An Academic Advisory Committee (AAC) submitted a report to the Virginia Department of Environmental Quality (DEQ) to suggest approaches to developing nutrient criteria for the state’s freshwaters.
For streams and rivers, the AAC recommends that criteria be defined to represent levels of algal biomass that impair the designated uses. The committee determined a process that could be applied to define criteria levels for these indicators but recommends against application of a relatively undisturbed reference or a percentile-distribution reference approach.
User perception surveys, if designed, administered, and analyzed in a scientifically valid manner, would be an appropriate mechanism for assessing suitability for recreational uses.
The committee also recommends that investigation of nutrient-algal biomass relationships be considered an integral component of the criteria development process because nutrient inflows both control algal biomass and are subject to direct management controls. If those relationships can be defined with statistical confidence, they could be applied by DEQ to defining numeric nutrient criteria. The committee recommends that the natural lakes and constructed impoundments be treated separately in the criteria development process. The committee recommends that the two natural lakes—Mountain Lake and Lake Drummond—have individual nutrient criteria developed because they are different from the constructed impoundments and from each other.
The AAC believes the constructed impoundments should be classified based on the types of fisheries that they support and (pending results of data analysis) possibly on morphometric features that influence nutrient-algal relationships and/or fish population response. To meet the objectives of the work plan for assisting DEQ with freshwater nutrient criteria, the AAC proposes to analyze DEQ monitoring and associated data. The primary purpose of the analysis will be to determine whether such data demonstrate linkages between water column nutrients (as represented by TN and TP concentrations, chlorophyll a as an indicator of algal populations, and Secchi depth as an indicator of water clarity) and the suitability of water bodies to support designated uses.
Virginia DEQ has provided the AAC with ambient monitoring data taken from the state’s lakes since the late 1970s. Parameters include phosphorous concentrations, nitrogen concentrations, chlorophyll a, and Secchi depth, as well as context variables such as sampling location, sampling date and time, sampling depth, water temperature, and pH.
All monitoring locations are aggregated by lake. For each variable, all observations from each lake will be reduced to a single data point that is considered to be representative of that lake over the period of interest using statistical methods appropriate to the variable’s distribution. Because algal impairment is a warm weather phenomenon, only observations representative of the warm-weather season will be considered.
The committee proposed to calculate trophic state index (TSI) using measured TP, chlorophyll a, and Secchi depth values for selected Virginia reservoirs and quantify the degree of correspondence among these measures. They will explore the effect of expressing candidate criteria for protection of recreational and aquatic life uses as TSI values (Zipper et al. 2004).
Reference:
Zipper, C.E., E.F. Benfield, T.A. Dillaha III, T.J. Grizzard, Jr., H.I. Kator, W-S, Lung, J.J. Ney, L.A. Shabman, E.P. Smith, L.A. Smock, J.L. Walker, E.R. Yagow, and T. Younos. 2004. Report of the Academic Advisory Committee to Virginia Department of Environmental Quality – Freshwater Nutrient Criteria. Prepared for Virginia Department of Environmental Quality. Accessed October 2016. http://www.deq.virginia.gov/Portals/0/DEQ/Water/WaterQualityStandards/AAC04report.pdf EXIT.