Effects of land use on water column bacterial activity and enzyme stoichiometry in stream ecosystems

Abstract

Fifty streams, located in southern Ontario, Canada, were visited in September 2008 to investigate the effect of varying land use, land cover, and associated resource inputs on water column bacterial abundance (BACT), production (BP), and extracellular enzyme activity and stoichiometry. Principle components analysis was used to summarize landscape data, producing three components (PCs), which explained 79.2% of the variability in the data. The PCs grouped into the following gradients: (PC1) urban land use and continuous annual cropping to wetland-like cover, (PC2) rotational cropping to forest-like cover, and (PC3) increasing rural and agricultural land uses with increasing watershed size. These landscape gradients created imbalanced resource availability. Nutrient resources were more abundant in streams with more intensive anthropogenic land uses, but carbon availability was primarily controlled by the abundance of natural land covers (wetland and wooded areas). BACT, BP, and enzyme activities were positively related primarily to nutrient availability and/or anthropogenic land use (Stepwise R 2 range: 0.33-0.73). The ratio of b-glucosidase to alkaline phosphatase activity approached a 1:1 balance with increasing anthropogenic land use, decreased wetland and forest cover, and increased total dissolved nitrogen. The ratio of leucine-aminopeptidase to alkaline phosphatase activity approached 1:1 with both increased dissolved organic carbon and nitrogen. Moreover, enzyme C:N:P ratios moved closer to 1:1:1 with faster water column bacterial turnover times. These results suggest that water column microbial communities are better able to balance resource availability with growth in streams receiving nutrient subsidies from anthropogenic sources and under these conditions when carbon resources increase.

Extracellular Enzyme Activity and Microbial Diversity Measured on Seafloor Exposed Basalts from Loihi Seamount Indicate the Importance of Basalts to Global Biogeochemical Cycling

“…Williams et al (58) found that this ratio approaches 1:1 with increased levels of dissolved organic C and dissolved organic N. In our study, the LAP/AP ratios were 1:50 at J2482 and 1:20 at J2477. Greater AP activity in this study can be interpreted as a higher demand for phosphorus and/or carbon.…”

Biochemical quality of basal resources in a forested stream: effects of nutrient enrichment

“…In general, forested streams (specifically Fuirosos) are primarily heterotrophic, with the DOM in the stream water primarily resulting from allochthonous sources (Thurman 1985;Butturini et al 2008). Higher enzyme activities in water with nutrient enrichment have also been observed (Williams et al 2012), but the temporal differences observed in our study are not related to light, as observed for biofilms.…”

Nutrient loading associated with agriculture land use dampens the importance of consumer‐mediated niche construction

“…The land cover and use in the catchments is a mix of forests, wetlands and agriculture and to a lesser extent developed (urban or suburban) land (see Supplemental Table 1 and Wilson & Xenopoulos ; Williams et al . for detailed watershed characteristics). Freshwater mussel populations, while somewhat ubiquitously distributed, are often observed as patches (~100 m long) called ‘mussel beds.’ Therefore, using an unpublished Fisheries and Oceans Canada database, site selection was initially filtered according to the presence of either or both focal mussel species E. complanata (Lightfoot 1786) and L. costata (Rafinesque 1820) (~80–90 sites), and then refined according to the desired range of agriculture intensity, watershed area and proximity to laboratory.…”