title: Classifying lakes to quantify relationships between epilimnetic chlorophyll a and hypoxia.
abstract: Excess nutrient loading increases algal abundance which can cause hypoxia in many lakes and reservoirs. We used a divisive partitioning approach to analyze dissolved oxygen profile data collected across the continental United States to increase the precision of estimated relationships between chlorophyll a (chl a) concentrations and the extent of hypoxia in the water column. Chl a concentrations predicted the extent of hypoxia most accurately in lakes that were stratified at the time of sampling with a maximum temperature gradient of at least 1.2 °C/m. Lake elevation, Secchi depth, and lake geometry ratio further refined the specification of groups of lakes with different relationships between chl a and the extent of hypoxia. The statistical relationships between chl a and the extent of hypoxia that were estimated can be used directly for setting management thresholds for chl a in particular types of lakes.
authors.affiliation: Office of Science and Technology, Office of Water, U.S. Environmental Protection Agency, 1200 Pennsylvania Ave NW, Washington, DC, 20460, USA, yuan.lester@epa.gov.
authors.forename: Lester L
authors.initials: LL
authors.lastname: Yuan
authors.forename: Amina I
authors.initials: AI
authors.lastname: Pollard
mesh_terms: D002734:Chlorophyll / Q000032:analysis*; D000077194:Chlorophyll A; D004784:Environmental Monitoring / Q000379:methods* / Q000592:standards; D060106:Lakes / Q000737:chemistry*; D009391:Nephelometry and Turbidimetry; D010100:Oxygen / Q000032:analysis*; D013696:Temperature; D014481:United States; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical; D002734:Chlorophyll; D010100:Oxygen; D000077194:Chlorophyll A