3.4.1 Treatments and Soil Preparation
Our demonstrations included seeding and fertilizing cold-tolerant grasses in POL-contaminated
soils. We compared the treatment effects of nutrient additions on a mix of three plant species and
of the interactions of plants with nutrients, with controls for each, resulting in four treatments: 1)
a control, (no plants and no nutrients added), 2) added nutrients, 3) plants without nutrients, and
4) plants plus nutrients.
We used a mixture of annual ryegrass (Lolium multiflorum, Lam.), Arctared red fescue (Festuca
rubra, L.), and white clover (Trifolium repens, L.) at each of the three sites. Low-maintenance
grasses and a legume were chosen to avoid the need for intensive agricultural practices. The
initial nutrient addition to the soil and watering are all that is usually required to create a viable
stand of these grasses in these climates. We followed the guidelines developed by the
Remediation Technologies Development Forum (RTDF) for seeding mixtures, which by weight
are approximately 8 lb/1000 ft2 tall fescue, 2 lb/1000 ft2 annual ryegrass, 1 lb/1000 ft2 legume
(such as white clover, yellow sweet clover, or birdsfoot trefoil). These mixes, in general,
provided a seed mix that had 10 to 15% ryegrass (annual or perennial), 20 to 25% legume
(alfalfa, clover, birds-foot trefoil), and 60 to 70% fescue (varieties chosen for local conditions)
on a seed quantity basis.
Minimal soil preparation was done prior to seeding. Seeds were surface applied by hand or by
hand-held seeders and pressed into the soil surface to promote reasonable seed-soil contact and
water imbibition. Nutrients were applied by hand or by hand-held seeders. Neither seeds nor
nutrients were mixed into the soil, eliminating the need for heavy equipment mobilization to
remote sites. Plot size varied at each site due to the constraints imposed by the local conditions.
Figure 3 shows an overview of Block 1 plots on Annette Island; Figures 1 and 2 show grass
growth in the plots at Campion; and Figure 4 shows plots at Barrow.
3.4.2 Fertilizer
Fertilizer requirements for bioremediation are controversial. A potential issue is that for highly
contaminated soils--which necessarily have high carbon levels--the amount of fertilizer
nitrogen that is needed to maintain many carbon:nitrogen ratios becomes quite high, leading to
osmotic stress on both microorganisms and plants.
We used standard agricultural fertilizer using as much nitrogen as could be added without
stunting the plants. The maximal level for nitrogen additions without inhibiting microbial
activity is approximately 2000 mg N / kg soil water (Walworth et al., 1997). The challenge to
this approach is that soil water content varies as soil wets and dries. A reasonable way to address
nutrient additions is to add nutrients based on soil water concentrations of 2000 mg nitrogen / kg
soil water, and use soil water content that is equivalent to a soil water matric potential of -33
KPa. We used this approach at our three demonstration locations. At Galena, the soil had been
fertilized earlier and some residual fertilizer remained. Our fertilizer additions inhibited seed
germination until microbial processes lowered the nitrogen in the soil.
3.5 Sampling and Monitoring Procedures
To initially characterize the general contaminant distribution at the site and to find the best
location for the demonstration plots, we analyzed an initial set of samples in a grid pattern by
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