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

Abstract

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.

A Longitudinal Study of Brazilian Food Production Dynamics

“…There has been a decline in deforestation, from approximately 18,309 km 2 yr −1 from 1990 through 2004, to just under 8877 km 2 yr −1 in 2005-2019, with the lowest rate (4571 km 2 yr −1 ) in 2012 [38]. Recent studies in the region address other concerns: green and blue water effects on productivity and efficiency [5], political mobilization and the legal arena [7], fire and deforestation on spatial and temporal dynamics [39], and land use effects on ecosystem function [40].…”

Sediment Infill of Tropical Floodplain Lakes: Rates, Controls, and Implications for Ecosystem Services

“…Population density in the tropics is projected to increase rapidly (e.g., Laurance et al, 2014), hence >50% of the world's population is expected to reside in the tropics by 2050. Land conversion for livestock and agriculture has intensified in the tropics since the "Green Revolution" in the second half of the 20th century (e.g., Evenson and Gollin, 2003;Le Huong and Thanh Son, 2020;Sinha et al, 2020;Alavez-Vargas et al, 2021;Jankowski et al, 2021), leading to increased sediment supply to some lowland lakes. Owens (2020) describes that greater sediment accumulation rates have become a threat to water security.…”

Land-use effects on aquatic macroinvertebrate diversity in subtropical highland grasslands streams

“…Human activities have negative impacts on inland aquatic systems (Allan, 2004;Rezende et al, 2014b). Some land uses [e.g., native vegetation replacement with pastures, agriculture or urbanization (Firmiano et al, 2021;Jankowski et al, 2021;Rezende et al, 2021)] may decrease stream bed stability (Allan, 2004;Shanafield et al, 2021) and alter both the organic matter dynamic (Burwood et al, 2021;Rezende et al, 2021) and water physicochemical characteristics [e.g., dissolved nutrient input, pH, electrical conductivity, and dissolved oxygen (Chen et al, 2021;Martins et al, 2021;Tonin et al, 2021)]. Anthropogenic land covers may also favor the best competitor, thereby increasing the abundance of a few organisms (Allan, 2004;Shanafield et al, 2021).…”

“…Anthropogenic land covers may also favor the best competitor, thereby increasing the abundance of a few organisms (Allan, 2004;Shanafield et al, 2021). Therefore, land covers resulting from different uses may affect stream habitats differently, altering the diversity and functioning of the ecosystem and its organisms (Kahirun et al, 2019;Jankowski et al, 2021). Among aquatic organisms that are sensitive to land use changes, macroinvertebrates are perhaps the main indicators of freshwater ecosystem health (Kahirun et al, 2019;Firmiano et al, 2021).…”