be used for quality assessment of the Mayotte rivers and require much less effort than taxonomy-based indices. There were differences between the two types of indices, which are discussed in this paper. As a perspective for further studies, tests of trait-based indices among different eco-regions would be challenging.

Cryptoprocta spelea (Carnivora: Eupleridae): What Did It Eat and How Do We Know?

The extent to which Madagascar’s Holocene extinct lemurs fell victim to nonhuman predators is poorly understood. Madagascar’s Holocene predator guild included several now-extinct species, i.e., crocodiles, carnivorans, and raptors. Here we focus on mammalian carnivory, specifically the roles of Cryptoprocta spelea and its still-extant but smaller-bodied sister taxon, C. ferox, the fosa. Cryptoprocta spelea was the largest carnivoran on Madagascar during the Quaternary. We ask whether some extinct lemurs exceeded the upper prey-size limits of C. spelea. We use univariate and multivariate phylogenetic generalized least squares regression models to re-evaluate the likely body mass of C. spelea. Next, we compare characteristics of the forelimb bones of C. ferox and C. spelea to those of other stealth predators specializing on small, mixed, and large-bodied prey. Finally, we examine humeri, femora, crania, and mandibles of extinct lemurs from six sites in four ecoregions of Madagascar to identify damage likely made by predators. We test the relative prevalence of carnivory by mammals, raptors, and crocodiles at different sites and ecoregions. Our data reveal that crocodiles, raptors, and the largest of Madagascar’s mammalian predators, C. spelea, all preyed on large lemurs. Cryptoprocta opportunistically consumed lemurs weighing up to ~85 kg. Its forelimb anatomy would have facilitated predation on large-bodied prey. Social hunting may have also enhanced the ability of C. spelea to capture large, arboreal primates. Cryptoprocta carnivory is well represented at cave and riverine sites and less prevalent at lake and marsh sites, where crocodylian predation dominates.