scholarly journals Land Use Change Influences Ecosystem Function in Headwater Streams of the Lowland Amazon Basin

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1667
Author(s):  
Kathi Jankowski ◽  
Linda Deegan ◽  
Christopher Neill ◽  
Hillary Sullivan ◽  
Paulo Ilha ◽  
...  
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Stream Function ◽  
Amazon Basin ◽  
Headwater Streams ◽  
Ecosystem Respiration ◽  
Riparian Forest ◽  
Light Availability ◽  
Nutrient Concentrations ◽  
Tropical Regions

Intensive agriculture alters headwater streams, but our understanding of its effects is limited in tropical regions where rates of agricultural expansion and intensification are currently greatest. Riparian forest protections are an important conservation tool, but whether they provide adequate protection of stream function in these areas of rapid tropical agricultural development has not been well studied. To address these gaps, we conducted a study in the lowland Brazilian Amazon, an area undergoing rapid cropland expansion, to assess the effects of land use change on organic matter dynamics (OM), ecosystem metabolism, and nutrient concentrations and uptake (nitrate and phosphate) in 11 first order streams draining forested (n = 4) or cropland (n = 7) watersheds with intact riparian forests. We found that streams had similar terrestrial litter inputs, but OM biomass was lower in cropland streams. Gross primary productivity was low and not different between land uses, but ecosystem respiration and net ecosystem production showed greater seasonality in cropland streams. Although we found no difference in stream concentrations of dissolved nutrients, phosphate uptake exceeded nitrate uptake in all streams and was higher in cropland than forested streams. This indicates that streams will be more retentive of phosphorus than nitrogen and that if fertilizer nitrogen reaches streams, it will be exported in stream networks. Overall, we found relatively subtle differences in stream function, indicating that riparian buffers have thus far provided protection against major functional shifts seen in other systems. However, the changes we did observe were linked to watershed scale shifts in hydrology, water temperature, and light availability resulting from watershed deforestation. This has implications for the conservation of tens of thousands of stream kilometers across the expanding Amazon cropland region.

scholarly journals Deforestation in Amazonia impacts riverine carbon dynamics

2016 ◽  
Vol 7 (4) ◽  
pp. 953-968 ◽  
Author(s):  
Fanny Langerwisch ◽  
Ariane Walz ◽  
Anja Rammig ◽  
Britta Tietjen ◽  
Kirsten Thonicke ◽  
...  
Keyword(s):  
Land Use ◽  
Organic Carbon ◽  
Land Use Change ◽  
Atlantic Ocean ◽  
Amazon Basin ◽  
Inorganic Carbon ◽  
Carbon Dynamics ◽  
Model System ◽  
Atmospheric Co2 ◽  
Terrestrial Productivity

Abstract. Fluxes of organic and inorganic carbon within the Amazon basin are considerably controlled by annual flooding, which triggers the export of terrigenous organic material to the river and ultimately to the Atlantic Ocean. The amount of carbon imported to the river and the further conversion, transport and export of it depend on temperature, atmospheric CO2, terrestrial productivity and carbon storage, as well as discharge. Both terrestrial productivity and discharge are influenced by climate and land use change. The coupled LPJmL and RivCM model system (Langerwisch et al., 2016) has been applied to assess the combined impacts of climate and land use change on the Amazon riverine carbon dynamics. Vegetation dynamics (in LPJmL) as well as export and conversion of terrigenous carbon to and within the river (RivCM) are included. The model system has been applied for the years 1901 to 2099 under two deforestation scenarios and with climate forcing of three SRES emission scenarios, each for five climate models. We find that high deforestation (business-as-usual scenario) will strongly decrease (locally by up to 90 %) riverine particulate and dissolved organic carbon amount until the end of the current century. At the same time, increase in discharge leaves net carbon transport during the first decades of the century roughly unchanged only if a sufficient area is still forested. After 2050 the amount of transported carbon will decrease drastically. In contrast to that, increased temperature and atmospheric CO2 concentration determine the amount of riverine inorganic carbon stored in the Amazon basin. Higher atmospheric CO2 concentrations increase riverine inorganic carbon amount by up to 20 % (SRES A2). The changes in riverine carbon fluxes have direct effects on carbon export, either to the atmosphere via outgassing or to the Atlantic Ocean via discharge. The outgassed carbon will increase slightly in the Amazon basin, but can be regionally reduced by up to 60 % due to deforestation. The discharge of organic carbon to the ocean will be reduced by about 40 % under the most severe deforestation and climate change scenario. These changes would have local and regional consequences on the carbon balance and habitat characteristics in the Amazon basin itself as well as in the adjacent Atlantic Ocean.

