Functional Condition Assessment
The RAN team is also investigating non-traditional methods for assessing stream condition. Historically, stream assessment methods have involved structural metrics which describe aquatic biological communities, water quality and quantity, and physical geometry and habitat values. Regulatory classification of stream condition is typically based upon biological assessments, which constitute one type of structural evaluation. There are, however, other methods for assessing stream condition that evaluate community-level ecosystem functions.
This aspect of the RAN Project involves a study that compares those traditional metrics of stream health with other functional assessment methods (specifically, whole-stream metabolism and solute injection experiments) that examine overall ecosystem processes (primary productivity, community respiration, and nutrient uptake). These experiments are being conducted on a set of six impaired and reference condition stream reaches in Vermont, selected via background research, field surveys, and consultation with Vermont Department of Environment Conservation (DEC) staff. These efforts will also help evaluate the effectiveness of using paired attainment and reference condition streams in Vermont.
The stream monitoring efforts at these 6 functional assessment sites share many parameters with the stream monitoring taking place at Butler Farms and Oak Creek. Field equipment installed at each site continuously monitors water level, dissolved oxygen content, specific conductivity, water temperature, light intensity (PAR), and rainfall. These data are currently being reduced for data analysis. It will be used in conjunction with the biological and physical data to explore how multiple factors influence stream condition from a structural perspective.
A majority of the field measurements are part of the calculation of Whole Stream Metabolism rates (WSM). WSM is calculated from a detailed budget of oxygen input, output and exchange over a specified stream reach. The experiments provide an integrated estimate of whole stream respiration, net photosynthesis, and gross photosynthesis. These data will be compiled in to daily WSM values which provide a long-term, general characterization of the study reaches to compare differences between the impaired and attainment condition streams.
The second functional assessment method used for this project is an assessment of nutrient uptake length. This method provides an estimate of the average amount of time a solute molecule remains in solution before it is taken up, absorbed or exchanged in the stream system. Thus, it is a metric of the rapidity with which a compound is cycled in a stream ecosystem, a concept that is referred to as spiraling. Excessively short or long uptake lengths (Sw) are indicative of systems that may be under stress or out of balance. We will focus on key forms of nitrogen (ammonium and nitrate) and - especially - phosphorus, which are critical to understanding how runoff from land affects eutrophication in Lake Champlain. Three rounds of Solute Injection Experiments (SIE) were conducted to study differences between impaired and attainment condition streams.