R/EH-16

Strategic focus area:

Description:

Land-use changes create numerous adverse impacts to stream ecosystems within the Chesapeake Bay watershed, including degrading water quality for both human and non-human use. Fish and benthic macroinvertebrates are traditionally used as indicators of biotic response to watershed disturbance.  However, these indicators do not necessarily reflect the status of key ecosystem processes such as the metabolism of nutrients and other pollutants that otherwise can flow to coastal waters. Conversely, microbial communities drive many ecosystem processes, including nutrient cycling, and thus their diversity and composition have great potential to assess and possibly mitigate impacts on aquatic ecosystems. Microbial pathogens are also important to human health, and identifying their prevalence and landscape associations may have profound implications for resource management and planning. However, almost nothing is known about the biogeography of microbial community diversity in stream ecosystems and how this varies with watershed alterations.

Robust methods to characterize the diversity of microbes, many of which cannot be cultured in the laboratory, have arisen recently due to high-throughput DNA sequencing of whole microbial communities. Our objectives for this study are to characterize microbial community diversity in headwater streams throughout the Chesapeake Bay watershed of Maryland to test the following predictions: (1) Microbial diversity declines along gradients of land use and urbanization; (2) Microbial diversity is a more sensitive and reliable indicator of stream impairment than traditional bioindicators such as fish and benthic macroinvertebrates; and (3) The taxonomic composition of microbial communities reflects specific impacts of anthropogenic land use such as high loadings of nutrients or sediments into aquatic ecosystems.

The Maryland Biological Stream Survey (MBSS) performs annual assessment of stream condition across the state's watersheds. In spring and summer of 2014, we will team with MBSS to sample microbial DNA from water and sediments of 96 headwater streams. An overlapping set of 24 "Sentinel Sites" will be sampled again in 2015. In addition, 96 sites will be sampled by 4 citizen watershed associations, who will help design studies to characterize microbial response to a local environmental stressor. Microbial DNA will be used for high throughput 16S amplicon sequencing to characterize the composition and diversity of the microbial metagenomic community at each site and season. Microbial diversity will then be related to water quality, traditional bioindicators, and measurements of land use using multivariate statistical models. Environmental predictors include a suite of physic-chemical and land use variables that define an environmental gradient within Maryland ranging from pristine forested, to primarily agricultural, to highly urbanized watersheds.

Our study will robustly characterize the relationships between microbial diversity and land use change within the Chesapeake Bay watershed. Our results will be accessible and useful to diverse stakeholders with interests in water quality, aquatic resource management, and the health of stream ecosystems.