Document Type

Conference Paper

Publication Date

1991

Publication Title

Proceedings of the Back Bay Ecological Symposium

Pages

60-96

Conference Name

Back Bay Ecological Symposium

Abstract

An investigation employing multivariate statistical techniques was conducted to determine major spatiotemporal patterns in water quality in Back Bay, Virginia. Water quality data collected by the Virginia Water Control Board (VWCB) over the past two decades and recent data collected by the Department of Game and Inland Fisheries and the Back Bay Restoration Foundation were consolidated for statistical analysis. Unfortunately, lack of continuity in sampling regimes prevented the use of many of the site/date/variable combinations in the statistical analyses. Nonetheless, a number of water quality patterns were characterized.

Long-term trends could be evaluated for a relatively few parameters (NO2, NH3, TKN, conductivity, DO, and pH) for which an adequate data base existed. Trend analysis of a 16-year data base for Hell Point Creek indicated a significant decrease in ammonia concentrations (-0.011 mg 1-1 yr-1) , possibly related to changes in land use activities in the region.

The TKN concentrations in the Bay almost doubled between the 1970's and 1980's (from 1.14 mg/1 to 1.97 mg/1). Indicators of eutrophication such as high daytime dissolved oxygen and pH measurements qualitatively appeared to decrease between 1970's and 1980's throughout the Bay, but lack of spatial and/or temporal continuity in the data sets prevented direct statistical comparisons.

Distinct seasonal patterns were characterized: "summer" conditions were characterized by high temperatures but lower suspended solids load and nutrient concentrations, while the converse was true for "winter" months. "Spring" and "fall" collection periods were intermediate in these characteristics but displayed elevated volatile suspended solids and depressed phosphorus concentrations, possibly due to seasonal phytoplankton blooms.

Overall spatial patterns indicated the tributary creeks appeared to be "source areas" for elevated nitrogen and phosphorus based nutrients, while the main Bay was characterized by a high organic-rich suspended solids load. The tributary of greatest concern was Nawney Creek, which displayed elevated nutrient concentrations and appeared to influence water quality in the proximate Bay region. In summary, two major problems appear to be associated with water quality conditions in Back Bay: elevated levels of nitrogen and phosphorus based nutrient in the tributary creeks and a high suspended solids load of organic-rich particles in the Bay. The full ecological significance of these conditions cannot be determined by the present study. However, consistent and comprehensive monitoring of water quality conditions, such as has been implemented in recent years, should permit observation of long-term trends in environmental conditions in various portions of the Bay. Only in this way can the success of any management or restoration actions be judged.

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