Roads are a pervasive form of disturbance with potential to negatively affect ecohydrological processes. Some of the most rapid growth in road networks is occurring in developing countries, particularly in the tropics, where political agendas are often focused on strengthening the economy, improving infrastructure, bolstering national security, achieving self‐sufficiency, and increasing citizen well‐being, often at the expense of the environment. We review what is known about road impacts on ecohydrological processes, focusing on aquatic systems, both temperate and tropical. We present seven cases that represent the broader trends of road development and impacts in tropical settings. Many of these process dynamics and impacts are not different from those experienced in temperate settings, although the magnitude of impacts in the tropics may be amplified with intense rainfall and lack of best management practices applied to road construction/maintenance. Impacts of roads in tropical settings may also be unique because of particular organisms or ecosystems affected. We outline a set of best practices to improve road network management and provide recommendations for adopting an agenda of research and road management in tropical settings. Importantly, we call for incorporation of transdisciplinary approaches to further study the effects of roads on ecohydrological processes in the tropics. Specific emphasis should also be placed on collaboration with governments and developers that are championing road development to help identify the drivers of road expansion and thresholds of negative impact, as well as methods of sustainable road construction and maintenance.

Concentrations of cations (Na ? , Ca 2? , Mg 2? , K ? , NH 4 ? ), anions (HCO 3 -, Cl -, NO 3 -, SO 4 2-, PO 4 3-) and suspended sediments in the Madeira River water were determined near the city of Porto Velho (RO), in order to assess variation in water chemistry from 2004 to 2007. Calcium and bicarbonate were the dominant cation and anion, respectively. Significant seasonal differences were found, with highest concentrations occurring during the dry season, as expected from the drainage of Andean carbonate-rich substratum. Interannual variations were also observed, but became significant only when annual average discharge was 25% less than normal. Under this atypical discharge condition, bicarbonate was replaced by sulfate, and higher suspended sediment concentrations and loads were also observed. Compared to previously published studies, it appears that no significant changes in water chemistry have occurred during the last 20-30 years, although differences in approaches and sampling designs among this and previous studies may not allow detection of modest changes. The calculated suspended sediment load reported here is close to the values presented elsewhere, reinforcing the relative importance of this river as a sediment supplier for the Amazon Basin. Seasonality has a significant control on the chemistry of Madeira River waters, and severe decrease in discharge due to anthropogenic changes, such as construction of reservoirs or the occurrence of drier years-a plausible consequence of global climate change-may lead to modification in the chemical composition as well in the sediment deliver to the Amazon River.

The Pantanal is the largest tropical wetland on the planet, and yet little information is available on the biome's carbon cycle. We used an automatic station to measure soil CO2 concentrations and oxidation‐reduction potential over the 2014 and 2015 flood cycles of a tree island in the Pantanal that is immune to inundation during the wetland's annual flooding. The soil CO2 concentration profile was then used to estimate soil CO2 efflux over the two periods. In 2014, subsurface soil saturation at 0.30 m depth created conditions in that layer that led to CO2 buildup close to 200,000 ppm and soil oxidation‐reduction potential below −300 mV, conditions that were not repeated in 2015 due to annual variability in soil saturation at the site. Mean CO2 efflux over the 2015 flood cycle was 0.023 ± 0.103 mg CO2‐C m−2 s−1 representing a total annual efflux of 593 ± 2690 mg CO2‐C m−2 y−1. Unlike a nearby tree island site that experiences full inundation during the wet season, here the soil dried quickly following repeated rain events throughout the year, which led to the release of CO2 pulses from the soil. This study highlights not only the complexity and heterogeneity in the Pantanal's carbon balance based on differences in topography, flood cycles, and vegetation but also the challenges of applying the gradient method in the Pantanal due to deviations from steady state conditions.

We review the biologically driven decomposition processes that take place in riverine ecosystems.• We identify important gaps in our understanding of decomposition processes in rivers from temperate and tropical biomes. • We propose a novel analytical approach to predict decomposition processes from metabolic scaling theory. • Using metadata from 30 rivers, we demonstrate that the slope of community size spectra can predict rates of decomposition.

Recebido em 28/10/09; aceito em 30/7/10; publicado na web em 17/11/10Groundwater quality of a riparian forest is compared to wells in surrounding rural areas at Urupá River basin. Groundwater types were calcium bicarbonated at left margin and sodium chloride at right, whereas riparian wells exhibited a combination of both (sodium bicarbonate). Groundwater was mostly solute-depleted with concentrations within permissible limits for human consumption, except for nitrate. Isotopic composition suggests that inorganic carbon in Urupá River is mostly supplied by runoff instead of riparian groundwater. Hence, large pasture areas in addition to narrow riparian forest width in this watershed may have an important contribution in the chemical composition of this river.