Agricultural land-use affects the nutritional quality of stream microbial communities

Abstract

We investigated how the lipid composition (fatty acids and sterols) of benthic microbial mats, which represent an important basal food resource for stream food webs, differs between tropical streams located in protected pristine and agricultural Cerrado savannah areas. The total microbial biomass and lipid composition differed significantly between pristine and agricultural streams in parallel with differences in water quality and hydrodynamic characteristics. Agricultural streams exhibited lower total biomass of benthic microbial mats than pristine streams. However, the higher concentrations of essential polyunsaturated fatty acids, such as linoleic acid (LIN, 18:2ω6), α-linolenic acid (ALA, 18:3ω3), and eicosapentaenoic acid (EPA, 20:5ω3), that were observed in agricultural streams suggest enhanced lipid complexity and a higher nutritional quality of the microbial community relative to pristine streams. Meanwhile, pristine stream microbial communities had higher total concentrations of saturated fatty acids and cholesterol than those of agricultural streams, reflecting their heterotrophic microbial communities. Moreover, stream morphotype and associated differences in the hydrodynamic characteristics affected the community composition and thereby also the lipid composition of microbial mats. Land-use-induced changes in the total biomass and lipid composition of microbial communities may affect the trophic transfer of energy in stream food webs, leading to changes in the composition and productivity of primary consumers and their predators, and thereby affecting stream ecosystem functioning.

Leaf decomposition and ecosystem metabolism as functional indicators of land use impacts on tropical streams

“…Moreover, exposed leaf material initially exhibited very low absolute N and P concentrations and molar N:P ratios compared to literature values (Wantzen et al, 2008), but accumulated N during the incubation, indicating that the incubated leaves acted as a substrate for microbial growth (Gessner et al, 1999;Stallcup et al, 2006). Effects of agricultural land use on microbial community composition and metabolism in tropical streams, such as decreases in bacterial and fungal biomass and heterotrophic activity, have been reported (Boëchat et al, 2011) and may also be the cause for land-use effects on microbial decomposition of leaf litter.…”

Fatty Acid Composition at the Base of Aquatic Food Webs Is Influenced by Habitat Type and Watershed Land Use

“…On the other hand, Müller-Navarra et al [20] found that lake trophic status (indicated by total phosphorus [P]) was negatively correlated to the amount of EPA and DHA in seston (per unit C). Agriculture and other human land uses tend to increase the nitrogen (N) and P available in downstream waters [19]–[21], and these nutrient increases are presumably influencing algal community dynamics (productivity and species composition) in these previous studies [19], [20]. Whether these changes in primary producer FA composition lead to variation among ecosystems in primary consumer FA composition has apparently not been assessed.…”

“…Boëchat et al [19] found that agricultural streams had higher per-mass amounts of essential PUFAs in biofilms than pristine streams, although biofilms were overall less extensive in agricultural streams (i.e., agricultural streams had small amounts of high-quality biofilms). On the other hand, Müller-Navarra et al [20] found that lake trophic status (indicated by total phosphorus [P]) was negatively correlated to the amount of EPA and DHA in seston (per unit C).…”

The necessity of management in a lake of the Atlantic Forest biodiversity hotspot: nitrogen levels connected to a persistent bloom of Cylindrospermopsis raciborskii

“…surroundings (Anderson 2014). The prompt responses allow the rapid detection of changes or impacts happening in the watersheds and could be helpful to understand the effects of land use, providing supporting data for the conservation of endangered environments, such as biodiversity hotspots (Boëchat et al 2011). The water quality in Marola Lake was connected to climate events, which was observed in the PCA ordination that clearly separated dry and rainy seasons.…”