Mercury emissions from artisanal and small-scale gold mining throughout the Global South exceed coal combustion as the largest global source of mercury. We examined mercury deposition and storage in an area of the Peruvian Amazon heavily impacted by artisanal gold mining. Intact forests in the Peruvian Amazon near gold mining receive extremely high inputs of mercury and experience elevated total mercury and methylmercury in the atmosphere, canopy foliage, and soils. Here we show for the first time that an intact forest canopy near artisanal gold mining intercepts large amounts of particulate and gaseous mercury, at a rate proportional with total leaf area. We document substantial mercury accumulation in soils, biomass, and resident songbirds in some of the Amazon’s most protected and biodiverse areas, raising important questions about how mercury pollution may constrain modern and future conservation efforts in these tropical ecosystems.

Climate change is driving ecological shifts in coastal regions of the world, where low topographic relief makes ecosystems particularly vulnerable to sea‐level rise, salinization, storm surge, and other effects of global climate change. The consequences of rising water tables and salinity can penetrate well inland, and lead to particularly dramatic changes in freshwater forested wetlands dominated by tree species with low salt tolerance. The resulting loss of coastal forests could have significant implications to the coastal carbon cycle. We quantified the rates of vegetation change including land loss, forest loss, and shrubland expansion in North Carolina’s largest coastal wildlife refuge over 35 yr. Despite its protected status, and in the absence of any active forest management, 32% (31,600 hectares) of the refuge area has changed landcover classification during the study period. A total of 1,151 hectares of land was lost to the sea and ~19,300 hectares of coastal forest habitat was converted to shrubland or marsh habitat. As much as 11% of all forested cover in the refuge transitioned to a unique land cover type—“ghost forest”—characterized by standing dead trees and fallen tree trunks. The formation of this ghost forest transition state peaked prominently between 2011 and 2012, following Hurricane Irene and a 5‐yr drought, with 4,500 ± 990 hectares of ghost forest forming during that year alone. This is the first attempt to map and quantify coastal ghost forests using remote sensing. Forest losses were greatest in the eastern portion of the refuge closest to the Croatan and Pamlico Sounds, but also occurred much further inland in low‐elevation areas and alongside major canals. These unprecedented rates of deforestation and land cover change due to climate change may become the status quo for coastal regions worldwide, with implications for wetland function, wildlife habitat, and global carbon cycling.

The exposure of freshwater-dependent coastal ecosystems to saltwater is a present-day impact of climate and land-use changes in many coastal regions, with the potential to harm freshwater and terrestrial biota, alter biogeochemical cycles and reduce agricultural yields. Land-use activities associated with artificial drainage infrastructure (canals, ditches, and drains) could exacerbate saltwater exposure. However, studies assessing the effects of artificial drainage on the vulnerability of coastal landscapes to saltwater exposure are lacking. We examined the extent to which artificial drainage infrastructure has altered the potential for saltwater intrusion in the coastal plain of eastern North Carolina. Regional spatial analyses demonstrate that artificial drainages not only lower the overall elevation in coastal landscapes, but they also alter the routing and concentration of hydrological flows. Together, these factors have the potential to increase the total proportion of the landscape vulnerable to saltwater intrusion, not only in areas adjacent to drainage infrastructure but also in places where no artificial drainages exist due to large scale effects of flow rerouting. Among all land cover types in eastern North Carolina, wetlands are most vulnerable to saltwater exposure. Droughts and coastal storms associated with climate change potentially exacerbate vulnerability to saltwater facilitated by artificial drainage.

Climate change, population growth, and agricultural intensification are increasing nitrogen (N) inputs, while driving the loss of inland water bodies that filter excess N. However, the interplay between N inputs and water body dynamics, and its implications for water quality remain poorly understood. Analyzing data from 1995 to 2015 across China, here, we find a 71% reduction in the area of small (<10^4.5 m²) water bodies (SWB), primarily in high-N-input agricultural regions. Preferential loss of SWBs, the most efficient nutrient filters, places 42% of China at high water quality risk due to increasing N inputs and declining SWB density. Currently, N removal by water bodies is 986 kilotonnes year⁻¹, but restoring 2.3 million hectares of SWB could increase removal by 21%, compared to just 5% for equivalent restoration of large water bodies. Targeted SWB restoration is crucial for improving water quality and mitigating N pollution in China.

Wetland restoration is a popular nutrient management strategy for improving water quality in agricultural catchments. However, a wetland’s ability to retain phosphorus is highly variable and wetlands can sometimes be a source of phosphorus to downstream ecosystems. Here, we used a meta-analysis approach to explore the source and sink capacity of 139 wetlands for both total phosphorus (TP) and the more bioavailable form, phosphate (PO₄ ³⁻), at seasonal and annual timescales. Median retention efficiency across all studies is 32% for TP and 28% for PO₄ ³⁻, however the range is extremely broad. We found that wetlands are often sinks for TP (84% of site-years) and PO₄ ³⁻ (75% of site years). The median TP retention within wetlands that are sinks (2.0 g·m⁻²·yr⁻¹) is greater than release by wetlands that are sources (−0.5 g·m⁻²·yr⁻¹). In contrast, for PO₄ ³⁻, median retention within wetlands that are phosphorus sinks (0.8 g·m⁻²·yr⁻¹) is of similar magnitude to that released by wetlands that are phosphorus sources (−0.7 g·m⁻²·yr⁻¹). We found that phosphorus release from wetlands coincides with higher hydraulic loading rates, lower influent phosphorus concentration, and legacy soil/sediment phosphorus. Phosphate releases were especially common in wetlands used for treating municipal wastewater, as well as restored and constructed wetlands with flashy, precipitation-driven flow. We found that experimental design may inherently bias our understanding of wetland performance for phosphorus retention as studies conducted in mesocosms outperform other wetland types. Analysis of monthly data demonstrated significant temporal variability in wetland phosphorus dynamics, often switching from retention to release many times within a year, but with no generalizable seasonal trends. Our results highlight the value of restoring wetlands for phosphorus retention and point to ways of furthering their utility towards improving water quality by simultaneously targeting retention enhancing measures and release avoidance.