Lead concentrations in hard antlers of adult European roebucks (Capreolus capreolus) were analyzed to assess lead exposure of roe deer roaming the floodplain of the Innerste River, a river system contaminated due to historical metal ore mining, processing, and smelting in its upper reaches. Antler lead concentrations of roebucks culled in the period 1939–2018 within or close to the Innerste floodplain ranged between <0.17 mg Pb/kg (limit of detection) and 51.5 mg Pb/kg (air-dry weight). Median lead concentration in antlers of roebucks culled within the floodplain was 11.1 mg Pb/kg, compared to 2.3 mg Pb/kg in antlers of bucks culled in the floodplain vicinity (P < 0.01). Sampling year had no significant effect on antler lead concentrations (P = 0.748). Lead isotope ratios of antlers from the Innerste downstream area (²⁰⁶Pb/²⁰⁷Pb: 1.179–1.181; ²⁰⁸Pb/²⁰⁶Pb: 2.083–2.085) fell within the range of those reported for hydrothermal vein deposits from the upper catchment area of the Innerste River in the Harz Mountains. Our study demonstrates the long-lasting impact of the historical metal ore mining, processing, and smelting in the Harz Mountains on lead pollution in floodplains of rivers draining this area and the lead exposure of wild herbivores inhabiting the floodplains. Furthermore, it highlights the suitability of roe deer antlers for monitoring environmental lead levels and the usefulness of lead isotope signatures in antlers for source apportionment of lead pollution.

Understanding the key drivers of eutrophication in floodplain lakes has long been a challenge. In this study, the Chlorophyll a (Chla) variations and associated relationships with environmental stressors along the temporal hydrological connectivity gradient were investigated using a 11-year dataset in a large floodplain lake (Poyang Lake). A geostatistical method was firstly used to calculate the hydrological connectivity curves for each sampling campaign that was further classified by K-means technique. Linear mixed effect (LME) models were developed through the inclusion of the site as a random effect to identify the limiting factors of Chla variations. The results identified three clear hydrological connectivity variation patterns with remarkable connecting water area changes in Poyang Lake. Furthermore, hydrological connectivity changes exerted a great influence on environmental variables in Poyang Lake, with a decrease in nutrient concentrations as the hydrological connectivity enhanced. The Chla exhibited contrast variations with nutrient variables along the temporal hydrological connectivity gradient and generally depended on WT, DO, EC and TP, for the entire study period. Nevertheless, the relative roles of nutrient and non-nutrient variables in phytoplankton growth varied with different degrees of hydrological connectivity as confirmed by the LME models. In the low hydrological connectivity phase, the Chla dynamics were controlled only by water temperature with sufficient nutrients available. In the high hydrological connectivity phase, the synergistic influences of both nutrient and physical variables jointly limited the Chla dynamics. In addition, a significant increasing trend was observed for Chla variations from 2008 to 2018 in the HHC phase, which could largely be attributed to the elevated nutrient concentrations. This study confirmed the strong influences of hydrological connectivity on the nutrient and non-nutrient limitation of phytoplankton growth in floodplain lakes. The present study could provide new insights on the driving mechanisms underlying phytoplankton growth in floodplain lakes.

River floodplain ecosystems host one of the highest freshwater molluscan biodiversity on Earth. However, multiple human disturbances, such as loss of hydrological connectivity and deterioration of water quality, are seriously threatening most floodplain lakes throughout the world. Given the high imperilment rate of freshwater molluscs but the scarcity of studies examining the anthropogenic effects on this fauna, we test the response of mollusc assemblages to river-lake disconnection and eutrophication in 30 lakes in the Yangtze River floodplain, China. The species richness of entire Mollusca, Gastropoda and Bivalvia and 6 dominant families were all much lower at disconnected lakes than that in connected lakes, and decreased with increasing water eutrophication. The assemblage structure differed significantly among four lake groups for datasets based on entire Mollusca, Gastropoda and Bivalvia, indicating the serious impacts of hydrological disconnection and eutrophication. Moreover, the connected lakes showed significantly lower values of average taxonomic distinctness (Δ⁺) but higher values of variation in taxonomic distinctness (Λ⁺) than disconnected lakes. Such variations were triggered by the extirpation of congeneric and endemic species (mainly from families Unionidae and Viviparidae), which giving a waring of the loss of mollusc endemism in this region. In general, the present study showed that river-lake disconnection and deterioration of water quality resulted in serious biodiversity declines of both gastropods and bivalves in the Yangtze River floodplain lakes. A systematic approach including restoration of river-lake connectivity and habitats and improvement of water quality should be implemented in the conservation planning in this large river floodplain.