Millennia-old carbon fluxes from degraded tropical peatland soils

2020 ◽  
Author(s):  
Stephanie Evers ◽  
Thomas Smith ◽  
Mark Garnett ◽  
Selvakumar Dhandipani ◽  
Massimo Lupascu
Keyword(s):  
Land Use ◽  
Organic Matter ◽  
Land Use Change ◽  
Ecosystem Respiration ◽  
Critical Element ◽  
Tropical Peatland ◽  
Agricultural Conversion ◽  
C Cycling ◽  
The Impact ◽  
Global Carbon

<p>Assessing the flux of carbon (C) from terrestrial ecosystems to the atmosphere represents a critical element of global carbon budgeting. In tropical peatlands this has been a fundamental part of assessing the impact of land use change on an ecosystem that represents a significant global carbon store, with peat accumulation being often many meters deep. These systems have formed over thousands of years as a function of incomplete decomposition of organic matter from water-logged swamp forests. However, intact tropical peat swamp forests (PSFs) are under increasing threat from agricultural conversion, deforestation, drainage practices and fires. The resultant alteration of the peat soil results in peat oxidation, increased rates of organic matter decomposition and greenhouse gas (GHG) emissions. Consequently, these peats are reverting from C stores to sources.</p><p>Radiocarbon (<sup>14</sup>C) abundance can be used to assess C cycling rates in varied ecosystems and identify rapid or slow C turnover rates from years to centuries, as well as shifts in cycling rates – for example with land use or hydrological alteration. Within intact peatlands, deep peats generally contain an increasing abundance of <sup>14</sup>C depleted content due to radioactive decay, conversely, shallower peats are more abundant in recently produced organic litter enriched with “Bomb C”; derived from nuclear testing in the 1960s. Similarly, root derived organic matter and the associated root respiration (autotrophic respiration) also have signatures resembling recent atmospheres, whereas microbial respiration of soil organic matter (heterotrophic respiration) will resemble the mean age of the soil carbon being utilised by the microbial community, and as such can be a tracer for sources of carbon being decomposed. </p><p>Yet while an increasing body of knowledge exists on tropical peatland carbon flux rates or net ecosystem respiration in association with land-use change, these approaches fail to delineate the sources of carbon being used within the soil profile and thus fully address questions linked to changing carbon cycling rates with land use change.</p><p>Here we provide what we believe to be the first data on <sup>14</sup>CO<sub>2</sub> fluxes from tropical peatland soils in relation to varying land use classes with the aim of determining if peats which were previously long-terms C stores are being utilised within short, fast C cycles and thus contributing to modern GHG budgets. CO<sub>2</sub> flux rates were measured using soil chambers and emitted CO<sub>2</sub> was subsequently trapped on a zeolite molecular sieve cartridge. An aliquot of the recovered CO<sub>2</sub> was graphitised and analysed for <sup>14</sup>C by accelerator mass spectrometry. Associated soil age profiles were also determined.</p><p>Results indicate significant fluxes of multi-millennia old carbon from peatlands under altered land use classes and clear evidence for a shift to C cycling speed, with previously long-term stored C contributing to modern C budgets. Result highlight the instability of the peat profile under altered land-use classes and minimal to no contribution of modern C from recently produced organic matter to these carbon budgets. Findings clearly indicate the unsustainability of these agricultural practices and the need for burn- and drain-free land-use strategies.</p>

Effects of intermittency and land use on the in-stream phosphorus and organic carbon uptake

2020 ◽  
Author(s):  
Gabriele Weigelhofer ◽  
Matthias Pucher
Keyword(s):  
Land Use ◽  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Hyporheic Zone ◽  
Agricultural Land ◽  
Headwater Streams ◽  
Phosphorus Release ◽  
Nutrient Concentrations ◽  
Agricultural Land Use ◽  
First Results

