Alexandra G. Ponette-González

Tropical land-cover change alters biogeochemical inputs to ecosystems in a Mexican montane landscape

In tropical regions, the effects of land-cover change on nutrient and pollutant inputs to ecosystems remain poorly documented and may be pronounced, especially in montane areas exposed to elevated atmospheric deposition. We examined atmospheric deposition and canopy interactions of sulfate-sulfur (SO4(2-)-S), chloride (Cl-), and nitrate-nitrogen (NO(3-)-N) in three extensive tropical montane land-cover types: clearings, forest, and coffee agroforest. Bulk and fog deposition to clearings was measured as well as throughfall (water that falls through plant canopies) ion fluxes in seven forest and five coffee sites. Sampling was conducted from 2005 to 2008 across two regions in the Sierra Madre Oriental, Veracruz, Mexico. Annual throughfall fluxes to forest and coffee sites ranged over 6-27 kg SO4(2-)-S/ha, 12-69 kg Cl-/ha, and 2-6 kg NO(3-)-N/ha. Sulfate-S in forest and coffee throughfall was higher or similar to bulk S deposition measured in clearings. Throughfall Cl- inputs, however, were consistently higher than Cl- amounts deposited to cleared areas, with net Cl- fluxes enhanced in evergreen coffee relative to semi-deciduous forest plots. Compared to bulk nitrate-N deposition, forest and coffee canopies retained 1-4 kg NO(3-)-N/ha annually, reducing NO(3-)-N inputs to soils. Overall, throughfall fluxes were similar to values reported for Neotropical sites influenced by anthropogenic emissions, while bulk S and N deposition were nine- and eightfold greater, respectively, than background wet deposition rates for remote tropical areas. Our results demonstrate that land-cover type significantly alters the magnitude and spatial distribution of atmospheric inputs to tropical ecosystems, primarily through canopy-induced changes in fog and dry deposition. However, we found that land cover interacts with topography and climate in significant ways to produce spatially heterogeneous patterns of anion fluxes, and that these factors can converge to create deposition hotspots. For land managers, this finding suggests that there is potential to identify species and ecosystems at risk of excess and increasing deposition in montane watersheds undergoing rapid transformation. Our data further indicate that montane ecosystems are vulnerable to air pollution impacts in this and similar tropical regions downwind of urban, industrial, and agricultural emission sources.

Influence of watershed‐climate interactions on stream temperature, sediment yield, and metabolism along a land use intensity gradient in Indonesian Borneo

Oil palm plantation expansion into tropical forests may alter physical and biogeochemical inputs to streams, thereby changing hydrological function. In West Kalimantan, Indonesia, we assessed streams draining watersheds characterized by five land uses: intact forest, logged forest, mixed agroforest, and young ( 10 years) oil palm plantation. We quantified suspended sediments, stream temperature, and metabolism using high-frequency submersible sonde measurements during month-long intervals between 2009 and 2012. Streams draining oil palm plantations had markedly higher sediment concentrations and yields, and stream temperatures, compared to other streams. Mean sediment concentrations were fourfold to 550-fold greater in young oil palm than in all other streams and remained elevated even under base flow conditions. After controlling for precipitation, the mature oil palm stream exhibited significantly greater sediment yield than other streams. Young and mature oil palm streams were 3.9°C and 3.0°C warmer than the intact forest stream (25°C). Across all streams, base flow periods were significantly warmer than times of stormflow, and these differences were especially large in oil palm catchments. Ecosystem respiration rates were also influenced by low precipitation. During an El Nino–Southern Oscillation-associated drought, the mature oil palm stream consumed a maximum 21 g O2 m−2 d−1 in ecosystem respiration, in contrast with 2.8 ± 3.1 g O2 m−2 d−1 during nondrought sampling. Given that 23% of Kalimantans land area is occupied by watersheds similar to those studied here, our findings inform potential hydrologic outcomes of regional periodic drought coupled with continued oil palm plantation expansion.

Managing water services in tropical regions: From land cover proxies to hydrologic fluxes

Watershed investment programs frequently use land cover as a proxy for water-based ecosystem services, an approach based on assumed relationships between land cover and hydrologic outcomes. Water flows are rarely quantified, and unanticipated results are common, suggesting land cover alone is not a reliable proxy for water services. We argue that managing key hydrologic fluxes at the site of intervention is more effective than promoting particular land-cover types. Moving beyond land cover proxies to a focus on hydrologic fluxes requires that programs (1) identify the specific water service of interest and associated hydrologic flux; (2) account for structural and ecological characteristics of the relevant land cover; and, (3) determine key mediators of the target hydrologic flux. Using examples from the tropics, we illustrate how this conceptual framework can clarify interventions with a higher probability of delivering desired water services than with land cover as a proxy.

