Compared to the period prior to the late 1980s, the Back River today is in far better condition than it was previously. Before the BNR upgrade was completed in 1998, algal blooms would sometimes turn the river a striking shade of iridescent green. During these blooms, as the wind swept across the river, algal cells and colonies would accumulate along the shoreline causing the water to look as though someone had poured green paint on the surface.
These were the days when the chlorophyll concentration would exceed 200 Ilg/L and occasionally 300 Ilg/L. Today, algal blooms still occur but they are not nearly as severe as they were with chlorophyll concentrations now averaging 50 to 75 1l9/L rather than the 200 to 300 1l9/L previously seen. Although this seems like good progress, chlorophyll concentration should be more in the range of 25 to 35 Ilg/L.
Water quality in Back River remains impaired for nutrients for two major reasons. The discharge from the Back River WWTP still contributes significant tonnages of
NOx to the river and legacy phosphorus pollution solubilizes from the sediment as the pH rises during times of peak biological activity. These two sources provide sufficient nutrients to support the algal growth still observed in Back River throughout the growing season.
These problems are being addressed as part of the overall Bay restoration strategy and also as part of the necessary steps to improve local water quality conditions in Back River. Currently under design are facilities to take the Back River Plant to enhanced nutrient removal (ENR) levels. When these facilities are competed and operating efficiently, effluent total nitrogen concentrations will be on the order of 3 to 4 mg/L rather than the 7 to 8 mg/L currently discharged. This will reduce by approximately half the concentration and therefore loadings to Back River. Several years are still needed before these facilities will be constructed and in-service but when complete, reductions in nutrients, particularly nitrogen (TKN and NOx), should occur along with concomitant reductions in chlorophyll concentration and increases in Secchi disk transparency.
These improvements in water quality will likely not make the river run clear again, however, as much of the observed turbidity is due to the sediment load in the water and not to the crop of phytoplankton and associated organisms in the biological community. Until sediment and erosion controls are fully in place, water quality in Back River will continue to suffer from the river turning brown after a hard rain.