An Optimised eDNA Protocol for Fish Biodiversity Assessment in a Tropical River System Using PCI Extraction

The dynamic of organic carbon in South Cameroon: fluxes in a tropical river system and a lake system as a varying sink on a glacial–interglacial time scale

Natural and Anthropogenic Drivers of Water Quality in the Normanby Basin and Princess Charlotte Bay, Cape York Peninsula, Australia

Supplementary material to "Dissolved organic carbon lability and stable isotope shifts during microbial decomposition in a tropical river system"

ABSTRACTRiparian vegetation plays a critical role in maintaining ecological integrity along river corridors, yet it is highly sensitive to changes in hydrological and geomorphic conditions, particularly in sediment‐influenced tropical river systems. In many Philippine rivers, increased sediment deposition and landscape disturbance have altered riparian structure and floristic composition, underscoring the need for site‐specific baseline assessments. This study aimed to document the floristic composition, vegetation structure, and spatial patterns of riparian vegetation along the downstream reach of the Amnay River in Occidental Mindoro, Philippines, as a baseline for understanding current riparian conditions in a sediment‐influenced river corridor. Vegetation surveys were conducted using transects and quadrats established along the riverbanks, where species composition, growth form, and structural attributes were recorded. Species importance values and diversity indices were calculated to characterize vegetation dominance and diversity patterns across sampling sites. Riparian vegetation communities were mapped to describe spatial distribution and fragmentation. A total of 125 plant species representing 40 families were recorded, with vegetation dominated by herbaceous and disturbance‐tolerant taxa, particularly members of Poaceae and Fabaceae. Woody vegetation was limited and occurred mainly as isolated remnant patches, resulting in low vertical complexity and fragmented spatial structure. Species diversity varied among sampling sites, reflecting localized differences in substrate stability and vegetation cover. The findings provide a baseline characterization of riparian vegetation in a sediment‐influenced tropical river system and highlight the persistence of remnant woody vegetation within an otherwise simplified riparian corridor. This baseline information is essential for future monitoring, comparative studies, and the evaluation of riparian management and restoration efforts.

Remote sensing of floodplain geomorphology as a surrogate for biodiversity in a tropical river system (Madre de Dios, Peru)

Emerging and persistent contaminants (EPCs) were detected at high concentrations in Chiang Mai’s Mae Kha Canal, identifying urban waterways as important sources of pollution in the Ping River system in northern Thailand. Maximum levels of metformin (20,000 ng/L), fexofenadine (15,900 ng/L), gabapentin (12,300 ng/L), sucralose (38,000 ng/L), and acesulfame (23,000 ng/L) point to inadequately treated wastewater as a plausible contributor. Downstream enrichment patterns relative to upstream sites highlight the cumulative impact of urban runoff. Five compounds—acesulfame, gemfibrozil, fexofenadine, TBEP, and caffeine—consistently emerged as reliable tracers of urban wastewater, forming a distinct chemical fingerprint of the riverine exposome. Median EPC concentrations were highest in Mae Kha, lower in other urban canals, and declined with distance from the city, reflecting spatial gradients in urban density and pollution intensity. Although most detected concentrations fell below predicted no-effect thresholds, ibuprofen frequently approached or exceeded ecotoxicological benchmarks and may represent a compound of ecological concern. Non-targeted analysis revealed a broader “chemical cocktail” of unregulated substances—illustrating a witches’ brew of pollution that likely escapes standard monitoring efforts. These findings demonstrate the utility of wide-scope surveillance for identifying key compounds, contamination hotspots, and spatial gradients in mixed-use watersheds. They also highlight the need for integrated, long-term monitoring strategies that address diffuse, compound mixtures to safeguard freshwater ecosystems in rapidly urbanizing regions.

Signals of typhoon induced hydrologic alteration in particulate organic matter from largest tropical river system of Hainan Island, South China Sea

The size distribution of soluble copper complexing ligands (<0.45 μm) present in water samples collected from a tropical river system was characterised using a combination of equilibrium dialysis and differential pulse anodic stripping voltammetry. The proportion of copper complexing capacity associated with small molecular weight (<1,000 Dalton) ligands increased progressively from 40% in the upper catchment to 79% at a lowland floodplain/wetland location. This increase indicated the dominant role of the floodplain as a source of low molecular weight ligands to the river system. Asignificant proportion of copper complexation was also associated with the >14,000 Dalton fraction. As the majority of soluble iron was also associated with this fraction, it is likely that this complexing pool contains organic ligands adsorbed to the surface of inorganic colloids as well as large molecular weight ligands. Destruction of dissolved organic matter by sample pre-treatment with UV light resulted in a complete loss in copper complexation capacity detectable by anodic stripping voltammetry. This confirmed that the observed complexation of copper was associated with organic ligands and not inorganic components of the sample. A statistically significant linear correlation was observed between copper complexation capacity and fluorescence (340 nm excitation/440 nm emission). This indicated that the ligands were most likely to be associated with humic and fulvic compounds having conjugated molecular structures. Overall, the study emphasises the role of low molecular weight organic ligands in controlling copper speciation in tropical freshwater systems.