Sediment quality monitoring is commonly used to assess for river pollution by industrial activities, but requires knowledge of pre-disturbance conditions. This has long been a critical knowledge gap for assessing pollution of the Lower Athabasca River within the Athabasca Oil Sands Region (AOSR) because sediment quality monitoring started 30 years after mining operations began in 1967. Here, we analyze oil-sands pollution indicator metals vanadium (V) and nickel (Ni) in sediment cores from five Athabasca River floodplain lakes spanning from 17 km upstream to 58 km downstream of central oil sands operations. These data are used to define pre-development baseline (i.e., reference) concentrations and assess for enrichment in sediment deposited after 1967. Measurements of organic and inorganic matter content were used to differentiate periods of strong and weaker Athabasca River influence in the sediment records, as needed to discern pathways of metal deposition. Numerical analyses reveal that post-1967 V and Ni enrichment factors have remained below the 1.5 threshold for ‘minimal enrichment’ (sensu Birch, 2017) in stratigraphic intervals of strong river influence in the floodplain lakes. Thus, concentrations of V and Ni carried by Athabasca River sediment have not become measurably enriched since onset of oil sands development, as demonstrated by our before-after study design with >99.99% power to detect a 10% increase above pre-development baselines. At the closest lake (<1 km) to oil sands operations, however, enrichment factors for V and Ni increased to 2.1 and 1.5, respectively, in the mid-1980s and have remained at this level when river influence was weaker, indicating contamination via atmospheric transport. Localized enrichment within the oil sands region via atmospheric pathways is a greater concern for ecosystems and society than local and far-field transport by fluvial pathways.

Excessive use of nitrogenous fertilizers and their improper management in agriculture causes nitrate contamination of surface and groundwater resources. This study was conducted along the seasonally flooded alluvial agricultural area of Indus River Basin to determine the spatial and temporal dynamics of nitrate concentrations in the groundwater along the river. Total of 112 samples were collected from shallow (30–40 ft) and deep groundwater (120–150 ft) wells at seven sites, 25 km apart from each other and covered an area of 170 km along the river, during four sampling campaigns between October 2016 to May 2017 i.e. in start, mid and end of dry season. The study period covered the whole agricultural cycle including the wet summer season with no agricultural activities under flooding and the sampling sites were always less than 2 km from the river bank. Nitrate concentrations of shallow wells were 15–54 and 20–45 mg L⁻¹ during the start and middle of dry season, respectively. However, at the end of the dry season, the highest nitrate concentrations of 35–75 mg L⁻¹ were recorded and 70% of these samples contained nitrate concentrations above the permissible limit 50 mg L⁻¹. Similar seasonal patterns of nitrate concentrations were observed in deep wells, however, δ¹⁸O data suggested lower recharge in deep well than shallow wells. The results illustrated that high nitrate concentrations in shallow wells were associated with high δ¹⁸O values indicating that the quantity of evaporated water infiltrated from the floodplain, possibly from distribution channels, along with the nitrate polluting shallow wells more than the deep wells. At the end of the dry season, nitrate concentrations exceeded the permissible limits in both shallow and deep wells, which possibly happened due to the horizontal movement of groundwater along with the nitrate mixing during vertical seepage of river water to the aquifers.

