The effect of agriculture on the seasonal dynamics and functional diversity of benthic biofilm in tropical headwater streams

Abstract

Tropical streams are one of the most endangered ecosystems in the world due to the constant pressures from human activities. Among these activities, agriculture represents a land use that is crucial for human development but also a key driver of stream degradation and biodiversity decline in the tropics. Against this background, we investigated indirect effects of agriculture (alterations in stream flow and nutrient availability) and climate characteristics (water temperature) on benthic biofilm communities in tropical streams (São Paulo State, Brazil). Three first‐order streams draining catchments dominated by agricultural land use (sugarcane for bioenergy production, pasture) with some remaining riparian forest were studied for 1 year. We focused on the relationships of benthic biofilm biomass, algal biomass, diatom community, and functional structure with streamflow dynamics, nitrate concentrations, and water temperature. Our results indicate that these biological responses were mainly mediated by flow and water temperature and not by resource availability in the studied headwater streams. This result could be explained by the heavy rains and elevated runoff generation in these tropical catchments under agricultural influence, which might override the known effects of nutrient enrichment on benthic biofilm communities. Considering forecast climate and land‐use changes in tropical streams, our findings may suggest potential shifts in benthic biofilm communities, with functional consequences for aquatic food webs in these environments. Abstract in Brazilian Portuguese is available with online material.

Trait‐based diatom functional diversity as an appropriate tool for understanding the effects of environmental changes in soda pans

“…Of the functional diversity metrics studied, FGR, FRic, FDis, and FDiv proved to be the most useful for assessing the ecological status and conservation value of soda pans. FEve was not related to changes in the environment, as has been shown in the case of diatoms in tropical headwater streams (Taniwaki et al, ), and over the long term by phytoplankton communities in a large river (Abonyi et al, ).…”

“…As forest shading of streams reduces functional diversity (Taniwaki et al, ), the light climate of soda pans on the basis of their color type (Lengyel et al, ) had a considerable effect on the trait composition and functional diversity, as also experienced in the diatom community composition of artificial bomb crater ponds (Földi et al, ). While the turbidity of lakes reduces light intensity, high levels of humic materials can modify the spectral composition of the incoming light (Kirk, ; V.‐Balogh, Németh, & Vörös, ).…”

The riverine bioreactor: An integrative perspective on biological decomposition of organic matter across riverine habitats

“…Flood pulses can be marked and predictable in some tropical rivers due to the extended wet season (Boulton et al, 2008). But, the higher annual precipitation in wet subtropical and tropical regions results in frequent and irregular flood pulses, which structure communities including biofilms (Taniwaki et al, 2019;Burrows et al, 2020) and benthic macroinvertebrates (Nessimian et al, 1998). Nonetheless, the higher frequency and magnitude of flood pulses has not been related to decomposition processes at low latitudes.…”

Fine sediment and flow velocity impact bacterial community and functional profile more than nutrient enrichment

“…Our experiment was performed over a relatively short period of time in a single mesocosm setup. Seasonality and geographical location are important determinants of microbial communities; therefore, studies across longer time periods and spanning multiple locations are necessary (Lear et al 2008, Taniwaki et al 2019). For example, a survey of four streams impacted by varying degrees of human modification (Lear et al 2009) found that macroinvertebrate community structure changed clearly across the entire gradient of human impact while bacterial communities could only separate the most impacted site from the other three.…”