<p>Understanding the consequences of the interplay between land use and climate change is among the most pressing challenges of the 21<sup>st</sup> century for river managers. Over the past decades, agricultural land use has altered nutrient concentrations and stoichiometric ratios in stream ecosystems, thereby affecting aquatic biogeochemical cycles and the coupling among carbon, phosphorus, and nitrogen. In addition, the frequency and duration of droughts has increased dramatically across Europe, causing perennial streams to shift to intermittency and changing the capacity of sediments for the uptake and storage of macronutrients.</p><p>Our study aims to understand the effects of drying and re-wetting on the uptake, storage, and release of phosphorus and organic carbon from the benthic and the hyporheic zone of headwater streams under the additional stressor of agricultural land use. In specific, we are interested in the potential coupling and decoupling of phosphorus and dissolved organic carbon cycling in autotrophic and heterotrophic benthic biofilms. We sampled headwater streams before, during, and after the dry period in 2018 and 2019 and performed laboratory experiments with artificial drying and re-wetting and additions of dissolved organic carbon. We measured nutrient uptake and release, microbial biomass, respiration, and the activity of extra-cellular enzymes. The first results show an increased phosphorus release from the sediments immediately after re-wetting, foolowed by a reduced uptake capacity. The uptake of DOC was correlated with phosphorus in autotrophic biofilms, but not in heterotrophic ones.</p>

scholarly journals Evaluation of soil carbon dynamics after land use change in CMIP6 land models using chronosequences

2021 ◽  
Author(s):  
Victor Brovkin ◽  
Lena Boysen ◽  
David Wårlind ◽  
Daniele Peano ◽  
Anne Sofie Lansø ◽  
...  
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Soil Carbon ◽  
Land Surface ◽  
Coupled Model ◽  
Quality Data ◽  
Tropical Regions ◽  
Nitrogen Levels ◽  
Decadal Scale ◽  
Crop Harvest

<p>Land surface models are used to provide global estimates of soil organic carbon (SOC) changes after past and future land use change (LUC). To evaluate how well the models capture decadal scale changes in SOC after LUC, we provide the first consistent comparison of simulated time series of LUC by six land models all of which participated in the Coupled Model Intercomparison Project Phase 6 (CMIP6) with soil carbon chronosequences (SCC). For this comparison we use SOC measurements of adjacent plots at four high-quality data sites in temperate and tropical regions. We find that initial SOC stocks differ among models due to different approaches to represent SOC. Models generally meet the direction of SOC change after reforestation of cropland but the amplitude and rate of changes vary strongly among them. Further, models simulate SOC losses after deforestation for crop or grassland too slow due to the lack of crop harvest impacts in the models or an overestimation of the SOC recovery on grassland. The representation of management, especially nitrogen levels is important to capture drops in SOC after land abandonment for forest regrowth. Crop harvest and fire management are important to match SOC dynamics but more difficult to quantify as SCC hardly report on these events. Based on our findings, we identify strengths and propose potential improvements of the applied models in simulating SOC changes after LUC.</p>

Land conversions and forest dynamics in a riparian forest zone in south east Nigeria

2020 ◽  
Vol 2 (4) ◽  
Author(s):  
Nwabueze Ikenna Igu ◽  
Joseph O. Duluora ◽  
Uzoamaka R. Onyeizugbe
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Surface Temperature ◽  
Land Surface Temperature ◽  
Land Surface ◽  
Agricultural Land ◽  
Riparian Forest ◽  
Agricultural Land Use ◽  
Forest Landscape ◽  
Sparse Vegetation