Cadmium, present locally in naturally high concentrations in the Northern Plains of the United States, is of concern because of its toxicity, carcinogenic properties, and potential for trophic transfer. Reports of natural concentrations in soils are dominated by dryland soils with agricultural land uses, but much less is known about cadmium in wetlands. Four wetland categories – prairie potholes, shallow lakes, riparian wetlands, and river sediments – were sampled comprising more than 300 wetlands across four states, the majority in North Dakota. Cd, Zn, P, and other elements were analyzed by ICP-MS, in addition to pH and organic matter (as loss-on-ignition). The overall cadmium content was similar to the general concentrations in the area's soils, but distinct patterns occurred within categories. Cd in wetland soils is associated with underlying geology and hydrology, but also strongly with concentrations of P and Zn, suggesting a link with agricultural land use surrounding the wetlands.

Arsenic and other trace element concentrations were determined for tube-well water collected in the Lao PDR provinces of Attapeu, Bolikhamxai, Champasak, Savannakhet, Saravane, and Vientiane. Water samples, especially from floodplain areas of central and southern Laos, were significantly contaminated not only with As, but with B, Ba, Mn, U, and Fe as well. Total As concentrations ranged from <0.5μgL⁻¹ to 278μgL⁻¹, with over half exceeding the WHO guideline of 10μgL⁻¹. 46% of samples, notably, were dominated by As(III). Samples from Vientiane, further north, were all acceptable except on pH, which was below drinking water limits. A principal component analysis found associations between general water characteristics, As, and other trace elements. Causes of elevated As concentrations in Lao tube wells were considered similar to those in other Mekong River countries, particularly Cambodia and Vietnam, where young alluvial aquifers give rise to reducing conditions.

Mercury (Hg) is a persistent environmental contaminant found in many freshwater and marine ecosystems. Historical Hg contamination in rivers can impact the surrounding terrestrial ecosystem, but there is little known about how far downstream this contamination persists. In 2009, we sampled terrestrial forest songbirds at five floodplain sites up to 137 km downstream of an historical source of Hg along the South and South Fork Shenandoah Rivers (Virginia, USA). We found that blood total Hg concentrations remained elevated over the entire sampling area and there was little evidence of decline with distance. While it is well known that Hg is a pervasive and long-lasting aquatic contaminant, it has only been recently recognized that it also biomagnifies effectively in floodplain forest food webs. This study extends the area of concern for terrestrial habitats near contaminated rivers for more than 100 km downstream from a waterborne Hg point source.

After flooding, iron reduction in riverine wetlands may cause the release of large quantities of phosphorus. As phosphorus is an important nutrient causing eutrophication in aquatic systems, it is important to have a tool to predict this potential release. In this study we examined the P release to the soil pore water in soil cores from floodplains in the Netherlands and from less anthropogenically influenced floodplains from Poland. During the inundation experiment, concentrations of P in the pore water rose to 2–90 times the initial concentrations. P release was not directly related to the geographic origin of the soils. An important predictor variable of P release was found in the ratio between the concentration of iron-bound P and amorphous iron. This ratio may provide a practical tool for the selection of new areas for wetland creation, and for impact assessment of plans for riverine wetland restoration and floodwater storage. Mobilisation of phosphorus in floodplain wetland soils can be predicted with easily measurable soil characteristics.

This paper details the distribution of Cu, Pb and Zn in aquatic systems draining Mount Isa Ag-Cu-Pb-Zn Mine in arid northern Queensland, Australia. Sediment-metal concentrations in the <2 mm grain-size fraction adjacent to and downstream of the mine significantly exceed background concentrations (Cu, 159; Pb, 36; Zn, 86 ppm) as well as Australian government sediment quality low trigger guidelines (Cu, 65; Pb, 50; Zn, 200 ppm). Overbank sediments are more contaminated than channel sediments with mean values of Cu, 480; Pb, 540; Zn, 750 ppm. Mean concentrations in cut riverbank samples from the <2 mm fraction were Cu, 195; Pb, 724; Zn, 807 ppm. Corresponding <180 μm samples returned concentrations of Cu, 321; Pb, 995; Zn, 1110 ppm. Delivery of contaminants during wet seasons from Mount Isa Mine and historically contaminated riverbanks remains an ongoing issue. The ease of dust entrainment in arid zones means that sediments enriched in toxic concentrations of metals may be widely dispersed and ultimately ingested and absorbed by biota.