Summary of main results for the 1995 Brome Lake Project By Doctors Yves Prairie and Paul del Giorgio, UQAM (1995)

a) Inflowing nitrogen and phosphorus concentrations have decreased by 9 and 18% respectively relative to 1994.

b) Lake nitrogen and phosphorus concentrations have decreased by 28 and 10 % respectively relative to 1994. The reasons for this substantial decline are unclear in that they cannot be entirely attributed to the decreasing nutrient loading.

c) These changes in nutrient conditions have led to a 30% decrease in average algal biomass relative to 1994. This decrease is in full agreement with theory although the concentrations are higher than expected.

d) Two distinct stratification-destratification cycles led to two episodes of hypolimnetic anoxia and concurrent P release. The internal release fueled most of the summer algal biomass increase.

e) Contrary to expectation, the hypolimnetic release of phosphorus does not appear to be the result of the reduction of iron-bound phosphorus (as we concluded last year - 1994) but rather the simple result of decomposition and the associated nutrient regeneration.

f) Benthic chamber experiments demonstrated the role of bacterial activity in the release of phosphorus but treatments with calcium carbonate or alum did not produce a consistent reduction in P release.

g) The dominance of blue-green algae in the phytoplankton community is likely the result of the very low N:P ratio of the diffusive nutrient flux from the sediments.

h) The rare and sudden bloom of Botrydiopsis arrhiza first developed in the nutrient rich hypolimnion and surfaced when the lake destratified.

i) From the microbiological point of view, total and fecal coliform counts were generally low in the lake throughout the summer except in Douglass Beach, where they often approached unacceptable limits, most likely related to the presence of large numbers of people using these waters.