Seasonality and trends in stream water quality in Gwinnett County, Georgia, 1996–2003
More than 400 water-quality samples col-lected during baseflow and stormflow conditions between 1996 and 2003 in six watersheds in Gwinnett County, Georgia, were analyzed for seasonality and long-term trends. Baseflow water quality did not have a statistically significant seasonal variation. Flow-adjusted stormflow concentrations of total suspended solids, total phosphorus, and total zinc showed a seasonal pattern between 1996 and 2003 in five of the six watersheds and typically peaked in late summer between July and August. The seasonal pattern may be related to seasonal land-disturbance activities and/or to seasonal rainfall intensity, both of which increased in summer. Graphical and statisti-cal analyses do not indicate a time trend from 1996 to 2003 in flow- and seasonally adjusted stormflow concen-trations of total suspended solids, total phosphorus, total zinc or total dissolved solids for the sampled streams in the six watersheds studied. The absence of a trend, when land use was changing rapidly, may reflect the time lag of impacts, natural variability and/or watershed management practices. The only long-term trend detected was a decline in baseflow concentrations of total zinc. The cause of this trend is currently unknown.