Freshwater Wetland Primary Productivity

Prep the students the week before:

1. wear long pants and long sleeves

Prep the students in the classroom before going out:

1. “what is a wetland” lecture 5-10 min

- PP – above ground is most important to upper trophic levels

2. map of how to get there

3. map in class of wetland and how to not trample everything

4. go over procedure

Introduction

All of the energy that enters living systems, with minor exception, is incorporated first by photosynthesis. One measure of the amount of energy thereby made available to consumers is the amount of plant biomass produced, or the net primary productivity. (This is the total amount of energy fixed by producers minus the energy they require for respiration).

This lab describes a method for estimating net primary production in a non-forested wetland ecosystem in which the producer organisms are mainly annual or perennial herbaceous plants. The estimate obtained by this method assumes no significant decomposition of plant material that dies between the initial and final sampling. The estimate is uncorrected for losses of shoot material as a result of herbivory by insects. The estimate also assumes that in each pair of samples (time 0 and time 1) at each site enclose vegetation that is as similar as possible. Thus, the method works best if measurements are made during a portion of the growing season in which a continuous increase of biomass of living plant material is occurring, and in situations where herbivore grazing is minimal.

Logistics:

5 groups of 4 students each

5 plant communities at differing elevations :

Cattail (Typha)

Burreed (Sparganium)/Arrow Arum (Sagittaria)

Burreed (Sparganium)

Rush (Juncus)/grass(Poaceae),

Terrestrial

2 plots required for each sample/community

3 replicates/community

Procedure:

This experiment will be carried out in two stages.

Week 1

1. Each group collects needed equipment from the vehicles (1 pr scissors, 3 chicken wire cages, 3 stakes, 1box ziplocks, one sharpie, 18 cable ties, a wire circle.

2. Each group will be responsible for sampling one of the above plant communities.

3. It is important that you stay on the “trail” through the marsh until your sites have been “caged”, to avoid trampling your sites. So enter the marsh single file in your groups and follow the trails. Once your group’s plant community has been pointed out to you, work on your cages as described back at school. You will set up 3 cages, and beside each cage, as close as possible but in an undisturbed area, you will use your wire circles to harvest within. The cages will be staying in the marsh for the next 7 weeks. Set the cages up by CAREFULLY lowering them over the vegetation, and arranging the vegetation carefully by pulling leaves away that shouldn’t be in the cages and putting ones in that should be (based on the area of the bottom of the cage. Do not push the cage down into the ground, because sprawling vegetation needs to be included if it is present, and if you cut it you will kill it). Remove any unattached detritus from the cage (without damaging any live vegetation) and throw it away. Insert one stake inside the cage and into the mud on the downstream (south) side of the cage, and attach it to the cage with a cable tie. Label the stake with the community name and replicate number. Cover the top of the cage with a wire lid and attach it with two cable ties.

4. Using your wire circles, enclose an area of vegetation as similar to your original replicate as possible. Carefully trim all vegetation, live and dead, from within the circle. Place it in labeled ziplock bags.

5.Back at the lab, take your plant material out and pat it dry (keeping replicates separate, and being sure not to loose plant material to the floor, etc…). Use a plastic bucket as a weighing container. Depending on which scale you use, you may have to divide your sample and add the weights up at the end (some of the scales will max out with the weights involved with these plants). Weigh and record your wet-weight data.

6. Once you have done that, combine material of your three replicates. Separate out approximately 50g of the total wet material (in approx. the same species proportions as in the field) (only live material… remove any dead material) and record the exact weight it has. Oven dry this sub-sample for about 48hr at 100oC, then obtain dry weights.

Week 2 (7 weeks later…)

At each site, at the #1 cages, living and dead shoot material are collected and weighed for wet-weights as before. As before, 50g sub-samples are oven dried and dry weights obtained after 48hrs.

After collecting your plants, survey the plant communities to find out their elevations.

Calculations

Vegetation varies in the amount of water it contains. The best way to compare primary productivity between the different elevations, then, is to compare the changes in the dry-weights rather than in the wet-weights. The first task, then, is to transform wet-weight data into dry-weight data. You know what 50gs of each material when wet becomes when it dries. By setting up proportions, you can calculate the dry-weight of each of your samples.

d = x

s ww

Where: d= dry-weight of 50g sub-sample

s =original exact wet weight of 50g sub-sample

ww= wet-weight of sample

x= dry weight of sample

Calculate the dry-weights for each of the samples you collected.

For each elevation (as represented by the different plant communities), calculate estimated Net Primary Productivity (NPP):

NPP = (l2 + d2) – l1

where:

NPP = net primary production

l2= living matter at 2nd date

d2= dead matter at 2nd date

l1= living material at 1st date

Because detritus has been removed from plots on first date, any organic matter in plots on second date is due to production before and after the first date, assuming no import, export, grazing or decomposition. Therefore, subtracting the amount of production standing at the first date yields the amount of organic matter produced over the study period.

Analysis and Report

Equipment:

Waders/old shoes

Scales- coarse – 5 would be great

Oven

Beakers for oven containers

Chicken wire (precut in lengths) (15 cages of about 3ft circumference)

15 lids for cages

15 Stakes

Zipties (asked for 90)

Lots of large ziplocks (5 boxes of 2 gallon (10 per box))

5 sharpies

Bugspray

scissors

5 buckets

real vegetation clippers, knives etc for Typha

water in cooler

cups

first aid especially bandaids

garden gloves

wire circles

Week 2:

Survey Flags

string

meter pole

line level

scissors

ziplocks