North Temperate Lakes
US Long-Term Ecological Research Network

South: Field Sampling Routine

A. Nutrient Sampling: Refer to the Field Sheet to see which bottles need to be sampled at which depths and the 'Southern Lakes LTER Bottle Codes’ for preservation, filtering, and coding information.
 
1.     Purge the lines: Whenever sampling from a new depth, the peristaltic pump tubing must be purged of the water from the previous depth. After reaching the proper sampling depth, use a graduated cylinder to measure the volume of water purged before beginning the sampling. Purge at least 1200 mL of water for each 20 meters of tu

South: Sampling Schedule

1. When to Sample: To determine the sampling dates, follow the same schedule as done in past years. It is best to make out the calendar for the whole year and sign-out a vehicle and boat far in advance. Check the past year’s sampling calendar for agreement in dates.
 
a.     The sampling schedule is made by working back from the Monday closest to September 1. 
1.     The September 1st week is considered a 'profile sampling' with more extensive nutrient and chlorophyll sampling (refer to the field sheets from the same sampling week

Color

We collect water samples for color at the deepest part of the lake four times per year: February under ice, spring mixis, August stratification, and fall mixis. The samples are surface water, filtered in the field through 0.45u polycarbonate membrane filters. We run a wavelength scan from 800 to 200nm, using a 5cm rectangular quartz cell in a Beckman Coulter Model DU800 spectrophotometer. Any samples that display absorbance values above 2AU are run again from 400 to 200nm using a 1cm quartz cuvette.
 
Protocol Log:  1990 -- we began running color scans, using

Total Particulate Matter

We measure water column total particulate matter (TPM) monthly during open water at the deepest part of the lake. The sample depths are selected based on thermal stratification: we sample top and bottom of the epilimnion, mid thermocline, and top, middle, bottom of the hypolimnion.  Using a peristaltic pump and tubing, we pump lake water through preweighed 0.45u membrane filters until the filters clog or until we have pumped 500ml.
Upon return to the lab we store the filters in the freezer until the following week at which time they are dried in a 60°C drying oven for at least

Temperature and Dissolved Oxygen

We sample at the deepest part of the lake, taking a temperature and oxygen profile at meter intervals from the surface to within 1 meter of the bottom using a YSI Pro-ODO temp/DO meter.  We sample biweekly during open water and approximately every five weeks during ice cover.

Protocol Log:  Prior to 2011, we used a YSI Model 58 temp/DO meter.

Light Extinction

Light (PAR) extinction coefficient is calculated by linearly regressing ln (FRLIGHT (z)) on depth z where the intercept is not constrained. FRLIGHT(z) = LIGHT(z) / DECK(z) where LIGHT(z) is light measured at depth z and DECK(z) is light measured on deck (above water) at the same time.

Water Color Scans

Sample Collection
The samples are surface water, filtered in the field through 0.45u polycarbonate filters into 125ml poly bottles.  The minimum amount needed is about 60ml; if filtering is easy, fill the bottles to allow for the possibility of running duplicate scans.  Color samples are collected four times per year, during the quarterly chemistry sampling weeks.  Quarterly sample dates include February under ice, spring mixis, August stratification, and fall mixis.  Store samples cold and dark, then allow them to warm to room temperature just before running the sca
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National Science Foundation | LTER Network | Center for Limnology        

This material is based upon work supported by the National Science Foundation under Cooperative Agreement #DEB-2025982, NTL LTER (ROR: 04gq8q482). Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.