Fracking vs Faucets: Balancing Energy Needs and Water Sustainability at Urban Frontiers

ewly accessible shale deposits have dramatically increasedglobal gas reserves and are touted as a bridge to a cleanenergy future. For example, in the U.S., where shale gas isprojected to comprise 49% of national natural gas productionby 2035, proponents argue that shale gas production canprovide energy independence, create employment, andstimulate regional economies.

Biomass burning drives atmospheric nutrient redistribution within forested peatlands in Borneo

This article quantifies the influence of fire on biogeochemical fluxes of nitrogen, phosphorus, and sulfur in a 12 ha forested peatland in West Kalimantan, Indonesia.

Snowlines and Treelines in the Tropical Andes

Examination of the dynamism of snowlines and treelines could provide insights into environmental change processes affecting land cover in the tropical Andes Mountains. Further, land cover at these ecotones represents a powerful lens through which to monitor and understand ecological processes across biophysical gradients while acknowledging their socioenvironmental dimensions. To illustrate this approach, we draw on recent research from two sites in the high tropical Andes where, at the regional scale, land cover assessments document retreating glaciers and changing amounts of forest cover, even though steep topographic gradients impose spatial shifts at much finer scales. Our results show that heterogeneous patterns of glacier recession open up new ecological spaces for plant colonization, potentially forming new grasslands, shrublands, and wetlands. In addition, treeline shifts are tied to changes in woody plant dominance, which can vary in rate and pattern as a result of aspect, past land use, and current livelihoods. We suggest that the telecoupling of regional and global biophysical and socioeconomic drivers of land use and land cover change to specific landscape combinations of elevation, aspect, and slope position might explain much of the spatial heterogeneity that characterizes landscape stasis and flux in mountains.

A Low-Cost GPS-Based Protocol to Create High-Resolution Digital Elevation Models for Remote Mountain Areas

Abstract Researchers and development practitioners in remote mountain areas rely on elevation data to study vegetation dynamics, natural hazards, land use, and other patterns. However, despite advances in technology, accurate digital elevation models (DEMs) with spatial resolution <30 m do not exist for most of the worlds montane regions. We used a low-cost GPS-based protocol to construct a high-resolution (10 m) DEM for a rugged, remote mountain site in the northern Peruvian Andes. Elevation data were collected with handheld GPS units and combined with digitized and interpolated points within a Geographic Information System to generate a 10 m DEM. Additional DEMs were generated using 50%, 20%, and 15% of the surface points collected and from a 1∶100,000 topographic map and ASTER GDEMv2 data. Estimated absolute vertical accuracy of the GPS surface-point DEMs was significantly lower than that of the ASTER GDEMv2 and topographic map DEMs. Relative vertical accuracy, a better measure of DEM quality, was considerably lower for all 6 DEMs than absolute vertical accuracy. Depending on project budget, time, and labor availability, this method can be used to produce DEMs with high spatial resolution and substantially improved relief maps for research, visualization, and communication purposes. Implementation of this method is practical in locations without access to electricity or post-processing correction facilities, open-canopy land covers, and projects with small budgets that involve local participants.

Nitrogen cycling in tropical Atlantic Forest differing in exposure to urban atmospheric nitrogen deposition

Background and aimsInorganic nitrogen (N)––ammonium (NH4+-N) and nitrate (NO3--N)––deposition to tropical forests near urban areas frequently exceeds 5-10 kg ha-1 yr-1, surpassing critical loads for many forest types. We hypothesized that throughfall N fluxes to Atlantic Forest and effects on soil N cycling and availability would increase with proximity to a megacity (population ~12 M) on Brazil’s Atlantic Coast.MethodsWe quantified N in rainfall and throughfall, soil nutrient status and N transformations, and relative N availability in three Atlantic Forest sites: an oceanic site ~100 km southwest, a coastal site in, and an inland site ~50 km northeast and downwind from Rio de Janeiro megacity.ResultsAnnual throughfall N flux did not increase with proximity to the megacity but increased along an ocean (7.6 ± 0.3 kg ha-1) to coast (8.7 ± 1.5 kg ha-1) to inland (14 ± 2.5 kg ha-1) gradient. Potential net N mineralization and nitrification rates did not differ among forests. However, NO3:NH4 and resin bag NO3- accumulation in soil were highest at the high-N site.ConclusionsOur results suggest that elevated rainfall and throughfall N increase relative N availability and potential NO3- leaching losses from Atlantic Forest soils downwind urban areas.