The hydrological status of river systems is expected to change due to dam operations and climate change. This will affect the riverine fluxes of sediment and carbon (C). In rivers with strong seasonal and inter-annual variability, quantification and extrapolation of sediment and C fluxes can be a challenge as measurement periods are often too short to cover all hydrological conditions. We studied the dynamics of the Tana River (Kenya) from 2012 to 2014 through daily monitoring of sediment concentrations at three sites (Garissa, Tana River Primate Reserve and Garsen) and daily monitoring of C concentrations in Garissa and Garsen during three distinct seasons. A bootstrap method was applied to calculate the range of sediment and C fluxes as a function of annual discharge by using daily discharge data (1942–2014). Overall, we estimated that on average, sediment and carbon were retained in this 600 km long river section between Garissa to Garsen over the 73 years (i.e., fluxes were higher at the upstream site than downstream): integration over all simulations resulted in an average net retention of sediment (~ 2.9 Mt year− 1), POC (~ 18,000 tC year− 1), DOC (~ 920 tC year− 1) and DIC (~ 1200 tC year− 1). To assess the impact of hydrological variations, we constructed four different hydrological scenarios over the same period. Although there was significant non-linearity and difference between the C species, our estimates generally predicted a net increase of C retention between the upstream and downstream site when the annual discharge would decrease, for example caused by an increase of irrigation with reservoir water. When simulating an increase in the annual discharge, e.g. as a potential effect of climate change, we predicted a decrease in C retention.

Comparing fishway designs for application in a large tropical river system

Abstract. A significant amount of carbon is transported to the ocean as dissolved organic carbon (DOC) in rivers. During transport, it can be transformed through microbial consumption and photochemical oxidation. In dark incubation experiments with water from the Tana River, Kenya, we examined the consumption of DOC through microbial decomposition and the associated change in its carbon stable isotope composition (δ13C). In 15 of the 18 incubations, DOC concentrations decreased significantly by 10 to 60 %, with most of the decomposition taking place within the first 24–48 h. After 8 days, the remaining DOC was up to 3 ‰ more depleted in 13C compared with the initial pool, and the change in δ13C correlated strongly with the fraction of DOC remaining. We hypothesize that the shift in δ13C is consistent with greater microbial lability of DOC originating from herbaceous C4 vegetation than DOC derived from woody C3 vegetation in the semi-arid lower Tana. The results complement earlier findings that the stable isotope concentration of riverine DOC does not necessarily reflect the proportion of C3 and C4-derived DOC in the catchment: besides spatial distribution patterns of different vegetation types, processing within the river can further influence the δ13C of riverine OC.

Integrating GIS–Based Inverse Distance Weighting and Multivariate Statistical Techniques to Assess Surface Water Quality Within a Sub–Tropical River System

Seasonal and inter-annual variations in carbon fluxes in a tropical river system (Tana River, Kenya)

The importance of predation risk as a key driver of evolutionary change is exemplified by the Northern Range in Trinidad, where research on guppies living in multiple parallel streams has provided invaluable insights into the process of evolution by natural selection. Although Trinidadian guppies are now a textbook example of evolution in action, studies have generally categorized predation as a dichotomous variable, representing high or low risk. Yet, ecologists appreciate that community structure and the attendant predation risk vary substantially over space and time. Here, we use data from a longitudinal study of fish assemblages at 16 different sites in the Northern Range to quantify temporal and spatial variation in predation risk. Specifically we ask: 1) Is there evidence for a gradient in predation risk? 2) Does the ranking of sites (by risk) change with the definition of the predator community (in terms of species composition and abundance currency), and 3) Are site rankings consistent over time? We find compelling evidence that sites lie along a continuum of risk. However, site rankings along this gradient depend on how predation is quantified in terms of the species considered to be predators and the abundance currency is used. Nonetheless, for a given categorization and currency, rankings are relatively consistent over time. Our study suggests that consideration of predation gradients will lead to a more nuanced understanding of the role of predation risk in behavioral and evolutionary ecology. It also emphasizes the need to justify and report the definition of predation risk being used.

Dam construction in the 1960s to 1980s significantly modified sediment supply from the Kenyan uplands to the lower Tana River. To assess the effect on suspended sediment fluxes of the Tana River, we monitored the sediment load at high temporal resolution for 1 year and complemented our data with historical information. The relationship between sediment concentration and water discharge was complex: at the onset of the wet season, discharge peaks resulted in high sediment concentrations and counterclockwise hysteresis, while towards the end of the wet season, a sediment exhaustion effect led to low concentrations despite the high discharge. The total sediment flux at Garissa (c. 250 km downstream of the lowermost dam) between June 2012 and June 2013 was 8.8 Mt yr‐1. Comparison of current with historical fluxes indicated that dam construction had not greatly affected the annual sediment flux. We suggest that autogenic processes, namely river bed dynamics and bank erosion, mobilized large quantities of sediments stored in the alluvial plain downstream of the dams. Observations supporting the importance of autogenic processes included the absence of measurable activities of the fall‐out radionuclides7Be and137Cs in the suspended sediment, the rapid lateral migration of the river course, and the seasonal changes in river cross‐section. Given the large stock of sediment in the alluvial valley of the Tana River, it may take centuries before the effect of damming shows up as a quantitative reduction in the sediment flux at Garissa. Many models relate the sediment load of rivers to catchment characteristics, thereby implicitly assuming that alterations in the catchment induce changes in the sediment load. Our research confirms that the response of an alluvial river to external disturbances such as land use or climate change is often indirect or non‐existent as autogenic processes overwhelm the changes in the input signal. Copyright © 2015 John Wiley &amp; Sons, Ltd.