The rate at which forest ecosystems are lost and modified across tropical landscapes are alarming, yet proper documentation and proactive measures to curtail this still remains a huge challenge in most areas. This research focused on elucidating the ongoing land use change patterns of a riparian forest landscape, its current impacts on the ecosystem and land surface temperature, as well as its likely future scenarios for the zone. LANDSAT images were downloaded for 1988, 2003 and 2018 and used to show the dynamics for the zone, its drivers and their varying temperatures. Maximum Likelihood Classification algorithm was used for the classification and the land-use classes were categorized as: Water body, Farms and Sparse Vegetation, Built-up Areas, Bare Surface, and Thick Vegetation. Furthermore, Markov Chain Analysis was employed for understanding the future patterns of land use change in the zone. Land use categories experienced changes over the three epochs, but among all, farmlands/ sparse vegetation and thick vegetation had the most significant changes from 7.70 to 58.67 percent and 73.56 to 20.58 percent, respectively; implying that much of the forestland use/cover (which constituted the bulk of the land initially; 73.56 percent) were converted to agricultural land use. This same trend at which agriculture grew in the zone was seen to affect the land surface temperature for zone (Pearson correlation coefficient of  0.99 with p = 0.0058 at 0.05 level of significance). Future projection for the zone equally showed that agricultural land use will likely dominate the entire landscape in the coming years and a consequent impact on the climate and ecosystem expected as well. On that note, intensive agricultural practices that seek to maximize allocated farm units were advocated. Such initiatives will help to ensure that agricultural growth is contained within delimited zones so that haphazard cultivations, reductions in ecological value of the forest landscape and consequent climatic impacts could be managed across the region.

scholarly journals Contributions of secondary forest and nitrogen dynamics to terrestrial carbon uptake

2010 ◽  
Vol 7 (2) ◽  
pp. 2739-2765 ◽  
Author(s):  
X. Yang ◽  
T. K. Richardson ◽  
A. K. Jain
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Secondary Forest ◽  
Nitrogen Dynamics ◽  
Carbon Uptake ◽  
Secondary Forests ◽  
Terrestrial Carbon ◽  
Tropical Regions ◽  
Forest Regrowth ◽  
Limiting Nutrient

Abstract. We use a terrestrial carbon-nitrogen cycle component of the Integrated Science Assessment Model (ISAM) to investigate the impacts of nitrogen dynamics on regrowing secondary forests over the 20th century. We further examine what the impacts of nitrogen deposition and land use change history are on terrestrial carbon uptake since preindustrial time. Our results suggest that global total net land use emissions for the 1990s associated with changes in cropland, pastureland, and wood harvest are 1.22 GtC/yr. Without considering the secondary forest regrowth, the estimated net global total land use emissions are 1.58 GtC/yr or about 0.36 GtC/yr higher than if secondary forest regrowth is considered. Results also show that without considering the nitrogen dynamics and deposition, the estimated global total secondary forest sink for the 1990s is 0.90 GtC/yr or about 0.54 GtC/yr higher than estimates that include the impacts of nitrogen dynamics and deposition. Nitrogen deposition alone is responsible for about 0.13 GtC/yr of the total secondary forest sink. While nitrogen is not a limiting nutrient in the intact primary forests in tropical regions, our study suggests that nitrogen becomes a limiting nutrient for regrowing secondary forests of the tropical regions, in particular Latin America and Tropical Africa. This is because land use change activities, especially wood harvest, removes large amounts of nitrogen from the system when slash is burnt or wood is removed for harvest. However, our model results show that carbon uptake is enhanced in the tropical secondary forests of the Indian region. We argue that this may be due to enhanced nitrogen mineralization and increased nitrogen availability following land use change in the Indian tropical forest ecosystems. Results also demonstrate that there is a significant amount of carbon accumulating in the Northern Hemisphere where most land use changes and forest regrowth has occurred in recent decades. This study indicates the significance of secondary forests to terrestrial carbon sinks, the importance of nitrogen dynamics to the magnitude of secondary forests carbon uptake, and therefore the need to include both primary and secondary forests and nitrogen dynamics in terrestrial ecosystem models.

scholarly journals Belowground changes to community structure alter methane-cycling dynamics in Amazonia

2020 ◽  
Author(s):  
Kyle M. Meyer ◽  
Andrew H. Morris ◽  
Kevin Webster ◽  
Ann M. Klein ◽  
Marie E. Kroeger ◽  
...  
Keyword(s):  
Land Use ◽  
Microbial Community ◽  
Land Use Change ◽  
Forest Soils ◽  
Amazon Basin ◽  
Surface Soil ◽  
Secondary Forest ◽  
Primary Forest ◽  
Forest Regrowth ◽  
Cattle Pasture

