Water properties and approximate sampling frequencies for National Stream Quality Accounting Network and Hydrologic Benchmark Network water-quality data on CD-ROM _____________________________________________________________________________ WATER PROPERTIES FREQUENCIES 1 (samples per year) _____________________________________________________________________________ Physical/field measurements: Temperature, specific conductance (field and lab), dissolved oxygen, pH (field and laboratory), suspended sediment, turbidity, instantaneous streamflow...............................................4 to 12 Streamflow, daily mean...................................... 365 Major ions: Calcium, chloride, magnesium, potassium, silica, sodium, sulfate, fluoride, dissolved solids, hardness, alkalinity, bicarbonate, and carbonate.........4 to 12 Nutrients and carbon (dissolved and total)2: Ammonia+organic (Kjeldahl) nitrogen, ammonia, nitrite, nitrate+nitrite, orthophosphate, phosphorus, and nitrogen.................................4 to 12 Organic carbon (includes suspended also)....................4 to 8 Radiochemicals (dissolved, suspended sediment): Gross alpha and beta, radium-226, tritium, uranium..........1 or 2 Biological measurements: Fecal coliform and streptococci............................4 to 12 Periphyton (chlorophyll A and B), periphyton biomass.....................................................4 Phytoplankton (chlorophyll A and B), phytoplankton (total count), identification of predominant forms........................................7 to 12 Inorganic trace elements (dissolved, total): Aluminum, arsenic, barium, beryllium, boron, cadmium, chromium, cobalt, copper, iron, lead, lithium, manganese, mercury, molybdenum, nickel, selenium, silver, strontium, vanadium, and zinc..........3 or 4 _____________________________________________________________________________ 1 The range of sample frequencies for any constituent group reflect differences in frequency among the two networks, changes in frequency with time, and differences among stations within a single network. See the section "Sampling Frequency" in the accompanying Open-File Report 96-337 for a discussion of temporal changes in sampling frequency. 2 Analyses for the "total" forms of nitrate+nitrite, nitrite, ammonia, and orthophosphate are based on samples "decanted" in the laboratory (see the section "National Network Laboratory Techniques" in the accompanying Open-File Report 96-337 for additional details). Total nitrogen is computed as the sum of total Kjeldahl nitrogen and "total" nitrate+nitrite.