Microbial stream ecology of Latah Creek watershed, WA

Background/Question/Methods

Although sediment microbes play key roles in decomposition and nitrogen (N) cycling, understanding how microbial communities vary in response to N additions within many watersheds is unknown. Agriculture has been shown to contribute excess N into stream systems, predominantly as ammonia, which is transformed through nitrification into nitrate by bacteria and Archaea that produce the ammonia monooxygenase enzyme (amoA). The Latah Creek watershed in WA State drains approximately 430,000 acres of land, of which half is agricultural. Because the tributary streams reside in forested, agricultural and mixed use drainages, samples from these stream sediments can capture microbial communities at different spatial gradients of land use. Our research aims to answer: To what extent does agriculture in a drainage affect microbial community compositions, and how does it affect the abundance of nitrifying bacteria? Water and sediment samples were collected from ten locations along the watershed in Spring and Fall 2012. Two PCR techniques will be used on the DNA: T-RFLP on the small ribosomal subunit 16S rRNA is useful for comparing differences among community compositions as it isolates hypervariable regions in this sequence and identifies differences in community constituents; qPCR on amoA will measure gene abundance to quantify functionally similar microbes.

Results/Conclusions

GIS was used to determine the percentage of agricultural land within each of the ten tributary drainages that were sampled. These percentages ranged from 0% at the headwaters to 98% along the Palouse. pH, temperature, conductivity and dissolved oxygen (DO) were measured in situ and showed the following ranges: pH (6.1 – 8.22); temperature ( 5.19°C -18.91°C); conductivity (0.07 ms/cm^c - 0.90 ms/cm^c); and DO mg/L (7.6 – 14.79). Nitrogen chemistry will be conducted in the lab. These physical characteristics of the streams and watersheds will be compared to microbial diversity and abundance of the amoA gene. We hope to better relate microbial communities and nitrification to patterns of land use and water quality.