US Long-Term Ecological Research Network
We collect samples at the deepest part of the lake using tubing and a peristaltic pump, filtering (where required) inline through 0.45u polycarbonate membrane filters. We sample for water chemistry monthly during open water and approximately every five weeks during ice cover.  The sample depths are selected based on thermal stratification. We take samples at the top and bottom of the epilimnion, mid thermocline, and top, middle, and bottom of the hypolimnion. When the lake is mixed, we sample at the surface, mid water column, and bottom.  We analyze for pH, phosphorus, nitrogen, silica, inorganic and organic carbon, ammonium, and nitrate/nitrite.  Four times per year we also sample for alkalinity, major anions and cations, conductivity, and color.
Protocol Log: Chem samples were collected biweekly before 1986.


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