ABSTRACTAmazonian rainforest is undergoing increasing rates of deforestation, driven primarily by cattle pasture expansion. Forest-to-pasture conversion has been associated with changes to ecosystem processes, including substantial increases in soil methane (CH4) emission. The drivers of this change in CH4 flux are not well understood. To address this knowledge gap, we measured soil CH4 flux, environmental conditions, and belowground microbial community attributes across a land use change gradient (old growth primary forest, cattle pasture, and secondary forest regrowth) in two Amazon Basin regions. Primary forest soils exhibited CH4 uptake at modest rates, while pasture soils exhibited CH4 emission at high but variable rates. Secondary forest soils exhibited low rates of CH4 uptake, suggesting that forest regrowth following pasture abandonment could reverse the CH4 sink-to-source trend. While few environmental variables were significantly associated with CH4 flux, we identified numerous microbial community attributes in the surface soil that explained substantial variation in CH4 flux with land use change. Among the strongest predictors were the relative abundance and diversity of methanogens, which both increased in pasture relative to forests. We further identified individual taxa that were associated with CH4 fluxes and which collectively explained ~50% of flux variance. These taxa included methanogens and methanotrophs, as well as taxa that may indirectly influence CH4 flux through acetate production, iron reduction, and nitrogen transformations. Each land type had a unique subset of taxa associated with CH4 fluxes, suggesting that land use change alters CH4 cycling through shifts in microbial community composition. Taken together, our results suggest that changes in CH4 flux from agricultural conversion could be driven by microbial responses to land use change in the surface soil, with both direct and indirect effects on CH4 cycling. This demonstrates the central role of microorganisms in mediating ecosystem responses to land use change in the Amazon Basin.

scholarly journals Variation of stream metabolism along a tropical environmental gradient

2018 ◽  
Author(s):  
Wesley A. Saltarelli ◽  
Walter K. Dodds ◽  
Flavia Tromboni ◽  
Maria do Carmo Calijuri ◽  
Vinicius Neres-Lima ◽  
...  
Keyword(s):  
Land Use ◽  
Total Phosphorus ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Canopy Cover ◽  
Tropical Streams ◽  
Nutrient Concentrations ◽  
Stream Metabolism ◽  
Mixed Effect ◽  
Single Station

Stream metabolism is affected by both natural and human-induced processes. While metabolism has multiple implications for ecological processes, relatively little is known about how metabolic rates are influenced by land use in tropical streams. In this study, we assessed the metabolic characteristics and related environmental factors of six streams located in a transition area from Cerrado to Atlantic Forest (São Carlos/Brazil). Three streams were relatively preserved, while three were flowing through more agriculturally and/or urban impacted watersheds. Surface water samples were analyzed for biological and physico-chemical parameters as well as discharge and percentage of canopy cover. Metabolism was determined through the single-station method to estimate gross primary production (GPP), ecosystem respiration (ER) and net ecosystem production (NEP) with BAyesian Single-station Estimation (BASE). Nutrient concentrations tended to be higher in impacted versus preserved streams (e.g., average total phosphorus between 0.028-0.042 mg L-1 and 0.009-0.038 mg L-1, respectively). Average canopy cover varied between 58 and 77%, with no significant spatial or seasonal variation. All streams were net heterotrophic (ER exceeded GPP) in all sampling periods. GPP rates were always lower than 0.7 gO2 m-2 d-1 in all streams and ER varied from 0.6 to 42.1 gO2 m-2 d-1.  Linear Mixed-Effect models showed that depth, discharge, velocity and total phosphorus are the most important predictors for GPP. For ER, depth, velocity and canopy cover are significant potential predictors. Canopy cover was the main light limiting factor and influenced stream metabolism. Our findings reinforced the concepts that shifts in the shading effect provided by vegetation (e.g., through deforestation) or changes in discharge (e.g., through land use conversion or water abstractions) can impact freshwater metabolism. Our study suggests that human activities in low latitude areas can alter tropical streams’ water quality, ecosystem function, and the degree of riparian influence. Our data showed that tropical streams can be especially responsive to increases of organic matter inputs leading to high respiration rates and net heterotrophy, and this should be considered to support management and restoration efforts.

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