Impact Index

 An impact index was constructed to compare the varying parameters on the same

scale and to allow the comparisons between the enriched and reference sites within each

area (Table 4-8). In general, impact index values above 0.5 reflect severe changes in a

specific parameter between the enriched and reference sites. Positive values reflect

increased values at the enriched site while negative values reflect higher values at the

reference site. The equation for each parameter is:

 Impact Index = log ((Enriched P site) / (Reference P site))

 As expected, the most responsive nutrient parameters to the P gradient were the P-

related biogeochemical indicators TP, C:P, N:P, PHO, and Ecell/Ep in both the benthic

and soil layers. TOC showed relatively little change in relation to the P gradient while

TN demonstrated a small response in the soil layer. Differences were also observed with

BGL in both layers. The majority of large impact indices in the benthic layer were within

ENP-TS, even though there is a less pronounced P gradient in this area. WCA-2A, a

heavily impacted area, did not exhibit the large differences that were expected. There

were greater index values associated with the benthic layer, indicating that this layer is

more responsive to changes in biogeochemical conditions.

Transitional Sites

 Large increases in several of the individual enzyme activities occurred at the

transitional sites in the four hydrologic units (Figure 4-la & 4-1b). The greatest increases

in benthic activity occurred at the WCA-2A TRANS site with BGL and LEU with 10 of

12 comparisons significant. Spikes in LEU were also observed within the transitional

sites in LNWR, WCA-2A, and ENP-TS. PHO also increased in the soil layer WCA-2A,