Responses of aquatic macrophyte cover and productivity to flooding variability on the Amazon floodplain

Abstract

Macrophyte net primary productivity (NPP) is a significant but understudied component of the carbon budget in large Amazonian floodplains. Annual NPP is determined by the interaction between stem elongation (vertical growth) and plant cover changes (horizontal expansion), each affected differently by flood duration and amplitude. Therefore, hydrological changes as predicted for the Amazon basin could result in significant changes in annual macrophyte NPP. This study investigates the responses of macrophyte horizontal expansion and vertical growth to flooding variability, and its possible effects on the contribution of macrophytes to the carbon budget of Amazonian floodplains. Monthly macrophyte cover was estimated using satellite imagery for the 2003-2004 and 2004-2005 hydrological years, and biomass was measured in situ between 2003 and 2004. Regression models between macrophyte variables and river-stage data were used to build a semiempirical model of macrophyte NPP as a function of water level. Historical river-stage records (1970-2011) were used to simulate variations in NPP, as a function of annual flooding. Vertical growth varied by a factor of ca. 2 over the simulated years, whereas minimum and maximum annual cover varied by ca. 3.5 and 1.5, respectively. Results suggest that these processes act in opposite directions to determine macrophyte NPP, with larger sensitivity to changes in vertical growth, and thus maximum flooding levels. Years with uncommonly large flooding amplitude resulted in the highest NPP values, as both horizontal expansion and vertical growth were enhanced under these conditions. Over the simulated period, annual NPP varied by ca. 1.5 (1.06-1.63 TgC yr(-1) ). A small increasing trend in flooding amplitude, and by extension NPP, was observed for the studied period. Variability in growth rates caused by local biotic and abiotic factors, and the lack of knowledge on macrophyte physiological responses to extreme hydrological conditions remain the major sources of uncertainty.

Influence of the aquatic vegetation landscape on larval fish abundance

“…S2E vs S2F). These relatively large interannual variations have also been observed in other large river ecosystems, like the Amazon (Silva et al, 2013). In LSP, the distribution, composition and productivity of AV beds are largely influenced by the inflow of nutrients from watershed land use (Hudon and Carignan, 2008), primarily agriculture, variation in transparency (Hudon et al, 2000), water retention time, geomorphology (i.e.…”

“…In addition to total biomass, AV community composition can also affect fish distribution (Chick and Mclvor, 1994;Weaver et al, 1997;Cvetkovic et al, 2010;Silva et al, 2013). Given that remote sensing and aerial imagery are becoming more available, the use of image texture metrics as a proxy of AV community composition may also provide additional and valuable information to evaluate the effect of AV landscape on fish communities.…”

Recent increase of river–floodplain suspended sediment exchange in a reach of the lower Amazon River

“…Herbaceous plant net primary productivity (NPP) is a significant component of the carbon budget in Amazon floodplains. Silva et al (2013) predicted increase in annual macrophyte NPP associated with increase in flood duration and amplitude, as NPP was determined based on both stem elongation (vertical growth) and plant cover changes (horizontal expansion). However, vegetation will be affected by changes in patterns of sedimentation, flow shear stress, and supply and residence times of nutrients.…”

“…The floodplain is vegetated by shrubs, woodland and sparse alluvial forest (Silva et al, 2013). Seasonal growth and decomposition of grasses and other aquatic plants are linked to the inundation dynamics (Silva et al, 2009).…”

Vegetation, rainfall, and pulsing hydrology in the Pantanal, the world’s largest tropical wetland

“…Rising temperatures and changes in rainfall can lead to alterations in hydrology within these ecosystems [4]. Further, intensification of land-use pressures can have a large impact on wetland geomorphology and ecology [9,11]. For example, dam construction changes flow paths, discharge dynamics, river stage, and sediment transport [12][13][14].…”